Interleaving Quasi-Sliding-Mode Control of Parallel-Connected Buck-Based Inverters

An interleaving fixed-switching-frequency quasi-sliding control algorithm based on the zero average dynamics approach is reported and applied to the design of a modular system of parallel-connected single-phase inverters. This approach is used in a laboratory prototype of three inverters with field-programmable gate array control-based implementation embedding this algorithm, as well as a power management strategy for handling the number of active inverters. Experimental results are provided to illustrate the design features in terms of ac output voltage regulation, balanced current sharing among mismatched modules, interleaved fixed-switching-frequency operation and robustness with respect to load variations, and inverter activation during system operation.      

Model Predictive Control of Parallel-Connected Inverters for Uninterruptible Power Supplies

Uninterruptible power supplies (UPSs) have been used in many installations for critical loads that cannot afford power failure or surge during operation. It is often difficult to upgrade the UPS system as the load grows over time. Due to lower cost and maintenance, as well as ease of increasing system capacity, the parallel operation of modularized small-power UPS has attracted much attention in recent years. In this paper, a new scheme for parallel operation of inverters is introduced. A multiple-input–multiple-output state-space model is developed to describe the parallel-connected inverters system, and a model-predictive-control scheme suitable for paralleled inverters control is proposed. In this algorithm, the control objectives of voltage tracking and current sharing are formulated using a weighted cost function. The effectiveness and the hot-swap capability of the proposed parallel-connected inverters system have been verified with experimental results.      

Robust Model-Following Control of Parallel UPS Single-Phase Inverters

This paper presents a robust control technique applied to modular uninterruptible power-supply (UPS) inverters operating in parallel. When compared to conventional proportional–integral (PI) control, the proposed technique improves the response of the output voltage to load steps and to high distorted output currents, reducing the distortion of the output voltage. Furthermore, an excellent distribution of currents between modules is achieved, resulting in fine power equalization between the inverters on stream. The crossover frequency of the different loop gains involved is moderate, so that robustness to variations of the operation point and to modeling uncertainties is achieved. A comparative study with a two-loop conventional PI control scheme is presented. Experimental results on a 1-kVA modular online UPS system confirm the viability of the proposed scheme.      

单相UPS逆变控制技术研究

为了进一步提高UPS(Uninterrupted Power Supply)输出的动态和稳态性能，介绍了一种采用电流环做内环的双环控制技术，实现了对负载电流扰动的解耦。同时为了补偿输入电压的不稳定，采用输入电压前馈控制。文中就提到的控制方法分别进行了时域和频域仿真分析，并以DSP(TMS320LF2407)为控制芯片进行了实验验证，结果显示逆变器输出电压在恶劣的负载条件下波形畸变很小。     

Weighted Control of Traction Drives With Parallel-Connected AC Machines

AC machines supplied in parallel by a common voltage source inverter are sometimes used in industrial drives and railway traction applications. This reduction of power and control electronics leads to a reduction of cost, weight, and dimensions that is very useful for on-board systems. But this common supply imposes common voltages to all machines and the possibilities of independent behavior are reduced. In this paper, a graphical modeling is suggested to model such parallel drives for a railway application. A weighted control is then systematically deduced from this modeling and different possibilities of control are highlighted. Experimental results are provided to compare two of the deduced controls     

A Three-Level Hysteresis Function Approach to the Sliding-Mode Control of Single-Phase UPS Inverters

A new approach to the sliding-mode control ofsingle-phase uninterruptible-power-supply inverters is introduced in continuous time. A three-level hysteresis sliding function is used to directly control the inverter switches, with the result that a transistor is switched during a half-cycle while it remains either on or off during the other cycle. An expression is derived for the predicted switching frequency. The performance of the proposed control method has been tested through computer simulations and experiments under different loads (a resistive load and a diode bridge rectifier load). Simulation and experimental results verify the correct operation of the proposed control strategy. In addition, the switching frequency prediction is seen to be quite accurate.      

Control Design Guidelines for Single-Phase Grid-Connected Photovoltaic Inverters With Damped Resonant Harmonic Compensators

The injection of low-harmonic current to the electrical grid is nowadays regulated by international standards. In order to accomplish these standards, selective harmonic compensation is carried out in grid-connected photovoltaic inverters by means of resonant harmonic compensators. This paper gives a systematic design procedure for selecting the gains and parameters of these harmonic compensators. Other factors considered in the design process include frequency deviation, grid synchronization, and transient response. Both a design example meeting the requirements of grid interconnection and selected experimental results from a digital-signal-processor-based laboratory prototype are also reported.     

