Current Weighting Distribution Control Strategy for Multi-Inverter Systems to Achieve Current Sharing

A current-weighting-distribution-control (CWDC) strategy for multi-inverter systems to achieve current sharing is presented in this paper. With a CWDC strategy, the inverters connected in parallel are allowed to have different power ratings and can achieve a weighted output current distribution by adding only simple circuits to each inverter. In such systems, each inverter has an outer voltage loop controller to govern system stability, an inner current loop controller to expedite dynamic response, and a weighting current controller to achieve current distribution and to reduce possible interactive effects among inverters. Experimental results from a two-inverter system and a three-inverter system have demonstrated the feasibility of the proposed strategy in weighting current distribution and fast regulation during a step-load change or hot-swap operation     

三相并网逆变器的双环控制策略研究

由于对高频谐波的抑制效果明显好于L型滤波器,因此LCL滤波器在电流源控制的并网逆变器中应用越来越广泛。而针对该类型的并网逆变器的控制策略更为复杂,为了简化控制策略一种基于电流双环的并网控制方案被提出来。与电压电流的双环控制器设计方法不同,设计电流双环控制器参数时除了考虑内外环控制器的相互影响以外,还需要考虑双环控制器带来的降阶和少自由度问题。因此本文在介绍基于高阶极点配置的电流双环控制器设计方法的基础上,重点分析在电流双环控制带来的少自由度的情况下如何合理的设计控制器参数。实验结果表明,根据该方案设计的控制器参数能够使三相并网逆变器安全、可靠运行且具有较快的动态响应速度。     

A novel communication strategy for decentralized control of paralleled multi-inverter systems

A new communication strategy for decentralized control of paralleled multi-inverter systems is introduced in this paper. The proposed strategy utilizes the common mode signal's circuit in the paralleled system as a channel of communication between individual inverters. Source voltage synchronization for paralleled inverters is presented to demonstrate its effectiveness. One inverter module acts as a source and a synchronized signal is sent by means of frequency modulation in this channel to all other modules via the common mode current. Each module will then receive and transform the signal to be used as a synchronized voltage command for individual inverters. The approach enables synchronization in the paralleled multi-inverter system and the method is not affected by external factors such as load change, output voltage variation, and different types of loads. The principle of operation, performance of the proposed strategy, as well as the experimental evaluation with three single-phase paralleled inverters are discussed and presented in this paper.     

Discrete pulse modulation strategies for high-frequency invertersystems

High-performance, high-frequency inverter systems for UPS (uninterruptible power system) applications cannot be easily realized using conventional hard-switched PWM inverter topologies. Adoption of typical soft-switched inverters such as the resonant DC link inverter, require the use of discrete pulse modulation strategies. New controller structures are necessary to cope with stringent voltage regulation and distortion constraints in the presence of unbalanced and nonlinear loads. A controller that utilizes a load current feedforward strategy with a cost function current regulator to achieve excellent transient performance characteristics is presented. Voltage regulation is ensured using a synchronous frame regulator. Detailed simulation and experimental results verifying the concepts are presented. Although this work focuses on soft-switching inverters, the control concepts can be applied to conventional hard-switching inverters as well     

Decoupling Control Strategy for Single Phase SPWM Parallel Inverters

A deconpling control strategy of inverter parallel system is proposed based on the equivalent output impedance of single phase voltage source SPWM （sinusoidal pulse width modulation） inverter. The active power and reactive power are calculated in terms of output voltage and current of the inverter, and sent to the other inverters in the parallel system via controller area network （CAN） bus. By calculating and decoupling the circumfluence of the active power and reactive power, the inverters can share load current via the regulation of the reference-signal phase and amplitude. Experimental results of an 110V/2kVA inverter parallel system show the feasibility of the decoupling control strategy.     

Improved and less load dependent three-phase current-controlledinverter with hysteretic current controllers

A concept of the so-called inner feedback in three-phase current-controlled inverters with hysteretic current controllers is introduced. Stability of the inverter at various frequencies under two different applied loads have been studied. An inertial feedback loop is added to each controller. This modification affects operating characteristics of the inverter by enforcing a switching pattern of low dependence on the load, resulting in significantly improved quality of the output current     

光伏并网多个逆变器并联运行控制及实现

传统的逆变器并联控制方案中各个模块相互之间存在连线.随着模块数目的增加和模块间距离的增大,各个模块之间的信号容易受到干扰.根据逆变器并联运行的原理,该文分析了几种逆变器并联的控制方案,比较了几种常见的PQ下垂法的优缺点,进一步研究了无互联线逆变器并联控制策略,介绍了一种更加适合光伏并网系统的无互联线逆变器并联控制方案,...     

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.     

基于极点配置的400Hz逆变电源系统设计

针对单相400Hz逆变电源系统的控制特点,引入输出电压瞬时值外环和电感电流内环的双环反馈控制,采用极点配置与PI控制相结合的方法对系统进行了设计,并根据状态空间理论建立了系统数学模型。仿真结果表明,该方案动态响应快、稳态精度高、THD小、带负载能力强。     

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     

双闭环逆变器控制策略仿真研究

针对开环逆变器波形畸变大的缺点,文中采用双闭环控制策略,并应用Matlab的Simulink工具对单相半桥、三相半桥逆变器的开环,双闭环控制条件下的逆变器进行仿真,结果验证了双闭环控制逆变器的优越性。     

Dead beat control of three phase PWM inverter

A novel method for microprocessor control of three-phase sinusoidal-voltage pulse-width-modulated (PWM) inverters is proposed. First, the discretized state equations of the inverter main circuit on the d-q frame are derived. An algorithm for dead beat control with a current minor loop that constrains the inverter current within the safety limit is subsequently developed. To compensate the computing time delay, a second-order prediction method and a novel discretization method using twice the time of the sampling period have been adopted. This method is especially suitable for inverters using high-speed switching devices and digital signal processors. The validity of the control system has been demonstrated by precise simulation using a hybrid computer     

