Passive system of cooling and refrigerant fluid circulation, assisted by capillary pumping

We propose a concept design of a cooling system, primarily targeting gas-insulated switchgear enclosures which use a mixture of a refrigerant fluid, such as Novec™ 649, and a non-condensable gas for electrical insulation. The novel open-loop system relies on evaporative cooling assisted by capillary pumping, and refrigerant vapor condensation on the walls of the system enclosure. The results of experiments on a laboratory prototype are presented and discussed. Besides cooling, a major benefit of the system is in facilitating the circulation of the gas mixture in the enclosure.

All-SiC ANPC Submodule for an Advanced 1.5 kV EV Charging System under Various Modulation Methods

This work is focused on the design and experimental validation of the all-SiC active neutral-point clamped (ANPC) submodule for an advanced electric vehicle (EV) charging station. The topology of the station is based on a three-wire bipolar DC bus (±750 V) connecting an ac grid converter, isolated DC-DC converters, and a non-isolated DC-DC converter with a battery energy storage. Thus, in all types of power converters, the same three-level submodule may be applied. In this paper, a submodule rated at 1/3 of the nominal power of the grid converter (20 kVA) is discussed. In particular, four different modulation strategies for the 1.5 kV ANPC submodule, exclusively employing fast silicon carbide (SiC) MOSFETs, are considered, and their impact on the submodule performance is analyzed. Moreover, the simulation study is included. Finally, the laboratory prototype is described and experimentally verified at a switching frequency of 64 kHz. It is shown that the system can operate with all of the modulations, while techniques PWM2 and PWM3 emerge as the most efficient, and alternating between them, depending on the load, should be considered to maximize the efficiency. Furthermore, the results showcase that the impact of the different PWM techniques on switching oscillations, including overvoltages, can be nearly fully omitted for a parasitic inductance optimized circuit, and the choice of modulation should be based on power loss and/or other factors.

Lifetime and reliability improvements in modular multilevel converters using controlled circulating current

Circulating current has been an inherent feature of modular multilevel converters (MMC), which results in second-order harmonics on the arms currents. If not properly controlled, the circulating current can affect the lifetime and reliability of a converter by increasing the current loading, loss distribution, and junction temperature of its semiconductor devices. This paper proposes controlled circulating current injection as a means of improving the lifetime and reliability of an MMC. The proposed method involves modifying the reference modulating signals of the converter arms to include the controlled differential voltage as an offset. The junction temperature of the semiconductor devices obtained from an electro-thermal simulation is processed to deduce the lifetime and reliability of the converter. The obtained results are benchmarked against a case where the control method is not incorporated. The incorporation of the proposed control method results in a 68.25% increase in the expected lifetime of the converter and a 3.06% increase on its reliability index. Experimental results of a scaled down laboratory prototype validate the effectiveness of the proposed control approach.

Design and Experimental Characterization of L-CADEL v2, an Assistive Device for Elbow Motion

An experimental characterization is presented for an improved version of a wearable assistive device for elbow motion. The design is revised with respect to requirements for elbow motion assistance, looking at applications both in rehabilitation therapies and exercising of elderly people. A laboratory prototype is built with lightweight, portable, easy-to-use features that are verified with test results, whose discussion is also provided as a characterization of operating performance.

A Dual Rising Edge Shift Algorithm for Eliminating the Transient DC-Bias Current in Transformer for a Dual Active Bridge Converter

This paper deals with a well-known problem of the transient DC-bias current occurring during a phase shift transition in dual active bridge (DAB) DC/DC converters. This phenomenon, if not compensated, can cause damage to the converter or deteriorate its performance. One aim of this paper is to present a solution which allows for the elimination of the undesired transient DC-bias component in current waveforms. This solution is the dual rising edge shift (DRES) compensation algorithm. It provides a very simple implementation and fast settling time within the first half of a switching period. Moreover, the solution is independent on any measurements or system parameter values. It is based on the double-sided single phase shift (DSSPS) modulation, which is described in detail along with a converter model in steady-state. Then, the mechanisms leading to the transient DC-bias are explained, and the compensation algorithm is derived. The performance of the algorithm has been tested using a laboratory prototype. A comprehensive set of tests, involving rapid step changes in power flow and frequency sweep, are provided. Finally, the features of the proposed algorithm are briefly discussed.

