In recent years, implementation of vector-controlled inverter for industrial servo control system is very common due to the development of microprocessors and power semiconductors. And variable speed control of motor using vector control algorithm is used even in consumer products such as refrigerators, air conditioners, and washing machines that require very simple speed control.
The vector-controlled inverter system consists of the converter part and the inverter part. The converter part performs the function of rectifying ac voltage and smoothing the output voltage waveform with inductor or capacitor to remove the ripple. The type of rectifier with a smoothing capacitor causes narrow pulse of current waveform only near the peak voltage of power supply. These pulse currents consist of fundamental and harmonic components. Fundamental current components have the disadvantage of degrading power factor due to the phase difference from the supply voltage waveform and harmonic components have the disadvantage of worsening THD of input current.
In this paper, in order to solve these problems in low cost, a boost converter to control power factor was add to converter part of conventional vector-controlled inverter. A microcontroller in this inverter system performs simultaneous vector-controlled algorithm of inverter part and power factor control algorithm of boost converter. In boost converter, excellent control function of power factor is performed regardless of changes in input voltage by using the PLL phase synchronization method. A digital average current control mode for input current control and PI control algorithm for output voltage control are used in power factor correction control program.
In order to process vector control and power factor correction algorithm in high speed, Cortex-M4 microcontroller with DSP function and a built-in FPU is used. In boost converter MOSFET is used for fast switching and in inverter part IPM, a miniaturized IGBT module, is used for simple and economic power circuit. In vector-controlled inverter, PI control algorithm is used for inverter current control and motor speed control. And the inverter used space vector PWM method which has less harmonic components and causes excellent current control response.
The computer simulations and experiments were carried out to investigate performance of the power factor correction circuit and characteristics of deceleration, acceleration and reverse rotation of 200[W] three-phase induction motor. The results of simulations and experiments show that the proposed boost-converter-type power factor correction circuit bring high power factor and low THD characteristics while inverter part is stably performing vector control. Therefore, this type of power factor correction method can be used in low cost vector-controlled inverter system for small three-phase induction motor.