6. HARDWARE PROTOTYPE AND EXPERIMENTAL RESULTS
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Transcript of 6. HARDWARE PROTOTYPE AND EXPERIMENTAL RESULTS
CHAPTER-6 HARDWARE PROTOTYPE AND EXPERIMENTAL RESULTS.
150
6. HARDWARE PROTOTYPE AND
EXPERIMENTAL RESULTS
Laboratory based hardware prototype is developed for the z-source inverter based
conversion set up in line with control system designed, simulated and discussed in earlier
chapters. The setup is used for the experimental verification of the results obtained through
simulation. The experimental setup shown in Figure 6.1 is broadly divided into following
sections:
Diode Rectifier-IGBT inverter power module
Z- network consisting of inductors and capacitors
Controller section consisting of number of modules
Three phase AC filter circuit
Three phase Load
Measuring digital meters, Digital Storage Oscilloscope (DSO)
PICKit3 programming module (with MPLAB software)
Variac
Figure 6.1 Hardware Prototype of ZSI
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For the experimental purpose a single phase variac is used for initializing variable power
source that rectifies through a bridge uncontrolled rectifier to generate variable dc voltage.
This dc source is connected to an IGBT based three phase bridge inverter through a z-
network. Main development in this hardware prototype is its controller section which senses
the voltage across a capacitor in z-network and through digital signal processing develops
shoot-through pulses. The capacitor voltage range 0-1000V is normalized to 0 to +5V. This
includes realization of PID controller through PIC microcontroller. With this variable pulse
width shoot-through pulse third harmonic injected (THI) maximum constant boost control
(MCBC) technique is used for switching the IGBTs. AC filters are used to suppress the
higher order harmonics in the three phase output. Digital meters are used to measure the
input ac voltage, DC bus Voltage, DC bus current, load current etc. DSO is used to verify
the waveforms in different sections. The programs code developed for different PIC
microcontrollers under MPLAB software The algorithm of which is presented in
Appendix-B.MPLAB Integrated Development Environment (IDE) is an integrated toolset
for the development of embedded applications on Microchip's PIC microcontrollers.
MPLAB IDE v8.87 is used to write the program for PIC16F886 (Peripheral interface
controller) microcontroller. The program code was uploaded and burned via the PICKit 3
module provided with the PID modules described later. Detailed description of the
hardware prototypes, their circuit diagram, components used including their photographic
view are presented in this chapter. It also presents the waveforms at different test points and
the results obtained through experiments for simple ZSI and Quasi-ZSI topologies.
6.1. Rectifier - Inverter power module
It consists of the following sections as sketched in Figure 6.2
(a)Diode Rectifier
Four 16NSR120 diode are used with heat-sink as full wave single phase bridge rectifier
circuit to rectify the variable ac input voltage. Two capacitors of value 470 microfarad, 450
maximum working voltages are connected at the output of the rectifier to get the smooth dc
bus output. Figure 6.4 shows the view of the rectifier section which includes a time-delay
circuit consisting of mainly a relay and microcontroller chip PIC16F. Time delay is
introduced to provide the power circuit a soft start through green LED. The delay is
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adjustable through the microcontroller program. The DC bus output is passed through a fast
switching diode to the inverter via z-network
(b) Three phase Inverter:
Three phase six switches bridge inverter consists of six IGBTs of model
FGA25N120ANTD as in
Figure 6.5 to generate three phase output which is to be connected with three phase load.
IGBTs are attached with suitable heat sink.
(c) IGBT driver circuit:
There are six driver circuits separately for six IBTS shown in the IGBT module in
Figure 6.5. includes 6N138 is a low input current high gain Darlington optocoupler. A
single driver circuit shown in Figure 6.6 includes an optocoupler and transistors. When an
electrical signal is applied to the input of the optocoupler, its LED lights, its light sensor
then activates and a corresponding electrical signal is generated at the output. Unlike a
transformer, the opto isolator allows for dc coupling and generally provides significant
protection from serious overvoltage condition in one circuit affecting the other. Pulses
coming out from the signal conditioner circuit are fed to pin 2 of the optocoupler. Output
from pin 8 is processed through various resistors, transistors and two back to back zener
diodes to generate required pulse for the gate of IGBT.
