quasi-PR Controller Research Articles

Single-phase photovoltaic off-grid inverter based on quasi-PR control

Given the rapid growth of renewable energy generation, photovoltaic inverters have gained widespread adoption in power generation systems. To achieve improved precision in control and enhanced quality in the output waveform of the inverters, this article presents a single-phase photovoltaic inverter designed for both grid-connected and off-grid systems. It utilizes a quasi-proportional-resonant control technique. Initially, the mathematical representation of the grid-connected and off-grid inverter is established. Following this, the quasi-proportional resonant control strategy is introduced, with the corresponding implementation method of the controller derived from its equivalent block diagram. Furthermore, the control block diagrams of the grid-connected and off-grid inverters undergo a detailed analysis, and the system’s transfer function is obtained from the control block diagram. The incorporation of grid voltage feedforward control is introduced for examining the system’s tracking performance. Ultimately, the proposed control approach is validated for its effectiveness and practicality through Simulink simulation.

A Cascade-Formed Accurate Quasi-PR Controller Realization by Pole-Zero Placement

A Cascade-Formed Accurate Quasi-PR Controller Realization by Pole-Zero Placement

Three-Leg Quasi-Z-Source Inverter with Input Ripple Suppression for Renewable Energy Application

Single-phase inverters are widely employed in renewable energy applications. However, their inherent 2ω-ripple power can substantially affect system performance, leading to fluctuations in the maximum power points (MPP) of photovoltaic (PV) systems and shortening the lifespans of fuel cell (FC) systems. To alleviate input ripple, a three-leg quasi-Z-source inverter (QZSI) and its associated control strategy are proposed. The QZSI consists of a quasi-Z-source network, an H-Bridge inverter, and an active power filter (APF). The active filtering structure comprises filtering capacitors and the third bridge leg. The proposed control strategy consists of three loops: open-loop simple boost control, output voltage control, and 2ω-ripple suppression control. Open-loop simple boost control is utilized for shoot-through state modulation, output voltage control is applied to the two bridge-legs of the H-Bridge, and the additional third bridge-leg adopts a quasi-PR control (QPR) method that injects specific frequency harmonic voltage and suppresses newly generated low-frequency components of the input current. This method effectively avoids the drawbacks of utilizing passive filtering strategies, such as high-value impedance networks, low power density, and weak system stability. A simulation platform of 300W 144VDC/110VAC50Hz is constructed. The simulation results indicate that the addition of the third bridge leg under full load conditions reduces the input-side inductor current ripple ΔI from 1.89 A with passive filtering to 0.513 A, representing a reduction of 72.86%. The second harmonic ripple of the input current is reduced from 18.2% to 4.5%, and the fourth harmonic ripple is reduced from 16.5% to 2.1%. The DC bus voltage ripple ΔVPN falls from 70.75 V to 6.54 V, representing a reduction of 90.76%. The Total Harmonic Distortion (THD) of the output voltage and current are both less than 1%. The simulation results validated the feasibility of the proposed approach.

Multi-resonant Controller Design for a PV-Fed Multifunctional Grid-Connected Inverter in Presence of Unbalanced and Nonlinear Load

The use of Active Power Filters (APFs) in future power grids with high penetration of nonlinear loads is unavoidable. Voltage Source Inverters (VSIs) interfacing Photovoltaic (PV) generator could play the APF role in addition to power supply. In this paper, the control of a PV-fed multifunctional grid-connected three-phase VSI is addressed with nonlinear and unbalanced load. The control objective is threefold. The first one is to deliver the maximum available power from the PV source to the grid satisfying power quality standards. The second one is the Voltage Balancing Control for DC-link capacitors to guarantee correct operation of the VSI. The last one is shunt APF control to compensate for nonlinear and unbalanced load harmonics, reactive power, and unbalanced sequences. A quasi-Proportional-Resonant (PR) controller with harmonic compensators is proposed for the current control loop. The quasi-PR controller parameters are determined through optimization algorithms such as Particle Swarm Optimization (PSO), Genetic Algorithm (GA), and a combination of both PSO and GA. The aim of the objective function is to improve static and dynamic behavior. The different gains at the fundamental resonant frequency and the selected odd harmonics are obtained for the proposed quasi-PR controller. The dynamic characteristics of the optimized quasi-PR controllers show superiority against conventional ones in terms of gain margin, phase margin, overshoot, and robustness. With the proposed control scheme, the harmonics, reactive power, and unbalanced sequences are appropriately compensated. The performance of the PV-fed VSI shunt APF under irradiance change, load change, and distorted grid voltage conditions is validated through numerical simulations performed on hbox {PSIM}^{copyright } software. The results show that the grid currents Total Harmonic Distortion for irradiance change case study are 4.57%, 4.57%, and 3.22% in phase a, b, and c with the proposed control method, while they are 9.25%, 5.65%, and 10.12% with conventional instantaneous p-q theory.

