JPS61170295A - Operation controller of motor - Google Patents

Abstract

PURPOSE:To accurately detect a load current and to simplify a circuit configuration by inserting a current detector between a DC power source and a power module, connecting the maximum value holder with the output side to discriminate an overload state. CONSTITUTION:In a circuit for controlling a motor 14 by a power module 13 made of switching elements 1-6 and circulating diodes 7-12 connected in a bridge, a current detecting resistor 15 for detecting a DC current Id is inserted between the module 13 and a DC power source. A detection voltage (v) generated at both terminals of the resistor 15 is input to the maximum value holder (capacitor C1) having arbitrary charging/discharging time constant. The maximum value is compared by a comparator 17 with the prescribed value, and when it exceeds the prescribed value, it is judged as an overload state to apply a signal to a control calculator 16 of the module 13, thereby reducing the rotating speed of the motor 14.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an operation control device for an electric motor, and particularly to a circuit suitable for detecting a load current of an inverter-driven electric motor.

[Background of the invention]

Since the conventional load current detection circuit directly detects the current IR flowing through the freewheeling diode of the lower arm as shown in FIG. 6, the power module requires a terminal for the freewheeling diode.

This will be explained in detail with reference to FIGS. 6 to 10.

In FIG. 6, 101 to 106 are power transistors, which are examples of switching elements.

Diodes 107 to 112 are connected to the power transistor in a forward direction opposite to that of the power transistor as shown in the figure. 1]
3 is a power module composed of power 1 helangisters 101 to 106 and diodes 107 to 112;
114 is a DC motor, which is connected to the power module 113 in three phases as shown. 115 is a current detection element, V
d is a DC power supply, and ■ is a voltage generated by the load current Tm flowing through the current detection element 115. A is the positive side of the DC power supply,
B is the negative side of the DC power supply. FIG. 7 shows the upper power 1 transistors 101 to 103 and the lower power transistor 10.
The combinations 4 to 106 are turned on.

In FIG. 8, the upper row shows the waveform of the direct current Td, the middle row shows the waveform of the circulating current Tr, and the lower row shows the waveform of the load current Im.

Further, t1 is the ON time when the upper power transistor is pulsing, and t is the chopper period.

In FIG. 9, 116 is a microcomputer that controls the rotation speed of the DC motor 114 (hereinafter referred to as microcomputer 116), and 117 is a current detecting element 115 in FIG. This is a comparator that serves to notify the microcomputer 116 that the magnitude of the voltage V exceeds a certain value.

The power transistors 101 to 106 in the 6th H are
Drive circuits (not shown) connected to the respective bases turn on each of the upper and lower power 1 transistors alternately as shown in FIG.

That is, 101 and 105 → 1.01 and 106 → 102 and 106 → 102 and 104 → 103 and 104 →
103 and 105 → 101 and 105, the combinations that are turned ON are changed in sequence, and six currents are supplied to the DC motor number 114.

Considering the state where power 1 - transistors 101 and 105 are ON, the DC current Id is as follows: DC power supply positive side A → power transistor 01 → DC motor 114 → power 1 - transistor 105 → current detection element 115 →
The current flows in the order of the negative side B of the DC power supply.

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, as shown in FIG. 7, the upper power transistor is turned OFF at a chopper cycle that is faster than the switching cycle of the ON combination of power transistors, and the ON time, that is, as shown in FIG. Change ON time t1 by 5. This controls the average voltage applied to the DC motor 114.

Therefore, the waveform of the DC current Id described above becomes an intermittent waveform as shown in FIG.

Next, in FIG. 6, the power transistor 105 is turned on,
Considering the OFF state when the power transistor 101 is in the OFF state, the freewheeling current Ir is as follows: DC motor 114 → power transistor 105 → current detection element 115 → freewheeling diode 110 → DC motor 1
It flows in the order of 14.

The waveform of the circulating current Tr at this time becomes a waveform that fills the gap between ○N times t1 and 11 of the DC current Id as shown in the middle part of FIG.

