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%.      

Practical Control Implementation of a Three- to Single-Phase Online UPS

A high-performance three- to single-phase online uninterruptible power supply (UPS) is proposed. The proposed UPS is composed of a rectifier, a battery charger/discharger, and an inverter. The rectifier has the capability of power-factor correction and regulates a dc-link voltage. When the rectifier becomes unavailable or when the current required by the load exceeds the output rating of the rectifier, the charger/discharger supplies the power demanded by the load to a dc-link capacitor. The inverter provides a regulated sinusoidal output voltage and limits an output current under an impulsive load. New control algorithms of the rectifier, the charger/discharger, and the inverter are proposed. The proposed algorithms of the rectifier and the charger/discharger improve dynamic performance at step load change. To improve the transient response of the output voltage at outage of an input source, a mode change method of the charger/discharger is also proposed. Additionally, the proposed current-limit algorithm of the inverter can be implemented without additional hardware, and it increases the reliability of the UPS.      

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     

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     

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     

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).      

A boost DC-AC converter: analysis, design, and experimentation

This paper proposes a new voltage source inverter (VSI) referred to as a boost inverter or boost DC-AC converter. The main attribute of the new inverter topology is the fact that it generates an AC output voltage larger than the DC input one, depending on the instantaneous duty cycle. This property is not found in the classical VSI, which produces an AC output instantaneous voltage always lower than the DC input one. For the purpose of optimizing the boost inverter dynamics, while ensuring correct operation in any working condition, a sliding mode controller is proposed. The main advantage of the sliding mode control over the classical control schemes is its robustness for plant parameter variations, which leads to invariant dynamics and steady-state response in the ideal case. Operation, analysis, control strategy, and experimental results are included in this paper. The new inverter is intended to be used in uninterruptible power supply (UPS) and AC driver systems design whenever an AC voltage larger than the DC link voltage is needed, with no need of a second power conversion stage     

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.      

基于电流控制的光伏太阳能充电器系统研究

提出一种基于电流控制的最大功率点跟踪方法用于光伏太阳能充电器,以DC/DC变换器中的Boost电路作为开关充电器,系统由一个光伏电池模块、一个基于Boost变换器开关电池充电器和电池组成.采用光伏电池输出电流控制实现系统的最大功率点跟踪,调整占空比,从而使太阳电池阵列输出功率最大,以输出稳定的电压对蓄电池进行充电,可以提高蓄电池使用寿命,有效地提高独立光伏系统的综合效率,降低整个系统的成本.     

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.      

Combined low-cost, high-efficient inverter, peak power tracker andregulator for PV applications

A novel compound power converter that serves as a DC-to-AC inverter, maximum power point tracker (MPPT), and battery charger for stand-alone photovoltaic (PV) power systems is introduced. A theoretical analysis of the proposed converter is performed, and the results are compared with experimental results obtained from a 1.5 kW prototype. The overall cost of PV systems can thus be reduced by using load management control and efficiency-optimization techniques. Power flow through the converter is controlled by means of a combination of duty cycle and output frequency control. With load management, large domestic loads, such as single phase induction motors for water pumping, hold-over refrigerators, and freezers, can be driven by day at a much higher energy efficiency. This is due to the high efficiency of the inverter with high insolation, and because the inverter uses the energy directly from the solar array. The battery loss component is thus reduced     

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     

基于DSP的UPS电源在线控制技术研究

文章针对单相PWM逆变器,建立了一种用IGBT半桥式逆变电路作为功率变换的电路方案,完成以TMS320LF2406为主控DSP芯片的UPS控制电路。实验表明,利用TMS320LF2406芯片,采用合适的控制方案对50HzUPS逆变电源进行数字化控制,在空载和带大负载的情况下,满足逆变输出电压稳定率〈3%的要求,能获得较理想的控制效果。     

Design and implementation of a cost-effective quasi line-interactive UPS with novel topology

This paper presents an improved single-phase passive-standby uninterruptible power supply (UPS) for low cost applications. The proposed system includes an input rectifier/charger and a switching inverter. It is basically an offline UPS structure, but has nearly the performance of a line-interactive UPS. It can continuously regulate the sustained voltage swells and sags by injecting a voltage in series with the source voltage in the normal mode, and can be switched smoothly to back-up mode when the utility voltage goes outside the specified range, or fails. The regulation range is also larger than conventional offline and line-interactive UPSs. Additionally, the proposed system has no low frequency transformer, which would involve a heavy and bulky structure. Theoretical analysis has been achieved based on the power flow theory. Case study is demonstrated by means of a prototype experiment to prove its performance and effectiveness.     

