Frederik De Belie

Adding Inverter Fault Detection to Model-Based Predictive Control for Flying-Capacitor Inverters

In this paper a method for fault detection for flying capacitor multilevel inverters is presented. When a single-switch open circuit fault occurs in one of the power electronic switches, the proposed algorithm can detect the fault and the switch that is causing it. The analysis is performed on a linear resistive inductive load, used as a simple and comprehensive reference frame. The proposed algorithm is an extension of an already available finite-set model based predictive control algorithm. Therefore no extra hardware or measurements are required. The paper also discusses a suggested method for reconfiguration after fault detection. Computer simulation and experimental verifications validate the proposed methods.

Original article: A sensorless PMSM drive using modified high-frequency test pulse sequences for the purpose of a discrete-time current controller with fixed sampling frequency

For electrical machines, accurate position estimations at low speed can be obtained from current responses on high-frequency voltage test pulses. Nevertheless, to apply these voltage test pulses the current controller is often interrupted. In this paper, a modified test pulse sequence is discussed for which the current can be controlled without interruption. To generate the modified test pulse sequence, an asymmetric pulse-width modulator is required. The improvement in the dynamic behaviour of the sensorless drive is discussed by simulations including a salient-pole permanent-magnet synchronous machine, the current control loop, the pulse-width modulator and the position estimator.

Improved Dynamic Behavior in BLDC Drives Using Model Predictive Speed and Current Control

Model-based predictive control is a powerful control strategy to drive electrical machines. Conventional cascade proportional-integral (derivative) [PI(D)] controllers are often used to control speed, torque, and current. However, for low-inertia machines, achieving a high-performance and wide speed range is far beyond the application conditions for which these controllers are designed for. Using two cascaded PI(D) controllers for the speed/current control of a low-inertia machine, changes in the speed set point should be slowly applied in order to avoid stability problems. In this paper, a model predictive control algorithm that is able to control the speed of a low-inertia brushless direct-current machine with a high bandwidth and good disturbance rejection properties is proposed. The algorithm is implemented on a SPARTAN 3E 1600 field-programmable gate-array board, and experimental results verify the performance of the proposed algorithm.

Effect of Multilevel Inverter Supply on Core Losses in Magnetic Materials and Electrical Machines

The effect of multilevel inverter supply on power losses in magnetic cores and electrical machines is studied. A dynamic numerical model for the hysteresis, eddy current, and excess losses in a core lamination is first developed. By both measurements and simulations for a ring-core inductor, we demonstrate how increasing the number of inverter voltage levels decreases the iron losses when compared with traditional two-level supply. Although the switching frequency has a significant impact on the iron losses in the case of a traditional two-level inverter, using three or five voltage levels makes the losses almost independent of the switching. Finally, finite-element simulations show that similar reductions are also possible for the core losses of 150-kVA and 12.5-MW wound-field synchronous machines, in which rather low switching frequencies are typically used. Calorimetric loss measurements are also presented for the 150-kVA machine in order to confirm the significant effect of switching frequency on the core losses with two-level inverter supply.

The Efficiency of Hybrid Stepping Motors: Analyzing the Impact of Control Algorithms

Stepping motors are used in numerous applications because of their low manufacturing cost and simple open-loop position control capabilities. It is well known that their energy efficiency is low, although the actual efficiency values are generally not available. Moreover, the bulk of the stepping motors are driven in a non-optimal way, e.g., in an open loop with a maximum current to avoid step loss and, thus, with low efficiency. In this article, the impact of the control algorithm on the efficiency of the motor is analyzed, measured, and discussed. The basic open-loop full-, half-, and microstepping algorithms are considered together with a more advanced vector control algorithm. For each algorithm, the torque/current optimization is discussed.

