JPS6331487A - Controller for dc brushless motor - Google Patents

Abstract

PURPOSE:To suppress a peak current and reduce an effective current, by controlling an inverter with the signal of inverter input current detection signal and chopper signal for output generated from a microcomputer which are combined with each other. CONSTITUTION:From a microcomputer 6, the output of chopper signal 6a controlling the increment or reduction of duty is generated according to a difference between the operationrotational frequency signal of a DC motor 4 and rotational frequency signal through a command source 8. From a combining circuit 10, the output of the logical product of the chopper signal 6a and suppressing signal 9a for output generated when the current of a set or more value flows with a current detector 9 is generated. By this logical product output 10a, an inverter section 3 is driven. As a result, the peak value of conductive current to the inverter section 3 can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a control device for a DC brushless motor.

[Conventional technology]

Conventionally, a control device for a DC brushless motor inputs a DC voltage obtained by rectifying a commercial power supply to an inverter unit, and uniformly increases or decreases the duty of a chopper signal of a fixed period according to an externally commanded rotation speed. ing.

However, the peak value of the input current to the inverter section changes depending on the pulsations of the rectified DC voltage, so the inverter section requires semiconductor elements with a relatively large capacity, and the current pulsations This causes problems such as an increase in effective current, an increase in motor copper loss, and unstable operation of a back electromotive voltage detection circuit that detects motor induced voltage and determines commutation timing.

In order to solve the problems of the prior art described above, a motor control device shown in FIG. 3 has been previously proposed.

In FIG. 3, an AC voltage from a commercial power supply 1 is converted into a DC voltage by a rectifier circuit 2, and then supplied to an inverter section 3. Further, the generated electromotive voltage of the DC motor 4 is inputted into the microcomputer 6 as an operating rotation speed signal via the back electromotive force detection circuit 5, and this operating rotation speed signal is combined with the rotation speed signal from the external rotation speed command source 8. A chopper signal with a duty corresponding to the difference is input to the synthesis circuit 10. Synthesis circuit 10
The other input signal is a modulation signal obtained by comparing the periodic function voltage created by the oscillation circuit 12 and the reference voltage created by the reference voltage creation circuit 11 from the AC voltage of the commercial power supply 1, The output signal of the synthesis circuit 10 is amplified by the base drive circuit 7 and supplied to the inverter section 3.

The current detector 9 detects the overload state of the system by monitoring the current I, and its detection signal is sent to the microcomputer 6.

FIG. 4 is a waveform diagram of the modulated output signal at the comparator section indicated by the reference numeral 13 in FIG.
becomes a pulse signal with a pulse width corresponding to the amplitude of the reference voltage signal 11a that changes in phase with the AC voltage, and the waveform peak value of the inverter section input terminal I can be suppressed.

[Problem that the invention seeks to solve]

However, in the conventional motor control device shown in Fig. 3, there is a specific configuration that suppresses the peak value of the current flowing to the inverter section and reduces the effective current without being affected by the pulsations of the rectified DC voltage. As, from the AC voltage to the reference voltage Ll
It was necessary to perform a level shift in order to create the signal a, and it was necessary to add a circuit for creating a modulated output signal, which made the circuit configuration complicated.

The present invention has been made in consideration of the above points, and includes:
The purpose of this is to suppress the peak value of the current flow to the inverter section and reduce the effective current without being affected by the pulsations of the rectified DC voltage. An object of the present invention is to provide an improved control device for a direct current brushless motor, which does not require the addition of a new circuit for generating a modulated output signal, and has a simpler circuit configuration than the conventional one. It is something.

[Means for solving problems]

The above object is achieved by a circuit configuration in which a part of the motor control device detects the input terminal of the inverter section, and controls the inverter section with a signal that is a combination of this detection signal and a chopper signal output from a microcomputer. .

[Effect]

Therefore, by adopting the above configuration, the present invention provides the following features:
When the current flow in the inverter section exceeds the set value, the chopper signal is suppressed against any current pulsation.
Since the peak current to the inverter section is suppressed, it is possible to reduce the effective current as a result.

Note that the rotation speed of the DC motor decreases by the current width suppressed by the peak current limit, but the difference between the operating rotation speed and the external command rotation speed widens, and the chopper duty uniformly increases. The drop in rotational speed is corrected.

〔Example〕

The present invention will be described below based on an embodiment shown in FIGS. 1 and 2. FIG. 1 is a block circuit diagram of a motor control device according to the present invention.

