Active Power Decoupling Research Articles

An Efficiency-Improved Single-Phase PFC Rectifier With Active Power Decoupling

Active power decoupling (APD) technology is an effective solution to store the double-line frequency ripple power in the single-phase system and remove the bulky aluminum electrolytic capacitors. However, APD introduces power loss because of adding extra switches operating at high frequency, which hurts the system efficiency inevitably. Addressing this issue, this article proposes an improved boost power factor correction (PFC) rectifier with a buck-type APD cell. An auxiliary circuit, composed of a resonant inductor and a diode, is added. With the developed modulation strategy, zero voltage switching of the switches both in the PFC and APD circuits is achieved, which improves the system efficiency significantly. This article first describes operating modes and then analyzes the soft-switching condition of each switch. Finally, a 300 W prototype is built and the experimental result shows that the efficiency is increased by 4%.

Control and Modulation of a Single-Phase AC/DC Converter With Smooth Bidirectional Mode Switching and Symmetrical Decoupling Voltage Compensation

In this article, a bidirectional single-phase ac/dc converter with active power decoupling (APD) and smooth mode switching is proposed. Power decoupling techniques have been proved efficient in the reduction of bulky dc bus electrolytic capacitors (E-caps) for single-phase low-power level conversion systems. However, it is found that when dealing with transient conditions such as sudden bidirectional switching or steep load changes, the whole system may be vulnerable and unstable under greatly reduced E-caps situation. None of the existing researches carefully examine such dc bus transient characteristics with bidirectionality under decoupling situation. By multiusing the APD cell, the proposed dc bus voltage suppression strategy is capable of both dc bus voltage ripple elimination and load disturbance rejection under transient conditions. Moreover, the proposed controller involves a dead-time compensation to achieve symmetrical power decoupling voltage without additional sensors for decoupling circuit, which ensures the maximum ripple power suppression ability as well as achieves minimum capacitance requirements. Finally, a 1-kW, 110-Vrms, and 50-Hz single-phase ac/dc prototype has been built and evaluated. Theoretical predictions are compared favorably with experimental results.

High voltage ride-through of doubly-fed induction generator based on grid side and rotor side converters cooperative control

In order to further improve the doubly-fed wind turbine high voltage ride-through ability, this article is different from the traditional control research only considering the rotor side converter in the power grid failure in stator flux dynamic changes of active and reactive power decoupling, the influence of the coupling current and the additional quantity of the stator flux changes as the feedforward compensation component in the current reference value. On this basis, an improved control strategy is also proposed for the grid-side converter, which takes into account the power imbalance between the two ends of the DC bus and the voltage mutation of the grid. Simulation in power grid voltage surge, coordinated control based on the grid-side converter and rotor-side converter control strategy of doubly-fed wind power generator of high voltage ride-through the active power and reactive power of wind power unit, the rotor over current, DC bus voltage fluctuations, etc all have better inhibition, effectively improve the doubly-fed wind turbine high voltage crossing ability.

Review and Comparison of Control Strategies in Active Power Decoupling

The active power-decoupling (APD) method is an effective solution to handle the inherent double-line frequency ripple power in single-phase power systems. It removes the bulky passive devices and facilitates the improvement of the system power density and even the reliability. This article provides a comprehensive review of the prior-art and state-of-the-art control strategies in APD. They are categorized into four groups according to the basic control ideas of “power balance,” “harmonic suppression,” “volt-second balance/charge balance,” and “virtual impedance.” And the specific control strategies under each control idea are discussed and compared. The pros and cons of each control idea are also presented . Finally, this article draws a sketch of the global trends in APD control.

