Sliding-mode control in voltage source inverter-based higher-order circuits

In this article, a new control methodology of sliding-mode control (SMC) for voltage source inverter (VSI)-based higher-order circuit is proposed. In this method, the SMC is used at the inner terminals for stable tracking of the voltage and current variables. An outer voltage control loop is included to reduce the steady-state error in tracking the reference load voltage. It is shown that when the SMC is applied on the load voltage terminal for higher-order VSI circuits, it leads to the instability. However, it well stabilises the system when the controller is implemented on the inner shunt capacitor terminals. Additional outer voltage control loop with proportional plus integral controller will ensure regulated voltage across the load. It has been shown that the controller is able to achieve good tracking accuracy with an acceptable stability margins. The performance of the proposed SMC has been verified on the fourth-order VSI circuit.     

基于双环控制的PWM逆变器的研究

文中比较了几种电流内环控制的方法,提出基于电感电流反馈的双环控制策略,利用极点配置的方法设计控制系统参数。这样的控制方法可以使得逆变器动态响应加快,非线性负载适应能力加强,输出电压的谐波含量减小。     

基于dsPIC单片机的单相逆变电源的设计

本文介绍的是一个PI控制单相逆变电源的设计过程。根据单相电压型逆变器电路模型,建立了逆变器开环系统的传递函数,利用dsPIC单片机设计了一个单相逆变电源。逆变电源的仿真和实验结果表明:增加了电压有效值反馈闭环后,逆变器对输出电压的控制能力明显提高。     

两种双环控制方式对并联逆变器的影响

电压电流双环控制策略对单相逆变电源有一定的优越性,不同的采样电流方式对逆变电源输出电压外特性有着不同的影响。在控制参数一致的情况下进行对比分析,电感电流反馈方式对其输出电压外特性的影响较大,对并联逆变电源的环流影响较小;电容电流反馈对输出电压外特性的影响较小,对并联逆变电源的环流影响较小,所以文中并联系统采用电容电流反馈方式作为内环调节;通过MATLAB软件中的simulink工具验证了理论的正确性。     

Output Impedance Design of Parallel-Connected UPS Inverters With Wireless Load-Sharing Control

This paper deals with the design of the output impedance of uninterruptible power system (UPS) inverters with parallel-connection capability. In order to avoid the need for any communication among modules, the power-sharing control loops are based on the$P/Q$droop method. Since in these systems the power-sharing accuracy is highly sensitive to the inverters output impedance, novel control loops to achieve both stable output impedance and proper power balance are proposed. In this sense, a novel wireless controller is designed by using three nested loops: 1) the inner loop is performed by using feedback linearization control techniques, providing a good quality output voltage waveform; 2) the intermediate loop enforces the output impedance of the inverter, achieving good harmonic power sharing while maintaining low output voltage total harmonic distortion; and 3) the outer loop calculates the output active and reactive powers and adjusts the output impedance value and the output voltage frequency during the load transients, obtaining excellent power sharing without deviations in either the frequency or the amplitude of the output voltage. Simulation and experimental results are reported from a parallel-connected UPS system sharing linear and nonlinear loads.     

Analysis and design of a multiple feedback loop control strategyfor single-phase voltage-source UPS inverters

This paper presents the analysis and design of a multiple feedback loop control scheme for single-phase voltage-source uninterruptible power supply (UPS) inverters with an L-C filter. The control scheme is based on sensing the current in the capacitor of the load filter and using it in an inner feedback loop. An outer voltage feedback loop is also incorporated to ensure that the load voltage is sinusoidal and well regulated. A general state-space averaged model of the UPS system is first derived and used to establish the steady-steady quiescent point. A linearized small signal dynamic model is then developed from the system general model using perturbation and small-signal approximation. The linearized system model is employed to examine the incremental dynamics of the power circuit and select appropriate feedback variables for stable operation of the closed-loop UPS system. Experimental verification of a laboratory model of the UPS system under the proposed closed-loop operation is provided for both linear and nonlinear loads. It is shown that the control scheme offers improved performance measures over existing schemes, It is simple to implement and capable of producing nearly perfect sinusoidal load voltage waveform at moderate switching frequency and reasonable size of filter parameters. Furthermore, the scheme has excellent dynamic response and high voltage utilization of the DC source     

An accurate approach of nonlinearity compensation for VSI inverter output voltage

An accurate nonlinearity compensation technique for voltage source inverter (VSI) inverters is presented in this paper. Because of the nonlinearity introduced by the dead time, turn-on/off delay, snubber circuit and voltage drop across power devices, the output voltage of VSI inverters is distorted seriously in the low output voltage region. This distortion influences the output torque of IM motors for constant V/f drives. The nonlinearity of the inverter also causes 5th and 7th harmonic distortion in the line current when the distributed energy system operates in the grid-connected mode, i.e., when the distributed energy system is parallel to a large power system through the VSI inverter. Therefore, the exact compensation of this nonlinearity in the VSI inverter over the entire range of output voltage is desirable. In this paper, the nonlinearity of VSI inverter output voltage and the harmonic distortion in the line current are analyzed based on an open-loop system and a L-R load. By minimizing the harmonic component of the current in a d-axis and q-axis synchronous rotating reference frame, the exact compensation factor was obtained. Simulations and experimental results in the low frequency and low output voltage region are presented.     

