Showing papers by "Srdjan Lukic published in 2016"

A SiC-based high-performance medium-voltage fast charger for plug-in electric vehicles

Abstract: This paper presents an isolated medium-voltage, high-power-quality and high efficiency (over 96%), fast charger for plug-in electric vehicles. The proposed fully modular fast charger uses off-the-shelf Silicon Carbide (SiC) power devices to convert the rectified single-phase 2.4 kV medium-voltage input to variable dc output. The adopted input-series-output-parallel unidirectional topology enables converter scalability in both the input voltage and the output power. Using wide bandgap (WBG) power devices enables 9 times reduction in volume and 6 times reduction in weight, compared to the state-of-the-art fast chargers, while exceeding the efficiency of the state-of-the-art fast chargers by more than 1.5% Based on the system requirements, the appropriate converter topology was selected, its operation was simulated and validated by experiments on the developed fast charger prototype.

Universal Restart Strategy for High-Inertia Scalar-Controlled PMSM Drives

Abstract: In many industrial settings, momentary power disruptions commonly occur, resulting in tripping of large electric machines, which then have to be brought to zero speed before the machine can be restarted. This can result in frequent interruptions in an industrial process, which can have negative effects on productivity. A more practical approach would restart the machine back to the original speed as soon as power is restored, not having to wait for the machine to be at a standstill. This concept is known as flying restart. In this paper, we propose an approach to implement the flying restart for permanent magnet synchronous machines (PMSM) by using an identification algorithm that determines the speed and position of the machine back-electromotive force so that the correct voltage vector can be applied, thus minimizing the inrush current during the restart. The novelty of the proposed method is that its implementation only requires nameplate machine parameters and needs no machine-specific tuning, making the approach suitable for implementation with both vector- and scalar-controlled PMSM.

A SiC-based power converter module for medium-voltage fast charger for plug-in electric vehicles

Abstract: This paper presents an isolated power converter module for medium-voltage (2.4 kV), high-power-quality (PF ≥ 0.98, current THD ≤ 2%), 50 kW fast charger for plug-in electric vehicles. The proposed high-efficiency (above 96%), and reduced-footprint converter module utilizes off-the-shelf Silicon Carbide (SiC) devices to step down the rectified single-phase medium-voltage input. The developed module can also serve as a building block for other medium voltage rectifier applications, including power supplies for data centers and other dc power distribution systems. Based on the system requirements, the appropriate unidirectional converter topology was selected, its operation was simulated and validated by experiments on the developed converter prototype.

Sensorless scheduling of the modular multilevel series-parallel converter: enabling a flexible, efficient, modular battery

Abstract: We present a control approach for the modular multilevel converter (MMC) with series and parallel module connectivity (MMSPC) that provides natural module balancing, reduced conduction losses, and enhanced robustness afforded by the parallel mode. In conventional MMC control, the voltage of each module's storage element has to be measured or estimated to enable the controller to equalize the voltages across all modules. This requirement has been one of the key barriers for MMCs in low and medium power applications. In contrast, we use the parallel connectivity of the MMSPC for module voltage balancing. It also enables robust operation in the presence of battery failure by supporting the module voltage with frequent parallelizations of the residual module capacitance. The parallel connectivity further reduces conduction losses at voltage levels below the system maximum by decreasing the effective source impedance. This approach renders attractive for the first time low and medium power MMC applications as well as MMC-based battery storage. These are illustrated with an experimental MMSPC system comprising eight battery modules that generates high-quality ac output without filtering magnetics.

Multilayer Tubular Conductor for High Q -Factor Wireless Power Transfer System Resonators

Abstract: In this paper, we investigate multilayer tubular conductor for multi-MHz Wireless Power Transfer systems high- Q (quality factor) resonators. The conductor layers’ thicknesses and current sharing between them are optimized at 13.56 MHz, showing significant reduction in conductor ac resistance ${R_{{{\rm AC}}}}$ . Capacitive ballast is used as a practical method for current sharing between layers and operation of coil near resonance. A two-layer conductor is designed, fabricated, and characterized at 27.93 MHz, showing 18.1% and 12.8% reduction in ${R_{{{\rm AC}}}}$ , compared with an identical conductor without capacitive ballast and a same size solid conductor, respectively.

Coated-Strand Litz Wire for Multi-Megahertz Frequency Applications

Abstract: Substantial induced eddy-current losses and the need for skin-depth-size strands leave litz wire out as an option for inductive applications at multi-megahertz frequencies. To address this, we analyze and minimize the litz-wire eddy-current losses by adding a coating layer to each strand while keeping the wire dimensions and packing factor constant. The skin and proximity effects of isolated and in-bundle coated strands are studied for various coating properties and dimensions. A new method is proposed for calculation of proximity losses inside coated-strand litz wire, which enables simple systematic approach for proximity loss and ac resistance ( ${R} _{\mathrm{ac}}$ ) determination. Three types of pure copper (Cu), silver-coated copper (Ag/Cu), and nickel-coated copper (Ni/Cu) strands are studied in isolation and inside a litz wire. The litz wires associated with these strands are fabricated and their power dissipations are measured. Analytical results followed by finite-element modeling and experimental results show 26% reduction in Ni/Cu litz wire ${R} _{\mathrm{ac}}$ , and 3% reduction in Ag/Cu litz wire ${R} _{\mathrm{ac}}$ at 13.56 MHz compared with same-size Cu litz wire.

A novel approach towards energy storage system sizing considering battery degradation

Abstract: Energy Storage System (ESS), with its fast ramping and bi-direction power flow capabilities, is playing a more vital role in the electric market. However, it still stands on the farther end of economic viability. As a result, a good estimate of battery service life, and therefore revenue, is necessary before the investment is made in any given application. In this paper, a set of improved degradation models are propose to estimate the useful life of an ESS when subjected to daily duty cycles (4-sec resolution). The models are validated and tuned for the target Li-Nickel Cobalt Aluminum Oxide (NCA) batteries. Time to End of Life (EOL) is estimated for batteries of different sizes to provide ancillary services and/or energy services in electric market, given different end-of-cycle state of charge. Finally, the strategies which can be used to size the battery for maximizing time to EOL are discussed.

A universal restart strategy for induction machines

Abstract: This paper presents an approach to implement the universal flying restart for an induction machine using a frequency search algorithm that determines the rotor speed so that the correct frequency and voltage can be applied to minimize the inrush current during the restart. This method only uses the measured phase current and the motor nameplate parameters, thus making it ideal for use with scalar-controlled motor drives. An additional benefit of the proposed approach is that the time to estimate the rotor speed is independent of the motor parameters, and is defined by the restart algorithm itself. Beyond the development of the algorithm, implementation issues will be considered to provide general guideline for the application of the developed algorithm.