Cge Korneel Wijnands

Reference frames fit for controlling PWM rectifiers

The authors argue that one should keep things simple when controlling bidirectional pulsewidth modulation rectifiers by considering the utility grid as a virtual electric machine. The advantage is that the air-gap flux of this big machine can be directly measured in a straightforward way. Therefore, as shown in this paper, principles of field orientation can be applied to control the power flow, yielding high-dynamic performance.

Performance Evaluation of a Three-Phase Dual Active Bridge DC–DC Converter With Different Transformer Winding Configurations

This paper investigates the impact of three transformer winding configurations, i.e., the Y-Y, the Y-Δ, and the Δ-Δ configuration, on the performance of a three-phase dual active bridge (DAB) dc-dc converter. For each configuration, equations for the phase currents, power flow, and zero-voltage switching (ZVS) boundaries are derived for all possible switching modes of the three-phase DAB. Thereafter, a comparison is made of the stress on the switches, the transformer, and the filter capacitors for the selected winding configurations. The comparison reveals that the Y-Y and Δ-Δ configuration perform equally regarding above aspects, with the only difference of a lower winding current for the Δ-Δ configuration. The Y-Δ configuration shows a constant commutation current for phase-shifts from 0 to 30 degrees. Therefore, this configuration features a wider ZVS region for low output powers. Overall, the Y-Δ configuration performs best for power levels between 50% and 80%, regarding the stress on the switches, the transformer, and the filter capacitors. The theoretical analysis is supported with measurements obtained from a high-power experimental setup.

Control of DC-excited flux switching machines for traction applications

Electrical traction motors face challenging torque-speed requirements. DC-excited flux switching machine (FSM) offers inherently a good torque capability along with an effective controllability thanks to its DC field windings. These machines have been evaluated mainly over their performance with little consideration on their control. This paper proposes a control strategy, applied on a 3-phase 6/5 DC-excited FSM for traction applications. To obtain the non-linear magnetic behavior of the machine, 2D finite element method (FEM) simulations are performed. The controller regulates the DC field current before reaching base speed to minimize the iron and copper losses. Due to the high armature reaction of the motor the speed range is extended by limiting both the field and armature currents as a function of the speed and inverter supply voltage. Torque control of the machine is performed throughout its complete speed range.

Dual voltage source inverter topology extending machine operating range

Field weakening operation of an electrical machine is a conventional method to extend the angular velocity range of a system above the peak output voltage of the inverter. A downside, however, is that an increased reactive current is required that creates losses but no output torque. A dual voltage source inverter topology is proposed, capable of driving an electrical machine without weakening its field in an extended speed range. For this purpose, a second inverter fed by a capacitor only is connected to the open-end side of the machine windings. Charging the floating capacitors is realized by adding an AC zero sequence current to the regular machine currents. The operating principles of the presented topology are demonstrated, showing their possible advantages when driving an electrical machine. Simulation results confirm the proposed ideas.

Single-stage three-phase AC to DC conversion with isolation and Bi-directional power flow

An approach for three-phase AC to DC conversion is proposed, which consists of a single-stage while offering galvanic isolation, soft-switching, bi-directional power flow and a significant reduction of inductive and capacitive energy storage. Two elements enable this approach, namely a neutral voltage-lift capacitor and a Quad Active Bridge (QAB) converter. Moreover, a control strategy is described and a detailed converter analysis is given.

Loss minimization of boost mode dual inverter drive system

A dual inverter drive system is proposed, which is capable of boosting the phase voltages applied to an open-winding electric machine. A zero sequence current at the third harmonic of the intended output frequency is added to increase the supply voltage of one inverter, thereby extending the operating range of the machine. The need for a reactive current to weaken the machine field is avoided as a result. A method is introduced for simultaneously optimizing the inverter voltages and minimizing the required boost current, to maximize the overall system efficiency. The analysis is explained and verified by simulation.

Charge-based ZVS modulation of a 3–5 level bidirectional dual active bridge DC-DC converter

This paper presents a charge-based Zero Voltage Switching (ZVS) modulation strategy for the 3 Level–5 Level (3–5L) Dual Active Bridge (DAB) DC-DC converter. The DAB combines a primary-side full bridge and a secondary-side mixed bridge (i.e. a 3-level T-type leg with a half-bridge leg), linked by a high-frequency transformer and an inductor. A ZVS modulation strategy is presented, in which a charge-based model of the non-linear parasitic output capacitances of the switches is used to accurately describe the ZVS constraints. Moreover, commutation inductances are included to extend the ZVS region to the entire operating range. The configuration of the secondary-side bridge facilitates increased flexibility compared to a full bridge configuration, in order to reduce the RMS current in the switches, inductor, and transformer. The nominal power of the investigated converter is 2.8 kW with input voltage range from 8 V to 16 V and output voltage range from 175 V to 450 V. The RMS currents of the 3–5L DAB are compared with those of a typical 3–3L DAB, applying the proposed modulation strategy in the 3–5L DAB, and a similar strategy previously proposed in literature in the 3–3L DAB.

Fault-tolerant operation of a fully electric gearbox equivalent

A fault-tolerant operation method for a dynamic electric vehicle (EV) propulsion system using variable torque/speed characteristics is presented. With this method, the electrically powered vehicle can continue driving with a minimum performance reduction, and without the need for redundant systems on machine or electronics level. One of the possible single module fault scenarios, during which the system must continue operation, is shown. The accompanying theoretical analysis of the fault scenario is presented, and simulations and preliminary measurements are executed to demonstrate the presented solution.

Quad-Active-Bridge Single-Stage Bidirectional Three-Phase AC–DC Converter With Isolation: Introduction and Optimized Modulation

This paper introduces the quad-active-bridge (QAB) ac–dc converter, which provides isolation and bidirectional power flow in a single-stage topology. While matrix-based topologies commonly use bipolar voltage switches, the proposed solution allows the use of unipolar voltage switches. Compared to a six-switch inverter, the average voltage stress is reduced by a factor of 2. A modulation scheme is derived for this converter, which is analytically optimized toward minimum conduction losses to improve the conversion efficiency. The modulation scheme consists of closed-form algebraic solutions such that no lookup tables are required for implementation. Considerations for the converter design and the main component selection procedures are given. The proposed topology and modulation strategy is implemented in a 20-kW prototype. Measurements are conducted and show that the methods operate as expected. Experimental results show that the load step is stable, the power factor is close to unity, and the phase current total harmonic distortion is less than 5%. Finally, it is shown that the circulating current can be controlled independent of the output power. The methods and tools provided can be used for the design and analysis of ac–dc power converters based on the QAB topology.

Operating Range Advancement of a Dual-Inverter Driven Machine Through Voltage Range Enhancement

Speed range maximization of a traction drive is one of the main focus points in transportation electrification research. This paper presents a range improvement method, suitable for each type of open-winding three-phase electric machine. A dual-inverter drive system is proposed, which is capable of enhancing the phase voltages applied to the open-winding electrical machine. A common-mode current at the third-harmonic of the intended output frequency is deliberately generated to boost the supply voltage of one inverter, thereby extending the operating range of the machine above the base angular velocity. The need for a reactive fundamental frequency current to weaken the machine field is avoided as a result. A method is introduced for simultaneously optimizing the inverter voltages and minimizing the required boost current, thereby maximizing the speed range and the overall efficiency. The analysis is explained and verified by experiments. A relative angular velocity advancement of a factor 1.6 is achieved using voltage range enhancement.