Research On The Integrated Control Of AC-DC-AC Converters

The diode and thyristor used in the rectifier brings low power factor in the grid side,current harmonics“pollution”in the grid side and big capacitance and size in the DC side,for the reason that rectifier adopt non-controlled or phase control method.if the rectifier is substituted by PWM rectifier and consist a back to back constructer of dual PWM system,that the power of the grid can run to unity power factor,motor power can flow backward to grid and the motor can run in four quadrant operation.It is a real green power converters.Integrate the rectifier and inverter of dual-PWM converters can realize the quick response so as to reduce the capacity of DC side,this paper foucs on the PWM rectifier strategy,and integrated-control strategy of dual PWM.First,this paper introduces the topology and principle of the dual PWM converters,and discusses the mathematics model PWM rectifier and PMSM.For the control strategy of dual PWM converters,Direct Power Control（DPC）theory,including instantaneous power theory,hysteresis loop and switch table,is discussed in details,due to the the switching frequency is not fixed in traditional DPC,this paper introduces a new predictive DPC based on space vector modulation.For the control strategy of PMSM is not the emphasis,just the i_sd=0rotor field oriented space vector modulation is discussed.Secondly,analyzing considering the energy flow among rectifier side,DC side and inverter side,power feedforward control feedforward the inverter power as compensation to the rectifier strategy.it is a easy way to realize integrated-control of dual PWM converters.As the capacitor power direct reflect the capacitor power fluctuation,this paper also analyses the integrated-control strategy of dual PWM based on direct capacitor power,the small signal model and the state observer model of dual PWM converters is established.Finally,establish the simulation model of dual PWM converters system in the MATLAB/SIMULINK environment,and compare the simulation result between independent control and inverter power feedforward to rectifier strategy and direct capacitor power control strategy respectively to verify the feasibility of two control strategy.