Proportional-integral Current Controller Research Articles

Super Twisting Sliding Mode Control of Four-Phase Interleaved Boost Converter

This paper presents a novel control method that integrates super-twisting sliding mode (STSM) voltage control with proportional-integral (PI) current control for a four-phase interleaved boost converter (IBC) in fuel cell applications. The STSM control, employed in the outer voltage loop, provides robust voltage regulation by generating precise reference currents for each phase. The conventional PI control in the inner current loop utilizes these reference currents to generate pulse width modulation (PWM) signals for each phase. The effectiveness of the proposed control strategy is evaluated through comprehensive simulation studies in MATLAB/Simulink, demonstrating an improvement in dynamic performance and enhanced robustness compared to conventional methods. Quantitative analysis shows that the output voltage quickly rises to the reference voltage within approximately 0.25 seconds in the proposed STSM-PI control method and improves transient response by 16 times compared to the conventional PI-PI method. This integrated STSM-PI control strategy offers significant advancements in reliability and efficiency making it a promising solution for high-performance fuel cell power systems.

Enhancing grid-connected photovoltaic system performance with novel hybrid MPPT technique in variable atmospheric conditions

This paper proposes an innovative approach to improve the performance of grid-connected photovoltaic (PV) systems operating in environments with variable atmospheric conditions. The dynamic nature of atmospheric parameters poses challenges for traditional control methods, leading to reduced PV system efficiency and reliability. To address this issue, we introduce a novel integration of fuzzy logic and sliding mode control methodologies. Fuzzy logic enables the PV system to effectively handle imprecise and uncertain atmospheric data, allowing for decision-making based on qualitative inputs and expert knowledge. Sliding mode control, known for its robustness against disturbances and uncertainties, ensures stability and responsiveness under varying atmospheric conditions. Through the integration of these methodologies, our proposed approach offers a comprehensive solution to the complexities posed by real-world atmospheric dynamics. We anticipate applications in grid-connected PV systems across various geographical locations and climates. By harnessing the synergistic benefits of fuzzy logic and sliding mode control, this approach promises to significantly enhance the performance and reliability of grid-connected PV systems in the presence of variable atmospheric conditions. On the grid side, both PSO (Particle Swarm Optimization) and GA (Genetic Algorithm) algorithms were employed to tune the current controller of the PI (Proportional-Integral) current controller (inverter control). Simulation results, conducted using MATLAB Simulink, demonstrate the effectiveness of the proposed hybrid MPPT technique in optimizing the performance of the PV system. The technique exhibits superior tracking efficiency, achieving a convergence time of 0.06 s and an efficiency of 99.86%, and less oscillation than the classical methods. The comparison with other MPPT techniques highlights the advantages of the proposed approach, including higher tracking efficiency and faster response times. The simulation outcomes are analyzed and demonstrate the effectiveness of the proposed control strategies on both sides (the PV array and the grid side). Both PSO and GA offer effective methods for tuning the parameters of a PI current controller. According to considered IEEE standards for low-voltage networks, the total current harmonic distortion values (THD) obtained are considerably high (8.33% and 10.63%, using the PSO and GA algorithms, respectively). Comparative analyses with traditional MPPT methods demonstrate the superior performance of the hybrid approach in terms of tracking efficiency, stability, and rapid response to dynamic changes.

Analysis of AWPI Based Hybrid Grid-tied Inverter for Smart Energy Management System

Renewable energy sources are gaining popularity in recent years for power generation. The world has an abundance of pollution-free solar and wind energy; batteries play vital role for energy storage and all these sources combine to form a hybrid power system. Efficient management of the hybrid system via controlling the operation of its components is essential. In this article, a smart energy management system is proposed, where the control is focused on the hybrid grid-tied inverter. The inverter module is controlled through an anti-windup proportional-integral (AWPI) current and voltage controller. The performance of the proposed control system has been analyzed through current, and voltage Total Harmonic Distortion (THD) before and after grid integration. The suggested AWPI controller effectively mitigated the voltage drop and maintained the THD within the appropriate level. In addition, the proposed scheme of interest enhanced the steady-state response of the smart-grid system. The comparative analysis made among the intended controller and its counterparts inferred its superiority.

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.

An optimal angle control strategy for switched reluctance motor drive in EV applications

In this study, a hybrid method of the Harris-Hawk optimisation method is used to simultaneously manage the speed of a switched reluctance motor and minimise the torque ripple. A proportional integral (PI) speed controller is used in the outer loop of the three-phase, six-phase switching reluctance motor, and a PI current controller is used in the inner loop. Turn-on and turn-off angles are also controlled. In order to decrease current parameter error measures, reduce torque ripples, and increase efficiency, the task of finding the turn-on and turn-off angles is treated as an optimisation problem. Using the suggested optimisation technique, a model with adjustable turn-on and turn-off angles under different load torques is produced. When contrasted to current optimisation methodologies, the suggested model is demonstrated to be efficient for torque ripple suppression and speed augmentation simultaneously.

