The Research On Control Method And Application In High Voltage Variable Frequency Field For Cascaded Inverter

The technology to adjust speed with variable frequency and high voltage is a commanding heights technology in the field of power electronic,which involves speed regulation and energy-saving for high power ac motor with all kinds of load.High voltage inverter has not a mature and consistent topological structure as low voltage inverter.H bridge cascaded multilevel inverter(HBCMI) is becoming the main topological structure of high-voltage inverter because of the features of the modular design.the use of low voltage components to realize high voltage output.the facilitating of fault redundancy design for inverter.etc.The modulation method is the hot issue and difficulty in study for HBCMI due to the need of real-time control to many power switch devices. This paper researchs and puts forward different modulation method suitable for HBCMI, and looks for the relationship and discipline between them.It makes the theory analysis, simulation and experimental validation for different modulation method,and provides some effective methods to improve the control performance for HBCMI in the field of high voltage variable frequency.This paper also makes research on feedback cascaded inverter with four quadrant operation.Because HBCMI has many H bridges and power switch devices which need synchronization control, it needs multiplied modulation pulse compared to low voltage inverter.In order to simplify the calculating of PWM pulse for HBCMI, the phase shift principle is the most simple and intuitive method which is in for the PWM pulses of other each layer H bridge after getting the first layer H bridge’ PWM pulse.The most commonly used modulation method-"phase shift SPWM" for HBCMI is taken as the foundation of this paper.The " new carrier reverse phase shift SPWM "and" new carrier same phase shift SPWM "are taken out by changing the double polarity carrier of phase shift SPWM to" reverse single polarity carrier "and" same phase polarity carrier " respectively.The modulation mode can effectively reduce switch loss because the power switching device remains on or off state for half a cycle in each cycle of modulation wave.With the launch of the new carrier phase shift SPWM,"variable ring width constant frequency current hysteresis control method" is taken out by changing its pulses producing way by the comparing of triangle carrier and sine wave to current hysteresis control which can realize the fast track of inverter actual output current to given current. In this paper, based on the phase shift SPWM of HBCMI,"phase shift SVPWM" is launched by the changing of implementing pulse to SVPWM.SVPWM is widely applied in high performance vector control for two level inverter.SVPWM actually is evolved by SPWM.SVPWM is only applied to two level inverter with eight switch states and can not be directly applied to HBCMI with a large switch states.The output voltage of HBCMI is the difference value between two level inverter group’output voltage formed by left bridge arms of all H bridges and two level inverter group’ output voltage formed by right bridge arms of all H bridges from the topology of HBCMI.So a suitable modulation of "phase shift SVPWM" is introduced for HBCMI by the use of phase shift principle and SVPWM.This paper also makes research on "rotor field-oriented vector control"to motor by the implementing of HBCMI’s phase shift SVPWM.Phase shift principle is focus on the simple and easy generation of modulation pulse for HBCMI which is hard to achieve inverter output performance optimization by improving modulation method.So this paper makes research on simplified space vector modulation and its performance optimization in450coordinate system for HBCMI.Because it needs to sample the inverter output voltage in every sampling period for HBCMI in simplified space vector modulation, the single voltage vector modulation method can be changed to improve the inverter’s output performance in each sampling period."optimization switch frequency modulation algorithm " and "inhibit inverter zero sequence voltage output modulation algorithn" in450coordinate system for HBCMI are researched,which can effectively reduce the inverter switch loss and reduce the common mode voltage forming by inverter output voltage in the motor respectively. This paper also makes research on HBCMI with the feedback function and provides some theoretical basis in the occasion which need four quadrant operation for HBCMI.The paper not only makes theoretical analysis to the above proposed all sorts of modulation methods,but also gives a large number of simulation waveform to prove the modulation methods correct and effective at the same time.This paper finally makes engineering design for the application of HBCMI in the field of high voltage variable frequency.The paper gives out the main circuit’s hardware and software design to HBCMI,which includes multi-channel pulse trigger design based on FPGA, the main control circuit’s hardware design and part software design based on DSP, etc.The proposed all kinds of modulation method for HBCMI are validated in the engineering device of high voltage inverter and it gives out all the waveforms which verifys the correctness of the proposed modulation methods.The paper can promote the very good industrial application prospect for HBCMI in high voltage variable frequency areas.