A high-power multitransistor-inverter uninterruptable power supply system

This paper presents a novel control strategy using a genetic algorithm optimized fuzzy logic controller with repetitive learning action for uninterruptible power supply (UPS) inverter applications. The repetitive learning action can reduce steady-state errors and distortions caused by unknown periodic disturbances. Considering its poor dynamic response with sudden load change, the fuzzy logic controller (FLC) is introduced. The parameters for the FLC are optimized by genetic algorithm (GA) in the proposed scheme. The presented digital control scheme measure only the output voltage, decreasing the amount of sensors and the overall system cost. The control laws and design procedure of the control scheme are discussed. Simulation and experimental results for a single-phase UPS inverter controlled by a TMS320F240 DSP are presented to verify the performance of the proposed control approach under different load conditions. It proves to be a cost-effective solution for common UPS products.

With the popularity of micro-processors, digital controllers are widely used in uninterruptible power supply (UPS) inverters. These digital control systems of UPS inverters require a time interval for sampling and computation, which sometimes affects the performance of inverters. In this paper, the problem of time delay in digital control of a UPS inverter is discussed. Then two novel pulsewidth modulation (PWM) methods, the two-polarity PWM method and the asymmetric PWM method, are proposed to handle the time-delay problem. Both of these PWM methods can achieve a wide range of duty ratio between 0.05-0.95, which is independent of inverter model. Furthermore, they are easy to implement using a digital micro-controller. Experimental results are presented in the paper to verify feasibility of the proposed PWM methods.

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.

This paper presents a discrete integral sliding mode control scheme with time-delay compensation for the output voltage regulation of an uninterruptible power supply (UPS) inverter. Since the inverter is subject to the parameter variation and the load disturbance and the time delay is introduced due to the adoption of digital control scheme, the controller is required to reject the disturbance as well as the influence of the time delay. This paper analyzes and models the discrete single-phase UPS inverter with time delay. To enhance the robustness of the inverter the discrete integral sliding mode control scheme is proposed. An integral controller is added to improve the steady performance of the controller and the time-delay compensation is considered to eliminate the influence of the time delay. The inverter has shown its excellent voltage tracking performance through the simulation results and the effectiveness of the scheme is verified..

Nowadays the use of Uninterruptible Power Supply (UPS) is common because UPS is able to provide a backup electrical power when the main source is disconnected or interrupted. With the use of a UPS, the supply of electrical power to the system will not be interrupted. When the UPS operates, the voltage go through dual conversion process, from AC to DC by the rectifier and from DC to AC by the inverter. The DC voltage in the UPS is used to supply the battery charger and the AC voltage is used to supply the load system. The switching process of the inverter can produce disturbances at high frequency. In this study, a 1 KVA UPS is connected to a capacitive load 3.6 µF, 7.2 µF, 14.4 µF and 28.8 µF which generate the highest disturbances voltage of 309.53 mV at a frequency of 9.8 kHz at a load of 28.8 μF and the lowest of 1.33 mV at a frequency of 110.6 kHz at a load of 3.6 μF. The disturbances voltage occur at three dominant frequencies of 19-24 kHz, 35-44 kHz and 105- 114 kHz and increases as the increase of capacitive load level.

This paper presents a nonlinear feed-forward controller applied to single-phase uninterruptible power supplies (UPS). The controller was conceived by using a one-cycle based PWM generator and an output-current feedforward, in order to cancel input-voltage disturbances and nonlinear load currents, respectively. It also includes an external control loop to ensure good output-voltage tracking. The controller design is based on a large-signal approach, introduced to achieve good transient response and stability in a wide range of parameter variations. Besides, in spite of the nonlinear nature of the controller, we obtain a linear average output-voltage dynamic response. The proposed control provides the following features: fast transient response, low THD sine-wave output-voltage, fixed switching frequency, and high robustness against load and line step changes. Simulation results show the effectiveness of this control technique for inverters in UPS applications, especially when nonlinear loads must to be supplied and UPS DC-link has large undesirable ripple.

Uninterruptible Power Supply (UPS) is widely used in industry and electronics field in order to improve power quality. However, the distortion and interruption of output voltage will occur when UPS is applied to instantaneous impulsive load. This paper proposes a novel dynamic control strategy to resist impulsive load. When the impulsive load is imposed on UPS instantaneously, the impulsive current can be quickly sensed by the digital controller and the supplying power for the load is switched from inverter to bypass immediately. Therefore, the output voltage of UPS can be maintained uninterruptible. The proposed control strategy is verified by a 30 KVA UPS prototype.

