Yonglu Liu

Review of Active Power Decoupling Topologies in Single-Phase Systems

Active power decoupling methods are developed to deal with the inherent ripple power at twice the grid frequency in single-phase systems generally by adding active switches and energy storage units. They have obtained a wide range of applications, such as photovoltaic (PV) systems, light-emitting diodes (LEDs) drivers, fuel cell (FC) power systems, and electric vehicle (EV) battery chargers, etc. This paper provides a comprehensive review of active power decoupling circuit topologies. They are categorized into two groups in terms of the structure characteristics: independent and dependent decoupling circuit topologies. The former operates independently with the original converter, and the latter, however, shares the power semiconductor devices with the original converter partially and even completely. The development laws for the active power decoupling topologies are revealed from the view of “duality principle,” “switches sharing,” and “differential connection.” In addition, the exceptions and special cases are also briefly introduced. This paper is targeted to help researchers, engineers, and designers to construct some new decoupling circuit topologies and properly select existing ones according to the specific application.

AC/DC Matrix Converter With an Optimized Modulation Strategy for V2G Applications

To adapt the battery voltage and increase charging efficiency in vehicle to grid (V2G) systems, an ac/dc matrix converter topology is presented. Aim to solve the problem of relatively large charging current ripple in the classical current space vector modulation strategy, a sectional optimized modulation strategy, is proposed, which can reduce the charging current ripple within the whole output range. And the comparative analysis is carried out between them. A simple controller with active damping is briefly introduced; it can work at two charging modes: constant voltage charging and constant current charging. The simulation and experimental results demonstrate the validity and effectiveness of the proposed method.

Active Power Decoupling Method for Single-Phase Current-Source Rectifier With No Additional Active Switches

This paper proposes an active power decoupling method without adding additional active switches for single-phase current source rectifiers. Two identical decoupling capacitors connected across the two bridge arms operate alternatively to buffer the ripple power at twice the line frequency. First the operational principle of the proposed circuit is presented. Thereafter, a hybrid modulation method, in which input current synthesis and ripple power buffering can be carried out simultaneously, is developed. Moreover, a new effective closed-control strategy is presented, in which the decoupling control is responsive for regulating dc-link current and the rectification control is in charge of power factor correction as well as maintaining the dc component of the decoupling capacitor voltages at a given level. Consequently, complete ripple power decoupling is achieved and sine input current is obtained. Finally, the theoretical analysis is favorably verified by the simulations and experimental results.

A Single-Phase Current-Source Bidirectional Converter for V2G Applications

Bidirectional power flow, reactive power compensation capability and high efficiency are essential for vehicle to grid (V2G) systems. In this paper, a single-phase/single-stage bidirectional AC/DC converter for V2G application is presented, which consists of a line frequency commutated unfolding bridge and an interleaved buck-boost stage. In addition to sinusoidal input current, bidirectional power flow, high efficiency and reduced battery current ripple, the proposed topology uses the direct power control and PWM modulation to provide wide output voltage range and excellent reactive power compensation capability. The topology structure and operating principles of the proposed converter are analyzed in detail. The feasibility of the converter is validated and tested by MATLAB simulation.

A Control Method for Bridgeless Cuk/Sepic PFC Rectifier to Achieve Power Decoupling

Bulky electrolytic capacitor is usually needed in bridgeless power factor correction rectifiers to buffer the double-frequency ripple power (DFRP). However, it reduces the system reliability and power density significantly. This letter proposed a control method to divert DFRP to the small energy transfer capacitor. Then, the bulky electrolytic capacitor can be replaced with a small film capacitor. The proposed method is realized by making the best of the existing switching states. Therefore, it needs no extra switches or energy storage components, which are usually required in other active power decoupling methods. The operating principle is explained, and a closed-loop control strategy is proposed. Finally, the effectiveness is verified by experimental results.

