Dynamic Response Improvement of a Three-Phase Line Interactive UPS System with Active Power Line Conditioning

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

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 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.

In this paper, a new real-time space-vector-based control strategy is presented for three-phase uninterruptible power supply systems powering nonlinear and unbalanced loads. The proposed control strategy generates the inverter reference and gating signals in closed loop and guarantees high-quality output voltages at the load terminals. The approach, which is implemented on a digital signal processor, adapts to a wide variation of nonlinear and unbalanced load conditions without specific knowledge of the output filter (L-C) component values. Analysis and experimental results on a 10-kVA prototype are presented. The results show that the output voltage is restored at heavy nonlinear and unbalanced load.

Low power quality and supply reliability within industrial grids cause severe economic damage to Europe's key industry sectors. A modular shunt connected power conditioning systems with the objective of locally improving quality of supply within industrial grids has been proposed. One of its voltage-fed power converter based modules implements functionalities which are comparable to those of well known line interactive uninterruptible power supply systems. This paper discusses the input filter topology choice, its application specific design and points out contrasts to optimization criteria derived for the LCL filter design of converters for permanent grid-connected operation.

This paper describes design considerations and performance analysis of a novel on-line singlephase to three-phase uninterruptible power supply (UPS) with reduced number of switches. The proposed topology uses only 5 active switches reducing the cost of the system compared to the traditional 10-switch topologies. The proposed UPS consists of a single-phase rectifier/charger, a two-leg/three-phase inverter connected to load, battery bank, DC link capacitor and an AC inductor. Detailed circuit operation and analysis as well as simulation results are also presented to verify its feasibility.

This work presents a Model Predictive Control (MPC) strategy for a Voltage Source Inverter (VSI) used in a three-phase Uninterruptible Power Supply (UPS) for critical loads. An MPC using continuous variables is proposed for solving this problem and the output of the controller is used as the reference voltage to be generated by a PWM modulator. The solution of this unconstrained MPC gives rise to an explicit solution that can be computed beforehand, allowing the prediction horizon to be easily extended. Therefore, the effect of the length of the prediction horizon over the system performance is also evaluated in the paper. This study addresses how this parameter should be chosen to minimize the error between the actual and the desired output voltage. The proposed control strategy has been tested on a simulated model of a UPS supplying a three-phase resistor load. This model has been developed using MATLAB/Simulink with PSIM software. The simulation results show that proposed continuous MPC controller achieves high performance and high degree of robustness.

This paper presents a design and an implementation of inverters with ultra-low total harmonic distortion (THD) under all kinds of loads. In this study, the ultra-low THD objective is achieved by combining the advantages of the repetitive controller, the predictive-PID controller and the reference signal feedforwarding method in a multi-loop structure. The high performance uninterruptible power supply (UPS) and the transformer test converter applications where the ultra-low THD is desired require the use of high performance controllers. This study successfully achieves the design of such a controller by means of computer simulation, which is based on the true model of the inverter system. The tuning of the controller and inverter parameters made through simulation has yielded a successful hardware design and a good performance during the experimental tests. The performance of controller is evaluated in terms of output voltage waveform distortion under actual linear and nonlinear loads. The experimental results that demonstrate the success of the controller are obtained from the voltage source inverters (VSI) built for a three-phase UPS application at 30 kVA and a transformer test converter application at 300 kVA. The maximum measured THD is less than 2.88% under the worst nonlinear load case. The converters employing the designed controller are currently in use with success in the field.

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.

The non-linear devices used in the present environment like computers, printers, lasers, smps, rectifiers etc. pollutes the power system by harmonics and reactive power. Due to the presence of harmonics in the power system a number of undesirable effects caused in the distribution network. To find the solution for this the active power filter (APF) is one of the suitable solutions, which compensates Harmonics as well as reactive power simultaneously. This paper presents a active power line conditioning system to improve the power quality in the distribution network and implementation of a digital controller using 8051 microcontroller. The active power line conditioner is implemented with Pulse Width Modulation (PWM) based current controlled voltage source inverter (VSI). The Digital Controller is designed using MCS 8051 microcontroller which becomes independent of process technology. Synchronous reference frame (SRF) is used for generation of reference current. The PI current algorithm is implemented using MATLAB platform. The shunt APF is modeled and investigated under different unbalanced non-linear load conditions in MATLAB/SIMULINK. The simulation results reveals that the active power filter is efficiently compensating the current harmonics and reactive power in the distribution network. The APF system is in compliance with the IEEE 519 and IEC 61000-3 recommended standards.

Various electronic circuits such as inverters, choppers, cyclo-converters, SMPS used by industrial and domestic purposes are non-linear in nature, which makes the load current to be distorted, causing undesirable effects like heating, equipment damages, EMI related problems in power system. The active power filter (APF) is the best solution for eliminating the harmonics caused by the non-linear loads. This paper presents about a three-phase four-wire active power filter for power line conditioning to improve power quality in the distribution network and implementation of a digitally controlled APF. The active power filter is implemented with PWM based current controlled voltage source inverter (VSI).The switching signals for APF are generated through proposed three-level hysteresis current controller (HCC). The shunt APF system is modeled and investigated under different unbalanced non-linear load conditions using MATLAB program. The Controller Design using Hardware Description Language (VHDL or VERILOG) becomes independent of process technology. Synchronous reference frame (SRF) is used for generation of reference current. Both PI current algorithm and HCC are written in VHDL code and implemented using FPGA platform.

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.

This paper proposes a reactive power control strategy for the active load balancer (ALB) in three-phase four-wire distribution systems. The proposed reactive power control strategy is based on constant DC capacitor voltage control, which is always used in active power line conditioners. Therefore, the proposed reactive power control strategy does not require active, reactive calculation blocks of load currents for the reference source current calculation. Balanced source currents with a predefined power factor can be achieved without unbalanced active and reactive components detection of the load currents. The basic principle of the reactive power control strategy for the ALB is discussed in detail, and then confirmed by digital computer simulation using PSIM software. A prototype experimental model is constructed and tested to validate the feasibility of the proposed control algorithm. Simulation and experimental results demonstrate that balanced source currents with a predefined power factor are achieved in three-phase four-wire distribution systems.

In the paper, a method for measuring the inactive powers of a three-phase power supply system based on operations with currents and voltages represented in the αβ - coordinate system is proposed. It is shown that measuring the four scalar powers and apparent power of a three-phase threewire system based on currents and voltages represented in the αβ-coordinate system requires four wattmeters, which is half as much as when using non-convertible values of currents and voltages. The six scalar powers of the three-phase four-wire power supply system can be determined based on the readings of six wattmeters. The experiment showed the adequacy of calculated and experimental data. Change in the nature of the load while preserving the value of the first load current harmonic does not affect the integral values of four scalar powers.

Fryze Current Controller Based Active Power Filter