Research On Dead-time Effects And Compensation Methods Of Inverters

The rapid development of modern power electronics makes a great contributionto the progress of AC drive technology. With the emergence of various pulse-widthmodulation techniques, many issues are increasingly prominent. Since powerswitches of inverter main circuit are not ideal components, the upper and lowerswitches may turn on at the same time. To avoid this situation, dead time added tothe driving signal of power switch is essential. Although the dead time is short, itcauses large distortion of inverter output voltage and current waveform in highswitching frequency system and affects control performance. Instability can evenhappen. In order to decrease the dead zone effect on the performance of inverter,reducing the harmonic component of output waveform is becoming an importanttechnical problem and has practical industrial application significance.The dead-zone effect leaded by dead-time is analyzed firstly. The effect causesthe change of output voltage and phase, low harmonic increasing and zero currentclamping in the zero current areas. Fourier analysis was carried out on the dead zonevoltage so that rationality of the dead zone average voltage method is verified. Theinfluence of the dead zone effect with different modulation modes is analyzed.Simulation indicates single polarity modulation mode has small effect on outputcurrent waveform.Existing main dead zone compensation method can be divided into threecategories, namely, direct pulse width adjustment method, the average voltagecompensation method and invalid switch elimination method. Through simulation itcan conclude that each method can suppress the dead-zone effect. Based on theanalysis of the traditional inverter dead time compensation method, this papercompares and discusses these methods used for inverter control system. Eachcharacteristic and improvement direction is pointed out. A modified invalid switch dead-time compensation circuit is presented on baseof invalid switch elimination method. Through the anti-parallel diode conductionmethod, the output current zero area is divided. It reduces the disadvantages of thedead zone effect. Compared to the traditional invalid switch elimination method, itdoesn’t affect the inverter output dynamic performance except zero area and prolongthe service life of power tube. More importantly, it can confirm current crossing zeroarea accurately and solve the disadvantages of the dead zone effect well.Based on microcontroller dsPIC30F4011/4012, a single-phase inverter controlsystem is developed. The control circuit, drive circuit, power supply circuit and adetection circuit is designed in details. The modified invalid switch dead-timecompensation circuit and related experiments are implemented. The experimentalresults show that output current waveform has greatly improved by adding thecompensation circuit. The effectiveness of the proposed circuit is verified.