DIAGNOSIS APPARATUS AND DIAGNOSIS METHOD FOR RELAY CIRCUIT
FIELD
The embodiments discussed herein are related to a
diagnosis apparatus and a diagnosis method for a relay circuit.
BACKGROUND
A DC power supply available to flow a large current with
a voltage of 200 V or higher may be used for electric.vehicles
or hybrid vehicles, for example. Accordingly, for the purpose
of security and the like, a relay contact may be provided in a
power supply line so as to completely separate the DC power
supply from a load circuit such as an inverter or a motor when
the DC power supply is not in use.
However, the relay contact may be welded due to
discharges occurred during on-off control of the relay contact.
As examples of technologies for diagnosing such welding,
technologies disclosed in JP 2000-278802 A and WO 2004/088696 A
are known.
JP 2000-278802 A discloses a system which determines a"
malfunction in a discharging system for discharging electric
charge accumulated in a capacitor by using a motor coil. This
determination system can determine whether discharge is
performed normally, whether there is an abnormality of the
motor coil, and whether there is an abnormality of a discharge
resistor, based on a change (slope) of the both-end voltage of
an inverter with respect to the time after start of the
discharge.
Meanwhile, WO 2004/088696 A discloses a method and an
apparatus for detecting the welding of a relay contact. This
detection method (or apparatus) performs sequence (turning
on/off) control on first and second main relays and a precharge
relay. The first and second main relays are provided in

positive and negative power supply lines of a DC power supply.
The precharge relay is provided in parallel with the contact of
the first main relay and is configured by a resistor and a
contact. In the sequence control, it is determined whether any
one of the first and second main relays is welded by checking
whether or not the both-end voltage of a load circuit decreases.
However, according to the technology disclosed in. JP
2000-278802 A, when relay welding occurs, there is no change in
the both-end voltage of the inverter, and accordingly, the
occurrence of the relay welding itself can be identified but a
welding-occurred relay would not be identified.
In contrast, according to the technology disclosed in WO
2004/088696 A, it can be determined which one of the first and
second main relays is welded. However, in a case where the
resistance value of the load circuit is much higher than the
resistance value of the resistor (precharge resistor) of the
precharge relay, the both-end voltage of the load circuit
decreases in low speed, and accordingly, quick or rapid
diagnosis would not be available.
For example, in a case where the resistance value of the
load circuit (discharge resistor) is 160 kΩ while the
resistance value of the precharge resistor is 300 Ω, it takes a
time to perform discharge through the load circuit, and
accordingly, the quick or rapid diagnosis would not be
available. In other words, according to the technology
disclosed in WO 2004/088696 A, the time required for the
diagnosis depends on the ratio between the resistance values of
the precharge resistor and the discharge resistor.
In addition, according to the technology disclosed in WO
2004/088696 A, it can be determined which main relay is welded,
however, a detection of an abnormality of a circuit component
(for example, an abnormality of the precharge resistor)"is not
available.

SUMMARY
It is an object in one aspect of the embodiment(s) to
enable a quick or rapid detection of an abnormality of a relay
circuit.
According to an aspect of the embodiment(s), there is
provided a diagnosis apparatus for a relay circuit. The relay
circuit includes: a load circuit supplied with a direct-current
(DC) voltage from a direct-current (DC) power supply; a
capacitor connected to both ends of the load circuit; a first
main relay provided for a power supply line between a positive
terminal of the DC power supply and one end of the load
circuit; a second main relay provided for a power supply line
between a negative terminal of the DC power supply and the
other end of the load circuit; a series circuit of a first
resistor and a precharge relay that are provided in parallel
with the second main relay; and a second resistor connected to
both ends of the load circuit. The diagnosis apparatus
includes: a voltage sensor configured to detect a both-end
voltage of the capacitor; a relay controller configured to
performs an on-off control on each of the relays in accordance
with a predetermined sequence; and a determiner configured to
detect an abnormality of the first resistor based on the
voltage detected by the voltage sensor and an equivalent
resistance value representing a discharge process in a sequence
including the discharge process, the discharge process being
performed by the relay controller to turn on both of the first
main relay and the precharge relay and turn off the second main
relay to apply a reactive current with an amount indicated by a
value stored in a memory to the load circuit.
According to the technology described above, an
abnormality of the resistor of the relay circuit can be
detected quickly or rapidly.

BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a block diagram illustrating an example of the
configuration of a vehicle according to a first embodiment
focusing on a motor driving system;
FIG. 2 is a diagram illustrating an example of the state
of Sequence #1 in the configuration illustrated in FIG. 1;
FIG. 3 is a diagram illustrating an example of the state
of Sequence #2 in the configuration illustrated in FIG. 1/
FIG. 4 is a diagram illustrating an example of the state
of Sequence #3 in the configuration illustrated in FIG. 1;
FIG. 5 is a graph illustrating an example of a change in
a discharge resistance value with respect to a discharge
current value;
FIG. 6 is a diagram illustrating an example of the state
of Sequence #4 in the configuration illustrated in FIG. 1;
FIG. 7 is a diagram illustrating an example of the state
of Sequence #5 in the configuration illustrated in FIG; 1; .
FIG. 8 is a diagram illustrating an example of the state
of Sequence #6 in the configuration illustrated in FIG. 1;
FIG. 9 is a diagram illustrating examples of a change in
the both-end voltage (C voltage) of a capacitor C with respect
to time, a change in the on-off state of each relay, and a.
change in a discharge current amount in Sequences #1 to #6;
FIG. 10 is a diagram illustrating examples of a change in
the both-end voltage (C voltage) of the capacitor C with
respect to time, a change in the on-off state of each relay,
and a change in the discharge current amount in Sequences #1 to
#6;
FIG. 11 is a diagram illustrating examples of a change in
the both-end voltage (C voltage) of the capacitor C with
respect to time, a change in the on-off state of each relay,
and a change in the discharge current amount in a case where a

