Johan Åström

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.

Improving the maximum torque per ampere in a BLDC motor accounting for transient and continuous operation using thermal boundary conditions

This paper investigates the impact on power density of a BLDC motor using different control strategies. The simulations are carried out using 2D electromechanical FEM calculations, including the frequency converter supply. The maximum steady state output power is determined using thermal FEM calculations. The obtained results shows that an increase of 5.9% in output power can be obtained by running a BLDC motor with sinusoidal currents at rated operation instead of using BLDC currents. In addition, an increase of 18% peak torque can be obtained at rated speed operation when sinusoidal feeding is used instead of BLDC supply. The result is verified with measurements showing a close correlation to the calculation, were 6.5% increase of output power was obtained at rated operation.

Time efficient FEM modeling of a PMSM by iteration between field calculations and state

This paper investigates a time efficient method for estimating the iron losses in a permanent magnet motor using FEM modeling. The methodology comprises of using iteration between FEM electromagnetic simulations and Analytical state space modeling. Results show that by using fast field calculations as input to the state space model accurate mean torque calculations can be made, even during high saturation, eg deviating only 0.7% at three times the rated torque. This high accuracy is reached due to an improved torque calculation method compared to models used in previous work. The methodology is based on that the current response obtained from the analytical calculations have been fed back to the FEM calculations for determination of the magnet and iron losses in the motor, reducing the simulation time significantly compared to a voltage fed FEM model. The temperature dependence of the magnet strength and stator resistance have also been taken into account when comparing the simulation result with measurements.

Design of an online temperature monitoring system for an experimental IPMSM

The overall performance of an electric machine is closely linked to the thermal design of the machine and there is a trend to include more thermal analysis into the machine design procedure in academic literature. Thus, there is also a motivation to prototype experimental machines for accurate validations of the thermal analysis. One of the challenges is to measure rotor temperatures online while the machine is in operation. This paper presents some of the experience from designing an online temperature monitoring system for an experimental IPMSM. In total, 32 sensors was successfully placed inside the 3.4 liter volume of the small IPMSM and temperature data was transmitted from the rotor in the end of the shaft, using infrared light. It was found that the online temperature monitoring system was very reliable. Both the used analog and digital sensors exhibit equal results and EMI immunity, when placed inside the electromagnetically noisy environment inside the machine.

Performance of the position control of a permanent magnet sensorless drive

A sensor less position control of a permanent magnet motor has been implemented. The permanent magnet motor is made with interior magnets and concentrated windings. The 4-pole machine can produce 0.4 Nm of continuous torque and have a top speed of 2000 rpm. The peak torque is 0.8 Nm and the system DC-link voltage is 24 V. Sensorless control is utilised with signal injection during low speed operation and at higher speed the induced emf is used for tracking the rotor angle. The estimated rotor angle is used for positioning an ordinary FOC, (Field Oriented Control). The performance of the system is simulated, including FEM-calculated values of saturated flux in d- and q-axes. Cascaded regulators for the speed and the position make it possible to control the mechanical position of the machine. Tests on the real application show a position error of 30 electrical degrees. In this case it corresponds to +/- 15 degrees on the mechanical shaft.

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.

Considerations when modernizing drives for buildings based on an energy efficiency and cost perspective

The efficiency consequence of keeping overdimensioned Induction Motors (IM) in Heating Ventilation and Air Conditioning (HVAC) applications, when modernizing such systems, using the potential that modern power electronic drives gives, is investigated in this paper. Five different Eff1 IM ratings in the range 1.1–4kW have been the target of the analysis. It is a common assumption that the motor efficiency drops rapidly as the load decreases below 75% its rated operation, which is the case for grid connected motors or motors operated with constant V/Hz ratio by an inverter. As a result, overdimensioning of the IM will result in increased energy cost compared to a smaller rating. However, by using a variable V/Hz ratio, it is shown here that the efficiency is in general highest for the largest IM regardless of the loading, despite the increase of the mechanical losses caused by increased cooling and friction. A conclusion found is that it is in principle always worth to keep an overdimensioned existing motor instead of replacing it with a smaller motor having a better efficiency class.

Modeling and measurements of loss components for different switching schemes in a three phase converter using CoolMOS transistors

This paper presents simulation and measurement loss determination results for different switching schemes in a frequency converter using CoolMOS transistors. Different Space Vector Modulation (SVM) schemes has been investigated. The simulation and measurement results show a close correlation. The losses in the MOSFETs have been determined with temperature measurement resulting in high accuracy. It has further been shown that the measured loss component in the MOSFETs can be divided into the switch loss and the conducive loss component using two different approaches. By measuring the on-state voltage drop as a function of current and temperature the conductive loss component can be determined. Furthermore, the switch loss component can be determined by measuring the switching transition of the component and calculating the switching losses as a function of the current. The second method, measures the loss component in the MOSFETs for a constant motor operation but with different switching frequencies. The obtained results of the conductive losses show an approximate error of 5%. Finally, the overall efficiency of a 4 kW Induction motor drive system were determined showing an approximate increase in efficiency of 1% using a discontinuous SVM.