Phase‐Locked Loop Using Complex‐Coefficient Filters for Grid‐Connected Inverter

Recently, photovoltaic (PV) power systems have attracted considerable attention in attempts to mitigate global warming. In a PV power system, it is necessary to synchronize the grid voltage when a PV inverter is interconnected with a grid. This paper proposes a high‐speed and high‐precision phase‐locked loop (PLL) using complex‐coefficient filters for a single‐phase grid‐connected inverter. The proposed PLL can detect the phase of grid voltage that has superimposed harmonic components for grid fault. Moreover, numerical results show the effectiveness of the proposed method.     

消除直流分量影响和谐波干扰的并网同步方法

在电网发生故障时,如何快速、准确的检测出电网同步信号,对逆变器电力电子控制至关重要。提出了一种基于多重复数滤波器(MCCF)与锁频环(FLL)的电网同步技术,复数滤波器分离出故障电网电压的正负序分量及谐波,锁频环进行电网锁相跟踪,并加入直流分量反馈环节。当电网故障时本文所提结构可以自动地在短时间内准确地跟踪电网电压频率,准确提取故障时电网电压正、负序分量和谐波成分,消除直流分量的影响,且具有较快的动态响应速度.确保并网电力电子器件的稳定、可靠运行。     

Control of Uninterrupted Switching Using a Virtual Synchronous Generator Between Stand‐Alone and Grid‐Connected Operation of a Distributed Generation System for Houses

The home applications of distributed generations facilities such as photovoltaic and gas engine cogeneration systems are growing and many distributed generations are connected to a grid by a DC/AC inverter. The DC/AC inverter is controlled by a phase‐locked loop (PLL) in order to be synchronized with the power system frequency. However, the control scheme of stand‐alone operation uses voltage control, and the PLL is unnecessary. Therefore, it is hard to realize uninterrupted change between stand‐alone and grid‐connected operation. In this paper, we propose a virtual synchronous generator control scheme in order to use the same control scheme in stand‐alone and grid‐connected operation. We carried out experiments to demonstrate the control characteristics.     

Grid synchronization and control of distributed generation unit with flexible load compensation capabilities using multi-output LMS-filter

This paper deals with grid synchronization and control of single-phase voltage source inverter in distributed generation (DG) systems using a multi-output adaptive filter. Besides the active power injection, the proposed control enables the inverter to compensate load harmonic and reactive currents based on the capacity of inverter. The currents to be compensated are obtained using a multi-output adaptive filter structure that operates on the principle of variable step size (VSS) least mean squares (LMS) algorithm. The main objective of VSS-LMS filter is to decompose the load current into harmonic and reactive current components and compute their RMS values. The currents extracted by the VSS-LMS filter are used in developing a flexible compensation based on load compensation factors. The load compensation factors are calculated based on the remaining capacity of the inverter and priority. Harmonic currents compensation is given first priority over the reactive currents. In addition to harmonic currents detection, the same VSS-LMS filter is used in developing a phase locked loop unit for synchronizing the inverter with fundamental point of common coupling (PCC) voltage. Synchronizing the DG inverter with fundamental PCC voltage would make the proposed control algorithm insensitive to grid voltage harmonics and frequency fluctuations. The feasibility and the efficacy of the proposed control algorithm are demonstrated using hardware-in-the-loop (HIL) based experiments.     

Output‐voltage feedback control topology for inverters dedicated to renewable energy systems

We present a new control topology for inverters, mainly dedicated to renewable energy applications. The originality is due to the integration in the inverter of an adaptive regulation of its output voltage controlled by a closed feedback loop allowing compensating the voltage drops induced by load variations. The feedback control is based on an adaptive pulse wave modulation (APWM) technique, that controls the power switches of the inverter to obtain the purest possible sine‐wave voltage. The APWM technique straightforwardly compares the inverter output voltage with a reference signal at the grid frequency. In this contribution, this technique is applied to a single‐phase push‐pull inverter but could have been integrated for the control of all kinds of inverter topologies in renewable energy systems. We have shown that the APWM technique allows generating pure sine‐wave voltage, with low total harmonic distortion compared with the generally obtained by classical systems and that load variations do not affect the quality of the output. An experimental prototype of a single‐phase inverter with an adaptive regulation based on APWM technique was developed. The experimental characterizations of the prototype confirm the simulations. Copyright © 2017 John Wiley & Sons, Ltd.     

