Permeance based modelling, design and optimization of supercapacitor assisted surge absorber (SCASA)
Silva Thotabaddadurage, S. U. (2021). Permeance based modelling, design and optimization of supercapacitor assisted surge absorber (SCASA) (Thesis, Doctor of Philosophy (PhD)). The University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/14602
Permanent Research Commons link: https://hdl.handle.net/10289/14602
Supercapacitor assisted (SCA) techniques are a unique set of circuit topologies designed to fulfil power conversion and protection tasks by circumventing the energy losses normally associated with RC based circuits. With million times larger capacitance compared to electrolytic type, supercapacitors (SCs) have shown a remarkable surge endurance as discovered by the University of Waikato (UoW) power electronics group. This thesis examines a patented SCA surge protector based on the novel use of SCs' surge withstanding capability, and investigates ways to optimize the present design based on the improvements made to circuit's magnetic components. The supercapacitor assisted surge absorber (SCASA) developed at UoW incorporates a coupled-inductor wound to a specially selected magnetic material—powdered-iron—that absorbs transients. Despite its high performance, the circuit generates a secondary effect of a negative voltage-peak due to inductive energy release by the core. One aim of our study is to eliminate this undesirable voltage spike using air-gapped ferrite cores. We first identified coupled-inductor transformer action under contrasting voltage conditions. In predicting the SCASA operation under both 50 Hz AC and transient conditions, a permeance based model is used. Our model highlights non-ideal characteristics of the coupled-inductor such as leakage and magnetizing inductances, and provides theoretical predictions based on the permeance coefficients extracted from manufacturer specifications. Inductance measurements are taken over a range of kilohertz frequencies to confirm the accuracy of modelling work. During initial investigations, we inserted air gaps to ferrite toroids to enhance surge energy storage capability and fringing losses associated with the core. Single- and double-gapped core approach we tested yielded positive test results showing a reduction in negative-surge effect. This encouraged us to develop circuit prototypes using commercially available (Magnetics Inc.) gapped cores of EER type which has an effective permeance comparable to original powdered-iron toroid. This new core configuration indicated improved performance under transient conditions while continually facilitating the passage of AC mains power. In particular, air-gapped cores resulted in optimizing SCASA performance by showing: • 95% depletion of the negative-surge effect associated with the coupled-inductor • ~10% reduction of MOV clamping improving the load-side voltage characteristics • improved surge endurance as per UL-1449 test standards • minimized inductance tolerance and reduced manufacturing cost To comprehend SCASA surge propagation, we applied a Laplace transform analysis to predict primary and secondary transient currents in the coupled-inductor. Compared to ideal transformer action, we quantify how the primary:secondary current ratio deviates from the turns ratio due to magnetic reluctance of powdered-iron. LTSpice numerical simulations further confirm our analytical predictions. All experimental procedures presented in this thesis are compliant with IEEE C62.41/IEC 61000-4-5 standards, and generated using a lightning surge simulator (Noiseken LSS-6230) coupled to 230 V, 50 Hz utility mains. Test results generated under these conditions were all within 10% of the predictions showing good consistency with the theorized models.
The University of Waikato
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