Power Decoupling Capability Research Articles

Enhanced four-port dual-active-bridge converter employing power decoupling capability for DC microgrid islanding mode operation

Enhanced four-port dual-active-bridge converter employing power decoupling capability for DC microgrid islanding mode operation

A Single-Phase Transformerless Common-Ground Type PV Inverter With Active Power Decoupling

To solve the problems of existing non-isolated PV grid-connected inverters such as leakage current, power pulsation and harmonic current, a single-phase common-ground-type non-isolated grid-connected inverter with power decoupling capability is proposed in this paper. The integration of the traditional boost converter and the switched capacitor technology obtains the structure that the neutral point of the grid is directly connected with the negative terminal of PV array, and the leakage current is eliminated. Due to the time-sharing multiplexing of circuit components, which can achieve power decoupling and high step-up, fewer semiconductor devices are required in proposed inverter. At the same time, the improved control strategy ensures that the inverter can adapt to the voltage ripple of large decoupling capacitor. This paper introduces the working principle, mode, performance and control strategy of the novel topology in detail. Finally, the experimental prototype with rated output power of 320W verifies the superior performance of the inverter.

Power Decoupling Strategy for Voltage Modulated Direct Power Control of Voltage Source Inverters Connected to Weak Grids

The grid voltage modulated direct power control (GVM-DPC)-based inverter is an attractive solution to regulate the instantaneous real and reactive powers injected into power grids. However, the power coupling in GVM-DPC, i.e., interactions between the real and reactive power loops, may deteriorate its transient performance. In this paper, a power decoupling strategy for GVM-DPC is proposed based on a dynamic feedforward power compensation (DFPC) algorithm. It is proved that the proposed strategy has better decoupling performance than that of the traditional virtual impedance method (VIM). Firstly, power coupling characteristics in GVM-DPC are analyzed, indicating that the ignorance of voltage angle variation at the point of common coupling (PCC) will result in severe power coupling. Then, power coupling magnitudes are derived according to relationships among the real power, reactive power and PCC voltage. Next, the coupling magnitudes are compensated into the power control loop of the GVM-DPC for the better decoupling performance. The transient performance of inverter using DFPC is studied based on the impedance analysis. Also, the relationship between coupling magnitude and grid side impedance is studied, which indicates the limited power decoupling capability of VIM. Finally, the proposed method is validated by the simulations and a hardware-in-loop system.

SiC-Based Improved Neutral Legs With Reduced Capacitors for Three-Phase Four-Wire EV Chargers

An electric vehicle (EV) charger can operate in an autonomous mode to create its own grid by utilizing the EV batteries during grid blackouts. This requires three-phase four-wire inverters as the grid-side ac/dc port of the EV charger to supply unbalanced loads. Although silicon carbide (SiC) metal–oxide–semiconductor field-effect transistors (MOSFETs) can be adopted to increase the power density of these inverters, the second-order ripples exhibited on the dc bus caused by unbalanced loads need to be mitigated by a large dc capacitance—increasing the size of inverters. In this article, an improved neutral leg for three-phase four-wire inverters is presented, which not only provides the neutral current for unbalanced loads, such as a conventional neutral leg, but also reduces the second-order ripples on the dc bus without the need for additional hardware components. Furthermore, it can reduce by 50% the dc capacitance compared to its conventional counterpart. A control strategy featuring power decoupling capability is included for the improved leg. It was built with SiC MOSFETs and experimentally assessed with a three-phase inverter, with results verifying its effectiveness. For completeness, the performance of the improved neutral leg is also evaluated through simulations in PLECS and compared to a conventional neutral leg.

Simplified Active Power Regulation Scheme for Grid Connected Solar Photovoltaic based Micro-Inverter

ABSTRACT A simplified active power regulation (APR) scheme for a single-stage grid-connected micro-inverter with pulsating power decoupling capability has been proposed and tested in this work. The versatility of the active power regulation control method makes it to contribute an analytical solution based on maximum power point (MPP) estimation and operate at the right-hand side (RHS) of the PV characteristics while giving reserve fraction. The injection of power to the grid with the help of an APR scheme can be witnessed using the reserve fraction. A test setup with 250 Wp solar panel feeding power to a 230 V, 50 Hz single-phase grid through a single-stage grid-connected micro-inverter has been utilized to test the proposed APR scheme. The entire system has been modeled in MATLAB/ SIMULINK and the same has been implemented and verified by hardware experimentation whose results have been reported with different environmental conditions.

