Multivariable control strategy for variable speed, variable pitch wind turbines

Reliable and powerful control strategies are needed for wind energy conversion systems to achieve maximum performance. A new control strategy for a variable speed, variable pitch wind turbine is proposed in this paper for the above-rated power operating condition. This multivariable control strategy is realized by combining a nonlinear dynamic state feedback torque control strategy with a linear control strategy for blade pitch angle. A comparison with existing strategies, PID and LQG controllers, is performed. The proposed approach results in better power regulation. The new control strategy has been validated using an aeroelastic wind turbine simulator developed by NREL for a high turbulence wind condition.     

闭环与开环方式相结合的柴油机正时优化控制

本文研究用电子控制系统对柴油机气门及供油正时进行以有效油耗率为目标函数的优化控制.为提高系统适应能力和响应速度,文中提出控制气门及供油正时的新往来帐策略,介绍在2135柴油机上的实验研究结果,还介绍作者研制的可调正时液压气门机构,该机构具有结构简单和便于采用电子控制的特点.     

基于5MW风机模型的变初值模糊PI变桨控制技术研究

针对传统PID变桨控制器参数自调整性能较差,适应性不强的问题,文章提出了风电机组变初值模糊PI变桨控制算法。通过模糊控制算法实现了PI参数的自动调节,根据风速大小设计了合理的变初值调整算法,实现了模糊控制器初值的在线调节。基于FAST风机软件中5 MW陆上风电机组非线性模型,分析了风电机组在额定风速以上运行时变桨系统的动态特性,从算法结构出发,设计了合适的模糊规则和量化、比例因子以及变初值调整算法,在Matlab/Simulink中搭建了变初值模糊PI变桨控制策略。通过仿真验证了控制策略在抑制转速波动和风机叶片、塔基受力力矩波动方面具有较好的效果。     

An adaptive sliding mode observer based near-optimal OER tracking control approach for PEMFC under dynamic operation condition

Tracking control of oxygen excess ratio (OER) is crucial for dynamic performance and operating efficiency of the proton exchange membrane fuel cell (PEMFC). OER tracking errors and overshoots under dynamic load limit the PEMFC output power performance, and also could lead oxygen starvation which seriously affect the life of PEMFC. To solve this problem, an adaptive sliding mode observer based near-optimal OER tracking control approach is proposed in this paper. According to real time load demand, a dynamic OER optimization strategy is designed to obtain an optimal OER. A nonlinear system model based near-optimal controller is designed to minimize the OER tracking error under variable operation condition of PEMFC. An adaptive sliding mode observer is utilized to estimate the uncertain parameters of the PEMFC air supply system and update parameters in near-optimal controller. The proposed control approach is implemented in OER tracking experiments based on air supply system of a 5 kW PEMFC test platform. The experiment results are analyzed and demonstrate the efficacy of the proposed control approach under load changes, external disturbances and parameter uncertainties of PEFMC system.     

Dynamical variable structure controller for power regulation of wind energy conversion systems

The paper addresses the problem of output power regulation of fixed-pitch variable-speed wind energy conversion systems. Operation is constrained by practical reasons to the low-speed side of the turbine power-speed curve. Unfortunately, this region is characterized by a nonminimum phase dynamics which is an obstacle to perform the regulation task. A dynamical variable structure controller is developed that accomplishes the control objective despite this limitation. The proposed control strategy presents attractive features such as robustness to parametric uncertainties of the turbine and generator as well as to electric grid disturbances.     

Filtered Smith predictor with feedback linearization and constraints handling applied to a solar collector field

Feedback linearization (FL) has recently been used to control the temperature in a solar field using the water flow rate as the manipulated variable. Nevertheless, the system shows undesirable control signal oscillation caused by a delay uncertainty. In this paper, the dynamics resulting from applying the FL transformation to the nonlinear process model is approximated by a first-order model plus dead-time, and a filtered Smith predictor (FSP) is proposed as the control strategy. This controller deals with dead-time errors but also includes control signal saturation caused by flow rate constraints. Simulations demonstrate the robustness of the FSP structure in comparison to a simple PID and a Smith predictor (SP) approach when a faster closed-loop is required in a system with delay uncertainties. Real experimental results included show the improved behavior of the proposed control scheme.     

