High-performance Current Control Research Articles

Pole Placement-Based Current Control Method for CSI-Fed PMSM Drive With Eliminating Capacitor Voltage Sampling

This article proposes a pole placement based current control method for the current source inverter (CSI) fed permanent magnet synchronous machine (PMSM) drive with eliminating capacitor voltage sampling. Firstly, a generalized <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N$</tex-math></inline-formula> -order feedback form of motor current and CSI output current is proposed in the stationary <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\alpha \beta$</tex-math></inline-formula> frame, for the arbitrary pole placement of the control plant. With the proposed pole placement method, the resonance frequency is moved closer to the Nyquist frequency and the resonance peak is damped. On this basis, a linear controller is proposed in the synchronous <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$dq$</tex-math></inline-formula> frame for the high-performance current control of PMSM. Moreover, the control parameter selection method is presented based on the consideration of open-loop crossover frequency and phase margin (PM). In this way, the desired PM and enough gain margin (GM) can be achieved, thus guaranteeing the stability and robustness of the system. Finally, the effectiveness of the proposed method is verified by lab-scaled experiments.

Comparative Stability Analysis of Synchronous Reference Frame Current Controllers Operated at High Fundamental Frequency

Synchronous reference frame (SRF) proportional-integral (PI) current controller (CC) is the most well-established solution for current regulation in AC machine drives and grid-connected voltage source converters. The design of high dynamic performance current control loop has several challenges in high-speed and high-power applications due to the effects of controller gain’s selection, non-linearities, parameters variations, disturbances, digital implementation, and time delays. These become more significant due to high operating frequencies, which severely degrade dynamics and stability of the current control system. Various structures of SRF PI CCs have been reported in the literature. However, the aforementioned effects on the dynamics at high frequency operation have not been thoroughly addressed. Therefore, a comparative analysis of different SRF PI CCs’ structures is proposed in this paper, which addresses the design principles and gains’ selection while also taking into account the heavy computational burden and PWM delays. Additionally, the paper thoroughly analyzes and evaluates the dynamics and stability of the system operating at high fundamental frequencies. The advantages and limitations of each SRF PI CC scheme are studied and reported. The performance of the SRF PI CCs is comprehensively tested to demonstrate the analytical outcome of this study.

Discrete Domain Design Scheme of Complex-Vector Current Controller for Induction Motor at Low Switching Frequency

The synchronous coordinates complex-vector proportional–integral (PI) controller is a high-performance current controller for vector-controlled ac motors, which is designed based on the continuous domain motor models. However, the application of digital signal processors in motor control necessitates the conversion of continuous domain models to discrete domain models. Moreover, the digital control itself has delay effects. Therefore, the original performance of continuous-domain-designed current controllers may be degraded. In order to improve the deteriorative performance, this article proposes corresponding delay compensation schemes for the forward Euler, backward Euler, and trapezoidal method discretized complex-vector PI controllers, respectively, which are analyzed based on discrete domain models. The root locus, frequency characteristics, and bandwidth are utilized to evaluate the performance of these three discretized controllers at the low switching frequency. Finally, the simulation and experimental results validate the analysis and the delay compensation methods proposed in this article.

Two-Degree-of-Freedom Active Disturbance Rejection Current Control for Permanent Magnet Synchronous Motors

In the control of permanent magnet synchronous motors, the active disturbance rejection control (ADRC) has attracted considerable attention due to its intrinsic ability for disturbance rejection. However, the existing ADRC methods have the problem of coupling the reference tracking performance and disturbance suppression performance. To simultaneously improve the current control's dynamic response speed and steady-state control accuracy, a two-degree-of-freedom ADRC current control method based on the improved extended state observer (IESO) is proposed in this article. First, the designed IESO cancels the error correction term in the observed current update law to realize the complete decoupling of the reference tracking performance and disturbance suppression performance. Under the decoupling structure, the observed disturbance update law of the IESO is designed as a proportional-integral-repetitive control structure to suppress periodic and aperiodic disturbances. Then, the system stability is proved by analyzing the distribution of characteristic roots, and a two-step parameter tuning guideline of the IESO is provided. The proposed method realizes the complete decoupling of the reference tracking performance and disturbance suppression performance, reducing the complexity of the controller parameter selection and facilitating the realization of the high-performance current control. Finally, the effectiveness of the proposed method is validated by experimental results.

