JP7191304B2 - STARTING CONTROL DEVICE AND CONTROL SYSTEM FOR INDUCTION MOTOR - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a start- up control device and control system for an induction motor, and more particularly to a start -up control device and control system for an induction motor for starting without disturbing a power system .

In an induction motor, the rotating magnetic field created by the stator causes the rotor to generate an induced current in a cage-shaped conductor, and the electromagnetic force between the magnetic field and the current generates rotational torque. It is an electric motor that generates rotational torque corresponding to the difference in rotational speed between the two, that is, the slippage.

When this induction motor is started with an AC power source via a switch, the rated voltage is applied to the stator coils, but since the rotor is not rotating, the starting current flowing through the induction motor stator coils is It is determined by the leakage reactance, and a current 5 to 8 times the rated current flows through the stator coil.
Moreover, this current is an inductive current, that is, a current with a poor power factor, which is not desirable because it adversely affects the power environment due to a voltage drop in the upstream power system and causes an overcurrent to flow through the protective fuse. In addition, the insulation performance of the motor windings adversely affects the service life of the induction motor.

Therefore, various methods such as inverter start, reactor start, star-delta ( Y−Δ ) start, and thyristor start have been adopted as start methods for preventing a large current from flowing through the induction motor.

JP-A-2009-33942 JP 2017-126544 A JP 2006-353079 A

However, inverter start-up is preferable, but in the case of motors that do not require variable speed operation after start-up is completed, insertion loss results. After starting and reaching the rated speed, if the inverter is short-circuited with a metal contact switch (hereinafter simply referred to as "metal contact") , there is no operation loss of the inverter. In the case of a water pump, if the pump head does not change, even if the pump rotation speed is adjusted with an inverter, the water will not rise if the water pressure is insufficient, so the rotation speed cannot be lowered. It is possible by operation, but it requires a start-up control device to start and stop it frequently .

The method described in Patent Literature 1 uses a magnetic energy regeneration switch to advance the current phase of each phase at startup to lower the voltage applied to the motor, thereby limiting the rush current at startup. By starting with the phase-leading current, the voltage of the upstream distribution system rises by the amount of the inductance, and the voltage does not drop, which is preferable. However, since the slip frequency with the rotor is high to obtain the starting torque, a large current is still required, and this does not eliminate the rush current of the starting current.

In order to solve the above-mentioned problems when starting an induction motor, the present invention uses V/f control (a control that keeps the ratio between the output voltage V and the output frequency f constant), which is soft control as an inverter at the time of starting. , it is possible to start without a starting current rush, and after the inverter stops operating, the switching metal contact turns on the short-circuit contact of each phase and immediately shifts to power supply direct connection operation. Eliminate insertion loss. Furthermore, in order to improve the power factor during operation , the inverter is separated into each phase and operated as a magnetic energy regeneration switch. The contact is opened after the current is bypassed by the semiconductor switch so as to be opened. If the current bypass by the semiconductor switch is stopped by gate control after opening without arcing, it will be cut off.

Furthermore, even if the shutdown is completed by the gate control of the semiconductor switch, in the case of a long stoppage, the accident breaker on the upstream side of the power supply is finally opened to ensure high insulation resistance for safety. do. This is also to prevent malfunction of the gate circuit. A fault circuit breaker can block the intrusion of a surge voltage greater than the withstand voltage of the semiconductor switch .

Here, since the metal contact provided in the activation control device according to the present invention is turned on / off without arcing, the electrode is not consumed and can be turned on/off frequently. As a result, the induction motor is started by the inverter, and when the rotation reaches the rated speed, the metal contacts are turned on to switch to direct operation. Since the metal contact can be opened and closed without arcing by adopting the method described in Document 2, frequent on / off is possible.

Star-delta starting and the method described in Patent Document 1 also had the drawbacks that the starting current was as large as several times the rated value, the torque was small due to the large slip, and the power factor was poor. Then, the semiconductor switch inverter controls the torque by V/ f control and operates only for a short time until the start-up is completed. , the cooling equipment becomes smaller and lighter.

With conventional metal contacts, contact wear is a problem due to repeated starting and stopping operations, but in the present invention, it is possible to avoid this problem by using parallel semiconductor switches to switch without arcing.
Before the metal contact closes , the semiconductor switch conducts, the metal contact can be closed without voltage , and before opening the metal contact, the semiconductor switch bypasses the current and becomes currentless before opening. When poled, the metal contact opens arc-free.

If the metal contact can be opened and closed without arcing, the metal contact can be opened and closed several hundred thousand times during the mechanical life of the metal contact, and the induction machine can be started / stopped frequently. A method of time-sharing operation of the induction machine becomes possible.