一种改进的单相逆变器重复控制方案

提出一种新的重复控制方案,通过电容电流内环反馈,消除逆变器固有的谐振峰,简化了重复控制器的设计;改进内模中的Q（z）,采用零相移低通滤波器,提高了系统的稳态精度。Matlab仿真结果表明,该控制方案可以获得高质量的电压输出,在非线性负载条件下THD仅为0.65%,稳态误差只有0.12%。     

A novel high-performance utility-interactive photovoltaic inverter system

This paper presents a novel photovoltaic inverter that cannot only synchronize a sinusoidal AC output current with a utility line voltage, but also control the power generation of each photovoltaic module in an array. The proposed inverter system is composed of a half-bridge inverter at the utility interface and a novel generation control circuit which compensates for reductions in the output power of the system that are attributable to variations in the generation conditions of respective photovoltaic modules. The generation control circuit allows each photovoltaic module to operate independently at peak capacity, simply by detecting the output power of the system. Furthermore, the generation control circuit attenuates low-frequency ripple voltage, which is caused by the half-bridge inverter, across the photovoltaic modules. Consequently, the output power of the system is increased due to the increase in average power generated by the photovoltaic modules. The effectiveness of the proposed inverter system is confirmed experimentally and by means of simulation.     

Wireless-Control Strategy for Parallel Operation of Distributed-Generation Inverters

In this paper, a method for the parallel operation of inverters in an ac-distributed system is proposed. This paper explores the control of active and reactive power flow through the analysis of the output impedance of the inverters and its impact on the power sharing. As a result, adaptive virtual output impedance is proposed in order to achieve a proper reactive power sharing, regardless of the line-impedance unbalances. A soft-start operation is also included, avoiding the initial current peak, which results in a seamless hot-swap operation. Active power sharing is achieved by adjusting the frequency in load transient situations only, owing to which the proposed method obtains a constant steady-state frequency and amplitude. As opposed to the conventional droop method, the transient response can be modified by acting on the main control parameters. Linear and nonlinear loads can be properly shared due to the addition of a current harmonic loop in the control strategy. Experimental results are presented from a two-6-kVA parallel-connected inverter system, showing the feasibility of the proposed approach     

Multilevel inverter by cascading industrial VSI

In this paper, the modularity concept applied to medium-voltage adjustable speed drives is addressed. First, the single-phase cascaded voltage-source inverter that uses series connection of insulated gate bipolar transistor (IGBT) H-bridge modules with isolated DC buses is presented. Next, a novel three-phase cascaded voltage-source inverter that uses three IGBT triphase inverter modules along with an output transformer to obtain a 3-p.u. multilevel output voltage is introduced. The system yields in high-quality multistep voltage with up to four levels and low dv/dt, balanced operation of the inverter modules, each supplying a third of the motor rated kVA. The concept of using cascaded inverters is further extended to a new modular motor-modular inverter system where the motor winding connections are reconnected into several three-phase groups, either six-lead or 12-lead connection according to the voltage level, each powered by a standard triphase IGBT inverter module. Thus, a high fault tolerance is being achieved and the output transformer requirement is eliminated. A staggered space-vector modulation technique applicable to three-phase cascaded voltage-source inverter topologies is also demonstrated. Both computer simulations and experimental tests demonstrate the feasibility of the systems.     

PWM整流器的PI^λ D^μ控制策略

针对常规控制适用场所的局限性,提出了一种基于分数阶控制的PWM整流方法,该方法有别于以往的双闭环控制策略,电流内环控制使用分数阶控制器取代传统控制器。通过MATLAB/Simulink仿真与实验验证了该控制策略的控制效果明显好于传统控制方法。此外,其不仅可以应用在控制精度要求高、控制参数多的非线性系统中,而且具有较好的跟随性、鲁棒性和稳定性,能够准确的跟踪指令电流,并且得到的网测电流谐波很少,近似于正弦波。     

Compensated synchronous PI current controller in overmodulationrange and six-step operation of space-vector-modulation-basedvector-controlled drives

Overmodulation enhances the power utilization of the installed capacity of a voltage-source inverter. A space-vector strategy is used for constant-switching-frequency inverters. In order to achieve the overmodulation, a modified reference signal with nonuniform angular velocity is generated using a preprocessor. Such a reference wave produces low-frequency harmonics in currents. The presence of current harmonics restricts the bandwidth of the synchronous proportional plus integral current controller in the overmodulation range. A compensating current control is presented to allow for high-bandwidth current control in synchronous coordinates during overmodulation and six-step. The proposed scheme allows for an easy upgrade of a conventional vector control scheme to include overmodulation and, thus, reduce the design-to-market time     

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.     

基于预测函数控制的无刷直流电机控制研究

由于无刷直流电机调速系统具有非线性、多变量、不确定时变系统等特点,在高控制精度和快响应速度的条件下,传统的PID控制方法已经不能满足无刷直流电机调速系统的要求,如果其中的参数变化超过一定范围,整个控制系统会出现不稳定。在分析无刷直流电机（BLDCM）的数学模型并将其简化的基础上,提出了一种无刷直流电机的预测函数控制（PFC）策略,并进行了Matlab仿真试验。该BLDCM系统采用双闭环调速,速度环中采用PFC控制,计算得到参考电流值作为电流环的输入,电流环采用离散PI控制,由滞环电流跟踪型PWM逆变器的原理实现电流控制。仿真试验结果显示,这种无刷直流电机调速系统可以取得良好的控制效果。