Sliding Mode Current Controller Research Articles

Islanded microgrid: hybrid energy resilience optimization

To maintain a dependable and sustainable power supply in a microgrid system, it is crucial to combine renewable energy sources with hybrid energy backup. To achieve maximum output power from solar source, a high gain DC-DC boost converter is managed using the dual Kalman filter based perturb and observe approach. A sliding mode current controller at a three phase inverter with an LC filter is intended to follow an undisturbed reference voltage. To effectively manage the power flow and optimize the utilization of available resources, a robust power management algorithm is required. The novel power management algorithm for a solo operated renewable distribution generation unit with hybrid energy backup in a microgrid is introduced. The algorithm aims to dynamically allocate power among various sources, storage systems, and loads, considering their characteristics and the overall system constraints. The algorithm utilizes sliding mode control techniques to regulate the current flow from the renewable generator and effectively manage the power allocation among different energy sources, storage systems, and loads.

Intelligent fuzzy back-stepping observer design based induction motor robust nonlinear sensorless control

Introduction. The control algorithm of Induction Motor (IM) is massively dependent on its parameters; so, any variation in these parameters (especially in rotor resistance) gives unavoidably error propagates. To avoid this problem, researches give more than solution, they have proposed Variable Structure Control (VSC), adaptive observers such as Model Reference Adaptive System, Extended Luenberger Observer (ELO) and the Extended Kalman Filter (EKF), these solutions reduce the estimated errors in flux and speed. As novelty in this paper, the model speed observer uses the estimated currents and voltages as state variables; we develop this one by an error feedback corrector. The Indirect Rotor Field Oriented Control (IRFOC) uses the correct observed value of speed; in our research, we improve the observer’s labour by using back-stepping Sliding Mode (SM) control. Purpose. To generate the pulse-width modulation inverter pulses which reduce the error due of parameters variations in very fast way. Methods. We develop for reach this goal an exploration of two different linear observers used for a high performance VSC IM drive that is robust against speed and load torque variations. Firstly, we present a three levels inverter chosen to supply the IM; we present its modelling and method of control, ending by an experiment platform to show its output signal. A block diagram of IRFOC was presented; we analyse with mathematic equations the deferent stages of modelling, showed clearly the decoupling theory and the sensorless technique of control. The study described two kinds of observers, ELO and EKF, to estimate IM speed and torque. By the next of that, we optimize the step response using the fuzzy logic, which helps the system to generate the PI controller gains. Both of the two observers are forward by SM current controller, the convergence of SM-ELO and SM-EKF structures is guaranteed by minimizing the error between actual and observed currents to zero. Results. Several results are given to show the effectiveness of proposed schemes.

Decoupled average model-based sliding mode current control of LC-filtered inverters in rotating frame

Recently, LC-filtered inverter has been a trendy research object towards the efficient exploitation and use of sustainable energy sources. The nested control scheme of the system includes a voltage control loop and a current one, which can be developed on the rotating frame. The conventional PI controller is employed for the outer loop voltage controller and it performs effectively. However, the PI current controller introduces delay to the system and overshoot occurs frequently due to the influence of nonlinear load. This paper proposes a novel method of decoupled average model-based sliding mode current control performing faster response and better tracking performance of the desired current. Besides, the comprehensive model of the nonlinear load is applied to examine the robustness of the proposed control scheme. This method is developed on the average model, fixed-frequency PWM can therefore be used to modulate the inverter. The novel method is compared with a conventional PI current controller. Offline simulation on MATLAB/Simulink and real-time simulation using Opal-RT experimental platform prove the advantages of the proposed current controller considering critical scenarios with the nonlinear load.

Robust and efficient control strategy for single-phase two-stage PV grid-tied system with improved power quality

In the last couple of decades, the integration of photovoltaic (PV) systems with the utility grid has gained significant attention due to its potential to harness renewable energy and contribute to sustainable power generation. However, the integration of the PV system into the grid leads to issues related to power quality and system stability under varying solar irradiation, dc offset, and distorted grid conditions. Therefore, this paper focus on the robust and efficient control of a single-phase, two-stage PV grid-tied system to improve power quality and stable system operation under abnormal grid conditions. These objectives can be achieved using the synchronization method, dc link voltage control, and grid current control. The hybrid PLL is proposed in this paper for synchronization and to mitigate the effect of dc offset and lower-order harmonics in the estimated phase and frequency. Further, the sliding mode voltage controller and integral sliding mode current controller are proposed for dc link voltage regulation and grid current tracking. The stability of voltage and current control loops is analyzed using the Lyapunov stability theory. Furthermore, the proposed schemes are validated using MATLAB simulation and experimental analysis. The proposed approach outperforms conventional methods and exhibits better disturbance rejection capability under both dynamic and steady-state conditions, making it a robust and efficient control strategy for grid-tied systems.

