Saverio Bolognani

Design and Implementation of Model Predictive Control for Electrical Motor Drives

This paper deals with a model predictive control (MPC) algorithm applied to electrical drives. The main contribution is a comprehensive and detailed description of the controller design process that points out the most critical aspects and also gives some practical hints for implementation. As an example, the MPC is developed for a permanent-magnet synchronous motor drive. Speed and current controllers are combined together, including all of the state variables of the system, instead of keeping the conventional cascade structure. In this way, the controller enforces both the current and the voltage limits. Both simulation and experimental results point out the validity of the design procedure and the potentials of the MPC in the electrical drive field.

Rotor Flux-Barrier Design for Torque Ripple Reduction in Synchronous Reluctance and PM-Assisted Synchronous Reluctance Motors

The torque produced by a synchronous reluctance machine (including the permanent-magnet-assisted machine) is studied analytically, with the aim of pointing out the effect of the position of the flux barriers on the torque ripple. It is verified that the position of the flux-barrier ends highly influences the torque waveform. With the aim of reducing torque harmonic contents, a new strategy is proposed based on the choice of couples of flux barriers of different shapes. The flux-barrier geometry is chosen so as to obtain a compensation between the torque harmonics produced by each couple. Experimental results on two prototypes confirm the analytical prediction.

A Distributed Control Strategy for Reactive Power Compensation in Smart Microgrids

We consider the problem of optimal reactive power compensation for the minimization of power distribution losses in a smart microgrid. We first propose an approximate model for the power distribution network, which allows us to cast the problem into the class of convex quadratic, linearly constrained, optimization problems. We then consider the specific problem of commanding the microgenerators connected to a microgrid, in order to achieve the optimal injection of reactive power. For this task, we design a randomized, leader-less, gossip-like optimization algorithm. We show how a distributed approach is possible, where microgenerators need to have only a partial knowledge of the problem parameters and of the state, and can perform only local measurements. For the proposed algorithm, we provide conditions for convergence together with an analytic characterization of the convergence speed. The analysis shows that, in radial networks, the best performance is achieved when we command cooperation among microgenerators that are neighbors in the electric topology. Numerical simulations are included to validate both the proposed model and the analytic results about the performance of the proposed algorithm.

Innovative remedial strategies for inverter faults in IPM synchronous motor drives

Interior permanent magnet (IPM) synchronous motors are used extensively in many industrial drives, and the development of fault-tolerant control techniques may extend their use to applications where high reliability, also in the flux-weakening region, is a key-feature. This paper proposes some innovative fault-remedial control strategies for failures occurring in the drive voltage inverter.

Analysis of PM synchronous motor drive failures during flux weakening operation

Under flux weakening operation, the phase emf of a PM synchronous motor can be extremely high; this paper investigates the effects on currents, voltages and torque of different drive failures occurring under flux weakening operation, as a starting point for a successful design of an effective system protection and a fault-tolerant control.

Torque Harmonic Compensation in a Synchronous Reluctance Motor

The torque behavior of a synchronous reluctance motor [including the permanent magnet (PM) assisted configuration] is deeply analyzed. An analytical model is developed, showing the dependence of the torque ripple on the rotor geometry. The results of this model allow to individuate the position of the flux--barrier ends so as to minimize the torque ripple. In addition, the proposed strategy to minimize the ripple is not only based on a suitable choice of the flux--barrier ends, but this choice is combined with the adoption of a rotor formed by two different laminations. This strategy allows an optimal compensation of the torque harmonics so that a smooth torque is achieved. Some motor prototypes have been manufactured and tested in a suitable testing bench. The torque versus position characteristics have been measured at very low speed, to avoid a reduction of the high-order torque harmonics. The experimental results confirm the effectiveness of the proposed strategy.

On the Existence and Linear Approximation of the Power Flow Solution in Power Distribution Networks

We consider the problem of deriving an explicit approximate solution of the nonlinear power equations that describe a balanced power distribution network. We give sufficient conditions for the existence of a practical solution to the power flow equations, and we propose an approximation that is linear in the active and reactive power demands of the PQ buses. For this approximation, which is valid for generic power line impedances and grid topology, we derive a bound on the approximation error as a function of the grid parameters. We illustrate the quality of the approximation via simulations, we show how it can also model the presence of voltage controlled (PV) buses, and we discuss how it generalizes the DC power flow model to lossy networks.

Distributed Reactive Power Feedback Control for Voltage Regulation and Loss Minimization

We consider the problem of exploiting the microgenerators dispersed in the power distribution network in order to provide distributed reactive power compensation for power losses minimization and voltage regulation. In the proposed strategy, microgenerators are smart agents that can measure their phasorial voltage, share these data with the other agents on a cyber layer, and adjust the amount of reactive power injected into the grid, according to a feedback control law that descends from duality-based methods applied to the optimal reactive power flow problem. Convergence to the configuration of minimum losses and feasible voltages is proved analytically for both a synchronous and an asynchronous version of the algorithm, where agents update their state independently one from the other. Simulations are provided in order to illustrate the performance and the robustness of the algorithm, and the innovative feedback nature of such strategy is discussed.

Design of a Fault-tolerant IPM Motor for Electric Power Steering

This paper deals with the design of an interior permanent magnet (IPM) motor for power steering. Such an application requires an imperative fault-tolerant capability that is obtained by means of a redundant solution with two motors on the same shaft. A ball-screw system converts the rotating movement into the linear movement of the steering rack. In addition, the IPM motor has to exhibit very low braking torque after a short-circuit fault. Useful relationships between the maximum braking torque and the motor parameters are found and used in the design of the motor

Identification of power distribution network topology via voltage correlation analysis

We consider the problem of reconstructing the topology of a portion of the power distribution network, given a dataset of voltage measurements. By using an approximate model for the grid voltage magnitudes, we show that these signals exhibit some specific correlation properties, that can be described via a sparse Markov random field. By specializing the tools available for the identification of graphical models, we propose an algorithm for the reconstruction of the grid topology. Via simulations, we show how the algorithm performs well also when an exact nonlinear model of the grid voltages is adopted, when realistic power demand profiles are considered, and when the voltage measurements are affected by measurement noise.