Microcontroller Based PWM Controlled Four Switch Three Phase Inverter Fed Induction Motor Drive

Transcription

1 SERBIAN JOURNAL OF ELECTRICAL ENGINEERING Vol. 7, No., November 00, UDK: Miroontroller Based PWM Controlled Four Swith Three Phase Inverter Fed Indution Motor Drive Nalin Kant Mohanty, Ranganath Muthu Abstrat: This paper presents PIC miroontroller based PWM inverter ontrolled four swith three phase inverter (FSTPI) fed Indution Motor drive. The advantage of this inverter that uses of 4 swithes instead of onventional 6 swithes is lesser swithing losses, lower eletromagneti interferene (EMI), less omplexity of ontrol algorithms and redued interfae iruits. Simulation and experimental work are arried out and results presented to demonstrate the feasibility of the proposed approah. Simulation is arried out using MATLAB SIMULINK and in the experimental work a prototype model is built to verify the simulation results. PIC miroontroller (PIC 6F877A) is used to generate the PWM pulses for FSTPI to drive the 0.5 hp 3-phase Indution Motor. Keywords: Four Swith Three Phase Inverter (FSTPI), Indution Motor (IM), Pulse Width Modulation (PWM), Total Harmoni Distortion (THD), Peripheral Interfae Controller (PIC). Introdution Indution motors are being used for many industrial and ommerial appliations beause it its easy build, high robustness, and generally satisfatory effiieny. AC indution motors, whih ontain a age, are very popular in variable-speed drives. They are simple, rugged, inexpensive and available at all power ratings. Progress in the field of power eletronis and miroeletronis enable the appliation of indution motors for high-performane drives. The speed of the indution motor an be ontrolled by varying its input AC voltage and frequeny using an Inverter. A standard six - swith three phase voltage soure inverter has six swithes in three legs with a pair of omplementary power swithes per phase. A redued swith ount voltage soure inverter i.e. four swith three-phase inverter Department of Eletrial and Eletronis Engineering, Anna University, Chennai 60005, India; nkmohanty003@yahoo.o.in Eletrial and Eletronis Engineering Department at SSN College of Engineering, Chennai 60005, India; ranganathm@ssn.edu.in 95

2 N.K. Mohanty, R. Muthu (FSTPI)] uses only two legs, with four swithes. The advantage of this inverter due to the use of 4 swithes instead of onventional 6 swithes is lesser swithing losses, lower eletromagneti interferene (EMI), less omplexity of ontrol algorithms and redued interfae iruits. Several artiles report on FSTPI struture [-5]. In reent years, with the inreasing use of miroontrollers in power eletronis, it beomes possible to use it to generate the pulse width modulation (PWM) signals to ontrol the speed of the indution motor. The miroontroller provides the variable frequeny signal that ontrols the applied voltage on the gate drive, whih provides the required PWM frequeny at the output of the power inverter. Low ost PIC6F877A miroontroller has been hosen for implementation for ease in development and fast response. In addition, PIC6F877A has high-performane RISC CPU with only 35 single-word instrutions, all single-yle instrutions exept for program branhes, whih are two-yles, and operating speed of 0 MHz. Proposed Topology In the simulation and experimental work, the single phase half bridge retifier onverts AC power to DC. The DC power is fed to FSTPI. The FSTPI onverts the DC power to ontrolled 3-phase AC power. The 3-phase indution motor is driven by the FSTPI. PIC miroontroller 6f877A is used to generate the ontrolled PWM pulse for FSTPI. The ontrolled PWM pulses of miroontroller are fed to the gate of MOSFETs of FSTPI through the driver iruit to drive the IM.. Priniple of FSTPI operation The power iruit of the FSTPI fed IM drive is shown in Fig.. The iruit onsists of 4-swithes S, S, S 3 and S 4 and split apaitors C and C. The 3-phase AC input, whih is of fixed frequeny, is retified by the retifier swithes. The power iruit is the three-phase four-swith inverter. Two phases a and b are onneted to the two legs of the inverter, while the third phase is onneted to the enter point of the d-link apaitors, C and C. The 4 power swithes are denoted by the binary variables S to S 4, where the binary orresponds to an ON state and the binary 0 orresponds to an OFF state. The states of the upper swithes ( S, S ) and lower swithes ( S 3, S 4 ) of a leg are omplementary that is S 3 = S and S 4 = S. The terminal voltages V as, V bs and V s of a 3-phase Y-onneted Indution Motor an be expressed as the funtion of the states of the upper swithes as follows: 96

