Vito Giuseppe Monopoli

Design of H-bridge multilevel active rectifier for traction systems

This paper is focused on the design of the controller for a high voltage-high power single phase front-end rectifier stage, for a large electric drive designed for, but not limited to, traction field applications. The rectifier should absorb current with low harmonic content to eliminate disturbances on the communication equipments and more generally to reduce environment electromagnetic pollution. Additional specification is the elimination of the heavy and bulky transformer to reduce encumbrances and cost. A multilevel H-bridge single phase configuration has been chosen. In this paper, the design has been fully investigated with the help of theoretical analysis and simulations.

A passivity-based multilevel active rectifier with adaptive compensation for traction applications

The control of a single-phase multilevel H-bridge rectifier suitable for traction applications is considered. Such a converter often presents instability problems making difficult its design and uncertain its behavior. In this paper the use of a passivity-based controller is experimentally investigated. Such a controller achieves stability, unity power factor, good balancing between the two DC links, and satisfactory behavior even in the presence of load changes. A right choice of the damping parameters allows the fulfilling of system requirements in terms of DC-link voltage error and grid current distortion.

Predictive Current Control for Multilevel Active Rectifiers With Reduced Switching Frequency

In this paper, a new low-frequency predictive current control is proposed for a single-phase cascaded H-bridge multilevel rectifier. The control method has been fully investigated with theoretical analysis, simulation, and experiments on a laboratory prototype with five series-connected H-bridges. However, the analysis and technique are valid for any general level structure. The simulations and experimental results presented demonstrate the excellent performance of the predictive control in terms of AC current waveform quality, power factor, and reduced switching frequency of each bridge, in comparison to traditional control schemes.

An energy-based control for an n-H-bridges multilevel active rectifier

This paper deals with the control of a multilevel n-H-bridges front-end rectifier. This topology allows n distinct dc buses to be fed by the same ac source offering a high loading flexibility suitable for traction applications as well as for industrial automation plants. However, this flexibility can lead the system to instability if the dc buses operate at different voltage levels and with unbalanced loads. Thus, linear controllers, designed on the basis of the small-signal linearization, are not effective any longer and stability can not be ensured as large-signal disturbances occur. The use of a passivity-based control (PBC) designed via energy considerations and without small-signal linearization properly fits stability problems related to this type of converter. The system has been split into n subsystems via energy considerations in order to achieve the separate control of each dc bus and its stability in case of load changes or disturbances generated by other buses. Then, a set of n passivity-based controllers (one for each subsystem) is adopted: the controllers are linked using dynamical parameters computed through energy balance equations. Hence, the system dc buses are independent and stable as experimental results demonstrate.

Overview of PI-based solutions for the control of the dc-buses of a single-phase H-bridge multilevel active rectifier

The H-bridge-based multilevel active rectifier is an attractive topology that allows feeding of multiple dc loads. The main control problem is to manage state variables (one current plus dc voltages) with only switching functions. In this paper, three PI-based solutions are discussed, and the tuning of the best solution is addressed in case resonant controllers are used instead of classical integrators. Moreover, practical problems such as the implementation and the influence of phase-locked-loop systems and of analog filters (first order and Butterworth) on the measurements are discussed.

Comparison of power converter topologies for permanent magnet small wind turbine system

Permanent magnet based wind generators are one of the more promising technology. This paper presents a comparison of power converter topologies for permanent magnet small wind turbine systems to improve the power quality and to extract the maximum power from wind. Two detailed models are presented and explained: the first configuration is made by a diode-bridge rectifier, a boost converter and an inverter connected to the grid, the second configuration is a back-to-back converter. The generator control is designed to maximize the power output and achieve a smooth torque and power profile. The operational characteristics of the two configurations are investigated through simulations.

Multilevel Phase-Shifting Carrier PWM Technique in case of Non-Equal dc-Link Voltages

This paper analyzes the phase-shifting carrier PWM techniques in case of multilevel cascaded H-bridges with non-equal DC-link voltages. In the past it has been demonstrated that these techniques succeed in cancelling the sideband harmonics in the produced multilevel voltage only if the DC-link voltages are equal. Two different approaches can be used to modulate the reference signal in multilevel converters when the DC-link voltages are different and in a non-integer ratio: the theory of symmetric polynomials and resultants, and the generalized hybrid modulation (GHM) technique, which extends the hybrid modulation technique to non-integer DC-link ratio. This paper extends the original PSC-PWM technique proposing a method to obtain the proper shifting angles in view of reducing the overall output voltage WTHD under every possible de-link voltages. The proposed new approach is compared, in simulation with the original phase-shifted cascaded multilevel technique

Design of a back-to-back multilevel induction motor drive for traction systems

This paper deals with the design of a single phase AC/DC/AC converter feeding an induction motor for traction applications. A cascade of H-bridge cells has been used to obtain a multilevel conversion structure. The front-end rectifier should absorb current with low harmonic content to eliminate disturbances on the communication equipments and, more in general, to reduce electromagnetic pollution. Additional specification is the elimination of the transformer such as to reduce encumbrance and cost. A similar H-bridge cascade has been used in the motor side. In fact, supplying the motor by multilevel voltages greatly reduce the current harmonic distortion, enhancing induction motor performance, and the switching frequency, improving efficiency and extending component life. In this paper the design of the converter has been described with the help of theoretical analysis and simulations, moreover some first partial experimental results are also shown.

Fuzzy controlled active filter driven by an innovative current reference for cost reduction

The aim of this work is to minimize the active power filters prime and operating costs by the means of a new current reference. Such a current reference is able to share the responsibilities in power quality deterioration between supply and customer, making the filter to deliver a current with a lower harmonic content, which means a lower power delivered and a lower switching frequency. The use of fuzzy logic may be helpful to achieve a good current control since this approach allows a control action to be carried out independent of electrical parameters. Fuzzy control has been designed in order to have different direct actions in each critical point of reference waveform using the nonlinear input-output mapping.

Passivity-Based Control by Series/Parallel Damping of Single-Phase PWM Voltage Source Converter

This paper describes a detailed design procedure for passivity-based controllers developed using the Brayton-Moser (BM) framework. Several passivity-based feedback designs are presented for the voltage-source converter, specifically for the H-bridge converter, since nowadays it is one of the preferred solutions to connect direct current (dc) loads or distributed sources to the alternating current (ac) grid. Independent of the operating mode, namely, the rectifier and regenerative operating mode, the achieved control aims are: high power factor correction in the ac-side and optimal dc voltage regulation capability in the dc-side. The proposed controllers can use series or parallel damping-based solutions for the error dynamics, naturally providing the conditions for stability and tuning of control parameters. In addition, the BM structure facilitates the addition of virtual resistance-inductance-capacitance (RLC) filter circuits to the control design for the rejection of low frequency harmonics. The effectiveness of series/parallel damping is investigated in case of abrupt changes in the load, using conductance estimators. Simulation and experimental results validate the analysis.