JPH11316249A - Current detecting circuit and excess current protecting circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current detecting circuit for detecting forward currents and backward currents inputted to an inverter circuit by using a single power supply voltage, and to provide an excess current protecting circuit using the current detecting circuit. SOLUTION: In the driving device of a brushless motor 42 in which a double voltage rectifier circuit 22 is combined with an inverter circuit 25, a serial circuit constituted of resistances 46 and 47 for detecting currents is inserted into a negative side current power line 24, and a voltage Va generated in the resistance 46 by forward currents is detected by a first detecting circuit 48, and a voltage Vb generated in the resistance 47 by backward currents is detected by a second detecting circuit 49 with the common connection of those resistances 46 and 47 as a reference potential (ground terminal). Those voltages Va and Vb are compared with reference voltages V3 and V4 by single voltage driving comparators 50 and 58, and a forward excess current signal Sa and a backward excess current signal Sb are obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current detection circuit for detecting a current flowing in a DC power supply line connecting a DC power supply and an inverter circuit, and an overcurrent protection circuit using the same.

[0002]

A conventional configuration of this type of current detection circuit will be described with reference to FIG. A three-phase inverter circuit 2 that outputs an AC voltage to the stator windings 1 u, 1 v, and 1 w of the brushless motor 1 includes a DC power supply 5 through a positive DC power supply line 3 and a negative DC power supply line 4.
, And a current detecting resistor 6 is inserted into the negative DC power supply line 4.

The current detecting circuit 7 comprises a current detecting resistor 6, comparators 8 and 9, and resistors 10 to 13. The common connection point between the negative terminal of the DC power supply 5 and the resistor 6 is ground. Set as a terminal. The comparator 8 is supplied with a power supply voltage of +5 [V], and the comparator 9 is supplied with a power supply voltage of -5 [V].

The common connection point between the resistor 6 and the negative input terminal of the inverter circuit 2 is connected to the non-inverting input terminals of the comparators 8 and 9. The inverting input terminal of the comparator 8 has a power supply voltage of +
A reference voltage V1 (> 0) generated by dividing 5 [V] by the resistors 10 and 11 is provided, and the inverting input terminal of the comparator 9 is supplied with a power supply voltage according to the reverse overcurrent threshold. A reference voltage V2 (<0) generated by dividing a certain -5 [V] by the resistors 12 and 13 is given. The output signal of the comparator 8 is used for overcurrent protection against a forward current, and the output signal of the comparator 9 is
Used for overcurrent protection against reverse current.

In the current detection circuit 7 having the above-described configuration, the comparator 8 operates between the two terminals of the resistor 6 by a forward current flowing from the negative input terminal of the inverter circuit 2 to the negative terminal of the DC power supply 5 through the DC power supply line 4. Is compared with the reference voltage V1. The comparator 9
Compares the reference voltage V2 with a reverse voltage generated between both terminals of the resistor 6 by a reverse current flowing from the negative terminal of the DC power supply 5 to the negative input terminal of the inverter circuit 2 through the DC power supply line 4. I do.

Therefore, the brushless motor 1 loses synchronism or the stator windings 1u, 1v, 1w of the brushless motor 1
Is short-circuited, the inverter circuit 2 can be stopped by obtaining an overcurrent flowing in the forward direction as an output signal of the comparator 8. Similarly, when the induced voltage of the brushless motor 1 is higher than the output voltage of the inverter circuit 2, the inverter circuit 2 is controlled by obtaining an overcurrent flowing in the reverse direction as a regenerative current as an output signal of the comparator 9. Therefore, the reverse current can be reduced.

However, in the above-described conventional configuration, a positive voltage generated between both terminals of the resistor 6 is applied to the non-inverting input terminals of the comparators 8 and 9 for a forward current, and is applied to a non-inverting input terminal for a reverse current. Since a negative voltage generated between both terminals of the resistor 6 is applied, a positive power supply voltage is required for the comparator 8 for detecting a forward overcurrent, and a comparator 9 for detecting a reverse overcurrent. Required a negative power supply voltage.

As described above, conventionally, in the current detection circuit 7 for detecting currents in the forward and reverse directions, a power supply having two positive and negative voltages is required. There is a problem that the size of the board to be mounted is increased and the efficiency of the entire system is reduced due to the loss of the power supply itself.

