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Featured researches published by Hua Ni.


ieee region 10 conference | 2013

Synchronization strategy of microgrid from islanded to grid-connected mode seamless transfer

Haizhen Xu; Xing Zhang; Fang Liu; Debin Zhu; Rongliang Shi; Hua Ni; Wei Cao

Microgrid should be operated in both grid-connected and islanded mode to ensure high voltage quality and reliability. In the case of continuous uninterrupted power supply, seamless transfer is important between the two modes,and synchronization of the voltage of the point of common coupling (PCC) and utility grid should be finished first to achieve the goal. In this paper varies of synchronization strategies used in different microgrid control structures from islanded mode to grid-connected mode are summarized, and a new method based on droop control is proposed. This method does not affect power sharing during synchronization procedure. Simulation and experiment results are presented to show the feasibility of the method.


IEEE Transactions on Power Electronics | 2017

Analysis and Control of Neutral-Point Voltage for Transformerless Three-Level PV Inverter in LVRT Operation

Zhangping Shao; Xing Zhang; Fusheng Wang; Renxian Cao; Hua Ni

The modulation strategy LMZVM (large, middle, and zero vector modulation) can be widely adopted in the three-level 7 photovoltaic (PV) inverter, because it reduces the ground current and produces little neutral-point (NP) voltage in normal operation. However, in low-voltage ride-through (LVRT) operation, the NP voltage fluctuation becomes large and has not been researched nowadays. In this paper, according to this problem, four critical weighing factors about the NP voltage based on symmetrical component method are proposed. We can see that the maximum peak-to-peak value among all dip types happens when the single-phase grid voltage dips to 0. Then, an original balancing strategy, which replaces the zero vector with two opposite P-type or N-type small vectors of equal duty cycle, is put forward. Experimental results are provided to validate that the proposed strategy can reduce the NP voltage fluctuation in LVRT operation.


IEEE Transactions on Power Electronics | 2017

Modeling and Resonance Analysis of Multiparallel Inverters System Under Asynchronous Carriers Conditions

Changzhou Yu; Xing Zhang; Fang Liu; Fei Li; Haizhen Xu; Renxian Cao; Hua Ni

With increasing penetration of renewable energy sources into modern power systems, multiparallel inverters are commonly employed in the interface to the utility grid, giving rise to potential resonance problems. In order to better understand the issue, resonance of multiparallel inverters is analyzed under an asynchronous carrier. First, multiparallel inverter equivalent circuits are modeled within a controlled bandwidth. In order to investigate resonance characteristics under an asynchronous carrier, a crossover filter function is used to separate output currents of different frequencies for a two-parallel inverter to analyze the output current frequency response. With this approach, resonance characteristics are focused under asynchronous conditions, and the impact of shifting LCL parameters on resonance is examined. The influence of paralleled inverter number on output currents is examined, and the analysis is expanded to multiparallel inverter systems to determine the resonance characteristics. Experimental results validate the developed models and the proposed resonance characteristics.


international power electronics and motion control conference | 2016

Research on power compensation strategy for diesel generator system based on virtual synchronous generator

Rongliang Shi; Xing Zhang; Liu Fang; Haizhen Xu; Chao Hu; Yong Yu; Hua Ni

Due to the large adjust inertia of the diesel generator set (DGS), the quality of power supply would decline when a large load disturbance occurs to the diesel generator system. This paper aims to improve the stability of the diesel generator system voltage amplitude and frequency under impact load conditions using a virtual synchronous generator (VSG) method. Firstly, a mathematical model of DGS is built, the dynamic performances of DGS under a variety of load conditions is analyzed. Secondly, a three-phase energy storage inverter based on VSG control is selected as the parallel power compensator to suppress the system voltage amplitude and frequency fluctuations. Finally, experimental results are given to verify the feasibility and validity of the proposed control strategy.


ieee pes asia pacific power and energy engineering conference | 2016

Virtual impedance design for virtual synchronous generator controlled parallel microgrid inverters based on a cascaded second order general integrator scheme

Rongliang Shi; Xing Zhang; Chao Hu; Jun Gu; Haizhen Xu; Yong Yu; Hua Ni

This paper explores the impact of the output impedance on the power-sharing stability between parallelized microgrid inverters (MGIs) operating with virtual synchronous generator (VSG) method. In these systems, a virtual output impedance is usually added to the control loop of each MGI to improve the power sharing, regardless of line impedance unbalances. The time derivative of the MGI output current is usually used to implement the virtual impedance, which makes the system highly sensitive to the output current with high slew rate. To solve this, the virtual impedance is designed based on a cascaded second order general integrator (CSOGI) scheme, which is less sensitive to the output current noise, avoids to perform the time derivative function, achieves better output voltage total harmonic distortion. The proposed strategy is demonstrated in detail and validated with a two 100kVA-MGIs parallel system under linear and nonlinear loads.


ieee international future energy electronics conference | 2015

A differential feedforward control of output current for high performance virtual synchronous generator in microgrid

Rongliang Shi; Xing Zhang; Fang Liu; Haizhen Xu; Chao Hu; Hua Ni; Yong Yu

This paper concentrates on the load disturbance in three phase microgrid inverter (MGI) with an isolated transformer based on virtual synchronous generator (VSG) control. The transformer can provide the VSG with inductive output impedance when placed behind the LC filter. But the load disturbance may lead to steady-state error and poor dynamic performance with only capacitor voltage feedback control. The capacitor voltage differential feedback control is proposed to damp the output LC filter resonance and thus increases the system stability margin. The output current differential feedforward control is proposed to eliminate the influence of load disturbance then obtains error-free steady-state output and excellent dynamic responses. These theoretical findings have been eventually verified experimentally both on simulation and laboratory prototypes.


international conference on electrical machines and systems | 2014

Leakage current reduction for transformerless three-level T-Type photovoltaic grid-connected inverter

Zhangping Shao; Xing Zhang; Fusheng Wang; Renxian Cao; Hua Ni

This paper proposed the common mode model of three-level T-Type inverter. Then a kind of improved LCL filter, where the capacitor common point was linked to the DC neutral point, was used to eliminate the leakage current. However, this improved LCL filter changes the mechanism of the neutral-point potential. Traditional algorithms, such as the distribution factor algorithm, are no longer applicable. In order to control the neutral-point potential, a new general distribution factor algorithm was proposed in this paper. Experimental results demonstrate the availability and correctness of the theoretical analysis and algorithm.


Archive | 2010

High-precision maximum power point tracing method

Renxian Cao; Wei Chen; Hua Ni; Lei Tao


Archive | 2010

Boosting method for synchronization without insulating photovoltaic grid-connected inverters

Renxian Cao; Xiaodong Mei; Hua Ni


ieee ecce asia downunder | 2013

A general active damping method based on capacitor voltage detection for grid-connected inverter

Changzhou Yu; Xing Zhang; Fang Liu; Haizhen Xu; Caixia Qiao; Zhangping Shao; Wei Zhao; Hua Ni

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Xing Zhang

Hefei University of Technology

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Haizhen Xu

Hefei University of Technology

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Fang Liu

Hefei University of Technology

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Rongliang Shi

Hefei University of Technology

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Zhangping Shao

Hefei University of Technology

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Changzhou Yu

Hefei University of Technology

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Chao Hu

Hefei University of Technology

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Fusheng Wang

Hefei University of Technology

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Caixia Qiao

Hefei University of Technology

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Debin Zhu

Hefei University of Technology

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