Mario Marchesoni

Diode-clamped multilevel converters: a practicable way to balance DC-link voltages

The converter topologies identified as diode-clamped multilevel (DCM) or, equivalently, as multipoint clamped (MPC), are rarely used in industrial applications, owing to some serious drawbacks involving mainly the stacked bank of capacitors that constitutes their multilevel DC link. The balance of the capacitor voltages is not possible in all operating conditions when the MPC converter possesses a passive front end. On the other hand, in AC/DC/AC power conversion, the back-to-back connection of a multilevel rectifier with a multilevel inverter allows the balance of the DC-link capacitor voltages and, at the same time, it offers the power-factor-correction capability at the mains AC input. An effective balancing strategy suitable for MPC conversion systems with any number of DC-link capacitors is presented here. The strategy has been carefully studied to optimize the converter efficiency. The simulation results related to a high-power conversion system (up to 10 MW) characterized by four intermediate DC-link capacitors are shown.

New DC–DC Converter for Energy Storage System Interfacing in Fuel Cell Hybrid Electric Vehicles

The use of energy storage devices such as batteries or supercapacitors is almost mandatory in fuel cell hybrid electric vehicles, in order to guarantee load leveling, assuring braking energy recovery and good performances in transient operations. To this end, converters with bidirectional power flows are needed to connect the accumulators to the dc-link of the motor drive system. In this paper, a new conversion structure for the bidirectional interfacing of two dc voltage sources with a higher voltage dc-link is presented, where only three controllable power electronic switches are needed and where the only limit is that the sum of the two dc voltages must be lower or equal than the motor drive dc-link voltage. The analysis of the converter structure, the control and modulation systems that have been developed, and simulations and experimental results are reported

Multilevel Converter for Traction Applications: Small-Scale Prototype Tests Results

In ac-supplied traction systems (e.g., 15 kV, 16.7 Hz), the energy supplied by a conventional transformer results in large volume, high weight, and relatively low efficiency. In this paper, an ac-dc multilevel converter is presented that allows the use of a medium-frequency transformer in the input section of a traction drive. The proposed solution seems particularly well adapted to the different requirements (volume, weight, EMC, losses) of the electric traction domain. The system is studied from a theoretical point of view, starting from the basic module up to the entire converter structure. Simulation results and reduced-scale (10-kVA four-stage converter) experimental results are presented.

Power conditioning system using sliding model control

A control system for power conditioning and uninterruptible power supply systems is presented. The design is based on the theory of variable-structure systems with sliding mode. Results of an analytical study and digital simulation of both the power and control systems are reported, showing good agreement. The high dynamics and the robustness of the implemented system, indicated by the simulation results, confirm the validity of the control scheme and suggest the possibility of adopting it for three-phase systems, variable frequency supplies, and measuring equipment.<<ETX>>

Speed Finite Control Set Model Predictive Control of a PMSM Fed by Matrix Converter

This paper presents a new speed finite control set model predictive control algorithm, which has been applied to a permanent-magnet synchronous motor driven by a matrix converter (MC). This method replaces the classical cascaded control scheme with a single control law that controls the motor currents and speed. Additionally, unlike classical MC modulation methods, the method allows direct control of the MC input currents. The performance of the proposed work has been verified by simulation studies and experimental results.

A new control strategy for neutral-point-clamped active rectifiers

A new control strategy has been developed for interfacing a neutral-point-clamped active rectifier with the mains. In particular, a method, based on the modulation of the input currents amplitudes, is proposed to compensate the dc-link capacitors voltages fluctuations. The proposed strategy gives good results in all the operating conditions, but it appears to be very useful especially in no-load or low-load operations, where other methods fail. Analytical, simulation, and experimental results, derived from a reduced-scale prototype, are presented and confirm the validity of the proposed approach.

A minimum-energy-based capacitor voltage balancing control strategy for MPC conversion systems

In AC/DC/AC power conversion, the connection of a multi point clamped (MPC) rectifier with an MPC inverter simplifies the balancing of the voltages on the series-connected DC link capacitors as well as giving input power-factor correction capability. This is only true provided that an alternative balancing PWM control strategy is adopted instead of the standard PWM one. A control strategy is proposed which is based on the development of an energy function which may be minimized in real time by exploiting the existing redundancies in power-converter switching states. This strategy may be easily implemented in a DSP controller and is usable with any number of voltage levels and input/output phases. A validation has been performed by simulating a 5-level 3-phase MPC system and the significant waveforms are presented.

AC locomotive conversion systems without heavy transformers: is it a practicable solution?

All actual AC locomotives have an onboard line transformer to reduce line voltages to levels suitable to power electronic devices and to guarantee galvanic insulation to the on board equipment. Unfortunately, such a transformer is heavy, expensive and represents one of main reasons why traction vehicles often exceed the targets for weight and dimensions. Two innovative conversion systems have been studied, which permit the use of transformers of greatly reduced size. Suitable control and modulation techniques have been also developed, and some simulation results are presented. In addition, a further analysis has been carried out to allow a fair comparison between one of the two innovative loco electrical drive systems and a conventional one, taking into account their reliability performances. Some important achievements are shown and the complete set of the results is presented and discussed.

About the DC-link capacitors voltage balance in multi-point clamped converters

The multi-point clamped converter (MPCC) represents an interesting technical solution to overcome the limitations in voltage and power posed by the existing semiconductor devices. However, if real power must be delivered to the load, DC-link capacitors exhibit a problematic voltage unbalance, that can be faced in both active or passive ways, that is, by using or not using additional components. Both approaches can be used together, in order to optimize the system performances. The authors have analyzed this problem from an analytical point of view and have developed a modulation control strategy that exploits the inherent redundancy in switching configurations to achieve a correct voltage sharing, in the case of a MPCC with four DC-link capacitors. The results obtained are presented and discussed in a critical way and they are correlated to the case where an active rectifier is used as an input stage to achieve near unity power factor and capacitors voltage balance.

A microcontroller-based sensorless stator flux-oriented asynchronous motor drive for traction applications

A sensorless stator flux-oriented asynchronous motor drive has been realized by using a low-cost single-chip microcontroller. A motor state observer has been implemented, which showed excellent performances, particularly at low-speed operation. Two different experimental realizations have been developed, with rated powers equal to about 1.5 and 30 kW, respectively, and good results have been obtained in both cases. The theoretical approach, main design choices, and most significant experimental results are presented.