JP2004147401A - Current detector and inverter device provided with current detecting function - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a current detector which can accurately detect the current of an inverter device with simple constitution. <P>SOLUTION: The inverter device is equipped with a switch circuit 10 for U phase, a switch circuit 20 for V phase, and a switch circuit 30 for W phase. The load of the inverter device is a three-phase AC motor 50. Each switch circuit 10, 20, and 30 is grounded via resistors 61, 62, and 63, respectively. An addition circuit 70 adds the voltage generated in each of resistors 61-63. A comparator 80 monitors the generation of an eddy current by comparing the output of the addition circuit 70 with specified threshold voltage. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD 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 to a device for detecting current of an inverter device for driving a three-phase AC motor and a three-phase device having a current detection function. It relates to an inverter device.
[0002]
[Prior art]
An inverter device is a device that generates an alternating current from a direct current, and is widely used for various purposes. A three-phase inverter device, which is one form of such an inverter device, is a device that generates three-phase alternating current from direct current, and is used, for example, for driving a three-phase alternating current motor.
[0003]
FIG. 9 is a diagram illustrating a basic configuration of a three-phase inverter device that drives a three-phase AC motor. The three-phase inverter device usually 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) connected in parallel with each other. Switch circuit) 30. Here, each of the switch circuits 10, 20, 30 includes a pair of switches (an upper-arm switch and a lower-arm switch) connected in series with each other. A diode is connected to each of the switches in parallel. A predetermined DC voltage is applied to each of the switch circuits 10, 20, and 30 by the power supply 40. The outputs of the switch circuits 10, 20, and 30 are connected to a motor (three-phase AC motor) 50.
[0004]
In the inverter device having the above configuration, 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. By appropriately controlling these switch circuits 10, 20, and 30, a three-phase alternating current is supplied to the motor 50.
[0005]
By the way, some inverter devices have a function of detecting a current. For example, a technique is known in which a shunt resistor is provided for each phase (U phase, V phase, W phase), and a voltage generated at each shunt resistor is monitored to detect a current for each phase. (For example, see Patent Document 1)
In addition, 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. 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 Application Laid-Open No. 9-229972 (FIGS. 1, 7, paragraphs 0002 to 0007)
[0007]
[Patent Document 2]
JP-A-6-284747 (FIG. 1, paragraphs 0024 to 0025)
[0008]
[Problems to be solved by the invention]
However, the technology described in Patent Literature 1 monitors the current of each phase in order to control an AC motor, and does not assume that an overcurrent is detected to perform a protection operation. Further, it is difficult to perform high-speed overcurrent detection / protection by this technique.
[0009]
In addition, the technology described in Patent Document 2 has a configuration in which the maximum current is detected by diode coupling, and therefore, accuracy may be reduced due to variations in the forward voltage of the diode and its temperature dependence. Also, in this technique, the current flowing through the switch and the current flowing through the diode are compared, but since these currents flow in opposite directions, an absolute value circuit is provided to compare these. There must be.
[0010]
An object of the present invention is to provide a current detection device capable of accurately detecting the current of an inverter device with a simple configuration, and an inverter device including such a current detection device (or a current detection function).
[0011]
[Means for Solving the Problems]
The current detection device of the present invention is a device for detecting a current generated by an inverter device having first to third switch circuits, and is connected in series to the first to third switch circuits, respectively. There are first to third resistors, and addition means for adding the voltages generated in the first to third resistors and outputting the addition result as a value representing the current flowing through the inverter device. .
[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 with the current flowing through the third resistor connected to the circuit matches the output current of the first switch circuit. Also, in this case, no current flows through the first resistor connected to the first switch circuit. Therefore, the positive-direction maximum current is detected by adding the voltages generated in the first to third resistors.
[0013]
On the other hand, when the output current of the first switch circuit is the maximum current in the negative direction, the current directly flows 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 maximum negative current is detected.
[0014]
Note that, in the current detection device, when the output of the addition unit is larger than a predetermined threshold, an overcurrent detection unit that outputs a signal indicating that an overcurrent has occurred is further provided. Is also good. According to this configuration, when an overcurrent is generated, it is detected immediately, so that protection of the load or components constituting the inverter device can be achieved.
