JPS5992799A - Control system for induction motor - Google Patents

Abstract

PURPOSE:To enable to always hold the maximum efficiency irrespective of a load state by providing the prescribed relationship to a current which flows to an induction motor and controlling the terminal voltage. CONSTITUTION:When a load is varied a control circuit 4 searches a function table 10 by data which represents a new current I and supplies a new gate signal in response to it to a voltage control circuit 2. When the storage content of the function table 10 is suitably determined and the relationship between the voltage V and the current I is maintained to produce the maximum efficiency, the maximum efficiency in response to the load state can be always automatically obtained even if the load of the IM3 varies, with the result that the IM3 can be always operated with high efficiency irrespective of the variations in the load.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a control method for an induction motor with large load fluctuations, and is a method of controlling an induction motor that always maintains the maximum efficiency under any load. This invention relates to a control system that allows the operation of an induced acid ψυ machine.

[Prior art]

In recent years, with the advancement of single-power semiconductor devices such as triacs, voltage control methods using tribooks and the like have become widely used for controlling induction motors (hereinafter simply referred to as IMs). It's starting to look like this.

As such a control method, a method is conventionally known in which a direct current of % IM is detected and the terminal voltage is controlled accordingly.

In the conventional control method, the phase difference (power factor) between the terminal voltage of l1VI and the current limit is detected, and the voltage is controlled so that the phase difference, l) power factor, becomes a preset value.

For this reason, the conventional control method has the disadvantage that when the IM load fluctuation is large, optical efficiency cannot be obtained.

To explain this t'L with reference to Figure 1, the figure is JISC4
The load-efficiency characteristic diagram calculated using the three-phase IM characteristic calculation method of 207 is designed so that maximum efficiency can be obtained when the load factor is 75 to 100% with respect to the general lA46-I rated terminal voltage. Therefore, its characteristics are expressed by curve a, and when the load factor becomes less than 75q6, the efficiency decreases rapidly. This is because the excitation input is also constant, and as the load becomes lighter, the proportion of this input in the total loss increases.

On the other hand, when the power factor is controlled to be constant as in the conventional control method described above, the terminal voltages of p and IM are controlled as shown by curve C in Figure 1. As a result, although a remarkable improvement is obtained compared to the case of characteristic curve a when the characteristic curve is constant, it can be seen that the condition is still not sufficient.

[Purpose of the invention]

The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to
To provide a control system for an IM that can always operate at maximum efficiency even when the load fluctuates.

[Summary of the invention]

To achieve this objective, the present invention provides an
The voltage is changed according to the current, and in this case,
The present invention is characterized in that the voltage is always controlled to achieve the maximum efficiency that should be obtained at that time depending on the load condition based on the relationship between the current of the IM and the load, and the efficiency and voltage in the load.

[Embodiments of the invention]

Hereinafter, an actual Mtt example of the IM control method according to the present invention will be explained with reference to the drawings.

FIG. 2 shows one embodiment of the present invention, and in the figure, 1 is a three-phase AC power supply, 2 is a voltage control circuit, 3 is an IM to be controlled, and 4 is an example of the present invention.
5 is a current detector, 6 is an A/D (analog-to-digital converter), 7 is a power synchronization circuit, an 8-digit gate circuit, and 9 is a ROM (read only memory) for storing a block. ), 1° is a function table.

The voltage control circuit 2 includes a semiconductor element such as a triac, and functions to control the voltage of the three-phase power supply from the power source 1 by controlling the conduction angle, etc., and supply it to the IiVi 3 as a CIEV.

The control device 4 has arithmetic processing functions such as a microcomputer, and performs various control functions according to programs stored in the ROM 9.

The current detector 5 detects a certain current supplied to the IM 3, converts the current signal into digital data using the A/D 6, and supplies the converted data to the input port of the control circuit 4.

The power supply synchronization circuit 7 synchronizes the gate signal calculated and outputted by the control device 4 with the power supply 1, and supplies it to the triac of the voltage control circuit 2 via the gate circuit 8.

The function table 10 is composed of ROM etc.:! tlJ
The output paper pressure of the voltage control circuit 2 is determined in accordance with the data representing the flow rate read by the gososan 4 from the current detector 5.

For example, the terminal Fi voltage V of p IM3 is M” 31 yen
It is possible to read out the data necessary to generate a gate signal 0 such that the relationship shown in FIG.

Next, the operation of this embodiment will be explained.

