A parameter determining apparatus for determining parameters for estimating temperature of a switching element of an inverter unit, comprising: an inverter unit including a power semiconductor module configured with at least one or more switching elements; and a control unit configured to determine an initial collector-emitter voltage of each of the at least one or more switching elements and collector-emitter resistance of each thereof by linearizing a curve of collector current as a function of collector-emitter voltage of each of the at least one or more switching elements at a certain temperature characterized in, that the control unit is further configured to determine (S71) a region of a current specified to a first current ( I A ) and a second current ( I B ) at a reference current region; determine (S72) a collector-emitter voltage of each of the at least one or more switching elements with respect to the first current and the second current at each of predetermined first and second temperatures ( V CE_AT1 , V CE_BT1 ; V CE_AT2 , V CE_B12 ); determine (S73) a collector-emitter voltage ( V CE_ATK , V CE_BTK ) of each of the at least one or more switching elements at the first current and the second current and a certain temperature ( T K ) using: T K − T 1 T 2 − T 1 = V CE _ BTK − V CE _ BT 1 V CE _ BT 2 − V CE _ BT 1 T2>T1 and representing temperatures reflected by manufacturer graphs V CE _ BTK = T K − T 1 T 2 − T 1 ∗ V CE _ BT 2 − V CE _ BT 1 + V CE _ BT 1 V CE _ ATK = T K − T 1 T 2 − T 1 ∗ V CE _ AT 2 − V CE _ AT 1 + V CE _ AT 1 determine (S74) a linear equation representing the collector-emitter voltage ( V CE ) at the temperature ( T K ) and a current I C from two points ( I A , V CE_ATK ) and ( I B , V CE_BTK ): V CE = R CE _ TK ∗ I C + V CE 0 _ TK ; and determine parameters R CE_TK and V CE0_TK for estimating the temperature of the junction of the switching element: R CE _ TK = V CE _ BTK − V CE _ ATK I B − I A V CE 0 _ TK = V CE _ BTK − R CE _ TK ∗ I B an inverter unit including a power semiconductor module configured with at least one or more switching elements; and a control unit configured to determine an initial collector-emitter voltage of each of the at least one or more switching elements and collector-emitter resistance of each thereof by linearizing a curve of collector current as a function of collector-emitter voltage of each of the at least one or more switching elements at a certain temperature characterized in, that the control unit is further configured to determine (S71) a region of a current specified to a first current ( I A ) and a second current ( I B ) at a reference current region; determine (S72) a collector-emitter voltage of each of the at least one or more switching elements with respect to the first current and the second current at each of predetermined first and second temperatures ( V CE_AT1 , V CE_BT1 ; V CE_AT2 , V CE_B12 ); determine (S73) a collector-emitter voltage ( V CE_ATK , V CE_BTK ) of each of the at least one or more switching elements at the first current and the second current and a certain temperature ( T K ) using: T K − T 1 T 2 − T 1 = V CE _ BTK − V CE _ BT 1 V CE _ BT 2 − V CE _ BT 1 T2>T1 and representing temperatures reflected by manufacturer graphs V CE _ BTK = T K − T 1 T 2 − T 1 ∗ V CE _ BT 2 − V CE _ BT 1 + V CE _ BT 1 V CE _ ATK = T K − T 1 T 2 − T 1 ∗ V CE _ AT 2 − V CE _ AT 1 + V CE _ AT 1 determine (S74) a linear equation representing the collector-emitter voltage ( V CE ) at the temperature ( T K ) and a current I C from two points ( I A , V CE_ATK ) and ( I B , V CE_BTK ): V CE = R CE _ TK ∗ I C + V CE 0 _ TK ; and determine parameters R CE_TK and V CE0_TK for estimating the temperature of the junction of the switching element: R CE _ TK = V CE _ BTK − V CE _ ATK I B − I A V CE 0 _ TK = V CE _ BTK − R CE _ TK ∗ I B <EOS>