[0015]
Further, in the current detection device, the first to third switch circuits are configured to include an upper-arm switch and a lower-arm switch that are connected in series with each other, and the adding means includes: The upper arm switch and the lower arm switch of the switch circuit are controlled to be in an on state and an off state, respectively, and the upper arm switch and the lower arm switch of the second and third switch circuits are in the off state and The maximum current of the inverter device may be detected while being controlled to the 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 switches of the second and third switch circuits. 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 at the second and third resistors.
[0016]
Further, in the current detection device, the first to third switch circuits are configured to include an upper arm switch and a lower arm switch, respectively, which are connected in series with each other, and the adding means includes: The upper arm switch and the lower arm switch of the switch circuit are controlled to be in an off state and an on state, respectively, and the upper arm switch and the lower arm switch of the second and third switch circuits are in the on state and the off state, respectively. The maximum current of the inverter device may be detected when the inverter device is turned off. 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. 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]
An inverter device with a current detection function according to the present invention includes first to third switch circuits connected to a DC power supply, and first to third switch circuits connected in series to the first to third switch circuits, respectively. There is provided a resistor, and an adding means for adding the voltages generated in the first to third resistors and outputting a result of the addition as a value representing a current flowing through the inverter device.
[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 maximum current and the negative maximum current with a simple configuration. Therefore, it is possible to reduce the size of the inverter device capable of accurately detecting the maximum current. In the inverter device, when the output of the adding means is larger than a predetermined threshold value, An overcurrent detection means for stopping the switch circuit may be further provided. According to this configuration, the load and the first to third switch circuits connected to the inverter device can be immediately protected from overcurrent.
[0019]
BEST MODE FOR CARRYING OUT 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 commonly in both FIG. 1 and FIG. 9 mentioned above points out the same thing. That is, the inverter device of the present 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 supply 40 as a DC power supply is connected to these switch circuits 10, 20, 30. Further, 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 to 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, for example, a transistor such as a MOSFET, and its on / off state is controlled by a control circuit (not shown). Each of the switches 11, 12, 21, 22, 31, and 32 is provided with a diode in parallel.
[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 resistors 62 and 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 lower arm switches of the switch circuits 10, 20, and 30 and the negative electrode (for example, ground) of the power supply 40. Here, the resistance values of the resistors 61 to 63 are basically the same as each other. The positive electrode of the power supply 40 is connected to the upper arm switches of the switch circuits 10, 20, and 30.
[0022]
The adding circuit (adding means) 70 adds the voltages generated at the resistors 61 to 63 (the voltages at both ends of the resistors) 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 adding circuit 70. The configuration of the addition circuit 70 and the reason that the maximum current of the inverter device can be detected from the output voltage of the addition circuit 70 will be described later in detail.
[0023]
The comparator (overcurrent detection means) 80 compares the output voltage of the addition circuit 70 with a predetermined threshold voltage, and when the output voltage of the addition circuit 70 is higher, changes the output from “H” to “H”. L ”. Here, the threshold voltage is a voltage corresponding to an overcurrent value to be monitored. On the other hand, the output voltage of the adding circuit 70 represents a current generated by the inverter device. Therefore, when an overcurrent occurs, the comparator 80 can output a signal indicating that. When an overcurrent is detected by the comparator 80, for example, each switch 11, 12, 21, 22, 31, 32 is forcibly controlled to be in an off state, so that each of the motors 50 or the inverter device is constituted. The control system operates so as to protect components (particularly, each switch itself).
[0024]
FIG. 2 is a diagram illustrating a control signal for driving the inverter device having the above configuration. The method of generating a control signal 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. Control signals for controlling the switches 11, 12, 21, 22, 31, 32 are generated by comparing the triangular wave with the signal wave of each phase. For example, the control signal for controlling the upper arm switch 11 becomes “H” when the U-phase signal wave is higher than the triangular wave, and “H” 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. Then, control signals for controlling the other switches 21, 22, 31, and 32 are generated in a similar manner.
[0025]
Then, by controlling the switches 11, 12, 21, 22, 31, and 32 using the control signal, a three-phase alternating current as shown in FIG. 2 is 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”. When the output current from the inverter device to the motor 50 for each phase is defined as “Iu”, “Iv”, and “Iw”, the following relationship is established.
