The Research On Four-quadrant Operation Cascade Multilevel Inverter

Since input of power unit input of traditional cascade multilevel inverter (CMLI)adopts uncontrolled rectifier bridge, CMLI can not reverse the power into the grid andlimits it’s the application of the four-quadrant operation occasion shuch as mine hoist.At the same time, because of higher harmonic is contained in the input current, so inthe case of without the phase shifting transformer, this will cause harmonic pollutionto power grid. To solve the former problems, a novel four-quadrant cascade multilevelinverter (FCMLI) topology which makes the high voltage electric machine operate infour-quadrant occasion is proposed in this dissertation.Firstly, study of power unit of the three-phase PWM rectifier is made, itsmathematical model under three kinds of coordinate system is analyzed and two vectorcontrol methods of PWM rectifier is put forward which are feed forward decouplingcontrol and sliding-mode structure direct power control based on the ac voltagesensorless technology. This provides energy bi-directional flow of FCMLI an effectiveway.In the second, to the in-depth analyzing of traditional unipolar SPWM modulationmethod and phase-shift carrier SPWM method in inverter section of the FCMLI, anovel phase-shift carrier unipolar SPWM modulation algorithm is introduced.Mathematical model and simulation model of the algorithm are given. Each H-bridge’spower switching devices in half of the half wave modulation cycle is in a normallyopen or normally closed state, which can greatly reduce the switching frequency andlower the switching loss of switch device. In addition, a phase-shift SVPWM controlalgorithm based on CMLI is proposed, in which pulse is generated by a simple wayand multilevel voltage output is realized under the premise of without any increase inprocessor computing complexity, under the premise of without any increase inprocessor computing complexity. Simulation result verifies the correctness of themethod.Thirdly, the paper deduces the mathematical model of power unit PWM rectifier andH-bridge inverter. Thus it gives the mathematical model of FCMLI drawingconclusion of simultaneity and uniformity of power unit when motor is in a state ofgenerating renewable energy distribution. The PWM rectifier power control algorithmis applied to four-quadrant power unit realizing unit power factor of input current. Finally, a FCMLI low voltage experiment device of which each phase consists offive power unit is built. For experimental verification of the proposed controlalgorithm, the multi-channel pulse trigger based on DSP and FPGA is designed. Theconsistency of experimental results and the simulation results illustrates the validity ofthe theory proposed in this paper providing a theory basis for the subsequent practicalengineering applications.