A Review of Direct Driven PMSG for Wind Energy Systems

This paper presents a comprehensive overview study of the DDPMSG （direct driven permanent magnet synchronous generator） for wind energy generation system. Wind turbine controls are provided. The PMSG （permanent magnet synchronous generator） is introduced as construction and model. Configurations of different power converters are presented for use with DDPMSG in wind systems at variable speed operation and maximum power capture. Control techniques for the system are discussed for both machine-side and grid-side in details. Grid integration is provided with focus on how to insure power quality of the system and the performance at disturbances.     

A Study on the Structure of Linear Synchronous Motor for 600 km/h Very High Speed Train

Recently, an interest in a hybrid system combining only the merits of the conventional wheel-rail system and Maglev propulsion system is growing as an alternative to high-speed maglev train. This hybrid-type system is based on wheel-rail method, but it enables to overcome the speed limitation by adhesion because it is operated through a non-contact method using a linear motor as a propulsion system and reduce the overall construction costs by its compatibility with the conventional railway systems. Therefore, a comparative analysis on electromagnetic characteristics according to the structural combinations on the stator-mover of LSM （linear synchronous motor） for VHST （very high speed train） maintaining the conventional wheel-rail method is conducted, and the structure of coreless superconducting LSM suitable for 600 km/h VHST is finally proposed in this paper.     

Control of variable speed wind turbines equipped with synchronous or doubly fed induction generators supplying islanded power systems

A control method for variable speed wind turbines (VSWTs) supplying islanded parts of electrical networks is presented. Active power/frequency and reactive power/voltage droops are applied in order to determine the active, reactive power production, thus downscaling to the VSWTs the conventional control concepts of the power plants. Two types of VSWTs comprising doubly fed induction generators or synchronous generators are considered. Electrical, aerodynamic and structural detailed dynamic models were developed and combined with the proposed control strategies ensuring fast regulation of the frequency and the voltage in the islanded mode of operation. The obtained models are used for the simulation of a representative simplified distribution network supplied by VSWTs.     

分布式光伏发电系统改进虚拟同步发电机控制

提出一种计及分布式光伏发电系统源端输出功率波动特征的改进虚拟同步发电机(IVSG)控制策略。对单台虚拟同步发电机功率平衡方程特征值进行分析,明确了光伏电源的基本运行特性,确定了光伏电源稳定运行区域。在传统虚拟同步发电机(VSG)的基础之上进一步采用了直流电压稳定控制技术,提出改进的虚拟同步发电机控制策略。当光伏电源输出功率低于负载需求时起到抑制直流母线电压跌落、维持直流电压稳定的作用,实现按照负荷或并网功率需求进行功率匹配的目的。仿真与实验结果验证了所提控制策略的可行性与有效性。     

Comparison of oscillation damping capability in three power control strategies for PMSG‐based WECS

With the aid of small signal analysis and digital simulations, this paper compares the mechanical and power oscillation damping performances of three power control strategies for the multi‐pole permanent magnetic synchronous generator (PMSG)‐based direct driven wind energy conversion system (WECS). Maximal power point tracking (MPPT) control implemented in the generator side has inherent abilities on the oscillation damping. For the smoothed or constant power requirements, power oscillations are hard to damp, and additional active damping controller is required. Active damping can be achieved with power control on the generator or grid side and DC link voltage control on the generator side. With additional compensator in the power or DC link voltage control loop, a damping torque is produced to suppress the oscillations. An improved control structure, which has inherent oscillation damping capability, is proposed for the power control of WECS. Combined with different power control strategies, this structure can be applied to achieve different power outputs. The validation of the proposed control structure is verified by the simulations. Copyright © 2010 John Wiley & Sons, Ltd.     

Innovative Control Strategy for Islanded Small Hydro Power Plant

In many developing countries, there are regions where the electrical grid is weak or nonexistent. However, in these areas, large amounts of distributed energy sources, such as hydro, are often available and could be suitably exploited. To this aim, the low head hydro power plants can play a significant role. In fact, recent technological advances in mini-hydro turbines and decreasing costs of static electricity conversion devices enable to realize suitable power plants for an efficient and profitable exploitation of these sites. One of the major challenges is the integration of the above-mentioned power plants into autonomous electrical systems, islanded and/or disconnectable from the main distribution network. In this paper, an innovative control strategy for a low head hydro power plant supplying users in small clusters of villages is proposed.     

