Development of a Current-Sensorless Multi-Loop Control for Standalone PWM Inverters

Yuan Yisheng,Liuchen Chang,Song Pinggang 전력전자학회 2007 ICPE(ISPE)논문집 Vol.- No.-

A current-sensorless multi-loop control method that estimates the capacitor current is proposed for standalone inverter applications. The theory of the control loop is given, and a mathematical model is analyzed. The effect of capacitor parameter mismatch on system characteristics was emphasized and discussed through modeling and simulation. Finally, experimental results comparing the characteristics of the output voltage under parameter mismatch conditions verified the operation and merits of the proposed controller.

Improved SVM for High Gain Tri-state CSI to Reduce DC Side Inductor Current Ripple

Chufeng Li,Liuchen Chang,Meiqin Mao 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5

Extending our previous work proposing a high gain tri-state current source inverter (CSI), in this paper, an improved space vector modulation (SVM) method is proposed in order to reduce the DC side inductor current ripple. By the proposed SVM method, the active state time is divided into four equal segments and the shoot-through state time is divided into six equal segments and inserted into the four equal active state segments, respectively. Theoretically, the maximum ripple can be obtained to 1/3 of that compared with the traditional SVM mode. The proposed improved SVM method is compared with the traditional SVM method. Simulation and experimental results verify the effectiveness of the proposed strategy.

Q-learning Algorithm Based Multi-Agent Coordinated Control Method for Microgrids

Yuanyuan Xi,Liuchen Chang,Meiqin Mao,Peng Jin,Nikos Hatziargyriou,Haibo Xu 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6

This paper proposes a Q-learning algorithm (Q-LA) based multi-agent coordinated control method for microgrids. By the method, Q-LA is adopted to calculate the power to be regulated, which is called the microgrid regulation error (MRE), in secondary control for real-time operation. And the generation schedule of distributed generators (DGs) as well as batteries is modified in real time with the MRE by the fuzzy theory and particle swarm optimization method, taking the economy and environmental benefits into consideration together. The simulation platform of Q-LA based multi-agent hybrid energy management system for microgrid (HEMS-MG) is established in C++ Builder. The simulation results verify the effectiveness and feasibility of the proposed method.

Multi-Agent Based Simulation for Microgrid Energy Management

Mao Meiqin,Dong Wei,Liuchen Chang 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5

This paper presents a general multi-agent based model for the hierarchical and distributed energy control of a Microgrid. In this model, the agents under three different levels are classified and defined in detail. And based on the model, a novel simulation platform for the energy management system of the Microgrid (EMS-MG) is designed in terms of Client-Server and implemented under C++ Builder environment. Taking the generation automatic control for example and by the proposed model and implemented EMS-MG, a simulation result is shown to illustrate the operation process of the simulation platform and present the benefits of the proposed method.

Economic Analysis of the Microgrid with Multi-energy and Electric Vehicles

Mao Meiqin,Sun Shujuan,Liuchen Chang 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5

Electric vehicles (EVs) may play dual roles when they plug in a microgrid. They appear as loads during charging, meanwhile they may also be used as storage units to supply energy to the rest loads in the microgrid if the batteries have the sufficient spare energy. Considering the characteristic of bidirectional energy flow of EVs in a microgrid, this paper proposes the energy dispatch model and strategies for the microgrid including Wind generators, Photovoltaic systems, Battery storages, EVs and other local loads to analyze the impact of incorporating vehicles within and without microgrid on the economic operation of the microgrid. The simulation results indicate that incorporating EVs within the microgrid can not only minimize the capital cost of storages and reduce operation cost of the microgrid’s operator, but also save the cost of EVs’s owners.

A Novel Soft-Switching Two-Stage Step-Up DC/DC Converter

Shaowu Du,Zhong Chen,Liuchen Chang 전력전자학회 2007 ICPE(ISPE)논문집 Vol.- No.-

In an electric vehicle power system, a step-up converter is required to increase the voltage from 24 V to 270 V. To achieve such a high voltage boost ratio, there are several challenges that must be overcome: tackling the leakage inductance of the isolation transformer; reducing the voltage stress on the power switches; and guaranteeing fast dynamic response and high efficiency. Thus, innovative approaches are needed. A novel two-stage step-up DC/DC converter has been developed. This device has the advantages of high power density, easy control, high efficiency, high transformer utilization, and fast dynamic response. The two-stage step-up DC/DC converter is composed of a boost converter cascaded with a push-pull converter. The boost diode and filter capacitor, as found in conventional boost converters, are eliminated. All switches achieve soft-switching by using a simple auxiliary circuit. Therefore, this novel converter is well-suited for applications where the input voltage level is significantly lower than the output voltage, for example, in the areas of electric vehicle power supplies, communication systems, aeronautic power, and power systems. Analysis, prototype development, and experimental tests have been conducted, and the results are presented in this paper. The results confirm the performance and features of the novel converter.

