Driving device for motor-driven compressor

Details Driving device for motor-driven compressor Driving device for motor-driven compressor

2000-12-12

2002-05-07

Nappi, Robert E. (Department: 2837)

Electricity: motive power systems

Automatic and/or with time-delay means

C318S800000, C318S441000

Reexamination Certificate

active

06384558

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a driving device for a motor-driven compressor having an electrolytic capacitor in its power unit, and particularly to the discharge of an electrolytic capacitor in an air-conditioning system in household and automobile applications where safety must be assured to protect human bodies from electric shocks, firing, burns, and other hazards.
BACKGROUND OF THE INVENTION
Conventionally, motor-driven compressors (herein after simply referred to as “compressors”) have been used mainly for household air-conditioning systems. However, with the recent penetration of electric vehicles, hybrid cars, fuel cell powered vehicles, or the like, an increasing number of compressors are also used for automobile air-conditioning systems.
FIG. 7
shows a circuit diagram of a driving device used for a compressor in a conventional air-conditioning system incorporated in an automobile.
In
FIG. 7
, compressor
501
of the air-conditioning system has a three-phase motor unit and a compressing unit therein. Battery
502
serves as a power source of both compressor
501
and a drive motor, and normally supplies voltages ranging from 100 V to 300 V.
Switch
504
turns on/off the power supplied from battery
502
as required, and is always closed when compressor
501
is operated. The power from battery
502
is supplied to driver
505
via switch
504
and electrolytic capacitor for smoothing current
503
. Driver
505
includes a plurality of switching elements for supplying power to compressor
501
and base (gate) drive circuit
511
for driving the elements.
Driver
505
performs inverter control and pulse width modulation (PWM) on DC voltages supplied from battery
502
thereby to convert them into pseudo AC voltages (sine wave) formed by positive and negative rectangular pulses. Then, the driver changes the voltages or frequencies to control the number of revolutions of compressor
501
. The values specifying the numbers of revolutions are given from air-conditioning controller
506
that controls the entire air-conditioning system. Controller
506
determines the numbers of revolutions of compressor
501
so that the inside of the automobile is always kept comfortable in accordance with its environmental conditions, and sends the specified values to driver
505
.
Hereinafter described is how capacitor
503
discharges for a conventional driving device after the operation of compressor
501
is stopped and switch
504
is opened.
During the operation of compressor
501
, driving current flows through driver
505
. On the other hand, even when compressor
501
is at rest, some amounts of current flows. That is, driver
505
includes a microcomputer for control and various protection networks therein and such circuits carry a small amount of current (hereinafter referred to as “dark current”), though it is weaker than the driving current for the compressor.
Capacitor
503
is discharged by this dark current after compressor
501
has stopped, and it takes a considerable period of time to discharge the capacitor completely. For example, when the supply voltage is 300 V, the capacitance of the capacitor is 1000 &mgr;F, and the dark current is 20 mA and constant, it takes 15 seconds to discharge the capacitor completely. It takes 13.5 seconds to discharge the capacitor to 30 V, which is said to a safety voltage at which human bodies do not get electric shocks in an automobile.
FIG. 8A
is a timing chart showing the operations of each component after compressor
501
starts its operation and then stops, and before capacitor
503
completes discharge. Now this timing chart is explained.
At timing A, the instruction from controller
506
is changed from “Stop” to “Operate”. Then, the signal is sent to switch
504
and the switch
504
is closed after time T
1
delay. This time T
1
delay is an operational delay of switch
504
. Upon closure of switch
504
, capacitor
503
is charged, output of driver
505
is switched on, and energization to compressor
501
is started.
Next, when the instruction from controller
506
is changed from “Operate” to “Stop” at timing B, switch
504
is opened after time T
1
delay, and at the same time, output from driver
505
is switched off and compressor
501
is de-energized. Since the voltage of capacitor
503
after that time depends on the natural discharge caused by the dark current as mentioned above, it slowly decreases over time T
4
. Thus, capacitor
503
is discharged completely. The time T
4
is 15 seconds under the above conditions.
FIG. 8B
is a control flow chart of driver
505
. Capacitor
503
is naturally discharged by the dark current and no special discharge control is performed on it.
With the recent penetration of electric vehicles, hybrid cars, and fuel cell powered vehicles, or the like, safety measures to protect not only crew but also mechanics engaged in maintenance of such vehicles from high voltages is becoming necessary.
However, with the above-mentioned conventional driving device for a motor-driven compressor, it takes about a dozen seconds to discharge the electrolytic capacitor. During maintenance work of an air-conditioning system, mechanics may misunderstand the system has been stopped and touch the circuits, even though the discharge of the capacitor has not been completed yet. Therefore, the conventional driver for a compressor has a problem that some safety measures must be taken for such a case.
When a capacitor that has not completely discharged yet is short-circuited with tools or the like, sparking occurs. Safety from such a case must be assured. Particularly, since hybrid cars carry gasoline, they require additional assurances of safety. Similarly, since fuel cell powered vehicles, or the like, use hydrogen as a fuel, they also require additional assurances of safety. Moreover, for hydrocarbons (e.g. propane) recently used as a new refrigerant for air-conditioning systems, maximum safety must be assured in the replacement of gas.
In addition, the conventional driver for a compressor has another problem that when an external resistor is installed to discharge the capacitor for a shorter period of time, the resistor carries current and thus increases the loss of the circuit and the size of the system.
SUMMARY OF THE INVENTION
The present invention addresses the problems discussed above. It is, therefore, an object of the present invention to provide a small and high-efficient driving device for a motor-driven compressor assuring safety of the crew and mechanics, in an air-conditioning system to be incorporated in an electric vehicle, hybrid car, or fuel cell powered vehicle, or the like, operating from a high-voltage source, and also in an air-conditioning system using flammable refrigerants.
A driving device for a motor-driven compressor of the present invention is comprised of:
(a) a motor-driven compressor for compressing a refrigerant;
(b) a DC power supply serving as a power source of the motor-driven compressor;
(c) a capacitor connected in parallel with the DC power supply;
(d) a switch provided between the DC power supply and the capacitor, and closed when the motor-driven compressor is operated and opened when the compressor is stopped;
(e) a driver for converting electric power supplied from the DC power supply via the switch and the capacitor into driving power for the motor-driven compressor, and for outputting the driving power thereto;
(f) a controller for instructing the driver to operate or stop the motor-driven compressor; and
(g) a discharge control unit provided in the driver and controlling the driver so that the capacitor is discharged using the motor-driven compressor as a medium, after the instruction to stop the motor-driven compressor is given.
The above structure allows the control of the driver so that the capacitor is discharged using the motor-driven compressor as a medium for discharge; thereby realizes a small and high-efficient driving device for a motor-driven compressor with maximum safety.


REFERENCES:
patent: 4463296 (1984-07-01), Tada et

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