Journal of Engineering Research and Studies

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Research Article PSPICE ANALYSIS OF A VARIABLE DC-LINK VOLTAGE WITH BUCK-BOOST CONVERTER TOPOLOGY FOR SWITCHED RELUCTANCE MOTOR DRIVE Souvik Ganguli * Address for Correspondence * Assistant

1 Research Article PSPICE ANALYSIS OF A VARIABLE DC-LINK VOLTAGE WITH BUCK-BOOST CONVERTER TOPOLOGY FOR SWITCHED RELUCTANCE MOTOR DRIVE Souvik Ganguli * Address for Correspondence * Assistant Professor, Department of Electrical & Instrumentation Engineering, Thapar University, Patiala , India. ABSTRACT This paper addresses the PSPICE analysis of a variable dc link voltage with buck-boost converter topology used for a switched reluctance motor drive. A general introduction of this converter, its operating principle as well as its merits and demerits are discussed in this article. The simulation for finding out the phase current rise and fall time and to perform the Fourier analysis is carried out using PSPICE at an operating temperature of 27 C. The total harmonic distortion is also calculated for this drive converter. The voltages across the different nodes and the currents across the different voltage sources have been found out from the SPICE circuit. The operating point information is also obtained for the different diodes and the BJTs used as per the SPICE circuit of the converter. KEYWORDS Switched reluctance motor, variable dc link voltage with buck-boost converter, Fourier analysis, total harmonic distortion, small signal bias solution, operating point information, PSPICE software. 1 INTRODUCTION Switched reluctance motor (SRM) drives have been paid renewed attention because of its manifold advantages over other ac motors viz. simple in construction and robust nature, high reliability, easy maintenance and good performance. The absence of permanent magnets and windings in rotor give possibility to achieve very high speeds (over rpm) and have turned switched reluctance motor drives into perfect solution for operation in harsh environments like presence of vibrations or impacts. The simple mechanical structure greatly reduces its price. Due to these features, switched reluctance motor drives are finding applications in aerospace, automotive and domestic appliances. However, switched reluctance motors suffer from few drawbacks as well like complicated algorithm to control it due to its high degree of nonlinearity. Moreover, switched reluctance motors always have to be electronically commutated and there is the need of a shaft position sensor in order to detect the shaft position. The other limitations include strong torque ripples and acoustic noise effects [1]. A typical switched reluctance motor drive essentially consists of four basic components: Power Converter Control Logic Circuit Position Sensor Switched Reluctance Motor. The essential features of the power switching circuit for each phase of the switched reluctance motor comprises of two parts: A controlled switch to connect the voltage source to the coil windings in order to build up the current. An alternative path for the current to flow when the switch is turned off, since the trapped energy in the phase winding can be used for the other strokes. In addition to this, it protects the switch from the high current produced by the energy trapped in the phase winding [2]. 2 CIRCUIT OPERATION OF A VARIABLE DC LINK VOLTAGE WITH BUCK-BOOST CONVERTER TOPOLOGY Fig. 1: Circuit Diagram for Variable DC Link Voltage with Buck-Boost Converter A variable dc link voltage converter circuit with four switches and diodes is shown in Figure 1 given below. There is only one switch per machine phase, and it is connected in series with the phase winding which prevents a shoot-through fault. The switch Tc, diode Dc, inductor L, and output capacitor C form the buck-boost, frontend power stage. The machine dc link voltage V i can be varied from zero to greater than (say, two times) the dc source voltage V dc to obtain the desirable input voltage to the machine windings. Further, this stage provides the isolation required for faster commutation of the current with the constant source voltage V dc. The energization mode is initiated by turning on the phase switch (say, T1) and thereby applying the voltage V i to machine phase A. To regulate the winding, switch T1 is turned off which initiates the routing of the current through the freewheeling diode D1, the dc source voltage V dc and phase A winding, regardless of the on or off condition of the chopper switch Tc. That would apply a fixed negative dc source voltage V dc across the machine phase winding. The energy in the output capacitor C will be able to cater to the oncoming phase (say, B) during the time that the switch Tc is turned off. In this manner, the independence between various machine phases is maintained in this converter topology.

