With the integration of large-scale distributed generators

the reactive power and voltage coupling between transmission network (TN) and distribution network (DN) is becoming more close. The reactive power optimization problems of TN and DNs are not suitable to be solved independently. Due to the independence of operation and control of TN and DNs

a heterogeneous decomposition (HGD) based distributed reactive power optimization method of global TN and DNs is presented. The global reactive power optimization problem can be decomposed into the TN reactive power optimization sub-problem

some DN reactive power optimization sub-problems and the boundary consistency coordination sub-problem. The duality theory based algorithms are adopted to solve the reactive power optimization sub-problems. The penalty function is used to handle the discrete variables and therefore the augmented Lagrangian functions are differentiable. The boundary sensitivities

which are constructed by using the boundary dual multipliers

are used to decouple the global reactive power optimization. The coordination between TN and DN is achieved by transferring the boundary variables and sensitivities. The simulation results of the IEEE 30-bus (TN) and IEEE 33-bus (DN) test system with multiple distributed generators show that the proposed method is effective.