JP2002034264A - Inverter current detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current detector which is not influenced by noise generated from switching elements Q1 to Q6 such as transistor. SOLUTION: An inverter current detector is constructed of an inverter circuit 2 including a plurality of switching elements Q1 to Q6, a current detecting circuit 4 for detecting a current of the inverter circuit 2 and an arithmetic means 1 for calculating a current detected value except for a detected value of the period corresponding to the ON-OFF switching time of the switching elements Q1 to Q6. Thereby, a current value can be calculated except for the detected value of the period corresponding to the ON-OFF switching time of the switching elements Q1 to Q6 on the occasion of sampling of a current value, and accurate current value can also be detected without any influence of noise generated at the time of ON-OFF switching time of the switching elements Q1 to Q6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current detecting device for an inverter capable of accurately detecting a current without being affected by switching noise caused by turning on and off a switching element such as a transistor.

[0002]

2. Description of the Related Art In an inverter device for controlling the rotation speed of a three-phase motor or the like, if an overcurrent flows in an inverter circuit, electronic components in the circuit may be damaged. Therefore, the current value is sampled so that overcurrent does not flow and monitored constantly, and if the current value exceeds a predetermined threshold, the drive of the inverter device is forcibly stopped to protect the circuit. I am trying to do it.

[0003]

However, in an inverter circuit for controlling the rotation speed of a three-phase motor or the like,
When a rising and / or falling signal (edge signal) is generated by turning on and off a switching element such as a transistor, noise is generated in a current flowing in the inverter circuit. When noise of this current value is sampled, accurate current detection cannot be performed, and there is a problem in that the function of the protection circuit for monitoring the current so that an overcurrent does not flow is lost.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems and has been improved and eliminated. Therefore, it is an object of the present invention to provide a current detecting device which is not affected by noise of a switching element such as a transistor. Is what you do.

[0005] In order to solve the above-mentioned problems, the present invention employs an inverter circuit having a plurality of switching elements, a current detection circuit for detecting a current of the inverter circuit, A current detecting device for an inverter, comprising: a calculating means for calculating a detected current value excluding a detected value during a period corresponding to a time when a switching element is turned on / off. By calculating the current detection value excluding the detection value during a period corresponding to the switching element on / off switching, the current value sampling is not affected by noise generated when the switching element is switched on / off. Therefore, accurate current detection is possible.

According to a second aspect of the present invention, in the period corresponding to the on / off switching of the switching element,
2. The current detection device for an inverter according to claim 1, further comprising fixing means for fixing a detection value of the current detection circuit to a constant value. According to this invention, the detection value of the current detection circuit is set to a constant value (for example, zero) during a period corresponding to the on / off switching of the switching element, which is a period during which noise is generated, and when the calculation unit calculates the current detection value, a plurality of times are set. Of the detected values of
Detection values that are constant values can be easily distinguished, and can be calculated excluding the detection values.

According to a third aspect of the present invention, there is provided an inverter circuit having a plurality of switching elements, a fixing means driving circuit for receiving a driving signal for switching the switching elements, and a current detecting means for detecting a current of the inverter circuit. A current detection circuit, a calculating means for calculating a current detection value excluding a detection value during a period corresponding to the on / off switching of the switching element, and a detection value of the current detection circuit constant during a period corresponding to the on / off switching of the switching element Fixed means for fixing to a value, the fixing means driving circuit,
An inverter current detecting device for outputting an operation signal to the fixing means for a predetermined time from a rise and / or a fall of the drive signal. According to the present invention, the fixing means driving circuit fixes the detection value of the current detection circuit to a fixed value (for example, zero) for a predetermined time after the rise and / or fall of the drive signal for switching the switching element. An operation signal is output. As a result, the detection value of the current detection circuit becomes a constant value (for example, zero) during a period corresponding to the time when the switching element is turned on and off, which is a period in which noise is generated. And the calculation means can accurately calculate the current detection value.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below with reference to the embodiments of the invention shown in the drawings. 1 to 3 relate to a first embodiment of the present invention. FIG. 1 is a block circuit diagram showing an entire configuration of a current detection device, and FIG. 2 is a current waveform of an inverter circuit 2 and a microcomputer (hereinafter referred to as a microcomputer). FIG. 3 is a diagram showing an on / off signal waveform output from the microcomputer 1 to the inverter circuit 2, and FIG. 3 is a flowchart of a current abnormality determination by the microcomputer 1 based on sampling data. The microcomputer 1 includes a central processing unit (CPU), a memory (ROM,
RAM) and an input / output port (I / O port).

