M 1 M sw M hw M 6 M 6a M CO M 7 M 7a M 7b M 5 M 5a M 5b unit. M 4 M 4a M 4b measurement Phasor M 3 M 3a M 3b PMU, PMU. the M 2 of M 2a M 2b Modeling 3.7 FIGURE