JPH06189561A - Control method for v/f-constant control-type inverter - Google Patents

Abstract

PURPOSE:To provide a control method for a V/f-constant control-type inverter capable of controlling an AC motor that drives a load with a large moment of inertia, and having smooth operation after recovery from a relatively short control power stoppage. CONSTITUTION:In a V/f-constant control-type inverter, a control circuit is operated by using a DC power voltage supplied through a rectifier. Within a period of time from a failure of a control power supply 1 until a DC voltage is lowered, the frequency of the inverter in operation is stored in a back-up RAM 6. When the control power supply 1 is recovered from the failure, the back-up frequency in the back-up RAM 6 is used as an initial value of a frequency set value on the basis of an inverter operation command, which still remains.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter control method for smoothly restarting the operation of a V / f constant controlled inverter when the control power source is restored after a power failure.

[0002]

2. Description of the Related Art FIG. 5 shows a conventional example of a V / f constant control type inverter, in which 10 is an inverter main circuit and 20 is a control circuit. The inverter main circuit 10 is an AC power supply 1
1, a rectifier 12 for converting AC power into DC power, a smoothing capacitor 13 of a DC intermediate circuit, and an inverter unit 14 for converting DC power into AC power of variable frequency and variable voltage.
And an AC motor M such as an induction motor.

On the other hand, the control circuit 20 for controlling the main circuit 10 includes a frequency setter 21, an acceleration / deceleration calculator 22 for increasing / decreasing the frequency set value at a constant speed, and a frequency set value output from the calculator 22. Voltage pattern set value 2 that outputs a preset voltage set value V _set using f _set as an input
3, the terminal voltage detection value V of the AC motor M detected by the voltage setting value V _set and the transformer 15 for the instrument on the main circuit side.
_An adder 24 that obtains a deviation from _act and a voltage controller 25 such as a PI controller that adjusts so that the deviation becomes zero
Then, the control signal from the adjuster 25 is input together with the frequency setting value f _set , and the PW for the inverter unit 14 is inputted.
The pulse width modulation circuit (PWM circuit) 26 that generates and outputs the M signal and the operation command switch 27 are included. The main part of the control circuit 20 is composed of, for example, a microcomputer.

[0004]

In the case where the AC motor M is driven by the above-mentioned conventional system, if the power supply of the control circuit 20 (control power supply) is interrupted and then restored, the control circuit 20 When configured by a microcomputer, all the contents will be cleared unless the memory has a backup function. Therefore,
When the operation command switch 27 is closed at the time of power recovery and is in the “operation command present” state, the frequency setting value f _set is output from the minimum frequency as in the case of starting the inverter.

On the other hand, since the AC motor M has a large moment of inertia, it takes a long time to completely stop even if the AC motor M is in a free-run state due to a power failure. Therefore, when the power is restored after a short power failure time, the rotational speed of the AC motor that has been in a free-run state due to inertia until then is generally high. In this case, a frequency setting value f _set lower than the primary frequency (rotation speed) of the rotating AC electric motor M is given and the difference becomes large, so that an overcurrent flows in the AC electric motor M, and depending on the case. The AC motor M breaks down and it becomes impossible to restart or continue the operation.

The present invention has been made to solve the above problems, and an object of the present invention is to control a V / f constant control type inverter that can smoothly resume operation when the control power is restored. To provide.

[0007]

In order to achieve the above object, the present invention controls a V / f constant control type inverter that operates a control circuit using a DC power source obtained from an AC control power source through a rectifier. In the method, during the period until the DC power supply drops after the loss of the control power supply, the operating frequency of the inverter at that time is stored in a backup memory, and when the operation command of the inverter exists when the control power supply is restored. The operating frequency in the backup memory is used as an initial value of the frequency setting value.

