Quasi-proportional Resonant Research Articles

Grid-Connected Inverter Grid Voltage Feedforward Control Strategy Based on Multi-Objective Constraint in Weak Grid

In weak grid, feedforward of grid voltage control is widely used to effectively suppress grid-side current distortion of inverters caused by harmonics in point of common coupling (PCC) voltage. However, due to its introduction of a positive feedback loop related to the grid impedance, it results in a significant reduction in the system phase margin. In view of this, in this paper, the output impedance of a three-phase LCL grid-connected inverter under a quasi-proportional resonant (QPR) controller is first modeled. Instead of the traditional grid voltage feedforward control strategy, a band-pass filter is added to the grid voltage feedforward channel. Secondly, a multi-objective constraint method is proposed to make improvements to the feedforward function. Then, a multi-objective constraint function is established with the constraints of base-wave current tracking performance, system stability margin, and low-frequency amplitude, and the feasibility of its function optimization design method is verified. Theoretical analysis shows that the optimized grid voltage feedforward control strategy can effectively reshape the phase characteristics of the system output impedance, which greatly broadens the adaptation range of the system to the grid impedance. Finally, the effectiveness of the proposed control strategy is verified by building a semi-physical simulation experimental platform based on RT-LAB OP4510.

Research on current harmonic suppression of permanent magnet synchronous motor using smith predictive controller

Abstract Due to the dead time added to the operation of the motor inverter, the generated current harmonics are introduced into the synchronous motor, increasing the harmonic content of the motor. The higher harmonic content is the 5th, 7th, 11th, and 13th current harmonics, which can cause motor torque ripple [1]. To suppress the current harmonics that cause torque ripple, a control method of using a PI controller and a quasi-proportional resonant controller in parallel is considered to suppress current harmonics. However, the introduction of a proportional resonant controller can cause greater overshoots in the current response, and external environmental influences can also generate current disturbances. Therefore, a method based on Smith prediction-PID and quasi-proportional resonance controller cascade control structure is proposed to suppress current harmonics and current overshoot in response to this problem. Finally, the effectiveness of this method was verified through simulation experiments, thereby improving the stability of synchronous motor operation.

Super-Twisting Extended State Observer-Based Quasi-Proportional-Resonant Controller for Permanent Magnet Synchronous Motor Drive System

For the purpose of realizing permanent magnet synchronous motor (PMSM) systems with strong robustness and smooth speed, the quasi-proportional-resonant (QPR) controller is combined with super-twisting extended state observer (STESO) in this paper. Although traditional active disturbance rejection control scheme generally selects a sufficiently large bandwidth of linear extended state observer (LESO) to enhance the time-varying disturbance rejection capacity, the bandwidth of LESO is limited by system stiffness. To solve this tough issue, the STESO using generalized super-twisting technique is developed to optimize the stability and anti-disturbance capacity of motor drive system. In addition, the QPR controller is combined with the proposed STESO to suppress the motor speed fluctuation. Experimental results show that the proposed STESO-based QPR control algorithm has satisfactory characteristics.

Adaptability enhancement of fractional‐order LLCL‐type grid‐connected inverter to weak grid based on grid voltage weighted feedforward scheme

SummaryGrid‐connected inverter with a novel fractional‐order LLCL filter has the advantage of high grid current tracking accuracy and low total harmonic distortion without passive or active dampers, and the grid voltage full feedforward scheme is an effective method to improve the quality of grid current. However, due to the digital control delay, the suppression of the grid current harmonics is weakened, and the inverter output impedance has an additional negative phase shift, which deteriorates the stability of grid‐connected systems under weak grid. In this paper, a weighted grid voltage fractional‐order feedforward control scheme is proposed based on a quasi‐proportional resonant (QPR) controller, which introduces two weighting factors in the full feedforward path of the grid voltage and compensates the phase lag of the output impedance by designing appropriate weighting factors. Then, an improved scheme combining the QPR controller with a phase compensator is presented. As a result, the suppression ability of grid current harmonics and the adaptability to grid impedance variations are enhanced. Simulation and experimental results verify the effectiveness of the proposed grid voltage fractional‐order weighted feedforward scheme.