Simulation of grid connection and maximum power point tracking control of brushless doubly-fed generator in wind power system

In this paper, based on the analysis of the mathematical model in a common synchronous reference frame of the brushless doubly-fed generator (BDFG), the grid connection strategy and maximum energy extraction control were both analyzed. Besides, the transient simulation of no-load model and generation model of the BDFG have been developed on the MATLAB/Simulink platform. The test results during cutting-in grid confirmed the good dynamic performance of grid synchronization and effective power control approach for the BDFG-based variable speed wind turbines.     

电厂负荷调度的智能决策方法

等微增法和动态规划法是目前常用的电厂负荷优化调度方法,文中对这两种方法进行了分析比较,指出了这两种方法在实际负荷调度过程中的缺点。在此基础上,提出了基于减小电厂发电成本并融合实际负荷调度经验的电厂负荷智能决策算法,并针对南通天生港发电有限公司的4台125MW机组,研制了基于负荷智能决策算法的优化负荷调度系统。     

Gain scheduling control of variable speed WTG under widely varying turbulence loading

Probabilistic paradigms for wind turbine controller design have been gaining attention. Motivation derives from the need to replace outdated empirical-based designs with more physically relevant models. This paper proposes an adaptive controller in the form of a linear quadratic Gaussian (LQG) for control of a stall-regulated, variable speed wind turbine generator (WTG). In the control scheme, the strategy is twofold: maximization of energy captured from the wind and minimization of the damage caused by mechanical fatigue due to variation of torque peaks generated by wind gusts. Estimated aerodynamic torque and rotational speed are used to determine the most favorable control strategy to stabilize the plant at all operating points (OPs). The performance of the proposed controller is compared with the classical proportional-integral-derivative (PID) controller. The LQG is seen to be significantly more efficient especially in the alleviation of high aerodynamic torque variations and hence mechanical stresses on the plant drive train. Simulation results validate the effectiveness of the proposed method.     

Direct Instantaneous Torque Control in Direct Drive Permanent Magnet Synchronous Motors—a New Approach

In this paper, a novel direct instantaneous torque control scheme for a direct drive (DD) permanent magnet synchronous motor (PMSM) is presented. A hybrid control structure combining the internal model principle and the variable structure control (VSC) approach is proposed. First, a variable structure torque controller is adopted to regulate the torque angle increment according to the torque feedback error. Second, the appropriate control voltage vector is determined using the reference stator flux vector and the estimated dynamic back electromotive force (EMF) vector, as an internal model, in a deadbeat control manner. Subsequently, better disturbance rejection can be obtained with the proposed cascaded control structure. To robustly obtain the instantaneous torque and flux information, a robust adaptive motor model is proposed. The Lyapunov stability theory is used to analyze the stability of the augmented robust adaptive motor model and to give a guideline for tuning model parameters. Experimental results are presented to demonstrate the validity and effectiveness of the proposed instantaneous torque control scheme.     

Varying load distribution impacts on the operation of a hydrogen generator plant

This study advances several methods to evaluate the operation of a hydrogen generator plant. The model developed helps customize plants that contain multiple generators of varying powers using a decision module, which determines the most efficient plant load distribution. Evaluation indices to assess individual devices within the plant are proposed and system flexibility maximizes the amount of renewable energy stored. Three case studies examined the variable load distribution of an electrolysis system connected to a 40 MW wind farm for energy storage purposes and incorporated a “night-valley” operational strategy. These methods facilitate the selection of the proper plant configuration and provide estimates for individual device effectiveness within the system.     

