Juan A. Martín-Ramos

Power Supply for a High-Voltage Application

In this paper, the guidelines to design a high-voltage power converter based on the hybrid series parallel resonant topology, PRC-LCC, with a capacitor as output filter are established. As a consequence of the selection of this topology, transformer ratio, and therefore secondary volume, is reduced. The mathematical analysis provides an original equivalent circuit for the steady-state and dynamical behavior of the topology. A new way to construct high-voltage transformers is also proposed, pointing out the advantages and establishing an original method to evaluate the stray components of the transformer before construction. The way to make compatible the characteristics of both, topology and transformer is illustrated in the frame of a practical application. To demonstrate the feasibility of this solution, a high-voltage, high-power prototype is assembled and tested with good performance and similar behavior to the one predicted by the models. Experimental results are shown on this particular.

Dynamic and Steady-State Models for the PRC-LCC Resonant Topology With a Capacitor as Output Filter

In high-voltage DC power supplies (hundreds of kilovolts), avoiding the inductance in the output filter is an important asset. Thus, a capacitor as a unique component of that filter is preferable. On the other hand, a high-voltage step-up transformer shows a high capacitance in its secondary, which can be included in a resonant stage. Both capacitances, i.e., one from the filter and the other from the transformer, are separated by the output rectifier. When this rectifier is on, they are in parallel; when it is off, they are disconnected. A resonant stage where a very large capacitor appears and disappears several times in one period is not linear and has not been dynamically modeled before. This paper shows two simple models for the parallel-series (LCC-type parallel resonant converter) resonant topology with a capacitor as output filter. Its dynamics and steady state are studied and constitute an important help for any designer.

An Online and Noninvasive Technique for the Condition Monitoring of Capacitors in Boost Converters

Capacitors usually determine the overall lifetime of power converters since they are mainly responsible for breakdowns. Their failure results from the deterioration of their dielectric, the production of gases, and, eventually, their explosion. This process leads to an increase in the capacitor equivalent series resistance (ESR) and a decrease in its capacitance value for both electrolytic and metalized polypropylene film (MPPF) capacitors. In this paper, a novel noninvasive technique for capacitor diagnostic in Boost converters is presented. It can easily be applied online and even in real time, and it is suitable for the operation in both continuous current mode (CCM) and discontinuous current mode (DCM). The technique is based on the double estimations of the ESR and the capacitance, improving the diagnostic reliability. This way, predictive maintenance is provided, and it is possible to alarm for capacitor replacement, avoiding downtime. As the method is intended for railway high-power applications, it has been conceived neither to add any additional hardware in the power stage nor to even slightly modify it. To demonstrate and validate the effectiveness and accuracy of the proposed technique, several simulations and experimental results are discussed in a small prototype. In this prototype, the software for real-time estimation is programmed in a low-cost digital signal processor (DSP).

Intelligent and universal fast charger for Ni-Cd and Ni-MH batteries in portable applications

In this paper, a new fast charger is presented for Ni-Cd and Ni-MH batteries, which are the most frequently used in portable applications. In this charger, the control and supervision of the process has been entrusted to a microcontroller, which provides a powerful and intelligent tool to undertake complex tasks, and reduces the requested circuitry to the microcontroller itself and a few additional components. The resulting charger is able to work out the initial battery state (detecting deteriorated devices), decide the suitable way to charge it (ensuring a long cyclic life), and determine when the charge process must be finished. This way, the state of the battery is always controlled, preventing any damage to it and providing a fully protected operation mode. This paper summarizes the design and construction of the presented charger, as well as shows the experimental results obtained in the prototype tests.