Table 6.1 Major components in Rectifier-Inverter Power Module
Name Specification/Type Quantity
Capacitor 470µF,450 V 2
Diodes for Rectifier,16NSR120 16A, 1200 V stud diode 4
Relay KT954 1
Microcontroller to introduce delay PIC16F-628A 1X 3
Optocoupler 6N138 1 X 6
Transistor for Driver circuit NPN, BC547 1 X 6
Transistor for Driver circuit PNP, BD140 1 X 6
Transistor for Driver circuit NPN, BD139 1 X 6
IGBT FGA25N120ANTD,25A,1200V 6
Driver power Supply IN 4007 / 470µF,35 V 4 X 6, 2 X 6
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Figure 6.2 Rectifier-Inverter power module and IGBT driver circuit schematic
Figure 6.3 Hardware circuit of Rectifier - Inverter power module
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Figure 6.4 Hardware circuit for Single phase Bridge rectifier
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Figure 6.5 IGBT Module with driver circuit
Figure 6.6 IGBT Driver circuit
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6.2. Triangle Wave generator
The function generator IC chip XR2206 has been used to generate high quality, high
frequency triangular wave. The output waveforms can be both amplitude and frequency
modulated by an external voltage. Frequency of operation can be selected externally over a
range of 0.01Hz to more than 1MHz. As shown in Figure 6.7 of the schematic, the fixed
capacitor of value 0.01 microfarad connected between the pin no 5 and 6 and 24.7 k
variable resistance across pin no 7 produces the desired frequency triangular wave at output
pin 2. A variable resistance is connected between pins 15 and 16 to adjust the symmetry of
the output waveform. Figure 6.6 represents the block diagram of the function generator IC
and Figure 6.9 show the view of the hardware circuit of the generator. The signal is then
amplified with the help of TL082 operational amplifier and offset is adjusted by 5K pot
connected with non-inverting terminal. Finally it produces a 6 KHz and 5 volt peak
triangular wave as captured in DSO and shown as Figure 6.10
Figure 6.7 Schematic of Triangle wave generator
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Figure 6.8 Block diagram of IC XR2206
Figure 6.9 Hardware circuit of triangle wave generator
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Figure 6.10 High frequency triangular wave of 5volt peak.
Table 6.2 Major components for triangle wave generator
Name Specification Quantity
Function generator, XR2206 Max operating frequency = 1 MHz
Adjustable Duty Cycle, 1% to 99% 1
Operational amplifier, TL082
Wide Gain Bandwidth: 4 MHz
High Slew Rate: 13 V/μs
Internally Trimmed Offset Voltage: 15 mV
1
Trim Pot 20K, 10K, 5K 2,1,1
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6.3. Voltage Sense
IC Chip ACPL-782T is used as voltage sensor to sense the voltage across capacitor of the z-
network. Capacitor voltage is passed through a voltage divider circuit of 1M x 4 and 50
ohm resistances and voltage across 50 ohm is connected to the 8-pin ACPL-782T IC chip.
ACPL-782T is an isolation amplifier applied mainly for voltage and current sensing. The
output from pin 6 and 7 of this chip is processed through LM358 op-amp to convert this in a
suitable level. It is then connected to the PID controller PCB to generate the shoot through
pulses to compensate the input voltage fluctuation. The schematic of the circuit is shown in
Figure 6.11 which also includes a 5V dc power supply for providing power to the ICs.
Figure 6.12 is the view of the PCB developed for the purpose.
Figure 6.11 Voltage Sense circuit diagram
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Table 6.3 Major components in voltage sense PCB
Name Specification Quantity
Diode IN4007 2
voltage regulator, 7805 Three terminal positive 5 V 1
Voltage Sensor chip, ACPL-
782T
8 pin isolation
amplifier DIP
2% Gain Tolerance
100 kHz Bandwidth
1
Operational Amplifiers,
LM358
Dual Differential Input
Large DC Voltage
Gain: 100Db
Wide Power Supply
Range
1
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Figure 6.12 Hardware circuit for Voltage Sense
6.4. Third Harmonic Injected (THI) Sine-wave modulating signal generation
PIC16F886 microcontroller is used to generate three phase 50 Hz sinusoidal waveform
which is then added with the third harmonic 16% of amplitude of same sinusoidal
waveform to get the third harmonic injected sine waveform. This total operation is made
through microcontroller program details of which is presented as APPENDIX-C. is
Presented in the circuit sketch in
Figure 6.13, terminals A1-A8, B1-B8 and C1-C8 generate the 8-bit three phase outputs
each 120 degree out of phase representing the THI sinusoidal digital signals. These signals
become the eight bit inputs to the three digital to analog converters DAC0800. The separate
analog outputs of DACs are processed through corresponding op-amp (LM358) to generate
variable maximum ±5 volt peak to peak THISIN three phase modulating signals. The
amplitude of these signals can be varied through program to adjust modulation index. The
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hardware view of this section is presented in Figure 6.14. The DSO captured view of these
three phase signals is shown in Figure 6.15.
