The International Maritime Organization (IMO) has mandated that the amendments to Annex VI of MARPOL – the Regulations for the Prevention of Air Pollution from Ships – be implemented from January 1, 2023.
Some ships have begun to adopt new technologies or equipment to improve energy efficiency and reduce emissions. Among them, ship shaft power generation technology is a simple and cost-effective solution.
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Efficiency Improvement and Emission Reduction | Shaft Belt Power Generation Technology
Marine shaft generator technology uses the ship's main engine to drive a shaft generator, utilizing the engine's surplus power to generate electricity, thus replacing the ship's auxiliary generator technology. This technology directly reduces the energy consumption of the auxiliary generator with almost no increase in the main engine's energy consumption, thereby helping ships achieve energy conservation and emission reduction.
Currently, there are two main types of shaft-driven power generation technology: one is gearbox-driven shaft-driven power generation technology and the other is direct-drive shaft-driven power generation technology.
Gearbox speed-up shaft power generation technology
Gearbox-driven shaft generator technology converts the low-speed kinetic energy of the main engine into high-speed kinetic energy through a gearbox, driving a high-speed synchronous generator to produce electricity. The advantages of this technology are small generator size and low cost, but it suffers from problems such as easy gearbox wear, high maintenance costs, and high mechanical stress. Furthermore, the commonly used uncontrolled rectifier inverter limits the speed range of the shaft generator, affecting the efficiency of the main engine.
★★★ Direct-drive shaft belt power generation technology
The main engine directly drives a coaxial shaft generator to generate electricity. This design simplifies the transmission structure and eliminates the gearbox in traditional systems, thereby reducing the need for routine mechanical maintenance and upkeep.
Furthermore, the frequency converter in this solution employs fully controlled rectification technology, which not only improves the overall efficiency of the system but also significantly expands the main engine speed range that the shaft generator system can adapt to, enhancing its adaptability and stability under different operating conditions. This innovative configuration makes the entire power generation process more efficient and reliable, and reduces long-term operating costs.
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Inverter | Core component of direct drive shaft technology
Based on the requirements of direct-drive shaft-driven power generation technology, Shanghai STEP Electric has developed the AS710M series frequency converter as the core component of shaft-driven power generation systems. This is a water-cooled engineering drive frequency converter with a common DC bus architecture. ❶ It adopts a modular design, featuring three-phase full-bridge rectifier units using thyristors and three-phase full-bridge inverter units using IGBT devices. Through flexible unit combinations, it can be configured as a two-quadrant frequency converter, a four-quadrant frequency converter, or a multi-drive frequency converter. ❷ Its control unit can be equipped with various types of control algorithms to meet the needs of various application scenarios from the ship's power generation side to the power consumption side. ❸ It meets CE certification requirements, and the product has already passed the China Classification Society certification.
AS710M unit appearance
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Technical Features | AS710M Series Frequency Inverters
Encoderless control technology
The AS710M series frequency converter adopts a rotor angle adaptive control algorithm, which eliminates the need for a speed sensor, allows for direct start-up, and ensures high stability.
PWM Fully Controlled Rectification Technology
The frequency converter outputs stable DC power within a range of 1.8 times the main engine speed, ensuring high-quality three-phase AC voltage.
Small grid-connected inrush current
The optimized grid-connected control loop results in an approximately 0 Ampere current surge during manual closing operations.
Long-term online networking technology
Virtual synchronous generator control technology enables long-term grid-connected operation with auxiliary generators, reducing shaft stress and extending service life.
Convenient power expansion
It features a common DC bus architecture, modular design, and a maximum output power that can be expanded to 6.4MW.
(Power Expansion System Diagram)
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Real-world application | Xinshida & Jiangsu Yuanshang Shipbuilding
ESTDA, in collaboration with Jiangsu Yuanshang Marine Electric Co., Ltd., has jointly developed a marine permanent magnet shaft-driven power generation system using the AS710M frequency converter unit as the core power conversion device. The system has been installed on board and has successfully completed sea trials and passed acceptance testing. This achievement aligns with the International Maritime Organization's initiative regarding the amendments to Annex VI of MARPOL, conforms to the national "dual-carbon" strategy, and provides a solution for building a global green shipping industry.
(Results of the axle system diagram)
All functions and performance indicators meet the shipyard's requirements. The main performance tests completed on board are as follows:
1) Long-term network test of axial-mounted and auxiliary-mounted generators
2) Shipwide power supply test at 1.42 times rotational speed range
3) Ballast pump sudden increase and decrease test
4) Main engine speed drop test
(Axle-driven frequency converter cabinet)
According to data provided by the shipowner, the installation of the shaft-driven generator system saves an average of 1 ton of fuel per day, resulting in daily savings of approximately 5,000 yuan, and an estimated annual savings of 1.25 million yuan (based on 250 operating days per year). The application of shaft-driven generators brings significant economic benefits to the shipowner and also has a significant effect on reducing carbon emissions. Each ton of heavy fuel oil produces approximately 0.8 tons of carbon dioxide, and it is estimated that carbon dioxide emissions will be reduced by 200 tons annually, demonstrating considerable environmental value.
(Actual ship)
With the global mandatory implementation of Annex VI of the International Maritime Organization (IMO) MARPOL regulations on January 1, 2023, shaft-driven power generation, as a solution with high cost-effectiveness, significant emission reduction effect and simple system architecture, can help ship owners easily achieve emission reduction targets and generate profits.
In highly complex applications like shaft-driven power generation, the STEP Electric team possesses considerable experience in product design, on-site commissioning, internal production, and quality management. STEP Electric's AS710M series frequency converters will play a significant role in building a global green shipping industry.