In this way, the DC current ■d and the circulating current Ir alternately flow through the current detection element 115, and eventually the load current Tm shown in the lower part of FIG. 8 flows. This load current Im is proportional to the current flowing through the DC motor 114, and the current detection element 115
Accordingly, the current flowing through the DC motor 114 can be accurately detected.

The motor current I
A voltage V proportional to m is generated.

Also, in FIG. 9, the voltage V is smoothed by an integrating circuit consisting of a resistor and a capacitor, becomes a voltage proportional to the average value of the load current Im, and is input to the negative input terminal of the comparator 1.17. Ru. On the other hand, comparator 1
The positive input terminal 17 is fixed at a certain potential by resistors R102 to R105. As a result, the load current m
When a certain value is exceeded, the output of the comparator 117 is inverted (in this case Hi-)Lo), and this signal is sent to the microcomputer 116.
It is input to the ○VL terminal of
operates in the direction of lowering the rotation speed. However, in such a conventional system, the power module 113 has one emitter terminal connected to each emitter of the power transistors 104, 105, and 106, and free-wheeling diodes 110, 111,
It is necessary to provide an anode terminal connected to each of the 112 anodes.

However, in general commercially available power modules, each emitter and each anode are connected internally, and only one terminal is provided.

For this reason, there was a disadvantage that a custom-made power module had to be used.

Next, an example of operation will be explained with reference to FIG. In FIG. 10, a and b are voltage waveforms induced in the current detection element 115 by the load current Tm in FIG. C is a voltage whose voltage waveforms a and b are smoothed by the resistor RIOI and capacitor clo in FIG. 9, and is input to the negative terminal of the comparator 117 in FIG. d is the maximum allowable voltage value that can flow through the power module.

The voltage waveform a has a small amount of ripple, and the voltage waveform a has a large amount of ripple, and in both cases, the average value voltage C is input to the comparator 117. But the maximum value of voltage,
That is, when comparing the maximum value of the load current and the maximum allowable current value d, in the voltage waveform a with few ripples, the difference from the maximum allowable current value d is as large as Sl, and in the voltage waveform with many ripples, the difference is S2. becomes smaller. In this method of detecting the average value of the load current, the difference from the maximum allowable current value d varies depending on the amount of current ripple, so the comparator 117
It was necessary to keep the detection level low considering the case where there are many current ripples. As a result, it is forced to operate at a low current even when the current ripple is small. Therefore, the ability of the electric motor could not be fully demonstrated.

[Purpose of the invention]

An object of the present invention is to provide a slave device for controlling the operation of an electric motor that is capable of detecting load current and does not require a freewheeling diode terminal in a power module.

[Summary of the invention]

Even if there is no circulating current, the maximum value of the load current flows through the detection element, so if this maximum value is held and used, it is possible to sufficiently achieve the purpose.

For this reason, the present invention provides a power module comprising a plurality of upper and lower switching elements that switch the drive current flowing through the motor, and a diode that maintains the current flow when one side of the switching elements is all turned off. and an arithmetic circuit that controls the rotational speed of the motor by controlling the upper and lower switching elements of the power module in ON-OFF state via a drive circuit. A current detection element inserted between the two, a maximum value holding circuit that can hold the maximum value of the voltage across the current detection element with an arbitrary charge/discharge time constant, and an overload operation when this maximum value exceeds a certain value. the output of the comparison circuit is connected to the input terminal of the arithmetic circuit, and when the overload operating state is input to the input terminal of the arithmetic circuit, the rotation speed of the motor is reduced. It was used as an operation control device for electric motors.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 to 5.

FIG. 1 shows a circuit using a power module that is generally available on the market. Reference numerals 1 to 6 are power 1 helangisters, and 7 to 12 are diodes, which are connected as shown. 13 is a power module composed of power 1-ranjistat-6 and diodes 7-12;
14 is an electric motor, which is connected to the power module 13 as shown in the figure.
The sum is connected. Reference numeral 15 denotes a current detection element, which uses a resistor in the embodiment. Vd is a DC voltage, and ■ is a voltage generated by the DC current Td flowing through the current detection element I5.

