JP4127014B2 - Current detection device and inverter device with current detection function - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a device for detecting current of an inverter device and an inverter device having a current detection function, and more particularly, a device for detecting current of an inverter device for driving a three-phase AC motor and a three-phase having a current detection function. It relates to the inverter device.
[0002]
[Prior art]
The inverter device is a device that generates alternating current from direct current, and is widely used in various applications. And the three-phase inverter apparatus which is one form of such an inverter apparatus is an apparatus which produces | generates three-phase alternating current from direct current, Comprising: For example, it is used in order to drive a three-phase alternating current motor.
[0003]
FIG. 9 is a diagram showing a basic configuration of a three-phase inverter device for driving a three-phase AC motor. In general, the three-phase inverter device includes a U-phase switch circuit (first switch circuit) 10, a V-phase switch circuit (second switch circuit) 20, and a W-phase switch circuit (third Switch circuit) 30). Here, each switch circuit 10, 20, 30 includes a set of switches (upper arm switch and lower arm switch) connected in series with each other, and each upper arm switch and lower arm. Each switch is connected in parallel with a diode. A predetermined DC voltage is applied to each switch circuit 10, 20, 30 by a power supply 40. The outputs of the switch circuits 10, 20, 30 are connected to a motor (three-phase AC motor) 50.
[0004]
In the inverter device configured as described above, the switch circuits 10, 20, and 30 are controlled by a control circuit (not shown). At this time, in each of the switch circuits 10, 20, and 30, the upper arm switch and the lower arm switch are alternately turned on / off so as not to be turned on at the same time. A three-phase alternating current is supplied to the motor 50 by appropriately controlling the switch circuits 10, 20, and 30.
[0005]
Incidentally, some inverter devices have a function of detecting current. For example, a technique for detecting a current for each phase by providing a shunt resistor for each phase (U phase, V phase, W phase) and monitoring a voltage generated in each shunt resistor is known. (For example, see Patent Document 1)
Also, the combined current of the current flowing through the lower arm switch of each phase and the combined current of the current flowing through the diode provided in parallel with the lower arm switch of each phase are obtained, and by diode coupling, A configuration is also known in which the larger of the two combined currents is output as the maximum current of the inverter device. (For example, see Patent Document 2)
[0006]
[Patent Document 1]
Japanese Patent Laid-Open No. 9-229972 (FIG. 1, FIG. 7, paragraphs 0002 to 0007)
[0007]
[Patent Document 2]
JP-A-6-284747 (FIG. 1, paragraphs 0024-0025)
[0008]
[Problems to be solved by the invention]
However, the technique described in Patent Document 1 monitors the current for each phase in order to control the AC motor, and it is not assumed that a protective operation is performed by detecting an overcurrent. Also, it is difficult to perform high-speed overcurrent detection / protection with this technology.
[0009]
Moreover, since the technique described in Patent Document 2 is configured to detect the maximum current by diode coupling, there is a risk that accuracy may be reduced due to variations in forward voltage of the diode and its temperature dependence. In this technique, the current flowing through the switch and the current flowing through the diode are compared. Since these currents flow in opposite directions, an absolute value circuit is provided to compare them. There must be.
[0010]
An object of the present invention is to provide a current detection device that can accurately detect a current of an inverter device with a simple configuration, and an inverter device including such a current detection device (or current detection function).
[0011]
[Means for Solving the Problems]
The current detection device of the present invention is a device that detects a current generated by an inverter device including first to third switch circuits, and is connected in series to each of the first to third switch circuits. 1st-3rd resistor, and the addition means which adds the voltage which arises in the said 1st-3rd resistor, and outputs the addition result as a value showing the electric current which flows through the said inverter apparatus .
[0012]
According to this configuration, for example, when the output current of the first switch circuit is the maximum current in the positive direction, the current flowing through the second resistor connected to the second switch circuit and the third switch The sum of the current flowing through the third resistor connected to the circuit matches the output current of the first switch circuit. In this case, no current flows through the first resistor connected to the first switch circuit. Therefore, if the voltages generated in the first to third resistors are added, the maximum positive current is detected.
