The research and development of an intelligent merging unit based on IEC61850-9-2

Merging unit (MU) is an important intelligent electronic device (IED) in digital substation and becomes research emphasis. The function of an MU is to collect multichannel digital signals output by electronic current transformers (ECT) and electronic voltage transformers (EVT) synchronously, and transmit these signals with the protocol of IEC61850 to protective devices and measure-control devices. Compared with IEC61850-9-1, IEC61850-9-2 has more flexible frame format. It means the meaning of each channel and the quantity of the channels can be both customized. Moreover, 9-2 supports not only unicast but also multicast. This paper gives an information model of merging unit which informs us how the MU operates. Besides, it introduces a realization method of sample pulse synchronization, sample values (SV) receiving, processing and transmitting based on Field-Programmable Gate Array (FPGA) EP3C25Q240C8, 10/100 Mbps Ethernet controller LAN9215 and 100 Mbps integrated physical layer chip ICS1889 in detail. This method simplifies circuit design and enhances circuit stability. Data frames transmitted by the MU follow the protocol of 9-2 and can be switched between the interfaces of fiber optic with ST connector and electrical system with RJ45 connector in terms of actual needs. The data frames can be captured and analyzed by MMS ethereal software which supports 9-2 protocol. The test results demonstrate the utility and flexibility of the MU.