A Review of Power Decoupling Techniques for Microinverters With Three Different Decoupling Capacitor Locations in PV Systems
TL;DR: In this paper, a thorough study for different power decoupling techniques in single-phase microinverters for grid-tie PV applications is presented, compared and scrutinized in scope of the size of decoupled capacitor, efficiency, and control complexity.
Abstract: The reliability of the microinverter is a very important feature that will determine the reliability of the ac-module photovoltaic (PV) system. Recently, many topologies and techniques have been proposed to improve its reliability. This paper presents a thorough study for different power decoupling techniques in single-phase microinverters for grid-tie PV applications. These power decoupling techniques are categorized into three groups in terms of the decoupling capacitor locations: 1) PV-side decoupling; 2) dc-link decoupling; and 3) ac-side decoupling. Various techniques and topologies are presented, compared, and scrutinized in scope of the size of decoupling capacitor, efficiency, and control complexity. Also, a systematic performance comparison is presented for potential power decoupling topologies and techniques.
Citations
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TL;DR: In this paper, the authors provide a comprehensive review of active power decoupling circuit topologies and their development laws from the view of the dual principle, switch sharing, and differential connection.
Abstract: 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.
395 citations
Cites background or methods from "A Review of Power Decoupling Techni..."
...tem performance, for example, reducing the maximum power point tracking (MPPT) efficiency of the photovoltaic (PV) panels [2], leading to light flicker in light-emitting diode (LED) lighting applications [3]–[5], causing overheating of batteries [6], [7], and shortening fuel cell’s lifetime [8], [9]....
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...Different from the review in [2], which presented a comprehensive review of the power decoupling techniques for microinverters in PV application, this paper mainly focuses on the development and construction laws of decoupling...
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...cations, such as PV generation systems [2] and LED lighting systems [3]–[5], are met....
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TL;DR: In this paper, a symmetrical half-bridge circuit was proposed to absorb the ripple power in a single-phase dc/dc system, where the only additional components are a pair of switches and a small filtering inductor.
Abstract: Single-phase ac/dc or dc/ac systems are inherently subject to the harmonic disturbance that is caused by the well-known double-line frequency ripple power. This issue can be eased through the installation of bulky electrolytic capacitors in the dc link. Unfortunately, such passive filtering approach may inevitably lead to low power density and limited system lifetime. An alternative approach is to use active power decoupling so that the ripple power can be diverted into other energy storage devices to gain an improved system performance. Nevertheless, all existing active methods have to introduce extra energy storage elements, either inductors or film capacitors in the system to store the ripple power, and this again leads to increased component costs. In view of this, this paper presents a symmetrical half-bridge circuit which utilizes the dc-link capacitors to absorb the ripple power, and the only additional components are a pair of switches and a small filtering inductor. A design example is presented and the proposed circuit concept is also verified with simulation and experimental results. It shows that at least ten times capacitance reduction can be achieved with the proposed active power decoupling method, and both the input current and output voltage of the converter can be well regulated even when very small dc-link capacitors are employed.
227 citations
Cites background from "A Review of Power Decoupling Techni..."
...More literature reviews regarding this research topic can be found in [12, 18]....
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TL;DR: A transformerless inverter topology, which is capable of simultaneously solving leakage current and pulsating power issues in grid-connected photovoltaic (PV) systems, and it is possible to use long-lifetime film capacitors instead of electrolytic capacitors to improve the reliability of the PV system.
Abstract: This paper presents a transformerless inverter topology, which is capable of simultaneously solving leakage current and pulsating power issues in grid-connected photovoltaic (PV) systems. Without adding any additional components to the system, the leakage current caused by the PV-to-ground parasitic capacitance can be bypassed by introducing a common-mode (CM) conducting path to the inverter. The resulting ground leakage current is therefore well controlled to be below the regulation limit. Furthermore, the proposed inverter can also eliminate the well-known double-line-frequency pulsating power that is inherent in single-phase PV systems. By properly injecting CM voltages to the output filter capacitors, the pulsating power can be decoupled from the dc-link. Therefore, it is possible to use long-lifetime film capacitors instead of electrolytic capacitors to improve the reliability of the PV system. The mechanism of leakage current suppression and the closed-loop control of pulsating power decoupling are discussed in this paper in detail. A 500-W prototype was also built and tested in the laboratory, and both simulation and experimental results are finally presented to show the excellent performance of the proposed PV inverter.
160 citations
Cites background from "A Review of Power Decoupling Techni..."
...A number of active power decoupling circuits have recently been proposed in order to reduce the dc-link capacitance requirement, so that long-lifetime film capacitors can be used instead of electrolytic capacitors in the dc-link to improve the reliability of single-phase power converters [25]–[32]....
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TL;DR: A comprehensive review of the most recent isolated topologies of grid-connected photovoltaic (PV) microinverters is presented in this article, where the power losses at different stages, control techniques, position of the decoupling capacitor, and cost analysis are analyzed.
