Machine Side Converter Research Articles

Improved Control Strategy for Dual-PWM Converter Based on Equivalent Input Disturbance

Aiming at the problems of jittering waveforms and poor power quality caused by external disturbances during the operation of a dual-pulse-width-modulation (PWM) converter, an improved terminal sliding mode control and an improved active disturbance rejection control (ADRC) are investigated. The method is based on mathematical models of grid-side and machine-side converters to design the controllers separately, and the balance between the two sides is maintained by the capacitor voltage. An improved terminal fuzzy sliding mode control and equivalent input disturbance (EID)-error-estimation-based active disturbance rejection control are presented on the grid side to improve the voltage response rate, and an improved support vector modulation (SVM)–direct torque control (DTC)–ADRC method is developed on the motor side to improve the robustness against disturbances. Finally, theoretical simulation experiments are built in MATLAB R2023a/Simulink to verify the effectiveness and superiority of this method.

Non‐linear coordinated control of LPMG‐based direct drive wave energy conversion system with supplementary energy storage system based on feedback linearization

AbstractThe linear permanent magnet generator (LPMG)‐based direct drive wave energy conversion system (DDWECS) works under perpetual fluctuations of ocean waves. Short‐term energy storage, such as electrochemical energy storage, is usually adopted in a supplementary energy storage system (SESS) to buffer power fluctuations. Since the investigated DDWECS consists of various non‐linear components such as insulated gate bipolar transistors (IGBTs)‐based power electronic converters, the unremitting changes of system working conditions caused by ocean wave effects will degrade the dynamic performance with conventional linear controllers which are implemented via local linearization around a single working condition. This paper proposes the multiple feedback linearization based non‐linear coordinated control (MFLNCC) scheme for coordinating non‐linear plants in DDWECS with SESS such as the machine‐side converter (MSC), the grid‐side converter (GSC) and DC/DC converter in SESS. The enhanced dynamic performance of the proposed MFLNCC in DDWECS with SESS is validated under different scenarios.

An Improved Collaborative Control Scheme to Resist Grid Voltage Unbalance for BDFG-Based Wind Turbine

This article presents an improved collaborative control to resist grid voltage unbalance for brushless doubly fed generator (BDFG)-based wind turbine (BDFGWT). The mathematical model of grid-connected BDFG including machine side converter (MSC) and grid side converter (GSC) in the αβ reference frame during unbalanced grid voltage condition is established. On this base, the improved collaborative control between MSC and GSC is presented. Under the control, the control objective of the whole BDFGWT system, including canceling the pulsations of electromagnetic torque and the unbalance of BDFGWT’s total currents, pulsations of BDFGWT’s total powers are capable of being realized; therefore, the control capability of BDFGWT to resist unbalanced grid voltage is greatly improved. Moreover, improved single-loop current controllers adopting PR regulators are proposed for both MSC and GSC where the sequence extractions for both MSC and GSC currents are not needed any more, and hence the proposed control is much simpler. In addition, the transient characteristics are also improved. Moreover, in order to achieve the decoupling control of current and average power, current controller also adopts the feedforward control approach. Case studies for a two MW BDFGWT system are implemented, and the results verify that the presented control is capable of effectively improving the control capability for BDFGWT to resist grid voltage unbalance and exhibit good stable and dynamic control performances.

A hybrid fuzzy logic-based MPPT algorithm for PMSG-based variable speed wind energy conversion system on a smart grid

Recently, wind power has gained popularity as a sustainable energy source. Wind energy conversion systems (WECSs) can accept fixed speed and variable speed (VS) operations. VS-WECSs are preferable to conventional WECSs because of their higher electricity collection capacity. Maximum power point tracking systems (MPPTs) are essential for maximizing the efficiency of wind energy generation in wind turbine installations linked to power grids. This study introduces a hybrid fuzzy logic controller-based MPPT (FLC-MPPT) for wind turbines (WTs) connected to permanent magnet synchronous generators (PMSGs) to accurately determine the maximum power output of WTs. This study employs a three-phase back-to-back converter to link a PMSG to a utility grid. The reference signals for pulse width modulation controllers comprise two-phase system currents. It constructs a converter that can transfer electrical energy in both directions using insulated-gate bipolar transistor technology and is powered by a battery. The machine-side converter uses model predictive control for the present control loop. Given the generator's susceptibility to changes in wind conditions, this factor is of the utmost importance. A WT simulation was conducted using MATLAB/Simulink and an FLC methodology was employed. The model used a PMSG. Measurements of rotor speed, power, induced voltage, and current were taken in relation to variations in wind speed. The simulation results show that the FLC-MPPT can maximize the output power over a wide range of wind speeds with a higher efficiency of 92.6% and performance of 95.7%.

