Uninterruptible Power Supply Inverter Research Articles

VOT and VFT-Based hybrid digital hysteresis control for UPS inverter

When the digital hysteresis current control (DHCC) strategy is applied to control the uninterruptible power supply (UPS) inverter, here are some issues such as large hysteresis tracking error caused by sampling interval and severe switching frequency swing caused by rapid change rate of inductor current. To address these issues, this paper presents a digital control strategy based on the hybrid digital hysteresis current control (HDHCC) of variable opening time (VOT) and variable falling time (VFT) for UPS inverter. Firstly, the HDHCC structure is established and the working principle of the inverter system is described in detail. Then, the tracking error and switching frequency error of the DHCC are derived. Based on the performance requirement of quasi-constant frequency control of UPS inverter, VOT and VFT control criteria without the dependency of circuit parameters are given. The experimental results demonstrate that the hybrid digital hysteresis control strategy based on VOT and VFT has the advantages of high current tracking accuracy, accurate switching frequency control, small output voltage waveform distortion, and simple implementation.

Sensorless Model Predictive Control of Single-Phase Inverter for UPS Applications via Accurate Load Current Estimation.

Single-phase inverters with an output LC filter, can generate low distortion output voltages, which are suitable for uninterruptible power supply (UPS) systems. The UPS system provides emergency power in the case of utility power failure, requiring high reliability and clean power. The sensorless control method is actually a soft-sensing technique, that reduces system cost, measurement-related losses, and, especially important for UPS systems, enhances the system reliability. This paper proposes a load current sensorless finite control set model predictive control (FCS-MPC) scheme for a single-phase UPS inverter. A time varying observer is proposed, which offers the accurate estimation for individual components simultaneously in periodic load current signal, without subsequent complex calculations. Compared with another two typical sensorless methods (the low-pass filter and the Kalman filter), the proposed observer-based FCS-MPC strategy has smaller load current estimation error and lower output voltage distortion, under both linear and nonlinear loads. The theoretical analysis is verified through simulation and experiment. A single-phase inverter rapid control prototype (RCP) is set up with the Speedgoat real-time target machine, to confirm the effectiveness of the system.

Processor-in-the-Loop Validation of an Observer Current-based Dead-Beat Control for a Single-Phase UPS Inverter

This paper presents a dead-beat control algorithm for Uninterruptible Power Supply (UPS) applications of single-phase inverters. The proposed control method requires the measurement of capacitor current and output voltage in order to keep the output voltage sinusoidal ensuring high dynamic performance even under load changes. The dead-beat controller optimizes the behavior of the system by eliminating the error between the output and the reference voltage without increasing the number of current sensors, which are costly, and eliminates load voltage distortions and restores the system state in the event of external shutdown-loop road interference. In this paper, we propose a capacitor current estimation based on the Luenberger observer. Processor-In-the-Loop (PIL) is a test method that allows us to create and evaluate controllers by running built-in C code on the DSP scheduled for the controller during simulated PSIM power phase control. It can be seen that the simulation results match the PIL test results, which proves the validity of the proposed controller.

Design of Uninterruptible Power Supply Inverters for Different Modulation Techniques Using Pareto Front for Cost and Efficiency Optimization

This work presents a design for uninterruptible power supply inverters using Pareto front optimization for improved cost and efficiency. Three PWM modulation techniques applied to the full-bridge inverter are analyzed. As a result, the best MOSFET design solution in terms of the cost and efficiency of the inverter is evaluated based on a database with 47 power MOSFETs. Using the Pareto front, the optimal and sub-optimal solutions are compared, considering the three modulation techniques and the characteristics of MOSFETs manufactured for different voltage levels. Thermal and electrical measurements are used to validate the models.

A Novel Control Strategy for Uninterruptible Power Supply Based on Backstepping and Fuzzy Neural Network

This paper proposes a novel control strategy for controlling the uninterruptible power supply (UPS) inverter, which is based on backstepping control theory combined with a fuzzy neural network (FNN). The advantage of backstepping control is that it can decompose a complex system into multiple subsystems, stabilize the control object according to Lyapunov stability theory, and simplify the controller design. However, it requires prior knowledge of multiple system parameters. FNN can approximate arbitrary nonlinear functions and system errors, which can reduce the parameters required for controller design. Hence, Combining the advantages of both methods, a UPS inverter control method with only a few parameters is designed. Then the sliding mode gain is added to compensate for the fuzzy neural network to reduce the chattering when the system operates and ensure the needed power quality. To verify the effectiveness of the proposed control system, the effectiveness of the proposed method is verified by a simulation experiment platform.

