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Axes cross-coupling in dq-frame will deteriorate the current control performance, especially for applications with low switching/sampling frequency. Decoupling methods based on inductor current state feedback and complex vector proportional-integrator controllers are usually performed to solve this problem. In this paper, an alternative decoupling method based on preprocessed reference current feed-forward...
Grid-connected Voltage Source Inverters (VSIs) equipped with LCL filters are attractive in utility applications for their better power quality features, while the inherent LCL resonance may limit the current control loop bandwidth or even threaten system stability. Simple but effective single-loop current control strategies have been studied for obtaining a stable system, where either the inverter-side...
VSG (Virtual Synchronous Generator) is a control method for inverters that mimics both the steady-state droop characteristic and transient characteristic of Synchronous Generators (SGs). Because the steady states of VSG and droop controlled inverters are similar, the deviation of frequency and voltage amplitude also exists in the VSG. This paper proposes a new secondary control method mimicking the...
The modular multilevel converter(MMC) is one of the most attractive converter topologies for high or medium voltage power system. In this paper, a combination of modular multilevel converter and dual active bridge(DAB) is discussed. The DAB assisted MMC(MMC-DAB) is capable of low frequency output with elimination of capacitor voltage fluctuations in submodules. This paper analyzes the MMC-DAB structure...
The recently proposed small-AC-signal droop based secondary control is very attractive for microgrids to restore the voltage and frequency of overall system and to share the output power between paralleled distributed generations (DGs). However, the previous work has not discussed the system stability of the novel secondary control method. This paper presents a small-signal model for the microgrids...
The well-known active power-frequency and reactive power-voltage amplitude droop control is widely used in the coordinative control of parallel inverters in Microgrids. However, this conventional droop method may cause deviation on the frequency and voltage amplitude, which will affect the accuracy of power supply. This paper proposes a novel secondary control method to compensate this deviation....
The PI-based current control scheme in dq-frame and PR-based one in αβ-frame are the two most popular current control schemes. It is commonly known that there exists axes cross-coupling in dq-frame, while in αβ-frame it doesn't. And decoupling terms are usually performed to decouple dq-axes cross-coupling. However, PR control scheme presents different performance, when compared with dq-frame PI control...
AC power electronics system are prone to instability due to the interaction between the power converters, and terminal characteristics of individual power converter based criteria are very attractive for analyzing stability of whole system. However, more and more AC power electronics systems emerge with the feature of variable fundamental frequency, while existing approaches for stability analysis...
The following two types of resonant controllers are mainly employed in stationary reference frame to obtain high performance in voltage-source converters: 1) proportional + resonant (PR) and 2) complex vector proportional + integral (cVPI). The performance analysis and parameter design of these two controllers has been researched in many papers. In this paper, these two groups of resonant controllers...
The well-known active power-frequency and reactive power-voltage amplitude droop control is widely used in the coordinative control of parallel inverters in microgrids. However, this conventional droop method may cause frequency and voltage deviation, which affects the accuracy of power supply. This paper proposes a novel secondary control strategy to compensate this deviation. This strategy mimics...
Harmonics are common power quality problems for series compensation devices. In this paper, a robust control scheme based on H∞ synthesis is designed and tested on a 2kW single-phase Active Voltage Quality Regulator (AVQR) system under distorted grid. The designed H∞ exhibit great robustness in the face of system parameter variations due to aging, thermal effect or saturation even the grid is distorted...
The conventional droop control method, which does not require communication lines, is an effective control scheme to dispatch power among inverters in the microgrid. However, this method has inherent tradeoffs: frequency vs. active power accuracy and amplitude regulation vs. reactive power sharing accuracy. To cope with this problem, this paper presents a novel active power control strategy to improve...
Cascaded H-bridge (CHB) multilevel inverter has gained more and more focus due to its adaptability to high-power, high-voltage applications and capability of fault tolerant. In this paper, modeling of the CHB multilevel inverter under RMS feedback control is presented. This particular control scheme is suitable for the control system that has a strong demand for the output voltage amplitude accuracy...
This paper presents a novel wireless load-sharing control strategy, active droop positioning, for islanding parallel inverters in an ac-distributed system. Normally, the microgrid is intended to operate in islanded mode when the disconnection from the upstream MV network occurs. In this condition, the inverter-interfaced microsources acts as a voltage source, with the magnitude and frequency of the...
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