Experimental investigation of predictive control for PMSM-based wind turbine generation system

The theoretical analysis of permanent magnet synchronous machine (PMSM)-based wind turbine generation system was presented by many researchers; nevertheless, although the practical setup is still quite difficult, it is more valid. Moreover, the main challenge facing wind power systems is figuring out how to extract the most energy from varying wind speeds. Since wind turbine maintenance is hard and expensive, using wind speed sensors is a challenging operation. Therefore, this research suggests an effective and practical control system based on the Model Predictive Control Scheme (MPCS) for both the grid-side converter (GSC) and the machine-side converter (MSC) to optimize power extraction from wind energy. Detailed exploration of the MPCS for the PMSM and predictive power control (PPC) for the GSC involves stages such as flux estimation, torque prediction, and cost function minimization. The results obtained validate the higher performance of MPCS in comparison to the direct torque control (DTC) method. Furthermore, excellent tracking with high accuracy is achieved in relation to simulation and experimental data. Additionally, an evaluation indices based on root mean square error (RMSE) and gross system efficiency are used for wind turbine performance. These indices are used to show that, the feasibility of the MPCS approach compared with DTC under the same WT conditions. This approach offers a promising avenue for cost-effective wind energy conversion. The control systems were designed and implemented utilizing a DSPACE 1104 card. Experimental results confirm the effectiveness of the proposed mechanism in achieving maximum power point tracking (MPPT).

Optimal predictive voltage control of a wind driven five phase PMSG system feeding an isolated load

Wind energy conversion systems (WECS) are considered to be a promising alternative to traditional power generation systems. The principal purpose of this study is to enhance the performance of a stand-alone wind-driven five-phase PMSG system. The initial step involves providing a clear explanation of the system model, which includes the wind turbine, five-phase PMSG, and a battery storage system. Then, the maximum power point tracking (MPPT) and pitch angle control (PAC) technique is employed to optimize the power delivered to an isolated load. Furthermore, the system incorporates the machine-side converter (MSC) and battery converter, which require control to efficiently regulate the power delivered from them to an isolated load. In addition, the MSC is regulated by two predictive control algorithms: predictive torque control (PTC) and a newly formulated predictive voltage control (PVC). The PTC faces limitations such as considerable ripple, significant load commutation, and the weighting factor of its cost functions. The proposed prediction technique aims to overcome these constraints by using a simple cost function and eliminating the need for weighting factors to address stability issues also another study's objective revolves around proposing a PVC controller that achieves an optimal design. The results demonstrate that the newly proposed predictive controller outperforms the conventional control method for the wind generator. The developed controller produces consistently distributed sinusoidal currents with significantly fewer ripples and current harmonics. This fact is verified mathematically as the total harmonic distortion (THD) is reduced to 1.168 % as an average value.

An optimal regulation of grid-connected doubly-fed induction generator angular speed and the DC-link voltage

In this work, a linear quadratic regulator controller is utilized to optimize the gains of the machine-side converter and grid-side converter controllers. The DC-link voltage and the rotational speed of the doubly-fed induction generator are optimally regulated by these controls. Additionally, the small-signal stability of the proposed system has been evaluated using the linearized model of the system. The small-signal stability analysis of the designed system has been accomplished through the application of the eigenvalues and participation factors technique. The suggested controller has been tested in a variety of operating conditions under small disturbances. MATLAB/SIMULINK simulation simulations have been used to evaluate the efficacy of the suggested optimal control system. Additionally, the generator-angular speed and DC-link voltage dynamic performances demonstrate the efficacy of the proposed controller. Finally, the robustness of the proposed controller has also been tested and validated using OPAL-RT technology under large perturbations at stator terminal voltage.