The present invention has been made in view of the above circumstances, and an object of the present invention is to detect a forward current and a reverse current input to an inverter circuit using a single power supply voltage. It is an object of the present invention to provide a current detection circuit that can be used and an overcurrent protection circuit using the current detection circuit.

[0010]

In order to achieve the above object, a current detecting circuit according to the present invention is connected to a DC power supply line connecting a DC power supply and an inverter circuit, and includes a first resistor and a first resistor. A series circuit composed of a second resistor and a common connection point between the first resistor and the second resistor are used as a reference potential, and a predetermined unidirectional current flowing through the DC power supply line is supplied to the first resistor. A first detection circuit for detecting as a generated voltage; and a current flowing in the DC power supply line in a direction opposite to the predetermined direction as a voltage generated in the second resistor. A second detection circuit; and a detection circuit power supply having a single voltage for operating the first detection circuit and the second detection circuit, using the common connection point as a reference potential.

With this configuration, the voltage generated in the first resistor by a predetermined one-way current flowing through the DC power supply line is set with the common connection point of the first resistor and the second resistor as a reference potential. Have the same polarity as the voltage generated in the second resistor by the reverse current flowing through the DC power supply line. Therefore, by providing a power supply for a detection circuit having a single voltage of that polarity, it is possible to detect currents in both forward and reverse currents.

In this case, as in the current detection circuit according to the second aspect, the first detection circuit includes a first reference voltage generated based on a voltage generated at the first resistor and a power supply for the detection circuit. And a first comparator for comparing
Is preferably configured to include a second comparator for comparing a voltage generated in a second resistor with a second reference voltage generated based on the detection circuit power supply.

[0013] With this configuration, the first comparator includes the first comparator.
, Ie, a predetermined one-way current value flowing through the DC power supply line, and a first reference voltage, that is, a reference current value, and outputs a comparison signal based on the magnitude of both. Similarly, the second comparator compares the voltage generated in the second resistor, that is, the value of the reverse current flowing in the DC power supply line, with the second reference voltage, that is, the reference current value. And outputting a comparison signal based on the comparison signal.

According to another aspect of the present invention, the first detection circuit detects a voltage generated in the first resistor by a current flowing in the DC power supply line in a direction opposite to a predetermined direction. A first limit circuit for limiting, and a second detection circuit includes a second limit circuit for limiting a voltage generated in a second resistor by the current in the predetermined direction flowing through the DC power supply line. Preferably, it is provided.

According to this structure, the first limit circuit generates a voltage generated in the first resistor by a current flowing in the DC power supply line in a direction opposite to a predetermined direction (a polarity opposite to the power supply voltage for the detection circuit). Is applied to the first detection circuit (first comparator). Similarly, in the second limit circuit, a voltage (a polarity opposite to the detection circuit power supply voltage) generated in the second resistor due to a predetermined one-way current flowing through the DC power supply line is
It is prevented from being applied to the second detection circuit (second comparator).

Further, an overcurrent protection circuit according to a fourth aspect includes the current detection circuit according to any one of the first to third aspects, and an excessive current flowing in one direction and the opposite direction of the DC power supply line. To protect the DC power supply, the inverter circuit, and the load of the inverter circuit.
With this configuration, the DC power supply, the inverter circuit, and the load of the inverter circuit can be protected against a bidirectional overcurrent flowing through the DC power supply line using the detection circuit power supply having a single voltage.

[0017]

(First Embodiment) A first embodiment of the present invention will be described below with reference to FIG.

FIG. 1 shows an electric configuration of a motor driving device using an overcurrent protection circuit.
An AC power supply 21 having a voltage of [V] is connected to an input terminal of the voltage doubler rectifier circuit 22 and outputs a positive DC power supply line 23 and a negative DC power supply line 24 as output lines of the voltage doubler rectifier circuit 22.
Are connected to the positive input terminal and the negative input terminal of the inverter circuit 25, respectively.