Analysis and Design of Multiple Resonant Current Control for Grid-Connected Converters

Including “generalized integrators” for sinusoidal signals, multiple resonant control (MRSC) scheme which can accurately compensate selected sinusoidal signals, is widely used as a high-performance current control method for grid-connected converters. In this article, the plug-in digital plug-in MRSC scheme is proposed to provide a general framework for housing various MRSC schemes, which plugs the MRSC controller into a stable feedback control loop. It can take advantages of both controllers—the feedback controller provides fast response and good robustness, and the MRSC controller offers accurate compensation of the periodic signals. More critically, based on a new type of sinusoidal signal model, the sufficient stability criteria and the gain tuning rules are developed to offer a simple universal approach to the design of the digital plug-in MRSC schemes. An application case study on the digital plug-in MRSC of a 5-kVA three-phase four-wire grid-connected inverter with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> filter is provided. Experimental results demonstrated that the proposed MRSC scheme can force the inverter to produce high-quality currents with high accuracy, fast transient response, and good robustness.

Variable Switching Frequency Control-Based Six-Step Operation Method of a Traction Inverter for Driving an Interior Permanent Magnet Synchronous Motor for a Railroad Car

Most railroad cars employ a natural ventilation cooling method. For this reason, severe problems occur in the control devices for the railroad cars due to the heat generated by the high-power switching loss. Therefore, the traction inverter for the railroad car requires a control method that can reduce the switching loss. In this paper, we propose a control method for an interior permanent magnet synchronous motor in consideration of the driving conditions of the railroad cars. The proposed method combines a variable switching frequency-based synchronous pulse width modulation control method, a flux-weakening control method that considers the maximum voltage modulation index, and an optimized over-modulation method. Through the proposed method, the utilization rate of the DC-link voltage can be maximized while lowering the switching frequency of the traction inverter as much as possible, and the high-performance current control can be performed in the entire speed region of the railroad car. The validity and effectiveness of the proposed method are verified by the simulation results and the experimental results.

Continuous terminal sliding mode control using novel fuzzy neural network for active power filter

This study aims to develop a continuous terminal sliding mode control using meta-cognitive fuzzy neural network for active power filter (APF). Different from conventional sliding mode-based APF current control strategy, high-performance current control can be assured using an integral-type terminal sliding surface to force the tracking error to zero in a finite time. Also, with the aim to reduce the chattering phenomenon owing to the large switching gain for typical sliding mode control, a novel sliding mode control design called continuous terminal sliding mode control (TSMC) is developed to soften the control signals. In addition, the control law is constructed based on meta-cognitive FNN rather than actual systems. Unlike the predefined structure approaches, meta-cognitive FNN can extract useful input data to adjust the networks structure and system parameters. Moreover, the stability and convergence analysis are presented to satisfy the control objectives and system stability requirements at the same time. Experimental results verify that proposed continuous TSMC using meta-cognitive FNN reveal superior features compared with other existing control approaches.

