电网电压不平衡下基于PMSG的风力发电机组功率限流控制

ABSTRACT —— Unbalanced grid voltage sags are the severe challenge for wind power generation system which connected to the grid successfully. The dc bus voltage and output power will fluctuate under unbalanced grid voltage. Moreover, the voltage sags will lead to the increase of peak current, which will bring potential safety hazards to the operation of wind power system. This paper proposes a simple current limiting control scheme without auxiliary equipment, which based on the detailed analysis of the excessive peak current. In this scheme, the machine side converter (MSC) controller adjusts the electromagnetic power according to the power transmitted to the grid by the grid side converter (GSC). Meanwhile, it converts the unbalanced power on the dc-link into the rotor kinetic energy, avoiding the dc-link overvoltage. The GSC controller can not only ensure that the three-phase inverter currents are in the maximum safe range that the converters can bear, but also provide reactive power support for the grid. Furthermore, the fluctuations on dc bus voltage and output power can be eliminated effectively by using the GSC controller. The feasibility of the proposed scheme and the superiority over the traditional control schemes have been verified by simulations under different types of unbalanced voltage.

大规模并网风电对电力系统的影响

Abstract —— The randomness and fluctuation of wind results in wind power generation with strong uncertainty. To ensure the power system operate safely and reliably, research on the impact of grid connected wind power on power system is necessary. From the perspective of system relay protection, system peaking, transmission capacity planning and reliability planning, this paper introduces the impact of centralized wind power integration on power system. 可用作毕设参考文献。

配电网无功补偿技术研究

Abstract —— The researches of reactive power compensation in distribution network mainly consist of two aspects: the research of reactive power compensation optimization theory and the research of reactive power compensation device. According to certain configuration principle and optimization principle, the mode and capacity of reactive power compensation can be optimized, which can effectively reduce the system loss and improve the power quality of distribution network. At present, reactive power compensation devices include shunt capacitor, static var compensator and static synchronous compensator (D-STATCOM). We could choose the appropriate reactive power compensation device to compensate the distribution network in the view of practice and economy. This article would introduce some aspects of reactive power compensation breifly, including several studies on compensation mode selection and capacity determination. In addition, we would also introduce the working principle and the reactive current detection technology of D-STATCOM which is the most advanced reactive power compensation device.

双馈异步发电机变速风力发电机组闪变研究

Abstract —— Grid connected wind turbines may produce flicker during continuous operation. This paper presents a simulation model of a MW-level variable speed wind turbine with a doubly fed induction generator developed in the simulation tool of PSCAD/EMTDC. Flicker emission of variable speed wind turbines with doubly fed induction generators is investigated during continuous operation, and the dependence of flicker emission on mean wind speed, wind turbulence intensity, short circuit capacity of grid and grid impedance angle are analyzed. A comparison is done with the fixed speed wind turbine, which leads to a conclusion that the factors mentioned above have different influences on flicker emission compared with that in the case of the fixed speed wind turbine. Flicker mitigation is realized by output reactive power control of the variable speed wind turbine with doubly fed induction generator. Simulation results show the wind turbine output reactive power control provides an effective means for flicker mitigation regardless of mean wind speed, turbulence intensity and short circuit capacity ratio.

带电压谐波补偿的双馈发电机转子电流控制器

Abstract —— The doubly fed induction generator is particularly appropriate to be used in wind power generation systems. However, in weak grids its stator connection to unbalanced or distorted voltages imposes low frequency and high amplitude rotor current harmonics. Also, the grid side converter must deal with the same voltage conditions. The paper addresses the first issue presenting a voltage harmonics controller in the dq reference frame to be included in the high dynamics rotor current controller. Simulation and experimental results demonstrate the performance of the proposed controller imposing a sinusoidal input current.

采用STATCOM的配电连接风电场闪变抑制

Abstract —— Renewable Energy is emerging as major Source of power throughout the world. Wind Energy is one of the most popular sources of renewable energy. Distribution-connected wind turbine is accompanied with various power quality issues. Flicker is one of the power quality issues in a distributionconnected wind turbine imposing technical limitations on amount of wind power to be integrated at particular point of common coupling (PCC). This paper details the flicker problems ncountered upon the connection of wind power to distribution networks and its effects on the network characteristics commensurate with the flicker severity. It describes the mitigation of flicker in a distribution connected wind-farm with the STATCOM.

