JPS6334709B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for applying anti-phase braking to an electric motor using a variable frequency, variable voltage inverter.

There are various braking control methods for AC motors, but
It is desirable that the braking time be short. Among these control methods, those that use an inverter to lower the frequency while the motor is running and apply regenerative braking require the rotational energy to be returned to the inverter, which may cause overvoltage to destroy the semiconductor elements inside the inverter. . Furthermore, DC braking has disadvantages such as the high cost of the braking control circuit and the loss of braking torque when the speed reaches zero. Because of these problems, regenerative braking requires gradual deceleration to avoid overvoltage, which has the disadvantage of prolonging braking time.

In addition, if brushing is applied at high speed, an overcurrent will occur, which will not only make it impossible to operate, but also reduce the motor loss due to the operating energy (1/2) during no-load rotation.
jω ² ), and the rotor generates a large amount of heat.

In view of the drawbacks of the prior art described above, the present invention provides a braking control method that enables sudden stop control of a motor without overloading circuit elements of an inverter and without causing excessive heat loss to the motor. It is in.

By using a three-phase output inverter whose output frequency and output voltage are both variable, immediately after applying a voltage in the first phase order to operate the three-phase AC motor, the inverter outputs a signal whose phase order is different from the first phase order. A reverse second phase order output is lowered in both frequency and voltage than the maximum value during the first phase order operation, and is applied to the three-phase AC motor to perform reverse phase braking. , samples the current of the motor during the anti-phase braking operation, compares two successive sampling currents, and cancels anti-phase operation when the later sampled current becomes larger than the first sampled current. and stopped it.

The present invention will be described in detail below with reference to the accompanying drawings. 1st
2 and 2 are diagrams for explaining the principle of the present invention, and as shown in the respective characteristic diagrams, while the motor is rotating in the first phase order, the voltage applied to the second phase order is It can be seen that the voltage is lower than the voltage corresponding to the maximum frequency in the phase sequence of 1, and the frequency is also low. In addition, in FIGS. 1 and 2, f is the applied frequency, V is the applied voltage,
T indicates torque and I indicates current.

Next, specific embodiments of the present invention based on the principles shown in FIGS. 1 and 2 will be described in detail with reference to FIGS. 3 to 10. FIG. 3 is an overall configuration diagram including an inverter circuit that controls the forward and reverse rotational drive of the electric motor.
Further, FIG. 4 shows a relay sequence for performing anti-phase braking in the circuit of FIG. 3. In Fig. 3, 1 is an electric motor, 2 is a 3-phase AC power supply,
3 indicates a three-phase output inverter circuit, which includes a rectifier circuit 4, a smoothing capacitor 5 inserted between the DC output terminals, a resistor 6 connected in series, transistors 7a to 7f for DC-AC conversion, and the transistor 7.
It consists of a control circuit 8 for controlling ON/OFF of a to 7f, a speed setting resistor 9, power switches 10a and 10b, and a contact 16a of a forward/reverse command relay to be described later. The sequence circuit shown in FIG. 4 is connected to the R and T terminals in FIG.
0 to 16 indicate relay coils, and each relay has contacts 10c, 11a, 11b, 12a, 12
b, 13a, 13b, 14a, 14b, 15a,
It has 15b, 15c, and 16a. Here, relay 10 is a relay for starting operation, and relay 16
is a relay for forward/reverse rotation command. Further, switch BS1 is a starting switch, BS2 is a sudden stop switch, and BSS is a stop switch, and the sudden stop circuit is constituted by a relay circuit as shown.

Next, the operation will be explained with reference to the circuits shown in FIGS. 3 and 4 and the waveform diagrams shown in FIGS. 5 to 8. Now, the start switch BS1 shown in Fig. 4 is closed,
It is assumed that by energizing the relay 10, the rotation speed of the electric motor 1 is increased through the inverter circuit 3 to the speed determined by the speed setting device 9.
Thereafter, when sudden stop control is performed by closing the sudden stop switch BS2, the relay 11 is energized to close the contact 11b, which energizes the relay 12 and opens the contact 12b. This cuts off the power line, and at the same time resistor 9 for speed setting
will be reset. Next, the relay 16 is closed by closing a forward/reverse rotation command switch (not shown).
is energized and self-maintained via the contact 15c of the relay 15. As a result, the relay 13 is deenergized and the relay 14 is energized, so that a motor rotation command opposite to that described above is issued. That is, if the previous rotation command was a forward rotation command, it is replaced with a reverse rotation command, and if it was a reverse rotation command, it is replaced with a forward rotation command.
Therefore, by closing the start switch BS1, the power is turned on again, and the speed setting increases from zero to the specified rotational speed over a timed period, and the rotation gradually increases due to the action of the so-called soft start circuit.

