A model reference resonant current controller for grid connected voltage source inverter

This paper presents a control scheme for grid-connected PWM voltage source inverters (VSIs) featuring fast load voltage regulation and effective mitigation of fast voltage disturbances. To ensure perfect regulation of the voltage at the point of common coupling, and provide means for rejecting voltage disturbances, the voltage control loop should offer a high disturbance rejection performance. Toward this, a hybrid voltage controller combining a linear with variable-structure control (VSC) element is proposed to generate the reactive current reference in a grid-connected VSI. The proposed voltage controller can embed a wide band of frequency modes through an equivalent internal model. Subsequently, wide range of voltage perturbations, including capacitor-switching transients, can be rejected. To optimally tune the proposed nonlinear voltage controller, the tuning problem is formulated as a constrained optimization problem, and solved via an evolutionary search algorithm based on the particle-swarm-optimization (PSO) technique. Therefore, a simple and structured tuning methodology can be obtained. Theoretical analysis and comparative evaluation tests are presented to demonstrate the effectiveness of the proposed control scheme.

This paper investigates the modeling and decoupling control of grid-connected voltage source inverter (GC-VSI) for wind energy conversion system (WECS) applications. Firstly, the typical configuration and operation principle of the direct-driven grid-connected WECS are analyzed. Then, by means of input-output modeling method and instantaneous active power theory, a time domain mathematical model of the GC-VSI is set up. Besides, in order to resolve the GC-VSI active current and reactive current cross-coupling nonlinear control problem, a vector decoupling control method for the GC-VSI firing pulse generation is deduced in the dq synchronous rotating coordinates. The proposed decoupling control method can realize the active power and reactive power of the GC-VSI injected into the grid are regulated independently. Finally, the performance of the proposed GC-VSI system is evaluated by using MATLAB/Simulink simulation.

Currently, the Passivity-Based Control (PBC) has been used successfully in Grid-Connected Voltage Source Inverter (GCVSI) with L or LC filter. In practice, an LCL filter is widely used for the GCVSI. However, only a few papers have discussed how to apply the PBC for the GCVSI with LCL filter, where there is a complex structure in a three phase system due to using six state variables, and the variation of grid impendence is not addressed at the same time. In this paper, a PBC controller with only two state variables is presented. Furthermore, an active damping (AD) method is inserted into the control loop to resist the reverse effect of grid impendence variation, and to achieve a wide control bandwidth. The modeling and controller design are detailed described. The simulation platform is carried out in Matlab/simulink to verify the theoretical analysis.

Grid-connected Voltage Source Inverter (VSI) with LCL filters, controlled by proportional-resonant compensator in αβ frame, is very popular in utility application for its better power quality feature, while the inherent LCL resonance characteristic limits the control loop bandwidth and threatens the system stability. The active damping is essential to dampen the LCL resonance. This paper investigates the active damping method with only grid current feedback. Compared with the most widely used capacitor current feedback active damping, this novel method avoids the use of extra sensors to detect the capacitor current, which possesses the merits of lower cost and higher reliability. By performing the equivalent control block diagram transformation, it is revealed that a virtual impedance in series or parallel with the grid-side inductor can ideally be implemented with specific active damping controllers, which also comprehensively reflects the physical circuit property of grid current feedback active damping. However, the second-order derivative terms are needed in the ideal forms of the active damping controllers which can hardly be realized in practice. To deal with this issue, a second-order transfer function is proposed to approximate the s2 term in the required frequency range for realizing the similar LCL resonance damping performance. Further, a straightforward design method to determine the parameters of the active damping controller is introduced. Finally, the effectiveness of the proposed control method and relevant design strategies are verified both in time and frequency domain.

