R. Bojoi

Improved current control strategy for power conditioners using sinusoidal signal integrators in synchronous reference frame

In this paper, an improved current control scheme for shunt type power conditioners is proposed, with the aim of simplifying current harmonic compensation for industrial implementations where strict limitations on the harmonic distortion of the mains currents are required. To compensate current harmonics, the proposed scheme is based on proportional-integral regulators using sinusoidal signal integrators, implemented to operate both on positive and negative sequence signals. One regulator, for the fundamental current component, is implemented in the stationary reference frame. The other regulators, for the current harmonics, are implemented in a synchronous reference frame rotating at the fundamental frequency. This allows to compensate simultaneously two current harmonics with just one regulator. The whole control algorithm has been implemented on a 16-bit, Fixed-point digital signal processor (DSP) platform controlling a 20 kVA prototype. Experimental results are presented to show the validity of the proposed solutions.

Digital field-oriented control for dual three-phase induction motor drives

A direct rotor-field-oriented control of a dual-three phase induction motor drive is described in this paper. The induction machine has two sets of stator three-phase windings spatially shifted by 30 electrical degrees. The stator windings are fed by a current-controlled pulsewidth-modulation (PWM) six-phase voltage-source inverter. Three key issues are discussed: (1) the machine dynamic model is based on the vector space decomposition theory; (2) the PWM strategy uses the double zero-sequence injection modulation technique which gives good results with low computational and hardware requirements; and (3) to eliminate the inherent asymmetries of the drive power section, a new current control scheme is proposed. Experimental results are presented for a 10-kW dual three-phase induction motor drive prototype.

Enhanced Power Quality Control Strategy for Single-Phase Inverters in Distributed Generation Systems

Power electronic converters are commonly used for interfacing distributed generation systems to the electrical power network. This paper deals with a single-phase inverter for distributed generation systems requiring power quality features, such as harmonic and reactive power compensation for grid-connected operation. The idea is to integrate the DG unit functions with shunt active power filter capabilities. With the proposed approach, the inverter controls the active power flow from the renewable energy source to the grid and also performs the non-linear load current harmonic compensation keeping the grid current almost sinusoidal. The control scheme employs a current reference generator based on Sinusoidal Signal Integrator (SSI) and Instantaneous Reactive Power (IRP) theory together with a repetitive current controller. Experimental results obtained on a 4 kVA inverter prototype demonstrate the feasibility of the proposed solution.

Complete analysis and comparative study of digital modulation techniques for dual three-phase AC motor drives

The main goal of the paper is to perform a complete analysis and a comparative study of different digital pulsewidth modulation (PWM) techniques for dual three-phase induction machine drives. Six different digital PWM strategies are considered: four of them are present in the literature, the other two have been introduced by the authors in this paper. The comparison between the modulation strategies is based on several criteria: current harmonic minimisation, hardware and software implementation complexity with low cost fixed-point DSP platforms. Simulation results are provided to emphasize the advantages and disadvantages of each method. Experimental tests have been carried out to validate the most promising strategy which gives satisfactory results in terms of current harmonic minimisation and low implementation complexity.

Direct torque control for dual-three phase induction motor drives

A direct torque control (DTC) strategy for dual-three phase induction motor drives is discussed in this paper. The induction machine has two sets of stator three-phase windings spatially shifted by 30 electrical degrees. The DTC strategy is based on a predictive algorithm and it is implemented in a synchronous reference frame aligned with the machine stator flux vector. The advantages of the discussed control strategy are: constant inverter switching frequency, good transient and steady-state performance and low distortion of machine phase currents respect to direct self control (DSC) and other DTC schemes with variable switching frequency. Experimental results are presented for a 10 kW DTC dual three-phase induction motor drive prototype.

Digital current-control schemes

The paper is about comparing the performance of digital signal processor-based current controllers for three-phase active power filters.

Analysis and Comparison of Phase Locked Loop Techniques for Grid Utility Applications

This paper presents an analysis and comparison of phase locked loop techniques used in grid utility applications to find the voltage vector angle generated from the supply voltages. The phase locked loop (PLL) has a wide range of applications as distributed generation (DG), flexible AC transmission systems (FACTS), static VAR compensators, cycloconverters, active power filters (APFs) and others systems connected to the utility. The performance of these systems in grid connected applications is strongly influenced by the adopted PLL strategy. For this reason, the goal of the proposed paper is to present a comparison of different PLL-based techniques for utility applications to indicate the appropriate solution dedicated to a specific application. The criteria to compare the phase locked loops techniques is the performance under distorted and unbalanced supply voltages.

Digital field oriented control for dual three-phase induction motor drives

A direct rotor field oriented control (DRFOC) of a dual-three phase induction motor drive is described in this paper. The induction machine has two sets of stator three-phase windings spatially shifted by 30 electrical degrees. The stator windings are fed by a current controlled PWM (CRPWM) six-phase voltage source inverter (VSI). Three key issues are discussed: (1) the machine dynamic model is based on the vector space decomposition theory; (2) the PWM strategy uses the double zero-sequence injection modulation technique which gives good results with low computational and hardware requirements; and (3) to eliminate the inherent asymmetries of the drive power section, a new current control scheme is proposed. Experimental results are presented for a 10 kW dual three-phase induction motor drive prototype.

Unified Direct-Flux Vector Control for AC Motor Drives

The paper introduces an Unified Direct-Flux Vector Control (UDFVC) scheme suitable for simusoidal AC motor drives. The AC drives considered here are the Induction Motor (IM) drives, Synchronous Reluctance (SyR) and synchronous Permanent Magnet (PM) drives of the Interior PM (IPM) and Surface-mounted PM (SPM) types. The proposed controller operates in stator flux coordinates: the stator flux amplitude is directly controlled by the direct voltage component, while the torque is controlled by regulating the quadrature current component. The control firmware is the same for all the motor under test with the only exception of the magnetic model used for flux estimation at low speed. The UDFVC is particularly convenient when flux-weakening is required, since it easily guarantees maximum torque production under current and voltage limitations. Experimental results on four different drives are provided.

Experimental Identification of the Magnetic Model of Synchronous Machines

This paper proposes and formalizes a comprehensive experimental approach for the identification of the magnetic model of synchronous electrical machines of all kinds. The identification procedure is based on controlling the current of the machine under test while this is driven at constant speed by another regenerative electric drive. Compensation of stator resistance and inverter voltage drops, iron loss, and operating temperature issues are all taken into account. A road map for implementation is given, on different types of hardware setups. Experimental results are presented, referring to two test motors of small size, and references of larger motors identified with the same technique are given from the literature.