Field of the invention:
[0001] The present invention relates to hybrid vehicle architecture and
particularly relates to operating strategy for a series hybrid vehicle.
Background of the invention:
[0002] In existing conventional series hybrid system, the generated energy is
used primarily to charge battery. So lots of energy conversion inefficiency is
added to the energy conversion chain i.e. from generated electrical energy to
chemical energy for battery charging and then to electrical energy to power the
inverter which in turn converts into mechanical energy by the motor. As per the
conventional series hybrid architecture, two modes of operation can be achieved,
powering the motor only from the battery and charging the battery from the
generator.
[0003] Further, in conventional series hybrid electric vehicles, an on-board
generator is used to charge the battery when the energy of the battery is depleted.
The issue is when generator power is used to charge battery and later used it to
drive the motor, various stages of energy conversion (electrical to chemical to
electrical to mechanical) happens in the process and associated inefficiency
creeps into the energy chain.
[0004] In order to charge the battery, the benefit of operating the engine in
best efficiency region is partially lost in the process.
[0005] According to a patent literature 0011/DEL/2013, a vehicle with hybrid
power system is disclosed. A motorcycle having at least one seat and at least two
wheels, an internal combustion engine, a generator, and a rechargeable battery
configured to be recharged by the internal combustion engine or generator, an
electric motor electrically connected to the rechargeable battery and configured
to drive at least one of a plurality of wheels of the vehicle, and an electronic
controller configured to start the internal combustion engine based upon a
monitored condition of the rechargeable battery.
[0006] Hence, there is a need for a device and a method to overcome the
limitations or inefficiencies in the conventional hybrid vehicles.

Brief description of the accompanying drawings:
[0007] An embodiment of the disclosure is described with reference to the
following accompanying drawing,
[0008] Fig. 1 illustrates a block diagram of a series hybrid vehicle with a
Power Distribution Unit (PDU) operating in a first mode, according to an
embodiment of the present invention;
[0009] Fig. 2 illustrates the series hybrid vehicle with the PDU operating in a
second mode, according to an embodiment of the present invention;
[0010] Fig. 3 illustrates the series hybrid vehicle with the PDU operating in a
third mode, according to an embodiment of the present invention;
[0011] Fig. 4 illustrates the series hybrid vehicle with the PDU operating in a
fourth mode, according to an embodiment of the present invention;
[0012] Fig. 5 illustrates the series hybrid vehicle with the PDU operating in a
fifth mode, according to an embodiment of the present invention;
[0013] Fig. 6 illustrates a method for controlling power flow in a series hybrid
vehicle, according to an embodiment of the present invention, and
[0014] Fig. 7 illustrates a process flow diagram, according to an embodiment
of the present invention.
Detailed description of the embodiments:
[0015] Fig. 1 illustrates a block diagram of a series hybrid vehicle with a
Power Distribution Unit (PDU) operating in a first mode, according to an embodiment of the present invention. The vehicle comprises an engine 102 coupled to a generator 104. The generator 104 is electrically connected to a battery 106. The generator 104 is further connected to a traction motor 116 through an inverter 114. The traction motor 116 is coupled to at least one wheel 118 of the vehicle. The PDU 110 is electrically connects/ connected to the generator 104, the battery 106 and the traction motor 116. The PDU 110 comprises a converter circuit 108 electrically connected to each of the generator 104, the battery 106 and the traction motor 116 through respective switches, i.e.

a first switch 120 between the generator 104 and the PDU 110, a second switch 130 between the battery 106 and the PDU 110 and a third switch 140 between the traction motor 116 and the PDU 110. The PDU 110 further comprises an Electronic Control Unit (ECU) 112 in communication with the switches 120, 130, 140 to selectively control power flow between the generator 104, the battery 106 and the traction motor 116.
[0016] The traction motor 116 is a type of electric motor, which produce
rotational torque and are used to drive wheels 118 in electric or hybrid vehicles with or without transmission gears. The traction motor 116 comprises but not limited to brushless electric motor such as a Brushless DC motor (BLDC) and a Permanent Magnet Synchronous Motor (PMSM). The traction motor 116 requires some form of Alternating Current to operate.
[0017] In another embodiment, the PDU 110 only comprises the converter
circuit 108. The ECU 112 is externally connected to the PDU 110 through the
switches 120, 130, 140. The switches 120, 130, 140 are either electronic switches
such as any transistor based switches i.e. MOSFETs, IGBTs or are
relays/contactors. The engine 102 is always operated at best or optimal Brake
Specific Fuel Consumption (BSFC) regions. The inverter 114 between the
traction motor 116 and the PDU 110 converts a Direct Current (DC) signal to
Alternating Current (AC) signal. Since the traction motor 116, such as BLDC or
the PMSM, does not have mechanical commutator or slip ring to convert DC
current to AC current, the traction motor 116 needs an external switching device.
The invertor 114 is the external switching device which converts DC current to
AC current of required frequency and amplitude, there by controlling speed and
torque of the traction motor 116. The present invention is equally applicable for
other variant of traction motors, and must not be understood in a limiting sense.
[0018] The first mode of PDU 110 comprises driving the traction motor 116
by generator 104 bypassing the battery 106. The ECU 112 determines the power demand by the wheel 118 considering current wheel speed and torque demand through torque estimation. Based on vehicle speed at that instance of time and change in throttle demand, the current drawn by the traction motor 116, the ECU

