Current controlling apparatus and method for air conditioning apparatus

A current control method and apparatus for use in an air conditioning apparatus is disclosed. A total current detection portion is mounted at the AC power supply portion and a peak current detection device is mounted between the conversion portion and the inverter. The total current detection portion detects a maximum current applied to the air conditioning apparatus and the peak current detection portion detects a peak current generated in the inverter. The limitation of the detected total current value is particularly preset in the heating and in the cooling operations. When the detected value surpasses the preset limitation, the inverter motor is stopped.

BACKGROUND OF THE INVENTION 
Field of the Invention 
This invention relates to a current control apparatus and method for air 
conditioning apparatus and, more particularly, to a current control 
apparatus and method which sets limitation of the total current in the 
cooling operation and heating operation and protects an inverter from 
excess current by detecting current in the inverter. 
Generally, the capacity of an outdoor air conditioning apparatus is 
determined by the capacity of the compressor. Operating capacity of a 
compressor is dependent on the speed of rotation of the compressor motor 
which is dependent on its supply frequency. The supply frequency is 
controlled by the switching operation of the inverter. 
When an inverter is used for controlling a compressor, an air conditioning 
apparatus accurately detects the total current flowing in the inverter 
and, if the detected current value is excessive to a predetermined current 
limitation, the compressor stops so that the current flowing in the 
inverter is not greater than the predetermined limit value. 
The switching elements of an inverter comprise semiconductor elements such 
as a power transistor. However, the physical characteristics of a 
semiconductor are sensitive to temperature change. Especially, where there 
is a wide difference between the outside temperatures during the cooling 
operation in summer and the heating operation in winter, an air 
conditioning apparatus with an inverter comprising semiconductor elements 
has a disadvantage in that, because the quantity of current applied to the 
compressor varies greatly, the air conditioning apparatus is set on 
parameter adapted to one of the two seasons malfunctions in other season. 
That is to say, if the parameter of the semiconductor is set to operate in 
the cooling mode, in the heating operation, the quantity of current 
applied to compressor by the inverter is less so that the rotation speed 
of the compressor is lower than that required in the heating operation. 
Therefore, the air conditioning apparatus malfunctions. If the 
semiconductor is set to operate in the heating mode, to the contrary of 
the above described case, excessive current flows in the inverter, 
resulting in the semiconductor element being damaged. 
A typical example of the above described air conditioning apparatus is 
disclosed in Japanese laid open publication No. 58-17997. This apparatus 
detects excessive current. It not only periodically stops the operation of 
the compressor but also fixes the rotation frequency of the motor every 
time an excessive current flows in the inverter. Thus, when the rotation 
of the inverter motor is reversed by an external power, even if it 
operates, the direction of its rotation is corrected to the normal 
rotation direction without halting the operation of the inverter. Thus, 
the inverter is protected from excessive current. 
However, the present invention differs from the above described apparatus 
in that the semiconductor elements are prevented from breakdown resulting 
from a large difference in current flowing in the inverter during the 
heating mode and the cooling mode. 
Also, there is an another problem. When a peak current is generated in the 
inverter, it causes a breakdown of the semiconductor element thereby 
disturbing normal operation. Accordingly, a conventional apparatus detects 
peak current by a current transformer or shunt resistor and prevents a 
malfunction caused by the peak current. However, a system using a current 
transformer does not detect a minute quantity of current because of the 
characteristics of transformer. Because current shunted by an resistor is 
detected by the shunt resistor, a system using a shunt resistor is the 
same. Therefore, these systems have a problem in that they do not guard 
against the problem caused by peak current. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to supply a current controlling 
apparatus and method which protects the inverter from excessive current 
caused by the total current and peak current applied to air conditioning 
apparatus. 
Another object of the present invention is to supply a current control 
apparatus and method which sets the limitation level of the current to a 
two step level according to the operating mode or to a multistage level 
according to the operating command frequency thereby preventing abnormal 
operation of the inverter generated by excessive current. 
