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. <EOS>