Active Power Decoupling Research Articles

Buck-Plus-Unfolder as the Superior Active Power Decoupling Solution for 400 Vdc/kW-Level Applications

In single-phase ac/dc applications where reliability and/or power-density are critical, active power decoupling (APD) circuits can be employed to reduce the required capacitance on the dc-link. Various APD circuits have been proposed so far, all with their advantages and disadvantages. However, many confusions still exist in the literature on this topic which is mainly attributed to a lack of unified and comprehensive assessment criteria. In this paper, first the decisive criteria for a modern APD circuit are established, and the buck APD is identified as the current state-of-the-art, based on them. Then the buck-plus-unfolder topology with triangular current mode (TCM) modulation is proposed as an improvement, and a simple, yet solid foundation is introduced to choose the superior decoupling solution at different specifications. The operation equations for the APD with TCM modulation are derived next, and the operation of the proposed solution is demonstrated using a hardware prototype.

A High-Performance Dynamic Controller For an Active Power Decoupler With AC-Side Storage Element

The instantaneous power in a single-phase system pulsates at double the supply frequency. With the effective use of the storage element, the electrolytic capacitor placed at the dc bus can be replaced by film capacitors, thereby improving the converter lifespan. Active power decoupling (APD) using an extra set of switches aims to attain the same. Recently, a promising APD topology has been reported, offering a lesser number of switches, as well as lesser stress on the switches for a wide range of power factor. However, the control of that converter poses a challenge as it has more number of states than the independent control variables. This paper focuses on the control aspect of the topology. It is shown that controlling two out of three states guarantees the overall system performance at the steady state. Also, ripple power in the dc bus is controlled in a closed-loop fashion so as to handle model uncertainty and thereby improve the steady-state performance. Furthermore, the solution to suppress the harmonic power, reflected on to the dc bus, under polluted grid condition is provided. The simulation and experimental results are presented supporting the analysis and design of the controller structure.

Reduced‐switch induction motor drive system with active power decoupling

This paper presents a reduced-switch motor drive system, which is made up of a single-phase half-bridge rectifier circuit, ripple power decoupling unit, three-phase inverter circuit, and three-phase motor. Due to the ripple power decoupling unit, the DC-bus of drive system could also provide DC power supply for other DC loads. The ripple power decoupling unit almost shares all components with rectifier and inverter circuit, so this is a low-cost solution. Considering the strong coupling of all kind of components in the system, a hybrid model predictive control (MPC) is introduced to coordinate the operation of the decoupling circuit, rectifier, and inverter circuits. The effectiveness of this scheme is verified with the experimental results.

A PFC Single-Coupled-Inductor Multiple-Output LED Driver Without Electrolytic Capacitor

In order to lower the system cost and reduce the form factor, single-inductor multiple-output (SIMO) converters are intensely developed for on-chip dc–dc converters and offline light emitting diode (LED) drivers. However, existing single-stage power factor correction (PFC) SIMO LED drivers are usually designed with electrolytic capacitors, leading to a short-life span and limited range of operation temperature. In this paper, based on a single dual-winding coupled inductor, a SIMO LED driver with PFC function is proposed without the requirement of electrolytic capacitors, where a small storage capacitance is used to actively decouple the ac and dc input powers. Compared with previous works, the proposed PFC SIMO LED driver has some additional benefits, including a smaller line filter, multiple output currents without double line frequency ripple, and a faster output regulation. With appropriate control strategy, an independent output regulation can be achieved for each output channel. Meanwhile, to improve the converter efficiency, the energy flow of the converter is optimized with an inductor current programming technique. Finally, the proposed electrolytic capacitorless PFC SIMO LED driver is developed, designed, tested, and compared with a single-stage SIMO design without active power decoupling.

