Aggregate load-frequency control of a wind-hydro autonomous microgrid

This paper presents an aggregate load-frequency controller for an autonomous microgrid (MG) with wind and hydro renewable energy sources. A micro-hydro power plant with a synchronous generator (SG) and a wind power plant with an induction generator (IG) supply the MG. Both generators directly feed power into the grid without the use of additional power electronics interfaces, thus the solution becoming robust, reliable and cost-effective. An original electronic load controller (ELC) regulates the MG frequency by a centralized load-frequency control method, which is based on a combination of smart load (SL) and battery energy storage system (BESS). SL and BESS provides the active power balance for various events that such systems encounter in real situations, both in cases of energy excess production and energy shortage. Moreover, the proposed ELC includes an ancillary function to compensate the power unbalance produced by the uneven distribution of the single-phase loads on the MG phases, without the use of extra hardware components. A laboratory-scale prototype is used for experimentally assessment of the proposed solutions. The experimental results emphasize the effectiveness of the ELC while also showing its limitations.     

Controller design for an induction generator driven by a variable-speed wind turbine

This paper presents the modeling, controller design and a steady-state analysis algorithm for a wind-driven induction generator system. An output feedback linear quadratic controller is designed for the static synchronous compensator (STATCOM) and the variable blade pitch in a wind energy conversion system (WECS) in order to reach the voltage and mechanical power control under both grid-connection and islanding conditions. A two-reference-frame model is proposed to decouple the STATCOM real and reactive power control loops for the output feedback controller. To ensure zero steady-state voltage errors for the output feedback controller, the integrals of load bus voltage deviation and dc-capacitor voltage deviation are employed as the additional state variables. Pole-placement technique is used to determine a proper weighting matrix for the linear quadratic controller such that satisfactory damping characteristics can be achieved for the closed-loop system. Effects of various system disturbances on the dynamic performance have been simulated, and the results reveal that the proposed controller is effective in regulating the load voltage and stabilizing the generator rotating speed for the WECS either connected with or disconnected from the power grid. In addition, proper steady-state operating points for an isolated induction generator can be determined by the proposed steady-state analysis algorithm. Constant output frequency control using the derived steady-state characteristics of the isolated induction generator is then demonstrated in this paper.     

New architecture and SCADA for stand‐alone hybrid (medium‐sized asynchronous wind turbine + UPS with battery + photovoltaic array) power system without diesel generator

In general, the commercialized medium‐sized asynchronous wind turbines are fully automated facilities designed to operate in parallel connection to the grid; in case of isolated operation, they need to be combined with diesel generator. This paper aims at studying the method of producing electricity of maximal quality with the wind, by constructing a new stand‐alone hybrid (medium‐sized asynchronous wind turbines, UPS with battery, and photovoltaic array) power system without diesel generator. This paper proposes a new architecture of stand‐alone hybrid power system that consists of medium‐sized asynchronous wind turbine, UPS, current limiter (reactor), photovoltaic array, and consumer and dump loads; accordingly, a supervisory control and data acquisition (SCADA) for this system is suggested along with the operation strategies depending on the output power of the UPS and wind turbine, consumer load, and the battery voltage of UPS. The case study was confirmed through the simulation results of the operation of a new stand‐alone hybrid (two 110 kW of asynchronous wind turbines, 250 kVA of UPS with battery, reactor, 36 kW of photovoltaic array, and consumer and dump loads) power system. The results of the simulation showed that the system frequency change of the new stand‐alone hybrid power system was 60 ± 0.5 Hz, and the one of the wind + diesel stand‐alone hybrid system was 60 ± 1 Hz, for the sudden change of consumer load and gust. This new system can be eligible as a standardizing option for the architecture of nondiesel stand‐alone hybrid system and its SCADA system.     

Distributed control system for frequency control in a isolated wind system

High wind penetration wind diesel hybrid systems (WDHS) have three modes of operation: diesel only (DO), wind diesel (WD) and wind only (WO). The control requirements for frequency control in WO mode are analysed and a distributed control system (DCS) is proposed for this frequency control, describing the actuation of its sensor and actuator nodes. A power system for WO mode consisting of a wind turbine generator (WTG), a synchronous machine (SM), the consumer load, a battery based energy storage system (ESS) and a discrete dump load (DL) along with the associated DCS have been simulated. By means of a 400 Hz reference power message that establishes the active power necessary for frequency regulation and a prescribed active power sharing between the ESS and DL actuators, graphs for frequency, voltage and active powers for consumer load and wind speed changes are presented. The results of the simulation show maximum settling times and frequency per unit variation of 1.5 s and 0.16% respectively, for the previous input changes. The DCS solution presented could constitute a proposal for the standardization of the control for WO mode in high wind penetration WDHS which rely on a SM to generate the voltage waveform in that mode.     

