FIELD OF THE INVENTION
The present invention relates to a digital three-phase secondary injection
simulation system for accurate testing and calibration of power electronics
control panels.
BACKGROUND OF THE INVENTION
In control and Instrumentation (C&I) field of technology, simulation of a current/
potential (CT/PT) transformer feedback of synchronous generator is required for
testing of Digital Automatic Voltage Regulator (DAVR) panels (for Generator
Controls) and other DCS panels. However, simulation of feedback from the
transformers with a rheostat has its limitations, mainly being a constant power
factor (PF). Hence, an Analog Secondary injection load device was introduced in
prior art simulators. Again, it was found that such devices use the input from
utility power, which fail to provide the desired stability, and hence there is no
repeatability of the test results. Moreover, due to use of various transformers in
their construction, the prior art load simulators are susceptible to frequent
breakdowns, and do not provide accurate results. One of the reasons could be
attributed to frequent defect developed in the carbon brushes due to internal
movement and repeated usage.
US Patent No. 4,158,808 teaches an apparatus for simulating large electrical
loads in alternating current systems incorporating power meters of the type
having separate voltage and current sensing inputs. The apparatus comprising: a
controlled current source operative to generate a selectively variable output
alternating current signal having a fixed phase angle; phase shift means
connected to receive said current signal and to generate a reference signal
having a phase angle which is selectively variable with respect to the phase

angle of said current signal; a controlled voltage source connected to receive
said phase reference signal and to generate a selectively variable output voltage
signal; current signal connector means for interconnecting said controlled current
source and the current sensing inputs of a power meter whereby said current
sensing inputs receive said current signal; and voltage signal connector means
for interconnecting said controlled voltage source and the voltage sensing inputs
of said power meter whereby said voltage sensing inputs receive said voltage
signal.
Thus, this prior published patent teaches a portable high power source simulator
in which a shunt is inserted electrically in series with the controlled current
source, the voltage across the shunt being proportional to the current flowing
through it. This voltage is amplified and fed through an Automatic Gain Control
(AGC) circuit to insure the independence of the current and voltage sources. The
output of the AGC circuit is fed through a conventional phase shift network,
amplified and connected to the primary coil of a step-up power transformer. By
regulating the amplifier gain, the voltage sensed by the voltage inputs of the
Device under test (DUT) can be varied independently of the current sensed by
the current inputs of the DUT.
Accordingly, this invention discloses a load simulator which employs independent
voltage and current sources to minimize power dissipation during the testing and
calibration of electrical power measuring devices.
US Patent No. 3,993,943 teaches a "There phase power circuit" which is
constructed to provide three-phase sinusoidal wave output the wye or delta
loads (balanced loads).
The three-phase power circuit of prior art comprising a pair of inverter circuits

each operable to convert a d.c. voltage to a square wave, a source of d.c. fed to
each of said inverters, a pair of constant voltage transformers each including a
primary with a center tap connection, said pair of inverters connected
respectively to said pair of primaries in an alternate connection relative to said
center tap; said constant voltage transformers each also including a secondary
winding, one of said secondary windings having a center tap and the other of
said secondary windings having a tap In order of one-third voltage magnitude;
the extreme ends of one of said secondary windings having said center tap
providing a first and second output and one end of the other of said secondary
windings providing a third output, said one-third tap on the other of said
secondary windings providing a neutral connection, the center tap on the one
secondary winding and the other end of the other secondary winding being
connected.
Thus, the power circuit is operable to provide a three-phase sine wave output, in
which the secondaries and the taps of two transformers are interconnected to
provide the three-phase output. Additionally, the tap on the one transformer is a
vectorial voltage distribution whereas the tap on the other transformer is a
center tap.
The pair of inputs is a filtered d.c. fed to a pair of inverters that converts the d.c.
to a square wave such as by switching. The square wave outputs of the two
inverters are fed to a pair of constant voltage transformers (CVT) primaries. The
secondary of each transformer together with a center tap on the one and a tap
in the order of one-third voltage magnitude on the other are interconnected to
provide a three-phase output.
Under a balanced load the circuit is operable for its intended purpose wye and
delta loads. However, to assure operability with unbalanced loads the phase of

