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

In the past large Uninterruptible Power Supply (UPS) applications requiring parallel operation of Pulse Width Modulated (PWM) inverters was not practical. New developments in PWM logic design have made load sharing of PWM inverters very precise. This paper addresses the critical factors of the inverter and system design which permit parallel operation and enhancement of system reliability. Taking full advantage of the PWM technique in control of an inverter is discussed. New methods of accomplishing parallel operation are discussed. Particular emphasis is given to improving the "fault tolerance" capabilities of a UPS system. The paper discusses in detail the design of a parallel-redundant UPS system which eliminates some of the "single point failure modes" present in most UPS system configurations. The logic design which permits precision sharing of load currents between parallel inverter; and, the methods of removing faulted inverters from the common bus are presented. Actual operating sequences are used to demonstrate the effectiveness of the system design and the improved fault tolerance characteristics.

In this paper, a high performance controller for parallel operation of uninterruptible power supplies (UPS) is proposed. The proposed controller is based on synchronous reference frame that is developed for parallel UPSs. Applying master-slave algorithm in this controller, power sharing and voltage regulation are controlled centrally by master UPS and commands are send through CAN bus to slave UPS. But each UPS performs voltage harmonic compensation locally and independently. Virtual impedance technique is used to share harmonic currents perfectly. Controller also is modified for unbalanced nonlinear loads. The performance of the proposed controller has been verified with simulation results for 20KVA, 380V three-phase parallel UPS.

This paper is concerned with the control of a line interactive Uninterruptable Power Supply (UPS) system in a Microgrid. In grid connected mode, power can be imported from the grid to charge the battery or it can be injected into the grid to boost the power supplied by the Microgrid. In island mode, the UPS supplies local critical load in parallel with other sources. Power flow is controlled using the frequency and voltage drooping technique to ensure seamless transfer between grid connected and parallel islanding modes of operation. When the power is imported from the grid, an outer voltage controller that regulates the DC link voltage sets the power demand for an inner power flow controller. The outer voltage loop is designed with the aid of small signal analysis which has been used to model the dynamics of the inner power flow controller. Due to the limited DC link capacitance, the drooping coefficients are chosen carefully to limit transient circulating active power from the grid to the UPS module or from one UPS module to another. The traditional way of measuring active and reactive power which is based on using a low pass filter is replaced by a real time integration method which is shown to improve the response of the controller. A virtual impedance is utilized in grid-connected mode to improve output current THD. Experimental results of two 60kW line interactive UPS modules are provided to validate the design.

Our daily life is supported by powerful information networks which are composed of computers and communication equipments. If they do not work correctly or completely, our daily life would be surely confused. Under some circumstances safety could not be kept. Uninterruptible Power Supply (UPS) systems are commonly equipped to supply stable power to the critical loads, for example, large computer center telephone and telecomnication center, aviation control system and so on. Several kinds of UPS systems are now used in many important fields as the above mentioned. But they almost do not have been evaluated numerically based on system reliability.This paper evaluates MTBF of parallel redundant UPS systems, and reports MTBF of 2 sets of parallel redundant UPS system is lower than that of 3 sets of parallel redundant UPS system under some circumstances. Continuous power supply reliability of the UPS system with bypass and uninterruptible transfer switch is much higher than any other UPS system without bypass circuit and uninterruptible transfer switch. And then the last some highly reliable parallel operation technology are shown.

This paper presents the digital control scheme of a single phase uninterruptible power supply (UPS). In order to obtain fast response in the current control, the authors propose the digital control scheme based on the instantaneous values. The inverter of the UPS is connected to the load in parallel to reduce the loss of the UPS. The controller is constructed by a DSP. The control schemes in all of the operations of the UPS are described. All operations of the UPS using the proposed control scheme have been verified by experiments.

A dual-motor electric power steering system suitable for commercial vehicles was designed. Based on ADAMS/Car, the multi-body dynamic model of the vehicle is established, and the basic assist characteristic curve of the commercial vehicle is given. Then, two kinds of electric current distribution and fault-tolerant control strategies of dual-motor EPS system are proposed. Finally, based on MATLAB/Simulink, the control model of EPS is established. The feasibility and fault tolerance of current distribution control strategy proposed in this paper are verified by co-simulation.

A current sharing method considering battery state of charge(SOC) for multi-module uninterruptable power supply(UPS) system is proposed. Modularized UPS system consists of a single master module and multi slave modules. A master module performs output voltage control and distributes current commands to slave modules. The current commands are generated by using the proposed current sharing algorithm to balance the SOC of each UPS module. Moreover, the UPS mode transfer time can be significantly reduced by using the predictive current control. The predictive current control method is mathematically verified by analyzing the UPS system. The validity of proposed balancing method and predictive control is verified by simulation results.

This paper presents the reactive power compensation with UPS. The most effective power quality improvement solution is analyzed in an uninterruptible power supply systems. The conventional UPS has three stages i.e rectifier converts AC to DC, Battery to store DC and Inverter to convert DC to AC. A novel technique has implemented in off-line UPS. The power is delivered to load via by-pass switch when main supply is available. Inverter does not operate during this period. So inverter function is same as conventional inverter. To overcome this problem, static change over switches has proposed. Hence it will get better voltage regulation and loss less in distribution system. The performance of simulation result is analyzed using MATLAB/SIMULINK.