Leakage Current Suppression of Single-Phase Power-Decoupled Current-Source Inverters

Recently, single-phase power-decoupled current-source inverters (PD-CSIs) have been proposed to eliminate the use of electrolytic capacitor (E-cap) having a short lifespan. This type of inverter also features a high-efficiency and compact circuit design via multiplexing use of circuit components. However, it is found in this article that component sharing inevitably renders coupled switching states for incorporating charging and discharging phases of decoupling buffers, e.g., film and ceramic capacitors. The resultant effect will be a significant increase in the common-mode voltage, which may lead to an unpleasant leakage current. In this article, a generalized modulation technique is proposed for the PD-CSIs to perform active power decoupling (APD) operation without generating much leakage current. The generic operating principles of the PD-CSIs are analyzed synthetically. The formation of leakage current in the coupled switching states is analyzed. The design of the proposed modulation technique and the power-decoupling controller is provided. Simulation and experimental results of typical types of PD-CSIs in a 110-V ac grid are performed to verify the effectiveness of the proposed modulation scheme. With the proposed modulation scheme, the leakage current of the PD-CSI can be reduced by 56%.

A High Power Density Multilevel Bipolar Active Single-Phase Buffer With Full Capacitor Energy Utilization and Controlled Power Harmonics

Active power decoupling in single-phase conversion systems reduces the required capacitance for twice-line frequency power ripple buffering by operating the energy buffering capacitors with high energy utilization ratios. The bipolar active buffer is the buffer topology that can achieve 100% energy utilization ratio. Yet, the conventional two-level full-bridge designs suffer from high switching and conduction loss and large filter inductor size due to the direct connection of the buffer across the high voltage dc-bus. Moreover, the high voltage swings across the buffer capacitor impose challenges for the control to regulate harmonics in the system. This article improves the power density and the efficiency of the bipolar active buffer through a buffer architecture incorporating the flying capacitor multilevel topology. Moreover, control techniques to regulate harmonics in the buffer are proposed to maintain low ripple in the dc-side current. The use of two common types of capacitors, the metal film capacitor and the X6S multilayer ceramic capacitor (MLCC) as buffer capacitors, is addressed with different harmonic control schemes. With MLCCs, we have also achieved a total passive component volume that is almost three times smaller than state-of-the-art solutions. The proposed approach is validated using a compact hardware for a 2-kW, 400-V dc-bus, 60-Hz single-phase inverter application.

Active and Reactive Power Control for Wind Turbines Based DFIG Using LQR Controller with Optimal Gain-Scheduling

This paper proposes an optimal gain-scheduling for linear quadratic regulator (LQR) control framework to improve the performance of wind turbines based Doubly Fed Induction Generator (DFIG). Active and reactive power decoupling is performed using the field-oriented vector control which is used to simplify DFIG’s nonlinearity and derive a compact linearized state-space model. The performance of the optimal controller represented by a linear quadratic regulator is further enhanced using the whale optimization algorithm in a multiobjective optimization environment. Adaptiveness against wind speed variation is achieved in an offline training process at a discretized wind speed domain. Lookup tables are used to store the optimal controller parameter and called upon during the online implementation. The control framework further integrates the effects of pitch angle control mechanism for active power ancillary services and possible improvements on reactive power support. The results of the proposed control framework improve the overall performance of the system compared to the conventional PI controller. Comparison is performed using the MATLAB Simulink platform.

Output Voltage Control of a Single-Phase UPS using an Active Power Decoupling Circuit

This paper proposes a method to control the output voltage of an online UPS system based on active power decoupling. The experimental results confirm that the proposed method reduces the DC voltage ripple by 72%. Moreover, this paper proposes a technique to control the output voltage during power failure.