2 The distinct advantage of this power converter compared to the converter with a buck converter front end is that the input voltage to the machine phases could be increased over and above the dc source voltage to accelerate the buildup of the current in the machine phases. But a much greater advantage is found in the generation mode of the machine because the phase energization instance coincides near the rotor and stator pole alignment where the inductance is many times greater than the unaligned inductance encountered initially in the motoring mode of operation. These advantages come with a penalty in the voltage rating of the switches. All the machine phase switches have to be rated at least to the maximum output voltage of the chopper. The chopper switch voltage rating is equal to the sum of the dc source and machine input voltages. For example, assuming that the machine input voltage (i.e., the output voltage of the chopper circuit) is equal to, say, twice the source voltage, then the voltage rating of the chopper rises to three times that of the source voltage. In the buck mode of operation, when the machine input voltage is less than that of the source voltage, the switch ratings are still higher than that of the buck front-end converter while retaining the advantages of the buck front-end converter topology [3]. 3 CIRCUIT ELEMENT VALUES The supply voltage chosen for the purpose of our analysis is 50 Volts (dc). The diode and transistor values are as per the specifications given in [4-5] and are listed below: Diode Specifications Saturation Current (IS=0.5 µa) Reverse breakdown voltage (BV=5.20 Volts) Reverse breakdown Current (IBV=0.5 µa) Parasitic Resistance (RS=1.0 ohms) Transistor Specifications P-N saturation current (IS=6.734 µa) Ideal maximum forward beta (BF=416.4) Base-Emitter leakage saturation current (ISE=6.734 µa) Ideal maximum reverse beta (BR=0.7371) Base-Emitter zero-bias P-N capacitance (CJE =3.638 Pico Farads) Base-Collector P-N grading factor (MJC=0.3085) Base-Collector built in potential (VJC=.75Volts) Base collector zero-bias P-N capacitance (CJC=4.493 Pico Farads) Base-Emitter P-N grading factor (MJE=0.2593) Base-Emitter built in potential (VJE=0.75 Volts) Ideal reverse transit time (TR=239.5 Nano Seconds) Ideal forward transit time (TF=301.2 Pico Seconds) The phase windings denoted by L2, L3 and L4 respectively are assumed to be inductances of 25mH each. The Transistor Base-drive Resistance equals 250Ω. For SPICE analysis, we have drawn Fig. 2 as given below. Fig. 2: PSPICE Circuit Diagram for Variable DC Link Voltage with Buck-Boost Converter 4 RESULTS As per the PSPICE circuit, the fourier analysis of the phase current for a variable dc link converter has been carried out at a temperature of 27 C. The voltage across the different nodes has been found out using small signal bias solution at the same operating temperature. The currents flowing through the different voltage sources along with their polarities have also been shown. The operating point information is obtained for the different diodes and the BJTs. Finally, the plot showing the variation of phase current with respect to time and frequency and the FFT of the phase winding has been conducted and shown in Figs 3-5. The results obtained are given as follows: 4. 1 Fourier Analysis FOURIER COMPONENTS OF TRANSIENT RESPONSE I (VZ) DC COMPONENT = E-04 Table 1: Fourier analysis of the Phase Current for Variable DC Link Voltage with Buck-Boost Converter Harmonic Number Frequency (Hz) Fourier Component Normalized Component Phase (Deg) Normalized Phase (Deg) E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+02 TOTAL HARMONIC DISTORTION = E+02 PERCENT So the input current THD=27.98%=

3 4. 2 Small Signal Bias Solution Table 2: Small Signal Bias Solution for Variable DC Link Voltage with Buck-Boost Converter Node Voltage (V) Node Voltage (V) Node Voltage (V) Node Voltage (V) E E E E E Voltage Source Currents Table 3: Voltage Source Currents in Variable DC Link Voltage with Buck-Boost Converter Name of the Voltage Source Magnitude of Current (A) VX E-13 VY 2.021E-30 VZ 2.021E-30 VA 3.133E-13 VG E-13 VG E-14 VG E-30 VG E Operating Point Information Table 4: Operating Point Information for Variable DC Link Voltage with Buck-Boost Converter Diodes Name of the Diode DC D1 D2 D3 MODEL DMOD DMOD DMOD DMOD ID 1.74E E E E-10 VD 2.37E E E E-01 REQ 9.38E E E E+07 CAP 0.00E E E E+00 Bipolar Junction Transistors Name of the QA QB QC QD Transistor MODEL MODQ1 MODQ1 MODQ1 MODQ1 IB 4.58E E E E-16 IC -7.96E E E E-16 VBE -6.47E E E E-28 VBC 2.37E E E E-04 VCE -2.37E E E E-04 BETADC -1.74E E E E+00 GM -3.90E E E E-15 RPI 5.66E E E E+12 RX 0.00E E E E+00 RO 6.06E E E E+11 CBE 4.49E E E E-12 CBC 3.95E E E E-19 CJS 0.00E E E E+00 BETAAC -2.21E E E E-02 CBX/CBX2 0.00E E E E+00 FT/FT -1.38E E E E Plot Results for Variable DC Link Voltage with Buck-Boost Converter Plot showing the variation of phase current with respect to time and frequency are given in Fig. 3 and 4 respectively. The Fast Fourier Transform (FFT) of the phase winding has been carried out and depicted in Fig mA 10mA 5mA 0A -5mA 180us 190us 200us 210us 220us 230us 240us 250us 260us 270us 280us 290us 300us Time Fig. 3: Variation of Phase Current for Variable DC Link Voltage with Buck-Boost Converter with respect to Time

