Direct-drive Wind Power System Research Articles

Research on Overvoltage Caused by Long Cable of Converter

Abstract Due to the impact of energy crisis and environmental pollution, wind power generation has developed rapidly as a clean and renewable energy source. The direct drive wind power system has attracted the attention of the country and wind power enterprises due to its simple structure and good reliability. This article conducts in-depth analysis on the overvoltage generated at the input end of the converter in the direct drive wind power generation system, and concludes that there are two reasons for the overvoltage: (1) there is a certain stray inductance in the direct drive wind power generation system. When the IGBT inside the converter is turned off too frequently, the induced electromotive force generated at both ends of the converter overlaps with the DC voltage, resulting in overvoltage pulses; (2) The long cable connection between the converter and the generator causes voltage reflection and generates overvoltage at the converter end. Therefore, if not suppressed in a timely manner, it will cause damage to the converter and generator. In order to prevent overvoltage damage, this article designs a new filtering circuit at the input of the converter to suppress overvoltage. A simulation model is built using Matlab simulation software to verify the advantages and disadvantages of the new filtering circuit. Finally, a comparative analysis of its simulation waveform shows that the new filtering circuit effectively suppresses the overvoltage at the input end of the converter, And the low energy consumption and wide filtering range effectively protect the safe operation of the converter.

Calculation Method and Characteristic Analysis for Fault Current of Permanent Magnet Direct-Drive Wind Power System considering Positive and Negative Sequence Decomposition

In view of the fact that the influence of positive and negative sequence decomposition, which is widely used in positive and negative sequence decoupling control in control system, on the fault current calculation process is not deeply considered in the existing transient analysis methods of permanent magnet direct-drive wind farm short circuit current, this paper proposes a transient short circuit current calculation model that takes into account positive and negative sequence decomposition. The influence of the transient characteristics of positive and negative sequence decomposition on the control system is studied, and the mechanism of its action on the transient change of short circuit current is revealed. The positive and negative sequence decoupling processes of the circuit equation are modified, and the characteristics of the coupling equation are analyzed. The difference in the converter output voltage between the circuit equation and the control equation and the depth of its influence on the calculation process is revealed. On the basis of quantifying the difference at the converter output voltage, the circuit equation and the control equation are combined to form a short-circuit current calculation model with positive and negative sequence decomposition, which accurately characterizes the transient characteristics of fault current under different voltage drops and effectively improves the accuracy of the calculation results.

Support Vector Regression Inverse System Control for Small Wind Turbine MPPT with Parameters’ Robustness Improvement

With the increasing penetration of the permanent-magnet direct-drive wind power system, the maximum wind-energy capture and the generation speed control are more and more important. In the literature, the dynamic performance of the generator speed is well documented by the inverse system method. However, conventional inverse system methods have parameter dependency that is not sufficient to meet the dynamic requirements for permanent magnet synchronous generator (PMSG) speed tracking. Therefore, this paper introduces a support vector regression machine (SVR) method, especially for the inverse system model, which could solve the inaccurate parameters problems. As the SVR has the nonlinear approximation ability to identify and adjust the parameters online, thus, the system robustness could be improved. Finally, the dynamic performance of generator speed is evaluated by using the SVR method. Proposed theoretical developments are verified by the Simulink Test and experimental test.

HOSMD and neural network based adaptive super-twisting sliding mode control for permanent magnet synchronous generators

To solve the maximum power tracking (MPT) control problem of the direct-driven wind power system, a super-twisting integral sliding mode controller with adaptive parameter estimation is designed. A high-order sliding mode differentiator is introduced as the virtual control variate filter, which solves the difficulty of obtaining the derivative of the control variate and the controller saturation in the nonlinear system with disturbances. Since the speed loop of permanent magnet synchronous generator (PMSG) is susceptible to disturbances, a radial basis function neural network (RBFNN) approximator and its adaptive algorithm are proposed to observe the unmodeled part of the system and external disturbances. In addition, the super-twisting algorithm is introduced to improve the robust performance. An improved adaptive parameter estimation algorithm is used to obtain real-time estimated values in the circumstances of uncertain stator parameters and parameters perturbation during operation, which enhances control accuracy and reduces undesirable chatting. The errors of RBFNN approximation and parameter estimation are taken into Lyapunov functions to guarantee the stability of the whole system. The effect of the proposed scheme is verified as compared to the adaptive backstepping terminal and new reaching law sliding mode controllers.