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.

A Novel Electrolytic Capacitor-Less MMC With Magnetic Power Decoupling Method

This article presents a novel flux-cancellation-based modular multilevel converter (MMC) with power decoupling capability. Conventional MMC suffers from low-frequency (fundamental and second-order) ripple power in the submodule (SM) capacitors. The low-frequency ripple power makes the SM capacitors bulky, responsible for a significant portion of the volume and weight of the whole system. The ripple power on the SM capacitor of the three-phase module is phase-shifted by 2π/3 rad from each other. The proposed flux cancellation is based on directing the low-frequency ripple power to a common core of a three-winding transformer to cancel out. A three-port bidirectional isolated dual half-bridge is introduced for flux cancellation. For this scheme, the main problem is the presence of leakage inductances of the transformer, and another one is three-port isolated bidirectional converter modeling as it has only input ports. The average model is proposed for the flux cancellation circuit. It provides a practically simple model for the complex circuit. Second, a virtual-capacitance-based power decoupling controller is proposed to overcome the leakage inductance problem by the benefits of simple current estimation and of no need for the current sensor. The proposed power decoupling method reduces the system size significantly and enables the MMC to operate with a nonelectrolytic SM capacitance of few microfarads. The operating principle and control design of the proposed MMC are presented. The proposed MMC is validated by simulation and experimentation.

Modular Multilevel Converter Grid Interface for Klystron Modulators: An Augmented Modulation Scheme for Arm Balancing

This paper discusses the control of a modular multilevel converter (MMC) used as a grid interface for the klystron modulators in the compact linear collider (CLIC). The converter has a DC side load which takes short-duration power pulses, causing high DC side power fluctuations that are not tolerable if seen by the AC grid. The DC–AC power decoupling capability of the MMC enables mitigation of the power ripple on the AC side, guaranteeing compliance with power quality requirements. However, the pulse repetition rate of the CLIC modulators is synchronized the 50-Hz AC grid and this induces permanent power imbalance in the arms of the MMC, causing voltage deviation and overmodulation unless appropriate balancing strategies are implemented. Unlike existing arm balancing methods that control 50-Hz circulating currents to balance the arm powers, the method proposed in this paper introduces an augmented modulation strategy where modulation signals are redistributed among arms based on the demand from a balancing controller. The resulting controller has lower complexity and its simple structure enables an easier design of the balancing loop, which guarantees predictable dynamics in operation. The effectiveness of the method has been demonstrated in simulation for the full-scale CLIC converter ratings and experimentally on a 7-kW MMC prototype operating with a 3.3-kA pulsed DC load.

DC to single‐phase AC grid connected inverter with boost‐type active buffer circuit operated in discontinuous current mode

AbstractA novel circuit topology for a single‐phase inverter with a power decoupling capability operated in discontinuous current mode (DCM) is proposed in this paper. An inverter connected to a single‐phase grid requires a power decoupling capability to compensate for a power ripple with twice the grid frequency. Bulky capacitors are used as DC‐link capacitors in conventional systems. In contrast, the proposed circuit topology can use ceramic capacitors instead of electrolytic capacitors by reducing the required capacitance based on the active buffer concept. Moreover, this active buffer requires no additional inductor because it uses DCM for the power decoupling capability. In this paper, a control method for the active buffer circuit operated in DCM is introduced. An experimental verification of a 1‐kW prototype shows that the proposed circuit reduces the input current ripple at twice the grid frequency by 96.8%, with a maximum efficiency of 95.2%. In addition, the Pareto optimization of power density and efficiency is used to clarify the maximum power density points. It is found that the maximum power density of the proposed circuit is 1.6 times higher than that of a conventional boost‐type active buffer.

Research of Thermoelectric Decoupling of Cogeneration Unit Based on Absorption Heat Pump

Due to a large number of new energy power generation, the contradiction of heat-electricity is prominent in the period of winter in north China. In order to effectively eliminate the renewable energy power generation and promote the healthy development of the electric power industry in China, it is urgent to improve the peak load capacity of cogeneration unit. In this paper, a new method of thermoelectric decoupling was proposed for traditional coal-fired power generation unit, which was the transformation of thermoelectric decoupling system of integrated absorption heat pump. The comparison tests before and after the transformation of the absorption heat pump was carried out for a pilot unit. Then, the thermal power decoupling capability, energy saving benefit and special advantages of this method were analysed. The result showed that this method can both improve the energy-saving and thermoelectric decoupling. Furthermore, it also can improve the thermal efficiency of the unit and maintain the characteristics of safe and stable operation and responsive of the power load.