Design and analysis of robust backstepping controller for DC suppression of parallel UPS inverter system

AbstractHere, an improved control strategy is proposed, which adopts a non‐linear robust backstepping controller to eliminate DC circulating current in a parallel uninterruptible power supply (UPS) system. The traditional active and reactive power sharing control can ideally suppress the AC circulating current, but cannot effectively restrict the DC circulating current. Based on the traditional active power and reactive power sharing control (TAPRPSC) of the parallel UPS system, the proposed control strategy is used in each parallel inverter module to suppress the DC component disturbance in the inverter output voltage, which varies within a certain range. Hence the desirable steady‐state and dynamic performance of the system can be obtained. Moreover, the Lyapunov method is utilized to ensure the stability and robustness of the system. A parallel system of two UPS inverters with the proposed control strategy is built by Matlab/Simulink, and further experiments are carried out on the semi‐physical simulation platform of the Modelling Tech. Both the simulation and experimental results verify the effectiveness of the proposed control strategy for DC circulating current suppression and ideal output voltage tracking.

A Novel VSG Control Strategy for UPS Voltage Source Inverter with Impulsive Load

This paper proposes a novel control strategy to alleviate the impulsive current for Uninterruptible Power Supply (UPS), which is designed based on the theory of virtual synchronous generator (VSG) and dynamic switching method. The power quality of UPS will become distortion when the instantaneous impulsive load is imposed on UPS. Especially, the output current of UPS will increase quickly in short time. In order to maintain the uninterrupted output voltage and reduce the distortion of output voltage of UPS under the action of instantaneous impulse load, Dynamic switching method is proposed to resist impulse load with large scale impulse current, Meanwhile, the VSG control strategy is adopted to deal with the slow power switching and provide virtual inertia for the system, so that the output voltage of UPS can remain uninterrupted and stable. Finally, simulation and experimental results show that this method can effectively suppress the impulse current, reduce the output voltage distortion of UPS inverter, and ensure the good performance of On-line UPS under impulse load.

Design and Implementation of PV Fed Local UPS Inverter

Locally manufactured Uninterruptible Power Supply (UPS) units are purchased as an alternative to rolling blackouts and load shedding in underdeveloped and developing countries like Pakistan. These locally manufactured UPS units are energy-inefficient, causing stress on the national grid and cost-intensive for the residential consumer in the form of high utility bills of electricity. In this regard, the authors have proposed the PV fed local UPS inverter to make the existing UPS unit more efficient through photovoltaic (PV) energy without disrupting its function of providing uninterrupted supply during load-shedding hours. In order to validate the performance of the proposed PV fed local UPS inverter, the maximum power point tracking (MPPT) PV charge controller module is designed and implemented practically in a hardware setup and simulated in MATLAB/Simulink and Proteus environment, respectively. Moreover, the installation of an MPPT PV charge controller module in an existing locally manufactured UPS unit is also discussed. The practical results demonstrate the superiority of the proposed PV fed local UPS inverter with an average efficiency of 81.51% and a lowest total harmonic distortion (THD) of 1.29% as compared to existing UPS inverters.

Internal Model Principle Method to Robust Output Voltage Tracking Control for Single-Phase UPS Inverters With Its SPWM Implementation

This article investigates output voltage tracking control, and harmonic distortion suppression in single-phase voltage-source uninterruptible power supply (UPS) inverters with an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$LC$</tex-math></inline-formula> -filter. The control scheme is based on sensing the output voltage across the UPS load, and using the voltage tracking error in a feedback loop of the internal model principle (IMP) framework. A robust controller is designed to drive <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$LC$</tex-math></inline-formula> -filter to operate with an adjustable amplitude, and adaptive resonant frequency. Specifically, the proposed controller basically employs an internal model with a filter to examine the incremental dynamics of the voltage tracking error, and regulate the voltage modulating signal in sine pulse width modulation (SPWM). With such a stable operation of the controlled UPS system, the inverter is able to achieve fast dynamics of voltage tracking, which results in the minimum harmonics while approaching the zero-error steady state under the external loads. The Matlab/Simulink simulation, and experimental validation are both provided for the prototype controlled UPS inverter under the closed-loop operation. It is shown that the controller offers improved performance over the existing schemes. By merely using the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">voltage error</i> to adjust the output voltage, the controlled inverter produces nearly perfect sinusoidal voltage at moderate switching frequency under a wide range of filter parameters, and consequently, the UPS operation has excellent dynamic response with both high voltage utilization of the DC source, and high power quality.