A Space Vector PWM Scheme for Multifrequency Output Voltage Generation With Multiphase Voltage-Source Inverters

Multiphase variable-speed drives, supplied from two-level voltage-source inverters (VSIs), are nowadays considered for various industrial applications. Depending on the drive structure and/or the motor design, the VSI is required to generate either sinusoidal voltages or voltages that contain a certain number of sinusoidal components (ldquomultifrequency output voltagesrdquo). The existing space vector pulsewidth-modulation (SVPWM) schemes are based on selection of (n-1) active space vectors (for odd phase numbers) within a switching period and they yield either sinusoidal voltage or sinusoidal fundamental voltage in combination with a limited amount of other harmonic terms. This paper develops a SVPWM scheme, which enables multifrequency output voltage generation with arbitrary values of various sinusoidal components in the output voltage. The method is based on initial selection of (n-1)²/2 active space vectors within a switching period, instead of the common (n-1) active vectors. By properly arranging the sequence of the vector application, it is possible to provide an automatic postreduction of the number of applied active vectors to (n-1), thus maintaining the same switching frequency as with the existing schemes while simultaneously avoiding the limiting on the generated sinusoidal output voltage components. Theoretical considerations are detailed using a five-phase VSI. The experimental verification is provided using a five-phase two-motor series-connected induction motor drive, supplied from a custom-designed five-phase DSP-controlled VSI.     

Control Strategy for Series and Parallel Output Dual-Buck Half Bridge Inverters Based on DSP Control

This paper presents a novel control strategy for series and parallel output dual-buck half-bridge inverters (DBHBIs). With the increasing concern of fossil fuel reserves and the environmental aspects, the 2005 International Future Energy Challenge, sponsored by U.S. the Department of Energy and the Institute of Electrical and Electronics Engineers, required that the grid-connected inverter should provide a single-phase utility line with 110–240 V at either 50/60 Hz. The proposed series and parallel output DBHBI can produce those kinds of voltage by series or parallel connection of two inverters and with digital signal processor (DSP) control to meet the aforementioned specifications. The load current of the two inverters at parallel output association and the load voltage of both at series output association can be shared. The waveform quality of the whole output voltage is high at both associations. Stability and relative stability of the inverter are unaffected at the two output associations. Operating principle, control strategy, stability and relative stability, and design guidelines and examples are illustrated. Experimental results of a 1-kVA DSP-based series and parallel output DBHBI at stand-alone mode verify the theoretical analysis. The comparisons between single and double inverter structures show that the proposed inverter is very promising in applications.      

一种大电流高输出阻抗电流镜的设计

设计一种增强型的共源共栅电流镜。通过放大器的负反馈,这里设计的电流镜在不增大基本电流镜输入阻抗的基础上,具有比传统电流镜更高的输出阻抗和更高的电流匹配精度,同时该电流镜也有高于传统共源共栅电流镜的输出电压摆幅。采用CSMC 0.5μm CMOS工艺,在3.3 V电源电压,输入电流为10 mA时,该电流镜的输出阻抗达到200 MΩ以上,输出电压摆幅为0.2~5 V,电流匹配精度误差小于0.016%,电流一致性误差小于0.5%。     

A Novel Switching Sequence Design for Five-Level NPC/H-Bridge Inverters With Improved Output Voltage Spectrum and Minimized Device Switching Frequency

This paper presents a novel switching sequence design for the space-vector modulation of high-power multilevel converters. The switching sequences are optimized for the improvement of harmonic spectrum and the minimization of device switching frequency. Compared to other commonly used switching sequences, the output spectrum of the proposed design shows higher inverter equivalent switching frequency. Meanwhile, the device switching frequency is reduced by using a flexible switching pattern. The proposed switching sequence has been simulated and experimentally tested on a 5-level neutral point clamped H-bridge based inverter. The results from both simulations and experiments consistently verify the above-mentioned features.     

中央无线覆盖工程大功率UPS设计安装及维护

目前,我国已发布实施强制性地面数字电视国家标准(DMB),加紧建设各级中央广播电视节目无线数字化覆盖,已成为当前一项重要而紧迫的任务,而UPS电源是确保无线数字电视信号的优质播出最关键环节.本文通过对此次的工程完工后试播近半年来的经验,来描述大功率UPS在中央无线覆盖工程当中存在的一些设计安装方法和维护经验,以供同行们参考使用.     

