A power conversion system comprising an over-current protection module and a power conversion device (20; 440) comprising at least one switching element, the power conversion device (20; 440) being operatively coupled to a direct current DC link that receives input power at a first input terminal and a second input terminal, the over-current protection module being operatively coupled to the power conversion device and comprising: an over-current threshold setting unit configured to receive at least one parameter in association with the operation of the power conversion device (20; 440) and generate an over-current threshold value (I oc) at least partly variable with respect to the received at least one parameter; and an over-current judging unit coupled to the over-current threshold setting unit, the over-current judging unit configured to compare an actual electrical current (I sw) flowing through the at least one switching element with the over-current threshold value (I oc) and provide an over-current flag signal if the comparison indicates that the actual electrical current (I sw) meets the over-current threshold value (I oc); wherein the at least one parameter used by the over-current threshold setting unit for generating the over-current threshold value (I oc) comprises the DC voltage (U dc) at the DC link; the power conversion system being characterised in that the over-current threshold setting unit is further configured to generate an over-current threshold value (I oc) that: - has a substantially constant value when the DC voltage (U dc) at the DC link is equal to or below a nominal DC voltage (U dc0) and the DC link experiences an under-voltage condition, and - decreases in a linear manner with an increasing of the DC voltage (Udc) when the DC voltage (U dc) at the DC link is above the nominal DC voltage (U dc0) and the DC link experiences an over-voltage condition. an over-current threshold setting unit configured to receive at least one parameter in association with the operation of the power conversion device (20; 440) and generate an over-current threshold value (I oc) at least partly variable with respect to the received at least one parameter; and an over-current judging unit coupled to the over-current threshold setting unit, the over-current judging unit configured to compare an actual electrical current (I sw) flowing through the at least one switching element with the over-current threshold value (I oc) and provide an over-current flag signal if the comparison indicates that the actual electrical current (I sw) meets the over-current threshold value (I oc); wherein the at least one parameter used by the over-current threshold setting unit for generating the over-current threshold value (I oc) comprises the DC voltage (U dc) at the DC link; the power conversion system being characterised in that the over-current threshold setting unit is further configured to generate an over-current threshold value (I oc) that: - has a substantially constant value when the DC voltage (U dc) at the DC link is equal to or below a nominal DC voltage (U dc0) and the DC link experiences an under-voltage condition, and - decreases in a linear manner with an increasing of the DC voltage (Udc) when the DC voltage (U dc) at the DC link is above the nominal DC voltage (U dc0) and the DC link experiences an over-voltage condition. - has a substantially constant value when the DC voltage (U dc) at the DC link is equal to or below a nominal DC voltage (U dc0) and the DC link experiences an under-voltage condition, and - decreases in a linear manner with an increasing of the DC voltage (Udc) when the DC voltage (U dc) at the DC link is above the nominal DC voltage (U dc0) and the DC link experiences an over-voltage condition.