Research On Multi-level Current Source PWM Rectifier Based On Hybrid Switching Devices

Rectifier is an important part which connects the power electronic devices to thegrid. Multi-level current source PWM rectifier has the advantages of flexible currentcontrol, large power capacity, low input current total harmonic distortion, fast transientresponse and so on. It has been widely used in the field of the electric vehicle charging,wind farms converter stations, industrial heat treatment and other high-powerapplications. Take these characteristics into account, a multi-level current source PWMrectifier using hybrid switching devices is mainly discussed and analyzed in this paper.1. Main circuit topology and mathematical model are studied, and an average modelfor hybrid switching three-level current source PWM rectifier topology is presented.Dynamic models of power converters are normally time-varying. Traditional approachesare applied to analyze the power converters to achieve the time-invariant models suitablefor system analysis and design via the classical control theory. The presented powersystem consists of a three-phase controlled rectifier and an IGBT-controlled buckconverter by using the dq and the generalized state-space averaging methods. The newtype of PWM buck rectifier dynamic model is described in detail, the proposed modelcan provide good performance in both transient and steady-state responses. Theoperational principle is analyzed at the same time, and the commutation mechanism ofhybrid switching rectifier is described in detail.2. Space vector pulse width modulation (SVPWM) method for three-phase hybridswitching rectifier is discussed, an improved SVPWM control strategy is put forward. Agiven approach which the q-axis current is assigned to nonzero is to regulate the powerfactor. The excellent performance of the presented rectifier is verified by simulation andexperimental waveforms, a low current total harmonic distortion (THD) and inputsinusoidal current are effectively achieved.3. Large current and high power can be obtained by parallelling current sourcerectifiers directly. An interleaving parallel system consists of some three-phase buck-typerectifiers is described in this paper, and sample time staggered SVPWM control isadopted to ensure small AC side harmonic at low switching frequency, sector signalselection current balancing strategy is put forward to effectively solve the problem ofcirculating current between the parallel units at the same time, which may result in alarge power loss. 4. An effective method using a hybid combination of a virtual harmonic damper andan improved SVPWM technology is proposed in this paper to reduce line currentharmonics and oscillation of current source PWM rectifier LC filter link. The virtualharmonic active damper control strategy, can supress the current distortion andoscillation caused by LC resonance without affecting the fundermental power flow. Thedistortion of the line current is effectively reduced and the stability of the system isimproved.5. A digital control for mulit-level rectifier system based on FPGA is designed.SVPWM control pulse generation, sector signal selection as well as active dampingcontrol procedures are realized by EP2C5Q208C8chip. Excellent working performanceof the hybrid switching current source PWM rectifier is verified.