As shown in FIG. 1, in this embodiment, the microcomputer 1 samples the current value of the inverter circuit 2 and stores the data in an internal memory. The inverter circuit 2 interrupts power supplied to the three-phase motor 3 at predetermined intervals by switching elements Q1 to Q6 in which transistors are connected in a three-phase bridge,
The rotation speed of the three-phase motor 3 is controlled by changing the width or frequency of the intermittent one pulse. Note that a rectifier circuit and an AC power supply (commercial power supply), not shown, are connected to the inverter circuit 2, and the AC voltage is converted into DC by the rectifier circuit and supplied.

The current detection circuit 4 is connected to an intermediate point A between the emitter of each of the switching elements Q1 to Q6 in the inverter circuit 2 and the resistor R.
To continuously output an analog voltage corresponding to the value of the current flowing through the intermediate point A through one of.
The current detection circuit 4 has an amplifier 5 for amplification and a transistor 6 as fixing means, and the output side of the bridge circuit of the inverter circuit 2 is connected to the positive terminal of the amplifier 5 for amplification. The collector of the transistor 6 is connected to the A / D converter 7 of the microcomputer 1. on the other hand,
A drive signal for turning on and off at a predetermined frequency is output from the microcomputer 1 to the inverter circuit 2 via the waveform generation circuit 8, and the switching elements Q1 to Q6 of the inverter circuit 2 control the speed of the three-phase motor 3 based on the drive signal. It is carried out. The waveform generation circuit 8 generates a drive signal by dividing the basic clock of the microcomputer 1 by hardware.

Further, the drive signal output to the inverter circuit 2 is also input to the fixing means drive circuit 9. The fixing means driving circuit 9 comprises an OR element 10, an edge detection circuit and a delay gate circuit 11, and the output side of the edge detection and delay gate circuit 11 is connected to the base side of the transistor 6 of the current detection circuit 4. . The OR element 10 inputs a drive signal for the inverter circuit 2,
A signal is output at the time of rising and / or falling. The OR element 10 is connected to the inverter circuit 2
Are input in parallel to all the switching elements Q1 to Q6 (six in the case of three phases). Therefore, this OR element 10 is connected to any of the switching elements Q
Even when the drive signals for 1 to Q6 rise and / or fall, a predetermined signal is output.

On the other hand, the edge detection and delay gate circuit 11
Detects an edge (rise and / or fall) of the drive signal from the output signal of the OR element 10 and outputs an operation signal for operating the transistor 6 until a predetermined delay time elapses from the edge. Things. For example, the delay time may be set to about 250 ns. As a result, the transistor 6 sets the output of the amplifier 5 for taking in the A / D converter 7 of the microcomputer 1 to zero for a predetermined delay time from the detection of the edge signal (cuts the output signal). That is, the value of the current flowing through the inverter circuit 2 is not output as the output value of the current detection circuit 4 for a predetermined time from the edge in the drive signal of the switching elements Q1 to Q6, and the noise generated when the edge occurs is reduced. It is possible to prevent the affected output value from being used for calculating the current detection value.

During the energizing period of the three-phase motor 3, the switching elements Q1 to Q6 of the inverter circuit 2 are turned on / off by a drive signal input from the microcomputer 1 via the waveform generation circuit 8, and the rotation of the three-phase motor 3 is performed. Controlling speed. Thus, during such an energizing period, as shown in FIG. 2, the current waveform flowing through the inverter circuit 2 has noise at the rising and / or falling (edge) of the drive signal that periodically turns on and off. Occurs and the current value changes greatly. The current value including such noise is directly used as sampling data of the overcurrent detection protection circuit by the microcomputer 1.
In this case, accurate calculation of the current detection value cannot be performed.