High performance current control of single‐phase grid‐connected converter with harmonic mitigation, power extraction and frequency adaptation capabilities

Grid-connected converters in distributed generation systems are required to operate under highly distorted voltage with a wide frequency range, and to provide active/reactive power information for ancillary services and power control. This paper presents multiple unbalanced synchronous reference frame control for regulating and mitigating the grid current distortion of a voltage source converter caused by grid voltage distortion and converter deadtime. The proposed control technique has intrinsic power extraction and frequency adaptation capabilities. The multiple unbalanced synchronous reference frame control is compared with the proportional multi-resonant control. A new controller which combines the unbalanced synchronous reference frame control for regulation of the fundamental component current and the multi-resonant control for harmonic compensation is presented. The proposed control techniques were verified with a 1.5-kVA LCL-filtered grid connected inverter. The multiple unbalanced synchronous reference frame control with odd harmonic orders 3rd to 13th exhibited excellent harmonic rejection with a total harmonic distortion (THD) less than 0.60% under a highly distorted voltage. The proposed combined control technique provided slightly inferior performance with the grid current THD less than 0.65%. The combined control scheme retains functionalities as the multiple unbalanced synchronous reference frame control with a significant reduction of computational effort.

Intelligent Global Sliding Mode Control Using Recurrent Feature Selection Neural Network for Active Power Filter

This study develops an intelligent global sliding mode control using recurrent feature selection neural network for active power filter (APF). First, the dynamic model of an APF is constructed. Second, a conventional global sliding mode control (GSMC) is introduced to achieve the aim to track the quick changing reference signal for an APF current control strategy. Since uncertain parameters of APF are unavailable in advance, high performance current control cannot be assured in practical applications. In this article, to improve conventional GSMC for APF, the recurrent feature selection neural network (RFSNN) is proposed to learn uncertain function. Unlike the classical neural network, RFSNN can select useful network parameters and delete unfavorable network parameters to adjust the structure and parameters of the neural networks. Based on Lyapunov stability analysis, the online learning laws for network parameters are derived to satisfy the control objectives. Finally, the superiority and robustness of the proposed GSMC using RFSNN are verified by detailed experimental results.

Multivariable sliding‐mode extremum seeking PI tuning for current control of a PMSM

High-performance current control is critical for obtaining smooth output torque in permanent-magnet synchronous motors (PMSMs). To this end, a new proportional–integral (PI) tuning method based on multivariable sliding-mode extremum seeking is proposed in this study and applied for current control of a PMSM. In the proposed method, a sliding-mode extremum seeking optimiser varies the PI gains by minimising a cost function based on the feedback error term. The resulting PI controller can achieve fast and accurate tracking response, high disturbance rejection, and low sensitivity to PMSM parameter variations. The stability of the proposed control strategy is investigated through a Lyapunov analysis and its performance is evaluated through experimental studies. The results indicate that the proposed controller can offer improved performance in terms of accuracy, parametric variations, and load torque disturbances when compared with a conventional PI and a recently proposed PI controller using the gradient-based extremum seeking tuning method.

Low-Switching-Loss Finite Control Set Model Predictive Current Control for IMs Considering Rotor-Related Inductance Mismatch

This paper develops a high-performance finite control set model predictive current control (FCS-MPCC) method for induction motors (IM) to ensure the system control performance over the low-switching-frequency (LSF) range, where the switching loss is low. The new controller is based on tripartite calculations in each control period and sliding mode (SM) rotor-related inductance observer. In detail, firstly, to solve the problem that the control performance of the traditional FCS-MPCC methods is low when they are used at low frequencies, tripartite calculations are employed in each control period to improve the prediction accuracy. By dividing one control period into three equal parts and executing the prediction algorithm in each subsection, the current estimation errors become lower compared to the conventional single-step Euler-discretization controller. Then, considering that the performance of an FCS-MPCC controller highly relies on the machine parameter values, but it is hard to directly obtain the accurate rotor-related inductances (mutual inductance and rotor inductance), this paper uses an online parameter observer based on the sliding mode (SM) principle to diagnose them in real time. It needs to be mentioned that when discussing the stability of the sigmoid-function-based SM observer, a new technique called estimation-error-limitation is initially adopted in this paper to simplify the analysis process. Finally, the proposed algorithms are verified by simulation, which is conducted on a three-phase IM at LSF situations.