Analysis and effective controller design for the cascaded H‐bridge multilevel APF with adaptive signal processing algorithms

The cascaded H‐bridge (CHB) multilevel inverter is being recognized as the most suitable topology for high‐power medium‐voltage power quality conditioning applications. This paper presents mathematical modeling and effective controller design methodology for the CHB‐based active power filters (APFs), which achieves dynamic reactive power and harmonic compensation. The most crucial problems in CHB‐APF control are the simultaneous requirements of both accurate harmonic current compensation and the dc‐link voltage stabilization among the H‐bridges, which is the prerequisite for the stable operation of CHB‐APF. To achieve dc‐link stabilization, a novel voltage balancing algorithm is proposed by splitting the dc‐link voltage control task into two parts, namely, the average voltage control and the voltage balancing control, where the sine and cosine functions of the phase angle of the fundamental component of the grid voltage are used, respectively. To ensure accurate phase tracking, a novel phase‐locked loop (PLL) is proposed by using the adaptive linear neural network (ADALINE), where the grid voltage background distortion is also taken into account. The superior performance of the ADALINE‐PLL is validated by comparison with the existing PLLs in literatures. Furthermore, the proportional‐resonant (PR) controller is used for the reference current tracking. A separate ADALINE algorithm is applied for reference current generation (RCG) for the CHB‐APF. The excellent performance of the ADALINE‐based RCG scheme is verified by comparison with the existing RCG schemes, namely, the low‐pass filter approach and the single‐phase p ? qmethod. The experimental results on the three modules CHB‐APF are presented, which verifies the effectiveness of the proposed control algorithms. Copyright © 2011 John Wiley & Sons, Ltd.     

弱电网下电压源型逆变器锁相环的改进

弱电网并网运行时会产生谐波干扰以及电网电压频率波动等问题,导致逆变器输出电流谐波失真。弱电网并网环境对锁相环(Phase Locked Loop, PLL)的性能提出了更高的要求。针对弱电网下并网逆变器的控制要求,在分析并网电压源型逆变器(Voltage Source Converter, VSC)控制模型基础上,提出一种弱电网下PLL的优化方案。该方案采用超前补偿器补偿平均滑动滤波器(Moving Average Filtering, MAF)的相位延迟以提高系统的动态响应;引入前馈频率估计环,提高系统在电网电压频率偏差较大时的锁相精度,仿真验证改进的PLL的有效性。建立并网VSC系统实验平台对文中所述改进方法进行验证。实验结果表明,经PLL改进后的VSC系统在弱电网条件下具有良好的鲁棒性,逆变器入网电能质量得到了保证。     

Filter‐based perturbation control of low‐frequency oscillation in voltage‐mode H‐bridge DC–AC inverter

This paper presents a new additional perturbation control method for suppressing low‐frequency oscillation in voltage‐mode H‐bridge DC–AC inverter. The stability boundary of the H‐bridge inverter is investigated from its small‐signal averaged model. High input voltage and light load would cause low‐frequency oscillation in this system. To this end, a filter‐based perturbation control (FBPC) is proposed for eliminating this oscillation, by using an analog filter to extract the unexpected signal and applying it to the control loop. Theoretical results show a larger stability range of the controlled system with the proposed FBPC. The simulation and experiment results show that the proposed controller can control the low‐frequency oscillation in H‐bridge DC–AC inverter well. Copyright © 2014 John Wiley & Sons, Ltd.     

