JPH01219373A - Compressor controlling method for refrigerator - Google Patents

Abstract

PURPOSE:To improve the extent of temperature control accuracy by performing operating frequency control only over a compressor being small in output when suction pressure of the compressor is lower than the setting one, and only over a compressor being large in the output when the suction pressure is larger than the setting one, respectively. CONSTITUTION:A suction pressure sensor 9 is installed in a refrigerant pipe P at the suction side of compressors 1, 2, and when suction pressure is lower than the setting one, operating frequency control only over a compressor 2 small in output is performed, and when the suction pressure is larger than the setting one, the operating frequency control only over a compressor 1 large in the output is performed. With this constitution, a capacity adjusting range is sundividable, so that temperature control accuracy becomes heightened and, what is more, operating efficiency is improvable.

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Application Field) The present invention has a plurality of compressors connected in parallel with each other and having different outputs, and an inverter device is used to control the operating frequency of each compressor. The present invention relates to a refrigerating machine that is controlled, and particularly to an improvement in a method of controlling the operation of each compressor.

(Prior Art) For example, in large showcases, so-called multi-type refrigerators, which constitute a refrigeration cycle that controls a plurality of evaporators, are often used. In this type of refrigerator,
The range of refrigerating capacity required by each evaporator is wide, and it is not possible to satisfy this requirement with just one large compressor. That is, the capacity of the material to be frozen is often different for each evaporator, and there are also cases where only one evaporator is activated while all other evaporators are stopped.

In order to meet these demands, rather than having one large compressor, multiple compressors with different outputs are connected in parallel to create a refrigeration cycle with a wide range of capacity according to the demands of each individual evaporator. A method of driving began to be adopted.

Moreover, by connecting an inverter to each compressor and controlling its operating frequency separately, the refrigeration capacity can be varied, making it possible to achieve more precise refrigeration.

By the way, conventionally, in such a refrigerator, as shown in Fig. 4 (A), a compressor with a large output (large kelp) and a compressor with a small output (small kelp) are operated simultaneously and at the same ratio. Inverter control was performed accordingly. Normally, the suction pressure, which is the pressure on the compressor suction side of the refrigeration cycle circuit, is detected and compared with a set pressure determined from empirical rules to determine the optimum operating conditions, which is useful for controlling the compressor. In the figure, PsS indicates the set pressure, and PsL is the suction pressure lower than the set pressure P5S.

PsH indicates a pressure higher than the set pressure P8S.

Over the entire operating range, the sum of the outputs of the compressor with a large output (large kelp) and the compressor with a small output (small kelp) directly appears as the refrigerating capacity.

However, in this type of control, two compressors are always driven at the same time, so the temperature control range becomes very wide, resulting in poor operational efficiency and a problem in that the so-called energy-saving operational control is not achieved.

Further, as shown in FIG. 2B, in order to finely control the temperature, it is conceivable to intentionally change the slope of the refrigerating capacity at the upper and lower pressures around the set pressure PsS. However, compressors with different outputs are operated simultaneously, which makes operation control more complicated.

(Problems to be Solved by the Invention) The present invention provides a refrigerator in which a plurality of compressors having different outputs as described above are connected in parallel to each other and each is electrically connected to an inverter device. By operating simultaneously, the adjustment range of refrigeration capacity becomes extremely large, eliminating the problem of refrigeration with rough temperature control accuracy, and by performing control corresponding to each compressor based on the set pressure, each compressor The purpose of the present invention is to provide a method for controlling a compressor of a refrigerator, which improves operating efficiency, improves temperature control accuracy, and helps save energy.

[Structure of the invention]

(Means for Solving the Problem) That is, the present invention provides a refrigerator in which a plurality of compressors with different outputs are connected in parallel to each other, and each compressor is electrically connected to an inverter device. When the suction pressure of the compressor is lower than the set pressure, the operating frequency is controlled only for the compressor with a small output, and when the suction pressure is higher than the set pressure, the operating frequency is controlled only for the compressor with a large output. This is a compressor control method for a refrigerator, which is characterized by the following.

(Function) In normal stable operating conditions, if the suction pressure is below the set pressure, the compressor with high output is held at a constant operating frequency, and only the compressor with low output is controlled. Manage temperature. Furthermore, when the suction pressure is higher than the set pressure, the compressors with low output are held at a constant operating frequency, and only the compressors with high output are controlled to achieve a certain level of fine temperature control.

