JPH0715992A - Ground-fault detection circuit of motor - Google Patents

Abstract

PURPOSE:To precisely discriminate the ground fault of a motor from the open state of a relay and to detect them. CONSTITUTION:FETs 1, 2 which are interposed respectively across a power supply 7 and both poles of a motor 5, FETs 3, 4 which are interposed respectively across both poles of the motor 5 and a ground and a current detection resistor RS which is interposed between the FETs 3, 4 and the ground are installed. In addition, a means 11 which measures a voltage across both the motor 5, a control means 12 which selectively drives the FETs 1, 4 and the FETs 2, 3 as sets and a means 13 which judges a ground fault when at least one of the detection value of the measuring means 11 is at a prescribed voltage or lower when the control means 12 drives two sets of the FETs 1 to 4 alternately are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground short circuit detecting circuit for a motor driven by an H-type bridge circuit.

[0002]

2. Description of the Related Art Conventionally, as one of DC-AC conversion circuits (inverter circuits) for driving a motor, an H-type bridge circuit using four amplification elements has been known, and as shown in FIG. An H-type bridge circuit is composed of field effect transistors (hereinafter referred to as FETs) as amplifying elements. In this circuit, FETs 1 and 4 arranged diagonally
The current to the motor 5 is controlled by alternately driving the FETs 2 and 3 as a set. And
The resistance RS _Y interposed between the FETs 1 and 2 and the power supply detects an overcurrent when the lead wire of the motor 5 is short-circuited to ground. The resistor RS _X arranged in series with the motor 5 is for detecting the current for controlling the FETs 1 to 4.

[0003]

However, in the above-mentioned conventional circuit, since the resistor RS _Y for detecting the overcurrent when the motor is short-circuited to the ground is constantly energized, the power loss is large and the overcurrent is directly detected. Therefore, there are cases where malfunction occurs due to overload. In addition, it is necessary to separately provide a switchgear such as a relay that operates after a ground short circuit is detected, which may complicate the circuit.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a motor ground short circuit detection circuit which can accurately detect a motor ground short circuit and can also detect an open state of a relay.

[0005]

According to the present invention, first and second amplifying elements are respectively provided between a power source and both poles of a motor, and between both poles of the motor and ground. Third and fourth amplifying elements, a current detection resistor RS interposed between the third and fourth amplifying elements and ground,
A means for measuring a voltage across the motor, a control means for selectively driving the first and fourth amplifying elements and the second and third amplifying elements as a set, and the control means. A means for determining a ground short circuit is provided when at least one of the detection values of the measuring means when the two sets of amplifying elements are alternately driven is equal to or lower than a predetermined voltage.

The first and second amplifying elements are provided with first and second resistors R1 and R2 arranged in parallel, respectively.

Further, a switching element is interposed between the first and second amplifying elements and the power source, and the judging means is arranged to operate when the control means alternately drives the two sets of amplifying elements. The open state of the switching element is determined when the detection values of the measuring means are both below a predetermined value.

[0008]

Therefore, when the control means alternately drives the first and fourth amplifying elements and the second and third amplifying elements one by one, if the motor is short-circuited to ground, the two amplifying elements are driven. By alternately driving, at least one of the detection values of the voltage measuring means becomes equal to or lower than a predetermined voltage, and the determining means can reliably detect the ground short circuit of the motor from the drive signal and the detected value of the voltage.

When the control means is not driving the amplifying element, the first and second resistors R1 and R2 introduce a predetermined power supply voltage across the motor, and at this time, a ground short circuit occurs in the motor. Then, the detected value of the voltage measuring means becomes less than a predetermined value (for example, zero), and the judging means can easily detect the ground short circuit of the motor.

Further, the open state of the switching element interposed between the first and second amplifying elements and the power source,
When the two sets of amplifying elements are driven alternately, the voltage across the motor is below a predetermined value, so that it can be easily identified as a ground short circuit of the motor.

[0011]

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

In FIG. 1, both ends of the motor 5 are connected to the sources of FETs 1 and 2 as amplifying elements, respectively, and are also connected to the drains of FETs 3 and 4, respectively.

The drains of the FETs 1 and 2 are connected to a power supply 7 via a relay 6 as a switching element,
The sources of the FETs 3 and 4 are grounded via the current detection resistor RS. The FETs 1 to 4 and the motor 5 form an H-type bridge. The relay 6 operates in an abnormal condition such as when an overcurrent flows through the H-shaped bridge.

The control means 12 is the FE of the FETs 1 to 4.
T1 and 4 and FETs 2 and 3 are alternately driven as one set, and the gates of FETs 1 and 4 and FETs 2 and 3 are pulse width modulated (hereinafter P
WM) drive signal is provided. Also, the control means 1
Reference numeral 2 controls the drive signal based on the current detection value of the current detection resistor RS interposed between the FETs 3 and 4 and the ground.

