Digital control scheme of single-phase uninterruptible power supply

The paper presents the single phase uninterruptible power supply (UPS) system with galvanic separated DC-AC-DC-AC converters operating in parallel. The CAN physical layer based system of communication between converters has been developed and applied, which allow to utilize a decentralized master-slave control providing high availability factor of the whole UPS system. The control system of particular converters has been developed to ensure a high quality of the output voltage for both linear and nonlinear load. The selected simulations and experimental results obtained for 5 kVA prototype modules are presented.

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.

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..

It is essential characteristics for uninterruptible power supply (UPS) to eliminate harmonic currents in its input current and to get unity power factor. Switched mode rectifier (SMR) with a high -frequency transformer link has promising characteristics as a AC/DC conversion circuit for UPS. It does not only eliminate harmonic currents but also provides an isolation between AC input and DC output with a small high frequency transformer. We applied the SMR for the development of UPS with capacity of 2kVA, 3kVA and 5kVA. This paper presents circuit configurations and control strategies of the SMR and the test results of the developed UPS.

In the article, based on the concept of increasing the reliability of the formed image of the complex of technical means for ensuring the operation of an unsolicited measuring station of the network of stations of the ground control complex, a solution is proposed for choosing the general scheme of an uninterruptible power supply as part of a complex of technical means of unsolicited measuring systems. The uninterrupted power supply system is designed to automatically provide a set of technical means for ensuring the operation of a non-demand measuring station with a guaranteed and uninterrupted power supply in accordance with the indicators of reliability, autonomy and quality of electricity specified in the terms of reference. A procedure for selecting the constituent elements of an uninterruptible power supply is proposed, the main stages and composition of the protection means for the power supply network are considered. A block diagram of protection over the power supply network is presented. It is noted that structurally, the uninterruptible power supply should be able to be placed both in a stationary room and in a block container.

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.

Increasing tendency in online businesses and work from home, attracted many businesses and individuals to consider single-phase uninterruptible power supplies (UPSs). However, low power UPSs are normally incapable of operating for extended time periods. In order to extend UPS ranges, researchers integrated auxiliary energy sources to UPSs. However, integrating auxiliary power sources require additional power electronics active and passive components. This will result in low power density and bulky UPSs. To overcome this issue, multi-port converters have been proposed as an alternative to employing multiple converters. Nevertheless, using multi-port converters require more advanced control methods. This paper proposes a novel multi-port UPS with a finite control set model predictive controller. Simulations are conducted to demonstrate the effectiveness of the proposed converter. The results show the load current THD of 0.77%, resilient transient response, and efficiencies up to 97.5% using SiC MOSFETs.

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.

A power converter topology suitable for online single-phase uninterruptible power supply (UPS) systems is presented. The converter uses only four switches, five if a low-voltage battery and resonant link operation are required, to realize very desirable features. These include independent control of the input and output currents a common neutral connection, line conditioning, sinusoidal input currents independent of load current, and battery charge/discharge regulation. Detailed simulation results and experimental results are included.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

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.

A photovoltaic (PV) grid-connected power conditioning system with the function of uninterruptible power supply (UPS) is presented in the paper. It can not only realize photovoltaic generation, but also has full function of shunt active power filter (APF). In addition, it can act as UPS when instantly power interruption occurs. The instantaneous reactive power theory is employed in harmonics current detecting and signal synthesis algorithm of reference current. The proposed control strategy has two control modes (Grid connection mode and UPS mode) which can switch to each other automatically. A dual instantaneous loop control strategy is applied to UPS mode so as to obtain fast responses. The whole system is constructed and simulated in Matlab / Simulink environment. The power qualities under different conditions are given and compared. By analysis of the simulation results, it is shown that the proposed system is feasible and practical.

As digital control may meet the increasingly rigorous requirements for power converters, more and more attention has been paid to the digitalization of traditional analog control uninterruptible power supply (UPS). However, time quantization and numerical quantization of discrete-time system result in a series of problems in digital control UPS, such as sampling delay, computational delay, serious dead time effect, and truncation error etc. In this paper, these issues are researched, and the corresponding techniques for designing a digital single-phase full-bridge on-line UPS are proposed. In digital UPS system, the flux imbalance of output transformer is induced by the accumulation of truncation error, and can be eliminated by modifying digital control algorithm with real time bias correction signals. Under the selection of optimal sampling mode, the sampling delay of control variables may be reduced apparently. The feed-forward compensation scheme is proposed to alleviate the dead time effect. By adjusting the frequency and phase of inverter output voltage alternately, the digital phase-locked loop is implemented in software. Theoretical analysis and experimental results are presented to demonstrate the validity and feasibility of these proposed control schemes.

A multi-objective control scheme of a voltage source converter with battery–supercapacitor energy storage system used for power quality improvement

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

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.