Sónia Ferreira Pinto

Matrix Converter-Based Unified Power-Flow Controllers: Advanced Direct Power Control Method

This paper presents a direct power control (DPC) for three-phase matrix converters operating as unified power flow controllers (UPFCs). Matrix converters (MCs) allow the direct ac/ac power conversion without dc energy storage links; therefore, the MC-based UPFC (MC-UPFC) has reduced volume and cost, reduced capacitor power losses, together with higher reliability. Theoretical principles of direct power control (DPC) based on sliding mode control techniques are established for an MC-UPFC dynamic model including the input filter. As a result, line active and reactive power, together with ac supply reactive power, can be directly controlled by selecting an appropriate matrix converter switching state guaranteeing good steady-state and dynamic responses. Experimental results of DPC controllers for MC-UPFC show decoupled active and reactive power control, zero steady-state tracking error, and fast response times. Compared to an MC-UPFC using active and reactive power linear controllers based on a modified Venturini high-frequency PWM modulator, the experimental results of the advanced DPC-MC guarantee faster responses without overshoot and no steady-state error, presenting no cross-coupling in dynamic and steady-state responses.

34 – Control Methods for Switching Power Converters

J. Fernando Silva, Ph.D. and Sonia Ferreira Pinto, Ph.D. Instituto Superior Tecnico, DEEC, A.C. Energia, Laboratorio de Maquinas Electricas e Electronica de Potencia, Centro de Automatica da Universidade Tecnica de Lisboa, AV. Rorisco Pais 1, 1049-001 Lisboa, Portugal 34.

Linear and Sliding-Mode Control Design for Matrix Converter-Based Unified Power Flow Controllers

This paper presents the design and compares the performance of linear, decoupled and direct power controllers (DPC) for three-phase matrix converters operating as unified power flow controllers (UPFC). A simplified steady-state model of the matrix converter-based UPFC fitted with a modified Venturini high-frequency pulse width modulator is first used to design the linear controllers for the transmission line active (P) and reactive (Q) powers. In order to minimize the resulting cross coupling between P and Q power controllers, decoupled linear controllers (DLC) are synthesized using inverse dynamics linearization. DPC are then developed using sliding-mode control techniques, in order to guarantee both robustness and decoupled control. The designed P and Q power controllers are compared using simulations and experimental results. Linear controllers show acceptable steady-state behavior but still exhibit coupling between P and Q powers in transient operation. DLC are free from cross coupling but are parameter sensitive. Results obtained by DPC show decoupled power control with zero error tracking and faster responses with no overshoot and no steady-state error. All the designed controllers were implemented using the same digital signal processing hardware.

Advanced Control of Switching Power Converters

Publisher Summary This chapter provides basic and advanced skills to control electronic power converters, considering that the control of switching power converters is a vast and interdisciplinary subject. State-space models provide a general and strong basis for dynamic modeling of various systems including switching converters. State-space models are useful to design the needed linear control loops and can also be used to computer simulate the steady state and the dynamic behavior of the switching converter fitted with the designed feedback control loops and subjected to external perturbations. Current-mode control in switching power converters is the simplest form of state feedback. Closed-loop control of resonant converters can be achieved using the outlined approaches if the resonant phases of operation last for small intervals compared to the fundamental period. The first step in the fuzzy controller synthesis procedure is to define the input and output variables of the fuzzy controller. This is done accordingly with the expected function of the controller. There are no general rules to select those variables, although typically the variables chosen are the states of the controlled system, their errors, error variation, and error accumulation.

Direct control method for matrix converters with input power factor regulation

This work presents the design of sliding mode controllers, considering the dynamics of the input filter, for three-phase AC-AC matrix converters, to guarantee input and output sinusoidal waveforms with controllable input power factor. The sliding mode control technique together with space vector modulation is used to ensure that the output voltages and input currents track their references, guaranteeing the desired input power factor of matrix converters, which may be useful in applications operating with unity input power factor, such as AC drives, or applications where fully controllable input power factor is useful, namely static VAR compensators (SVC) or phase shifters. The obtained simulation and experimental results show that the designed controllers, associated with the state-space vector technique, guarantee the direct control of matrix converters output voltages, as well as their input currents.