Observer-Based Second-Order Sliding Mode Current Controller for Thyristor-Controlled LC-Coupling Hybrid Active Power Filter

In this paper, a second-order sliding mode observer (SOSMO) based second-order sliding mode controller (SOSMC) for the TCLC-HAPF is proposed. The proposed SOSMO based SOSMC ensures the TCLC-HAPF low steady-state error, fast dynamic response, fixed switching frequency, and good system robustness under parameter variation and non-ideal grid conditions. First, the SOSMO for the TCLC-HAPF system model is proposed, and its parameter design is provided. Based on the SOSMO model, the SOSMC for the TCLC-HAPF is proposed and designed accordingly. Then, simulation studies and experiments on a three-phase TCLC-HAPF are carried out to verify the steady-state and dynamic performance of the proposed SOSMO based SOSMC compared with the other existing current controllers: proportional-integral controller, hysteresis current controller and multi-quasi-proportional-resonant controller. Finally, the system robustness, unbalance compensation capability, and DC-link voltage control performance of the proposed SOSMO based SOSMC under different non-ideal grid conditions are also verified by simulation and experimental results.

A step-by-step full-order sliding mode controller design for standalone inverter-interfaced cleaner renewable energy sources

Power electronic inverters are one of the most significant components for the integration of clean energy systems and the proper control of these power electronic interfaces helps to enhance power quality. This paper presents a robust step-by-step full-order sliding mode voltage control strategy for standalone single-phase inverters that can be interfaced with cleaner renewable energy sources. The proposed controller employs a cascaded method through outer- and inner-loops to facilitate tracking of the desired load voltage. In contrast to the most commonly used sliding mode techniques for interfacing these cleaner energy sources, which usually utilize the canonical-form of the system’s state-space model, the designed controller uses a block-controllable model that mitigates unwanted noises. To design the controller, the capacitor voltage and the inductor current of the LC filter are measured to be employed in the outer second-order sliding mode voltage control loop and the inner first-order sliding mode current control loop, respectively. The utilization of such full-order sliding surfaces in each step effectively reduces the chattering in the control signals as well as facilitates the transient and steady-state responses with less harmonic distortion and thereby, promoting the effective integration of renewable energy sources. To verify the performance of the proposed controller under various loading conditions as external disturbances, a 2.2 kW standalone single-phase inverter is simulated using MATLAB/Simulink platform along with a microcontroller-based processor-in-loop through the digital signal processing. In terms of internal disturbances, the proposed controller is also tested under different filter parameters’ variations over a wider range. The results indicate a better alignment for coupling with clean energy sources and the comparisons with other control techniques show better performance of the proposed controller.

Encoderless Five-phase PMa-SynRM Drive System Based on Robust Torque-speed Estimator with Super-twisting Sliding Mode Control

In this paper, a robust torque speed estimator (RTSE) for linear parameter changing (LPC) system is proposed and designed for an encoderless five-phase permanent magnet assisted synchronous reluctance motor (5-phase PMa-SynRM). This estimator is utilized for estimating the rotor speed and the load torque as well as can solve the speed sensor fault problem, as the feedback speed information is obtained directly from the virtual sensor. In addition, this technique is able to enhance the 5-phase PMa-SynRM performance by estimating the load torque for the real time compensation. The stability analysis of the proposed estimator is performed via Schur complement along with Lyapunov analysis. Furthermore, for improving the 5-phase PMa-SynRM performance, five super-twisting sliding mode controllers (ST-SMCs) are employed with providing a robust response without the impacts of high chattering problem. A super-twisting sliding mode speed controller (ST-SMSC) is employed for controlling the PMa-SynRM rotor speed, and four super-twisting sliding mode current controllers (ST-SMCCs) are employed for controlling the 5-phase PMa-SynRM currents. The stability analysis and the experimental results indicate the effectiveness along with feasibility of the proposed RTSE and the ST-SMSC with ST-SMCCs approach for a 750-W 5-phase PMa-SynRM under load disturbance, parameters variations, single open-phase fault, and adjacent two-phase open circuit fault conditions.

