Grid-connected Permanent Magnet Synchronous Generator Research Articles

Direct Predictive Voltage Control for Grid-Connected Permanent Magnet Synchronous Generator System

In this paper, a direct predictive voltage control (DPVC) is proposed for the grid-connected permanent magnet synchronous generator (PMSG) system. In the proposed strategy, the dc-link voltage regulation and power regulation terms are merged into one cost function, thereby eliminating the conventional cascade control structure. The strategy selects the voltage vector that not only will generate a dc-link voltage closer to the setpoint at instant <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$k+2$</tex-math></inline-formula> , but will generate an active power that can further reduce that voltage error for the future instant. To cope with the mismatch between the actual and nominal parameters, Kalman filter has been added to compensate for the steady-state error. Besides, to enhance the dynamic performance and to save the effort of parameter tuning, the weighting factor is further eliminated from the cost function by sorting the terms into two groups and independently evaluating each group in turn. To fully validate the effectiveness of the proposed strategy, the experimental test waveforms of the DPVC strategy with and without weighting factor have been presented and compared with that of the conventional PI-MPC strategy in various testing conditions.

Performance analysis of modeling scale on multiband oscillations in grid-connected wind farm

Grid-connected permanent magnet synchronous generator (PMSG) wind farms may be susceptible to oscillation when connected to weak grids. This paper explores the root causes of the oscillations from two perspectives: the model and the oscillation frequency band. First, the small signal model of PMSG wind farm grid-side system is established, and the small disturbance comparison with the PMSGA full-order electromagnetic transient model in MATLAB/Simulink is carried out. Then, we calculatue the eigenvalues of the small signal model and use model analysis techniques such as participation factors calculation and root locus method to identify the critical factors that cause the oscillation modes to be dominant. Finally, time-domain simulation is used to verify the theoretical analysis. Two dominant modes are identified: the subsynchronous oscillation mode and the low-frequency oscillation mode. The subsynchronous oscillation mode is closely related to the direct current (DC) voltage control and the dynamics of DC link. The low-frequency oscillation is significantly weakened with the decrease in grid strength, and it is closely related to the phase-locked loop (PLL) control. The conclusions can provide a reference for tuning the control parameters of PMSG converter.

Exploring Dynamic P-Q Capability and Abnormal Operations Associated with PMSG Wind Turbines

With the proliferation of large-scale grid-connected wind farms, subsynchronous oscillation (SSO) incidents associated with Type-4 wind turbines (WTs) with a permanent magnet synchronous generator (PMSG) have occurred frequently. These incidents have caused severe reliability risks to the power grid. Conventionally, P-Q capability charts are utilized to ensure the safety operating region of a synchronous generator. However, a PMSG WT exhibits completely different and dynamic P-Q capability characteristics due to the difference in energy conversion technique and several critical factors related to the WT power converters. This paper presents a comprehensive dynamic P-Q capability study of a PMSG WT with sufficient and accurate considerations of the WT control and operation in the dq reference frame, its power converter constraints, and grid dynamics. Models of a PMSG WT are first developed based on its control principle in the dq reference frame. Then, algorithms for obtaining the P-Q capability charts of the WT are developed with the considerations of complete WT constraints in different aspects. The study analyzes the root cause of many abnormal operations of grid-connected PMSG WTs, reported in the literature, from the dynamic P-Q capability perspectives. The proposed study is verified via an electromagnetic transient (EMT) model of a grid-connected Type-4 WT.

Improving the performance of grid connected wind generator with a PI control scheme based on the metaheuristic golden eagle optimization algorithm

• A novel Golden Eagle optimization algorithm (GEOA) is proposed. • GEOA is used to improve the Transient and Dynamics stability of wind farm. • Transient and Dynamics stability of grid-tied PMSG-VSWT is investigated during symmetrical, unsymmetrical faults and Stochastics wind variation at that site. • The results of GEOA are compared with the results of NR, PSO and GOA. • The results shown that the GEOA is robust and competitive. Wind power installations are globally established thoroughly, resulting in significant electrical power penetration into power grids. Consequently, tremendous efforts are expended to improvise the performance of the grid-connected Permanent Magnet Synchronous Generator driven by a Variable-Speed Wind Turbine (PMSG-VSWT). In this work, eight cascaded Proportional Integral (PI) controllers in the machine side and grid side converters are optimally tuned by the golden eagle optimization algorithm with the purpose of enhancing the dynamics and transient stability performances of the grid connected PMSG-VSWT.The integration of the square error criterion was utilised as a fitness function in the optimization process, which was processed using the simulation-based optimization technique. The proposed control technique's efficacy was compared to various optimal PI controllers under symmetrical and unsymmetrical fault conditions. This study also employed the measured real-time events collected at the Coimbatore wind farm in Tamil Nadu (India) to produce realistic results and aid in the pursuit of higher performance. The wind farm modelling and simulation were processed using the DIgSILENT power factory/MATLAB Simulink environment and was utilized to test the proposed control approach's achievability. Finally, the study demonstrates that the golden eagle optimization technique improves the wind farm's performance when compared to observed events and other techniques.