precharge relay is welded before the start of Sequences #1 to
#6;
FIG. 12 is a flowchart illustrating Sequences #1 to #5
according to the first embodiment;
FIG. 13 is a flowchart illustrating Sequences #5 and #6
according to the first embodiment;
FIG. 14 is a flowchart illustrating Sequences #1.to #5
according to a second embodiment;
FIG. 15 is a flowchart illustrating Sequences #5 and #6
according to the second embodiment;
FIG. 16 is a diagram illustrating examples of a change in
the both-end voltage (C voltage) of a capacitor C with respect
to time, a change in the on-off state of each relay, and a
change in a discharge current amount in Sequences #1 to #6
according to the second embodiment;
FIG. 17 is a diagram illustrating examples of a change in
the both-end voltage (C voltage) of the capacitor C with
respect to time, a change in the on-off state of each relay,
and a change in the discharge current amount in a case where a
positive-side main relay is welded in the second embodiment;
FIG. 18 is a flowchart illustrating a third embodiment;
FIG. 19 is a flowchart illustrating Sequences #1 to #5
according to a fourth embodiment;
FIG. 20 is a flowchart illustrating Sequences #5 and #6
according to the fourth embodiment;
FIG. 21 is a diagram illustrating examples of a change in
the both-end voltage (C voltage) of a capacitor C with respect
to time, a change in the on-off state of each relay, and a
change in a discharge current amount in Sequences #1 to #6
according to the fourth embodiment;
FIG. 22 is a flowchart illustrating Sequences #1 to #5
according to a fifth embodiment; and
FIG. 23 is a flowchart illustrating Sequences #5 and #6

according to the fifth embodiment.
DESCRIPTION OF EMBODIMENTS
Hereinafter, exemplary embodiments will be described with
reference to the appended drawings. Here, the following
embodiments are merely exemplary, and are not intended to
exclude applications of various modifications or techniques
which are not described below. In the drawings used in the
following embodiments, the same components are denoted by the
same reference numerals unless otherwise set forth.
(First Embodiment)
FIG. 1 is a block diagram illustrating an example of the
configuration of a vehicle according to a first embodiment
focusing on a motor driving system. For example, the motor
drive system 1 illustrated in FIG. 1 is used in a next- ,
generation vehicle such as an electric vehicle (EV) or a hybrid
vehicle (HEV). The motor drive system 1, for example, includes
a vehicle control unit (VCU) 10, a motor control unit (MCU), 2.0,
an inverter 30, a three-phase motor 40, and a lithium ion
battery (LiB) 50.
The VCU 10 controls the traveling of the vehicle by
transmitting a drive control signal such as a torque
instruction value to the MCU 20 based on an accelerator sensor
signal and a brake sensor signal acquired by an accelerator
sensor and a brake sensor not illustrated in the figure. For
example, the VCU 10 performs an instruction for the calculation
or regeneration of a drive torque based on the accelerator
sensor signal, an instruction for the calculation of a
regenerated energy amount based on the brake sensor signal,
control of drivability, and the like.
The MCU 20 is communicably connected to the VCU 10
through a serial peripheral interface (SPI) or the like. The
MCU 20 controls the inverter 30 based on a traveling control

signal given from the VCU 10 through SPI communication, thereby
drive power given to the three-phase motor 40 is controlled.
For example, the MCU 20 performs feedback control, of the
three-phase motor 40 based on a torque instruction value and
sensor signals of an angle sensor (resolver) and a current
sensor 60 provided in the three-phase motor 40 such that the
torque of the three-phase motor 40 coincides with the torque
instruction value given from the VCU 10.
The inverter 30 receives a power source voltage (battery
voltage: VI) from the LiB 50, generates a drive voltage of the
three-phase motor 4 0 in accordance with drive power control
performed by the MCU 20, and supplies drive power to' the three-
phase motor 40 as the three-phase AC. For example, the inverter
30 is configured using an IGBT module in which a switching
element such as an insulated gate bipolar transistor (IGBT) and
a free wheel diode forms an anti-parallel connection.
As illustrated in FIG. 1, the inverter 30 includes, for
example, three IGBT elements UH, VH, and WH forming upper arms
of the U phase, the V phase, and the W phase and three IGBT
elements UL, VL, and WL forming lower arms of the U phase, the
V phase, and the W phase. The gate voltages of the six IGBT
elements UH, VH, WH, UL, VL, and WL are individually controlled
by the MCU 20, whereby the drive power of the three-phase AC
given to the three-phase motor 40 is controlled.
In addition, the inverter 30 detects a battery voltage
VDC received from the LiB 50 using an isolation amplifier and
supplies the detected battery voltage VDC to the MCU 20 as an
inverter voltage. The MCU 20 is operable to notify the VCU 10
of the inverter voltage, for example, through the SPI
communication, and accordingly, the VCU 10, for example, is
operable to detect (monitor) an abnormality of an inverter
voltage.
A capacitor C and a resistor R2 are connected to both of

positive and negative ends of the inverter 30 in parallel.'.The
capacitor C is a smoothing capacitor and suppresses a variation
of the input voltage input from the LiB 50 to the inverter 30.
When both of a first main relay and a precharge relay are
turned on, and a second main relay is turned off, a divided
voltage ratio of the battery voltage VI supplied from the;.LiB
50 is determined by the resistor R2 together with the resistor
(precharge resistor) Rl. This will be described later in detail.
The three-phase motor 40 is an example of a driving
source of the vehicle and is provided with the resolver and the
current sensor 60 described above. The inverter 30 and the
three-phase motor 40 are examples of the load circuit.
The LiB 50 is an example of the DC power supply and, for
example, applies a DC voltage of 200 V or higher (for example,
300 V or the like) to the inverter 30. A first main relay (LIB .
P) 81 is disposed in the power supply line between the positive
terminal of the LiB 50 and one terminal of the inverter 30.
Further, a second main relay (LIB N) 82 is disposed in the
power supply line between the negative terminal of the LiB 50
and the other terminal of the inverter 30. When both of the.'
main relays 81 and 82 are turned on, power is supplied from the
LiB 50 to the inverter 30. On the other hand, when both of the
main relays 81 and 82 are turned off, the LiB 50 is
electrically disconnected from the inverter 30 and the three-
phase motor 40.
Furthermore, a series circuit configured by a resistor
(precharge resistor) Rl and a precharge relay (LIB PRE) 83 is
connected to the second main relay 82 in parallel therewith.
The precharge resistor Rl is an example of a first resistor and
the aforementioned resistor R2 is an example of a second
resistor. Upon controlling both of the main relays 81 and 82
turned on, the precharge relay 83 may be turned on. However,
the precharge relay is turned on after the positive-side main