Steady-State and transient assessments of integral back-stepping current controllers in high-voltage direct current transmission systems

In the last five decades, proportional-integral (PI) controller remains dominant in control of high-power converters in industrial and utility power systems despite its bandwidth, hence, the performance is coupled to power circuit parameters and degrades in parts of operating range. Consequently, further mitigation measures such as fine-tuning or loop reshaping might be needed. In contrast, integral back-stepping (IBS) decouples controller bandwidth and performance from the system parameters; hence, leads to consistent performance throughout the operating range and simplifies tuning of controllers with complex structures with multiple loops. Therefore, this paper investigates the suitability of IBS for implementation of inner current controllers of the voltage source converter (VSC)-based high-voltage direct current (HVDC) transmission systems. The paper presents step-by-step synthesis of back-stepping current controller and supporting theoretical bases, and assesses its performance against the conventional PI current controller. Theoretical analysis and discussions and comparative simulations reveal that the characteristics of IBS technique enjoys unique characteristics: decouples the controller gains from the converter parameters; restricts closed loop poles to real axis; and exhibits larger closed loop bandwidth than the PI counterpart. It has been shown that the gains of IBS current controllers are explicitly specified in terms of the desired natural frequency and damping ratio, which are advantageous compared to that of the PI equivalent, in which the closed loop bandwidth are limited by converter parameters. For ease of illustration of similarities and differences, only inner current controllers of the converter stations were designed using integral back-stepping technique and compared against PI equivalents. The outer control loops such as dc link voltage, active and reactive power controllers are designed based on proportional-integral controllers. MATLAB-SIMULINK models of the point-to-point VSC-HVDC system, in which the current controllers implemented using integral back-stepping and proportional-integral controllers (active/reactive power and DC link voltage controllers) have been developed and subsequently used for performance comparison. Results of the one-to-one comparison show that the integral back-stepping current controller can match and even outperform its proportional-integral equivalent during normal and abnormal conditions, including current limitation during ac faults. Selected experiments conducted on grid connected voltage source converter that employs IBS current controller have confirm its viability.

Study of novel parallel H-bridge and common-emitter current-source inverters for photovoltaic power conversion system

A novel operation of three-level H-bridge and common-emitter current source inverters (CSIs) proposed for photovoltaic power converters is presented in this paper. Two photovoltaic systems with two different inverter circuits, i.e. H-bridge and common-emitter CSIs, were connected in parallel to supply a sharing ac power load. In order to regulate the power supplied by each inverter system, proportional integral current controllers were employed. Triangular carrier and sinusoidal signals-based modulation techniques were implemented to both inverters. Some parameters such as load current, inverter’s output current, total harmonics distortion (THD), and efficiency were tested and analyzed. Test results showed that in the parallel operation of these inverters, the average THD percentage of the load current was 0.34% for load power factor 0.996 and 0.62 % for load power factor 0.782. Minimum waveform distortion of inverter ac currents during parallel operation can be achieved if the current magnitudes of both inverters were set the same. In the case of efficiency, the maximum efficiency of the system was 89.07%. Operating the H-bridge CSI with a higher magnitude of the output current will result in higher efficiency of the system.

Parameter Tuning of Sliding Mode Speed Controller of Induction Motor Drive Using Teaching-Learning Based Optimization Algorithm

The optimal settings of the Sliding Mode Controller for three-phase Induction Motor speed regulation are proposed in this paper using a Teaching-Learning Based Optimization Algorithm. It is a straightforward metaheuristic algorithm that simulates the teaching-learning processes in a classroom. Indirect Field Oriented Control is used in this induction motor drive, which allows the motor torque and the flux to be separated, similar to a DC motor. The inner loop uses proportional-integral current controllers, whereas the outside loop uses a sliding mode speed controller. In this paper, the sliding mode controller uses a tanh function as a switching function. Integral Time Absolute Error and Zwe-Lee Gaing's parameters are used as objective functions for tuning sliding mode controller settings. Performances of the proposed scheme in terms of the transient response analysis are compared with the swarm intelligence-based algorithms, namely the modified Particle Swarm Optimization and Grey Wolf Optimization. MATLAB/ SIMULINK software is used to build the three algorithms and sliding mode controller-based induction motor drive models, which are then analysed using simulation experiments. In comparison to the modified Particle Swarm Optimization and the Grey Wolf Optimization algorithms, Teaching-Learning Based Optimization yields the lowest value of the objective function Zwe-Lee Gaing's parameter and it converges quickly.

