Water Electrolysis System and Method for Controlling the Same

A method for controlling a water electrolysis system comprising:

• a power converter capable of converting AC and DC to transmit and receive power between an AC-side connection end and a DC-side connection end;
• an electrolysis stack which electrolyzes water to generate hydrogen and oxygen;
• a circuit breaker which is connected to a DC circuit on a DC-side connection end side and enables connection and disconnection of the DC circuit by an external signal or an external operation;
• and a control device which controls the power converter and the circuit breaker, wherein
• the AC-side connection end of the power converter is connected to an AC power grid,
• a series circuit constituted by at least one electrolysis stack and the circuit breaker connected to the at least one electrolysis stack is connected to the DC-side connection end of the power converter,
• the power flowing to the DC-side connection end is reduced before the electrolysis stack is isolated from the series circuit, while maintaining a speed at which the power converter reduces the power flowing to the DC-side connection end below a speed that allows a difference of an amplitude of a voltage of the AC power grid from a reference value to be less than a predetermined value, and
• when reaching a power level enabling disconnection of an internal DC circuit by the circuit breaker, the circuit breaker connected to the DC circuit is disconnected and the electrolysis stack is isolated from the series circuit.