Iu + Iv + Iw = 0
Next, a method of detecting the maximum value of the current generated by the inverter device will be described.
[0026]
First, a method of detecting the maximum value of the forward 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 is the maximum current in the positive direction, the currents Iv and Iw flow in the negative direction. Here, the switching frequency of each switch 11, 12, 21, 22, 31, 32 is the same as that of the triangular wave shown in FIG. 2 and is sufficiently faster than the frequency of the three-phase alternating current. A small current change due to turning on / off of the device can be ignored.
[0027]
Before time T1 in FIG. 3, as shown in FIG. 4A, the upper arm switches 11, 21, and 31 are controlled to be on, and the lower arm switches 12, 22, and 32 are each turned off. Is controlled. In this case, no current flows through each of the resistors 61 to 63. Therefore, the added value of the voltages generated at the resistors 61 to 63 output from the adding circuit 70 is “0 (zero)”.
[0028]
Subsequently, from time T1 to T2, as shown in FIG. 4B, the upper arm switch 31 is controlled to be off, and the lower arm switch 32 is controlled to be on. 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 sum of the voltages generated in the resistors 61 to 63 is a voltage value representing the “current Iw”.
[0029]
Further, during times T2 to T3 (period A), as shown in FIG. 4C, the upper arm switches 21 and 31 are controlled to be off, and the lower arm switches 22 and 32 are turned on. 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 sum of the voltages generated in the resistors 61 to 63 is a voltage value representing “current Iv + current Iw”.
[0030]
At this time, the total sum of the output currents (Iu, Iv, Iw) of each phase of the inverter device becomes 0 (zero). That is, “current Iv + current Iw” is equal to “− (current Iu)”. However, as shown in FIG. 4C, the current Iu flows in the positive direction, while the currents Iv and Iw flow in the negative directions. Therefore, between times T2 and T3, the output of the adding circuit 70 indicates the current Iu.
[0031]
The operation after time T4 is basically the same as the operation before time T3. That is, from time T4 to T5 (period B), the output of the adding circuit 70 represents the current Iu.
As described above, in the examples illustrated in FIGS. 3 and 4, the output of the adder circuit 70 represents the current Iu that is the U-phase output current in the periods A and 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 only necessary to monitor whether or not the output voltage of the adder circuit 70 exceeds a predetermined threshold value without paying attention to the period A or the period B. Good. In the present embodiment, as shown in FIG. 1, a configuration is employed in which the output voltage of the adder circuit 70 is compared with a predetermined threshold voltage using a comparator 80, and an overcurrent is detected according to the comparison result. are doing.
[0032]
Next, a method of detecting the maximum value of the negative 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.
Prior to time T1 in FIG. 5, as shown in FIG. 6A, the upper arm switches 11, 21, and 31 are controlled to be on, and the lower arm switches 12, 22, and 32 are each turned off. Is controlled. In this case, no current flows through each of the resistors 61 to 63. Therefore, the added value of the voltages generated at the resistors 61 to 63 output from the adding circuit 70 is “0 (zero)”.
[0033]
Subsequently, from time T1 to T2 (period C), as shown in FIG. 6B, the upper arm switch 11 is controlled to be off, and the lower arm switch 12 is controlled to be on. . 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 sum of the voltages generated in the resistors 61 to 63 is a voltage value representing “Iu”.
[0034]
Further, from time T2 to time T3, as shown in FIG. 6C, the upper arm switches 11, 21 are controlled to be off, and the lower arm switches 12, 22 are controlled to be on. 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. Therefore, the added value of the voltage generated at each of the resistors 61 to 63 at the time T2 to T3 is smaller than the added value at the time T1 to T2.
[0035]
The operation after time T4 is basically the same as the operation before time T3. That is, from time T4 to T5 (period D), the output of the adding circuit 70 represents the current Iu.
As described above, in the examples illustrated in FIGS. 5 and 6, the output of the addition circuit 70 represents the current Iu that is the U-phase output current in the periods C and 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]
Note that, in the examples shown in FIGS. 3 to 6, the case where the U-phase output current has reached the maximum current has been described, but the operation when the V-phase or W-phase output current has reached the maximum current is also fundamental. Is the same as
As described above, in the inverter device according to 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, the function of detecting the maximum current as described above is realized by the resistor and the adder circuit, so that the circuit configuration is simple.