Dynamic Voltage Restorer with Active Disturbance Rejection Control

Power quality is one of the major concerns among consumers and electric utility companies. CUPS （custom power systems） devices are used to improve the quality of power and enhance the reliability of the power supply in the distribution networks. The DVR （dynamic voltage restorer） is an important CUPS device used to mitigate voltage sag/swell and imbalances. Various control techniques have been implemented to control the DVR, among which the PID （proportional-integral-derivative） controller is dominant because of its model independent property and its error driven technique. In this paper, a new controller based on the ADRC （active disturbance rejection control） concept is developed, and its performance is compared to that of the PID controller. The model of the DVR and its ADRC and PID controllers were developed under the MATLAB （matrix laboratory）/Simulink environment. The simulation results demonstrated the effectiveness of the ADRC over the PID controller.     

Examination for Experimental Verification of Improvement of Power Quality in Distribution System by PCS

In the future, the power quality will decrease by the introduction of a lot of renewable energy sources. The topic of this research is a new method of operation of PCS （power conditioning systems） in the future distribution system. The purpose of this research is development of PCS with a function of improvement of the distribution system. Therefore, the authors propose a method of the power quality improvement of the distribution system by PCS. In addition, the authors construct the control logic to use in PCS The control logic suggests adding harmonic restraint function to conventional control. These were verified by simulation and an experiment. As the results, we confirmed that basic operation of PCS being carried out, harmonics were restrained, and power quality had improved.     

Effect of Load Models on AC/DC System Stability and Modulation Control Design

This paper investigates important aspects related to the effect of load models on the modulation control design and stability of a modulated ac/dc system. Static load is modeled as a nonlinear function of load bus voltage and dynamic load is modeled by an equivalent induction motor. DC power and reactive power modulations are considered for the modulation controllers. A method for eigenvalue sensitivity calculation is developed to predict the effect of load characteristics on system stability. Eigenvalue sensitivity and simulation results show that static and dynamic load characteristics may have a considerable effect on the system stability. Figure 1 shows an ac/dc power system model used for studying the effect of nonlinear load on system stability. Reactive power modulation gain is obtained via optimal control theory. Figure 2 shows speed response of synchronous generator for a 5% change in reference current (Iref) of the rectifier terminal. Reactive power modulation by static var compensator improves system stability with constant impedance load model. However, reactive power modulation makes the system unstable when the modulation gain is based on constant impedance load model and the actual load is represented by induction motor. Important conclusions resulting from the computations and simulations performed for an integrated ac/dc system are listed below. 1. The dynamic behavior of induction motor load has a significant effect on the system stability. Induction motor in most cases reduces the overall system damping.     

Advanced Reactive Power Control at Individual Residences to Smooth Energy Loss Fluctuation for a Clustered Grid-Interconnected PV System

Reactive power control can control voltage within the proper range from the power network side or from the distribution generation （PV （photovoltaic）） side. Reactive power control from the power network side is simpler because little controlled object apparatus, such as STATCOM, is required. However, it is difficult to optimize the individual voltages of residential consumers because few data have been obtained by the power network side as compared with the power generation side. Energy loss at each residence with PV is different due to the difference in the grid-interconnection condition, such as distribution line impedance when the same operating voltage is set at all residences. Therefore, in this paper, the authors propose an advanced reactive power control method for residential PV systems in order to optimally control the voltage at individual residences so as to minimize energy loss fluctuation. The effectiveness of the proposed reactive power control is demonstrated by numerical simulation.     

Nonlinear Control Model of Synchronous Motor with Excitation and Damper Windings

In this paper, a new control method for synchronous motor with excitation and damper windings is presented. It is based on one type of nonlinear control; feedback linearization control. To make a realization in the sense of electric drive, symmetricM space vector PWM （pulse width modulation） is applied. Estimation of damper winding currents via Lyapunov function for the whole estimated system is done. The aim of control is to make tracking system for rotor speed and square of stator flux. Simulation of motor starting to predefined operating points is done, and also maintaining these points during step change of load torque is obtained. Simulations give good results.     

