Richard Beddingfield

Performance investigation of hybrid converter systems for mobile mining applications

To supply the AC high power drive systems, several Active Front-Ends (AFEs) with DC choppers are currently used to ensure reliable operation and an acceptable harmonic current spectrum. Recently, integration of the energy storage system with the mining equipment as an example of large mobile multimotor applications has received industry attention, especially for peak load shaving and energy management of the mines. Currently, the regenerative energy is often burnt into the choppers. The industry is motivated to capture this regenerative energy since it can be as high as 60% of the motoring power, as high as 3MJ in every operation cycle and 24 MW peak power. Hybrid approach for the front-end converter system has shown a technology path to deploy on-board energy storage without sacrificing the efficiency and reliability of the entire system. This paper addresses the dynamic performance analysis of such systems through detailed simulation and laboratory scale experiments.

Investigation of series DC active filter and hybrid AC active filter performance in medium voltage DC amplfier

To further improve energy management, the US navy is exploring medium-voltage DC as the power supply of choice for next generation integrated power systems (NGIPS). Using the mature technology of multi-pulse thyristor bridge rectifiers, viable topologies are proposed that meet power density expectations. However, due to the non-linear ripple associated with thyristor commutations in such active front-ends (AFEs), a high bandwidth series AC active filter is used to smooth out the current harmonics. Similarly, a high bandwidth hybrid DC active filter is used for DC bus smoothing and improved dynamic performance. This paper will investigate the combined performance and consequential interactions of both active filters.

A novel dual voltage source converter for magnetic material characterization with trapezoidal excitation

A magnetic core testbed is intended to provide a variety of induction curves to fully characterize a magnetic material. Off the shelf solutions are prohibitively expensive and limited in testing range for research purposes. Mainly, high voltages and/ or currents and the ability to create a variety of induction profiles, beyond sinusoidal, is needed for full core characterization. This paper establishes the need for a novel magnetic core testing apparatus to explore high frequency trapezoidal excitation. Then a solution is presented using a novel dual voltage source converter circuit. The authors validate the topology in simulation and present a laboratory prototype. Specifically, the induction profile seen in many dual active bridges is of immediate interest and generated with this approach.

Distributed fiber-optic sensor for real-time monitoring of energized transformer cores

Real-time temperature mapping is important to offer an optimized thermal design of efficient power transformers by solving local overheating problems. In addition, internal temperature monitoring of power transformers in operation can be leveraged for asset monitoring applications targeted at fault detection to enable condition based maintenance programs. However transformers present a variety of challenging environments such as high levels of electromagnetic interference and limited space for conventional sensing systems to operate. Immersion of some power transformers within insulation oils for thermal management during operation and the presence of relatively large and time varying electrical and magnetic fields in some cases also make sensing and measurement technologies that require electrical wires or active power at the sensing location highly undesirable. In this work, we investigate the dynamic thermal response of standard single-mode optical fiber instrumented on a compact transformer core by using an optical frequency-domain reflectometry scheme, and the spatially resolved on-line monitoring of transformer core temperature rise has been successfully demonstrated. It is found that spectral shifts of the fiber-optic sensor induced by the temperature rises are strongly related to the locations inside the transformer as would be expected. Correlation between thermal behavior of the transformer core as derived from standard IR-based thermal imaging cameras and fiber-optic sensing results is also discussed. The proposed method can easily be extended to cover situations in which high accuracy and high spatial resolution thermal surveillance are required, and offers the potential for unprecedented optimization of magnetic core designs for power transformer applications as well as a novel approach to power transformer asset monitoring.

Active elimination of DC bias flux in series DC active filter coupling transformer

The Medium-voltage DC amplifier is a thyristor based power converter with a series DC active filter that provides a highly controllable and responsive platform to establish a high power dc bus. Having bulk power flow through the thyristor converter offers an economical and high power density solution over PWM converters. By designing the system to meet standards requested by the US Navy for the Next Generation Intelligent Power System, this paper will show a platform applicable to many high power DC microgrid fields. In particular, there are promising applications in mobile mining equipment, electric aircraft and ships. This paper proposes a novel control technique to actively mitigate the DC flux that is generated by the load current. This control approach yields significant reductions in the core volume and required transformer turns. The proposed solutions will be evaluated in a 4 kVA 400 VDC laboratory scale test-bed.

