JPH0352593A - Method for controlling motor-driven inverter - Google Patents

Abstract

PURPOSE:To omit the labor hour of once stop and restart, and to return rotational speed to original one by directly inputting a set frequency command to a control circuit without through an adjustable-speed computing element at the time of the recovery of service power and gradually rising a voltage command from zero when service interruption exceeding a fixed time is executed to an AC motor during operation at inverter set frequency. CONSTITUTION:In an induction motor (I) 5 driving load having a large flywheel effect, revolution is continued even when service interruption is continued for a time exceeding a fixed time, and operating speed is returned to original one immediately after the recovery of service power. Since a signal from a frequency setter (F) 9 is input to a control circuit through an adjustable-speed computing element (S) on the driving of (I) 5, AC voltage and frequency from an inverter to (I) 5 are increased gradually. When service interruption is continued for the time exceeding the fixed time, a logic element 8 is operated, and the set signal of the F9 is input directly to a service-interruption recovery-time control circuit 6 without through S while a voltage command value in specified functional relation to the control circuit 6 is also risen from zero gradually, thus smoothly recovering revolution to set frequency speed quickly in (I) 5.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to a method of controlling an inverter driving a motor when a power outage occurs in the power supply of the inverter that drives the motor coupled to a load with a large flywheel effect. ．． [Prior Art] By using an inverter that outputs variable voltage/variable frequency AC power, it is possible to freely control the speed of an induction motor, which was difficult to control in the past, so it has become widely used. By the way, such an inverter generally converts DC power into DC power using a rectifier connected to a commercial power source, absorbs and removes the free pull contained in this DC power using a smoothing capacitor, and then converts the smoothed DC power into DC power using a smoothing capacitor. The system is designed to supply DC power to the inverter, but commercial 'r
t. s may experience short-term power outages due to lightning strikes, line changes, etc. When the commercial power supply goes out, the induction motor is disconnected from the inverter and rotates freely, so its speed gradually decreases, and the speed of the induction motor when the power outage is restored is unknown. Therefore, when trying to restart the motor immediately after the power outage is restored, it is impossible to match the frequency corresponding to the speed of the induction motor with the frequency of the inverter output AC. If the above-mentioned frequencies do not match when restarting operation, for example, if the frequency of the inverter output AC is higher, an excessive rush current will flow from the inverter to the induction motor, causing the inverter to trip due to overcurrent. Put it away. Conversely, when the frequency of the inverter output AC is lower, power is regenerated from the induction motor to the inverter, and the so-called DC This increases the voltage in the intermediate circuit, causing the inverter to trip due to overvoltage. Therefore, in the event of a power outage in the commercial power supply, even if the power outage is only for a short time, the induction motor is stopped and then restarted, but the flywheel effect of the load driven by this induction motor is When driving large machines such as centrifuges and spinning machines, it takes a long time to stop and to reach the specified speed after stopping, which reduces the operating rate of the equipment. .

Therefore, if a speed transmitter is attached to the motor, the speed of the motor at the time of power restoration can be detected, and by matching the frequency of the inverter output AC to this speed, operation can be resumed immediately.

[Problem to be solved by the invention]

However, when attempting to connect a load and this speed transmitter to an induction motor, this motor requires a double shaft type and a standard type cannot be used, making it expensive. Furthermore, depending on the device, it may be difficult to secure a space to install the speed transmitter, or even if it is installed, maintenance and inspection may not be possible. Therefore, when a load with a large flywheel effect is coupled, if the power outage is not long, the motor speed will only decrease slightly during the power outage, so set the maximum speed at which the motor operates. Then, when the power is restored, the frequency of the inverter output AC will be set to the frequency corresponding to this maximum speed setting value. However, there is a risk that the inverter will trip over current due to the inconsistency of the frequency of the inverter output AC and the motor speed. The voltage of the inverter output AC is gradually raised from zero when restarting operation so that the current does not exceed this limit value. However, if the motor speed immediately before the power outage is much lower than the maximum speed setting value mentioned above, the motor speed will increase to this maximum speed setting value as soon as the power is restored, and then decrease to the original speed. Not only does it take a long time for the speed to stabilize, but the current limit value (which is usually larger than the rated current) continues for a long time while the speed is increasing, which may cause the inverter to exceed its overload capacity. There is also a risk of tripping. If the power outage becomes even longer (generally about 2 seconds), the above-mentioned smoothing process will occur. The control circuit, which operated using the capacitor as a power source, stopped as the charge was discharged, and the maximum speed setting was also lost. In this case, the motor must be stopped and then restarted. Therefore, the purpose of this invention is to enable the inverter, which drives the induction motor connected to the load with a large flywheel effect, to immediately operate without stopping once the power outage is restored, even if the power outage of the inverter that drives the induction motor is extended. The purpose is to enable a smooth return to the original speed upon restart. [Means for Solving the Problems] In order to achieve the above object, the control method of the present invention includes the following:
By passing through the acceleration/deceleration calculation means, the output of the frequency setting means is converted into a frequency command signal and a voltage command signal having a predetermined functional relationship with this, and AC power with a voltage and frequency corresponding to these two command signals is generated. Using an output inverter to connect an AC motor with a load that has a large flywheel effect,
In the method for controlling a motor-driven inverter that operates at a speed corresponding to the output of the frequency setting means, the condition is that if the power supply to the inverter continues to fail for a predetermined period or more, a command to operate the AC motor is issued. and
When the power outage is restored, the output of the frequency setting means becomes a frequency command signal without passing through the acceleration/deceleration calculation means, and the voltage command signal is gradually increased from zero.