the output voltage of one transformer is compared with the phase of the output
voltage of the other transformer. This is done in a feedback circuit that includes
converting the oscillator output to a sawtooth wave and the sine wave output of
the transformer to a d.c. voltage level dependent on the sine wave phase
relationship for comparison. The phase of the output of the one transformer is
then adjusted to the phase of the other.
US Patent No. 6,218,853 Bl teaches an alternating current load simulating
device for generating a load current with a phase difference to an electrical
phase angle of an alternating current power source voltage. The device
comprising: a voltage zero-crossing detecting circuit electrically connected across
the alternating current power source voltage for generating a counting pulse at
each positive half cycle of the alternating current power source voltage; a
current waveform generating circuit coupled to the voltage zero-crossing
detecting circuit for receiving the counting pulse and then generating a phase
control signal; a voltage and current phase control circuit for receiving the phase
control signal generated by the current waveform generating circuit and the
counting pulse of the voltage zero-crossing detecting circuit, and then generating
a first and a second switching control signals; a switch circuit having two input
ends coupled to the alternating current power source voltage in parallel for
receiving the alternating current power source voltage and an output end, the
switch circuit comprising a first switch and a fourth switch being paired and
controlled by the first switching control signal, and a second switch and a third
switch being paired and controlled by the second switching control signal, to
generate a load voltage at the output end of the switch circuit; a rectifying circuit
coupled to the output end of the switch circuit for rectifying the load voltage
generated by the switch circuit and then generate a direct current voltage; and a
voltage to current converting circuit for converting the direct current voltage
outputted from the rectifying circuit into a load current with a phase difference to

the phase angle of the alternating current power source voltage under control of
the phase control signal generated by the current waveform generating circuit.
Thus, the device of the prior published patent discloses an alternating current
load simulating device capable of simulating a resistive load, an inductive load, or
a capacitive load.
US Patent No. US 2011/0175876 Al, teaches a "DIGITALLY CONTROLLED
VOLTAGE GENERATOR" which is designed for use in application requiring fine
resolution voltage control such as generating a common voltage for a liquid
crystal display (low VA rating).
US Patent No. 4,940,930 teaches a "DIGITAL CONTROLLED CURRENT SOURCE"
which is designed to provide a digitally controlled current source for supplying
current to a load impedance using one each Digital to Analog converter and
Operational amplifier.
In summary, the prior art simulators used for testing of synchronous generators
and other controls and Instrumentation modules, are of analog type and
comprises many inductors, variacs, network transformers and other electrical
components which not only makes the systems considerably heavy but also
makes them liable for breakdown on movement from one place to another. Since
the power source is 3-ϕ Utility supply, there are continuous fluctuations in the
input supply resulting in an unstable output. Hence the prior art systems are
virtually immobile and have poor accuracy, and not suitable for calibration grade
measurements.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a digital three-phase

secondary load simulator system for accurate testing and calibration of power
electronics control panels.
Another object of the invention is to propose a digital three-phase secondary
load simulator system for accurate testing and calibration of power electronics
control panels, which is capable to generate 3 phase voltages and current
adapting digital Signal processing methods.
A still another object of the invention is to propose a digital three-phase
secondary load simulator system for accurate testing and calibration of power
electronics control panels, which provides highly stable and accurate Voltages,
Currents, Power factors and frequency of the 3 phase signals being operable
under negative feedback closed loop method for auto tuning of voltages,
currents and phase errors.
Yet another object of the invention is to propose a digital three-phase secondary
load simulator system for accurate testing and calibration of power electronics
control panels, in which the Human Machine Interface (HMI) is extremely simple
and User friendly, and having multiple modes of display as well as control and
operations.
A further object of the invention is to propose a digital three-phase secondary
load simulator system for accurate testing and calibration of power electronics
control panels, which exhibits a graphical display of Sinusoidal waveforms and
Phasor diagrams for all the three-phase voltages and current.
A still further object of the invention is to propose a digital three-phase
secondary load simulator system for accurate testing and calibration of power
electronics control panels, which is capable of independent control of Voltage,

