Calorimetry for Power Electronics

In the EEMG, we have proposed the Bristol Calorimeter, an alternative Closed Single-Jacket Surface-Heated calorimeter topology, which decouples the measurement chamber from the instrumentation and minimises heat leakage using a surface heater. This approach enables a standardised set of instrumentation to be used with low-cost measurement chambers which are tailor made to suit a particular DUT volume resulting in minimised measurement time whilst maintaining a similar accuracy to a double-jacket topology.

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The accurate and reliable determination of power losses is of great importance to the design, optimisation and performance evaluation of power electronic systems and the validation of component loss models [link to loss modelling section]. Common techniques for loss measurement can be grouped into electrical and calorimetric methods.

In electrical methods, the input and output voltage and current of the Device Under Test (DUT) are measured and multiplied to yield input and output power, the difference giving an indication of loss and efficiency. Accurate measurements are readily achieved for dc and low-frequency ac circuits. However, when measuring high frequency signals with distortion such as those exhibited by Pulse Width Modulation (PWM) driven circuits, high-bandwidth digital instruments capable of simultaneous voltage and current sampling are required. These instruments provide a simple means of measuring losses under both transient and steady-state conditions, however, Electromagnetic Interference (EMI) originating from the DUT along with practical implementation issues such as non-linearity of the Analogue to Digital Converter (ADC), time and phase delays and sampling errors contribute to measurement error. In high-efficiency systems, where the input and output power are similar in magnitude, the measurement errors can lead to unacceptable inaccuracies in loss and efficiency calculations, as a  result calorimetric methods are often adopted as an alternative.

Reference

[1] Paper published in IEMDC.

What is Calorimetry?

The procedure of measuring the heat of chemical reactions or physical changes is called calorimetry.  The apparatus used to measure the change in energy is called a calorimeter. Differential scanning, titration, isothermal and accelerated rate calorimeters are amongst the most common types.

A calorimeter measures the power lost from a DUT as heat by monitoring the change in temperature of a cooling medium such as air or water. However, the practical realisation of a precise calorimeter is challenging since all heat leakage must be accounted for.

Contact

For more information please email energy-management@bristol.ac.uk or contact Dr Nick Simpson.

Fig.1 Calorimeter Setup
Fig.2 Inside the chamber
Fig.3 Comparison of power analyser and calorimeter results based on a single calibration
Fig.4 Double jacket calorimeter
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