Proposal Description

Ship shaft-driven power generation technology uses the ship’s main engine to drive a shaft-driven generator, harnessing the main engine’s surplus power to generate electricity and thereby replacing the conventional auxiliary generator-based power generation system. This technology virtually eliminates the energy consumption of auxiliary generators without significantly increasing the main engine’s fuel consumption, thus helping ships achieve energy savings and emission reductions.

Currently, there are two mainstream shaft-driven power generation technologies: one is the gearbox-based shaft-driven power generation technology, and the other is the direct-drive shaft-driven power generation technology.

The gear-box-based speed-increasing shaft-generation technology uses a gearbox to convert the low-speed kinetic energy of the main engine into high-speed kinetic energy, thereby driving a high-speed synchronous generator to produce electricity. This technology has the advantages of a compact generator design and low cost; however, it also suffers from issues such as easy wear and tear of the gearbox, high maintenance costs, and significant mechanical stress. Moreover, commonly used uncontrolled rectifier-based variable-frequency drives limit the speed range of the shaft-driven generator, thereby hindering the full utilization of the main engine's performance. An alternative approach is the direct-drive shaft-generation technology, which directly couples the main engine to a coaxial shaft-driven generator for power generation. This design simplifies the transmission structure by eliminating the need for a traditional gearbox, thus reducing the demands for routine mechanical maintenance and upkeep. Additionally, the variable-frequency drive employed in this solution adopts fully controlled rectification technology, which not only enhances the overall system efficiency but also significantly broadens the range of main-engine speeds that the shaft-generation system can accommodate, improving its adaptability and stability under various operating conditions. This innovative configuration makes the entire power-generation process more efficient and reliable, while also lowering long-term operational costs.

Illustration of the gearbox speed-increasing shaft with power generation technology

Diagram of direct-drive shaft generator technology

Scheme advantages

Based on the requirements of direct-drive shaft-generator technology, Shanghai New Motion has developed the AS710M series frequency converter as the core component of the shaft-generator system. This is an engineered drive frequency converter with a common DC bus architecture and water-cooling thermal management.

● It adopts a modular design, featuring a three-phase full-bridge rectifier unit with thyristors and a three-phase full-bridge inverter unit with IGBT devices. Through flexible combinations of these units, it can be configured as a two-quadrant frequency converter, a four-quadrant frequency converter, or a multi-drive frequency converter.

● Its control unit can be equipped with various types of control algorithms, enabling it to meet the requirements of diverse application scenarios—from the power generation side to the power consumption side of ships.

● With encoderless control technology, the AS710M series variable frequency drives employ a rotor-angle adaptive control algorithm that eliminates the need for a speed sensor, enabling direct startup and ensuring high stability.

● PWM full-control rectification technology enables the inverter to deliver stable DC power within a range of 1.8 times the main engine’s speed, ensuring high-quality three-phase AC voltage.

● Small inrush current during grid connection; optimized grid-connection control loop ensures an inrush current of approximately 0 amperes under manual closing operations.

● Long-term online networking technology and virtual synchronous generator control technology enable long-term networked operation with auxiliary generators, reducing the working stress on the shaft generator and extending its service life.

● Easy power expansion: featuring a common DC bus architecture and modular design, the maximum output power can be expanded up to 6.4 MW.

● Meets CE certification requirements and is certified by the China Classification Society.

All functions and performance indicators meet the shipowner’s requirements. The main performance test items completed onboard are as follows:

● Long-term networking test for main shaft and auxiliary shaft drives

● Full-ship power supply test over a speed range of 1.42 times the rated speed

● Ballast pump sudden increase and sudden decrease tests

● Main engine speed drop test

According to data provided by the shipping company, after installing an axle-driven power generation system, the vessel can save an average of 1 ton of fuel per day, resulting in daily cost savings of approximately 5,000 yuan. Over a full year—assuming 250 days of operation—the estimated annual savings amount to 1.25 million yuan. The application of axle-driven power generation brings significant economic benefits to shipowners and also has a notable impact on reducing carbon emissions. Each ton of heavy fuel oil produces roughly 0.8 tons of carbon dioxide; therefore, the vessel is expected to reduce its annual carbon dioxide emissions by 200 tons, yielding substantial environmental benefits.

With the global mandatory implementation of the amendments to MARPOL Annex VI by the International Maritime Organization (IMO) on January 1, 2023, shaft generator systems—featuring high cost-effectiveness, significant emission reduction benefits, and a simple system architecture—offer shipowners both an easy path to achieving their emission reduction targets and a straightforward way to generate additional revenue. In the application of this highly sophisticated technology—shaft generators—the Xinshida team has accumulated considerable experience in product solution design, on-site commissioning, internal production, and quality management.

Shaft-driven variable-frequency cabinet