This paper is concerned with power reduction control which is used to avoid DC over-voltage for multiterminal HVDC transmission of offshore wind power. Voltages and frequencies of offshore AC wind farm networks are used for transmitting control signals for the power reduction control. These methods do not require fast communication. Power reduction sharing among the offshore wind farms using the different control signals is analysed. The control systems are also compared against the DC chopper method to prevent a DC overvoltage. Simulation and experiments are carried out to evaluate the control systems.