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This paper proposes a virtual series impedance emulation control strategy for current controlled remote PV or wind farms, in order to enhance the power transfer capability of the transmission line. This approach can be regarded as integrating the functions of the FACTS devices, such as series capacitors, into the grid-side converters of PV or wind farms, by utilizing the reactive power capability...
This paper concentrates on the control of the integrated battery storage Power Conditioning Systems (PCS) parallel system in Microgrid (MG). The theoretical analysis of the different operation modes are clearly studied, including grid-connected and islanded mode. To improve the power sharing accuracy during the islanded operation, an enhanced droop controller is introduced. The proposed approach is...
In this paper, an improved control loop based on feedforward is proposed to reduce the total harmonic distortion of the input current (THDi), realizing power factor correction (PFC) in MCM. The frequency responses of the input impedance for a wide frequency range are improved and unified by adding feedforward duty-ratio to the output of the original current-loop. A 5 kW experimental prototype is built...
In recent years, embedding ancillary functions of distributed generation (DG) have drawn great attention due to the increasing penetration of renewable energy based DG such as photovoltaic, wind turbines and fuel cells. Among these ancillary functions, harmonics compensation is becoming more interesting and important with the growth of nonlinear loads in today's power distribution system. When controlled...
V2 control and its variety named ripple-based control, are popular control schemes in point-of-load Buck converters and Voltage Regulators for microprocessor. This control scheme is elegant when output capacitors with sufficient ESR are employed, such as OSCON capacitors. However, in most cases with small-ESR capacitors, such as ceramic capacitors, instability problem will occur. Up to now, no equivalent...
The output voltage transient of a buck regulator during a load current step is often a key performance specification. However, many practical design approaches are based on frequency domain specifications like bandwidth and phase margin, without explicitly considering the constraints of the output filter. This paper derives an analytical expression for the peak transient output voltage due to a load...
A new equivalent circuit model is presented to predict the small-signal characteristic of current-mode control with DCR current sensing accurately, and a simple auto-tuning method is proposed to solve the issue of time constant mismatch in DCR current sensing. The model shows that the mismatch between the current sensing RC network and the output inductor makes the output impedance deviate away from...
This paper introduces a new modular master-less active control method for current share in digitally controlled DC-DC converters that communicate over single wire bus. Current balance among paralleled converters is achieved with new current error zeroing method. Experimental results show the new scheme exhibiting excellent static and stable dynamic current matching performance. The paper also includes...
This paper derives closed-loop input and output impedances of a number of dc-dc power electronic converters when operating in a dc distribution network. The derived impedances can be used for stability analysis and control design for dc distribution networks. In this paper, first the small-signal model of a power converter operating in a dc power system is introduced and the open-loop transfer functions...
DC distribution systems consist of several feedback-controlled converters interconnected to form a complex power distribution system. While the analysis and design of a single power converter and its control is well understood, in a DC distribution system the situation is different. Analyzing and designing a complex multi-converter system in such a way as to guarantee both system stability and performance...
Conventional droop controls have been widely studied for load sharing in dc Microgrids. However, unlike ac Microgrids, transmission line impedances can undermine the controller's performance, and it might fail to provide regulated rated voltage and proportional load sharing. Herein, a distributed secondary controller is introduced that includes two modules; a voltage regulator and a current regulator...
This paper presents a decoupled and adaptive droop strategy to coordinate parallel operation of inverters. This strategy neatly combines a novel decouple method and an adaptive power sharing strategy. The decouple method guarantees the system stability by defining a pair of virtual power and utilizing a low pass filter to achieve dynamic decoupling. And the adaptive power sharing method is included...
The small-signal modeling of dual active bridge (DAB) converter dynamics in discrete time is a useful analysis tool due to the ability to incorporate behavior during zero-voltage switching (ZVS) intervals explicitly, and is advantageous for the direct design of digital compensators. While the control-to-output transfer function has been modeled previously, accurate models of the output impedance of...
In order to improve the input impedance of stacked boost converter (SBC) that processes only a part of the total power delivery, the traditional three-capacitor structure is optimized as single-capacitor structure in this paper. Then small signal models of push-pull SBC based on these two capacitor structures are set up, the loop gain and input impedance are analyzed and compared. Finally, the effectiveness...
Power hardware-in-the-loop (PHIL) simulation techniques are being increasingly applied in the power system field for novel equipment testing and validation. To ensure the accuracy and stability of the overall simulation, special care must be taken in the control of the virtual power interface between the hardware under test and software simulated system. The application of wideband system identification...
Grid synchronization instability issues and low frequency oscillations between synchronous generators exist in electrical power system. This kind of stability issue happens between paralleled power converters is also reported. Analysis based on small-signal model of inverters with phase-locked loops (PLL) has been proposed. Different from that approach, which needs detailed inverter and controller...
A new isolated push-pull very high frequency (VHF) resonant DC-DC converter is proposed. The primary side of the converter is a push-pull topology derived from the Class EF2 inverter. The secondary side is a class E based low dv/dt full-wave rectifier. A two-channel multi-stage resonant gate driver is applied to provide two complementary drive signals. The advantages of the converter are as follows:...
This paper discusses the characteristics of a series-series compensated inductive power transfer system (IPT) with theoretical analysis and experimental results. To maximize system efficiency, two-stage structure, which includes a PFC stage and a resonant DC-DC stage operating in ZVS region, is proposed. One of the major design challenges in implementation of a practical contactless EV charger is...
Small-signal stability in balanced three-phase systems can be analyzed using the Generalized Nyquist stability Criterion (GNC), which is based on source and load impedance in the synchronous rotating (d-q) frame. This paper models the d-q frame impedance of three-phase grid-tied inverters with current feedback control and Phase-Locked Loop (PLL). The result unveils a very interesting and important...
Three-phase ac systems can be transferred into dq axis, where stability analysis becomes much simpler. In order to apply the stability criterion in AC system, an equivalent DQ admittance model for the ATRU system has been developed in this paper, based on the ABC impedance model in paper [1]. Compared to the literature work, this model has two better features: (1) it is valid in a wide frequency range,...
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