Navid Amiri

An Improved Direct Decoupled Power Control of Doubly Fed Induction Machine Without Rotor Position Sensor and With Robustness to Parameter Variation

In this paper, coupling between active and reactive powers in conventional direct power control (DPC) strategies is analyzed and a new direct DPC method for doubly fed induction machine without rotor position sensors is presented. Coupling analysis is done on an improved DPC strategy with rotor flux controllers in the stator reference frame. The presented control strategy is done by controlling the rotor flux in the grid flux reference frame. The rotor flux command is calculated using a predicted stator flux, the stator current command, and the stator resistance. Moreover, the rotor position is estimated by comparing measured and estimated values of the rotor current. Furthermore, to reduce the methods sensitivity to the parameter inaccuracies, the mutual inductance of the machine is updated during the machine operation by the error between the magnitudes of the measured and estimated values of the rotor current.

Verification of Parametric Average-Value Model of Thyristor-Controlled Rectifier Systems for Variable-Frequency Wind Generation Systems

Line-commutated thyristor-controlled rectifiers are often used in many industrial and renewable energy applications where controllable dc voltage is required. The derivation of accurate dynamic average-value models for thyristor-controlled systems is challenging. The recently proposed parametric average value modeling (PAVM) avoids the discrete switching states of the converters and results in computationally efficient models that are suitable for system level studies. This paper extends the PAVM recently developed for synchronous-machine-fed thyristor-controlled-rectifier systems to a permanent magnet synchronous machine wind generation system where the operation in variable speed and frequency is required.

Constant parameter VBR model of permanent magnet synchronous machine wind generation system

Modeling renewable energy generation systems with electrical machines has been an active area of research, wherein interfacing the machine models with power electronic converters is a known challenge area. As an alternative to traditional qd models, the coupled-circuit phase-domain (CCPD) and voltage-behind-reactance (VBR) models have been recently proposed. The permanent magnet (PM) generator has internal saliency and damper structures, which results rotor-position-dependent inductances in both CCPD and VBR models, and interfacing qd models requires snubber circuits, all of which reduces the simulation efficiency. This paper presents a constant-parameter voltage behind reactance (CPVBR) model in order to achieve a numerically-efficient interface with the rectifier circuit. The model is demonstrated on a grid-connected variable-speed wind generation system, wherein significant computational advantages are demonstrated compared with existing models.

Dynamic Phasor Modeling of Line-Commutated Rectifiers With Harmonics Using Analytical and Parametric Approaches

Line-commutated rectifiers (LCRs) are widely used in various industrial applications, wherein they are also known to be a significant source of harmonics. The dynamic phasor (DP) modeling approaches have been well studied in the literature to simulate the dynamics of power systems and their components including harmonics. In this paper, the state-of-the-art analytical DP (ADP) models of LCRs, which relate the ac and dc subsystems through complicated switch functions, are first investigated. Then, a new parametric DP (PDP) model of LCRs is proposed, wherein the DP dynamics of rectifier/dc-link are represented using a set of explicit algebraic functions that are numerically established. Rigorous computer studies demonstrate that the proposed PDP methodology is capable of accurately predicting the steady-state and transient responses of LCR systems under a wide range of loading conditions, while providing significant computational advantages over the conventional detailed model and the established ADP models.

Interfacing SFA- and GAM-type dynamic phasors for modeling of integrated AC-DC power systems

This paper focuses on the modeling of integrated ac-dc backup and generation power systems, which has received increasing attention due to the emergence of microgrids and distributed generations. The conventional shifted-frequency analysis (SFA) type dynamic phasors (DPs) assume a bandpass spectrum of power system signals, and thus are only suitable to model system components wherein the 60Hz fundamental frequency is dominant. To account for high-order harmonics of interest in ac-dc systems, this paper considers another type of DPs based on the generalized averaging method (GAM), and proposes a possible interface between the SFA- and GAM-type DP models. Computer studies demonstrate that the proposed DP interface allows for accurate simulations of both fundamental frequency components and high-order harmonics in integrated ac-dc power systems, while providing significant numerical advantages over the conventional time-domain detailed models.

