An inverter contains the following structure: an inverter circuit having upper-arm switching elements connected on the positive side of a DC power source and lower-arm switching elements connected on the negative side of the DC power source; a current sensor that detects current flowing between the DC power source and the inverter circuit; and a control circuit that not only effects control of the inverter circuit so that AC is fed to a motor from the inverter circuit according to an ON-period controlled by a PWM system, but also makes a correction to the ON-period so as to allow the current sensor to detect phase current. The control circuit determines an amount of the correction by judging a direction of current of a phase having an intermediate length of the ON-period.
1. An inverter comprising:
an inverter circuit having upper-arm switching elements connected on a positive side of a DC power source and lower-arm switching elements connected on a negative side of the DC power source;
a current sensor for detecting current flowing between the DC power source and the inverter circuit; and
a control circuit energizing the inverter circuit by a PWM system for the inverter circuit to supply an AC to a motor, and detecting a phase current with the current sensor through a correction of a time, during which an ON-signal is supplied to only one or only two of the upper-arm switching elements, into a predetermined time necessary for detecting the phase current by the current sensor within a carrier cycle;
wherein, the control circuit judges a direction of current, which is a direction flowing into the motor or a direction flowing out of the motor, of a phase having an intermediate length of an ON-period in the carrier cycle and changes the predetermined time according to the direction.
2. The inverter of claim 1 , wherein the direction of current is judged by a phase of current flowing to the motor.
3. The inverter of claim 1 , wherein the direction of current is judged by a phase of applied voltage to the motor.
4. The inverter of claim 1 , wherein the correction is carried out in a case where the PWM system operates with a modulation degree smaller than a predetermined modulation degree.
5. The inverter of claim 1 , wherein the correction is carried out in a case where the motor operates at an rpm lower than a predetermined rpm.
6. The inverter of claim 1 , wherein the PWM system is a three-phase modulation.
7. The inverter of claim 1 , wherein the motor drives an electric mechanism section and forms an electric compressor.
8. The inverter of claim 7 , wherein the inverter is mounted on the electric compressor.
9. The inverter of claim 8 , wherein the electrical compressor is formed as a vehicle-mounted structure.