Apparatus for supplying an isolated DC load from a variable-speedself-excited induction generator

This paper describes the design and laboratory testing of novel generation apparatus for supplying an isolated DC load from a self-excited induction generator operable at variable speed. The variable-speed generating apparatus consists of a self-excited induction machine, a controlled Graetz bridge rectifier, a voltage-boost power converter, and a control system. The induction generator supplies the rectifier. The voltage-boost power converter interfaces the variable output voltage of the rectifier to the fixed DC voltage required for the load. The rectifier is operated at levels of average DC current and voltage which control machine voltage to the rated AC voltage and which also draw the necessary power to supply the DC load. Performance is enhanced with respect to earlier apparatus in that both the DC voltage supplied to the load and the AC voltage on the machine are simultaneously controlled to fixed reference levels over broad operating ranges of load and speed     

Neural network controller for a permanent magnet generator applied in a wind energy conversion system

In this paper a neural network controller for achieving maximum power tracking as well as output voltage regulation, for a wind energy conversion system (WECS) employing a permanent magnet synchronous generator, is proposed. The permanent magnet generator (PMG) supplies a DC load via a bridge rectifier and two buck–boost converters. Adjusting the switching frequency of the first buck–boost converter achieves maximum power tracking. Adjusting the switching frequency of the second buck–boost converter allows output voltage regulation. The on-times of the switching devices of the two converters are supplied by the developed neural network (NN). The effect of sudden changes in wind speed, and/or in reference voltage on the performance of the NN controller are explored. Simulation results showed the possibility of achieving maximum power tracking and output voltage regulation simultaneously with the developed NN controller. The results proved also the fast response and robustness of the proposed control system.     

虚拟同步发电机技术控制的MMC型固态变压器

针对在大容量直流负荷和高渗透率分布式电源接入固态变压器低压侧时,高压并网接口易呈惯量低、阻尼特性差的问题,提出一种虚拟同步发电机技术控制的模块化多电平换流器（MMC）型固态变压器。首先,分析虚拟同步发电机原理并推导MMC与虚拟同步发电机的等效数学模型,并将虚拟同步发电机技术融入到输入级的控制中,使并网接口的惯性与阻尼增强,在输出端功率变化时对上级电网呈现出友好的柔性缓冲能力。其次,为提升MMC型固态变压器对上级电网的频率支撑能力,在低压直流环节配置储能装置,通过改变充放电功率主动响应一次调频。然后,通过输入级的无功控制环节,验证其具备一定的调压能力。最后建立仿真模型验证了所提控制策略的有效性与可行性。     

Maximum power point tracker of wind energy conversion system

In this paper, a simple control strategy for an optimal extraction of output power from grid connected variable speed wind energy conversion system (WECS) is presented. The system consists of a variable speed wind turbine coupled to a permanent magnet synchronous generator (PMSG) through a gear box, a diode bridge rectifier, a dc-to-dc boost converter and a current controlled voltage source inverter. The maximum power point tracker (MPPT) extracts maximum power from the wind turbine from cut-in to rated wind velocity by sensing only dc link power. The MPPT step and search algorithm in addition to the DC–DC and DC–AC converters PWM controllers are simulated using MATLAB-SIMULINK software. The obtained simulation results show that the objectives of extracting maximum power from the wind and delivering it correctly to the grid are reached.     

Frequency support capability of variable speed wind turbine based on electromagnetic coupler

In the variable speed wind turbine based on electromagnetic coupler (WT-EMC), a synchronous generator is directly coupled with grid. So like conventional power plants WT-EMC is able to support grid frequency inherently. But due to the reduced inertia of synchronous generator, its frequency support capability has to be enhanced. In this paper, the frequency support capability of WT-EMC is studied at three typical wind conditions and with two control strategies—droop control and inertial control to enhance its frequency support capability. The synchronous generator speed, more stable than the grid frequency which is the input signal for Type 3 and Type 4 wind turbine frequency support controller, is used for the calculation of WT-EMC supplementary torque command. The integrated simulation environment based on the aeroelastic code HAWC2 and software Matlab/Simulink is used to build a 2 MW WT-EMC model and study the frequency support capability of a wind farm consisting of WT-EMC.     