Current and Power factor for all the three phases.
Yet another object of the invention is to propose a digital three-phase secondary
load simulator system for accurate testing and calibration of power electronics
control panels, which is enabled to calibrate and simulate the CT/PT feedback of
synchronous Generators used in Static Excitation System (Direct Excitation) and
digital automatic voltage regulator (DAVR).
SUMMARY OF THE INVENTION
According to the invention, there is provided a Digital 3-Phase Secondary Load
Simulator system to generate 3-phase Sinusoidal voltage and current using a
digital means, which produces a highly accurate and stable output, required for
calibration grade equipment. Additionally, the system comprises a feedback
control mechanism for auto tuning of the output voltage, current and phase
angle to eliminate error in actual output and a set value, which gets introduced
by the circuit device and loading conditions. This system is capable to accurately
test and precisely calibrate Load Measuring Units (LMU), Load Shedding Relays
(LSR), Energy meters, Multifunction meters and various transducers viz Active
power, Reactive power and Power factor transducers. Due to its modular
construction, the system can be expanded for higher VA rating, by inserting
additional cards. The system is enabled to conduct a power on calibration
including self-check.
The system is capable to exercise an independent control of three-phase
voltages, current and power factor, and operable under two frequencies, 50 Hz
and 60 Hz, which are most common frequency standards used in various
countries.

The present invention utilizes digital controlled methods for simulation of
electrical loads in an embedded system, and simulate independent 3-ϕ voltage
and current sources with different power factors (Unity, Lead, and Lag).
It may be noted that the present invention is not specific to balanced load or
unbalanced load as the voltage, rather the current sources are independent and
hence provide three-phase sinusoidal wave output for both type of load i.e.
balanced and unbalanced load. It does not require any inverter to convert DC
signals to AC signals.
The present invention teaches a 3-ϕ current source and 3- 0 voltage source with
phase control means to simulate all type of Alternating electronic loads.
Independent control of phase angle between voltage and current signals is
implemented in an embedded system having accuracy up to 3 decimal places.
According to the present invention, the 3- 0 current source is controlled by the
disclosed embedded system. A Digital to analog converter and a High Power
Operational amplifier supply current to load up to 50VA burden per phase.
The present invention therefore includes developing of hardware and software
for a 3 phase Secondary Injection Simulation System generating 3 phase output
voltage 3 phase current 3- 0 power factors (unity, lead and lag) and output
frequency selectable between 50 Hz and 60 Hz to test Static Excitation System
(Direct Excitation) and DAVR (Indirect Excitation), including testing and precise
calibration of Load Measuring Units (LMU), Load Shedding Relays (LSR), Energy
meters, Multifunction meters).
The Digital 3-Phase Secondary Load Simulator of the invention, simulates the
CT/PT feedbacks of synchronous Generator used in Static Excitation including

Digital Automatic Voltage Regulator (DAVR) panels (indirect excitation) for
testing and precise calibration of Load Measuring Units (LMU), Load Shedding
Relays (LSR), Energy meters, Multifunction meters and various transducers viz
Active power, Reactive power and Power factor transducers.
• The system of the invention generates three-phase Sinusoidal Voltages
varying from 0 to 155 V rms up to 20 VA burden.
• It generates three-phase Sinusoidal Currents varying from 0 to 1.2 Amps
rms up to 50 VA burdens and 0 to 6.0 Amps rms up to 50 VA burden.
The system is operable under following two modes which is selectable by a
toggle button in a human-machine interface (HMI):-
> Synchronous Mode: In this mode, voltage, currents and Power factors
for all three phases are same.
> Normal Mode: In this mode Independent control of three-phase
voltages, currents, and Power factors are implemented.

• The system generates two frequencies namely, 50 Hz and 60 Hz of
voltage and current signals, which are most common frequency standards
being used worldwide. These frequencies are also selectable in HMI using
the toggle button.
• The system negative feedback closed loop method for auto tuning of
voltages, currents and phase errors which are commonly introduced by
undesired conditions and thereby ensures highly stable and accurate
Voltage, Currents and frequency for all the three phases.

