Development of Power Semiconductors: The Quest for the Ideal Switch
From the beginning, the development of power semiconductors has centered around finding the ideal switch—one with the lowest on-state and commutation losses, the highest possible commutation frequency, and a simple drive circuit. While low-voltage applications have consistently benefited from advancements, medium-voltage users were limited to GTOs (Gate Turn-Off thyristors). However, the emergence of IGBTs (Insulated Gate Bipolar Transistors) for higher powers has brought new hope.
ABB's Exploration: The Evolution from GTO to GCT
ABB Switzerland explored new avenues, aiming to leverage the advantages of IGBTs for higher power while retaining the strengths of GTOs. This exploration led to the development of the GCT (Gate Commutated Thyristor), an evolution of the GTO. The GCT introduced several improvements, including a new gate connection, advanced housing technology, monolithically integrated diodes, and a simplified power circuit.
The Secret of the GCT: Overcoming Control Challenges
The GCT resolves the primary challenge of the GTO—control during turn-off. Traditional GTOs experienced instability during the transition from conducting to non-conducting states, requiring snubber circuits for stability. The GCT addresses this with a hard drive approach, ensuring stable and fast turn-off without the need for snubber circuits.
IGCT Technology: A Quantum Leap in High-Power Converters
ABB's IGCT (Integrated Gate Commutated Thyristor) technology represents a significant advancement in high-power converters. By integrating low-inductance drive circuits, optimizing silicon technology, and enhancing converter integration, IGCTs offer a range of benefits, including reduced losses, smaller size, and higher reliability. The technology enables the creation of modular, scalable converters with clear and coordinated development processes.
Integration and Modular Design: The Future of High-Power Converters
IGCT technology introduces two levels of integration—monolithic on the wafer and hybrid for the GCT periphery. This integration simplifies converter design, reduces size, and improves reliability. The modular approach also extends the range of applications, with IGCT converters capable of handling power levels from 250 kW to 100 MW.
Reducing Circuit Complexity: Simplifying Converter Design
GCTs turn off like transistors, eliminating the need for snubber components required in GTO converters. This simplification reduces circuit complexity and overall costs, making IGCT converters competitive with conventional IGBT converters.
IGCT Converters in Operation: Proven Reliability
The first IGCTs were installed in ABB-built plants, with the most prominent example being the 100 MW "Bremen" railway system inter-tie. These IGCTs have operated without failure since 1996, demonstrating their superior reliability and ease of series connection.
The Advantages of IGCT Technology: A Worthy Successor to the GTO
IGCT technology combines the strengths of GTOs and IGBTs, offering high voltage ratings, low losses, high commutation frequency, and excellent reliability. With its modular design, simplified circuit, and high efficiency, IGCT technology is poised to be the ideal successor to GTOs in high-power applications.