Axis Current Reference Research Articles

Probabilistic Robust Damping Controller Optimization for Mitigating Subsynchronous Control Interaction in DFIG and PMSG‐Based Wind Farms

ABSTRACTAdvanced control and mitigation solutions are required due to the enormous challenges posed by sub‐synchronous control interaction in wind farms. These concerns include system instability, potential damage to turbines, and grid stability issues. This research presents the probabilistic robust damping controller, an adaptive control approach, to address the issues in grid‐connected wind farms. The innovation employs the balanced remora optimization algorithm to optimize controller parameters, ensuring system stability under various conditions. For permanent magnet synchronous generator‐based wind farms with weak grid circumstances, critical elements such as the DC‐link voltage, the d‐q axis current reference, and the actual values in the grid‐side converter are essential for problem mitigation. The controller generates controlled output using these input signals. The MATLAB‐based implementation demonstrates the controller effectiveness in damping issues within a series‐compensated doubly fed induction generator. Comparative analysis with conventional controllers under different grid conditions and disturbances validates its superior performance. Time‐domain simulations, both with and without time delay, further confirm the controller's ability to enhance system stability and dampen the issues. Four schemes are used to evaluate the doubly fed induction generator‐based wind farms: wind speed at 13 m/s with 75% series compensation, 7 m/s with 75% compensation, 9 m/s with 45% compensation, and 9 m/s with 60% compensation. Under short circuit ratio, the wind farms based on permanent magnet synchronous generators are analyzed in three scenarios: normal, strong, and weak cases.

A Simple Model Predictive Instantaneous Current Control for Single-Phase PWM Converters in Stationary Reference Frame

The traditional proportional–integral (PI) based current control for single-phase pulsewidth-modulation (PWM) converters in railway traction applications either has a steady-state error or a poor dynamic response. Deadbeat instantaneous current control (ICC) cannot eliminate the steady-state error due to approximation errors of the linear extrapolation. Compared with PI-based direct current control, continuous-control-set (CCS) model predictive control (MPC) implemented in a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d-q</i> frame offers better performance, but its dynamic response is still slower than ICC. To solve these problems, a simple model predictive (MP) ICC scheme for single-phase PWM converters is proposed in this article. The optimal modulation function is calculated in the stationary reference frame by the CCS-MPC principle without <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">β</i> -axis current estimation and reference frame transformation. The proposed MP-ICC scheme can keep the fast dynamic response characteristics of ICC and achieve zero steady-state error. In addition, it has the advantages of low current harmonics and low computational complexity. The influence of the inductance parameter mismatch on the current loop is analyzed in detail, and a phasor-method-based inductance parameter online estimation is developed. This solution can be executed during the idle time of the digital processor without making the control delay longer. Finally, a comprehensive experimental comparison with four existing current control schemes is conducted to verify the feasibility and effectiveness of the proposed scheme.

Torque Pulsation Reduction During Magnetization in Variable Flux Machines

This paper proposes two methods to minimize the pulsating torque during magnetization in a variable flux - permanent magnet synchronous machine (VF-PMSM). The VF-PMSM is demagnetized and remagnetized by injecting a current pulse to achieve the high speed and high torque requirements. During demagnetization and remagnetization, a d – axis current pulse is injected to change the magnetization state (MS). These MS changing current pulses will change the magnet flux linkage based on the amplitude of the pulse. However, the injected d – axis current abruptly changes the magnet torque as well as reluctance torque and results in a pulsating torque. Since the remagnetization current is much higher than the machine rated current, the pulsating torque is more severe during the remagnetization process. Thus, it is preferred to magnetize the magnet at zero speed and unloaded conditions. To solve this problem, a q – axis current reference during the remagnetization is determined by two different methods: voltage limit method and load torque method. The derived q – axis current reduces the torque pulsation during the remagnetization. The effectiveness of the proposed scheme is experimentally verified on a manufactured VF-PMSM prototype.