112 determines the mechanical torque being produced. Using the torque and the present speed the ECU 112 determines the power at that instance of time. Further, a change in throttle demand is mapped to change in torque and thereby change in power. The ECU 112 also determines a power range of the generator 104, i.e. comprising a minimum and a maximum power generated by the generator 104 when the engine 102 is operating in best BSFC regions.
[0019] When a power requirement of the traction motor 116 is within the
power range of the generator 104, the ECU 112 isolates the battery 106 from the PDU 110 and connects the generator 104 to the converter circuit 108 to directly drive the traction motor 116. The ECU 112 closes the first switch 120 and the third switch 140, and opens the switch 130.When the demanded wheel power is in the power range of minimum and maximum generated power in the best engine operating regions, the traction motor 116 is directly powered from the output of the generator 104. Thereby, the traction motor 116 is getting powered by bypassing the battery 106. By doing this, the energy is retained in the battery 106 and energy conversion inefficiency by charging back the battery 106 is reduced.
[0020] In the present invention, the output power of the generator 104 and the
output of the battery 106 are coupled to the PDU 110 to deliver the power to the traction motor 116. The PDU 110 is a PWM based switching circuit or it may be a bidirectional/ unidirectional buck-boost DC-DC convertor or a simple DC bus bars connected to route the power to the loads i.e. traction motor 116 via the inverter 114, which powers the wheel 118. The bi-directional power flow is required between the battery 106 and the PDU 110 for charging and discharging. The power distribution is achieved by controlling the switches 120, 130, 140 by the ECU 112. A dashed line 150 represents the flow of power from the generator 104 directly to the traction motor 116.
[0021] Fig. 2 illustrates the series hybrid vehicle with the PDU operating in a
second mode, according to an embodiment of the present invention. The second mode comprises the generator 104 powering the traction motor 116 and also charging the battery 106. The second mode may be referred to as power

distribution mode. The ECU 112 connects the generator 104 to the converter circuit 108 to drive the traction motor 116 and charge the battery 106, when a terminal voltage of the battery 106 is less than a generated voltage of the generator 104, and a power requirement of the traction motor 116 is less than minimum power generated (of the power range), by the generator 104. The operation of the engine 102 could get into inefficient region outside the optimal BSFC region. To prevent inefficient operation, the engine 102 is operated at best BSFC regions and the generator 104 is loaded to higher power point thereby distributing the generated power for charging battery 106 and providing power to the traction motor 116.
[0022] When demanded wheel power is less than the minimum power
generated by the generator 104 in the power range, the generator 104 is loaded with battery 106 apart from powering the traction motor 116. The power from the generator 104 is distributed between charging the battery 106 and powering the traction motor 116. The ECU 112 closes all the switch 120, 130 and 140. The terminal voltage of the battery 106 is regulated such that the generator 104 charges the battery 106 with safe charging current. Two dashed line 250 and 260 represents the power flow from generator 104 to the traction motor 116, and to the battery 106, respectively.
[0023] Fig. 3 illustrates the series hybrid vehicle with the PDU operating in a
third mode, according to an embodiment of the present invention. The third mode comprises the generator 104 and the battery 106 powering the traction motor 116. The third mode may also referred to as power distribution mode or load sharing mode. The ECU 112 connects the generator 104 and the battery 106 to the converter circuit 108 to drive the traction motor 116, when a power requirement of the traction motor 116 is more than any one of, the maximum power generated in the power range by the generator 104 and the power/energy available in the battery 106.
[0024] When demanded wheel power is greater than maximum power
generated by the generator 104 in the power range, the required additional power is provided from the battery 106. Hence, the power is distributed to wheels 118

