Research On Modulation And Control Strategies Of Three-level Active Power Filter

With the fast development of power electronics, power quality problems likeharmonic current had become worse day by day. To solve problems of power quality,the active power filter was invented. With the traditional two-level inverter topologycompared, the three-level active power filter has become a hot research focus as itsapplication in high power for high voltage and lower output harmonic distortion.The LCL filter diode neutral point clamped three-level active power filter basedon timing multi-comparison control strategy and space vector pulse width modulationstrategy PR control strategy was researched separately.The LCL filter installed to the three-level active power filter as output filter forrestricting indeterminate-frequency high order harmonic. Initially, the work principleand operational modal analysis of three-level active power filter were analyzed; thechoice of two common methods to detect the compensation current is analyzed, whichshows with current hysteresis control the system is stable only when detectinginverter-side current as compensation current; a LCL filter Plane iterative designalgorithm in consider of switching frequncy fluctuation and a virtual resistor controlstrategy based on grid current feedback was proposed.The three-level active power filter based on constant switching frequncy controlstrategy was researched with three-level space vector pulse width modulation strategybased on two-level SVPWM strategy and a neutral-point potential balance controlmethod based on capacitor charge balance. An improved PR controller was proposed,its stability and parameter design was analyzed.The three-level active power filter prototype was debugged, a simulation basedon Matlab/Simulink was done to verify the modulation and control strategy above,and the experiment results have proved the strategy above is reliable.