The Thyristor Switched Parallel Capacitors (TSPC) Converter for Power Factor Correction in Wind Power Systems

This paper presents a novel power factor correction circuit suitable for low-speed electric generators usually used in direct drive wind turbines. The Thyristor Switched Parallel Capacitors (TSPC) circuit belongs to the Controlled Series Capacitor (CSC) circuits. Those circuits have been used in power transmission lines to correct the power factor and improve the performance of the electrical system. Such a circuit can be used in wind power systems to improve and maximize the efficiency of a wind turbine. A typical direct-drive wind power system employs variable speed electric generators, but the downside is that systems like that suffer from high and variable inductive reactance. In order to correct the power factor and to improve the efficiency of the system, the inductive reactance of the generator must become equal in value to the capacitive reactance. A TSPC circuit uses a set of capacitors, connected in series with anti-parallel thyristors. In every cycle, a controller triggers the appropriate thyristors, allowing the current to pass from the capacitor which then provides the system with the capacitive reactance that matches the generator’s inductor reactance. Therefore, the TSPC circuit is able to counteract for any reactive losses and improve the power factor, as well as, the efficiency. This paper introduces this novel power factor correction circuit that employs capacitors in parallel configuration. This circuit was simulated in PSPICE and was implemented and tested in the lab. Based on the simulation and implementation results, we discuss the benefits as well as the drawbacks of the proposed circuit

Comparison between Thyristor Switched Series Capacitors and Thyristor Switched Parallel Capacitors for wind power systems - A Simulation Study

This paper compares by simulation the Thyristor Switched Series Capacitors (TSSC) Circuit with the Thyristor Switched Parallel Capacitors (TSPC) Circuit for wind turbines. The well-known TSSC circuit belongs to the Controlled Series Capacitor (CSC) circuits that have been used in power transmission lines in order to correct the power factor and improve the performance of the electrical system. Such a circuit can be used in wind power systems to improve and maximize the efficiency of a wind turbine. A typical direct-drive wind power system employs variable speed electric generators, but the downside is that systems like that suffer from high inductive reactance. A TSSC circuit, therefore, is able to counteract for any reactive losses, and improve the power factor as well as the efficiency. The main issue with the TSSC circuit is the use of a high number of capacitors that must be connected in series, which can increase the cost and the maintenance of the controller. This paper introduces a novel circuit with different control technique than the TSSC that employs capacitors in parallel configuration. The novel TSPC circuit was simulated in PSPICE and the benefits as well as the drawbacks are described

A hybrid sensorless control of PMSG wind-power generator with frequency signal injection method and extended Kalman filter

Based on the rotating high-frequency voltage-signal injection technique this paper introduces and compares two different approaches to extract the rotor position information for sensorless low speed control of direct-drive permanent magnet synchronous generator-based wind power system. One of the approaches is to extract the rotor position information from the carrier current of permanent magnet synchronous generator (PMSG) by the traditional bandpass filter. The other one is to use an extended Kalman filter algorithm. The effectiveness of the proposed sensorless low speed control is shown by numerical simulations using MATLAB/Simulink environment. The simulation results show that both control schemes provide an accurate estimate of the position of the PMSG-wind turbine and shaft speed. But extended Kalman filter algorithm improves the efficiency of the high-frequency voltage-signal injection method by eliminate the phase shift introduce by the traditional bandpass filter.