A resistor R1 is provided in parallel between the drain and source of the FET1, and the resistor R is similarly provided to the FET2.
Two are provided. These resistors R1 and R2 are FETs 1 and 2
When the motor 5 is not driven, the voltage of the power source 7 is introduced to both ends of the motor 5, and when the motor 5 is driven, it is set to a predetermined resistance value capable of suppressing the current to the resistors R1 and R2.

The voltage measuring means 11 measures the voltages V1 and V2 in the figure on both ends of the motor 5, and the measured values of the voltages V1 and V2 are sent to the judging means 13.

The determination means 13 determines the ground short circuit of the motor 5 and the relay based on the measured values of the voltages V1 and V2 and the duty ratio of the drive signal from the control means 12 (for example, the time ratio at which the pulse of one cycle is turned on). Determine the open state of 6,
If the motor 5 is short-circuited to the ground, a short circuit signal is generated.

Here, the ground short circuit of the motor 5 will be briefly described.

The motor 5 includes FETs 1 to 4 and resistors R1 and R
Is connected to the H-shaped bridge circuit via a lead wire or the like (not shown), the contact between the lead wire with the missing coating and the body of the motor 5, the winding of the motor 5 and the body of the motor 5 Or a brush (not shown) of the motor 5 comes into contact with the main body of the motor 5 to cause a ground short circuit.

This ground short-circuit often occurs in the portion A or the portion B connected to the motor 5 through the lead wire in FIG. 1, and for example, when the ground short-circuit occurs in the portion B, FIG. As shown in, when the FETs 1 and 4 are driven (each gate is turned on), the current from the power supply 7 flows from the portion B to the ground side after passing through the FET 1 and the motor 5, while the current passing through the motor 5 is Part is FET4,
It flows through the current detection resistor RS to the ground side, and the terminal voltage V between V1 and V2 of the voltage measuring means 11 becomes substantially equal to the power supply voltage V _CC .

On the other hand, as shown in FIG. 3, when the FETs 2 and 3 are driven, the current from the power supply 7 flows from the FET 2 to the ground side through the portion B, while a part of the current from the FET 2 is supplied to the motor 5, the FET 3 and the FET 3. It flows through the current detection resistor RS to the ground side, and the voltage V between the terminals V1 and V2 of the voltage measuring means 11
Is 0.

When the portion A is short-circuited to ground, although not shown, when the FETs 2 and 3 are turned on, the inter-terminal voltage V≈V _CC is obtained, while the FETs 1 and 4 are turned on. Then, the voltage between terminals becomes V≈0.

In FIGS. 2 and 3, since the current passing through the current detection resistor RS decreases, the control means 12 controls the FET 1
Since the duty ratio of the drive signal to 4 is increased, that is, the control is performed in the direction of increasing the current, an overcurrent flows at the time of the ground short circuit.

Here, as shown in FIG. 3, the motor 5
It suffices if the ground short circuit can be determined when the inter-terminal voltage V is 0, but as shown in FIGS. 5 and 6, the voltages V1 and V2 are 0 when the relay 6 is open, and therefore the inter-terminal voltage is 0. Since V also becomes 0, the ground short circuit cannot be easily determined.

Therefore, the judging means 13 detects the ground short circuit or the open state of the relay 6 based on the flowchart of FIG. Hereinafter, description will be given with reference to the flowchart of FIG.

To detect a ground short circuit, first, the duty ratio of the drive signal supplied to each of the FETs 1 to 4 of the control means 12 is a predetermined ratio N% or more and the detection value of the current detection resistor RS is less than a predetermined current A ₀ . Sometimes it is started (step S1).

The voltages V1 and V2 across the motor 5 are measured with the drive signal from the control means 12 stopped and the gates of the FETs 1 to 4 turned off (step S2). In this state, if the section A or the section B is not short-circuited to ground, the voltages V1 and V2 are the power source 7 supplied by the resistors R1 and R2.
While it is equal to the power supply voltage V _{CC of the above} , V1 and V2 are 0 when the ground is short-circuited or the relay 6 is open.

In step 3, it is determined whether the measured V1 and V2 are lower than a predetermined voltage L, that is, whether the ground is short-circuited or the relay 6 is open, and both V1 and V2 exceed a predetermined value L. If V1 and V2 are both less than or equal to the predetermined value L, the process is terminated assuming that the power is normally supplied, and the process proceeds to step S4.

In step 4, the control means 12 is driven and F
The ETs 1 and 4 are turned on to energize the motor 5. In this state, the energization state shown in FIG. 2 or FIG. 4 is obtained, and if a ground short circuit occurs in the B portion as shown in FIG. 2, V1≈V _CC , V2≈0, and the terminal voltage V ≒ V
While the _CC, V1, V2 if the earth short circuit occurs in an open state or A part of the relay 6 are both substantially zero.

The V1 and V2 thus read are substituted into the variables VM1 and VM2, respectively (step S5).

Next, the control means 12 is driven to drive the FET 2,
3 is turned on to energize the motor 5 (step S
6). In this state, the energization state shown in FIG. 3 or FIG. 5 is obtained. As shown in FIGS. 3 and 5, if a ground short circuit occurs in the portion B or the relay 6 is open, V1≈0,
While V2≈0 and the inter-terminal voltage V≈0, V1≈0, V2≈V _CC
Thus, the inter-terminal voltage V≈V _CC .