In order to achieve the above objects, a total current detection portion is 
mounted at the AC power supply portion and a peak current detection device 
is mounted between the rectifying portion and the inverter. The total 
current detection portion detects a maximum current applied to the air 
conditioning apparatus and the peak current detection portion detects a 
peak current generated in the inverter. The limitation of the detected 
total current value is particularly preset in the heating and cooling 
operations. When the detected values surpass the preset limitation, the 
inverter motor is stopped.

DETAILED DESCRIPTION OF THE INVENTION 
The invention will be described in more detail hereinafter with reference 
to the accompanying drawings. 
FIG. 1 shows the control portion of an air conditioning apparatus according 
to the present invention. FIG. 2 is a detailed drawing of FIG. 1. The 
rectifying portion 2 is connected to a commercial power source and 
rectifies A.C. power supplies rectified A.C. power as D.C. power. The 
inverter portion 3 converts the pulsating D.C. output of the rectifying 
portion into three phase A.C. which is supplied to the motor of the 
compressor 4. The base drive portion 5 supplies a control signal to the 
bases of transistors TR1-TR6 of the inverter portion 3. The microprocessor 
6 outputs a control signal to the base drive portion 5 which is obtained 
by processing outdoor temperature data and current data received from the 
below described detection portions. The total current detection portion 7 
detects current by a current transformer mounted between the commercial 
power source and the rectifying portion 2 and outputs the detected total 
current value to the microprocessor 6. The peak current detection portion 
8 detects peak current flowing in a shunt resistor mounted between the 
rectifying portion 2 and the inverter portion 3 and outputs the detected 
peak current value to the microprocessor 6. The temperature sensing 
portion 9 senses indoor and outdoor temperature, indoor and outdoor piping 
temperature and compressor discharging gas temperature and so on and 
outputs the sensed data to the microprocessor 6. The interface portion 12 
connects the microprocessor 6 of outdoor device and microprocessor of 
indoor device. 
Here, the microprocessor 6 includes an inverter control portion 10 for 
determining compressor operation frequency depending on external data and 
outputs a control data and PWM (Pulse Width Modulation) wave synthesizing 
portion 11 for varying the pulse width of the signal driving the base 
drive portion 5 according to the operation command frequency of the 
inverter control portion 10. 
The operation of the apparatus according to the present invention is 
described as follows: 
A.C. power applied to the apparatus from a commercial power source is 
rectified in the rectifying portion 2. The rectified power is applied to 
the inverter portion 3. At this time, the inverter control portion 10 
outputs a control signal to the PWM wave synthesizing portion 11, so the 
PWM wave synthesizing portion 11 forms a PWM wave. The PWM wave is applied 
to the base drive portion 5. The transistors TR1-TR6 of the inverter 
portion 3 are particularly turned on and off by the PWM wave, so the three 
outputs of the inverter portion 3 output the three phase A.C. power 
supply. An induction motor for compressor 4 is driven by the three phase 
A.C. power supply. The D.C. output of the rectifying portion 2 is applied 
to the inverter portion 3 and returns to the rectifying portion 2 through 
the shunt resistor R1 forming a current loop. At this time, current 
flowing in the shunt resistor R1 is detected by the peak current detection 
portion 8. The detected peak current value is output to the microprocessor 
6. 
When the detected value is above the predetermined value, the 
microprocessor 6 transmits a halt signal to the base drive portion 5, 
turning off transistors TR1-TR6 of the inverter portion 5 thereby halting 
the operation of the induction motor of the compressor 4. Also, when the 
detected value is below the predetermined value, it is inquired as to 
whether the total current value detected by the total current detection 
portion 7 is below the predetermined value. When the total current value 
is below the predetermined value, the induction motor of the compressor 4 
is powered. When the total current value is above the predetermined value, 
the operation of the motor is halted after a predetermined time. The 
predetermined values are separately set by the external environment data 
detected by the temperature sensing portion 9 in heating mode and cooling 
mode. 
FIG. 3 is a schematic diagram showing the peak current detection portion 8 
according to the present invention. As shown in FIG. 3, the peak current 
detection portion 8 comprises a zener diode ZD and a resistor R2 connected 
to the shunt resistor R1 with a resistor R3 connected to the common 
terminal of zener diode and resistor R2 and capacitors C2 and C3, diode 
D11, photo-coupler 14 and, resistor R4 connected to the output end of 
photo-coupler and power terminal Vcc. 