from two different power sources, i.e. the generator 104 and the battery 106. The terminal voltage of the battery 106 and the generator 104 is regulated to same voltage level of common bus bar of the traction motor 116. The ECU 112 closes all the switches 120, 130 and 140.
[0025] The voltages are regulated in order to maintain the same voltage points,
when the generated voltage is lesser than the battery voltage. By this combination, the requirement of larger capacity battery 106 is be eliminated. The dashed lines 350 and 360 depicts the power flow from the generator 104 and the battery 106, respectively, to the traction motor 116.
[0026] Fig. 4 illustrates the series hybrid vehicle with the PDU operating in a
fourth mode, according to an embodiment of the present invention. The fourth
mode comprises the battery 106 alone powering the traction motor 116. When
energy of the battery 106 is full and the demanded wheel power is within the
discharge power of the battery 106 or when the fuel in the vehicle is completely
exhausted, the traction motor 116 is completely powered from the battery 106.
During fourth mode, the engine 102 is not operational, hence no power is
generated by the generator 104 even though the generator 104 is connected. The
ECU 112 opens the first switch 120, and closes the second switch 130 and the
third switch 140. The fourth mode is achievable with / without the PDU 110.
[0027] In other words, if the demand wheel power is less than the minimum
power generated by the generator 104 in the power range where engine operation is inefficient BSFC region and the battery 106 cannot be charged further, the demanded wheel power is completely provided by the battery 106 until a level where it can be charged again. The dashed line 450 depicts power flow from the battery 106 to the traction motor 116.
[0028] Fig. 5 illustrates the series hybrid vehicle with the PDU operating in a
fifth mode, according to an embodiment of the present invention. The fifth mode comprises the generator 104 charging the battery 106 alone. When the battery 106 is depleted to a threshold and the required wheel power demand is zero, the generator 104 is driven by the engine 102 to charge the battery 106 to a required level. The ECU 112 opens the third switch 140, and closes the first switch 120

and the second switch 130. In the fifth mode, the electric powertrain i.e. traction
motor 116 is isolated i.e. vehicle is stationary. Similar to the fourth mode, the
fifth mode is also achievable with / without the PDU 110. The dashed line 550
shows the power flow from the generator 104 to the battery 106 for charging.
[0029] In all the above modes explained from the Fig. 1 through Fig. 5,
whenever required, the converter circuit 108 regulates voltage to maintain same voltage between the generator 104, the battery 106 and the traction motor 116. The engine 102 is coupled to the generator 104 is the prime source of power supply and the battery 106 is used as a support. The battery 106 acts as a load and as a power source based on the conditions. The ECU 112 is shown connected to switches 120, 130, 140 through dotted lines. In an embodiment, the switches 120, 130, 140 are either internally connected to the PDU 110 or external to the PDU 110.
[0030] Fig. 6 illustrates a method for controlling power flow in a series hybrid
vehicle, according to an embodiment of the present invention. The method comprising the steps of, a step 602 comprising operating the engine 102 coupled to the generator 104 at best Brake Specific Fuel Consumption (BSFC) regions. The step 602 further comprises determining terminal voltage of the battery 106 and the voltage generated by the generator 104. A step 604 comprises determining power requirement of a traction motor 116. A step 606 comprises determining a power range comprising minimum and maximum power generated by the generator 104 when the engine 102 is operated at best BSFC regions. A step 608 comprises controlling power flow between the battery 106, the generator 104 and the traction motor 116 in a selective manner. The step 608 moves to step 610 when the power requirement of the traction motor 116 is within the power range of the generator 104. The step 610 refers to first mode comprising supplying power from the generator 104 to drive the traction motor 116.
[0031] The step 608 moves to a step 612 when the terminal voltage of the
battery 106 is less than the terminal voltage of the generated voltage of the generator 104, and the power requirement of the traction motor 116 is less than