Assume that the load on IM3 is approximately 85 cm, and the terminal voltage V at this time is V, . At this time, the magnitude of the voltage V1 for the electric current is determined by searching the function table 10 using the data read by the control circuit 4 from the current detector 5 via the A/D 6, and thereby As mentioned above, it is determined by the gate signal, that is, the control signal, which is supplied to the voltage control circuit 2 through the power synchronization circuit 7 and the gate circuit 8 after processing the given data. be.

Next, it is assumed that the load on IM3 is small and the supplied current (2) drops below 11.

Then, the control circuit 4 changes the function table 10 according to the data representing the new current I, and accordingly supplies a new gate signal to the voltage control circuit 2 to correspond to the new current, fc, and the new voltage V. is supplied to 1M3.

As a result, the current I and voltage ■ of 4M3 are controlled like the third factor according to the functional relationship stored in advance in the function table 10, and for example, for an electrician, When the voltage is Vl-I2, the voltage is V2-I3, which is 3.

By the way, as already explained, the efficiency of l1vf changes depending on the load ratio and terminal voltage, and as shown in Fig. 4, the voltage ■ changes from vi to ■t -vs (however, Vl>
Vz > va), the state of change in efficiency η with respect to changes in load also changes, and its maximum value also changes as η8. η1. η3, and at the same time the current ■ also changes to L - It - In (however, L > I2 > Is)
This is changing.

Therefore, if the memory contents of the function table 10 are appropriately determined so that the relationship between the voltage ■ and the turtle AI in Figure 3 is maintained, even when the load of 1M3 changes, the maximum Efficiency will always come automatically,
As a result, according to the embodiment shown in FIG. 2, as already shown by the curve shown in FIG. 1, the I1vI3 operation can be performed while maintaining efficiency regardless of changes in the load.

In addition, according to this embodiment, 1M3
Since the terminal voltage V changes, the total vector characteristic with respect to the load becomes like characteristic b' in Figure 1, which is larger than characteristic a' when the terminal voltage is kept constant. The size can be kept within a range that does not cause any practical problems.

Next, FIG. 5 shows another embodiment of the present invention, in which:
11 is a power supply switch, 12 is a switch drive circuit, and the rest is the same as the embodiment shown in FIG.

When the switch drive circuit 12 receives a power cutoff signal from the control circuit 4, it operates the power switch 11 to disconnect the voltage control circuit 2 from the power supply 11.

In the embodiment shown in FIG. 5, when an open phase occurs in one of the three phase inputs of 1M3 and the current of the phase input to which the current detector 5 is provided increases abnormally, the current of this phase input increases. It is designed to provide protection when the current becomes zero or when the 1M3 becomes overloaded and the current increases abnormally.
A program is added to the program stored in the ROM 9 so that when the data input from the current detector 5 shows an abnormal value, a cutoff signal is output from the control device 4 to the switch drive circuit 12. be.

Therefore, according to the embodiment shown in Fig. 5, 1M3 can be operated at maximum efficiency at all times, and 1M3 operation can be stopped in the event of phase loss or overload, thereby preventing accidents due to overheating of 1M3. can do.

Furthermore, FIG. 6 shows another embodiment of the present invention, in which 13 is a cushion start selection switch, and the rest is the same as the embodiment of FIG. 2.

The cushion start selection switch 13 functions to select the cushion start mode, and depending on the load condition of 1M3 and the condition of the power supply 1, the cushion start selection switch 13 functions to select the cushion start mode.
This is to select and set the start-up time of No. 3 in advance.

Then, in accordance with this, a cushion start program is stored in the ROM 9 and added to the alphrogram, and at the time of starting, the control device 4 adjusts the voltage according to the mode set with the cushion start selection switch 13. A control signal to the control circuit 2 is controlled, and the rise time of the voltage V is set in advance by the switch 13 to perform cushion start control as a time corresponding to a certain mode.

Therefore, according to this embodiment, the operation of the 1M3 can be efficiently controlled, and the shock that occurs to the 1M3, the load, and the power source 1 at the time of starting can be sufficiently reduced.

Next, the operation of the above embodiment will be explained according to the flowchart of FIG.

First, in the embodiment shown in FIG. 2, after the operation has started, the result in step 2 is No, so that fC'l The number is read into the control device 4, and the data stored in the function table 10 is read into the control device 4 in step
The gate control is read in and compared with the signal proportional to the magnitude of the current mentioned above, and the voltage is removed for maximum efficiency, and in step (3), the gate control is processed so that the voltage is obtained from the output port of the control device 4. A signal is output, and the voltage V is automatically controlled by the voltage control circuit 2. Below are the steps ■→■→■→
In the loop (2), the above operation is repeated in the same way.

