Single-phase UPS Research Articles

Continuous switching sliding mode controller design for single-phase UPS inverter circuit

Continuous switching sliding mode controller design for single-phase UPS inverter circuit

Single phase UPS systems loaded with nonlinear circuits: analysis of topology in the context of electric power quality

Single phase UPS systems loaded with nonlinear circuits: analysis of topology in the context of electric power quality

Proportional Integral Control Realized in Stationary and Synchronous Reference Frames for a Single-Phase UPS Inverter System: A Comparative Study

ABSTRACTVoltage regulation of the single-phase UPS inverter has design challenges in terms of dynamic performances and control complexity. Widely used conventional integral controllers, such as proportional integral and proportional resonant in stationary frame (SF) of reference have limitations of either steady state error or implementation difficulties. Although a mature technique in three-phase applications, the synchronous reference frame (SRF) control scheme has not been exhaustively investigated for single-phase UPS inverters due to complex multiple transformations. This paper suggests a voltage control scheme which can be alternatively used in both stationary and synchronous reference frames. Three integral controllers namely, SF-proportional integral (SF-PI), SF-proportional resonant (SF-PR) and SRF-proportional integral (SRF-PI) are comparatively evaluated for steady state and transient performances. A systematic procedure for the design of control parameters with stability analysis in the frequency domain for the closed loop control system is also presented. Respective controllers are simulated in discrete time frame using MATLAB/Simulink and experimentally implemented using the TMS320F2812 Digital Signal Processor based laboratory prototype.

A digital dual-modulation control for single-phase UPS inverters

ABSTRACTA trip-point modulation strategy is proposed for single-phase uninterruptible power supply inverters with an LC filter, which operates simultaneously with pulse-width modulation, named dual-modulation (DM) control. Current estimation and offset current approximation are used conjointly to facilitate the proposed control law. It is shown analytically that the DM control leads to reduced total harmonic distortion (THD) and gains fast transient-state recovery. The simulation and experimental results demonstrate significant amelioration to THD and dynamic state compared to proportional–integral–derivative control under both linear and non-linear loads.

A single-phase on-line UPS system for multiple load transformers

A single-phase on-line UPS system for multiple load transformers

An Extended Lyapunov-Function-Based Control Strategy for Single-Phase UPS Inverters

In this study, an extended Lyapunov-function-based control strategy that assures global asymptotic stability is proposed for single-phase UPS inverters. The Lyapunov function is formed from the energy stored in the inductor and capacitor due to the fact that the system states converge to the equilibrium point if the total energy is continuously dissipated. It is shown analytically that the classical Lyapunov-function-based control leads to a globally asymptotically stable system at the expense of steady-state errors in the output voltage, which exist due to the lack of outer voltage loop in the control input. Therefore, an extended Lyapunov-function-based control strategy is proposed, which eliminates the steady-state error without destroying the global stability of the closed-loop system. The steady state and dynamic performance of the proposed control strategy has been tested by simulations and experiments under resistive and diode bridge rectifier loads. The results obtained from a 1-kW inverter demonstrate that the developed control strategy not only offers global stability, but also leads to good quality sinusoidal voltage with a reasonably low THD, almost zero steady-state error in the output voltage, and fast dynamic response under linear and nonlinear loads.

비선형 부하에서 커패시터 전류 궤환을 통한 고성능 UPS 설계

This paper presents a digital control solution to process capacitor current feedback of high performance single-phase UPS for non-linear loads. In all UPS the goal is to maintain the desired output voltage waveform and RMS value over all unknown load conditions and transient response. The proposed UPS uses instantaneous load voltage and filter capacitor current feedback, which is based on the double regulation loop such as the outer voltage control loop and inner current control loop. The proposed DSP-based digital-controlled PWM inverter system has fast dynamic response and low total harmonic distortion (THD) for nonlinear load. The control system was implemented on a 32-bit Floating-point DSP controller TMS320C32 and tested on a 5[KVA] IGBT based inverter switching at 11[Khz]. The validity of the proposed scheme is investigated through simulation and experimental results.