the minimum power generated by the generator 104. The step 614 refers to the second mode comprises supplying power from the generator 104 to drive the traction motor 116 and to charge the battery 106.
[0032] The step 608 proceeds to a step 614 when the power requirement of
the traction motor 116 is more than any one of the maximum power generated by the generator 104 and the power available in the battery 106, and the terminal voltage of the battery 106 is less than the generated voltage of the generator 104. The step 614 refers to the third mode comprising supplying power from the generator 104 and the battery 106 to drive the traction motor 116.
[0033] The step 608 moves to a step 616 when the demand wheel power is
less than the minimum power generated by the generator 104 in the power range, and the battery 106 cannot be charged further. The step 616 is referred to as the fourth mode comprising supplying the demanded wheel power completely from the battery 106 until a level where the battery 106 needs to be charged again during efficient conditions of operating the engine 102.
[0034] The step 608 proceeds to a step 618 when the battery 106 is depleted
to a threshold and the required wheel power demand is zero, the generator 104 is driven by the engine 102 to charge the battery 106 to a required level. The step 618 is referred to as the fifth mode comprising only charging the battery 106 where the traction motor 116 is isolated.
[0035] Fig. 7 illustrates a process flow diagram, according to an embodiment
of the present invention. A block 702 represents the wheel power demand
determined by the ECU 112. A block 704 represents determination of the power
range of the generator 104, i.e. the minimum power generated and the maximum
power generated when the engine 102 is operated in best BSFC regions.
[0036] A step 706 is performed, if the wheel power demand is within the
power range. The ECU 112 isolates the battery 106 from the PDU 110. The power generated by the generator 104 drives the traction motor 116 through the inverter 114.
[0037] A step 708 is performed, if the power requirement from the traction
motor 116 is less than the minimum power generated by the generator 104 as in

the power range. So, instead of operating the engine 102 at low efficiency or outside the best BSFC regions, the generator 104 is loaded with the battery 106 apart from the traction motor 116. The generator 104 charges the battery 106 and also drives the traction motor 116. In another embodiment, instead of battery 106, other in-vehicle electrical loads are powered. In yet another embodiment, along with the battery, the in-vehicle electrical loads are supplied with generated power. The in-vehicle electrical loads comprises, wiper, infotainment system, radio, blower, etc.
[0038] A step 710 is performed, if the power demand from the traction motor
116 is more than the maximum power generated by the generator 104 during the engine operation in best BSFC regions. The generator 104 is supported by the battery 106 to meet the power requirement of the traction motor 116. Apart from the traction motor 116, other in-vehicle electrical loads/accessories may increase the power demand.
[0039] In present invention, a battery bypassing technique is proposed with /
without the PDU 110 which effectively bypasses major portion of demanded wheel energy from battery 106 by directly providing electrical energy from the generator 104 and distribute the power between the loads. The engine 102 is still operated in best efficiency region. The present invention enables 80% or more of the required wheel power demand to be provided by engine 102 coupled generator 104. By operating the engine 102 in best efficiency region thereby improving overall fuel economy and reducing emissions. Thereby losses involved in energy conversion is eliminated. The intermediate inefficient energy conversion chain i.e. electrical to chemical then to electrical energy is completely eliminated. The present invention avoid oversizing of the battery pack there by reducing the overall cost of the vehicle. Thereby enabling to reduce the size of the battery pack (capacity of the battery 106) and improve the energy chain efficiency.
[0040] It should be understood that embodiments explained in the description
above are only illustrative and do not limit the scope of this invention. Many such embodiments and other modifications and changes in the embodiment

explained in the description are envisaged. The scope of the invention is only limited by the scope of the claims.
Claims:We claim:
1. A Power Distribution Unit (PDU) (110) for a series hybrid vehicle, said vehicle comprising an engine (102) coupled to a generator (104), said generator (104) is connected to a battery (106), said generator (104) is further connected to a traction motor (116) which is coupled to at least one wheel (118), said PDU (110) electrically connected to said generator (104), said battery (106) and said traction motor (116), and comprises:
a converter circuit (108) electrically connected to each of said generator (104), said battery (106) and said traction motor (116) through respective switches (120, 130, 140), and
an Electronic Control Unit (ECU) (112) in communication with said switches (120, 130, 140) to selectively control power flow between said generator (104), said battery (106) and said traction motor (116).

2. The PDU (110) as claimed in claim 1, wherein said ECU (112) determines a power range of said generator (104) comprising a minimum and maximum power generated when said engine (102) is operated at best Brake Specific Fuel Consumption (BSFC) regions.

3. The PDU (110) as claimed in claim 2, wherein said ECU (112) isolates said battery (106) and connects said generator (104) to said converter circuit (108) to directly drive said traction motor (116), when a power requirement of said traction motor (116) is within said power range.

4. The PDU (110) as claimed in claim 2, wherein said ECU (112) connects said generator (104) to said converter circuit (108) to drive said traction motor (116) and charge said battery (106), when
a. a terminal voltage of said battery (106) is less than a generated voltage of said generator (104), and
b. a power requirement of said traction motor (116) is less than minimum power generated by said generator (104).

