Research On ANPC Three-level Active Power Filter

With harmonic and reactive power pollution in the grid become increasingly serious and the strict power quality demand of electrical energy, active power filter is studied and applied as an effective resolution. Tradition neutral-point-clamped active power filter has loss distribution unbalancing problem. Some devices generate more heat energy than others, which prevent active power filter from increasing capacity and robustness. Active neutral-point-clamped topology overcomes the deficiency of neutral-point-clamped topology with the ability to balance loss distribution among power electronics. This article applies active neutral-point clamped three-level topology to active power filter, analyzes the loss distribution and neutral-point balancing control of the APF.This article firstly explains the operating principle of ANPC three-level active power filter, compares the two traditional PWM modulation strategies of ANPC converter, designs PI and repetitive controller as well as corresponding parameters based on the advantages and disadvantages of PI control method and repetitive control method, analyzes the stability of the controller.Then this article chooses a loss calculation method of power electronics that is relatively precise and easy to realize, establishes equivalent thermal res istance model to get temperature parameters of power electronics which will increase accuracy of loss calculation result. Under the circumstances that total loss of converter is invariant, an improved PWM modulation strategy is proposed to realize loss balance among power electronics based on comparison of power electronics loss distribution between two PWM modulation methods. This method is also available for loss balancing control of ANPC converter with IGBT module.At last, active power filter neutral-point voltage fluctuation model is studied. Neutral-point voltage balancing control skeme is proposed based on current reference using zero-sequence current injection method, needed zero-sequence current calculation method is also deduced. Neutral-point voltage self-balancing ability of three-phase four-wire system APF is proved by theory deduction and simulation. The differences and correlation of neutral-point voltage balancing control methods of three-phase three-wire system and three-phase four-wire system is analyzed, neutral-point voltage balancing control method of three-phase three-wire system is applied to three-phase four-wire system to attenuate DC side neutral-point voltage fluctuation. Suspended capacitor is introduced to improve ANPC converter topology in order to solve the limitation that neutral-point voltage balancing control based on zero-sequence injection method has controllable region, the influence of suspended capacitor on DC side capacitor voltage is discussed and neutral-point voltage balance under extreme situation is guaranteed.