Advanced control methods for power electronics systems

The application of modeling methods suitable for control and simulation of power electronic systems is outlined as a self-contained approach to solve the simulation and control problems of novel structures of power electronics converters. The straightforward non-linear modeling for controller design and simulation uses switched state-space models avoiding the averaging task, needs few linear control concepts, derives the stability study from geometric properties and leads to an integrated design of the control, modulators and simulation tasks. On-line sliding mode control techniques are well suited to power converters as they are inherently variable structure systems. Obtained controllers are robust concerning converter parameter variations, semiconductor non-ideal characteristics, load and line disturbances. Main modeling and design steps are summarized and some examples given. Results show fast dynamics, no steady-state errors and robustness against semiconductor non-idealities and dead times.

Single stage inverter for PV applications with One Cycle Sampling technique in the MPPT algorithm

This paper introduces a single-stage, single-phase, inverter, for maximum efficient photovoltaic grid connection. The inverter is based in a full-bridge converter where a few diodes and one inductor have been added to enable single stage operation. The new topology provides an additional buck-boost converter function at the bridge level in order to extract the maximum power from photovoltaic (PV) panel. Non linear control is used to regulate the sinusoidal current injected in the grid and the PV voltage, so that maximum power point tracker, MPPT, is obtained. The new MPPT algorithm uses one cycle sampling technique to obtain the average value of the voltage and current in the panel with a small time delay. This technique eliminates errors introduced in the MPPT calculation, due to the switching ripple. The proposed algorithm also allows the operation of the control circuit at a lower frequency than the high switching frequency of the bridge converter transistors.

Constant-frequency sliding-mode and PI linear controllers for power rectifiers: a comparison

Constant-frequency sliding-mode and linear proportional integral (PI) cascaded controllers (internal current loop and external output voltage control loop) for 12-pulse thyristor rectifiers are designed, using new models and convenient assumptions, and their performances compared. The use of sliding-mode control on line-commutated power converters implies the use of fixed-frequency sliding-mode design, originating steady-state errors. These are eliminated using a higher order switching function, with fourth-order Bessel polynomial coefficients, to minimize the response time and to eliminate the overshoot in the reaching mode. Comparisons are made using simulations (MATLAB/SIMULINK blocks) and experimental results. The sliding-mode controllers, as well as the PI controllers, need almost the same hardware and present no steady-state errors and no output voltage overshoots. Besides allowing a faster dynamics than the PI controllers, the proposed sliding-mode approach provides a new, nonlinear theoretical frame for solving the control problem of power rectifiers with output filters.

Direct Controlled Matrix Converters in Variable Speed Wind Energy Generation Systems

This paper presents a variable speed wind energy generation system with a doubly-fed induction generator (DFIG), using a direct controlled matrix converter in the rotor circuit. The main aim is to extract the maximum energy from the wind (Maximum Point Power Tracking - MPPT). In order to achieve a decoupled control between the torque and the rotor excitation current, the induction machine equations are obtained using the Stator Flux Oriented Control (SFOC) approach. The matrix converter will be used to control the rotor currents, guaranteeing the necessary torque, to extract the maximum energy from the wind (MPPT). The obtained results show that the proposed variable speed wind energy generation system has the expected performance, guaranteeing the MPPT.

P-Q decoupled control scheme for unified power flow controllers using sparse matrix converters

The main aim of this paper is to improve the dynamic control performance of power systems, using an advanced control approach for Unified Power Flow Controllers (UPFC). The proposed controller, based on sliding mode control technique, guarantees fast response times, precise control actions and an almost completely decoupled active and reactive power control. To reduce energy storage equipment, with consequent reduction of power losses and lifetime increase of UPFC systems, AC-AC converters with minimum storage requirements are used. These converters, usually known as Sparse Matrix Converters, are based on Matrix Converter technology and guarantee AC/DC and DC/AC conversion without the intermediate bank of capacitors, present in most AC/DC - DC/AC converters association. UPFC model is presented, using Sparse Matrix Converters, and the system controllers are designed to allow both a good steady-state and dynamic response.