1 is a circuit block diagram showing the configuration of an activation control device of the present invention, and a main circuit configuration diagram omitting a gate control circuit; FIG. 2 is a diagram for explaining that the induction motor enters a circuit state of inverter operation with Sa, Sb, and Sc in the circuit of FIG. 1 turned off and Sp1, Sp2, Sn1, and Sn2 closed; FIG. When Sp1 and Sp2 are off, Sn1 and Sn2 are off, and Sa, Sb, and Sc are also off, the single-phase MERS circuit for improving the power factor of Patent Document 1 is provided for each of the three phases. All the semiconductor switches are gate-blocked, Sa, Sb, and Sc are closed, and a three-phase power source is used for direct operation. When opening and closing metal contacts Sa, Sb, and Sc, it is explanatory drawing which turns on the gate of a semiconductor switch beforehand, and makes it a hybrid switch which cuts off/conducts with a semiconductor switch after that. FIG. 2 is a configuration diagram in which a plurality of activation control devices are controlled by an integrated control device; It is FIG. 1 of the said patent document 1. FIG.

The present invention will now be described in detail with reference to the drawings.
FIG. 1 is a circuit block diagram showing the configuration of an activation control device according to the present invention, showing a first embodiment.
The circuit of FIG. 1 has an accident circuit breaker from the distribution line, an accident circuit breaker that opens due to an overcurrent or a ground fault current at the time of an accident, and the start control device of the present invention is located downstream thereof. In this startup control device, a single-phase magnetic energy recovery bidirectional current switch (Magnetic Energy Recovery Switch, hereinafter referred to as "MERS") is connected to each of the three phases, and the positive side of the MERS capacitor There are metal contacts Sp1 and Sp2 that connect to each other, and metal contacts Sn1 and Sn2 that connect to each other on the negative side of the MERS capacitor. These four metal contacts are DC switches that are turned on/off simultaneously.
Furthermore, there are metal contacts Sa, Sb, and Sc that directly connect the inputs A, B, and C of the three-phase AC 1 and the three-phase inputs a, b, and c of the induction motor 2 . Collectively, the three metal contacts are an AC switch that is turned on and off.

FIG. 2 shows the opening and closing states of the metal contacts when the start control device of the present invention drives the inverter. The metal contacts Sa, Sb, Sc are open, and Sp1, Sp2 and Sn1, Sn2 are closed. If this configuration is rewritten, it can be rewritten as shown in the lower circuit diagram of FIG. It can be seen that this is a conventional three-phase input inverter-converter configuration.
FIG. 2 also shows a circuit diagram showing a modified configuration. This control supplies the current that generates the torque required for the induction motor to start, and accelerates from a low rotational speed to near the rated rotational speed. If the inverter is operated only at start-up, the semiconductor switch cooling device becomes simple, and if it is a SiC (silicon carbide) semiconductor switch, the high temperature characteristics are good, so the cooling device becomes even more convenient and can be made smaller. is.

FIG. 3 is a diagram in which Sa, Sb, and Sc are in the open state, and Sp1, Sp2 and Sn1, Sn2 are also in the open state. This is the situation with single phase MERS on each phase. This circuit has the configuration of the above -mentioned Patent Document 1, but here, the operation from the inverter configuration to the short circuit by the metal contacts Sa, Sb, and Sc will be further explained.
1: When the speed becomes close to the rated speed due to the start of the inverter in FIG. 2, all gates of the inverter are turned off and the inverter operation is stopped.
2: Then, since the charge/discharge current of the capacitor stops, Sp1, Sp2 and Sn1, Sn2 are opened in a non-current state.
3: When Sp1, Sp2 and Sn1, Sn2 are turned off, the state shown in FIG. 3 is reached, and the capacitor 5 is charged with the AC peak voltage. If either the positive side or the negative side of the semiconductor switch is gated on, the semiconductor switch bypasses the alternating current, so the metal contacts Sa, Sb, and Sc can be opened and closed without an arc. I can.

FIG. 4 is a diagram showing a state in which a three-phase AC power supply and an induction motor are directly connected by metal contacts Sa, Sb and Sc . If the metal contacts Sa, Sb, and Sc are closed as shown in FIG. 4, the controller of the inverter is in the gate stop state, the controller can reduce the power consumption to zero, and there is no semiconductor loss. .

In order to stop the operation of the induction motor, it is sufficient to open the contacts Sa, Sb, and Sc. Alternatively, if the contacts Sa, Sb, and Sc are opened while any two gates of the lower arm are turned on, the contacts are opened without an arc and without current. This is disclosed in the hybrid switch described in Patent Document 2 above .
The start control device of the present invention makes it possible to start and stop the induction motor frequently without considering the wear and tear of the metal contacts.

