| Nowadays,with the global environmental pollution and energy crisis increasingly prominent issues,pollution-free,renewable energy concerns more intense.For example,new energy generation technology,led by solar energy,has become a hot topic in today’s society due to its huge storage capacity,direct development and utilization,and clean and pollution-free advantages.As a bridge between new energy and power grid,grid-connected inverter can effectively convert the energy from new energy into ac that can be directly connected to the power grid.Therefore,the research on grid-connected inverter has become one of the key technologies to develop new energy generation.In this paper,the control strategy of single-phase grid-connected inverter is studied.Aiming at how to reduce system harmonics and improve system dynamic response,this paper proposes a double-loop PI control and repetitive control method based on dq transformation.The single-phase grid-connected inverter studied in this paper is discussed from the following aspects:(1)In this paper,single-phase grid-connected inverter is taken as the research object,single-phase full-bridge inverter is adopted,and LC type second-order low-pass filter is selected to make the output voltage be the sine wave under low-frequency signal.Sinusoidal PWM(SPWM)switching mode is adopted to generate the trigger signal of the switch.The parameters of dc voltage,busbar capacitance,LC filter and grid-connected voltage of the system are designed.(2)In view of the problems existing in the traditional double loop control method,such as: due to the ripple of the grid connected power,there will be a second ripple on the DC bus,resulting in serious third harmonic in the grid connected current,which is one of the main reasons for the increase of the harmonic in the grid connected inverter.In addition,the traditional double loop control can not directly control the inverter current through PI(proportional integral)controller,which usually uses P(proportional)controller to track,so that the system has a large steady-state error.In view of the above problems,this paper proposes a dual loop PI control method based on dq transformation to realize the independent control of active power and reactive power.In order to reduce the harmonic of the system,the method of restraining the ripple of DC bus is added to the voltage loop control.(3)In order to realize DQ conversion in single-phase inverter,it is necessary to construct an AC quantity which is orthogonal to the inverter side current before the coordinate change.Compared with three-phase inverter,the conversion process is more complicated.In view of the above problems,this paper proposes a single loop repetitive control method to control the inverter side current repeatedly.On the premise of ensuring the stability of the system,the repetitive control structure and compensation link are designed,and the harmonic suppression ability of the controller is analyzed.Compared with the double loop control method,the repetitive control is more simple and the harmonic suppression ability is stronger.(4)Build the simulation model of single-phase inverter under the environment of PSIM,and conduct simulation analysis on the double-loop PI control and repetitive control of dq transformation.The simulation results show that the power decoupling function of single-phase inverter can be realized by coordinate change,and the power grid can realize both active and reactive power output.(5)TMS320TM28335 is used as the control chip of the system to design the sampling circuit,drive circuit and protection circuit;At the same time,the Sim Coder module in PSIM is used to generate the C program code,which is directly downloaded to DSP for experimental verification of the system. |