PIC16F886 is a 28 pin CMOS Microcontrollers with nanoWatt technology having 24
numbers I/O pins, 8192 flash word memory, 368 bytes SRAM and 256 bytes EEPROM
memory with maximum operating speed of 20 MHz. The block diagram of the
microcontroller is copied in Figure 6.16. Program is developed for the microcontroller
through the MPLAB IDE software and burning of program is done through PICkit3
programmer shown in Figure 6.17.The DAC0800 is a commonly used 8-bit high-speed
current-output digital-to-analog converters (DAC) featuring typical settling times of 100 ns.
Figure 6.13 Circuit Diagram of THI Sine wave Generation Schematic
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Figure 6.14 Hardware circuit for THI Sinewave Generation PCB
Figure 6.15 THI Sine wave waveform
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Figure 6.16 Block Diagram of PIC16F886
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Figure 6.17 PIC kit-3 programmable module
6.5. PID Controller section
The signal which is coming from the voltage sense PCB is connected as input for this
section which through a voltage follower and zener is connected to the microcontroller
PIC16F886. It is supported by a 20 MHz crystal oscillator connected between pin 9 and 10.
A program is developed with extensive logics for the PID operation of the whole system.
There is a provision of burning the program in this PCB through a 6-pin connector. PID set
points like KP, KI and KD are set through 4 push-switches K1, K2, K3 and K4. The four
numbers seven segment displays are used to display the set values (SV) and also present
value (PV) by adjusting the push-switches a number of times. Five LEDs connected
alongside indicate the mode of display i.e. whether it is PV, SV, KP, KI or KD. The four
switches are used for selecting the parameter, setting the parameters i.e. increase and
decrease the values and entering the final value respectively. The 8 bit output from
microcontroller section is then connected to the DAC0800 for digital to analog conversion
of the control output signal. Finally through LM358 opamps this is processed and limited
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within a range of 0 to 5 V control signal which is fed to the signal conditioner circuit. The
schematic diagram of this section is shown in Figure 6.18 and photographic view in Figure
6.19.
Figure 6.18 PID Controller section
Figure 6.19 Hardware circuit for PID Controller section
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Table 6.4 Major components in PID Controller Section
Name Specification Quantity
DAC0800 8-Bit Digital-to-Analog Converters 1
LED Seven segment Display board 4×7 Segment Display 4x1
LM324 Low power quad op amp 1
Microcontrollers PIC16F886 Details given in THI sinewave generator
section 1
LM358 Low power dual operational amplifier
Details given earlier 2
LED Board 5 red LEDs for SP, PV, KP, KI and KD 1 X 5
Push switch board Push to connect ground switches 1X4
Crystal Oscillator for PIC 20 MHz 1
Connector for Programmer 6- pin 1
6.6. Signal Conditioner
Three phase third harmonic injected (THI) sinusoidal modulating signals are compared
separately by LM358 opamp comparators with a high frequency triangular carrier signal
coming from triangular signal generator card. Across the non-inverting and inverting input
terminals modulating and carrier signals are fed respectively to obtain high frequency PWM
switching pulses. Across the output terminals 5.1V zener diode is connected to ensure the 5
volt peak switching pulses. This comparison and generation of pulse for a single phase are
captured in a DSO and presented as Figure 6.22. These pulses are then fed to Schmitt
Trigger inverter IC7414. The 7414 IC is composed of six independent Schmitt-Triggered
single-Input inverter gates. Schmitt Trigger logic gates have a greater immunity to noise in
the input lines. With noise suppression, the logic gates (in this case inverters) are more
likely to remain in their current state unless a true change to the input was intended.
Glitches and high speed random noise in the line is less likely to toggle the status of the
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output. Pin 14 of IC7414 is connected to +5volt supply and pin no 7 is grounded. Across
pin no 1,5,11 the PWM pulses are applied as shown in the circuit schematic Figure 6.20.
Pin 2 is the complemented output of pin 1. Pin 2 and 3 are shorted and hence the output at
pin 4 is similar to the input at pin1 (because of double inversion). So pulses at pin 2 and pin
4 are complement to each other. Similarly pulses at pin 10 and 12 as well as pin 6 and 8 are
complement to each other. The six PWM pulses are fed to two OR gate IC7432 at pin 1,
4,9,12 and 1, 4 respectively.