relay 81 is turned on and before the negative-side main relay
82 is turned on. Thereby, a charge current charging the
capacitor C flows through the resistor Rl, and the capacitor G
is gradually charged. Therefore, even when the negative-side,
main relay 82 is turned on, a large inrush current toward the
capacitor C is not generated. Thus, it is possible to prevent
one or both of the main relays 81 and 82 from being welded.
The LiB 50, the resistors Rl and R2, the capacitor C, and
the relays 81 to 83 described above configure an example of a
relay circuit.
The on-off control on each relay 81 to 83, for example,
is performed in accordance with a control signal (relay control
signal) provided from the VCU 10. In this embodiment, as will
be described later, by performing an on-off control on each of
the relays 81 to 83 in accordance with a predetermined
switching sequence and monitoring a change in the both-end
voltage V of the capacitor C in the switching sequence, it is
possible to detect whether or not any one relay is welded.
Further, by monitoring a change in the both-end voltage V, it
is possible to detect an abnormality of the precharge resistor
Rl.
For this, a voltage sensor 70 that senses (detects) a
voltage is connected to both ends of the capacitor C (resistor
R2). A voltage detection result obtained by the voltage sensor
70, for example, is supplied to the VCU 10. The VCU 10 detects
whether a relay is welded and whether there is an abnormality
of the precharge resistor Rl based on the voltage detection
result (in other words, a change in the both-end voltage of the
capacitor C (the resistor R2)) during the aforementioned
switching sequence.
For this, the VCU 10 includes, for example, a relay
controller 101, a determiner 102, a memory 103, and a discharge
controller 104. These units 101 to 104 configure an example ""of

the diagnosis apparatus for a relay circuit together with the.
voltage sensor 70.
The relay controller 101 performs an on-off control on
each of the relays 81 to 83 in accordance with a switching
sequence represented in Table 1 set out below.
The amount of a reactive current to flow during
discharging in the sequence may be stored in the memory 1.03. '
The memory 103 may be installed in the MCU 20. The relay
controller 101 performs control so that a reactive current of
an amount indicated by a value read from the memory 103 flows.
The amount of the reactive current stored in the memory
103 in advance, for example, may be determined based on values
of the precharge resistor Rl, the capacitor C, the LiB voltage,
the determination time, and the discharge resistor Rdis- The
amount of the reactive current may be stored in the memory 103
when the product is shipped.
In Embodiments 4 and 5 to be described later, the amount
of the reactive current in Sequences # 1 to #4 and Sequences #5
and #6 may be changed. In such a case, the amount of the
reactive current stored in the memory 103 may be read before
start of the discharge in the sequence.
FIGS. 2 to 4 and 6 to 8 illustrate connection states of
the relays 81 to 83 and current paths corresponding to
Sequences #1 to #6. In FIGS. 2 to 4 and 6 to 8, the voltage
sensor 70 is not illustrated.
[Table 1]



In other words, before start of the sequence (before the
inrush) and in Sequence #1, as illustrated in FIG. 2, the relay
controller 101 controls both of the main relays 81 and 82
turned on and controls the precharge relay 83 turned off. In
this case, the battery voltage is applied to both ends of- the
capacitor C (the resistor R2) from the LiB 50 (in other words,
a voltage V detected by the voltage sensor 70 is VI), and self-
discharge occurs in a path illustrated by a dotted-line arrow
501. In other words, a current flows in a path 501 starting
from the LiB 50, passing through the positive-side main relay
81, the resistor R2, and the negative-side main relay 82, and
returning to the LiB 50.
Thereafter, in Sequence #2, the relay controller 101, as
illustrated in FIG. 3, controls the negative-side main relay 82
turned off. Further, the discharge controller 104 gives a
discharge start instruction to the MCU 20. Thereby, the MCU 20
controls the IGBT element such that a reactive current flows
into a d-axis of the three-phase motor 40 through the inverter
30.
In that case, a current flows in a path denoted by a
solid-line arrow 502 in FIG. 3 (discharge). In other words,
electric charge accumulated in the capacitor C flows from the
positive side of the capacitor C to the d-axis of the three-
phase motor 40 through the IGBT element configuring the upper
arm of the inverter 30 (reactive current) and flows to the
negative side of the capacitor C through the IGBT element
configuring the lower arm of the inverter 30. Also, a part of

the electric charge accumulated in the capacitor C flows to the
resistor R2 in a path denoted by a dotted-line arrow 503 (self-
discharge) . The both-end voltage (in other words, a voltage
detected by the voltage sensor 70) V of the capacitor (the
resistor R2) at this time is decreased toward V = 0.
Thereafter, in Sequence #3, the relay controller 101, as
illustrated in FIG. 4, controls the precharge relay 83 turned
on. In that case, a current flows in a path illustrated by a
dotted-line arrow 504 in FIG. 4. In other words, a current
(discharge current) flows from the positive side of the LiB 50
to the negative side of the LiB 50 through the main relay 81,
the inverter 30, the three-phase motor 40 (d axis), the
precharge resistor R1, and the precharge relay 83. Further, a
current flows from the positive side of the LiB 50 to the
negative side of the LiB 50 through the main relay 81, the
resistor R2, the precharge resistor Rl, and the precharge relay
83. At this time, electric charge is accumulated (charged) in
the capacitor C. In conclusion, the current flows to the d-axis
of the three-phase motor 40 through the inverter 30, and the
capacitor C is charged. The both-end voltage (in other words, a
voltage detected by the voltage sensor 70) V of the capacitor C
(the resistor R2) at this time is represented in the following
Equation (1) .
V = V1x { (Rdis-R2)/(Rdis + R2)}/{R1 + (Rdis-R2 ) / (Rdis +
R2)} ... (1)
Here, Rl and R2 respectively represent resistance values
of the resistors Rl and R2. For example, Rl is 300 Ω and R2 is
180 kΩ. Rdis represents a resistance value in a case where the
discharge is simulated as a resistor. For example, RdiS-can be
represented as a variable resistance value which changes in the
range of about 1 kΩ to 8 kΩ in a case where the discharge
current IdiS changes in the range of 5 to 15 A (ampere), as
illustrated in FIG. 5. The reason for the decrease in the both-