Disturbance observer‐based quasi‐proportional resonant composite control strategy for high‐frequency LCLC inverters

SummaryA quasi‐proportional resonant (QPR) composite control strategy based on disturbance observer (DOB) is proposed to improve the power quality and dynamic performance of the high‐frequency AC distribution system source side. The load DOB normalizes the controlled object while suppressing the load disturbance and improving the system's robustness and dynamic performance of the system. The QPR control strategy is proposed based on the internal mode principle, which improves the tracking capability of the system for the operating frequency band signal, reduces the system output steady‐state error, and suppresses the inverter output voltage harmonics. To adapt to the high bandwidth requirement of the controller for high‐frequency AC inverters, the proposed control strategy based on analogy devices implementation circuit is designed, and the corresponding controller parameters design method is given. Compared with the traditional control strategy, the proposed control strategy can reduce the inverter output voltage harmonics, effectively suppress the load disturbance, and improve the dynamic performance and steady‐state performance of the system. Finally, the experimental platform verifies the feasibility and effectiveness of the proposed control strategy and the designed circuit.

Control Strategy for Array Buoy Type Wave Energy Converters' Power Conversion

In order to solve the problem of complex inner‐loop control structure, difficult debugging of control parameters and poor anti‐interference ability in the double PI power conversion control method of array buoy type wave energy converter, this article proposes a power conversion control strategy in which the one step delay compensation model predictive current control strategy is proposed for the machine side rectifier and the three closed‐loop control structure with PI voltage outer‐loop, quasi‐proportional resonant (QPR) current inner‐loop and proportional capacitor current inner‐loop is proposed for the grid‐side LCL inverter. In addition, this article proposes a graded power generation scheme for a single oscillating buoy and two power generation branches, which aims to address the issue of a restricted safe working pressure range for the accumulator in the single buoy and single power generation branch mode. Based on the mathematical model of the system's key components, the MATLAB/Simulink program is applied for modeling and simulation. The results indicate that the recommended graded power generation scheme and power conversion control mechanism may accomplish stable operation of the system under three diverse wave conditions, showing the scheme's practicality. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Adaptive quasi-proportional resonant control with parameter estimation for PMSM sensorless control

Conventional sliding mode control (SMO) utilizes a sign function and a low-pass filter (LPF) to achieve sensorless control of a permanent magnet synchronous motor (PMSM). However, the introduction of the sign function generates a large number of high harmonics, resulting in a significant system output chattering, whereas the addition of the LPF generates control delays and phase shifts. These degrade the PMSM speed and the position estimation accuracy and reduce the system control performance. To improve the performance of the PMSM, adaptive quasi-proportional resonant sensorless control with parameter estimation (AQPR_PE) is proposed. In this control model, an adaptive quasi-proportional resonance controller is used reduce the system output error and to weaken the chattering phenomenon. Meanwhile, the system PMSM parameters are estimated online and fed back to the control model to improve the system parameter robustness and the control accuracy. The Bode diagram, Popov theory, and root trajectory are used to analyze the stability of AQPR, parameter estimation, and AQPR_PE, respectively. Finally, the effectiveness of the proposed method is demonstrated by experimental validation.

Enhanced Voltage Regulation for PV Power Conversion Using Quasi-Proportional Resonant Extended State Observer

Extended state observer (ESO) is a promising control technology thanks to its robustness against model inaccuracy. This article expands the application of an ESO-based control scheme to digitally regulate a grid-tied photovoltaic (PV) power converter. It focuses on mitigating the steady-state disturbance resulting from the dc to single-phase ac conversion and dynamic disturbances caused by solar irradiance and voltage reference changes. The development is based on an in-depth analysis of PV power systems regarding the nonlinear and time-variant features. Thanks to the disturbance rejection loop, the active damping function is naturally offered, which boosts the system damping without extra sensors or complex model-based tuning. A new ESO scheme, namely quasi-proportional resonant ESO, is developed by the frequency-domain analysis, which enables the precise tracking and rejection of fast-varying sinusoidal disturbance at the targeted frequency. The advantages include simple and intuitive tuning, easy implementation, and enhanced transient and steady-state control performance. A 1.5-kW laboratory platform is built to verify the effectiveness and practicality of the proposed control scheme.