MMC circulating current suppression strategy based on improved quasi-PR control

The internal circulation of modularized multilevel converter will affect waveform quality and increase system loss. In this paper, the basic principle and topological structure of MMC as well as the causes of the internal circulation are briefly analyzed. A method of harmonic component extraction based on the second-order generalized integrator and the suppression strategy of MMC circulation based on feedforward compensation quasi-proportional resonant control are proposed. The feasibility of this strategy is verified in MATLAB/Simulink, and the simulation results show that the circulation and capacitor voltage fluctuation are controlled within a reasonable range.

Harmonic Compensation of APF Three-phase Three-line System Based on Quasi-PR Control

The Active power filter (APF) plays an important role in reducing the harmonic distortion rate of grid current and improving grid stability. However, the APF based on traditional methods such as deadbeat control and hysteresis control has poor tracking accuracy for the load harmonic current, and it is difficult to achieve efficient compensation. In this regard, this paper proposes a current inner loop quasi-proportional resonant (PR) control method to achieve fast-tracking of the compensation current and high control precision. Then, according to the equivalent mathematical model of the three-phase APF in the continuous domain, the parameters of the quasi-PR control method are designed. Finally, the effectiveness of the proposed method is verified by simulation.

A High Power Quality Buck-H Auxiliary Power Converter in Railway Applications

DC voltage utilization and AC voltage harmonics are important evaluation indexes for Auxiliary Power Converter in Railway Applications. To improve the above two indicators, a novel switch-mode modulation method and quasi-PR control strategy for Buck-H three-phase inverter is proposed in this paper. The Buck-H three-phase inverter integrates the AC side filter circuit into the DC Buck circuit, which reduces the volume of the filter capacitor and improves the filtering effect. This novel switch-mode modulation method uses only one high frequency switch per phase, which reduces the switching losses and thereby increases overall efficiency. In addition, this switch-mode modulation absence of shoot-through menace eliminates the dead time requirement. Meanwhile, the quasi-proportional-resonance (PR) controller and its control parameters are optimized to improve the AC voltage tracking performance. The influence of PR control parameters on system performance is analyzed in detail. The proposed switch-mode modulation method and control method can effectively reduce the harmonic distortion rate of the system. The effectiveness is verified through the StarSim hardware-in-the-loop experimental results.

Research on control method of three-phase inverter based on LQR optimal tracking control

According to the linear quadratic optimal control principle, the idea of optimal tracking control is applied to the three-phase inverter control system, which can effectively improve the output characteristics of the system. Based on the establishment of mathematical model, the nonlinear load and load mutation are regarded as the uncertain factors affecting the performance of three-phase inverter, and the parameter optimization design of state feedback and input feedforward is carried out based on the linear quadratic optimal control method. The simulation results show that the LQR optimal tracking control can better adapt to the adverse effects of nonlinear load and load mutation than the traditional quasi-PR control, and the system has good harmonic performance, dynamic performance and the ability to resist load disturbance.

An optimized parameter control method of resonance corrector for improving the output characteristics of singlephase inverter

According to the principle of internal mode, the resonant corrector is applied to the control system of single-phase inverter, which can effectively improve the output characteristics of the system. Based on the mathematical model, the dc input voltage fluctuation and load change are taken as the uncertain factors affecting the performance of the inverter, and the parameter optimization design of the resonant corrector is carried out based on pole assignment. The simulation results show that compared with the traditional quasi-PR controller, the controller designed with the resonance corrector parameter optimization can better adapt to the continuous large range of voltage fluctuation at the DC input end, and the system has good dynamic performance, waveform stability, and the ability to resist load disturbance.