end voltage of the capacitor C due to discharge (in other words,
a decrease in the energy collected in the capacitor C). is that
energy is consumed as heat in accordance with heat dissipation
of the coil of the three-phase motor 40 in a coil resistor due
to conduction and heat dissipation due to conduction of the
IGBT and the diode and switching. The effect of the consumption
of energy as such heat is equivalently simulated as discharge,
according to the resistor Rdis. Further, since the amount of
consumption as heat is proportional to the amount of the
discharge current, Rdis can be considered as a variable
resistance value which is monotonously decreased in accordance
with an increase in the discharge current (the amount of heat
dissipation increases as the resistance value decreases)-.
Accordingly, in Sequence #3, the both-end voltage V of
the capacitor C (the resistor R2) increases toward a value,
which is represented in the above-described Equation (1),
acquired by dividing the battery voltage V1 by the precharge
resistance value R1 and the discharge resistance value Rdis-
Next, in Sequence #4, the relay controller 101, as
illustrated in FIG. 6, controls the positive-side main relay 81
turned off. In that case, a current flows in a path represented
by a solid-line arrow 505 in FIG. 6 (discharge). In other words,
electric charge accumulated in the capacitor C flows from the
positive side of the capacitor C to the d-axis of the three-
phase motor 40 through the IGBT element configuring the upper
arm of the inverter 30 (reactive current) and flows to the
negative side of the capacitor C through the IGBT element
configuring the lower arm of the inverter 30. A part of the
electric charge accumulated in the capacitor C also flows to
the resistor R2 in a path denoted by a dotted-line arrow 506
(self-discharge). The both-end voltage (in other words, a
voltage detected by the voltage sensor 70) V of the capacitor
(the resistor R2) at this time is decreased toward V =0.

Thereafter, in Sequence #5, the relay controller 101, as
illustrated in FIG. 7, controls the positive-side main relay 81
turned on. In that case, similar to the case of Sequence #3, a
current flows in a path illustrated by a dotted-line arrow 508
in FIG. 7. In other words, the current flows to the.d—axis of
the three-phase motor 40 through the inverter 30, and the.
capacitor C is charged. The both-end voltage (in other words, a
voltage detected by the voltage sensor 70) V of the capacitor C
(the resistor R2) at this time is represented in Equation (1)
described above.
Accordingly, in Sequence #5, the both-end voltage V of
the capacitor C (the resistor R2) increases toward a value,
which is represented in the above-described Equation (1),
acquired by dividing the battery voltage V1 by the precharge
resistance value R1 and the discharge resistance value Rais.
Next, in Sequence #6, the relay controller 101, as
illustrated in FIG. 8, controls the precharge relay 83 turned
off. In that case, similar to Sequence #2, a current flows in a
path represented by a solid-line arrow 509 in FIG. 8
(discharge). In other words, electric charge accumulated in the
capacitor C flows from the positive side of the capacitor C to
the d-axis of the three-phase motor 40 through the IGBT element
configuring the upper arm of the inverter 30 (reactive current)
and flows to the negative side of the capacitor C through the
IGBT element configuring the lower arm of the inverter 30. A
part of the electric charge accumulated in the capacitor C also
flows to the resistor R2 in a path denoted by a dotted-line
arrow 510 (self-discharge). The both-end voltage (in other
words, a voltage detected by the voltage sensor 70) V of the
capacitor (the resistor R2) at this time is decreased toward V
= 0.
FIG. 9 illustrates examples of a change in the both-end
voltage (C voltage) of the capacitor C with respect to time, a

change in the on-off state of each of the relays 81 to 83, and
a change in the discharge current amount in Sequences #1 to #6.
In FIG. 9, #1 to #6 represent periods corresponding to
Sequences #1 to #6, respectively. Further, a solid line 601.
represents a change in the C voltage, a dotted line 602
represents a change in the on-off state of the negative-side
main relay 82, and a dashed line 603 represents a change in the
on-off state of the positive-side main relay 81. Furthermore, a
two-dot chain line 604 represents a change in the on-off state
of the precharge relay 83, and reference numeral 605 represents
a change in the amount of the discharge current during the
discharge period (a period corresponding to Sequences #2 to #6).
The VCU 10 is available to detect (diagnose) an
abnormality of the battery voltage and whether any one of the
relays 81 to 83 is welded by comparing the C voltage with a
predetermined voltage threshold during the period corresponding
to each of Sequences #1 to #6 by using the determiner 102.
Further, as illustrated in FIG. 10, during the period
corresponding to each of Sequences #3 to #5, the VCU 10 is also
available to diagnose whether there is no abnormality of the
precharge resistor R1 by comparing the C voltage with the
predetermined voltage threshold by using the determiner 102.
A case in which the precharge relay 83 has already been
welded before the start of Sequences #1 to #6 may also be
considered. In such a case, as illustrated in FIG. 11, the VCU
10 is available to diagnose whether or not the precharge relay
83 is welded by comparing the C voltage with a predetermined
voltage threshold during the period corresponding to Sequence
#6 by using the determiner 102. More specifically, it can "be
determined that the precharge relay 83 is welded in a case
where the C voltage is not below the predetermined voltage
threshold.
However, when the precharge relay 83 is welded, a voltage

