M.M. Hernando

Different Purpose Design Strategies and Techniques to Improve the Performance of a Dual Active Bridge With Phase-Shift Control

This paper addresses the performance of the bidirectional Dual Active Bridge (DAB) converter. One of the advantages of the DAB is the possibility to achieve Zero Voltage Switching (ZVS) operation in all the switches of this converter. However, the ZVS operation range can be lost for light loads, especially if high voltage is required in at least one of the DAB ports and the phase-shift control is used to regulate the power processed by the converter. Theoretically simple averaged model is presented for the DAB converter. Using the study presented in this paper, the boundaries of ZVS operation can be easily evaluated. The proposed models and analysis of the ZVS boundaries allow the proposal and evaluation of two different design strategies with different purposes: on the one hand, increasing the ZVS operation range and, on the other, improving efficiency at full load. Moreover, some techniques are presented for increasing the ZVS operation range and improving the efficiency of the DAB at full load (both using phase-shift control) employing the aforementioned analysis to obtain certain design criteria and conclusions. Finally, the proposed models, design strategies and techniques to improve the performance of the DAB are experimentally tested using a 1kW prototype with input and output voltages of 48V and 400V, respectively.

An overall study of a Dual Active Bridge for bidirectional DC/DC conversion

The increase demand of an intermediate storage of electrical energy in battery systems, in particular due to the use of renewable energy, has resulted in the need of bidirectional DC/DC power converters with galvanic isolation. Uninterruptible Power Supplies (UPS), battery charging systems, photovoltaic equipment and auxiliary power supplies in traction applications are examples of some fields of application of this kind of converters. A Dual Active Bridge (DAB) bidirectional DC/DC converter is a topology with the advantages of decreased number of devices, soft-switching commutations, low cost, and high efficiency. The use of this topology is proposed for applications where the power density, cost, weight, and reliability are critical factors. In the present paper the steady-state analysis of the converter has been carried out, giving some guidelines for the design (considering soft switching limits and the amount of reactive current) and a small-signal model of the topology. Simulations and experimental results are also presented.

EMI Radiated Noise Measurement System Using the Source Reconstruction Technique

One of the requirements that electronics circuits must satisfy comprises conducted and irradiated noise specifications. Whereas conducted noise is well covered in the literature, radiated noise is not. Radiated noise regulations impose limits on the noise measured 3 or 10 m away from electronic equipment. These measurements are usually made in anechoic rooms, which are very expensive. Moreover, the measurement procedure is not a ldquoplug-and-playrdquo feature, but requires a strict measuring protocol. Once the electronic circuit has been tested, the designer remains ignorant of the source of the problem should the regulation not be met. Hence, the procedure to make an electronic circuit comply with regulations is usually one of trial-and-error, in which the experience of the designer is essential. A new radiated noise measurement technique is proposed in this paper with a twofold objective: to simplify the measurement procedure and to obtain more information about noise sources. The main idea is to scan the electric/magnetic field at two arbitrary although known distances. From these measurements, the source reconstruction technique enables the identification of the noise sources in the surface of the circuit and the field estimation at any distance and the assessment of compliance with regulations. Moreover, if regulations are not met, the effect of modifying the noise source can be tested in order to ascertain how the circuit should be modified to comply with regulations.

Single Stage Inverter for a Direct AC Connection of a Photovoltaic Cell Module

There are several possibilities to transfer the energy taken from a photovoltaic cell to the grid. In the past, several cell modules used the same centralized inverter to transfer the energy to the grid. Nowadays, decentralized modules are preferred because of their versatility to harvest a larger amount of power, even when some of the modules of the total surface are covered and do not receive the same solar irradiation. This paper presents an inverter topology that can be used to connect a photovoltaic cell module directly to the grid. The inverter is based on a single stage Flyback topology and it is quite simple. Furthermore, a maximum power point tracking algorithm is proposed. The system can be implemented in a very simple microcontroller and the output current, although it is not sinusoidal, its harmonic content is lower than the limit imposed by IEC 61000-3-2 regulations. A prototype of the topology has been built and tested.

Steady-State Analysis and Modeling of Power Factor Correctors With Appreciable Voltage Ripple in the Output-Voltage Feedback Loop to Achieve Fast Transient Response

