Large-scale green hydrogen production system combining wind farms and electrolysis systems is an important way to low-carbon energy system. The flexible and fast ramping capability of the electrolysis system provides the possibility for a wind-electrolysis joint system (WEJS) to provide secondary frequency regulation (SFR) to reduce the production cost of green hydrogen. To increase the biddable capacity and improve the full load hours, this paper proposes a cooperative power allocation strategy for wind turbines and electrolyzers responding to the down and up AGC signals respectively. Furthermore, this paper proposes a more accurate method for estimating the daily hydrogen production due to response to the up ramping of automatic generation control (AGC) signals to ensure that the joint system meets the hydrogen production contract when providing SFR. Based on the above two points, this paper proposes a multi-timescale control framework and robust bidding optimization for a WEJS participating in energy and regulation markets. Case studies demonstrate that the relative error of daily hydrogen production can be controlled at 3.37%. The full load hours of the electrolysis systems can be increased by 50.21% compared with only participation in the energy market.