• The Simulation device generates Sinusoidal currents at leading and
lagging power factor with accuracy up to 3 decimal places, continuously
variable from 0 to 1.
• Due to the modular construction of the system, it can be expanded for
Higher VA rating, by inserting additional modules.
• The system has means for power on calibration, self-check and energy
and power calculation
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1- Functional block diagram of a Digital 3-Phase Secondary injection
simulation System according to the invention.
Figure 2 - A block diagram of a High Speed Signal Processing Board of the
system of Figure 1.
Figure 3 - A block diagram of a 3-ϕ PT Interface driver Board with feedback
means of the System of Figure 1
Figure 4 - A block diagram of a 3-ϕ CT Interface driver Board with feedback
means of the system of Figure 1
Figure 5 - A block diagram of an Auto Phase and Voltage Correction circuit for
automatic phase correction for the phase of sinusoidal voltage from
the pressure transmitter
Figure 6 - A block diagram of an Auto Phase and Current Correction circuit for

automatic phase correction for the phase of sinusoidal current from
the current transformer.
Figure 7- Process Flow of the "Digital 3-ϕ Secondary load Simulator" of Figure
1
Figure 8 - Process of the "Digital 3-Phase Secondary Load Simulator" of Figure
1.
DETAIL DESCRIPTION OF THE INVENTION
An overall functional block diagram of the inventive three-phase secondary
injection simulation system is illustrated in Figure 1. The Simulation system
consists of a High Speed Embedded system, an Interface board, a High speed
Signal Processing Board, a three-phase pressure transmitter, an Interface driver
Board with feedback, a three-phase current transformer Interface driver Board
with feedback, and an Auto Phase circuit for correction of Voltage and Current.
The system having 1GHz CPU operating frequency. The entire system runs on a
touch screen based monitor. The monitor is attached to the High speed
embedded device using a VGA cable and the layer of touch screen operates
using a serial interface cable. The system runs on LINUX operating system which
is installed on a Single board computer. The application code for simulation
system is loaded into a Flash memory of the Embedded system to generate
three-phase Sinusoidal voltages, and currents with required power factors. It
operates in two modes 'Synchronous' and 'Normal'. In synchronous mode, the
value of voltages, currents and power factors for all the three phases are same.
In Normal mode, the Voltages, currents and power factors can be independently
controlled. It can generate two frequencies 50 Hz and 60 Hz of voltage and
current signals. These frequencies are also selectable in HMI using a toggle
button. The Sinusoidal voltages and currents with adjustable power factor are

fed to the Generator panel in DCS system and Static excitation transformer,
DAVRs panels for testing and calibration purpose. 0
The system basically comprises five innovatively hardware modules as explained
below.
(1) Interface board;
(2) High Speed Signal Processing Board;
(3) 3-ϕ PT Interface driver Board with feedback;
(4) 3-ϕ CT Interface driver Board with feedback; and
(5) Auto Phase, Voltage and Current Correction circuit device.
The brief description of each of the above modules is explained below.
(1)Interface Board:
Interface board is designed to integrate both High Speed Embedded
System and High Speed Signal Processing board using a PC-Bus. The PC-
Bus used in the interface board utilizes address, data and control bus
using high speed Opto-isolation to integrate the embedded system and
Signal processing board. Because of opto-isolation used in the design, all
the signal paths address, data and control bus of the embedded system
are noise free signals and also all the signals are shielded to prevent noise
interference.
(2)High Speed Signal Processing Board:
Signal Processing Board is the hardware component that communicates
with the High Speed embedded system via a bus interface. It contains
address buffers, Data bus buffer, Control bus buffer for buffering the
address, data and control respectively. The board also includes Address
decoders to generate the chip selects for timers, DACs and Energy

metering IC and parallel port. The Timer used in the design generates
square wave of required time period for example, of 56μs for generating
interrupt signal, which is given to an interrupt pin of high speed
embedded system. In order to generate 3-ϕ sinusoidal voltage and
currents, Bi-polar DACs (Digital to Analog Converters) having very fast
settling time of for example 80 ns are used. The timer maintains the
interval of 56μs for outputting the sine samples. Final stage of output
contains AC Voltage follower circuits to block any DC Voltages present in
the signal. The output of High Speed signal processing board is 3-ϕ
sinusoidal voltages and currents of magnitude (0-7 Volts rms).
In order to communicate between the High Speed embedded system and
the High Speed signal processing board, a Linux driver is provided the
function of the driver and associated user program is to communicate
with the Embedded system using the PC-bus. It has two components:
(a)Driver Program:
This takes care of opening, closing, and reading from, writing to, the
device which is the High speed signal processing board.
It is a regular Linux driver routine file that runs in the operating
system (OS) to communicate with the device.
(b)User Program
This initializes the program by inserting the driver and waits for the
upper layered software, the HMI to write the data to its standard input
stream.
It transmits the variables from the HMI to the device and outputs sine
samples on the device.