Design and Implementation of High Power Factor LED Driver with Hot Swap,Smart Output Voltage Regulation and Dimming Control

In this paper, a high power factor LED driver with hot swap, smart output voltage regulation and dimming control is proposed. The dimming control is used to change LED brightness. During converter is working, the hot swap function supply users to remove and insert LED module. The smart output voltage can regulate quickly and rightly output voltage in different number of LED series connection. The system consists two stages, one is 50 W flyback converter which is used as power factor corrector, it is input source is 110-220 V, PF （power factor） is about 0,994. The other is Boost DC/DC converter, it can offer 35-60 V of output voltage. Finally, a prototype has been built and tested. The simulation and experimental results are shown to verify the feasibility of the proposed method.     

Permanent-magnet machines

This paper explores the use of an interior permanent-magnet synchronous machine (IPM) as a source of controlled DC power. A three-phase diode rectifier converts the generated AC power into DC, which is further processed by a buck or boost DC-DC converter with a pulse-width modulation voltage controller for load voltage and output power regulation. The modeling and analysis of the generator system set forth are confirmed to accurately predict the generator characteristics by experimental results derived from a 2 hp interior permanent-magnet generator controlled separately by a buck and a boost DC-DC converter     

A Real-Time Power Controller for Grid-Connected Inverters in LV Smart Microgrids

This paper presents a real-time power flow controller for VSIs （voltage source inverters） interfaced to low voltage microgrids. The proposed controller is modular, flexible, intelligent, inexpensive, portable, adaptive and designed to positively contribute in low voltage microgrids in which the lines R/X ratio is greater than the transmission lines. Therefore, the proposed control strategy is developed for operation in distribution lines. The controller strategy is different from the conventional grid-connected inverters which are designed based on transmission line characteristics. This controller, using a Texas Instrument general purpose DSP （digital signal processor）, is programmed and tuned using MATLAB/SIMULINK in order to enhance self-healing, reliability and stability of the grid. This general purpose controller makes proper decisions using its local measurements as the primary source of data. The controller has the capability of communicating with the adjacent controllers and sharing the information if/when needed. The power flow output of the inverter is tested for both islanded and grid-connected modes of operation. The inverter positively contributes to active and reactive power supply while operating in grid-connected mode. The proposed control method has been implemented on a Texas Instrument DSC （digital signal controller） chip and tested on a hardware test bench at the Alternative Energy Laboratory at WVU1T （West Virginia University Institute of Technology）. The system＇s experimental results veri~ the validity and efficiency of the proposed controller.     

A robust direct current control of DFIG wind turbine with low current THD based predictive approach

This paper presents a simple and robust direct current control based predictive approach for rotor side converter (RSC) of the doubly fed induction generator (DFIG), which operates at a constant switching frequency and has a fast dynamic response. First, sector of required rotor voltage vector is predicted in this strategy, and according to this predicted sector, two active vectors and two zero vectors are elected in each switching period. Derivatives of rotor current in the synchronous frame are determined for each predicted voltage vector in every period. These derivatives are used to compute the duration of the vectors in such a way that the current error at the end of the switching period gets minimized. The accuracy of the proposed control strategy under variation of rotor speed is evaluated in Matlab/Simulink environment for a 2 MW DFIG. Moreover, the impact of parameter variations on the system is examined for this suggested technique. Furthermore, the dynamic response and stator current total harmonic distortion (THD) of proposed strategy is compared with traditional vector control (VC), direct power control (DPC) and predictive direct power control (PDPC) methods. Finally, the performance of the proposed method is evaluated under disturbance voltage. The results demonstrate that suggested control technique has the lowest stator current THD and operates perfectly near the synchronous speed and under grid voltage dip. Copyright © 2015 John Wiley & Sons, Ltd.