Parallel connected GaN E‐HEMT VSI‐based servo drives for PMSMs

The operation of parallel-connected servo drives has the advantages of increasing the torque (hence the power) capacity, reliability, redundancy and modularity. However, smaller discrepancies of the system clocks of the independent microcontrollers, asynchronous pulse width modulation (PWM) carrier signals and hardware differences can make the output voltages of the parallel modules non-identical, which results in circulating currents. These circulating currents limit the parallel operation, introduce additional power dissipation, cause unbalanced power distribution and degrade the control performance. To eliminate the circulating currents separated DC supplies, coupled inductors (CIs), PWM techniques, modified control techniques etc. are proposed in the literature. In this study, a fault-tolerant parallel-connected gallium nitride enhancement-mode high electron mobility transistor voltage source inverter-based servo drive scheme that eliminates the need for CIs and separate DC supplies and also enables the use of a standard proportional-integral current control and a standard space vector PWM approach is proposed and tested. To evaluate the performances of the proposed scheme, up to six servo drives (limit-6 × 7 Arms) are connected in parallel and tested under various conditions with a 24 V permanent magnet synchronous motor (nominal-61.9 Arms). The results show that the parallel operation not only increases the torque capacity of the system but also increases modularity, flexibility, reliability and also redundancy.

Design and Development of Experimental Based Phase Modulated Model Predictive Control for Torque Ripple Reduction of MMC Fed BLDC Motor

This article represents the torque ripple performance of modular multilevel converter (MMC) fed brushless dc (BLDC) motor using different current control technique. For reducing the ripple current in BLDC motor, a phase-modulated model predictive control (PMMPC) technique has been proposed. The stator ripple current is almost negligible using PMMPC. This PMMPC current control method is a significant minimization of torque ripple in BLDC motor. A comparative torque ripple behaviour of MMC fed BLDC motor has been done using phase-modulated model predictive control, model predictive control (MPC) and proportional integral (PI) control at different switching frequency. It has been observed that a PMMPC current control technique is more efficient as compared to the MPC as well as PI current control technique. It has also been observed that the torque ripple performance is improved while using PMMPC as compared to the MPC and PI controller. Simulation results have been verified with the help of experimental result and these results are obtained in good agreement to the simulated results.

A Novel DSP-Based MPPT Control Design for Photovoltaic Systems Using Neural Network Compensator

In this study, based on the slope of power versus voltage, a novel maximum-power-point tracking algorithm using a neural network compensator was proposed and implemented on a TI TMS320F28335 digital signal processing chip, which can easily process the input signals conversion and the complex floating-point computation on the neural network of the proposed control scheme. Because the output power of the photovoltaic system is a function of the solar irradiation, cell temperature, and characteristics of the photovoltaic array, the analytic solution for obtaining the maximum power is difficult to obtain due to its complexity, nonlinearity, and uncertainties of parameters. The innovation of this work is to obtain the maximum power of the photovoltaic system using a neural network with the idea of transferring the maximum-power-point tracking problem into a proportional-integral current control problem despite the variation in solar irradiation, cell temperature, and the electrical load characteristics. The current controller parameters are determined via a genetic algorithm for finding the controller parameters by the minimization of a complicatedly nonlinear performance index function. The experimental result shows the output power of the photovoltaic system, which consists of the series connection of two 155-W TYN-155S5 modules, is 267.42 W at certain solar irradiation and ambient temperature. From the simulation and experimental results, the validity of the proposed controller was verified.

Model Predictive Current Control of Multiphase Motor at Low Carrier Ratio

Multiphase motors have multiple control planes, and harmonics are decoupled in different planes. Multiphase motors can improve magnetic field distribution, power density and core utilization by injecting certain harmonic currents into the harmonic planes. In the harmonic plane control process, due to the switching frequency of the inverter being limited, the ratio of the switching frequency to the current frequency (the carrier ratio) of the harmonic plane is low, the digital control delay increases, and the inverter output current contains more harmonics, which makes it difficult for the proportional-integral (PI) current controller to effectively control the d-axis and q-axis currents of the harmonic plane and thus unable to track the given values stably. Moreover, the PI current controller is relatively dependent on the motor parameters. For these reasons, a model predictive current control method with predictive error compensation is proposed. Taking a nine-phase induction motor as an example, the control voltage is calculated by the cost function and corrected by the current predictive error, which realizes the current control method at a low carrier ratio. Additionally, the robustness of the control method is analyzed after the parameters of the multiphase motor have large errors. The experimental results show that the proposed method can control the current of the harmonic plane at low carrier ratio, accurately track the harmonic current commands and attain strong robustness for the motor parameters.

