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This paper proposes a lag-lead Active Voltage Positioning (AVP) technique that can be used in buck converters to minimize their output voltage transients during dynamic events, such as load pulses. The proposed technique is based on optimizing the output impedance of the converter across a wide range of frequencies, and therefore, output voltage transients in response to both narrow and wide load...
The flipped voltage follower (FVF), a variant of the common-drain transistor amplifier, comprising local feedback, finds application in circuits such as voltage buffers, current mirrors, class AB amplifiers, frequency compensation circuits and low dropout voltage regulators (LDOs). One of the most important characteristics of the FVF, is its low output impedance. In this tutorial-flavored paper, we...
In DC Microgrid, the majority of the loads are connected to the grid via power electronic converters. These loads act as constant power loads (CPLs) when tightly regulated. If the voltage changes, the CPLs behave negative incremental impedance characteristic during dynamic periods, and could cause system instability. To guarantee the system stability and simultaneously maintain the CPLs good performances,...
As a significant part of electrical load, air conditioners draw attentions for their sometimes-unfriendly load characteristics, especially their dynamic responses during grid voltage disturbances. In this paper, a novel under-voltage control strategy for variable-speed air conditioners is introduced, which can keep air conditioners load characteristic as constant impedances when unexpected voltage...
The performance of reactive power sharing in an islanded microgrid is significantly affected by feeder impedance, mismatch parameters and unbalanced local load. To reduce the negative impact of mismatched link impedance on reactive power sharing, the adaptive virtual impedance strategy for voltage compensation is proposed with paralleled inverters in an islanded mode. The on-line adaptive control...
It is known that the constant power load (CPL) property of load converter can degrade the stability of DC bus voltage of cascaded power converters system. An idea by combining virtual capacitor (VC) based active damping control (ADC) method with DC bus voltage conditioner (DBVC) technique for load converter is proposed in this paper. Through implementing common virtual capacitance volume requirement,...
The constant power load (CPL) property of load converter with tight control can cause instability in the DC bus voltage of cascaded power converters system. To solve this problem, an idea by combining virtual resistor (VR) based active damping control (ADC) method for load converter with hardware DC bus voltage conditioner (DBVC) is proposed in this paper. By establishing common compensation index...
The proposed circuit aims to harvest energy from freight railcars, in which a three-phase electromagnetic generator (EMG) is used to harvest kinetic energy. The key idea of the proposed circuit is to extract maximum power from the EMG through impedance matching until the charge level of the battery reaches 90%. Once, the battery reaches the charge level, it switches the operation mode and regulates...
Microgrid (MG) consists of distributed generation (DG) units, which supply MG loads via the power network. Droop-based control system has been proposed for power sharing implementation among DG units in MGs. The droop control performance is based on the power network variables, which makes it easy to implement. As the control system at the primary level, the droop controller plays a major role in...
In high voltage (HV) flyback charging circuits, the importance of transformer parasitics holds a significant part in the overall system parasitics. The resonance between magnetising inductance and resonant capacitance cause significant deviations in voltage gain. This effect is predominant in the case of very lightly loaded high voltage flyback converters when used for bipolar output voltages. In...
In order to ensure three-phase grid-connected inverter output voltage symmetry under unbalanced grid voltage, an improved control strategy is proposed in this paper. The proposed control strategy includes power, voltage and current three loops. The complex coefficient-filter (CCF) is used to obtain the positive and negative sequence of unbalance output voltage and current during the grid faults. By...
Under the condition of low short circuit capacity and high grid impedance of weak grid, the grid voltage is easily fluctuated due to the load change, affecting the power quality of the grid. In view of this problem, firstly, this paper analyzes the principle of the grid-connected voltage change caused by the load change. Secondly, an improved voltage-power control method (PQ-U) for three-phase grid-connected...
The high line impedance and load fluctuations of weak grid can easily lead to grid voltage fluctuations and other issues. In order to make the grid-connected PV inverter have strong robustness and improve the dynamic response speed, the active power control method of PV inverter based on passive theory is proposed. Firstly, the control strategy of the power outer loop is given, and the Euler-Lagrange...
This paper proposes a control strategy for sharing load requirements in a low voltage islanded microgrid with converter interfaced distributed energy resources. In high voltage lines with large X/R ratio, real and reactive power are decoupled and thus conventional droop control can effectively share the power needs of the load. However, the same strategy cannot be applicable in dominantly resistive...
In this paper, proposed an adaptive droop control method using estimated the line impedance in real time and compensate for the mismatch in voltage drops across line impedance, to enhance reactive power sharing accuracy in island microgrids. The block of line parameter estimation using the current and voltage parameters in the microgrid and estimation algorithm recursive least squares method (LSM)...
In the distributed generation systems, three-phase inverters are the basement because they are used as power electronics interface between the generators and the grid. Cascaded multi-level H-bridge inverters are widely used for industrial application due to the simple topology and good power quality. However, unbalanced power source problem will easily happen in such an application. In this paper,...
This article presents the design of a 4.5-V, 450-mA low drop-out (LDO) voltage linear regulator based on a two-stage cascoded operational transconductance amplifier (OTA) as error amplifier. The aforementioned two-stage OTA is designed with cascoded current mirroring technique to boost up the output impedance. The proposed OTA has a DC gain of 101 dB under no load condition. The designed reference...
In this paper, proposed an adaptive droop controller using compensate for the mismatch in voltage drops across line impedance, to enhance reactive power sharing accuracy in island microgrid. Communication is used to facilitate the tuning of adaptive controller for the change of load. The method will ensure in accurate reactive power sharing even the communication is interrupted if the load does not...
Supercapacitors (SCs) are widely utilized as energy storage units (ESUs) to compensate the transient power fluctuations. In this paper, an improved virtual impedance based coordinated control strategy for distributed SCs is proposed to achieve accurate power distribution. Unlike the existed strategy which can hardly adjust the output power of each SC if the energy storage system contains several distributed...
The technology of microgrid has been developed by the progress of new energy technology, the new energy connected to the microgrid by (distributed generator) DG. Microgrid represents the new direction of the power grid as the great complements of traditional power supply network. This paper presents that using several photovoltaic grid-connected inverters as the DG, and control the microgrid by controlling...
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