Electrical performance characteristics of high power converters for space power applications

The first goal of this project was to investigate various converters that would be suitable for processing electric power derived from a nuclear reactor. The implementation is indicated of a 20 kHz system that includes a source converter, a ballast converter, and a fixed frequency converter for generating the 20 kHz output. This system can be converted to dc simply by removing the fixed frequency converter. This present study emphasized the design and testing of the source and ballast converters. A push-pull current-fed (PPCF) design was selected for the source converter, and a 2.7 kW version of this was implemented using three 900 watt modules in parallel. The characteristic equation for two converters in parallel was derived, but this analysis did not yield any experimental methods for measuring relative stability. The three source modules were first tested individually and then in parallel as a 2.7 kW system. All tests proved to be satisfactory; the system was stable; efficiency and regulation were acceptable; and the system was fault tolerant. The design of a ballast-load converter, which was operated as a shunt regulator, was investigated. The proposed power circuit is suitable for use with BJTs because proportional base drive is easily implemented. A control circuit which minimizes switching frequency ripple and automatically bypasses a faulty shunt section was developed. A nonlinear state-space-averaged model of the shunt regulator was developed and shown to produce an accurate incremental (small-signal) dynamic model, even though the usual state-space-averaging assumptions were not met. The nonlinear model was also shown to be useful for large-signal dynamic simulation using PSpice

Improved methodology for conducted EMI assessment of power electronics and line impedance measurement

Electromagnetic Interference (EMI), primarily common mode (CM), is problematic in a wide range of electronic circuits due to its propensity to radiate, particularly in high power applications. It is routine for much effort and resources to be dedicated to its characterization and reduction as EMI compliance is a requirement for most electronic systems and devices, including power electronics. Many well-known factors contribute to a system’s EMI performance including intentional coupling from system components as well as unintentional coupling from parasitics. Sources of intentional coupling may include Y-capacitors intended to mitigate EMI as part of a filter. Unintentional coupling is more elusive and can exist throughout the system in PCB layout, cabling, load construction, and internal to components such as inverter bridges. Lesser-known contributions to EMI performance irregularities can be EMI filter asymmetries, switching asymmetries, line impedance variances, and galvanic coupling from the metrology intended to measure EMI. It is critical to understand these contributors to facilitate designs with optimal EMI performance. EMI filters are often added to designs with no consideration to asymmetries in construction and component tolerances. This proposal evaluates the impact to CM currents in cases of coupling or leakage inductance imbalances of a CM choke. Similarly, CM currents are also evaluated for cases when EMI filter Y-capacitor imbalances span the components tolerance band. Also analyzed are switching asymmetries in a typical converter topology to understand EMI impact and evaluate potential benefits if intentional asymmetric switching is applied. A practical method is introduced to measure line impedance upstream of devices under test as line impedance variation can impact the performance of EMI filter design. However, few documented practices exist to measure line impedance without specialized instrumentation. Finally, this work proposes a streamlined method for conducted emissions evaluation employing an oscilloscope, differential voltage probes, and post-processing software implemented in MATLAB. This method eliminates unintended metrology ground coupling that can significantly impact EMI measurements and minimizes risk of instrumentation damage particularly in high power systems

A general magnetic-energy-based torque estimator: validation via a permanent-magnet motor drive

This paper describes the use of the current–flux-linkage ($i{-}psi$ ) diagram to validate the performance of a general magnetic-energy-based torque estimator. An early step in the torque estimation is the use of controller duty cycles to reconstruct the average phase-voltage waveform during each pulsewidth-modulation (PWM) switching period. Samples over the fundamental period are recorded for the estimation of the average torque. The fundamental period may not be an exact multiple of the sample time. For low speed, the reconstructed voltage requires additional compensation for inverter-device losses. Experimental validation of this reconstructed waveform with the actual PWM phase-voltage waveform is impossible due to the fact that one is PWM in nature and the other is the average value during the PWM period. A solution to this is to determine the phase flux-linkage using each waveform and then plot the resultant $i{-}psi$ loops. The torque estimation is based on instantaneous measurements and can therefore be applied to any electrical machine. This paper includes test results for a three-phase interior permanent-magnet brushless ac motor operating with both sinusoidal and nonsinusoidal current waveforms

Low voltage dc to dc converter-regulator with minimum external magnetic field disturbance third quarterly progress report, 1 dec. 1964 - 28 feb. 1965