Performance evaluation of coupled-inductor DC-DC converter for wind energy conversion system

ABSTRACT This paper studies the performance of single-switch-coupled inductor-based quadratic DC-DC converter employed in the machine side converter of wind energy conversion system. The performance of the converter is evaluated in terms of voltage conversion ratio, voltage and current stress on the switch of the converter. The detailed circuit analysis, power loss analysis, modelling and integration issues have been elaborated in this work. The DC-link voltage regulation of wind energy conversion system is carried out using closed-loop control scheme including maximum power point tracking scheme and dual-loop control scheme. Simulation results and experimental results have been provided in this work.

Artificial neural network-based direct power control to enhance the performance of a PMSG-wind energy conversion system under real wind speed and parameter uncertainties: An experimental validation

With the increasing emphasis on embedding advanced technology into system controls, the Direct Power Control (DPC) approach has garnered considerable attention due to its simple and highly adaptable algorithm. This approach has been increasingly recognized in numerous applications. However, the variable frequency, harmonic distortion of the currents, and power ripples caused by Hysteresis controllers and switching tables decrease its effectiveness and robustness, affecting the system’s performance. For this reason, this paper proposed a new DPC based on Artificial Neural Network (ANN) approaches. In this approach, the hysteresis comparator and the switching table are substituted with ANN controllers and then applied on both sides: machine-side converter (MSC) and grid-side converter (GSC) of a Permanent Magnet Synchronous Generator based Wind Energy Conversion System (PMSG-WECS). Moreover, to make the system more efficient in varying wind conditions, this study expands the utilization of the artificial neural networks (ANN) to encompass the maximum power point tracking (MPPT) control strategy. To demonstrate the effectiveness of the proposed approach on the system behaviors, a simulation test was carried out in the Matlab/Simulink environment, using a real wind profile of a Moroccan city (Essaouira). In comparison to the classical DPC control, the simulation results showed the superior performance of the proposed ANN-DPC control in terms of reference tracking, response time, overshoot, precision, and its capacity to reduce the rate of power ripples and total harmonic distortion (THD) in the injected currents. Furthermore, a robustness test was also included in this work to check the robustness of the proposed control against parameters variation. In conclusion, the feasibility and effectiveness of the ANN-DPC control approach were confirmed through experimental validation using the dSPACE DS1104 board.

Control Method of Load Sharing between AC Machine and Energy Storage Bank in the DC Grid

The article presents the issues related to load-power sharing in direct-current grid and a novel control method has advantages over known solutions. Unlike many similar-sounding papers, this article shows an attempt at creating fully controllable non-isolated system that allows for load-power sharing between a permanent magnet alternator equipped with machine-side converter (MSC) and a dual active bridge (DAB) tied to batteries or supercapacitor. The current-based load-power sharing is an essential feature of parallel-connected direct-current generators, and all types of voltage sources, in this way are contributing power to the system. To keep the optimal efficiency of the alternator, the rotational speed changes rely on proper mapping of the driving combustion engine. System components include a self-excited synchronous generator (SESG), operating at variable shaft speed, as well as batteries and supercapacitors that provide electricity for sudden electrical-load changes on the distribution grid. The core of the presented system is in a power-distribution method that consists of a programmed-controller structure allowing precise current distribution. A novelty of the proposed method is the use of a cascaded system of current and DC voltage regulators that allows for precise power-distribution control. In contrast with previously presented solutions, the proposed system allows for fast and accurate control of currents, loading parallel-connected DC voltage sources for wide-range generator speed changes. In the presented solution, both converters have been equipped with Schottky diodes, preventing the flow of equalizing currents between closed transistors in the parallel mode of operation. An experimental test-stand of the described system is presented with its theoretical basis and experimental results.