Fault-Tolerant Current Control of Six-Phase Permanent Magnet Motor With Multifrequency Quasi-Proportional-Resonant Control and Feedforward Compensation for Aerospace Drives

To improve the current tracking performance, this article proposes a new fault-tolerant current control for the six-phase fault-tolerant permanent magnet synchronous motor (FTPMSM) system with multifrequency quasi-proportional-resonant (QPR) control and back electromotive force (EMF) feedforward compensation, which can track the time-varying sinusoidal and nonsinusoidal reference currents in the stationary reference frame (SRF) under normal and fault conditions. First, the multifrequency QPR current controller with shunt topology is proposed to track the time-varying reference current in SRF, which can guarantee the current control performance regardless of the motor speed variation and the load torque change. Second, the optimized feedforward compensation method for the back EMF is proposed to further reduce the steady-state current tracking error, which takes the time delay of the digital implementation into consideration. Finally, the effectiveness of the proposed approach is verified on a 3 kW six-phase FTPMSM platform. The resulting six-phase FTPMSM system with the proposed current control has great current tracking performance, strong robustness to various external/internal disturbance, as well as low computational burden, which can guarantee the multiphase FTPMSM system performance in normal and fault conditions.

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.

Stability analysis of microgrid inverter off-grid mode considering nonlinear load

With the large-scale utilization of distributed generation in microgrid, inverter as the connection hub of new energy grid connection, directly affects the operation performance of microgrid. In order to improve the output voltage quality and load capacity of the inverter in the off-grid mode of distributed energy, the stability region of the inverter with load is analyzed by using the impedance analysis method of cascade converter and control theory. The quasi proportional resonant (QPR) double loop control is adopted to realize no static error tracking voltage while increasing bandwidth, and the influence of control parameters on performance is analyzed. At the same time, in order to improve the capacity of inverter with nonlinear load, odd harmonics are introduced into the controller to suppress the influence of low harmonics of load current on output voltage. Finally, the influence of inverter output impedance change, load level, controller parameters and filter parameters on system stability is analyzed through impedance ratio Nyquist curve, which provides corresponding theoretical support and parameter optimization reference for the design of actual system.

Improved PR Control Strategy for an LCL Three-Phase Grid-Connected Inverter Based on Active Damping

Aiming at the problem of power coupling and complicated decoupling in the d-q coordinate system of a three-phase grid-connected inverter, a current closed-loop control strategy based on an improved QPIR (quasi-proportional integral resonant) controller in the α-β two-phase static coordinate system is proposed. Firstly, the mathematical model of an LCL three-phase grid-connected inverter is established, and its instantaneous power calculation equation is deduced. Secondly, the frequency method is applied to compare and analyze the proportional resonant, quasi-proportional resonant, and improved current controller, and the appropriate improved controller parameters are obtained according to the traditional proportional integral controller parameter design method and the weight coefficient. Finally, the improved controller is compared with the traditional controller in the simulation model of the LCL three-phase grid-connected inverter based on active damping. The results show that the proposed improved current control strategy has good dynamic response characteristics, can realize the non-static error control of grid-connected current, and realizes the decoupling control of active power and reactive power when the load jumps. At the same time, the results also prove the superiority of the proposed control strategy and verify its effectiveness.

Analysis, Design, and Implementation of Multi-Quasi-Proportional-Resonant Controller for Thyristor-ControlledLC-Coupling Hybrid Active Power Filter (TCLC-HAPF)

Compared with the conventional active power filter, the thyristor-controlled <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> -coupling hybrid active power filter (TC <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> -HAPF) has a distinct characteristics of low dc-link operating voltage, which can lower the system and operational costs in the medium-voltage-level system. It also has a wider operational range than the conventional hybrid active power filter. Besides that, the TC <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> -HAPF can provide reactive, harmonic, and unbalanced powers compensation simultaneously. In this article, the modeling of the TC <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> -HAPF is investigated based on the linear control aspect. Then, the analysis, design, and implementation of a multi-quasi-proportional-resonant (MQPR) controller with gain scheduling for the TC <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> -HAPF will be proposed, which can automatically change the resonant gain between the inductive and capacitive loads operation to improve its compensation performances. The proposed controller can significantly reduce the TC <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> -HAPF steady-state current tracking errors and output current ripple. Finally, the simulation and experimental results are also provided to verify the effectiveness and performance of the MQPR controller for the TC <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> -HAPF in comparison with the hysteresis current controller and quasi-proportional-resonant (QPR) controller, which shows superior compensating performances.