[0013]
On the other hand, when the output current of the first switch circuit is the maximum current in the negative direction, the current flows as it is through the first resistor connected to the first switch circuit. In this case, no current flows through the second and third resistors connected to the second and third switch circuits. Therefore, if the voltages generated in the first to third resistors are added, the negative maximum current is detected.
[0014]
The current detection device may further include overcurrent detection means for outputting a signal indicating that an overcurrent has occurred when the output of the adding means is greater than a predetermined threshold value. Also good. According to this configuration, when an overcurrent occurs, it is immediately detected, so that the load or the components constituting the inverter device can be protected.
[0015]
In the current detection device, the first to third switch circuits include an upper arm switch and a lower arm switch connected in series with each other, and the adding means includes the first switch. The switch for the upper arm and the switch for the lower arm of the switch circuit are respectively controlled to be on and off, and the switch for the upper arm and the switch for the lower arm of the second and third switch circuits are respectively in the off state and You may make it detect the maximum electric current of the said inverter apparatus, when being controlled to an ON state. When the first to third switch circuits are in the above state, the current flowing through the upper arm switch of the first switch circuit is the current flowing through the lower arm switch of the second and third switch circuits. Is equal to the sum of Therefore, the maximum output current of the inverter device can be detected by calculating the sum of the voltages generated in the second and third resistors.
[0016]
Further, in the current detection device, the first to third switch circuits include an upper arm switch and a lower arm switch that are connected in series with each other, and the adding means includes the first switch. The switch for the upper arm and the switch for the lower arm of the switch circuit are controlled to be in the OFF state and the ON state, respectively, and the switch for the upper arm and the switch for the lower arm in the second and third switch circuits are respectively in the ON state and You may make it detect the maximum electric current of the said inverter apparatus, when it is controlled by the OFF state. When the first to third switch circuits are in the above state, the current flowing through the lower arm switch of the first switch circuit is the current flowing through the upper arm switch of the second and third switch circuits. Is equal to the sum of Therefore, the maximum output current of the inverter device can be detected based on the voltage generated in the first resistor.
[0017]
The inverter device with a current detection function of the present invention is an inverter device for driving a three-phase AC motor, and includes first to third switch circuits each including an upper arm switch and a lower arm switch, A value representing the current flowing through the inverter device by adding the first to third resistors connected in series to the third switch circuit and the voltage generated in the first to third resistors, respectively. Adding means for outputting the addition result, and a control circuit for controlling the upper arm switch and the lower arm switch of the first to third switch circuits. A first phase current flowing between the first switch circuit and the three-phase AC motor; a second phase current flowing between the second switch circuit and the three-phase AC motor; and the third switch circuit. Of the third phase current flowing between the motor and the three-phase AC motor is zero. The control circuit controls the upper arm switch and the lower arm switch of the first switch circuit to an on state and an off state, respectively, and the upper arm switch of the second and third switch circuits. When the switch for the lower arm and the switch for the lower arm are controlled to the off state and the on state, respectively, the adding means detects the maximum current of the first phase current.
The control circuit controls the upper arm switch and the lower arm switch of the first switch circuit to an off state and an on state, respectively, and the upper arm switch and the lower switch of the second and third switch circuits. The adding means may detect the maximum current of the first phase current when the arm switch is controlled to the on state and the off state, respectively.
[0018]
The inverter device has a function provided by the above-described current detection device of the present invention, and can accurately detect both the positive direction maximum current and the negative direction maximum current with a simple configuration. Therefore, the inverter device capable of accurately detecting the maximum current can be reduced in size. In the inverter device, when the output of the adding means is larger than a predetermined threshold value, You may make it further have an overcurrent detection means which stops a switch circuit. According to this configuration, it is possible to immediately protect the load and the first to third switch circuits connected to the inverter device from overcurrent.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating a configuration of an inverter device according to an embodiment of the present invention. In addition, the code | symbol used in common in both FIG. 1 and FIG. 9 mentioned above has shown the same thing. That is, the inverter device of this embodiment includes a U-phase switch circuit (first switch circuit) 10, a V-phase switch circuit (second switch circuit) 20, and a W-phase switch circuit (third switch circuit). ) 30. Further, a power source 40 that is a DC power source is connected to the switch circuits 10, 20, and 30. Furthermore, it is assumed that a motor (three-phase AC motor) 50 is connected to this inverter device as a load.