In FIG. 1, the same symbols as in the conventional motor control device shown in FIG. 3 indicate the same parts, and the difference from FIG. 3 lies in the wiring system of the current detector 9. Current detector 9 has conventionally been used only to detect overload conditions in the system, but in the illustrated embodiment it is input to synthesis circuit 10 in place of the conventional modulation signal. That is, in the present invention, a chopper signal that controls whether the duty is increased or decreased according to the difference between the operating rotation speed signal of the DC motor 4 and the rotation speed signal from the external rotation speed command source 8, and the current detector 9 The inverter unit 3 is driven by the AND output with the suppress signal that is output when a current exceeding a set value flows.

FIG. 2 is an output signal waveform diagram of each part of the control device shown in FIG. 1.

Now, assuming that AC voltage 1a is input to the rectifier circuit indicated by numeral 2 in FIG. The chopper signal 6a of the microcomputer 6 is represented by a pulse train with a --like duty. However, since the rectified DC voltage 2a is pulsating, if the large winding inductance is L, approximately di
/dt=E/L, which is different for each pulse position, and since the current is limited in a portion where the rectified DC voltage 2a is relatively high, the suppress signal from the current detector 9 becomes as shown in 9a. Furthermore, since the energization indicated by the dotted line is suppressed, the voltage applied to the DC motor 4 as a whole becomes insufficient.In order to compensate for this, the duty of the chopper signal 6a is increased in the negative direction, and the externally commanded rotation speed is changed. The operation of the DC motor 4 is controlled.

As described above, the present invention uses the chopper signal 6a, which controls the increase/decrease of the duty according to the difference between the operating rotation speed signal of the DC motor 4 and the rotation speed signal from the external rotation speed command #8, and the current The inverter unit 3 is driven by the AND output with the suppress signal 9a outputted by the detector 9 when a current exceeding a set value flows.
Unlike the conventional example shown in the figure, it is not necessary to perform a level shift to create a reference voltage signal from an AC voltage, and the peak value of current flowing to the inverter section 3 can be suppressed without adding a new modulated output signal. Therefore, in addition to reducing the size of the control semiconductor element, it is possible to reduce the effective value of the current flow, thereby reducing the DC motor copper loss.

In addition, with a circuit configured to detect the motor-generated electromotive force and determine the commutation timing, it is possible to suppress the peak current below a certain value, reducing the spike current when switching off and reducing commutation. Further stabilization of timing detection can be achieved.

〔Effect of the invention〕

The present invention is as described above, and as is clear from the explanation of the illustrated embodiments, according to the present invention, the peak value of the current flowing to the inverter section can be adjusted without being affected by the pulsation of the rectified DC voltage. When reducing the effective current, there is no need to perform a level shift to create a reference voltage signal from AC voltage, and there is no need to add a new circuit to create a modulated output signal, making the circuit configuration simpler than before. As a result, an improved control device for a DC brushless motor can be obtained.

[Brief explanation of drawings]

Fig. 1 is a block circuit diagram showing an embodiment of the motor control device according to the present invention, Fig. 2 is an output signal waveform diagram of each part of the control device shown in Fig. 1, and Fig. 3 is a block diagram of a conventional motor control device. The circuit diagram of FIG. 4 is a waveform diagram of the modulated output signal at the comparator section indicated by reference numeral 13 in FIG. DESCRIPTION OF SYMBOLS 1... Commercial power supply, 2... Rectifier circuit, 3... Inverter part, 4... DC motor, 5... Back electromotive force detection circuit, 6... Microcomputer, 7... Base Drive circuit, 8... External rotational speed command source, 9... Current detector, 10... Synthesis circuit. ＼、Representative Patent Attorney Masaru Ogawa Men 3 Zutomi 240

Claims (1)

[Claims] 1. An inverter section in which a plurality of semiconductor switches are bridge-connected, a motor rotation speed detection circuit, a signal from the motor rotation speed detection circuit and a command rotation speed signal, and an output according to the difference therebetween. a control circuit unit that increases or decreases the duty of the chopper signal to be input; and current detection means that detects the input current of the inverter unit and generates a suppress signal when the input current value exceeds a predetermined value; A control device for a direct current brushless motor, comprising means for driving an inverter section using an AND signal of a chopper signal and a suppress signal. 2. The invention as set forth in claim 1 has a back electromotive voltage position detection circuit that inputs the motor terminal voltage and detects the rotor magnetic pole position, and this back electromotive voltage position detection circuit detects the commutation of the inverter section. A control device for a direct current brushless motor, comprising means for inputting timing and motor rotation speed into a control circuit section.