Active Harmonic Filter & Static Var Generator application in Marine Electrical Systems

A ship, particularly a modern, advanced vessel, is essentially a floating, highly concentrated town of power systems. The stability, efficiency, and reliability of its electrical system are directly related to the ship's operational safety, operating costs, and mission. The SVG, as a dynamic, precise, and high-performance reactive power compensation device, plays an irreplaceable role in addressing the special challenges of marine electrical systems.

I. Characteristics and Challenges of Marine Electrical Systems

Before discussing SVG applications, one must understand the unique aspects of a marine power grid:

1. "Islanded" Operation Mode: The ship's power grid is a typical islanded microgrid. Its power is entirely supplied by onboard synchronous generators (diesel generators, gas turbine generators). The grid has limited capacity and a small short-circuit capacity, making issues of voltage fluctuation and frequency stability far more pronounced than in large land-based grids.

2. Complex and Dynamic Load Characteristics:

   • High-power impact loads: Thrusters, steering gears, winches, cranes, and elevators generate massive, rapidly changing reactive power surges during start-up and operation, causing grid voltage sags.

   • Abundant non-linear loads: Variable Frequency Drives (VFDs) are widely used in main thrusters (for electric propulsion ships), pumps, fans, etc., generating significant harmonics and absorbing reactive power.

   • Pulsating loads: Equipment like radar and sonar generate pulsed power during operation.

3. Space and Weight Constraints: Ship space is extremely valuable. Any equipment must have high power density, small footprint, and light weight.

4. Harsh Environment: Equipment must withstand high temperatures, high humidity, salt spray corrosion, and continuous vibration and tilting.

Traditional capacitor/reactor bank compensation methods (TSC/TCR) are slow-responding, imprecise, bulky, and prone to harmonic resonance with grid impedance, making them unsuitable for modern vessels. This is precisely where the SVG excels.

II. Specific Application Scenarios for SVG in the Maritime Industry

SVGs use power electronic converters to instantaneously (response time <5ms) generate or absorb reactive current, thereby dynamically stabilizing grid voltage. Their main applications are as follows:

1. Reactive Power and Voltage Support for Electric Propulsion Systems

• Target Vessels: Large ships with electric propulsion (Azipod or other podded thrusters) such as icebreakers, research vessels, cruise liners, offshore support vessels (OSVs), and LNG carriers.

• Problem: The main propulsion converters are huge reactive loads whose demand varies drastically with speed and load. This causes:

  • Generator terminal voltage fluctuations, affecting other sensitive equipment.

  • Forces multiple generators to run in parallel to provide sufficient reactive capacity, leading to very poor fuel efficiency at low load operation ("low-load running").

• SVG Solution:

  • Install SVGs centrally near the main switchboard (MSB) to provide dynamic reactive power support for the propulsion system, stabilizing grid voltage.

  • Enables "N-1" or even "N-2" operation: The SVG can replace one or even two generators in providing the required reactive power, allowing diesel engines to run at higher, more efficient load factors, significantly reducing fuel consumption and emissions. This is one of the most economically valuable applications of SVG on ships.

2. Suppressing Voltage Fluctuations and Flicker

• Target Vessels: All ships with high-power fluctuating loads, such as container ships (ship cranes), research vessels (A-frames, CTD rosettes), dredgers, and Anchor Handling Tug Supply (AHTS) vessels.

• Problem: Thrusters and deck cranes draw massive reactive currents during start-up and sudden loading, causing voltage sags and light flicker across the entire ship's grid, severely affecting the operation of other equipment and crew comfort.

• SVG Solution:

  • Install SVGs near the distribution circuits of fluctuating loads (e.g., thruster boards).

  • The instant the load starts, the SVG immediately injects the required capacitive reactive current, perfectly offsetting the inductive reactive power absorbed by the load, thereby limiting voltage fluctuations to a very small range (e.g., ±1%) and eliminating flicker.

3. Dynamic Power Factor Correction (PFC)

• Target Vessels: All commercial vessels, to meet the power factor requirements of classification societies (e.g., DNV, ABS, LR, CCS).

• Problem: Numerous motor loads (pumps, fans) cause low overall power factor, even when running at line frequency. Traditional capacitor banks cannot track load changes, risking over-compensation or under-compensation.

• SVG Solution:

  • The SVG can precisely control the entire ship's grid power factor to a set value (typically 0.98 lag or lead), avoiding utility penalties (onshore) and optimizing generator performance.

4. Working in Concert with Harmonic Filtering Equipment (APF + SVG)

• Problem: Non-linear loads like VFDs generate both harmonics and reactive power.

• Solution:

  • Integrated Solution: Modern power quality devices often integrate Active Power Filter (APF) and SVG functionalities into a single unit (called an Active Power Conditioner or Hybrid Harmonic and Reactive Compensation Device).

  • Division of Labor: The APF module filters harmonic currents, while the SVG module compensates for reactive power. One device solves two major power quality issues simultaneously, saving space and simplifying system structure. This is highly attractive for space-constrained ships.

III. Summary of SVG Advantages Over Traditional Solutions

IV. Key Points for Selection and Implementation

Selecting an SVG for marine use requires additional considerations:

1. Environmental Suitability: Equipment must meet Classification Society certifications (e.g., DNV-GL, ABS, LR, CCS, etc.), have sufficient Ingress Protection (IP) rating (e.g., IP22 or higher), and use designs and materials suitable for a marine environment (anti-salt spray, anti-corrosion).

2. Capacity Calculation: Must be based on the most severe operating conditions (e.g., thruster starting at full power while the main propulsion is also accelerating).

3. Installation Location:

   • Centralized Compensation: Installed near the Main Switchboard (MSB) to address global issues.

   • Local Compensation: Installed near specific fluctuating loads (e.g., thruster distribution board) for more targeted and effective mitigation.

4. System Integration: The SVG needs to be integrated into the ship's Power Management System (PMS) or Energy Management System (EMS) for intelligent coordinated control.

In the maritime industry, the Static Var Generator (SVG) is no longer merely a "power factor correction" device but a key core technology that enhances the stability, safety, economy, and environmental performance of the ship's electrical system.

It is particularly suitable for:

• Electric propulsion vessels, to achieve energy savings and stable operation.

• Working vessels (e.g., research vessels, construction vessels), to ensure mission execution and equipment safety under high-power fluctuating loads.

• All high-end commercial vessels, as a signature configuration of a modern intelligent grid, meeting future stricter efficiency and environmental standards (e.g., EEXI, CII).

Investing in SVG is an investment in the reliability, efficiency, and long-term competitiveness of vessel operations.