Case Details

Photovoltaic power generation November 22, 2025

MPPT Current Detection Scheme for String Inverters of a PV Inverter Manufacturer

The technical challenge
PV inverter MPPT requires ±0.5% current measurement accuracy, high multiplex consistency requirements, high annual demand cost-sensitive
prescription
FL-2 type 2mΩ shunt, batch consistency control ±0.2%, cost optimization for high volume production
Project results
MPPT efficiency >99.5%, annual supply of more than 1 million pieces, products sold to 30+ countries around the world

Project Background

A well-known domestic PV inverter manufacturer ranks among the world's top manufacturers in terms of product shipments, with products sold to more than 30 countries and regions around the world, and annual shipments exceeding 10 GW. string inverters are its main product line, with power ranging from 50kW to 250kW, and adopting a multi-way MPPT (Maximum Power Point Tracking) design, which requires accurate DC side current detection for MPPT control and string monitoring.

Technical specification requirements:

  • Product Series: 50kW-250kW String Inverter
  • Number of MPPT channels: 4-12 channels
  • Maximum single circuit current: 30A (550W module × 12 strings)
  • Current measurement accuracy: ±0.5%
  • Working Temperature: -25℃ ~ +60℃

Technical challenges faced

1. MPPT accuracy requirements

The MPPT algorithm calculates power based on the product of current and voltage, and current measurement error directly affects the MPPT efficiency.11 TP3T of current measurement error may result in 0.1-0.21 TP3T of power generation loss, which means considerable economic loss in a MW-class plant.

2. Multiple coherence

A single inverter has multiple MPPTs, and the consistency of multiple current measurements directly affects the accuracy of string monitoring and fault diagnosis. If there are deviations between different roads, it may lead to false or missed alarms.

3. Cost control

The PV industry is highly competitive, and the price of inverters is decreasing, with strict cost control for each component. The shunt, as the core component of the multiplexed MPPT, needs to optimize the cost while ensuring the performance.

4. Global accreditation

The products are sold to the global market and need to meet the certification requirements of different countries and regions, including CE, UL, TÜV, etc.

Technical Solutions

1. Shunt sizing

Each MPPT is configured with one FL-2 splitter. key parameters:

  • Resistance value: 2mΩ ±0.5%
  • Rated current: 50A
  • Rated voltage drop: 100mV @50A
  • Temperature coefficient:<30ppm>
  • Power loss: 1.8W @30A

Select a higher resistance value (2mΩ) to obtain sufficient signal amplitude (100mV) to simplify the signal conditioning circuit, while the single circuit power consumption is only 1.8W, which has an impact on the overall efficiency of the inverter.<0.01%.

2. Accuracy and consistency control

  • Adopt 0.5 grade precision shunt, factory 100% testing
  • Multiple shunts for the same inverter selected from the same production lot
  • Resistance deviation between batches is controlled within ±0.2%.
  • Matching resistance grouping labels, easy to match the use of the client

3. Cost optimization

  • Standardized design, mass production to reduce costs
  • Optimize material ratios to reduce material costs while ensuring performance
  • Automated production line improves production efficiency
  • Annual supply of more than 1 million, the scale effect is significant

4. Certification and quality

  • Products through the CE, UL certification
  • Cooperate with customers to complete TÜV, CQC and other certifications
  • IATF 16949 Quality Management System Assurance

Project results

  • MPPT efficiency:Current measurement accuracy ±0.5%, support inverter MPPT efficiency >99.5%
  • Consistency:Consistency of multiple current measurements<±0.3%, accurate and reliable string monitoring
  • Scale of supply:With an annual supply of more than 1 million units, we are the largest supplier of shunts to our customers.
  • Global Markets:The products are sold with inverters to more than 30 countries around the world, including Europe, America, Asia-Pacific and other major markets.
  • Long-term cooperation:More than 8 years of cooperation and in-depth strategic partnership established