Abstract: Galvanic isolation in grid-connected photovoltaic (PV) microinverters is a very important feature concerning power quality and safety issues However, high-frequency transformers and high switching losses degrade the efficiency of the isolated types of microinverters Recently, several isolated topologies were proposed to increase the efficiency and lifetime of PV converters This paper presents a comprehensive review of the most recent isolated topologies of PV microinverters These topologies are categorized into two groups in terms of their power processing stages: 1) single-stage microinverter and 2) multi-stage microinverter Various topologies are presented, compared, and scrutinized in terms of the power losses at different stages, control techniques, position of the decoupling capacitor, and cost analysis Recommendations are provided to improve the existing topologies and select the suitable control techniques to obtain a clear picture of the framework for next-generation isolated PV microinverters
152 citations
Cites background from "A Review of Power Decoupling Techni..."
...Hence, the reliability of the microinverter can be increased by either placing the capacitor on a high voltage DC link or by adopting a decoupling circuit on the PV side [62]....
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TL;DR: In this paper, a three-phase dc-ac converter with two-stage zero voltage switching (ZVS) operation for grid-tied PV system is proposed which will reduce cost per watt, improve reliability, and increase scalability of MW-class solar farms through the development of new solar farm system architectures.
Abstract: Module integrated converters (MICs) in single phase have witnessed recent market success due to unique features such as improved energy harvest, improved system efficiency, lower installation costs, plug-and-play operation, and enhanced flexibility and modularity. The MIC sector has grown from a niche market to mainstream, especially in the United States. Assuming further expansion of the MIC market, this paper presents the microinverter concept incorporated in large size photovoltaic (PV) installations such as megawatts (MW)-class solar farms where a three-phase ac connection is employed. A high-efficiency three-phase MIC with two-stage zero voltage switching (ZVS) operation for the grid-tied PV system is proposed which will reduce cost per watt, improve reliability, and increase scalability of MW-class solar farms through the development of new solar farm system architectures. The first stage consists of a high-efficiency full-bridge LLC resonant dc-dc converter which interfaces to the PV panel and produces a dc-link voltage. A center points iteration algorithm developed specifically for LLC resonant topologies is used to track the maximum power point of the PV panel. The second stage is comprised of a three-phase dc-ac inverter circuit which employs a simple soft-switching scheme without adding auxiliary components. The modeling and control strategy of this three-phase dc-ac inverter is described. Because the dc-link capacitor plays such an important role for dual-stage MIC, the capacitance calculation is given under type D voltage dip conditions. A 400-W prototype was built and tested. The overall peak efficiency of the prototype was measured and found to be 96% with 98.2% in the first stage and 98.3% in the second stage.
141 citations
Cites background from "A Review of Power Decoupling Techni..."
...However, with the presence of the power decoupling capacitor, MIC can support the ac grid not only as an ac power source, but as a VAR and possibly a harmonics compensator as well [5]....
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...The MIC with its high-frequency transformer can be grouped into three architectures based on the dc-link configurations: dclink, pseudo-dc-link, and high-frequency ac [3]–[5]....
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...In addition, MIC and ac PV systems greatly simplify system design, eliminate safety hazards, and reduce installation costs [3], [5], [6]....
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References
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TL;DR: In this article, the authors focus on inverter technologies for connecting photovoltaic (PV) modules to a single-phase grid and categorize the inverters into four classifications: 1) the number of power processing stages in cascade; 2) the type of power decoupling between the PV module(s) and the single phase grid; 3) whether they utilizes a transformer (either line or high frequency) or not; and 4) the kind of grid-connected power stage.
Abstract: This review focuses on inverter technologies for connecting photovoltaic (PV) modules to a single-phase grid. The inverters are categorized into four classifications: 1) the number of power processing stages in cascade; 2) the type of power decoupling between the PV module(s) and the single-phase grid; 3) whether they utilizes a transformer (either line or high frequency) or not; and 4) the type of grid-connected power stage. Various inverter topologies are presented, compared, and evaluated against demands, lifetime, component ratings, and cost. Finally, some of the topologies are pointed out as the best candidates for either single PV module or multiple PV module applications.
3,530 citations
"A Review of Power Decoupling Techni..." refers background or methods in this paper
...9 mF in order to achieve a 98% PV utilization factor [4]....
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...In grid-connected PV applications, the electrical isolation is necessary for safety issues [4]....
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...The grid-connected inverter for PV system is categorized into three categories: centralized inverter, string inverter, and ac-module “microinverter” [4], [5]....
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TL;DR: In this paper, a topology study of the PV MICs in the power range below 500 W and covers most topologies recently proposed for MIC applications is presented, where the MIC topologies are classified into three different arrangements based on the dc link configurations.