基于神经元自适应控制的动态电压恢复器研究

针对微电网并网系统中存在的电压跌落电能质量问题,研究了一种基于神经元自适应控制的蓄电池储能动态电压恢复器(DVR)。主要由蓄电池、逆变器、LC滤波器、变压器4个部分组成。其中,为了提升该DVR的控制性能,引入神经元自适应控制算法改进了外环电压PI调节器,实现了外环控制参数的自适应调节,从而得到新的双闭环控制策略。然后,结合空间电压矢量调制法最终实现控制。最后,在MATLAB/Simulink仿真软件中搭建了基于神经元自适应控制的蓄电池储能DVR的并网系统模型。试验结果表明,采用神经元自适应控制的蓄电池储能DVR能够补偿微电网的电压跌落,具有较强的动态响应能力和抗扰能力。     

Stabilization of a Power System Including Inverter‐Type Distributed Generators by a Virtual Synchronous Generator

The capacity of distributed generators (DGs) connected to the grid by inverters is growing year after year. The inverters are generally controlled by a phase locked loop (PLL) in order to achieve synchronization with the power system frequency. Power systems may become unstable as the capacity of the inverter‐type DGs continues to increase, because the inverter frequency is controlled just to follow the frequency determined by other synchronous generators. It has been suggested that inverters be controlled to behave like a synchronous generator. This concept is referred to as the virtual synchronous generator (VSG). In this paper, a control scheme for a VSG is presented, and the design method for the required energy storage and the capacity for grid stabilization control by a VSG is investigated by computer simulations.     

Three-phase grid voltage synchronization using sinusoidal amplitude integrator in synchronous reference frame

Synchronization with the grid voltage is critical in the control of grid-connected power converters. Under unbalanced grid condition, the conventional synchronous reference frame phase-locked loop (SRF-PLL) does not work well due to the effect of the fundamental negative sequence component. This paper proposes a new synchronization method, the sinusoidal amplitude integrator based phase locked loop (SAI-based PLL), to efficiently eradicate the effect of the fundamental negative sequence component. As a result, it can accurately and quickly estimate the amplitude and phase angle of the fundamental components of grid voltages in unbalanced grid conditions. In addition, when dc offset and harmonics are contained in the grid voltage, a multi-SAI-based PLL method is developed to extract the synchronization signal. The proposed SAI-based PLL incorporates the sinusoidal amplitude integrator into the conventional SRF-PLL. Its operation is analyzed using the complex-vector notation. Simulation and experimental results on the performance of the proposed SAI-based PLL and comparison with other synchronization methods are presented.     

Wavelet technique based islanding detection and improved repetitive current control for reliable operation of grid-connected PV systems

Recent years have witnessed a thrust towards the use of solar energy as the major renewable energy source for distributed power generation. The proposed system requires reliable detection technique and suitable current control strategy for proper operation. This paper focuses on plug-in repetitive current (RC) control strategy for grid connected inverter system and wavelet technique for electrical grid status identification. The performance of proposed current control technique employed for grid connected inverter system under distorted and unbalanced grid voltage is compared with the existing conventional methods like PI and PR controller. This controller uses the feedback control system for attenuating periodic disturbances, improving high quality sinusoidal output current and high power factor. The proposed scheme employs fourth order infinite impulse response (IIR) filter for maintaining its resonance frequency, output frequency matching with grid fundamental frequency and reduction of harmonics. The DC-DC boost converter implements incremental conductance based (INC) maximum power point tracker (MPPT) algorithm. The effects of LCL filter for improving disturbance rejection capability and dynamic performance of the proposed system is also demonstrated. Grid connected PV inverter employs wavelet technique for an islanding detection functionality in order to determine the status of the electrical grid. In order to show the effectiveness of the proposed algorithm, modeling and simulation for grid connected PV system is performed using MATLAB/SIMULINK and its PowerSim toolbox.     

