Rosario Casanueva

Microcontroller Power Mode Stabilized Power Factor Correction Stage for High Intensity Discharge Lamp Electronic Ballast

This paper presents new design considerations and a control strategy for a two-stage ballast system; power factor correction (PFC) and resonant inverter (RI), for high intensity discharge lamps. The ballast includes a microcontroller whose proposed algorithm implements a power loop and a voltage loop, both to control the PFC, and generates the transistor drive signals of the RI. The power loop adjusts the lamp power in steady state and the voltage loop controls the PFC during the ignition and warm-up time. System stability is studied to verify that the PFC stage provides the ballast with the required stability in long and medium term, while the short term stability is assured by the high output impedance of the LCC inverter, operating in open loop at constant switching frequency. The resulting performance of the ballast shows improvements in ignition repeatability, warm-up time reduction, robustness of the resonant inverter operation, and simple and accurate power control, including dimming operation

Digital Control of a Low-Frequency Square-Wave Electronic Ballast With Resonant Ignition

This paper proposes a two-stage low-frequency square-wave (LFSW) electronic ballast with digital control. The first stage of the ballast is a power factor correction (PFC) stage, and the second is a full-bridge (FB) converter used for both lamp ignition and LFSW drive. As a novelty for LFSW ballasts, ignition is achieved without an additional igniter circuit by operating the FB during start-up as a high-frequency resonant inverter. After ignition, the converter operates as an LFSW inverter to avoid exciting acoustic resonances by controlling the FB as a buck converter and regulating alternately positive or negative current to the lamp. Lamp power is regulated by adjusting the average current supplied by the PFC stage. Another contribution of this paper is to utilize digital control as a simple solution to achieve multimode control, including resonant lamp ignition, LFSW transitions, and lamp current and power regulation.

Power-mode-controlled power-factor corrector for electronic ballast

Medium- to high-power electronic ballasts are designed with two power conversion stages. The power-factor corrector (PFC) stabilizes the voltage supplied to the second stage and forces the utility current to meet the required standard. The inverter section stabilizes the arc in the lamp, and keeps the lamp power under the specified values. This paper proposes that the PFC section is to provide the power stability of the system while the inverter section operates in open loop. Consequences of this solution are: the power variation in the lamp caused by its aging is prevented, the complex dynamic of the lamp has no influence in the design, some extra voltage is available to achieve the lamp ignition, warmup time is reduced, and dimming control is easily implemented by modifying either the power reference or the bias value in the PFC control circuit. The inverter section is a half-bridge LC/sub p/C/sub s/ resonant inverter designed to require minimum variation of the input voltage to supply constant power to the lamp. In this way the operation point suffers little changes and no overdimensioning of the PFC and inverter components is necessary to meet the power source condition.

Teaching Resonant Converters: Properties and Applications for Variable Loads

This paper summarizes a lesson on resonant converters included in the new course, Advanced Power Conversion Techniques, within the M.Sc. program in electrical engineering at the University of Cantabria, Spain. The course has recently received the National Accreditation for official programs. The M.Sc. program, along with the Ph.D. thesis, forms a Ph.D. program in industrial engineering. The contents motivate the students to find suitable resonant converter applications of industrial interest. A new approach to teaching resonant converters is presented that focused on their properties at certain frequencies, such as for voltage sources, current sources, or sink and power source operation with very variable loads. The analysis of the converters enables the identification of these operating points and, by means of a sensitivity analysis with respect to the components of the resonant tank, explains the robustness of their behavior. Using as a starting point the fulfillment of the desired property, we propose that the students develop open-loop designs, with stable behavior, or closed-loop designs, with very small variation in the operating point. Two practical application examples are shown: electronic ballasts for high-intensity discharge lamps and power supplies for electrical discharge machining.