Enhanced Boost Factor for Three-Level Quasi-Switched Boost T-Type Inverter

A new modulation strategy has been introduced in this paper in order to enhance the boost factor for the three-level quasi-switched boost T-type inverter (3L-qSBT2I). Under this approach, the component rating of power devices is significantly decreased. Moreover, the use of a larger boost factor produces a smaller shoot-through current. This benefit leads to reducing the conduction loss significantly. Furthermore, the neutral voltage unbalance is also considered. The duty cycle of two active switches of a quasi-switched boost (qSB) network is redetermined based on actual capacitor voltages to recovery balance condition. Noted that the boost factor will not be affected by the proposed capacitor voltage balance strategy. The proposed method is taken into account to be compared with other previous studies. The operation principle and overall control strategy for this configuration are also detailed. The simulation and experiment are implemented with the help of PSIM software and laboratory prototype to demonstrate the accuracy of this strategy.

Independent Double-Boost Interleaved Converter with Three-Level Output

This paper introduces a novel converter topology based on an independent controlled double-boost configuration. The structure was achieved by combining two independent classic boost converters connected in parallel at the input and in series at the output. Through proper control of the two boost converters, an interleaved topology was obtained, which presents a low ripple for the input current. Being connected in series at the output, a three-level structure was attained with twice the voltage gain of classic boost and interleaved topologies. A significant feature of the proposed converter is the possibility of independent operation of the two integrated boost converters, in both symmetrical and asymmetrical modes. This feature may be particularly useful in voltage balancing or interconnection with bipolar DC grids/applications. The operation principle, simulations, mathematical analysis, and laboratory prototype experimental results are presented.

High Step-Up Converter Based on Non-Series Energy Transfer Structure for Renewable Power Applications

In this paper, a high step-up boost converter with a non-isolated configuration is proposed. This configuration has a quadratic voltage gain, suitable for processing energy from alternative sources. It consists of two boost converters, including a transfer capacitor connected in a non-series power transfer structure between input and output. High power efficiencies are achieved with this arrangement. Additionally, the converter has a common ground and non-pulsating input current. Design conditions and power efficiency analysis are developed. Bilinear and linear models are derived for control purposes. Experimental verification with a laboratory prototype of 500 W is provided. The proposed configuration and similar quadratic configurations are compared experimentally using the same number of components to demonstrate the power efficiency improvement. The resulting power efficiency of the prototype was above 95% at nominal load.

A novel self-powered supply for GCT gate drivers

This thesis is devoted to the development of a novel self-powered supply (SPS) for the gate driver of integrated Gate Commutated Thyristors (GCT). In commercial GCT power supplies, a high-voltage isolation transformer is an indispensable device. Since the GCT devices are normally for high-power converters operating at a voltage level of 2.3KV to 13.8KV, the high-voltage isolation transformer is expensive in cost and bulky in size. The SPS proposed in this thesis transfers energy from GCT snubber circuits and generates a regulated dc supply for the GCT gate driver. Since the snubber circuit is at the same potential as the GCT device, the insulation level of the self-powered supply is reduced from a few thousand volts to a couple of hundred volts, leading to a significant reduction in cost and size. In this thesis, the configuration of the proposed SPS is presented, and its operating principle is elaborated. The strategy for maximizing the SPS output power is analyzed. It is demonstrated that SPS can provide a regulated output up to 60W for most commercial GCT gate drivers. The performance of the SPS is verified by experiments on a 60W laboratory prototype.