JPS5999996A - Power source switching control circuit for plural motors - Google Patents

Abstract

PURPOSE:To effectively protect a motor without flowing an overcurrent to the motor by automatically deciding the current limiting value flowed out from an inverter in response to the number of the motors. CONSTITUTION:When a signal is applied to a motor number detector 20, the output of an adder 21 becomes a value corresponding to the sum of the motors which are driven by an inverter. Further, the output of the adder 22 is applied with a bias 23, and becomes an input of a limiter 24. The limiter 24 limits the maximum value of a proportional amplifier 16 in response to the input signal. In other words, a load current has no margin to exceed the current limiting value Ip. In this manner, two motors are stabilized in the same rotating speed while the load current is limited to the current limiting value Ip.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control circuit for switching the power supply source from a commercial power supply to an inverter for only some of a plurality of motors.

In recent years, in order to utilize energy to control the amount of feng shui, control of the amount of feng shui based on adjusting the degree of opening of a valve placed in a path of feng shui is no longer adopted. In other words, in feng shui volume control, the torque load becomes the square of the speed, and therefore, the required power is proportional to the 8th power of the speed, so rotation speed control is optimal, and conventional valve control results in a large energy loss. It is from. Therefore, in "Now", the opening of the valve is 1-1.
The amount of feng shui is controlled based on the speed control of the motor for controlling the amount of feng shui, without employing speed control. However,
For feng shui volume control based on motor control, alternating current power is supplied by a variable mlE, variable frequency (hereinafter referred to as F, VVVF) type inverter, and when variable speed control is performed, the speed is 100% from the point of view of efficiency. In the case of odor, it is necessary to directly supply electric power from the commercial power source to the motor for controlling the amount of feng shui.

To this end, it is necessary to achieve smooth switching between the commercial power source and the inverter power source for the power source for the load. Conventionally, when switching from an inverter power source to a commercial power source, a synchronous switching method based on various methods has been adopted. 3, but 1.
For example, in a series of blowers used in the steel industry, the drive motor is operated by commercial power only when a large amount of air is required depending on the operating condition of the line, and when a large amount of air is not required, the drive motor is operated at a low speed using an inverter to save energy. Measure. At this time, the blower may be stopped by stopping only the motor that operates at low speed, but it may not be preferable to stop the blower if the frequency of operation of the blower reaches a certain level.

Page 5 In addition, when the blower of a steel scorching furnace is stopped 1-, the blower may malfunction or die due to the heat, so it is necessary to perform low-speed rotation.Next, the core is Since the blower motor can be driven at low speeds sequentially based on the power from the inverter, the blower motor is driven sequentially.Such inverters generally use current source inverters, or When a given blower motor is repeatedly stopped and operated, the following problem arises: A series of a large number of blower motors.

When synchronously drawing only some motors from a commercial power source to an inverter power source without synchronously drawing all motors all at once, some motors are already being driven by the inverter, so the current must be set to 0 as in the conventional method. On the other hand, the method of applying inrush current to the motor at the time of switching requires that the inverter has a commutation ability that can commutate the inrush current of 71L, and this commutation In order to increase the capacity, a separate commutation auxiliary circuit is required, which increases the price of the entire inverter.Furthermore, the inrush current flowing into the motor makes the motor operation unstable.

9 to the same applicant as a means to eliminate such drawbacks.
J: Ru Sukyu 1'''' R6-58276 is available, i.e. ■ Turn off the motor power W++ After turning on the motor, increase the inverter current in a ramp function. O After turning on the motor, temporarily increase the frequency of the inverter. After lowering the voltage, switch the motor running on commercial power to inverter power. 3, θ
When switching the motor power supply, it is detected that the rotation speed of the motor disconnected from the commercial power supply is higher than the rotation speed of the motor driven by the output frequency of the inverter, and the power supply is switched to the inverter power supply. It is based on methods such as

However, even with @ and θ of the above improvement means, the motor is turned on when the difference between the rotation speed of the motor disconnected from the commercial power supply and the rotation speed of the motor operated by the inverter becomes large when the motor power is switched. When this happens, the inverter current increases like a ramp function, but a large amount of current flows, and depending on the situation, the current may even flow up to the inverter's current limit value, which has an adverse effect on the motor. ■When the power is turned off,
Or, if the motor is overloaded or loses synchronization for some reason during normal operation, the inverter current will increase like a ramp function as described above, but the motor current may flow up to the inverter's current limit value, causing damage to the motor etc. There is a risk.

The purpose of this invention is to solve the problems mentioned in the above section ``■'' based on a circuit means for setting a current limit value when a large number of motors are operated using an inverter power supply. The objective is to accurately protect the inverter and motor group.

The illustrated embodiment will be specifically described below. 1st
The figure shows the basic circuit configuration for carrying out the present invention. In the figure, 1 is a commercial power supply, 2 is a forward conversion circuit, which receives power from the commercial power supply 1, and controls the current control zyristor included therein. The supply current is adjusted by controlling the firing phase.