Hybrid ANFIS‐PI‐Based Robust Control of Wind Turbine Power Generation System

This paper introduces a novel hybrid controller designed for a wind turbine power generation system (WTPGS) that utilizes a permanent magnet synchronous generator (PMSG). This hybrid controller combines the adaptability of an adaptive neuro‐fuzzy inference system (ANFIS) with the simplicity of a proportional‐integral (PI) controller. The PI controllers are traditionally used for stability and noise handling. ANFIS adds adaptability, making it more suitable to cope with the variable nature of wind energy. The primary objective of this hybrid strategy is to augment the overall control performance and reliability of PMSG‐based WTPGS when encountered with continuous variable wind conditions. However, implementing the PI controller alone with the WTPGS often suffers from high overshoot and sluggish response in nonlinear systems like WTPGS. In contrast, ANFIS controllers offer superior performance to PI and other artificial intelligence controllers but are still susceptible to noise issues. In this paper, the proposed WTPGS system is designed in MATLAB/Simulink software where a hybrid controller (ANFIS‐PI) is implemented in the machine‐side converter (MSC) and grid‐side converter (GSC) of a variable speed PMSG‐based wind turbine to enhance its performance subjected to wind variations. The hybrid controller is implemented in such a way that the ANFIS controller is implemented in the outer layers while the PI controller is applied in the inner layers of both MSC and GSC. The simulation results for this hybrid controller in the MSC outperform those of the conventional PI controller. They demonstrate minimal overshooting and settling time, maintaining consistent stability even when subjected to various test signals at different intervals. Similarly, the GSC also surpasses conventional PI controllers, achieving a significant 6.4% reduction in maximum overshoot and a decrease of 4.36 seconds in settling time. This highlights its strong suitability for wind turbine applications.

Dynamic Performance Enhancement of a Self-Excited Induction Generator Connected to the Grid Using an Effective Control Algorithm

The current study aims to present a comprehensive analysis of a control technique used for improving the dynamic performance of a grid connected self-excited induction generator (SEIG). All components in the control system are modelled and explained in details. The management of SEIG operation is achieved through controlling the machine side converter using a new formulated predictive voltage control scheme (PVC). The proposed (PVC) is compared to field oriented control (FOC), model predictive current control (MPCC) and model predictive direct torque control (MPDTC) systems. MPDTC and MPCC have several drawbacks like high ripple, high load commutation, and using a weighting factor in their cost function, While FOC systems depend on machine parameters for variable estimation factors, need to use PI regulators and co-ordinate transformations, which complicate the system and slow down the dynamic response. The results obtained indicate that the proposed PVC is effective, as the ripples are reduced by 43% when compared to the MPDTC-used one and by 30% when compared to MPCC. Additionally, PVC's time response is less than that of the FOC by 15%, MPCC by 9%, and MPDTC by 4%. Furthermore, PVC produces 38% fewer commutations than MPCC and 40% fewer commutations than MPDTC. Consequently, the generator's efficiency and dependability both increased as a result of its better performance.

Analysis of Small-Disturbance Stability of Onshore Wind Power All-DC Power Generation System and Identification of Leading Factors

The application of conventional AC collection for the integration of large-scale renewable energy sources may lead to issues concerning harmonic resonance and reactive power transmission. Conversely, the utilization of an all-DC power generation system for wind power (WDCG) can effectively circumvent such issues. In contrast to the conventional power system, the interdependence among subsystems in the WDCG renders it susceptible to oscillation instability in the presence of minor disturbances. To address this concern, this paper first establishes a small-signal model for the WDCG, and validates the accuracy of this model by comparing it with an electromagnetic transient model based on PSCAD/EMTDC. Secondly, employing the eigenvalue analysis method, the principal oscillation modes of the WDCG are identified, and the state variables strongly correlated with these modes are analyzed using the participation factor method. Moreover, a quantitative assessment of the impact of operational and control parameters closely associated with the strongly correlated state variables on the negative damper oscillation model is conducted. The findings of the analysis reveal that the small-disturbance stability of the WDCG is significantly influenced by the operational parameters of the outlet capacitance of the ma-chine-side converter (MSC), the outlet capacitance of the direct current wind turbine (DCWT), the sub-module capacitance of the modular multilevel converter (MMC), and the inductance of the bridge arm. Additionally, the stability is al-so affected by the control parameters of the constant DC voltage control on the DCWT side, the voltage outer-loop–current inner-loop control, and the circulation suppression on the MMC side. The simulation results based on PSCAD validate the efficacy of the proposed method in identifying the dominant factors.

