JPS60241781A - Controller for variable speed pump - Google Patents

Abstract

PURPOSE:To improve the responsiveness of an induction motor by lengthening the accelerating time of the motor in a low speed portion and shortening it in a high speed portion. CONSTITUTION:A controller 9 calculates a deviation between the pressure signal 4b of a discharge unit of a pump 3 output from a pressure oscillator 4 and a set signal 8b by a PI regulating function, processes the results by function generating function, manual and automatic mode switching function to apply a frequency command to an inverter 1. The frequency command is set to the minimum starting frequency f4 when the start signal of the pump 3 to the inverter 1 is received, increased by the increasing rate A until exceeding the minimum frequency f0, and increased by the increasing rate B when exceeding the minimum frequency f0. Thus, the responsiveness of the pump is improved to reduce the variation in the discharge output of the pump for the variation in the flow rate of the pump.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a control device for an induction motor connected to a variable speed pump.

[Prior art]

Conventionally, there has been a device of this type as shown in FIG.

In the figure, 1 is an inverter connected to a power source via a switch SW, 2 is an induction motor whose rotation speed is variably controlled by the inverter 1, 3 is a variable speed pump driven by the induction motor 2, and 4 is piping. A pressure transmitter that measures the pressure of water flowing in the passage 4a, 5 a PI controller that converts the pressure signal 4a from the pressure transmitter 4, 6 a switching device that selects manual or automatic operation, and 7 a manual speed control. Setting device to set,
8 is a setting device for setting the pressure, and FR is an output frequency meter of the inverter 1.

When controlling the pump 3 in the manual operation mode, the switching device 6 is set to manual, and the arbitrary amount of speed command 7 set by the setting device 7 - t - The frequency setting input FK of the inverter 1 is transmitted through the switching device 6. and operate the inverter l according to the speed command 7a. Thereby, the induction motor 2 drives the pump 3 at a rotational speed according to the frequency of the current supplied from the inverter 1, and the pump 3 changes the pressure inside the piping 4a.

On the other hand, when controlling pump 3 in automatic operation mode 1
setting the switching device 6 to fully automatic, inputting the pressure signal 4b from the pressure transmitter 4 to the PI controller 5, and detecting the difference with the setting signal 8a from the setting device 8. The PI controller 5 applies a control signal 511 to the frequency setting manual power F of the inverter 1 via the gold switching device 6 to minimize this difference. Inverter Itl! , frequency setting human power F [supplied control signal 5a [Therefore, the rotation speed of the induction motor 2 is controlled to control the pump 3
to control the pressure inside the piping line 4a.

In this way, the frequency of the output that drives the induction motor 2 is increased or decreased by the control signal 5a of the inverter 1'' controller 5.However, when accelerating or decelerating the induction motor 2, the t current is In order to suppress the permissible limit within the current range, the control device 6 determines the rate of change in the frequency of the output of the inverter 1 so that it starts or decelerates slowly according to the setting signal 7a.Therefore, the acceleration/deceleration time varies from low speed to high speed. The acceleration torque of the induction motor 2 is set based on the point where the acceleration torque of the induction motor 2 is the smallest so that the acceleration is constant up to the point where the acceleration torque of the induction motor 2 is the smallest.

Since the conventional control device is configured as described above,
At startup when there is a large difference between the pressure in the piping and the set pressure value, the output from the PI controller, that is, the frequency command to the inverter becomes a speed increase command, but the time set with the acceleration/deceleration setting switch in the inverter is In other words, since the acceleration time is determined by the minimum acceleration torque, the rotational speed of the induction motor cannot be rapidly increased, and the pump pressure, that is, the specific capacity of the control system, is slow.

[Summary of the invention]

This invention was made to eliminate the drawbacks of the conventional ones as described above, and by installing a function generator for setting the frequency in the inverter, the acceleration time can be reduced in the low speed section where the acceleration torque of the induction motor is small. The variable speed pump control device is designed to be longer, and to shorten the inverter's acceleration/deceleration time in high-speed areas where the acceleration torque is large enough to improve the response of the induction motor and minimize pump pressure fluctuations. The purpose is to provide.

[Funny example of invention]

An embodiment of the present invention will be described below with reference to the drawings. Second
In the figure, the same symbols as in FIG. 1 indicate the same parts, and 9 is, for example, a computer, which converts the pressure signal 4b into a voltage signal, compares it with the setting signal 8a of the setting device 8, and amplifies the difference signal between the two. This control device is equipped with a PI adjustment function, a function generation function for controlling the difference signal amplified by the PI adjustment function and using it as a frequency command for the inverter 1, and a switching device 6 function.

When performing constant pressure control with respect to a change in flow rate at the discharge section of the pump 3, the pressure at the discharge section of the pump 3 is detected by the pressure transmitter 4. The control device 9 controls P by the detected pressure signal 9b.
I activate the controller function, perform processing to make it equal to the setting signal 8a of the setting device 8, and send the result to the function generation function,
A frequency control command to be processed by the manual and automatic mode switching function and supplied to the frequency setting manual F of the inverter 1 is obtained. Inverter 1 controls the rotation speed of induction motor 2 based on this frequency command. The control device 9 thus performs the PI controller function, mode switching function, and frequency command output function to the inverter 1. However, the PIp1 metering function and mode switching function were explained in the prior art section, so they will not be explained here. The explanation will be omitted, and the process of converting the result of executing the PI controller function into an optimum frequency command for the inverter 1 will be explained in detail with reference to the flowchart shown in FIG.