Multi-stage dual priority regulator for photovoltaic systems

The design and application are investigated of an array shedding voltage regulator for use in photovoltaic (PV) systems with two separate loads of different priority. The multistage dual-priority regulator charges two separate battery systems for high- and low-priority loads. This controller switches the array modules from the main battery to the auxiliary battery as the main battery nears full charge, thus utilizing the PV panels to the maximum without jeopardizing the reliability of the critical load. Both the main and auxiliary voltage settings are adjustable, allowing the use of different types of batteries. A dual-priority voltage regulator is useful in any stand-alone system with multiple loads. Uses include PV-powered homes, medical clinics, and recreational vehicles     

Neuro-fuzzy control for autonomous wind–diesel systems using biomass

This paper deals with the development of a neuro-fuzzy controller for a wind–diesel system composed of a stall regulated wind turbine with an induction generator connected to an ac bus-bar in parallel with a diesel generator set having a synchronous generator. A gasifier is capable of converting tons of wood chips per day into a gaseous fuel that is fed into a diesel engine. The controller inputs are the engine speed error and its derivative for the governor part of the controller, and the voltage error and its derivative for the automatic voltage regulator. These are readily measurable quantities leading to a simple controller which can be easily implemented. It is shown that by tuning the fuzzy logic controllers, optimal time domain performance of the autonomous wind–diesel system can be achieved in a wide range of operating conditions compared to fixed-parameter fuzzy logic controllers and PID controllers.     

双PWM全功率变流器机侧控制策略研究

双脉宽调制(PWM)全功率变流器机侧的开关频率低,其电流谐波含量高,且同步电机反电动势中产生了大量谐波.为了降低发电机的铜铁损耗,降低系统成本,弱化网侧滤波器设计的难度,抑制机侧谐波具有重要意义.传统比例积分(PI)调节器难以抑制直驱永磁同步发电系统机侧谐波,针对这一现象,提出将PI与准比例谐振(PR)调节器联合,形成新型的调节器,并在转子定向的旋转坐标系下对定子电流特定次谐波进行了抑制.运用PSCAD/EMTDC软件进行了仿真验证,结果表明:采用经典PI控制时,机侧电流谐波含量为17.28%;采用新型调节器时,机侧电流谐波含量为5.86%.同时,通过分析实验结果验证了该机侧控制策略的可行性,可有效地抑制机侧谐波.     

A smooth co-ordination control for a hybrid autonomous power system (HAPS) with battery energy storage (BES)

The standalone hybrid power system constitutes a synchronous generator driven by a diesel engine, renewable energy source (wind) apart from a battery energy storage system. A coherent control strategy to regulate the voltage and frequency of the standalone grid is proposed in this paper. The system is simulated using Matlab/Simulink for preliminary validation and further tested on a laboratory prototype which involves a TMS320LF2407A DSP controller to digitally implement the control strategy. The dynamic behavior of the system is perused through the direct connection of an induction machine. The control strategy is verified for step changes in load and variation in wind power.     

Adaptive fuzzy control for wind-diesel weak power systems

This work is concerned with the development of an adaptive fuzzy logic controller for a wind-diesel system composed of a stall regulated wind turbine with an induction generator connected to an AC busbar in parallel with a diesel generator set having a synchronous generator. In this work we propose to use an adaptive network based inference system (ANFIS) in order to generate fuzzy membership functions and control rules for the controller. A feedback linearized proportional integral controller is used to provide the required expert knowledge. A controller design process is identified; it consists of generating input-output data pairs to identify the control variables range and initial fuzzy memberships, and then to tune or adapt them using an ANFIS network structure. The controller inputs are the frequency error and its integral for the governor part of the controller, and the voltage and frequency errors for the automatic voltage regulator. These are readily measurable quantities leading to a simple controller which can be easily implemented     

An input‐output linearization–based control strategy for wind energy conversion system to enhance stability

