Robust Output Voltage Tracking with Prescribed Performance for Single-Phase UPS Inverters

Design concept of FPGA based hardware controller is proposed with basic modules for the development of power electronics applications. Also an autonomous decentralized control system for single phase UPS inverter with FPGA based hardware controller using software CPU core is described. Progress of FPGA technology makes it possible to include the software macro CPU core into the FPGA chip, a high flexibility can be realized for the construction of the control processor in power electronics application. But the basic modules for power electronics application are not enough in the environment of FPGA development platform. In this paper, several modules are presented for power electronics applications, and also proposed an autonomous distributed control system for single phase UPS inverter with FPGA based hardware controller using CPU core. The advantages of FPGA based hardware control system are discussed.

It is common practice to measure the instantaneous load current for realizing current trajectory control for UPS inverters. A recent paper describes an interesting sliding control mode scheme for 1-ph inverters with an LC filter in which the A.C. load current needs to be monitored. A modification to the scheme is presented in this paper which enables sliding mode control by monitoring the instantaneous D.C. line current and the load voltage. A simple observer can estimate the load current. The use of the observer helps in overcoming the problem of high voltage swings experienced by current sensors and errors due to common mode signals.

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.

This study introduces an innovative disturbance observer to tackle external disturbances and model uncertainties, along with a control strategy based on Lyapunov functions, ensuring global asymptotic stability for a single-phase multilevel inverter for UPS applications. The stability analysis of the proposed method is presented, based on two theorems. The first Theorem guarantees presents a disturbance observer, provides a bounded estimation error for the unknown disturbance, in the single-phase UPS inverter (UPSI). The bounded estimation is then used in designing an observer-based robust controller in the second Theorem, which ensures the convergence of tracking error to a small neighborhood of the origin. The numerical and practical results indicate that the developed control scheme ensures global stability and leads to the desired sinusoidal voltage with an almost low THD. Meanwhile, almost zero steady-state error in the output voltage (OV), and robust dynamic performance under uncertainties and disturbances are attained.

A previously reported (Campos-Canton and Espinosa-Perez, 1999) control law that solves the output voltage control problem for a single-phase voltage-source UPS inverter is experimentally evaluated. The adaptive nonlinear controller was developed considering a half-bridge DC-AC power converter connected to a (linear) resistance load. The evaluation procedure considers the following topics: verification of the stability and convergence theoretical properties, evaluation of the dynamic practical response, disturbance (load change) rejection capability, behavior under low size (and then cost) passive elements and (relative) low switching frequency. It is shown that the controller under study satisfies in a remarkable way all the above evaluation criteria.

Sequences having the minimum peak aperiodic autocorrelation sidelobe level one (1) are called Barker Sequences. Such sequences have been used in numerous real-world applications such as channel estimation, radar and spread spectrum communication etc. Unfortunately, the longest known biphase and quadriphase Barker sequences are of lengths 13 and 15 respectively. In this paper Modified Simulated Annealing Algorithm (MSAA) is used to design thirty-two phase sequences, which have good autocorrelation properties. Some of the synthesized results are presented here. The properties of the sequences up to length 24 have Barker properties which were not reported in literature earlier. The sequences of lengths from 4 to 289 have autocorrelation properties better than Frank codes. The synthesized 32-phase sequence sets are promising for practical application to radar and spread spectrum communication systems.

A quasi-continuous-time approach to the design of a digital PID control for DC/AC inverters with LC filter that use semiconductor switches producing PWM output voltage is presented. It is shown that an appropriately chosen continuous-time model of the digital controller with the PWM converter behaves like the actual discrete-time system, which allows for a simple controller design. SIMULINK models are used to validate this approach for a nonlinear rectifier load. The outcomes are compared with a real inverter experiment.

This paper presents a single uninterruptible power supply topology that overcomes some drawbacks of the previous reported ones. Among the desired features of the proposed UPS topology are: small number of semiconductors, low battery voltage, flexibility for the selection of the input and output voltages, common neutral between the incoming AC line and the load. The proposed UPS is composed of three bi-directional step-up converters, where both the incoming AC line and the load are connected in differential mode across the output terminals of these step-up converters. A current limiter is introduced to improve robustness and reliability of the proposed UPS. In this paper, analysis and experimental results for both the line operating mode and backup mode are presented. In addition, the current limiter operation is experimentally verified under several load transient conditions.

This paper describes a control method of UPS inverters connected in parallel. The UPS output voltage is controlled by an algorithm with an inverter current. A minor loop using two types of observers. Only the following two points are added to the algorithm for realizing parallel operations: (1) feedback of a common load current instead of the UPS output current; and (2) adjusting the phase of the output voltage to make the reactive component of the circulating currents zero. The proposed method has the following features, compared with conventional methods; (1) it does not need an additional output voltage control for parallel operation; (2) the impedances among UPSs are resistive so that the circulating currents caused by phase difference among UPSs have only reactive components; and (3) increase of software for parallel operation control is minimal.

Learning-based robust output tracking control for unknown discrete-time nonlinear systems with dynamic uncertainty

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. >

Uninterruptible power supplies have been used in many installations for critical loads that can not afford power failure or surge during operation. It is often difficult to upgrade the UPS system as the load grows over time. Due to lower cost and maintenance, as well as ease of increase system capacity, the parallel operation of modularized small power UPS has attracted much attention in recent years. This paper presents a state space based model predictive controller for controlling two or more parallel connected single phase UPS. In the proposed approach, the controller gains are determined by minimizing a cost function that reduces the output voltage tracking error, the control signals and equal sharing of the load currents among the inverters. The developed system has been evaluated through simulation study and experimental verification. The results under various loading conditions have demonstrated that the system performs well.

The paper presents the single phase 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.

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 systems (UPSs) compared to large conventional UPSs that are based upon bulky transformers that operate at the grid frequency, and due to the increasing interest in renewable energy integration and distributed generation (DG), it can also be a suitable solution for energy storage in microgrids or renewable-power-conditioning interface applications. The main features are soft commutation of the controlled switches, reduced weight and volume of magnetics, simple control strategy that can be implemented with well-know integrated circuits, use of a few batteries in series due to the same reference of the step-up stage, and connection between input and output enabling by-pass. A theoretical analysis, the implemented control strategy and the simulation results for main grid and photovoltaic solar energy applications obtained from an 1-kVA lab model are presented.

Robust output tracking control of Van der Pol oscillator is an important practical problem from an application point of view. An output feedback based robust tracking control strategy is proposed in this work for that purpose. First, a High-Order Sliding-Mode (HOSM) differentiator is used to estimate the oscillator states from the measurable output. Then, the Continuous Singular Terminal Sliding Mode (CSTSM) algorithm is used as a robust tracking controller based on the estimated states. Through numerical simulation, it is shown that the proposed control strategy outperforms a passivity based robust nonlinear tracking controller. Finally, experimental validations are also provided to show the feasibility of the proposed control in real-time.