Figure 2 shows the load current detection circuit that forms the core of the present invention.
Reference numeral 6 indicates a microcomputer (hereinafter referred to as a microcomputer) equipped with an arithmetic circuit serving as a central part in controlling the rotational speed of the DC motor 14, and 17 indicates the magnitude of the voltage V generated in the current detection element 15 in FIG. This is a comparator that serves to notify the microcomputer 16 that the value exceeds a certain value.

FIG. 3 shows the voltage waveform at V in FIG.

In FIG. 4, the solid line is the voltage waveform input to the negative terminal of the comparator 17 in FIG. 2, the broken line is the waveform of the voltage V shown in FIG. The charging time for charging the capacitor C1 through R1 and t2 represent the discharging time for discharging the shutter C'l through the resistor R2. In reality, since the resistor R2 is made sufficiently large, the voltage waveform is input to the comparator 17 in a nearly straight line as shown by the dashed line in FIG.

FIG. 5 shows the relationship between the detection level of the comparator 17, the maximum allowable current value d of the power module, and the load current.

In FIG. 1, power transistors 1 to 1 to 6 are alternately driven by a drive circuit (not shown) connected to their respective bases to alternately drive one each of the upper and lower power transistors in the same way as in FIG. Turn on.

That is, 1 and 5 → 1 and 6 → 2 and 6 → 2 and 4 are supplied.

Considering the state where power 1 to transistors 1 and 5 are ON, the DC current rd is as follows: DC power supply positive side A → power 1 -
The current flows in the following order: transistor 1 → DC motor 14 → power 1 to transistor 5 → current detection element r-15 → DC power supply negative side B. At this time, a direct current Id flows through the current detection element 15.

In order to convert the rotation speed of the DC motor 14,
It is necessary to change the voltage applied to the DC motor 14. As a means for this purpose, as in FIG.
The N time, that is, the ON time 11 shown in FIG. 8 is changed. This controls the average voltage applied to the DC motor 14.

Next, in FIG. 1, when power transistor 5 is ON and power 1 - transistor 1 is timisoping, O
Considering the state of the FF, the freewheeling current Ir is
4 → Power 1 Helangister 5 → Freewheeling diode 1
The current flows in the order of 0 → DC motor 14. At this time, no circulating current Tr flows through the current detection element I5.

In this manner, in this circuit system, only the DC current ■d flows through the current detection element 15, and the load current Im, which is proportional to the current flowing through the DC motor 14, cannot be directly detected by the current detection element.

In FIG. 2, a voltage V (not shown in FIG. 3) is applied to the anode side of the diode D1, and a current due to the voltage V passes through the diode DI and the resistor R1 to charge the capacitor C1. The charging speed depends on the time constant determined by RI×C1. To increase the detection sensitivity, the time constant may be decreased, and to decrease the detection sensitivity, the time constant may be increased. for example,
When detecting the maximum allowable current value d in Figure 5, it is necessary to increase the detection sensitivity as much as possible, and when suppressing overload operation as in the present invention, it is necessary to prevent malfunctions due to surge current and noise. Therefore, it is advantageous to lower the detection sensitivity slightly.

The current charged in the capacitor CI is discharged through the resistor R2. The discharge rate is influenced by the time constant determined by R2XC1. This discharge time constant also depends on the purpose of use of the circuit, as in the case of the charge time constant described above.
P^^ You can choose freely.

Resistors R3 and R4 are resistors for determining the potential of the positive terminal of the comparator 17, and determine the detection level of the load current.

Resistor R5 is a pull-up resistor, and R6 is a feedback resistor.