Small-Signal Modeling of Discharge Lamps Through Step Response and Its Application to Low-Frequency Square-Waveform Electronic Ballasts

In this paper, a simple method to obtain the small-signal model of discharge lamps, and particularly metal halide (MH) lamps, is proposed. A dc voltage source with a series resistor is used to supply the lamp at the required power level. Then, the lamp response against an input voltage step transient is analyzed. From this analysis, the parameters of the equivalent lamp model can be calculated. The proposed method allows obtaining the lamp model in a straight manner from a single test. With this technique, a 35-W MH lamp is modeled at two different power levels. A validation circuit, which includes a resistive ballast and a capacitance, is analyzed to evaluate the possibilities of the proposed modeling technique. The obtained experimental results are in good agreement with the theoretical analysis. The derivation of a time domain lamp model for SPICE-based computer simulators is also introduced. Finally, an example of application in low-frequency square-waveform electronic ballasts is presented

A new control strategy for an AC/DC converter based on a piezoelectric transformer

Piezoelectric transformers (PTs) are an attractive solution to reduce size and weight in ac/dc converters. In this paper, a PT-based topology is presented together with a control method. As an application, an 8-W ac/dc adapter (110 V/sub AC/ input, 12 V/sub DC/ output) is presented operating at frequencies around 500 kHz.

Multiple output AC/DC converter with an internal DC UPS

The usual way to avoid a computer shutdown during a mains failure is to connect an ac uninterruptible power system (UPS). However, there are other possibilities, such as using a dc UPS to obtain the dc output voltages directly from the battery instead of generating an ac voltage to feed the whole power supply. Thus, the topology must operate either from the ac mains or from a battery. A complete design of an ac/dc power supply with an internal dc UPS is presented in this paper. The solution is based on the coupling of the UPS to the main transformer. Moreover, the power supply meets all the requirements needed to be used as an Advanced Technology eXtended (ATX) PC power supply-multiple outputs, power and voltage ratings, size, protections, etc. A prototype has been fully developed and tested as a PC power supply. The autonomy achieved at full power is around 7 minutes.

A new full-protected control mode to drive piezoelectric transformers in DC-DC converters

Due to their high power density and their low EMI generation, piezoelectric transformers (PTs) are an attractive solution to replace magnetic transformers in AC/DC power converters. However, this substitution implies changes in the power topology and the control strategy because of the very frequency-dependent behavior of PTs, and their capacitive features. In previous works, some power topologies have been presented to deal with this new component, and frequency modulation has been assumed as the natural way to control the output voltage, sometimes in combination with pulse width modulation (PWM), to achieve both line and load regulation. In the frame of a particular application, this paper presents a new control method for PT-based converters. This control method is very simple to design, requires very few components and regulates the output voltage maintaining constant the frequency and the pulse width, trying to obtain the best characteristics from the piezoelectric device.

A modular PV regulator based on microcontroller with maximum power point tracking

We can find many different types of commercial regulators in the market, these devices basically can be divided into two categories according to their operation mode: The first ones modulate the input voltage with PWM (pulse width modulation) to hold the constant voltage in the output necessary to charge the battery. The other ones operate in the MPP (maximum power point) of the PV (photovoltaic) array, tracking it by different ways depending on the type of regulator; these regulators are called MPPTs (maximum power point trackers). The increase of power using a maximum power point tracker can be up to 25%. This paper presents a regulator which can operate in the maximum power point of PV arrays regardless of the meteorological conditions and the effects of them in the dispersion of the PV array characteristics. Parallel connection of this kind of regulators is also proposed, which allows installation without the need to get rid of previous equipment.

Condition Monitoring of Metallized Polypropylene Film Capacitors in Railway Power Trains

A novel technique for monitoring the condition of metallized polypropylene film (MPPF) capacitors installed in the dc link of railway power trains is proposed in this paper. The technique is based on the capacitance estimation of the two different capacitors used in the dc link (dc filtering and 2F filter capacitors), and it is done without adding any extra sensor or filter to the respective traction drive scheme. Therefore, the proposed method is implemented using software but not additional hardware for the different trains. Two other important passive component parameters of the traction drive are also monitored, all of them by means of curve fitting based on the least-mean-square (LMS) algorithm. The proposed technique is implemented and validated at simulation and experimental levels, using MATLAB/Simulink and a 1.2-MW traction drive test bench. Very accurate results are obtained, and the predictive maintenance of MPPF capacitors for different topologies of railway power trains can be set through the proposed technique.