A new active power‐decoupling topology and control mechanism to extend the lifespan and reduce the number of passive components

In this article, a new active power‐decoupling (APD) circuit without an additional discharging inductor is proposed for single‐phase power systems. In an APD circuit, a small film capacitor is used to extend the lifespan and remove ripple power derived from power systems. However, to manipulate power pulsation, additional circuits such as inductors, capacitors, and switches are required, which increase the manufacturing cost and parametric uncertainties. In the proposed circuit, rectification and a decoupling function are conducted on a coupled‐inductor at the same time to reduce the number of passive elements. Furthermore, a sliding mode control is used to ensure stable operation under parameter variation and disturbance. A design example is presented and the operation of the proposed topology is also verified with a simulation study and experimental results. The results show that the proposed APD method was able to remove passive components and reduce the withstand voltage of a buffer capacitor and insulated gate bipolar transistors (IGBT) while ensuring that both the input current and output voltage of the converter were well regulated under load variation. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Active power decoupling and controlling for single‐phase FACTS device

Single-phase FACTS device has a bulky and short-life electrolytic capacitor to absorb the ripple pulsating at twice of the line frequency in DC side, resulting in lower power density. This paper introduced a structure of three-phase bridge which added an additional leg connected to an AC capacitor based on single-phase H-bridge. The 2-ripple energy of the electrolytic capacitor in single-phase H-bridge could be transformed to the film capacitor of the AC side in three-phase H bridge. The size of single-phase FACTS is reduced by ten times compared to the single-phase H-bridge. A simple control strategy had been studied, through two kinds of controllers: the digital quais-PR controller had been used to control gird current and AC capacitor voltage and current; the two cosine controller had been used to eliminate the rest of two-ripple harmonic in the DC side, there was no controller to maintain DC voltage. The experiments verified the feasibility of the control strategy.

Design and Analysis of the Low Device Stress Active Power Decoupling for Single-Phase Grid Connection for a Wide Range of Power Factor

Single-phase power converters suffer from the double frequency power pulsation. In voltage source inverters, the dc bus capacitor is designed to supply this double frequency current. The stringent dc bus voltage ripple specifications call for larger capacitance. This implies larger electrolytic capacitors. However, the electrolytic capacitor suffers from short-term life span, which consequently brings down the lifetime of the converter. As an alternative, active power decoupling (APD) ensures significant reduction in dc buffering requirement, thereby reducing the bus capacitance. This can make use of the film capacitors with better lifespan. In this paper, an APD scheme is designed and developed for the grid-connected system. Another important feature of the proposed scheme is that, it reduces the stress on the switches significantly while compared with existing APD solutions for all load power factors. The system is analyzed further to arrive at APD control conditions including the effect of grid filter inductance. The simulation and experimentation have been done to validate the proposed method. Additionally, the stress on the switches as a function of grid filter inductance is predicted theoretically and verified practically. The average stress on the switches is shown to be lesser than the existing solutions.

Single-Phase Differential Buck–Boost Inverter With Pulse Energy Modulation and Power Decoupling Control

This paper presents a single-phase differential buck–boost inverter that possesses both buck–boost and active power decoupling functions without adding any power electronics or increasing the complexity of driver circuits, as compared with the previous differential inverters. Two types of operating principles are introduced: the unipolar operation with new pulse energy modulation technique enabling the inverter to operate under both discontinuous conduction mode and continuous conduction mode, and the bipolar operation with energy-based active power decoupling delivering the second-order ripple power into the output film capacitors, thus eliminating the large electrolytic capacitor at the dc side. Small-signal modeling analysis is conducted to show the characteristics of the proposed system and control. Simulation and experimental results verified the feasibility of operating principles for the differential buck–boost inverter and successful power decoupling with substantial reduction of second-order component in the dc current.

