JPH03145995A - Control of inverter - Google Patents

Abstract

PURPOSE:To facilitate adjustment of setting of predicted resonance frequency by sequentially lowering the carrier frequency, by a predetermined amount with predetermined interval, based on a command from a frequency operating circuit receiving a frequency lowering command from a vibration detecting circuit upon occurrence of vibration in the motor current. CONSTITUTION:Upon detection of resonance through a detecting circuit 2 during operation, carrier frequency correcting operation is started through a frequency operating circuit 1 based on an output command from the detecting circuit 2. Operating point of carrier frequency fc makes transition such that P1 P2 P3... and the carrier frequency fc lowers sequentially such that fc1 fc2...-fc3... with predetermined interval until resonance ceases. If resonance does not cease even if the carrier frequency fc lowers to the lower limit, the frequency operating circuit 1 provides an inverter operation stop command BS thus stopping operation of an inverter. By such arrangement, adjustment concerning to setting of predicted resonance frequency can be facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an inverter device control method for suppressing current vibration in an AC motor driven by an inverter.

[Conventional technology]

As a conventional control method of this type, one is known in which control is performed according to a control characteristic diagram illustrated in FIG. 4 using a frequency calculation circuit 1a as illustrated in an input/output relationship diagram in FIG.

In Fig. 3, f and fo are the set value of the inverter output frequency and the frequency command converted into the required form, respectively, and f□ is the difference between the inverter, the AC motor serving as its load, and its drive mechanical system. This is the setting value of the predicted value of the resonant frequency of the control system consisting of

Next, as shown in FIG. 4, the command f0 is set to the set value f0.
The set value f corresponds to the range of ±Δr0.

The inverter output frequency is flat and unchanged in the range of f, ±Δf, and setting of the inverter output frequency in an appropriate range before and after the predicted resonance frequency as described above is prohibited. Note that the setting Δf0 is appropriately determined from the aspect of resonance avoidance of the control system, and the setting Δf is determined corresponding to the setting Δf0.

[Problem to be solved by the invention]

However, in the above conventional method, it is necessary to reset the predicted resonance frequency each time the configuration of the control system having the above-mentioned configuration changes, which results in a lack of versatility in application to various control systems. Even in the case where the configuration of the control system remains unchanged, it is often necessary to correct the setting of the predicted resonance frequency value after the inverter starts operating, resulting in complicated adjustment. In view of the above, the present invention
It is an object of the present invention to provide an inverter device control method that easily and automatically adjusts the predicted value setting of the resonance frequency.

[Means to solve the problem]

In order to achieve the above object, an inverter device control method of the present invention includes an inverter device that drives and controls an AC motor. A frequency calculation circuit that performs a frequency change calculation and a motor current vibration detection circuit that detects a vibration state in the current flowing through the motor and issues a command to reduce the carrier frequency are provided, and when vibration occurs in the motor current, the vibration detection circuit is provided. The carrier frequency is sequentially reduced by a predetermined value and at intervals in response to a command from the frequency calculation circuit that receives a reduction command from the circuit.

[Effect]

A resonant state of a control system consisting of an inverter, an AC motor serving as its load, and a mechanical system driven by the motor causes significant vibration in the current flowing through the motor.

Further, the resonance of the control system as described above can be suppressed or avoided by reducing the carrier frequency of the PWM-controlled inverter.

According to the above, in the present invention, when the occurrence of the resonance is detected from the vibration of the motor current, a correction value Δfc having an appropriate value and output interval provided for correction is automatically calculated from the carrier frequency fc during operation. If the resonance state continues even after reaching the lower limit of the carrier frequency fc, the operation of the inverter is stopped.According to the above, the frequency calculation circuit and the motor current vibration detection circuit are It shall be established.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block circuit diagram showing an embodiment of the present invention, and FIG.
The figure is a control characteristic diagram corresponding to FIG. 1.

In Fig. 1, 1 is a frequency calculation circuit that performs various calculations regarding the inverter output frequency set value f5, its output command f0, and carrier frequency fc, and 2 detects the vibration state of the motor current I. The frequency calculation circuit 1
This is a motor current vibration detection circuit that outputs a correction signal of carrier frequency fc for .

Next, in FIG. 2, if the inverter now sets its output frequency setting value r1 to f, I and the carrier frequency fc to f
If the occurrence of a resonance state is detected by the detection circuit 2 during operation as cl, the carrier frequency correction calculation in the frequency calculation circuit 1 is started by the output command of the detection circuit 2, and the carrier frequency f, The operating point of is shifted as shown in the figure as P+-Pz-h..., and the carrier frequency fc is sequentially reduced at predetermined intervals as fCI-fc2-fcff... until the resonance disappears.

Furthermore, if the resonance is still not eliminated even when the carrier frequency fe reaches its operating permissible lower limit value fefi, the frequency calculation circuit 1 issues an inverter operation stop command BS, and the inverter device stops its operation. Note that the illustrated base carrier frequency fcl+f c 2 + f
Frequency difference Δfci(i
= 1.2...) can be determined as appropriate whether to set it as a fixed planting or to set it as a variable value.

[Effects of the Invention] According to the present invention, when current oscillations based on control system resonance occur in the current flowing through an AC motor driven by a PWM inverter, the PWM control rear 9 oscillation is automatically and sequentially reduced. Control eliminates the need to set the resonance prediction frequency and correct it, and from the perspective of avoiding resonance in the control system, expands the versatility of inverter application to mechanical systems driven by AC motors, and simplifies adjustment. It is possible to aim for

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram showing an embodiment of the present invention, and FIG.
3 is a control characteristic diagram corresponding to FIG. 1, FIG. 3 is a human output relationship diagram of a frequency calculation circuit in the prior art, and FIG. 4 is a control time ti diagram corresponding to FIG. 3. 1.18...Frequency calculation circuit, 2...Motor current vibration detection circuit. Office error e liquidation circulation diagram f. Diagram

Claims (1)

[Claims] 1) In an inverter device that drives and controls an AC motor, a frequency calculation circuit that receives an inverter output frequency setting signal, calculates and outputs the required command signal, and also calculates a change in carrier frequency for inverter PWM control, and energizes the motor. a motor current vibration detection circuit that detects an oscillation state in the current and issues a command to reduce the carrier frequency, and when the motor current oscillates, the frequency calculation circuit receives a reduction command from the vibration detection circuit; An inverter device control method, characterized in that the carrier frequency is sequentially decreased and changed at predetermined intervals.