JPS6040582B2 - Control method for variable capacity refrigeration and air conditioner - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control method for improving the operating efficiency of a variable capacity refrigeration and air conditioner at rated output.

Conventional variable capacity refrigeration and air conditioners employ a method of turning the refrigeration cycle on and off to control capacity.

On the other hand, recently, in order to improve the controllability of capacity control, methods of controlling capacity continuously or in stages according to air conditioning load fluctuations have become increasingly required. A method of controlling the rotational frequency of an AC motor of a refrigeration compressor according to fluctuations has been considered. That is, as shown in FIG. 1, a commercial AC power supply 11 is converted to a frequency different from the power supply frequency by a frequency converter 14 consisting of a vertical striped connection of a DC converter 12 and an AC inverter 13, and the converted output is used to convert the AC motor for the compressor. (Synchronous or yielding electric conduction machine) Controls the rotation speed of 15. On the other hand, temperature information, humidity information generated in response to refrigeration and air conditioning load fluctuations,
Based on the air volume information, the capacity control circuit 16 generates a necessary refrigerating capacity control signal, and in response to this control signal, the conversion frequency control circuit 17 generates a necessary conversion frequency control signal. Then, by controlling the conversion frequency of the AC inverter 13 through this conversion frequency control, the rotation speed of the AC motor 15 is controlled. With the control method described above, when the air conditioning load is large and it is necessary to increase the refrigeration capacity, the rotation speed of the electric motor 15 is increased to increase the capacity of the refrigeration compressor, and conversely, the air conditioning If the load is small and the refrigeration capacity is small, the electric motor 15
This control is performed to reduce the rotation speed of the refrigeration compressor and reduce the capacity of the refrigeration compressor.

By the way, in the control system of the above-mentioned control method, if the efficiency of the DC converter 12 is represented by tc, the efficiency of the AC inverter 3 is represented by ri, and the efficiency of the AC motor 15 is represented by rim, then the overall efficiency of these is expressed as: riCX riiX sword m
…Indicated by 〇).

However, in the above control method, the energy loss in the frequency converter 14 (Rc and Ri are both 1 or less) in the control system.

), the total efficiency is lower, which is disadvantageous in terms of energy usage effect. The present invention has been made in view of the above-mentioned circumstances, and its purpose is to control the AC motor to be directly driven by the commercial power supply when the refrigeration capacity is operating for a relatively long time, thereby reducing the energy loss of the frequency converter. The purpose of the present invention is to provide a control method for a variable capacity refrigeration and air conditioner that can significantly improve the overall energy use efficiency by excluding the above from the overall efficiency. An embodiment of the control method according to the present invention will be described below with reference to the control system diagram shown in FIG. Second
In the control system diagram shown in the figure, parts that are the same as those in FIG. 1 are given the same reference numerals and their explanations are omitted, but they differ from FIG. 1 in the following points.

That is, the first switching switch S, is connected to the commercial AC power supply 11.
and the frequency converter 14, and a second changeover switch S2 is inserted between the frequency changer 14 and the AC motor 15, and these switches S, S2 switch between the AC power supply 11 and the AC motor 15. A frequency converter 14 is inserted between the two, or the input and output terminals of the frequency converter 14 are switched and selected to be short-circuited. On the other hand, a rotation speed detection circuit 21 is provided for detecting the rotation speed of the AC motor 15, and generates a detection output when the detection circuit 21 detects that the AC motor rotation speed approximately matches the AC power frequency. do. This detection output is led to the slit judgment circuit 22 together with the output of the conversion frequency control circuit 17. This determination circuit 22 determines whether the rotational speed information of the electric motor 15 and the frequency information of the conversion frequency control signal substantially match the AC power supply frequency, respectively, and generates a determination output based on the coincidence determination, and outputs a determination output to switch off the sliding door. Supply to 23. This switching circuit 2
3, when the judgment output is supplied, the switches S, , S
2 is controlled to select the short-circuit connection side (the side other than the frequency converter side). However, it is assumed that the refrigeration system is designed so that when a predetermined refrigeration load is applied, the electric motor 15 is directly driven by the AC power supply 11 to exhibit a predetermined refrigerating capacity.

