JPS6114758B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an emergency operation method for an AC motor drive system in which one or more AC motors are connected to each of a plurality of inverter devices connected to a DC bus. It is.

This type of device is widely used in the textile and steel industries to control the speed of multiple electric motors.
However, when driving an AC motor with an inverter device, if the energy supply to the DC bus stops, that is, if a power outage occurs on the DC bus,
Even if the power outage is only for a very short time, the motor may experience problems such as out-of-step or out-of-step operation, causing the motor to stop operating, and it is impossible to restart the motor automatically even after the power outage is restored. is common. When such a problem occurs, for example, yarn breakage occurs in the spinning process of the textile industry, resulting in huge losses and requiring long recovery work. In order to prevent such problems, an emergency storage battery or generator may be connected to the DC bus, but this is very expensive equipment and is not generally used.

In addition, when controlling the speed of an AC motor that has a large flywheel effect on the load side of the drive motor with a single inverter, the energy of the flywheel effect on the motor load side is used during short power outages. A method of continuing operation has also been proposed, but if a flywheel effect cannot be expected on the motor load side, the motor will stop even during a short power outage.

In order to solve the problem that occurs during such a short power outage, the present invention allows the inverter device and the AC motor to continue operating if a flywheel effect can be expected on the load side of at least one of the multiple AC motors. This paper proposes an emergency operation method that enables Furthermore, the present invention aims to maintain stable operation by keeping the voltage and frequency of the AC voltage supplied to each AC motor substantially constant even during emergency operation.

Therefore, in the present invention, the drive system for the AC motor group is configured as follows. That is, at least one of the AC motors in the AC motor group has a relatively large flywheel effect connected to the load, and the inverter device that supplies power to at least this one motor is an inverter device that can regenerate power, and each inverter device Each is provided with a control device that controls the voltage and frequency in substantially proportional manner.
In the drive system configured as described above, in the present invention, when the power supply to the DC bus stops, the voltage control closed loop in the control device of each inverter device is switched to an open loop, and any one of the AC A common frequency reduction command signal is provided to each inverter device by an additional closed-loop control system that acts to keep the voltage/frequency ratio of the electric system substantially constant. By doing this, when the power supply to the DC bus stops, the output voltage value of each inverter device is proportional to the voltage value of the DC bus because the voltage control system is open loop. It starts to change. When the power supply to the DC bus is stopped, the voltage value of the DC bus starts to decrease, and the voltage/frequency ratio decreases accordingly. However, an additional closed-loop control system comes into play to keep the voltage/frequency ratio constant.
As the voltage decreases, the frequency decreases. As a result, at least the AC motor connected to a relatively large load with a flywheel effect enters generator operation, and the energy generated by this motor is supplied to the DC bus via an inverter device capable of power regeneration. . This allows stable operation while keeping the voltage/frequency ratio approximately constant.

The invention will now be described in more detail with reference to illustrated embodiments.

In FIG. 1, 3 is a DC bus bar, and a rectifier 2 connected to an AC power source 1 is installed as a device for feeding power to this DC bus bar. An inverter device group 4 is connected to the DC bus 3 . One or more AC motors are connected to each of the inverter devices 4-1 to 4-n. The AC motor group is shown schematically at 5, and the individual motors are shown at 5.
-1 to 5-m. The loads on the motors are indicated collectively at 6, and the loads on the individual motors are correspondingly indicated at 6-1 to 6-m. The number n of inverter devices and the number m of electric motors do not necessarily match.

It is necessary that at least one of the motors in the group is connected to a load having a relatively large flywheel effect, and that the inverter device that supplies power to at least one of the motors is an inverter device that can regenerate power.

The inverter device is a variable voltage variable frequency inverter device, such as a combination of a DC chopper and an inverter, or a pulse width controlled inverter. Each inverter device is provided with a control device for voltage and frequency, including for example a voltage regulator 8, a frequency controller 9, a setting device 10 and a voltage detector 11.

The output voltages of the setters 10-1 to 10-n in the individual inverters 4-1 to 4-n are respectively guided to the voltage regulators 8-1 to 8-n as voltage target values, and are also supplied to the frequency controller 9-n. 1 to 9-n as frequency command inputs. Each voltage regulator 8-
1 to 8-n are inverter devices 4-1 to 4-n that match the actual voltage values detected by the voltage detectors 11-1 to 11-n with their respective target values.
4-n. In other words, the voltage control system is a closed loop. Each frequency controller 9-1 to 9-n has a voltage
Each corresponding setting device 10 includes a frequency converter.
The inverter device is controlled at a frequency proportional to the input voltage from -1 to 10-n. Therefore, the voltage/frequency ratio of the AC voltage supplied from each inverter device to the motor is kept substantially constant.

Furthermore, for emergency operation in the event of a power outage according to the present invention, a loop switch 7 for switching the voltage control system from a closed loop to an open loop is provided on the output side of the voltage regulator 8 in the control device of each inverter. The individual loop switches 7-1 to 7-n are shown here in principle with switches and storage capacitors. When the switch is closed, the voltage control system is in closed-loop control, but when the switch is opened, the voltage control system switches to open-loop control using the voltage operation command signal stored by the memory capacitor immediately before the switch was opened. It will be done. Further, a power outage detector 21 is provided, and this power outage detector 21 generates a power outage detection signal when the magnitude of the voltage of the AC power supply 1 falls below a predetermined level. Furthermore, an additional closed-loop control system is provided, consisting of a voltage-frequency ratio detector 22, a voltage-frequency ratio regulator 23, and a voltage-frequency ratio setter 24. The detector 22 is connected to one predetermined AC motor (in the illustrated example, five
-m) detects the voltage/frequency ratio of the AC voltage supplied to the AC voltage. Upon receiving the power failure detection signal from the power failure detector 21, the regulator 23 controls each inverter so that the voltage/frequency ratio detected by the detector 22 matches the target value set by the setting device 24. An additional input voltage in the frequency decreasing direction is applied to the frequency controller of the device. Furthermore, the output voltage of regulator 23 is fed to each voltage regulator as an auxiliary input voltage.