Advanced Building Blocks of Power Converters for Renewable Energy Based Distributed Generators

Riming Shao,Mary Kaye,Liuchen Chang 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5

The power converter is a critical component of a distributed generation (DG) system, particularly for a renewable energy based distributed generator. With the rapid development and growing applications of DG systems, power converters have evolved from a traditional “power conversion device” to a “system integrator”. This paper outlines the basic and advanced building blocks of power converters for distributed generation systems, with an emphasis on the new algorithms developed especially for grid-connected single-phase power converters in small wind turbines and photovoltaic systems. A grid-connected power converter should feed power of a high quality into a grid with a low total harmonic distortion (THD), and fast dynamic response to the variations of a renewable energy resource. The newly developed space vector based pulse-width-modulation (PWM) with predictive current control provides a direct cycle-by-cycle regulation of the current waveform feeding into the grid. Effective anti-islanding is an essential function of a power converter, in compliance with the grid interconnection requirements. As active islanding detection methods exert disturbances to the grid and passive islanding detection methods generally have large non-detection zones, new and hybrid islanding detection methods have been developed. A power spectral density method has been developed to continuously monitor and identify the possible features of an islanding formation. Maximum power extraction from renewable energy resources is vitally important for distributed generators. Many algorithms have been developed for maximum power point tracking (MPPT) of photovoltaic and wind energy systems. A new MPPT method has been developed by integrating the fast extremum-finding method of Golden Section Search (GSS) into a multi-stage MPPT algorithm. The proposed MPPT algorithm provides fast response (in the order of 40 msec) and high tracking accuracy (99.9%) as compared to the existing algorithms.

A Single-Stage High Gain Current Source Inverter for Grid-Connected Photovoltaic System

Meiqin Mao,Yajun Zheng,Liuchen Chang,Haibo Xu 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6

The output voltage range of PV cells is widely influenced by the environment factors, such as temperature, solar radiation, etc. The lower output voltage of solar array can hardly meet the requirements for grid-connected operation of the system. To achieve high voltage gain and a steady ac output voltage in spite of the low dc input voltage, this paper presents a novel single-stage high gain current source inverter (CSI). The topology of the proposed inverter is derived from conventional tri-state current source inverter by introducing an impedance network with two symmetrical inductors and diodes separately. Theoretical analysis of operation modes and high voltage gain performance for the proposed inverter is presented, followed by the simulation of the proposed inverter in grid-connected photovoltaic (PV) system carried out on MATLAB.

Novel Nonlinear DC-Link Voltage Control for Small-Scale Grid-Connected Wind Power Converters

Guanhong Song,Bo Cao,Liuchen Chang,Riming Shao 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5

A novel nonlinear observer-based DC-link voltage control algorithm is proposed in this paper for smallscale grid-connected variable-speed wind power converters to minimize the voltage fluctuation across DC-link capacitors caused by wind power variations. The DC-link capacitors, in wind power converters, are normally used to buffer the difference between the input and output power. However, the DC-link voltage varies significantly under rapidly changing working conditions. Hence, a proper DC-link voltage controller is essential to regulate the DC-link voltage in order to minimize these fluctuations. The proposed algorithm estimates the power fed into the converter system using a nonlinear observer integrated with a PI controller, combining the advantages of fast dynamic response capability offered by the proposed observer and control robustness from the PI controller without any additional measurement components. The effectiveness of the proposed control algorithm is verified by both simulation and experimental results.

Predictive current controller and compensator‑based discrete current controller for single‑phase bridge inverters

Jinghua Zhou,Shuang Xu,Riming Shao,Liuchen Chang 전력전자학회 2022 JOURNAL OF POWER ELECTRONICS Vol.22 No.9

Transfer efficiency and power quality are two critical factors when it comes to grid-connected distributed generation systems. Single-phase inverters are commonly used in distributed generation systems under 10 kilowatts as the connection between the gird and renewable energy sources (RESs). In this application, grid current distortion plays a pivotal role in determining inverter performance. In this article, an improved current control strategy based on a predictive current controller (PCC) and a compensator is presented to decrease current harmonic distortion and increase power quality. The controller design method inspects a single-phase inverter system as a digital platform, and designs the controller in discrete time in order to obtain a more precise and effective controller than that in continuous time. The discretization procedures using sampling and hold (S&H) are taken into consideration in the design process. The improved current controller is a DSP-based digital current controller for grid-connected single-phase bridge inverters, whose performance is optimized by considering the time delay caused by analog–digital conversion (ADC) and computations. A comparison has been made to analyze the performance of the single-phase grid-connected inverter system with PCC and ICC. Experimental results are shown to validate the effectiveness of the designed current controller.