Calorimetric Power Loss Measurement of a Small Power Converter

Miniaturisation - is the key word in technology today and the general trend in all industries is to seek for smaller and compact electrical and magnetic components. With the increase in energy density, the loss density does too, and so does the need to achieve greater measurement accuracy of device losses. Calorimeters are the way to accomplish this effectively, as proven by the prevailing calorimetric watt-meters for electrical systems. The undertaking of this thesis work was to build a simple yet accurate calorimetric system to measure power losses in highly efficient power converters and similar small devices belonging to a power class of <1 kW. An improved closed, water cooled calorimeter with flow control and input water temperature control has been implemented, as an alternative to the accepted, yet complicated double jacketed calorimeter. The balance tests with the calorimeter yielded the calibration curve, which was followed by the actual test with a 0.75 kW frequency converter. From the power losses measured by the calorimeter, the tested device was confirmed to have a high efficiency of 97%. The calorimeter that was built is characterised by low flow rates and can measure loss powers in range of 25 W - 520 W with an accuracy better than 1.5% for power losses <50 W

High Speed Peltier Calorimeter for the Calibration of High Bandwidth Power Measurement Equipment

Accurate power measurements of electronic components operating at high frequencies are vital in determining where power losses occur in a system such as a power converter. Such power measurements must be carried out with equipment that can accurately measure real power at high frequency. We present the design of a high speed calorimeter to address this requirement, capable of reaching a steady state in less than 10 minutes. The system uses Peltier thermoelectric coolers to remove heat generated in a load resistance, and was calibrated against known real power measurements using an artificial neural network. A dead zone controller was used to achieve stable power measurements. The calibration was validated and shown to have an absolute accuracy of +/-8 mW (95% confidence interval) for measurements of real power from 0.1 to 5 W

Modeling Controlled Switches and Diodes for Electro-Thermal Simulation

Designers of advanced power converters may choose from a variety of switching device models for simulation. Some situations call for simple idealized models, while others require physics-based models. When evaluating thermal system performance, a behavioral model that includes both conduction and switching losses is desired. A set of models has been developed to include both unidirectional devices, such as IGBTs, BJTs, and diodes, and bidirectional devices, such as MOSFETs. Logic and timing elements are used to insert voltage and current sources into the circuit at appropriate times. All losses affect circuit operation, so simulation can accurately predict losses when the load affects the switching pattern. The model was constructed in Dymola and included thermal ports to be attached to a model of the thermal system. Temperature dependency of device parameters can be included with minor modifications. Experimental verification is shown

A Method of Including Switching Loss in Electro-Thermal Simulations

Often, power electronics systems are simulated with ideal switching elements, perhaps augmented with conduction loss models. A behavioral model is proposed that also includes switching loss and is independent of switching frequency. Therefore, it is suitable for variable frequency control methods, including hysteresis, delta modulation, and random PWM. Models have been realized in Dymola using voltage-controlled voltage sources, current sources, logic, and additional ideal switches. Thermal ports are included to facilitate electro-thermal simulation. A method for parameter extraction is demonstrated using experimental data from standard PWM

A comparison of the hard-switching performance of 650V power transistors with calorimetric verification

We compare the switching losses of four equivalent silicon and wide-bandgap 650V power transistors operated in a hard-switched half-bridge configuration, switching 400V at 40A. Each transistor is mounted on an identical PCB and driven by a gate drive circuit matched to its requirements. Switching speed is maximised by a PCB design featuring very low parasitic inductance and the use of zero external gate resistance (where possible). Switching losses are measured electrically using a Double Pulse Test (DPT) method. However, high-bandwidth electrical measurements are prone to error and so we assess the gain accuracy, offset accuracy, and the bandwidth requirements of the DPT measurements, and then verify the DPT results by calorimetry. The electrical and calorimetric measurements are shown to agree to within 5%. Comprehensive plots of gate-source voltage, drain-source voltage, and source current are provided for all transistors over a junction temperature range of 50-150°C. The ratio of the total half-bridge switching losses is 1:3.2:14:31 for the GaN HEMT, SiC MOSFET, Si IGBT, and Si superjunction MOSFET, respectively

Analytical Conduction Loss Calculation of a MOSFET Three-Phase Inverter Accounting for the Reverse Conduction and the Blanking Time

The reverse conduction capability of MOSFETs is beneficial for the efficiency of a three-phase inverter. In this paper analytical expressions in closed form are presented which allow to quickly evaluate the conduction losses, considering the effect of the reverse conduction and blanking time for both sinusoidal PWM operation with and without third harmonic injection. The losses of a three-phase SiC MOSFET inverter suitable for traction applications are estimated with the proposed method and show good agreement of about 98.5 % with measurements, performed with a calorimetric setup

Calorimetric measurement methodology for comprehensive soft and hard switching loss characterisation

Accurate measurement of soft and hard switching losses is challenging. Electrical methods are prone to errors and calorimetric measurements most often cannot separate turn-on and turn-off energies. We present a calorimetric test setup capable of measuring and separating turn-on and turn-off energies in soft and hard switching regimes. The resulting loss map can be used to accurately predict power semiconductor losses, even when the converter is not fully in the soft-switching regime

Comparison of Several Methods for Determining the Internal Resistance of Lithium Ion Cells

The internal resistance is the key parameter for determining power, energy efficiency and lost heat of a lithium ion cell. Precise knowledge of this value is vital for designing battery systems for automotive applications. Internal resistance of a cell was determined by current step methods, AC (alternating current) methods, electrochemical impedance spectroscopy and thermal loss methods. The outcomes of these measurements have been compared with each other. If charge or discharge of the cell is limited, current step methods provide the same results as energy loss methods

Graphene-based Josephson junction single photon detector

We propose to use graphene-based Josephson junctions (gJjs) to detect single photons in a wide electromagnetic spectrum from visible to radio frequencies. Our approach takes advantage of the exceptionally low electronic heat capacity of monolayer graphene and its constricted thermal conductance to its phonon degrees of freedom. Such a system could provide high sensitivity photon detection required for research areas including quantum information processing and radio-astronomy. As an example, we present our device concepts for gJj single photon detectors in both the microwave and infrared regimes. The dark count rate and intrinsic quantum efficiency are computed based on parameters from a measured gJj, demonstrating feasibility within existing technologies.Comment: 11 pages, 6 figures, and 1 table in the main tex