The voltage doubler rectifier circuit 22 functions as a DC power supply together with the AC power supply 21.
And 24, rectifying diodes 26 and 27 connected in series with the polarity shown in the figure, and smoothing capacitors 28 and 29 connected in series between the DC power supply lines 23 and 24. The common connection point of the diodes 26 and 27 and the common connection point of the capacitors 28 and 29 are input terminals for the AC power supply 21.

The inverter circuit 25 is constructed by connecting a switching element, for example, transistors 30 to 35, and a free wheel diode 36 to 41 in a three-phase bridge connection, and has a three-phase motor, for example, a brushless motor as a load at its output terminal. Stator windings 42u, 42 of motor 42
v and 42w are connected. This brushless motor 4
2 has a rotor (not shown) provided with a permanent magnet.

The position detecting circuit 43 includes a stator winding 42u,
The terminal voltages Vu, Vv, Vw of the respective 42v, 42w are input, and the position signals Hu, Hv, Hw indicating the rotational position of the rotor are detected based on the induced voltage of the brushless motor 42.

A control circuit 44 as a control means controls the commutation of the inverter circuit 25 so that the brushless motor 42 is driven to rotate in accordance with a speed command, and is constituted mainly by a microcomputer, for example. The control circuit 44 receives an external speed command value ωr *, position signals Hu, Hv, and Hw from the position detection circuit 43, and a forward overcurrent signal Sa and a reverse overcurrent signal Sb, which will be described later. Each transistor 3 constituting the circuit 25
The commutation signals Sup, Svp, Swp, Sun,
Svn and Swn are output. Control circuit 44
Is a PI for generating a voltage command value required for speed control.
The control circuit includes a control circuit, a commutation control circuit for controlling an output voltage of the inverter circuit 25, a commutation signal cutoff circuit as an overcurrent protection circuit, and the like (none is shown).

The current detection circuit 45 constitutes an overcurrent protection circuit together with the commutation signal cutoff circuit of the control circuit 44, and is configured as follows. That is, the first resistor 46 for current detection and the second
And the resistor 47 are inserted in series. A common connection point (node c) between the resistors 46 and 47 is used as a ground terminal, and a first detection circuit 48 and a second detection circuit 49 that operate with a single-voltage, for example, 5 [V] detection circuit power supply are provided. Is provided.

The first detection circuit 48 is configured as follows. The non-inverting input terminal of the 5 [V] -driven comparator 50 as the first comparator is connected to the node a via the resistor 51, and the inverting input terminal is connected to the power supply terminal Vcc of the detection circuit power supply and the ground. It is connected to a common connection point of voltage dividing resistors 52 and 53 connected in series between the terminals. The anode of the diode 54 and the diode 55
Are connected to the power supply terminal Vcc via the resistor 56, and the cathode of the diode 54 and the cathode of the diode 55 are connected to the ground terminal and the non-inverting input terminal of the comparator 50, respectively. . Here, the resistors 51 and 56 and the diode 54,
55 constitutes a first limit circuit 57.

Similarly, the second detection circuit 49 is configured as follows. The non-inverting input terminal of a 5 [V] -driven comparator 58 as a second comparator is connected to the node b via a resistor 59, and the inverting input terminal is connected in series between the power supply terminal Vcc and the ground terminal. It is connected to a common connection point between the connected voltage dividing resistors 60 and 61. Also,
The anode of the diode 62 and the anode of the diode 63 are connected in common, connected to the power supply terminal Vcc via the resistor 64, and the cathode of the diode 62 and the cathode of the diode 63 are connected to the ground terminal and the non-inverting terminal of the comparator 58, respectively. Connected to input terminal.
Here, the resistors 59 and 64 and the diodes 62 and 63 form a second limit circuit 65.

Next, the operation of the present embodiment will be described. When the brushless motor 42 is driven to rotate, the position detection circuit 43 outputs position signals Hu, Hv, and Hw having a phase difference of 120 [deg] and a duty of 50%. In the control circuit 44, first, the position signal H
The rotational speed ωr is calculated based on u, Hv, and Hw, and the speed deviation between the externally applied speed command value ωr * and the detected speed detected value ωr is calculated.
It is input to the I control circuit to generate a voltage command value.

