ACS580 & ACS880 Marine Propulsion & Thruster Solutions

High-Performance Variable Frequency Drives for Main Propulsion, Bow Thrusters, Azimuth Thrusters, and Dynamic Positioning

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Overview

Marine propulsion and thruster systems are the heart of any vessel — from cargo ships and tankers to offshore supply vessels, research vessels, ferries, and luxury yachts. Whether you need precise dynamic positioning, fuel-efficient transit, or rapid maneuvering in confined harbors, the performance of your electric propulsion system directly impacts operational costs, safety, and environmental compliance.

At Inomax Technology, we provide dedicated marine propulsion and thruster VFD solutions using our ACS580 (general purpose) and ACS880 (high-performance with Direct Torque Control) drive platforms. Our drives are available with type approval certificates from all major classification societies (CCS, DNV, ABS, BV, LR, RS, RINA, Class NK, KR), ensuring seamless compliance with international maritime regulations.

What we deliver for marine propulsion and thrusters:

• Ultra-low harmonic AFE technology – THDi <3% at typical loads, eliminating interference with sensitive navigation, communication, and DP equipment

• Direct Torque Control (DTC) – Full torque at zero speed, <5 ms torque response, perfect for dynamic positioning and precise maneuvering

• Regenerative energy savings – Return >95% of braking energy to the grid during crash stops or thrust reversal, reducing fuel consumption and generator loading

• Common DC bus multidrive configurations – Energy sharing between propulsion and thruster axes, reducing installed power and footprint by up to 50%

• Liquid-cooled options – Ultra-compact design for engine room space constraints, up to 50% higher power density than air-cooled equivalents

• Proven in harsh marine conditions – Conformal-coated circuit boards, IP54/IP66 enclosures, -20°C to +50°C operation, designed to withstand continuous vibration

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Thruster Types We Support

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Core Technologies for Marine Propulsion

Direct Torque Control (DTC) – ACS880

• Full torque at zero speed – Essential for dynamic positioning where thrusters must hold position against wind, waves, and current

• Torque response <5 ms – Propeller thrust changes almost instantly when the bridge commands a heading change or crash stop

• Speed accuracy ±0.01% with encoder – Precise control for DP class 2 and class 3 operations

• No encoder needed for most applications – Higher reliability in salty, vibrating environments

Active Front End (AFE) – Ultra-Low Harmonics

• THDi <3% at 80-100% load – Protects sensitive navigation (GPS, radar, gyrocompass), communication, and DP equipment

• Unity power factor (>0.99) – Reduces generator loading and fuel consumption

• Regenerative braking – Returns >95% of braking energy to the grid during crash stops or thrust reversal

• Meets IEEE 519 and IEC 61000 – Compliant with strictest harmonic standards without external filters

Common DC Bus Multidrive

• Energy sharing between axes – When one thruster regenerates, energy is available to other thrusters that are motoring

• Reduced installed rectifier power – Smaller generators, lower capital cost

• Space savings – Up to 50% reduction in cabinet footprint

• Simplified braking – No braking resistors needed if regeneration is balanced

Master-Follower Torque Control for Twin-Thruster Vessels

• Perfect load sharing – Both thrusters produce identical torque; vessel tracks straight without helm correction

• Redundant master capability – If master drive fails, any follower can assume master role

• Eliminates “nodding” and “shaking” – Common problem with mechanically coupled twin propellers

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Classification Society Approvals

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Marine Propulsion & Thruster Case Studies (Inomax Real Projects)

Case Study 1: National Scientific Research Vessel – Xiangyanghong (10,000m Winch & Propulsion Integration)

Customer: Ministry of Science & Technology, China
Vessel: Xiangyanghong – world-class oceanographic research ship
Application: Main propulsion + 10,000m deep-sea cable winch system
Drive power: 75 kW – 900 kW AFE multidrive

Challenge: This vessel carries extremely sensitive scientific instruments (sonar, magnetometers, seismic equipment). Harmonic distortion from propulsion drives had to be kept below 3% to prevent interference. The propulsion and winch systems also required perfect torque coordination during deep-sea sampling operations.

Solution: Inomax supplied ACS880 multidrive system with AFE active rectification (AIM + ALM) and multiple SMM motor modules. Common DC bus allows energy sharing between propulsion and winch. Direct Torque Control (DTC) enables precise torque response without encoders. Master-follower torque distribution coordinates twin propulsion thrusters.