A wideband low‐spur 0.18‐µm CMOS phase‐locked loop with bandwidth calibration

This paper presents a 0.18‐µm complementary metal‐oxide‐semiconductor wideband phase‐locked loop with low reference spurs. The dual‐level charge‐pump current calibration technique is proposed to maintain a constant loop bandwidth for wide operation frequency range and achieve low reference spurs. The first level charge‐pump current calibration is seamlessly incorporated in the automatic frequency band hopping control and the mechanism also ensures enough negative transconductance for the voltage‐controlled oscillator to function throughout the whole frequency range. The charge‐pump current mismatch is calibrated by the second level charge‐pump current calibration combined with the pulse‐width scaling technique. The operation frequency range of the phase‐locked loop covers from 4.7 GHz to 6.1 GHz. The measured phase noise is?116 dBc/Hz at 1‐MHz offset and the reference spurs are below?66.8 dBc. Copyright © 2015 John Wiley & Sons, Ltd.     

H‐infinity controller for frequency and voltage regulation in grid‐connected and islanded microgrid

This paper presents a study on a grid‐connected and islanded multiple distributed generation (DG) system for frequency and voltage regulation. The multiple DG system includes solar cells, wind turbine, fuel cell, and battery storage. The H‐infinity controller is used whose weighting parameters are optimized to minimize voltage and frequency deviation. The performance of the system is analyzed under different conditions for both grid‐connected and islanded modes of operation. In case of the load variations, the inner voltage and current loop react based on the H‐ infinity control strategies. The outer power loop uses the droop characteristic controller. The design is simulated using MATLAB/SIMULINK. The simulation results show that the multiple DG system can supply high‐quality power both in grid‐connected and islanded modes. Also, we show that the proposed control methodology will make the system to transit smoothly between the islanded mode and the grid‐connected mode. The results indicate that the frequency and voltage deviations meet the nominal values as per IEEE standard. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A novel modulation technique with interleaved‐and‐shifted shoot‐through state placement for quasi‐Z‐source inverters

In this paper, a single‐phase quasi‐Z‐source (qZS) inverter (qZSI), integrating the pulse width modulation (PWM) control with interleaved‐and‐shifted shoot‐through state (STS) placement modulation technique, is proposed to simultaneously achieve both dc voltage boost and dc‐ac inversion. Instead of placing the STS in both inverter legs simultaneously, the addressed method inserts the STS only in left/right inverter leg separately during the positive/negative half cycle of the output voltage to reduce switching losses and thermal stresses of the power devices. The STS shift is also studied to decrease the switching numbers of power devices and thus can improve the efficiency further. Theoretical analysis and design guidelines of the studied inverter are included. Improvement in effectiveness and performance of the devised scheme and modulation strategy are proved experimentally and compared with the previous studies on a built laboratory prototype.     

基于交叉解耦双复系数滤波器的频率自适应锁相环

锁相环PLL(phase-locked loop)是控制逆变器实现并网同步的重要方法之一。针对准1型锁相环QT1-PLL(quasi-Type-1 PLL)在电网电压频率偏移时抗干扰能力不佳、导致检测频率和相位误差较大的问题,本文提出一种新型的基于交叉解耦双复系数滤波器DCCF(double complex coefficient filter)的QT1-PLL(DCCF-QT1-PLL)。将具有频率反馈回路的交叉解耦DCCF作为QT1-PLL的前置滤波环节;采用窗长为0.0033 s的滑动平均滤波器MAF(moving average filter)作为DCCF-QT1-PLL的环内滤波环节;进而建立了DCCF-QT1-PLL的小信号模型,通过该模型得到了设计参数。提出的DCCF-QT1-PLL结构可消除电压不平衡和谐波分量,实现频率自适应。在Matlab/Simulink平台中搭建仿真模型,仿真结果证实DCCF-QT1-PLL结构具有频率自适应和更强的滤波能力。     