[Effect]

In this invention, the electric charge in the smoothing capacitor that serves as the power source for the inverter control circuit is discharged as the commercial power outage time passes, so even if the maximum speed setting value is lost when the power outage is restored, the keep relay By the function of , the output of the frequency setting means that sets the frequency value of the inverter output AC is given as a frequency command to the control in circuit, bypassing the acceleration/deceleration calculation means, and the voltage command is gradually raised from zero. Therefore, even if the power outage is prolonged, the motor speed is restored to the frequency setting value immediately before the power outage, thereby eliminating the need to restart the motor after it has stopped.

〔Example〕

Figure 1 is a circuit diagram showing an embodiment of the present invention. In FIG. 1, AC power from a commercial power source 1 is input to an inverter device 3 via a circuit breaker 2. In FIG.

Although detailed illustrations are omitted, this inverter device 3 includes a rectifier that converts alternating current from all commercial electricity into direct current, a smoothing capacitor that smoothes the direct current output of this rectifier, and a variable voltage converter that converts the smoothed direct current into a variable voltage. It is composed of an inverter that converts into variable frequency alternating current, a control device for these, and a power failure recovery control circuit 6 shown as part of this control device. The induction motor 5 can be driven at variable speed. When driving the induction motor 5, first close the circuit breaker 2 and connect the commercial power i! When the AC power from 11 is applied to the inverter device 3 and the operation command contact 4 is closed, an operation command signal is applied to the inverter device N3 and the keep relay 7. At this time, a logic H signal is input from the keep relay 7 to the AND element 8, but a logic L signal is input to the AND element 8.
Since the signal remains the same, the frequency reading contact lO which receives the output of the AND element 8 remains in the state shown. As a result, the frequency setting signal set by the frequency setting device 9 is given to the control circuit as a frequency command value via the acceleration/deceleration calculator, so that the voltage and frequency of the AC power from the inverter device 3 to the induction motor 5 are gradually increases until it reaches a predetermined value and enters the operating state. If the commercial power supply 1 is interrupted here, the induction motor ll5 will be in a free rotating state. As mentioned above, if the power outage time is short, the induction motor 5 can immediately resume operation, but if the power outage continues beyond a predetermined time, the smoothing capacitor will be discharged and the control device's 1i source will be lost. , the maximum speed setting value when restarting operation disappears.

However, in the present invention, the keep relay 7 remembers that the operation command signal is being issued. Then, after a predetermined power outage time has passed, both the two human input signals to the AND element 8 become logic H signals, and the frequency reading contact IO
The state is changed from that shown in the figure. In other words, the frequency setting value from the frequency setter 9 is input to the control circuit 6 at the time of power failure recovery. This power failure recovery control circuit 6 provides the manually inputted frequency setting value to the control circuit as a frequency command value as it is (i.e., without going through an adjustment/subtraction calculation unit), and also maintains a predetermined functional relationship with this frequency command value. The circuit structure is such that only a certain voltage command value is gradually raised from zero. As a result, even if the power outage is long, the frequency command value is immediately given to the control circuit, the voltage command value gradually increases from zero, and the current flowing from the inverter device 3 to the induction motor 5 may exceed the limit value. There is no. Therefore, when the power is restored, the induction motor 5 can smoothly recover to its original speed and continue operating. [Effects of the Invention] According to the present invention, an induction motor driven by an inverter enters a free rotation state and reduces its speed at the same time as a power outage. If the operation command signal has been issued in The circuit is carefully designed so that it gradually rises from As a result, the motor returns to the speed corresponding to the frequency setting immediately before the power outage, but because the voltage gradually increases, the motor returns to its original speed smoothly and in the shortest possible time without overcurrent. be able to.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... AC power supply, 2... Circuit breaker, 3... Inverter device, 4... Operation command contact, 5... Induction motor,
6...Control circuit at power outage recovery, 7...Key relay
8...Logic product element, 9...Frequency setter, lO...
・Frequency reading coloring 1 figure

Claims (1)

[Claims] 1) Through the acceleration/deceleration calculation means, the output of the frequency setting means is converted into a frequency command signal and a voltage command signal having a predetermined functional relationship with this, and an alternating current of voltage and frequency corresponding to these two command signals is generated. In a method of controlling an electric motor drive inverter for operating an AC motor to which a load with a large flywheel effect is coupled using an inverter that outputs electric power at a speed corresponding to the output of the frequency setting means, the power source of the inverter is If a power outage continues for a predetermined period of time or more, the output of the frequency setting means is routed through the acceleration/deceleration calculating means when the power outage is restored, provided that an operation command for the AC motor has been issued. 1. A method for controlling an electric motor drive inverter, characterized in that the voltage command signal is gradually increased from zero, and the voltage command signal is gradually increased from zero.