Results:

• Harmonic distortion maintained below 3% – scientific instruments operate without interference

• Vessel holds position within 1 meter during winch deployment in sea state 4

• Torque balance between dual propulsion thrusters achieved within ±3%

• Regenerative energy from winch lowering reused for propulsion – fuel savings estimated at 15%

• System successfully passed multiple sea trials in Arctic, Equatorial, and high-salinity environments

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Case Study 2: COSCO Shipping – Azimuth & Bow Thrusters for Large Container Vessels

Customer: China COSCO Shipping – one of the world‘s largest shipping lines
Application: Azimuth thrusters and bow thrusters
Power range: 1,200 kW – 3,600 kW per thruster

Challenge: Large container vessels require powerful thrusters for maneuvering in congested ports. Thrusters needed high starting torque, wide speed range, and very low harmonics to avoid interference with bridge electronics. Power levels up to 3.6 MW demanded liquid-cooled drives.

Solution: Inomax supplied ACS880 AFE liquid-cooled multidrives with common DC bus. Each thruster drive includes AFE front end maintaining THDi <4% even at low load. High-frequency output (up to 500 Hz) enables high-speed permanent magnet thruster motors.

Results:

• Thruster response time <100 ms from zero to full thrust

• Harmonic distortion meets DP class 2 requirements (<5% THD)

• Liquid cooling reduces cabinet footprint by 40%

• AFE regeneration during thruster reversal returns energy to grid – estimated 10% fuel savings during maneuvering

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Case Study 3: ZPMC – Low Harmonic Windlass & Thruster Integration (4 × 250 kW AFE)

Customer: ZPMC (Zhenhua Heavy Industries) – world‘s largest port machinery manufacturer
Application: 4 × 250 kW AFE drives for windlass with integrated thruster control

Challenge: Vessel required extremely low harmonics from all drive systems (windlass + thrusters) to avoid interference with DP systems. Traditional 6-pulse rectifiers would generate THDi >40%. Space in engine room was extremely limited.

Solution: Inomax provided four AFE series drives with common DC bus. Each drive uses AFE (AIM+ALM) with LCL filter, achieving THDi <3% at 80-100% load. Common DC bus allows energy sharing between windlass (regenerating when lowering anchor) and thrusters (motoring during maneuvering).

Results:

• Harmonic distortion measured at <3% – well below classification society requirements

• Modular AFE design simplified installation – no external charging circuit needed

• Four AFE units connected to double-winding transformer with redundant design

• Cabinet size reduced by 30% compared to conventional 12-pulse + filter solution

• Energy sharing reduces peak generator load by 15%

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Case Study 4: Jiangsu Aerospace – 3200T & 3500T Crane Ship Propulsion & Thruster Integration

Customer: Jiangsu Aerospace
Vessels: Yuhang 32 (3,200T crane ship), Aerospace 53 (3,500T crane ship)
Application: Main propulsion, bow thrusters, and crane drives (integrated common DC bus)
Drive power: 75 kW – 560 kW (multiple axes)

Challenge: These crane ships require coordinated control between propulsion thrusters (for vessel positioning) and crane drives (for load lifting). When crane lifts a heavy load, vessel must hold position precisely – requiring instant thruster response.

Solution: Inomax supplied complete ACS880 multidrive system with common DC bus. Main propulsion: ACS880-R88-571A-6 + SMM (2 units). Bow thruster: ACS880-R88-571A-6 + SMM. Crane drives: multiple SMM modules. All drives share common DC bus with AFE front end.

Results:

• Vessel position maintained within 0.5 meters during 400T crane lifts

• Energy sharing between crane (regenerating when lowering) and thrusters (motoring during positioning) – 18% reduction in generator fuel consumption

• All drives CCS type-approved

• System reliability proven over 2+ years of continuous offshore operation

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Case Study 5: Nantong Liwei – Crane Ship Thruster & Winch Control System

Customer: Nantong Liwei
Vessels: HT4000-282 (250/355 kW cranes), Giant 78 (8 × 400 kW)
Application: Main propulsion integration with winch electrical control system

Solution: Two 75 kW VFDs for traction reel, two 55 kW VFDs for friction storage cable reel, plus servo control for cable discharge. Integrated with Xinjie XD5E PLC and HMI. Features include automatic constant tension follow control, real-time detection of cable length/speed/tension, automatic fault diagnosis.