Parallel processing inverter system

A novel method of instantaneous voltage and power balance control of a parallel processing inverter system is proposed. It consists of a high-speed switching PWM (pulsewidth modulated) inverter with an instantaneous current minor loop controller, a voltage major loop controller, and a power balance controller. This system realizes the following functions with only one inverter: constant AC output voltage control with reactive power control, active filtering to absorb load current harmonics, DC voltage and current control as AC-to-DC converter, and uninterruptible power supply (UPS) for stand-alone operation. This system covers a wide application range, including UPS systems, new energy systems, and active filters with voltage control functions     

Novel unity power factor circuits using zero-vector control forsingle-phase input systems

This paper proposes two novel circuits which realize a unity input power factor single-phase to three-phase converter with a motor load. The power supply is connected to the neutral point of the motor, and the three-phase inverter is controlled to act also as a virtual AC/DC power converter leg. This virtual leg is controlled by zero vectors of the three-phase inverter. The main features of these circuits are as follows: no inductive components are required; a reduction in the number of switching devices compared with conventional topologies; and motor current increases because converter input current also flows through the motor windings. A full-bridge converter can be built using the same number of switching devices as the conventional half bridge and with no need for a capacitive leg with an accessible neutral point. In this paper, the proposed full-bridge-type circuit is experimentally tested using a 750-W induction motor as load     

High performance series-parallel type on-line UPS

An improved single-phase uninterruptible power supply (UPS) is proposed that is composed of a series converter and a parallel converter. The series converter regulates the output voltage, and then the parallel converter provides reactive current compensation and battery charging. A fast detection technique of the line voltage is proposed, which has almost zero transition time from the line power mode to the power failure mode. Furthermore, a current controller of the parallel converter for unity power factor is suggested and it is derived using the feedback linearization technique. A current limit technique in the power failure mode is proposed to protect the parallel converter without a system trip under any impulsive load. All control algorithms are implemented in software with a single-chip microcontroller. Experimental results obtained under a 3?kVA prototype show good transient and steady-state performance such as almost negligible transition time, 97% power efficiency and 99% power factor.     

TRIAC dimmable ballast with power equalization

A two-stage, two-wire TRIAC dimmable electronic ballast for fluorescent lamps is presented in this paper. It is constructed by using a flyback converter as the input power factor corrector to supply a half-bridge series-resonant parallel-loaded inverter to ballast the lamp. The flyback converter is operated in discontinuous conduction mode so that the filtered input current profile is the same as the TRIAC-controlled voltage waveform. The switches in the inverter are switched at a constant frequency slightly higher than the resonant frequency of the resonant tank. Based on the constant average input current characteristics of the inverter, the dimming operation is simply achieved by pulsewidth modulation control of the magnitude of the flyback converter output voltage. No synchronization network is required between the input and output stages. In addition, a linear power equalization scheme is developed so that the dc-link voltage (and hence the lamp power) is in a linear relationship with the firing angle of the TRIAC. The average output voltage of the dimmer controls the equalized flyback converter output voltage. Modeling, analysis, and design of the ballast will be described. A prototype was implemented to verify the experimental measurements with the theoretical predictions.     

Reduced Switch Count DC-Link AC–AC Five-Leg Converter

This paper investigates a reduced switch count dc-link ac–ac five-leg converter for three-phase power conversion. The converter provides both an input rectifier and an output inverter by sharing a leg in order to reduce the number of power switches. Scalar and vector pulsewidth modulation techniques are presented and the concepts of local and global apportioning factors are introduced. A control technique that aims at maximizing the utilization of the dc-link voltage is proposed. A hysteresis current controller that allows operating with one leg being shared by the load and grid sides is developed. In addition, several relevant characteristics of the converter are addressed, such as voltage capability, harmonic distortion, shared-leg and capacitor currents, and power rating. The features of such a converter are compared to those of the six-leg and four-leg converters. Selected experimental results are presented.     

无逆变高效率UPS电源

液晶显示器已取代传统CRT显示器,个人电脑的主机和显示器都由直流供电;在新型UPS中可将交流220V整流滤波成300V直流电,或将电池电压经DC/DC升压至300V,后将300V直流电经DC／DC转换成计算机所需的各组直流电,无需再逆变回交流220V;这种利用高效率的DC／DC转换器设计无逆变电路的UPS电源,可节省UPS电源的能量损耗和成本,并进一步提高电路的可靠性。