Power decoupling capability with PR controller for Micro-Inverter applications

Micro-inverters have been known as promising structures for small-scale PV systems. However, these structures need energy storage elements to balance the instantaneous output and input power. Demanding a large size capacitor forces using an electrolytic type at the dc-link that affects the micro-inverter lifetime. This paper presents a new Active Power Decoupling (APD) circuit for the micro-inverters to reduce the capacitor size at the dc-link and utilize film capacitors instead of electrolytic types. The proposed APD circuit is based on a single-phase flyback converter. This structure is controlled based on the PQ theory and a Proportional Resonant (PR) controller for delivering the PV panel energy to the grid and eliminating the pulsation power through the switching pattern control. Simulations and experimental results of a 180 W single-phase micro-inverter prototype were performed to evaluate the performance of the proposed structure and the control scheme. It was found that this controller can accurately regulate the switching pattern to remove the ripples of input current and voltage. Furthermore, the robustness and fast dynamic performance of the proposed configuration have been confirmed during input power variation. In conclusion, this single-phase micro-inverter structure has an efficiency of ∼ 91%, THDi of 3.6%, and a long lifetime.

An active parallel power decoupling circuit with a dual loop control scheme for micro‐inverters

AbstractAn important challenge in single‐stage single‐phase micro‐inverters is reducing required capacitance by various active power decoupling (APD) techniques in order to use film capacitors with a longer lifetime instead of electrolytic capacitors. In this paper, a photovoltaic (PV)‐side parallel APD circuit based on a bidirectional flyback converter is proposed. This topology is able to increase the average and ripple voltages for the capacitor due to having a transformer and thus can reduce the required capacitance. In the control scheme, dual control loops on the main and decoupling circuits manage the micro‐inverter operation. The primary control loop is based on the instantaneous active and reactive power theory and a proportional resonant (PR) controller that is responsible for delivering the PV panel energy to the grid. The secondary control loop regulates the pulsation power on the dc‐link capacitor through the PR controller. Simulation results demonstrated that the proposed APD circuit and the control method could properly damp the pulsation power in the normal and reference tracking operations. Furthermore, the good robustness of the micro‐inverter was confirmed in shutdown and start‐up. Finally, the experimental results with a 180‐W single‐phase micro‐inverter prototype are presented, which validates the advantages of the proposed configuration.

A Composite Power Decoupling Method for a PV Inverter With Optimized Energy Buffer

A composite passive and active power decoupling method is proposed and optimized for a photovoltaic (PV) inverter. The proposed composite power decoupling (CPD) method has the following merits: 1) the dc side passive power decoupling (DC-PPD) can be automatically activated/deactivated according to the solar power to maintain more than 99% maximum power point tracking efficiency and low total harmonic current distortion (THDi); 2) the film capacitor with high reliability can be used due to the optimization of the energy buffer, e.g., a reduction of 52% and 23% in capacitance (or buffer energy) compared to DC-PPD and ac side active power decoupling, respectively; 3) control scheme developed in the d-q frame has more simple structure and requires less measurements than the existing methods. The experimental results show that the proposed CPD can dynamically control the dc-link voltage ripple under various conditions such as the abrupt change of the solar power and the load. Besides, low dc-link voltage ripple and low THDi are achieved in both steady-state and transient periods. Particularly when the solar power is less than 74%, the proposed CPD (with 261 μF) has better performance than the traditional used PPD (with 1120 μF). This article is accompanied by a video demonstrating the parameters optimization and measured waveforms.

Active Power-Decoupling Circuit to Reduce Ripple Currents of Recycling Batteries used with Single-Phase Voltage Source Inverters

Active Power-Decoupling Circuit to Reduce Ripple Currents of Recycling Batteries used with Single-Phase Voltage Source Inverters

A generalized switching function-based SVM algorithm of single-phase three-leg converter with active power decoupling

In this paper, a generalized switching function-based space vector modulation (SVM) algorithm is presented and evaluated to minimize the dc voltage utilization and the ac utility grid current total harmonic distortion. This paper explores the control and modulation techniques of a single-phase three-leg converter with an active power decoupling method, where a generalized SVM algorithm is proposed and evaluated for easy implementation in a digital control platform. The active power decoupling method with the proposed converter can be achieved via dependent control and modulation techniques. The control method is separated into the ac active power control part and the dc power ripple control part, which can maintain a unity power factor at the ac utility grid and reduced the double-frequency ripple power effect on the dc-side. Simulation results validate the performance of the modulation algorithm and its control and demonstrate the feasibility of the proposed power converter, as well as the two mentioned operation modes of the power converter.

