JPS60237886A - Overload protective circuit of motor - Google Patents

Abstract

PURPOSE:To practically sufficiently detect accurately a current flowed to a DC motor by integrating a chopper signal to obtain a mean current, thereby using a power module available in the ordinary market. CONSTITUTION:A voltage V is a voltage generated at a current detecting resistor 115 via a current Id in the waveform similar to the current Id. The output of an integrator having a resistor R101 and a capacitor C101 is input to the negative side input terminal of a comparator 117. A chopper signal is output from a power terminal of upside from a CHO terminal of a microcomputer 116, and a power transistor of upside is turned ON and OFF by the chopper signal. A resistor R102 and a capacitor C102 are an integrator for obtaining the mean value of the chopper signal, and the output is input through a resistor R103 to the positive input terminal of the comparator. The mean value of Im can be indirectly obtained from the output of the comparator 117.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a system for controlling the rotation speed of an electric motor (using an inverter), and in particular detects an overcurrent using a current detection resistor to control the rotation speed of the electric motor. The present invention relates to a circuit suitable for reducing the load by lowering the load.

[Prior art]

A conventional example will be explained with reference to FIGS. 1 to 3. ,.

In Figure 1, 1 to 6 are power transistors, and 7 to 6 are power transistors.
12 is a diode connected as shown. 13 is a power module composed of power transistors 1 to 6 and diodes 7 to 12; 141d i&m;
, the power module output resistance in the electric motor, vd is the DC power supply,
(2) is a voltage generated by the current (2) m flowing through the current detection resistor 15.

In FIG. 2, the upper row shows the waveform of the current d, the middle row shows the waveform of the current r, and the lower row shows the waveform of the current Im.

Further, 11 is 08 hours when the upper power transistor is chopping, and t is the chopper period.

In FIG. 3, 16 is a microcomputer (hereinafter referred to as microcomputer 16) that is the central part in controlling the rotation speed of the DC motor 14, and 17 is a current generated in the current detection resistor 15 in FIG. This is a comparator that serves to notify the microcomputer 16 that the magnitude of the voltage V exceeds a certain value.

In FIG. 1, power transistors 1 to 6 are connected to a drive circuit (not shown) connected to their respective bases, and two power transistors are turned on alternately as follows.

That is, the combinations that are turned ON are changed in sequence, such as 1 and 5 → 1 and 6 → 2, 6 → 2, 4 → 3, 4 → 3, 5 → 1 and 5, and alternating current is supplied to the DC motor 14.

Now considering the state in which Hower transistors 1 and 5 are ON, current id flows in the order of A -> power transistor 1 -> DC motor 14 -> power transistor 5 -> current detection resistor 15 -> B.

However, in order to convert the rotation speed of the DC motor 14,
It is necessary to change the voltage at which DC is applied to the motive 14. As a means to prevent this, the power transistor O
The average voltage applied to the DC motor 14 is controlled by turning on and off the upper power transistor at a cycle faster than the switching cycle of the N combinations.

Therefore, the waveform of the current Jd described above becomes an intermittent waveform as shown in the upper part of FIG.

Next, in Figure 1, power transistor 1 is set to 0FF1.
Considering the state in which the power transistor 5 is ON, the current ir flows in the order of the DC motor 14 → the power transistor 5 → the current detection resistor 15 → the freewheeling diode 10 → the DC motor 14.

The waveform of the current r at this time is as shown in the middle part of FIG.

In this way, Id and current r alternately flow through the current detection resistor 15, and eventually current flow m shown in the lower part of FIG. 2 flows.

This current 1 m is the same as the current flowing through the DC motor 14, and the current flowing through the DC motor 14 can be accurately detected by the current detection resistor 15.

A voltage (2) proportional to the current Im is generated across the current detection resistor 150 in FIG.

Also, in FIG. 3, the voltage V is smoothed by an integrator circuit consisting of C and C, and is input to the negative input terminal of the comparator 17 as a voltage proportional to the average value of the current Im. . On the other hand, the positive input terminal of the comparator 17 is fixed at a certain potential by R2-R5. As a result, when the current m exceeds a certain value, the output of the comparator 17 is inverted, and in this case, 1 (i → LO), this signal is
6 is input to the OVL terminal of the microcomputer 16.
The chopper signal output from the motor is changed to lower the rotational speed of the DC motor 14.

It is necessary to provide one emitter terminal connected to the emitter and an anode terminal connected to each anode of the freewheeling diodes 10, 11, and 12. This is because a commercially available power module has only one terminal, with each emitter and each anode connected internally. The disadvantage was that a power module had to be used.

[Purpose of the invention]

An object of the present invention is to use a commercially available power module and to detect the current flowing through the DC motor 14 with sufficient accuracy for practical use.

[Fake invention]

In FIG. 2, the following relational expression holds true.

Average value of 1m - (average value of Id)・(t/it), that is,
Im can be calculated if the ratio of Id and the time during which Id is flowing is known.

The present invention achieves this principle with a simple circuit configuration.

An embodiment of the present invention will be described below with reference to FIGS. 4 to 7.

FIG. 4 shows a circuit when a commercially available power module is used, in which power transistors 101 to 106 and diodes 107 to 112 are connected as shown. 113 is by power transistors 101-106 and diodes 107-112! l
A power module 114 consisting of a DC motor is connected to the power module 113 as shown.

115 is a current detection resistor, ■d is a DC power supply, and ■ is a voltage generated by ■d flowing through the current detection resistor 115.