A GENERAL DESCRIPTION OF HIGH-FREQUENCY POSITION ESTIMATORS FOR INTERIOR PERMANENT-MAGNET SYNCHRONOUS MOTORS

This paper discusses fundamental equations used in high-frequency signal based interior permanent-magnet synchronous motor (IPMSM) position estimators. For this purpose, an IPMSM model is presented that takes into account the nonlinear magnetic condition, the magnetic interaction between the two orthogonal magnetic axes and the multiple saliencies. Using the novel equations, some recently proposed motion-state estimators are described. Simulation results reveal the position estimation error caused by estimators that neglect the presence of multiple saliencies or that consider the magnetizing current in the d-axis only.

Field-Oriented Control for an Induction-Machine-Based Electrical Variable Transmission

An electrical variable transmission (EVT) is an electromagnetic device with dual mechanical and electrical ports. In hybrid electric vehicles (HEVs), it is used to split the power to the wheels in a part coming from the combustion engine and a part exchanged with the battery. The most important feature is that the power splitting is done in an electromagnetic way. This has the advantage over mechanical power splitting devices of reduced maintenance, high efficiency, and inherent overload protection. This paper gives a conceptual framework on how the torque on both rotors of the EVT can be simultaneously controlled by using a field-oriented control (FOC) scheme. It describes an induction-machine-based EVT model in which no permanent magnets are required, based on classical machine theory. By use of a predictive current controller to track the calculated current reference values, a fast and accurate torque control can be achieved. By selecting an appropriate value for the flux coupled with the squirrel-cage interrotor, the torque can be controlled in various operating points of power split, generation, and pure electric mode. The conclusions are supported by simulations and transient finite-element calculations.

A Comparative Study of the Effect of Different Converter Topologies on the Iron Loss of Nonoriented Electrical Steel

In this paper, a comparative study of the effect of different converter topologies on the iron loss of nonoriented electrical steel is presented. Three converter topologies are considered in this investigation; namely: two-, three-, and five-level power converters. Moreover, the effect of the carrier frequency on both the iron loss and converter loss is introduced. The experimental results show a dramatic increase of the iron loss for the two-level converter, especially for low levels of the carrier frequency. Furthermore, the increase of the iron loss is negligible for the multilevel converter topologies. Specifically, the use of the five-level converter, even at a low value of the carrier frequency, results in lower iron losses than the three-level converter at a relatively higher carrier frequency.

Torque Analysis on a Double Rotor Electrical Variable Transmission With Hybrid Excitation

An electrical variable transmission (EVT) can be used as a power splitting device in hybrid electrical vehicles. The EVT analyzed in this paper is a rotating field electrical machine having two concentric rotors. On the outer rotor, permanent magnets (PMs) are combined with a dc-field winding, being the first implementation of its kind. The magnetic field in the machine as well as the electromagnetic torque on both rotors are a function of the q- and d-axis currents of the stator and inner rotor, as well as the dc-field current. To describe and fully understand this multiple-input multiple-output machine, this paper gives an overview of the influence of the different current inputs on the flux linkage and torque on both rotors. Focus is given to the hybrid excitation in the d-axis by combining the dc-field current and the alternating currents. This has the advantage compared to other EVT topologies that unwanted stator torque can be avoided without stator d-axis current flux weakening. Results of the analysis are presented by means of the torque to current characteristics of a double rotor PM-assisted EVT, as well as the torque to current ratios. The machine characteristics are finally experimentally verified on a prototype machine.

Compensating the influence of the stator resistor and inverter nonlinearities in signal-injection based sensorless strategies

Among the sensorless position estimation methods in electrical machines drives, the injection of voltage test pulses is a promising strategy. Several papers are studying and applying this strategy, in particular for permanent magnet synchronous machine (PMSM) at low speed or standstill. Recently, an adaptive test pulses sequence reducing the current distortions has been proposed. However, the test pulses can be influenced by the voltage drops such as across stator resistor and semiconductor switches. By neglecting these voltage drops, the distortion in the current samples can not be fully reduced. In this paper, we improve the adaptive test pulses strategy by estimating and compensating the resistive drops. We also discuss the impact of the inverter nonlinearities. Finally, we present experimental results on a PMSM.