5. The PDU (110) as claimed in claim 2, wherein said ECU (112) connects said generator (104) and said battery (106) to said converter circuit (108) to drive said traction motor (116), when
a power requirement of said traction motor (116) is more than any one of said maximum power generated by said generator (104) and power available in said battery (106).

6. A method for controlling power flow in a series hybrid vehicle, said method comprising the steps of:
determining a terminal voltage of a battery (106) and a voltage generated by said generator (104);
determining power requirement of a traction motor (116);
determining a power range comprising minimum power and maximum power generated by said generator (104) when said engine (102) is operated at best BSFC, and
selectively controlling power flow between said battery (106), said generator (104) and said traction motor (116).

7. The method as claimed in claim 6, wherein controlling power flow comprises supplying power from said generator (104) to drive said traction motor (116), when
said power requirement of said traction motor (116) is within said power range by said generator (104);

8. The method as claimed in claim 6, wherein controlling power flow comprises supplying power from said generator (104) to drive said traction motor (116) and charge said battery (106), when
said terminal voltage of said battery (106) is less than said generated voltage of said generator (104), and
said power requirement of said traction motor (116) is less than said minimum power generated by said generator (104);

9. The method as claimed in claim 6, wherein controlling power flow comprises supplying power from said generator (104) and said battery (106) to drive said traction motor (116), when
said power requirement of said traction motor (116) is more than any one of said maximum power generated by the generator (104) and power available in said battery (106), and

10. The method as claimed in claim 6, wherein controlling of said power flow is performed by an Electronic Control Unit (ECU) (112) using switches (120, 130, 140).
, Description:Field of the invention:
[0001] The present invention relates to hybrid vehicle architecture and particularly relates to operating strategy for a series hybrid vehicle.

Background of the invention:
[0002] In existing conventional series hybrid system, the generated energy is used primarily to charge battery. So lots of energy conversion inefficiency is added to the energy conversion chain i.e. from generated electrical energy to chemical energy for battery charging and then to electrical energy to power the inverter which in turn converts into mechanical energy by the motor. As per the conventional series hybrid architecture, two modes of operation can be achieved, powering the motor only from the battery and charging the battery from the generator.
[0003] Further, in conventional series hybrid electric vehicles, an on-board generator is used to charge the battery when the energy of the battery is depleted. The issue is when generator power is used to charge battery and later used it to drive the motor, various stages of energy conversion (electrical to chemical to electrical to mechanical) happens in the process and associated inefficiency creeps into the energy chain.
[0004] In order to charge the battery, the benefit of operating the engine in best efficiency region is partially lost in the process.
[0005] According to a patent literature 0011/DEL/2013, a vehicle with hybrid power system is disclosed. A motorcycle having at least one seat and at least two wheels, an internal combustion engine, a generator, and a rechargeable battery configured to be recharged by the internal combustion engine or generator, an electric motor electrically connected to the rechargeable battery and configured to drive at least one of a plurality of wheels of the vehicle, and an electronic controller configured to start the internal combustion engine based upon a monitored condition of the rechargeable battery.
[0006] Hence, there is a need for a device and a method to overcome the limitations or inefficiencies in the conventional hybrid vehicles.

Brief description of the accompanying drawings:
[0007] An embodiment of the disclosure is described with reference to the following accompanying drawing,
[0008] Fig. 1 illustrates a block diagram of a series hybrid vehicle with a Power Distribution Unit (PDU) operating in a first mode, according to an embodiment of the present invention;
[0009] Fig. 2 illustrates the series hybrid vehicle with the PDU operating in a second mode, according to an embodiment of the present invention;
[0010] Fig. 3 illustrates the series hybrid vehicle with the PDU operating in a third mode, according to an embodiment of the present invention;
[0011] Fig. 4 illustrates the series hybrid vehicle with the PDU operating in a fourth mode, according to an embodiment of the present invention;
[0012] Fig. 5 illustrates the series hybrid vehicle with the PDU operating in a fifth mode, according to an embodiment of the present invention;
[0013] Fig. 6 illustrates a method for controlling power flow in a series hybrid vehicle, according to an embodiment of the present invention, and
[0014] Fig. 7 illustrates a process flow diagram, according to an embodiment of the present invention.