A hybrid sensorless control of PMSG wind-power generator with frequency signal injection method and extended Kalman filter

Based on the rotating high-frequency voltage-signal injection technique this paper introduces and compares two different approaches to extract the rotor position information for sensorless low speed control of direct-drive permanent magnet synchronous generator-based wind power system. One of the approaches is to extract the rotor position information from the carrier current of permanent magnet synchronous generator (PMSG) by the traditional bandpass filter. The other one is to use an extended Kalman filter algorithm. The effectiveness of the proposed sensorless low speed control is shown by numerical simulations using MATLAB/Simulink environment. The simulation results show that both control schemes provide an accurate estimate of the position of the PMSG-wind turbine and shaft speed. But extended Kalman filter algorithm improves the efficiency of the high-frequency voltage-signal injection method by eliminate the phase shift introduce by the traditional bandpass filter.

Dual Closed-Loop Linear Active Disturbance Rejection Control of Grid-Side Converter of Permanent Magnet Direct-Drive Wind Turbine

In the permanent magnet direct-drive wind power grid-connected system, in order to solve the coupling problem between d -axis and q -axis currents and to improve the disturbance rejection performance of direct current (DC) bus voltage under grid faults, a new dual closed-loop structure based on linear active disturbance rejection control (LADRC) is proposed. This new dual closed-loop control includes current inner loop decoupling control and DC bus voltage outer loop control with first-order LADRC. As the LADRC has the advantages of decoupling and disturbances rejection, it is applied to the control of wind power grid-connected inverter. Through analysis, it is demonstrated that the current decoupling control is simpler than proportional integral (PI) control algorithm, the dynamic response speed is faster, and the DC bus voltage control has better anti-disturbance. Finally, a 1.5 MW direct-drive permanent magnet wind power system was established through digital simulation, and the control effects of the two control modes under different working conditions are compared. The simulation results verify that the proposed dual closed-loop control based on first-order LADRC is superior to PI double closed-loop control in terms of decoupling performance and disturbance rejection performance under grid faults.

Analysis and Design of PI Plus Repetitive Control for Grid-Side Converters of Direct-Drive Wind Power Systems Considering the Effect of Hardware Sampling Circuits

In inverters based on a single proportional-integral (PI) or deadbeat (DB) controller, an inherent resonance peak may emerge near their current loop cut-off frequency, which results in harmonic amplification or even resonance. Additionally, inappropriate filter circuits implemented in sampling circuits may result in the expansion of the resonance peak. Thus, this paper further investigates the influence of the sampling circuits on a PI- or DB-based control loop. Then, the RC filter in the sampling circuit is designed to reduce the inherent resonance peak. Moreover, a compound control strategy based on an improved repetitive controller (IRC) plus a PI controller is adopted for the grid-side converter of a direct-drive wind system. This strategy enhances the harmonic and reactive compensation performance by reconstructing the internal model of the classic repetitive controller (CRC) and limiting the bandwidth of the PI-based loop to a low level. The parameters of the presented IRC-plus-PI control are designed for the purpose of resonance peak elimination and system stability. Furthermore, the non-integer delay problem is solved with an inserted fraction compensator (FC), which plays the role of a low-pass filter in the IRC. Finally, the feasibility and effectiveness of the presented control method is verified by the experimental results.

Simulation study on direct‐drive wind power system

Direct-drive wind turbine is an important type of wind power technology. In recent years, it has also become the development trend of large-capacity wind turbines. It is difficult and expensive to establish physical simulation for wind in reality, which makes the real-time simulation model necessary in the study its power generation control strategy and operation characteristics. Here, the structure and basic principles of the direct-drive wind power system was studied, mathematical model of the dq generator and converter using coordinate transformation was built, and control methods including the wind turbine pitch angle control, maximum power tracking control, and generator-side variable flow control were simulated. Furthermore, a control strategy of generator-side converters and grid-side converters was proposed and studied based on the model in the real-time simulation system RTDS. Different working conditions as grid-connected normal operation and operation with grid fault were simulated within the strategy. Waveforms of current, voltage, power, torque were obtained and analysed. The simulation results showed that the simulation model reflected the operating characteristics of the direct-drive wind power generation system well, the control strategy performed successfully, and the features of the system in normal and faulted operation were preliminarily revealed.

