发电机典型调速器模型结构和一次调频特性比较

在电力系统频率特性仿真研究中,水、火常规发电机采用何种类型的调速器模型是影响仿真结果的重要因素。为此,比较了工程实际中广泛采用的传统推荐模型和现代数字电气液压式调速模型(DEH)的结构差异;并以送端电网与主网解列后频率升高的场景为例,比较了两类典型调速器模型一次调频的效果。结果表明,DEH模型因增加了PID控制、电功率反馈、多种限幅环节等的模拟,较传统推荐模型更为细致和全面;在较大幅度功率过剩条件下,水电与火电DEH模型限幅环节均导致其一次调频效果较传统推荐模型要弱,对应到实际电网中,在DEH类型调速器投入比例较高时,若大量使用传统推荐模型会产生偏乐观的结果。     

汽轮机及调速器对共振型低频振荡的影响及改进措施

汽轮机调速器采用转速和功率作为控制信号,在调速器的控制下汽轮机输出功率会引入附加机械同步转矩和阻尼转矩,进而影响共振型低频振荡。分析了共振幅值与机械同步转矩系数Km、阻尼转矩系数Dm的关系,基于汽轮机及调速器的数学模型采用复转矩系数法推导了Km和Dm的表达式,并分析了汽轮机及调速器相频特性和转矩系数之间的关系。在此基础上提出了一种改进措施,通过在控制环路中加入超前滞后环节,使汽轮机在共振频率处输出的机械同步转矩和阻尼转矩为正值,从而有利于消除汽轮机及调速器对共振振荡的不利影响。在Matlab/Simulink中搭建典型单机无穷大系统进行仿真,仿真结果验证了理论分析的正确性和改进措施的有效性。     

Multimachine System Transient Stability Improvement using Transient Power System Stabilizers (TPSS)

Power system stabilizers (PSS) have been designed and installed [1,2] to improve the dynamic (smnall signal) response of multimachine systems. This paper presents the theory and test results for improving the transient (large disturbance) behaviour of a multimachine system by supplementing the conventional PSS with a transient power system stabilizer (TPSS). Each generator unit is fitted with a TPSS which, after computation, injects supplementary control signals into both the automatic voltage regulator (AVR) and speed governor control loops.     

Tuning method for governor control parameters of hydropower generator in isolated grid considering primary frequency performance and small-signal stability

This paper presents a method of tuning governor control parameters of an isolated hydropower generator considering the primary frequency performance and small-signal stability. First, generators that can be operated in isolated state are identified. Second, different schemes are proposed for generator mode switching from on-grid to off-grid state through comparison and mechanism analysis. Third, the time domain model and frequency domain model of the isolated generator governor are constructed to respectively estimate the primary frequency performance and small signal stability. Parameter sets that satisfy the primary frequency performance and small signal stability are acquired as optimal values of governor control parameters. Finally, the measurement-based parameters of the governor are identified and validated using simulations to demonstrate the feasibility and effectiveness of the method.     

Co-Ordinated Governor/Exciter Stabilizer Design in Multi-Machine Power Systems

This paper describes the application of multi-variable control design methods to the problem of designing co-ordinated stabilizers in a multi-machine environment. Linear state space methods are used to design co-ordinating stabilizing inputs for the exciter and governor loops, based on a number of local outputs. The dynamics of the multi-machine power system are taken into account by determining a dynamic equivalent model of the power system as seen from the transformer bus of the design generator. This is accomplished using identification techniques as described in a previous paper[2]. The generator equations are linearized and combined with this dynamic equivalent of the remainder of the power system, resulting in a reduced order representation of the combined system. Linear optimal control methods are then used to determine the co-ordinated controller. The effects of nonlinearities are taken into account by experimenting with different cost function weightings. The method is demonstrated by applying it to a generating station in an example 63 bus power system with a total of 59 generators represented.     

Design of an optimal robust governor for hydraulic turbinegenerating units

Design and analysis of a hydraulic turbine generator governor using optimal robust control methodology are presented. The approach is unique in the sense that the nonlinear characteristics of the turbine are first modelled as multiplicative uncertainties; and an optimal robust governor is designed by taking into account such uncertainties explicitly. The advantage of this approach is that the designed governor will guarantee the stability and the performance of the speed control loop for the entire turbine operating range. The performance of the new governor is shown to be superior to that of the conventional PID controller during large load disturbances. The resulting governor is only a third order. Hence, it has the same level of complexity as any other electrical-hydraulic governor in use today     

Multiple Input Governor Control for a Diesel Generating Set

The paper presents a multiple-input single-output fuzzy logic governor algorithm that can be used to improve the transient response of a diesel generating set, when supplying an islanded load. The proposed governor uses the traditional speed input in addition to voltage and power factor to modify the fueling requirements during various load disturbances. The use of fuzzy logic control allows the use of proportional–integral–derivative (PID) type structures that can provide variable gain strategies to account for nonlinearities in the system. Fuzzy logic also provides a means of processing other input information by linguistic reasoning and a logical control output to aid the governor action during transient disturbance. The test results were obtained using a 50 kVA naturally aspirated diesel generator testing facility. Both real and reactive load tests were conducted. The complex load test results demonstrate that, by using additional inputs to the governor algorithm, enhanced generator transient speed recovery response can be obtained.      