This paper describes a high performance voltage controller for 3-phase 4 wire UPS (uninterruptible power supply) system, and proposes a new scheme of synchronous reference frame controller in order to compensate for the voltage distortions due to unbalanced and nonlinear loads. Proposed scheme in this paper is able to completely eliminate the negative sequence voltage distortion due to unbalanced loads and also reduce the harmonic voltage distortion due to non-linear loads, even if the bandwidth of voltage control loop is a very narrow. Therefore, the proposed scheme is especially appropriate for a fully digital controlled UPS or a high power UPS with limited voltage control bandwidth. In order to compensate for the effects of unbalanced loads, the synchronous reference frame controller with the positive and negative sequence computation block is proposed, and the synchronous frame controller with a bandpass filter is proposed to compensate for the selected harmonic frequency of output voltage. The effectiveness of the proposed scheme has been investigated and verified through computer simulations and experiments by a 30 kVA UPS

Uninterruptible power supply (UPS) is an electronic power device that delivers voltage to critical loads and whose application must satisfy standardized performance requirements. Usual control techniques demand the UPS model. In this article, we propose a simple, model-free procedure based on the generalized forced oscillation method to design the control system of a UPS output stage. The procedure involves the design of an inner current loop with a proportional gain and a proportional-multiresonant controller in the output voltage loop. We also compare the closed-loop results obtained in a single-phase 3.5 kVA UPS with the IEC 62040-3 performance criteria and show that the results are equivalent to model-based approaches.

To achieve proper operation of an online static uninterruptible power supply (UPS) system, feedforward and feedback (FF/FB) controls are introduced. Feedforward control is applied to reduce the low order harmonics in the output voltage due to the ripples included in the input DC voltage to the UPS inverter resulting from the controlled rectifier, while feedback control is applied mainly for stabilizing the output voltage. In this paper, a feedforward technique is selected that was found to give free ripple output, and two types of feedback techiques are compared and the most suitable one is considered. The paper gives the modeling and simulation results of the whole system, that compare the performance without and with FF/FB under different steady state and transient conditions.

PWM inverters are increasingly being applied to general power system loads, both as uninterruptible power supplies (UPS) and in serving dedicated load from alternative energy sources. The size of motors that can be served from these inverters is limited by the inrush requirements of the motors and the limited overload capability of the inverters. This paper presents two methods to limit motor starting inrush currents within an appropriate range, in order to allow increased motor starting capability without exceeding the inverter overload limits. Both methods work by introducing voltage sags during the motor starting. Comparisons are made between the two methods, and are also compared with the existing method which has no current limitation. Both methods are also compared with acceptable sag and harmonic distortion limits. Conclusions are offered regarding the viability of these methods.

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.

The paper highlights the reliability estimation tool for power system's reliability estimation study. The reliability estimation tool was applied to the different configurations of Uninterruptible Power Supply (UPS) systems Capacity, Isolated Redundant, Parallel Redundant, Distributed Redundant, and System plus System Redundant configurations. UPS reliability parameters such as failure rates, Mean Time Between Failures, and Availability can be estimated from the proposed system's reliability estimation methods. The suggested reliability estimation methods in this paper are the Reliability Block Diagram (RBD) and the Monte-Carlo simulation methods. The UPS system reliability estimation study found that the System plus System Redundant configuration gives the highest reliability and availability values compared to all other configurations. Studies has been conducted to investigate the effects of the reliability level of every component in the UPS system onto the overall system's reliability, thus making it possible to rank their contribution to system's reliability and thereby useful in establishing the area of improvement in the design of the highest UPS system's reliability.

In the modern world, when there is a power outage or a power failure, telecommunication systems, computer systems, and many other critical equipment, such as medical equipment, require uninterrupted power to support their operation. Uninterruptible power supply (UPS) systems are used for this purpose. Over the years, research on UPS systems and related publications have increased. Also, new opportunities for UPS systems have emerged with the development of novel storage technologies, power electronic topologies, rapid electronic devices, high-performance digital apps, and other technological advances. Servers and storage systems, personal computers, medical equipment, telecommunication systems, and industrial equipment all require clean, stable, and uninterrupted power supply from UPS systems. Several recent studies have focused on the design of UPS systems to provide continuous power under normal or abnormal power conditions, including power outages. Such UPS systems use energy storage technologies such as batteries or flywheels to provide power to loads in the absence of applied power. Typically, static power electronics such as fast-switching high-current insulated gate bipolar transistors (IGBTs) are used to convert power. This article discusses the most typical power line issues and how they relate to the various types of UPS systems available today.

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