If AC power supply 1 causes a power outage for some reason,
This is detected by the power failure detector 21. The power failure detection signal issued from the power failure detector 21 stops the rectifier 2 and at the same time switches the voltage control system of each inverter device from the conventional closed loop to the open loop. Thereby, the voltage operation command value of each inverter device is kept constant at the value immediately before the loop switching. As a result, the output voltage of each inverter device changes in proportion to the DC bus voltage Vde. As the power supply from the AC power supply 1 to the DC bus 3 via the rectifier 2 is stopped, the DC bus voltage begins to decrease, and accordingly, the output voltages of the individual inverter devices also begin to decrease.

However, in the illustrated example, a decrease in the output voltage of each inverter device appears as a decrease in the voltage/frequency ratio at the terminals of the electric motor 5-m, which is detected by the detector 22. The power failure detection signal emitted from the power failure detector 21 is also guided to the regulator 23, whereby the zero hold state of the regulator 23 is released, and the regulator 23 adjusts the voltage/frequency detected by the detector 22. The ratio starts operating so as to match the target value set in the setter 24. The output voltage of the regulator is set at the input end of each frequency controller 9-1 to 9-n, respectively, to the corresponding setting device 10-1 to 10.
-n is superimposed on the frequency command input voltage, thereby reducing the frequency of the inverter device. In this way, the frequency is also lowered following the voltage drop, and the voltage and frequency are kept constant. In this case, the motor to which a load with a relatively large flywheel effect is connected will be in a state in which the frequency decrease precedes the decrease in the motor rotational frequency, causing it to rotate at a speed higher than the synchronous speed, and as a result, the generator Start driving. The energy generated by the electric motor that has entered generator operation is supplied to the DC bus 3 via an inverter device capable of power regeneration. This allows the DC bus voltage to be maintained within an operable range for a relatively long period of time. An inverter device that has only a motor connected to a load with a small flywheel effect or an inverter device that cannot regenerate power will be operated by receiving power from the DC bus. Since the frequency reduction signal from the regulator 23 is simultaneously given to the frequency controllers of other inverters that do not perform voltage/frequency ratio detection, the voltage/frequency ratios of the motor groups connected to these inverters are also approximately the same. As a result, all electric motors can operate stably.

When the power supply voltage is restored in this state and the power failure detection signal is released, the rectifier 2 is turned on and each voltage control system is returned to its original closed loop.
Zero hold of the regulator 23 is performed. In this case, it is preferable to avoid saturation of the integral characteristics of the voltage regulators 8-1 to 8-n during a power outage. Various means for this are known in the art, but in this embodiment it is provided that the output voltage of the regulator 23 is superimposed on the input of each regulator with a polarity that reduces the voltage setpoint value. Furthermore, it is preferable that the regulator 23 not be held at zero suddenly at the time of power restoration, but held at zero after a delay. As a result, when power is restored from the power supply side to the DC bus 3 and the DC bus voltage rises, the frequency drop signal is gradually extracted in response to this and the original operating frequency is restored. A complete recovery is guaranteed.

If the frequency settings on the setting device 10 of each inverter device are distributed over a wide range, applying exactly the same frequency reduction signal to each frequency controller will keep the voltage frequency ratio of all motors within the desired range. In such a case, it is advisable to add a ratio divider 25 as shown in FIG. 2. In FIG. 2, the same elements as in FIG. 1 are given the same reference numerals. Each ratio divider 25-1 to 25-n converts a common frequency reduction signal into a frequency reduction signal proportional to the operating frequency (set frequency) of the inverter device to which it belongs.

[Brief explanation of the drawing]

1 and 2 are block diagrams showing different embodiments of the present invention. DESCRIPTION OF SYMBOLS 1... AC power supply, 2... Rectifier, 3... DC bus, 4... Inverter device, 5... AC motor, 6... Load, 7... Loop switch, 8... Voltage regulator, 9 ...Frequency controller, 10...Voltage and frequency setting device, 11...Voltage detector, 21...
...Power failure detector, 22...Voltage/frequency ratio detector,
23... Voltage/frequency ratio adjuster, 24... Voltage/
Frequency setter.

Claims (1)

[Scope of Claims] 1. A device that supplies power to a DC bus, a plurality of variable voltage variable frequency inverter devices connected in parallel to the DC bus, and an AC motor connected to each inverter device. , at least one of these AC motors is connected to a load having a relatively large flywheel effect, and the inverter device that supplies power to at least one AC motor is an inverter device that can regenerate power, and each In a drive system for a group of AC motors in which each inverter is equipped with a control device that controls the voltage and frequency in approximately proportion to each other, the voltage control loop in the control device of each inverter is closed to an open loop in the event of a power outage. At the same time as switching, a common frequency reduction signal is given to the control device of each inverter device by an additional closed loop control system that acts so that the voltage/frequency ratio of any one AC motor is approximately constant. An emergency operation method in an AC motor group drive system characterized by: 2. In claim 1, the common frequency reduction signal guided by the additional closed-loop control system to the control device of each inverter device has a coefficient proportional to the respective operating frequency in the control device of each inverter device. An emergency operation method for a drive system of an AC motor group, characterized in that the drive system is driven by an alternating current motor group.