The International Maritime Organization (IMO) has mandated the mandatory implementation of amendments to “MARPOL Annex VI—Regulations for the Prevention of Air Pollution from Ships,” effective January 1, 2023.

Some ships have already begun adopting new technologies or equipment to improve energy efficiency and reduce emissions, among which... Ship shaft-driven power generation technology is an architecture that is simple and offers high cost-effectiveness in terms of investment. 。

PART/1 Enhancing Efficiency and Reducing Emissions | Shaft-Driven Power Generation Technology

Ship shaft-driven power generation technology uses the ship’s main engine to drive a shaft-driven generator, harnessing the main engine’s excess power to generate electricity and thereby replacing the conventional auxiliary generator-based power generation system on board. This technology directly eliminates the energy consumption of auxiliary generators without significantly increasing the main engine’s energy consumption. Thus achieving the goal of helping ships conserve energy and reduce emissions.

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.

• Gearbox speed-increasing shaft power generation technology

The gear-box-driven generator technology converts the low-speed kinetic energy of the main engine into high-speed kinetic energy via a gearbox, thereby driving a high-speed synchronous generator to produce electricity. The advantages of this technology include a small generator size 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 frequency converters limit the speed range of the shaft-driven generator, thereby hindering the full utilization of the main engine's performance.

• Direct-drive shaft-generator technology (high efficiency/reliable/low cost)

The design employs a coaxial shaft-mounted generator directly driven by the main engine to generate electricity. This approach simplifies the transmission structure and eliminates the gearbox typically found in conventional systems, thereby reducing the need for routine mechanical maintenance and upkeep. Moreover, the frequency converter used in this solution adopts full-controlled rectification technology, which not only enhances the overall system efficiency but also significantly broadens the range of main engine speeds that the shaft-generator 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.

PART/2 Inverter | Core Component of Direct-Drive Shaft Generation Technology

Based on the requirements of direct-drive shaft-generator technology, Shanghai New Motion has developed the AS710M series of variable-frequency drives as the core component of shaft-generator systems. This is an engineered drive product featuring a common DC-bus architecture and liquid-cooled thermal management. ❶ It adopts a modular design, incorporating 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, the drive can be configured as either a two-quadrant, four-quadrant, or multi-drive variable-frequency system. ❷ Its control unit can be equipped with various types of control algorithms, enabling it to meet the diverse application scenarios—from the power generation side to the power consumption side on ships. ❸ The product complies with CE certification requirements and has already been certified by the China Classification Society.

(AS710M unit appearance)

PART/3 Technical Features | AS710M Series Inverters

• Encoderless control technology

The AS710M series inverters employ a rotor-angle adaptive control algorithm that eliminates the need for a speed sensor, enabling direct startup with high stability.

• PWM Full-Control Rectification Technology

The inverter 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

Optimized grid-connected control loop delivers an approximate zero-ampere current surge during manual closing operations.

• Long-term online networking technology

Virtual synchronous generator control technology enables long-term networked operation with auxiliary generators, reducing the working stress on the shaft generator and extending its service life.

• Power expansion is convenient.

Common DC bus architecture, modular design; maximum output power can be expanded up to 6.4 MW.

(Power Expansion System Diagram)

PART/4 Real-Ship Application | STEP & Jiangsu Yuanshang Shipbuilding

STEP, in collaboration with Jiangsu Yuanshang Ship Electrical Co., Ltd., has jointly developed a marine permanent-magnet shaft-driven generator system, using the AS710M variable-frequency drive unit as the core power conversion device. The system has now been installed on board a vessel, successfully undergone trial voyages, and passed acceptance testing. This achievement aligns with the International Maritime Organization’s initiative to amend Annex VI of MARPOL, supports the nation’s “Dual Carbon” strategy, and provides a viable solution for building a globally sustainable shipping industry.

(Achievement Axis System Diagram)

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

1) Long-term networking test of the main shaft and auxiliary shaft drives

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

3) Ballast pump sudden start-up and sudden shutdown tests

4) Main engine speed drop test

(Shaft-driven variable frequency cabinet)

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.

(Actual vessel)

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—offering high cost-effectiveness, significant emission reductions, and a simple system architecture—provide shipowners with an easy way to achieve their emission reduction targets while also helping them generate additional revenue. In the highly complex technical application of shaft generators, the STEP team has accumulated considerable experience in product solution design, on-site commissioning, internal production, and quality management. The STEP AS710M series of frequency converters will play a pivotal role in advancing green shipping worldwide.

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