Extended State Observer-Based Sliding-Mode Control for Three-Phase Power Converters

A new approach to the control of three-phase two-level grid-connected power converters is proposed in this paper. The proposed control is an extended state observer (ESO)based second order sliding mode (SOSM), which comprises two control loops: the outer loop is a voltage regulation loop, as well as inner loop is an instantaneous power tracking loop. The outer loop is accomplished by an H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> controller plus an ESO, which is designed to regulate dc-link capacitor voltage of the converter and asymptotically reject external disturbances and parameter perturbations. The SOSM strategy is employed in the inner loop to drive the active and reactive power convergence to their desired values. Control objectives of nearly unity power factor and dc-link capacitor voltage regulation are simultaneously satisfied. Availability of the ESO-based SOSM is compared with the classic proportional-integral control in simulations, and the comparison implies that the proposed strategy not merely achieves an almost perfect tracking performance, but also provides a complete robustness against resistance load variation.

In this paper, a novel scheme of disturbance observer based second order sliding mode (SOSM) control for DC-DC buck converters is proposed. A cascade-control structure is established to regulate the output voltage and force the inductor current to track its reference, which comprises two control loops. The voltage regulation loop which is based on an SOSM controller combined with extended state observer (ESO) is the external loop. The current tracking loop also accomplished by SOSM controller is the internal loop. The fast motion is dominated by the dynamics of the current tracking loop whereas the slow motion stems from the dynamics of the output voltage. In addition, the load resistance that influences significantly the dynamics of whole system is regarded as the external disturbance in this papper. A disturbance observer, ESO, aims at asymptotically rejecting disturbances to converter. The proposed control strategy is verified using simulation test.

A novel scheme for the control of three-phase two-level grid-connected power converters is presented in this paper. A cascade-control structure, based on H ∞ control and sliding mode control (SMC), is proposed, which simultaneously achieves output voltage regulation and unity power factor under dc-load variations. The overall control strategy contains two main loops: first, a current tracking loop (internal loop) based on sliding mode control that guarantees the input currents to follow the desired references; second, a dc-link voltage regulation loop (external loop) based on an H ∞ controller integrated with an extended state observer (ESO), which regulates the output voltage and provides current references for the internal loop. Simulation results are provided to assess the efficiency of the proposed method.

This paper employs second-order sliding mode control (SOSMC) to carry out the current tracking and voltage regulation tasks of a grid-connected three-phase two-level power converter. For dc-link voltage regulation, a disturbance observer is adopted to improve the whole control performance. In this paper, four different types of disturbance observers are proposed for comparison, which are conventional linear observer (LINO), second-order sliding mode observer (SOSMO), linear extended state observer (LESO) and nonlinear extended state observer (NESO). To ensure fair comparison, the parameters of the observers are tuned to make the power converter achieve almost same current total harmonic distortion (THD) and steady error of dc-link voltage. The performances are compared in the term of transient response of the dc-link voltage. The simulation results show: first, the disturbance observers improve the control performance of SOSMC; second, SOSMO outperforms the other three observers.

The parametric uncertainties and external disturbances in the buck converter would cause degradation of the control performance. In this paper, a disturbance observer based second order sliding mode (SOSM) control strategy for buck converter is proposed to solve this problem. The double-loop control strategy is set up to force the output voltage and inductor current to their references. The load variation which significantly influences the control performance can be considered as the external disturbance. The parametric uncertainty of the capacitor and the load variation are estimated by an extended state observer (ESO), and the parametric uncertainty of the inductor is dealt by the SOSM controller. The strategy has good tracking performance and disturbance rejection ability against parametric uncertainties and external disturbances. Simulation results verifies the performance of the presented control strategy.

In this paper, a model based robust control for three-phase three-level Neutral Point Clamped (NPC) power converters is studied. Based on the continuous averaged model of the system, a Second Order Sliding Mode (SOSM) technique is employed to the control design. The control objectives are to achieve desired dc-link capacitor voltage regulation, voltage balance in the two dc-link capacitors and the instantaneous active and reactive power tracking. In order to achieve fast dynamic response of the proposed controller in the presence of external disturbances, an Extended State Observer (ESO) is employed to asymptotically reject the disturbances which are integrated in the controller design. The proposed control strategy has a cascaded structure which consists of power tracking (inner loop) ESO-based dc-link voltage regulation and capacitors voltage balance (outer loop). Multi-rate simulation illustrates the effectiveness and robustness of the proposed controller under parametric uncertainties and load variations.

In order to obtain a simple and efficient control strategy for three-phase two-level grid-connected power converters with improved system performance including reduced computation and communication burdens, an event-triggered continuous control set-model predictive control (CCS-MPC) is proposed in this paper. In the DC-link voltage regulation loop, a simple but efficient controller is designed to track the DC-link voltage to its reference value. In the power tracking loop, a simple event-triggered CCS-MPC is utilized to ensure that the active power and reactive power also track their reference values. The control signals to the converter are updated and transmitted only when the triggering condition is satisfied. Compared with periodic sampling control strategies, which require the calculation and transmission of control signals in each sampling period, the proposed controller reduces the utilization of limited computation and communication resources while maintaining good tracking performance. By comparing with the periodic sampling proportional-integral strategy, the effectiveness and superiority of the proposed strategy are shown through simulation results.

