Real-Time Prediction of Power Electronic Device Temperatures Using PRBS-Generated Frequency-Domain Thermal Cross Coupling Characteristics

This paper presents a technique to predict the temperature response of a multielement thermal system based on the thermal cross coupling between elements. The complex frequency-domain cross coupling of devices is first characterized using a pseudorandom binary sequence technique. The characteristics are then used to predict device temperatures for a known input power waveform using a discrete Fourier transform-based technique. The resulting prediction shows good agreement with an example practical system used for evaluation. To reduce the computational complexity of the initial method, a digital infinite impedance response (IIR) filter is fitted to each cross coupling characteristic. A high correlation fit is demonstrated that produces a near-identical temperature response compared to the initial procedure while requiring fewer mathematical operations. Experimental validation on the practical system shows good agreement between IIR filter predictions and practical results. It is further demonstrated that this agreement can be substantially improved by taking feedback from an internal reference temperature. Additionally, the proposed IIR filter technique allows the efficient calculation of future device temperatures based on simulated input, facilitating future temperature predictions

Positive Feedforward Control Design For Stabilization Of A Single-Bus DC Power Distribution System Using An Improved Impedance Identification Technique

Due to recent advances in power electronics technology, DC power distribution systems offer distinct advantages over traditional AC systems for many applications such as electric vehicles, more electric aircrafts and industrial applications. For example, for the All-Electric ship proposed by the U.S. Navy the preferred design option is the adoption of a Medium Voltage DC power distribution system, due to the high power level required on board and the highly dynamic nature of the electric loads. These DC power distribution systems consist of generation units, energy storage systems and different loads connected to one or more DC busses through switching power converters, providing numerous advantages in performance and efficiency. However, the growth of such systems comes with new challenges in the design and control areas. One problem is the potential instability caused by the interaction among feedback-controlled converters connected to the same DC bus. Many criteria have been developed in the past to evaluate system stability. Additionally, passive or active solutions can be implemented to improve stability margins. One previously proposed solution is to implement Positive Feed-Forward (PFF) control in the load-side converter; with this technique it is possible to introduce a virtual damping impedance at the DC bus. A recently proposed design approach for PFF control is based on the Passivity Based Stability Criterion (PBSC), which analyzes passivity of the overall bus impedance to determine whether the system is stable or unstable. However, since the PBSC does not provide direct information about system’s dynamic performance, the PFF control design based on PBSC might lead to lightly damped systems. Therefore, a disturbance in the system may result in long-lasting lightly damped bus voltage oscillations. Moreover, in order to study the system dynamic performance it is necessary to know the bus impedance. A method has been proposed that uses digital network analyzer techniques and an additional converter that acts as a source for current injection to perturb the bus. The present work provides original contributions in this area. First of all, the effect of the dominant poles of the bus impedance on the system dynamic performance is analyzed. A new closed-form design procedure is proposed for PFF control based on the desired location of these dominant poles that ensures a desired dynamic response with appropriate damping. Regarding bus impedance identification using a switching converter for perturbation injection, a new technique is proposed that eliminates the need for an external converter to provide the excitation. The technique combines measurements performed by existing converters to reconstruct the overall bus impedance. Additionally, an improved perturbation technique utilizes multiple injections to eliminate the problems of injected disturbance rejection by the converter feedback loop at low frequency and the problem of attenuation due to reduced loop gain at high frequencies. The proposed methods are validated using time domain simulations, in which the bus impedance of a single-bus DC power distribution system is estimated and then utilized for the design of a PFF controller to improve the dynamic characteristics

Measurement and characterisation technique for real-time die temperature prediction of MOSFET-based power electronics

