W.G. Odendaal

Overview of Power Loss Measurement Techniques in Power Electronics Systems

Measuring power loss accurately is of great importance for power electronics systems design and for assessing system performance and reliability. This paper reviews various power loss measurement techniques in power electronics systems. A brief overview of electrical methods for loss measurements is given. Calorimetric methods, the most accurate of all instruments for measuring power loss, are described along with their implementations. The pros and cons of various techniques are discussed and compared for estimating the losses in integrated power electronic modules (REM).

Overview of power loss measurement techniques in power electronics systems

Measuring power loss accurately is of great importance for power electronics systems design and for assessing system performance and reliability. This paper reviews various power loss measurement techniques in power electronics systems. A brief overview of electrical methods for loss measurements is given. Calorimetric methods, the most accurate of all instruments for measuring power loss, are described along with their implementations. The pros and cons of various techniques are discussed and compared for estimating the losses in integrated power electronic modules (REM).

An apparatus for loss measurement of integrated power electronics modules: design and analysis

A calorimetry-based apparatus for accurate loss measurement of integrated power electronics modules (IPEMs) is presented. The IPEM is placed in a closed chamber, and a heat flux sensor is implemented to measure the total heat generated in the IPEM. Thermoelectric modules are introduced to cool the IPEM and control the operating temperature of the IPEM. The temperature difference between two polished covers in the apparatus is controlled in order to reduce the measurement error caused by convection and radiation. The design and analysis of the proposed apparatus, which can measure losses up to 50 W is described below.

Leakage impedance design as function of frequency scaling in power transformers

The paper describes the relationships that exist for leakage impedance as function of frequency scaling a power transformer by either adjusting its size or by adjusting the number of cores in a distributed transformer. The frequency dependency of losses in ferrite materials are also taken into account. It is demonstrated that the leakage inductance of a lumped transformer is generally larger than that of a comparable distributed transformer. At high power levels and frequencies, it is beneficial in terms of power density and cooling to subdivide a transformer into smaller transformers. A new approach to achieving high leakage inductance in a distributed assembly is introduced. Finally, a case study of two 70 kHz stacked core transformers with high leakage inductance, for application in a 40 kW plasma burner, is presented.

Combined numeric and analytic methods for foil winding design

A new approach to eddy current analysis in foil windings, using a combination of numerical and closed form analytical solutions, is proposed. The method requires less computing power, is faster than finite element methods and is more accurate than traditional one-dimensional closed form analytical techniques. The method is applied to a foil winding inductor and its accuracy is compared to a finite element solution of the same problem.<<ETX>>

Utilizing stray capacitances of a litz wire

In power electronics applications, litz wire is widely used for reducing ohmic losses due to skin- and proximity effect eddy currents. Litz wire also introduces stray capacitance that can be utilized in the design of such devices as niters and inverting, matching and balun transmission line transformers (TLTs). This paper focuses on a set of solutions that is obtained through finite element modeling for predicting the per unit length capacitance as a function of the fractional thickness of the strand insulation, its relative permittivity, and the number of strands used in a litz wire conductor. A simple statistical approach is used to account for the unknown distribution of strand position along the lengths of litz bundles, and measured results of prototype samples are presented. Prototype structures are built using litz wire and their frequency dependent characterization is presented.

Litz Wire Pulsed Power Air Core Coupled Inductor

A methodology for designing high-current air core pulsed power coupled inductors is presented with emphasis on simplicity. Standard inductor design is based on derated current densities and magnetic flux densities to make the most efficient utilization of materials, but the presented pulsed power inductors have low duty cycle and are designed based on impedance and physical size. The frequency content of applied pulses manifests as strong eddy currents that cause high ac resistance. The use of litz wire is justified for extremely low-resistance inductors and, in our case, resulted in a design that is smaller, lighter, and less costly than when using conventional conductors. Wheelers formula is used to estimate the optimal geometry, and finite-element analysis is used to verify and finalize the design. Several 2.2-μH inductors were successfully designed and built to within 10% tolerance.

A plasma torch converter based on the partial series resonant converter

Converters for plasma torches generally operate at power levels above 30 kW, and hard switching topologies are normally used. The switching frequency at these power levels is restricted due to high switching losses and the unavailability of suitable high power transformers. While significant progress was made in soft switching by using resonant techniques, the applications were restricted mostly to lower power applications. The zero voltage switching partial series resonant converter has properties that make the application at high power levels attractive. In this paper the converter is applied to a plasma torch application where power levels can go up into the megawatt range. To increase the power rating per unit, a distributed transformer and parallel operation of a number of converters are proposed. An improved dynamic controller is introduced and experimental results are presented on a 30 kW, 40 kHz, DC plasma torch converter using an IGBT partial series resonant converter.Power converters for plasma torch applications generally operate at power levels above 30 kW, and hard switching topologies are normally used. The switching frequency at these power levels are restricted due to high switching losses and the unavailability of suitable high power transformers. While significant progress has been made in recent years in soft switching by using resonant techniques, the applications have been restricted mostly to low power applications. The zero voltage switching partial series resonant power converter has properties that make its application at high power levels attractive. In this paper, such a power converter is applied to a plasma torch application where power levels can go up into the megawatt range. To increase the power rating per unit, a distributed transformer and parallel operation of a number of converters are proposed. An improved dynamic controller is introduced. Experimental results are presented on a 30 kW, 40 kHz, DC plasma torch converter using an IGBT partial series resonant converter.

Scant modelling: a new method for optimizing functionality and form of transformers

A new approach to high frequency power transformer design, called scant modelling is proposed. It is a specially engineered transformer model which allows interactive graphical optimization of a transformer form in the presence of derating factors influenced by heating due to conduction losses, eddy currents in windings and core losses.<<ETX>>