JPH1070897A - Control circuit for direct-current motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the over-rotation and the generation of overvoltage, even if a motor is rotated by external force when power supply is interrupted. SOLUTION: A control circuit is provided with protective circuit 10, 20. The control circuit controls the forward and backward rotation of a direct- current permanent motor PM through a H-type bridge circuit, wherein a switching element TR1-TR4 is contained each arm. If the motor PM is rotated, for example, forward by external force, and the potential at point P2 is increased when a relay RY is opened and a main circuit is interrupted, a Zenar diode Z2 in the protective circuit 20 breaks down to make current flow through resistors R3, R4. For the reason, voltage drop produced in the resistor R4 is inputted to the switching terminal on the switching element TR4, which is then brought into conduction. As a result, current flows from the motor PM through the switching element TR4. This prevents overvoltage from being applied to the elements and produces electrical braking force in the motor PM.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control circuit for a DC motor, and more particularly to a control circuit for controlling the induced voltage of a DC motor below a certain value even when the motor is rotated by an external force when the main circuit is cut off and the motor is over-rotated. , And over-rotation can be automatically braked automatically. The present invention is particularly effective when applied to a permanent magnet type DC motor (hereinafter abbreviated as “DC permanent motor”).

[0002]

2. Description of the Related Art A control circuit as shown in FIG. 5 is generally used as a control circuit for controlling a DC permanent motor to rotate forward and reverse. That is, the control circuit is configured to control the DC permanent motor PM to rotate in the forward and reverse directions using a so-called H-bridge circuit. The H-type bridge circuit connects the first series circuit α and the second series circuit β in parallel to a battery B (for example, a battery having a voltage of 24 V) as a DC power supply, and A DC permanent motor PM is connected between P1 and a point P2 of the series circuit β.

The first series circuit α includes a switching element T
A first upper arm composed of R1 and a flywheel diode D1 connected in anti-parallel to this, and a switching element TR2 and a first lower arm composed of a flywheel diode D2 connected in anti-parallel to this. It is configured by connecting in series. The point P1 is a connection point between the first upper arm and the first lower arm. The second series circuit β is
A second upper arm including a switching element TR3 and a flywheel diode D3 connected in anti-parallel thereto, and a second lower arm including a switching element TR4 and a flywheel diode D4 connected in anti-parallel to the switching element TR4 Are connected in series. The point P2 is
A connection point between the second upper arm and the second lower arm.

The above switching elements TR1, TR2, T
Transistors, FETs, IGBs are used as R3 and TR4.
Various switching elements such as T are employed (in the circuit of FIG. 5, FETs are employed as the switching elements).

In FIG. 5, a capacitor C is a capacitor for absorbing a surge generated when the switching elements TR1, TR2, TR3 and TR4 perform a switching operation. The relay RY is interposed between the battery B and the bridge circuit, and is opened when not operating or in an emergency to cut off the main circuit.

The DC permanent motor PM rotates forward when current flows from point P1 to point P2,
When the current flows from point P2 toward point P1, the motor rotates reversely.

In the control circuit having the above configuration, when the DC permanent motor PM is rotated forward, the relay RY is turned on to make the switching elements TR1 and TR4 conductive and to switch the switching element T1.
R3 and the switching element TR2 are turned off. In this way, a current flows from point P1 toward point P2, and DC permanent motor PM rotates forward.

When the DC permanent motor PM is rotated in the reverse direction, the relay RY is turned on to make the switching elements TR3 and TR2 conductive and to switch off the switching elements TR1 and TR4. In this way, current flows from point P2 toward point P1, and DC permanent motor PM rotates in the reverse direction.

[0009]

In the control circuit having the above structure, when the motor is rotated by an external force when the main circuit is shut off by opening the relay RY in an emergency or the like, the number of rotations is reduced. If the motor terminal voltage (induced voltage) rises due to excessive rise or excessive rotation, the following problems occur.

That is, in the control circuit having the above configuration, the main circuit may be shut off by opening the relay RY in an emergency or the like. For example, the relay RY is opened when a circuit or system for generating a command for rotating the DC permanent motor PM is down. More specifically, the control of a hoist motor such as a medical hoist,
In the control circuit shown in FIG. 5, when the hoist cannot be lowered by an electric command due to a circuit failure or the like, the mechanical brake is manually released, and the relay RY is manually operated for safety. To shut off the main circuit. After this, the hoist is manually lowered.

