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A selection switch based cell-to-cell voltage equalizer requires only one dual-port dc-dc converter shared by all the cells. A cell-to-cell voltage equalizer is proposed that utilizes a capacitively level-shifted Cuk converter and low-frequency cell selection switches. The absence of isolation transformer and diodes in the equalizer leads to high efficiency, and the use of low-frequency selection switches significantly reduces the cost of the drive circuits. A low-frequency cell selection network is proposed using bipolar voltage buses, where the switch count is almost half, compared to the existing low-frequency cell-to-cell equalizers for the case of a large number of cells. A novel approach for cell voltage recovery compensation is proposed, which reduces the number of operations of the selection switches and the equalization time. The proposed equalizer is implemented with relays and verified with an 8-cell Li-ion stack. The developed prototype shows the efficiency of over 90\% and good voltage balancing performance during charging, discharging, and varying load conditions. Experimental results also show about one order of magnitude reduction in the number of relay switchings and a significant reduction in equalization time using the proposed voltage compensation.

In this paper, a photovoltaic (PV) reconfigurable grid-tied inverter (RGTI) scheme is proposed. Unlike a conventional GTI that ceases operation during a power outage, the RGTI is designed to act as a regular GTI in the on-grid mode but it is reconfigured to function as a DC-DC charge-controller that continues operation during a grid outage. During this period, the RGTI is tied to the battery-bank of an external UPS based backup power system to augment it with solar power. Such an operation in off-grid mode without employing communication with the UPS is challenging, as the control of RGTI must not conflict with the battery management system of the UPS. The hardware and control design aspects of this requirement are discussed in this paper. A battery emulation control scheme is proposed for the RGTI that facilitates seamless functioning of the RGTI in parallel with the physical UPS battery to reduce its discharge current. A system-level control scheme for overall operation and power management is presented to handle the dynamic variations in solar irradiation and UPS loads during the day, such that the battery discharge burden is minimized. The design and operation of the proposed RGTI system are independent of the external UPS and can be integrated with an UPS supplied by any manufacturer. Experimental results on a 4~kVA hardware setup validate the proposed RGTI concept, its operation and control., Comment: 8 pages, 10 figures. This manuscript is under review in IEEE Transactions

Batteries are connected in series to meet the voltage requirement in many applications. A voltage equalizer circuit is necessary to ensure that none of the batteries is over-charged or over-discharged. A novel fast soft-switched cell-to-cell voltage equalizer topology is proposed in this work. This topology can transfer charge from multiple over-charged batteries to multiple under-charged batteries simultaneously avoiding any unnecessary charging or discharging of a battery to achieve fast voltage equalization. The proposed circuit topology and modulation method ensure zero voltage switching under all battery conditions. The circuit operation and soft-switching are analyzed and experimentally verified with a four battery voltage equalizer prototype. The prototype is tested with a battery bank and a hybrid ultra-capacitor bank, and a high conversion efficiency is verified., Comment: 15 pages, 20 figures

Many high voltage applications are realized with series connected thyristors. Voltage imbalance among series connected thyristors during steady state as well as in transients is one of the major concerns. This voltage imbalance is mitigated by using static and dynamic balancing network. Dynamic balancing networks are typically designed based on reverse recovery charge of the thyristor during turn-off, which suits many applications. But this is not the case for a crowbar application, where turn-off of the thyristor is not a major circuit constraint. This paper proposes the design method for dynamic balancing network considering gate turn-on delay time and the balancing network component tolerances. The paper derives two models for the dynamic balancing network based on its charge-discharge cycle. The importance of charge-discharge cycle in the design of dynamic balancing network during high di/dt operation is emphasized. Influence of dynamic balancing resistance and crowbar current limiting inductance on voltage imbalance, charging current and discharging current is studied using the analytical model. The proposed design method also offers flexibility to incorporate differences in propagation delays among the thyristor drivers that are used to trigger individual thyristors. Such delays cannot be directly incorporated in the conventional balancing network design method based on reverse recovery. Further, it is also analytically shown that designing the dynamic balancing network based on reverse recovery charge makes the balancing network lossy and bulky for crowbar application. Simulation studies and experimental results on a 12kV , 1kA crowbar consisting of six series connected thyristors confirms the theoretical analysis and validates the proposed approach for crowbar applications., Comment: This paper is a preprint of a paper accepted by IET Power Electronics and is subject to Institution of Engineering and Technology Copyright. When the final version is published, the copy of record will be available at IET Digital Library"

