The "Intelligent Heart" and "Scavenger" of PV Plants: An Application Analysis of High-Voltage SVG and Passive Filtering Equipment

The "Intelligent Heart" and "Scavenger" of PV Plants: An Application Analysis of High-Voltage SVG and Passive Filtering Equipment

With the acceleration of the global energy transition, photovoltaic (PV) power plants, as a mainstay of clean energy, are rapidly developing towards large-scale and clustered configurations. However, integrating unstable solar power into the grid efficiently and with high quality presents a complex technical challenge. Among these, the reactive power compensation and harmonic mitigation are two core issues ensuring the safe, compliant, and efficient operation of a plant. This article delves into the application of key equipment addressing these issues—High-Voltage SVG (Static Var Generator) and Passive Filtering Equipment—in PV systems.

I. The Challenge: Why Do PV Plants Need These "Supporting Role" Devices?

Many believe that PV plants simply need to generate power, but the reality is far more complex:

1. Reactive Power Demand: PV inverters themselves consume reactive power. Furthermore, long collection lines and step-up transformers also cause reactive power losses or charging power. This can lead to the plant's power factor failing to meet grid codes (often required to be within ±0.95) and cause voltage fluctuations at the Point of Common Coupling (PCC), potentially resulting in grid penalty fees.

2. Harmonic Pollution: PV inverters, being power electronic devices, are potential sources of harmonics, injecting specific order harmonic currents (such as 5th, 7th, 11th, 13th, etc.) into the grid. Harmonics can cause overheating of transformers and cables, accelerate equipment aging, interfere with protection devices, and degrade grid power quality.

3. Low Voltage Ride-Through (LVRT) Requirement: When grid faults cause a sudden voltage dip, the plant must not only remain connected but also provide reactive power support to help restore grid voltage. This is a mandatory requirement in modern grid codes.

To solve these problems, High-Voltage SVG and Passive Filtering Equipment are elevated from "supporting roles" to "key players" crucial to plant performance.

II. The Intelligent Heart: High-Voltage SVG - The King of Dynamic Reactive Power Compensation**

The High-Voltage SVG can be regarded as the "intelligent heart" of a PV plant, capable of instantaneously and precisely injecting or absorbing reactive power.

1. Core Functions:

Voltage Stabilization: When sudden changes in PV output (e.g., passing clouds) cause voltage fluctuations, the SVG can respond within milliseconds to generate or absorb reactive power, rapidly balancing the system voltage like a "sponge" to ensure PCC voltage stability.

Power Factor Improvement: It continuously tracks the reactive power exchanged between the plant and the grid, providing counter compensation to ensure the power factor always meets grid requirements.

Grid Fault Support: During grid voltage dips, the SVG can utilize its short-term overload capability (typically 1.3 to 1.5 times its rated capacity) to inject significant reactive current into the grid, meeting LVRT requirements and acting as the plant's "guardian."

2. Application Scenarios and Sizing Recommendations:

Applicable Scenarios: A standard device for almost all medium and large-scale (typically ≥10MW) PV plants. Especially suitable for:

   *   Plants in regions with strong solar resources and high output fluctuation.

   *   Remote plants with weak grids and low short-circuit capacity.

   *   Regions with stringent LVRT requirements.

*  Capacity Sizing: As discussed before, sizing is not a simple proportional calculation. It requires comprehensive consideration of:

   *  Empirical Estimation: 10%-30% of the PV capacity (e.g., 10-30 Mvar for a 100MW plant).

   *  Technical Calculation: Reactive power losses from transformers and lines.

*  Mandatory Verification: Meeting LVRT requirements is often the most critical factor determining the capacity, potentially leading to a final size larger than the empirical estimate.

III. The Power Scavenger: Passive Filtering Equipment – The Cost-Effective Solution for Harmonic Mitigation

Passive filtering equipment, typically referring to finely tuned  LC Filters composed of capacitors, reactors, and resistors, acts like a "scavenger" in the grid, specifically tasked with "filtering out" specific harmonic impurities.

1. Core Functions:

Filtering Specific Order Harmonics: The filter is designed to create a high-pass  resonance harmonic filter path, preventing it from injecting into the public grid.

Providing Fundamental Reactive Power Compensation: While filtering harmonics, the filter itself acts as a capacitor bank, providing fixed capacitive reactive power to compensate for the system's reactive power deficit.

2. Application Scenarios and Selection Advice:

Applicable Scenarios:

Prominent Harmonic Issues: When assessment or field measurements identify severe exceeding limits for certain harmonics, especially characteristic harmonics.

Cost-Sensitive Scenarios without Need for Fast Dynamic Compensation**: Situations where dynamic response is not critical, or as a supplement to SVG.

Collaborative Use with SVG: Forming a "Passive + Active" hybrid filtering and compensation system for optimal cost-performance.

Important Considerations:

Resonance Risk: Passive filters can potentially cause parallel or series resonance with grid impedance, amplifying other order harmonics. Therefore, detailed simulation analysis is essential.

Fixed Compensation: Its compensation characteristic is fixed and cannot dynamically track changing reactive power demands like an SVG.

Capacitive Compensation Only: It can only generate capacitive reactive power and cannot absorb it. This might be unsuitable for plants with extensive cable lines where capacitive charging power can cause voltage rise at night.

IV. Combining of the The Hybrid Application of SVG and Passive Filters

For large, complex PV plants, the ideal solution often involves having SVG and passive filters "team up," leveraging their respective advantages.

Typical Architecture:

Passive Filters: Responsible for filtering the main, high-magnitude characteristic harmonics (e.g., 5th, 7th) and handling a portion of the basic, fixed reactive power compensation.

High-Voltage SVG: Acts as the core for dynamic compensation, "filling the gaps":

Rapidly compensates for fast-changing reactive power in the system, stabilizing voltage.

Further filters harmonics not completely eliminated by the passive filters, especially non-characteristic harmonics.

Suppresses potential resonances, enhancing system security.

Advantages:

Cost-Effectiveness: Utilizing lower-cost passive equipment for the bulk of filtering and fixed compensation reduces the required SVG capacity, lowering the overall investment.

Excellent Performance: Achieves both "symptomatic and root cause" treatment for harmonic mitigation and reactive power compensation, reaching the highest standard of system power quality.

Safety and Reliability: The active control capability of the SVG can effectively avoid the potential resonance risks associated with passive equipment.

V. Conclusion and Outlook

In the pursuit of grid parity and efficient operation today, selecting the right "supporting role" equipment for PV plants has become key to determining their overall benefits.

High-Voltage SVG, with its dynamic, precise, and intelligent compensation capabilities, is the preferred choice for ensuring voltage stability and meeting grid ride-through requirements, serving as the "intelligent heart" of modern PV plants.

Passive Filtering Equipment, with its advantages of “mature technology and low cost” still plays an indispensable "scavenger" role in targeted harmonic mitigation and fixed reactive power compensation scenarios.

Looking forward, with advancements in power electronics technology, SVGs integrating Active Power Filter (APF) functionality (i.e., STATCOM+APF integrated devices) will become more prevalent. These can perfectly solve various power quality issues like reactive power, harmonics, and unbalance on a single platform. However, in large-scale PV bases, the "SVG + Passive Filter" hybrid scheme, due to its excellent economy and reliability, will remain a mainstream technical route for a long time, safeguarding the stable grid integration of clean energy.