Active front end converter based on MMC

Active front end converter based on MMC


Modular multilevel converter for hybrid grids.

Design of highly reliable modular multilevel converters

Due to their higher efficiency, improved power quality, inherent fault tolerance and higher density, modular multilevel converters are used in MV and HV applications.

The challenge 

Today, power electronic semiconductors and capacitors thermally limit the service life and overload capacity of power electronic converters. Therefore, the temperature peaks of the semiconductors can be reduced by appropriate control, thereby expanding the overcurrent operating range of the modular multilevel converter (MMC) in the headend. However, to achieve this performance, the junction temperature of the semiconductors must be known. That is why we offer measurement techniques to indirectly determine the junction temperature without having to measure it directly.

Our Solution

We offer a measurement technique to indirectly determine the junction temperature of the semiconductors via thermal-electrical sensitivity parameters (TSEP). By connecting the measurement technology to the gate drivers of the MMC cells, the junction temperature can be output as a function of the collector-emitter voltage, for example, and used for overcurrent operation or for self-protection of the power converter.

Yout benefits at a glance

The MMC is a key technology for AC/DC applications in the medium-voltage range. Because this type of topology requires a large number of power electronic devices, it is important to provide a highly reliable converter that ensures uninterrupted operation and reduced maintenance time. Then we offer an MMC with overload capability that uses an independent TSEP for variables other than temperature. Such a solution indirectly monitors the temperature of the semiconductor, which allows management of the overload and extends the life of the converter.


Research and Development

  • Investigation of the external connection mechanism for measuring the voltage drop of power semiconductors during operation.
  • Evaluation of different modulations in the MMC and their effects on the DC-side current and on the wiring of the converter.
  • Investigation of protection strategies using the device's temperature inference based on its TSEP.
  • Development of a methodology that correlates device temperature and circulating current.


Lab Facilities

  • DC voltage: 10kV
  • AC Voltage: 6kV
  • Active power: 500 kW
  • Number of bipolar cells: up to 48
  • Semiconductor Blocking Voltage: 1.7kV
  • Semiconductor Rated Current: 300A
  • Maximum semiconductor junction temperature: 175°C
  • Switching frequency: 1 kHz
  • MMC overload capability
  • Independent TSEP from variables other than temperature