drop during the period corresponding to Sequence #2 is slow.
Accordingly, by comparing a voltage drop value of the C voltage
after the elapse of a predetermined time with a threshold, a
welding diagnosis is available during the period corresponding
to Sequence #2. This aspect will be described later in a third
embodiment.
Each of the thresholds described above may be stored in,
for example, the memory 103 and may be read by the determiner
102 appropriately.
Hereinafter, a specific example of the above-described
diagnosis will be described with reference to a flowchart
illustrated in FIGS. 12 and 13. In FIGS. 12 and 13, #1 to,#6
represent periods corresponding to Sequences #1 to #6,
respectively.
First, as illustrated in FIG. 12, during the period
corresponding to Sequence #1, the VCU 10 determines whether "V
> Vth1" is satisfied by comparing the C voltage V detected by
the voltage sensor 70 with a voltage threshold Vthl using the
determiner 102 (Process P10). For example, when the battery
voltage V1 of the LiB 50 is 300 V, the voltage threshold Vthl
may be set to 290 V.
As a result, in a case where "V > Vthl" is not satisfied
("No" in Process P10), the determiner 102 determines that there
is an abnormality of the battery voltage of the LiB 50 (Process
P70) . In this case, the VCU 10 (the relay controller 101) ends
the process without performing subsequent Sequences #2 to #6
(discharge stop: Process P80).
On the other hand, in a case where V > Vthl is satisfied
("Yes" in Process P10), the VCU 10 controls the negative-side
main relay 82 turned off using the relay controller 101
(Process P20), and discharge is started by the discharge
controller 104 (Process P30).
Thereafter, when a predetermined time (for example, 800

ms) elapses (Process P40), the VCU 10 determines whether V <
Vth2 is satisfied by comparing the C voltage V detected by the
voltage sensor 70 with a predetermined voltage threshold Vth2
(< Vthl) using the determiner 102 (Process P50) . For example,
in a case where the battery voltage V1 is 300 V, the voltage
threshold Vth2 may be set to 250 V. Here, the predetermined
time may be set in comprehensive consideration of the
capacitance of the capacitor C, the discharge resistance value
Rdis, a steady-state voltage value, switching control of the
IGBT, the determination time, and the like (hereinafter, this
similarly applies).
As a result, in a case where "V < Vth2" is not satisfied
(in a case where the C voltage V is not below the voltage
threshold Vth2: "No" in Process P50), the determiner 102
determines that the negative-side main relay 82 is welded,
(process P60). In such a case, the VCU 10 (the relay controller
101) stops discharge using the discharge controller 104 without
performing subsequent Sequences #3 to #6 (Process P80) and ends
the process.
On the other hand, in a case where "V < Vth2" is
satisfied ("Yes" in Process P50), the VCU 10 controls the
precharge relay 83 turned on using the relay controller 101
(Process P90). Thereafter, when a predetermined time (for
example, 800 ms) elapses (Process P100), the VCU 10 determines
whether "Vth4 < V < Vth5" is satisfied by comparing the C
voltage V with predetermined voltage thresholds Vth4 and Vth5
by using the determiner 102 (Process P110). Here, for example,
the voltage threshold Vth4 satisfies Vth2 < Vth4 < Vthl, and
the voltage threshold Vth5 satisfies Vth4 < Vth5 < Vthl. For
example, in a case where the battery voltage V1 is 300 V, the
voltage thresholds Vth4 and Vth5 may be set to 265 V and 285 V,
respectively.
As a result, in a case where "Vth4 < V < Vth5" is not

satisfied ("No" in Process P110), the determiner 102 determines
that there is an abnormality of the precharge resistor R1
(Process P180) . In such a case, the VCU 10 (the relay-
controller 101) stops discharge by using the discharge
controller 104 without performing subsequent Sequences #4 to.#6
(Process P190) and ends the process.
On the other hand, in a case where "Vth4 < V < Vth5" is
satisfied ("Yes" in Process P110), the VCU 10 controls the
positive-side main relay 81 turned off by using the relay
controller 101 (Process P120). Thereafter, when a predetermined
time (for example, 800 ms) elapses (Process P130), the VCU 10
determines whether "V < Vth6" is satisfied by comparing the C
voltage V with a predetermined voltage threshold Vth6 by using
the determiner 102 (Process P140). Here, for example, the
voltage threshold Vth6 satisfies Vth6 < Vth2. For example, in a
case where the battery voltage V1 is 300 V, the voltage
threshold Vth6 may be set to 230 V.
As a result, in a case where "V < Vth6" is not satisfied
("No" in Process P140), the determiner 102 determines that the
positive-side main relay 81 is welded (process P170). In such a
case, the VCU 10 (the relay controller 101) stops discharge by
using the discharge controller 104 without performing
subsequent Sequences #5 and #6 (Process P190) and ends the
process.
On the other hand, in a case where "V < Vth6" is
satisfied ("Yes" in Process P140), the VCU 10 controls the
positive-side main relay 81 turned on by using the relay
controller 101 (Process P150). Thereafter, when a predetermined
time (for example, 800 ms) elapses (Process P160), as
illustrated in FIG. 13, again, the determiner 102 determines
whether "Vth4 < V < Vth5" is satisfied by comparing the C
voltage V with the predetermined voltage thresholds Vth4 and
Vth5 (Process P200).

As a result, in a case where "Vth4 < V < Vth5" is not
satisfied ("No" in Process P200), the determiner 102 determines
that there is an abnormality of the precharge resistor R1
(Process P260). In such a case, the VCU 10 (the relay,
controller 101) stops discharge by using the discharge
controller 104 without performing the subsequent Sequence #6
(Process P270) and ends the process.
On the other hand, in a case where "Vth4 < V < Vth5".is
satisfied ("Yes" in Process P200), the VCU 10 controls the
precharge relay 83 turned off by using the relay controller 101
(Process P210) . Thereafter, when a predetermined time (for
example, 800 ms) elapses (Process P220), the VCU 10 determines
whether "V < Vth7" is satisfied by comparing the C voltage V
with a predetermined voltage threshold Vth7 by using the
determiner 102 (Process P230). Here, for example, the voltage
threshold Vth7 satisfies Vth7 < Vth2. For example, in a case
where the battery voltage V1 is 300 V, the voltage threshold
Vth7 may be set to 230 V. In other words, the voltage threshold
Vth7 may be set to the same value as that of the voltage
threshold Vth6 (= 230 V).
As a result, in a case where "V < Vth7" is not satisfied
("No" in Process P230), the determiner 102 determines that the
precharge relay 83 is welded (process P250). In such a case,
the VCU 10 stops discharge by using the discharge controller
104 (Process P270) and ends the process.
On the other hand, in a case where "V < Vth7" is
satisfied ("Yes" in Process P230), a normal end process is
performed (Process P240). For example, the discharge controller
104 stops the discharge (Process P270), and the process ends.
As described above, according to the aforementioned
embodiment, the discharge process is controlled in which a
reactive current of a reactive current amount corresponding to
the value stored in the memory 103 is caused to flow in the