Results:

• Tension accuracy maintained within ±5% of setpoint

• Operator intervention reduced by 70% due to automation

• Fault diagnosis reduces troubleshooting time by 80%

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Case Study 6: Dalian Jialin Shipbuilding – Shaft Generator for Propulsion System

Customer: Dalian Jialin Shipbuilding Heavy Industry
Application: Shaft generator (200 kW / 315 kW) integrated with main propulsion

Challenge: When main engine drives propeller, shaft generator must produce stable 380/690V 50/60Hz power regardless of engine speed variations. Harmonic distortion must be low to power sensitive onboard equipment.

Solution: Inomax supplied ACS880 AFE drives configured as shaft generator controllers. AFE rectifier maintains constant DC bus voltage while controlling generator excitation to output constant voltage and frequency across wide speed range (60-110% of nominal shaft speed).

Results:

• Voltage regulation within ±2% from 60% to 110% shaft speed

• THDi <5% at full load

• Eliminates need for separate auxiliary generator when main engine is running – fuel savings of 15-20%

• Seamless transition between shaft generator and auxiliary generator modes

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Why Choose Inomax Technology for Marine Propulsion & Thrusters?

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Frequently Asked Questions

Q1: What harmonic distortion levels can I expect with Inomax AFE drives for thrusters?
At 80-100% load, THDi is <3%. At light loads (20-50%), THDi remains below 5%. This meets the most stringent requirements for vessels with DP systems and sensitive navigation equipment.

Q2: Do I need an encoder for thruster torque control with ACS880?
No. Direct Torque Control provides excellent torque accuracy (±5%) without an encoder for >95% of marine propulsion applications. For DP class 2 or class 3 operations requiring higher precision, we recommend adding an encoder.

Q3: What is the advantage of common DC bus for multiple thrusters?
When one thruster regenerates during a turn, that energy is immediately available to other thrusters that are motoring – reducing generator loading, saving fuel (typically 10-20% during maneuvering), and reducing cabinet footprint by 30-50%.

Q4: Can I retrofit an existing diesel-mechanical vessel with electric propulsion using Inomax drives?
Yes – PTO/PTI (Power Take-Out / Power Take-In) retrofit. A shaft generator/motor is added between main engine and propeller, controlled by ACS880 AFE drive. In PTO mode, it produces power for hotel load. In PTI mode, it assists main engine or provides full electric propulsion.

Q5: How do you protect drives against salt spray and humidity?
All marine drives feature conformal-coated circuit boards. For engine rooms: IP54 enclosures. For exposed locations: IP65/IP66 enclosures with stainless steel hardware. Liquid-cooled drives are fully sealed with no fans.

Q6: What is the typical payback period for AFE regenerative drives on thrusters?
For vessels that maneuver frequently (tugs, OSVs, DP vessels), fuel savings of 10-20% typically deliver payback in 18-30 months. We provide free ROI analysis based on your vessel‘s operating profile.

Q7: What communication protocols are supported for DP system integration?
We support Modbus RTU/TCP, Profibus DP, Profinet IRT, EtherCAT, EtherNet/IP, and CANopen. For DP systems, we recommend Profinet IRT or EtherCAT with <1 ms cycle times.

Q8: Can a single ACS880 multidrive control both main propulsion and bow thruster?
Yes. Multiple inverter modules (SMMs) share a single AFE rectifier module. For example: two 1.5 MW inverters for azimuth thrusters plus one 300 kW inverter for bow thruster – all sharing common DC bus.

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Ready to Power Your Vessel with Inomax Propulsion Drives?

Whether you are building a new vessel, retrofitting an existing propulsion system, or upgrading thrusters for better DP performance, our marine propulsion specialists are ready to help.

Contact us today for:

• Free marine propulsion drive assessment

• Classification society pre-approval documents (CCS, DNV, ABS, BV, LR, RINA, RS, KR, NK)

• Retrofit proposal for replacing obsolete drives

• Hybrid and battery-ready propulsion system design

• Onboard commissioning and global service support

Inomax Technology