Sliding Mode Current Controller Research Articles

PIDR Sliding Mode Current Control with Online Inductance Estimator for VSC-MVDC System Converter Stations under Unbalanced Grid Voltage Conditions

This study aims to present a novel proportional-integral-derivative-resonant law-based sliding mode current control strategy with online inductance estimator (PIDR-SMCC-OIE) for voltage source converter medium voltage direct current (VSC-MVDC) system converter stations under unbalanced grid voltage conditions. A generalized current reference calculation method, by which the ratio of the amplitude of the active power ripple to that of the reactive power ripple can be continuously controlled without current distortion is presented. A dynamic model of the current control errors in the positive sequence synchronous reference frame is developed, and a PIDR law-based sliding mode current controller is designed, where derivatives of the current references are obtained by simple algebraic operations. An OIE adopting the dynamic filtering method and gradient algorithm is proposed to further improve system robustness. In this OIE, the converter pole voltages are obtained by computation utilizing the gate signals of the switching devices and the DC bus voltage, so that no additional voltage sensors are needed. To verify effectiveness of the PIDR-SMCC-OIE strategy, simulation studies on a two-terminal VSC-MVDC system are conducted in PSCAD/EMTDC. The results show it can provide satisfactory performance over a wide range of operating conditions.

Model-Based Current Sharing Approach for DCM Interleaved Flyback Micro-Inverter

Current sharing control is a challenge for a discontinuous conduction mode (DCM) micro-inverter based on interleaved flyback topology. To solve this problem, this study proposes a novel and systemic model-based approach. Firstly, an accurate fourth-order model is presented for the interleaved flyback circuit, which takes the two flybacks’ parameter mismatch and coupling into account. Secondly, based on the presented model, a continuous time sliding mode current controller is proposed to tackle the output imbalance caused by parameter mismatch, coupling and disturbance. The proposed controller is derived from the Lyapunov function without switching conditions. Finally, the effectiveness of the proposed model and control method is validated by simulation tests using MATLAB/SIMULINK. Simulation results show that the proposed approach improves the current sharing for the interleaved flyback micro-inverter when compared to the conventional current sharing approach.

Fixed Switching Period Discrete-Time Sliding Mode Current Control of a PMSM

A fixed switching period sliding mode control (SMC) for permanent-magnet synchronous machines (PMSMs) is presented. The aim of this paper is to design an SMC that improves the traditional PI-based field-oriented control transient response, as well as to reduce the switching frequency variations of the direct torque control. Such SMC requires a decoupling method of the control actions, which also brings constant switching functions slopes. These constant slopes allow to calculate the required hysteresis band value to control the switching frequency. The digital implementation degrades the performance of the hysteresis comparator, and as a consequence, the previously calculated band becomes inaccurate to regulate the switching frequency. In order to recover the analogue hysteresis band comparator performance, a predictive algorithm is proposed. Finally, a set of experimental results with constant switching frequency during a torque reversal and speed control tests are provided.

A Sliding Surface-Regulated Current-Mode Pulse-Width Modulation Controller for a Digital Signal Processor-Based Single Ended Primary Inductor Converter-Type Power Factor Correction Rectifier

To efficiently supply wide-range DC voltage from a pulse-width modulation (PWM) rectifier, this paper presents a single-phase, full-wave, diode-bridge, single-ended primary-inductor converter-type (SEPIC-type) power-factor-correction (PFC) rectifier in continuous conduction mode with a sliding surface-regulated current-mode PWM controller. According to the switched-mode operation of the rectifier, a fourth-order switch model of the SEPIC is derived. From the fourth-order model, a simplified state-averaged model which approximately describes the dynamic behaviors of both the output voltage and inductor current is proposed. Then, from the simplified state-averaged model, the sliding surface-regulated current-mode PWM controller for the SEPIC-type PFC rectifier is proposed. The sliding surface-regulated current-mode PWM controller comprises a sliding-mode voltage controller in outer loop for robust control of the output DC-voltage and a sliding-mode current controller in inner loop for phase-synchronized control of the inductor current. For experimental studies, implementation of the proposed control algorithm in a DSP controller and a laboratory prototype of the SEPIC-type rectifier with the DSP-based PWM controller were carried out. Experimental results from the DSP controller-applied SEPIC-type rectifier are illustrated to confirm the validity of the proposed controller for practical applications.