The signal processing board consists of:
• Timers to generate square wave of required time period for example of
56μs for generating Interrupt signal.
• Buffers for buffering the address, data and control bus.
• Decoder to generate the chip selects for timers, DACs, and Energy
metering IC and parallel port.
• High speed Opto-isolators to integrate embedded system and Signal
processing board.
• Energy metering ICs: for energy and power calculation
• High speed DACs: having very fast settling time of 80 ns.
The schematic diagram of High speed signal processing board is shown in
Figure 2.
(3)3-ϕ PT Interface driver Board with feedback:
This module of the simulation system consists of some buffers, phase lead-
lag network, comparators, power amplifiers and Potential transformers.
Output of this module which is a pure Sinusoidal Voltages of desired
amplitude and is directly fed to the generator test load in DCS panels. The
PT interface circuit acts as an interface between the Signal processing board
& Step up Potential transformer. Operational amplifier is used as buffer
amplifier to block any DC signal which might have been generated because
of any intermediate stage saturation or failure of any component. The O/p
from Buffer is passed through voltage comparator, which compares the
input signal with the feedback signal from Auto Phase/ Voltage correction
circuit The Voltage comparator produces an error signal, which acts as
input for voltage controller circuit which produce controlled voltage as

output. Output of voltage controller is amplified to suitable level by power
Op-Amp and then passed through High value electrolytic capacitor to
suppress the inrush current produced at the startup. Inrush current
protection circuit protects the power amplifier from sudden spike in current
drawn from Toroidal core Potential transformer. The output voltage from
the power amplifiers is fed to the primary winding of a potential transformer
(for each phase) for voltage amplification. The secondary of Potential
transformer is connected to measurement transformer, which provides the
feedback voltage for automatic voltage tuning. The output voltage from
measurement transformer is passed through Automatic phase/voltage
correction circuit for any phase & voltage compensation if required. The
output from Automatic phase/voltage correction circuit is fed to voltage
comparator circuit for producing error signal and this completes closed loop
for voltage.
The 3-ϕ PT Interface driver Board with feedback consists of:
• Power Amplifiers: High current power amplifiers to boost the voltage
level to desired value.
• High speed Op-amps.
The schematic diagram of Potential transformer interface circuit for VR is
shown in Figure 3. The block diagram for other phase voltages i.e. VY and
VB can also be obtained in same way after replacing VR with VY and VB
respectively.
(4)3-ϕ CT Interface driver Board with feedback:
This module is an ideal current source which generate 3-ϕ sinusoidal

currents independent of load up to maximum 50 VA burden. The CT
Interface driver Board acts as an interface between signal processing board
and Current transformer. An Operational amplifier is used as buffer to block
any DC signal which might have been generated because of any
intermediate stage saturation or failure of any component. The O/p from
Buffer is passed through voltage comparator, which compares the input
signal with the feedback signal from an Auto Phase/ Current correction
circuit. The Voltage comparator produces an error signal, which acts as
input for voltage controller circuit which produce controlled voltage as
output. Output of voltage controller is amplified to suitable level by power
Op-Amp and then is fed to TWO independent Ideal current source
consisting of a Power amplifier, an inrush current protection circuit and a
wire wound resistor of appropriate value. Inrush current protection circuit is
also implemented to protect the power amplifier from sudden spike in
current drawn from Toroidal core Current transformer. Output from first
Ideal current source is Sinusoidal current of magnitude 0-2.5Amps and is
fed to one primary winding of current transformer (Si, El) for further
current scaling and the output current from second Ideal current source is
fed to second primary winding of current transformer (S2, E2) for further
current scaling. The current transformer used in the circuit consists of Two
Independent primary winding & split winding on the secondary side to
provide output current as either 1.2 Amps or 6.0 Amps. Each primary
winding is capable of driving 50 VA burden. The secondary of current
transformer is connected to High precision measurement current
transformer, which provides the feedback current for automatic current
tuning. The feedback voltage is passed through a current selector switch to
select either 1.2 Amps or 6.0 Amps current range for providing feedback.
The feedback voltage from this stage is passed through Automatic
phase/current correction circuit for any phase & current compensation if