3 Miroontroller Based PWM Controlled Four Swith Three Phase Inverter Fed... V Vas = ( 4S S ) 3 () V Vbs = ( S + 4S ) 3 () V Vs = ( S S + ) 3 (3) where V as, V bs, V s are the inverter output voltages, V is the voltage aross the d link apaitors, V d is the voltage aross the apaitors C and C ( V = V /). d Fig. FSTPI with Indution Motor. In matrix form the above equations an be written as: V 4. (4) as V S V Vbs 4 = 3 S + 3 V s Table shows the different modes of operation and the orresponding output phase voltages of the inverter. Table Swithing states and output phase voltages. Swithing states Output voltages S S V as V bs V s 0 0 V /3 V /3 V /3 0 V V 0 0 V V 0 V /3 V /3 V /3 97

4 N.K. Mohanty, R. Muthu. PWM generation in PIC miroontroller 8-bit PIC6F877A miroontroller was hosen to obtain the pulses for the FSTPI to drive the Indution Motor. This Miroontroller has a 5 MHz proessor, 33 input/output (I/O) pins, interrupts, ounters, timers, I/O ports, RAM, and ROM/EPROM. The peripheral interfae ontrollers (PICs) are the integrated iruits based on CMOS tehnology. The main omponents of a PIC are RAM, EPROM, EEPROM, and Peripheral Interfae Adaptor (PIA). These omponents are inserted in the same integrated iruit to redue the size, the ost of the system and make design of the system easier. The address bus, the data bus and the ontrol bus onneting the omponents are plaed in the PIC iruit by the manufaturer. Beause of these advantages, PICs have been preferred devies in pratial ontrol appliations. PIC6F877A used in this work operates at 0 MHz lok frequeny and runs eah instrution as fast as 00 ns. Flash Program Memory is up to 8K 4 words. Data memory is partitioned into four banks whih ontain the General Purpose Registers and the Speial Funtion Registers. Bits RP and RP0 are the bank selet bits. Eah bank extends up to 7Fh (8 bytes). It ontains K EEPROM as a program memory, 5 speial hardware registers, 36 general purpose registers and 64 byte EEPROM as a data memory. PICs have been preferred ontrol devies beause of their low ost, less energy onsumption and small volume. The miroontroller has been programmed to vary the frequeny of the PWM signal that ontrols the frequeny of the voltage applied at the gate drives, and as a result of this the swithing frequeny of the inverter is ontrolled. 3 Simulation Work and Results Digital omputer simulation model using MATLAB-SIMULINK has been developed to test the proposed FSTPI fed IM drive blok as shown in Fig.. Simulation iruit diagram of the system is shown in Fig. 3. The FSTPI fed drive system onsists of a three-phase diode bridge retifier, a split apaitor, four swith three phase inverter and 3-phase squirrel age Indution Motor. Input three-phase supply voltage: 400 V (rms), 50 Hz; Three-phase indution motor: 3 hp, 400 V, 50 Hz, 500 rpm. The 3-phase output urrents i a, i b and i of FSTPI with IM are shown in Fig. 4. The torque speed harateristi of the indution motor without load is shown in Fig. 5. The speed inreases linearly and reahes the rated speed 500 rpm at steady state in 0.75 s. At starting, the torque inreases and redues to a minimum value when the speed reahes the rated value. In Fig. 6 the torque speed harateristis is shown for a full load of 0 N -m. The performane is seen on the basis of Total Harmoni Distortion (THD) with load and without load. It is found that THD without load is 9.4% and with load is 5.70%, as shown in Figs. 7 and 8. 98

5 Miroontroller Based PWM Controlled Four Swith Three Phase Inverter Fed... Fig. Simulink blok diagram of FSTPI fed drive system. Fig. 3 Complete Simulation Ciruit diagram of FSTPI fed IM Drive system. Fig. 4 Three phase output urrent i a, i b and i waveform of FSTPI with IM. 99

6 N.K. Mohanty, R. Muthu Fig. 5 Rotor speed in rpm vs. time in s and Eletromagneti torque in Nm vs. time in s without Load. Fig. 6 Rotor speed in rpm vs time in s and Eletromagneti torque in Nm vs time in s with 0 Nm Load. Fig. 7 THD without Load for phase urrent i a. 00

