Research On Controlling Strategy Of Single Phase Frequency Variable Inverter Based On Active Damping

The frequency variable inverter has been widely used in household appliances,electric drive and test power supply etc. The frequency variable inverter designed inthis paper is used in electric energy meter calibration field, and the inverter demandsa high quality of the output voltage and a wide range of the output voltage frequency.The frequency variable inverter mostly adopts the dual-loop control strategy based oninner inductor current loop and outer instantaneous voltage loop. The control strategyhas a fast dynamic response, simple design, small rate distortion of output voltageand the protection circuit is easy to design etc. But for the inverter designed in thispaper, there will be three problems in dual-loop control: the output filter resonance,the output voltage of the steady-state error and the DC component of the outputvoltage. Therefore, this article mainly studies the controlling strategy of single phasefrequency variable inverter based on active damping.This article first establishes a single-phase full-bridge inverter mathematicalmodel with the use of state-space averaging method and chooses of the unipolardouble frequency modulation. Secondly, the filter parameters are designed byanalyzing the magnitude-frequency characteristics of the filter frequency. Wherever,by increasing the damping ratio of the resonant, this article adopts active dampingcontrol algorithm in order to suppress the filter resonance peak of no-load. Bytransforming the active damping control block diagram equally into the inductorcurrent feedback form, the dual-loop control strategy based on inner inductor currentloop and outer instantaneous voltage loop is established and the regulator parameterdesign method is given.Based on the analysis of the output characteristics of the inverter, acquiring highsteady precision by adjusting the dual-loop PI controller parameters is more difficult.We introduced output voltage RMS loop based on dual-loop control. By analyzingthe RMS-loop control block diagram, the simplified model of RMS loop isestablished and parameters of the RMS loop regulator is designed.In order to suppress the DC component of the output voltage inverter withdual-loop control, the paper proposes a new method for the DC component detectionand suppression. We introduced a DC component closed loop and used the feedback control method for suppressing by detecting the DC component of the output voltageof the output voltage. The impact of a given reference voltage on the DC componentof output voltage is analyzed. The DC component control model is established andthe regulator parameter calculating method is given.Based on the analysis of control strategy and the results of simulationexperiments, experimental platform is built. The active damping control experimentand improved control strategy combined with RMS loop and DC component loopexperiment is completed. Experimental results show that the inverter with suchcontrol strategy meets the requirements of technical indicators.