Novel Resonant Transition Soft-Switching Three-Phase PWM Inverters

Investigations on soft-switching three-phase inverters are overviewed, generalized, and evaluated, and the key problems on novel soft-switching three-phase PWM inverters are discussed in detail.A novel topology of DC-rail ZVT voltage source three-phase PWM inverter is advanced. The principle, design considerations, modulation index and efficiency of the proposed inverter are discussed in detail. All the power devices including main switches and auxiliary switches are in soft-switching condition (ZVS or ZCS), while the freewheeling diodes are turned off in zero current condition. Besides, the control of resonance between inductance and capacitor can be easily realized without needing of setting the threshold values of the inductance current. The proposed inverter can work in four-quad, as well.Influence of DC-rail zero-voltage notch on the output of the inverter is investigated, and an important conclusion is obtained that the direction of output current of the inverter is not effected by the voltage deviation produced by DC-rail zero-voltage notch, on the basis of which, a new simple correction approach is put forward. Experiment results show that the proposed correction method is effective.A novel resonant pole ZVT three-phase PWM inverter circuit for three-phase AC motor driving is presented. The proposed circuit has the feature of being more flexible with three inverter arms in ZVT process. Using only one resonant inductance, the inverter can not only reduce the power loss of inductance but also avoid possibility of unbalance in motor's three stator windings. The residuary energy in the resonant inductance can be feedback to the power source, as well. In addition, all of the auxiliary switches in the inverter are in ZCS mode. The control logic of the auxiliary switches is much simple. Based on the analysis of the proposed inverter, the zero-transition condition is obtained. Aprototype is made verifying the feasibility of the new inverter.Switching loss and efficiency of the proposed resonant pole ZVT three-phase PWM inverter are analyzed and discussed. Results of calculation and testing of the prototype together with a hard-switching inverter with the same specification show that an improvement of 2%~3% is obtained.Based on the analysis of drawbacks of existing SVPWM technique in resonant pole ZVT three-phase PWM inverters, several improved SVPWM methods are presented. A new control method, which can reduce the switching number of times of auxiliary switches to one half, is put forward. The new approaches are verified by experimentation.A generalized method to design a soft-switching VVVF is also discussed in the end.