Nadir Idir

Active gate voltage control of turn-on di/dt and turn-off dv/dt in insulated gate transistors

As the characteristics of insulted gate transistors [like metal–oxide–semiconductor field-effect transistors and insulated gate bipolar transistors (IGBTs)] have been constantly improving, their utilization in power converters operating at higher and higher frequencies has become more common. However, this, in turn, leads to fast current and voltage transitions that generate large amounts of electromagnetic interferences over wide frequency ranges. In this paper, a new active gate voltage control (AGVC) method is presented. It allows us to control the values of at turn-on and at turn-off for insulated gate power transistors, by acting directly on the input gate voltage shape. In an elementary switching cell, it enables us to strongly reduce over-current generated by the reverse recovery of the free-wheeling diode at turn-on, and oscillations of the output voltage across the transistor at turn-off. In the following sections, the AGVC in open and closed-loop for IGBT is presented, and its performance is compared with that of a more conventional method, i.e., increasing the gate resistance. Robustness of the AGVC is estimated under variations of dc-voltage supply and transistor switched current.

A New Carrier-Based PWM Providing Common-Mode-Current Reduction and DC-Bus Balancing for Three-Level Inverters

Adjustable-speed drives involve common-mode voltages, which generate common-mode currents flowing to the ground through stray capacitances of electric machines. These currents are known to provoke premature motor-bearing failures, as well as electromagnetic interferences disturbing neighbor electronic devices. Furthermore, high-voltage applications involve high levels of these conducted emissions, which must be lowered by using bulky and expensive filters. This paper aims at elaborating a new pulsewidth-modulation (PWM) strategy in order to reduce the common-mode currents generated by three-level neutral-point-clamped inverters. The proposed strategy also provides the ability to balance the neutral point of the dc-bus capacitors. Experimental results both in time and frequency domains confirm that the new PWM improves the electromagnetic-compatibility behavior of the drive compared with conventional strategies.

Modeling of Conducted EMI in Adjustable Speed Drives

This paper deals with conducted electromagnetic interferences (EMIs) in adjustable-speed drive (ASD) systems. For some years, the use of high-speed switching power devices in ASDs induces high-voltage ( dv/dt) and high-current ( di/dt) variations that excite the parasitic elements of the power circuit, inducing conducted emissions. The advent of these devices has thus generated several unexpected problems, such as premature deterioration of motor ball bearings and high increases in the EMI levels, which are caused by the circulation of the high-frequency currents. In order to evaluate the level of the common-mode (CM) and the differential-mode (DM) currents in the ASD system, it is necessary to use a precise model of the pulse width modulation (PWM) inverter, power cable, and ac motor that takes into account various phenomena, which appear when the frequency increases. First, a PWM inverter and shielded four-wire power cable model are presented. Then, a new high-frequency modeling method of the ac motor is proposed. Finally, the ASD system is simulated and the obtained results are compared to the experimental measurements in the frequency and time domains.

Turn- on Performance of Reverse Blocking IGBT (RB IGBT) and Optimization Using Advanced Gate Driver

Turn-on performance of a reverse blocking insulated gate bipolar transistor (RB IGBT) is discussed in this paper. The RB IGBT is a specially designed IGBT having ability to sustain blocking voltage of both the polarities. Such a switch shows superior conduction but much worst switching (turn- on) performances compared to a combination of an ordinary IGBT and blocking diode. Because of that, optimization of the switching performance is a key issue that makes the RB IGB not well accepted in the real applications. In this paper, the RB IGBT turn-on losses and reverse recovery current are analyzed for different gate driver techniques, and a new gate driver is proposed. Commonly used conventional gate drivers do not have capability for the switching dynamics optimization. In contrast to this, the new proposed gate driver provides robust and simple way to control and optimize the reverse recovery current and turn-on losses. The collector current slope and reverse recovery current are controlled by the means of the gate emitter voltage control in feedforward manner. In addition, the collector emitter voltage slope is controlled during the voltage falling phase by the means of inherent increase of the gate current. Therefore, the collector emitter voltage tail and the total turn- on losses are reduced, independently on the reverse recovery current. The proposed gate driver was experimentally verified and the results presented and discussed.

