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This paper proposes discrete time voltage and current controllers for three-phase PWM inverters used in UPS applications. An accurate state space discrete model of the PWM inverter-filter-load, which takes into account nonlinearities and propagation delays associated with a real time digital implementation, is derived for the controller design. The output voltages and inductors currents are dynamically limited by means of MIMO controllers designed using optimal servo linear quadratic regulators, which ensure stability for the system at all operating conditions. In order to ensure smooth transitions among the different modes of operation, a nonlinear MIMO anti-windup method is proposed to update the servo variables. A 15kVA PWM inverter fully controlled by the DSP controller TMS320F241 has been used to validate the proposed approach. Simulations and experimental results show a good transient and steady state performances from no-load to short circuit operation. I. INTRODUCTIONThe main goal of an UPS is to provide high quality output voltage for critical loads even under disturbances coming from both AC line or from the load. Many controllers have been proposed to obtain an output voltage with low total harmonic distortion for three phase PWM inverters [1-6]. Among them, deadbeat and OSAP controllers [1-3] presents a fast transient response, however, they are sensitive to parametric variations and model uncertainties, which often results in undesirable transient performance, or even instability. On the other hand, nonlinear state feedback controller in the synchronous frame [4-5] have been described, however, the design is usually carried out in the continuous time domain, and the relevant delays associated with a digital implementation are not taking into account, which can degrade its final performance [6]. In addition, in none of the case reported the output voltage controller and the current limiter controller, which is required to clear faulty loads and to protect the inverter against overloads, are simultaneously designed with systematic procedure. This paper proposes a rotating frame fully digital voltage and current controllers for PWM inverters where good performance from no load to short circuit is assured by the proper selection of the cost functions of the voltage and current linear quadratic regulator. The impact of the weighting matrices on the converter performance are thoroughly investigated and a systematic procedure for the controller design in the state space is derived. The remainder part of this paper is organized as follows: Section II presents a discrete model in the rotating frame for the space vector modulated inverter and LC filter and load,

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O objetivo deste trabalho é de que ele possa ser utilizado como tutorial da modulação space vector para profissionais da área de Eletrônica de Potência. Nesse sentido, este artigo apresenta uma abordagem unificada para a modulação space vector aplicada a inversores alimentados em tensão. Cinco inversores de tensão são apresentados para exemplificar a metodologia proposta, são eles: inversor monofásico em ponte completa, inversor trifásico a três fios de dois e três níveis, inversor trifásico a quatro fios de três e quatro braços. Para cada um dos inversores são apresentados os vetores de comutação, os planos de separação, os planos limites para operação na região linear, bem como algumas possíveis seqüências de comutação. Resultados experimentais são apresentados para validar a metodologia proposta.
This paper presents a unified approach of the space vector modulation for voltage-source inverters. To demonstrate the proposed unified approach, five fundamental inverters topologies are analyzed, that are: single-phase full-bridge; three-phase three-wire; three-phase four-wire, three-phase four-leg and three-phase three-level inverters. Switching vectors, separation and boundary planes in the inverter output space as well as decomposition matrices and possible switching sequences are derived for each one of these inverters. Experimental results are shown to validate the proposed approach

This paper presents a design procedure of discretetime plug-in repetitive controllers for single-phase PWM inverters. The presented methodology can be applied to inverters with different servo controller and takes into consideration the most usual nonlinear cyclic loads. The basic principles of the repetitive controllers used in PWM inverters are discussed as well as the design guidelines to obtain a stable closed-loop controller with suitable steady-state performance and improved rate of convergence. To illustrate the proposed procedure is presented a design example of a repetitive controllers using a PID-feedforward as the servo controller. Experimental results have been provided to show the response of the controllers under different load conditions.

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This study investigates the rotor speed estimation problem for induction motor drives. The authors propose the design of a scheme based on a discrete-time sliding mode observer which provides the rotor speed estimative. A new algorithm for discrete-time rotor speed estimation is developed and analysed. The conditions for the existence of a discrete-time sliding switching hyperplane are analysed. Moreover, conventional algorithms aiming at the chattering reduction and high-frequency switching on discrete-time implementation are discussed for use with the proposed technique. The stability analysis and parameter convergence of the proposed method are investigated for discrete-time solution. The algorithms developed are tested by experimental results based on fixed-point digital signal processor (DSP) platform (TMS320F2812). Therefore the results demonstrate the good performance of the proposed scheme.

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