Andreas Karvonen

MOSFET modeling adapted for switched applications using a state-space approach and internal capacitance characterization

This paper presents a new approach to MOSFET modeling using a state-space technique. The model is based on discrete elements whose values are extracted from measurements, datasheet parameters and SPICE® equations. The switching characteristics of the component are strongly determined by the gate-drain capacitance (CGD). With help of thorough impedance measurements, characterization of this capacitance as a function of the applied external voltages is possible. Simulations and measurements show good agreement and the model gives possibilities for e.g. controller design thanks to the state-space implementation.

Reduction of EMI in Switched Mode Converters by Shaped Pulse Transitions

An idea of reducing the amplitude of higher order harmonic frequencies from PWM switching pattern is presented and analyzed in this paper. For experimental studies a flexible curve shaping circuit was developed and implemented for achieving and controlling smooth transitions in a DC/DC PWM controlled converter for a 12 V system. A comparison between trapezoidal and sinusoidal transitions is made and it is found that a sinusoidal transition gives better EMI performance without increasing the switching losses. In order to further reduce the EMI, a strategy of controlling the output voltage transitions in a MOSFET by ”pre-charging” its gate is derived and investigated. The developed practical circuit is tested with sinusoidal reference for a purely resistive load and an R-L load. Frequency responses obtained from simulations and measurements are compared and discussed.

Simulating the EMI characteristics of flyback DC/DC converters

In this article, the influence of diode reverse recovery on EMI performance of a low power flyback converter is investigated. Two different diode models (SPICE and SABER®) are analyzed and the conducted emissions from a simulated converter with a thorough characterization of the parasitic elements are compared to measurements. It is concluded that the emission levels to a large extent is determined by the mutual couplings within the input filter. The proposed simulation model predicts EMI levels up to 20MHz with good accuracy. Furthermore, it is concluded that the diode reverse recovery is reflected into the conducted emissions. For the investigated case, a recovery peak of IRR=2.8A gives an increase in emission levels with 3dB around 10MHz compared to a diode with IRR=1.0A. Finally, it was found that Schottky diodes may decrease the EMI performance of the converter; the large inherent capacitance can cause large oscillations in the circuit that are reflected into the conducted emissions.

Harmonic Modeling of a Vehicle Traction Circuit Towards the DC Bus

Different converters such as the traction inverter and DC/DC converter are connected to the dc bus of an electric or hybrid electric vehicle. Harmonic models of these devices towards the dc bus are needed to investigate different phenomena like the dc bus transients and ripples. A high-frequency harmonic model of a traction circuit, a drive system based on a three-phase inverter connected to an ac motor, is presented and explained. The model is extracted from an analytical approach developed for a three-phase inverter with a sinusoidal PWM controller. In addition to the analytical formulation, simulations and experimental results of a plug-in vehicle are provided to verify the spectrum of the dc bus waveforms.

Parameter analysis of current and voltage ripple in a hybrid vehicle traction system

In a modern hybrid vehicle where several switched converters are connected to a common high voltage DC-bus, current and voltage harmonics will arise due to the switching events in the inverter. In order to determine the behavior of the complete system, models that include switching characteristics, control parameters of each device and high frequency behavior of the cabling and the battery must be incorporated. The complete system model can then be used to e.g. quantify ripple components and analyze resonance effects. In this paper, a model of a drive system is set up and the results are verified by measurements. The model is then used to verify the interaction of the different subsystems and to investigate the complete system behavior. It is concluded that interaction of the different systems can be foreseen and that the battery inductance in combination with the DC-link capacitance contribute most to the DC-bus current ripple.

Co-Simulation and Harmonic Analysis of a Hybrid Vehicle Traction System

In a modern hybrid vehicle where a traction inverter is connected to a high voltage battery, current and voltage harmonics will arise due to the switching events. In order to determine the high frequency system behavior, simple analytical models are no longer adequate due to difficulties in parameter estimation. In this paper, a co-simulation model of a drive system is implemented in Ansys Maxwell/Simplorer and the results are verified by measurements. It is concluded that the machine model affects the system performance to such an extent that a co-simulation of the electric and magnetic domain is needed to capture all relevant effects on the DC-bus of the system.

EMI reduction using symmetrical switching and capacitor control

An EMI reduction technique using two MOSFETs instead of a single MOSFET in a step-down converter is investigated in this article. A circuit that implements this technique together with external capacitor control was designed and measurement results were compared against simulations. The switching element in the proposed circuit is an IRF7309 that consists of a p-channel and an n-channel MOSFET in the same package. The entire circuit also consists of an input circuit for the control pulses and a controller circuit responsible for optimizing the turn-on and turn-off of the p-channel MOSFET and n-channel MOSFET. The effect of difference in the threshold voltage between the two MOSFETs is controlled by external capacitances in a configuration referred to as capacitor control. The analyzes of simulations and measurement results show that the symmetrical switching (or double MOSFET switching) technique can successfully be applied to reduce the RF emission in the low frequency and medium frequency range when compared to the single MOSFET switching.

Semiconductor component reduction in AC/DC converters with transmission lines

By replacing the power inductor in a traditional converter topology with a transmission line, new functions such as inverting and non-inverting output voltage polarity from the same converter will arise. In this paper, the proposed technology was investigated in an AC/DC converter where the traditional topology (diode bridge and secondary DC/DC converter) was replaced with a single converter with a transmission line as an energy storage device. The transmission line was realized with lumped elements and the major benefit was found to be a reduced number of semiconductors; the same functionality could be achieved with only half the original amount. Due to practical reasons, the operating principle was verified in a DC/AC-circuit which was simulated in LTspice. The simulations showed that a switch mode converter with transmission line is possible to use for the suggested application with a power stage efficiency of ηPwSt=87%. To verify the simulations, a prototype was built and tested which showed that the principle works in practice with a measured power stage efficiency of ηPwSt=85%.

Simulating the EMI characteristics of step-down DC/DC converters

This paper addresses a complete analysis of the EMI problems associated with step down DC/DC converters and evaluate the effectiveness of solutions that aim to minimize the conducted emissions. Different simulation model of diodes are analyzed and a full converter including PCB stray elements is implemented in Simplorer. To increase the accuracy and account for higher frequencies in the conducted emissions, the coupling between circuit elements in the input filter is taken into account. If the EMI performance of the simulation model is compared with measurements, both for synchronous and non-synchronous rectification, it is concluded that the complete EMI signature can be simulated with satisfactory accuracy by a detailed model including stray elements and mutual couplings. Synchronous rectification can help to lower the conducted emission levels and a co-packaged Schottky diode in the low-side switch can decrease the emission levels even further by reducing the influence of the reverse recovery of the inherent body diode.

On dynamic diode characteristics and EMI performance of an inverter with Undeland snubber

In this paper, two different power diodes were modeled in SPICE and implemented in a 100kW inverter. The reverse and forward recovery characteristics of the diodes were simulated and compared with hardware measurement to verify the validity of the SPICE diode models. The diodes showed different dynamic and static performance and simulations were performed to investigate which parameters that influence the losses and EMI-performance most. The simulations showed that the conducted emissions were reduced with approximately 3dB by selecting a diode with softer dynamic characteristics on expense of increased losses. Furthermore, an Undeland snubber was implemented which resulted in a reduction of the conducted emissions, recovery of the snubber energy and reduction of the losses in the switching elements. However, the forward and reverse recovery characteristics of the snubber diodes must be considered when designing the circuit since they also have an impact on the conducted emissions and the losses in the circuit.