Models that accurately predict the output voltage ripple magnitude are essential for applications with stringent performance target for it. Impact of dc input ripple on the output ripple for a Series Resonant Converter (SRC) using discrete domain exact discretization modelling method is analysed in this paper. A novel discrete state space model along with a small signal model for SRC considering 3 state variables is presented. The audiosusceptibility (AS) transfer function which relates the input to output ripple is derived from the small signal model. Analysis of the AS transfer function indicates a resonance peak and an expression is derived connecting the AS resonance frequency for input ripple with different SRC component values. Further analysis is done to show that a set of values for SRC parameter exists, which forms a design region, for which the normalized gain offered by the SRC for input ripple is less than unity at any input ripple frequency. A test setup to introduce the variable frequency ripple at the input of SRC for the experimental evaluation of AS transfer function is also proposed. Influence of stray parameters on AS gain, AS resonance frequency and on SRC tank resonance frequency is addressed. An SRC is designed at a power level of 10kW. The analysis using the derived model, simulations, and experimental results are found to be closely matching., Comment: Submitted to IEEE Trans. on Industry Applications

Many applications that use high energy plasma are realized using Microwave tubes (MWT) that operate at peak power in the range of hundreds of MW and frequency in GHz. One failure mode of the MWT is due to the excess energy in the tube during internal arcing events. Crowbar is used to protect the MWT by diverting the energy during fault. To compute the energy released into the MWT, the dc fault current model and the MWT model are essential. An equivalent fuse wire model is utilized for the MWT for the crowbar applications. The paper proposes a model for the dc fault current, the analysis for which is based on Joules Integral energy concept. The model provides flexibility to choose a range of practically observed reactance to resistance ratio (X/R) of transformer and also allows the use of a range of dc current limiting resistances that are utilized in the High Voltage (HV) power supply circuits in Microwave applications. The non-linearity of the system due to the multipulse diode rectifier is also considered by introducing a correction factor in the model. This paper shows that the same correction factor can be applied for both dc side parallel and series connected rectifier circuits. Both dc fault current and MWT models are verified experimentally. Using the model a 10kV , 1kA crowbar is built to limit the energy in MWT below 10J., Comment: Submitted to IEEE Trans. on Industry Applications

Grid-interactive power converters are normally synchronized to the grid using phase-locked loops (PLLs). The performance of the PLLs is affected by the non-ideal conditions in the sensed grid voltage such as harmonics, frequency deviations and dc offsets in single-phase systems. In this paper, a single-phase PLL is presented to mitigate the effects of these non-idealities. This PLL is based on the popular second order generalized integrator (SOGI) structure. The SOGI structure is modified to eliminate of the effects of input dc offsets. The resulting SOGI structure has a high-pass filtering property. Hence, this PLL is termed as high-pass generalized integrator based PLL (HGI-PLL). It has fixed parameters which reduces the implementation complexity and aids in the implementation in low-end digital controllers. The HGI-PLL is shown to have least resource utilization among the SOGI based PLLs with dc cancelling capability. Systematic design methods are evolved leading to the design that limits the unit vector THD to within 1% for given non-ideal input conditions in terms of frequency deviation and harmonic distortion. The proposed designs achieve the fastest transient response. The performance of this PLL has been verified experimentally. The results are found to agree with the theoretical prediction., Comment: 22 pages, 13 figures and 2 tables