JPS60196541A - Rotational frequency control device of heat pump type air conditioner - Google Patents

Abstract

PURPOSE:To contrive to reduce the cost by making the current capacity of a semiconductor smaller by lowering motor current immediately when the motor current exceeds a limit value. CONSTITUTION:Input current to the motor 1 of a compressor during space heating operation is detected by a current transformer 3 as a motor current detecting means, which is provided between an inverter 2 as a frequency-to-voltage converting device and the motor 1. The signal from the current transformer is inputted through an analog-to-digital converter 4 to a CPU5 so as to be compared with current limit value memorized in a ROM6. Simultaneously when the value of the input current exceeds the current limit value, the CPU5 lowers the frequency and outputs the lowered frequency through an I/O8 to the inverter 2 under the condition that the voltage is kept fixed. At the same time, the CPU5 starts the time counting. After a certain period of time, the CPU5 outputs a signal to lower the voltage through the I/O8 to the inverter 2. In addition, the CPU5 outputs a signal to raise the rotational frequency to an inverter 10 to control the rorational frequency of a motor 9 to drive an indoor fan.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention is applied to a heat pump type air conditioner that can change the rotation speed of a compressor by changing the power frequency using a semiconductor element, and can change each state of the compressor. be able to.

Conventional configuration and its problems Conventionally, in a heat pump type air conditioner that uses semiconductor elements to change the power supply frequency and change the rotation speed of the compressor to change its capacity, the discharge during heating operation is When the pressure increases and the load on the motor increases, the current flowing through the motor, that is, the current flowing through the semiconductor increases. At this time, in order to protect the semiconductor from this overcurrent, the rotation speed of the compressor is reduced and the discharge pressure is lowered.

However, with this method, even if the rotation speed of the compressor is reduced, the discharge pressure does not start to drop immediately; there is a slight delay (1
0 to 30 seconds), the current value begins to drop 10 to 30 seconds after the frequency is lowered.

7. In general, electric motors that change frequency are shown in Figure 1.
It is operated with the characteristics shown in FIGS. 2 and 3.

FIG. 1 shows the relationship between the voltage of the power supply applied to the motor and the same wave number. FIG. 2 shows the output characteristics of the motor when driven by the power supply shown in FIG. 1, and FIG. 3 shows the relationship between load torque and current when a load is applied to the motor. For example, when the discharge pressure increases and the load on the motor reaches point a while operating at 90% in Figure 2, the current flowing through the motor at that time reaches a' as shown in Figure 3. If the limit value is exceeded, the power supply frequency is reduced to 6or%.

Then, as described above, the discharge pressure does not drop immediately, so the load torque on the motor does not change and moves to point b, which is the same as point a, as shown in FIG. 2. Since the current value at this time remains at point a' shown in FIG. 2, the operation of lowering the frequency continues. In this way, the frequency decreases one after another until the compressor stops. In order to prevent this phenomenon, the current limit value is set lower than point a', and a delay circuit is provided that stops the next frequency lowering operation during the time period 1 when the discharge pressure decreases after the frequency is lowered.

As described above, in the conventional method, the current must be limited to a lower current value than the current limit value of the semiconductor. That is, if torque at point -a is required, a semiconductor with a larger current capacity than point a' must be used, resulting in high cost.

OBJECTS OF THE INVENTION An object of the present invention is to eliminate the drawbacks of conventional rotation speed control devices for heat pump type air conditioners and to provide a rotation speed control device that is lower in cost.

Structure of the Invention In order to achieve this object, the present invention provides a rotational speed control device that includes: an air conditioning load detection means for detecting an air conditioning load; a motor current detection means flowing through a motor of a compressor; and the air conditioning load detection means. a comparison calculation means for inputting both outputs of the motor current detection means and performing a comparison calculation; a frequency-voltage conversion means for converting the frequency and voltage of a power source that drives the compressor; Determine the frequency of the conversion means. a driving frequency determining means; a driving voltage determining means for determining a driving voltage by inputting both outputs of the one driving frequency determining means and the comparison calculation means; and a timing driving means operated by the output of the driving voltage determining means. , this word 1
a clock means for cutting and cutting for a certain period of time by a time drive means and outputting a timing completion signal to the drive voltage determining means; an indoor fan rotation speed determining means operated according to the output of the drive voltage determining means; and a rotation speed of the indoor fan. The indoor fan rotation speed control means operates based on the output of the determination means.