[0020]
The U-phase switch circuit 10 includes an upper arm switch 11 and a lower arm switch 12 connected in series with each other. Similarly, the V-phase switch circuit 20 includes an upper arm switch 21 and a lower arm switch 22, and the W-phase switch circuit 30 includes an upper arm switch 31 and a lower arm switch 32. Here, each of the switches 11, 12, 21, 22, 31, 32 is a transistor such as a MOSFET, for example, and its on / off state is controlled by a control circuit (not shown). In addition, a diode is provided in parallel to each of the switches 11, 12, 21, 22, 31, and 32.
[0021]
The resistor 61 is a shunt resistor for detecting a U-phase current, and is connected in series to the U-phase switch circuit 10. Similarly, the resistor 62 and the resistor 63 are connected in series to the V-phase switch circuit 20 and the W-phase switch circuit 30, respectively. That is, the resistors 61, 62, and 63 are provided between the switch for the lower arm of the switch circuits 10, 20, and 30 and the negative electrode (for example, ground) of the power supply 40, respectively. Here, the resistance values of the resistors 61 to 63 are basically the same. The positive electrode of the power supply 40 is connected to the upper arm switch of each switch circuit 10, 20, 30.
[0022]
The adding circuit (adding means) 70 adds the voltages (voltages across the resistors) generated in the resistors 61 to 63 and outputs the result. Here, the voltages generated in the resistors 61, 62, and 63 represent U-phase, V-phase, and W-phase currents. Therefore, the maximum current of the inverter device can be detected from the output voltage of the adder circuit 70. The configuration of the adder circuit 70 and the reason why the maximum current of the inverter device can be detected by the output voltage of the adder circuit 70 will be described in detail later.
[0023]
The comparator (overcurrent detection means) 80 compares the output voltage of the adding circuit 70 with a predetermined threshold voltage, and when the output voltage of the adding circuit 70 is larger, the output is changed from “H” to “ Switch to “L”. Here, the threshold voltage is a voltage corresponding to the overcurrent value to be monitored. On the other hand, the output voltage of the adder circuit 70 represents a current generated by the inverter device. Therefore, the comparator 80 can output a signal indicating that when an overcurrent occurs. When an overcurrent is detected by the comparator 80, for example, each switch 11, 12, 21, 22, 31, 32 is forcibly controlled to be turned off, so that each of the motor 50 or the inverter device is configured. The control system operates to protect the components (particularly, each switch itself).
[0024]
FIG. 2 is a diagram for explaining a control signal for driving the inverter device having the above-described configuration. The control signal generation method described below is an example, and the present invention is not limited to this.
In FIG. 2, a triangular wave is a periodic wave having a predetermined frequency and is a reference signal for generating a control signal. On the other hand, the signal waves for each phase are sine waves having the same frequency, but their phases are shifted by 120 degrees from each other. And the control signal for controlling each switch 11, 12, 21, 22, 31, 32 is produced | generated by comparing the said triangular wave and the signal wave for every phase. For example, the control signal for controlling the upper arm switch 11 is “H” when the U-phase signal wave is higher than the triangular wave, and “U” when the U-phase signal wave is lower than the triangular wave. L ". The control signal for controlling the lower arm switch 12 is an inverted signal of the control signal for controlling the upper arm switch 11. Control signals for controlling the other switches 21, 22, 31, and 32 are also generated in the same manner.
[0025]
And by controlling each switch 11, 12, 21, 22, 31, 32 using the said control signal, three-phase alternating current as shown in FIG. 2 is produced | generated. In the following description, as shown in FIG. 1, the direction from the inverter device to the motor 50 is referred to as “positive direction”, and the direction from the motor 50 to the inverter device is referred to as “negative direction”. Further, if the output current for each phase from the inverter device to the motor 50 is defined as “Iu”, “Iv”, and “Iw”, the following relationship is established.