Controlling PMSG Wind Turbine Connected to Three Level Neutral Point Clamped Inverter Based on MPC

Wind energy generation systems are facing increasing importance in terms of harmonic distortion control and power quality standards. In recent years, variable speed has also risen rapidly due to advancements in power electronics. The three key elements of a wind power conversion system (WECS) are electrical generators, machine-side converters, and grid-side converters. It should be noted that the permanent magnet synchronous generator is one of the most often used types of electrical generators due to its special qualities. When wind energy is converted to the proper electrical power, it may be injected into the utility grid using either synchronous generators or grid-side converters. Therefore, an investigation of several topologies and control strategies is required to determine which is the best for the machine-side converter. The use of model predictive control (MPC) for a surface mount permanent magnet synchronous machine wind turbine is the main topic of this work. The machine's electrical model is the one that was utilized. The power converters are selected considering the intricate and highly nonlinear aerodynamic system of the wind turbines. MPC is a promising control technique despite being a relatively recent application in power electronics. In addition, MATLAB and Simulink are used to build the MPC code and offer a simplified model of the turbine.

Enhanced DC-link voltage control of PMSG-based wind turbine generators by machine-side converter during asymmetrical grid faults

Under asymmetrical grid fault conditions, oscillating active power can occur on the grid-side converter (GSC) of permanent magnet synchronous generator (PMSG)-based wind turbine generators. The oscillating active power flows into the DC-link, causing voltage oscillations that can lead to a shortened lifetime of DC-link capacitors and additional harmonics injected into the grid. While conventional methods can mitigate the oscillating active power through negative sequence current injection by the GSC, this hinders the grid support of the GSC regarding negative sequence reactive current during grid fault. To address this issue, a novel control scheme is proposed that uses the machine-side converter (MSC) to transfer the oscillating power to the motor. Firstly, the active power capacity of the MSC is analyzed and compared with that of GSC, and the results show that MSC has enough capacity to accommodate the oscillating active power. On this basis, a novel MSC control scheme is proposed to transfer the oscillating active power on the DC-link to the motor, which has a much larger inertia to buffer the power oscillation. Compared with conventional methods, the proposed control scheme relieves the GSC from mitigating the power oscillation to support the grid. Simulation studies using DIgSILENT PowerFactory are presented to verify the effectiveness of the proposed control scheme for PMSG-based wind turbine generators.

Configuration and control strategy for an integrated system of wind turbine generator and supercapacitor to provide frequency support

Wind turbine generators (WTGs) can provide fast frequency support to power systems through inertial control via the release of kinetic energy stored in rotating masses. However, because the kinetic energy is limited, the frequency support from WTGs based on inertial control cannot last until the system frequency recovers to the nominal value. Thus, it must be terminated during system frequency control, which results in adverse effects on the system frequency response. To guarantee sufficient energy and fast response for the frequency support of a permanent magnet synchronous generator based WTG, this study proposed the integration of a DC/DC converter-interfaced supercapacitor (SC) at the DC link of the WTG and consequently formed an integrated system of WTG and SC (WTG-SC system). First, the configuration of the SC was proposed based on the evaluation of the energy consumption of the WTG-SC system for frequency support and the available kinetic energy of the WTG. Second, a control structure that coordinates the machine-side converter (MSC), grid-side converter (GSC), and DC/DC converter of the SC was proposed. Finally, a “dual-droop” frequency support control scheme for the WTG was proposed to enhance the WTG-SC system’s frequency support capability and the efficiency of energy utilisation during frequency support. The efficacy of the proposed approach was validated using a modified IEEE 39 bus system with a wind farm comprising 100 WTG-SC systems under different operating conditions.

Coordinated Control for Seamless Integration of Wind Energy Conversion System With Small Hydrogenerator Through Modified Notch Filters

This paper deals with the seamless integration of doubly fed induction generator (DFIG) based wind energy conversion system (WECS) with local grid constituted by a permanent magnet based small hydrogenerator (PMHG). The seamless integration is carried out using a solid state static transfer switch (SSSTS). The WECS-PMHG system is operated using a coordinated control strategy based on modified notch filters. The modified notch filters are adopted for the computation of (a) sensorless speed and position of the DFIG rotor, (b) fundamental constituents of unbalanced/nonlinear load current and (c) filtered DFIG stator voltages and phase angle. Moreover, the notch filters are also used for mitigating the effects of unbalance/nonlinearity in load currents on the stator and rotor currents of DFIG as well as PMHG currents. Additionally, the control methodology ensures no power interaction between the WECS and the PMHG during the synchronization process. This enables transient-free WECS and PMHG currents. Further, the coordinated control regulates the amplitude and frequency of system voltages even amidst wide variations in wind speed and load. The DFIG stator and wind currents are injected at unity power factor with the system voltages, while the excitation requirement of the DFIG is met by its machine side converter. The validness of the control is demonstrated experimentally through a developed laboratory-scale test bench.