When the mass controller receives a starting signal for the pump 3 to the inverter 1, the lowest starting frequency f4 of the inverter 1 is supplied to the inverter 1 as the output frequency f2 of the inverter 1 in step S1. In step S2, the command frequency f1 from the controller function is compared with the output frequency f2 of the inverter I, and when +'+>f2, step S3 is executed and the acceleration timer provided in the control device 9 is reset. , in step S4, set the acceleration timer to time setting 1 and set the pump l.
Set the value according to the load, and then proceed to step s5.
．． Output frequency f2 with time amplifier of acceleration timer in s6
1 step up (“2+1 step → fz)”
. In step S7, the minimum speed frequency fo for ensuring the minimum discharge pressure of the pump 3 set in advance is compared with the output frequency f2.

If ro<r2 does not hold, the process advances to step S8. In step S8, the inverter IVc output frequency f2 is output, and the process returns to step S2.

In the above manner, the speed comparison f, ) f2 is performed, and the output frequency f2 is increased by one step in the loop of setting the acceleration timer for one hour - increasing the output frequency f2 by one step - comparing the lowest speed until the lowest speed is exceeded. The output frequency f2 of the inverter 1 is determined by a function, that is, according to the acceleration fA as shown in FIG. When the output frequency f2 exceeds the lowest frequency fo, the process proceeds from step S7 to step S9, and the command frequency f by the PI controller function is output to the inverter 1. From then on, the acceleration time setting TI+ in the inverter 1 shown in FIG. The output frequency f2 of the reimperter 1 is increased or decreased by the deceleration time setting T2.

FIG. 4 is a characteristic diagram of the inverter acceleration/deceleration pattern formed by the series of processes described above.

Output frequency f2 from increase rate AK until lowest speed frequency fo
increases.

FIG. 5 is a characteristic diagram showing an enlarged view of portion C shown in FIG. 4. The output frequency f2 of the inverter 1 increases according to the time setting T5 of the adjustable acceleration timer. In addition, when the lowest speed frequency is 10 or more, the command frequency f is switched by the PIvI4 metering function, so the frequency increases at the rate of increase B according to the acceleration time setting TI and deceleration time setting T2 in the 5 inverter 1, so the pump pressure Improved response.

In the above embodiment, a frequency setter that changes linearly is shown, and only one point, the lowest frequency, is shown as the acceleration switching point. Several switching points may be provided to effectively use the torque characteristics of the induction motor 2.

In addition, in the above embodiment, the PI controller, frequency setter, etc.
Although the control device is shown as one unit, these may be separated by function, or even if these functions are built into the inverter 1, the same effect will be achieved.

〔Effect of the invention〕

As described above, according to the present invention, since the acceleration/deceleration of the induction motor is changed depending on the rotation speed of the induction motor, the responsiveness of the pump is improved, and the fluctuation of the pump discharge pressure with respect to changes in the pump flow rate is small, and a constant trap is maintained. dripping Further, since the torque generated by the induction motor is effectively used for acceleration, the inverter capacity can be small, and the device can be made at a low cost and has the advantage of being highly accurate.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional variable speed pump control device, Fig. 2 is a block diagram of a variable speed pump control device according to an embodiment of the present invention, and Fig. 3 outputs a frequency command by the device shown in Fig. 2. 4 and 5 are characteristic diagrams of acceleration/deceleration patterns according to the present invention. 1... Inverter, 2... Induction motor, 3... Pump, 4... Electric motor, 1, 8... Setting device, 9...
Control device. Note that the same reference numerals in Figure 1 indicate the same parts. Patent Applicant Mitsubishi Electric Co., Ltd. Agent Patent Attorney 1) Hiroshi Sawa (2 others) -□ Figure 4 Figure 5 Procedural Amendment (Voluntary) 1, □1116 Shimo 6. Old. Commissioner of the Japan Patent Office 1, Indication of the case Japanese Patent Application No. 59-73015 2, Name of the invention Variable speed pump control device 3, Person making the amendment 5, Detailed description of the invention in the specification subject to amendment 6, Amendment amend the statement of contents as follows. Pe

Claims (1)

[Claims] A pressure signal indicating the pressure in the piping connected to the pump driven by the induction motor and a preset pressure command in the piping are input, and a speed command for commanding the rotational speed of the pump is sent to the inverter. 1. The control device changes the speed command according to a certain function when the pump does not reach a preset minimum speed depending on the frequency of the output of the inverter after starting the pump, When it is indicated that the minimum speed has been reached, the speed command is controlled according to the pressure signal so that the operating speed corresponds to the pressure command within a preset acceleration/deceleration time, and the inverter A variable speed pump control device that changes the rotation speed according to a speed command.