In many fields of science and engineering. partial differential equation (PDE) constrained optimal control problems are widely used. We mainly solve the optimization problem constrained by the time-periodic eddy current equation in this paper. We propose the three-block splitting (TBS) iterative method and proved that it is unconditionally convergent. https://www.roneverhart.com/BJORK-VULNICURA-2LP-Deluxe-Edition/