Grid-Voltage-Feedback Active Damping With Lead Compensation for LCL-Type Inverter Connected to Weak Grid

To improve the robustness and stability of the LCL inverter connected to weak grid, this paper proposes a novel active damping based on voltage of point common coupling ( v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pcc</sub> ) feedback. A phase lead compensator is proposed in the v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pcc</sub> feedback loop to compensate system phase margin (PM). Theoretical analysis of the effectiveness, detailed parameter setting, stability analysis for proposed active damping adopting lead compensator, named as LC AD, are all described. Simulation and experiment results show that comparing to conventional high pass filter (HPF) AD, the proposed LC AD provides more effective damping effect for the LCL inverter adopting quasi-proportional resonant (QPR) controller under weak grid.

Application of Repetitive Control in Electric Spring

With the increasing of the grid-connected capacity of renewable energy such as wind energy and solar energy, its instability, intermittence and uncontrollability have a serious impact on the stable operation of power system, such as voltage fluctuation, frequency flicker, etc. Therefore, Electric Spring (ES) system has become a current research hotspot. Aiming at the deficiencies of the resonance control strategy, a control method that combines quasi-proportional resonance (QPR) control and repetitive control is proposed. The quasi proportional resonance control is used to realize the tracking without static error, and the internal model principle of repetitive control is used to suppress the periodic disturbance of the grid voltage, so as to improve the power quality of the grid. Compared with the traditional quasi proportional resonant control, the introduction of repetitive control can effectively improve the steady-state accuracy, reduce the system harmonic and enhance the ability of anti-harmonic interference. The modeling of ES and the design method of repetitive controller parameters are discussed in detail. The simulation model is built using MATLAB / Simulink, and the ES experimental platform is built with dSPACE as the control core, the results verify the feasibility and effectiveness of the proposed control strategy.

Design of Double-Line-Frequency Ripple Controller for Quasi-Single-Stage AC–DC Converter With Audio Susceptibility Model

Power factor correction (PFC) converter suffers from serious double-line-frequency output voltage ripple due to the difference between instantaneous ac input power and dc output power. To suppress such double-line-frequency output voltage ripple, a ripple cancellation circuit (RCC) is utilized to generate the same magnitude but 180° phase shifted double-line- frequency voltage ripple. This paper provides an insight into the relationship between control scheme and double-line-frequency ripple suppression from the perspective of audio susceptibility model. For the purpose of reducing the double line frequency ripple, the closed-loop audio susceptibility of series RCC should be designed relatively low at double line frequency. According to such requirement, a ripple controller with improved voltage feed-forward (FF) scheme and quasi-proportional-resonant (QPR) compensator is designed. As QPR compensator can increase the denominator of the closed-loop audio susceptibility, while voltage FF scheme can reduce its numerator, its magnitude at double line frequency is thus greatly reduced and double-line-frequency ripple is also significantly suppressed. Moreover, due to the flexibility of QPR compensator, the proposed ripple controller presents good ripple suppression in a different line frequency application. Finally, experimental results of a flyback PFC with buck-type RCC quasi-single-stage ac–dc converter are provided to verify the validity of the proposed ripple controller.