When the hoist is manually lowered in this way, the DC permanent motor PM is rotated by an externally applied rotational force and functions as a generator. At this time,
Since the switching elements TR1 to TR4 are in the off state, the terminal of the DC permanent motor PM is in an open state, and the terminal between the terminals of the DC permanent motor PM is proportional to the motor speed as shown in the following equation. A voltage (induced voltage) _Eo is generated. _{E o = K a · Φ o} · ω m However K _a: induced voltage coefficient Φ _o: magnetic flux ω _m: rotational speed

[0012] For example, if the rating of the DC permanent motor PM were DC24 [V], when rotating at nominal speed, the terminal voltage E _o is DC24 [V], and the the rotational speed is equal to or greater than rated speed, terminal The voltage _Eo further increases beyond 24 [V] (the voltage increases in proportion to the rotation speed).

(1) After all, when the hoist is manually lowered, the terminals of the DC permanent motor PM are in an open state, so that no electric braking occurs and only the mechanical resistance of gears and the like is generated. However, only the braking force acts as a braking force, so that the rotation speed is excessively increased, and the speed at the time of manual lowering is increased, which is dangerous.

[0014] (2) When the rotational speed in the manner described above becomes too high, the terminal voltage E _o is high, may exceed the withstand voltage of the switching element TR1～TR, there may become element destruction . Switching elements TR1 to TR
The like 4, there is a demand that want to use those possible low voltage in consideration of the cost reduction, also, since the switching element of large current is generally low withstand voltage, because such a problem occurs when the terminal voltage E _o becomes high is there.

The present invention has been made in view of the above-mentioned prior art, in that when a relay is opened to disconnect a power supply and a bridge circuit and a main circuit is disconnected, a DC motor is rotated by an external force to function as a generator. The present invention provides a control circuit for a DC motor in which a terminal voltage (induced voltage) is suppressed to a certain value or less and an electrical braking is generated to prevent the DC motor from over-rotating in the event that the DC voltage becomes excessive. And

[0016]

According to a first aspect of the present invention, there is provided a first series circuit comprising a first upper arm including a switching element and a first lower arm including a switching element connected in series. Circuit and a second element including a switching element
A second series circuit formed by serially connecting an upper arm and a second lower arm including a switching element are connected in parallel to a DC power supply via a relay, and a first upper arm and a first lower arm are connected. In a control circuit of a DC motor connecting a DC motor between a connection point of the DC motor and a connection point of a second upper arm and a second lower arm, an anode is connected to one terminal of the DC motor. A diode, a Zener diode connected to the one terminal in a reverse blocking state via the diode, a resistor that causes a current flowing when the Zener diode breaks down to flow to the ground potential line, and a resistor generated in the resistor. A drive line for inputting the reduced resistance voltage to a switching terminal of a predetermined switching element among the switching elements to make the switching element conductive. Characterized by comprising a protection circuit consisting of.

Further, the configuration of the present invention is characterized in that the DC motor is a permanent magnet DC motor.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows a control circuit of a DC motor according to an embodiment of the present invention. The control circuit according to the present embodiment controls a motor for hoisting a medical hoist (DC permanent motor PM), and has a control circuit configuration for controlling the DC permanent motor PM to rotate forward and reverse by a so-called H-shaped bridge circuit. . The H-type bridge circuit connects the first series circuit α and the second series circuit β in parallel to a battery B (for example, a battery having a voltage of 24 V) as a DC power supply, and P1
And a point P2 of the series circuit β, a DC permanent motor PM is connected.

The first series circuit α includes a switching element T
A first upper arm composed of R1 and a flywheel diode D1 connected in anti-parallel to this, and a switching element TR2 and a first lower arm composed of a flywheel diode D2 connected in anti-parallel to this. It is configured by connecting in series. The point P1 is a connection point between the first upper arm and the first lower arm. The second series circuit β is
A second upper arm including a switching element TR3 and a flywheel diode D3 connected in anti-parallel to the switching element TR3, and a second lower arm including a switching element TR4 and a flywheel diode D4 connected in anti-parallel to the switching element TR4. The arm is connected in series. The point P2 is
A connection point between the second upper arm and the second lower arm.

