Design of Low-Ripple and Fast-Response DC Filters in DC Distribution Networks

Abstract

The design and parameter selection of low-ripple and fast-response direct current (DC) filters are discussed in this study with the aim of alleviating the influence of a DC-side low-frequency voltage pulsation on a sensitive load in a DC distribution network. A method for determining the DC filter parameters by using a mofatching most flat response algorithm is presented. The voltage transfer function of the DC-side filter in the DC distribution network is deduced to analyze its voltage transfer characteristics. The resonance peak value of the filter network is an important factor affecting the transfer speed of a filter. A pole-circle-based parameter optimization method is proposed to move the poles of the filter transfer function down and to the left of pole plane for finding the appropriate capacitance, inductance, and damping parameters. This approach effectively restricts the resonance peak value, accelerates the transfer speed, and maintains steady filtering results. Simulation and test results verify that the filter has low resonance value, rapid convergence ability, and an excellent filtering effect.Energies 2018, 11, 3128 2 of 20 into two categories: active power filtering (APF) [19][20][21][22][23] and passive power filtering (PPF) [24][25][26][27][28][29]. APF can eliminate DC voltage fluctuation dynamically by paralleling the voltage converter on the DC side. For example, Wang et al. [20] proposed eliminating harmonics in the DC bus voltage with a DC electric spring. This approach adjusts the consumption power of a non-critical load to make it follow the power variation of renewable energy. However, the ability of this method to eliminate voltage harmonics is limited considering the restricted power of non-critical loads. In Li et al. [19], a pluggable voltage pulsation suppression device was designed to realize flexible control of the voltage ripple in an AC/DC hybrid distribution network. However, adding a device at each node evidently increased the cost of investment. Lee et al. [21] suggested suppressing DC voltage pulsation using an energy storage device in the DC distribution network and controlling the converters. However, the control method is complex and the operation and maintenance costs of the energy storage device are high. In Li et al.[23], a ripple eliminator, which is a bidirectional buck-boost converter terminated with an auxiliary capacitor, was adopted to replace bulky capacitors in DC systems. Although the APF is effective at eliminating voltage harmonics, designing and controlling DC APF is complex and costly [22]. In addition, APF is rarely used in DC distribution networks with large capacity and high voltage given its limitations. The DC passive filter design is simple without the additional of a controller, acting as the main DC voltage filter in the DC distribution network. DC passive filters are mainly divided into tuned and low-pass filters. The former has a large occupational area and minimal flexibility [27]. The latter can filter the harmonics after a cut-off frequency...