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.

Single‐stage AC module with series power decoupling capability for connecting PV to a single‐phase power grid

In single-phase grid-connected photovoltaic inverters, the input power is constant during the grid period, whereas the output power oscillates at double-line frequency. Therefore, electrolytic capacitors are widely used to handle the input and output power differences. However, these capacitors have short lifetime which degrade the inverter reliability. This paper proposes a control strategy to turn a conventional four-switch flyback-based inverter to an inverter equipped with a series power decoupling circuit. Therefore, a long lifetime film capacitor can be used as the main energy storage. The modified inverter has an inherent snubber circuit, which can restore energy of the transformer leakage inductance and improves its overall efficiency. The control strategy can realise maximum power point tracking and inject a sinusoidal low total harmonic distortion current to the grid. A 100 W prototype inverter has been built to verify operation and feasibility of the proposed control strategy.

Development of Electrolytic Capacitor Less Photovoltaic Grid Connected Inverter with Boost‐Up Type Active Buffer Circuit

SUMMARYThis paper proposes a configuration of a single‐phase voltage source inverter that features power decoupling capability. Generally, the converter connected to a single‐phase grid employs bulky dc link capacitors such as electrolytic capacitors in order to decouple the power ripple with twice the frequency of the power supply. The power ripple in the proposed circuit is compensated by an active buffer with small capacitors. In this paper, the fundamental operations of the proposed converter are confirmed by experimental results. From the experimental results, the output current total harmonic distortion (THD) is 3.51%, the ratio of the input current is 14.3%, and the output power factor is over 99%. In addition, the volume of the proposed circuit is reduced by 61% when the carrier frequency is 64 kHz compared to that with a carrier frequency of 16 kHz. Finally, from an evaluation of the power density using Pareto front curves, the proposed circuit achieves high power density in comparison with the conventional circuit.

Review of three port micro-inverter with power decoupling capability for photovoltaic (PV) systems applications

The Photovoltaic (PV) systems have been realized using different architectures, starting with the string and centralized PV system to the modular PV system. Presently, decentralized inverters are being developed at the PV panel power level (known as AC – PV Modules). Such new PV systems are becoming more attractive and many expect this will be the trend of the future. The AC-Module PV system consists of an inverter attached to one PV panel. This integration requires that both devices have the same life-span. Although, the available commercial inverters have a relatively short life-span (10 years) compared to the 25 –year PV. It has been stated in literature that the energy storage capacitor (electrolytic type) in the single-phase inverter is the most vulnerable electronic component. Hence, many techniques such as (power decoupling techniques) have been proposed to solve this problem by replacing the large electrolytic capacitor with a small film capacitor. This paper will present a quick review of these power decoupling techniques, and proposes a new three-port micro-inverter with power decoupling capability for AC-module PV system applications.

昇圧形アクティブバッファを有する電解コンデンサレス太陽光発電用系統連系インバータの開発

This paper proposes a configuration of a single-phase voltage source inverter that features power decoupling capability. Generally, the converter connected to a single-phase grid employs bulky DC link capacitors such as electrolytic capacitors in order to decouple the power ripple with twice the frequency of the power supply. The power ripple in the proposed circuit is compensated by an active buffer with small capacitors. In this paper, the fundamental operations of the proposed converter are confirmed by experimental results. From the experimental results, the output current total harmonic distortion (THD) is 3.51%, the ratio of the input current is 14.3% and the output power factor is over 99%. In addition, the volume of the proposed circuit is reduced by 61% when the carrier frequency is 64kHz compared to that with a carrier frequency of 16kHz. Finally, from an evaluation of the power density using Pareto front curves, the proposed circuit achieves high power density in comparison with the conventional circuit.

A Three-port Flyback for PV Microinverter Applications With Power Pulsation Decoupling Capability

A novel single-stage photovoltaic (PV) microinverter with power decoupling capability is proposed in this paper. The proposed topology is based on three-port flyback with one port dedicated to power decoupling function so as to reduce the decoupling capacitance, thus allowing for long lifetime film capacitor to be used. Operation principle is analyzed in details. Key design considerations, including key parameter selections, predictive control strategy, and the dc voltage balance control across the power decoupling capacitor, are given in this paper. A 100-W microinverter prototype is built to verify the proposed topology. Experimental results show the proposed topology can achieve power decoupling, while maintaining good efficiency.