Frequency Coupling Admittance Modeling of Quasi-PR Controlled Inverter and Its Stability Comparative Analysis Under the Weak Grid

This paper intends to comparatively study the stabilities of grid-connected inverters with three closely related controllers: quasi-proportional resonance (quasi-PR), proportional integral (PI), and proportional resonance (PR) under the weak grid. Firstly, considering the influence of frequency coupling characteristic, a frequency coupling admittance model of quasi-PR controlled inverter is established. Then, the admittance characteristics of the quasi-PR, PI and PR controlled inverters are compared. Admittance characteristics of the PI and PR controlled inverters are similar while the quasi-PR controlled inverter is quite different: the amplitude of the quasi-PR controlled inverter is larger than that of the PI controlled inverter and the phase difference between the two inverters is obvious in the mid-high frequency areas, which are mainly caused by the resonance bandwidth of the quasi-PR controller. Furthermore, the stabilities of the quasi-PR, PI and PR controlled inverters are analyzed. The stabilities of the PI and PR controlled inverters are similar but the quasi-PR controlled inverter is more sensitive to weak grid and high inverter output power. To achieve the same system stability, the voltage outer-loop bandwidth of the quasi-PR controlled inverter should be designed narrower than that of the PI and PR controlled inverters. Finally, experiments verify the correctness of the analyses.

A Novel Grid-Connected Current Control Method Based on Frequency Adaptive Proportional Resonance

In this paper, a novel quasi-proportional resonance (quasi-PR) controller for grid-connected current control is proposed. For the traditional quasi-PR controller, the performance decreases in cases when a large gird frequency deviation is going through. To solve the problem, a frequency adaptive structure is applied in the current control method to achieve online correction on the resonance frequency, so that a high control accuracy is maintained and the robustness of the control system is enhanced. The feasibility of the proposed method has been verified by experimental results.

RETRACTED: Control strategy and security of small and medium-sized wind power grid-connected inverter

Smart city has become an important direction of urban development. Focusing on the construction of smart city, it can reflect the ideal practical effect in many aspects, effectively improve the level of urban development and operation, and also show better in urban planning. Strong influence requires urban planning for adaptive adjustment. This paper from the core of a small wind power system is the grid-connected inverter. According to the main topology of small wind power generation inverter and grid-connected system, a systematic modeling of small wind power generation system is built. In order to make up for the deficiency of the traditional control strategy for small wind power grid-connected inverter, this paper puts forward a fuzzy control and quasi-PR control method to be applied to the synchronization control of grid-connected inverter. The simulation experiment is conducted by using MATLAB/SIMULINK platform, and the test is conducted by means of combining self-designed system hardware circuit, and the results show that compared with the PR method, the grid current synchronization error can be reduced to smaller, adaptability, and anti-disturbance can be greatly improved through the proposed method and, consequently, has a better application value for small wind power grid-connected inverter.

Harmonic Control for Variable-Frequency Aviation Power System Based on Three-Level NPC Converter

At present, three-phase 115V/360-800Hz variable frequency AC power system is mostly used in the main power system of More-Electric Aircraft. With the increase of EMA (Electro-Mechanical Actuator), EHA (Electro-Hydrostatic Actuator), DC/DC power supply and power electronic devices in More-Electric Aircraft, harmonic and reactive power problems are brought, which seriously affect the power supply quality of variable frequency power supply for aircraft. According to the characteristics of high frequency and wide range of aviation variable frequency power supply, this paper studies a three-level active filter which can effectively improve the power quality of aviation variable frequency power supply system. This paper analyzes the working principle of the diode clamped three-level topology active filter, and deduces its mathematical model; proposes the frequency detection of the aviation variable frequency power supply based on the improved Rife method; the ip-iq method based on the instantaneous reactive power theory, accurately detects the harmonic current of the aviation variable frequency power supply system; uses the quasi PR controller to track the current, and improves the harmonic suppression effect. Finally, the experimental hardware platform is built to verify the feasibility of the proposed control strategy.

Improved QPR Power Controller With Harmonic Compensator For Wind Grid-Connected Inverter

The grid-connected inverter plays an important role in wind turbine grid-connected power generation system. The performance of inverter control strategy directly affects the grid-connected current quality. For quasi-proportional resonant(QPR) control, the output signal step of controller exists owing to the input signal step, and the grid current will be distorted by the low-frequency noise in the input signal. In order to solve these problems, the performance of quasi-PR control should be improved, so a method of constructing quasi-PR controller with two degrees of freedom is adopted, by which the improved controller can effectively suppress the influence of the step and low-frequency noise in the input signal on the grid-connected current. The improved controller is simulated on MATLAB, and the results show that the applied method can effectively improve the property of the existing problems of quasi-QPR controller and the quality of grid-connected current. Keywords: Grid-connected inverter, Harmonic compensator, Matlab/Simulation, 2-DOF,QPR. DOI: 10.7176/CTI/8-05