The switching elements TR1, TR2, T
Transistors, FETs, IGBs are used as R3 and TR4.
Various switching elements such as T are employed (in the circuit of FIG. 1, FETs are employed as the switching elements).

In FIG. 1, a capacitor C is a capacitor for absorbing a surge generated when the switching elements TR1, TR2, TR3, and TR4 perform a switching operation. The relay RY is interposed between the battery B and the bridge circuit, and is opened when not operating or in an emergency to cut off the main circuit.

The DC permanent motor PM rotates forward when current flows from point P1 to point P2,
When the current flows from point P2 toward point P1, the motor rotates reversely.

In the control circuit having the above-described structure, when the DC permanent motor PM is rotated forward, the relay RY is turned on to make the switching elements TR1 and TR4 conductive and to switch the switching element T4.
R3 and the switching element TR2 are turned off. In this way, a current flows from point P1 toward point P2, and DC permanent motor PM rotates forward.

When the DC permanent motor PM is rotated in the reverse direction, the relay RY is turned on to turn on the switching elements TR3 and TR2 and to turn off the switching elements TR1 and TR4. In this way, current flows from point P2 toward point P1, and DC permanent motor PM rotates in the reverse direction.

Each switching element TR1, TR
2, TR3 and TR4 perform a switching operation when a gate control signal is input from a gate control circuit (not shown) via terminals t1, t2, t3 and t4 in a power-on state where the relay RY is turned on. do.

Up to this point, the configuration is similar to that of the prior art shown in FIG. Further, in the present embodiment, a first protection circuit 10 and a second protection circuit 20 are added.

The first protection circuit 10 includes a diode D5
, A Zener diode Z1, resistors R1 and R2, and a drive line DL1. Diode D
5, the Zener diode Z1, and the resistors R1 and R2 are connected in series, and the anode of the diode D5 is connected to the point P1.
, And the resistor R2 is connected to the ground potential line. A diode D5 is arranged in the forward direction and a Zener diode Z1 is arranged in the reverse blocking direction with respect to the current flowing from the point P1 toward the protection circuit 10. The drive line DL1 is connected to a resistor R
1, a connection point P3 with R2 and a switching element (FE
T) The gate terminal (switching terminal) of TR2 is connected.

When the relay RY is opened and the voltage of the battery B is not supplied to the bridge circuit, the first protection circuit 10 controls the DC permanent motor P by external force.
When M rotates forward and a positive voltage (positive induced voltage) is generated at point P1, overvoltage damage to switching element TR2 is prevented and DC permanent motor P
An electric brake is generated for the forward rotation of M.

The second protection circuit 20 includes a diode D6
, A Zener diode Z2, resistors R3 and R4, and a drive line DL2. Diode D
6, the Zener diode Z2, and the resistors R3 and R4 are connected in series, and the anode of the diode D6 is connected to the point P2.
, And the resistor R4 is connected to the ground potential line. A diode D6 is arranged in the forward direction and a Zener diode Z2 is arranged in the reverse blocking direction with respect to the current flowing from the point P2 toward the protection circuit 20. The drive line DL2 is connected to a resistor R
3, a connection point P4 with R4 and a switching element (FE
T) The gate terminal (switching terminal) of TR4 is connected.

When the relay RY is opened and the voltage of the battery B is not supplied to the bridge circuit, the second protection circuit 20 activates the DC permanent motor P by an external force.
When M rotates in the reverse direction and a positive voltage (positive induced voltage) is generated at the point P2, the overvoltage of the switching element TR4 is prevented and the DC permanent motor P
An electric brake is generated for the reverse rotation of M.

Here, when the relay RY is opened to shut off the main circuit and the switching elements TR1 to TR4 are turned off, the protection operation when the hoist is manually lowered is shown in FIG. 1 and FIG. This will be described with reference to FIG. 3 which is a flow chart showing the generation state of current and voltage). In FIG. 2, elements and the like through which no current flows are not shown.

When the relay RY is opened and the hoist is manually lowered (step 1), the DC permanent motor P
M is reversed rotated by an external force (Step 2), it generates an induced voltage V _M to the point P2 side is positive voltage polarity (Step 3).