Detailed description of the embodiments:
[0015] Fig. 1 illustrates a block diagram of a series hybrid vehicle with a Power Distribution Unit (PDU) operating in a first mode, according to an embodiment of the present invention. The vehicle comprises an engine 102 coupled to a generator 104. The generator 104 is electrically connected to a battery 106. The generator 104 is further connected to a traction motor 116 through an inverter 114. The traction motor 116 is coupled to at least one wheel 118 of the vehicle. The PDU 110 is electrically connects/ connected to the generator 104, the battery 106 and the traction motor 116. The PDU 110 comprises a converter circuit 108 electrically connected to each of the generator 104, the battery 106 and the traction motor 116 through respective switches, i.e. a first switch 120 between the generator 104 and the PDU 110, a second switch 130 between the battery 106 and the PDU 110 and a third switch 140 between the traction motor 116 and the PDU 110. The PDU 110 further comprises an Electronic Control Unit (ECU) 112 in communication with the switches 120, 130, 140 to selectively control power flow between the generator 104, the battery 106 and the traction motor 116.
[0016] The traction motor 116 is a type of electric motor, which produce rotational torque and are used to drive wheels 118 in electric or hybrid vehicles with or without transmission gears. The traction motor 116 comprises but not limited to brushless electric motor such as a Brushless DC motor (BLDC) and a Permanent Magnet Synchronous Motor (PMSM). The traction motor 116 requires some form of Alternating Current to operate.
[0017] In another embodiment, the PDU 110 only comprises the converter circuit 108. The ECU 112 is externally connected to the PDU 110 through the switches 120, 130, 140. The switches 120, 130, 140 are either electronic switches such as any transistor based switches i.e. MOSFETs, IGBTs or are relays/contactors. The engine 102 is always operated at best or optimal Brake Specific Fuel Consumption (BSFC) regions. The inverter 114 between the traction motor 116 and the PDU 110 converts a Direct Current (DC) signal to Alternating Current (AC) signal. Since the traction motor 116, such as BLDC or the PMSM, does not have mechanical commutator or slip ring to convert DC current to AC current, the traction motor 116 needs an external switching device. The invertor 114 is the external switching device which converts DC current to AC current of required frequency and amplitude, there by controlling speed and torque of the traction motor 116. The present invention is equally applicable for other variant of traction motors, and must not be understood in a limiting sense.
[0018] The first mode of PDU 110 comprises driving the traction motor 116 by generator 104 bypassing the battery 106. The ECU 112 determines the power demand by the wheel 118 considering current wheel speed and torque demand through torque estimation. Based on vehicle speed at that instance of time and change in throttle demand, the current drawn by the traction motor 116, the ECU 112 determines the mechanical torque being produced. Using the torque and the present speed the ECU 112 determines the power at that instance of time. Further, a change in throttle demand is mapped to change in torque and thereby change in power. The ECU 112 also determines a power range of the generator 104, i.e. comprising a minimum and a maximum power generated by the generator 104 when the engine 102 is operating in best BSFC regions.
[0019] When a power requirement of the traction motor 116 is within the power range of the generator 104, the ECU 112 isolates the battery 106 from the PDU 110 and connects the generator 104 to the converter circuit 108 to directly drive the traction motor 116. The ECU 112 closes the first switch 120 and the third switch 140, and opens the switch 130.When the demanded wheel power is in the power range of minimum and maximum generated power in the best engine operating regions, the traction motor 116 is directly powered from the output of the generator 104. Thereby, the traction motor 116 is getting powered by bypassing the battery 106. By doing this, the energy is retained in the battery 106 and energy conversion inefficiency by charging back the battery 106 is reduced.
[0020] In the present invention, the output power of the generator 104 and the output of the battery 106 are coupled to the PDU 110 to deliver the power to the traction motor 116. The PDU 110 is a PWM based switching circuit or it may be a bidirectional/ unidirectional buck-boost DC-DC convertor or a simple DC bus bars connected to route the power to the loads i.e. traction motor 116 via the inverter 114, which powers the wheel 118. The bi-directional power flow is required between the battery 106 and the PDU 110 for charging and discharging. The power distribution is achieved by controlling the switches 120, 130, 140 by the ECU 112. A dashed line 150 represents the flow of power from the generator 104 directly to the traction motor 116.