In this way, the electric motor 1 starts plugging at the lowest frequency and lowest voltage, suddenly stops, and rotates in reverse. Then, if the timer relay 11 is timed up in anticipation of this transition to reverse rotation, and the relay 10 is shut off before the reverse rotation occurs, an abrupt stop is achieved, and the sudden stop control is achieved.

In addition, in the waveform diagram showing the rotational state of the motor rotation speed in Fig. 6, A indicates from normal rotation to anti-phase braking, B indicates from reverse rotation to anti-phase braking, A',
B' indicates the time when the vehicle is idling, and Q indicates the time when anti-phase braking is applied. Also, Figure 7 shows
This is a current waveform diagram flowing through the electric motor at that time, and the eighth
The figure shows the voltage waveform between the terminals of the capacitor 5 shown in FIG. 3.

Next, the reason why the control circuit system is not destroyed by the maximum current flowing when the motor is braked in reverse phase will be explained using an example. The reason why the control circuit system is not destroyed by the maximum current as shown in Figure 7 is that
This is because since the starting frequency is the lowest and the applied voltage is small, only the current sufficiently limited by the primary resistance of the motor flows.

As an example, the stator resistance per phase of a 3.7KW induction motor is 0.35~
0.45Ω, and the primary equivalent resistance of the rotor is 0.25~
Since it is about 0.40Ω, the resistance value of the resistor 6 connected to the capacitor 5 shown in FIG. 3 is about 0.6Ω in a star-shaped connection even if the rotor resistance is ignored, that is, even if S=∞. The output voltage of an inverter around 2~3Hz is about 15V in effective value, so 15V/
0.6Ω = 25A, which is not a large current that would short-circuit the load, but a current that can be easily output by an inverter circuit of about 5KVA.

In addition, when stopping by normal plucking, the slippage changes from S=2 to S=1, so kinetic energy of 3/2jω ² is dissipated as heat in the rotor, but with low frequency plucking using an inverter, S≒1
Since (S>1), it is placking up to S=1, so in the generated loss formula, W=1/2jω ² (S ² ₁ −S ² ₂ ),
If S ₁ = 1.1, S ₂ = 1.0, W = 1/2jω ² (1.1 ² −
1.0 ² ) = 1/2jω ² ×0.21.

In other words, normally an energy loss of about 0.21/3 = 1/15 occurs in the motor rotor, and the rest is loss due to the primary winding, wiring loss in the inverter, mechanical loss of the motor, and iron loss, and the rotational energy is It can be seen that it absorbs and stops. If there is surplus power in the output current of the inverter, it is possible to increase the braking frequency and consume rotational energy within the rotor of the motor, thereby controlling the braking time.

In addition, in order to realize sudden stop control by lowest frequency and lowest voltage plucking using only software without relying on the relay sequence shown in Fig. 4, following the flowchart shown in Fig. 9, What is necessary is to control the activation of the control circuit configured as described above. Figure 10 shows the sudden stop control circuit configuration when using a microcomputer.
21 is a microprocessor; 22 is a storage device consisting of ROM and RAM that are read and written under the control of the microprocessor 21; 23 is connected to the input/output circuit; A power amplifier controls on/off the transistor circuit shown in the figure, 24 is a speed setting resistor,
Reference numeral 25 indicates a contact point of a forward/reverse rotation command relay (not shown).

The operation will be explained below with reference to FIGS. 9 and 10. In the flowchart of FIG. 9, the reason why the minimum point of the motor current is detected is to capture the moment when the motor finishes anti-phase braking and shifts to power running. In addition, the minimum point detection principle is
As mentioned above, during anti-phase braking, the slip S = 1.1, but after the anti-phase braking is completed, the slip S becomes 0 (because the synchronous speed has shifted to a low frequency), and the resistance on the secondary side increases. This is because the impedance inside the motor increases and the current decreases due to the large change.