Model Predictive Control for ARC Motors Using Extended State Observer and Iterative Learning Methods

The arc permanent magnet motor (arc motor) is widely used in large telescope for its high efficiency and high power density. Due to the unique structure, the periodic end torque, cogging torque and flux harmonics will cause certain speed ripples which can affect the performance of the drive system. To solve these problems, the paper proposes a novel model predictive control (MPC) based on extended state observer and iterative learning control, where the MPC is equipped in speed loop and the disturbances estimated by the conventional extended state observer (ESO) are fed forward to the controller to improve the ability of disturbance rejection. A position dependent iterative learning control (ILC) is used to estimate the periodic disturbances at different speeds. The MPC calculates the q axis current reference with the compensation of ESO and ILC, which can have a fast response and disturbance rejection ability for periodic and nonperiodic disturbances. The stability of the proposed method is demonstrated by theoretical analysis. The experimental results validate the effectiveness of the proposed method at different speeds.

Improved Voltage Flux-Weakening Strategy of Permanent Magnet Synchronous Motor in High-Speed Operation

This paper presents an improved voltage flux-weakening strategy of a permanent magnet synchronous motor (PMSM) in a high-speed operation. The speed control performance using voltage flux-weakening control is not affected by the motor parameters, so it is used in various motors for high-speed operations. In general, the voltage flux-weakening control uses voltage references to generate a flux axis current reference. However, there may be errors between the voltage reference and the actual voltage flowing into the motor. This causes an error in the current reference generation and reduces the efficiency of the inverter and motor due to the use of more current. In this paper, the problems that can occur due to voltage errors were analyzed through theoretical approaches and simulations, and improved voltage flux-weakening control to resolve these problems was presented. This method’s advantage is that the error between the voltage reference and the voltage applied to the motor can be minimized, and the target speed can be reached with minimum current. As a result, it was possible to increase the energy efficiency by reducing the amount of current flowing through the motor. The effect of the improved voltage-based flux-weakening control method was verified through simulations and experiments. As a result, the voltage errors were reduced by approximately 2.16% compared to the general method. Moreover, the current used in the field-weakening control region was reduced by up to 27.17% under the same torque condition.

D-STATCOM d-q Axis Current Reference Control Applying DDPG Algorithm in the Distribution System

The high penetration level of renewable energy in large-scale power systems could adversely affect power quality, such as voltage stability and harmonic pollution. This paper assesses the impacts of Distribution Static Compensator (D-STATCOM), one of the Flexible AC Transmission System (FACTS) devices, on power quality of 4.16kV-level distribution systems via transient and steady-state analysis. Carrier-based Pulse Width Modulation (PWM) control in D-STATCOM generates d-q axis current reference via the PID (Proportional-Integral-Differential) controller to control d-q axis current and voltage. A new control method, via the Deep Deterministic Policy Gradient (DDPG) algorithm-based reinforcement learning (RL), is studied to create a new d-q axis current reference applying to the voltage control, which can improve voltage stability and transient response and derive fast convergence of current and voltage at the D-STATCOM bus. The real-time simulations on an IEEE 13-bus system show that the proposed approach can better control the D-STATCOM than the conventional control methods for enhancing voltage stability and transient performance.

Evaluation of Efficient Operation for Electromechanical Brake Using Maximum Torque per Ampere Control

This paper deals with efficient operation method for the electromechanical brake (EMB). A three-phase interior permanent magnet synchronous motor (IPMSM) is applied to the EMB operation. A current controller, speed controller, and position controller based on proportional-integral (PI) control are used to drive the IPMSM. Maximum torque per ampere (MTPA) control is applied to the current controller to perform efficient control. For MTPA control, the angle β is calculated from total input current, and the synchronous frame d–q axis current reference is determined by the angle β. The IPMSM is designed and analyzed with finite element analysis (FEA) software and current control is simulated by Matlab/Simulink using a motor model designed by FEA software. The simulation results were verified to compare with experimental results that are input current and clamping force of caliper. In addition, the experimental results showed that the energy consumption is reduced by MTPA.