[0021] Fig. 2 illustrates the series hybrid vehicle with the PDU operating in a second mode, according to an embodiment of the present invention. The second mode comprises the generator 104 powering the traction motor 116 and also charging the battery 106. The second mode may be referred to as power distribution mode. The ECU 112 connects the generator 104 to the converter circuit 108 to drive the traction motor 116 and charge the battery 106, when a terminal voltage of the battery 106 is less than a generated voltage of the generator 104, and a power requirement of the traction motor 116 is less than minimum power generated (of the power range), by the generator 104. The operation of the engine 102 could get into inefficient region outside the optimal BSFC region. To prevent inefficient operation, the engine 102 is operated at best BSFC regions and the generator 104 is loaded to higher power point thereby distributing the generated power for charging battery 106 and providing power to the traction motor 116.
[0022] When demanded wheel power is less than the minimum power generated by the generator 104 in the power range, the generator 104 is loaded with battery 106 apart from powering the traction motor 116. The power from the generator 104 is distributed between charging the battery 106 and powering the traction motor 116. The ECU 112 closes all the switch 120, 130 and 140. The terminal voltage of the battery 106 is regulated such that the generator 104 charges the battery 106 with safe charging current. Two dashed line 250 and 260 represents the power flow from generator 104 to the traction motor 116, and to the battery 106, respectively.
[0023] Fig. 3 illustrates the series hybrid vehicle with the PDU operating in a third mode, according to an embodiment of the present invention. The third mode comprises the generator 104 and the battery 106 powering the traction motor 116. The third mode may also referred to as power distribution mode or load sharing mode. The ECU 112 connects the generator 104 and the battery 106 to the converter circuit 108 to drive the traction motor 116, when a power requirement of the traction motor 116 is more than any one of, the maximum power generated in the power range by the generator 104 and the power/energy available in the battery 106.
[0024] When demanded wheel power is greater than maximum power generated by the generator 104 in the power range, the required additional power is provided from the battery 106. Hence, the power is distributed to wheels 118 from two different power sources, i.e. the generator 104 and the battery 106. The terminal voltage of the battery 106 and the generator 104 is regulated to same voltage level of common bus bar of the traction motor 116. The ECU 112 closes all the switches 120, 130 and 140.
[0025] The voltages are regulated in order to maintain the same voltage points, when the generated voltage is lesser than the battery voltage. By this combination, the requirement of larger capacity battery 106 is be eliminated. The dashed lines 350 and 360 depicts the power flow from the generator 104 and the battery 106, respectively, to the traction motor 116.
[0026] Fig. 4 illustrates the series hybrid vehicle with the PDU operating in a fourth mode, according to an embodiment of the present invention. The fourth mode comprises the battery 106 alone powering the traction motor 116. When energy of the battery 106 is full and the demanded wheel power is within the discharge power of the battery 106 or when the fuel in the vehicle is completely exhausted, the traction motor 116 is completely powered from the battery 106. During fourth mode, the engine 102 is not operational, hence no power is generated by the generator 104 even though the generator 104 is connected. The ECU 112 opens the first switch 120, and closes the second switch 130 and the third switch 140. The fourth mode is achievable with / without the PDU 110.
[0027] In other words, if the demand wheel power is less than the minimum power generated by the generator 104 in the power range where engine operation is inefficient BSFC region and the battery 106 cannot be charged further, the demanded wheel power is completely provided by the battery 106 until a level where it can be charged again. The dashed line 450 depicts power flow from the battery 106 to the traction motor 116.
[0028] Fig. 5 illustrates the series hybrid vehicle with the PDU operating in a fifth mode, according to an embodiment of the present invention. The fifth mode comprises the generator 104 charging the battery 106 alone. When the battery 106 is depleted to a threshold and the required wheel power demand is zero, the generator 104 is driven by the engine 102 to charge the battery 106 to a required level. The ECU 112 opens the third switch 140, and closes the first switch 120 and the second switch 130. In the fifth mode, the electric powertrain i.e. traction motor 116 is isolated i.e. vehicle is stationary. Similar to the fourth mode, the fifth mode is also achievable with / without the PDU 110. The dashed line 550 shows the power flow from the generator 104 to the battery 106 for charging.
[0029] In all the above modes explained from the Fig. 1 through Fig. 5, whenever required, the converter circuit 108 regulates voltage to maintain same voltage between the generator 104, the battery 106 and the traction motor 116. The engine 102 is coupled to the generator 104 is the prime source of power supply and the battery 106 is used as a support. The battery 106 acts as a load and as a power source based on the conditions. The ECU 112 is shown connected to switches 120, 130, 140 through dotted lines. In an embodiment, the switches 120, 130, 140 are either internally connected to the PDU 110 or external to the PDU 110.
