Sliding Mode Direct Power Control Research Articles

Improved sliding mode direct power control for low-carbon oriented MMC-HVDC of asymmetric offshore wind power flexible systems

The modular multilevel converter based high voltage direct current (MMC-HVDC) is a dynamic power balancing system. The control system of MMC generally adopts a dual closed-loop vector control strategy based on the traditional instantaneous power model under asymmetric grid state, which has complex control structure and low control accuracy. This paper introduces a flexible instantaneous power model and establishes a general power equation with active power and new reactive power as control objects. Based on this, an improved sliding-mode MMC-HVDC direct power control strategy based on the new instantaneous power model is proposed which combines the flexible instantaneous power model and the improved sliding-mode control method to eliminate the twice grid-frequency ripples in both active and reactive power under asymmetric grid states. Furthermore, it omits the inner-loop controller and power compensation terms while optimizing the control structure. Simulation results show that the proposed method has better dynamic responsiveness, control accuracy and robustness under operating conditions such as asymmetric grid state and parameter perturbation which can better exploit the advantages of the flexible instantaneous power model.

Torque Ripple Reduction of Nonsinusoidal Brushless DC Motor Based on Super-Twisting Sliding Mode Direct Power Control

In this paper, a second-order sliding mode control, based on super-twisting algorithm, is proposed for direct power control of the brushless DC (BLDC) motor. The proposed controller uses a super-twisting scheme that requires only sliding surface information and can handle system uncertainties and external disturbances, well. This scheme can improve the BLDC motor torque ripple by solving the disadvantages of the conventional sliding mode control method, such as the chattering effect and high frequency switching control. This method is simple and robust for the BLDC motor’s biggest challenge, torque ripple, which does not require any voltage and current control loops or complex reference frame transformations. The simulation results of the proposed method are compared with the direct power control (DPC) and model predictive control (MPC) methods, which indicate the superiority of the proposed method in both the steady- and transient-states. Moreover, the motor parameters variation in the tracking of active and reactive power are discussed. In addition, the practical results of the proposed method in both cases of speed and load variation show the effectiveness of this method in reducing power (torque) ripple and current total harmonic distortion (THD) and increasing the system’s efficiency compared to other methods.

Power Quality Improvement Based on Third-Order Sliding Mode Direct Power Control of Microgrid-Connected Photovoltaic System with Battery Storage and Nonlinear Load

Power Quality Improvement Based on Third-Order Sliding Mode Direct Power Control of Microgrid-Connected Photovoltaic System with Battery Storage and Nonlinear Load

An Improved Sliding Mode Direct Power Control Strategy Based on Reactive Power Compensation for Vienna Rectifier

Vienna rectifiers are widely used in electric vehicle charging systems, wind power generation systems and other fields due to their excellent high-voltage resistance, small size and high efficiency. Aiming at the problems of the Vienna rectifier’s long response time, low anti-disturbance ability, and current zero-crossing distortion, a new sliding mode direct power control strategy based on disturbance compensation is proposed. Firstly, a model considering the uncertainty is established, and the neural network is used to estimate and compensate the uncertain disturbance. Secondly, aiming at the slow approach speed and slow system convergence of traditional control methods, a new approaching law sliding mode direct power control strategy is designed. Aiming at the current zero-crossing distortion, the reason is analyzed and a compensation method is proposed. Finally, simulations and experiments show that the proposed method has no voltage overshoot and converges faster, effectively improving the problem of different phases of voltage and current. The rectifier operates at unit power, has better steady-state performance and stronger anti-load disturbance ability. The current total harmonic distortion is controlled below 2%, and the current quality is effectively improved.

Adaptive-Gain Second-Order Sliding Mode Direct Power Control for Wind-Turbine-Driven DFIG under Balanced and Unbalanced Grid Voltage

In a wind turbine system, a doubly-fed induction generator (DFIG), with nonlinear and high-dimensional dynamics, is generally subjected to unbalanced grid voltage and unknown uncertainty. This paper proposes a novel adaptive-gain second-order sliding mode direct power control (AGSOSM-DPC) strategy for a wind-turbine-driven DFIG, valid for both balanced and unbalanced grid voltage. The AGSOSM-DPC control scheme is presented in detail to restrain rotor voltage chattering and deal with the scenario of unknown uncertainty upper bound. Stator current harmonics and electromagnetic torque ripples can be simultaneously restrained without phase-locked loop (PLL) and phase sequence decomposition using new active power expression. Adaptive control gains are deduced based on the Lyapunov stability method. Comparative simulations under three DPC schemes are executed on a 2-MW DFIG under both balanced and unbalanced grid voltage. The proposed strategy achieved active and reactive power regulation under a two-phase stationary reference frame for both balanced and unbalanced grid voltage. An uncertainty upper bound is not needed in advance, and the sliding mode control chattering is greatly restrained. The simulation results verify the effectiveness, robustness, and superiority of the AGSOSM-DPC strategy.