The operation of the peak current detection portion 8 is described as 
follows: 
When current flows in the shunt resistor R1, a voltage difference exists 
between the two ends of the shunt resistor R1. When the voltage is below 
the zener voltage of the zener diode ZD, the zener diode ZD is turned off, 
so the light emitting element of the photo-coupler 14 is not activated. 
The high level signal is applied to the microprocessor 6, so the 
microprocessor 6 recognizes that current flowing in the apparatus is 
normal. If excessive current flows in the shunt resistor R1, the voltage 
applied to the shunt resistor R1 is above the zener voltage of the zener 
diode ZD, so the zener diode ZD is conducted. Because of the conduction of 
the zener diode ZD, current flows in the light emitting element PD of 
photo-coupler 14 through the resistor R3, so the light emitting element 
lights. Because the light receiving element PT is turned on by the light, 
the low level signal is applied to the microprocessor 6, so the 
microprocessor 6 senses an abnormal state due to excessive current. 
FIG. 4 is a flow chart showing the current controlling method according to 
the present invention. 
After supplying power and initializing, in step 101, it is inquired as to 
whether the user's selecting mode is in the heating mode or the cooling 
mode. In the cooling operation, in step 102, environment data is inputed 
from the indoor microprocessor and the temperature sensing portion 9. The 
input data corresponding to the air conditioning load includes indoor 
temperature and indoor piping temperature transmitted from the indoor 
device, and outdoor temperature, and outdoor piping temperature and 
compressor discharging gas temperature detected in the outdoor device and 
so on. In step 103, the environment data is inputed from the detecting 
portions, and the suitable operation frequency is read in the ROM table 
according to the environment data and the operation frequency of the 
inverter portion 3 is determined. In step 104, the total current 
limitation I.sub.A is set to the limitation current value I.sub.1 suitable 
to cooling operation. 
In the heating operation, in step 105, environment data corresponding to 
the air conditioning load are inputed. In step 106, the operation 
frequency of the inverter portion 3 is determined according to the inputed 
data. In step 107, the total current limitation I.sub.A is set to the 
limitation current value I.sub.2 adapted to the heating operation. At this 
time, in reference to the temperature characteristics of the 
semiconductor, the total current limitation values are set so that they 
have the relation of I1&lt;I2. 
In above description, the total current limitation value is particularly 
set to the two levels, that is the heating and cooling operations. 
However, the total current limitation value and the peak current value are 
divided into a multitude of level every frequency band thereby setting the 
total current limitation value and the peak current value to those adapted 
to the corresponding frequency band. 
In step 108, the detected peak current ID is inputed from the peak current 
detection portion 8. In step 109, when the detected peak current ID is 
above the peak current limitation value IB, the operation halt routine is 
executed stopping the motor of the compressor 4. When the detected peak 
current ID is not above the peak current limitation value IB, the timer 
buffer is cleared to "0" (step 110). In step 111, the detected total 
current IS is compared with the total current limitation value IA. When 
the detected total current IS is not above the total current limitation 
value IA, the normal operation routine is executed. When the detected 
total current IS is above the total current limitation value IA, timer 
buffer is increased by 1 (step 112). 
In step 113, it is inquired whether the value of timer buffer is above the 
predetermined value (for example, 2). When the value of timer buffer is 
below the predetermined value, it is regarded as an instant current 
increment, so step 110 is repeated. If the detected total current IS is 
not above the total current limitation value IA, the normal operation 
routine is executed and this program returns to the step inquiring whether 
the operation mode is heating mode or cooling mode after executing 
operation routine. When the value of timer buffer is above the 
predetermined value, the halt routine is executed stopping the operation 
of the motor of the compressor 4. 
As above described, the present invention accurately detects a total 
current applied to the air conditioning apparatus and a peak current 
applied to the inverter, so the inverter is protected from excessive 
current. The total current limitation value is particularly set in heating 
and cooling operations. Both the total current limitation value and the 
peak current limitation value are particularly set to the multistage value 
according to the operation frequency band. Thus, the compressor is 
controlled in a multitude of limitation values to not only protect the 
inverter elements but also to control the operation of the air 
conditioning apparatus.