This paper presents a technique to predict the die temperature of a MOSFET based on an empirical model derived following an offline thermal characterization. First, a method for the near-simultaneous measurement of die temperature during controlled power dissipation is presented. The method uses a linear arbitrary waveform power controller which is momentarily disconnected at regular intervals to allow the forward voltage drop of the MOSFET's antiparallel diode to be measured. Careful timing ensures the power dissipation is not significantly affected by the repeated disconnection of the power controller. Second, a pseudorandom binary sequence-based system identification approach is used to determine the thermal transfer impedance, or cross coupling between the dice of two devices on shared cooling using the near-simultaneous measurement and control method. A set of infinite impulse response digital filters are fitted to the cross-coupling characteristics and used to form a temperature predictor. Experimental verification shows excellent agreement between measured and predicted temperature responses to power dissipation. Results confirm the usefulness of the technique for predicting die temperatures in real time without the need for on-die sensors

Real-time temperature estimation in a multiple device power electronics system subject to dynamic cooling

This paper presents a technique to estimate the temperature of each power electronic device in a thermally coupled, multiple device system subject to dynamic cooling. Using a demonstrator system, the thermal transfer impedance between pairs of devices is determined in the frequency domain for a quantised range of active cooling levels using a technique based on pseudorandom binary sequences. The technique is illustrated by application to the case temperatures of power devices. For each cooling level and pair of devices, a sixth order digital IIR filter is produced which can be used to directly estimate temperature from device input power. When the cooling level changes, the filters in use are substituted and the internal states of the old filters are converted for use in the new filter. Two methods for filter state conversion are developed—a computationally efficient method which is suited to infrequent changes in power dissipation and cooling, and a more accurate method which requires increased memory and processing capacity. Results show that the temperature can be estimated with low error using a system which is suitable for integration on an embedded processor

Recent advances in radio resource management for heterogeneous LTE/LTE-A networks

As heterogeneous networks (HetNets) emerge as one of the most promising developments toward realizing the target specifications of Long Term Evolution (LTE) and LTE-Advanced (LTE-A) networks, radio resource management (RRM) research for such networks has, in recent times, been intensively pursued. Clearly, recent research mainly concentrates on the aspect of interference mitigation. Other RRM aspects, such as radio resource utilization, fairness, complexity, and QoS, have not been given much attention. In this paper, we aim to provide an overview of the key challenges arising from HetNets and highlight their importance. Subsequently, we present a comprehensive survey of the RRM schemes that have been studied in recent years for LTE/LTE-A HetNets, with a particular focus on those for femtocells and relay nodes. Furthermore, we classify these RRM schemes according to their underlying approaches. In addition, these RRM schemes are qualitatively analyzed and compared to each other. We also identify a number of potential research directions for future RRM development. Finally, we discuss the lack of current RRM research and the importance of multi-objective RRM studies

Advanced thermal modelling and management techniques to improve power density in next generation power electronics

This thesis sets out a series of new techniques to improve the thermal management of power electronics. The work is motivated by the increasing impetus to design smaller, more energy efficient electronic power systems for a range of applications, notably electric vehicles. Thermal management is an increasingly important tool which can facilitate improvements in power density through better monitoring and control of system temperatures. This thesis seeks to deliver improvements in implementing this strategy. A review of the state of the art in thermal management is reported, focussing on temperature measurement, thermal characterisation and system modelling techniques. In addition, novel techniques for arbitrary dissipation control and die temperature measurements in semiconductor devices are presented. A novel analysis of the limitations of low-order thermal models is also described. Improvements and applications of these techniques form the basis of this thesis. The pseudorandom binary sequence (PRBS) technique for system identification is applied throughout the thesis to characterise thermal systems. A mathematical analysis is provided, together with a novel technique to determine the minimum gain which can be identified by PRBS techniques in the presence of noise. A novel improvement to the PRBS technique for typically ten times more noise resilient measurements is then developed based on mathematical mixing of different frequency PRBS signals. In parallel, a novel technique is formulated to estimate the temperature throughout a multiple device system using digital IIR filters and PRBS thermal characterisation, which achieves errors of 3-5% when demonstrated practically. By combining these techniques, a comprehensive temperature estimation and control methodology is implemented for a multiple device system under active cooling. Finally, the expansion of the proposed methodologies to steady-state die temperature estimation is presented with comparable accuracy to surface temperature measurements, increasing the usefulness of the developed techniques in a practical setting