22-08-2012, 02:19 PM
PROGRAMABLE LABORATORY INVERTOR AND SPACE VECTOR PWM
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ABSTRACT
This paper describes space vector pulse width modulation. For implementation this technique is use programmable laboratory inverter that was designed on Department of Power Electrical and Electronic Engineering on VUT Brno. This sort of algorithm for control of AC drives serve as demonstration exercise in curse of microprocessor control of electric motor. This exercise demonstrates usage of digital signal processors for control of speed of AC motors.
INTRODUCTION
Sinusoidal PWM has been a very popular technique used in AC motor control. This relatively unsophisticated method employs a triangular carrier wave modulated by a sine wave and the points of intersection determine the switching points of the power devices in the inverter. However, this method is unable to make full use of the inverter’s supply voltage and the asymmetrical nature of the PWM switching characteristics produces relatively high harmonic distortion in the supply.
Space Vector PWM (SVPWM) is a more sophisticated technique for generating a fundamental sine wave that provides a higher voltage to the motor and lower total harmonic distortion, it is also compatible for use in vector control (Field orientation) of AC motors. This application note describes the theory of SVPWM and applies it to a practical example using a 56F803 16-bit digital signal processor and Programmable laboratory inverter designed on Dept. of Power Electrical And Electronic Engineering [8], [9].
PROGRAMMABLE LABORATORY INVERTOR
Programmable laboratory inverter was designed on Department of Power Electrical and Electronic Engineering. It consists of Digital Signal Processor DSP56F803, DC supply (for supply power electronics, sensors and other electronics), driver for power transistors and set of sensors. Programmable laboratory inverter is described in [8], [9].
SPACE VECTOR PWM GENERATION
An example of use of SV PWM has been created a program that SV PWM is used together with Constant Volts/Herzt control of an AC induction motor. The program is divided into three main parts. First part is an initialization process that is responsible for initialization the system after RESET. It configures the clock settings of the devices, intialises the
peripherals that are used for the application and enables the appropriate interrupts.Second part is responsible for calculating the SVPWM timing parameters(it means : calculate ta, tb and t0). Third part provides the Motor Speed demand (V/Hz). To this purpose is used one pin of A/D converter and provides a 12-bit resolution from an external Potentiometer.
CONCLUSION
This document has presented an overview of SV PWM theory and one way of SV PWM implementation. Program example is given for Motorola DSP56F803 DSP microprocessor and Programmable Laboratory Inverter. Example program of use of SV PWM serve to student’s introduction with Programmable Laboratory Inverter and as demonstrational exercise for students. It has been shown that the SV PWM technique utilizes DC bus voltage more efficiently and generates less harmonic distortion in a three-phase voltage-source inverter.