A new unified control strategy for inverter-based micro-grid using hybrid droop scheme

Micro-grid (MG) operation using voltage control methods (VCMs) has been widely recommended for parallel operation of three phase voltage source inverters, especially during islanded mode to maintain the voltage level in the MG. In contrast, this paper presents a new unified control strategy for MG parallel operation using a current control method (CCM). A hybrid control scheme which combines a universal robust droop controller (URDC) and quasi-proportional resonant (QPR) regulator is introduced. It ensures equal power sharing among parallel operated inverters during all MG's operating modes. Moreover, an improved adaptive estimator for the reference current magnitude is integrated to meet dynamic load variations. Furthermore, the scheme is enhanced with a self-synchronized capability using a simple synchronous reference frame phase locked loop (SRF-PLL). This obviates the necessity of communication links and external synchronous clocks required for synchronization process. In addition, a decentralized control action is locally managed to restore the inverter's frequency upon any reactive load change. Modeling and simulation results using MATLAB/SIMULINK software are presented to show the effectiveness of the proposed strategy.

Hierarchical voltage imbalance control for single‐/three‐phase hybrid multimicrogrid

With the rapid development of distributed generation (DG), microgrids and multimicrogrids (MMGs) appear at the end of distribution networks. For the islanded operation of a single-/three-phase hybrid MMG, a hierarchical coordinated control scheme is proposed in this study that includes primary and secondary levels. A compound control strategy based on quasi-proportional resonant and robust control is proposed for the primary voltage/frequency control to suppress voltage fluctuations caused by sudden changes in load power and DG output power; a coordinated strategy regarding tie-line power at the point of common coupling (PCC) is proposed for the secondary control to simultaneously improve voltage imbalance at the terminal of the master power supply, PCC, and load terminal. The proposed hierarchical coordinated control scheme is compared with conventional proportional–integral control and a control method based on the PCC to verify its performance. Test studies verify the superior robustness and voltage imbalance control performance of the proposed control scheme in coping with a sudden change in power and unbalanced loads.

A Neutral-Point Voltage Controller With Hybrid Parameters for NPC Three-Level Grid-Connected Inverters Under Unbalanced Grid Conditions

To solve the neutral-point (NP) voltage unbalancing problem, a conventional proportional integral (PI) controller is used for NP clamped (NPC) three-level grid-connected inverters under balanced grid conditions. However, when the three-phase grid voltage is unbalanced, the NP voltage unbalancing problem becomes more serious and complex, which cannot be solved by a conventional PI controller with the variation of the unbalanced grid. Based on the transfer function of the injected zero-sequence component to the NP voltage, the NP voltage module has different characteristic performances in frequency-domain, which is a leading or lagging system with the variation of the unbalanced grid and output power factor. Besides, being appropriate for this NP voltage module in two cases, a PI controller with hybrid parameters (HP-PI controller) is proposed to balance the NP voltage in this paper. According to varied unbalanced grid and output power factor, hybrid parameters are designed for this controller in two cases by the Lagrange multiplier method appropriately. Furthermore, frequency-domain characteristics and the balancing time of the proposed HP-PI control method are analyzed. Experimental and simulation results show that, compared with conventional PI and quasi-proportional resonant (PR) control methods, the proposed HP-PI controller has a strong ability to balance NP voltage with a good dynamic and steady-state performance under varied unbalanced grid conditions, which also improves the quality of grid currents.

Quasi-Proportional-Resonant Controller Based Adaptive Position Observer for Sensorless Control of PMSM Drives Under Low Carrier Ratio

The position and speed estimation performance of the sliding mode observer (SMO) for permanent magnet synchronous motor (PMSM) drives under low carrier ratio degrades, due to the inherent chattering and enlarged control delay. To improve estimation performance, this paper proposes a quasi-proportional-resonant (QPR) based adaptive observer to obtain back electromotive force with adaptive harmonics cancellation. In this observer, the QPR controller is employed to eliminate errors between the observed currents and the actual ones in the αβ reference frame, replacing sign function and low pass filter (LPF) of the SMO to cancel the chattering, and harmonics immune performance can also be achieved thanks to frequency selection characteristic of the QPR controller. Besides cancelling the chattering, the proposed observer can also eliminate phase shift produced by the LPF, since the QPR controller is a zero phase-shift amplifier at the resonant frequency. Comparative experiments are carried out in a 3-kW PMSM drive, and the results validate the effectiveness of the proposed adaptive position observer.