Iu + Iv + Iw = 0
Next, a method for detecting the maximum value of the current generated by the inverter device will be described.
[0026]
First, a method for detecting the maximum value of the positive current will be described with reference to FIGS. Here, it is assumed that the current Iu, which is the U-phase output current, is maximized.
In the three-phase alternating current, basically, as shown in FIG. 2, the output current of each phase becomes the maximum current in order. During the period when the current Iu becomes the maximum current in the positive direction, the current Iv and the current Iw flow in the negative direction. Here, the switching frequency of each of the switches 11, 12, 21, 22, 31, and 32 is the same as that of the triangular wave shown in FIG. 2, and is sufficiently faster than the three-phase AC frequency. A small change in current due to turning on / off can be ignored.
[0027]
Prior to time T1 in FIG. 3, as shown in FIG. 4A, the upper arm switches 11, 21, and 31 are controlled to be in the on state, and the lower arm switches 12, 22, and 32 are in the off state. Is controlled. In this case, no current flows through each of the resistors 61-63. For this reason, the added value of the voltage generated in each of the resistors 61 to 63 output from the adding circuit 70 is “0 (zero)”.
[0028]
Subsequently, at time T1 to T2, as shown in FIG. 4B, the upper arm switch 31 is controlled to the off state and the lower arm switch 32 is controlled to the on state. At this time, the current Iw flows through the lower arm switch 32 and the resistor 63. That is, a voltage representing the current Iw is generated in the resistor 63. Therefore, the added value of the voltages generated in the resistors 61 to 63 becomes a voltage value representing “current Iw”.
[0029]
Further, at time T2 to T3 (period A), as shown in FIG. 4C, the upper arm switches 21 and 31 are controlled to be in the off state, and the lower arm switches 22 and 32 are in the on state. Be controlled. At this time, the current Iv flows through the lower arm switch 22 and the resistor 62, and the current Iw flows through the lower arm switch 32 and the resistor 63. That is, a voltage representing the current Iv is generated in the resistor 62, and a voltage representing the current Iw is generated in the resistor 63. Therefore, the added value of the voltages generated in the resistors 61 to 63 becomes a voltage value representing “current Iv + current Iw”.
[0030]
At this time, the sum of the output currents (Iu, Iv, Iw) of each phase of the inverter device becomes 0 (zero). That is, “current Iv + current Iw” coincides with “− (current Iu)”. However, as shown in FIG. 4C, the current Iu flows in the positive direction, whereas the current Iv and the current Iw each flow in the negative direction. Accordingly, at time T2 to T3, the output of the adder circuit 70 represents the current Iu.
[0031]
The operation after time T4 is basically the same as the operation before time T3. That is, during the times T4 to T5 (period B), the output of the adder circuit 70 represents the current Iu.
As described above, in the example illustrated in FIGS. 3 to 4, the output of the adder circuit 70 represents the current Iu that is the U-phase output current in the period A and the period B. Therefore, if the output of the adder circuit 70 is monitored in the period A or the period B, the current Iu can be detected. However, in order to check whether or not an overcurrent has occurred, it is merely necessary to monitor whether or not the output voltage of the adder circuit 70 exceeds a predetermined threshold without being aware of the period A or the period B. Good. In this embodiment, as shown in FIG. 1, the comparator 80 is used to compare the output voltage of the adder circuit 70 with a predetermined threshold voltage, and an overcurrent is detected according to the comparison result. is doing.
[0032]
Next, a method for detecting the maximum value of the negative direction current will be described with reference to FIGS. Here, it is assumed that the current Iu, which is the U-phase output current, is maximized.
Before time T1 in FIG. 5, as shown in FIG. 6A, the upper arm switches 11, 21, and 31 are controlled to be in the on state, and the lower arm switches 12, 22, and 32 are in the off state, respectively. Is controlled. In this case, no current flows through each of the resistors 61-63. For this reason, the added value of the voltage generated in each of the resistors 61 to 63 output from the adding circuit 70 is “0 (zero)”.