Stability Improvement for Three-Phase Grid-Connected Converters Through Impedance Reshaping in Quadrature-Axis

Three-phase AC−DC and DC−AC power converters have been extensively employed as grid-interfaces in various applications, e.g., distributed generation and energy storage systems. In these applications, power converters should always synchronize with the mains grid so that active and/or reactive power can properly be regulated while maintaining desired waveforms of grid currents. Grid synchronization necessitates accurate information of grid voltages, which is normally obtained through phase-locked-loops (PLLs). However, the employment of PLLs may bring in stability concerns. Previous research revealed that the inclusion of PLLs shapes the impedance of power converters into a negative resistance in the quadrature-axis ( q -axis), and this should be responsible for instability. To resolve the instability issue caused by PLLs, this paper proposes an impedance controller for reshaping the q -axis impedance into a positive resistance in the low-frequency band. Without any extra burden on system hardware, the proposed controller can easily be implemented by directly relating the q -axis voltage to the q -axis current reference. As a result, the presented three-phase power conversion system can operate stably even under a severely weak grid condition, which are verified by simulation and experimental results.

Direct DC-Link Current Control Considering Voltage Saturation for Realization of Sinusoidal Source Current Waveform Without Passive Components for IPMSM Drives

In order to reduce the cost and the size of a single-phase to three-phase power converter, an electrolytic capacitor-less single-phase to three-phase inverter is proposed. As the system does not have energy storage, such as an electrolytic capacitor, it results in source current harmonics due to the spatial harmonics of the motor. Adding an inductor for filtering the source current harmonics increases the cost and size of the system. In order to improve the source current waveform without adding passive components, it is necessary to reduce the source current harmonics via inverter control. However, when the inverter control reduces the source current harmonics, voltage saturation of the inverter causes source current distortion. At the rated speed and load, the voltage saturation region amounts to 40-50% of the source period, and the source current harmonics do not meet the guideline of IEC 61000-3-2. This paper proposes a direct dc-link current control (DDCCC) considering voltage saturation and the dq -axis current reference calculation for applying the DDCCC, which reduces the source current harmonics below the guideline. The effectiveness of the proposed method is verified through experiments.

Realization of Maximum Torque per Ampere Control for IPMSM Based on Inductance Segmentation

In order to solve problems associated with inductance parameter changes on traditional maximum torque per ampere (MTPA) control method for interior permanent magnet synchronous motor, such as large amount of computation, complicated control system, and low control precision, an MTPA control method based on inductance segmentation is proposed. Considering the effects of magnetic saturation, the inductance parameters are processed by segmentation analysis. The Newton iteration method is used to solve the correspondence between the electromagnetic torque and the optimum ${d}$ – ${q}$ axis current components, and the subsection curve is fitted to achieve MTPA control. By analyzing and processing inductance parameters, this control method improves the accuracy of control system. The ${d}$ – ${q}$ axis current reference is realized by piecewise curve fitting to improve the dynamic performance of the system. Finally, the dynamic performance of this method is compared with that of the traditional method through simulation and experiment. The simulations and experiments results show that this method has the advantages of fast dynamic response, high control accuracy, and simple implementation.

Cancellation of Torque Ripples With FOC Strategy Under Two-Phase Failures of the Five-Phase PM Motor

This paper investigates torque ripples cancellation of a five-phase (5Ph) permanent magnet (PM) motor under open fault of two phases, where failure phases are either adjacent or nonadjacent. In recent works, torque ripples cancellation is performed at a stationary frame and postfault current solutions for constant output torque are complicated. To implement field-oriented control (FOC) and carrier-based pulse width modulation, reduced-order Clarke and Park transformations are proposed. With the coordinate transformation, a 5Ph motor model under unbalanced conditions has been decoupled. Along with this, the fundamental torque at the d-q frame also remains the same as the healthy case. However, third harmonic of winding density distribution results in torque ripples. To reduce dependence on mathematical model of torque ripples, sliding mode control is employed to calculate q -axis current reference while keeping constant the rotor speed. Decoupled models corresponding to two types of faults, which are adjacent and nonadjacent open fault, are confirmed by finite element analysis, and effectiveness of proposed torque ripples cancellation method is verified on the 5Ph drive in the laboratory.

