Why we should apply SVG & APF in DC charge piles

We can definitively state that for high-power DC charging piles in gas stations or service areas, it is highly recommended, and in many cases essential, to install a Static Var Generator (SVG) or an Active Power Filter (APF) alongside them. The ideal solution is often a hybrid device that combines both functions, such as a Hybrid-APF or an Active Reactive Compenser (ARC).

This is not an "optional upgrade" but a fundamental safeguard to ensure the safe, reliable, and efficient operation of the charging station. The following analysis breaks down the reasons, necessity, solutions, and selection criteria.

I. The Root Cause: How DC Charging Piles "Pollute" the Grid

A DC charging pile is essentially a high-power non-linear rectifying load. Its core function is to convert grid Alternating Current (AC) into Direct Current (DC) to charge electric vehicle batteries. This AC/DC conversion process, primarily performed by IGBT rectifier circuits, creates two major power quality issues:

1. Significant Harmonic Currents:

   • The charging piles draw non-sinusoidal, distorted current from the grid, generating rich harmonics, particularly characteristic harmonics like the 5th, 7th, 11th, and 13th.

   • Hazards: Harmonic currents cause line overheating, accelerate the aging of cable and transformer insulation, and can lead to neutral line overload (due to triple-n harmonic summation), which in severe cases can cause fires. Crucially, harmonics interfere with sensitive control equipment within the gas station (e.g., tank level monitoring systems, payment systems, surveillance systems), causing data errors or system crashes.

2. Reactive Power Demand:

   • Charging piles also absorb reactive power during operation, leading to a lower power factor.

   • Hazards: Reactive current consumes transformer capacity, increases line losses, and can lead to higher electricity costs (if the utility company imposes penalties for a low power factor). When multiple high-power charging piles operate simultaneously at high speed, the massive reactive power surge can cause grid voltage fluctuations and flicker, resulting in flickering lights and unstable operation of other equipment within the gas station.

II. Why are Gas Stations/Service Areas Particularly Vulnerable?

1. Relatively Limited System Capacity: The distribution transformer capacity of a gas station or service area is typically in the range of a few hundred kVA to one or two thousand kVA. A single 120kW DC charger can have a peak current of nearly 200A. Starting multiple units simultaneously imposes a much greater strain on the grid compared to a large industrial park or commercial complex (which have larger transformers and a "stronger" grid).

2. Extremely High Safety Requirements: Gas stations contain flammable and explosive environments. Any equipment failure or spark caused by power quality issues (e.g., line overheating, voltage instability) poses a potential catastrophic risk. Ensuring pure and stable power supply is a lifeline for safe operation.

3. High Sensitivity to Voltage Fluctuations: Equipment such as point-of-sale systems, fuel pump controllers, and level gauges are highly sensitive to voltage sags. A voltage dip can cause a fuel dispenser to freeze or measure inaccurately, directly impacting business and user experience.

4. Avoiding Cross-Interference: Without mitigation, harmonics and reactive power generated by the chargers can travel through the grid and interfere with other equipment like fuel dispensers, and vice versa. Mitigation ensures "harmonious coexistence" between all devices.

III. The Roles of SVG vs. APF and How to Choose

Conclusion: For charging station scenarios, both harmonic and reactive power issues typically need to be addressed. Therefore, the best choices are:

1. Install separate APF and SVG units for dedicated mitigation.

2. Preferred Solution: Install a Hybrid Active Power Filter (Hybrid-APF) or a comprehensive power quality correction device. These integrated units combine APF and SVG functionality, allowing for simultaneous and independent compensation of harmonics and reactive power. They offer a better cost-performance ratio and a smaller footprint, making them ideal for the compact space of a gas station electrical room.

IV. Solution Design and Implementation Recommendations

1. Mitigation Approach: Centralized mitigation at the low-voltage side of the station's main distribution transformer is recommended. Connecting the APF/SVG in parallel to the main distribution panel provides a clean, stable power environment for the entire gas station (including both chargers and original fuel equipment), achieving global governance.

2. Capacity Calculation:

   • APF Capacity: Estimated based on the total rated current of all chargers and their typical current distortion rate (THDi, usually 30-35%). Formula: APF Rated Current ≥ Total Charger Current × THDi × Safety Factor (1.2-1.3).

   • SVG Capacity: Calculated based on the total reactive power demand of the chargers. This often requires measurement or calculation based on rated power and power factor.

   • Recommendation: Conduct a professional power quality assessment to accurately determine the required capacity based on measured data.

3. Key Product Selection Criteria:

   • Response Speed: Must be extremely fast (<5ms) to track the rapid load changes of the charging piles.

   • Protection Rating: Outdoor installation requires at least IP54; indoor installation requires IP20 or higher to handle dusty, humid environments.

   • Certification & Safety: Products must have relevant certifications and comply with electrical installation codes for potentially hazardous areas.

   • Smart Monitoring: Preferably supports cloud platform monitoring for remote viewing of power quality data and device status, enabling unattended operation.

Summary

For DC charging pile projects in gas stations/service areas, installing power quality mitigation equipment (APF/SVG) is not a question of "if," but rather "how to select and install."

This is a crucial investment whose returns are realized through:

• Safety: Elimination of fire hazards, protection of life and property.

• Reliability: Ensures stable operation of all charging station and gas station equipment, preventing downtime losses.

• Economy: Saves on extra electricity costs caused by harmonics and reactive power, avoids utility penalties, and extends equipment lifespan.

• Compliance: Meets the mandatory requirements of the national grid for power quality (harmonics, power factor).

The cost and space for power quality mitigation should be integrated into the overall design from the initial project planning stage, thereby creating a safe, efficient, and reliable green energy refueling point.