[0008]

In the present invention, the operating state and operating frequency (frequency setting value) when the control power is lost when the control power is restored
Is called from the backup memory and the operation of the inverter is restarted using this frequency as the initial value of the frequency setting value.Therefore, when the power failure time is short, the difference between the rotational speed of the AC motor and the frequency setting value is small, and the operation is smooth. Can be resumed.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the main part of this embodiment. In the figure, 1 is an AC control power supply, and a rectifier 2 and a power failure detection circuit 3 are connected to the output side thereof. The output side of the rectifier 2 and the power failure detection circuit 3 is connected to a CPU 4 which performs PWM calculation and the like, and the output side of the rectifier 2 stores an operation command for the inverter and a frequency set value f _set. A RAM 5 serving as a main memory and a backup RAM 6 are connected. In addition, 7 is CPU4, RAM5 and backup R
AM6 is a data bus mutually connected, 8 is a diode, and 9 is a capacitor for preventing discharge.

Next, this operation will be described with reference to FIGS. First, as shown in FIG. 2, when the control power supply 1 loses power at time t ₁ , its effective value V ₁ immediately decreases, but the DC voltage V ₂ output from the rectifier ₂ is generally from time t ₁ to time T _1. After a lapse of time, it starts to decrease from time t ₂ . That is, since the DC power supply of the CPU 4 has not disappeared during the time T, the present invention focuses on this.

That is, as shown in the flow chart of FIG. 3, when the power failure detection circuit 3 detects a power failure of the control power source 1, that is, the start of the time T (step S1 YES),
If the inverter is in operation, the CPU 4 outputs an inverter off command for commanding pulse off of the switching element (S2). After that, the current operating state (information during driving or stopping) and the operating frequency (frequency set value f _set ) at that time are transferred from the RAM 5 to the backup RAM 6 and stored (S3, S4). Perform these processes at time T
The DC power supply of the CPU 4 also disappears after that.

Next, as shown in the flow chart of FIG. 4, when the control power supply 1 is restored, first, the backup R
It is determined from the contents of AM6 whether or not the inverter was in operation at the time of the previous power failure, and if it was in operation (S11
(YES) It is determined whether or not there is an operation command after power recovery (S12). If there is a driving command (S12YE
S), backup RA of frequency setting value f _set at power failure
It is read from M6 and is set as the initial value of the output frequency setting value of this time after power recovery (S13). Then, the inverter on command is output to restart the inverter (S14).

In the above embodiment, the backup RAM
The operating frequency stored in 6 is the frequency set value f _set at the time of power failure.
However, the actual frequency value (detection value) at the time of power failure may be used.

[0014]

As described above, according to the present invention, when the control power is restored, the operating state and the operating frequency (frequency setting value) when the control power is lost are called from the backup memory, and the operation command is issued after the power is restored. At some times, the frequency is set to the initial value of the frequency set value to restart the operation of the inverter. For this reason, in a system in which a load with a large moment of inertia is driven by an AC motor, the difference between the rotational speed of the AC motor and the frequency setting value becomes small when the power supply failure time of the control power supply is short, and overcurrent flows to the motor. The operation can be restarted smoothly without any inconvenience such as flowing.

[Brief description of drawings]

FIG. 1 is a block diagram showing a main part of a control circuit to which an embodiment of the present invention is applied.

FIG. 2 is an explanatory diagram of a control power supply voltage.

FIG. 3 is a flowchart when a power failure occurs in the embodiment.

FIG. 4 is a flowchart at the time of power recovery in the embodiment.

FIG. 5 is a functional block diagram of an inverter main circuit and a control circuit for explaining a conventional technique.

[Explanation of symbols]

 1 Control Power Supply 2 Rectifier 3 Power Failure Detection Circuit 4 CPU 5 RAM 6 Backup RAM 7 Data Bus 8 Diode 9 Capacitor M AC Motor

Claims (1)

[Claims] 1. A control method for a V / f constant control type inverter, wherein a control circuit is operated using a DC power supply obtained from an AC control power supply via a rectifier, wherein the DC power supply drops after the control power supply is lost. In the period up to, the operating frequency of the inverter at that time is stored in the backup memory, and when the control command of the inverter is restored, if there is an operation command of the inverter, the operating frequency in the backup memory is used as the initial value of the frequency setting value. A method for controlling a V / f constant control type inverter, which is characterized by being used.