Variable speed DFIG wind energy system for power generation and harmonic current mitigation

This paper presents a novel approach for simultaneous power generation and harmonic current mitigation using variable speed WECS with DFIG. A new control strategy is proposed to upgrade the DFIG control to achieve simultaneously a green active and reactive power source with active filtering capability. To ensure high filtering performance, we studied an improved harmonic isolator in the time-domain, based on a new high selectivity filter developed in our laboratory. We examined two solutions for harmonic current mitigation: first, by compensating the whole harmonic component of the grid currents or second, by selective isolation of the predominant harmonic currents to ensure active filtering of the 5th and 7th harmonics. Simulation results for a 3 MW WECS with DFIG confirm the effectiveness and the performance of the two proposed approaches.     

Modeling and control of photovoltaic energy conversion connected to the grid

This paper presents modeling and control of a photovoltaic generator (PVG) connected to the grid. The parameters of the PVG have been identified in previous work (series and parallel resistance, reverse saturation current and thermal voltage) using Newton-Raphston and the gradient algorithm. The electrical energy from a PVG is transferred to the grid via two static converters (DC/DC and DC/AC). The objective of the proposed control strategy is to maximize energy captured from the PVG. The adapted control law for extracting maximum power from the PVG is based on the incremental conductance algorithm. The developed algorithm has the capability of searching the maximum photovoltaic power under variable irradiation and temperature. To control the DC/AC inverter, an intelligent system based on two structures is constructed: a current source control structure and a voltage source control structure. The system has been validated by numerical simulation using data obtained from the PVG installed in the laboratory research (INSAT, Tunisia).     

极端风况下双转子风力机降载复合控制策略

为降低双转子风力机在极端风况下的大波动载荷,基于双转子风力机气动与控制仿真系统,提出了基于独立变桨自抗扰控制器和偏航模糊控制器的降载复合控制策略,并分析了正常风况和极端风况下该策略的控制效果。结果表明：与传统PID独立变桨控制相比,在极端运行阵风和极端湍流模型下,独立变桨自抗扰控制方法使叶根挥舞弯矩标准差减小18%以上;与传统恒速偏航控制相比,在极端风向变化下,偏航模糊控制方法使偏航轴承滚动力矩标准差减小约27%。降载复合控制策略有效降低了极端风况下双转子风力机的大载荷,抑制了功率波动。     

基于神经元PID的风力发电机组独立变桨控制

针对传统统一变桨距控制策略存在的不足,基于风力机空气动力学原理,提出了基于神经元PID的独立变桨距控制策略,将测量的桨叶根部My方向载荷通过神经元PID控制算出d、q轴的桨距角,经反Park变换得到3个桨叶的附加桨距角,将其与统一变桨距角相加作为独立桨距角的设定值。并借助Fast软件平台以2MW变速变桨风力发电机组为例,仿真比较了独立变桨距控制策略与统一变桨距控制策略。结果表明,独立变桨距控制策略能有效保证在额定转速下机组输出功率稳定,且能有效降低风力发电机组各零部件的疲劳载荷。     

An Approach to Fault-Tolerant Three-Phase Matrix Converter Drives

Despite numerous research efforts in matrix converter-based drives, a study of fault-tolerant topology and control strategy for a matrix converter drive has not been presented in the literature. This paper proposes a matrix converter structure and a modulation technique for the remedial operation in case of opened switch faults and single-phase open circuits. The fault compensation is achieved by reconfiguring the matrix converter topology with the help of a connecting device. Based on the redefined converter structure, a fault-tolerant modulation algorithm is developed to reshape output currents of two unfaulty phases for obtaining continuous operation. The proposed method allows improved system reliability and fault-tolerant capability with no backup leg and no parallel redundancy. Simulation and experimental results are shown to demonstrate the feasibility of the proposed fault-tolerant approach to the matrix converter drives.     

