G. Scarcella

A Novel Converter System for Fuel Cell Distributed Energy Generation

To interface the fuel cells (FCs) to grid/loads a DC/AC energy conversion system is required with the capability to act as an energy buffer for matching generator-load dynamics. A new power converter design is proposed based on cascade connection of a DC/DC and a DC/AC converter. The DC/DC converter has to control the FC current ripple and regulate the power flow from the FC. It is characterized by only two main switches of low side type, operated with an interleaved control technique which requires the use of two boost inductance chokes. Such a control strategy provides input current ripple cancellation, which is mandatory in fuel cell systems. A regenerative active clamp circuit is also used in order to prevent high peak voltages on the two main switches, maintaining a high efficiency. The proposed DC/DC converter is tested on a laboratory prototype and represents a new cost effective topology, able to operate under a wide range of input voltages and load conditions with high efficiency

Sensorless field oriented control using common mode currents

A simple sensorless field oriented control technique of an induction motor drive is presented, that estimates the angular frequency of the main flux from common mode currents. The proposed technique is effective at any load level and any speed, ranging from zero to rated value and beyond, in the flux weakening region. Moreover, no motor parameter estimation procedures are required, neither additional sensors, nor the availability of the motor neutral point. The consistency of the proposed technique is practically evaluated by experimental results obtained on a standard induction motor drive.

Zero frequency rotor position detection for synchronous PM motors

The paper presents a simple but effective approach to determine the position of the rotor in synchronous PM machines at any operating condition, including very low and zero speed. The proposed approach is based on the addition of a high frequency stator voltage component and on a demodulation of the zero sequence voltage. Compared to previous sensorless schemes, it allows zero speed operations, does not need any initial identification of the rotor position, and can be inexpensively implemented. Experimental tests are shown in order to practically confirm the expected features of the proposed system.

Induction motor sensorless control based on a maximum torque per ampere approach

The paper proposes a new position sensorless control approach for induction motor drives able to generate correct field orientation through continuous minimization of the stator current amplitude, holding the system in a maximum torque per ampere state. In such conditions an estimation of the angular position of the rotor flux, insensitive to rotor speed and motor parameter variations, is univocally carried out from the known angular position of the stator current. According to the proposed approach a sensorless field oriented control scheme with variable rotor flux amplitude has been developed featuring direct detection of the position of the rotor flux and working at very low stator frequency with no additional high frequency excitation. Experimental results are presented in order to evaluate the performance of the proposed approach in terms of dynamic response.

Sensorless Airgap Flux Position Estimation by Injection of Orthogonal Stationary Signals

A new method to compute the airgap flux position of induction motors at very low and zero stator frequency is presented that merges a sensorless third harmonic approach with the injection of a suitable pair of stationary sinusoidal stator voltage components. These two components feature different frequencies (245 and 135 Hz) and provide the machine with a permanent excitation that causes a modulation of the saturation level of the magnetic core according to the angular position of the airgap flux. As a result, the amplitude of the third harmonic of the stator voltage shows a ripple that contains information about the position of the airgap flux. Such a ripple includes two components having respectively the frequencies of the two injected signals and is demodulated using suitable filters and a closed loop state observer approach derived from the resolver to digital (R/D) conversion. The proposed technique is suitable to provide an estimation of the position of the airgap flux at zero speed using a relatively simple hardware, such that equipping standard constant V/f industrial drives or automotive electromechanical actuators

Energy management optimization in stand-alone power supplies using online estimation of battery SOC

With the aim to improve the energy management of battery packs in stand-alone power supply applications, a simple but effective model-based algorithm for battery state estimation has been developed. The method can be classified into the category of PI-based observers and exploits a Thevenin-based equivalent circuit to model the battery behavior associated with a simple start-up identification process. The algorithm provides a real-time accurate SOC estimation which can be used to evaluate the actual power capability and to predict the amount of energy flows in a long term time horizon. Moreover, useful information about battery aging such as SOH value can be obtained. Thanks to its straightforward implementation, the proposed algorithm can be conveniently integrated in the battery management systems of charge regulators and other power converters which are part of stand-alone power supplies. In such a way, it is possible to increase the harvested energy without increase the hardware requirements. A comprehensive validation has been carried out by performing several experimental comparisons between the battery state estimation performed by suggested approach and standard methods.

High frequency modeling of DC/AC converters

The paper proposes a new method to measure the high frequency (HF) current components in electronic converters and defines a model able to address the converter operation on a wide frequency range (100 kHz divide 30 MHz). The developed model is calculated by an automatic procedure that performs the measurements during the normal operations of the converter, instead of using HF circuital sub-models of the power devices, that are only related to the parasitic inner parameters, connection wires, and diodes. By this approach, the HF admittance of the converter is calculated taking into account the instantaneous switches configuration and, therefore according to the switching PWM strategy. The proposed dynamic HF model of the power converter is composed by several black boxes, each related to a single converter status or a groups of states with the same response. Each box acts differently to a HF voltage excitation, according to the number of devices that are contemporary on and off, while the converter is modulated. By knowing the PWM modulation strategy, the sequence of the states is unambiguous and therefore the model of the converter is entirely defined. Simulations and experimental results are presented in order to evaluate the consistence of the proposed approach

A single to three-phase converter for home appliances featuring four switches and an active power factor control

Three switch, unipolar power converters have been presented in the past with the aim to reduce cost and circuital complexity of induction motor drives for low power applications in household appliances or in the automotive field. However, such topologies to be of practical use, require an extra switch to control the voltage of the dump capacitor or special winding arrangements. Moreover, they generally require closed loop current and speed control. In the present paper a new converter topology is presented, aimed to equip household appliances, where the additional switch required to control the dump capacitor voltage is also exploited to improve the input power factor. Therefore, the presented topology is equivalent, from the point of view of the amount of power switches, to a true three switch unipolar converter with an active power factor control input stage. In addition, a simple constant V/f speed regulation is introduced thus avoiding expensive current and speed sensors. Finally, the proposed converter topology featuring only switches of the low side type, makes noticeably simpler the design of driver circuits and opens the perspective for a full integration of the converter power stage on a single chip, exploiting smart power technologies.