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3-phase string inverter solutions

Enhance 3-phase string inverter solutions design with the right semiconductor solutions

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Overview

3-phase string inverters perform power conversion on series-connected photovoltaic panels. Usually, these inverters are rated around a few kilowatts up to 350 kW. In general, most inverter designs are transformerless or non-isolated. String inverters typically rely on two-stage power conversion.

Benefits

  • Saving energy
  • Reduction of cost of electricity
  • Great design flexibility
  • Higher robustness
  • Higher efficiency
  • Higher switching operation

Block diagram

About

Explanation of the two-stage power conversion

First, the DC-DC stage converts variable DC voltage into a suitable or fixed voltage required by the DC-AC inverter stage. At the same time, it ensures maximum power, which has been extracted from the PV string via MPPT technique.

Second, the DC-AC stage converts DC power into grid-compatible AC power. Either 2-level or 3-level topology is preferred in this stage. In particular, 3-level topology is widely used for its higher efficiency. Mainly for 1000 V PV array system, 3-level NPC1 / NPC2 is preferred. 3-level NPC1 enables use of 650 V devices and allows more than 20 kHz switching frequency operation even for oversized PV panels. 3-level NPC2 uses 650 V and 1200 V devices, the best-fit topology for less than 20 kHz switching frequency operation. For the 1500 V PV system, 3-level ANPC and NPC1 is widely used for their higher robustness against cosmic ray, and in particular, ANPC topology is widely used due to its higher efficiency over the full range of power factor operation. The size and weight of the inverter depend highly on the DC and AC filter and cooling system. Therefore, higher switching operation is desirable to reduce the size and cost of the system.

Our offerings for designs up to 350 kW

Usually, these inverters are rated from 6 kW up to 350 kW. For power up to 20 kW, Infineon¡¯s discrete IGBTs, CoolSiC? MOSFETs, and CoolSiC? Schottky diodes are the preferred choice to achieve the best price-to-performance ratio.

In power ranges above 20 kW, the Easy module family of products is the best choice for customers looking for a flexible and scalable power module solution, such as CoolSiC? Easy Modules, Easy Booster modules, and Easy 3-level modules. The flexible pin grid system is perfect for customizing the layout and pinout. In addition, it is a great choice for power density and ease of manufacturing.

All switches need a driver, and all drivers need to be controlled. We also offer the right EiceDRIVER? gate driver and the XMC? and PSoC? microcontroller for your inverter design. Finally, each functional block needs a sensor and auxiliary power supply, so we offer CoolSET? together with our 1.7 kV CoolSiC? MOSFET and the TLI4971 and TLE4971 current sensor. A smart combination to address connectivity is provided by the AIROC? family, which offers Bluetooth? and Wi-Fi in a single device. OPTIGA? products complete the portfolio and ensure data protection and security.

More about power solutions
More about microcontroller
More about sensors
More about security solutions
Trends and requirements of 3-phase string inverters - part 1

Generally, for residential and small commercial applications up to 30 kW, the user generates and consumes electricity. Improved self-consumption and avoiding expensive load peaks are highly important to save up on the electricity bill. The hybrid inverter type is gaining popularity due to the improved self-consumption of solar power. Like string inverters, hybrid inverters can connect multiple photovoltaic panels and convert DC to AC. But, on top of that, hybrid inverters can also supply DC currents directly to a battery or another energy storage system. This eliminates unnecessary power conversions, which saves energy.

For large commercial and utility-scale installations, PV system voltage increased over time to help reduce the levelized cost of electricity (LCoE). Like in the past, from 1000 V to 1500 V, even higher voltage standards may emerge in the near future. Further DC/AC ratio or oversizing of PV power plants is becoming the clear trend.

Trends and requirements of 3-phase string inverters - part 2

Lightweight string inverters are gaining popularity in these markets up to 20 MW. They enable great design flexibility and easy transportation and are also quickly and easily replaced by two persons with a few clicks.

