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Under the high penetration of renewable energy, the power grid may features as the weak grid, which contains a large set of grid impedance values and varies of harmonics. The grid-connected inverter can be greatly challenged by this weak grid condition when it is operated as the interface to inject the generated power into the grid. Particularly, the stability problem may be aroused by the grid impedance...
The internal nodes of switched capacitor converters can be used to provide multiple pulsed width modulated voltages that, in combination with filter inductors, can extend the available dc outputs. Such converter architecture requires models that accurately predict the behaviour of switched capacitor converters operated in current output mode. Based on the well-known output impedance model, a new circuit...
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...
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,...
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...
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...
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:...
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 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...
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 proposes a small signal model for active droop control in equivalent circuit form. Active droop control is an average current mode control with proportional output voltage feedback. The proposed model takes the switching ripple of the voltage and current feedback into account, and the model is valid up to half of switching frequency. The features of the active droop controlled converters...
Datacenter power consumption makes up two percent of United States electricity consumption or 80TWhr. Roughly half of this energy is spent on cooling or lost in power conversion. Further as datacenters try to maximize compaction, the need for small and highly efficient power supplies is highlighted. Telecom power supplies often rely on large and lossy transformers to achieve large conversion ratios...
This paper addresses the stability issues and some control solutions in solid-state transformers (SST). An SST is built using three cascaded stages, including an ac-dc rectifier, a dual active bridge (DAB) converter, and a dc-ac inverter. Multistage cascaded converters are highly prone to instabilities due to the interaction between stages. Hence, the control system must be designed in a way that...
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...
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...
This paper proposes the simple and seamless operation technique for bi-directional LLC converter. Generally, bi-directional operation of LLC converter is complicated and difficult to control. Because, the switching frequency has to be changed across fsr (series resonant frequency) and the switching sequences has to be also changed due to resonant characteristics. In order to simplify the switching...
In this paper, an improved power flow analysis algorithm for distributed generation (DG) units controlled with P/Q droop functions and virtual impedances in a low voltage (LV) microgrid is proposed. The proposed analysis provides in contrast to conventional power flow calculation techniques: (i) consideration of virtual impedance parameters and (ii) higher accuracy in reactive power flow calculation...
Noise separators have been wildly used in separating the common mode and differential mode signals in conducted EMI measurements. The high frequency performance of a single phase noise separator is improved in this paper. It is realized by a detailed calculation of the impedance characterization of the transmission line transformer. Then an impedance matching capacitance is added at the output terminal...
Wireless power transfer (WPT) technology has become a popular idea in battery charging for both low- and high-power applications, such as mobile-phones and electric vehicles (EV). For charging portable devices, common ideas apply location sensing and turn on specific coils under the loads. This paper proposes a universal WPT system for multiple electronics devices. The system is based on LLC circuit,...
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