Joachim Druant

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.

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.

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.

An advanced multilevel converter topology with reduced switching elements

Smart grid applications, renewable energy utilization and electric vehicles (EVs) are attracting researchers due to their importance nowadays as well as in the future. An efficient power electronic converter is a main and common topic for research in this area. In this paper, a prototype of the electrical part of a power-train for EVs using an advanced multilevel converter topology is introduced, discussed and analysed. A comparison between the advanced converter, two-level and conventional multilevel converter topology is discussed as well. A switch function model is derived and discussed for the proposed converter. A mathematical model for the converter supplied by a fuel-cell (FC) and boost-converter (BC) is implemented with Matlab/Simulink. The simulation results are analysed to evaluate the converter. The evaluation is based on the harmonic analysis and power loss calculations. The converters are tested at different switching frequencies to show the effect of this variable on the converter loss. The results indicate that the proposed converter is 1.32% more efficient compared to conventional five-level DCC. Moreover, the lowest harmonic content, for all of the studied converters, is the proposed one.

Power flow in 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. Depending on the operating point part of the power is transmitted in an electromagnetic way, while the rest is transmitted electrically using two back to back inverters. The power flow determines the power rating of the inverters, the cooling and the machine design. This paper gives an overview of the different operating points and the corresponding power flow.

Optimal Control for a Hybrid Excited Dual Mechanical Port Electric Machine

An electrical variable transmission (EVT) is an electrical machine consisting of a stator and two concentric rotors. It is a competitive alternative for power split devices used in current series–parallel hybrid electric vehicles (HEVs). Although tending to have high power densities, permanent magnet (PM) machines suffer from no-load iron losses. Since the torque interaction between stator and outer rotor is low during large time intervals, the EVT in this paper possesses a flux bridge with dc-field winding to modulate the stator field, while maintaining the inner rotor flux linkage. In this paper, a torque controller is proposed that optimally combines the stator, dc-field, and inner rotor currents in order to minimize the copper and iron losses in every operating point of torque and speed on both rotors. Also the electromagnetic coupling between both rotors is considered. It turns out that there are two optimal load angles for the stator currents, of which one of the two is dominant depending on speed and torque. The control is tested on a 120 kW prototype EVT, and measurement results are given to illustrate the optimal performance obtained with the proposed torque control. In addition, efficiencies are measured in order to support the statements made concerning the proposed method.

Adding inverter fault detection to model-based predictive control for flying-capacitor inverters

As inverters are often used in critical applications, reliability is an important issue. In particular, the power electronic switches and gate drivers, the most essential components of the inverter, are vulnerable parts in real live operation. Therefore, this paper focuses on open-switch fault detection for multilevel inverters. When a single-switch open-circuit fault occurs in one of the power electronic switches, the algorithm can detect the fault and the switch that is causing it. The detection is worked out for both a linear resistive inductive load and an induction motor. 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. This paper also discusses a suggested method for reconfiguration after fault detection. Computer simulation and experimental verifications validate the proposed methods.

Loss Identification in a Double Rotor Electrical Variable Transmission

An electrical variable transmission (EVT) is an electromagnetic power-split device with two mechanical and two electrical ports. It can be used in hybrid electric vehicles to split the power to the wheels in a part coming from the combustion engine and a part exchanged with the battery. Although crucial for the EVT design and evaluation, no papers are found to give a detailed overview of the different loss components in such a machine and how they can be calculated and measured. In contrast to conventional electrical machines, this machine has more degrees of freedom, which can be exploited to measure the different loss contributions separately. This paper proposes a methodology to identify and measure the different loss components in this kind of machines. The proposed method is able to identify the iron losses in stator and inner rotor, the copper losses, bearing losses, and slip ring friction losses separately. To this end, measurements of both torque and speed sensors in different operating points are combined. The methods are applied to identify the different loss contributions in a prototype permanent magnet assisted EVT, both in no-load operation as under load where its functionality as power-split device is evaluated.

Concept study of a double rotor induction machine used as continuously variable transmission

In a drive train a continuously variable transmission (CVT) has the advantage that the combustion engine can be driven in its optimal point along the requested power curve, which enhances overall efficiency. Moreover there is no power loss during shifting of gears which is often demanded in off highway applications. Several mechanical and hydraulic CVTs exist that have already proven their functionality, each having their pros and cons. This paper introduces the concept of an electromagnetic CVT which has some inherent advantages compared to mechanical systems being the absence of friction and the need for lubrication, only two moving parts and inherent overload protection. The machine can be seen as a conventional induction motor with two rotors. The rotors are arranged in a concentric way and are electromagnetically coupled. The working principle is explained, and an efficiency map is calculated for a scaled test case. It is concluded that with a smart choice of the interrotor flux a good efficiency can be achieved in a broad range of torque and flux of the interrotor.

Modeling and control of an induction machine based electrical variable transmission

An electrical variable transmission (EVT) is an electromagnetic device with multiple rotors and multiple shafts. In hybrid electric vehicles it is used to split the power to the wheels in a part coming from the combustion engine and a par exchanged with the battery. This paper summarizes how an induction machine based EVT can be modeled and controlled using field oriented control.