Low voltage dc to dc converter regulator with minimum external magnetic field disturbance - choke cell assembly and magnetic disturbance mapping of choke cell and coaxial converte

Calibration of seven-hole pressure probes for use in fluid flows with large angularity

Described here is the calibration of a non-nulling, conical, seven-hole pressure probe over a large range of flow onset angles. The calibration procedure is based on the use of differential pressures to determine the three components of velocity. The method allows determination of the flow angle to within 0.5 deg and velocity magnitude to approximately 1.0 percent. Also included is an examination of the factors which limit the use of the probe, a description of the measurement chain, an error analysis, and a typical experimental result. In addition, a new general analytical model of pressure probe behavior is described and the validity of the model is demonstrated by comparing it with experimentally measured calibration data for a three-hole yaw meter and a seven-hole probe

Optimisation of a Near-Field Scanning System

In this thesis, the optimisation of a near field scanning system is discussed. This system, which consists of a stationary transmitter and a movable receiver, is in use in the Experimental Physics Department at NUI Maynooth. The position of the receiver is controlled by a two axis mechanical actuator. The function of the near field scanning system is to characterise and verify different optical components in the W-Band (75¡110 GHz). The measurements are generally used as a comparison with optical set-ups that have been modelled in commercial optical packages such as CST, GRASP and ZEEMAX. Primarily this project is concerned with improving the overall efficiency of the scanning system. At first the original set-up will be introduced along with the reasoning behind subsequent upgrades. In Chapter 3 these upgrades to the system will be outlined along with the problems that arose as a result. In particular, a study of the mechanical vibration caused by the driving of the actuator is discussed. This vibrational study is split into two parts; displacement analysis and spectral analysis. Both methods are used in an attempt to understand the source of these new excitations. The implications that these vibrations have on the quality of measurements being made by the near field scanner will also be outlined. Finally, the development of a new computational tool for alignment will be discussed. The purpose behind this work is to develop a robust alignment tool that will be the centrepiece of a standardised alignment method. The construction of this tool along with its step by step testing will be outlined in Chapter 4

Optimisation of a Near-Field Scanning System

In this thesis, the optimisation of a near field scanning system is discussed. This system, which consists of a stationary transmitter and a movable receiver, is in use in the Experimental Physics Department at NUI Maynooth. The position of the receiver is controlled by a two axis mechanical actuator. The function of the near field scanning system is to characterise and verify different optical components in the W-Band (75¡110 GHz). The measurements are generally used as a comparison with optical set-ups that have been modelled in commercial optical packages such as CST, GRASP and ZEEMAX. Primarily this project is concerned with improving the overall efficiency of the scanning system. At first the original set-up will be introduced along with the reasoning behind subsequent upgrades. In Chapter 3 these upgrades to the system will be outlined along with the problems that arose as a result. In particular, a study of the mechanical vibration caused by the driving of the actuator is discussed. This vibrational study is split into two parts; displacement analysis and spectral analysis. Both methods are used in an attempt to understand the source of these new excitations. The implications that these vibrations have on the quality of measurements being made by the near field scanner will also be outlined. Finally, the development of a new computational tool for alignment will be discussed. The purpose behind this work is to develop a robust alignment tool that will be the centrepiece of a standardised alignment method. The construction of this tool along with its step by step testing will be outlined in Chapter 4

Generalised multistage modelling and tuning algorithm for class EF and class Φ inverters to eliminate iterative retuning

The additional complexity of Class EF and Class Φ inverters compared to their Class E counterparts, combined with parasitic effects becoming more prevalent as frequency and power levels increase, results in poor accuracy from traditional design methods, and usually additional iterations of manual retuning are required. In this work we propose an approach to simulating and tuning Class EF/Φ inverters, with various levels of accuracy depending on the level of knowledge of the system parasitics. Our method is comprised of a combination of analytic and numerical solving methods thus providing both insight on the progression of the algorithm and computational robustness. The aim of our algorithm formulation is to enable solutions to be found in an automated and fast way. The novelty in our work lies in the design method's concurrent capability to provide a generalised set of design inputs (e.g. DC to AC current gain, arbitrary drain voltage slope at turn on, Φ- branch resonance, etc.), inclusion of board and device non-linear parasitics, and the ability to design within the set of preferred component values. An example is shown for the design of a 50 W, 13.56 MHz inverter where the experimental setup approaches the theoretical efficiency of 97%. The algorithm changes the values of the components over 5% to 50% and improves the simulated waveform accuracy by 2 to 12 times compared to the design method based on first order approximations