Then, you can program the software as follows. That is, the measured current is A/D converted,
Temporarily stored in random access memory RAM.
At the next sampling period, the measured current is A/D-converted again, compared in size with the previously stored data, and if the previous data is smaller, the later sampled data is stored in the RAM area at the same address, and the previous data is Erase the , and repeat the above operation as many times as you like. then,
If the later data is smaller than the previous data, it is determined that the minimum point has been passed, that is, the reverse rotation has started, and software suppression is applied to bring the vehicle to a natural stop. Since the frequency at this time is the minimum, the motor immediately stops due to mechanical friction.

Next, the first circuit is the circuit for running the above software.
Figure 0 will be explained. First, various programs are stored in the memory device (ROM) 22 of the circuit configured as shown in the figure, and transient data is stored in the memory device (RAM) 22. The microprocessor 21 processes scheduled programs, judges and processes various data, and input/output circuit (I/O) 2
Give commands to 0. Inside the input/output circuit 20,
It has a reference and transient register and a comparator as an arithmetic logic unit, performs a comparison operation between the reference register and the transient register, outputs the result to the power amplifier 23, and at the same time outputs a status signal indicating the completion of program processing. Answer back to microprocessor 21. At this time, the contents of the reference register of the input/output circuit 20 are changed to the microprocessor 2 by software.
It has been rewritten with instructions from 1. The input/output circuit 20 also includes an A/D converter, which converts the current, voltage, and speed commands of the motor into data, and serves as a basis for changing the reference register. That is, the motor current is A/D converted, the result is notified to the microprocessor 21, and the microprocessor 21
stores the data based on the amount of A/D converted data, and performs comparison judgment with past data. According to the soft flowchart shown in Figure 9,
The entire system operates in the same manner as the circuit shown in FIGS.

In this way, when applying anti-phase braking to a motor using a variable frequency, variable voltage inverter circuit, it is possible to control the motor in the shortest possible time by creating a state in which there is no regenerative energy in the inverter and without increasing the loss on the secondary side of the motor. Performs stop control.

As is clear from the above-mentioned embodiments, according to the present invention, braking can be applied within an extremely short period of time and a sudden stop can be achieved without returning braking energy to the inverter circuit, thereby reducing the heat generated inside the motor. The advantage is that the loss is only about 1/3 of that of normal plucking.

Note that it is also possible to perform anti-phase braking by changing the connection of any two wires among the wires connecting the inverter and the AC motor.

[Brief explanation of the drawing]

The attached drawings are diagrams for explaining the present invention, and
Figures 1 and 2 are rotational characteristic diagrams of an electric motor to explain the principles of the present invention, Figure 3 is an overall circuit configuration diagram for driving and controlling the electric motor via an inverter circuit, and Figure 4 is an embodiment of the present invention. A relay sequence circuit when implementing anti-phase braking using an inverter circuit showing an example,
5 to 8 are time charts for explaining the operation of the circuit shown in FIG. 4, and FIGS. 9 and 10 show other embodiments of the present invention, and FIG. FIG. 10, a flowchart during anti-phase braking, is an inverter circuit diagram having a microcomputer that operates based on the flow shown in FIG. 9. 1...Motor, 2...Power supply, 3...Inverter circuit, 4...Rectifier, 5...Capacitor, 6...
Resistor, 7a to 7f... Transistor, 8... Control circuit, 9, 24... Speed setting device, 10 to 16...
Relay, BS1...start switch, BS2...sudden stop switch, BSS...stop switch, 20...input/output circuit, 21...microprocessor, 22
...Memory circuit, 23...Power amplifier.

Claims (1)

[Claims] 1. By using a three-phase output inverter whose output frequency and output voltage are both variable, immediately after applying a first phase-sequence voltage to operate a three-phase AC motor, the phase-sequence is output from the inverter. An output of a second phase order that is opposite to the first phase order is applied to the three-phase AC motor with both frequency and voltage lower than the maximum value during the first phase order operation, and the output is reversed. Phase braking is performed, and the current of the motor during the reverse phase braking operation is sampled.
A method for anti-phase braking of an electric motor using an inverter, in which two successive sampling currents are compared, and when the sampling current taken in later becomes larger than the sampling current taken in first, the anti-phase operation is canceled and stopped. 2. A method for anti-phase braking of an electric motor using an inverter according to claim 1, characterized in that the inverter is one in which the phase order of output can be changed. 3. When switching from the first phase to the second phase, the connection of two phases of the wires connecting the inverter and the three-phase AC motor is changed. A method for reverse phase braking of an electric motor using an inverter according to item 1.