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

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

Critical Design Criterion for Achieving Zero Voltage Switching in Inductorless Half-Bridge-Driven Piezoelectric-Transformer-Based Power Supplies

A methodology for predicting the ability of inductor-less driven piezoelectric transformer (PT) based power supplies to achieve zero voltage switching (ZVS) is presented. A describing function approach is used to derive an equivalent circuit model of the PT operating in the vicinity of ZVS and the subsequent application of the model provides a quantitative measure of a PT's ability to achieve ZVS when driven by an inductor-less half-bridge inverter. Through detailed analysis of the analytical model, the limitations of the inductor-less half-bridge driven PT are exposed from which guidelines for designing both the PT and inverter are derived

Minimum charge-recovery time control with parallel connected buck converters

Optimal-time control to minimise a converter’s recovery time has thus far been reported only for single power module converters. This paper adapts the optimal-time control problem and applies it to converters based on multiple power modules. Additionally, a novel minimum charge-recovery time control is also proposed for the multiple power module converter which produces a recovery time shorter than that in the optimal-time control. A 20 W converter is used to demonstrate the improved characteristics under primary regions of operation. Results show that the transient recovery time during a load step change is improved by 75% compared to traditional optimal time control

Assessment of thermal runaway in commercial lithium iron phosphate cells due to overheating in an oven test

Overheating by oven exposure testing is a fundamental method to determine the severity of thermal runaway (TR) in lithium-ion cells. The TR behavior of lithium iron phosphate (LFP) cells under convection oven exposure is quantified and a comparison is made of their stability and severity against that of lithium metal oxide cells under similar conditions presented in the literature. The convection oven test is carried out at 180°C and 220°C, the TR response of the LFP cells is shown to be significantly more stable and less severe than lithium cobalt oxide cells tested in the literature. Also, under an oven abuse test a cylindrical cell is shown to have near uniform surface temperature along its length

Evaluation of silicon MOSFETs and GaN HEMTs in soft‐switched and hard‐switched DC‐DC boost converters for domestic PV applications

Hard‐switched high‐gain DC‐DC converters such as the boost converter play an important role in renewable energy systems. Research to increase their efficiency is important and can be achieved using soft‐switching techniques; however, that approach requires an auxiliary circuit. The auxiliary circuit decreases power density and reliability while increasing the cost. Moreover, soft‐switching topologies usually cannot improve the efficiency for all power and voltage ranges. Wide bandgap (WBG) devices, such as gallium nitride (GaN), result in lower switching losses than silicon (Si), can be used while retaining the simple structure of a hard‐switched topology. However, the high cost of these devices is problematic for their frequently cost‐sensitive applications. To quantify the cost and efficiency, this study compares soft‐switching techniques and WBG‐based switches in DC‐DC boost converters for a photovoltaic (PV) energy application. The performance of four prototypes including the soft‐switched and hard‐switched DC‐DC converters with both state‐of‐the‐art Si and GaN switches are evaluated in terms of cost, power density, efficiency, and reliability using theoretical analysis, simulation and experimental results. It is shown that the GaN‐based hard‐switched converter provides higher efficiency and power density; it is more expensive than its Si‐based counterpart, yet is cheaper than soft‐switched converters

Analysis, design and modelling of two fully- integrated transformers with segmental magnetic shunt for LLC resonant converters

To achieve a precise, high leakage inductance for an integrated magnetic transformer, a magnetic shunt (based on low- permeability materials) is usually added to the planar transformer. However, high-performance low-permeability power materials are not readily available in the market. Therefore, two new topologies for shunt-inserted planar transformer are proposed in this paper. In the proposed topologies, the magnetic shunts are based on high-permeability materials like ferrite, which is widely available, and use multiple small gaps to approximate a low-permeability material as an alternative to a low-permeability magnetic shunt. The analysis, design and modelling of the proposed planar transformers are presented in detail. It is shown that the magnetizing inductance can be controlled by vertical air gaps and the leakage inductance value can be controlled by the thickness of the shunt. Hence, the desirable leakage inductance and magnetizing inductance values for the integrated transformer can be obtained for use in LLC resonant converters. The theoretical analyses are verified by finite element analysis (FEA) and the AC resistance for the proposed topologies is discussed

Equivalent circuit parameter extraction of low-capacitance high-damping PTs

Existing equivalent circuit extraction techniques are inaccurate for piezoelectric transformers (PTs) with low-input capacitance or high damping. A new method is presented, offering improved accuracy in both damping resistance and resonant frequency extraction compared with state-of-the-art methods. Effectiveness is evaluated on two sample PTs, with the proposed method achieving up to 84% decrease in error compared with previous methods

Present and Future Bounds on Non-Standard Neutrino Interactions

We consider Non-Standard neutrino Interactions (NSI), described by four-fermion operators of the form $(\bar{\nu}_{\alpha} \gamma {\nu}_{\beta}) (\bar{f} \gamma f)$, where $f$ is an electron or first generation quark. We assume these operators are generated at dimension $\geq 8$, so the related vertices involving charged leptons, obtained by an SU(2) transformation $\nu_{\delta} \to e_{\delta}$, do not appear at tree level. These related vertices necessarily arise at one loop, via $W$ exchange. We catalogue current constraints from $\sin^2 \theta_W$ measurements in neutrino scattering, from atmospheric neutrino observations, from LEP, and from bounds on the related charged lepton operators. We estimate future bounds from comparing KamLAND and solar neutrino data, and from measuring $\sin^2 \theta_W$ at the near detector of a neutrino factory. Operators constructed with $\nu_\mu$ and $\nu_e$ should not confuse the determination of oscillation parameters at a $\nu$factory, because the processes we consider are more sensitive than oscillations at the far detector. For operators involving $\nu_\tau$, we estimate similar sensitivities at the near and far detector.Comment: Erratum added at the end of the documen