This paper investigates the control of an uninterruptible power supply (UPS) using a combined measurement of capacitor and load currents in the same current sensor arrangement. The purpose of this combined measurement is, on one hand, to reach a similar performance as that obtained in the inductor current controller with load current feedforward and, on the other hand, to easily obtain an estimate of the inductor current for overcurrent protection capability. Based on this combined current measurement, a voltage controller based on resonant harmonic filters is investigated in order to compensate for unbalance and harmonic distortion on the load. Adaptation is included to cope with uncertainties in the system parameters. It is shown that after transformations the proposed controller gets a simple and practical form that includes a bank of resonant filters, which is in agreement with the internal model principle and corresponds to similar approaches proposed recently. The controller is based on a frequency-domain description of the periodic disturbances, which include both symmetric components, namely, the negative and positive sequence. Experimental results on the output stage of a three-phase three-wire UPS are presented to assess the performance of the proposed algorithm.

Paper presents a novel topology of a grid-connected back-up uninterruptible power supply (UPS) system with multilevel converters. The star-configuration three-phase "back-to-back" topology with a five-level diode-clamped rectifier (5LDCR) and a five-level diode-clamped inverter (5LDCI) supplies a three phase output load. The proposed multi-level current mode control techniques in both converters provide an effective solution to an imbalance problem with the capacitor voltages in a DC link network. The interfaced battery energy storage (BES), which constitutes an integral part of the entire UPS system, supplies the DC link capacitor voltages to the 5LDCI in a standby emergency mode because the proposed balancing method is constrained to the "back-to-back" operation only. Importantly, the UPS system is able to operate with an asymmetrical, a nonlinear and an impact loads in three phases and it provides the power factor correction on the grid side

This paper discusses a repetitive based controller for uninterruptible power supplies (UPS) to compensate for unbalance and harmonic distortion on the load. We propose to use a combined measurement of capacitor and load currents using the same current sensor with the purpose of, on one hand, reaching a similar performance as that obtained in a capacitor current based controller, and, on the other hand, to obtain an estimate of the load current for protection purposes. The proposed controller is composed of a proportional term plus a repetitive scheme. The latter is implemented with a simple feedback array of a delay line, thus making the implementation relatively easy. The repetitive scheme acts as a refinement term to reject the harmonic distortion caused by the unbalanced and distorted load current, and thus, allowing the UPS to deliver an almost pure sinusoidal balanced voltage. Experimental results are included to show the performance of the proposed controller

This paper investigates the control of a four-wire three-phase Uninterruptible Power Supply (UPS) inverter using the internal model principle by applying multiple resonant controllers in the stationary abc-frame for zero-error tracking of sinusoidal reference and harmonic disturbances rejection due to nonlinear and unbalanced loads. The synthesis of such controllers is accomplished in a robust control framework where the controller parameters are determined by means of a convex optimization problem subject to a set of Linear Matrix Inequality (LMI) constraints. Simulation results from a 15.0-kVA UPS inverter are considered to illustrate and validate the performance and behavior of the controller design under nonlinear and unbalanced loads.

The current distribution had remarkable effect on the microstructure and properties of MgAlON composites in the process of spark plasma sintering (SPS). MgAlON composites, using alumina, magnesia and aluminum as starting materials, were prepared by SPS. Based on the current distribution method, the current distribution model on samples and single grain was established, and the basic electric current control principle was analyzed. It was found that the current conveyance by sample or single Al grain could be expressed by a formula including B and I.In the formula, B was the Al volume fraction and I was the total current. When the Al volume fraction was controlled within 12%, the current conveyance by sample increased significantly with the Al addition increasing. Meanwhile, the current conveyance by single Al grain decreased significantly. The sintering speed and properties of MgAlON composites by SPS would show a significantly change.

This paper focuses on the development and experimental validation of a single-phase modular multilevel converter (MMC) based on a battery energy storage system (BESS) for residential uninterruptible power supply (UPS) with two-level active SoC balancing control. The configuration and mathematical modeling of the single-phase MMC-BESS are first presented, followed by the details of the control strategies, including dual-loop output voltage and current control in islanded mode, grid-connected control, circulating current control, and two-level active state-of-charge (SoC) balancing control. The design and optimization of the quasi-proportional-resonant (QPR) controllers were investigated by using particle swarm optimization (PSO). Simulation models were built to explore the operating characteristics of the UPS under islanded mode with an RL load and grid-connected mode and assess the control performance. A 500 W experimental prototype was developed and is herein presented, including results under different operating conditions of the MMC-BESS. The experimental results show that for both RL load and grid-connected tests, balancing was achieved. The response time to track the reference value was two grid periods (0.04 s). In the islanded mode test, the THD was 1.37% and 4.59% for the voltage and current, respectively, while in the grid-connected mode test, these values were 1.72% and 4.24% for voltage and current, respectively.

In this paper, the uninterruptible power supply(UPS) mode transfer method of three-phase energy storage system (ESS) using the silicon-controlled rectifier(SCR) is applied. In the three-phase ESS using the SCR, the three-phase grid is not blocked because each-phase has a difference of 120 degree. Therefore, the ESS needs the UPS transfer method which is blocking the three-phase grid at the same time when the grid fault occurs. So the UPS mode transfer method which is blocking the SCR by changing the direction of the power flow is applied. The applied UPS mode transfer method is verified by simulation results using the PSIM ver.9.1.4.