Efficient simulation of wind farms using switching reduced models of converters and VBR formulation of six-phase PM synchronous generators

Wind generation systems with variable frequency generators commonly utilize several power electronics converters. Using numerically efficient models for converters and electrical machines can decrease simulation time of wind farms. In this paper, a voltage-behind-reactance model is developed for a six-phase permanent magnet synchronous generator. Then, a multiresolution simulation methodology is presented which utilizes different combinations of detailed and average-value models of twelve-pulse rectifier and three-phase inverter systems in conjunction with different six-phase machine models. The presented models are verified through simulations to provide superior performance in terms of speed and numerical efficiency.

A parametric dynamic phasor model of line-commutated rectifier systems

Recently, the generalized averaging method (GAM) has received significant attention to effectively model and simulate dynamics of ac-dc power systems using dynamic phasors (DPs). The conventional analytical DP (ADP) models of line-commutated rectifiers (LCRs) have been derived based on switch functions, which are only valid for certain operating mode. In this paper, a new parametric DP (PDP) model of LCRs is presented, which relates the ac-dc subsystems through a set of parametric algebraic functions that account for various loading conditions. Simulation results validate the advantageous accuracy of the proposed PDP model of LCRs, and demonstrate its superior numerical efficiency over the time-domain detailed model and the prior ADP model.

Parametric average value modeling of high power AC/AC cyclo converters

Line-commutated thyristor-controlled AC/DC and AC/AC converters are commonly used in high power industrial applications. Therefore, analyzing industrial distribution systems requires accurate and computationally efficient models that may be easily implemented in simulation software packages. Average-value models (AVMs) avoid the discrete switching of the converters, provide accurate system-level steady-state and transient simulation results, which make such models particularly suitable for large scale studies of power electronic systems. Parametric average value modeling (PAVM) is one of very promising techniques resulting in accurate models that are also considerably simpler in terms of mathematical complexity. The PAVMs for AC/DC converter systems have been thoroughly analyzed in literature. This paper proposes a new PAVM for AC/AC cyclo-converters which supply the load at lower AC frequencies. The superior performance and computational advantages of the proposed PAVM of cyclo-converters are verified against the detailed model in terms of CPU efficiency as well as numerical accuracy.

Direct decoupled active and reactive power control of Doubly Fed Induction Machine without rotor position sensors and with robustness to saturation and parameter variation

In this paper a new Direct Power Control method of the Doubly Fed Induction Machine without the use of rotor position sensors is presented. The method is based on estimating the stator flux in the rotor reference frame, and then applying the correct rotor voltages to obtain the desired rotor flux and power. Estimation of the rotor position is done by comparing the measured values with the estimated values of the rotor current. For this control method to have minimal sensitivity to parameter inaccuracies, the mutual inductance of the machine is also corrected during the process by an error signal produced by comparing the magnitudes of the measured and estimated rotor current. This will also ensures robustness against machine saturation and can be used to detect saturation in the machine.

Generalized Parametric Average-Value Model of Line-Commutated Rectifiers Considering AC Harmonics With Variable Frequency Operation

Line-commutated rectifiers are often utilized in machine-converter systems and many energy conversion applications. Simulation of such power systems using detailed switching models of rectifiers is computationally expensive, and as an alternative for system-level studies, the so-called average-value modeling (AVM) techniques have become indispensable. The parametric AVM (PAVM) uses a computerized approach for establishing the key relationships between the averaged ac and dc variables. In this paper, a generalized PAVM (GPAVM) is proposed, which extends several previously proposed models. The new GPAVM includes the ac harmonics in thyristor-controlled rectifier models considering their nonlinear dependency on the line frequency. The new model is verified using detailed simulations and experimental results and is demonstrated to have better accuracy in a wider range of operating conditions and speeds/frequencies.