Research on grid-connected photovoltaic inverter based on quasi-PR controller adjusting by dynamic diagonal recurrent neural network

The single-phase grid-connected photovoltaic inverter system is studied in this paper. In view of the non-linear and time-varying characteristics of this system, the three-closed-loop control strategy consisting of DC voltage outer loop, grid-connected current inner loop and capacitive current inner loop based on quasi-PR control is proposed. Since the quasi-PR controller of fixed parameters is unable to adapt to changes of parameters in power network, a quasi-PR control method of dynamic self-tuning based on a dynamic Diagonal Recurrent Neural Network (DRNN) is presented. DRNN is based on the Recursive Prediction Error (RPE) algorithm with second-order gradient, which has a faster convergence rate than the BP algorithm. The simulation and experiment results prove that the grid-connected photovoltaic inverter with the above control algorithm has a good quality of the output current and fast performance in dynamic response.

Research on grid-connected photovoltaic inverter based on quasi-PR controller adjusting by dynamic diagonal recurrent neural network

Research on grid-connected photovoltaic inverter based on quasi-PR controller adjusting by dynamic diagonal recurrent neural network

Grid Connected Control Strategy of Microgrid

The Combination of large power grid and distributed power supply is recognized by electric power experts as the development direction of power industry, which can save energy consumption, improve the reliability and flexibility of power system. Therefore, it is of great value to study distributed power supply. According to the shortcomings of PI control gain at the fundamental frequency of small, poor control effect, introducing the band-pass quasi PR controller, and improve the algorithm in order to improve the control effect, and finally through the MATLAB simulation software to test the improved algorithm, verify the feasibility of the algorithm and accuracy.

A Method for the Suppression of Fluctuations in the Neutral-Point Potential of a Three-Level NPC Inverter With a Capacitor-Voltage Loop

This paper investigates the problem of fluctuation of the neutral-point potential (NPP) in a three-level NPC inverter with a capacitor-voltage loop. The phase pulse width duty cycle disturbance pulse width modulation (PWM) method is proposed to suppress the NPP fluctuation efficiently. Based on the basic carrier-based phase-disposition PWM method, the average pulse neutral-point current model is established. Then, the frequency, amplitude, and equivalent initial phase of the NPP fluctuation are analyzed based on the current model. According to the alternating error of the dc-link capacitor voltages, a capacitor-voltage loop with a quasi-proportional resonant (PR) controller is presented. The control variable, which varies with the modulation index, phase current, load power factor, etc., can be obtained from the quasi-PR controller. Finally, an experimental three-level NPC inverter is described and the validity and feasibility of the proposed method are verified by experimental results.

Analysis, Design, and Implementation of a Quasi-Proportional-Resonant Controller for a Multifunctional Capacitive-Coupling Grid-Connected Inverter

The capacitive-coupling grid-connected inverter (CGCI) is coupled to the point of common coupling via a second-order LC branch. Its operational voltage is much lower than that of a conventional inductive-coupling grid-connected inverter (IGCI) when it serves as a multifunctional inverter to compensate reactive power and transfer active power simultaneously. It is a promising solution for microgrid and building-integrated distributed generator systems. A quasi-proportional-resonant (quasi-PR) controller is applied to reduce the steady-state current tracking errors of the CGCI in this paper. The quasi-PR controller generates the voltage reference for use of carrier-based pulse-width modulation, which can effectively reduce output current ripples. The second-order coupling impedance of the CGCI causes its modeling and controller design to differ from that of the conventional IGCI. A comprehensive design method for the quasi-PR controller in a CGCI is developed. The quasi-PR controller is also compared with a proportional-integration current controller. Simulation results are provided to verify the effectiveness of the quasi-PR controller and its design method in a CGCI. The current tracking errors are greatly reduced when the quasi-PR controller rather than the proportional-integration controller is applied. Experimental results are also provided to validate the CGCI as a multifunctional grid-connected inverter.

Analysis and control of MMC-HVDC under unbalanced voltage conditions

A vector current controller based on quasi-proportional resonant (PR) in α β stationary reference frame is used to control the positive and negative sequence currents uniformly. Through analyzing the power characteristics under unbalanced grid conditions, control strategies to suppress negative sequence current and active power ripples are realized without the additional transformation between α β and d q reference frame. A more general method is proposed to analyze the circulating current features and sequence components; then a circulating current controller is designed based on quasi-PR controller. The traditional voltage-balancing algorithm is also improved to reduce switching times by adjusting the voltage sorting frequency according to the capacitor voltage standard deviation (CVSD).