4 10mA 1.0mA 100uA 10uA 1.0uA 0Hz 0.2MHz 0.4MHz 0.6MHz 0.8MHz 1.0MHz 1.2MHz 1.4MHz 1.6MHz 1.8MHz 2.0MHz 2.2MHz Frequency Fig. 4: Variation of Phase Current for Variable DC Link Voltage with Buck-Boost Converter with respect to Frequency 4.0mA 3.0mA 2.0mA 1.0mA 0A 0Hz 0.2MHz 0.4MHz 0.6MHz 0.8MHz 1.0MHz 1.2MHz 1.4MHz 1.6MHz 1.8MHz 2.0MHz 2.2MHz Frequency Fig. 5: Fast Fourier Transform of the Phase Winding Current for Variable DC Link Voltage with Buck- Boost Converter 4. 6 Calculation of Input Power Factor Input current THD= 27.98% = o Displacement angle φ 1= o DF = cos( φ ) = cos(79.34 ) = Input 1 PF = cos( φ 2 1) = ( leading ) 1 + ( THD). 5 CONCLUSIONS This topology has the advantages of using lesser number of switches and diodes that results in reduction of logic power supplies and gating circuits, and hence offers compactness, lower overall cost and higher reliability of the drive. The converter needs only (n+1) switches, supports single pulse operation, provides suppressing voltage of nearly negative V dc, requires no additional control for regulating the dump capacitor voltage and the dump capacitor is robust to the chopper switch failure. As a result of the single pulse operation, acoustic noise and core loss of the switched reluctance motor can be considerably reduced. Its higher phase demagnetization voltage gives improved performance. This converter is targeted for variable-speed drives in consumer appliances where low acoustic noise is sought for. The SPICE simulations produce satisfactory results reflecting the true characteristics of this converter. 6 REFERENCES 1. R. Krishnan, Switched Reluctance Motor Drives: Modeling, Simulation, Analysis, Design and Applications. Industrial Electronics Series, CRC Press, M.Asgar, E. Afjei, A.Siadatan and Ali Zakerolhosseini, A New Modified Asymmetric Bridge Drive Circuit Switched Reluctance Motor, European Conference on Circuit Theory and Design, pp , S. Vukosavic and V. R. Stefanovic, SRM inverter topologies: a comparative evaluation, IEEE IAS, pp , Muhammad H. Rashid, Power Electronics: Circuits, Devices and Applications, Pearson Prentice Hall, Muhammad H. Rashid, SPICE for Power Electronic Circuits, Pearson Prentice Hall, APPENDIX PSPICE PROGRAM FOR VARIABLE DC LINK VOLTAGE WITH BUCK-BOOST CONVERTER TOPOLOGY VDC 1 0 DC 50V CIRCUIT DESCRIPTION CD MF DC 2 6 DMOD D1 1 9 DMOD D DMOD D DMOD L UH C UF VX 10 0 DC 0V

5 VY 15 0 DC 0V VZ 20 0 DC 0V VA 5 0 DC 0V QA MODQ1 QB MODQ1 QC MODQ1 QD MODQ1 L UH L UH L UH RB RB RB RB VG1 4 0 PULSE (0V 20V 0 1NS 1NS 12.24US 40US) VG2 8 0 PULSE (0V 20V 0 1NS 1NS 12.24US 40US) VG PULSE (0V 20V 0 1NS 1NS 12.24US 40US) VG PULSE (0V 20V 0 1NS 1NS 12.24US 40US) * DMOD DEFINES THE DIODE MODEL PARAMETERS.MODEL DMOD D (IS=100E-15 RS=16 BV=100 IBV=100E-15) * MODQ1 DEFINES THE TRANSISTOR MODEL PARAMETERS.MODEL MODQ1 NPN (IS=6.734F BF=416.4 ISE=6.734F BR= CJE=3.638P MJC=.3085 VJC=.75 CJE=4.493P MJE=.2593 VJE=.75 + TR=239.5N TF=301.2P).TRAN 2US 300US 180US 1US UIC.PROBE.OPTIONS ABSTOL=1.00N RELTOL=0.01 VNTOL=0.1 ITL5=20000.FOUR 120HZ I (VZ).OP.END

PSPICE ANALYSIS OF A SPLIT DC SUPPLY CONVERTER FOR SWITCHED RELUCTANCE MOTOR DRIVES Souvik Ganguli *

Research Article PSPICE ANALYSIS OF A SPLIT DC SUPPLY CONVERTER FOR SWITCHED RELUCTANCE MOTOR DRIVES Souvik Ganguli * Address for Correspondence * Assistant Professor, Department of Electrical & Instrumentation