José Fernando Silva

Multilevel Optimal Predictive Dynamic Voltage Restorer

This paper presents an optimal predictive controller for a multilevel converter-based dynamic voltage restorer (DVR), which is able to improve the voltage quality of sensitive loads connected to the electrical power network. The optimal predictive controlled multilevel DVR can restore sags and short interruptions while reducing the total harmonic distortion (THD) of the ac line voltages to values lower than 1%. The DVR is based on a three-phase neutral point clamped converter to dynamically inject a compensation voltage vector in series with the line voltage, through series-connected transformer secondary windings. To assure high-quality voltages for sensitive loads, we devise optimal predictive control laws for the injected compensation ac voltages. A suitable quadratic weighed cost functional is used to choose the voltage vector, minimizing both the ac voltage errors through current injection and the dc side capacitor voltage unbalancing. The performance of the proposed predictive controller is compared to classical proportional integral (PI): synchronous frame and stationary frame (P+resonant) controllers. The line-side filter capacitor topology is compared to the regular converter-side filter capacitor. Obtained experimental results show that the ac voltages are almost sinusoidal in steady-state operation when facing balanced and unbalanced sags and short interruptions with unbalanced loads. Voltage THD is reduced to values lower than 1%; the DVR is behaving also as a series active power filter for the ac voltages.

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.

Fixed frequency sliding mode modulator for current mode PWM inverters

A fixed frequency current mode PWM modulator that provides output current limiting in sliding mode voltage controlled DC-AC power converters is presented. The modulator is considerably simpler than previous solutions and well adapted for sliding mode control, which is advantageous when the inverter feeds nonlinear or wide ranging loads and performs as a switching power operational amplifier or power operational transconductance amplifier.<<ETX>>

Generalized solid-state marx modulator topology

A generalized circuit topology for bipolar or unipolar high voltage repetitive pulse power applications is proposed. This circuit merges the negative and positive solid state Marx modulator concepts, which take advantage of the intensive use of semiconductor devices to increase the performance of the original dissipative Marx modulators. The flexibility of the proposed modular circuit enables the operation with negative and/or positive pulses, selectable duty cycles, frequencies and relaxation times between the positive and negative pulse. Additionally, the switching topology enables the discharge of the parasitic capacitances after each pulse, allowing the use of capacitive loads, and the clamping of inductive loads, recovering the reset energy back to the main capacitors. Analysis of efficiency and power loss will be addressed, as well as experimental details for different conditions based on laboratory prototype, with 1200 volt Insulated Gate Bipolar Transistors (IGBT), diodes, and 4.5 muF capacitors.

Repetitive High-Voltage Solid-State Marx Modulator Design for Various Load Conditions

The analysis of a solid-state Marx modulator (S2M2) topology, which have been developed for repetitive high-voltage (in kilovolts) applications, needing positive or negative rectangular pulses, is presented. The proposed topology benefits from the intensive use of semiconductors, allowing kilohertz operation with different load conditions. In addition to resistive loads, capacitive loads can be discharged to ground after each pulse and inductive loads can be clamped and the energy recovered to the main capacitors. Furthermore, the presented topology and proposed switching sequence enables the use of typical half-bridge semiconductor structures currently integrated in modular packages, which is advantageous for circuit assembling and triggering the semiconductors. Discussion on the advantages and limitation will be given. Finally, experimental results of some modulator features will be presented.

Three-phase single-stage four-switch PFC buck-boost-type rectifier

This paper proposes a new three-phase single-stage power-factor corrector buck-boost-type rectifier topology. The typical topology uses a bridge configuration with six switches. This new topology only requires four switches, improving the rectifier efficiency as only one reverse-blocking power semiconductor conducts at any time. A vector-based sliding-mode control method for the three-phase input currents is also proposed. This fast and robust technique uses sliding mode to generate /spl alpha//spl beta/ space-vector modulation, which forces the input line currents to track a suitable sinusoidal reference. A near-unity power-factor operation of the rectifier is obtained using a sinusoidal reference in phase with the input source voltages. A proportional-integral controller is adopted to regulate the output voltage of the converter. This external voltage controller modulates the amplitude of the current references. The characteristics of the new rectifier are verified with experimental results.