Robust Speed Controller for PMSG Wind System Based on Harris Hawks Optimization via Wind Speed Estimation: A Real Case Study

Modern wind power systems have recently tended to focus on achieving fast-tracking wind speeds (WSs), high maximum power point tracking (MPPT) efficacy without mechanical sensors, and high performance under uncertain WS together with an effective control system. Therefore, a sensorless MPPT method is introduced, which calculates the actual WS to save system installation costs and boost performance levels. The implemented MPPT method is based on the approximating of the 3-order polynomial to the aerodynamics torque power coefficient. In this study, three-speed control strategies (SCSs) for a grid-connected permanent magnet synchronous wind generator (PMSWG) are examined and assessed. Harris Hawks’ algorithm (HHA)-based PI controller (HHA-PIC) is used in place of (the conventional proportional-integral controller (CPIC), and adaptive fuzzy logic controller (AFLC)) as a speed controller to overcome their drawbacks. To track the generator speed to the desired speed, the HHA-PIC is used. All the CPIC, AFLC, and HHA-PIC have been carefully thought out and constructed to satisfy the speed control loop’s responsive performance. Additionally, a comparison of SCSs amongst the categories under investigation is done. The effect of HHA on the functionality of SCS is verified using MATLAB/SIMULINK. To ensure the efficacy and supremacy of the HHA-PIC over the CPIC and AFLC, a wide variety of WSs (step change, ramp, and real fluctuations) are applied. The HHA-PIC boosts system efficiency over AFLC and CPIC by 0.81% and 8.48%, respectively. Finally, it can be said that HHA is a crucial remedy for the problems with CPIC and is superior to AFLC.

Power Oscillation Analysis of PMSG Wind Power Generation System Considering Power Control Nonlinearity

High proportion of renewable energy generation, especially wind power generation, has changed the dynamic behavior of power systems and leads to emerging stability issues such as oscillation accidents. The commonly used stability analysis methods based on linear system theory cannot tackle the influence of nonlinear elements in the control loop. To fill this gap, the describing function method is used to analyze the stability and power oscillations of a grid-connected permanent magnet synchronous generator (PMSG) wind power generation system in this paper. A complete PMSG system model is taken into consideration, including a wind turbine, a generator, a machine-side converter, a grid-side converter, and a weak grid. Particularly, the nonlinear element introduced by maximum power point tracking control in the power control loop is modeled and analyzed, and the influences of critical system parameters are studied. With the high accuracy of the describing function method, it is revealed that the machine-side converter mainly influences the oscillation amplitude, while the grid-side converter mainly influences the oscillation frequency. Furthermore, the following results can be obtained: 1) High bandwidth of maximum power point tracking control and rotation speed control may enlarge the oscillation amplitude, while a fast current loop of the machine-side converter is beneficial to the stability; 2) Grid-side voltage loop can significantly affect the frequency of the oscillation, and improper high bandwidth of a phase-locked loop (PLL) is harmful to system stability; 3) A stronger grid is not always beneficial to the system stability, and the influence of grid strength should be carefully analyzed and examined when nonlinear elements are considered. All analyses are verified by simulations based on MATLAB/Simulink.

Improving the Performance of PMSG Wind Turbines During Grid Fault Considering Different Strategies of Fault Current Limiters

The wind energy conversion technology of a Permanent Magnet Synchronous Generator (PMSG) is very promising in renewable power generation. However, the performance of the grid-connected PMSGs is greatly affected by grid disturbances because their stator windings are interfaced with the grid directly. There are different Fault Current Limiter (FCL) topologies that are capable of improving the Fault Ride Through (FRT) capability of PMSG wind turbines during short circuit faults. This study investigates three types of FCLs connected to the grid side of the PMSG wind turbine: Series Dynamic Braking Resistor (SDBR), traditional Bridge Fault Current Limiter (BFCL), and Capacitive Bridge Fault Current Limiter (CBFCL). Complete modeling of FCLs was derived in order to understand their behaviors accurately during normal conditions and fault periods. The performance of the three FCLs in the PMSG wind turbine was analyzed and compared using a severe three-phase to ground fault at the terminal of the PMSG wind turbine in Power System Computer Design and Electromagnetic Transient Including DC (PSCAD/EMTDC) platform. The same conditions of operation were used in investigating the various FCL strategies in the PMSG wind turbine considered in this study during grid fault for effective comparison.