(Example) Hereinafter, an example of the present invention will be described based on FIG. In the figure, 1 is a first compressor with a large output (also called a kelp large), and 2 is a second compressor with a small output (also called a kelp small). Both the discharge side and the suction side are connected in parallel via a refrigerant pipe P. Further, the first and second compressors 1.2 are electrically connected to a first inverter device 3 and a second inverter device 4, respectively, so that their operating frequencies are controlled by each other. . 1st. The discharge side refrigerant pipe P and the suction side refrigerant pipe P of the second compressor 1.2 both merge and communicate through one refrigerant pipe P. In the middle of this refrigerant pipe P, there is a condenser 5. expansion valve 6
．． The evaporator 7 and the gas-liquid separator 8 communicate with each other in sequence, thus forming a refrigeration cycle. In addition, the above 1. A suction pressure sensor 9 is provided in the refrigerant pipe P on the suction side of the second compressors 1 and 2. This suction pressure sensor 9 and the first
．． Both second inverter devices 3 and 4 are electrically connected to control circuit C. Further, a plurality of evaporators (not shown) having the same capacity may be connected in parallel to the evaporator 7.

However, the refrigerant is the first. It is compressed by the second compressor 1.2, and conducts sequentially in the direction shown by the solid arrow, so that each component performs the necessary refrigeration cycle action. The suction pressure sensor 9 detects the suction pressure of the refrigerant sucked into each compressor 1, 2, and constantly sends a detection signal to the control circuit C. The control circuit C receives this, calculates a comparison with the set pressure PsS, and sends a necessary operation command signal to each inverter device 3, 4. Therefore, each compressor 1, 2 has a first . The operating frequency is always controlled to the optimum operating frequency by the second inverter device 3.4.

When starting the refrigerator, as shown in FIG. 3(A), the operating frequency of the first and second compressors 1 and 2 is increased and maintained in order to quickly reach a predetermined temperature. Control to maximize ability. If this state continues, the predetermined freezing temperature will be reached quickly, and the freezing action will no longer be necessary.

Therefore, the refrigerating capacity of each compressor 1, 2 is temporarily lowered to perform a so-called energy-saving operation. Then, after a certain amount of time has passed and the refrigeration effect becomes weaker, the operation frequency is raised again to increase the refrigeration capacity and the operation is repeated to achieve so-called stable operation.

The first condition during such a period of stable operation. Second compressor 1
, 2 is performed as shown in FIG. 2(B). The suction pressure Ps detected by the suction pressure sensor 9 is Ps
If the pressure is between L and the set pressures P and S, the control circuit C
is the first. The following operation command is issued to the second inverter device 3.4. That is, the first compressor 1 (large kelp) with a large output is maintained at a constant operating frequency, and only the second compressor 2 (small kelp) with a small output is controlled. Therefore, the refrigerating capacity can be increased or decreased only in the second compressor 2, which has a small output, and the range of the refrigerating capacity can be adjusted very finely, resulting in extremely fine temperature control.

Furthermore, when the suction pressure Ps exceeds the set pressure PsS and is between PsH, the second compressor 2 (small comb) with a small output is maintained at a constant operating frequency, and the first compressor with a large output is maintained at a constant operating frequency.
Only compressor 1 (large kelp) is controlled. From this,
Although the refrigerating capacity adjustment range is slightly larger than in the state described above, a certain degree of finer temperature control is possible compared to the conventional method in which two compressors are controlled at the same time.

In other words, the suction pressure Ps has increased to the set pressure 258 or higher.
In this case, for example, a plurality of evaporators 7 are operated at the same time, and therefore, very strict temperature control is not required.

The control method for each of the compressors 1 and 2 can be explained from FIG. 2 as well. As in the present invention, the first . If the operating frequencies of the second compressors 1 and 2 are controlled, the range of capacity adjustment becomes narrower, the temperature control accuracy becomes higher, and an optimal refrigerating effect can be achieved depending on the object to be frozen.

〔Effect of the invention〕

As explained above, according to the present invention, each inverter device detects the pressure on the suction side of the compressor, and
Since the operating frequency is controlled to change based on the set pressure, the capacity adjustment range can be narrowed, temperature control accuracy is increased, and the optimal freezing effect on the frozen object is achieved. .

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a refrigeration cycle of a refrigerator showing an embodiment of the present invention, and FIG. 2 is a diagram specifically explaining its control method.
Figure 3 (A) is a characteristic diagram showing the relationship between refrigerating capacity and suction pressure especially at startup, Figure 3 (B) is a characteristic diagram showing the relationship between refrigerating capacity and suction pressure during stable operation, and Figure 4. (
A) and (B) are characteristic diagrams showing the relationship between refrigerating capacity and suction pressure, showing mutually different conventional examples of the present invention. 1... First compressor (large kelp), 2... Second compressor (small kelp), 3... First inverter device, 4
...Second inverter device, C...Control circuit. Applicant's agent Patent attorney Takehiko Suzue Figure 2 (A) (B) Figure s4

Claims (1)

[Claims] In a refrigerator in which multiple compressors with different outputs are communicated in parallel with each other and each compressor is electrically connected to an inverter device, each of the inverter devices is A compressor control method for a refrigerating machine, characterized in that the operating frequency of only a compressor with a small output is controlled, and when the suction pressure is higher than a set pressure, the operating frequency of only a compressor with a large output is controlled.