This paper proposes a novel control strategy for doubly fed induction generator (DFIG)‐based wind energy conversion system to investigate the potential of enhancing the stability of wind energy transmission system, a synchronous generator weakly integrated to a power system with a DFIG‐based wind farm. The proposed approach uses state feedback to exactly linearize the nonlinear wind energy transmission system from control actions (active power and reactive power control order of DFIG) to selected outputs (power angle and voltage behind transient resistance of synchronous generator) at first. Then, on account of the linearized subsystem, the stability enhancement controller is designed based on linear quadratic regulator algorithm to contribute adequate damping characteristics to oscillations of the synchronous generator system under various operation points. The proposed control strategy successfully deals with the nonlinear behaviors exist from the inputs to outputs and improve the robustness with respect to the variation of system operation points. Furthermore, not only the rotor angle stability but also the voltage stability is enhanced by using the proposed control strategy. The simulation results carried on the studied system verify the effectiveness of the proposed control strategy of wind energy conversion system for system stability enhancement and the robustness against various system operation points.     

A new control strategy for a stand-alone self-excited induction generator driven by a variable speed wind turbine

This paper presents a new control strategy of a stand-alone self-excited induction generator (SEIG) driven by a variable speed wind turbine. The proposed system consists of a three phase squirrel-cage induction machine connected to a wind turbine through a step-up gear box. A current controlled voltage source inverter (CC–VSI) with an electronic load controller (ELC) is connected in parallel with the main consumer load to the AC terminals of the induction machine. The proposed control strategy is based on fuzzy logic control principles which enhance the dynamic performance of the proposed system. Three fuzzy logic PI controllers and one hysteresis current controller (HCC) are used to extract the maximum available energy from the wind turbine as well as to regulate the generator terminal voltage simultaneously against wind speed and main load variations. However, in order to extract the maximum available energy from the turbine over a wide range of wind speeds, the captured energy is limited due to electrical constraints. Therefore the control strategy proposed three modes of control operation. The steady state characteristics of the proposed system are obtained and examined in order to design the required control parameters. The proposed system is modeled and simulated using Matlab/Simulink software program to examine the dynamic characteristics of the system with proposed control strategy. Dynamic simulation results demonstrate the effectiveness of the proposed control strategy.     

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.     

Load control of a wind-hydrogen stand-alone power system

A new generation of load controllers enable stand-alone power systems (SAPS) to use one or many standard (grid connected) wind turbines. The controllers use fuzzy logic software algorithms. The strategy is to use the control loads to balance the flow of active power in the system and hence control system frequency. The dynamic supply of reactive power by a synchronous compensator maintains the system voltage within the limits specified in EN50160. The resistive controller loads produce a certain amount of heat that is exchanged down to the end user (hot water). It was decided to investigate the implementation of a hydrogen subsystem into the SAPS that can work in parallel with the Distributed Intelligent Load Controller (DILC). The hydrogen subsystem can then function as energy storage on long-term basis and an active load controller on short-term basis.     

Single-Stage Dual Priority Regulator for photovoltaic systems

In this paper the design and application of a voltage regulator for use in Photovoltaic Systems with two separate loads of different priority is presented. The Single-Stage Dual Priority Regulator (SSDPR) charges two separate battery systems for high and low priority loads. The controller always charges the main battery first. It toggles between the two batteries when the main battery is nearly charged, and reduces the charge duty cycle of the main battery as it approaches full charge. The SSDPR utilizes the PV more efficiently by supplying low priority loads without jeopardizing the reliability of the critical load. Both the main and auxiliary voltage settings are adjustable, allowing the use of different types of batteries. The SSDPR is being tested in the University of Lowell Vaccine Refrigerator Laboratory. A dual priority regulator is useful in any stand-alone system with multiple loads. Uses include photovoltaic powered homes, medical clinics, and recreational vehicles.     

An Autonomous System Supplied Only by a Pitch-Controlled Variable-Speed Wind Turbine

This paper presents a control strategy for a variable-speed pitch-controlled wind turbine (WT) generation scheme for the supply of an autonomous system with no energy storage units. The synchronous generator includes two three-phase stator windings displaced by 30deg that are connected to the transformer load through two dc links with voltage source inverters (VSI). Following priority rules, the load is divided into steps. Each load step can be supplied by the WT when the wind speed varies between two predefined speed levels. The first goal of the WT control system is to supply the load with constant real power under constant voltage as the wind speed varies between two levels and the second is to operate smoothly interchanging the load steps when the wind speed breaks through a speed level. There are two controllers: the inverter controller that keeps the load voltage constant and the pitch controller acting on the blade's angle. Using simulation techniques, the operation of the WT system and the efficiency of the proposed control strategy are demonstrated for a wide range of wind speeds.     