load circuit. Accordingly, speedy discharge can be performed,
whereby a quick or rapid diagnosis can be achieved. Further,' in
the sequence performing the discharge process, an abnormality
of the precharge resistor R1 can be detected based on the both-
end voltage of the capacitor C, which is detected by the
voltage sensor 70, and the resistance value RdiS that is an
equivalent representation of the discharge process. Accordingly,
the equivalent resistance value RdiS can be freely set without
depending on the resistance value of the precharge resistor Rl
and the like.
In the first embodiment described above, the switching
control of the relays 81 to 83 is performed in order of
Sequences #1 to #6, however; the order of the sequences may be
changed. For example, a set of Sequences #3 and #4 and a set of
Sequences #5 and #6 may be interchanged in the execution order.
Further, in a case where the precharge relay 83 is turned on in
a stage before the start of the sequences, a set of Sequences
#1 and #2 and a set of Sequences #3 and #4 (or a set of
Sequences #5 and #6) may be interchanged in the execution order.
(Second Embodiment)
In the first embodiment described above, in the case of
normal end, for example, as illustrated in FIG. 10, while
discharge is continuously performed during the period
corresponding to Sequences #2 to #6, for example. However, as
denoted by reference numeral 605 in FIG. 16, inverter control
may be performed such that discharge is intermittently
performed by the discharge controller 104.
In such a case, the discharge controller 104 serves as an
example of a discharge period controller that controls a period
during which electric charge accumulated in the capacitor C or
the electric charge supplied from the LiB 50 is discharged
through the inverter 30 and the three-phase motor 40 for each
sequence.

FIGS. 14 and 15 illustrate an example of the intermittent
discharge operation. As can be understood by comparing FIGS. 14
and 15 and FIGS. 12 and 13 with each other, in the second
embodiment, in each of Sequences #2 to #6, discharge is stopped
when a predetermined time (for example, 500 ms) elapses from
the start of discharge, which is different from the first
embodiment.
For example, as illustrated in FIG. 14, in Sequence #2,
after the negative-side main relay 82 is turned off (Process
P20), discharge is started (Process P30), and, when a
predetermined time elapses (Process P31), the discharge is
stopped (Process P32).
Further, in Sequence #3, after the precharge relay 83 is
turned on (Process P90), discharge is started (Process P91),
and, when a predetermined time elapses (Process P92), the
discharge is stopped (Process P93).
Furthermore, in Sequence #4, after the positive-side main
relay 81 is turned off (Process P120), discharge is started
(Process P121), and, when a predetermined time elapses (Process
P122), the discharge is stopped (Process P123).
Further, in Sequence #5, after the positive-side main
relay 81 is turned on (Process P150), discharge is started
(Process P151), and, when a predetermined time elapses (Process
P152), the discharge is stopped (Process P153).
Furthermore, as illustrated in FIG. 15, after the
precharge relay 83 is turned off (Process P210), discharge is
started (Process P211), and, when a predetermined time elapses
(Process P212), the discharge is stopped (Process P213).
The other processes (the determination process and the
like) to which the same reference numerals as those of the
first embodiment (FIGS. 12 and 13) are depicted in FIGS. 14 and
15 are the same as those of the first embodiment. FIG. 16
illustrates an example of a change (see reference numeral 601)

of the C voltage in a case where the above-described
intermittent discharge is performed. FIG. 17 illustrates a case
where the positive-side main relay 81 is determined as being
welded because the C voltage is not below the predetermined
voltage threshold Vth6 in Sequence #4.
As described above, during the period corresponding to
Sequences #2 to #6, by intermittently performing discharge, the
discharge period can be shorter than that of the first
embodiment. Accordingly, the amount of the consumed current
according to the discharge can be suppressed.
In the second embodiment described above, in each of the
periods corresponding to Sequences #2 to #6, the start and the
stop of discharge are performed, however; the start and the
stop of discharge may be performed only for some of the periods.
(Third Embodiment)
FIG. 18 illustrates an example of a flowchart of a relay
welding diagnosis according to a third embodiment. The
flowchart illustrated in FIG. 18 is different from the
flowchart according to the first embodiment illustrated in FIGS.
12 and 13 in that Processes P51 and P52 are added. Further, in
the case illustrated in FIG. 18, Processes P160, P190, P200,
P210, P220, P230, and P250 illustrated in FIGS. 12 and 13 are
unnecessary (deleted).
The reason for this is that, in Processes P51 and P52, in
a case where the C voltage V is determined as not being below
the predetermined threshold Vth3 by the determiner 102 ( "No"
in Process P51), it can be determined that the precharge relay
83 is welded in Process P52. In a case where the precharge
relay 83 is determined as being welded, the discharge is
stopped by the discharge controller 104 (Process P80).
In a case where the C voltage V < Vth3 is satisfied
("Yes" in Process P51), Process P90 and subsequent processes
illustrated in FIG. 18 are performed. For example, the

