Research of hybrid active power filter based on FBD method detection
To fast and effectively detect harmonic current of power system, FBD method is proposed. Compared with method which is based on instantaneous reactive power, FBD method has no complex transformation and transformation, it can be used to detect harmonic current for single-phase, three-phase three-wire and three-phase four-wire system. But FBD method needs a low-pass filter to extract the DC current, it causes delay and phase-shifting problems, to solve these problems, this paper presents a real-time sliding window to extract the DC current instead of low-pass filter. At the same time, shows the principle of hybrid active power filter, and corresponding mathematical model is established. Finally, take a new composite control strategy. Simulation results show correctness of the detection and effectiveness of the new composite control strategy.
DEFINITION AND COMPENSATION OF GENERALIZED INSTANTANEOUS REACTIVE CURRENT AND REACTIVE POWER IN abc COORDINATES
A new definition method for generalized instantaneous reactive current and reactive power of three-circuits in abc coordinates is presented and the detection and compensation method for generalized instantaneous reactive current is proposed. The results of simulation and research demonstrate that any additional hardware is not needed for the detection of the generalized instantaneous reactive current. For abrupt change of current the accurate detection of generalized instantaneous reactive current can be implemented in one power frequency period by the proposed method, meanwhile, the transmission loss is minimal and the distortion factor of the voltage is reduced to the minimum.
Parallel operation of capacity-limited three-phase four-wire active power filters
Three-phase four-wire active power filters (APFs) are presented that can be paralleled to enlarge the system capacity and reliability. The APF employs the PWM four-leg voltage-source inverter. A decoupling control approach for the leg connected to the neutral line is proposed such that the switching of all legs has no interaction. Functions of the proposed APF include compensation of reactive power, harmonic current, unbalanced power and zero-sequence current of the load. The objective is to achieve unity power factor, balanced line current and zero neutral-line current. Compensation of all components is capacity-limited, co-operating with the cascaded load current sensing scheme. Multiple APFs can be paralleled to share the load power without requiring any control interconnection. In addition to providing the theoretic bases and detailed design of the APFs, two 6 kVA APFs are implemented. The effectiveness of the proposed method is validated with experimental results.