A new UPS topology employing a PFC boost rectifier cascadedhigh-frequency tri-port converter

A new uninterruptible power supply (UPS) topology using the high-frequency tri-port UPS technique is proposed which presents the advantages of no-break power, low cost, input unity power factor, high power density, and high power conversion efficiency. Through the proposed circuit configuration, charging concept, and control strategy, the battery management is easily obtained by controlling the output voltage of the power-factor-correction (PFC) converter, which results in no additional power device being required for charging. The implementing circuit of the charging method is submitted to perform the two-stage charging, constant current charging, and constant voltage charging. The proposed technologies can be applied to the switching power supply with built-in UPS function featuring a low-cost solution for computer equipment, Finally, an experimental AC online UPS is built to verify the proposed concept, analysis, and control strategy     

Single-Phase Uninterruptible Power Supply Based on Z-Source Inverter

This paper presents a new topology of uninterruptible power supply (UPS) by using a Z-source inverter, where a symmetrical LC network is employed to couple the main power circuit of an inverter to a battery bank. With this new topology, the proposed UPS can maintain the desired ac output voltage at the significant voltage drop of the battery bank with high efficiency, low harmonics, fast response, and good steady-state performance in comparison with traditional UPSs. The simulation and experimental results of a 3-kW UPS with the new topology confirm its validity.      

Performance of a single-stage UPS system for single-phasetrapezoidal-shaped AC-voltage supplies

A high-performance single-stage UPS system for single-phase AC power supply systems is presented. The topology generates a trapezoidal-shaped load voltage that is synchronized with the AC supply; therefore, a small DC-link capacitor is required. This feature leads to a high-input power factor (0.94 at nominal voltage), and due to the single-stage structure, high efficiency (93% at nominal voltage) is also achieved. Moreover, in both cases the supply current spectrum presents low-order harmonics, all of which satisfy IEC 555. The high performance is validated using both resistive (linear) and diode RC (nonlinear) loads. The dynamic performance of the UPS system is also analyzed under different transient conditions. Specifically, the supply to battery, battery to supply transition, load transient, and supply/battery-voltage transients are performed. They show a transfer time of 500 μs (from AC supply to battery) and overvoltages of at most 15%. The dynamic and static evaluations are performed on a 1 kVA UPS system. The design guidelines for the key components and control parameters are also included     

A novel on-line UPS with universal filtering capabilities

A novel line-interactive uninterruptible power supply (UPS) is proposed that offers the characteristics of an “on-line” or “inverter-preferred” UPS (which incorporates a pulse-width modulation (PWM) rectifier) at a reduced cost. This new UPS is based on the combination of two full-bridge VSI converters: one in series with the input and the other in parallel with the load. The UPS acts as a line conditioner and output-voltage stabilizer in the presence of input power while charging the battery at a controlled rate. In case of loss of input power, the UPS can make a seamless transition to backup mode while supplying the load with a controlled sinusoidal voltage, drawing power from the battery. The series converter sees only a small percentage of the input voltage (typically, 10%-20%) while carrying the input current and therefore has a small kilovoltampere rating. The parallel converter supplies the load during blackout and hence determines the total kilovoltampere rating of the UPS. The reduced kilovoltampere rating of the series converter results in reduced system cost compared to conventional on-line systems without sacrificing any desirable characteristics. A laboratory version of the proposed UPS has been built to demonstrate the claimed capabilities, and both simulation and experimental results are included in the paper     

Consumption power feedback unit for power electronics burn-in test

Power electronics burn-in testing consumes a huge amount of energy and adds to a significant part of the manufacturing cost. To improve this situation, a pulsewidth modulation (PWM) DC/AC inverter using current-mode control is proposed to feedback burn-in test power to the electric utility system. To implement the proposed idea, a new control strategy and system design are presented in this paper. Case studies using uninterruptible power systems (UPS) and battery chargers are demonstrated by means of prototype experiments to prove the method's performance and effectiveness     

Improved single-phase line-interactive UPS

An improved single-phase line-interactive uninterruptible power supply (UPS) is proposed for low-power applications with low cost. The proposed UPS is comprised of two push-pull converters based on a low-voltage battery for reduced cost: one in series with the input and the other in parallel with the load. In the presence of input power, the UPS acts as an output voltage regulator and at the same time as an active filter while charging the battery. In case of loss of input power, the UPS supplies a regulated sinusoidal voltage to the load, drawing power from the battery. The series converter compensates only a small percentage of the input voltage carrying the input current and, therefore, a reduced rating is made. The parallel converter always supplies a nominal voltage and makes a seamless transition to backup mode. In the voltage determination of the parallel converter, the nominal voltage is derived using the feedback linearization concept and then a perturbed voltage is determined for the reactive power control or output voltage regulation. Experimental results obtained from a 1-kVA prototype are discussed     