风电并网变流器谐波抑制机理分析及控制策略研究

Abstract —— In order to improve adaptability for wind power gridconnected converter under non-ideal grid conditions and reduce the harmonic influence, harmonic suppression mechanism for grid-connected converter is depth analyzed and harmonic suppression method and theory is derived. Be limited by complexity of the control system, compound control strategy composed by repetitive controller paralleled with PI controller is proposed for grid-connected converters control in this paper. System stability is analyzed, Geometric representation for repetitive controller stability is shown in figure and Control system difference equation is deduced. Using the proposed control strategy, no difference tracking current control is achieved in the fundamental positive sequence reference frame. The gird current harmonic can be effectively reduced and the converter grid adaptability is improved. The simulation and experimental results verified the effectiveness of the proposed control strategy.

一种新型的风电双馈发电机并网控制方案

Abstract ——This article deals with a phase-locked loop (PLL)- based novel control for wind turbine driven doubly fed induction generator interfaced to utility grid with a battery energy storage (BES) connected at the dc link. The control of grid-side converter (GSC) is modified to export/import constant power to/from the grid. The state of charge of BES helps in deciding the reference export power to the grid apart from the manual selection using averaged wind power in a particular period of time. An off maximum power point tracking logic is incorporated in the rotor-side converter (RSC) control to operate the BES within its constraints and, moreover, to feed constant power to the grid. In addition, the energy management scheme of the system is presented in the form of flowchart for both exporting and importing power to/from the grid. The RSC and GSC have taken care of unity power factor operation at stator terminals and to mitigate harmonics and grid currents balancing, respectively. The system performance is found robust as the PLL response is not affected even under grid voltages with dc offset. The system is modeled and simulations are carried out in MATLAB using SimPowerSystems tool box. Moreover, the control scheme performance is compared with conventional control algorithms both in terms of PLL and converter controls. To validate the effectiveness of the control scheme, a prototype of the system is developed. Test results demonstrate the satisfactory performance of the system under various operating conditions.

电网电压畸变条件下双馈发电机的动态建模与改进控制

Abstract —— This paper presents a mathematical model of a doubly fed induction generator (DFIG) in the positive synchronous reference frame under distorted grid voltage conditions. The oscillations of the DFIG’s electromagnetic torque and the instantaneous stator active and reactive powers are fully described when the grid voltage is harmonically distorted. Four alternative control targets are proposed to improve the system responses during grid harmonic distortions. A new rotor current control scheme implemented in the positive synchronous reference frame is developed. The control scheme consists of a proportional–integral (PI) regulator and a harmonic resonant (R) compensator tuned at six times the grid frequency. Consequently, the fundamental and the fifth- and seventh-order components of rotor currents are directly regulated by the PI–R controller without sequential-component decompositions. The feasibility of the proposed control strategy is validated by simulation studies on a 2.0-MW wind-turbine-driven DFIG system. Compared with the conventional vector control scheme based on standard PI current controllers, the proposed control scheme leads to significant elimination of either DFIG power or torque oscillations under distorted grid voltage conditions.

一种双馈风力发电机软并网同步控制技术

Abstract —— Due to network events and power system emergencies, doubly-fed induction generator (DFIG) based wind turbines can suffer from low voltage ride through which may result to the disconnection of the DFIG. Before connecting to the electricity grid again, DFIG has to be synchronized to minimize the transient effects and ensure smooth connection to the power grid. In this paper, a direct voltage control based synchronization technique is proposed for DFIG based wind turbines. Additional control features are added to original direct voltage control method for implementation of the proposed synchronization strategy. A grid connection logic is designed and presented for soft connection of DFIG to the grid. The proposed technique is implemented in a DFIG based wind turbine model and tested through simulations with various practical scenarios. Voltage transients, frequency analysis, voltage phase and system stability are analyzed in details and simulation results presented. From the results, it can be revealed that the proposed synchronization technique functions effectively and efficiently. It is also shown that by using the proposed technique, the process of synchronization and grid connection do not introduce any changes into the system, which may cause protection devices to trip or mal-operation.