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The design of a digital state-space controller employing a deadbeat state observer is presented for uninterruptible power source (UPS) inverter applications with inductor-capacitor (L-C) filters. Conventionally, the inductor current and capacitor voltage values are utilized as the measured feedback variables for the controller, and the load current is either measured or estimated. In the proposed...
Uninterruptible Power Supplies (UPS) have several closed loop control topologies for control of Voltage Source Inverter (VSI). The topologies vary mainly due to choice of control/feedback variable. This paper attempts to categorize different control topologies and highlights the similarities/differences between them. Further, an analytical study on the basis of steady-state and transient performance,...
This paper proposes an optimised design approach for Multi-Modular (M-M), single-phase UPS inverters system. The Voltage Source Inverters (VSIs) have low output impedance for good voltage regulation, which conflict with the requirement of high impedance in the parallel configuration to restrain Inter-Modular (I-M) circulating currents. Conventional dual-loop approach of Proportional-Resonant (PR)...
This paper proposes a novel autonomous control scheme for equal load current distribution between n parallel-connected, LCL-based, three phase UPS units. The control is based on varying the capacitor reference voltage of each inverter as a function of its own output current, without exchanging information between the inverters. The load voltage is maintained fixed at the specified reference value...
A control strategy for PWM inverters used in double conversion UPS systems is proposed. The objectives of this control strategy are to control the inverter output voltage to comply with performance specification given by standards, and control the inductor current to achieve short-circuit and overload protection. The control strategy is composed by two feedback loops, where the inner current loop...
This paper presents a three-phase transformerless uninterruptible power supply (UPS) with sinusoidal pulse width modulation (SPWM) based division-summation (D-Σ) digital control. A transformerless UPS controls the power flow between dc link and utility grid, as well as tracks the ac reference voltage. The proposed control law derived with D-Σ digital approach takes into account the effects of dc-link...
Parallel connected multi-modular (M-M) singlephase UPS inverter system is an attractive choice for a reliable and scalable power delivery for critical loads. However, a proper current sharing control technique is required to avoid the inter-modular circulating (IMC) currents without use of any extra power circuit components. The output current of an UPS module is used as load disturbance compensation...
This paper proposes an active method to balance the voltage and to filter low-order current harmonics on the DC-link Bus capacitors of a three-phase half-bridge transformerless UPS. These low-frequency current components occur due to utility unbalanced voltage conditions or even under the connection of non-linear and/or unbalanced loads. They increase the DC bus capacitors losses and also may cause...
A novel single-phase current fed full-bridge converter with split DC output voltage, multifunctional input source (main grid, photovoltaic modules or battery bank), power factor correction for main grid applications and high-frequency transformer (HFT) isolation topology is presented in this paper. This converter might be a suitable alternative when used as an input stage of uninterruptible power...
This paper proposes a bypass transfer method without parallel feeding between utility power line and uninterruptible power supply (UPS). This system has ACSWs consists of a bi-directional thyristor and a magnetic contactor both utility power line and UPS line. The control board observes the condition of utility power and UPS to operate ACSWs. A proposed method has instantaneous interruptible period...
This paper presents the predictive control of single-phase UPS system for fast dynamic characteristic. When occurring grid fault, UPS system has to transfer UPS mode and supply power to the load. In PI controller, it has a disadvantage rather low dynamic characteristic, which is caused increasing transient time. To solve this problem, the predictive control is proposed. By adopting predictive control...
An adaptive current-sharing control strategy with virtual circulating impedance for single-phase parallel connected UPS is proposed in this paper. The current-sharing scheme of the paralleled system is developed and the theoretical analysis of the virtual circulating impedance is studied. The impact of the virtual circulating impedance on the stability of the paralleled system is also discussed. Moreover,...
This paper proposes an inductor current feedback plus load current decoupling scheme for single-phase uninterruptible power supply (UPS) applications using a single current sensor. At first, the inductor current feedback with and without load current decoupling are compared in the view point of the output voltage control performance. The output impedance of the entire control system is analytically...
This paper presents cascaded buck-boost converter for improving power quality at ac mains input in terms of improved power-factor (PF), reduced total harmonics distortion (THD) of input current and regulated output dc voltage at 380 V for high frequency uninterruptible power supply (HF-UPS). Discontinuous conduction mode (DCM) of operation is used to achieve inherent power factor correction (PFC)...
In UPS, Battery mode and electric mode usually use a common boost converter to translate different input voltage into a same DC bus voltage. In this paper, the mathematic model of the boost converter based on PWM three-terminal switch device is derived. To obtain good dynamic performance during the input voltage changes, a directly digital dual-loop controller design method based on Matlab/Simulink...
A single-stage power converter for dc uninterruptible power supply (UPS) is proposed in this paper. Basically the proposed converter is an integration result of a power factor correction circuit with a dc-to-dc converter to achieve simple hardware circuit, high efficiency, and low cost for extra UPS function. Under normal operation, a two-switch CUK converter operates as an ac to dc converter with...
This paper presents a three-phase uninterruptable power supply (UPS) based on the high performance Z-source inverter (ZSI). The proposed control strategy is based on two loops. The first loop is dedicated to regulate the dc voltage of the Z-network capacitor and limiting the peak value of the dc link voltage by controlling the shoot-through duty cycle. The second loop employs the instantaneous voltage...
This paper deals with the basic options of suitable control method for power structure operating in island mode. A brief description of power structure and its utilization possibilities is presented. The simulation of selected control method and power structure was created in Matlab/Simulink for verification the proper function of control method and for comparison the properties of selected controllers...
Paralleling converters is normally employed to increase power capacity in different applications, such as autonomous micro grid systems and unininterruptible power supplies. These systems share the current between the different converters, but it must be in an equalized manner, no matter different type of loads or conditions. This paper propose an alternative to operate parallel inverters, the proposal...
This paper proposes a novel Control strategy based on decoupled control scheme to eliminate DC loop current of paralleled uninterrupted power supply (UPS) inverter system. On the basis of the original paralleled system for load-sharing by active and reactive power control, a separate control circuit is added in each parallel inverter module to eliminate the DC component of output voltage. The voltage...
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