The ○vL terminal of the microcomputer 16 inputs the output inversion of the comparator 17 based on load current detection, and changes the ratio of Hi and Lo of the chopper signal output from the CHO terminal (hereinafter referred to as chopper duty) to adjust the rotation speed of the motor 14. It works to maintain the load current at an appropriate value.

According to this detection circuit, the detection level theoretically shows a waveform consisting of charging time t1 and discharging time t2 as shown by the solid line in FIG. 4, but in this embodiment, the discharging time constant is set to an appropriate value of 1 second or less Since the length is set sufficiently long so that the chopper period as shown in FIG. Therefore, the current level detected by the comparator 17 is the average value of the load current in the conventional example, whereas in this embodiment, it is the maximum value of the load current. However, the load current Trn can be detected using the DC current 1d in FIG.

Next, an example of operation will be explained with reference to FIG.

In Figure 5, a is the load current when the ripple is small;
b is the load current when the ripple is large, C is the detection level by the comparator 17, and d is the maximum allowable current value that can flow through the power module.

According to the load current detection circuit according to this embodiment, in order to detect the maximum value of the load current, the detection level C is set at a point obtained by subtracting a constant value S from the maximum allowable current value d, regardless of the magnitude of the current ripple. It can be determined without being influenced by the magnitude of the current ripple. Furthermore, as shown in a, if there are few ripples, the average current can be larger than b, where there are many ripples, so the operating range of the motor 14 can be expanded. Therefore, the ability of the electric motor can be fully demonstrated. Furthermore, the detection level C is set to the maximum allowable value d
By setting the value at a point obtained by subtracting a more constant value S, reliable overload protection can be achieved. In addition, if you want to reduce the base current of the power transistor of the power module, the first
Just make a Darlington connection as shown in Figure 1. Further, when switching a large current using the power transistor 9, if the transistors are connected in parallel as shown in FIG. 12, it is not necessary to use a large capacity and expensive power transistor.

〔Effect of the invention〕

According to the present invention, the load current can be accurately known by holding and detecting the maximum value of the load current.

Therefore, it is possible to provide a motor operation control device that can use a power module that does not have a terminal for detecting circulating current.

[Brief explanation of drawings]

□ Figure 1 shows the motor drive circuit of the present invention, Figure 2 shows the load current detection circuit of the present invention, Figure 3 shows the waveform of the voltage V in Figure 2, and Figure 4 shows the negative terminal of the comparator in Figure 2. 5 shows a comparison of current levels in the present invention, FIG. 6 shows a conventional motor drive circuit using an inverter, and FIG. 7 shows a comparison of current levels in the present invention. Figure 8 showing the ON state of the side and lower side power transistors.
The figure shows the current waveforms of each part of Fig. 6, Fig. 9 shows the conventional load current detection circuit, Fig. 10 shows a comparison of the conventional current levels, and Fig. 11 shows the power transistor in place of the power transistor in Fig. 1. 12 shows a side port in which the power transistors shown in FIG. 1 are connected in parallel. 1... Power 1 ~ transistor, 7... Freewheeling diode,
13... Power module, 14... DC motor,
15... Current detection resistor, 16... Microcomputer, 17.
··comparator. Representative Patent Attorney Katsuo Ogawa '-7 No. 1 #2

Claims (1)

[Claims] A power module consisting of a plurality of upper and lower switching elements that switch the drive current flowing to the motor and a diode that maintains the current flow when one side of the switching elements are all turned off; and the upper and lower switching elements of the power module. O through the element drive circuit
A motor operation control device including an arithmetic circuit that controls the rotation speed of the motor through N/OFF control, comprising: a current detection element inserted between a DC power source and a power module;
A maximum value holding circuit that can hold the maximum value of the voltage across the current detection element with an arbitrary charging/discharging time constant, and a comparison circuit that determines that the maximum value exceeds a certain value and is in an overload operation state. An operation control device for an electric motor, characterized in that the output of the comparison circuit is connected to an input terminal of the arithmetic circuit, and the rotation speed of the motor is lowered when an overload operating state is input to the input terminal of the arithmetic circuit.