A bidirectional DC-DC converter topology for low power application

This paper presents a bidirectional DC-DC converter for use in low power applications. The proposed topology is based on a half-bridge on the primary and a current-fed push-pull on the secondary side of a high frequency isolation transformer. Achieving bidirectional flow of power using the same power components provides a simple, efficient and galvanically isolated topology that is specially attractive for use in battery charge/discharge circuits in DC UPS. The DC mains (provided by the AC mains), when presented, powers the down stream load converters and the bidirectional converter which essentially operates in the buck mode to charge the battery to a nominal value of 48 V. On failure of the DC mains (derived from the AC mains), the converter operation is comparable to that of a boost and the battery regulates the bus voltage and thereby provides power to the downstream converters. Small signal and steady state analyses are presented for this specific application. The design of a laboratory prototype is included. Experimental results from the prototype, under different operating conditions, validate and evaluate the proposed topology. An efficiency of 86.6% is achieved in the battery charging mode and 90% when the battery provides load power. The converter exhibits good transient response under load variations and switchover from one mode of operation to another     

An integrated flyback converter for DC uninterruptible power supply

An integrated flyback power converter performing the combined functions of uninterruptible power supply (UPS) and switch-mode power supply (SMPS) is presented. This power converter has a high voltage main power input and a low voltage backup battery input. DC output is obtained from the main input via a flyback power converter during normal operation and from the backup battery via another flyback power converter when input power fails. High conversion efficiency is achieved in normal, backup, and charging modes as there is only a single DC-DC conversion in each mode. The power converter circuit is very simple, with two switching transistors, a relay for mode switching, and a single magnetic structure only. This new design offers substantial improvement in efficiency, size, and cost over the conventional cascade of UPS and SMPS due to single voltage conversion, high frequency switching, and removal of design redundancy. The operation, design, analysis, and experimental results of the power converter are presented     

Control of Distributed Uninterruptible Power Supply Systems

In the last years, the use of distributed uninterruptible power supply (UPS) systems has been growing into the market, becoming an alternative to large conventional UPS systems. In addition, with the increasing interest in renewable energy integration and distributed generation, distributed UPS systems can be a suitable solution for storage energy in micro grids. This paper depicts the most important control schemes for the parallel operation of UPS systems. Active load-sharing techniques and droop control approaches are described. The recent improvements and variants of these control techniques are presented.     

应用于户用储能系统的电池功率自适应下垂控制

以户用储能系统为研究对象,采用下垂控制调节电池功率,即由逆变器控制直流母线,电池的双向DC/DC控制器根据母线电压调节电池功率,该控制方法的优势在于方便实现多直流源并联。双向DC/DC变换器的电路拓扑采用交错式双向Boost变换器,并给出了下垂控制器的具体设计方法。针对系统中普遍存在的因电压采样偏差(逆变器与DC/DC变换器的电压采样是独立的,存在偏差)导致的功率控制偏差问题,提出了两种电池功率自适应控制策略:电压补偿和功率补偿,并给出了具体的实施方法。最后设计了一台5 kW样机,分别实现了两种策略,并进行了对比分析,实验结果验证了所提出策略的有效性。     

Design of a Reflex-Based Bidirectional Converter With the Energy Recovery Function

In this paper, a reflex charging strategy with the energy recovery function for a bidirectional converter (BC) is proposed to build a novel reflex-based BC (RBC) for increasing the battery charging efficiency in an uninterruptible power supply (UPS). The proposed RBC can provide a reflex charging current profile to charge the battery to obtain a high battery charging efficiency and prolong the battery life cycle. In particular, the negative pulse energy of the reflex charging current profile in the proposed RBC is recovered to reduce the battery charging dissipation. A soft transfer method is also developed in this paper to really erase the spike current in the RBC. A 400 W prototype is designed and implemented to verify the feasibility of the proposed RBC. Compared with a typical bidirectional converter, the battery charging efficiency, the battery charging speed, and the battery thermal deterioration effect are improved by about 10%, 8.8%, and 7%, respectively, with the proposed RBC.      

High-frequency link inverter for fuel cells based on multiple-carrier PWM

Fuel-cell inverter applications typically have a relatively low voltage input, and require a battery bus for energy buffering. Circuit topology issues are examined based on these needs. The need for high step-up ratios, current control, low ripple, and battery storage leads to a current-sourced link converter as perhaps the best choice of conversion topology. High-frequency ac link conversion offers a possible way to reduce the number of power stages, in the form of a cycloconverter, known from previous work. It is shown that the control complexity in this converter can be addressed by adapting pulse-width modulation (PWM) techniques. Here, a multicarrier PWM approach is introduced as a convenient way to implement a high-frequency link inverter. The approach is a direct extension of conventional PWM, and supports square-wave cycloconversion methods that have appeared in prior literature. Simulation and experimental results are developed for a low-voltage ac link inverter, leading to a 48-V fuel cell input design.     