Voltage Control Technique for the Extension of DC-Link Voltage Utilization of Finite-Speed SPMSM Drives

This paper presents a new voltage control technique which extends dc-link voltage utilization for finite-speed surface-mounted permanent magnet synchronous motor drives. Therefore, significantly increasing the output power and torque under flux-weakening operation can be achieved. The switching period and summation of active switching times for inverter pulsewidth modulation control are used to modify the -axis current reference under the flux-weakening region such that the voltage trajectory of inverter output can be extended to move to the hexagon of the space vector modulation, thereby extending the utilization of dc-link voltage. Moreover, it will be shown that the proposed voltage control technique has some additional special features, such as not sensitive to motor parameter, no need of voltage and current feedback, and no need of lookup table. The presented method is realized by software and does not require additional hardware. Comparisons of experimental results will be presented for confirming the presented technique.

Optimum Trajectory Control of the Current Vector of a Nonsalient-Pole PMSM in the Field-Weakening Region

Industry-proven field-weakening solutions for nonsalient-pole permanent-magnet synchronous motor drives are presented in this paper. The core algorithm relies on direct symbolic equations. The equations take into account the stator resistance and reveal its effect on overall algorithm quality. They establish a foundation for an offline calculated lookup table which secures effective <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis current reference over entire field-weakening region. The table has been proven on its own and in combination with a PI compensator. Usage recommendations are given in this paper. Functionality of the proposed solutions has been investigated theoretically and in practice. The investigation has been carried out in the presence of motor magnetic saturation and parameter tolerance, taking into account the change of operating temperature. The results and analysis method are included in this paper.

Sensorless Position Control of Permanent-Magnet Motors With Pulsating Current Injection and Compensation of Motor End Effects

The sensorless position control of permanent-magnet motors is successfully implemented by superimposing a high-frequency voltage signal on the voltage reference or adding a high-frequency current signal to the current reference. The former approach is usually preferred because of its simplicity, although the latter one may allow better performance. This paper presents a new algorithm for the sensorless control of low-saliency permanent-magnet synchronous motors based on high-frequency sinusoidal current signal injection into the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis. Different from the related literature, the position information is derived by analyzing the measured high-frequency currents. The amplitude of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis voltage reference is also exploited to improve performance. A proportional-integral (PI) controller plus a resonant term (PI-RES) is adopted to ensure the accurate tracking of both the dc and high-frequency components of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis current reference. The main advantages of the proposed approach are the increased accuracy and sensitivity with respect to the approach based on voltage injection, the insensitiveness to inverter nonlinearities that are compensated by the current regulation loop, the actual control on the injected current value, and the practical absence of acoustic noise. Experiments on a linear tubular permanent-magnet synchronous motor prototype have been carried out to verify the aforementioned advantages. This paper also presents a discussion of the parameters of the PI-RES.

Online Minimum-Copper-Loss Control of an Interior Permanent-Magnet Synchronous Machine for Automotive Applications

This paper presents an algorithm to calculate the current references on line, considering the inherent nonlinear nature of the saturation effect in an interior permanent-magnet synchronous machine for the minimum-copper-loss control under the current and voltage limit of the drive system. This paper basically approaches this issue as a nonlinearly constrained optimization problem where the torque command imposes the nonlinear equality constraint and the voltage limit imposes the nonlinear inequality constraint. Depending on the operating region, it solves the corresponding set of nonlinear equations in real time derived from the Lagrange multiplier method. Newton's method among various techniques is adopted to implement the numerical solution. This scheme gives accurate results not only in motoring but also in generating operation of the machine, since the voltage drop of the stator resistance is taken into account, which is hardly applicable to a two-dimensional lookup table where the inputs are the torque command and the maximum flux amplitude, and the output is each axis current reference in the rotor reference frame. The simulation and experimental results show the feasibility and performance of the proposed technique