Enhanced Low Voltage Ride Through Capability for Grid Connected Wind Energy Conversion System

It is obvious that the current era has received much attention in the fields of science and technology, besides the continuous endeavor to provide environmentally friendly and resource-saving alternatives for conventional energy conversion systems. The rapid development of Wind Energy Conversion Systems (WECS) has made Permanent Magnet Synchronous Generator (PMSG) a primer choice because of its advantages. The current trend on WECS necessitates wind turbines to maintain continuous operation during voltage drops, which is referred to as Low Voltage Ride Through (LVRT). The PMSG control technique is a widely used approach for improving conversion efficiency as well as LVRT capability. This paper provides LVRT and power enhancement for grid-connected PMSG based WECS using control techniques. The LVRT capability has been investigated by using PI and Residue controllers. The simulation results show improved active power delivery and better LVRT capability during voltage dips when the Residue controller is implemented.

Dynamic performance analysis of grid-connected PMSG based on nonlinear control

This paper presents nonlinear control of a Wind Energy Conversion System (WECS) based Permanent Magnet Synchronous Generator (PMSG) and Five-Level Neutral Point Clamped Voltage Source Converter (5L-NPC-VSC). For WECS, the Maximum Power Point Tracking (MPPT) is a very important requirement in order to maximise the effectiveness. Therefore, the MPPT approach and grid-connected control methods are discussed. On the other hand, the proposed control techniques are based on Sliding Mode Approach (SMA) and Vector Control (VC) to achieve the MPPT, to keep the dc-link voltage constant and to the control active and reactive powers. The stability of the regulators is obtained using Lyapunov analysis. An extensive simulation study, using MATLAB/Simulink, is conducted on a 4-MW wind farm composed of two 2 MW PMSG based wind turbines.

A Novel Stability Analysis Approach for the Gird-connected Wind Generator Based on Impedance Ratio Criterion

A novel stability analysis approach is proposed for a gird-connected Wind generator system based on the impedance criterion, which can consider the dynamic characteristics of permanent magnet synchronous generator (PMSG). Firstly, the stability analysis criteria for the grid connected power system with electronic converters is deduced based on the impedance stability analysis principle. Secondly, the small signal model of a PMSG with consideration of the dynamic characteristics of PMSG is established by the state-space equation of PMSG, and the output impedance of a grid-connected PMSG system is derived. On this basis, the stability analysis method for the gird-connected PMSG is obtained. Numerical simulation are performed to validate the proposed control method.

Design of robust MPPT controller for grid-connected PMSG-Based wind turbine via perturbation observation based nonlinear adaptive control

This paper presents a robust maximum power point tracking (MPPT) control scheme for a grid-connected permanent magnet synchronous generator based wind turbine (PMSG-WT) using perturbation observation based nonlinear adaptive control. In the proposed control scheme, system nonlinearities, parameter uncertainties, and external disturbances of the PMSG-WT are represented as a lumped perturbation term, which is estimated by a high-gain perturbation observer. The estimate of the lumped perturbation is employed to compensate the actual perturbation and further achieve adaptive feedback linearizing control of the original nonlinear system, without requiring the detailed system model and full state measurements. The effectiveness of the proposed control scheme is verified through both simulation studies and experimental tests. The results show that, compared with the conventional vector controller and the standard feedback linearizing controller, the proposed control strategy provides higher power conversion efficiency and has better dynamic performances and robustness against parameter uncertainties and external disturbances.

A new control approach to improve the dynamic performance and ride through capability of PMSG wind energy system

The increasing penetration of wind power into the modern power system forces many countries to adopt and revise grid codes for wind farms. The latest grid codes demand the wind energy systems to remain online during grid disturbances to meet the Low Voltage Ride-Through Capability (LVRT). The disconnection of the grid connected wind farm under abnormal grid disturbances significantly impacts the stability of the grid system. This paper proposes the robust active disturbance rejection control for permanent magnet synchronous generator (PMSG) based wind energy systems to enhance the dynamic performance and ride through capability under abnormal grid disturbances. The proposed approach is applied to the machine and grid side converter of PMSG to improve its ride through capability in compliance with the grid codes. Besides external grid disturbances, the proposed approach also considers the internal disturbances such as random parameter variations, parameter uncertainties, and cross-coupling terms to improve the dynamic performance of the wind energy system. The proposed approach is particularly effective in real-time estimation and compensation of the internal and external disturbances. The simulation results are performed in Matlab/Simulink to support the theoretical considerations, demonstrating the potential contributions of the proposed control strategy. The superiority of the proposed control strategy to improve the LVRT potentiality for the grid-connected PMSG wind energy system is verified by comparing with the traditional vector PI control scheme.