With this configuration, when the motor current exceeds the limit value, the motor current can be immediately reduced, and the current capacity of the semiconductor can be reduced.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 4, 6, and 6. An input current r1 to the motor 1 of the compressor during heating operation is provided at a known frequency '·l-1, and a current transformer 3 is provided between the inverter 2, which is a pressure converter, and the motor 1, and which is a motor current detection means. is detected.

This signal (through the analog/digital converter 4) is input to the CPU 5 of the microcomputer. When it is determined that the current value has exceeded the limit value, a signal from thermistor 7, which is an air conditioning load detection means, is sent.
Immediately, the CPU 6 decides to fix the voltage and lower the frequency by 4 cm, and changes the frequency to l10s')if+l
.

and output to inverter 2. At the same time, the CPU 5 starts counting time, and after a certain period of time has elapsed, outputs a signal to lower the voltage to the inverter 2 through the I 108. At the same time, the CPU 5 outputs a signal to increase the rotation speed of the electric motor 9 driving the indoor fan to the inverter 10 that controls the rotation speed. FIG. 5 is a flowchart 1 showing these operations.

Next, how the motor current changes by controlling the voltage and frequency described above will be explained using FIGS. 6 and 7. FIG. 6 shows the relationship between frequency and voltage. This relationship d: is stored in the ROM 6 in advance. For example, at the 0 point of 90H2, ■71 (the current is ff1 in the width
11 If the limit value is exceeded, the voltage is 901-i,'i'tj:
Lower the frequency to 60I17.

Then, after a certain period of time has elapsed, the voltage drops to the lci point.

Next, in Figure 7, the frequency and electric power 1F are shown in Figure 6.
This shows the motor current when the motor moves. 90I (7,
When the frequency is lowered to the fixed voltage switch 6011□ during freeze expansion, the current kl immediately drops from c' to d'. Then, when the voltage is lowered after the load on the motor is reduced, the current further drops and moves to the zero point. Furthermore, since the rotation speed of the indoor fan is increased at the same time as these operations, the discharge pressure immediately begins to drop.1. The time during which the load torque on the compressor motor decreases can be shortened. In this way, the motor current can be reduced in a short time.

In this embodiment, the rotation speed of the indoor fan is controlled by an inverter, but the rotation speed may also be controlled by well-known tap switching.

As described in detail, according to the present invention, the current flowing through the motor can be immediately reduced, and there is no need to provide a margin for the current capacity of the semi-conductor, so a low current capacity can be used. Semiconductors can be used, and a low-cost rotational speed control device can be provided.

[Brief explanation of drawings]

Figure 1 is a voltage-frequency characteristic diagram when operating with a conventional rotation speed control device, and Figure 2 is a diagram of the same rotation speed control device. FIG. 3 is a current-torque characteristic diagram of the electric motor; FIG. 4 is a circuit diagram of an air conditioner equipped with a rotation speed control device according to an embodiment of the present invention; Figure 5 is a flowchart showing the signal flow of the rotation speed control device, Figures 6 and 7d are voltage-frequency characteristic diagrams and current-voltage characteristic diagrams of the rotation speed control device, respectively. FIG. 2 is a claim correspondence diagram expressing the present invention using a function realizing means. 1... Electric motor, 2... Inverter, 3...
...Current transformer, 6... CPU0 Fig. 1 Fig. 2 Fig. 3 'IC' = L Fig. 4 ■ Fig. 5

Claims (1)

[Claims] A rotation speed control device that varies the operating speed of the compressor according to fluctuations in air conditioning load is provided, and the rotation speed control device is combined with air conditioning load detection means for detecting the air conditioning load and detecting the current flowing through the electric motor of the compressor. motor current detection means; - comparison calculation means for inputting both outputs of the air conditioning load detection means and the motor current detection means and performing a comparison calculation; and a frequency/voltage for converting the frequency and voltage of the power source that drives the compressor. a converting means, a driving frequency determining means for determining the frequency of the frequency/voltage converting means based on the output of the comparing calculating means, and determining a driving voltage by inputting both outputs of the driving frequency determining means and the comparing calculating means. a driving voltage determining means, a timing driving means operated by the output of the driving voltage determining means, a timing driving means for measuring a certain period of time by the timing driving means and outputting a timing end signal to the driving voltage determining means, and the driving voltage determining means. A rotation speed control device for a heat pump type air conditioner, comprising an indoor fan operating rotation speed determining means and an indoor fan rotation speed control means, which are operated based on the output of the means.