Research On MMC DC Generation System For SSPS

The sunlight in space is not attenuated by the atmosphere,nor affected by seasonal and day and night changes.In geosynchronous orbit,solar radiation can be stably received continuously for 99% of the time.The space solar power station will be a huge renewable energy system that collects and converts solar energy into electrical energy in Earth orbit and then transmits it to the ground via microwaves for users to use.Since Glaser proposed the space solar power station in 1968,it has begun to attract widespread attention from various space powers.The space segment of the system consists of three main components: a solar energy harvesting device,a power transmission section,and a transmitting antenna.The power transmission and management system of the space solar power station is responsible for transmitting the electric energy collected by the solar array to ultra-high power and distributing it to the transmitting antenna and other electrical equipment.This paper proposes an MMC DC generation system,based on the DC power supply of the transmitting antenna in the ground-based demonstration system of the actual engineering project SSPS-OMEGA.In this paper,the reason of the traditional MMC capacitor voltage fluctuation is analyzed by the method of power conservation,and the cause of the circulation is obtained by mathematical expression.Then,an isolated MMC sub-module structure suitable for the present scheme is proposed.The isolated sub-module in this paper can also meet the requirements of buck and isolation required for the power supply of the transmitting antenna.Compared with the traditional MMC common DC bus,this system can work in bipolar modulation mode.The implementation of high DC level voltage can be realized by connecting the secondary sides of the sub-modules in series.The DC circulating current is not required to provide energy for the load,which can greatly reduce the loss caused by the circulating current.Then the paper deduces the expression of the capacitor voltage of the sub-module in the MMC DC generation system under different operating conditions.It is proved that the voltage fluctuation of the capacitor on the sub-module can be greatly reduced when the three laterally isolated sub-modules of the MMC are used in parallel.Moreover,the injection of the zero sequence component can further reduce the fluctuation of the capacitor voltage of the isolation sub-module,thereby reducing the loss of the sub-module capacitance and improving the efficiency and life of the MMC power supply system.Finally,the feasibility of the scheme and the injection of zero-sequence components are reduced by simulation to reduce the voltage fluctuation of the isolation sub-module.An Ether CAT-based MMC DC power supply device is built,which verified the Ether CAT network real-time data transmission and distributed clock functions.