基于状态空间的PWH逆变器的PI数字双环控制方法研究

本文分析了正弦波PWM逆变器的实际应用情况和数字控制的特点,在建立了逆变器及其控制系统的状态空间模型基础之上,采用了一种带输出电流前馈的PI数字双环控制方案（电感电流内环输出电压外环）,并对控制系统直接离散化后利用极点配置的方法设计了控制系统参数,最后给出了在各种实验条件下的仿真波形。仿真结果表明,该方案设计简单可行,井能很好地达到逆变电源的各项性能指标要求。     

Improved control for high power static var compensator using novel vector product phase locked loop (VP-PLL)

This paper presents a new dual loop control using novel vector product phase locked loop (VP-PLL) for a high power static var compensator (SVC) with three-level GTO voltage source inverter (VSI). From a simple dq-axis equivalent circuit obtained by circuit DQ-transformation method, steady-state analysis is achieved for maximum controllable phase angle α_max per unit current between AC source and switching function of inverter. In addition, the system parameters L and C are designed and thus transient analysis is made for open-loop transfer function. This paper proposes software VP-PLL for more accurate α control than conventional hardware PLL because α_max becomes very small in high power SVC. Therefore, the overall controller has dual loop structure of inner VP-PLL for synchronizing the phase angle with AC source and outer Q-loop for compensating reactive power of load. Finally, the usability of the proposed control method is verified through the experiment of 100kvar power capacity with both stand alone and load linked operation.     

基于滞环电流控制的串联型双Buck逆变器

为了使分布式发电系统更有效更稳定地利用自然资源,文章提出了一种适用于风光发电系统(WPGS)的逆变器模型,它由两个双Buck结构串联组成。通过理论分析和模型仿真研究了该逆变器的工作过程。系统由电压外环和电流内环调节输出电压和输出功率,滞环电流控制消除了斜坡交截SPWM控制所需的的偏置电流,提高了效率,增强了系统稳定性。仿真结果表明该逆变器具有克服桥臂直通的优点,可以在两输入电压不稳的情况下为负载提供稳定的电压,具有一定的实用价值。     

An Investigation on Design and Switching Dynamics of a Voltage Source Inverter to Compensate Unbalanced and Nonlinear Loads

In this paper, design aspects of various passive components and switching dynamics of a voltage source inverter (VSI) for compensating unbalanced and nonlinear load are presented. The design method for VSI to track desired reference currents smoothly, is illustrated. By using the proposed method, it is possible to design the passive components of different VSI topologies used for load compensation. The results are supported by detailed simulation studies on a three-phase four-wire compensated system using PSCAD 4.2.1. The design steps are also verified by conducting experiments using a prototype model developed in the laboratory.      

Active input-voltage and load-current sharing in input-series and output-parallel connected modular DC-DC converters using dynamic input-voltage reference scheme

This paper explores a new configuration for modular DC/DC converters, namely, series connection at the input, and parallel connection at the output, such that the converters share the input voltage and load current equally. This is an important step toward realizing a truly modular power system architecture, where low-power, low-voltage, building block modules can be connected in any series/parallel combination at input or at output, to realize any given system specifications. A three-loop control scheme, consisting of a common output voltage loop, individual inner current loops, and individual input voltage loops, is proposed to achieve input voltage and load current sharing. The output voltage loop provides the basic reference for inner current loops, which is modified by the respective input voltage loops. The average of converter input voltages, which is dynamically varying, is chosen as the reference for input voltage loops. This choice of reference eliminates interaction among different control loops. The input-series and output-parallel (ISOP) configuration is analyzed using the incremental negative resistance model of DC/DC converters. Based on the analysis, design methods for input voltage controller are developed. Analysis and proposed design methods are verified through simulation, and experimentally, on an ISOP system consisting of two forward converters.     

单相光伏逆变器的改进型并网控制方法

单相光伏并网逆变器通常采用双闭环控制和电网电压前馈控制的策略,其中双闭环的外电压环为采用PI恒压控制逆变前直流侧电压,分析比较了准比例谐振调节和PI调节两种电流内环的输出外特性,通过对电流内环采用准比例谐振控制的控制系统进行分析建模,建立了逆变器的单相并网仿真模型。仿真结果显示电流内环采用准比例谐振控制能实现并网电流的无静态误差控制,并减小电网频率偏移对并网电流的影响。仿真及实验得到的输出正弦电流波形良好,基于该并网控制策略的光伏逆变器能以高功率因数向电网发电,动态响应快、鲁棒性强、跟踪精度高、并网电流的THD明显优于传统方法,从而验证了改进后模型的可行性和实用性。     