Abstract: The annual world photovoltaic (PV) cell/module production is growing at almost an exponential rate and has reached 1727 MW in 2005. Building integrated PV (BIPV) projects are emerging as the strongest part of the PV market and grid interactive inverters are a key component in determining the total system cost. Module integrated converter (MIC) technology has become a global trend in grid interactive PV applications and may assist in driving down the balance of system costs to secure an improved total system cost. This paper concentrates on the topology study of the PV MICs in the power range below 500 W and covers most topologies recently proposed for MIC applications. The MIC topologies are classified into three different arrangements based on the dc link configurations. A systematic discussion is also provided at the end of the paper that focuses on the major advantages and disadvantages of each MIC arrangement. These are considered in detail and will provide a useful framework and point of reference for the next generation MIC designs and applications.
1,158 citations
"A Review of Power Decoupling Techni..." refers background or methods in this paper
...Microinverter configurations with high-frequency transformer fall into three basic categories based on the dc-link configurations [5]: dc link, pseudo dc link, and high-frequency ac, as shown in Fig....
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...The grid-connected inverter for PV system is categorized into three categories: centralized inverter, string inverter, and ac-module “microinverter” [4], [5]....
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TL;DR: In this paper, a flyback-type utility interactive inverter circuit topology was proposed for photovoltaic (PV) power generation systems when its lifetime under high atmospheric temperature is taken into account.
Abstract: In recent years, interest in natural energy has grown in response to increased concern for the environment. Many kinds of inverter circuits and their control schemes for photovoltaic (PV) power generation systems have been studied. A conventional system employs a PV array in which many PV modules are connected in series to obtain sufficient dc input voltage for generating ac utility line voltage from an inverter circuit. However, the total power generated from the PV array is sometimes decreased remarkably when only a few modules are partially covered by shadows, thereby decreasing inherent current generation, and preventing the generation current from attaining its maximum value on the array. To overcome this drawback, an ac module strategy has been proposed. In this system, a low-power dc-ac utility interactive inverter is individually mounted on each PV module and operates so as to generate the maximum power from its corresponding PV module. Especially in the case of a single-phase utility interactive inverter, an electrolytic capacitor of large capacitance has been connected on the dc input bus in order to decouple the power pulsation caused by single-phase power generation to the utility line. However, especially during the summer season, the ac module inverters have to operate under a very high atmospheric temperature, and hence the lifetime of the inverter is shortened, because the electrolytic capacitor has a drastically shortened life when used in a high-temperature environment. Of course, we may be able to use film capacitors instead of the electrolytic capacitors if we can pay for the extreme large volume of the inverter. However, this is not a realistic solution for ac module systems. This paper proposes a novel flyback-type utility interactive inverter circuit topology suitable for ac module systems when its lifetime under high atmospheric temperature is taken into account. A most distinctive feature of the proposed system is that the decoupling of power pulsation is executed by an additional circuit that enables employment of film capacitors with small capacitance not only for the dc input line but also for the decoupling circuit, and hence the additional circuit is expected to extend the lifetime of the inverter. The proposed inverter circuit also enables realization of small volume, lightweight, and stable ac current injection into the utility line. A control method suitable for the proposed inverter is also proposed. The effectiveness of the proposed inverter is verified thorough P-SIM simulation and experiments on a 100-W prototype
493 citations
"A Review of Power Decoupling Techni..." refers background in this paper
...Given the cascaded conversion process, the projected efficiency will be low, as indicated in [15], where 70% is achieved as the peak efficiency....
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TL;DR: In this paper, a hybrid fuel cell/battery system is proposed to improve the slow transient response of a fuel cell stack, which can be used for an autonomous device with quick load variations.
Abstract: The implementation of a hybrid fuel cell/battery system is proposed to improve the slow transient response of a fuel cell stack. This system can be used for an autonomous device with quick load variations. A suitable three-port, galvanic isolated, bidirectional power converter is proposed to control the power flow. An energy management method for the proposed three-port circuit is analyzed and implemented. Measurements from a 500-W laboratory prototype are presented to demonstrate the validity of the approach
416 citations
TL;DR: In this paper, two methods of reducing the storage capacitance in the ac/dc power supplies for light emitting diode (LED) lighting were proposed to achieve a long power suppliespsila lifetime.
Abstract: This paper proposes two methods of reducing the storage capacitance in the ac/dc power supplies for light emitting diode (LED) lighting. In doing so, film capacitors can be adopted instead of electrolytic capacitors to achieve a long power suppliespsila lifetime. The voltage ripple of the storage capacitor is intentionally increased to reduce the storage capacitance. The method of determining the storage capacitance for ensuring that the boost power factor correction converter operates normally in the whole input voltage range is also discussed. For the purpose of further reducing the storage capacitance, a method of injecting the third harmonic current into the input current flow is proposed. While ensuring that the input power factor is always higher than 0.9 to comply with regulation standards such as ENERGY STAR, the storage capacitance can be reduced to 65.6% of that with an input power factor of 1. A 60-W experimental prototype is built to verify the proposed methods.
380 citations
"A Review of Power Decoupling Techni..." refers methods in this paper
...The authors in [26] used this concept to minimize the dc-link capacitance in ac/dc application, and also proposed a third-harmonic injection method to further reduce the size of the capacitance by compromising the power factor and capacitance [27], [28]....
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