A simplified time-domain design and implementation of cascaded PI-sliding mode controller for dc–dc converters used in off-grid photovoltaic applications with field test results

A time-domain design methodology for voltage regulation control of dc–dc boost and buck-boost converters based on a multi-loop controller with PI regulator for the outer loop and an inner loop with sliding mode current controller has been developed for renewable energy applications such as photovoltaic (PV)-fed dc–dc converters. This paper proposes a new method for the design of PI regulators in such multi-loop control scheme. The proposed design presents a simple analytical method for selecting controller gains and has been validated by simulation as well as hardware implementation. Also, this paper presents an illustrative example based on the proposed design for the voltage regulation control of PV-fed boost converters for off-grid applications. The simulation results for varying irradiation, temperature and load along with stability analysis have been presented in this paper. The proposed controller is implemented in hardware for a 1.1 kW PV-array-fed boost converter. Performance analysis based on field test results using real-time weather data validates the proposed design. Therefore the proposed controller could be considered as an attractive solution for off-grid renewable energy applications like PV- or fuel-cell-fed dc–dc converter, where the variations are stochastic in nature.

Sliding Mode Fixed Frequency Current Controller Design for Grid-Connected NPC Inverter

In this paper, a fixed-frequency pulsewidth modulation (PWM) based on sliding-mode current controller is designed and applied to a utility interface three-phase/wire/level neutral-point-clamped inverter. The proposed design methodology of the sliding-mode control is based on a constant switching frequency operation and on Gao’s reaching law that allows chattering compensation. The aim of the controller is to inject a controlled active power from renewable energy sources into the grid while controlling the power factor and minimizing supply current harmonics. Moreover, the dc-link voltages across the split capacitors are controlled with a simple proportional–integral (PI) regulator. Experimental results show the advantages of the proposed control algorithm in terms of fast dynamic response, low voltage ripple on the dc bus, low current Total Harmonic Distortion, and robustness toward external perturbations from the dc and ac sides; moreover, a comparison with a PWM–PI current controller is presented.

Non-linear control of the output stage of a solar microinverter

ABSTRACTThis paper presents a proposal to control the output stage of a two-stage solar microinverter to inject real power into the grid. The input stage of the microinverter is used to extract the maximum available power of a photovoltaic module enforcing a power source behavior in the DC-link to feed the output stage. The work here reported is devoted to control a grid-connected power source inverter with a high power quality level at the grid side ensuring the power balance of the microinverter regulating the voltage of the DC-link. The proposed control is composed of a sinusoidal current reference generator and a cascade type controller composed by a current tracking loop and a voltage regulation loop. The current reference is obtained using a synchronized generator based on phase locked loop (PLL) which gives the shape, the frequency and phase of the current signal. The amplitude of the reference is obtained from a simple controller regulating the DC-link voltage. The tracking of the current reference is accomplished by means of a first-order sliding mode control law. The solution takes advantage of the rapidity and inherent robustness of the sliding mode current controller allowing a robust behavior in the regulation of the DC-link using a simple linear controller. The analytical expression to determine the power quality indicators of the micro-inverter's output is theoretically solved giving expressions relating the converter parameters. The theoretical approach is validated using simulation and experimental results.

Fuzzy-Logic Sliding-Mode Control Strategy for Extracting Maximum Wind Power

A fuzzy-logic sliding-mode control strategy is proposed to capture the maximum wind energy and reduce the generator-side current harmonics for a direct-driven wind power system. The control strategy mainly consists of a fuzzy logic controller for generating the optimum dc-side current and a double integral sliding-mode current controller capable of accurately tracking the optimum dc-side current. A resonant filter is also incorporated into the fuzzy logic controller to eliminate the generator-side current harmonics. Detailed design procedure, existence, and stability conditions of the proposed control strategy have been thoroughly investigated and presented. The capability and effectiveness of the proposed control strategy have been validated by comparative experimental results.

Auto-tuning of PV controllers to improve the speed response and stability of the P&O algorithm

<span>This paper proposes an auto-tuning control system to ensure a fast response of the photovoltaic (PV) voltage by reducing the <span>perturbation time of a P&O algorithm. This solution accelerates the tracking of the maximum power point and, at the same time, <span>guarantees the system stability, which increases the amount of energy produced by the PV system. The control system consists of three <span>cascaded controllers: a P&O algorithm dynamically parameterized by the adaptive law in order to guarantee stability; an adaptive <span>PI controller whose parameters are modified by the adaptive law, depending on the operating conditions, to reduce the settling <span>time of the system as much as possible; and a sliding mode current controller to mitigate environmental and load perturbations and <span>ensure global stability. The design of the new control structure is supported by mathematical analyses and validated with simulations <span>performed in PSIM in order to demonstrate the robustness of the proposed solution.</span></span></span></span></span></span></span><br /><br class="Apple-interchange-newline" /></span>

