Flow Calorimeter for Power Electronic Converters Alex Van den Bossche EPE 2001 – Graz P. 1 Flow Calorimeter for Power Electronic Converters Alex Van den Bossche Ghent University, Laboratory for Electrical Machines and Power Electronics ELMAPE, Sint-Pietersnieuwstraat 41 Gent Belgium Tel.+32-9-2643419/fax. 32-9-2643582 alex.vandenbossche@rug.ac.be http://elmape.rug.ac.be/elmape Keywords «Measurements, thermal design, efficiency, converter circuits» Abstract A flow calorimetric system is proposed which measures the temperature rise of the air across the room of the device under test. The mass flow of the air is stabilised by controlling a fan in such way, that the temperature rise of a known dissipation is kept constant. The efficiency of power electronic converters is continuously increasing. The current and voltage waveforms contain frequencies that can disturb a wattmeter. This is in particular true for variable speed drives. The output voltage of frequency converters contains indeed slopes up to 20V/ns, which reduce the accuracy of a wattmeter. The accuracy of a wattmeter is also limited due to the fact that two similar values are subtracted. With an efficiency of 95% and a wattmeter accuracy of 1%, the accuracy for the losses is only about 40%. A calorimeter based direct loss measurement can be much more accurate. Calorimeters are mentioned as a possible method for magnetic materials [1], inductors [2], for transformers [3], as a method for measuring motor losses [4] and for general apparatus and systems [5][6]. 1. Inertia calorimeter The inertia calorimeter is well known and is used mainly for material research in chemistry and physics, where the sample is quite homogeneous in nature and has a good thermal conductance. The total energy of a phenomenon is calculated and compensated for the heat losses of the thermal insulation. The inertia calorimeter has a few drawbacks. Normally, the heat capacity of the device under test has to be known or must be low. The principle is not suited for devices with multiple masses with long internal thermal time constants. 2. Flow calorimetric principle The device under test (d.u.t.) is thermally insulated from the environment but with a mass flow of a cooling fluid. In the steady state case, the loss of the device under test is the mass flow of the cooling fluid multiplied with the temperature rise of the cooling fluid and the specific heat capacity of the cooling fluid. (1) (2) T1 : temperature before the d.u.t. ; T2 : temperature after the d.u.t.; Td: temperature difference. Td c m P p ⋅ ⋅ =  1 2 T T Td - =