JPH04285496A - Frequency control method for inverter - Google Patents

Abstract

PURPOSE:To improve frequency control for inverter. CONSTITUTION:Power of a three-phase AC power supply 1 is fed through a noise filter 2 and converted through a converter 3 into DC power which is then fed through a reactor 4 and a smoothing capacitor 5 and inverted through a switching element section 6 into AC power to be fed to a motor. The switching element section 6 is switched through a driving circuit 8 based on a command delivered from a control circuit 9 comprising a CPU 10 and a memory 11. The memory 11 contains a data table previously stored with waveform data for each operating frequency. The control circuit delivers a command, based on the waveform data for each operating frequency stored on the table, to the driving circuit 8. For an operating frequency not stored on the table, data on the table closest to that operating frequency is utilized for driving the switching element section 6 with time ratio of waveform pattern being varied. At that time, variation width of the operating frequency is decreased immediately before or after modification of the waveform data whereas it is increased during modification.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency control method for an inverter used for a motor such as a compressor of an air conditioner.

0002

2. Description of the Related Art In inverter control of a compressor motor of an air conditioner or the like, a PWM pattern is generally generated by storing an optimal waveform pattern for each frequency in a ROM or internal memory of a microcomputer.

In this case, by having waveform data for every operating frequency or by calculating waveforms in real time, a PWM pattern that matches the V/F characteristics of the motor can be obtained, allowing smooth and efficient operation. but,
Storing many patterns and performing real-time calculations requires additional memory and a high-performance microcomputer, which poses a cost problem.

Conventionally, therefore, a ROM table has data for every several Hz of operating frequency, and in a steady state where the operating frequency is in the data table, reference data is output as is. In addition, when outputting an operating frequency that is not stored in the data table because it is necessary to change the frequency gradually, such as when changing the frequency, select the closest frequency among the operating frequencies on the data table. Using one pattern data, the frequency is changed by changing the time ratio of the waveform pattern at a constant rate, for example, 0.5 Hz/second.

[0005]

[Problem to be Solved by the Invention] However, since waveform data can only be stored every few Hz, it is not possible to reduce the change in the inverter output voltage by changing the reference data, especially when the impedance of the motor is small. However, if the voltage and frequency are greatly changed at the same time, there are problems such as overcurrents occurring, and if the frequency is changed slowly to prevent overcurrents, the response to frequency changes deteriorates.

[0006]

[Means for Solving the Problems] The present invention takes the following means to solve the above problems. That is, when inverter controlling a motor as an inverter frequency control method, waveform data for each operating frequency is stored in advance on a data table, and at the operating frequency stored on the table, the waveform data is In the inverter that drives the motor, at an operating frequency that is not stored on the data table, such as when changing the frequency, the waveform data of either the previous or the previous one with the closest frequency on the data table is used, and the waveform pattern is The motor is driven by varying the frequency by changing the time ratio of , and the operating frequency is controlled to a small change width immediately before or after the waveform data change, and a large change width is controlled during that time. .

[0007]

[Operation] With the above means, when the operating frequency of the motor is on the data table, the inverter is controlled based on the waveform data of the operating frequency to drive the motor. When the motor is driven at an operating frequency that is not on the data table, the motor is driven by using the closest operating frequency on either the front or back table and changing the time ratio of the waveform pattern. At this time, immediately before or after the waveform data change, the operating frequency is controlled to be changed in a small range, and immediately before and immediately after, the operating frequency is controlled to be changed in a large range.

[0008] Immediately before the voltage increases and/or
Or immediately after, control is performed in fine steps, and where the voltage between them becomes small, control is performed in coarse steps, thereby preventing the generation of excessive current in the motor.

[0009]

[Embodiment] An embodiment of the present invention will be explained with reference to FIGS. 1, 2, and 3.

In FIG. 1, a three-phase AC voltage input from a power source 1 is converted into a DC voltage by a converter 3 via a noise filter section 2, passed through a reactor 4, and smoothed by a smoothing capacitor 5. . The smoothed DC voltage is sent to the switching element section 6 and converted into three-phase AC at the operating frequency. The compressor motor 7 is driven by an inverter by this three-phase alternating current. This switching element section 6 is connected to the CPU 1
0 and a control circuit 9 having a memory 11, it is driven via a drive circuit 8, performs a switching operation, and outputs three-phase alternating current at the above frequency.

Waveform data of the operating frequency is input into the memory 11 in advance on a data table at predetermined frequency intervals.

Here, the i-th frequency of the data table is f
Assume (i) that the data tables are arranged in order of increasing operating frequency.

[0013] In the above, for example, when increasing the rotational frequency of the motor 7 from f(i) to f(i+1), the control circuit 9 shifts to f(i+1) based on the i-th data in the memory 11 according to a command from the CPU 10. Until just before, the frequency (waveform) increases in small steps △f1 as shown in Figure 2.
The drive circuit 8 is driven by the command. Then from f(i) to f(
i+1), a coarse step △f2 (>△f1)
The drive circuit 8 is driven by the frequency command stored in the memory 11. Furthermore, immediately after reaching f(i+1), the drive circuit is driven with a frequency command that increases in narrow steps Δf1 based on the i+1th data in the memory 11. For comparison, an example of conventional same step driving is shown in FIG.

[0014] In this way, the frequency is changed in detail immediately before and/or immediately after the frequency change where the voltage increases, and it is changed coarsely where the voltage between them becomes small, thereby preventing the generation of excessive current in the motor. . Furthermore, according to this embodiment, good control can be performed without increasing the memory capacity of the control circuit.

[0015]

[Effects of the Invention] As explained above, according to the present invention, even when waveform data can only be stored at intervals of several Hz due to memory limitations, the frequency change response can be maintained without deteriorating.
It is possible to drive the motor and prevent overcurrent from occurring in the motor.

[Brief explanation of the drawing]

FIG. 1 is a configuration block diagram of an embodiment.

FIG. 2 is an explanatory diagram of the operation of the same embodiment.

FIG. 3 is an explanatory diagram of the operation of a conventional example.

[Explanation of symbols]

1 Power supply 2 Noise filter 3 Converter 4 Reactor 5 Smoothing capacitor 6 Switching element section 7 Compressor motor 8 Drive circuit 9 Control circuit 10 CPU 11 Memory

Claims (1)

[Claims] 1. When controlling a motor with an inverter, waveform data for each operating frequency is stored in advance on a data table, and at the operating frequency stored on the table, the motor is controlled based on the waveform data. In the inverter that performs driving, at an operating frequency that is not stored in the data table, such as when changing the frequency, the waveform data of either the previous or the previous one with the closest frequency on the data table is used, and the time ratio of the waveform pattern is The inverter is characterized in that the motor is driven by varying the frequency by changing the waveform data, and the change width of the operating frequency is controlled to be small immediately before or after the change of the waveform data, and the change range is controlled to be large during that time. Frequency control method.