Improving output current of inductor-cell based five-level CSI using hysteresis current controller

Current source inverter (CSI) operates to output a specified ac current waveform from dc current sources. Talking about power quality, harmonics distortion of ac waveform is a problem of an inverter circuit. Generating a multilevel current waveform will have less harmonics content than a traditional three-level current waveform. In addition to non-ideal conditions of power switches, i.e. voltage drop in diodes, conductors or controlled switches, the performance of current controller applied in an inverter circuit will considerably affect the ac waveform quality produced by inverter circuit. This paper presents and discusses application of hysteresis current controller in the five-level H-bridge with inductor-cell current source inverter. The current controller performance was compared with the proportional integral current controller. Some test results are presented and discussed to explore the advantages of hysteresis controller in reducing the current ripple and harmonics distortion of output current.

Design and Analysis of Vector Proportional–Integral Current Controller forLC-Coupling Hybrid Active Power Filter With Minimum DC-Link Voltage

In this article, a vector proportional-integral (VPI) current controller for the LC-coupling hybrid active power (LC-HAPF) with ideally zero steady-state error, optimal transient response, and good robustness is proposed. First, the transfer function of the proposed VPI current controller is introduced, and its parameter design for obtaining optimal transient response is discussed. Second, a detailed robustness analysis of the VPI current controller, including the system parameter variation, distorted grid voltage, and grid frequency variation conditions, is proposed. Third, the digital implementation method of the VPI controller and an overall control block diagram for the LC-HAPF with the proposed VPI current controller are presented. Moreover, a comparative study and analysis between the VPI current controller and the other representative current controllers under the minimum dc-link voltage is discussed in which the VPI current controller obtains the best performances under the minimum dc-link voltage operation. The simulation and experimental results are provided to verify the advantages and effectiveness of the proposed VPI current controller for a three-phase four-wire LC-HAPF in comparison with the other representative current controllers under different dc-link voltage conditions. Finally, the robustness under different grid conditions and unbalanced compensation capability of the proposed VPI-controlled LC-HAPF are also verified by the experimental results.

Fast and Simple Tuning Rules of Synchronous Reference Frame Proportional-Integral Current Controller

Synchronous reference frame proportional-integral (PI) current controller (CC) is considered the most well-established solution for the current regulation in electrical drives. However, the gain selection of the PI CC is still regarded to be poorly reported, particularly in relation to the effect of the inevitable execution time taken by the controller and inverter. Mostly, tuning process of PI CC is done by trial and error or using simple rules based on pole zero cancelation and pole placement methods which ignore time delays through the controller and inverter. Hence, PI CC delivers significantly different performance compared to the expected one during the digital implementation, especially if high bandwidth or low ratio between the switching and operational frequency are required. Therefore, this paper firstly addresses and analyses the common tuning rules of PI CC which ignore the existence of time delays followed by a rigorous analysis for PI CCs' robustness to the influence of computational and modulation delays. Based on this analysis, generic recommendations have been proposed to select the PI CCs' gains as a function of the electrical drive switching frequency considering the delay effect. A set of simple, generic, and fast tuning rules were derived that guarantee fast dynamic performance with reasonable stability margins. Moreover, the effects of model uncertainties on these developed rules have been analyzed and reported. Comprehensive experimental results are provided to prove the key analytical results of this study and to validate the proposed design recommendations.

A Novel Voltage Injection Based Offline Parameters Identification for Current Controller Auto Tuning in SPMSM Drives

This paper presents a comprehensive study on a novel voltage injection based offline parameter identification method for surface mounted permanent magnet synchronous motors (SPMSMs). It gives solutions to obtain stator resistance, d- and q-axes inductances, and permanent magnet (PM) flux linkage that are totally independent of current and speed controllers, and it is able to track variations in q-axis inductance caused by magnetic saturation. With the proposed voltage amplitude selection strategies, a closed-loop-like current and speed control is achieved throughout the identification process. It provides a marked difference compared with the existing methods that are based on open-loop voltage injection and renders a more simplified and industry-friendly solution compared with methods that rely on controllers. Inverter nonlinearity effect compensation is not required because its voltage error is removed by enabling the motor to function at a designed routine. The proposed method is validated through two SPMSMs with different power rates. It shows that the required parameters can be accurately identified and the proportional-integral current controller auto-tuning is achieved only with very limited motor data such as rated current and number of pole pairs.