Based on our deep application know-how in solar and related industries, we can reduce learning cycles and provide fast customization through proven short-flow processes. In combination with the strength of Infineon¡¯s 650 V, 1200 V, and 2000 V CoolSiC? MOSFET, and TRENCHSTOP? IGBT7 enable our customers not only to reduce system and operational cost significantly but furthermore help to harness never before seen levels of efficiency and power density.

Explanation of the two-stage power conversion

First, the DC-DC stage converts variable DC voltage into a suitable or fixed voltage required by the DC-AC inverter stage. At the same time, it ensures maximum power, which has been extracted from the PV string via MPPT technique.

Second, the DC-AC stage converts DC power into grid-compatible AC power. Either 2-level or 3-level topology is preferred in this stage. In particular, 3-level topology is widely used for its higher efficiency. Mainly for 1000 V PV array system, 3-level NPC1 / NPC2 is preferred. 3-level NPC1 enables use of 650 V devices and allows more than 20 kHz switching frequency operation even for oversized PV panels. 3-level NPC2 uses 650 V and 1200 V devices, the best-fit topology for less than 20 kHz switching frequency operation. For the 1500 V PV system, 3-level ANPC and NPC1 is widely used for their higher robustness against cosmic ray, and in particular, ANPC topology is widely used due to its higher efficiency over the full range of power factor operation. The size and weight of the inverter depend highly on the DC and AC filter and cooling system. Therefore, higher switching operation is desirable to reduce the size and cost of the system.

Our offerings for designs up to 350 kW

Usually, these inverters are rated from 6 kW up to 350 kW. For power up to 20 kW, Infineon¡¯s discrete IGBTs, CoolSiC? MOSFETs, and CoolSiC? Schottky diodes are the preferred choice to achieve the best price-to-performance ratio.

In power ranges above 20 kW, the Easy module family of products is the best choice for customers looking for a flexible and scalable power module solution, such as CoolSiC? Easy Modules, Easy Booster modules, and Easy 3-level modules. The flexible pin grid system is perfect for customizing the layout and pinout. In addition, it is a great choice for power density and ease of manufacturing.

All switches need a driver, and all drivers need to be controlled. We also offer the right EiceDRIVER? gate driver and the XMC? and PSoC? microcontroller for your inverter design. Finally, each functional block needs a sensor and auxiliary power supply, so we offer CoolSET? together with our 1.7 kV CoolSiC? MOSFET and the TLI4971 and TLE4971 current sensor. A smart combination to address connectivity is provided by the AIROC? family, which offers Bluetooth? and Wi-Fi in a single device. OPTIGA? products complete the portfolio and ensure data protection and security.

More about power solutions
More about microcontroller
More about sensors
More about security solutions

Trends and requirements of 3-phase string inverters - part 1

Generally, for residential and small commercial applications up to 30 kW, the user generates and consumes electricity. Improved self-consumption and avoiding expensive load peaks are highly important to save up on the electricity bill. The hybrid inverter type is gaining popularity due to the improved self-consumption of solar power. Like string inverters, hybrid inverters can connect multiple photovoltaic panels and convert DC to AC. But, on top of that, hybrid inverters can also supply DC currents directly to a battery or another energy storage system. This eliminates unnecessary power conversions, which saves energy.

For large commercial and utility-scale installations, PV system voltage increased over time to help reduce the levelized cost of electricity (LCoE). Like in the past, from 1000 V to 1500 V, even higher voltage standards may emerge in the near future. Further DC/AC ratio or oversizing of PV power plants is becoming the clear trend.

Trends and requirements of 3-phase string inverters - part 2

Lightweight string inverters are gaining popularity in these markets up to 20 MW. They enable great design flexibility and easy transportation and are also quickly and easily replaced by two persons with a few clicks.

Based on our deep application know-how in solar and related industries, we can reduce learning cycles and provide fast customization through proven short-flow processes. In combination with the strength of Infineon¡¯s 650 V, 1200 V, and 2000 V CoolSiC? MOSFET, and TRENCHSTOP? IGBT7 enable our customers not only to reduce system and operational cost significantly but furthermore help to harness never before seen levels of efficiency and power density.

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Design resources

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