一种新型UPS无互联线并联下垂特性控制

传统的UPS无互联线并联下垂特性控制是采用频率下垂和幅度下垂来调节输出电压。这种控制方法虽然是有效的，但是它容易导致系统正反馈。文中提出了一种基于神经网络解耦控制的下垂特性控制方案。这种新的控制方法能有效地克服传统下垂特性控制的局限性。由仿真结果得，该方案下逆变电源均分负载电流的效果好，而且系统动态响应性能高。     

大脉宽单稳态触发器的设计

提出了一种不用大电容实现大脉宽单稳态触发器的电路，并重点对其电压特性和温度特性进行了分析。     

Design of a Flexible Control Platform for Soft-Switching Multilevel Inverters

In modern high-power medium voltage drives, multilevel converters are increasingly used. Employing slight topological modifications, soft-switching technology can be applied to multilevel converters to reduce the switching losses. As a result, the switching frequency can be increased, thereby reducing the output filter size. However, common converter controls have to be modified. In this paper, a flexible control platform is presented that allows rapid prototyping of soft-switching topologies. An analysis of different auxiliary resonant commutated pole (ARCP) topologies shows that all switching commands can be synthesized with synchronized signals of two-level ARCP converters. Therefore, a flexible state-machine for two-level converters was developed first, which can also be used to build controls for multilevel topologies. It supports drivers with built-in intelligence as well as the control of additional switches that are required in some ARCP neutral-point-clamped (NPC) topologies. The switching commands for the state machines can be generated by standard multilevel modulation methods. Illegal switching states are filtered and multiple simultaneous commutations per phase are prevented for ARCP NPC converters. To verify the functionality, the control scheme was realized in a field programmable gate array and a completely modular test converter was developed. This test converter can be used to quickly implement all common multilevel topologies and test different modulation strategies. Experimental results are presented in this paper.     

Loop Gain, Input Impedance and Output Impedance of Feedback Amplifiers

Introductory treatments of feedback amplifiers commonly contain inconsistencies, or present results as universal when in fact they need qualification. Loop gain, overall gain, input impedance and output impedance are instances. A case can therefore be made for rigorous development, even in a first course, provided mathematical rigor can be combined with physical insight. A feedback factor H is first defined for ideal circumstances. The corresponding forward-path gain G has an obvious physical interpretation: the amplifier without feedback, the external source and load impedances, and the feedback network are all involved, and the form of G is such as to suggest best practice for the various feedback configurations. Stability considerations, and precise values for overall gain, sensitivity, input impedance and output impedance follow directly from GH.     

并联逆变器输出滤波器的分析和改进

简述了输出滤波器在逆变器并联中的作用,对传统LC输出滤波器在逆变器并联中存在的问题进行了分析,并提出了改进的非对称T型滤波器。改进的滤波器在逆变器并联的环流抑制和控制量的选择等方面优于LC输出滤波器。理论分析和仿真结果证明提出的输出滤波器改进方法简单而有效,并将其应用到并联电路试验中,起到了较好的效果。     

Distributed Control for UPS Modules in Parallel Operation With RMS Voltage Regulation

A novel distributed control for uninterruptible power supply (UPS) modules in parallel operation is proposed in this paper, in which the voltage reference synchronization control and load current distribution control are decoupled by a local feedback. The voltage reference is presynchronized beyond the current distribution control with a microcontroller unit and a wired-and circuit. Both instantaneous current distribution and hot swapping of any module are allowed with all the UPS modules electrically isolated. The transfer function of the circulating current regulator is analyzed and equivalent to a first-order low-pass filter. The control characteristics of the root-mean-square voltage regulator (RMSVR) in each UPS module in parallel operation are researched, as well as the coupling effect between the RMSVR and the load balance performance. The RMSVR's impact on current distribution is compensated by introducing the amplitude of the output current or the circulating current into the amplitude adjustment of the sinusoidal voltage reference signal. As a result, both the current sharing and the output-voltage performance of the whole system are effectively improved. Theoretical analysis and experimental results are provided to demonstrate the validity and feasibility of the proposed control.      

A Nonisolated Single-Phase UPS Topology With 110-V/220-V Input–Output Voltage Ratings

A circuit configuration of a single-phase nonisolated online uninterruptible power supply (UPS) with 110-V/220-V input–output voltage ratings is proposed, allowing the bypass operation without a transformer even if the input voltage is different from the output voltage. The converter consists of an ac–dc/dc–dc three-level boost converter combined with a double half-bridge inverter. In this type of configuration size, cost and efficiency are improved due to the reduced number of switches and batteries, and also, no low-frequency isolation transformer is required to realize bypass operation because of the common neutral connection. Both stages of the proposed circuit operate at high frequency by using a passive nondissipative snubber circuit in the boost converter and insulated-gate bipolar-transistor switches in the double half-bridge inverter, with low conduction losses, low tail current, and low switching losses. Principle of operation and experimental results for a 2.6-kVA prototype are presented to demonstrate the UPS performance.      

全数字化UPS并联运行系统的保护控制策略

为保证模块化电源并联系统能独立、稳定地长期运行，详细分析了全数字化UPS中SPWM逆变电源并联运行过程中故障的判断技术及保护处理措施，并提出了系统保护控制策略及控制流程。