The commutation control circuit of the control circuit 44 synchronizes with the position signals Hu, Hv, Hw to generate commutation signals Sup, Svp, Swp, Sun, Svn,
Swn is generated. Of these, the commutation signals Sup, Svp, Swp for the upper arm transistors 30, 31, 32 of the inverter circuit 25 are on / off controlled at the carrier frequency during the 120 [deg] energizing period, and the duty ratio is the voltage. It is controlled to increase in proportion to the command value. The commutation signals Sup to Swn are output from the inverter circuit 2
5, the inverter circuit 25 outputs an AC voltage equal to the voltage command value, and the brushless motor 42 is rotationally driven to follow the speed command value ωr *. .

In such a steady operation state, the brushless DC power supply line 24 is connected in a brushless direction from the negative input terminal of the inverter circuit 25 to the negative output terminal of the voltage doubler rectifier circuit 22 (forward direction). A direct current Idc (forward current) having a magnitude corresponding to the load torque of the motor 42 flows. The DC current Idc causes a voltage drop in the resistors 46 and 47. That is, with the potential of the node c (ground terminal) as a reference (0 [V]), a positive voltage Va proportional to the DC current Idc is generated at the node a, and the DC current Idc is generated at the node b.
, A negative voltage Vb is generated.

The voltage Va is applied to the non-inverting input terminal of the comparator 50 via the resistor 51.
A reference voltage V3 generated from the resistors 52 and 53 based on the power supply for the detection circuit is applied to the inverting input terminal. This reference voltage V3 is a current larger than the DC current Idc flowing when the brushless motor 42 is driven at the maximum rotational speed while giving the maximum load torque, that is, the brushless motor 42
Is set as a voltage corresponding to the current flowing only when the stator windings 42u, 42v, and 42w short-circuit or step out.

The comparator 50 outputs a high-level (5 [V]) forward overcurrent signal Sa when the voltage applied to the non-inverting input terminal is higher than the voltage applied to the inverting input terminal. When the voltage applied to the non-inverting input terminal is smaller than the voltage applied to the inverting input terminal, a low-level (0 [V]) forward overcurrent signal Sa is output. Note that the first limit circuit 57
Since the input voltage Va is positive, the diode 54 is on, the diode 55 is off, and the comparator 50
Is applied as it is to the non-inverting input terminal.

Accordingly, the first detection circuit 48 outputs a high-level forward overcurrent signal Sa when a forward overcurrent occurs, and outputs a low-level forward overcurrent signal Sa at other times. The control circuit 44 always receives the forward overcurrent signal Sa from the current detection circuit 45, and outputs the forward overcurrent signal Sa.
Becomes high level, the commutation signals Sup to Swn are turned off by the commutation signal cutoff circuit, and the voltage doubler rectifier circuit 22, the inverter circuit 25, and the brushless motor 42 are protected from overcurrent.

The negative voltage Vb is applied to the input of the second detection circuit 49. However, in the second limit circuit 65, both the diodes 62 and 63 are turned on. The potential of the terminal is limited to approximately 0 [V], and the comparator 58 is protected from the negative input voltage Vb.

On the other hand, if the frequency of the inverter circuit 25 is reduced stepwise or the load torque of the brushless motor 42 is reduced stepwise during steady operation, the output voltage of the inverter circuit 25 is reduced. , And a current generated by power generation, that is, a regenerative current flows through the DC power supply lines 23 and 24. This regenerative current flows through the negative DC power line 24
The DC current Idc (reverse current) flows from the negative output terminal of the voltage doubler rectifier circuit 22 to the negative input terminal of the inverter circuit 25 (reverse direction). That is, with reference to the potential of the node c (ground terminal), a negative voltage Va proportional to the DC current Idc is generated at the node a, and a positive voltage Vb proportional to the DC current Idc is generated at the node b.

In this case, the first detection circuit 48 operates similarly to the above-described second detection circuit 49 for the forward current, and the second detection circuit 49 performs the first detection for the above-described forward current. It operates similarly to the circuit 48. A reference voltage V4 corresponding to the protection current value of the reverse current is applied to the inverting input terminal of the comparator 58. As a result, during the regenerative operation, the second detection circuit 49 sets the high level when an overcurrent in the reverse direction exceeding the protection current value occurs,
Otherwise, the low-level reverse overcurrent signal Sb
Is output. The control circuit 44 always receives the reverse direction overcurrent signal Sb from the current detection circuit 45. When the reverse direction overcurrent signal Sb goes to a high level, the commutation signals Sup to Swn are turned off by the commutation signal cutoff circuit. Thus, the voltage doubler rectifier circuit 22, the inverter circuit 25, and the brushless motor 42 are protected from overcurrent in the reverse direction.