Modeling and control of DC microgrid system based on hydrogen production load

For the intermittent output of wind turbine and photovoltaic power, aming at the problem of abandoning wind and abandoning light, this paper proposes a DC microgrid system model and control strategy based on hydrogen production load. The DC microgrid system consists of a permanent magnet direct drive wind power system, a photovoltaic power generation system, a buffer energy storage system and an alkaline water electrolysis cell hydrogen production load. The hydrogen production load can adapt to the intermittent fluctuation power supply, make better use of the abandoned wind and light power and be environmentally friendly. Both wind power system and photovoltaic power generation system adopt MPPT control. The battery buffer energy storage device adopts constant voltage charge and discharge control. They are all controlled by their own converters to the DC bus, by producting hydrogen to store the unstable electrical energy generated by distributed generation in the DC microgrid. Based on Matlab/Simulink, results show that the system operates flexibly, the control strategy adopted by the system can maintain the stable operation and load of the system under various power fluctuations and different power supply combinations.

Operating performance analysis on wind turbines with the speed regulating differential mechanism

In this paper, a hybrid transmission system is presented for variable-speed constant-frequency wind turbines (WTs). This approach employs an electrically controlled speed regulating differential mechanism (SRDM) so that the synchronous generator is able to rotate at a stable speed and, thus, generate electricity in constant frequency regardless of the changing wind rotor speed. In order to find out the operating performance of the proposed SRDM-based WT, a detailed 1.5 MW simulation model is established by which the speed-regulating accuracy, the electrical harmonic pollutions, and the system low-voltage ride-through (LVRT) capability are all studied in depth and then compared with those of the existing direct-drive or double-fed wind power systems. Simulation results indicate that, under various wind conditions, SRDM can efficiently regulate the output power frequency with satisfactory deviations by using a low-power (less than 262 kW) permanent magnet synchronous motor. Compared to the existing WTs, the 5th, 7th, 11th, and 13th current harmonics of the proposed WT are all ideally reduced to 0.4% of the fundamental current. Moreover, around 0.45 p.u., reactive power can be provided for the rapid recovery of the grid during severe voltage sags. The output power quality, system transient stability, and LVRT capability are all improved. Theoretical analysis and case studies give good verifications of the feasibility and superiority of the proposed SRDM-based WT.

Switched model based control of dual-PWM converters in the direct-drive permanent magnet synchronous wind turbine system

Nowadays, permanent magnet synchronous generator (PMSG) based direct drive wind power generation systems are developing rapidly and are attracting more and more attention. Dual-PWM (pulse width modulation) converters, as full power converters of the direct-drive wind power system, have excellent performance and have been widely used in recent years. The effective control of the back-to-back Dual-PWM converters plays an important role in generating the wind power efficiently. As the back-to-back Dual-PWM converters of the direct-drive wind power generation system can be considered as switched systems according to their working characteristics, this study presents one switched model based control strategy for the control of the Dual-PWM converters. First, the switched dynamic models of the converters on the PMSG side and the grid side are established, respectively. In contrast to the traditional averaged or linearized models, the proposed models can be more precise because no approximation will be introduced when the wind speed changes. Then, in order to realize the highest convergent rate, the min-projection strategy based switched control laws are derived. Furthermore, the stability analysis is done to assure the global stability of the proposed control strategy. Finally, detailed simulations and experiments are available to verify the proposed control method. The simulation and experimental results demonstrate that the proposed models and the control strategy are correct and effective. Comparing with the conventional proportional-integral control method, this paper integrates the back-to-back Dual-PWM converters as part of the proposed controller and utilizes the states of the converters as control variables, and thus, faster torque dynamics can be achieved.

