Implementation of Pulse Width Modulation Control using Digital Technique for Three-Phase Voltage-Source Inverter fed AC Drives

Abstract
- This paper explores the advantages and implementation of Digital Signal Processing (DSP) TMS 320F2812 to generate gate pulses. The main features of this DSP are elaborated. The technique to obtain gate pulses in different pulse width modulation methods in order to control three-phase voltage source inverter is explained systematically. The steps needed to develop the program are highlighted in detail to control frequency and the duty cycle of PWM waveform. Further Fabrication of gate driver circuit is presented. Experimental results of three-phase voltage source inverter controlling ac drive in variable voltagevariable frequency mode are also given.
INTRODUCTION
Pulse Width Modulated (PWM) converters are used to overcome the problem of low order harmonics associated with input line current rectifier circuit. PWM converter shift the frequency of the dominant harmonics to a higher value so that, these harmonics can be eliminated by employing a small passive filter. Furthermore, the PWM rectifier can markedly cut down the devices' bulk and weight, and get dynamic response faster remarkably. The PWM converters can be operated in variable frequency mode and duty ratio control mode. The analog circuits used for variable frequency control consists of voltage-controlled oscillator, logic circuits, deadband circuits, frequency limiter circuit and overload protection circuits. The analog control systems can experience performance degradation due to aging, component tolerances and drift. They lack in the flexibility to adoption of different control strategies and precision adjustment of the equal dead-bands is difficult. Hence, digital circuit is built. The digital control using a digital signal processor (DSP) provides precision and improvement in the system performance. The DSP controller offers reliability, programmability and the flexibility to adapt to the different control strategies with the same hardware. Moreover, the high-speed central processing unit allows the designer to process the control algorithms in real time. Owing to these reasons the digital control of the three-phase voltage source converter to control output threephase ac voltage is realized using a digital signal processor TMS 320F2812. A three-phase voltage source converter feeding three phase inverter is shown in Fig. 1. View of DSP is shown in Fig. 2. In this paper the algorithm development methodology to build DSP program to control the output voltage is explored. In addition to this control circuit, the high performance gate drive circuit using MOSFETs for driving the IGBTs in the three-phase HF inverter is elaborated. The experimental results three-phase VSI are also discussed.
CONCLUSION
In this paper the digital control circuit used to control threephase voltage-source converter is presented. The PWM waveform generation using DSP TMS 320F2812 is discussed step-by-step. The algorithm to develop DSP program is discussed in simplified way. The variable frequency control strategy under 180° wide gate control (square wave operation) is explained using an example. The control circuit is also used to operate ac drive in variable voltage-variable frequency mode. Finally a high performance, bipolar gate driver scheme using ultra-high speed MOSFETs IRF 510 and IRF9510 is given. The experimental results on the laboratory prototype of the three-phase VSI controlling three-phase induction motor are also presented. The digital techniques are flexible to adopt different control strategies and do not sacrifice the precision as well as system performance.