As described above, according to the present embodiment, in the driving device of the brushless motor 42 in which the voltage doubler rectifier circuit 22 and the inverter circuit 25 are combined, the current detecting resistor 46 is connected to the negative DC power supply line 24. A first detection circuit 48 for detecting a forward overcurrent and a reverse overcurrent are detected by inserting a series circuit with a 47 and using a common connection point of the resistors 46 and 47 as a reference potential (ground terminal). A feature is that a current detection circuit 45 including the second detection circuit 49 is provided.

If an overcurrent protection circuit is formed by using the current detection circuit 45, one overcurrent protection circuit having a single voltage (5 [V]) can be used.
By using only one power supply, it is possible to detect both forward current and reverse current flowing in the DC power supply line 24. As a result, the cost of the power supply can be reduced and the size of the substrate on which the power supply is mounted can be reduced as compared with a conventional circuit using a positive power supply and a negative power supply. Further, since the number of power supplies can be reduced, the efficiency of the entire driving device can be improved.

Further, the first and second detection circuits 48,
The first and second limit circuits 5 are connected to the input section 49 respectively.
7 and 65, the negative voltage outside the power supply voltage range is applied to the inputs of the comparators 50 and 58 constituting the first and second detection circuits 48 and 49 for both forward and reverse currents. Is not applied, and the comparator 50,
58 can be protected. Note that when the voltage Va due to the forward current or the voltage Vb due to the reverse current exceeds the power supply voltage (5 [V]), the first and second voltages are used.
In addition to the limit circuits 57, 65, the comparator 50,
What is necessary is just to provide the limit circuit which limits the input voltage of 58 to below the power supply voltage.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG. 2 with respect to portions different from the first embodiment.

The current detecting circuit 66 includes a resistor 4 for detecting a current.
With the common connection point (node c) between 6 and 47 as the reference potential,
First detection circuit 67 to which voltage Va of node a is input
And the second detection circuit 6 to which the voltage Vb of the node b is input
And 8. These first and second detection circuits 67 and 68 are operated by a detection circuit power supply of a single voltage, for example, 5 [V] with the node c as a ground terminal.
Then, the first detection circuit 67 includes an amplifier, for example, 5 [V].
Driving operational amplifier 69 and first limit circuit 5 described above
The operational amplifier 69 has an inverting input terminal and an output terminal connected thereto. Similarly, the second detection circuit 68 includes an amplifier, for example, an operational amplifier 70 driven by 5 [V].
The operational amplifier 70 has an inverting input terminal and an output terminal connected to each other.

According to the above configuration, the first detection circuit 67
Is a resistance 46 due to a forward current flowing through the DC power supply line 24.
, And outputs the voltage Va (> 0) to the control circuit 44 while maintaining the voltage Va. Similarly, the second detection circuit 68 detects a voltage Vb generated across the resistor 47 by a reverse current flowing through the DC power supply line 24.
(> 0), and outputs the voltage Vb to the control circuit 44.

Therefore, according to the present embodiment, both the forward current and the reverse current flowing through the DC power supply line 24 are detected by using only one power supply having a single voltage (5 [V]). And the same effects as in the first embodiment can be obtained.

(Other Embodiments) The present invention is not limited to the embodiment described above and shown in the drawings.
For example, the configuration may be as follows.

The devices connected to the inverter circuit 25 are:
The motor is not limited to the brushless motor 42, but may be another type of motor such as an induction motor or a synchronous machine, or an induction coil. The current detection resistors 46 and 47 of the current detection circuits 45 and 66 may be inserted into the DC power supply line 23 on the positive side.

The first limit circuit 57 provides another limit as long as the input voltage of the comparator 50 or the operational amplifier 69 is limited to about 0 [V] or more with respect to the negative input voltage Va due to the reverse current. It may be a circuit. Similarly, the second limit circuit 65 sets another limit as long as the input voltage of the comparator 58 or the operational amplifier 70 is limited to substantially 0 [V] or more with respect to the negative input voltage Vb due to the forward current. It may be a circuit.

