phase coupling for power line communications 电力线载波.pdfVIP

Application Note #0050 Phase Coupling for Power Line Communications Introduction Throughout North America, electric power distribution containing center tap transformers is provided for residential use. This arrangement supplies “split phase” 120V/240V with three wires coming from the utility: Line ( L1, L2), and Neutral (N). 120V power is available between L1 and N, and between L2 and N, and 240V is available between L1 and L2. At the distribution panel of each residence, the National Electrical Code requires that a local earth ground be supplied and connected to the neutral wire within the distribution panel. For normal 120V distribution within the house, the electrical code requires a three wire configuration: Line, Neutral and a bare copper protective Ground ( GND). With this type of distribution network, if two nodes on the communication bus are on opposite phases, the only direct current path between them is through the secondary windings of the distribution transformer. At commonly used power line carrier frequencies (i.e., 20KHz) this is an extremely poor channel, resulting in signal attenuation of 30dB or more. This combined with other noise sources, may degrade communication performance. CEBus Communications and the Distribution Network When two CEBus devices are connected to the same phase of the power line, communication is straightforward because there is a simple current path between the two devices as shown in Figure 1. Distribution Transformer L1 Current Path CEBus CEBus