This paper proposes a down-sampled discrete-time internal-model-based controller in the synchronous reference frame with a reduced number of poles. This controller is suitable for three-phase pulsewidth modulation inverters with output transformer for double-conversion uninterruptible power supply applications. It is demonstrated that the use of a down-sampled rate and fewer poles in the internal model results in a number of benefits, among which are the following: 1) improvement of the transient response; 2) increase of the stability margin of the closed-loop system; 3) a straightforward implementation in fixed-point digital signal processor (DSP) and microcontroller implementation as well as a reduction of the required memory space; and 4) a simple solution for the saturation of the output transformer. As a result, it is possible to obtain output voltages with reduced total harmonic distortion while ensuring good transient performance for both linear and nonlinear loads. To confirm the advantages claimed for the proposed synchronous reference dq frame internal-model-based controller and to demonstrate the steady-state and transient performance under the test conditions of the International Electrotechnical CommissionStandard 62040-3, the experimental results from a 10-kVA space-vector-modulated three-phase inverter, which is fully controlled by a DSP TMS320F241, are presented.Index Terms-Digital control, discrete-time control, internal model principle, power transformers, uninterruptible power systems (UPSs).

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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,

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

A new methodology to design discrete-time multiple resonant controllers for single-phase uninterruptible power supply inverters is proposed in this study. This methodology is based on classical linear tools and consists on the synthesis of the inverter output impedance according to standard specifications. This synthesis is performed using a multi-loop control strategy composed of an inner current control loop using a proportional controller, and an outer voltage control loop using the multiple resonant controller. A prototype was built to demonstrate the practical feasibility of the theoretical proposal. A significant reduction of the output impedance at determined harmonic frequencies resulted in a low-voltage total harmonic distortion of the output voltage of about 1.76%, for IEC 62040-3 reference non-linear load.

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A control strategy to achieve fault ride-through capability and to provide high performance of the output voltage of a single-phase uninterruptible power supply (UPS) inverter is proposed in this study. This strategy consists in controlling the voltage and current waveforms measured at the inverter output filter, with an inner current control loop and an outer voltage control loop, using a plug-in structure based on multiple resonant stages in addition with proportional controllers. In order to achieve stability from no load to short-circuit conditions, the implementation of the multiple resonant controllers includes a compensation of the system phase lag. Moreover, it presents a comparative analysis between two controller structures, the proposed plug-in and the classical proportional + resonant. From this analysis, it can be concluded that the plug-in structure presents improved characteristics of closed-loop output impedance and output voltage dynamic response during fault ridethrough events. A controller design methodology to achieve robustness to parametric uncertainties and UPS standard compliance, is detailed. Experimental results from a single-phase 2 kVA inverter prototype are presented to validate the feasibility of the proposal.