As the rotational speed of the DC permanent motor PM increases, the voltage V _DS between the terminals of the switching element TR4 (voltage between the drain and source) becomes larger than the breakdown voltage V _Z2 of the Zener diode Z2 (step). 4), the Zener diode Z2 breaks down (conducts) (step 5).

Then, the current i _G flows through the resistors R3 and R4, and the resistance drop voltage V _G (=
i _G × R4) occurs (step 6). This voltage V _G
Is input to the gate terminal (switching terminal) of the switching element TR4 via the drive line DL2.

[0036] When the voltage V _G is greater than the operating voltage V _TH of the switching element TR4 (step 7), the switching element TR4 is turned (step 8).

[0037] Thus, current i _D flows through the switching element TR4, the induced voltage V _M is not rise any further. For this reason, the voltage applied to the switching element TR4 does not become an overvoltage and the switching element TR4
Is protected. Further, since the current i _D flows, an electric braking force is generated in the DC permanent motor PM, and the increase in the rotation speed is suppressed (step 9).

FIG. 4 shows that the above operations (steps 1 to 9) are performed.
The rotation speed N and the voltage V _DSAnd the current i_DStrange
It shows chemical properties. As can be seen from FIG.
The rotation speed increases due to the conduction of the switching element TR4.
In addition, the rise of the induced voltage can be suppressed.

When the DC permanent motor PM rotates forward with the relay RY open, the protection circuit 10
Operates in the same manner as the protection circuit 20 to protect the switching element TR2 from overvoltage and generate electric braking.

The protection circuit 1 is provided to the first upper arm (TR1, D1) and the second upper arm (TR3, D3).
A protection circuit having the same configuration as 0, 20 may be connected.

As a matter of course, a bipolar transistor, an IGBT, or the like can be employed as a switching element constituting the bridge circuit, in addition to the FET. Also, the present invention can be applied to control other types of DC motors.

[0042]

According to the present invention, when the power supply voltage is not applied to the bridge circuit and the main circuit is shut off, the DC motor is rotated by an external force, as described in detail with the above embodiments. The protection circuit that turns on the switching element provided on the arm is provided on condition that the induced voltage generated by the switching element becomes large, so that the induced voltage can be suppressed to a certain value or less, and the switching element is prevented from being damaged by overvoltage. be able to. For this reason, the withstand voltage of the switching element can be designed to be low, and a control circuit capable of controlling a large current at a reduced cost can be provided.

Also, when the induced voltage is increased, the switching element is turned on to allow the DC motor current to flow, so that an electric braking force is generated in the DC motor and the DC motor is prevented from being over-rotated by an external force. Can be.
Until electric braking occurs, the DC motor can be rotated with a light load.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a control circuit of a DC motor according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing voltage and current states during a protection operation in the control circuit according to the embodiment;

FIG. 3 is a flowchart showing an operation state of the control circuit according to the embodiment;

FIG. 4 is a characteristic diagram showing rotation speed, voltage, and current characteristics when a protection operation is performed.

FIG. 5 is a circuit diagram showing a conventional technique.

[Explanation of symbols]

 10, 20 Protection circuit PM DC permanent motor RY Relay α, β Series circuit B Battery TR1 to TR4 Switching element C Capacitor D1 to D4 Flywheel diode D5, D6 Diode Z1, Z2 Zener diode R1 to R4 Resistance DL1, DL2 Drive line

Claims (2)

[Claims] 1. A first series circuit comprising a first upper arm including a switching element and a first lower arm including a switching element connected in series, a second upper arm including a switching element, and a switching element. A second series circuit formed by serially connecting a second lower arm including: a connection point of the first upper arm and the first lower arm, which is connected in parallel to a DC power supply via a relay; In a control circuit of a DC motor connecting a DC motor between a connection point of a second upper arm and a second lower arm, a diode having an anode connected to one terminal of the DC motor; A Zener diode connected to the one terminal in a reverse blocking state via this diode, a resistor for flowing a current flowing when the Zener diode breaks down to the ground potential line, And a drive line for inputting the same resistance drop voltage to a switching terminal of a predetermined switching element among the switching elements to make the switching element conductive, and a protection circuit comprising: Control circuit. 2. The DC motor control circuit according to claim 1, wherein said DC motor is a permanent magnet DC motor.