Augmented grey wolf optimizer for grid-connected PMSG-based wind energy conversion systems

The grey wolf optimizer (GWO) is a new meta-heuristic algorithm inspired from the leadership and prey searching, encircling, and hunting of the grey wolves’ community. The GWO algorithm has the advantages of simplicity (less control parameters), flexibility, and globalism. In this paper, a simple and efficient augmentation for the GWO (AGWO) algorithm is proposed for better hunting performance. The AGWO algorithm focuses on increasing the possibility of the exploration process over the exploitation process by modifying the behavior of the control parameter (a) and position updating. The AGWO is suitable to the low number of search agents such as the electric power system application. The proposed AGWO algorithm is verified using twenty-three benchmark test functions and is applied to the grid-connected permanent magnet synchronous generator driven by variable speed wind turbine (PMSG-VSWT). The obtained results of the AGWO algorithm are compared with the results of the original GWO and other algorithms. The comparisons verified that the proposed AGWO is significantly augmented the performance of the original GWO algorithm without affecting its simplicity and easy implementation.

Fault Ride-Through and Power Smoothing Control of PMSG-Based Wind Generation Using Supercapacitor Energy Storage System

This paper proposes an efficient power smoothing and fault ride-through control strategy for variable-speed grid-connected permanent magnet synchronous generator (PMSG)-based wind turbine generator (WTG) with supercapacitor energy storage system (SCESS). As WTG installations are increasing, these systems need to have a fault ride-through capability to stay alive during grid faults. As the wind speed is varying, power smoothing is needed as well. The controller proposed has twofold advantage for WTG equipped with SCESS. That is the SCESS is exploited to minimize the short-term fluctuation to have a smooth power profile during normal operation. In addition during grid side fault, the proposed controller stores the generated power from the WTG into the SCESS to ride-through the fault. Two back-to-back-connected three-level neutral-point-clamped (NPC) converters are used for the power conversion. The system model and the control strategy have been developed for the NPCs, the buck-boost converter and the variable-speed WTG system. The real time digital simulator (RTDS)-based results conducted on 2 MW/4 kV PMSG verify the effectiveness and superiority of the proposed controller.

Sub-synchronous interactions caused by the PLL in the grid-connected PMSG for the wind power generation

A phase locked loop (PLL) functions to connect a grid-connected permanent magnet synchronous generator (PMSG) for wind power generation to a power system. This paper investigates the sub-synchronous interactions (SSIs) caused by a PLL. A closed-loop interconnected model for the power system with the PMSG is established, wherein, the PLL and the rest of power system are modelled as two open-loop subsystems. Analysis in the paper indicates that when an open-loop complex pole of the PLL subsystem is close to an open-loop sub-synchronous oscillation (SSO) mode of the rest of power system, this open-loop modal resonance may cause strong SSIs between the PLL and power system. It is very likely that the strong SSIs may degrade the damping of power system SSOs. Hence, the mechanism that the grid connection of the PMSG may cause the SSO instability of the power system is revealed from the perspective of open-loop modal resonance introduced by the PLL. In the paper, a method of open-loop modal analysis is proposed to identify the instability risk of open-loop modal resonance brought about by the PLL. Study cases are presented in the paper to demonstrate and evaluate the analysis and conclusions.

PLL-Induced Modal Resonance of Grid-Connected PMSGs With the Power System Electromechanical Oscillation Modes

This study investigates the impact of a grid-connected permanent magnet synchronous generator (PMSG) for wind power generation on the power system electromechanical oscillation modes (EOMs) caused by a phase-locked loop (PLL). A closed-loop interconnected model of a power system with the PMSG is established, where the PLL and rest of the power system are modeled as two separate open-loop interconnected subsystems. Analysis based on the established model indicates that, when an open-loop PLL oscillation mode (POM) is close to an open-loop EOM of concern on the complex plane, the dynamic interactions between the PMSG and the power system may become strong. It is very likely that the modal resonance due to the closeness of the open-loop POM and EOM may degrade the small-signal stability of the power system. In this paper, case studies of an example power system with PMSGs are presented. It is demonstrated that open-loop modal resonance occurs when power system operating conditions change and the PLL parameters are tuned. Strong dynamic interactions between the PMSGs and power system are caused by the open-loop modal resonance, resulting in considerable damping degradation of the low-frequency electromechanical oscillations.

