Poster Competition – Spring 2017 Modular Multilevel Converter for Wind Energy Storage Systems Bora Novakovic Adel Nasiri 1 Slideshow and powerpoint viewer: Poster Competition – Spring 2017 I

Poster Competition – Spring 2017 Introduction • Motivation – Problems introduced by new grid codes for Wind Energy Systems • • • Fault ride through capabilities Power smoothing Frequency and reactive power support – Problems introduced by increased size of wind turbines • Paralleling of low voltage systems • Efficiency • Objective – Power converter topology that Is suitable for the high power (multiMW) wind energy application – Power conversion system topology that solves or diminishes problems related to new grid codes. 2

Poster Competition – Spring 2017 Approach • Make the conversion system medium voltage – Solves paralleling problems of low voltage systems – Solves efficiency problem • Integrate energy storage system into wind turbines – Solves or alleviates issues introduced by new grid codes • Find appropriate conversion topology to fulfill the requirements stated above. 3

Poster Competition – Spring 2017 Converter topology – MMC • Modify the MMC topology to integrate storage system • MC supports high number of levels – Modules (cells) can operate at low voltage for HV and MV systems – Allows integration of storage. 4

Poster Competition – Spring 2017 MMC Modifications • MMC is modified to include energy storage into the cell structure • Cell can also be divided in modules for easier analysis • Any module combination is possible and each has its benefits and drawbacks • Energy storage is assumed to be string of ultra-capacitors. 5

Poster Competition – Spring 2017 Simulation • To test the performance if the converter single leg was simulated – High detail switching model was used – It is assumed that the converter operates in a 5MW off shore wind turbine Description Base Converter Power Generator Power Generator Power Factor Base Voltage Base Impedance Base Frequency DC Bus Voltage min. Cell Voltage max. Number of levels Value 6.25MVA 5MW 0.8 13.8kV 30 60Hz 23kV 800V 32 • The power imbalance between the AC and DC side is simulated – The excess power goes to the integrated energy storage – This kind of condition can be found in cases of: • Low voltage ride through conditions • Power smoothing . 6

Poster Competition – Spring 2017 Results Cell DC voltage illustrates charging of the storage system Zoomed region for the cell DC voltage. Illustrates good balancing DC side power and AC side current to illustrate the power imbalance and the dynamic system behavior Output voltage illustrates 32 level switching. 7