Inner Loop Design for PMLSM Drives With Thrust Ripple Compensation and High-Performance Current Control

To realize the precise thrust force control in permanent magnet linear synchronous motor (PMLSM) drives, this paper studies a novel design method of the high-performance current inner loop. First, to increase the control bandwidth, an optimized predictive current controller, which takes account of the one-step delay issue, is presented on the basis of the discrete-time model of the PMLSM. Second, as disturbance factors, the thrust ripple and parameter variation can influence the input and output command of the current controller, respectively. Therefore, an improved sliding mode algorithm with the variable exponential reaching law is introduced to suppress these two disturbances simultaneously, and the stability analysis is given to prove the convergence of the algorithm through the Lyapunov stability theory. Finally, a precise experimental platform on account of the aerostatic guide is established, and experimental results are given to demonstrate the feasibility of the proposed control scheme.

Deadbeat control based on a multipurpose disturbance observer for permanent magnet synchronous motors

Robustness against parameter mismatches and position-sensorless operation are two important research topics for permanent magnet synchronous motor (PMSM) drives. Usually, the existing observers are designed for achieving a specific function. While here, both the above two functions are integrated into the proposed sliding-mode disturbance observer: (i) if a position sensor is equipped, accurate current regulation can be achieved by deadbeat predictive current control despite mismatched motor parameters; (ii) if the position sensor is not equipped but with a good estimation of motor parameters, the observer can serve as a back electromotive force estimator. Then, the rotor position can be extracted for position-sensorless control. Usually, a low-pass filter is required to suppress high-frequency noises in the conventional sliding-mode observer. This inevitably leads to phase delay in the estimation. By comparison, a complex coefficient filter is inherently embedded in the proposed method, which can provide accurate estimation without phase delay or magnitude error. Experimental results obtained from a 2.4 kW PMSM drive platform indicate that high-performance current control can be achieved with good robustness for position sensor-based operation. Also, rotor position can be accurately estimated with good steady and dynamic performance for position-sensorless operation.

High-Bandwidth and Strong Robust Current Regulation for PMLSM Drives Considering Thrust Ripple

This paper presents a high-performance current controller for the permanent-magnet linear synchronous motor considering the bandwidth and disturbances caused by the parameter variation and thrust ripple. First, an improved predictive current control (PCC) scheme based on the discretized model is proposed to increase the current control bandwidth. Besides the time-delay issue, it is noteworthy that the parameter variation in the PCC method can degrade the steady-state response. Through utilizing the information of first two sampling periods, the proposed PCC strategy can overcome such two issues at the same time. Second, a new discrete-time linearization observer is designed to estimate the thrust ripple. Then, the ripple can be suppressed by injecting the estimated value into the control system. Meanwhile, the stability analysis is given by the Lyapunov stability theory. A precise test platform based on the aerostatic guideway is established, and experimental results are shown to demonstrate the effectiveness and correctness of the proposed scheme.

A Robust Predictive Current Controller for PMSM Drives

High-performance current control is required to obtain a smooth output torque in permanent-magnet synchronous motor (PMSM) drives. In this manner, a new discrete-time robust predictive current controller is presented for PMSM drives. Controller and current prediction schemes are designed based on the dead-beat structure. The dead-beat control has good transient response, but it suffers from parametric uncertainties and unmodeled dynamics. In order to provide robustness, a discrete-time integral term is added to the dead-beat current prediction. The stability analysis is carried out considering the prediction error dynamics, nonlinear uncertain model of PMSM, and the integral action as the states of the overall system. The designed robust predictive controller is tested through numerical simulations and experiments. The proposed controller is easy to implement and suitable for high-performance PMSM applications.

Inductor Compensation in Three Phase PFC Control with Decoupling the Input Voltage and Bus Voltage

As the nonlinear structure of the boost ac/dc topology, the PFC is difficult to be controlled. The average state space theory has revealed that the choke current is determined by duty-ratio coupled with input voltage and bus voltage, which makes the high-performance sine-wave current track control more challenging. To remove disturbing variables and reduce the zero-crossing distortion, the decoupling control strategy is presented. Also, it is shown in this paper that the variable inductance has a great influence on PFC and THDI. As the inductor in boost converter varies with the current, a compensating coefficient of current is also proposed. The decoupling strategy and the inductor compensation strategy are implemented on a UPS with three phase input voltage. Numerical simulation and experimental results has indicated the high-performance of these control strategy.