Validation of Novel PLL-driven PI Control Schemes on Supporting VSIs in Weak AC-Connections

The integration of distributed energy resources (DERs) in modern power systems has substantially changed the local control capabilities of the grid since the majority of DERs are connected through a controlled dc/ac inverter interface. Such long-distance located DER installations, usually represented by current regulated dc sources, can inject large amounts of power into the main ac grid at points where the strength of the ac connection is low. The efficient and stable performance of such a power scheme is related to the capability of the control applied to retain the power extraction close to the maximum and simultaneously to regulate the dc-side voltage as well as the ac-side voltage magnitude at the weak ac connection point. This is implemented by designing the controllers of the voltage source inverters (VSIs) in a manner that reliably satisfies the above tasks. To this end, decentralized cascaded control schemes, driven by novel, locally implemented phase locked loops (PLLs), suitable to work in weak ac connections, are proposed for the VSI performance regulation by using new fast inner-loop proportional-integral (PI) current controllers. A decisive innovation is proposed by inserting an extra damping term in the inner-loop controllers to guarantee stability and convergence to the desired equilibrium. This is analytically proven by a rigorous analysis based on the entire nonlinear system model, where advanced Lyapunov-based methods are deployed in detail. As a good transient response of the VSI interface is indeed critical for the energy and grid system management, the conducted simulation and experimental results confirm that the proposed scheme efficiently supports the ac- and dc-side voltages of the VSI under different varying conditions in the power production or any voltage changes of the main grid.

Investigations on Three-phase Grid-Connected Inverter using PWM Controllers

In recent years, a Multilevel Inverter (MLI) topology is highly preferred in the various renewable energy applications for converting power due to their merits. In this paper, a three-phase inverter has been designed for grid-connected applications using Proportional Integral (PI) current controller scheme. To generate a sequence, the Level shift (LS) and Phase Shift (PS) Pulse Width Modulation (PWM) methodologies are adapted. This topology has been designed with two stages: the DC-DC conversion stage and DC-AC conversion stage. The DC-DC conversion stage is used to enrich input DC voltage which is obtained from the solar PV array. The PI current controller has been designed to regulate the grid current with park transformation. The performances of the inverter have been examined in terms of Total Harmonic Distortion (THD) using different PWM techniques and also investigated with existing research works. The developed results are verified using MATLAB/ Simulink.

Comparative Study of Discrete PI and PR Controls for Single-Phase UPS Inverter

This paper presents a comparative study of discrete proportional integral (PI) and proportional resonant (PR) current control for single-phase uninterruptible power supply (UPS) inverters. There is an increasing requirement for current and voltage-controlled UPS inverters with very low or zero steady-state error, improved transient response and lower total harmonic distortion (THD). The most promising type of current regulator for single-phase inverters is PR control because it can introduce an infinite gain at a selected resonance frequency such as the fundamental frequency to eliminate the steady-state error, which cannot be achieved by well-known proportional integral (PI) control. Note that PI control has limitations in terms of the steady-state magnitude and phase errors. In addition, PI control also has limited harmonic rejection capability, unlike the PR control, also can compensate for low-order harmonics. Imperfections in the current and voltage control scheme results in higher harmonic distortion of the output current and voltage. In this paper, performance of PR control parameters ($K_{p}$ , $K_{i}$ , and $\omega _{c}$ ) and filter parameters ($L_{f}$ and $C_{f}$ ) are optimally tuned to obtain a very low THD current with reduced output voltage ripple and steady-state error. The analysis, design and implementation of both PI and PR current control in single-phase UPS inverter applications through simulations and experiments are also presented in this paper. The performance of both of these control schemes are analyzed in terms of steady-state response, transient response, and level of current harmonics.

A Strongly Robust and Easy-Tuned Current Controller for PMSM Considering Parameters Variation

This paper proposes an improved internal-model-control (IMC)-based proportional-integral (PI) current controller for a permanent magnet synchronous motor (PMSM) drive system to solve the parameter dependence problem. The parameter sensitivity of the conventional IMC-based PI controller is analyzed, which indicates that the parameters mismatch would cause oscillation or overshoot. Therefore, this paper utilizes an uncertainty and disturbance estimator to eliminate the impact of the parameters mismatch disturbance caused by the parameters variation. The proposed controller includes an IMC-based PI controller, which is responsible for tracking, and a disturbance estimator, which deals with other control difficulties. The performance and robustness are easily achieved by separately tuning the only two parameters (the desired closed-loop bandwidth and the estimator bandwidth). The frequency-domain characteristic of the proposed current controller indicates that it can effectively suppress the parameters mismatch disturbance. Simulations and experiments have verified the effectiveness of the proposed method.