Single-phase single-stage dual-buck photovoltaic inverter with active power decoupling strategy

Abstract This paper proposes a single-phase single-stage dual-buck photovoltaic (PV) inverter with an active power decoupling (APD) strategy. Using this strategy, the dc-link voltage pulsating caused by a low-frequency power fluctuation in single-phase systems can be reduced without using a bulky dc-link storage. A simple active damping control is adopted to suppress the resonance of the APD circuit, so that the design of the feedback control becomes simple and reliable. Furthermore, the APD circuit directly regulates the dc-link voltage, which is identical to the PV voltage in single-stage PV inverters. Hence, the dc-link voltage control in the given power stage, where the unidirectional dual-buck topology is employed, is supplemented. The APD strategy can be universally applied in single-stage PV inverters regardless of the topology connected to the utility grid. To verify the proposed scheme, both simulations and experiments on a 2.1 kW single-phase single-stage dual-buck PV inverter are conducted. The results confirm that the proposed method not only reduces the dc-link voltage pulsating but also improves the MPPT accuracy. Compared to the power stage using electrolytic capacitors, the proposed scheme decreases the physical size and implementation cost of the dc-link storage.

Virtual Flux Based Direct Power Control on Vienna Rectifier

This paper proposes the virtual flux based direct power control for Vienna rectifier. No need for the input voltage sensors, the current regulation loop and PWM voltage modulation block along with the active and reactive power decoupling are some of the salient advantages of this method that make it suitable for controlling the conventional active rectifiers. However, due to the three-level nature of the Vienna configuration, balancing the output capacitors voltages is inevitable leading to a modified virtual flux based technique. Applying this modification, a separate switching table has been jammed into the proposed technique in order to control the capacitors voltages. Simulation results show the superiority of the virtual flux technique over the conventional Vienna control techniques from point of the mentioned advantages.

Switching strategy for improving the lifetime of dc‐link capacitor in a fault‐tolerant active power decoupling topology

Reliability is an important requirement for a grid-connected photovoltaic (PV) system in remote military-secured areas, which are difficult to access for system maintenance. However, the reliability of the PV system is reduced by the use of electrolytic capacitors in inverters. Active power decoupling (APD) topologies eliminate the need for these capacitors by using an additional decoupling circuit. However, the vulnerability of switching devices to failure is another reason for reduced reliability of inverters, which is not addressed in these topologies. Several fault-tolerant topologies are proposed in literature to address this limitation. However, these topologies use electrolytic capacitors in dc-link, which affects the overall reliability of inverter. To address these limitations, a fault-tolerant strategy is proposed in this study. In the proposed strategy, a conventional APD topology is used along with an electrolytic capacitor in the dc-link. The lifetime of the capacitor is improved using the decoupling circuit of the APD topology. In this regard, a switching strategy is proposed, using which the current flowing through dc-link capacitor is reduced. Furthermore, in the event of a device fault, the topology continues to function like the conventional H-bridge inverter. The operation of proposed strategy is validated through simulation and experimental studies.

Micro‐inverter based on single‐ended primary‐inductance converter topology with an active clamp power decoupling

The reliability and lifespan of micro-inverters are two significant features of AC-module photovoltaic systems. One of the most effective methods to enhance the reliability and life duration of micro-inverters is achieved by substituting their electrolytic power decoupling capacitor with the film capacitors. In this study, a new DC/AC inverter based on an isolated single-ended primary-inductance converter with an active clamp power decoupling is introduced. The proposed converter has no electrolytic capacitor which results in long lifetime and high reliability. Moreover, the inverter has simple structure and low number of semiconductor switches which improve the efficiency and make it cost effective. The sufficient stepping up ability for output voltage without increasing turns ratio excessively, non-pulsating input current, and appropriate isolation make the proposed micro-inverter a proper choice for grid-connected applications. The converter operating modes are discussed and design considerations are presented. Finally, experimental results of the implemented prototype validate aforementioned features and performance of the proposed micro-inverter.