两种逆变器双环反馈控制技术分析与比较

为了提高逆变器的稳定性和供电质量,文中介绍了一种基于极点配置的逆变器瞬时电压电流PI控制器的设计方法,建立了系统模型,比较分析了基于电感电流反馈控制和基于电容电流反馈控制技术。仿真结果表明,基于电感电流电压双环控制技术具有较好的输出特性。     

基于前馈加双环控制的逆变电源设计

介绍一种前馈加双环控制技术的逆变器,它的双环控制包括一个电容电流内环控制和一个瞬时电压外环控制。通过分析该控制策略的工作原理,应用DSP TM320F2812对控制系统进行了设计。试验结果显示逆变器有很好的正弦波输出波形,快速的动态响应,优良的负载特性和高精度的输出电压。     

Deadbeat controlled PWM inverter with parameter estimation usingonly voltage sensor

A technique based on deadbeat control theory is proposed to obtain a nearly sinusoidal PWM (pulsewidth-modulated) inverter output voltage using only a voltage sensor. The closed loop sampled-data feedback scheme inherently results in very fast response to load disturbance and nonlinear load, producing low total harmonic distortion. Parameter estimation of the plant provides a type of self-tuning of the proposed controller. A theoretical analysis, simulation, and experimental results are presented for a single-phase PWM inverter controlled by an Intel 8086 microprocessor     

Measuring the real parameters of single-phase voltage source inverters for UPS systems

The design of a voltage source inverter (VSI) control system requires knowledge about its continuous or discrete model. The output filter inductance and the equivalent serial resistance, which is partly the result of power losses in the core, have values at the operating point that are significantly different from the assigned nominal values, particularly for iron-powder cores. Measurements using standard laboratory equipment are not sufficient because it is impossible to get the voltage and current of the operating point. So the best solution is to measure the Bode plots of the inverter control function at the operating point, to estimate the results of the measurements using the proper analytic function and to calculate the real values of the inverter parameters. Knowledge about the equivalent serial resistance enables the estimation of the inverter power losses. Two approaches to measurements are shown – one that does not require any additional equipment and the other that uses a specialised system to automatically measure the Bode plots. The advantages and disadvantages of both approaches are presented. These measurements enable the validation of the coil core magnetic material by taking into account the power losses. The applications of the measurements in the control design are shown.     

A discretized current control technique with delayed input voltagefeedback for a voltage-fed PWM inverter

A current control technique for a voltage-fed PWM inverter is presented. The discretized state equation of an inverter and a load independent of operating conditions with the delayed input voltage feedback has been derived using the averaging concept. The discretized current controller is proposed to reduce the current error as fast as possible using the deadbeat control strategy and to stabilize the closed loop system asymptotically when the variations of load parameters are given in the predetermined stabilized region. This proposed control scheme is realized by the symmetrical uniform sampling method and is easily implemented using a microprocessor-based system. Computer simulation for the proposed controller has been carried out and the results show good static and dynamic performances     

不平衡负载条件下三相四桥臂逆变器的控制

三相四桥臂逆变器具备外接三相不平衡负载的能力。为改善逆变器系统在严重不平衡负载情况下输出电压的对称性,文中提出一种新颖的控制策略——旋转坐标系下的PIR-P双环控制。当系统接不平衡负载时,电压外环的PI控制器保证系统的动态性能,谐振控制器保证其稳态精度。最后在旋转坐标系下对系统分别采用PI-P和PIR-P两种双闭环控制器情形作对比仿真。结果表明系统在严重不平衡负载情况下,输出电压负序不平衡度由2.41%减小到0.129%,零序不平衡度由2.25%减小到0.032%。     

Implementation of a New Linear Control Technique Based on Experimentally Validated Small-Signal Model of Three-Phase Three-Level Boost-Type Vienna Rectifier

In this paper, the design and implementation of a new multiple-input-multiple-output linear control technique based on a theoretically established and experimentally validated small- signal model for the three-phase three-level boost-type ac/dc Vienna converter are presented. Averaging and local linearization techniques are used to derive the dynamic model expressed in the dqo reference frame. The resulted transfer functions are discretized for the sake of a digital controller design. Multiple-loop control strategy is adopted and consists of inner current feedback loops, which are based on the straightforward looping technique that neglects interactions between the dq components of control inputs and currents, respectively, and of an outer voltage loop, which is designed to ensure dc voltage regulation by adjusting the magnitude of the references for the inner current loops. The output dc voltage unbalance is also controlled in the inner loops. The proposed modeling and control approaches are first simulated and then validated on a 1.5-kW laboratory prototype supported by the DS 1104 digital real-time controller board of dSPACE. The obtained results prove the accuracy of the proposed new small-signal model and, therefore, its reliability for dynamic analysis and control design purposes. It is also proved that a judicious choice of controller parameters, as well as an adequate rating of boost inductors, allows one to meet the IEEE standard requirements in terms of ac line-current total harmonic distortion and power factor. The efficiency of the proposed control technique is maintained in case of disturbances occurring on both source and load sides.