In modern photovoltaic (PV) systems, string inverters not only convert DC to AC energy but are also the core of the entire power generation system. Their stability and reliability directly impact power generation efficiency and grid connection safety.

However, due to long-term exposure to outdoor environments and complex grid conditions, inverters are susceptible to multiple threats, including lightning surges, transient overvoltages, grid disturbances, and electrostatic discharge at communication ports.

This article will comprehensively analyze the key protection strategies of string inverters from the input end to the communication end and introduce how Semiware provides precise and reliable protection components for PV customers worldwide.

I. Input Protection: Handling Lightning Strike, Surge, and ESD

Photovoltaic module terminals are exposed outdoors, making them most vulnerable to lightning strikes, grid transient overvoltages, and ESD. Input protection design needs to balance withstand voltage, energy handling capacity, and response speed.

⭐ Recommended Protection Components and Their Functions

  • TVS Diode: Nanosecond-level response speed, quickly clamping high-voltage spikes.
  • MOV (Metal Oxide Varistor): Absorbs high-energy surges, preventing overvoltage damage to front-end circuits.
  • Gas Discharge Tube (GDT): Provides a protective path for high-current lightning strikes, improving overall lightning protection.

⭐ Engineer's Focus

  • Select MOVs with sufficient energy handling capacity (8/20 μs, 10/350 μs curves)
  • Series-parallel connection schemes reduce residual voltage.
  • TVS needs to balance reverse leakage current and clamping voltage.

II. DC-DC Boost and MPPT: Protecting Switching Devices and Energy Tracking Modules

MPPT modules use high-speed MOSFETs or IGBTs, which are susceptible to transient surges, reverse currents, and other shocks. Inadequate protection can lead to decreased module efficiency or even failure.

⭐ Recommended Protection Components and Their Functions

  • MOSFET (with overcurrent and overtemperature protection): Ensures stable high-frequency switching.
  • TVS Diode: Clamps overvoltage at the MPPT input/output ports.
  • NTC Thermistor: Suppresses power-on surges, protecting the switching transistors from impacts.

⭐ Engineer Focus

  • MOSFET SOA Safe Operating Area
  • TVS Selection of Appropriate VRWM (Operating Voltage) and Pppm (Surge Capability)
  • Cold Resistance and Hot Recovery Time of High-Power NTCs

III. Inverter DC-AC Main Power Stage: Handling Grid Disturbances and Load Sudden Changes

The inverter's main bridge arms (IGBT/MOSFET) directly face the complex grid environment. Overvoltage or switching transient spikes can lead to breakdown.

⭐ Recommended Protection Components and Their Functions

MOSFET/IGBT: Capable of handling high current and high switching speeds.

TVS Diode: Suppresses transient spikes during DC-AC conversion, protecting the main power devices.

⭐ Engineer Focus

  • dv/dt control and gate protection
  • TVS diodes require higher clamping accuracy and peak power capability.

IV. Output Protection: Addressing Grid Fluctuations and Lightning Coupling

Since the inverter output is directly connected to the grid, high-energy surge protection components are required.

⭐ Recommended Protection Components and Their Functions

  • MOV/GDT: Absorbs lightning coupling and high-energy surges.
  • TVS Diode: Protects sensitive electronic modules, such as SPCs and communication modules.

⭐ Engineer Concerns

  • MOV residual voltage and lifespan (pay attention to degradation after multiple surges).
  • GDT can be used in combination with MOV/TVS to form three levels of protection.

V. Communication and Interface Protection: Maintaining Stable RS485/Ethernet Communication

Communication ports are low-voltage signal links. ESD can cause communication interruptions or even damage to the main control board.

⭐ Recommended Protection Components and Their Functions

  • Low-Capacitance TVS Array
  • Designed for high-speed communication (RS485, CAN, Ethernet, Wi-Fi)
  • Maintains complete signal quality while providing protection
  • Prevents ESD-induced restarts, disconnections, and bit errors

⭐Engineer Concerns

  • Capacitance < 1pF (for high-speed interfaces)
  • IEC 61000-4-2 Level 4 ESD Waveform
  • Differential line TVS requires matched pair impedance

🛡️ Build a comprehensive security architecture to improve the reliability of photovoltaic systems

From the input of the photovoltaic modules to the DC-DC/DC-AC circuitry within the inverter, and then to the output and communication interfaces, a comprehensive protection scheme is crucial to ensuring the stable operation of the inverter.

Semiware's TVS, GDT, MOV, NTC, and MOSFET devices are widely used by photovoltaic inverter manufacturers worldwide, helping customers reduce maintenance costs and extend system lifespan thanks to their high reliability, surge capability, and consistency.

Visit Semiware ↗️https://en.semiware.com/applications/string-inverters/ to explore full solutions for lightning, surge, and ESD protection in string inverters, or contact us now!

📩 sales29@semiware.com