Christian Brañas

Solid-State Lighting: A System Review

T his article presents the background on the development of solid-state lighting technology, which is gaining popularity as a light source application. This review focuses on the main characteristics of solid-state lighting devices as well as their supply requirements and the effect of temperature on light-emitting diode (LED) performance. LED drivers are designed to achieve the best operation conditions without degrading the longer lifetime that this technology achieves in comparison to other popular light sources. Offline LED drivers include active power factor correction while current control with low ripple is required to supply the LED units or string arrangements. Methods to achieve balanced current sharing on paralleled LED strings and some of the latest contributions on LED drivers are also explained.

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.

Contributions to the design and control of LC/sub s/C/sub p/ resonant inverters to drive high-power HPS lamps

This paper presents the design criteria for full-bridge series-parallel (LC/sub s/C/sub p/) resonant inverters suitable for driving high-power high-intensity discharge lamps. By using the properties derived from the transfer functions of the inverter, a soft startup method is proposed. The lamp ignition is carried out maintaining the voltage and current variables below prefixed peak values, with the addition of no extra components to the power stage for this purpose. In steady-state operation, the proposed control minimizes the reactive voltamperes in the resonant tank. Moreover, the variation of the power delivered to the lamp, caused by the lamp aging, is limited in order to fulfil the standard. This design provides cost-effective circuits, simplifying the DC-AC power stage of an electronic ballast. The experimental results are given for high-pressure sodium lamps of the Sylvania SHP250W type.

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.

Design of Resonant Inverters for Optimal Efficiency Over Lamp Life in Electronic Ballast With Phase Control

The paper presents the design guidelines of phase controlled resonant inverters to drive high intensity discharge lamps. Considering the variation of the lamp resistance over its lifetime, the resonant phase is determined and the condition of minimum phase lag is imposed to minimize the current through the circuit. The optimum input voltage is analyzed according to phase lag, frequency variation, and control complexity. A design procedure is presented and experimentally validated with results from two electronic ballast designs operating from 300-V and 400-V dc bus and driving a 150-W high pressure sodium lamp

Experimental study of HPS lamp ignition by using LC network resonance

This paper presents a study of the HPS lamp behavior before ignition is achieved. The voltage generated by a LC network is applied to the lamp leads using the soft-start-up method. Modifications of the off state lamp equivalent resistance are observed when applying different ignition sequences. From the experiments, a breakdown characteristic is defined.

Power-Mode Control of Multiphase Resonant Electronic Ballast

A wide-bandwidth power-mode-controlled triple LCpCs resonant inverter is proposed for minimizing the light flicker caused by utility voltage fluctuation in industrial environments and compensating the dc bus ripple as an alternative rather than increasing the dc bus capacitance. To keep its efficiency, the inverter is controlled at a constant switching frequency by the phase displacement Ψ of the output voltage of one class-D section referred to the others. An approximate explicit form of the small-signal transfer function from the control angle Ψ to the output power is obtained by using a reduced-order model. This transfer function presents the main pole at a frequency high enough for the loop gain to exhibit wide bandwidth with a simple integral control action that compensates the voltage fluctuations in the frequency range where human perception is sensitive to light flicker. Experimental results are given using a 400-W high-pressure sodium lamp as the load.