That is, at a predetermined refrigeration load, the output of the capacity control circuit 16, which is determined by temperature information, humidity information, and air volume information, and the frequency information of the conversion frequency control output of the conversion frequency control circuit 17 approximately match the frequency of the AC power source 11. Assume that the characteristics of the control system are set as follows. Therefore, when the refrigeration system is exhibiting a predetermined refrigeration capacity, the output frequency information of the conversion frequency control circuit 17 and the output frequency information of the rotation speed detection circuit 21 each substantially match the power supply frequency, so the determination circuit 22 The judgment condition is satisfied and a judgment output is generated, and therefore the switching circuit 23 switches the switch S. so that the AC power supply 11 directly drives the electric motor 15. , S2
is under control. Note that the rotation speed n of the electric motor 15 is expressed by the following equation as is well known. n;12 is written-SZ...
■ However, f: Drive power frequency P: Number of poles S: Slip (S = 〇 in the case of synchronous electric motors) On the other hand, when a change in the refrigeration load occurs, at least one of the temperature information, humidity information, and air volume information changes. occurs, and in response to this information variation, the capacity control circuit 16 generates a required capacity control signal, and the conversion frequency control circuit 17 generates a required conversion frequency control signal.

Then, the output voltage V and output frequency f of the AC inverter 13, which is a variable frequency power source, are controlled by this conversion frequency control signal. When this world frequency f leaves the range that approximately matches the conversion frequency, the judgment condition of the judgment circuit 22 no longer holds true and no judgment output is generated, and the switching circuit 23 switches the switches S, S2 to the frequency converter 14. Control to choose side. Therefore, frequency converter 1
The electric motor 15 is driven by the output of 4. In this case, the electric motor 1
The number of rotations of the electric motor 15 is increased to increase the capacity of the refrigeration compressor, and conversely, when the refrigeration load is small and the refrigeration capacity needs to be weakened, the number of rotations of the electric motor 15 is decreased to reduce the capacity of the refrigeration compressor. A converter 14 output is generated. Note that during such variable control of the refrigerating capacity, rotation speed information of the electric motor 15 may be supplied from the rotation speed detection circuit 21 as comparison information for determining the conversion frequency in the conversion frequency control circuit 17.

Furthermore, when supplying a variable frequency drive output to the AC motor 15, the frequency converter 14 generates an output voltage V and an output frequency f such that the magnetic flux of the AC motor 15 is constant.

As is well known, the magnetic flux of this AC motor 15 must be determined by the driving voltage V
Since it is proportional to the drive frequency f and inversely proportional to the drive frequency f, the frequency converter 14 generates a drive output with V/f=constant. When the temperature information, humidity information, and air volume information each become constant values by controlling the refrigeration capacity as described above, the frequency information of the conversion frequency control signal approximately matches the frequency of the AC power supply 11, and the rotation speed of the electric motor 16 also increases. Since it approximately corresponds to the AC power frequency,
The determination condition of the determination circuit 22 is satisfied, and the switching circuit 23 connects the switches S, S2 to the short-circuited succeeding side, so that the AC power supply 11 directly drives the AC motor 15. According to the control method for a variable capacity refrigeration and air conditioner as described above,
At a predetermined refrigeration load, the AC motor for driving the refrigeration compressor is driven by a commercial AC power supply to achieve a predetermined refrigeration capacity, and when the refrigeration load fluctuates, the frequency converter for the variable frequency power supply is connected to the commercial AC power supply and the AC motor. The refrigeration and air conditioning capacity is variably controlled by inserting the motor between the Therefore, when the motor is directly driven by a commercial AC power source, the energy loss of the frequency converter can be eliminated from the overall efficiency.Moreover, by exerting the required refrigerating capacity that requires a relatively long operating time during this direct drive, the overall energy can be reduced. Utilization efficiency can be significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a control system diagram for explaining a conventionally considered control method for a variable capacity refrigeration and air conditioner, and FIG. 2 is a control diagram showing an example of the control method for a variable capacity refrigeration and air conditioner according to the present invention. It is a system diagram. 11... AC power supply, 14... Frequency converter, 15... AC motor, 16... Capacity control circuit, 17... Conversion frequency control circuit, 21...
...Rotation speed detection circuit, 22...Switching judgment circuit,
23... Switch switching circuit. Figure 1 Figure 2

Claims (1)

[Claims] 1 At a predetermined refrigeration load, the AC motor for driving the refrigeration compressor is driven with a commercial AC power source to exhibit a predetermined refrigeration capacity, and when the refrigeration load fluctuates, the frequency converter for the variable frequency power source is switched between the AC power source and the AC power source. A method for controlling a variable capacity refrigeration and air conditioner, characterized by inserting the power supply between the power supply and the electric motor to variably control the output of a variable frequency power supply according to fluctuations in the refrigeration load.