Research On The Vector Control System Of High Power Three-level Inverter

The high-voltage inverters mainly adopts V/F control of multi-cell-cascade structure in China.The difficulty of braking in control process limits the usage cover of the inverters, which mainly applied in the speed-controlling situations for saving energy. While in the case of high performance, the V/F control system cannot satisfy the need. So the vector control or direct torque control systems of three-level, which are usually purchased from abroad are applied in the above situation. Therefore, to solve the above problem, it is a compulsory path to research on vector control of high-voltage three-level inverter.The problems incurred in the high power three-level vector control are the followings: forming the PWM control signal quickly, measuring the voltage and current, observing flux, compensating the effect of output filter, compensating the lag of digital control and so on. According to the above problems, it will propose some solutions in the essay.It will propose three simple and effective PWM control methods based on the deep research on different control methods of three-level inverter. Via the different process methods to the carry-waveform and modulation-waveform, the different control schemes can be found out. And the principles of dead-time compensation, neutral-point control and narrow pulse elimination are analyzed deeply; meanwhile the solution methods are presented accordingly.It also analyses the current problems of high-power vector control. Meanwhile, it offers some solution methods: a) The voltage and current sensor based on∑/△type A/D converters can solve the isolation and EMC problems owing to high power and voltage. b) The calculating method of motor voltage and current can count the influence of output filter. c) The calculating method of motor emf can compensate the delay of current differential signals. d) The new motor voltage model (VMO) for observing flux can overcome delay and drift problem. e) The current pre-control can reduce torque response time.At the end of the essay, it will list experiment system design methods, and set up the control system using the TMS320C32. Via experiment results, the effectiveness of the proposed solutions is proved.