A current transformer 8 is linked to a circuit connecting the commercial power source and the forward conversion circuit 2, detects the current therebetween, and obtains a current return via the rectifier circuit 4.

5 on page 7 is an inverse conversion circuit whose DC input side is connected to the output side of the forward conversion circuit 216 via a constant current reactor 6.

. 7 is a transformer, which receives the output voltage of the inverse conversion circuit 5 as human power, and its output is passed through the rectifier circuit 8 to obtain voltage feedback ■0 1, ~ 11, λ2...M n is for load Each motor has its own selector switch S], S2...
Sn is connected to each movable contact SIC, S2C, . . . Snc.

On the other hand, the fixed contacts Sla, Slb, S2a, 821) or Sn of the changeover switches 31, 32...Sn
1, S n T), contacts S1a, S2a...
Sn+i is connected to commercial power supply], and the remaining fixed contact S
Ib, S2b...5nT) is the inverse conversion circuit 5
3, which is connected to the output side of r11 in Figure 1.
Does it represent one line, or actually two lines depending on the signal phase and three phases?
It shall have between 3 and 3 contact points. .

Next, a specific configuration of the gate control circuit for the thyristor group constituting the forward conversion circuit 2 in FIG. 1 will be described with reference to FIG. 2. In FIG. 2, reference numeral 11 denotes an adder, into which the voltage command Vx and -]22 constant voltage feedback 0 are inputted with the polarities shown. ]2 is a voltage control amplifier which amplifies the input from the adder [1].

Reference numeral 13 on page 9 is a transistor, the collector and emitter of which are connected to the input and output terminals of the voltage control amplifier 12, respectively. 14 is an integrating circuit, which is configured by connecting an amplifier 1 d fl and a capacitor 14 c in parallel;
- The output side of +a is led to the base of the transistor 13. ] 5 is an adder, into which the output command of the voltage control amplifier 12 and the command obtained via the proportional amplifier 1G of the current feedback circuit 0 are inputted as human input signals in the 41m direction shown in the figure, and the output command is 'r1i. Flow control amplifier 18
be guided by. Reference numeral 19 denotes a drive circuit for each thyristor constituting the forward conversion circuit 2, which controls the phase of each thyristor in the forward conversion circuit 2 according to the command level from the current control amplifier 18 described in -1, that is, Drive circuit 1! ] is controlled so that the value of the flow '11 flowing out from the forward conversion circuit 2 increases as the command level applied to it increases. 2
0 is a motor number detection circuit that detects the number of motors to be driven by the inverter. 21 is an adder which calculates the number of operating motors in the motor number detection circuit 20; It is a 23-digit bias setting device. The outputs from the adder 21101 (and the bias setter 23) are input to the adder 22 via resistors R1 and R2, respectively. 24 is a limiter circuit, and the output of the proportional amplifier 16 is input to the adder 22.
There are limits depending on the output. 25 is a comparator,
It is detected that the number of motors receiving power from the inverter has become O, and the current command of the current control amplifier II is set to O through the transistor I3 to reduce the current of the inverter. This comparator 250 input command includes the number detection setter 26 and addition 'a2'.
1 output signal is led through resistors R3 and R4, respectively.

In the above configuration, for example, the motor M2 is connected to the inverse conversion circuit 5.
Receives power supply from
Assume that the switch receives power from the commercial power supply l and is driven at 100% speed, and the operation at this time is as shown in FIG.
0. S2C! Fixed contacts S1a and S2b respectively
With the operation of the control circuit shown in Figure 2, -
A constant load current r continues to flow. That is, motor M2
In the operating state of the adder 15, the transistor 13 is conductive through the current minor loop including the proportional amplifier 16 and the integrating circuit 14, so that the output of the voltage control amplifier 2 is a voltage value corresponding to the output of the adder 15 ( The output of the amplifier 12 and the current feedback are regulated by the saturation voltage (below the saturation voltage).
The forward conversion circuit drive circuit 19 is automatically controlled by the comparison command of 0 through the current control amplifier 18. Now, in FIG. S1 IT industrial contact Slc
It is assumed that the fixed contact Sla is turned off, and the movable contact Slc is turned on to the fixed contact Slb at time t2 after a certain period of time has elapsed. At this time, the motor M1 moves from time t1 to time t.
During the period up to 2, it is possible that the rotation speed may decrease to the rotation speed regulated by the inverter frequency due to inertia, but other motors that are normally operated with inverter power source 81
The rotational speed is higher than that of one or more of the motors M2 to Mn, and as a result, the motor M1 enters a regenerative operation state. In this case, if the difference in the rotational speed between the motor ski and the motor that has been driven by the inverter up until now is 1/3, then it is regeneration. The load current from the impark increases as a function of Suu/jib, -C.