Super-Twisting Sliding Mode Direct Power Control of a Brushless Doubly Fed Induction Generator

This paper proposes and implements a super-twisting sliding mode direct power control (SSM-DPC) strategy for a brushless doubly fed induction generator (BDFIG). DPC has fast and robust response under transient conditions; however, it suffers from active and reactive power ripples and current distortions, which degrades the quality of the output power. In contrast, vector control has good steady-state current harmonic spectra; however, it is not robust to machine parameters variations, and thus needs a phase-locked loop for synchronous coordinate transformations. The SSM-DPC strategy controls active and reactive power directly without the need of the phase-locked loop. Moreover, its transient performance is similar to DPC and its steady-state performance is the same as vector control. The proposed controller is robust to uncertainties toward parameter variations and achieves constant converter switching frequency by using space vector modulation. Simulation and experimental results of a 2 MW and 3 kW laboratory-scale BDFIG are provided and compared with those of integral sliding mode and DPC to validate the effectiveness, correctness, and the robustness of the proposed strategy.

A Sliding-Mode Direct Power Control Strategy for DFIG Under Both Balanced and Unbalanced Grid Conditions Using Extended Active Power

This paper proposes a sliding-mode direct power control (SMDPC) strategy for doubly fed induction generator (DFIG) under both balanced and unbalanced grid conditions using extended active power. When the traditional power theory is used under unbalanced grid condition, the control strategies usually need to be modified and become more complicated. Therefore, an extended active power is proposed in this paper, which is effective under both balanced and unbalanced grid conditions with a simple control strategy. Based on the extended active power, elaborated analysis of the mathematical model of DFIG is obtained. Furthermore, an SMDPC strategy using the extended active power is proposed, which can obtain sinusoidal stator currents and restrain electromagnetic torque ripples under unbalanced grid condition without the need of decomposition process and phase-locked loop (PLL). Comparative experimental studies of the SMDPC using the extended and traditional active powers for DFIG are conducted to validate the effectiveness of the proposed strategy under both balanced and unbalanced grid conditions. In addition, the dynamic performance and robustness of the proposed SMDPC are also proved to be satisfying by the experimental results.

Adaptive integral sliding mode direct power control for VSC-MVDC system converter stations

Adaptive integral sliding mode direct power control for VSC-MVDC system converter stations

Integral Plus Resonant Sliding Mode Direct Power Control for VSC-HVDC Systems under Unbalanced Grid Voltage Conditions

An integral plus resonant sliding mode direct power control (IRSMC DPC) strategy for voltage source converter high voltage direct current (VSC-HVDC) systems under unbalanced grid voltage conditions is proposed in this paper. Through detailed instantaneous power flow analysis, a generalized power compensation method, by which the ratio between the amplitude of active and reactive power ripples can be controlled continuously, is obtained. This enables the system to provide flexible power control, so that the desired performance of the system on both the ac and dc sides can be attained under different operating conditions. When the grid voltage is unbalanced, one or both of the active and reactive power terms contain ripples, oscillating at twice the grid frequency, to obtain non-distorted ac current. A power controller consisting of the proportional, integral and resonant control laws is designed using the sliding mode control approach, to achieve accurate power control objective. Simulation studies on a two-terminal VSC-HVDC system using MATLAB/SIMULINK (R2013b, Mathworks, Natick, MA, USA) are conducted to verify the effectiveness of the IRSMC DPC strategy. The results show that this strategy ensures satisfactory performance of the system over a wide range of operating conditions.

Sliding‐mode DPC using SOGI for DFIG under unbalanced grid condition

A sliding-mode direct power control (SMDPC) strategy using second-order generalised integrator (SOGI) for doubly fed induction generator is proposed, which can achieve various objectives without the decomposition process of negative and positive sequence components when the grid voltage is unbalanced. The impact of the non-ideal grid voltage to the SM controller is studied, and an improved strategy is proposed by combining an SOGI-based compensator with the SMDPC strategy. Different control targets can be achieved by selecting different variables as the compensation. Experimental studies based on the proposed and traditional SMDPC are implemented to verify that the proposed strategy is effective when the grid voltage is unbalanced.

Sliding mode direct power control of RSC for DFIGs driven by variable speed wind turbines

In spite of its several advantages, a classic direct power control (DPC) of doubly fed induction generators (DFIGs) driven by variable speed wind turbines has some drawbacks. In this paper, a simple and robust total sliding mode controller (TSMC) is designed to improve the classical DPC performance without complicating the overall scheme. The TSMC is designed to regulate the DFIG stator active and reactive powers. Two integral switching functions are selected for describing the switching surfaces of the active and reactive powers. Reaching phase stability problem of the classical sliding mode controller is avoided in the proposed TSMC. Neither current control loops nor accurate values of machine parameters are required in the proposed scheme. In addition, axes transformation of the stator voltage and current are eliminated. The grid side converter is controlled based on DPC principle to regulate both DC-link voltage and total reactive power. The feasibility of the proposed DPC scheme is validated through simulation studies on a 1.5MW wind power generation system. The performance of the proposed and conventional DPC schemes is compared under different operating conditions.

Sliding mode direct power control strategy of a power quality based on a sliding mode observer

The first problem in our third millennium is energy. For this raison, we try to find a new solution to develop different ways of distribution and energy use. This article presents the design of a sliding mode controller using sliding mode observation technique which aims to simplify the control procedure. According to the justified tendency of reduction of the number of the sensors. The sliding mode observer has been presented as a robust estimation method. We propose a new multi-function converter as an efficient solution to improve the power quality. For improving the quality of the energy transfer from the power supply to the load, and reducing the harmful effects of the harmonics generated by nonlinear load. The good dynamic and static performance under the proposed control strategy is verified by simulation and experiment.