Carrier-Based Generalized Discontinuous PWM Strategy for Single-Phase Three-Legs Active Power Decoupling Converters

Three-legs active power decoupling (APD) converters are widely studied in the single-phase grid-connected systems to enhance the circuit lifetime by creating an alternative path for the typical existing dc-side power pulsating ripple. Therefore, this reduces the requirement of smoothing dc capacitors allowing compact designs even with the implementation of long life metalized film technology. In this article, to allow enhancement of the system power density by improving power conversion efficiency and thus reducing the requirement of thermal management of the semiconductors, a carrier-based generalized discontinuous PWM strategy is proposed. This method detects the converter ac currents and ac reference voltages to determine the optimum clamped duration in each one of the three bridge-legs, which will minimize the converter overall switching losses. The proposed modulation method is analyzed and validated on a PLECS simulation and a 2 kVA single-phase three-legs APD converter.

A Power-Decoupled Current-Source Inverter for PV Energy Harvest and Grid Voltage Regulation

The single-phase microinverter (SMI) is becoming one of the most cost-efficient interfaces for bridging photovoltaics (PV) and power systems. However, in the maximum power point tracking operation, the SMI injects an intermittent active power to the grid, which leads to voltage variations at the point of common coupling (PCC). This certainly dampens the power quality of grids. Besides, the power mismatch between the dc and ac terminals of SMIs will render a double-line-frequency pulsating power at the dc terminal, which inevitably increases the power ratings of the circuit components of the SMIs. To address these issues simultaneously, a power-decoupled current-source inverter (PD-CSI) is proposed in this article. The PD-CSI can provide the required reactive power compensation for regulating the PCC voltage. Meanwhile, it is imbedded with an active power decoupling circuit, which can actively store the double-line-frequency pulsating power in a film capacitor so that the PV can be operated at a constant dc current. The state-space model and steady-state operation of the PD-CSI are elaborated. The controllers are designed for achieving the active power decoupling operation and the PCC voltage stabilization. Experimental and simulation results in an 110-V ac microgrid have been provided to validate the simultaneous functionalities of the active power decoupling and grid voltage regulation for the proposed PD-CSI.

A Novel SiC-Based Multifunctional Onboard Battery Charger for Plug-In Electric Vehicles

This article proposes a simple and effective method to reduce the bulky capacitor in onboard battery charger (OBC) where low-voltage (LV) battery charging circuit is utilized as an active power decoupling (APD) circuit to filter out the second-order ripple power. When the OBC is connected to the grid to charge the high-voltage (HV) battery, the switches on the primary side of the LV charging circuit are operated as those of an ac-dc converter with APD function. Consequently, small dc-link capacitors can be used instead of large capacitor banks. In the proposed OBC, the switching devices are shared for the ac-dc converter, APD circuit, and primary-side of the LV charger. For a simultaneous charging of the LV and HV batteries, a dc-dc converter is added, which shares the same transformer core and secondary side with the LV charging circuit. So the functions of the OBC are maintained in the proposed topology whereas the volume and cost are decreased by 52.3% and 46.9% compared with the conventional nonisolated OBC, respectively. A 2-kW SiC-based prototype has been designed and tested to verify the validity of the proposed system. The peak efficiencies of the OBC and LV charger are 96.1% and 95.3%, respectively.

