JPH03164657A - Air conditioner - Google Patents

Abstract

PURPOSE:To obtain a stable operation over the entire range of the operating frequency of a compressor from low to high frequencies by setting the coefficient of PiD operation for regulating the opening of an electronic expansion valve in terms of the operating frequency. CONSTITUTION:The operation of opening of an electronic expansion valve 4 is carried out by a control calculator 9, and an opening change is output to the valve 4. The calculator 9 reads a delivery gas temperature Td from a delivery gas temperature sensor 8 and a condensing temperature Tc from a discharge pressure sensor 9, and operates a differential temperature (Td-Tc) as the degree of superheat SH. It reads a frequency Hz from an inverter 6 and sets a predetermined degree of superheat SH0. It operates the opening change PO of the expansion valve with this information. Its operational formula has three types of terms of a proportional term of a difference between the SH and the SH0, a differentiating term of variation amount of the SH, and an integral value of the accumulated values of the differences of the SH and the SH0, and used in the form of multiplying the calculated value of adding the proportional term, the differentiating term and the integrating term by a coefficient for converting to the change PO. If the frequency is low, an output opening change is reduced to perform a smooth control, while if the frequency is high, the output opening change is increased to perform a fast control.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an expansion valve control method in an air conditioner in which a compressor is driven by an inverter and the operating frequency of the compressor is variable.

[Conventional technology]

Conventionally, the control method for expansion valves involves integrating the difference between a predetermined degree of superheat and the actual degree of superheat, and controlling the valve opening of the expansion valve according to the output to keep the degree of superheat constant. was.

[Problem to be solved by the invention]

The above conventional technology simply integrates the difference between the target value and the actual value, and does not take into account the responsiveness of the refrigeration cycle.In the case of an air conditioner where the compressor is driven by an inverter to form the refrigeration cycle, The same control constants are used for all cases, from slow refrigeration cycle response when the compressor operating frequency is low to fast refrigeration cycle response when the compressor operating frequency is high. Also, at high frequencies, the followability of the expansion valve is poor and it takes time for the expansion valve to stabilize in an optimal state.

The purpose of the present invention is to provide stable operation in the entire compressor operating frequency range from low frequency to high frequency, and to quickly control the expansion valve even when the frequency fluctuates rapidly. The objective is to improve the temperature to a predetermined degree of superheating.

[Means to solve the problem]

In order to achieve the above object, the present invention provides an influence factor for frequency in the calculation method, and when the compressor operating frequency is low and the response of the refrigeration cycle is slow, the number of expansion valve opening/closing operation outputs is reduced. When the value is low, slow refrigeration cycle control is performed, and when it is high, the expansion valve opening/closing operation output number is increased to perform fast refrigeration cycle control.

[Effect]

Expansion valve control performs PiD calculation (proportional/integral/derivative operation) based on the difference between the target value of the degree of superheat and the actual degree of superheat, and multiplies it by a coefficient to convert it into a change in the opening degree of the expansion valve. Therefore, the coefficient is set according to the operating frequency, and when the frequency is low, the coefficient is set small, so that the opening change is small, and when the frequency is increased, the opening change is large, and the refrigeration cycle response changes depending on the frequency. Since it is possible to follow
A stable degree of superheat can be maintained.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. Compressor 1 with variable operating frequency by inverter 6. Four-way valve 2. Outdoor heat exchanger 3. Electronic expansion valve 4. Air heat exchanger 5
are sequentially connected to form a refrigeration cycle, and a high-pressure pressure sensor 7 and a discharge gas temperature sensor 8 are installed on the discharge side of the compressor 1, and this sensor information is taken in and the output frequency of the inverter 6 is In an air conditioner equipped with a control calculator 9 that can take in the following information, the control calculator 9 calculates the opening degree of the electronic expansion valve 4 and outputs the change in the opening degree to the electronic expansion valve.

The control calculator 9 performs electronic expansion valve opening control according to the flowchart shown in FIG. 2. First, the discharge gas temperature sensor 8
The discharge gas temperature Td from the inverter 6 and the condensation temperature Tc from the discharge pressure sensor 9 are read, and the temperature difference between Td and Tc is calculated as the superheat degree SH. Set the superheat degree SHo. The expansion valve opening change P○ calculation is performed using such information, but the calculation formula includes a proportional term consisting of the difference between SH and SHo, and S
It consists of three types of terms: a differential term consisting of the amount of change in H, and an integral value consisting of the similar product value of the difference between SH and SHo.The calculated value of the proportional term, differential term, and integral term is the expansion valve opening change Po. It is used in the form multiplied by the coefficient to be converted. This coefficient is set to the compressor frequency Hz by setting coefficient a1 when Hz is low, setting aZ when Hz is medium, and setting a8 when Hz is high. On the other hand, the coefficients are divided so that the influence of frequency is expressed in the operation of changing the opening degree of the expansion valve. Furthermore, the coefficient is at<ax<a
If the frequency is low, the output opening change is made low to reduce the influence of this control on the refrigeration cycle, and gentle control is performed.If the frequency is high, the output opening change is made high. This control will have a greater influence on the refrigeration cycle and will be controlled quickly.

According to this embodiment, when the compressor operating frequency is low, the movement of refrigerant circulating in the refrigeration cycle is slow, and it takes time for a reaction to a change in the expansion valve opening to appear. It is possible to control this and stabilize the refrigeration cycle. on the other hand.

When the compressor operating frequency is high, the movement of the refrigerant circulating in the refrigeration cycle is fast, and the expansion valve responds quickly to changes in the opening degree.According to the situation, the width of the opening change is accelerated and the degree of superheat converges quickly to the target value. becomes possible.

Furthermore, even when the behavior of the refrigeration cycle changes suddenly due to a single frequency change, such as when the compressor frequency suddenly changes from a low frequency to a high frequency, the expansion valve opening degree change can be followed, and the predetermined value can be quickly adjusted. The degree of superheating can be converged.

〔Effect of the invention〕

According to the present invention, in a refrigeration cycle having an inverter-driven compressor, the opening degree change control of the expansion valve is changed depending on the frequency, thereby providing refrigeration cycle control that can follow frequency fluctuations and transient conditions such as startup. and can be operated stably and efficiently.

[Brief explanation of the drawing]

Fig. 1 is a refrigeration cycle system diagram according to an embodiment of the present invention;
The figure is a control flowchart of the expansion valve. DESCRIPTION OF SYMBOLS 1... Compressor, 2... Four-way valve, 3... Outdoor heat exchanger, 4... Electronic expansion valve, 5... Air heat exchanger, 6...
・・Inverter, 7・High pressure sensor, 8・Discharge gas temperature sensor

Claims (1)

[Claims] 1. A compressor whose operating frequency is variable by an inverter;
Four-way valve, outdoor heat exchanger, electronic expansion valve, air heat exchanger,
In an air conditioner, the electronic expansion valve is opened in order to control the degree of superheat to a predetermined value, in an air conditioner equipped with a refrigeration cycle connected in sequence, a degree of superheat and the operating frequency, and a control calculator having a calculation function. An air conditioner characterized in that a change in the opening degree of the electronic expansion valve follows the operating frequency by setting a coefficient of PiD calculation for adjusting the operating frequency with respect to the operating frequency.