[0033]
Subsequently, at time T1 to T2 (period C), as shown in FIG. 6B, the upper arm switch 11 is controlled to be in the off state and the lower arm switch 12 is controlled to be in the on state. . As a result, the current Iu flows through the lower arm switch 12 and the resistor 61. That is, a voltage representing the current Iu is generated in the resistor 61. Therefore, the added value of the voltages generated in the resistors 61 to 63 becomes a voltage value representing “Iu”.
[0034]
Further, at time T2 to T3, as shown in FIG. 6C, the upper arm switches 11 and 21 are controlled to be in the off state, and the lower arm switches 12 and 22 are controlled to be in the on state. At this time, the current Iu flows through the lower arm switch 12 and the resistor 61, and the current Iv flows through the resistor 62 and the lower arm switch 22. That is, a voltage representing the current Iu is generated in the resistor 61, and a voltage representing the current Iv is generated in the resistor 62. However, the current flowing through the resistor 61 and the current flowing through the resistor 62 flow in opposite directions. For this reason, the addition value of the voltage which arises in each resistance 61-63 in time T2-T3 becomes smaller than the addition value in time T1-T2.
[0035]
The operation after time T4 is basically the same as the operation before time T3. That is, during the time T4 to T5 (period D), the output of the adder circuit 70 represents the current Iu.
As described above, in the example illustrated in FIGS. 5 to 6, the output of the adder circuit 70 represents the current Iu that is the U-phase output current in the period C and the period D. Therefore, if the output of the adder circuit 70 is monitored in the period A or the period B, the current Iu can be detected.
[0036]
In the examples shown in FIGS. 3 to 6, the case where the U-phase output current becomes the maximum current has been described. However, the operation when the V-phase or W-phase output current becomes the maximum current is also fundamental. Is the same.
As described above, in the inverter device of the embodiment, both the maximum current in the positive direction and the maximum current in the negative direction can be detected by monitoring the output of the adder circuit 70. Further, since the function of detecting the maximum current as described above is realized by a resistor and an adding circuit, the circuit configuration is simple.
[0037]
FIG. 7 shows an embodiment of the adder circuit 70. Note that the circuit configuration shown in FIG. 7 is one example, and the present invention is not limited to this.
The adder circuit 70 includes a U-phase circuit unit 71U, a V-phase circuit unit 71V, and a W-phase circuit unit 71W. Here, the configurations of the U-phase circuit unit 71U, the V-phase circuit unit 71V, and the W-phase circuit unit 71W are basically the same as each other. Therefore, here, the configuration of the U-phase circuit unit 71U will be described.
[0038]
The amplifier 72 is a differential amplifier and amplifies the voltage generated at both ends of the resistor 61. Here, the inverting input terminal of the amplifier 72 is connected to the ground-side terminal of the resistor 61 via the input resistor R1, and the non-inverting input terminal is connected to the switch-side terminal of the resistor 61 via the input resistor R2. The The non-inverting input terminal of the amplifier 72 is connected to a predetermined voltage source via the resistor R5. Further, a resistor R3 is provided as a feedback resistor between the output terminal and the inverting input terminal of the amplifier 72. The signal amplified by the amplifier 72 is output through the resistor R4.
[0039]
The outputs of the U-phase circuit unit 71U, the V-phase circuit unit 71V, and the W-phase circuit unit 71W are voltage-added to each other and guided to the comparator 80. As a result, an added value of the voltages generated in the resistors 61 to 63 is given to the comparator 80.
As described above, the current detection device (resistors 61 to 63, the addition circuit 70, the comparator 80) of the embodiment does not include an absolute value circuit as used in the publicly known document 2, and the positive direction maximum current and the negative direction. Since both of the maximum currents can be detected, the configuration is simple and can be realized at low cost.
[0040]
In addition, since the current detection circuit of the embodiment detects the maximum current without using a diode circuit as used in publicly known document 2, there is no influence such as variations in the forward voltage of the diode. Detection accuracy is improved.