Study of nonlinear control schemes for an automotive traction PEM fuel cell system

To be practical in automotive traction applications, fuel cell systems must provide power output levels of performance that rival that of typical internal combustion engines. In so doing, transient behavior is one of the keys for success of fuel cell systems in vehicles. The focus of this paper is on the air/fuel supply subsystem in tracking an optimum variable pressurization and air flow for maximum system efficiency during load transients. The control-oriented model developed for this study considers electrochemistry, thermodynamics, and fluid flow principles for a 13-state, nonlinear model of a pressurized fuel cell system. For control purposes, a model reduction is performed, and several multi-variable control designs are examined. The first technique uses an observer-based linear optimum control which combines a feed-forward approach based on the steady-state plant inverse response, coupled to a multi-variable LQR feedback control. An extension of that approach, for control in the full nonlinear range of operation, leads to the second technique, nonlinear gain-scheduled control. Some enhancements were applied to overcome the fast variations in the scheduling variable. Finally, a rule-based, output feedback control, implemented with fuzzy logic, is coupled with a nonlinear feed-forward approach, and is examined under the same conditions applied to the first two techniques. The control designs developed are compared in simulation studies to investigate robustness to disturbance, time delay, and actuator limitations.     

变速变桨风力发电机组的优化控制

提出了大型变速变桨风力发电机组在不同控制阶段的优化控制策略。在低风速时,采用自适应转矩控制方式,实现机组的变速运行,追踪最佳风能利用系数。在额定风速以上时,为了解决传统桨距控制方式系统超调量大的问题,提出了一种新型气动转矩观测器,并将气动转矩与发电机转矩偏差输入控制器。通过Bladed外部控制器模块编程并进行仿真,结果表明,所提出的控制策略能够更好地追踪最大功率点,并改善桨距控制效果,稳定功率输出。     

An integrated “Reservoir-Plant” strategy for a sustainable and efficient use of geothermal resources

A multidisciplinary approach for the design of geothermal power plants for water dominant resources is here proposed. The importance of a strategic approach is underlined, considering all the connections between the analysis of the geothermal potential of the reservoir (geophysical exploration and geochemical analysis) with the design of the plant based on thermodynamic and energy considerations, mainly regarding ORC (Organic Rankine Cycles) power plants.This multidisciplinary approach is fundamental for the objective of a sustainable exploitation of medium to low enthalpy sources. The aim of this study is to propose the optimization and management of the global system “reservoir-power plant” as the task of geothermal projects.This approach can be pursued only in a multidisciplinary perspective in which both Engineering and Geological aspects are involved. Numerical simulation appears to be an essential interacting step. After analyzing the problems caused by an incorrect characterization of geothermal source, reinjection temperature and strategy, a method for the numerical simulation of geothermal reservoirs long-term behavior/capacity is discussed. This could be the key instrument to synthesize the strategy inputs. A numerical modeling is performed, using as reference data the history matching of a well known and completely analyzed geothermal field.     

An improved thermal control of open cathode proton exchange membrane fuel cell

Proton exchange membrane fuel cell is a well-known technology that has shown high efficiency and performance as a power system compared to conventional sources such as internal combustion engines. Especially, open cathode proton exchange membrane is growing more popular thanks to its simple structure, low cost and low parasitic losses. However, the open cathode fuel cell performance is highly related to the operating temperature variation and the airflow rate which is adjusted through the fan voltage. In this regard, the present study investigates the thermal management of an open cathode proton exchange membrane fuel cell. The objectives are the stack performance improvement and the stack degradation prevention. Indeed, a safety and optimal operating zone governed by the load current, the stack temperature and the air stoichiometry, is designed. This optimal operating zone is defined based on the system thermal balance and the operating constraints. Hence, the proposed control strategy deals concurrently with the stack temperature regulation and the air stoichiometry adjustment to guarantee the goals achievement. The performance of the proposed control strategy is verified through experimental studies with different operating conditions and results prove its efficiency. To properly design an appropriate control strategy, a multiphysic fuel cell model is developed based on acausal approach by mean of Matlab/Simscape and experimentally validated.