Power System Electromechanical Oscillation Modes as Affected by Dynamic Interactions From Grid-Connected PMSGs for Wind Power Generation

Dynamic interactions between a grid-connected permanent magnet synchronous generator (PMSG) and power system are normally weak. This paper reports a special condition of modal resonance, under which the grid-connected PMSG may dynamically interact with power system strongly to affect power system electromechanical oscillation modes (EOMs). The special condition of modal resonance reported in this paper is that an open-loop converter oscillation mode (COM) of PMSG is close to an open-loop EOM of a power system on the complex plane. Damping torque analysis is carried out to explain why strong dynamic interactions between PMSG and power system may occur under the condition of modal resonance. Results of theoretical analysis in this paper indicate that occurrence of modal resonance may possibly cause the damping of either closed-loop COM or EOM to decrease such that power system small-signal angular stability is affected negatively by grid connection of PMSG. Responsible COMs for modal resonance are found to be related with active/reactive power control systems of a grid-side converter of PMSG. In the paper, an example multimachine power system with PMSGs is presented to demonstrate and validate analysis and conclusions made.

Reliability comparison of different power electronic converters for grid-connected PMSG wind turbines

Reliability is becoming more important as the size and number of worldwide installed wind turbines (WTs) increase. In offshore WTs, reliability evaluation is vital due to their hard and expensive repair and maintenance. Wind turbine producers, if consider reliability, can warrant that their productions will ensure high availability. Power electronic converters play an important role in reliability evaluation of grid connected variable speed WTs. This paper presents a reliability comparison between 3 types of power electronic converters that are conventionally used in the grid-connected permanent magnet synchronous generator–based wind turbines. Type 1 is back to back converter, type 2 is a pulse width modulation inverter with a conventional boost DC/DC converter and a simple diode rectifier, and type 3 is a pulse width modulation inverter with an interleaved boost DC/DC converter and a simple diode rectifier. The failure rate is calculated for each type of the converters, and then, reliability is calculated and compared. Results show that the type 3 is the most reliable and has the lowest failure rate between the above mentioned types of converters.

Wind Velocity Sensorless Maximum Power Point Tracking Algorithm in Grid-connected Wind Energy Conversion System

This article proposes a wind velocity sensorless hill-climb searching algorithm in the grid-connected field-oriented controlled permanent magnet synchronous generator based wind energy conversion system. The proposed method improves the speed and accuracy of initial tracking. Pseudo-optimum points are used to track the exact optimum points using the power versus speed characteristics of a wind turbine for various wind velocities. This research emphasizes that the pseudo-optimum points using the power versus speed characteristics are always less than and much nearer to the exact optimum points. The small-step forward tracking after pseudo-optimum points improves the accuracy of this algorithm. Moreover, this method improves the tracking speed for various wind velocities. The system used for this research consists of a back-to-back sinusoidal pulse-width modulation converter between the generator and the grid. The performance of the proposed method is analyzed mathematically and verified by simulation using MATLAB/Simulink software (The Mathworks, Natick; Massachusetts, USA).

Power Electronic Interface with Maximum Power Point Tracking Using Line-commutated Inverter for Grid-connected Permanent Magnet Synchronous Generator

—This article presents a simple grid interactive system that extracts maximum power from a wind-driven permanent magnet synchronous generator using an integrated cascade boost converter and a three-phase line-commutated inverter. The firing angle of the line-commutated inverter is held constant at an appropriate value that provides a constant DC-link voltage, and only DC-link current is sensed for maximum power point tracking. For wide wind variation, maximum power from the permanent magnet synchronous generator is achieved using a simple load current (DC-link current) perturb and observe maximum power point tracking technique. This is obtained by varying the duty ratio of the integrated cascade boost converter with an adaptive incremental step that varies the load on the permanent magnet synchronous generator in accordance with changing wind. Experiments have been conducted on a 3-phase, 750-W, 500-rpm laboratory size permanent magnet synchronous generator. The operation and analysis of the proposed topology with a fixed firing angle for a line-commutated inverter is presented. The results obtained from MATLAB (The MathWorks, Natick, Massachusetts, USA) simulation are verified with experimental results, and a close correlation has been found, proving the efficacy of the system.