[0030] Fig. 6 illustrates a method for controlling power flow in a series hybrid vehicle, according to an embodiment of the present invention. The method comprising the steps of, a step 602 comprising operating the engine 102 coupled to the generator 104 at best Brake Specific Fuel Consumption (BSFC) regions. The step 602 further comprises determining terminal voltage of the battery 106 and the voltage generated by the generator 104. A step 604 comprises determining power requirement of a traction motor 116. A step 606 comprises determining a power range comprising minimum and maximum power generated by the generator 104 when the engine 102 is operated at best BSFC regions. A step 608 comprises controlling power flow between the battery 106, the generator 104 and the traction motor 116 in a selective manner. The step 608 moves to step 610 when the power requirement of the traction motor 116 is within the power range of the generator 104. The step 610 refers to first mode comprising supplying power from the generator 104 to drive the traction motor 116.
[0031] The step 608 moves to a step 612 when the terminal voltage of the battery 106 is less than the terminal voltage of the generated voltage of the generator 104, and the power requirement of the traction motor 116 is less than the minimum power generated by the generator 104. The step 614 refers to the second mode comprises supplying power from the generator 104 to drive the traction motor 116 and to charge the battery 106.
[0032] The step 608 proceeds to a step 614 when the power requirement of the traction motor 116 is more than any one of the maximum power generated by the generator 104 and the power available in the battery 106, and the terminal voltage of the battery 106 is less than the generated voltage of the generator 104. The step 614 refers to the third mode comprising supplying power from the generator 104 and the battery 106 to drive the traction motor 116.
[0033] The step 608 moves to a step 616 when the demand wheel power is less than the minimum power generated by the generator 104 in the power range, and the battery 106 cannot be charged further. The step 616 is referred to as the fourth mode comprising supplying the demanded wheel power completely from the battery 106 until a level where the battery 106 needs to be charged again during efficient conditions of operating the engine 102.
[0034] The step 608 proceeds to a step 618 when the battery 106 is depleted to a threshold and the required wheel power demand is zero, the generator 104 is driven by the engine 102 to charge the battery 106 to a required level. The step 618 is referred to as the fifth mode comprising only charging the battery 106 where the traction motor 116 is isolated.
[0035] Fig. 7 illustrates a process flow diagram, according to an embodiment of the present invention. A block 702 represents the wheel power demand determined by the ECU 112. A block 704 represents determination of the power range of the generator 104, i.e. the minimum power generated and the maximum power generated when the engine 102 is operated in best BSFC regions.
[0036] A step 706 is performed, if the wheel power demand is within the power range. The ECU 112 isolates the battery 106 from the PDU 110. The power generated by the generator 104 drives the traction motor 116 through the inverter 114.
[0037] A step 708 is performed, if the power requirement from the traction motor 116 is less than the minimum power generated by the generator 104 as in the power range. So, instead of operating the engine 102 at low efficiency or outside the best BSFC regions, the generator 104 is loaded with the battery 106 apart from the traction motor 116. The generator 104 charges the battery 106 and also drives the traction motor 116. In another embodiment, instead of battery 106, other in-vehicle electrical loads are powered. In yet another embodiment, along with the battery, the in-vehicle electrical loads are supplied with generated power. The in-vehicle electrical loads comprises, wiper, infotainment system, radio, blower, etc.
[0038] A step 710 is performed, if the power demand from the traction motor 116 is more than the maximum power generated by the generator 104 during the engine operation in best BSFC regions. The generator 104 is supported by the battery 106 to meet the power requirement of the traction motor 116. Apart from the traction motor 116, other in-vehicle electrical loads/accessories may increase the power demand.
[0039] In present invention, a battery bypassing technique is proposed with / without the PDU 110 which effectively bypasses major portion of demanded wheel energy from battery 106 by directly providing electrical energy from the generator 104 and distribute the power between the loads. The engine 102 is still operated in best efficiency region. The present invention enables 80% or more of the required wheel power demand to be provided by engine 102 coupled generator 104. By operating the engine 102 in best efficiency region thereby improving overall fuel economy and reducing emissions. Thereby losses involved in energy conversion is eliminated. The intermediate inefficient energy conversion chain i.e. electrical to chemical then to electrical energy is completely eliminated. The present invention avoid oversizing of the battery pack there by reducing the overall cost of the vehicle. Thereby enabling to reduce the size of the battery pack (capacity of the battery 106) and improve the energy chain efficiency.
[0040] It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention. Many such embodiments and other modifications and changes in the embodiment explained in the description are envisaged. The scope of the invention is only limited by the scope of the claims.