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For the islanded microgrid which is connected with nonlinear loads, an effective harmonic sharing method should be designed to guarantee the system stable operation. In this paper, a novel method of virtual impedance and PCC voltage compensation are proposed to achieve the harmonic sharing and voltage quality improvement at the point of common coupling (PCC). The fundamental and each harmonic currents...
In this paper, an improved control strategy for three-phase inverter is proposed, which ensures three-phase output voltage symmetry under unbalanced grid voltage. Firstly, the positive and negative sequence separation module is used to obtain unbalance output voltage and current during the grid faults. By calculating output power of the inverter, an improved P-ƒ, Q-U and Q-G droop control strategy...
DC power distribution gains popularity in future residential, renewable energy, transportation and data centers. Such dc system can be connected to ac system through bidirectional interface converter. Compared with isolated converters, transformerless solutions have the advantages of higher power density, efficiency, and lower cost. One concern about the non-isolated connection is the coupled common-mode...
In the previous studies, it has been shown that the steady-state operation of a class-E resonant inverter can be rapidly simulated in the frequency domain by extending the concept and mathematical form of electrical impedance. This paper provides a more comprehensive solution for the efficient simulation of practical class-E resonant inverter, which is driven by a MOSFET switch. The parasitic components,...
Many efforts have been made to improve the performance of power electronic systems with active capacitive DC-link module in terms of power density as well as reliability. One of the attractive solution is an active capacitive DC-link with the series-connected circuit because of handling small-rated power. However, in the existing control method of this circuit, the DC-link current of the backward-stage...
This paper presents a new technique to detect the junction temperature of Silicon Carbide (SiC) MOSFET devices. The process of detection is based on injecting a high frequency/low amplitude sweep signal into the gate lead of a SiC device during its OFF-state period. A frequency response analysis is carried out to determine the variation in the impedance which is a function of temperature change. The...
The harmonic performance of the slim dc-link adjustable speed drives has shown good performance in some studies but poor in some others. The contradiction indicates that a feasible theoretical analysis is still lacking to characterize the harmonic distortion for the slim dc-link drive. Considering the shortcomings of the present harmonic analysis methods, such as the time-domain simulation, or the...
This paper explores the interconnection of multiple microgrid with “tie-line”. Tie-line control can be managed to control the power flow from microgrid and voltage at respective microgrid buses at the point of interconnection. Formation of such DC microgrid cluster ensures higher reliability of power supply and flexibility to manage distributed energy resources and loads in the system. Two identical...
This paper proposes a design method of the wireless power transfer system which obtains high power and high efficiency by using LC filter circuit in the transmitting side. This study forcuses on the maximum efficiency point of impedance. In the simulation, the proposed design achieved 2.5kW output power with the efficiency of 73%. In the experiment, the proposed circuit achieved 1.8kW wireless power...
A wireless power transfer (WPT) converter for ‘Energy Hub’ system is proposed in home applications. For high power factor capability, the proposed system adopts an additional secondary power factor correction (PFC) circuit. It can operate both of resistive AC load and capacitive DC load, which is multi-functional in the energy hub system. The proposed WPT converter can obtain high power factor without...
A newly proposed concept for CM impedance boosting has been developed and demonstrated. The impedance boosting is through a three-winding common mode(CM) choke with its auxiliary winding connected to an negative impedance circuit. However, in practical CM choke the imbalance of the windings will lead to impedance variations. The aim of this paper is to analyze these impedance variations. The DM and...
This paper presents a division-summation (D-Σ) digital controlled three-phase four-leg voltage source inverter with load impedance estimation for uninterruptible power supply applications. The D-Σ digital control developed for current tracking can accommodate wide filter inductance variation, which has been successfully adopted in grid-tied applications. This paper proposes a load impedance estimation...
This work will present a novel photovoltaic (PV) inverter with integrated short-term storage. The topology combines advantages of microinverter topologies, such as module-specific maximum-power-point tracking, failure-tolerance, safety due to limited voltages, modularity, use of low-cost low-voltage components such as silicon field-effect transistors (FET), and simple expandability, with those of...
The microgrid can operate in grid-connected mode and islanded mode, and the parallel operation of inverters will be involved in both modes. However, due to the differences of output characteristic among various inverters, the load power can't be shared equally. As a result, some methods without communication lines such as droop control and VSG (virtual synchronous generator) control have been proposed...
This paper proposes a frequency scanning-based impedance analysis for stability assessment of grid-connected inverter system, which is able to perform stability assessment without using system mathematical models and inherit the superior feature of impedance-based stability criterion with consideration of the inverter nonlinearities. Small current disturbance is injected into grid-connected inverter...
Inverters in voltage control mode including droop control and virtual synchronous generator (VSG) are promising for interconnecting the renewable energy to the grid, which are both emulating the frequency and voltage regulating functions of synchronous generators through droop method. However, improper transient impact current and reactive power output are observed for inverters in voltage control...
Researches to control water content of Polymer Electrolyte Membrane(PEM) are actively performed for increasing performance & durability of Fuel cell. This Research to control water content focused on measurement of PEM impedance. In this paper, The measurement system of PEM Impedance based on AC impedance method is proposed. Bi-directional DC/DC converter is designed to measurement of PEM impedance...
This paper proposes a novel control method to realize unbalanced load power sharing in an islanded microgrid. The proposed method consists of typical real-power-frequency (P-f) and reactive-power-voltage (Q-V) droop control, virtual impedance control which only functions at fundamental negative sequence, and unbalanced-power-small-signal-frequency (SU-ωss) droop control. The typical droop control...
Due to the high frequency nature and constant power load characteristics, stability issue exists widely in contemporary power electronic systems. Impedance-based criteria can be used in stability prediction. Thus, the accurate extraction of impedance becomes significantly important. For AC systems, impulse injection method has been proposed for its short measurement duration, but the accuracy needs...
The nonlinear loads in microgrid not only distort the voltage but also degrade the harmonic power distribution in a conventional droop-controlled microgrid. This paper starts with analyzing the trade-off between voltage total harmonic distortion (VTHD) and harmonic sharing effectiveness. A multi-framed droop controller is proposed to improve the harmonic power sharing without deteriorating VTHD by...
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