Design methodology of series DC coupling transformer in a medium-voltage DC amplifier system

The medium-voltage dc amplifier is a controllable dc source for the purpose of testing medium-voltage dc system technologies for shipboard applications. In a medium-voltage dc amplifier system, a dc active filter with a series dc coupling transformer is an integral component of the system required for both steady-state and dynamic voltage injection. This paper describes the design aspects and methodology for the series dc coupling transformer in such a system. The design of the transformer is one of the most critical aspects of this system as it has to withstand large continuous dc current offset without saturating. Based on system performance requirements, design criteria for the transformer is defined and two transformer designs based on two Iron-based magnetic materials are evaluated for a 12 kVA, 300 Vdc laboratory-scale amplifier test bed. An optimal design methodology is also proposed in this paper. Various design compromises have been studied and reported. The practical transformer design considerations and feasibility study for a medium-voltage dc amplifier system are given.

Enabling energy storage integration in high power multi-motor applications with active filter solutions

AC drive systems have gained popularity in multi-motor applications including mining industry because the production rate of mines increases by almost 20% compared to DC drive systems. Typically, to supply the AC drive systems several Active Front Ends (AFE) with DC choppers are used to insure a reliable and acceptable harmonic current spectrum operation. Recently, energy storage system integration with the mining equipment has received industry attention, especially for peak load shaving and smarter energy management of the mine. The energy storage system is intended to capture the regenerative energy and reuse it for the motoring operation of the drive. Currently, the regenerative energy is often burnt into the choppers and is not fed back to the grid‥ The industry is motivated to capture this regenerative power since it can be as high as 60% of the motoring power and as high as 24 MW. Therefore, there is a possibility of large cost reduction and component downsizing. However, present status of development seems not to be very promising mainly because energy storage systems, (such as ultracapacitors) are still considered as an add-on part to existing products. In this paper, we propose power conversion configurations, yet robust and reliable for development of the multi-motor mobile mining equipment that has encouraging incentives for both the manufacturer and the mine operator.

Performance investigation of hybrid active filter during low load condition

A hybrid active filter with a new voltage synchronization control loop is proposed to improve the harmonic content of nonlinear active front end converters for mobile mining equipment. This hybrid filter topology utilizes the DC bus established by the AFE and provides load harmonics at the PCC. Unlike traditional hybrid active filters, this topology uses no real power or control loops to maintain a DC link as this is provided by the AFE. This paper investigates the hybrid active filters performance in two compensation modes, harmonic current only, and both harmonic current and reactive power injection. Necessary considerations for the medium voltage dc testbed topology, real power flow minimization, and the active filter control during worst case load harmonic currents are also discussed.

Multi-Parameter Magnetic Material Characterization for High Power Medium Frequency Converters

With the rapid availability of new magnetic materials and even more options in post-processing techniques such as field and strain annealing, full property maps of materials and final fabricated components are needed for proper system design. This is especially critical in modern wide bandgap power electronics based converters where medium switching frequencies are used to deliver high power. In these systems, the magnetic design has a significant impact in the overall losses. The magnetics constitute a majority of the losses and magnetic properties have a defining influence on the overall systems, e.g. available power flow and soft switching regions. A new lossless structural harness that allows easy testing of cores and the development of property maps is presented. The harness also enables the testing of mechanical variations such as gapping and clamping pressure on the core.

Seamless black start and reconnection of LCL-filtered solid state transformer based on droop control

The solid state transformer (SST) is an emerging technology that can replace conventional passive transformers and actively manage renewable energy resources, energy storage devices, and loads. In this paper, a seamless black start control strategy is proposed for an SST-based smart grid system that has fault ride-through capability when it is islanded from the grid. Also, a method is developed to achieve smooth reconnection to the grid after a fault is cleared. The main component of the proposed control strategy is control of the high-voltage side converter of the SST (HV SST), which is based on a combination of droop control and an LCL filter. A single-loop controller for the capacitor voltage of the LCL filter is proposed, and simple criteria for setting compensator gains are provided. A low-voltage scaled SST system is introduced, and the controllers of the converters within the system are described. The proposed control strategy has been tested in simulation and experimentally on a low-voltage scaled testbed.