Carrier-Based Modulation Strategies With Reduced Common-Mode Voltage for Five-Phase Voltage Source Inverters

Two modulation strategies based on carrier-based modulation (CBM) scheme (named RCMV-CBM1 and RCMV-CBM2) are proposed to reduce the common-mode voltage (CMV) of a five-phase voltage source inverter. The basic characteristic of them is that two kinds of carriers with opposite phase are adopted. By applying the opposite carrier to some specific phases, the switching states with higher CMV absolute value can be avoided. In RCMV-CBM1, the output phase with the third largest modulated signal uses the opposite carrier, and the peak-to-peak value of CMV is reduced by 40%. In RCMV-CBM2, the output phases with the second largest and fourth largest modulated signals use the opposite carrier, and the peak-to-peak value of CMV is decreased by 80%. However, the ripple analysis reveals that RCMV-CBM1 has an advantage over RCMV-CBM2 in current quality. In addition, the optimized RCMV-CBM1 and RCMV-CBM2 are presented for reducing the output current ripple. Finally, a scaled-down prototype is built to verify the correctness and effectiveness of the proposed modulation strategies.

A Single-Phase PFC Rectifier With Wide Output Voltage and Low-Frequency Ripple Power Decoupling

This paper proposes a single-phase power factor correction (PFC) rectifier to achieve high power factor, wide output voltage range, and ripple power decoupling without using electrolytic capacitors. It consists of two parts: PFC circuit and output voltage regulation circuit. The load side is involved in both parts, which is different from the regular two-stage conversion structure. The proposed rectifier can be directly applied to low voltage cases due to the wide output voltage range. And the decoupling capacitor voltage can be smaller than the peak grid voltage, which reduces the voltage stress. Besides, the low-frequency ripple power buffer is implemented without a dedicated power-buffering controller. This paper first introduces the circuit structure, operation principles, and control method. Then, the system design consideration is given. Finally, the effectiveness of the proposed topology is verified by the simulations and experimental results.

Control Method for the Sheppard–Taylor PFC Rectifier to Reduce Capacitance Requirements

Sheppard–Taylor power factor correction (ST-PFC) rectifier could obtain a high power factor due to its capability of overcoming the control detuning issue. However, it needs a bulky electrolytic capacitor at the load side to buffer the double-frequency ripple power (DFRP), which reduces the reliability and power density significantly. This paper proposes a control method to divert the DFRP to the small energy transfer capacitor. Consequently, the bulky electrolytic capacitor is replaced with a small film capacitor. The proposed method is carried out by introducing the freewheel state (one switch is turned on and the other is turned off) into the control. So no extra hardware is added, which makes the proposed method cost-effective. A low electromagnetic interference emission is also achieved due to the continuous input–output currents. In addition, the proposed method can be extended to other topologies easily. This paper first gives the detailed analysis of the proposed control method, and then introduces the controller design. The selection of the passive components is also briefly discussed. Finally, the simulation and experimental results verify the effectiveness of the proposed control method.

A Single Phase AC/DC/AC Converter With Unified Ripple Power Decoupling

In single phase ac/dc/ac converters, the low frequency ripple powers exist both at the source and load sides. Usually, large dc-link filter components are used to buffer the ripple powers, which increases volume and weight. To overcome the drawback, this paper presents a single phase ac/dc/ac current source converter with unified ripple power decoupling. The converter only consists of three bridge arms and a decoupling circuit. The three bridge arms play the role of rectification and inversion with sharing a bridge arm. And the decoupling circuit is in series with the dc-link energy storage unit to buffer the ripple powers. The circuit configuration and operation principles are introduced first. Then, a modulation strategy based on Cartesian space is developed to achieve sinusoidal input and output currents. The control idea that the dc-link current is regulated by the decoupling circuit and the averaged decoupling capacitor voltage is maintained by the rectifier is adopted. The ripple power buffer is automatically achieved. Finally, the theoretical analysis is favorably verified by the simulations and experimental results.

Leakage current suppression and ripple power reduction for transformer-less single-phase photovoltaic inverters

Transformer-less single-phase grid-tied inverter is attractive due to low cost, high efficiency, and small size. However, leakage current and second-order ripple power have to be well dealt with. Because the leakage current is a potential threat for body safety and the ripple power will decrease overall efficiency and system reliability. Both issues become obstacles for practical applications. This paper proposes a method to achieve leakage current suppression and ripple power reduce simultaneously. The main circuit is formed by adding an extra arm and a decoupling capacitor to the traditional single-phase voltage source inverter. The additional arm is controlled to keep the common voltage constant and divert the ripple power to the decoupling capacitor. A decoupled control method is also developed to achieve independent control of power factor correction and power decoupling. Finally, simulation results are presented to show the effectiveness.