Search

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. Index Terms--Acoustic resonance, digital control, dimming control, low-frequency square-wave (LFSW) converter, metal halide (MH) lamps, resonant ignition.

A generalized study of the parallel connection of N Class-D parallel resonant (L[C.sub.p]) inverters is presented. Steady-state analysis and design considerations are provided in detail, evaluating the current distribution, output power and efficiency of the circuit as a function of the number, N, of phases. Inductor equivalent series resistance and MOSFET conduction losses are considered in order to foresee and optimize the inverter efficiency. The power supplied to the load can be controlled at constant switching frequency by using the phase displacement of the output voltages of each Class-D leg, although for the interests of this specific application, only one inverter is phase shifted. The applicability of the general analysis is demonstrated on two practical designs with three and five phases, resulting in 400-W and 1-kW high-pressure sodium lamp ballasts, respectively. Index Terms--Conduction losses, electronic ballast, high efficiency, high-power applications, high-pressure sodium (HPS) lamps, mnltiphase parallel resonant inverter, resonant inverters.

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 (L[C.sub.p] [C.sub.s]) 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. Index Terms--Current-source mode, Monte Carlo method, resonant power conversion, sensitivity analysis.

This paper presents the analysis and design method of a new configuration of resonant inverter suitable for high-intensity discharge (HID) lamp ballast applications. The proposed inverter results from the parallel connection of four class D L[C.sub.p] resonant inverters, sharing the total load current. In this way, the conduction losses are reduced and high frequency operation is achieved for high power lamps. The power control is implemented at constant frequency, modifying the phase displacement among the output voltages of each inverter section. Considering that the deviation of the operation point caused by the control action deteriorates the converter efficiency, this design guarantees minimum control action to correct the lamp power deviation caused by the lamp aging. A 600-W prototype has been built to validate the design proposal. Index Terms--High-intensity discharge (HID), high-pressure sodium (HPS).

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. Index Terms--Dimming, electronic ballast, lighting, power factor correction (PFC).

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. Index Terms--High intensity discharge (HID), high pressure sodium (HPS).

This paper presents a new criterion for the design of resonant inverters for driving high-intensity-discharge (HID) lamps. The proposed converter behaves almost as a power source, for a wide load range, regardless of the lamp aging. In order to achieve good repeatability, the analysis of lamp power sensitivity regarding the tolerance of the circuit components is carried out. The design is validated with experimental results and a statistical simulation by the Monte Carlo method. Index Terms--Electronic ballast, lighting, power source, resonant inverters, sensitivity study, tolerance analysis.

The L[C.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. Index Terms--Electrical discharge machining (EDM) power supply, switching frequency.

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 L[C.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. Index Terms--Dimming, electronic ballast, lighting, power-factor correction.

The aim of this paper is to incorporate the analysis of component tolerance in the design criteria of resonant inverters applied to the control of high-pressure sodium (HPS) lamps. This method may also be considered for metal halide (MH) lamps. The design accepts a large load variation without exceeding the lamp power limits given by the standard. The analysis is focused on the selection of the most suitable value of the resonant network in order to achieve a good repeatability of the circuit performance. The study is based on the analysis of the lamp power sensitivity regarding the lamp aging and the tolerance of the circuit components. The proposed design is validated with experimental results and a statistical study by the Monte Carlo method. Index Terms--Electronic ballast, lighting, sensitivity study, series-parallel resonant inverters, tolerance analysis.

The study of the stability of frequency sources is a matter of major interest due to the evolution of communication and instrumentation systems resulting in increasing the number of channels in a limited spectrum, and reducing size and power consumption. The paper relates laboratory experiences that explain the behavior versus temperature of thickness-mode quartz crystal resonators (AT- and SC-cut crystals) that are applied to the control of frequency sources, and the performance of digital compensation techniques. Prototypes of Microcomputer-Compensated Crystal Oscillators (MCXO's) have been developed to compare the compensation performance using the resonator as the temperature sensor against the use of an external sensor and verify the reduction of compensation errors due to thermal lags and hysteresis. The design of a CMOS integrated circuit for the MCXO is also included. A frequency correction method that does not modify the crystal resonance has been implemented in the circuit. This allows sensing the temperature by means of the crystal and improving its long-term stability (aging). A new frequency comparator is also introduced. Its aim is to obtain the difference between two very close frequencies at its output, without being affected by the phase variations that the new frequency correction method and the digital circuit introduce. This detector has been implemented to get a high-resolution thermometric frequency and to realize a frequency-locked loop that includes a crystal controlled local oscillator, allowing the use of the MCXO as good short-term stability source.

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. Index Terms--Electronic ballast, high-pressure sodium lamps, lighting, series-parallel resonant inverters, soft startup.