Onboard Battery Chargers for Plug-in Electric Vehicles With Dual Functional Circuit for Low-Voltage Battery Charging and Active Power Decoupling

This paper proposes a single-phase onboard battery charger (OBC) for plug-in electric vehicles, where the low-voltage (LV) battery charging circuit is utilized for an active power decoupling function. The OBC is operated in three different modes by sharing the transformer, switches, and capacitors. For a grid-to-vehicle mode or a vehicle-to-grid mode, the LV battery charging circuit serves as an active filter to eliminate the low-frequency power ripple at the DC link. Thus, the small film capacitors can be employed instead of large capacitors at the DC link. For the third operating mode, where the LV battery is charged from the HV battery, the isolation is provided by the dual active bridge (DAB) DC-DC converter. Since some components in the proposed OBC are used in common, the size and cost of the OBC can be reduced significantly. The simulation and experimental results have verified the validity of the proposed system.

Active Power Decoupling for Submodules of a Modular Multilevel Converter

The modular multilevel converter (MMC) is receiving wide acceptance in both high- and medium-voltage (MV) applications. However, due to the low (fundamental and second-order) frequency ripple powers in the submodule (SM) capacitors, large capacitance is required to smooth the SM voltage. The SM capacitors account for a large portion of volume and weight in the MMC system. Present methods (e.g., circulating current control, power channels linking upper and lower arms) cannot eliminate the fundamental and second-order ripple powers simultaneously. This paper investigates the feasibility of an active power decoupling technique for solving this issue. By adding a buck-type active power filter (APF) circuit (which contains another energy-storage capacitor), the low-frequency ripple powers can be transferred to the APF capacitor. This significantly reduces the SM voltage ripple and therefore the total capacitance of the SM. To enhance voltage ripple suppression, APF capacitor voltage reference is modified in a closed-loop manner, and a proportional-integral plus repetitive controller is proposed. Simulations and experimental results prove the validity of the method. A comparison with the traditional MMC shows that it can significantly reduce system volume and improve power density. The method is best suited for MV applications where power density is given a high priority.

Modeling and control for new LLCL filter based grid-tied PV inverters with active power decoupling and active resonance damping capabilities

LLCL filters utilization decreases single-phase transformerless inverters’ AC-Side volume significantly. Conversely, the inherent 2nd order power harmonic ripples burden inverters’ DC-Side. In fact, the passive solution to buffer these ripples imposes a threat to inverter’s reliability and power density. Hence, varieties of active power decoupling methods were introduced in the literature to improve inverter’s DC-Side volume and system’s reliability. Yet, most existing techniques require auxiliary power electronics and energy storage elements. This contradicts the goal of optimizing system’s overall power density. Therefore, a novel LLCL filter for grid-connected applications is introduced that merges AC-Side and DC-Side volume minimization methods without additional power electronics devices. Precisely, the common-mode (CM) operation is harnessed for active power decoupling and the differential-mode (DM) is utilized for active power injection. Besides, the stability analysis of the proposed system revealed that the CM and DM are resonating. Thus, an active resonance damping control scheme based on decoupled CM and DM capacitor currents feedbacks was developed. With the proposed topology, the DC-link capacitor was reduced 40 times compared to the passive solution. The robustness of the proposed solution to the grid-side inductance variation was also verified and validated on 750W prototype system.

A Single-Stage Two-Switch PFC Rectifier With Wide Output Voltage Range and Automatic AC Ripple Power Decoupling

Conventional single-phase power-factor-correction (PFC) rectifiers with active power decoupling capability typically require more than three active switches in their circuits. By exploring the concept of power-buffer cell, a new single-stage PFC rectifier with two active switches, one inductor and one small power-buffering capacitor is reported in this paper. The proposed converter can achieve high-power factor, wide output voltage range, and power decoupling function without using electrolytic capacitor. Additionally, an automatic power decoupling control scheme that is simple and easy to implement is proposed in this paper. The operating principle, control method, and design considerations of the proposed rectifier are also provided. A 100-W prototype with ac input voltage of 110 Vrms and a regulated dc output voltage ranging from 30 to 100 V has been successfully designed and practically tested. The experimental results show that with only a 15 μ F power-buffering film capacitor, the proposed converter can achieve an input power factor of over 0.98, peak efficiency of 93.9%, and output voltage ripple of less than 3%, at 100-W output power.