Improvement of synchronous generator damping throughsuperconducting magnetic energy storage systems

Stabilization of a synchronous generator through control of firing angle of the power converters in superconducting magnetic energy storage (SMES) systems is considered. An optimum strategy of the firing angle control is designed so as to eliminate the transients in minimum time. A nonlinear model of a synchronous generator, its governor and exciter systems, and an SMES system connected to the generator terminal is considered. The optimum firing angle control is derived retaining the nonlinearities of the system dynamics. Digital simulation results indicate that the proposed strategy controls the slowly growing as well as first swing instabilities very effectively     

Automatic generation control for hydro systems

The authors present the decision of an automatic generation control (AGC) system implemented with digital computers that periodically sample tie-line real power flows, line frequency, and generator power outputs. These analog signals are measured at 2-5 intervals and combined with desired interchange to obtain the area control error (ACE). The ACE digital quantity is allocated to regulating hydro turbines and transmitted via telemetry to the remote terminal units (RTU). The RTUs convert the raise/lower megawatts (MW) into timed relay contact closures to the governor which result in wicket gate open/close movement to change the generator output power. The output power of each generator is monitored by the digital AGC, which closes a feedback loop around the governor-turbine-generator to assure that the desired power level is attained. The feedback loop design, which is essentially a sampled-data control, is described. Additional feedback loops due to the ACE and load regulation are also analyzed. A method for allocating water usage between reservoirs on a generator command-time basis is presented. The theoretical designs are verified by online measurements     

Dynamic characteristics of autonomous wind–diesel systems

In this paper the dynamics of a small autonomous system, comprising a diesel generator and a wind turbine, are investigated. The analysis is performed both in the frequency and time domain, using simplified models of the system components and taking into account the diesel engine speed governor and the wind turbine pitch controller (for pitch regulated machines). The investigation is extended to include different types of wind turbines, equipped with induction or synchronous generator and using pitch or stall regulation, as well as operation of the wind turbine in an autonomous or infinite system. The objective is to determine the main factors affecting the behaviour of the system and to illustrate the effect of the speed governor and pitch controller settings on the expected performance. Particular emphasis is placed on identifying the main modes of the system and determining their dependence on the controllers' parameters. A comparative assessment of the dynamic characteristics of different types of wind turbines is also included and the operation of the wind turbine in a small system and against an infinite bus is addressed and discussed.     

电站柴油机双机并联调速系统的仿真研究

建立了电站柴油机双机并联调速系统的模型 ,对柴油机的调速控制、负荷前馈控制、负荷均衡控制进行了 MATL AB仿真研究。结果表明 :采用负荷前馈控制可明显提高柴油机电子调速器的调速性能 ,引入负荷均衡控制后 ,可以在零稳态调速率条件下实现双机之间的负荷均匀分配     

分数阶PID混合算法的水轮机调速系统优化控制与建模分析

为深入研究水轮机调速系统的非线性动态特征,分析水轮机在负荷波动时调速系统对水轮机转速、出力及输出电压电流波形的控制情况,提出一种采用混合算法(BP-FOA)的分数阶PID(FOPID)双目标函数控制系统;并利用Matlab平台建立了能够反映动态负荷变化及发电机情况的水轮机模型,使其更具实际适应性。仿真及实例分析表明,经混合算法优化后的水轮机调速器在调节性能与鲁棒性上均有一定的提升,同时亦为水轮机动态模型建模提供了借鉴。     

Nonlinear dynamic model of a solar steam generator

A thermal-hydraulic model of a once-through subcritical steam generator has been developed for predicting dynamic characteristics of solar thermal power plants as well as for control system design. The purpose of the model is to evaluate the overall system performance and component interaction with sufficient accuracy for controller design, rather than to describe the microscopic details occurring within the steam generator.The three-section (compressed water, two-phase mixture, and superheated steam) model with time-varying phase boundaries is described by a set of nonlinear differential equations derived from conservation of mass, momentum and energy. Local stability of the model has been examined at different levels of insolation. Transient response of six plant variables due to independent step disturbances in three input variables are presented as typical results.     

