What is claimed is:1. A power conversion device comprising:a case comprising a first protrusion and a second protrusion;a switching unit comprising a plurality of switches disposed on one surface of the case; anda clip for fixing the plurality of switches; andwherein the clip comprises:a body part which extends in a first direction; andelastic parts which extend from one side of the body part and are for pressing the plurality of switches to the case,wherein the body part comprises:a plurality of first through holes, which are disposed in the first direction and into which screws are coupled;a first coupling groove disposed on one end of the body part in the first direction; anda second coupling groove disposed on the other end of the body part in the first direction,wherein the first protrusion is coupled to the first coupling groove and the second protrusion is coupled to the second coupling groove,wherein the first coupling groove is longer than the second coupling groove in the first direction,wherein the first through holes are disposed between the first coupling groove and the second coupling groove, andwherein a total number of the plurality of first through holes is a half of a total number of the plurality of switches.2. The power conversion device of claim 1, wherein the case comprises a stepped portion on which the body part is disposed, and a straight-line distance from an end of the switches facing the stepped portion to the stepped portion is shorter than a straight-line distance from the end of the switches to a point where the elastic parts press the switches.3. The power conversion device of claim 1, wherein the clip further comprises a support part, which extends from the body part and is bent to face a sidewall of the case.4. The power conversion device of claim 1, further comprisinga transformer disposed on one surface of the case,a cooling channel disposed on the other surface of the case, anda coolant inlet and a coolant outlet, which are connected to the cooling channel, wherein the cooling channel comprises a first channel region connected to the coolant inlet and a second channel region connected to the coolant outlet.5. The power conversion device of claim 4, wherein the cooling channel comprises a divergence part disposed between the first channel region and the second channel region, and the divergence part has a width that decreases as it gets farther away from the coolant inlet and the coolant outlet.6. The power conversion device of claim 4, wherein the cooling channel comprises a guide protrusion disposed inside the cooling channel.7. The power conversion device of claim 6, wherein the guide protrusion extends from the coolant inlet to the coolant outlet.8. The power conversion device of claim 6, wherein the guide protrusion comprises a first end part facing the coolant inlet and a second end part facing the coolant outlet, and the first end part and the second end part are bent as they get farther away from each other.9. A power conversion device comprising:a case comprising a first protrusion and a second protrusion;a switching unit comprising a plurality of switches disposed on one surface of the case;a clip for fixing the plurality of switches;a transformer disposed on one surface of the case;a cooling channel disposed on the other surface of the case; anda coolant inlet and a coolant outlet, which are connected to the cooling channel,wherein the clip comprises:a body part which extends in a first direction; andelastic parts which extend from one side of the body part and are for pressing the plurality of switches to the case,wherein the body part comprises:a plurality of first through holes, which are disposed in the first direction and into which screws are coupled;a first coupling groove disposed on one end of the body part in the first direction; anda second coupling groove disposed on the other end of the body part in the first direction,wherein the first protrusion is coupled to the first coupling groove and the second protrusion is coupled to the second coupling groove,wherein the first coupling groove is longer than the second coupling groove in the first direction,wherein the first through holes are disposed between the first coupling groove and the second coupling groove,wherein the cooling channel comprises a first channel region connected to the coolant inlet and a second channel region connected to the coolant outlet.10. The power conversion device of claim 9, wherein the cooling channel comprises a divergence part disposed between the first channel region and the second channel region, and the divergence part has a width that decreases as it gets farther away from the coolant inlet and the coolant outlet.11. The power conversion device of claim 9, wherein the cooling channel comprises a guide protrusion disposed inside the cooling channel.12. The power conversion device of claim 11, wherein the guide protrusion extends from the coolant inlet to the coolant outlet.13. The power conversion device of claim 11, wherein the guide protrusion comprises a first end part facing the coolant inlet and a second end part facing the coolant outlet, and the first end part and the second end part are bent as they get farther away from each other.