A Lifetime Improvement Active Thermal Control Strategy for Wind Turbine Parallel Converters Based on Reactive Circulating Current

When the wind turbine operates under frequently fluctuating mission profiles, the power semiconductors of its converter will generate low-frequency junction temperature fluctuations, resulting in accumulation of damage to the devices and affecting the converter’s lifetime. To address the above issues, an active thermal control (ATC) strategy based on reactive circulating current for the parallel converter of permanent magnet synchronous generator wind power system was proposed in this paper, by introducing reactive circulating current during sudden wind speed drops, the thermal cycle of the power semiconductor can be effectively smoothed. On the other hand, considering the impact of the proposed strategy on the voltage vector and modulation index of the converter, both the machine-side converter (MSC) and the grid-side converter (GSC) during the control process will be analyzed in detail, then the reactive current of GSC will be limited to prevent excessive modulation index and maintain system stability without reducing the filter size. Finally, a 2 MW wind power system is utilized as a benchmark, and both short-term simulation analysis and long-term numerical results reveal the effectiveness of the control strategy proposed in this paper.

MAXIMUM POWER EXTRACTION USING TWISTING SLIDING MODE CONTROLLER FOR WIND ENERGY SYSTEMS

This paper presents a systematic control scheme for a wind energy conversion system with variable speed and describes a permanent magnet synchronous generator PMSG with five phases. The machine employs back-to-back converters, while the grid-side converters are used. Stator current and mechanical rotation speed control are employed to accomplish maximum power point tracking operation on the machine side converter at wind speed below the rated speed. The pitch of the angle is used to limit the extracted wind energy when the wind surpasses the specified wind. The grid current control loop regulates both active and reactive power injection at the unity power factor for the grid side converter. The five-phase PMSG rotor speed is controlled by the twisting sliding mode controller in order to maintain the reference speed in various wind speeds. Performance comparisons between the twisting sliding mode controller, conventional proportional integral controller, and integral sliding mode controller show that the twisting sliding mode controller is superior to the other controllers in steady state error. According to this study, the overall efficiency is increased to 94% when using the TSMC controller rather than the ISMC and PI controllers, which are currently at 92.45% and 88.12% respectively. MATLAB/Simulink simulation results are used to verify the effectiveness of the suggested control technique.

An adaptive control strategy for grid-forming of SCIG-based wind energy conversion systems

One of the crucial issues in the expansion of isolated wind energy conversion systems (WECSs) is the design of a grid forming control structure that is robust to changes of the system’s operating point in the steady-state as well as transient conditions. This paper has addressed the voltage/frequency control of a local microgrid as well as flux and slip control of a squirrel cage induction generator that feeds the microgrid via a back-to-back converter in an isolated WECS. An adaptive nonlinear voltage control structure has been proposed for load side converter (LSC) consists of a constant frequency voltage regulator and a current controller based on the Lyapunov function method (LFM), which are connected in cascade. In an outer loop, the reference current of LSC is generated by the voltage regulator designated for maintaining the voltage/frequency of the microgrid. In an inner loop, the reference signals are robustly tracked by the current controller. In a novel reference frame that its angle difference with the stationary reference frame is determined by a dual loop DC link voltage controller, an LFM-based nonlinear flux controller is proposed for the machine side converter (MSC). Using the proposed flux control structure, in addition to maintaining the flux magnitude at a nominal value, by controlling the generator slip through adjusting the speed of the proposed reference frame, the power balance is established and the DC voltage is maintained at a pre-set value. The performance of the proposed controllers has been investigated through simulation in the MATLAB® software. The obtained results confirm the robustness and stability of the proposed control structure with respect to various disturbances and uncertainties.