Analysis, design and experimental results of a high-frequency power supply for spark erosion

The LC/sub s/C/sub p/ resonant converter finds a new application in an electrical discharge machining (EDM) power supply, which is designed for the purpose of developing small size EDM systems. The switching frequency is tuned to the natural resonant frequency where the converter tends to act as a current source. In this way, three effects are achieved: 1) the necessary over-voltage is generated, first to ionize the dielectric and then to establish the electric discharge, 2) a constant current is supplied during the machining of the workpiece, providing the circuit with inherent protection under short circuit conditions, and 3) overall stability is guaranteed despite the equivalent negative resistance of the dielectric breakdown. The proposed control achieves an optimum and stable operation using tap water as dielectric fluid preventing the generation of undesired impulses and keeping the distance between the electrode and the workpiece within the optimum stable range. The EDM power supply has been validated to perform operations in a nuclear power plant application.

Approaches to modeling converters with current programmed control

In this paper, we present an overview of previously published approaches to dynamic modeling of current programmed converters, including basic low-frequency averaged models, as well as treatments of sampling and aliasing effects. The modeling assumptions are examined and the differences among the approaches are highlighted, with the objectives of making it easier to present these topics in power electronics courses and applying the models in practice.

Digitally Controlled Low Frequency Square Wave Electronic Ballast with Resonant Ignition and Power Loop

This paper proposes a digital controller for a low-frequency square-wave (LFSW) electronic ballast that includes the ignition sequence, a double control loop, and the selection of the positive and negative operation modes. The whole ballast is a two-stage circuit, where the first part is a power factor correction (PFC) stage and the second is a full-bridge (FB) converter used for both ignition and square-wave drive. Ignition is achieved by approaching the resonant frequency of the LC filter when the lamp is in the off state and the FB is working as a resonant inverter. After ignition, the converter operates as an LFSW inverter by controlling the FB to act alternately as a buck converter supplying positive or negative current. While ignition occurs at the LC filter resonance frequency (fo = 20 kHz), the buck converter switching frequency (fsw = 200 kHz) is selected significantly higher than fo to attenuate high-frequency harmonics and avoid exciting acoustic resonance. Lamp stability is achieved by controlling the inductor current of the LC filter, and power mode control is achieved by adjusting the average current and voltage supplied by the PFC stage. The solution is experimentally validated for different types of 150-W high-intensity discharge lamps. A coupled-inductor single-ended primary inductance converter operating in continuous conduction mode is used for the PFC stage.

Current mode controlled LCC resonant converter for electrical discharge machining applications

In this paper, a contribution to the electrical discharge machining (EDM) technology is presented. The final aim of this research is to develop small size EDM systems and determine the influence of the voltage and current of the output electrical arc on the quality and efficiency of the workpiece machining. The proposed system is a DC to DC LCC resonant converter intended to generate current controlled arc pulses at a constant frequency that erode the workpiece. The benefits of this proposal are: (1) the system has inherent protection under short circuit; (2) a simple linear controller results in a highly robust feedback control under load changes; and (3) the transistors turn-on at zero voltage is guaranteed at any load value. The output voltage is intended to be adjusted by an external system that controls the arc distance.

Current source LCC resonant converter for an EDM power supply

In this paper, the design of a low size power supply prototype for electrical discharge machining is presented. The system is a DC to DC LCC resonant converter whose switching frequency is tuned at the natural resonant frequency where the converter tends to act as a current source. In this way, two effects are achieved: (1) the necessary over-voltage, first to ionize the dielectric and then to establish the electric arc is generated, and (2) a constant current is supplied during the erosion of the workpiece, providing the circuit with inherent protection under short circuit conditions. The output voltage is intended to be adjusted by an external system that controls the arc distance.

Output Current Sensitivity Analysis of the

The sensitivity analysis of the output current of the parallel-series resonant inverter is presented with the objective of including the analysis of component tolerances in the design criteria of current-source resonant inverters. The effects of the tolerance of circuit elements in the parallel-series (LCpCs) resonant inverter are studied to optimize the design parameters that ensure the circuit performance with minimum deviation of the operating point, i.e., minimum control action or even no feedback, and also good repeatability. The analysis shows that the capacitor ratio affects the sensitivity values. Conclusions are confirmed with experimental results and a statistical study by the Monte Carlo method