Dynamic modeling of DC–DC converters with peak current control in double‐stage photovoltaic grid‐connected inverters

In photovoltaic (PV) double‐stage grid‐connected inverters a high‐frequency DC–DC isolation and voltage step‐up stage is commonly used between the panel and the grid‐connected inverter. This paper is focused on the modeling and control design of DC–DC converters with Peak Current mode Control (PCC) and an external control loop of the PV panel voltage, which works following a voltage reference provided by a maximum power point tracking (MPPT) algorithm. In the proposed overall control structure the output voltage of the DC–DC converter is regulated by the grid‐connected inverter. Therefore, the inverter may be considered as a constant voltage load for the development of the small‐signal model of the DC–DC converter, whereas the PV panel is considered as a negative resistance. The sensitivity of the control loops to variations of the power extracted from the PV panel and of its voltage is studied. The theoretical analysis is corroborated by frequency response measurements on a 230 W experimental inverter working from a single PV panel. The inverter is based on a Flyback DC–DC converter operating in discontinuous conduction mode (DCM) followed by a PWM full‐bridge single‐phase inverter. The time response of the whole system (DC–DC + inverter) is also shown to validate the concept. Copyright © 2011 John Wiley & Sons, Ltd.     

一种改进型一阶广义积分锁频环的研究

稳定可靠的并网控制策略是提高光伏逆变器故障穿越能力的关键,对锁相技术的研究尤为重要。提出一种改进型一阶广义积分锁频环FOGI-FLL(frequency-locked loop based on first order generalized integrator)技术,首先利用滑动平均滤波器MAF(moving average filter)滤除电网电压中的谐波分量,消除谐波对FOGI-FLL的影响,再利用FOGI-FLL进行基波正、负序分离。仿真结果表明:在发生谐波畸变的电网中,所提出的方法能够在电网电压不平衡、频率突变和相位跳变的故障情况下,准确提取出电网电压的基波正、负序分量,并快速跟踪电网频率和相位。     

Three‐stage multiphase‐switched‐capacitor boost DC‐AC inverter

A closed‐loop scheme of a three‐stage multiphase‐switched‐capacitor boost DC‐AC inverter (MPSCI) is proposed by combining the multiphase operation and sinusoidal‐pulse‐width‐modulation (SPWM) control for low‐power step‐up DC‐AC conversion and regulation. In this MPSCI, the power unit contains two parts: MPSC booster (front) and H‐bridge (rear). The MPSC booster is suggested for an inductor‐less step‐up DC‐DC conversion, where three voltage doublers in series are controlled with multiphase operation for boosting voltage gain up to 2³ = 8 at most. The H‐bridge is employed for DC‐AC inversion, where four solid‐state switches in H‐connection are controlled with SPWM to obtain a sinusoidal AC output. In addition, SPWM is adopted for enhancing output regulation not only to compensate the dynamic error, but also to reinforce robustness to source/loading variation. The relevant theoretical analysis and design include: MPSCI model, steady‐state/dynamic analysis, voltage conversion ratio, power efficiency, stability, capacitance selection, total harmonic distortion (THD), output filter, and closed‐loop control design. Finally, the closed‐loop MPSCI is simulated, and the hardware circuit is implemented and tested. All the results are illustrated to show the efficacy of the proposed scheme. Copyright © 2011 John Wiley & Sons, Ltd.     

带有滤波电容电流补偿的风电并网逆变器控制

分析了并网逆变器的控制策略,采用电网电压矢量定向和d, q轴电流闭环控制实现有功功率和无功功率的解耦控制。重点对输出滤波电容对并网电流相位的影响进行了分析,并对此提出了一种采用滤波电容电流补偿的方法。对比仿真结果表明,该补偿方法很好地消除了电网电压和并网电流的相位差。理论分析与仿真结果表明,带有滤波电容电流补偿的并网逆变器能够快速实现功率解耦控制,具有良好的动静态性能。