Similarly, V1 and V2 read in are substituted into variables VM3 and VM4, respectively (step S7).

Thus, a set of FETs 1, 4 and FET
The voltages across the motor 5 when 2 and 3 are alternately turned on are stored in variables VM1 to VM4. When all of these VM1 to VM4 are 0, the relay 6 shown in FIGS. If at least one of the VMs 1 to 4 is V _CC, it can be determined that there is a ground short circuit in the B portion shown in FIGS.

From this, if all of VM1 to VM4 are equal to or less than the predetermined value L, it is determined that the relay 6 is in the open state and the process proceeds to step S10, while all of VM1 to VM4 are equal to the predetermined value L. If not, that is, if at least one exceeds the predetermined value L, it is determined that there is a ground short circuit and the process proceeds to step S9.

In step S9, although not described in detail, a short-circuit signal is generated and, for example, the relay 6 is driven to open so as to prevent an overcurrent from flowing through the H-type bridge circuit. In step S10 in which 6 is in the open state, the relay 6 is closed and the current supply to the H-type bridge circuit is restored in the same manner.

In this way, the voltages V1 and V2 across the motor 5 measured by the voltage measuring means and the control means 12
By selectively driving the two sets of FET1, 4 and FET2, 3 by the above, not only can the ground short circuit of the motor 5 be reliably detected, but also the H-type bridge circuit and the power supply 7
It is also possible to detect the open state of the relay 6 that is interposed between and, and in the detection of ground short circuit, the resistor for detecting the overcurrent, which is conventionally required, becomes unnecessary, and the power loss of the H-type bridge circuit is eliminated. Can be suppressed.

FIG. 7 shows another embodiment, which is a current detection resistor R obtained by dividing the current detection resistor RS in the first embodiment.
S1 and RS2 are respectively interposed between the FETs 3 and 4 and the ground side, and other configurations and operations are the same as those in the first embodiment.
While the current is controlled by using the detection value of the current detection resistor RS2 when driving, the detection value of the current detection resistor RS1 is used when driving the FETs 2 and 3.

FIG. 8 shows still another embodiment, wherein the first
The current detection resistor RS in the above embodiment is interposed in series with the motor 5, and other configurations and operations are the same as those of the first embodiment.
It is similar to the embodiment of.

In the above embodiment, the voltage V across the motor 5 is used to judge whether the earth short circuit or the relay 6 is open.
Although 1 and V2 are used, the same applies when the terminal voltage V of the motor 5 is used.

[0040]

As described above, according to the present invention, the voltage across the motor measured by the voltage measuring means and the driving means for selectively driving the two sets of amplifying means selectively detect the ground short circuit of the motor. In addition to the above, it is possible to suppress the power loss of the drive circuit of the motor because a resistor for detecting an overcurrent, which is conventionally required, is unnecessary.

Since the resistors R1 and R2 are arranged in parallel with the first and second amplifying elements, the ground short circuit of the motor can be easily detected even when the amplifying elements are not driven.

Further, it becomes possible to detect the open state of the switching element interposed between the first and second amplifying elements and the power supply, and it is possible to reliably detect the ground short circuit of the motor and the open state of the switching element. It becomes possible to identify.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an operation showing a ground short circuit.

FIG. 3 is an explanatory view of the same operation.

FIG. 4 is an explanatory diagram of an operation showing when the relay is open.

FIG. 5 is an explanatory diagram of the same operation.

FIG. 6 is a flowchart showing the flow of control.

FIG. 7 is a circuit diagram showing another embodiment.

FIG. 8 is a circuit diagram showing still another embodiment.

FIG. 9 is a circuit diagram showing still another embodiment.

[Explanation of symbols]

 1 to 4 FET 5 motor 6 relay 7 power supply 11 voltage measuring means 12 control means 13 determination means R1, R2 resistance RS current detection resistance

Claims (3)

[Claims] 1. A first and second amplifying element interposed between a power source and both poles of a motor, respectively, and a third and fourth amplifying element interposed between both poles of the motor and a ground, respectively. A current detection resistor RS interposed between the third and fourth amplifying elements and ground, a means for measuring the voltage across the motor, the first and fourth amplifying elements and the fourth At least one of the control means for selectively driving the second and third amplification elements as one set and the detection value of the measurement means when the control means alternately drives the two sets of amplification elements is predetermined. And a means for determining a ground short-circuit when the voltage is less than or equal to the voltage. 2. The ground short circuit of the motor according to claim 1, further comprising first and second resistors R1 and R2 arranged in parallel with the first and second amplification elements, respectively. Detection circuit. 3. A switching element is interposed between the first and second amplification elements and the power source, and the determination means is configured to operate the switching means when the control means alternately drives the two sets of amplification elements. The ground short circuit detection circuit for a motor according to claim 1 or 2, wherein the open state of the switching element is determined when both detection values of the measuring means are equal to or less than a predetermined value.