Research On The Three Phase Grid-connected Inverter With Direct Power Control Strategies

Inverter is the last part of using renewable energy and the power output can be used directly for electrical equipment or be connected to the grid via a transmission line for users.The output power quality of inverter will directly affect and even determine the grid power quality when the inverter is connected to the grid.studying the grid inverter-controlled to increase the use of renewable energy was of great practical significance because power quality of the electricity sector was strict requirements of the utility grid in the power system.There are many control method about grid inverter,this paper main studies direct power control(DPC)method,which directly control inverter output power according to desired power of the inverter AC side.This method can separately control active and reactive power,also have strong controllability and adjustable power factor.Based on three-phase grid-connected inverter DPC,this paper have done some work:Firstly,power decoupling control is brought forward based on the traditional SVM-DPC.It improves dynamic response speed of the system,and reduces the steady-state error.Learning sensorless control method of AC motor,a concept of virtual flux (VF) is introduced in this paper.By constructing the grid virtual flux estimated the grid voltage angle,and using zero vector initialize the virtual flux to accurate positioning,which cancel AC side voltage sensor of traditional DPC in grid inverter.Moreover,we build traditional DPC and VF-DPC simulation model in Simulink platform,Simulation results showed that grid inverter VF-DPC has better dynamic performance and can achieve high energy efficiency converts,thereby,verify the correctness of the VF-DPC program.Secondly,this paper studied specific implementation way of the predictive direct power control(P-DPC)in order to overcome switching frequency is not fixed and AC side reactance design difficulties and other issues.Combines with space vector PWM,internal model control method with error compensation has been introduced predictive power control,which make system power output track the giving power in the next cycle begins or at the end of the current period.And building grid-connected inverter P-DPC and the inner-mode feedback P-DPC simulation model in Matlab/Simulink.Simulation results of two methods showed that system almost have no difference for steady power deviation,and have good stability,power factor is adjustable after addition internal model control.Finally,building three-phase inverter with VF-DPC,internal mold P-DPC and power decoupling SVM-DPC real-time simulation model on RT-LAB.Compared with the corresponding Matlab/Simulink simulation results,the feasibility of the above method is verified further.