As shown in the sketch in Figure 6.20, there are three microcontrollers PIC16F628A
connected in between and the three inverted PWM signals from IC7414 are passed through
them. There are two three pins jumpers connected at the output of each set of pulses. This
circuitry is made to introduce the options of dead time during switching. Though dead time
is not necessary in case of shoot-through switching, a provision is kept to include it, in case
of operating the circuit as conventional PWM inverter. A programmable dead time is
inserted to the three PIC16F628A separately. Dead time can be bypassed in case of shoot-
through operation with the help of jumper arrangements as shown in the sketch.
Again, in the lower half of the sketch in Figure 6.20, control voltage from the PID controller
PCB is compared with the same carrier triangular signal to generate the shoot through
pulses. Negative shoot through pulses for the lower half switches is generated by comparing
with the negative PID control voltage. Two sets of shoot-through pulses are then passed
through scmitt-trigger buffers (IC7414) without any inversion and are then ORed with the
PWM switching pulses by OR gate IC7432. Six output signals after OR-ing are fed to 20
pin IC74244 octal 3-state buffer/line driver to generate desired switching pulses which are
fed to individual IGBT driver circuit. The photoview of the signal conditioner Board is
shown in Figure 6.21.
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Figure 6.20 Signal Conditioner
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Table 6.5 Major components in Signal Conditioner PCB
Name Specification/Schematic diagram
Quantity
Microcontrollers PIC16F628A
8-Bit CMOS, 18 pin Microchip Microcontroller
Flash word memory 2048, SRAM 224 EEPROM
128 I/O 16, 20 MHz operating max speed.
3
Operational Amplifiers LM358 Details given earlier
4
Schmitt Trigger Inverter, 7414
Six inverting buffers with Schmitt-triggerLow-
power dissipation.
2
OR Gate IC chip 7432
Quad 2-Input OR
Gate 2
Buffer/Line Driver IC chip,
74244
Octal non-inverting buffer/line driver with 3-state
outputs.
1
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Figure 6.21 Signal Conditioner
Figure 6.22 THI SINPWM and Triangular wave comparator to produce single IGBT pulse
Figure 6.22 presents the DSO captured view of the THI Sine wave, triangular signal and
resulting PWM pulses together through three channels.
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Figure 6.23 The Controller section
Figure 6.23 shows the overall view of the controller section developed for the system and
Figure 6.24 represents the PWM pulse, shoot through pulse and the resulting pulses going
to the driver circuit of the single IGBT.
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Figure 6.24 pulse across single IGBT(Top- PWM pulses, Middle-shoot through pulses,
Bottom-pulse for each IGBT)
The impedance network and ac filter parameters for the experiment are chosen as
𝐿1 = 𝐿2 = 1𝑚𝐻 𝐶1 = 𝐶2 = 500𝜇𝐹
𝐿𝑓 = 10𝑚𝐻 𝐶f = 10𝜇𝐹
Table 6.6 and 6.7 present the experimental results of the simple ZSI system selecting two
different values of shoot through duty ratios D. With increase of D the output voltage as
well as capacitor voltage is increasing. Table 6.8 presents a closed loop experimental results
where the input single phase ac voltage is varied in steps from the variac and corresponding
output voltage is recorded. Output remains almost steady with little variation and this
satisfies the perfect working of the prototype under closed loop condition. Experiments are
carried out both for simple ZSI and Quasi ZSI. Figure 6.25 and Figure 6.26 are the DSO
captured waveforms separately taken without ac filter and with ac filter respectively.
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Table 6.6 Experimental results of ZSI(M=0.8,Shoot through duty ratio D=0.32)
𝑽𝒅𝒄(𝐕𝐨𝐥𝐭) 𝑽𝒄𝟏(Volt) 𝑽_𝒂𝒄 (Volt)
260 470 275
280 500 290
340 620 350
360 655 380
380 680 400
Table 6.7 Experimental results of ZSI (M=0.7,D=0.37)
𝑽𝒅𝒄(𝐕𝐨𝐥𝐭) 𝑽𝒄𝟏(Volt) 𝑽_𝒂𝒄 (Volt)
260 635 360
280 680 380
340 825 470
360 880 500
380 920 520
Table 6.8 Performance of the regulator
ZSI
Single phase
ac
input(Vrms)
DC Bus voltage(V) Three phase output line
voltage(Vrms)
60 141 250.5
75 177 255
95 225 258
110 260 258.5
130 308 263
150 351 260
QZSI
60 140 221
75 175 223
95 225 224
110 260 225.5
130 310 227
150 350 227.5
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Figure 6.25 Output line voltage without filter
Figure 6.26 Output line voltage with filter