Research On Double Closed Loop Strategy Of Three-phase Independent Inverter With LC Filter For Harmonic Suppression

The basic control idea of the traditional three-phase inverter is that AC is controlled by proportional integral by equivalent to DC after the two coordinate conversion from the three-phase static coordinate system.This kind of control strategy can achieve a certain control effect,but it has a limited effect on the harmonic suppression of the output waveform for the inverter.For the new controller,such as deadbeat controller,repetitive controller and predictive controller and so on,they have some advantages and some disadvantages in application.In order to suppress the voltage harmonics,the double closed loop control strategy of three-phase independent inverter with LC filter has been researched.The main contents have been listed as follows:(1)The proportional resonant controller has been researched in detail.The quasi proportional resonant controller has been added a cutoff frequency to avoid the tracking the frequency shifting,and low gain at fundamental frequency after the controller was discretized.The inverter can get a better output characteristic by using quasi proportional resonant controller.However,the harmonic suppression effect of quasi proportional resonant controller is not satisfactory for other frequency.The 5 subharmonic and 7 subharmonic can be effectively suppress by adding the quasi resonance controllers to become a multi quasi proportional resonant controller.(2)The proportional complex integral controller has been researched in detail.According to the principle of the system output tracking input in the classical control theory,the principle of the proportional complex integral controller's infinite gain at the fundamental wave' frequency has been described in detail through the method of solving the steady-state error of the AC,and the view of linear system's superposition principle and frequency domain analysis.On the basis of proportional complex integral controller,the quasi proportional complex integral plus integral controller has been proposed by added a cutoff frequency and a integral controller.(3)The software simulation model has been built by MATLAB/simulink software and the simulations of the double closed loop proportional integral control strategy,the double closed loop multi quasi proportional resonant control strategy,the double closed loop quasi proportional complex integral control strategy and the double closed loop quasi proportional complex integral plus integral control strategy have been carried out.(4)Improvement of experiment platform and experiment.A LC filter has been designed and fabricated based on TLI-X00 modular power electronic platform in the laboratory.The LC filter is used to filter and obtain the capacitor voltage and the inductance current in real time.The space vector pulse width modulation process has been realized with software.The ePWM module register and the ADC module register of TMS320F28335 have been configured to generate the PWM drive signal,and realize sampling function.The experiment of the double closed loop multi quasi proportional resonant control strategy and the double closed loop quasi proportional complex integral plus integral control strategy have been implemented by the inverter experimental platform.The simulations and experimental results have showed that the double closed loop quasi proportional complex integral plus integral control strategy can not only effectively suppress harmonic,but also effectively suppress the current disturbance caused by load mutation,and achieve good control effect compared with the other three control strategies.