7 Miroontroller Based PWM Controlled Four Swith Three Phase Inverter Fed... Fig. 8 THD with load for phase urrent i a. 4 Experimental Work and Results 4. Software implementation In the experimental work, soure ode is written in the C language using MPLAB s inbuilt text editor. The soure file is then ompiled by invoking the PCB or PCM ompiler in the MPLAB window. The ode was tested using MPLAB s simulator. Finally the miroontroller is plaed in the PICSTART programmer and programmed. 4. System hardware design The omplete prototype of the experimental setup is shown in Fig. 9. The details of the omponents used in this experiment are given in Table. The potential transformer is used to provide the power to PIC miroontroller board and driver iruit board. A single phase diode bridge retifier and filter iruit is used to onvert AC to DC. Four MOSFETs and -split apaitors are used to form FSTPI. The output of FSTPI is onneted to the 0.5 hp 3-phase Indution Motor. Osillosope is used to display the PWM pulses and the output urrent waveform of i a. Table Hardware omponents. Components Ratings Capaitor 000 μf, 50v Inverter MOSFET (IRF 460) Indution Motor 0.5 hp, 3-phase, 50Hz, 400v, 430 rpm Miroontroller 6F877A Retifier 0 V, 5 A, Single phase Bridge Retifier The miroontroller based ontrol system hardware has been programmed to vary the frequeny of the PWM signal that ontrols the frequeny of the FSTPI. The PWM module gets two inputs duty yle and frequeny. The 0

8 N.K. Mohanty, R. Muthu frequeny is onfigurable within the range 0Hz khz and the duty yle an be varied from 0% to 00%. The PWM signals of the MCU are applied to the gate of MOSFET through gate driver iruit. The gate driver provides isolation, low impedane and high urrent supply to drive the MOSFET. By ontrolling the input voltage to the analog ADC, the output frequeny of the Miroontroller an be ontrolled. Fig. 9 Complete hardware setup of PIC miroontroller based FSTPI fed IM Drive. 4.3 Experimental results The experimental results obtained are shown in Figs. 0-. Figs. 0 and show the ontrolled output PWM pulses of MCU for swithes S and S, with adjustable pulse width and frequeny. Pulses of S 3 and S 4 are similar but reverse of S and S. The output urrent i a of the single phase system fed to an indution motor is shown in Fig.. Fig. 0 Pulses to swith S. 0

9 Miroontroller Based PWM Controlled Four Swith Three Phase Inverter Fed... Fig. Pulses to swith S. 5 Conlusion Fig. Output urrent i a of FSTPI with IM. A PIC miroontroller based PWM ontrolled FSTPI fed Indution Motor drive has been designed and implemented suessfully. The simulation and hardware implementation results are presented to verify the feasibility of the system. The implementation of the proposed work shows the pratial industrial appliation FSTPI. 6 Referenes [] J. Kim, J. Hong, K. Nam: A Current Distortion Compensation Sheme for Four-swith Inverters, IEEE Transations on Power Eletronis, Vol. 4, No. 4, April 009, pp [] M.B.R. Correa, C.B. Jaobina, E.R.C. Silva, A.M.N. Lima: A General PWM Strategy for Four-swith Three-phase Inverters, IEEE Transations on Power Eletronis, Vol., No. 6, Nov. 006, pp [3] M.N. Uddin, T.S. Radwan, M.A. Rahman: Fuzzy-logi-ontroller-based Cost-effetive Four-swith Three-phase Inverter-fed IPM Synhronous Motor Drive System, IEEE Transation on Industry Appliation, Vol. 4, No., Jan/Feb. 006, pp. 30. [4] C.T. Lin, C.W. Hung, C.W. Liu: Position Sensorless Control for Four-swith Three-phase Brushless DC Motor Drives, IEEE Transations on Power Eletronis, Vol. 3, No., Jan. 008, pp

10 N.K. Mohanty, R. Muthu [5] F. Blaabjerg, D.O. Neasu, J.K. Pedersen: Adaptive SVM to Compensate DC-link Voltage Ripple for Four-swith Three-phase Voltage-soure Inverters, IEEE Transations on Power Eletronis, Vol. 4, No. 4, July 999, pp [6] Mirohip Tehnology, 00, PIC6F877A Data sheet, [7] M. Vasudevan, R. Arumugam, S. Paramasivam: High-performane Adaptive Intelligent Diret Torque Control Shemes for Indution Motor Drives, Serbian Journal of Eletrial Engineering, Vol., No., May 005, pp [8] M. Bounadja, A. Mellakhi, B. Belmadani: A High Performane PWM Inverter Voltage-fed Indution Mahines Drive with an Alternative Strategy for Speed Control, Serbian Journal of Eletrial Engineering, Vol. 4, No., June 007, pp [9] K. Rathnakannan, V. Ranjan: The Modeling and the Analysis of Control Logi for a Digital PWM Controller based on a Nano Eletroni Single Eletroni Transistor, Serbian Journal of Eletrial Engineering Vol. 5, No., Nov. 008, [0] MATLAB, Simulink User Guide, Math Works In.,