In the above-described embodiment, the resistors 61, 62, and 63 are provided between the negative electrode of the power supply 40 and the switch circuits 10, 20, and 30, but the present invention is not limited to this. That is, as shown in FIG. 8, the resistors 61, 62, and 63 may be provided as the resistor 64 between the negative electrode of the power supply 40 and the switch circuits 10, 20, and 30. As a result, the current flowing through the resistor 64 is the sum of the currents flowing through the resistors 61, 62, and 63, and the voltage generated at the resistor 64 is equivalent to the output of the adding circuit 70, so that the adding circuit 70 can be omitted. .
[0041]
Moreover, although the above-mentioned Example demonstrated the case which drives a three-phase alternating current motor, this invention is not limited to this. That is, the present invention can supply current to a load other than an AC motor under the condition that the sum of output currents becomes 0 (zero).
[0042]
【The invention's effect】
According to the present invention, it is possible to accurately detect both the positive direction maximum output current and the negative direction maximum output current of the inverter device with a simple configuration.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an inverter device according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a control signal for driving an inverter device.
FIG. 3 is a timing diagram of a period in which a maximum current in the positive direction is detected.
FIG. 4 is a diagram illustrating a state of the inverter device when the maximum current is flowing in the positive direction.
FIG. 5 is a timing diagram of a period during which a negative maximum current is detected.
FIG. 6 is a diagram illustrating a state of the inverter device when the maximum current flows in the negative direction.
FIG. 7 is an embodiment of an adder circuit.
FIG. 8 is a diagram illustrating a configuration of an inverter device according to another embodiment.
FIG. 9 is a diagram showing a basic configuration of a three-phase inverter device for driving a three-phase AC motor.
[Explanation of symbols]
10 U-phase switch circuit (first switch circuit)
20 V-phase switch circuit (second switch circuit)
30 W-phase switch circuit (third switch circuit)
11, 21, 31 Upper arm switch 12, 22, 32 Lower arm switch 40 Power supply 50 Motor (3-phase AC motor)
61-63 resistor 70 addition circuit (addition means)
72 Amplifier 80 Comparator (Overcurrent detection means)

Claims (3)

An inverter device for driving a three-phase AC motor,
First to third switch circuits each including an upper arm switch and a lower arm switch;
First to third resistors connected in series to the first to third switch circuits, respectively;
Adding means for adding the voltages generated in the first to third resistors and outputting the addition result as a value representing a current flowing through the inverter device;
A control circuit for controlling the upper arm switch and the lower arm switch of the first to third switch circuits,
A first phase current flowing between the first switch circuit and the three-phase AC motor; a second phase current flowing between the second switch circuit and the three-phase AC motor; and the third switch circuit. And the sum of the third phase currents flowing between the motor and the three-phase AC motor is zero,
The control circuit controls the upper arm switch and the lower arm switch of the first switch circuit to an on state and an off state, respectively, and the upper arm switch and the lower switch of the second and third switch circuits. The adding means detects the maximum current of the first phase current when the arm switch is controlled to the off state and the on state, respectively.
An inverter device with a current detection function. An inverter device for driving a three-phase AC motor,
First to third switch circuits each including an upper arm switch and a lower arm switch;
First to third resistors connected in series to the first to third switch circuits, respectively;
Adding means for adding the voltages generated in the first to third resistors and outputting the addition result as a value representing a current flowing through the inverter device;
A control circuit for controlling the upper arm switch and the lower arm switch of the first to third switch circuits,
A first phase current flowing between the first switch circuit and the three-phase AC motor; a second phase current flowing between the second switch circuit and the three-phase AC motor; and the third switch circuit. And the sum of the third phase currents flowing between the motor and the three-phase AC motor is zero,
The control circuit controls the upper arm switch and the lower arm switch of the first switch circuit to an off state and an on state, respectively, and the upper arm switch and the lower switch of the second and third switch circuits. The addition means detects the maximum current of the first phase current when the arm switch is controlled to be in an on state and an off state, respectively.
An inverter device with a current detection function. The inverter device according to claim 1 or 2 ,
It further has overcurrent detection means for stopping the first to third switch circuits when the output of the adding means is larger than a predetermined threshold value.
An inverter device with a current detection function .

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