Power Loss Reduction in Buck Converter Based Active Power Decoupling Circuit

Active power decoupling (APD) circuits enable the use of long lifetime capacitors (film or ceramic capacitors) in single-phase power converters. Owing to the inclusion of the APD circuits, the literature reports 1.5%-1.8% drop in efficiency of single-phase converter at rated power. This reduction in conversion efficiency is one of the significant challenges in the practical use of APD circuits. This article proposes an approach to reduce the power loss in the bidirectional buck converter based APD circuit. This approach is presented with the help of analytical calculations and graphical representation of operation of APD circuit. The proposed approach requires rapid variation in the average voltage of the buffer capacitor with a change in inverter power. To achieve this, an enhanced control technique is suggested with a duty ratio injection controller. The steady state and transient response of the proposed control technique are validated with simulation and experimentation. Further, the reduction in power losses realized by the proposed approach is verified with the help of a developed laboratory prototype. The proposed approach obtains up to 1% improvement in efficiency of single-phase converter at rated power, when compared with existing APD approaches.

Zero-Voltage-Switching Single-Phase Full-Bridge Inverter With Active Power Decoupling

Single-phase zero-voltage-switching (ZVS) inverter with wide bandgap devices has higher efficiency and power density. However, the dc-side capacitor of the inverter will suffer double line frequency ripple and reduces the lifetime of the dc bus capacitor. Active power decoupling (APD) is an effective method to replace the short lifetime electrolytic capacitor with a smaller film capacitor. In order to help achieving the ZVS condition for ZVS inverter and the additional APD circuit, this article presents a ZVS topology for single-phase full-bridge inverter with APD circuit by adding an auxiliary branch between the dc source and the bridge legs. The auxiliary branch is composed of a clamping capacitor, an auxiliary switch, and a resonant inductor. A ZVS pulsewidth modulation scheme is proposed for a single-phase inverter with APD. The gate drive pulses are designed to realize the ZVS turn-on for the main switches of both APD circuit and single-phase full-bridge inverter. Circuit operation stages are analyzed and ZVS conditions are given. Finally, the proposed ZVS inverter with APD circuit is verified on a 1.5-kW inverter prototype.

Single‐phase current source converter with high reliability and high power density

For single-phase current source converter (SCSC), at least one upper device and one lower device have to be gated on and maintained at any time. Otherwise, an open-circuit of the DC-link current would occur and destroy the devices. In addition, a bulky DC-link inductor is usually required to obtain a smooth DC-link current. To address these issues, this study proposes a novel SCSC with high reliability and high-power density. In the proposed circuit, even all the switches are turned on or turned off simultaneously, neither short-circuit nor open-circuit will happen. The inductance in DC-side is reduced significantly byadopting the active power decoupling technique. First, the operation principle of the proposed converter is introduced in detail. Then, a closed-loop control method is presented to regulate the DC-link current, maintain the DC component of the decoupling capacitor voltage, and achieve sinusoidal grid current. Besides, the parameter design of the circuit and controller is investigated. Moreover, the efficiency comparison between the proposed and other SCSCs is carried out. Finally, the effectiveness of the proposed topology is verified by the experimental results.

Integration of Boost-Type Active Power Decoupling Topology With Single-Phase Switched Boost Inverter

In this article, ripple energy of a single-phase switched boost inverter (SBI) is analyzed, and the amount of low-frequency ripple present in the switch-impedance network parameters is estimated. It is found that larger passive components are required to maintain smaller ripples resulting in poor power density. Therefore, integration of the single-phase SBI with an independent boost-type active power decoupling (APD) topology is proposed to deflect the low-frequency ripple to an auxiliary capacitor. Thus, the low-frequency ripple on inductor current and capacitor voltage of the switch-impedance network is significantly reduced, and much smaller passive elements are required only to filter high-frequency ripple. A passive element selection procedure for the switch-impedance network and the APD topology is presented to reduce ripple power. To properly mitigate the low-frequency ripple for varying ac loads of the SBI and also to avoid overcharging of the auxiliary capacitor, a closed-loop control strategy is developed for the APD topology. The proportional-resonant (PR) current controller is chosen due to its low steady-state error while tracking ac signals. The parameters of the PR controller are designed based on the small-signal analysis of the APD topology. A hardware prototype of the proposed system is fabricated, and its performance is demonstrated.