The performance of model-free predictive control (MFPC), which is based on the ultra-local model, is highly dependent on the effectiveness of the extended-state observer (ESO). The standard linear ESO has a high-gain which enhances disturbance rejection attributes. Nevertheless, this ESO has two main limitations: i) it amplifies high-frequency measurement noises, and ii) it deteriorates disturbance rejection performance when the noise immunity is improved. Therefore, this article introduces a new technique to improve both the disturbance rejection and noise suppression of ESO without increasing the bandwidth: the multi-frequency-based ESO (MF-ESO). Two novel ESO structures that operate on the MF-ESO principle are analyzed: parallel and cascade ESOs. Extensive frequency domain analyses unravel the comparative capabilities of the MF-ESO structures for improved disturbance rejection and/or high-frequency noise suppression. A novel adaptive gain is proposed to improve CESO's dynamic performance. The superior features of the proposed MF-ESO are experimentally validated by the model-free predictive control of a grid-connected power converter.

In this article, a two-stage control scheme consisting of an adaptive-gain second-order sliding mode (SOSM) controller and a switched high-gain observer (HGO) is proposed for the three-level neutral-point-clamped (NPC) converter. The adaptive-gain SOSM control method is applied both in the voltage regulation loop and instantaneous power tracking loop, thus, the boundary of the disturbance derivative does not need to be known <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a priori</i> . Compared with the fixed-gain SOSM, it provides a faster dynamic and a better steady-state response for the NPC converter. On the other hand, the conventional disturbance compensation observer used in the power system suffers from the adverse effects of measurement noise, which limits the performance of the observer. A switched HGO is combined with the adaptive-gain SOSM controller in the voltage regulation loop to address this issue. By using a switched observer gain, the switched HGO greatly diminishes the performance degradation induced by the inevitable measurement noise. Finally, several experiments between the representative extended state observer-based SOSM control scheme and the proposed control method are carried out for a comparison. The results demonstrate the feasibility and effectiveness of the proposed approach.

In this paper, a model based robust control for three-phase two-level grid connected power converters is studied. The proposed controller uses a Second Order Sliding Mode (SOSM) technique to develop the control law. The control objectives are to achieve desired dc-link capacitor voltage regulation and unity power factor. This requires controllers with fast response in the presence of external disturbances. An Extended State Observer (ESO) is employed to asymptotically reject the disturbances which are integrated in the controller design. The proposed control strategy has a cascaded structure which consists of current tracking (inner) and voltage regulation (outer) loops based on ESO. Multi-rate simulation illustrates the effectiveness and robustness of the proposed controller under parametric uncertainties and load variations.

According to the number of modulation levels, power converters can be divided into two-level and multi-level converters. Power converters with AC side include single-phase and three-phase converters, and grid-connected power converters are three-phase converters. Although there are various circuit topologies for converters, the three-phase two-level topology is most common in the industrial field due to its topological simplicity and full power ranage controllablity, as well as high reliability, high efficiency and high power capacity [1]. This chapter investigates the grid-connected three-phase two-level power converter, and adopts the disturbance observer based sliding mode control strategy to carry out the current tracking and voltage regulation of the converter. The voltage regulation loop adopts a super twisting sliding mode controller, which is compensated by a disturbance observer. The current control loop is controlled in synchronous reference frame (SRF), and two super twisting sliding mode controllers are used to track the d-axis and q-axis currents. Four different disturbance observers are designed for comparison, including linear observer, second-order sliding mode observer, linear extended state observer and nonlinear extended observer. Then through simulation, the performance of the observers is compared according to the transient response of the DC-link voltage. In order to ensure a fair comparison, the parameters of the observers are adjusted to make the converter have almost the same current distortion level and DC-link voltage steady-state error.

This paper proposes an Extended State Observer (ESO) based predictive direct power control strategy for three-phase two-level grid connected power converters. The proposed control is in cascade structure which consists of two control loops, instantaneous power tracking loop (inner loop) and voltage regulation loop (outer loop). A proportional integral (PI) controller integrated with an ESO is designed for the outer loop. In the inner loop, the finite-control-set model predictive control (FCS-MPC) strategy is employed to directly force the active and reactive powers of the system to track their desired values. Simulation results are provided to demonstrate the effectiveness and feasibility of the proposed control strategy.

In this paper, a second order-sliding mode (SOSM) control strategy for Field Oriented Control (FOC) of induction motor (IM) is proposed that satisfying requirements of reliable dynamics and steady state performance. The proposed control structure is a state of the development of FOC utilized SOSM in the inner loop that employ the artificial neural network (ANN) to estimate the rotor flux and motor speed. The SOSM controller designed based on model of induction motor (IM) that include torque control loop (inners loop) and speed tracking control (outer loop). Based on the sliding state convergence property, the state variables track the reference values. By analyzing the theory, the desired performance of the proposed control system proven for various situations. The proposed control considerably ameliorates specified disadvantages of the FOC and DTC, such as the sensitivity to motor parameter variations. The simulation results indicate the correctness of the control algorithm under the uncertainty in parameters and load variations. Keywords, (FOC, ANN's, Uncertainty, estimation, SOSM, Robust)

Practical second order sliding modes in single-loop networked control of nonlinear systems

In this article, a linear extended state observer (LESO) based second-order sliding mode (SOSM) control strategy with the direct power control is proposed for a three-phase neutral-point-clamped (NPC) power converter connected to a dc microgrid. Comparing with the PI control method, the proposed approach implements the advanced SOSM controller into the voltage regulation loop and instantaneous power tracking loop to enhance the dynamic and steady state performance. Furthermore, saturation function is applied in the SOSM method to weaken the chattering phenomenon. On the other hand, since the dc load is regarded as an external disturbance, an efficient LESO is designed in the voltage regulation loop to reject this disturbance. The design process of the proposed control strategy is shown based on the continuous averaged model of the NPC converter. Finally, comparison experiments among PI, LESO-based PI, and proposed LESO-based SOSM control strategies are implemented, which validate the superiority of the proposed approach.