FIG. 5 shows the central part of the present invention; 116 is a microcomputer (hereinafter referred to as a microcomputer) which is the central part in controlling the rotational speed of the DC motor 114; 117;
is a comparator that serves to notify the microcomputer 116 that the magnitude of the voltage V generated across the current detection resistor 115 in FIG. 4 exceeds a certain value.

FIG. 6 shows the voltage waveforms at V and CHO of FIG.

FIG. 7 shows a graph in which the vertical axis represents the average value of the voltage V (4av), and the horizontal axis represents the average value of the chopper output (Nt+/1)aV).

In FIG. 4, power transistors 101 to 106
In this case, two power transistors are turned on alternately as follows by a drive circuit (not shown) connected to each base.

That is, 101 and 105 → 101 and 106 → 102 and 10
6 → 102 and 104 → 103 and 104 → 103 and 105
→The combination of 1st-order ON like 101 and 105 is 9
, supplies alternating current to the DC motor 114.

Considering the state where power transistors 101 and 105 are now ON, the current ■d is A → power transistor 101 → DC motor 114 → power transistor 1
The current flows in the order of 05→current detection resistor 115→BL:D. At this time, a current Id flows through the current detection resistor 115.

However, in order to convert the rotation speed of the DC motor 114, it is necessary to change the voltage applied to the DC motor 114. As a means for this purpose, the average voltage applied to the DC motor 114 is controlled by turning the upper power transistor ON and OFF at a cycle faster than the switching cycle of the ON combination of the power transistors described above.

Next, in Fig. 4, power transistor 1゛01 is
Considering the state in which F'F and power transistor 105 are ON, current r flows in the order of DC motor 114 -> power transistor 105 -> free wheel diode 110 -> DC motor 114.

At this time, no current r flows through the current detection resistor 115.

In this way, in this circuit system, the current IdL does not flow through the current detection resistor 115, but the current m flows through the DC motor 114.
The current cannot be detected directly by the sensing resistor.

Therefore, in the present invention, in FIG. 2, the average value of Im = (average IdO value) · (t/lt)
...1 We focused on the fact that the following relationship holds true, and realized this as shown in Fig. 5.

In FIG. 5, V is the stain current detection resistor 11 due to the current
The voltage generated at the current 1d has a waveform similar to that of the current 1d, as shown in FIG. R101 and C101 are integral circuits for determining the average value (vav) of the voltage V, and the output thereof is input to the negative input terminal of the comparator 117.

On the other hand, from the CHO terminal of the microcomputer 116, a chopper signal with a peak value ■ddX)(time t11 period t of i as shown in FIG. Therefore, the ratio (11/1) of time (tl) and period (tl) at voltage V is 11/1 in the chopper signal.
It is the same as R102 and ClO2 in Fig. 5 are an integrating circuit for calculating the average value Ntl/1)aV) of the chopper signal, and its output is sent to the comparator 1 via R103.
It is included in the positive input terminal of 17.

Therefore, this input voltage value is proportional to t's/t of the chopper signal. Note that PvR is a semi-fixed resistor for adjusting the input voltage value to the comparator 117, and R104 is a pull-up resistor.

According to this circuit configuration, a samurai relationship is established in which the output of the comparator 117 is inverted.

vav=a −(tl/1)av …−= 2 However, a
is a constant of proportionality. Figure 7 is a graphical representation of the two equations.

Transforming equation 2, a=l:dav・(t/11)av -----・3
Also, the average value of v7tvαd... 4(t/1l
)av”(t/11) +・++++ s1 formula, 3 formula,
According to equations 4 and 5, the average value of aCxIm... 6 That is, the average value of 1 m can be calculated indirectly by this circuit configuration.

〔Effect of the invention〕

According to the present invention, the current flowing through the electric motor connected to the power module can be detected without providing a special terminal for detecting the return current in the power module as in the conventional example. This has the effect of allowing the use of existing power modules.

[Brief explanation of drawings]

Figure 1 is a circuit diagram around the power module in a conventional example, Figure 2 is a current waveform of each part in Figure 1, Figure 3 is an overload protection circuit diagram around a microcomputer in a conventional example, Figure 4 is a circuit diagram around the power module in an embodiment of the present invention, Figure 5 is an overload protection circuit diagram around a microcontroller in an embodiment of the present invention, and Figure 6 is a diagram of each part in Figure 5. FIG. 7 is a graph showing the relationship between the input voltage values to the plus and minus terminals when the output of the comparator 117 is inverted. 101... Power transistor, 107... Freewheeling diode, 113... Power module, 114...
...DC motor, 116...Microcomputer, 117...
Con'$1's I preference ν T=, 30 $4 figure u5 tt3

Claims (1)

[Claims] A circuit consisting of two power transistors connected in series and a diode connected between the core and emitter of each of the power transistors so that the forward direction of current flows is opposite to each other. A transistor circuit consisting of three sets connected in parallel, a motor connected to the intermediate point of the two power transistors connected in series, and a drive circuit connected to the base of the power transistor for switching the power transistor. , a DC power source that supplies power to the motor through the transistor circuit, a current detection resistor inserted between the DC power source and the transistor circuit, an output terminal that outputs a chopper signal for controlling the drive circuit; Equipped with an input terminal for inputting the overload operating state, the overload operating state signal is 1,170. It is equipped with a comparator circuit that compares the average value of the voltage across the resistor and the average value of the chopper signal, and the output of the comparator circuit is used to control the overload operation of the microcomputer. A motor overload protection circuit that is connected to an input terminal that inputs the status.