In this manuscript it is proposed and demonstrated that how an ANFIS (Adaptive Neuro Fuzzy Inference System) can be used in the control of a Voltage Source Inverter (VSI) connected to the grid. Volatile changes in the gird parameters rising by its variable demands and other related issues may humiliate the efficiency with which power can be injected into the grid. The system becomes a higher order one with the filters used at the terminal of the Voltage Source Inverter (VSI) along with the parameters of the grid which change from time to time. Single time tuned mathematical controllers like the PID variants are not suitable for such applications. Considering the increased order of the system and the associated non-linearity we have to look out for intelligent controllers. An ANFIS based control is found to be promising; the development and implementation of one such are demonstrated in this paper using the MATLAB SIMULINK platform and through experimental verification using the Reduced Instruction Set Computer (RISC) Microcontroller Advanced RISC Machine (ARM) processor as the central controller for the VSI.

This paper addresses the stability of discrete controlled grid connected voltage source inverters with LCL-filter usually found in wind power generation systems. First a theorem that relates the controllability of the discrete dynamic equation with the LCL-filter parameters and the sampling frequency is derived. Then, a robust partial state feedback design on the linear matrix inequalities framework guarantee the stability damping the LCL-filter resonance for a large set of grid conditions without requiring tuning procedures. Finally, an internal model controller is added to ensure asymptotic reference tracking and disturbance rejection, therefore reducing significantly the impact of grid background voltage distortion on the line currents. Simulation and experimental results are presented to support the theoretical analysis carried out and to demonstrate the system performance.

This paper proposes the use of an alternative current control strategy for grid connected Voltage Source Inverters (VSIs) via LCL-filters. In this strategy, the weighted average current flowing through the LCL-filter inductors is used as a control variable, droping the order of the plant transfer function, from three to one, similar to the obtained from an L-filter. A Model Reference Control (MRC) is used for reference tracking in short circuit, while an Adaptive Feedforward cancellation scheme (AFC) is used to compensate for the voltage disturbances effect at the point of commom coupling with the grid.

Purpose The purpose of this study is to present a new methodology of selective harmonics elimination (SHE) technique suitable for single-phase photovoltaic (PV) tied pulse width modulated (PWM) inverter. Design/methodology/approach In the proposed SHE, switching angles for inverter control are determined offline through numerical techniques and stored in a microcontroller memory as a function of modulation index (md). The methodology uses the solution that leads to a lower change of switching angles from the previous modulation index (md) for storing in the processor memory for multiple solutions. This leads to a smaller number of sections when a piecewise mixed model is considered for storing the entire switching angle curve for the online inverter control. The proposed idea is simulated and experimentally validated on a laboratory prototype of PV (500 W) grid-tied PWM inverter. The control environment is then realized in NI c-RIO 9082. Findings This proposed technique is suitable for limiting voltage total harmonics distortion (THD) in single-phase PV tied grid connected voltage source inverter (VSI). Moreover, it is found that filter (L-C) size requirement is less. Originality/value The proposed SHE with piecewise mixed model technique effectively reduces voltage THD with less filter size (L-C) in a single-phase PV-tied system.

The control of a grid connected voltage source inverter (VSI) with an LCL filter is a very challenging task, since the LCL network causes a resonance phenomenon near to the control stability boundary. While many active damping methods have been proposed to overcome this issue, the role that PWM transport delay plays in the effectiveness of these strategies is still not fully resolved. This paper presents a theoretical discrete time analysis frame work that identifies three distinct regions of LCL filter resonance - a high resonant frequency region where active damping isn't required; a critical resonant frequency where a controller cannot stabilise the system; and a low resonant frequency region where active damping is essential. Suitable controllers are then proposed for the two stable regions, with gain calculations that allow for the greatest system bandwidth and damping. Simulation and experimental results verify the presented analysis.

In this chapter, the properties of the transfer function and frequency response of first and second order systems are studied on some examples from electrical circuit laws. We show that their properties are governed by the poles (i.e., the zeros of the denominator) of the transfer function which is a rational fraction. A geometric argument based on the location of the poles of the transfer function in the complex plane allows a qualitative interpretation of the behavior of the frequency response with varying frequency. This geometric interpretation is easily generalized to situations with any number of zeros and poles. It proves useful for the understanding of the general behavior of filters. The study begins here with the simplest system, the first order system. Then the second order circuit system is presented thoroughly. The logarithmic Bode representation of the frequency gain is introduced and its advantages demonstrated. The quality factor Q of a resonant circuit is defined.