As shown in FIG. 5, a pair of semiconductor switches on the positive side arm is gated on to prepare a bypass circuit for both currents, and then, if the contact is opened or closed, the contact is disclosed in Patent Document 2 above . As shown, it opens and closes with no arc. After the contacts are opened and closed, the gate of the semiconductor switch is turned off.

If the load becomes overloaded, it can be handled by shifting to this circuit. In order to form the MERS circuit, the metal contacts Sa, Sb, and Sc are opened. After opening without arcing using the method of Patent Document 2, the MERS configuration is established. In the MERS configuration of FIG. 7, if gate control is performed in synchronization with the voltage phase of each phase and the induction motor is driven with a phase leading current, the voltage will increase, the current of the induction motor will increase, and the torque will increase. For example, in a coal crushing plant, the coal may be contaminated with rocks. Biting rocks to overload and stop. At this time, transient torque generation during overload can be achieved by increasing the input voltage of the induction machine by the MERS function.

Fig. 6 shows an example of the overall control system configuration. When multiple induction motors are operating in the same system, if the system voltage drops due to the start-up inrush current of other nearby consumers, etc., the reactance of the transmission line to the system If the voltage drops due to a large torque, the voltage of the induction motor drops and the required torque cannot be supplied to the load. be able to.

FIG. 6 shows an application of the present invention. In an industrial plant or a construction plant with a large number of induction machine groups, when the power contract amount is expected to be exceeded, as described in the above-mentioned Patent Document 3, Using the communication system to stabilize the power and voltage in the plant, the integrated control device of the start-up control device of the present invention is flexibly turned on and off to continue operation within the contract amount and voltage fluctuation.
Induction motors with flywheels or induction motors with a large load with a flywheel effect are designed to avoid lightning strikes in power system transmission lines. It can generate power for a short period of time to prevent voltage drop.

Even in a small-scale plant, the induction motors of drainage pumps and water pumps can be easily started and stopped according to the present invention, so voltage stabilization and energy-saving operation can be achieved by considering the order of startup and by time-sharing operation. .
In plants and distributed power sources having a large number of induction motors, the starting control device and the integrated control device of the present invention enable more effective use of electric power.

1 Three-phase AC power supply 2 Induction motor 3 Semiconductor switch (MOSFET)
4 DC switch (metal contact)
5 capacitor 6 AC switch (metal contact)
7 controller

Claims (6)

A start control device for an induction motor (hereinafter referred to as a "start control device") connected between a three-phase AC power supply and an induction motor, the start control device comprising:
A magnetic energy regeneration bidirectional current switch in which four reverse conduction type semiconductor switches are arranged in a bridge configuration and a capacitor is connected to a DC terminal, and this is connected to each phase,
Two DC switches (Sp1, Sp2) connecting the positive sides of the capacitors to each other, two DC switches (Sn1, Sn2) connecting the negative sides of the capacitors to each other, and the reverse conduction type A gate of a semiconductor switch and a controller for controlling on/off of each DC switch,
The controller is
The current phase is advanced by gate control of the reverse conducting semiconductor switch, and when the induction motor is started, the DC switch is turned on at the same time to form a three-phase reversible inverter configuration, and the induction motor is started. An activation control device characterized by: Further, an AC switch ( Sa, Sb, Sc ) is provided for connecting each phase of the three-phase AC power supply and the induction motor, and the controller turns on these switches at the same time to switch the three-phase AC power supply and the induction motor. 2. The activation control device according to claim 1, wherein the directly connects the . The starting control device becomes a three-phase reversible inverter configuration at the time of starting, generates the starting torque necessary for the induction motor , accelerates to near the rated rotation speed, and the controller controls all the reverse conduction type inverters there. 3. The activation control device according to claim 2, wherein the AC switches ( Sa, Sb, Sc ) are closed after the gates of the semiconductor switches are cut off to continue the three-phase AC operation. When the controller closes or opens the AC switches (Sa, Sb, Sc), the two opposite sides of either the positive side or the negative side of the magnetic energy recovery bidirectional current switch of each phase. 3. The activation control device according to claim 2 , wherein the conductive semiconductor switch is put in a gate-on state so that bidirectional current is put in a bypass state before closing or opening.
The controller controls the operation of the inverter, the operation of the magnetic energy regeneration switch, and the selection and transition of direct operation at the frequency of three-phase alternating current, and the start, operation, and stop are controlled by an external communication line. 3. The activation control device according to claim 1, wherein the activation is performed through. A plurality of the activation control devices according to claim 5 are provided, and an overall control device is further provided above the controller that performs activation, operation, phase advance operation, and operation stop via a communication line, and the overall control device controls electric power. A starting control system for an induction motor , wherein a voltage drop in a system is detected and a command is issued to the controller to increase the voltage by means of phase-advancing operation.

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