Applying an LCL-filter to a four-wire active power filter

Especially in the case of voltage source shunt four-wire active power filters, the switching frequency current ripple is a significant problem and cannot be completely suppressed with an L-filter without impairing the harmonic filtering performance of the system. An LCL-filter is a third-order low-pass filter, which is commonly used with PWM rectifiers and inverters. When properly designed, an LCL-filter offers a much better suppression of the switching frequency current ripple than a simple inductor. However, there are many matters to consider when designing an LCL-filter. The wide control bandwidth of active power filters makes the design of an LCL-filter even more challenging. This paper studies the suitability of an LCL-filter for four-wire active power filter topologies, presents an example LCL-filter structure and discusses matters related to design and accurate modeling of an LCL-filter. Finally, the proposed LCL-filter structure is applied to two common voltage source shunt four-wire active power filter topologies and the performance of the systems is verified by computer simulations and experimental tests