Low-voltage Direct Current Power Research Articles

MW-Scale High-Voltage Direct-Current Power Conversion for Large-Spacecraft Electric Propulsion

This paper proposes a megawatt (MW)-scale high-voltage (HV) electrical power-conversion element for large-spacecraft electric propulsion (EP) systems. The proposed scheme is intended for long-term and crewed missions, and it is driven by a nuclear electric propulsion (NEP) that acts as a heat source. The scheme includes (i) A two-rotor generator (TRG), (ii) A rectification stage, and (iii) An isolated dual output DC-DC (iDC2) converter. The TRG is a high-reliability electric machine with two rotors, a permanent magnet rotor (PMR), and a wound field rotor (WFR). The PMR has a fixed flux and hence back-EMF, while the back-EMF due to the WFR is controlled by injecting a direct current (DC) into the WFR winding. The total TRG output voltage, which is the sum of voltages due to the PMR and WFR, is controlled over a prescribed region of spacecraft operation. The output of the TRG is rectified and connected to the input of the iDC2 converter. The iDC2 converter uses a three-winding transformer, where the primary winding is fed from the rectified output of TRG, the secondary winding processes the propulsion power to an electric thruster via a high-voltage DC (HVDC) link and a tertiary winding that is connected to the spacecraft’s low-voltage DC (LVDC) power system. Three controllers are proposed for the system: an HVDC voltage controller, an HVDC current controller that controls the voltage and current processed to the thruster, and an LVDC controller that adjusts the current to the LVDC system. Detailed analytical models for the TRG, iDC2 converter, and controllers are developed and verified via simulations under different conditions. The analytical studies are further validated via results from a laboratory prototype.

Thermoelectric Refrigeration System

A thermoelectric refrigerator, also known as a thermoelectric cooler module or Peltier cooler, is an electric component made of semi-conductors that acts as a tiny heat pump. When a thermoelectric cooler module is powered by a low voltage direct current power source, heat is transferred from one side to the other. As a result, one module face will be cooled while the opposite face is heated at the same time. The same fundamental laws of thermodynamics govern both thermoelectric and mechanical refrigerators, and both refrigeration systems, despite their vastly different appearances, operate on the same principles.

Preliminary Design of a Superconducting LVDC Power Cable for Tokamak Application

Tokamak device requires a very high current power supply from the local power distribution sources to the targeted magnets such as toroidal field (TF) coils and poloidal field (PF) coils. This paper presents a preliminary design of a 30-m/1-kV/10-kA low voltage direct current (LVDC) superconducting cable for the potential in Tokamak applications. The outer diameter of the DC cable is 122.41 mm, and the pressure drop of liquid nitrogen (LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) in the inner and outer channels is about 6.59 kPa. The flow velocity of inner and outer LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> channels are 0.5 m/s and 0.25 m/s, respectively. The temperature rise of the entire cable was designed to be less than 5 K, which enhances the electricity supply safety and reliability. These preliminary design lays some technical bases for achieving high current and low loss power transmission. The designing results show that the LVDC superconducting cable has significant potentials for Tokamak applications compared with conventional copper cables.

A loop-analysis theory based power flow method and its linear formulation for low-voltage DC grid

As in alternative-current (AC) networks, the power flow (PF) task is the backbone of direct-current (DC) networks with the development of DC power system. In this paper, it proposes a loop-analysis theory based iterative power flow method for the low-voltage DC (LVDC) power grids. And further the linear power flow model via Taylor's series expansion has also been developed. Based on the node-branch incidence matrix, the relationship between the branch powers and node injection powers has been established. The formation of the proposed iterative method and its linear approximation are derived based on the branch powers rather than the injected currents. ZIP loads and V buses (multi-slack buses) have been taken into account. Simulation results verified the accuracy and speed of the proposed methods in comparison with the classical Newton-Raphson method and two other existing linear methods for both radial and meshed networks.

Service life extension of SH16 bridges – New Zealand's first hybrid corrosion protection

State Highway 16 (SH16) is a motorway of significant strategic importance, connecting central Auckland to the city's western suburbs and beyond. It carries an average of 90 000 vehicles per day and runs through an environmentally sensitive coastal marine reserve. Two bridges on the route – Whau River Bridge and Causeway Bridge – were rehabilitated due to extensive chloride contamination as a result of exposure to the marine environment. This paper offers a holistic review of the inspection, durability assessment and design processes, and discusses construction, operation and maintenance details. The durability assessment considered deterioration mathematical modelling with regard to service life extensions of 25 and 50 years. A hybrid corrosion protection (HCP) system was selected as the preferred corrosion management solution. The system operates in two phases, initially energised using low-voltage direct current power to arrest ongoing corrosion and thereafter in galvanic mode to provide corrosion prevention. A structural health monitoring system was also designed and installed to offer long-term performance monitoring. The HCP system minimised physical works on site, negated the requirement for extensive replacement of chloride-contaminated concrete, allowed work to take place around the natural tide cycles and offers long-term protection. This is the first HCP system designed and installed in New Zealand and is believed to be the first of its kind for prestressed concrete in tidal waters.

On Optimal Cost Planning of Low Voltage Direct Current Power Distribution Networks

In this article, optimal planning problem of large-scale urban power distribution network, in the presence of low-voltage direct current (LVDC) distribution technology, is formulated. The problem is modeled as a minimization of cost function comprising construction and loss costs. Simulations are performed on an urban test-case; spatial load forecasting is adopted and imperialist competitive algorithm (ICA) is utilized to find the optimal solution. Results show that the smaller sizes (large numbers) of MV substation (distribution transformer and rectifier) give the optimal solution. MV substations have standard sizes up to 2500 kVA; the proposed planning approach opted substations of size up to 315 kVA—for a total cost function comprising costs of LV feeders and MV substations.

Load Characteristics in Low Voltage DC Power Supply Systems

Low voltage direct current (LVDC) power supply systems have brought new growing point to low voltage power supply systems due to the high efficiency, improved reliability and power quality. In order to realize the extensive advancement of LVDC power supply systems, it is necessary to discuss several issues on the load side in LVDC systems, to reflect the advantages of LVDC systems on the load side. Based on the above purpose, this paper compares the electrical efficiency, power quality and reliability of load side between LVDC and traditional AC power supply systems, analyzes the compatibility of existing load in LVDC systems and finally, summarizes the load operating characteristics and load model in the LVDC systems. The research shows feasibility and superiority for the existing load when supplying from LVDC systems.