Marx-Type Solid-State Bipolar Modulator Topologies: Performance Comparison

The operation of generalized Marx-type solid-state bipolar modulators is discussed and compared with simplified Marx-derived circuits, to evaluate their capability to deal with various load conditions. A comparative analysis on the number of switches per cell, fiber optic trigger count, losses, and switch hold-off voltages has been made. A circuit topology is obtained as a compromise in terms of operating performance, trigger simplicity, and switching losses. A five-stage laboratory prototype of this circuit has been assembled using 1200 V insulated gate bipolar transistors (IGBTs) and diodes, operating with 1000 V dc input voltage and 1 kHz frequency, giving 5 kV bipolar pulses, with 2.5 μs pulse width and 5 μs relaxation time into resistive, capacitive, and inductive loads.

Rise time reduction in high-voltage pulse transformers using auxiliary windings

Today high-voltage pulses are reaching more fields of application. High-voltage pulse transformers are often used in association with high-voltage pulse generating circuits to further increase the pulse output voltage level. However, because of the transformer parasitic elements involved, the transformer is the critical device in shaping the rising characteristics of the output pulse. One of the techniques usually adopted to decrease the leakage inductance of the transformer adds two auxiliary windings to the transformer. If properly used, these auxiliary windings reduce the leakage flux and, therefore, the leakage inductance. As a result the pulse rise time is reduced. In this paper, a mathematical model is used to describe the observed behavior of a transformer operating with auxiliary windings, based on the theory of electromagnetic coupled circuits. The model is discussed regarding the experimental results obtained from a high-voltage test transformer associated with a high-voltage pulse generating circuit, and the simulation results obtained from the numerical evaluation of the developed differential equations implemented in Matlab/Simulink with the measured transformer parameters.

New solid-state Marx topology for bipolar repetitive high-voltage pulses

A novel bipolar high-voltage modulator topology, based on the Marx generator concept, is proposed for high-voltage repetitive pulsed power applications. The proposed topology is a generalized version of the negative and positive all-solid-state Marx modulator concepts, which takes advantage of the intensive use of power semiconductor switches to increase the performance of the classical circuit, strongly reducing losses and increasing the pulse repetition frequency. Additionally, the proposed topology enables the use of typical half-bridge semiconductor structures while ensuring that the maximum voltage blocked by the semiconductors is the voltage of the capacitor in each stage. Due to semiconductor topology used the output voltage is very flexible. Hence, it is possible to change from negative to positive unipolar to bipolar pulse, with different duty cycles and different switching patterns. Experimental results are presented and discussed. A laboratory prototype with 10 kW peak power, of this bipolar solid-state modulator circuit, was assembled 1200 V IGBTs and diodes, operating with 1000 V d-c input voltage and 10 kHz frequency, giving 2 kV bipolar pulses, 5 A, with 5 mus into a resistive load.

Pulse Shape Improvement in Core-Type High-Voltage Pulse Transformers With Auxiliary Windings

High-voltage pulsed power technologies are rapidly emerging as a key to efficient and flexible use of electrical power for many industrial applications. One of the most important elements in high-voltage pulse-generating circuit technology is the transformer, generally used to further increase the pulse output voltage level. However, its nonideal behavior has significant influence on the output pulse shape. The most attractive winding configuration for high-voltage, the core-type transformer with primary and secondary on different core legs, is seldom used in pulsed applications, because of its weak magnetic coupling between windings, which would result in a slow-rising output voltage pulse. This paper shows that auxiliary windings, suitably positioned and connected, provide a dramatic improvement in the pulse rise time in core-type high-voltage pulse transformers. The paper derives a mathematical model and uses it to describe the observed behavior of the transformer with auxiliary windings. It discusses experimental results, obtained from a high-voltage test transformer associated with a high-voltage pulse generating circuit, and the simulation results obtained from the numerical evaluation of the developed differential equations implemented in Matlab and taking into account the measured transformer parameters