Solar energy can be effectively utilized as the grid-connected photovoltaic (PV) generation system. But in weak grid, the non-ignorable network equivalent impedance is a great challenge for the stability of grid-connected voltage source inverters (VSIs). This paper focuses on the single-stage three-phase grid-connected PV inverter, presents a small signal model of PV inverter, and gives a physical insight by making an analogy between synchronous machine rotor movement and DC-link voltage dynamics of PV VSI to analyze the stability of DC-link voltage in VSI when connect to weak grid. The impact of P-V characteristic of PV array on single-stage PV inverter is discussed. Simulation results of PV power system, which includes grid-connected PV VSI and PV array, are given to verify the analysis.

Grid connected voltage source inverters require both current regulation and synchronisation to control the power flow and to maintain stability during grid disturbances. For this type of application, non-linear current control of VSIs using techniques such as hysteresis current regulation offer advantages compared to linear current regulation, such as inherent over-current protection, robustness to load/filter parameter variation and very rapid dynamic response. However these techniques suffer from variable switching frequency and their implementation can require significant analog circuitry. Furthermore, sensorless grid synchronisation can improve the inverter's robustness to disturbances such as electrical line interference, sensor failure and rectifier commutation voltage notches. This paper presents a fully digital constant frequency three-level hysteresis current regulator for single phase PV inverters that addresses these issues. The proposed control strategy also uses the average inverter voltage to adjust the hysteresis band to maintain a constant frequency, detect the output voltage polarity and estimate the grid voltage. The result is a robust current regulator with increased flexibility and easy adaptability for grid connected inverters.

This paper presents a control scheme for a grid-connected three-phase voltage source inverter with an LCL filter, which is suited for renewable energy applications. The proposed method has the following properties: fast tracking, optimized dynamics, grid disturbance rejection, and active resonance damping. The controller is based on an augmented linear quadratic regulation (LQR) scheme, which is optimized based on a weighted cost function. The LQR controller is augmented to include two complex conjugate poles at the grid frequency for sinusoidal voltage disturbance rejection upon connection to the grid. Furthermore, this control scheme actively damps the resonance introduced into the closed-loop system through the third-order LCL filter. Finally, the current reference is found by calculating the instantaneous power, which allows for faster power tracking compared to using the technique of measuring average power. Results verify the validity of the proposed control scheme.

This paper proposes a robust predictive resonant current control (RPRCC) to improve the dynamic and anti-disturbance performance of the permanent magnet synchronous linear motor (PMSLM). First, the disturbance caused by parameter variation is considering in modeling PMSLM. Based on this model, a robust predictive current control (RPCC) with mover current and disturbance estimation (MCDE) is derived, which is used to simultaneously overcome the time-delay and estimate the parameter disturbance. Then, in order to further suppress periodic disturbance caused by voltage source inverter (VSI) nonlinearity, an appropriate resonant controller is embed to RPCC. The combined controller is called RPRCC. Finally, a precise test platform based on semi-physical system AD5435 is established, and experimental results show the validity of the proposed approach.

The proportional–integral (PI) control is usually applied in synchronous reference frame to regulate the output voltage of three-phase voltage source inverter (VSI). However, the PI controller is constrained by the capability of suppressing harmonic and negative sequence components; besides, its direct application in single-phase VSI is limited. While the proportional–resonant (PR) control can track ac reference and achieve harmonic suppression in stationary frame for both single-phase and three-phase VSI. Due to the high order of the resonant controller, lots of efforts are needed during the parameter design to get a satisfactory performance, such as trial-and-error. In this article, the way to approximately reduce the order of the resonant controller in the discrete time domain is presented, and then a method of selective pole placement and cancellation for the PR control design used in VSI is proposed. With the proposed method, the closed-loop pole-zero distribution of the PR control structure used in the VSI is well handled, and the parameters of the feedback controller and the reference feedforward controller are directly calculated by placing the selected poles and zeros in desired positions. The procedure of the parameter design is facilitated, and the performance of the VSI with PR control is improved.