Arnaud Videt

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.

A Simple Carrier-Based Modulation for the SVM of the Matrix Converter

Today, industry has not fully embraced the matrix converter solution. One important reason is its high control complexity. It is therefore relevant to propose a simpler but efficient modulation scheme, similar as three phase voltage source inverter modulators with the well-known symmetrical carrier-based ones. The modulation presented in this paper is equivalent to a particular space vector modulation (SVM) and takes into account harmonics and unbalanced input voltages, with the same maximum voltage transfer ratio (86%). The aim of this work is to propose a simple and general pulse-width-modulation method using carrier-based modulator for an easier matrix converter control. Furthermore, a simple duty cycle calculation method is used, based on a virtual matrix converter. Finally, simulations and experimentations are presented to validate this simple, original and efficient modulation concept equivalent to matrix converter SVM.

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.

Motor Overvoltage Limitation by Means of a New EMI-Reducing PWM Strategy for Three-Level Inverters

Pulsewidth-modulated (PWM) voltage-source inverters are known to provoke high-frequency disturbances in motor-drive applications, particularly when long cables are used. Indeed, the parasitic elements of the cable, along with steep voltage transitions due to semiconductor switchings, are responsible for the conducted electromagnetic emissions and high overvoltages on the motor terminals. Therefore, several specific PWM schemes have been proposed in order to reduce these phenomena without requiring large passive filters. However, strategies that reduce common-mode currents (mainly conducted electromagnetic emissions) tend to increase the overvoltages generated on the motor. This paper focuses on a new PWM strategy that reduces the common-mode currents generated by three-level inverters. It provides a control algorithm that makes sure that the motor overvoltages never exceed those of conventional strategies while improving the electromagnetic-compatibility performance of the drive.

Modeling of switching transients for frequency-domain EMC analysis of power converters

Since the early 1990s, electrical energy tends to replace pneumatic and hydraulic energy aboard aircrafts. This is lead by MEA project and allows to reduce weight and volume of the actuators. But an increase of onboard electric energy leads to EMI issues. To comply with EMC standards, an EMI filter is often added to the electrical systems. In order to reduce the weight and volume impact of EMI filters, it is interesting to perform an optimization of the embedded electrical system at the design stage, based on EMC criteria, using a simulation approach. In order to perform these simulations, HF model of the system is necessary. Two approaches exist: either time-domain or frequency-domain simulations, each one having advantages and drawbacks. This paper presents a frequency-domain modeling method. The proposed method is based on the use of two linear equivalent noise generators topologies. The results obtained with the two topologies are combined, to obtain a good representation of power converters. This method increase the validity range of the simulation above 30MHz.

Using Current Surface Probe to Measure the Current of the Fast Power Semiconductors

With the advantage of high bandwidth and small insertion impedance, a current surface probe (CSP) used to measure switching current waveforms is presented in this letter. Its transfer impedance is characterized and validated by measuring an IGBT switching current that is compared with those obtained with a current probe and a Hall effect current probe. Furthermore, by comparing with a current shunt to measure a GaN-HEMT switching current, it is shown that CSP is able to measure a switching current of a few nanoseconds, while it brings no influence on transistor voltage waveform measurement. The obtained results show that the use of CSP brings little parasitic inductances in the measurement circuit and it does not bring the connection of the ground to the power converter.

NIF-Based Frequency-Domain Modeling Method of Three-Wire Shielded Energy Cables for EMC Simulation

This paper focuses on the modeling method of energy cables used in power conversion systems, in the aim of EMC simulation and overvoltage analysis. Based on the node-to-node functions method, a simple frequency-domain model with a reduced number of equivalent impedances is considered and applied to three-wire shielded cables, along with a fast identification method based on a cascaded-cell model. Even though the model eventually includes nonphysical virtual impedances, simulation in frequency domain provides accurate results when compared to equivalent experimental measurements, for various cable lengths and in short simulation times. Time-domain waveforms are then extracted from frequency-domain simulation and confirm the effectiveness of the proposed method in a wide frequency range up to 50 MHz. Finally, a good match has been found between experimental and simulation results of voltage overshoots on a buck power converter system.

Modeling the Residual Common-Mode Voltage Generated by 3-Phase Inverters with Simultaneous-Switching PWM Strategies

In the simulation of power electronics systems, for reasons of computing time and convergence, it may be necessary to use ideal components which generate ideal voltage switchings (steep edges). However, in reality, these voltage variations are far from ideal and to reproduce a voltage closer to reality, it is necessary to model these variations. This is especially important for the study of residual voltage obtained by simultaneous switching, which are present in PWM strategies developped to reduce the impact of the common-mode voltage generated by 3-phase inverters. This paper is focused on the required model accuracy, in order to take into account these residues obtained by the synchronization of switching voltages.

PWM strategy for common-mode voltage reduction in three-phase variable-speed drives with active front end

This paper presents a PWM strategy for the reduction of common-mode (CM) voltage generated by variable-speed motor drives composed of two-level, three-phase active-front-end rectifier and three-phase inverter. This method theoretically provides complete elimination of the CM voltage by synchronizing all inverter commutations with rectifier commutations, so that the resulting CM voltage does not vary. The degrees of freedom of this strategy are studied and an experimental implementation is provided on a 15 kW prototype to validate the method effectiveness. Taking into account dead-time compensation, measurements in time and frequency domains show that the CM voltage is strongly reduced and that more than 15 dB reduction is achieved in a wide frequency range.

GaN-HEMT fast switching current measurement method based on current surface probe

With the advantage of high bandwidth and small insertion impedance, a current surface probe (CSP) used to measure switching current waveforms is presented in this paper. Its transfer impedance is characterized and validated in the first time by measuring an IGBT switching current with a passive current probe (CP) and a Hall effect current probe (HECP). It is also shown that a return current beneath the PCB on which is put the CSP can reduce its transfer impedance. In the second time, the CSP is used to measure a GaN-HEMT switching current and the obtained results are compared with those measured with a current shunt (CS). The comparison of these results prove that CSP and CS are able to measure fast switching current (of the order a few nanoseconds). However, the advantage of the CSP is that it has no influence on the power device VDS voltage measurement. Also, the CSP brings less parasitic inductance in the commutation mesh than the CS and it does not have the ground connection drawback, which is the case for the CS.