The classical design of an active power factor corrector (PFC) leads to slow transient response in this type of converter. This is due to the fact that the compensator placed in the output-voltage feedback loop is usually designed to have narrow bandwidth to filter the voltage ripple of twice the line frequency coming from the PFC output. This feedback loop is designed with this filtering effect because a relatively high ripple would cause considerable distortion in the reference of the line current feedback loop, and hence in the line current. However, the transient response of the PFC can be substantially improved if the bandwidth of this compensator is relatively wide, thus permitting certain distortion in the line current that leads to a tradeoff between transient response (and hence voltage ripple at the output of the compensator) and harmonic content in the line current. As a consequence of the voltage ripple at the output of the compensator (which is considered the control signal), both the static and the dynamic behaviors of the PFC change in comparison with the standard case, i.e., with no voltage ripple on the control signal. The static behavior of a PFC with appreciable voltage ripple in the output-voltage feedback loop is studied in this paper using two parameters: the amplitude of the relative voltage ripple on the control signal and its phase lag angle. The total power processed by the PFC depends on these parameters, which do not vary with the load and which determine the total harmonic distortion and the power factor at the input of the PFC. Furthermore, these parameters also determine the maximum power that can be processed by the converter while still complying with EN 61000-3-2 regulations for Class A and Class B equipment. When the converter comply with the aforementioned regulations for Class C or Class D equipment, however, the compliance does not depend on the power processed by the PFC. In the case of Class C equipment, not all the possible combinations of the relative ripple of the control signal and its phase lag angle manage to comply with these regulations. Finally, the study was verified by simulation and in a real prototype.

Input current shaper based on the series connection of a voltage source and a loss-free resistor

A new input current shaper is proposed in this paper. The operating principle is based on the connection of a voltage source and a loss-free resistor (LFR) between the input rectifier and the bulk capacitor in a conventional switching mode power supply with no power-factor correction. Both the voltage source and the LFR are obtained as an additional output from the converters transformer. This additional output is a forward-type one with one extra inductor. With the final topology, a good tradeoff between capacitor voltage, recycling energy, and harmonic content can be established in order to comply with IEC 1000-3-2 specifications.

A new input current shaping technique using converters operating in continuous conduction mode

A new input current shaping technique has been proposed. Its operating principle is based on the connection of an additional DC output, obtained from the converters transformer, between the input rectifier and the bulk capacitor in a conventional switching-mode power supply with no power factor correction. This additional output is a forward-type one with one extra inductor, which provides an effective duty cycle modulated by the input current. Thus, the voltage-current characteristic of this output consists of a voltage source and a loss-free resistor, connected in such a way that they help the diodes of the line rectifier to conduct. The main difference with other input current waveshapers lies in the fact that the filter inductor of the additional output operates in continuous conduction mode. Thus, the current stress in the power transistor is minimized. With the final topology, a good trade-off between bulk capacitor voltage, re-cycling energy, power factor and harmonic content can be established in order to comply with the IEC 1000-3-2. Many aspects in the design and operation of this type of converter are analyzed in this paper.

Very efficient two-input DC-to-DC switching post-regulators

A study of the two-input post-regulators is carried out in this paper. In these post-regulators, only a part of the total power undergoes a switching conversion process, whereas the remainder of the power comes up to the load directly, with no power conversion process. Due to this fact, very high efficiency is achieved. Moreover, the stress in the semiconductors and the filter size are both much lower than in standard post-regulators. Two-input post-regulators require two-output main converters. However, many converter topologies can be easily adapted to supply two output voltages with no efficiency penalty. Two-input post-regulators can be used in many power converters. Multiple-output DC-to-DC converters and AC-to-DC power factor correctors are two good examples.

Simplified Voltage-Sag Filler for Line-Interactive Uninterruptible Power Supplies

There are three types of static uninterruptible power supplies (UPSs): passive standby, line interactive, and double conversion. The last one protects the load against all types of line disturbances, but it is the most expensive and the one with the lowest efficiency. On the other hand, passive-standby and line-interactive UPSs have higher efficiency and lower cost, but they show an important drawback: a switching time from normal to stored-energy mode. As a consequence, there is a notch in the UPS output voltage during this switching time. In a previous paper, the authors proposed a method for filling these voltage notches with a sinusoidal waveform generated by a switch-mode converter. In this one, a simplified notch filler is proposed. It consists of two capacitors, one charged with positive voltage and the other with negative voltage. If the fault occurs in the positive period, the positive-charged capacitor is connected to the load. This connection is then modulated in order to obtain a sinusoidal waveform at the load. In the negative period, the other capacitor is used in the same way.

On the Use of the Source Reconstruction Method for Estimating Radiated EMI in Electronic Circuits

Electromagnetic interference (EMI) regulations are a very important issue in the design of almost any electronic circuit. Over the years, “cut-and-try” procedures have been adopted by electronic designers to make circuits comply with these regulations, mainly due to the lack of reliable theoretical models of radiated noise and clear design rules. To gain new insight into this field, a novel approach is presented in this paper based on a well-known technique in the field of antenna design, i.e., the source reconstruction method (SRM). Its application allows a set of equivalent currents to be obtained that behave exactly like the circuit under consideration with regard to radiated noise. From these currents, magnetic and electric radiated fields can be obtained at any point in space, even at 3 or 10 m away from the circuit where the regulations must be met. Moreover, the equivalent currents accurately represent noise sources in the circuit, thus permitting the elements responsible for generating radiated noise to be located. The aforementioned method would enable designers to reduce the use of anechoic-chamber facilities when testing their designs, thereby leaving the chamber only for final certification purposes.