Switch yard and isolation control design for DC/AC/DC converter operating at power reversal condition in LCC-HVDC system

As one type of the interconnected device between HVDC systems, the DC/AC/DC converter is able to achieve high-voltage connection and bulk-power transportation, which makes this device fit the interconnection of LCC-HVDCs. To achieve an efficient interconnected LCC-HVDC system, the DC/AC/DC converter is possible to operate under the condition that one LCC-HVDC runs at normal operation and the other at the operation of power reversal. This requests the DC/AC/DC converter to regulate power in terms of the interconnection between positive voltage and the negative. Considering the economy of the interconnection, the DC/AC/DC converter uses half-bridge sub-modules, which is not able to connect the negative-voltage system. To achieve the ability of negative-voltage connection, a switch yard is proposed to reverse the voltage polarity of DC/AC/DC converter. And a control system of the DC/AC/DC converter is proposed to protect the normal LCC-HVDC from the influence of LCC-HVDC during power reversal.