Frequency deviation control by coordination control of FC and double-layer capacitor in an autonomous hybrid renewable energy power generation system

In this paper, a novel control strategy for frequency control in stand-alone application based on coordination control of fuel cells (FCs) and double-layer capacitor (DLC) bank in an autonomous hybrid renewable energy power generation system is implemented. The proposed renewable energy power generation subsystems include wind turbine generator (WTG), photovoltaic system (PV), FC system and DLC bank as energy storage system. The system performance under different condition has been verified by using real weather data. Simulation results demonstrate the validity of proposed studied hybrid power generation system feeding isolated loads in power frequency balance condition.     

基于DSP实现风力发电机组并网运行

提出了一种风力发电机组并网运行系统;研究了基于数字信号处理器-DSP(TMS320F240)控制的发电机转速驱动控制系统;详细介绍了该系统的DSP控制器的硬件电路设计,实现了对发电机转轴的速度检测和滑差离合器励磁线圈的电流检测;最后给出了该系统的软件设计方案及控制策略,完成对整个系统的控制,使发电机转速稳定,且输出稳定的频率和电压.     

Autonomous frequency regulation by controllable loads to increase acceptable wind power generation

Output power fluctuation of high penetration of wind power causes demand and supply imbalance in electric power systems and results in frequency deviation if the fluctuation is not fully compensated by other regulable power plants. In Japan, some electric utilities have started to accept only the wind farms which disconnect and give up generating power during light‐load periods with less adjustable reserve. Otherwise, wind farms are required to employ battery energy storage systems (BESSs) to charge the generated power during the light‐load periods. Instead of these uneconomical solutions, this paper proposes autonomous frequency regulation by controllable loads such as electric water heaters (EWHs). In the paper, the acceptable increase of wind power generation by the proposed load control has been evaluated quantitatively in the power system of the Hokkaido Island in Japan. The result indicates that the acceptable increase of wind power generation goes from 250 to 675 MW by applying the proposed autonomous frequency regulation on all EWHs, and the total cost to implement the autonomous frequency regulation on the EWHs is around 1/26 compared with a solution using BESSs. Copyright © 2009 John Wiley & Sons, Ltd.     

Energy management and control of a hybrid water pumping system with storage

This paper aims to define a control and management strategy for water pumping system which would be powered by a hybrid PV/diesel generator system with battery storage. The particularity of the proposed power management method is to ensure the water volume in need and to maximize the use of PV generator while limiting the use of the diesel generator. In order to capture the maximum power from PV generator, a fuzzy logic maximum power point tracking controller is applied. On the other hand, a PI regulator is used with a boost converter in order to adapt the voltage of the battery bank to the DC bus. The water flow of the pump is also controlled. The developed power management and control strategy has been implemented using SIMPOWER toolbox in Matlab/Simulink. The obtained satisfying simulation results prove the efficiency of the proposed solution that assures continuous supply of water and electricity.     

Reinforced Control and Operation of DFIG-Based Wind-Power-Generation System Under Unbalanced Grid Voltage Conditions

This paper proposes an enhanced control and operation of a doubly fed induction generator (DFIG) based wind power generation system under unbalanced grid voltage conditions. System behaviors of grid-side and rotor-side converters (GSCs and RSCs) are described. The RSC is controlled to eliminate the electromagnetic torque oscillation at double the grid frequency. Meanwhile, three selective control targets for the GSC, i.e., reducing the pulsations in the total active or reactive power, or unbalanced current outputs from the overall system, are identified and analyzed during voltage imbalance. A new current-control scheme is presented for the GSC and RSC without involving the decomposing of positive and negative sequence currents. The controller consists of a proportional (P) regulator and a resonant (R) one tuned at the grid frequency, which is implemented in the stator stationary reference frame. Finally, simulation studies are carried out on a 1.5-MW wind-turbine-driven DFIG system. The validity of the presented current controller and the feasibility of the proposed control targets are all confirmed by the simulated results.