High-Frequency Model of the Coupled Inductors Used in EMI Filters

This paper deals with a high-frequency modeling method of the coupled inductors used in electromagnetic interference (EMI) filters. These filters are intended to reduce conducted emissions generated by power static converters towards the power grid. To model the EMI filters, it is necessary to identify the various parameters of the passive elements: inductors and capacitors. Because of their major impact on filter efficiency, these elements must be identified with accuracy. In this study, high-frequency model of common-mode-coupled inductors is proposed. The identification of the model parameters is based on the experimental approach. Simulation results of the proposed model are compared to the experimental data obtained using the specific experimental setup. These results made it possible to validate the EMI filter model and its robustness in a frequency range varying from 9 kHz to 30 MHz. The proposed high-frequency inductor models will be very helpful for design and optimization of EMI filters, since the high-frequency behavior of the filter mainly depends on magnetic materials used and on the geometrical characteristics of winding.

Skin effect and dielectric loss models of power cables

In power electronics applications, power cables spread paths of conducted disturbances throughout the system. This paper proposes a high frequency modeling method for power cables that takes into account phenomena which appear when the switching frequency of the static converter increases, such as skin effects, proximity effects and dielectric losses. The proposed power cable models are obtained by the series association of n identical RLCG basic cells. The skin and proximity effects are represented as the impedance of an R-L ladder and the dielectric losses as the admittance of an R-C ladder. The proposed method was successfully applied to a three-wire unshielded cable and extended to a four-wire shielded cable.

A High Frequency Equivalent Circuit and Parameter Extraction Procedure for Common Mode Choke in the EMI Filter

Power converters with high switching frequency generate conducted electromagnetic interference (EMI) noise. EMI filters are thus widely used to reduce these conducted noises for the compliance with electromagnetic compatibility standards. In this paper, a high-frequency (HF) equivalent circuit model for common mode (CM) chokes used in EMI filters is proposed together with its parameter extraction procedure. This procedure is based on impedance measurements and it incorporates an iterative rational function approximation fitting algorithm to extract the parameters in the model. The proposed model and procedure is applied to a planar CM choke which is used to realize an EMI filter. The simulated results of the filter show good agreement with the experimental ones. This extraction procedure is quite general and it can also be extended to identify the HF model of other passive components.

A New Carrier-Based PWM for the Reduction of Common Mode Currents Applied to Neutral-Point-Clamped Inverters

Inverters used in adjustable speed drives create common mode voltages with high dv/dt transitions resulting in high frequency common mode currents which flow to the ground through stray capacitances. These common mode currents are known to damage the bearings of electric machines and cause malfunctions in other surrounding electronic devices, and therefore need to be confined by using bulky and expensive electromagnetic compatibility (EMC) filters. The presented work focuses on the three levels neutral-point-clamped (NPC) inverter and proposes a new pulse width modulation (PWM) strategy for the reduction of common mode currents by lowering the number of step variations of the common mode voltage. Unlike previous strategies, this carrier-based PWM pays attention to the real phenomena involved in the generation of common mode currents so as to efficiently reduce them by avoiding dead time effects. The new strategy has been implemented in a 20 kVA prototype and the experimental results presented in this paper confirm its best EMC behavior compared with classical PWM.

High frequency model of a shielded 4-wire energy cable

In adjustable speed drive (ASD) applications, most cables connecting the electronic voltage source to the AC-motor are multi-wire and shielded. The various inductive and capacitive effects are at the origin of high frequency phenomena that require models with distributed parameters as in transmission lines. From curves showing the evolution of the cable impedance with frequency, and under the assumption of choosing appropriate models, it is possible to calculate the values of the numerous parameters of the model from design tool software. This paper deals with the modelling of a shielded 4-wire energy cable, with the determination of the values of the parameters R, L, C and G of the energy cable, in order to obtain an equivalent electric model which is valid both in the time and frequency domains. The obtained results show that the proposed model reproduces the oscillations of current induced by the hard switchings of the power converter with a difference lower than 10% when compared to experimental measurements

A Common-Mode Choke Using Toroid-EQ Mixed Structure

Electromagnetic interference (EMI) filters are main solutions to suppress the conducted emissions from static power converters. For some years, integration techniques for EMI filters have been widely investigated to realize more compact systems. In this letter, a common-mode (CM) choke with toroid-EQ mixed structure is presented. This structure is constituted of a toroidal CM choke embedded into an EQ core. The proposed toroid-EQ CM choke presents threefold advantages. First, it effectively increases the leakage inductance of the toroidal CM choke and hence increases the differential-mode inductance. Second, it reduces the parasitic coupling between the choke and the filter capacitors. Finally, the component can be easily fabricated with low cost. Experimental verifications have been carried out to validate the effectiveness of the proposed toroid-EQ CM choke.