Luis Jose Garces

Parameter Adaption for the Speed-Controlled Static AC Drive with a Squirrel-Cage Induction Motor

The performance of speed-controlled induction motor drives, without a direct sensing of the flux, depends heavily on the accuracy with which the motor parameters are known. They change widely with the temperature, frequency, and current amplitude. With a control based on rotor position measurement and inner current control loops, the rotor resistance is the most essential changing parameter. A method of automatic adaption of the control to the changes in this parameter is presented. The proposed strategy is based on the measurement of only motor voltages and currents and is implemented by analog means. It does not make use of transducers or probes to measure the temperature or the flux in the motor.

Study and Development of Anti-Islanding Control for Grid-Connected Inverters

This is a report on the development of anti-islanding control for grid-connected inverters from distributed generation sources. Islanding occurs when a distributed generation source continues to provide electricity to a portion of the utility grid after the utility experiences a disruption in service. Since the utility no longer controls this part of the distribution system, islanding can pose problems for utility personnel safety, power quality, equipment damage, and restoration of service. This report proposes a new family of anti-islanding schemes that meet IEEE 1547 interconnection standards, that can detect all disruptions in service, have minimum power-quality impact, require low-cost implementation, work for multiple distributed generators, and work for any multi-phase inverters. It also provides design guidelines for the schemes, and evaluates and validates the proposed schemes for practical applications.

A new family of active antiislanding schemes based on DQ implementation for grid-connected inverters

Unintentional islanding protection of distributed generation is a key function for standards compliance. For those distributed generations that use an inverter as grid interface, the function can be implemented as part of the inverter control. Existing antiislanding schemes used in inverters have power quality and nondetection zone issues. This paper proposes a new family of schemes that have negligible power quality degradation and no nondetection zone. Design guidelines based on frequency-domain analysis is also provided. Finally, both simulation and experimental results validate the proposed schemes.

Modular High-Power Shunt-Interleaved Drive System: A Realization up to 35 MW for Oil & Gas Applications

This paper describes the experimental results of a medium-voltage modular 35-MW drive for oil and gas applications realized by interconnecting voltage-source three-level converters equally sharing the motor current. Drives rated for tens of megawatts are increasingly needed as torque helpers for gas turbines in the oil and gas industry, and one envisions that they will replace them completely in the future. These drives must be very reliable, often capable of reversible power flow and high power quality when connected to weak grids in remote areas. The pronounced torsional eigenmodes of large compressors and gas turbines demand for very low torque harmonic content.

A Four-Level Converter with Optimized Switching Patterns for High-Speed Electric Drives

High-speed electrical machines at multi-MW power level are being designed to drive high-speed compressor trains in oil and gas industry applications and for directly driving generators with gas turbines for shipboard and mobile power generation applications. The paper describes a converter topology to address such high power high frequency drive requirements. The proposed topology uses a three-phase bridge with series-connected single-phase bridges in each phase to obtain a four-level configuration. Optimized low pulse-count synchronous switching is used to limit the switching frequency of the individual devices; yet obtain the required power quality under all operating condition of the machine without use of external harmonic filters. Method of switching optimization and predicted performance of the drive are presented. Experimental results from a lab-scale prototype are provided to validate the concept.

Series-Input Parallel-Output Modular-Phase DC–DC Converter With Soft-Switching and High-Frequency Isolation

Multiphase soft-switching high-frequency isolated dc-dc converter is proposed for power conversion in modular stacked HVDC power transmission and distribution system. Input-series output-parallel connection of current-fed full-bridge dc-dc converter modules is proposed to increase voltage blocking capability at the input and decrease current ripple at the output. Basic power electronic building block is zero-current switching (ZCS) full-bridge phase-shift pulsewidth-modulated (PWM) dc-dc converter. Phase shift between switches in each leg of the converter is adjusted to control power flow, while phase shift between gate signals of individual phases is selected according to the number of phases in order to minimize ripple of the output voltage. Converter analysis is carried out to develop a simple equivalent boost converter model of the three-phase soft-switching converter suitable for system-level analysis and simulation. Strategies are developed to ensure fast detection of faults and continued operation of the converter in the case of fault in one phase module. To verify the proposed system design and analysis, experimental results on scaled-down laboratory prototype are presented for a three-phase ZCS dc-dc converter.

A Modular Stacked DC transmission and distribution system for long distance subsea applications

A new power transmission and distribution concept-Modular Stacked DC (MSDC) - architecture is described. Its main application is subsea oil and gas processing, where marinization of system components, their reliability and retrieval are the most critical requirements. In contrast to conventional HVDC systems, the proposed MSDC technology achieves the required DC transmission voltage by stacking a number of power converter building blocks in series that are easy to marinize. Since each building block is similar to a standard VFD, the MSDC technology has potentially much lower cost and higher reliability. Moreover, the modular architecture renders the system fault-tolerant and capable of operating in a degraded mode. The architecture is also highly reconfigurable as the field matures and the loads evolve over time. A generic subsea field scenario for oil and gas has been designed and analyzed. The MSDC architecture and associated system control strategy are developed and tested using a real-time simulation platform together with an experimental scaled down prototype of 160 kVA.

A high efficiency PV micro-inverter with grid support functions

This paper presents a new photovoltaic (PV) micro-inverter topology. The topology is based on a partial power processing resonant front end dc-dc stage, followed by an interleaved inverter stage. The input stage provides high efficiency, and flexibility of design for wide input voltage range and the output stage provides an effective switching ripple of twice the PWM frequency, which reduces the output filter requirement. The designed micro-inverter can also provide grid Volt/VAR support functions according to commands received by the grid. Circuit topology and operation are presented as well as experimental results for the micro-inverter. The overall micro-inverter efficiency is 96%.

A High Power Medium Voltage Resonant Dual Active Bridge for MVDC Ship Power Networks

This paper presents the design and control of a megawatt scale, medium voltage, medium frequency resonant dual active bridge dc–dc converter operating as a bus-tie converter in a dc distribution network. The high voltage (HV) side of the converter is designed using series connected low voltage (LV) devices to efficiently operate at higher switching frequencies. A combined variable frequency and phase-shift control method is proposed to achieve input–output power flow and voltage control, while maintaining soft switching operation for both the HV and LV bridges. Two 1 MW converter prototypes operated in a back-to-back arrangement are presented to validate the proposed topology and control.

A multi-objective study for down selection of a micro-inverter topology for residential applications

Micro-inverter based photovoltaic (PV) systems now represent about 8% of the U.S. residential market, and offer many advantages including safety, performance, and simplified installation. This paper presents a detailed trade-off study of micro-inverter circuit topologies. In addition to standard criteria of efficiency, reliability and cost, this study takes into account grid Volt/VAR support functions of each topology. The trade-off study concludes in the identification of a new micro-inverter architecture with high efficiency and Volt/VAR support capability suitable for application over a wide range of PV module technologies.