Research on the Control Method of UPS Inverter Circuit Considering Additional Filtering Branch

Improving the electric power quality of the Uninterruptible Power Supply (UPS) is an important part of ensuring the reliability of the power system. In order to optimize the output voltage waveform of the UPS, a filtering branch can be added to the existing UPS inverter circuit. This paper studies the circuit control problem after adding the RLC filter branch in the UPS inverter circuit. Through the analysis of the inverter circuit directly considering the added filtering branch, the system state function of the circuit is constructed. A double closed-loop PI control strategy is designed to control the inverter circuit, and the effectiveness of the method is verified by simulation. Using the method in this paper, the output of the inverter circuit with the added filter branch can reach a stable state quickly. The research conclusions of this paper are helpful to improve the output power quality of UPS.

An Adaptive Dual-Loop Lyapunov-Based Control Scheme for a Single-Phase UPS Inverter

This letter proposes an adaptive Lyapunov-based control strategy for a single-phase uninterruptible power supply inverter with inherent dual control loops. The control law is derived via a proposed Lyapunov function which takes both dual-loop requirements and the global large-signal stability demand into account. Besides, in the proposed control scheme, the load disturbance is suppressed adaptively without any additional load-current sensors or observers. The load voltage is regulated with better steady-state and dynamic performance, as well as with great robustness against the parametric variations. Finally, experimental results verify the effectiveness of the proposed control scheme.

Comparative Study of Discrete PI and PR Controls for Single-Phase UPS Inverter

This paper presents a comparative study of discrete proportional integral (PI) and proportional resonant (PR) current control for single-phase uninterruptible power supply (UPS) inverters. There is an increasing requirement for current and voltage-controlled UPS inverters with very low or zero steady-state error, improved transient response and lower total harmonic distortion (THD). The most promising type of current regulator for single-phase inverters is PR control because it can introduce an infinite gain at a selected resonance frequency such as the fundamental frequency to eliminate the steady-state error, which cannot be achieved by well-known proportional integral (PI) control. Note that PI control has limitations in terms of the steady-state magnitude and phase errors. In addition, PI control also has limited harmonic rejection capability, unlike the PR control, also can compensate for low-order harmonics. Imperfections in the current and voltage control scheme results in higher harmonic distortion of the output current and voltage. In this paper, performance of PR control parameters ($K_{p}$ , $K_{i}$ , and $\omega _{c}$ ) and filter parameters ($L_{f}$ and $C_{f}$ ) are optimally tuned to obtain a very low THD current with reduced output voltage ripple and steady-state error. The analysis, design and implementation of both PI and PR current control in single-phase UPS inverter applications through simulations and experiments are also presented in this paper. The performance of both of these control schemes are analyzed in terms of steady-state response, transient response, and level of current harmonics.

Performance enhancement of Uninterruptible Power Supply inverter through Neural Network control strategy

Performance enhancement of Uninterruptible Power Supply inverter through Neural Network control strategy

Design and implementation of an optimal switching controller for uninterruptible power supply inverters using adaptive dynamic programming

In this study, a new approach based on adaptive dynamic programming (ADP) is proposed to control single-phase uninterruptible power supply inverters. The control scheme uses a single function approximator, called critic, to evaluate the optimal cost and determine the optimal switching. After offline training of the critic, which is a function of system states and elapsed time, the resulting optimal weights are used in online control, to get a smooth output AC voltage in a feedback form. Simulations show the desirable performance of this controller with linear and non-linear loads and its relative robustness to parameter uncertainty and disturbances. Furthermore, the proposed controller is upgraded so that the inverter is suitable for single-phase variable frequency drives. Finally, as one of the few studies in the field of ADP, the proposed controllers are implemented on a physical prototype to show the performance in practise.