One-Cycle Controlled Single Phase UPS Inverter

Abstract A one-cycle controlled single-phase full-bridge DC-AC inverter is proposed. One-cycle control is a nonlinear control method which has fast transient response and good tracking performance. The one-cycle control immunizes the inverter against the perturbation of input dc bus and provides well system dynamic regulation with hybrid sinusoidal PWM control. The basic operational theory and control method are discussed in this paper. Finally, simulation waveforms and experimental results are given. The simulation and experimental results demonstrate the effectiveness of this control technique for inverters in UPS applications, especially when nonlinear loads must to be supplied and line has large undesirable harmonic components.

Comparative Study of Different Switching Surfaces for Sliding Mode Control of a 40 kVA Single-phase UPS Inverter

In this paper, the effect of switching surface on sliding mode control of a single phase inverter is studied. Capabilities of three switching surfaces in chattering elimination, THD reduction and steady state error improvement are compared. The performance of these switching surfaces has been investigated through simulation. Simulation results show that after chattering improvement by adding first integral term, adding second integral term is not advisable.

단상 UPS 인버터의 강인한 전압제어기 설계

In this paper a robust voltage controller for a single-phase UPS inverter is newly presented. The voltage controller is designed using -based robust control scheme to simultaneously guarantee robust stability and robust tracking performance in the presence of load variations. Firstly the robust performance of the resulting controller is theoretically confirmed via -analysis. Then simulations and experiments for the single-phase inverter system with linear and nonlinear loads demonstrate feasibility of the proposed control method providing improved performance - good regulation and fast dynamic response.

A Non-isolated Single Phase Ups Topology With 110v/220v Input Output Voltage Ratings

A circuit configuration of a single phase non-isolated on-line uninterruptible power supply (UPS) with 110V/220V input output voltage ratings is proposed, allowing the bypass operation without a transformer even if the input voltage is different of the output voltage. The converter consists of an AC-DC/DC-DC three level boost converter combined with a double half bridge inverter. In this type of configuration size, cost and efficiency are improved due to reduced number of switches and batteries, as well as no low frequency isolation transformer is required to realize bypass operation because of the common neutral connection. Both stages of the proposed circuit operate in high frequency, using a passive non-dissipative snubber circuit in the boost converter and IGBTs switches in the double half bridge inverter, with low conduction losses, low tail current and low switching losses. Principle of operation and experimental results for a 2.6kVA prototype are presented to demonstrate UPS performance.

Control strategy for single-phase UPS inverters

A simplified control strategy is proposed for single-phase uninterruptible power supplies in continuous time. In this strategy the controller has command feedforward and feedback components. Only proportional controllers are employed in the inductor current and output voltage control loops. This controller yields zero output impedance of the UPS, provided that estimated filter parameters match their actual values. Robustness of the control system is investigated. Simulation and experimental results are presented for linear and non-linear loads.

H/sub /spl infin// loop-shaping controller designs for the single-phase UPS inverters

This paper proposes the H/sub /spl infin// loop-shaping approach to the designs of sinusoidal output voltage tracking controllers for single-phase UPS inverters. Selection of weighting functions is introduced, which is quite different from the case of step tracking. By modeling the uncertainty in load as plant output multiplicative perturbation, two H/sub /spl infin// loop-shaping control schemes that use only a capacitor voltage sensor are presented. The first design adopts a single-loop control scheme which has the advantage of simple control structure and easy implementation. But its transient performance and robustness are not satisfactory. The second controller with a dual-loop structure, additionally employing output of a capacitor current estimator as feedback, provides improved performance over the single-loop scheme and has the feature of low distortion, good regulating performance and insensitivity to the variation in load. Simulation and hardware experimental results, with comparison to the PI-based multiple feedback loop design, are given to validate the robustness property and regulating performance of the proposed controllers.

A Novel Single-Phase UPS Inverter by Error-Tracking Mode PWM Scheme

This paper proposes a novel single-phase UPS inverter modulated by Error-Tracking Mode PWM scheme. An ac voltage regulation scheme which matches the PWM scheme is newly developed in a theoretical way. Since Error-tracking Mode PWM is based on constantly-sampled data, the controller is suited to be digitally implemented. The equivalent circuit of the UPS inverter controlled by the schemes is derived. The output impedence is found to be composed mainly of resistance differently from general ac apparatus.According to the newly-developed schemes, a 3kVA, 100V, 50Hz UPS inverter is experimentally fabricated in which the sample period is 10μs and the average switching frequency is 6kHz. No load, linear load and non-linear load characteristics are measured. The output voltage remains almost sinusoidal even for the rated non-linear load. The output impedences are also measured and well agreed with the intended values.