Fast Terminal Sliding Mode Current Control With Adaptive Extended State Disturbance Observer for PMSM System

This article proposes a current decoupling control strategy by combining a fast terminal sliding mode control (FTSMC) and an adaptive extended state observer (AESO). First, the voltage errors and external disturbances caused by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$d$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$q$ </tex-math></inline-formula> -axis current coupling and motor parameter variations are regarded as the lumped disturbance of the system, which facilitates the decoupling of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$d$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$q$ </tex-math></inline-formula> -axis currents. Next, an equivalent control-based FTSMC strategy is used to track the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$d$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$q$ </tex-math></inline-formula> -axis currents to obtain the proper <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$d$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$q$ </tex-math></inline-formula> -axis voltages and improve the current dynamic performance. Then, the AESO method is utilized to observe the lumped disturbance and compensate for the input signal. Afterward, the FTSMC and AESO algorithms are combined to obtain the appropriate current and voltage signals in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$d$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$q$ </tex-math></inline-formula> -axis. Finally, simulation and experimental results show that the proposed method not only achieves complete decoupling of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$d$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$q$ </tex-math></inline-formula> -axis currents, but also has good performance in terms of dynamic response, steady-state accuracy, and robustness.

Simplified Nonlinear Current-Mode Control of DC-DC Cuk Converter for Low-Cost Industrial Applications.

This paper presents a robust nonlinear current-mode control approach for a pulse-width modulated DC-DC Cuk converter in a simple analog form. The control scheme is developed based on the reduced-state sliding-mode current control technique, in which a simplified equivalent control equation is derived using an averaged power converter model in continuous conduction mode. The proposed controller does not require an output capacitor current sensor and double proportional-integral compensators as in conventional sliding-mode current controllers; thus, the cost and complexity of the practical implementation is minimized without degrading the control performance. The simplified nonlinear controller rejects large disturbances, provides fast transient response, and maintains a constant switching frequency. The nonlinear control scheme is developed using an analog circuit with minimal added components, which is suitable for low-cost industrial applications. The control law derivation, control circuit design, controller gains selection, and stability analysis are provided. The proposed control methodology is verified via simulating the closed-loop nonlinear power converter model in MATLAB/SIMULINK under abrupt changes in load current and input voltage. The simulation results show that the proposed control scheme provides robust tracking performance, a low percentage overshoot, fast transient response, and a wide operating range. The maximum percentage overshoot and settling time of the closed-loop power converter response during line disturbance are 5.6% and 20 ms, respectively, whereas the percentage overshoot and settling time during load disturbance are 2.8% and 15 ms, respectively.

Improved Sliding Mode Traction Control Combined Sliding Mode Disturbance Observer Strategy for High-Speed Maglev Train

To improve the robustness and dynamic tracking performance of the stator current control for the long stator linear synchronous motor (LSLSM) used in high-speed maglev train traction system, a composite current control strategy combining a sliding mode current controller (SMCC) and a sliding mode disturbance observer (SMDO) is proposed in this article. First, the LSLSM mathematical model in double feed mode is optimized. Then, an SMCC is designed based on the model. An improved stability criterion is proposed and the SMCC switching gain is obtained quantitatively to meet the current following speed required for the stator changeover process. As disturbance factors, parameter perturbation of the LSLSM and the stator changeover will bring about transient current fluctuations and chattering. Therefore, an SMDO is designed to estimate the disturbances and perform feed-forward compensation for the SMCC, thereby improving the robustness and suppressing the current chattering. Finally, the hardware-in-the-loop experiments verify the effectiveness of this strategy and compare it with the traditional current control strategy.