determination of the abnormality of the precharge resistor R1
(Processes P110 and P180) and the determination of therwelding
of the positive-side main relay 81 (Processes P140 and P170)
are performed. Here, the voltage threshold Vth3 satisfies "Vth3
< Vth2 < Vthl".
According to the third embodiment described above, the
welding of the precharge relay 83 can be detected more, quickly
than that of each of the aforementioned embodiments.
(Fourth Embodiment)
FIGS. 19 and 20 illustrate an example of the flow of a
relay welding diagnosis according to a fourth embodiment. The
flowchart illustrated in FIGS. 19 and 20 is different from the
flowchart according to the first embodiment illustrated in FIGS.
12 and 13 in that the discharge current is controlled to
different current values in Sequences #2 and #5. The control of
the discharge current may be performed by the discharge
controller 104.
The discharge controller 104 according to this embodiment
is an example of a discharge current amount controller
configured to control the amount of electric charge accumulated
in the capacitor C or the electric charge supplied from, the LiB
50 during the electric charge is discharged through the
inverter 30 and the three-phase motor 40, for each sequence.
For example, in Sequence #2, after the negative-side main
relay 82 is turned off (Process P20), discharge with 10 ampere
(A) is started (Pr ocess P30a). On the other hand, in Sequence
#5, after the C voltage V is determined as being below the
voltage threshold Vth6 ("Yes" in Process P140), the discharge
with 10A is stopped (Process P141), and discharge with 15 A is
started (Process P142). Accordingly, as illustrated in FIG. 21,
a discharge current increases to a value higher than that of
the periods corresponding to Sequences #2 to #4.
As described above, by differentiating (changing) the

discharge current, as illustrated in FIG. 21, there is a.
difference between C voltages of periods corresponding to
Sequences #3 and #5. The determiner 102 can distinctively
determine an abnormality of the precharge resistor Rl and an
abnormality of the discharge based on the voltage difference.
For this, in a case where the C voltage V does not
satisfy "Vth4 < V < Vth5" in process P110 (Sequence #3)
illustrated in FIG. 19, the determiner 102 according to the
fourth embodiment does not determine an abnormality of the
resistor R2 in this stage but sets a "flag 1" to "On" (Process
P180a). For example, "flag 1" is stored in the aforementioned
memory 103.
Then, as illustrated in FIG. 20, after it is determined
whether the C voltage V satisfies Vth8 < V < Vth9 in the
subsequent Sequence #5 (Process P200a), the determiner 102
checks whether or not the "flag 1" is set to "On" (Processes
P201 and P261). Here, voltage values Vth8 and Vth9, for example,
satisfy "Vth8 < Vth9 < Vth4 < Vth5". As a non-limited example,
in a case where the battery voltage V1 is 300 V, Vth8 and Vth9
may be set to 252 V and 267 V, respectively.
In a case where the C voltage V does not satisfy "Vth8 <
V < Vth9", and the "flag 1" is set to "On" ( "No" in Process
P200a and "Yes" in Process P261), the determiner 102 determines
that there is an abnormality of the precharge resistor Rl
(Process P263).
On the other hand, in a case where the C voltage V does
not satisfy "Vth8 < V < Vth9", and the "flag 1" is set to "Off"
( "No" in Process P200a and "No" in Process P261), the
determiner 102 determines that there is an abnormality of the
discharge (Process P262). Further, in a case where the C
voltage V satisfies "Vth8 < V < Vth9", and the "flag 1" is set
to "On" ( "Yes" in Process P200a and "Yes" in Process P261),
the determiner 102 determines that there is an abnormality of

the discharge (Process P262).
As described above, according to the fourth embodiment,
the amount of the discharge current during the discharge period
is changed (differentiated). Thus, the determiner 102.'can
distinctively detect an abnormality of the precharge resistor
R1 and an abnormality of the discharge based on a change in the
C voltage between Sequences #3 and #5 in which current amounts
are controlled to be mutually-different.
(Fifth Embodiment)
FIGS. 22 and 23 illustrate an example of the flow of a
relay welding diagnosis according to a fifth embodiment. The
flowchart illustrated in FIG. 22 is different from the
flowchart according to the fourth embodiment illustrated in FIG.
19 in that Processes P53 and P54 are added. Further, the
flowchart illustrated in FIG. 23 is different from the
flowchart according to the fourth embodiment illustrated in FIG.
20 in that Processes P264 and P265 are added.
As illustrated in FIG. 22, in Process P53, in a case
where the C voltage V is determined as being below the voltage
threshold Vth2 ("Yes" in Process P50), the determiner 102
further determines whether the C voltage V drops to a voltage
according to the resistance value Rdis acquired by simulating
the discharge as a resistor and the capacitance value of the
capacitor C. For example, the determiner 102 determines whether
or not the C voltage V satisfies "VthlO < V < Vth11". Here,
voltage thresholds Vth10 and Vthll, for example, may be set
based on the following Equation (2) in consideration of the
capacitance of the capacitor C, the resistance value Rdis, and a
variation in the C voltage V. As a non-limited example, in a
case where the battery voltage V1 is 300 V, VthlO and Vthll may
be set to 230 V and 250 V, respectively.
V = Vl*[exp{-0.8/(C-Rdis) }] ... (2)
In Equation (2), V1 represents the battery voltage of the

Lib 50, and C represents the capacitance of the capacitor C.
As a result of the above-described determination, in a
case where "VthlO < V < Vthll" is satisfied (the C voltage V
does not drop into a predetermined voltage range during
discharge) ("No" in Process P53), the determiner 102 sets a
"flag 2" to "On" (Process P54). The "flag 2" is stored in, for
example, the memory 103.
On the other hand, as the result of the above-described
determination, in a case where "VthlO < V < Vthll" is satisfied
("Yes" in Process P53), the VCU 10, similar to the fourth
embodiment, performs Process P90 and subsequent processes.
Next, as illustrated in FIG. 23, in Process P264, the
determiner 102 determines whether or not the "flag 2" is set to
"On". This determination is made in a case where the "flag 1"
is set to "Off" (in the case of "No" in Process P201).
As a result of the determination made in Process P264, in
a case where the "flag 2" is set to "On" (in the case of "Yes"),
the determiner 102 determines that there is an abnormality of
the capacitor C (Process P265). On the other hand, in a case
where the "flag 2" is set to "Off" ("No" in Process P264),
Processes P210, P22, P230, P240, P250 and P270 described above
are performed.
As described above, according to the fifth embodiment,
the same advantages as those of the fourth embodiment can be
achieved, and additionally, by determining whether or not the C
voltage satisfies "Vth10 < V < Vthll" during the discharge, a
discharge abnormality and an abnormality of the capacitor C can
be distinctively detected. Accordingly, an abnormality of the
precharge resistor R1, an abnormality of the capacitor C, and a
discharge abnormality can be detected individually.
According to the technology described above, an
abnormality of the resistor of the relay circuit can be
detected quickly or rapidly.