[0037]
FIG. 7 shows an embodiment of the adding circuit 70. Note that the circuit configuration shown in FIG. 7 is one example, and the present invention is not limited to this.
The addition 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. Therefore, here, the configuration of the U-phase circuit unit 71U will be described.
[0038]
The amplifier 72 is a differential amplifier and amplifies a voltage generated between both ends of the resistor 61. Here, the inverting input terminal of the amplifier 72 is connected to the ground terminal of the resistor 61 via the input resistor R1, and its non-inverting input terminal is connected to the switch side terminal of the resistor 61 via the input resistor R2. You. The non-inverting input terminal of the amplifier 72 is connected to a predetermined voltage source via a resistor R5. Further, a resistor R3 is provided between the output terminal and the inverted input terminal of the amplifier 72 as a feedback resistor. The signal amplified by the amplifier 72 is output via 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 added to each other in voltage, and guided to the comparator 80. Thus, the 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 (the resistors 61 to 63, the addition circuit 70, and the comparator 80) according to the embodiment includes the maximum positive current and the negative current without using the absolute value circuit used in the known document 2. Since both of the maximum currents can be detected, the configuration is simple and can be realized at low cost.
[0040]
Further, the current detection circuit of the embodiment detects the maximum current without using a diode circuit as used in the known document 2, so that there is no influence such as variation in the forward voltage of the diode, The detection accuracy is improved.
In the above-described embodiment, the resistors 61, 62, 63 are provided between the negative electrode of the power supply 40 and the switch circuits 10, 20, 30. However, 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 becomes equal to the output of the adding circuit 70, so that the adding circuit 70 can be omitted. .
[0041]
In the above-described embodiment, the case where the three-phase AC motor is driven has been described, but the present invention is not limited to this. That is, the present invention can supply current to loads other than the AC motor under the condition that the sum of the output currents becomes 0 (zero).
[0042]
【The invention's effect】
According to the present invention, both the positive maximum output current and the negative maximum output current of the inverter device can be accurately detected 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 chart of a period during which a maximum current in a positive direction is detected.
FIG. 4 is a diagram illustrating a state of the inverter device when a maximum current flows in a positive direction.
FIG. 5 is a timing chart of a period in which a maximum current in a negative direction is detected.
FIG. 6 is a diagram illustrating a state of the inverter device when a maximum current flows in a negative direction.
FIG. 7 is an embodiment of an adding 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 that drives 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 (6)

An apparatus for detecting a current generated by an inverter device including first to third switch circuits,
First to third resistors respectively connected in series to the first to third switch circuits;
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 current detection device having: The current detection device according to claim 1,
When the output of the adding means is larger than a predetermined threshold value, there is further provided an overcurrent detecting means for outputting a signal indicating that an overcurrent has occurred. The current detection device according to claim 1,
The first to third switch circuits each include an upper arm switch and a lower arm switch connected in series with each other,
The adding means includes an upper arm switch and a lower arm switch of the first switch circuit which are controlled to be in an on state and an off state, respectively, and the upper arm switch of the second and third switch circuits. When the lower arm switch and the lower arm switch are controlled to be in the off state and the on state, respectively, the maximum current of the inverter device is detected. The current detection device according to claim 1,
The first to third switch circuits each include an upper arm switch and a lower arm switch connected in series with each other,
The adding means includes an upper arm switch and a lower arm switch of the first switch circuit which are controlled to be in an off state and an on state, respectively, and wherein the second and third switch circuits have an upper arm switch. When the switch for the lower arm and the switch for the lower arm are controlled to the ON state and the OFF state, respectively, the maximum current of the inverter device is detected. First to third switch circuits to which a DC power supply is connected;
First to third resistors respectively connected in series to the first to third switch circuits;
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;
Inverter device with current detection function having The inverter device according to claim 5, wherein
An overcurrent detecting means for stopping the first to third switch circuits when an output of the adding means is larger than a predetermined threshold value is further provided.

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