Full-Order Sliding-Mode Current Control of Permanent Magnet Synchronous Generator With Disturbance Rejection

To address the stochasticity issues of wind power generation, this article proposes an anti-disturbance full-order sliding-mode control (FOSMC) strategy for the current control of permanent-magnet synchronous generator (PMSG)-based wind energy conversion systems (WECSs). An extended state observer (ESO) is designed to estimate the uncertainty of the external disturbances and internal model parameters in real time. An FOSMC strategy is designed for the current control of the PSMG. The FOSMC uses a continuously controlled sliding mode to solve the chattering problem and the disturbances estimated by the ESO to improve the antidisturbance capability while ensuring finite-time convergence of the system states. Experimental results for a 900 W emulated PMSG-based WECS are provided to validate the superior current tracking, chattering suppression, and antidisturbance performance of the proposed ESO-FOSMC strategy over a sliding-mode current controller using the same ESO for antidisturbance.

Convergence Trajectory Optimization of Supertwisting Sliding-Mode Current Control for Induction Motor Drives

For the induction motor (IM) current loop, the supertwisting sliding-mode control (ST-SMC) has been considered as an effective approach to achieve chattering suppression and steady-state errorless control. However, due to the system disturbance, the conventional ST-SMC suffers from control delay in the convergence trajectory, resulting in decreased antidisturbance capability. To address this problem, this article proposed a ST-SMC with convergence trajectory optimization. First, a nonlinear sliding-mode manifold is designed to achieve the ideal ST-SMC convergence trajectory. Then, a disturbance compensation term is added into the control law to eliminate the system control delay. Compared with the conventional ST-SMC, the studied method can effectively enhance the antidisturbance capability of IM current loop, leading to improved transient performance. Finally, the superiority of the investigated method is verified by the experimental results from a 3.7 kW IM test bench.

Sliding-Mode Current Control with Exponential Reaching Law for a Three-Phase Induction Machine Fed by a Direct Matrix Converter

The direct matrix converter (DMC) is considered to be an exciting power converter topology option for electric motor drives in industrial applications (elevators, hoists and cranes) and applications where size and weight are critical (e.g., the aerospace industry). Several control techniques have been developed to exploit the DMC’s benefits and achieve the desired performance with classic control techniques, such as field-oriented control and direct torque control, and more sophisticated ones, such as model predictive control and sliding mode control (SMC). SMC is attractive due to its robustness and fast response. However, this control strategy suffers from a phenomenon called chattering. Thus, a solution based on the exponential reaching law (ERL) is implemented to resolve this issue. The proposed method was validated using simulation and experimental results from tests on a three-phase induction machine.

A novel sliding mode observer-based compound sliding mode current control with active damping for single phase grid-tied inverter system in weak grid

This paper proposes a novel sliding mode observer (SMO)-based compound sliding mode current control (CSMCC) strategy with active damping for the single-phase grid-tied inverter system in weak grid. To decrease the number of measurement sensors and thus reduce system cost, the SMO with rapid response and low chattering level is designed for estimating the inverter-side current and capacitor voltage of LCL-type filter, which is used for feedback control. To enhance robustness against the parameter variation of grid-tied inverter system, the CSMCC is put forward, which is composed of two parts. One part is the equivalent control for grid-tied inverter system with nominal parameters, and the other part is the reaching law-based second-order nonsingular terminal sliding mode control (NTSMC) for compensating the disturbance due to the parameter variations. Since an adaptive gain of switching function is employed and there is integral operation for this discontinuous switching function, the proposed NTSMC strategy not only speed up system response but also attenuate the system chattering level significantly. Moreover, for inhibition of inherent resonance resulting from LCL-type filter, the weighted average current-based active damping is used to provide feedback current for CSMCC. Comprehensive simulation and experimental results show that the proposed strategy can enable the grid-tied inverter system to not only have strong robustness against the filter parameters & grid impedance variations but also improve the quality of grid current, and have satisfactory suppression effect of background grid voltage harmonics on grid current.

Robust Sliding Mode Control of the Permanent Magnet Synchronous Motor with an Improved Power Reaching Law

To improve the suppression ability of uncertain disturbance of the sliding mode control driving system of the surface-mounted permanent magnet synchronous motor (SPMSM) and to reduce the chattering of the control output, a robust sliding mode control strategy with an improved power reaching law (IPRL) is proposed in this paper. Compared with the traditional fast power reaching law (FPRL), the IPRL incorporates the sum of the power terms of the system state variables into the conventional power terms, and uses hyperbolic tangent saturation function to replace the piecewise function, which can effectively suppress the sliding mode chattering and improve the convergence speed of the system state to the sliding mode surface. Furthermore, the robust sliding mode speed controller and sliding mode current controller of the SPMSM are designed separately with the IPRL, and detailed simulation verification is carried out to reveal the effectiveness of the IPRL. Simulation and experimental results show that compared with the FPRL, the proposed IPRL can reduce the inherent chattering phenomenon in sliding mode control, and the IPRL-based speed and current control strategy can effectively improve the dynamic performance and robustness of the system.