Research on the virtual synchronous generator control strategy of grid-connected permanent-magnet direct-driven wind power system

Renewable energy, distributed generation, and micro-grid technology have been widely concerned for a long time. The traditional grid-connected inverter control strategy does not take into account the problem of inertia which is short and fast to cause the frequency change. The virtual synchronous generator control strategy is adopted to simulate the synchronous generator characteristics, which enhanced the inertia and damp of the system. For the micro-grid of wind power grid-connected, the storage battery is arranged on the AC side of the permanent magnet direct-drive wind turbine, and the model of the virtual synchronous generator is established. Thus the grid-connected performance of large-scale wind farm is improved. Here, the effect of moment of inertia in the virtual synchronous generator and the grid-connected regulation of virtual synchronous generator are verified by using PSCAD/EMTDC. The simulation results show that the grid-connected inverter controlled by the virtual synchronous generator is approximately equivalent to the synchronous generator in external characteristic. The grid-connected inverter based virtual synchronous generator control has a beneficial to adjust frequency and voltage, and can enhance the standby inertia of new energy and grid power generation

Fuzzy-Logic Sliding-Mode Control Strategy for Extracting Maximum Wind Power

A fuzzy-logic sliding-mode control strategy is proposed to capture the maximum wind energy and reduce the generator-side current harmonics for a direct-driven wind power system. The control strategy mainly consists of a fuzzy logic controller for generating the optimum dc-side current and a double integral sliding-mode current controller capable of accurately tracking the optimum dc-side current. A resonant filter is also incorporated into the fuzzy logic controller to eliminate the generator-side current harmonics. Detailed design procedure, existence, and stability conditions of the proposed control strategy have been thoroughly investigated and presented. The capability and effectiveness of the proposed control strategy have been validated by comparative experimental results.

Research on Inverter Side Steady Operation of Direct-Drive Permanent Magnet Synchronous Wind Power System

Currently, back-to-back converter is widely used in rectifier and inverter of direct-drive permanent magnet synchronous wind power system. But there are two shortages in the system, not stable of control effect and higher ripple of DC voltage. The dual-channel parallel boost converter can shunt the DC current, reduce the ripple effectively, and improve the quality of inverter side DC current. The paper uses the space vector pulse width modulation control strategy to control the inverter. Simplifying and decoupling the complex control system and control the DC bus voltage to remain stable. The simulation results confirm that dual-channel parallel boost converter have a better control effect than back to back converter, it through control the inverter to make power quality reached the grid connected requirement, verified the correctness of the design of inverter.

A Review on Low Voltage Ride-Through Solutions for PMSG Wind Turbine

The exiting of wind turbines will cause the adverse effect on the power grid and its assembling unit in network voltage drops. So, direct-drive wind power generation system should meet the requirement of the certain ability of low voltage. This paper introduces the influence of wind power system with different structure by voltage drop as well as the disadvantage and advantage on LVRT. The relate regulations based on LVRT are analyzed. The existing LVRT technologies of direct-drive wind power systems are briefly presented. The characteristics of each scheme from the different LVRT technology are analyzed. Moreover, further study of LVRT for PMSG is pointed out.

Maximum Wind Power Tracking Control Based on PID and Feedback Linearization

Based on the mathematical model of permanent magnet synchronous generator, the paper discussed the effect of the simplifying torque coefficient equation on direct-drive permanent magnet synchronous wind power generator. On the basis of feedback linearization principle, designed a PID and feedback linearization compound controller in this paper, and validated under varying wind speed, power coefficient remains at a constant value, which reached the maximum wind power capture purposes. Using MATLAB/simulink tool to build direct-drive permanent magnet synchronous wind power system simulation model, the paper verify the stability of the system when the external applied load mutate. The result shows that the control strategy of the composite is effective and timely when tacking the maximum power.

Introduction of the Direct Drive Wind Power Generation System

With the development of economy, the energy demand is becoming bigger and bigger, the development of wind energy is one of the main ways to solve energy crisis. In terms of energy utilization, high power wind power connected to the grid is currently one of the most effective ways of wind energy utilization. The wind power generation system connected to the grid plays the role of the changing wind energy into mechanical energy by wind turbines, and then converts mechanical energy into electrical energy by a generator. Because CSCF wind turbine works with the gearbox, which is low efficiency, noise and mechanical loss. And it has not been able to meet the needs of the times. Therefore, the direct drive wind power technology capable of tracking the maximal power point of wind power at rated wind speed has become one of the hot spots in the present research. This paper introduces the converter of the direct drive wind power system and analyzes the working principle of the direct driven permanent magnet synchronous wind power system.