Active power decoupling with reduced converter stress for single-phase power conversion and interfacing

Single-phase DC–AC power electronic converters suffer from pulsating power at double the line frequency. The commonest practice to handle the issue is to provide a huge electrolytic capacitor for smoothening out the ripple. However, the electrolytic capacitors having short end of lifetime limit the overall lifetime of the converter. Another way of handling the ripple power is by active power decoupling (APD) using the storage devices and a set of semiconductor switches. Here, a novel topology has been proposed in implementing APD. The topology claims the benefit of (1) reduced stress on converter switches and (2) using smaller capacitance value, thus alleviating the use of electrolytic capacitor and in turn improving the lifetime of the converter. The circuit consists of a third leg, a storage capacitor and a storage inductor. The analysis and the simulation results are shown to prove the effectiveness of the topology.

CAPACITANCE REDUCTION USING RIPPLE SUPPRESSION CONTROL OF SINGLE PHASE ENERGY STORED QUASI-Z-SOURCE INVERTER

The energy stored Quasi-Z-source Inverter (qZSI) allows integrate energy storage in addition to the other energy source mainly for output power smoothening. Single phase inverter suffers from double-frequency power ripple in the input side and also in the energy storage that is transferred there from the ac-side. In qZSI must be used large electrolytic dc capacitors in the impedance network to suppress this 100 Hz ripple. Also to suppress this ripple can be applied two types of power decoupling: passive power decoupling and active power decoupling. In this paper is analyzed passive power decoupling that is realized by means of the modified control strategy that produces the time-varying shoot-though duty cycle to mitigate power ripple without deteriorating of the output power quality. The validity of proposed control strategy was confirmed by simulation results that were obtained in PSIM software.

Improved power decoupling control strategy based on virtual synchronous generator

Virtual synchronous generator (VSG) control scheme, which can be regarded as an extension of droop control, has received much attention from researchers as the introduction of rotational inertia to inverters. This study discusses an active and reactive power decoupling technique for VSGs in microgrid, as an important aspect of VSG. The traditional power decoupling mechanism is initially analysed. Subsequently, the properties of the line impedance at different voltage degrees are compared. Results indicate that the traditional power decoupling method is unsuitable for medium- and low-voltage microgrids. Thus, an improved power decoupling method is proposed. By estimating the voltage at the point of common coupling and tracking their reference values, the output active and reactive power of inverters can perform dynamic decoupling. Furthermore, the stability of the new control structure and selection of relevant coefficients are analysed. The simulation and experimental results verify the enhanced decoupling strategy for VSGs.

Control of a Hybrid AC/DC Microgrid Involving Energy Storage and Pulsed Loads

This paper presents a real-time coordinated control of the hybrid ac/dc microgrids involving energy storage and pulsed loads. Grid-isolated hybrid microgrid applications require special considerations due to the intermittent generation, online energy storage control, and pulsed loads. In this study, we introduce a comprehensive frequency and voltage control scheme for a hybrid ac/dc microgrid consisting of a synchronous generator, solar generation emulator, and bidirectional (ac/dc and dc/dc) converters. A bidirectional controlled ac/dc converter with an active and reactive power decoupling technique is used to link the ac bus with the dc bus, while regulating the system voltage and frequency. A dc/dc boost converter with a maximum power point tracking function is implemented to maximize the intermittent energy generation from solar generators. Current-controlled bidirectional dc/dc converters are applied to connect each lithium-ion battery bank to the dc bus. Lithium-ion battery banks act as energy storage devices that serve to increase the system resiliency by absorbing or injecting power. Experimental results are presented for verification of the introduced hybrid ac/dc power flow control scheme.