A PWM converter is known as a device which performs switching control performed by PWM to thereby suppress a harmonic current included in a load current for an AC power source driving a motor driving device in order to improve power.
A PWM converter outputs a square wave AC voltage including high frequencies of several kHz or more on a path between the AC power supply and the PWM converter to perform switching control by the PWM. As the square wave AC voltage includes high frequency components not included in the power supply frequency, this type of PWM converter is generally configured to provide a low pass filter (LC filter) which allows a high frequency square wave AC voltage to pass between the AC power source and the converter in order to remove the high frequency waves.
FIG. 1 illustrates an example of a basic configuration of an LC filter. FIG. 1 illustrates a configuration where the LC filter 1001 is positioned between the PWM converter 1002 and a three-phase AC power supply 1000.
The LC filter 1001 for the PWM converter is configured to be equipped with a so called T-filter which comprises capacitors C1 to C3 whose ends have an inductance of La1 to La3 and Lb1 to Lb3 respectively. Generally two AC reactors 1010 and 1020 for realizing two inductances have similar configurations (the cores are positioned in the same direction). Further, in general, AC reactors are of a natural air cooling type (for example Japanese unexamined patent publication No. 2007-221858 (JP 2007-221858 A)).
Regarding the inductances L of the two AC reactors 1010 and 1020, in order to suppress the peak of the high frequency current flowing in from the PWM converter 1002 side, the L of the PWM converter side increases and the L of the AC power source 1000 side decreases. Therefore, in general, the volume of the AC reactor B (1020) on the PWM convertor side is comparatively larger than that of the AC reactor A (1010) of the AC power source side. Further, in general, the outer shape of the AC reactor is a parallelepiped about which the coil is wound.
Further, a large part of the loss generated in inductance is on the PWM convertor side where high frequency current flows. Therefore, high frequency current only flows through the AC reactor B on the convertor side (1020) which further increases the temperature rise.
Conventionally, due to AC reactors being large and heavy, two AC reactors and a capacitor, etc., constituting an LC filter were not housed in the same casing.
If these two AC reactors were to be housed in the same casing, there would be a problem that a useless space would be created due to the difference in the height between the small AC reactor on the power source side and the large AC reactor on the convertor side and the volume of the casing would be large.
The object of the present invention is to enable efficient cooling of the AC reactors and provide an LC filter which allows miniaturization and reduction in weight of a casing which houses the LC filter part.