(Others)
The voltage thresholds used in each of the aforementioned
embodiments may be determined in comprehensive consideration of
the battery voltage V1 of the LiB 50, variations of components
such as the resistor and the capacitor, a determination time,
switching control of the IGBT, and the like. The voltage
thresholds may be determined (set) as absolute values as
described in each embodiment and may also be determined using a
voltage value before the determination such as the battery
voltage V1 x RdiS/ (Rdis + R1) ±5% (variation tolerance).
Further, in each of the embodiments described above, all
of the relay controller 101, the determiner 102, the memory 103,
and the discharge controller 104 are provided in the VCU 10.
However, for example, a part of or all of the units 101 to 104
may be provided in the MCU 20. For example, by providing the
relay controller 101 and the discharge controller 104 into the
MCU 20, the communication amount using the SPI communication
between the VCU 10 and the MCU 20, which is made during the
discharge period or at the time of controlling the amount of
the discharge current, can be suppressed.
Furthermore, in each of the embodiments described above,
the motor driving system 1 (the diagnosis apparatus and the
diagnosis method for a relay circuit) is applied to a vehicle
such as an EV or a HEV, however; the motor driving system 1 may
be generally applied to other ridable machines such as a train
and a ship.

We Claim:
What is claimed is:
1. A diagnosis apparatus for a relay circuit, the relay circuit
comprising:
a load circuit supplied with a direct-current (DC)
voltage from a direct-current (DC) power supply;
a capacitor connected to both ends of the load circuit;
a first main relay provided for a power supply line
between a positive terminal of the DC power supply and one end
of the load circuit;
a second main relay provided for a power supply line
between a negative terminal of the DC power supply and the
other end of the load circuit;
a series circuit of a first resistor and a precharge
relay that are provided in parallel with the second main relay;
and
a second resistor connected to both ends of the load
circuit,
the diagnosis apparatus comprising:
a voltage sensor configured to detect a both-end voltage
of the capacitor;
a relay controller configured to perform an on-off
control on each of the relays in accordance with a
predetermined sequence; and
a determiner configured to detect an abnormality of the
first resistor based on the voltage detected by the voltage
sensor and an equivalent resistance value representing a
discharge process in a sequence including the discharge process,
the discharge process being performed by the relay controller
to turn on both of the first main relay and the precharge relay
and turn off the second main relay to apply a reactive current
with an amount indicated by a value stored in a memory to the

load circuit.
2. The diagnosis apparatus according to claim 1, wherein the
determiner determines whether any one of the relays is welded
based on a state change of the both-end voltage in each of
sequences performed by the relay controller, the sequences
comprising:
a sequence turning off the second main relay after a
sequence turning on both of the main relays and turning off the
precharge relay;
a sequence turning off the first main relay after turning
on both of the precharge relay and the first main relay and
turning off the second main relay; and
a sequence turning off the precharge relay after turning
on both of the precharge relay and the first main relay and
turning off the second main relay.
3. The diagnosis apparatus according to claim 1, wherein the
determiner determines an abnormality of the first resistor in
response to an out-of-range detection of the both-end voltage
from a predetermined voltage range during the sequence
performed by the relay controller to turn on both of the
precharge relay and the first main relay and turn off the
second main relay.
4. The diagnosis apparatus according to claim 1, further
comprising a discharge period controller configured to control
a period during which electric charge accumulated in the
capacitor or electric charge supplied from the DC power supply
is discharged through the load circuit for each sequence.
5. The diagnosis apparatus according to claim 1, further
comprising a discharge current amount controller configured to

control the amount of discharge of electric charge accumulated
in the capacitor or electric charge supplied from the DC power
supply through the load circuits for each sequence,
wherein the determiner distinguishes abnormalities of the
first resistance and the discharge based on a change of the
both-end voltage between sequences controlled to mutually-
different discharge current amounts by the discharge current
amount controller.
6. The diagnosis apparatus according to claim 5, wherein the
determiner determines whether or not the both-end voltage drops
to a voltage according to a resistance value numerically-
modeling the discharge as a resistance and the capacitance
value of the capacitor during the discharge to detect an
abnormality of a capacitance value of the capacitor.
7. A method of diagnosing a relay circuit, the relay circuit
comprising: a load circuit supplied with a direct-current (DC)
voltage from a direct-current (DC) power supply; a capacitor
connected to both ends of the load circuit; a first main relay
provided for a power supply line between a positive terminal of
the DC power supply and one end of the load circuit; a second
main relay provided for a power supply line between a negative
terminal of the DC power supply and the other end of the load
circuit; a series circuit of a first resistor and a precharge
relay that are provided in parallel with the second main relay;
and a second resistor connected to both ends of the load
circuit, the method comprising:
performing a discharge process to turn on both of the
first main relay and the precharge relay and turn off the
second main relay to apply a reactive current with an amount
indicated by a value stored in a memory to the load circuit;
and

detecting, in the discharge process, an abnormality of
the first resistor based on a both-end voltage of the capacitor
detected by a voltage sensor and an equivalent resistance value
representing the discharge process.

ABSTRACT

An example of a relay circuit includes: a capacitor
connecting both ends of a load circuit; first and second main
relays disposed in power supply lines between a direct-current
power supply and the load circuit; a series circuit configured
by a first resistor and a precharge relay disposed in parallel
with the first main relay; and a second resistor connecting
both ends of the load circuit. A discharge process is performed
in which both the first main relay and the precharge relay are
turned on, the second main relay is turned off, and a reactive
current is caused to flow through the load circuit. In this
discharge process, an abnormality of the first resistor is
detected based on a both-end voltage of the capacitor detected
by a voltage sensor and a resistance value that is an
equivalent representation of the discharge process.