UPS电池系统的配置与维护探讨

UPS可单机运行，也可多机联合运行。多机联合工作又分为：并机、串机。并机既可主备并机，又可冗余并机。UPS中蓄电池容量的选配也至关重要。文中结合在实际工作中的维护经验，论述了UPS的选型和配置，UPS及其电池系统的维护检测方法，推荐一种安全的电池放电方法和一种简易的采用电池离线模拟放电的测量电池电压方法。     

中、大型UPS蓄电池监测管理和容量配置

中、大型UPS系统中蓄电池为交流不间断供电提供了能源保证。对蓄电池组进行监测管理与合理配置容量,有利于延长其寿命,保证UPS系统稳定、安全运行。本文论述了UPS系统的蓄电池监测管理的几个方面,以及蓄电池容量的合理配置计算。     

High-performance online UPS using three-leg-type converter

A high-performance single-phase online uninterruptible power supply (UPS) is proposed. The UPS is composed of a three-leg-type converter which operates as a battery charger and an inverter. The first leg is controlled to charge the battery, and the third leg is controlled to make the output voltage. The common leg is controlled in line frequency. The charger and the inverter are controlled independently. The charger has the capability of power-factor correction while charging a battery. The inverter regulates output voltage and limits output current under an impulsive load. The three-leg-type converter reduces the number of switching devices. As a result, the system has less power loss and a low-cost structure. In the determination of the charger voltage, the nominal voltage is derived using the feedback linearization concept and then a perturbed voltage is determined for the reactive power control. The disturbance of input voltage is detected using a fast sensing technique of the input voltage. Experimental results obtained with a 3-VA prototype show a normal efficiency of over 87% and an input power factor of over 99%.     

UPS蓄电池的选择

蓄电池是UPS系统中的一个重要组成部分。因此，UPS电池的选择不仅关系到经济成本问题、还直接影响UPS电源的不间断供电。根据UPS电池的特点，从电池类型、容量计算、配置方式、寿命及品牌等五个方面分析了如何选择满足负载需要的既经济又可靠的UPS电池，对通信系统长效型UPS电池的选择具有一定的借鉴意义。     

Two-Stage Uninterruptible Power Supply With High Power Factor

An uninterruptible power supply (UPS) with high power factor and two conversion stages is suggested. The double-conversion configuration has three stages, but normally, only two stages are operating at the same time. The first stage of the proposed scheme integrates the power-factor-correction stage and the battery charger of the double-conversion configuration, obtaining a two-stage UPS. The second stage is based on the theory of inverter with boosting capabilities. The battery set has not only been completely isolated, but it has also been charged with a small change at the controller set point; these particular characteristics facilitate the system maintenance and simplify its operation. Additionally, the battery-set voltage is low, reducing the weight and size. The converter operation, analysis, design, and experimental results are shown. The proposed UPS approach is practical in low-power applications ($leq 500$ W).      

High-Performance Transformerless Online UPS

In this paper, a high-performance single-phase transformerless online uninterruptible power supply (UPS) is proposed. The proposed UPS is composed of a four-leg-type converter, which operates as a rectifier, a battery charger/discharger, and an inverter. The rectifier has the capability of power-factor collection and regulates a constant dc-link voltage. The battery charger/discharger eliminates the need for the transformer and the increase of the number of battery and supplies the power demanded by the load to the dc-link capacitor in the event of the input-power failure or abrupt decrease of the input voltage. The inverter provides a regulated sinusoidal output voltage to the load and limits the output current under an impulsive load. The control of the dc-link voltage enhances the transient response of the output voltage and the utilization of the input power. By utilizing the battery charger/discharger, the overall efficiency of the system is improved, and the size, weight, and cost of the system are significantly reduced. Experimental results obtained with a 3-kVA prototype show a normal efficiency of over 95.6% and an input power factor of over 99.7%.      

A Comparison of Diode-Clamped and Cascaded Multilevel Converters for a STATCOM With Energy Storage

The progression of distributed generation within a bulk power system will lead to the need for greater control of transmission-line power flows. Static synchronous compensators (STATCOMs) provide a power-electronics-based means of embedded control of transmission-line voltage and power flows. The integration of energy storage with a STATCOM can extend traditional STATCOM capabilities to four-quadrant power flow control and transient stability improvement. This paper discusses energy storage systems (ESSs) integrated with conventional and multilevel bidirectional power converters for a hybrid STATCOM/ESS. Conventional, diode-clamped, and cascaded multilevel converter-based STATCOM/ESSs are developed, and their performances for a variety of power system applications are compared using battery energy storage. The advantages and disadvantages of each topology are presented. Both simulation and experimental results are provided to validate the conclusions     

应用于UPS的3 kW Boost电路研究

提出了基于UC3842的Boost(升压)电路控制策略,运用开关函数法建立了Boost功率电路的高频数学模型,进而给出了状态空间平均模型,基于这一模型,从控制理论的角度分析了Boost电路的能控、能观测性。文中给出了占空比的输入到输出的小信号传递函数,为设计校正补偿网络提供了理论依据。这一电路可应用于中小型UPS(不间断电源)中,给蓄电池升压,为UPS中的逆变器提供输入电压,可以满足掉电时UPS的动态性能。最后给出的仿真和实验结果,证明了文中分析的正确性和UC3842控制的实用性。