Auto-tuning of PV controllers to improve the speed response and stability of the P&O algorithm

<span>This paper proposes an auto-tuning control system to ensure a fast response of the photovoltaic (PV) voltage by reducing the <span>perturbation time of a P&O algorithm. This solution accelerates the tracking of the maximum power point and, at the same time, <span>guarantees the system stability, which increases the amount of energy produced by the PV system. The control system consists of three <span>cascaded controllers: a P&O algorithm dynamically parameterized by the adaptive law in order to guarantee stability; an adaptive <span>PI controller whose parameters are modified by the adaptive law, depending on the operating conditions, to reduce the settling <span>time of the system as much as possible; and a sliding mode current controller to mitigate environmental and load perturbations and <span>ensure global stability. The design of the new control structure is supported by mathematical analyses and validated with simulations <span>performed in PSIM in order to demonstrate the robustness of the proposed solution.</span></span></span></span></span></span></span><br /><br class="Apple-interchange-newline" /></span>

Seamless sliding‐mode control for bidirectional boost converter with output filter for electric vehicles applications

This study analyses the feasibility of a unique sliding-mode control law to regulate a bidirectional boost converter with output filter in a seamless manner. The output voltage of the converter is effectively regulated by means of a proportional–integral controller, while the inner current loop has a sliding-mode current controller. The stability of this converter is verified for both step-up and step-down operation modes, considering the converter is part of a determined powertrain arrangement for an electric vehicle. Simulation and experimental results have proven the stability of the system in both operating modes and also during transitions, confirming that sliding-mode control is an appropriate control strategy for a bidirectional boost converter with output filter.

Fuzzy terminal sliding mode control for extracting maximum marine current energy

A new fuzzy terminal sliding mode control strategy is proposed to extract the maximum marine current energy. The control strategy mainly consists of a fuzzy logic controller for deriving the reference q-axis generator current and a non-singular terminal sliding mode current controller capable of accurately tracking the derived reference generator current. A swell filter is also involved in the control strategy to improve the generator power quality in case of swell effects. The detailed design process and stability condition analysis of this control strategy have been thoroughly investigated. The effectiveness of the proposed control strategy has been evaluated in a 60 kW marine current power system. Comparative results demonstrate that the proposed control strategy can be employed to more effectively capture the maximum marine current power and to considerably eliminate the generator power fluctuations as compared with a conventional second-order sliding mode control method.

Reduced state feedback sliding‐mode current control for voltage source inverter‐based higher‐order circuit

This study presents a reduced state feedback sliding-mode current controller (RSFSMCC) for a voltage source inverter (VSI)-based higher-order circuit. The proposed controller consists of an inner current loop and an outer voltage loop. The reference for the inner input inverter current is generated from the outer voltage loop through a proportional plus integral controller. The stability of the system is ensured by using feedback of only two state variables, that is, input inverter current and output capacitor voltage of the VSI circuit. A reduced state feedback analysis is used to obtain the gain matrix for the higher-order circuit. The tracking control convergence criterion of the system is examined through the eigen values of the resultant state matrix derived for the VSI circuit. The frequency response plot shows that the proposed RSFSMCC is robust with good stability margins. The simulation results show that the output voltage well tracks the reference voltage with reduced steady-state error for both linear and non-linear loads. The simulation results obtained in power systems CAD/electromagnetic transients including DC (PSCAD/EMTDC) v4.2.1 software are verified through the experimental results conducted on a single-phase VSI circuit using field programmable gate array implementation of the RSFSMCC.

A Fixed-Switching-Frequency Integral Sliding Mode Current Controller for Switched Reluctance Motor Drives

A fixed-switching-frequency model-based sliding mode current controller with an integral switching surface for switched reluctance motor (SRM) drives is presented in this paper. Based on the equivalent circuit model of SRM, including the magnetic saturation and mutual coupling, an integral sliding mode current controller is designed. The stability of sliding mode controller is analyzed in two scenarios: 1) one with known motor parameters and 2) the other with bounded modeling error. In order to analyze the robustness of the sliding mode controller, the motor controller parameter constraints are derived and the stability analysis is demonstrated by considering motor parameter modeling errors. The sliding mode controller is validated by both simulation and experimental results with a 2.3-kW, 6000-r/min, three-phase 12/8 SRM over the wide speed range in both linear and magnetic saturation regions. Compared to the hysteresis current controller, the sliding mode controller demonstrates comparable transient response and steady-state response in terms of torque ripples, current ripples, root-mean-square error of current and torque. Moreover, the sliding mode controller has some advantages over the hysteresis controller, including constant switching frequency and much lower sampling rate.