Current Harmonics From Single-Phase Grid-Connected Inverters—Examination and Suppression

Environmental conditions and operational modes may significantly impact the distortion level of the injected current from single-phase grid-connected inverter systems, such as photovoltaic (PV) inverters, which may operate in cloudy days with a maximum power point tracking, in a nonunity power factor, or in the low-voltage ride-through mode with reactive current injection. In this paper, the mechanism of the harmonic current injection from grid-connected single-phase inverter systems is thus explored, and the analysis is conducted on single-phase PV systems. In particular, the analysis is focused on the impacts of the power factor and the feed-in grid current level on the quality of the feed-in grid current from single-phase inverters. As a consequence, an internal model principle-based high-performance current control solution is tailor-made and developed for single-phase grid-connected systems to produce high-quality currents in different operation conditions, where a design procedure is also provided. The developed current controller in this paper can achieve a minimum steady-state error while maintaining a relatively fast transient response, and also being feasible in other single-phase applications as a promising harmonic mitigation solution. Experiments on single-phase grid-connected systems have verified the correctness of the relevant analysis and also the effectiveness of the tailor-made control solution in terms of good harmonic mitigation.

PQ변동을 이용한 개선된 계통 임피던스 추정기법

In a weak grid condition, the precise grid impedance estimation is essential to guaranteeing the high performance current control and power transfer for a grid-connected inverter. This study proposes a precise estimation method for grid impedance by PQ variations by employing the variation method of reference currents. The operation principle of grid impedance estimation is fully presented, and the negative impact of the phase locked loop is analyzed. Estimation error by a synchronization angle in the park`s transformation using the phase locked loop is derived. As a result, the variation method of reference currents for accurate estimation is introduced. The validation of the proposed method is verified through several simulation results and experiments based on a 2-kW voltage source inverter prototype.

High Performance Current Controller for Sparse Matrix Converter Based on Model Predictive Control

A novel predictive current control strategy for a sparse matrix converter is presented. The sparse matrix converter is functionally-equivalent to the direct matrix converter but has a reduced number of switches. The predictive current control uses a model of the system to predict the future value of the load current and generates the reference voltage vector that minimizes a given cost function so that space vector modulation is achieved. The results show that the proposed controller for sparse matrix converters controls the load current very effectively and performs very well through simulation and experimental results.

왜곡된 전원 전압하에서 Composite 관측기를 이용한단상 PWM 컨버터의 정현파 전류 제어

본 논문에서는 composite 관측기를 이용하여 전원전압 왜곡시 단상 PWM 컨버터의 고성능 전류제어를 제안한다. composite 관측기를 적용함으로써 전원 전압 및 전류의 기본파와 고조파 성분을 시간지연 없이 추출할 수 있다. 추출된 기본파 성분은 전원단의 페이저 각을 찾는 PLL시스템에 이용된다. 멀티 비례-공진 제어기로 단상 입력전류를 정현파로 제어하고 고조파 성분을 제거한다. 시뮬레이션과 실험 결과로 제안된 방법의 타당성을 검증한다. In this paper, a high-performance current control for the single-phase PWM converter under distorted source voltages is proposed using a composite observer. By applying the composite observer, the fundamental and high-order harmonic components of the source voltage and current are extracted without a delay. The extracted fundamental component is used for a phase-lock loop (PLL) system to detect the phase angle of the source voltage. A multi-PR (proportional-resonant) controller is employed to regulate the single-phase line current. The high-order harmonic components of the line current are easily eliminated, resulting in the sinusoidal line current. The simulation and experimental results have verified the validity of the proposed method.