Discrete-Time Super-Twisting Sliding Mode Current Controller With Fixed Switching Frequency for Switched Reluctance Motors

This article from a discrete-time model and stability analysis is developed using a Lyapunov approach, taking into account the one sample implementation delay present in digital control applications. Experimental results are provided to demonstrate the effectiveness of the proposed approach, where a conventional hysteresis controller is used as a benchmark. Results show that the proposal is able to deliver adequate reference tracking while using significantly lower sampling frequencies. Moreover, when compared to the hysteresis controller, superior tracking is observed at low speeds, while maintaining a similar level of computational complexity.

Zero Speed Sensorless Scheme for Permanent Magnet Synchronous Machine Under Decoupled Sliding-Mode Control

Position estimation at low/zero speed for permanent magnet synchronous machines is commonly achieved with the injection of high-frequency signals. This article presents a new sensorless scheme that accurately observe the rotor angle at low speeds, including standstill condition, without injecting high-frequency signals. The algorithm is built upon a previous sliding-mode current controller and uses the switching functions slopes inaccuracies produced by the saliency effect to determine the rotor position and speed. Thanks to the equivalent control concept and together with a sliding-mode-based phase-locked loop observer defined by a complex switching function, the algorithm provides both rotor position and speed in a compact form. This article includes the main working principle and defines the operational range of the proposed scheme. Finally, the feasibility of the method is corroborated through experimental results in sensorless configuration.

Higher‐order sliding mode current controller for grid‐connected distributed energy resources with LCL$\mathrm{LCL}$ filters under unknown grid voltage conditions

The control of the current injected into the grid with lower harmonics is considered as one of the most important issues for the grid integration of distributed energy resources (DERs). The unbalances and harmonics in the grid voltage usually pollute the current injected into the grid due to the power electronic interfaces, for example, inverters. To address such problems, the present paper proposes a nonlinear higher order sliding mode controller (HOSMC) for grid-connected three-phase inverters with LCL $\mathrm{LCL}$ filters in order to control the current injected into grid and improve the power quality. The proposed current controller injects the desired current into the grid with lower values of total harmonic distortions (THDs) under any grid voltage condition as well as it reduces the harmonics in the grid voltage. Apart from these, the proposed scheme is developed to provide robustness against parametric uncertainties where these uncertainties are modeled using the Taylor series expansion method. Finally, the performance of the system is evaluated using processor-in-loop (PIL) simulations via MATLAB/Simulink platform through the implementation on a system considering the capacity of the DER as 2 kVA per phase and compared with other existing control strategies.

Adaptive Fractional Order Sliding Mode Speed and Current Control for Switched Reluctance Motor

Adaptive Fractional Order Sliding Mode Speed and Current Control for Switched Reluctance Motor

Position and Cross-Coupling Factors Estimation for Sliding Mode Current Control Based Position-Sensorless Control of IPMSM

This paper presents a control method with an estimation method of cross-coupling factors of Interior Permanent Magnet Synchronous Motors (IPMSM) inductance for position-sensorless servo drive systems. The cross-coupling factors are from dq-axis mutual inductance. Conventionally, the cross-coupling factors have been ignored in the IPMSM model and deteriorate control performance. That has caused decreasing robustness and velocity vibration in the low-speed range. Since the cross-coupling factors vary with the rotor position and the current, it is hard to measure them. Therefore, the proposed method utilizes a high-frequency voltage injection method to estimate the cross-coupling factors online. In addition, the proposed current control method utilizes a sliding mode control and voltage disturbance observer based on the voltage equation, including the dq-axis mutual inductance model. The estimated cross-coupling factors are reflected in the proposed current controller instantaneously. Experimental results show that the proposed method considering cross-coupling factors increases the robustness to the disturbance force and reduces the velocity vibration.