required. The output from Automatic phase/current correction circuit is fed
to voltage comparator circuit for producing error signal and this completes
closed loop for current.
The 3.5 CT Interface driver Board with feedback consists of:
• Power Amplifiers: to boost the voltage level to desired value and High
current power amplifiers to boost the current level to desired value.
• Op-amps:
The schematic diagram of Current transformer interface circuit for IR is shown
in Fig.4
The block diagram for other phase currents i.e. IY and IB can also be
obtained in same way; replacing IR with IY and IB respectively.
(5) Auto Phase Voltage and Current Correction circuit:
An auto phase, voltage and current correction module is also incorporated
in the design of 3-ϕ secondary injection simulation system. This provides
automatic phase correction for the phase of sinusoidal voltages and
currents introduced by various load. The VR voltage output from Signal
processing board and feedback voltage signal from measurement
transformer are passed through respective zero crossing detectors and after
that through phase comparator to produce an output voltage square wave
pulse of duration equal to phase difference between original signal source's
voltage and feedback voltage. Two outputs from respective zero crossing
detectors is fed to Flip Flop to determine the nature of phase error as Lead
or Lag. After determination of nature of phase error and also the value of
phase error, this information is used by a digitally controlled resistor used in

Phase Lead-lag network to correct the phase error.
The Auto Phase, Voltage and Current Correction circuit consists of:
• Digitally controlled resistor: value of the resistor varies based on the
input pulse width and hence it changes phase lead or lag angle.
• Zero crossing detector
• Phase Comparator
• Flip-Flops:
The schematic diagram of Auto Phase/Voltage correction circuit is shown in
Figure 5.
The schematic diagram of Auto Phase /Current correction circuit is shown in
Figure 6.
The above hardware modules are assembled and integrated in a suitable
enclosure.
Technical advantages of Digital 3-phase secondary load simulator:
1) Microprocessor based three-phase Sinusoidal voltage and current
generation with different power factor.
2) Independent control of Voltage, Current and Power factor for all the three
phases.
3) It generates two frequencies 50 Hz and 60 Hz of voltage and current
signals. These frequencies are also selectable in HMI using toggle button.

4) Due to its modular construction it can be expanded for Higher VA rating,
by inserting additional cards.
5) The Human Machine Interface (HMI) runs on LINUX environment.
6) Extremely simple and User friendly HMI having two different modes of
operations (Normal and Synchronous mode).
7) Graphical display of Sinusoidal waveforms and Phasor diagrams for all the
three-phase voltages and currents.
8) 3-Phase AC energy measurement feature is incorporated.
9) Automatic Voltage and Current tuning with the help of negative feedback.
10)Automatic Phase error correction for all three-phase voltage and current.
ll)Housed in portable cabinet made of Aluminum for light weight, good
strength and EMI shielding. Suitable fans are provided for cooling the unit.
12)Fully Capacitive Touch screen display for faster and convenient user
operations.
13)Input supply to the unit is regular single phase 230 V AC, 50 Hz.
14)The Systems has facility for power on self-check and auto calibration.

WE CLAIM
1. A digital three-phase secondary injection simulation system for accurate
testing and calibration of power electronics control panels comprising:
- a high-speed embedded device with a central processing unit enabled
to generate three-phase sinusoidal voltages and currents with desired
power factor both in synchronous and normal modes, the sinusoidal
voltages, currents and power factors so generated can be fed to the
power electronics panels for testing and calibration;
- a signal processing device communicating with the embedded device
via a bus interface and having means for buffering address, data, and
controls; address decoders; bi-polar digital to analog converters;
integrated circuits for energy metering; a timer; parallel ports; a.c.
voltage follower circuit; a driver with associated user program, and a
multiple opto-isolators to integrate the embedded device and the
signal processing device, the timer generating square wave of desired
time period and transferring to the embedded device to produce 3-
phase sinusoidal voltage and current;
- a 3-phase potential transformer interface driver device with feedback
means acting as an interface between the signal processing device and
the potential transformer, and comprising a plurality of power
amplifiers to boost the voltage level; a voltage comparator; a voltage
controller; a current protection circuit to suppress sudden spike in
current received from the power amplifiers; and
- an automatic phase/voltage correction circuit device for phase or
voltage compensation, the output of the device being a pure sinusoidal