A novel fuzzy integral sliding mode current control strategy for maximizing wind power extraction and eliminating voltage harmonics

A novel fuzzy integral sliding mode current control strategy is proposed to extract the maximum wind power and eliminate the high-order voltage harmonics at the generator side for a direct-driven wind energy system. In this control strategy, a fuzzy logic generator is employed to derive the peak power points based on the variations of measured DC-side voltage and current. An integral sliding mode current controller is then designed in this control strategy to track the peak power points. A harmonic compensator is also built inside the fuzzy logic generator for minimizing the voltage harmonics. Major issues in the design and implementation of the control strategy such as detailed design procedure and stability condition have been presented. Comparative experimental results have demonstrated the achievable significant improvements on the maximum power extraction and harmonic elimination by using the proposed control strategy as compared with a conventional control method.

Maximum power point tracking in PV systems based on adaptive control and sliding mode control

Photovoltaic (PV) systems are commonly controlled using PI or PID structures, which cannot ensure global stability and a constant settling time. Therefore, the optimization algorithms, e.g. Perturb and Observe (P&O), are designed using the highest settling time in the operating range, which produces a slow tracking of the maximum power point (MPP) for the largest part of the operation range, introducing dynamic power losses to the system. This paper proposes to combine an adaptive controller and a sliding mode current controller (SMCC) to guarantee global stability and a constant settling time for any operation condition, which enable to increase the generated power in comparison with PI and PID controllers. The SMCC enables to mitigate the system perturbations and guarantee global stability, while the adaptive controller defines the reference of the SMCC to ensure a constant settling time. The design of the new control structure is supported by mathematical analyses and simulations made in Matlab®, where the robustness of the system is validated.

Direct sliding mode current control of feed drives

Dealing with cascade control of electrical feed drives involves optimizing the current loop regarding precision, dynamics, robustness and energy efficiency. This is challenging using switching inverters with pulse width modulation. A direct method based on a switching controller is presented, which needs no downstream modulator. Control takes place in field-oriented as well as in phase-oriented coordinates of the machine, providing benefits compared to other direct methods. Control rules and structures are derived and a comparison between conventional and novel approach is shown. Implementation and measurement were performed in a practical setup, proving higher dynamics and less energy consumption.

Bidirectional direct current-direct current converter for fuel cell and renewable energy hybrid systems

A bidirectional dc-dc power converter is an essential part of a HFCEV (Hybrid Fuel Cell Electric Vehicle) and renewable energy hybrid system. This paper presents a new bidirectional dc-dc power converter for HFCEV and renewable energy hybrid systems. The proposed converter is called four phases floating interleaved boost converter. Two control strategies of the dc-bus voltage are discussed. In the first one, a dual loop with linear current and voltage controllers is developed, based on the frequency response of the system. In the second one, the linear current controller is replaced by a non-linear sliding mode current controller, to improve the system performance from the robustness point of view. The non-linear sliding mode controller is designed based on the average model of the proposed topology. The proposed control strategies have been validated by simulation and experimental results.

An efficient sliding-mode current controller with reduced flickering for quadratic buck converter used as LED lamp driver

This paper presents mathematical analysis, design and simulation of a quadratic buck converter used as LED lamp driver, and the performance of the converter is compared with two different control strategies. The objective is to provide tight regulation of the LED current that can operate over a wide range of DC input voltages. The first control strategy is the non–linear Sliding–Mode (SM) current controller, and its design aspects include choice of sliding surface, deriving existing and stability conditions, control parameter selection and their analysis. This paper also throws light on Average Current–Mode (ACM) controller. The operation, modelling, designing and transfer function derivation for the inner current and outer voltage loops of the quadratic buck converter are presented. The tuning of controllers for the ACM controller is done using Bode plots, for achieving desired phase and gain margins. The simulation is done using PSIM software and the results are presented.

FPGA-Based Dynamic Reconfiguration of Sliding Mode Current Controllers for Synchronous Machines

This paper presents the concept of dynamic reconfiguration between two sliding mode current controllers for synchronous motor drives. The first one is a Direct Sliding Mode (DSM) current controller, which is based on a switching table synthesized via sliding mode theory. The second one is an Indirect Sliding Mode (ISM) current controller that computes a reference voltage vector via sliding mode theory. The computed reference voltage is then applied to the terminals of the synchronous machine through a Pulse Width Modulation (PWM) process. This item studies and discusses the reconfiguration criteria and presents the main interest of using FPGA digital solutions for dynamic reconfiguration process implementation between the two sliding mode current controllers. Numerous experimental results are presented in order to confirm the interest and performances of the proposed reconfigurable sliding mode current controller.