[0045]

According to the current detection circuit of the present invention, a series circuit consisting of a first resistor and a second resistor is inserted into a DC power supply line connecting a DC power supply and an inverter circuit, and the first resistor and the second resistor are connected to each other. A first detection circuit for detecting a current flowing in the DC power supply line in a predetermined direction as a voltage generated in the first resistance, using a common connection point with the second resistor as a reference potential, and a reverse current flowing in the DC power supply line As a voltage generated in the second resistor. According to this current detection circuit, using one detection circuit power supply having a single voltage,
It is possible to detect current flowing in both directions in the DC power supply line. Therefore, the cost of the power supply can be reduced, the size of the substrate on which the power supply is mounted can be reduced, and the loss occurring inside the power supply can be reduced as compared with the conventional configuration using the positive and negative power supplies.

Further, the first detection circuit includes a first limit circuit for limiting a voltage generated at the first resistor by a current flowing in the DC power supply line in a direction opposite to a predetermined direction,
The second detection circuit includes a second detection circuit configured to limit a voltage generated at the second resistor by a current flowing in the DC power supply line in a predetermined direction.
Of limit circuit. Therefore, it is possible to prevent the input voltage exceeding the power supply voltage range from being applied to the first and second detection circuits.

Further, according to the overcurrent protection circuit of the present invention constituted by using the above-described current detection circuit, the overcurrent in both directions flowing through the DC power supply line can be controlled by using the detection circuit power supply having a single voltage. The DC power supply, the inverter circuit, and the load of the inverter circuit can be protected.

[Brief description of the drawings]

FIG. 1 is an electric configuration diagram of a motor drive device using an overcurrent protection circuit according to a first embodiment of the present invention;

FIG. 2 is an electrical configuration diagram of a current detection circuit according to a second embodiment of the present invention;

FIG. 3 is a diagram corresponding to FIG. 1 in a conventional configuration.

[Explanation of symbols]

22 is a voltage doubler rectifier circuit (DC power supply), 23 and 24 are DC power supply lines, 25 is an inverter circuit, 42 is a brushless motor (load), 44 is a control circuit (overcurrent protection circuit), 45
Is a current detection circuit (overcurrent protection circuit), 46 is a first resistor, 47 is a second resistor, 48 and 67 are first detection circuits,
49 and 68 are second detection circuits, 50 is a comparator (first comparator), 57 is a first limit circuit, 58 is a comparator (second comparator), 65 is a second limit circuit, 66 is It is a current detection circuit.

Claims (4)

[Claims] 1. A series circuit comprising a first resistor and a second resistor inserted into a DC power supply line connecting a DC power supply and an inverter circuit, and a common connection between the first resistor and the second resistor. A first detection circuit for setting a point as a reference potential and detecting a predetermined one-way current flowing through the DC power supply line as a voltage generated in the first resistor; A second detection circuit for detecting a current flowing in a line in a direction opposite to the predetermined direction as a voltage generated in the second resistor; a common connection point serving as a reference potential; 2. A current detection circuit, comprising: a detection circuit power supply having a single voltage for operating the two detection circuits. 2. The first detection circuit includes a first comparator for comparing a voltage generated at a first resistor with a first reference voltage generated based on a detection circuit power supply. The second detection circuit is configured to include a second comparator that compares a voltage generated at a second resistor with a second reference voltage generated based on the detection circuit power supply. The current detection circuit according to claim 1, wherein 3. A first detection circuit comprising: a first limit circuit for limiting a voltage generated at a first resistor by a current flowing in a DC power supply line in a direction opposite to a predetermined one direction; 3. The detection circuit according to claim 1, further comprising a second limit circuit configured to limit a voltage generated at a second resistor by the current flowing in the DC power supply line in the predetermined direction. 4. Current detection circuit. 4. A DC power supply, an inverter circuit, and a load of the inverter circuit for an excessive current flowing in one direction and a reverse direction of the DC power supply line, comprising the current detection circuit according to claim 1. An overcurrent protection circuit characterized by protecting the circuit.