Next, in the embodiment shown in FIG. 5, after the result becomes NO in step (2), a signal proportional to the magnitude of the current detected by the current detector 5 is sent to the control device 4 in step (2). , step■
In step (2), it is determined whether the small current has increased due to an open phase in IM3 or due to an overload, and in step (2), it is determined whether the small current has become zero due to an open phase in the motor (2). When it is determined that the signal proportional to the size of the sludge is an overcurrent or an abnormal value of zero, a cutoff signal is output from the output port of the control device ILT 4 to the switch drive circuit 12 in step (3). The switch 11 is activated to automatically cut off the power supply 1.

In the embodiment shown in FIG. 6, the cushion start selection switch 13 is first checked in step (2), and the selected position is determined. Therefore, it is assumed that the selection positions of the cushion start selection switch 13 are set to the following 1 to 3.

1. Cushion start ■ Speed of rise to the rated value of voltage V → Small 2, Cushion start speed of rise to the rated value of voltage V → Medium 3, Cushion start 0 Speed of rise of voltage ■ to the rated value → Dog-t Then, in steps ■ and ■, the cushion start is determined to be one of the above, ■, and ◎, and based on this determination result, in step ■, a predetermined gate control signal is output from the output port of the control device 4, and the voltage is increased. Cushion start control is performed by controlling the increase in the terminal voltage V of IM3 by the control circuit 2.

It should be noted that the embodiments shown in FIGS. 2, 5, and 6 may all be combined to form another embodiment of the present invention, and the operation in this case is shown in the entire flowchart of FIG. 7. In addition to being able to control the operation of the IM3 at maximum efficiency at all times, it is also possible to obtain a 1LTU control system for 7'CI fVI, which is equipped with a protection function against abnormal wax light and a cushion start function.

Manhi, all of the above embodiments have been explained with respect to three-phase IM, but the present invention is not limited to three-phase IM.
Needless to say, this can also be applied to M.

〔Effect of the invention〕

As explained above, the present invention maintains maximum efficiency regardless of the load condition with a simple configuration in which the terminal voltage is controlled by giving a predetermined functional relationship to the current flowing through the induction motor. Since operation control is possible, eliminating the shortcomings of conventional technology, there is no wasted power consumption even when the load changes significantly, and the amount of heat generated by the motor is reduced. It is possible to provide a low-cost control method for the lvl guide mechanism that extends the lifespan of the lvl and the equipment to which it is attached.

[Brief explanation of drawings]

Fig. ε61 is a characteristic diagram showing an example of the characteristics of d4 Kamido i-sen, Fig. 2 is a block diagram showing an example of the control method of Noriyoshi Hiroshi according to the present invention, and Fig. 3 is a diagram showing an example of the function table Ichiten. 1+l
Figure 4 is a detailed explanation of the present invention; Figures 5 and 6 are block diagrams showing other embodiments of the present invention; , FIG. 7 is a flowchart for explaining the operation of the present invention. DESCRIPTION OF SYMBOLS 1... Power supply, 2... Voltage control circuit, 3... Induction motor (IM), 4... Control device, 5... Current detector, 6... Analog-digital converter, 7 ...α source synchronous circuit, 8...Gate circuit% 9...ROIV [
, 10...Function table, 11...Shagen switch, 1
2... Switch drive circuit, 13... Cushion start selection switch. 11 Technique r% Fig. 2 Current I Fig. 4 0 25 50 75
10011 Load c% Figure 5 Figure 6: I-'

Claims (1)

[Claims] 1. Means for arbitrarily controlling the terminal voltage of the induction motor to be controlled in accordance with a control signal, and means for detecting a DC signal representing the magnitude of the current supplied to the induction motor; means for generating the control signal according to a predetermined function iA with respect to the current signal; A control system for an induction motor, characterized in that the induction motor is configured such that the maximum efficiency according to the load of the induction motor MJJ machine is always maintained. 2. In claim 1, means is provided for detecting an abnormal value of the current flowing through the induction motor, and when the induction motor is in an abnormal motion state such as an overload state or an open phase state, the terminal A control method for an induction motor that is characterized by a configuration that cuts off the voltage. 3. The induction motor according to claim 1, characterized in that means is provided for detecting the starting state of the induction motor, and the terminal voltage at the time of starting the induction motor is controlled to a cushion start state. Electric motor control method.