Frequency converting apparatus and control method for the apparatus

Abstract

The difference between internal processes of a power converting apparatus may bring about a heat difference in the apparatus. In the cooling process, it is presumed that the temperature change of the inverter or converter module may be made so great that the power converting apparatus may be less reliable. In order to overcome this shortcoming, the temperature of the internal module is measured and a cooling control of a cooling fan or the like is carried out on the measured result. This cooling control of the cooling fan causes the life of a switching element of the inverter or converter to be longer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing an arrangement of a power converting apparatus according to an embodiment of the present invention;

FIG. 2 is a flowchart showing a cooling control of a control unit located in the power converting apparatus according to the embodiment of the present invention;

FIG. 3 is a circuit diagram showing an arrangement of a power converting apparatus according to another embodiment of the present invention;

FIG. 4 is a circuit diagram showing an arrangement of the power converting apparatus according to the embodiment in which a water-cooling or an oil-cooling operation is used for cooling the cooling fins; and

FIG. 5 is a chart showing relation between the speed occurring when the conventional power converting apparatus controls the speed of its motor at a constant torque characteristic, the inverter loss and the converter loss.

Claims

1. A power converting apparatus comprising: a converter for converting ac power from a commercial power supply into dc power;a smoothing unit for smoothing the dc power sent from the converter;an inverter for converting an output of said smoothing unit into another ac power;a control unit for controlling said inverter;a current detector for detecting an output current of said inverter; anda cooling fan for cooling said converter and said inverter,wherein a detection signal sent from said current detector is inputted into said control unit so that said control unit estimates a temperature of said inverter or converter based on said detection signal and control said cooling fan based on the estimated temperature.

2. The power converting apparatus as claimed in claim 1, wherein said control unit estimates the temperature of said inverter or converter according to the operations of the following expressions; Estimation of the temperature of the converter=αc×[the output current×an output frequency]Estimation of the temperature of the inverter=αi×[the output current]wherein αc and αi are proportional constants.

3. The power converting apparatus as claimed in claim 1, wherein a water-cooling device is used instead of said cooling fan.

4. The power converting apparatus as claimed in claim 1, wherein an oil-cooling device is used instead of said cooling fan.

5. The power converting apparatus as claimed in claim 1, wherein said current detector uses a Hall element.

6. The power converting apparatus as claimed in claim 1, wherein said current detector uses a shunt resistor.

7. A power converting apparatus comprising: a converter for converting ac power from a commercial power supply into dc power;a smoothing unit for smoothing the dc power sent from said converter;the inverter for converting an output of said smoothing unit into another ac power;a control unit for controlling said inverter;a cooling fan for cooling said converter and said inverter; anda temperature sensor of said converter and said inverter for measuring a temperature of said converter or said inverter,wherein said temperature sensor applies its temperature sensing information into said control unit so that said control unit controls said cooling fan based on said temperature sensing information.

8. The power converting apparatus as claimed in claim 7, wherein said temperature sensor of said converter and said inverter is provided in cooling fins for scattering out heat of said converter or said inverter.

9. The power converting apparatus as claimed in claim 7, wherein as said temperature sensor of said converter and said inverter, a converter temperature sensor is provided for measuring a temperature of said converter; and an inverter temperature sensor is provided for measuring a temperature of said inverter.

10. The power converting apparatus as claimed in claim 7, wherein a water-cooling device is used instead of said cooling fan.

11. The power converting apparatus as claimed in claim 7, wherein an oil-cooling device is used instead of said cooling fan.

12. A control method for controlling a power converting apparatus for applying an output of an inverter into a load, said power converting apparatus including a converter for converting ac power from a commercial power supply into dc power, a smoothing unit for smoothing the dc power of said converter, an inverter for converting the output of said smoothing unit into another ac power, a control unit for controlling said inverter, and a current detector for detecting an output current of said inverter, the method comprising the steps of: applying a detection signal from said current detector into said control unit so that said control unit estimate a temperature of said inverter or said converter;storing as a value given when a drive is started the temperature of said converter or said inverter estimated by said control unit when the drive is started;obtaining a difference between said temperature estimated at any time of the drive and the value stored given when the drive is started; andif said difference is greater than a predetermined value, controlling said cooling fan for cooling down said converter or said inverter.

13. The control method as claimed in claim 12, wherein for cooling said converter or said inverter, an operation is executed to cool down cooling fins for scattering out heat of said converter or said inverter

14. The control method as claimed in claim 12, wherein a water-cooling device is used instead of said cooling fan.

15. The control method as claimed in claim 12, wherein an oil-cooling device is used instead of said cooling fan.

16. The control method as claimed in claim 12, wherein said current detector uses a Hall element.

17. The control method as claimed in claim 12, wherein said current detector uses a Shunt resistor.