Lyapunov Energy Function Based Control Method for Three-Phase UPS Inverters With Output Voltage Feedback Loops

In this study, a Lyapunov energy function based control method with output voltage feedback loops is proposed for three-phase uninterruptible power supply (UPS) inverters. The presented paper demonstrates that the traditional Lyapunov-energy-function-based control method not only leads to considerable steady-state error in the output voltage, but also distorts the output voltage waveforms. Therefore, a modification has been performed on the traditional Lyapunov-energy-function-based control by incorporating the output voltage feedback loops in the control variables. The robustness of the proposed control method has been studied analytically through transfer functions which are expressed as the ratio of the output voltage to its reference. These analytical results are validated experimentally. In addition, the steady-state and dynamic performances of the proposed control method are also tested experimentally on a three-phase UPS inverter operating with linear (resistive) and nonlinear (diode-bridge rectifier) loads. As a consequence of incorporating output voltage feedback loops into the control variables, the proposed control method offers strong robustness against variations in LC filter parameters, high-quality sinusoidal output voltage along with acceptable total harmonic distortion (THD) values under linear and nonlinear loads, fast dynamic response under abrupt load changes, and negligibly small steady-state error in the output voltage.

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.

Hybrid iterative learning control strategy for single‐phase UPS inverter using inductor current active damping

This study proposes a hybrid iterative learning (HIL) control scheme for single-phase uninterruptible power supply (UPS) inverters using inductor current active damping technique. A UPS inverter maintains a tightly regulated output voltage independent of loading conditions and disturbances. To achieve such performance, a fast transient recovery time with a minimum steady-state error is desired. Fast control techniques, such as proportional integral (PI), are not always known for good steady-state performance in single-phase applications. As the load voltage and current are periodic, therefore a hybrid control strategy has been proposed in which a PI controller is combined with an iterative learning controller to produce better transient and steady-state dynamics. Adoption of such a strategy enables the UPS inverter control to be realised with one voltage and one current sensor, respectively. System modelling, filter magnitude-frequency characteristics shaping and control design with stability analysis have been presented in this study. The designed HIL control strategy is examined through simulations in a MATLAB environment in the discrete time frame and experimentally verified for a single-phase UPS inverter system prototype using a Texas TMS320F2812 digital signal processor.

Experimental assessment of UPS battery load model considering harmonics and its investigation in the distribution systems

Uninterruptible Power Supply (UPS) inverter battery systems in the recent years are playing significant role in achieving protection against power interruptions and in improving efficiency and cost effectiveness of the power networks. In this article, an assessment of harmonic load model of battery energy storage system is carried out by a detailed experimentation on 10kVA single-phase UPS inverter battery. Experimental results are obtained for fundamental powers drawn by the battery during charging, along with harmonic currents generated at various voltage levels. From the measured values, functional relations between voltage and power (real and reactive) have been developed. Results of experimentation are then integrated with radial distribution systems to investigate the impact of harmonic load model of UPS battery on the distribution network. The proposed method is tested on a radial distribution feeder integrated with UPS battery system. Load flow results of integrated distribution system demonstrate that non-linear load model of UPS battery can cause considerable harmonic distortion in the distribution network and increase power losses.

Grid-Connected Control Strategy of Five-level Inverter Based on Passive E-L Model

At present, the research on five-level inverters mainly involves the modulation algorithm and topology, and few articles study the five-level inverter from the control strategy. In this paper, the nonlinear passivity-based control (PBC) method is proposed for single-phase uninterruptible power supply inverters. The proposed PBC method is based on an energy shaping and damping injection idea, which is performed to regulate the energy flow of an inverter to a desired level and to assure global asymptotic stability, respectively. Furthermore, this paper presents a control algorithm based on the theory of passivity that gives an inverter in a photovoltaic system additional functions: power factor correction, harmonic currents compensation, and the ability to stabilize the system under varying injection damping. Finally, the effectiveness of the PBC method in terms of both stability and harmonic distortion is verified by the simulation and experiments under resistive and inductive loads.

A Single-Loop Repetitive Voltage Controller with an Active Damping Control Technique

This paper proposes a single-loop repetitive voltage control strategy which incorporates the active damping control feature for single-phase uninterruptible power supply (UPS) applications. The proposed method reduces the effect of the LC resonant peak, which limits the control bandwidth and deteriorates the stability of the entire control loop by effectively increasing the damping component. Due to the increased stability margin, a repetitive controller working together with a proportional-resonant (PR) controller can be easily adopted. Moreover, the voltage error is minimized even under severe non-linear load conditions. It is confirmed that the proposed single-loop controller achieves excellent and stable voltage regulation performance by evaluating the entire loop-gain of the system and the output impedance. Both the simulation and the experimental results for a 1.5 kW UPS inverter show agree well with the analyses, and the excellence of the proposed method has been verified.