Feasible single-phase UPS incorporating switched-mode PFC rectifier with high-frequency transformer link

The general purpose high performance single phase UPS topologies are indispensable for the considerable reduction of harmonic current components in a.c. mains as well as the realization of unity power factor correction (PFC). In particular, the single phase PFC rectifier with a high-frequency isolation transformer link has some feasible advantages as an electrically isolated a.c./d.c. conversion circuit for small scale UPS. This UPS is capable of eliminating harmonic currents and realizing an isolation between a.c. input and d.c. output power stage as well as matching the d.c. side input voltage of the PWM inverter by means of incorporating a compact high-frequency transformer into high-frequency intermediate stage. Electrically isolated PFC rectifiers designed for 2 kVA, 3 kVA and 5 kVA UPSs are put into practical use as new topological versions. This paper presents a circuit configuration of high-frequency link PFC rectifier for small scale UPS, its operating principle and related control strategy. The steady state and dynamic state performances of three power classes of UPSs which incorporate this type of PFC converter are evaluated from a practical point of view.

Deadbeat control method for single-phase UPS inverters with compensation of computation delay

In existing deadbeat control techniques for single-phase UPS inverters, the pulse width of the inverter output voltage is limited by the computation time of the controlling processor. This limits the utilisation of the DC source voltage and slows the response of the control system. A deadbeat control technique is presented which eliminates these limitations by allowing the application of the newly computed pulse width with time delay. During this delay, the previously applied pulse width is preserved until it is updated by the new pulse width. This method requires the use of a load-dependent reference function for the inverter output voltage. However, the error in the load voltage caused by using a fixed reference function is shown to be negligible. Computer simulations are performed to verify the theoretical results and for comparison with existing methods. Experimental results are also presented to support the theoretical considerations.

A Method of Digital Control for Single-phase UPS systems with Voltage Drop Compensation

A Method of Digital Control for Single-phase UPS systems with Voltage Drop Compensation

Simple topologies for single phase AC line conditioning

This paper presents a variety of single phase AC line conditioning approaches. The topologies use a minimal number of devices and feature buck-boost voltage regulation capability without a transformer, while preserving a neutral connection which is common with the input AC line. The simplest form of the converter is seen to be an AC voltage regulator with output voltage range of 0-2 p.u. with reasonable line current waveform. Modifications allow the circuit to operate with fully controlled input current. The circuit can be further extended to provide significant ride-through capability without using a battery. Finally, a full function single phase UPS can also be realized if required. The paper contains analytical, simulation and experimental results. >

A method to apply current source inverter to single-phase UPS.

At present, most of all inverters used in UPS are voltage-source types. In this case, a series reactor is an essential component of the output filter of the inverter because the waveforms of the output voltages consist of trains of voltage pulses. One of major issues of this type of system is magnetic noises, which are produced by the output voltage and appear at the series reactor and the output transformer.The use of the current-source inverter has merits not only reducing noises when compared to the case of voltage-source type but also getting a quasi-sinusoidal output voltage without any series reactors. However, there are few cases of applying the current-source inverters to the UPSs because built-in batteries of constant voltage are utilized as a voltage supply in the system.The feasibility of applying the current-source inverter to the UPSs is attempted in this paper, and a new circuit topology suitable for the UPSs is proposed. At the output terminal of the inverter only a capacitor is connected in parallel with a load, and the output voltage of the inverter is controlled so as to make it coincide with reference sinusoidal voltage. In order to realize this strategy, two choppers have to be connected between the DC input voltage source and the inverter.After showing the circuit configuration, the validity of the proposed method is confirmed by means of both simulation and measurement. When this type of the inverter is applied to an UPS, the waveforms of the inverter output voltage and the switching frequency depend strongly on the circuit constants and output voltage error. Then, these are discussed in quantity to get a design guide. A comparison with conventional current-source inverters shows that the new inverter system has a plenty of merits.

A fast acting detector for abnormal output voltages of an UPS system

A new method of sensing the abnormal output voltage conditions of a single phase UPS system is presented, which provides the information almost instantaneously, so that a fast load transfer can be initiated. A continuous monitoring of the UPS output instantaneous voltage is used so that any under/over voltage, transients, or waveform distortion present can be detected.