Study On The Three Phase Current-source PWM Rectifier With Voltage-source Load And Its Control Strategy

Nowadays most of the Uninterruptible Power System (UPS) are based on highpower factor rectifier. The rectifiers are divided into Voltage Source Rectifier (VSR) andCurrent Source Rectifier (CSR) according to the energy-storage component in the dc-link.The UPS with a CSR front-end has some excellent properties such as parallel operationability and implicit short-circuit protection. The back-end inverter of UPS can be seen asvoltage source load of CSR. This dissertation studies the Current Source Rectifier withVoltage Source Load (CSR-VSL) and its control strategies. The main contributions are asfollows..This dissertation founds the mathematical model of CSR-VSL in abc stationarycoordinate, αβ coordinate and dq coordinate. The model in dq coordinate can besimplified differently when referenced to the capacitor voltage synchronous frame andthe grid voltage synchronous frame. Then two kinds of modulation methods of CSR-VSLare introduced and design procedures of the parameters of the main circuit are proposed.Efficiency is a very important qualification of UPS. Switching losses andconduction losses are two critical factors which affect the efficiency of CSR-VSL. Thisdissertation studies the transfer procedure of switches, draws the ideal switchingtrajectories and furthermore, deduces the theoretical computational formula ofswitching losses and conduction losses in the basis of transfer procedure analysis andspace vector modulation method.To deal with the nonlinearity and serious state variables coupling of the model ofCSR-VSL in dq coordinate, the inverse system decoupling method is introduced. Thedc-link and ac-link inverse system decoupling control strategy is designed to achieveindependent control of dc-link voltage, active power and reactive power.A singularity is found when linearizing the mathematical model of CSR-VSL in dq coordinate by using inverse system decoupling method, which means the workingrange of this method is limited. This dissertation references the dq coordinate to thecapacitor voltage. Thus, the simplified model achieves decoupling of dc-link and ac-link.So the dc-link and ac-link can be controlled separately. State variables feedback controlis proposed to dc-link control and active damping with virtual resistor is fulfilled inac-link. Under this kind of control strategy, the working range of CSR-VSL is widened.The system has zero static state error, fast dynamic response, grid side current of lowtotal harmonic distortion and high power factor.