Omar Abdel-Baqi

A Dynamic LVRT Solution for Doubly Fed Induction Generators

Doubly fed induction generators have become the most common type of wind turbine generators. However, this type of generator is susceptible to grid-side low voltage and short circuits due to existence of a power electronics converter on the rotor side. When a short circuit or voltage sag happens on the grid side, the rotor current of the generator tends to rise, which could cause damage to the rotor converter. Design and implementation of a series converter on the stator side is presented in this paper to limit the current rise in the rotor. This system includes an active AC/DC inverter, three series transformers, and a DC-bus capacitor. To lower the rating of the components and make the system viable for practical solutions, an exponential decaying sinusoidal voltage, instead of a pure sinusoidal voltage, is applied by the converter during short circuit.

Series Voltage Compensation for DFIG Wind Turbine Low-Voltage Ride-Through Solution

This paper introduces a new solution for doubly fed induction generators to stay connected to the grid during voltage sags. The main idea is to increase the stator voltage to a level that creates the required flux to keep the rotor side converter current below its transient rating. To accomplish this goal, a series compensator is added to inject voltage in series to the stator side line. The series converter monitors the grid voltage and provides compensation accordingly to accomplish this aim. Since the turbine and converter stay connected, the synchronization of operation remains established during and after the fault and normal operation can be resumed immediately after the fault is cleared. To keep the current at its minimum, a control strategy has been developed to keep the injected voltage and line voltage in phase during and after the fault.

A Hybrid System of Li-Ion Capacitors and Flow Battery for Dynamic Wind Energy Support

Wind farm output power fluctuations create adverse effects on the voltage, frequency, and transient stability of the utility grid. Short-term wind farm power variations with high ramp rates can cause voltage instabilities, particularly if the farm is located in weak-grid areas. The integration of wind energy with energy storage devices to support the short-term shortcomings of wind energy is discussed in this paper. A turbine level hybrid configuration of an energy storage system is used to limit the power ramp rates and apply power smoothing. The proposed energy storage devices are the zinc bromide flow battery and lithium-ion capacitors. The actual models for the battery and capacitors used in this study are derived from laboratory tests. The wind farm power is also modeled using measured wind speed data. A new concept has been introduced to evaluate the effectiveness of energy storage system for wind energy support. The analysis shows that significant improvements can be made to shape the output power of the farm using energy storage systems.

Dynamic Performance Improvement and Peak Power Limiting Using Ultracapacitor Storage System for Hydraulic Mining Shovels

This paper presents a concept to improve the dynamic response, efficiency, productivity, and fuel consumption of hydraulic mining shovels (HMSs) using a high power energy storage system to supplement the existing diesel-powered generators. A 2.25-MW ultracapacitor system is applied to improve the sluggish dynamic response of the diesel engine during sudden load changes and to limit the engine power requirements by maintaining an optimal engine speed. When the load rate of change increases above a specified rate limit, the ultracapacitor system supplements power to support loads in order to limit the power ramp rate for the generator. In addition to the engine dynamic improvement, the ultracapacitor system supports the engine during peak power demand, allowing for a smaller engine size for the machine, which results in higher fuel savings and less exhaust emissions. An interleaved bidirectional dc/dc converter is designed to interface between the ultracapacitor bank and main dc bus. Sophisticated multilayer control strategies are designed, implemented, and applied to the system to perform complete machine power management while keeping the dc bus voltage stable. Modeling and experimental results for an 8000-hp HMS with the novel electrification architecture have also been presented.

Digital control of three-phase series converter for DFIG wind turbine low voltage ride-through solution

This paper introduces a new solution for Doubly-Fed Induction Generators (DFIG) to stay connected to the grid during short circuit condition. The main idea is to increase the stator voltage to a level that creates the required flux to keep the rotor side converter current below its transient rating. To accomplish this goal, a series compensator is added to inject voltage, during the short circuit, in series to the stator side line. Digital deadbeat controller is designed, implemented, and applied to a three-phase series converter. The proposed controller adjusts the series converter voltage with four sampling periods. Since the turbine and converter stay connected, the synchronization of operation remains established during and after the fault and normal operation can be resumed immediately after the fault is cleared. Simulation and experimental results are presented, which show the feasibility of the proposed controller for this topology.

Energy Management for an 8000 hp Hybrid Hydraulic Mining Shovel

There has been an increasing interest in concept of hybrid architecture which is penetrating the heavy industry machines, in recent years, including for hydraulic mining shovels (HMSs). Achieving increased machine efficiency, productivity, and performance, reduced emissions, and prolonged lifetime are the main goals in developing hybrid shovel structures. This paper presents the energy management concept for an electric HMS, which uses high power density energy storage systems to supplement the diesel-powered generators. A 2.25-MW ultracapacitor system is applied to improve the sluggish dynamic response of the diesel engines during sudden load changes and to reduce the engine power requirements by maintaining an optimal engine speed. In addition to the engine dynamic improvement, the ultracapacitor system supports the engine during peak power demand allowing for a smaller engine size, which results in higher fuel savings and less exhaust emissions. Detailed control schemes for the converters and system are described. Results of simulations, off-board testing, and on-board testing for an implemented 8000 hp mining shovel are provided and discussed. The machine operates smoothly at varying load conditions. The initial assessments indicate a 30% increase in machine productivity and 26% increase in fuel efficiency compared with a 120-ton conventional hydraulic machine.

The effect of available short circuit capacity and trail cable length on substation voltage amplification in surface excavation industry

The use of long-length medium-voltage portable trailing cables in the surface extraction industry to power the major excavation tools, such as electric rope shovel (ERS), electric drills, electric hydraulic mining shovel (HMS), and dragline is indispensable. Since these cables are highly capacitive with low X/R ratio, it is very important to conduct voltage stability analysis before adding a new machine to an existing power system. This paper investigates the effect of the trailing cable length on the mine substation voltage quality. An overvoltage condition that causes the failure of an auxiliary power supplies onboard one of the high-power machines is investigated. The possible causes of the overvoltage, predominantly the interaction between current harmonics generated by the use of variable speed drives and the long-cable capacitance and substation inductance, are described theoretically and simulated. Power requirements and installation guidelines for high-power electrically driven mining shovels are established. Onsite measurements are used to validate the theoretical analysis and confirm recommendations.

A dynamic LVRT solution for Doubly-Fed Induction Generator

Doubly-Fed Induction Generators (DFIG) have become the most common type of wind turbine generators. However, this type of generator is susceptible to grid side low voltage and short circuits, due to existence of a power electronics converter on the rotor side. When a short circuit or voltage sag happens on the grid side, the rotor current of the generator tends to rise, which could cause damage to the rotor converter. Design and implementation of a series converter on the stator side is presented in this paper to limit the current rise in the rotor. This system includes an active DC/AC inverter, three series transformers and a DC bus capacitor. To lower the rating of the components and make the system viable for practical solutions, an exponential decaying sinusoidal voltage instead of a pure sinusoidal voltage is applied by the converter during short circuit.