Here, the motor that has been driven by an inverter until now, has a large difference in rotational speed between the motors that are driven by an inverter, and has a large inertia.When connected to an inverter, it corresponds to the inverter frequency. It takes some time to reach the desired rotational speed, and during this time the output voltage of Inno-1 is 1.
:In order to increase this output voltage, the load current from the inverter increases, and ζh exceeds the current limit value [p] for the two motors.

By the way, in the circuit of the present invention, when the motor M1 is connected to the inverter power source by switching from the movable contact SIC of the changeover switch S1 to the fixed contact S1a to the fixed contact S11], a signal is given to the motor number detection circuit 20,
The output of the adder 21 is sent to the motor M2 which is being driven by the inverter and to the dryer 11 which is currently being driven by the inverter.
The value corresponds to the sum of . Furthermore, a bias 23 is added to the output of the adder 22, and it becomes an input JJ signal to a limiter circuit 24. The limiter circuit 24 then limits the maximum value of the proportional amplifier 16 in response to the input signal. , i.e. load? There is no room for the iE current to exceed the current limit value 11), so the load current from the inverters is at points 1 and 2.
increases more like a ramp function over time,
This load current is limited to a current limit value Ip. This ia rod 0 is switched from the commercial power source 1 to the inverter power source, and the rotational speed of the ia rod 0 is switched to the inverter power source 11 at the time [-1
As V gradually decreases, the load current of the inverter suddenly reaches M 1 , h(2), the value responsible for steady operation, and at the time t, 2 the motor M2 rotates at the same speed. Be stable at speed.

On the other hand, at the -inverter electric i/hara
From the said inverter 'Ichigen to all-C motors, 11~M
, n is disconnected, the setter 26 and the adder 21 receive the comparison "aif 25 wander signal (
-C voltage control amplifier 1z is short-circuited by the signal obtained by decreasing the output from addition a 2 + and current commands E, o are used to image the inverter.

In the above explanation, we have explained the case where one power source is disconnected from the commercial power source 1, and then the inverter power source (/Crj) is connected.
When the cores of the motor are overloaded, the load current increases like a ramp function, but since the current limit value corresponding to the motor base only flows out from the inverter, a large amount of current flows through the motor. Never.

As described above, the power supply switching control circuit for multiple motors according to the present invention (a basic circuit comprising an inverter, a commercial power supply, a plurality of motors, and switch means for individually connecting the motors to the inverter or commercial power supply) In the configuration, the inverter controls the forward conversion section in the inverter by automatically determining the current limit value that flows out from the inverter according to the number of motors that the inverter is responsible for supplying power to, and when no converter is connected to the inverter. L7 is used to throttle the current from the inverter.

Based on the power structure, ■ When operating multiple motors with an inverter, the current limiting effect may occur depending on the number of motors in operation, and the inertia of the motor may increase. (In case 1-2, it takes time for the rotation speed of the motor to decrease, and the H↓1 load current increases by -1-C, but the increase is limited and the motor receives an excessive current. 4. When multiple motors are running with an inverter, the current flowing out from the inverter is approximately (rJ). 0 and adversely affects the inverter.
J, I would like to see the effect of being able to open and close the motor without having to move.

[Brief explanation of the drawing]

FIG. 1 is a basic circuit according to the present invention, FIG. 2 is a control circuit of FIG. 1, and FIG. 8 is a graph for explaining the operation. 1...Commercial power supply 2...J@conversion circuit S...
...Inverse conversion circuits M1 to Mn... Motors 81 to 3n... Changeover switch 12... Voltage amplifier 18... Transistor 14... ......Integrator circuit 1G...Proportional amplifier 15 Page 18...Current intensifier lfi + 9-, , , ,, lli" complete circuit Controller 20 ...... Number detection circuit 24 ...
... Limiter circuit 25 ... - Original axis DG 2G ... Number of units detection setting device output] Gunyu Kami 1911 "& * 44, Shiki company agent, patent attorney Haruya Saito

Claims (1)

[Claims] 1. In the basic circuit configuration 1C that freely switches multiple motors individually and independently for a commercial power source and an inverter,
A basic control circuit that compares the voltage setting value of the inverter and the comparison signal on the voltage feedback signal with the current feedback port through the voltage amplifier 1, and controls the forward conversion circuit in the inverter through the current amplifier, and the current feedback described above. circuit means for controlling the amplification of the voltage amplifier so as to be inversely proportional to the feedback current through an integrator circuit using a signal obtained from the output of the voltage amplifier and the ratio Ml- through a proportional amplifier; A motor number detection circuit that supplies an output proportional to the number of motors that receive electric power, and a current limit signal that is proportional to the number of motors involved in inverter operation is supplied to the proportional amplifier circuit based on the output from the motor number detection circuit. A power supply switching control circuit for a plurality of motors 1, characterized in that it comprises a circuit means and a circuit means for reducing the amplification degree of the voltage amplifier when the number of motors involved in inverter operation is zero;