voltage of desired amplitude is directly fed to the panels under test;
- a three-phase current transformer driver device with feedback means
acting as an interface between the signal processing device and the
current transformer, and comprising power amplifiers including high
current power amplifiers respectively to block DC-signal boost the
voltage level and current level to desired values; an auto-phase
current correction circuit; a voltage controller; an inrush current
protection circuit;
- an auto phase voltage and current correction circuit; and
- a display device operably connected to the embedded device to exhibit
the measurement values relating to testing calibration of the power
electronics of the panels.

2. The system as claimed in claim 1, wherein the sinusoidal voltages and
currents produced by the drivers of the potential transformer and current
transformers are fed to the power electronics panel for testing and
calibration purpose.
3. The system as claimed in claim 1, wherein the three-phase voltage
transformer receiving output voltage from the power amplifier in the
primary winding for voltage amplification, wherein the secondary winding
of the transformer is connected to a measurement transformer to provide
the feedback voltage for automatic voltage tuning, and wherein the
output voltage from the measurement transformer is passed to the
voltage comparator via the automatic phase/voltage correction circuit for
producing an error signal and completes the closed loop for the voltage.

4. The system as claimed in claim 1, wherein the output of the voltage
controller of the three-phase current transformer driver module upon
amplification is fed back to two independent current sources, wherein the
output from the first current source is fed to the primary winding of the
transformer for current scaling, wherein the secondary winding of the
current transformer is connected to a high precision measurement current
transformer to provide feedback current for automatic current tuning,
wherein the feedback voltage is passed through a current selector switch
to select a current range to provide the feedback and whereas the
feedback voltage from this stage is passed through the automatic
phase/current circuit to the voltage comparator circuit for producing error
signal to complete the closed-loop for current.
5. The system as claimed in claim 1, wherein the nature and value of the
phase errors as determined via the CT/PT interface modules are fed to the
auto phase voltage and current correction module to provide automatic
phase correction for the phase of sinusoidal voltages and currents
introduced by different loads.
6. The system as claimed in claim 1 or 5, wherein the auto phase voltage
and current correction module comprises a digitally controlled resistor, a
zero-crossing detector, a phase comparator, and at least one flip flop.

ABSTRACT

The invention relates to a digital three-phase secondary injection simulation system for accurate testing and calibration of power electronics control panels comprising a high-speed embedded device with a central processing unit enabled to generate three-phase sinusoidal voltages and currents with desired power factor both in synchronous and normal modes, the sinusoidal voltages, currents and power factors so generated can be fed to the power electronics panels for testing and calibration; a signal processing device communicating with the embedded device via a bus interface and having means for buffering address, data, and controls; address decoders; bi-polar digital to analog converters; integrated circuits for energy metering; a timer; parallel ports; a.c. voltage
follower circuit; a driver with associated user program, and a multiple opto-isolators to integrate the embedded device and the signal processing device, the timer generating square wave of desired time period and transferring to the embedded device to produce 3-phase sinusoidal voltage and current; a 3-phase
potential transformer interface driver device with feedback means acting as an interface between the signal processing device and the potential transformer, and comprising a plurality of power amplifiers to boost the voltage level; a voltage comparator; a voltage controller; a current protection circuit to suppress sudden spike in current received from the power amplifiers; and an automatic
phase/voltage correction circuit device for phase or voltage compensation, the output of the device being a pure sinusoidal voltage of desired amplitude is directly fed to the panels under test; a three-phase current transformer driver device with feedback means acting as an interface between the signal processing device and the current transformer, and comprising power amplifiers including high current power amplifiers respectively to block DC-signal boost the voltage level and current level to desired values; an auto-phase current correction circuit;
a voltage controller; an inrush current protection circuit; an auto phase voltage and current correction circuit; and a display device operably connected to the embedded device to exhibit the measurement values relating to testing and calibration of the power electronics panels.