D.K.W. Cheng

Bio: D.K.W. Cheng is an academic researcher from Hong Kong Polytechnic University. The author has contributed to research in topics: Capacitor & Switched capacitor. The author has an hindex of 2, co-authored 4 publications receiving 20 citations.

Harmonic compensation for nonlinear loads by active power

Abstract: This paper studies a single phase shunt active power filter (APF) using a bi-directional full-bridge converter with capacitive energy storage to compensate for the harmonics generated by nonlinear loads. The usage of a capacitor as a reactive power source for the APF simplifies the circuitry. The harmonic current reference is obtained by feeding the load current signal into a 50 Hz notch filter. The simple and fast hysteresis control strategy involving only a few analog and logic components makes it attractive for the low power domestic application. The usefulness of the proposed control algorithm is confirmed by simulation as well as by experimental results.

On the performance improvement for design optimization of buck convertors

Abstract: In the design of PWM DC/DC convertors, standard design formulae are used but the final design is not necessarily an optimized design. Efficiency of convertors can widely change with variations in component values or frequency. Extensive information or literature is unavailable which assist the designer in visualizing the effect of component value variation or switching frequency variation. In this work, dependence of efficiency of buck convertors on different circuit parameters has been reported in both continuous and discontinuous mode. Experimental results have been presented in a way to clearly indicate the variation in efficiency with change in component values or switching frequency. Significant improvements can be obtained by adjustment of frequency only, indicated by the results obtained. Analysis results are in close agreement with simulation results.

On the reduced component count and low loss switched capacitor DC/DC convertors

Abstract: A very large number of components, in the conventional switched capacitor DC/DC stepdown convertor, make them unsuitable for practical applications and implementation in the integrated circuit form. Large ripple and charge-up losses result because of the in-series charging and parallel discharging into the load. We propose a new modified topology by inclusion of switches and capacitors, extendible to a matrix of switches and capacitors. Large component count can be reduced up to one-third of various designs. Ripple can be reduced and charge up losses per step can be reduced. Analysis and simulation results are reported.

Effects of the PCB layout on the surge suppression in power convertors with coordinated surge suppressor devices

Abstract: Random selection of PCB layout and placement of the surge protection devices in the protection circuitry results in a large overshoot with oscillatory response. The clamped output voltage level includes the overshoot due to distant placement of the suppressor devices and EMI filter capacitors. This degrades the performance of transient voltage surge suppression systems. The three fold decrease in track width deteriorates the performance substantially. An experimental study with supporting formulae is reported. Effects of different PCB layouts and placement of varistors driven with a 1.2/50 /spl mu/s combination wave is reported. The effect on the performance due to location of the EMI filter capacitors and varistors on the PCB track is discussed along with the results. The resulting waveforms are reported to depict the effect and results are discussed with conclusions.

On the reduction of component count in switched capacitor DC/DC convertors

Abstract: Conventional switched capacitor power convertors are unsuitable for many practical applications because of their large component count. A new modified topology is proposed for step-down DC/DC switched capacitor power convertors using a multistage structure of switches and capacitors. The component count can be reduced by up to one third or more for various designs. The ripple output and inrush current also are reduced. Simulation results and their analysis are provided.

Reciprocal effects of the distorted wind turbine source and the shunt active power filter: full compensation of unbalance and harmonics under ‘capacitive non-linear load’ condition

Abstract: Available compensating algorithms for shunt active power filters (SAPFs) and unified power quality conditioner perform somehow improperly in practice under certain circumstances. Typical examples could be any distorted `non-linear loads' showing low impedances at certain frequencies; also, there are technological limitations for the SAPF in modulating switching frequencies, including microcontroller processing speed, the employed control and modulation techniques, delays and so on. This study proposes an advanced universal power quality conditioning system (AUPQS) to fine tune the available solutions for generating purely sinusoidal wind turbine-end currents under both distorted-unbalanced load-terminal voltages and non-linear load conditions (capacitive loads leave much worse consequences than those of the inductive). It is shown that both series and SAPF are capable of full compensation of microgrid by the SAPF using the advanced generalised theory of instantaneous power. Meanwhile, the resultant source currents could be somehow non-sinusoidal. However, the proposed AUPQS will be able to fully eliminate the consequence of voltage asymmetry and unbalanced waveforms on the SAPF, generated because of the wind turbine operation by performing certain corrections on these solutions. Moreover, an independent single-phase rectifier is proposed at the load-end to regulate DC-link voltage. Effectiveness of the proposed AUPQS is confirmed by Simulink simulations.

Zero-sequence harmonics current minimization using zero-blocking transformer and shunt LC passive filters

Abstract: This paper presents a method for zero-sequence harmonics current minimization using zero-sequence blocking transformer and passive filters. The zero-sequence blocking transformer placed in series with the source provides high zero-sequence impedance while the shunt- passive filters placed parallel with the load provides low zero-sequence impedance. Thus, the zero-sequence harmonics currents tend to flow through the filter instead of the source. The effectiveness of this method depends on the ratio of zero-sequence blocking transformer impedance to filter impedance. This method offers relatively low-cost solution, while the passive components used make this. method relatively more reliable. The analysis is confirmed by simulation. The simulation result is verified through experiment work.

Implementation of shunt active power filter using sliding mode controller

Abstract: In this paper control of shunt active power filter with sliding mode controller is considered. The compensation by shunt active power filter involves harmonics mitigation due to three phase non linear loads. The sliding mode controller is used to regulate voltage of the capacitor used in inverter. The sliding mode controller improves the dynamic response of the system and provides faster convergence. The performance of the sliding mode controller is compared with the conventional PI controller. The realization of the system is implemented for balanced and unbalanced load conditions using MATLAB/Simulink. From the analysis it can be observed that the shunt active power filter with sliding mode controller gives a better response than the conventional PI controller. The simulation results prove the effectiveness of the proposed system.

Analysis and implementation of shunt active power filter based on synchronizing enhanced PLL

Abstract: This paper addresses the analysis and software implementation of synchronizing circuit enhancement phase locked loop (EPLL) designing for use in controller of shunt active power filter (SAPF) for harmonics mitigation Advantages of EPLL structure over conventional PLL's including its capability to made and maintain zero phase difference between input signal and voltage controlled oscillator (VCO) output signal Proposed PLL architecture is extract individual harmonic component and track amplitude as well as phase angle of its input signal The extracted currents are used for reference current generation in SAPF The shunt active power filter is implemented using EPLL and investigated for three phase non-linear loads using MATLAB/Simulink platform Simulation results show effectiveness and performance robustness synchronization using EPLL for improve power quality