Strategies for Operating Wind Power in a Similar Manner of Conventional Power Plant

As installed capacity of wind power retains a significant proportion of generation mix in the electric system, operators have the increasing expectation that wind turbines should function in some ways similar to the conventional plants. In addition to some basic capabilities to regulate reactive power for voltage support, the counterpart in active power control is also the major concern. This paper presents a control strategy to regulate active power for doubly fed induction generator under various operating conditions. Testing results showing the control performance in the simulated conditions validate the feasibility of the operation in power dispatch upon operator's request, and maintain stability under variant wind speed. Additionally, supplemental functions in generation margin assessment, in spinning reserve support, and in governor droop are presented to make the wind farm operation more like a conventional power plant.      

基于状态观测器的调速器液压系统故障诊断

水轮机调速器是水电厂重要控制设备,其工作的稳定性直接关系到水轮发电机组乃至电力系统的安全稳定运行。应用现代故障诊断技术,提出了一种基于状态观测器的故障检测与诊断方法,以实现调速器液压系统的故障检测。通过仿真验证了这种方法依然具有较好的故障检测和诊断能力。     

Single-phase operation of a three-phase induction generator using a novel line current injection method

By using two capacitances and a current injection transformer, a three-phase induction generator can operate with good phase balance and line power factor while delivering power to a single-phase power grid. This paper presents a systematic analysis on this novel induction generator configuration. The solution of the system's inspection equations using the method of symmetrical components enables the steady-state generator performance at any speed to be computed. The conditions for achieving perfect phase balance are deduced from the phasor diagram. It is shown that the capacitances that result in perfect phase balance depend on the generator admittance, power factor angle, as well as the turns-ratio of the current injection transformer. Where possible, the computed results are verified by experiments conducted on a 2-kW induction machine. An experimental investigation on the system waveforms and harmonics is also carried out.     

Turbine generator laboratory model tests to damp torsionaloscillations with supplementary signals

The improvement of generator stability by the use of supplementary signals into the voltage regulator and governor loops using discrete-time linear optimal control theory has been studied with particular emphasis on providing better damping for torsional oscillations. A multi-inertia laboratory model equipped with data acquisition and control computers was constructed to model the shaft dynamics of a 660 MW Drax turbine-generator. It is shown that the shaft torsional phenomena can be adequately simulated on a micro-synchronous-generator at least as far as the dominant shaft torsional modes of vibration are concerned. The practical implementation of multi-mode linear quadratic Gaussian (LQG) controllers has been shown to enhance system stability and provide better damping to the lower frequency torsional modes, which are those most susceptible to excitation     

An adaptive neuro-control system of synchronous generator for powersystem stabilization

This paper proposes a nonlinear adaptive generator control system using neural networks, called an adaptive neuro-control system (ANCS). This system generates supplementary control signals to conventional controllers and works adaptively in response to changes in operating conditions and network configuration. Through digital time simulations for a one-machine infinite bus test power system, the control performance of the ANCS and advanced controllers such as a linear optimal regulator and a self-tuning regulator is evaluated from the viewpoint of stability enhancement. As a result, the proposed ANCS using neural networks with nonlinear characteristics improves system damping more effectively and more adaptively than the other two controllers designed for the linearized model of the power system     

Integrated fuzzy logic generator controller for stabilityenhancement

An integrated fuzzy logic controller is proposed in this paper for the generator excitation and speed governing control. The proposed controller has three control loops: the first one is the voltage control loop which has the function of automatic voltage regulator (AVR), the second one is the damping control loop which has the function of power system stabilizer (PSS), and the last one is the speed governing control loop which has the function of governor (GOV). A simple fuzzy logic control scheme is applied to all these three loops. The control scheme is simple enough so as not to require heavy computation for the controller, therefore, its real time application is feasible. The effectiveness is demonstrated through nonlinear simulations using a one machine infinite bus system. Comparison studies are also performed to show the advantages of the proposed controller with conventional excitation and speed governing control systems     

Transient power characteristic measurement of a proton exchange membrane fuel cell generator

An experimental study on the transient power characteristics of a fuel cell generator has been conducted. The generator is hybridized by a proton exchange membrane (PEM) as the main power source and a lithium-ion battery as the secondary power source. power-conditioning module consisting of a main bidirectional converter and an auxiliary converter has been designed to manage the hybrid power of the generator that copes with fast dynamics of variable loads. Sensors embedded in the generator have measured the electrical properties dynamically. It was found that the present power-conditioning scheme has well controlled the power flow between the fuel cell stack and the battery by regulating the power flow from or to the battery. In addition, the thermal management system using pulse width modulation (PWM) schemes could limit the operation temperature of the fuel cell generator in a designed range. Furthermore, the dynamics of electrical efficiency of the generator are found to be parallel with those of the net system power. Finally, the stability and reliability of the fuel cell generator is proven by the rational dynamic behaviors of thermal and electrical properties for over 30-h demonstration.