Therefore, in this embodiment, the fixed drive means 9 causes the rising and / or falling of the on / off signal.
Alternatively, the falling edge (edge) is detected, and the transistor 6 as a fixing means is fixed for a predetermined delay time from the time of detection of the edge.
Is output. As a result, the transistor 6 operates via the analog port of the microcomputer 1 for a predetermined delay time from the detection of the edge signal.
The output of the current detection circuit 4 input to the / D converter 7 becomes zero (is cut). That is, the current value of the inverter circuit 2, which is the output value of the current detection circuit 4, is set to a constant value for a predetermined time from the rise and / or fall of the switching elements Q1 to Q6.
When the current detection value is calculated by the above, it is possible to prevent the detection value affected by noise from being included. Although the example of FIG. 1 shows a case where the microcomputer 1 includes the A / D converter 7, an A / D conversion circuit is provided separately from the microcomputer 1, and the value after being converted into a digital value is used as the microcomputer. One digital input port may be used.

The microcomputer 1 calculates an average value from a plurality of sampling data taken every predetermined time (sampling cycle), excluding data when the operation (ON) of the transistor 6 overlaps (value is zero). Then, the average value is compared with a preset threshold value to determine whether the current is abnormal. FIG. 3 shows a flowchart of the processing in the microcomputer 1.
First, the number of samplings n is set to zero (initial value), and it is determined whether or not the motor is operating from the state of the motor operation signal (ON or OFF). If the motor is not running, return immediately after starting. If the motor is running, it is determined whether the period measurement timer has expired. The period measurement timer has a preset period of time for the sampling period, and when the time is up, it is possible to detect that the sampling period has elapsed. If the period measurement timer has not timed out, the sampling period has not yet elapsed, so the process returns to the determination of whether or not the motor is operating.

When the period measurement timer expires, the number of samplings, n, is counted by one (n = n + 1).
At the same time, the output value (waveform data) of the current detection circuit 2 is fetched from the input port, and the value is stored in the memory as sampling data (current value). Thereafter, it is determined whether or not the number of samplings n has reached the set number of times. If the number has been reached, the average value calculating means calculates the average value of the sampling data stored in the memory. At this time,
An average value is calculated excluding data having a value of zero among the plurality of stored sampling data. If the number of samplings n has not reached the set number of times, the process returns to the determination of whether or not the motor is running, and thereafter, the same processing is performed until the set number of times is reached. When the calculated average value (current detection value) exceeds the threshold value, the motor may be stopped and an alarm signal may be output. At this time, it is possible to determine whether to stop the motor by making the time exceeding the threshold value and the current detection value effective.

FIG. 4 relates to a second embodiment of the present invention, in which a digital signal processor (hereinafter referred to as DSP) 12 is used to monitor overcurrent of an inverter circuit. It is. The DSP 12
In addition to the functions of a normal microprocessor, an arithmetic unit having a function specialized in floating-point arithmetic, a timer control function, and an input / output control unit with the outside are built in, and the fixing means driving circuit 9 shown in FIG. Even if not separately provided, the processing can be performed inside the DSP 12, and the current value is not sampled for a predetermined time from the occurrence of the rise and / or fall of the drive signal. That is,
Even without providing the transistor 6 for fixing the output value of the current detection circuit 4 to a constant (zero), the internal processing of the DSP 12
An output value is not taken in a specific period. This is because the DSP 12 has a high-speed operation circuit.
When this DSP 12 is used, the entire system configuration becomes extremely simple.

[0018]

As described above, in the present invention,
An inverter circuit having a plurality of switching elements, a current detection circuit for detecting a current of the inverter circuit,
The current detection device of the inverter is constituted by the calculating means for calculating the current detection value excluding the detection value of the period corresponding to the on / off switching of the switching element, so that the period corresponding to the on / off switching of the switching element upon sampling the current value It is possible to calculate the current value except for the detected value, and it is possible to accurately detect the current value without being affected by noise generated when the switching element is turned on and off.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing an overall configuration of a current detection device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing waveforms of a current value and an on / off signal of the current detection device according to the first embodiment of the present invention.

FIG. 3 is a flowchart of the current detection device according to the first embodiment of the present invention in the case where data of a current value is stored.

FIG. 4 is a block circuit diagram illustrating an overall configuration of a current detection device according to a second embodiment of the present invention.

[Explanation of symbols]

1 ... microcomputer, 2 ... inverter circuit, 3 ... three-phase motor,
4 ... current detection circuit, 5 ... amplification amplifier, 6 ... transistor (fixing means), 7 ... A / D converter, 8 ... waveform generation circuit, 9 ... fixing means driving circuit, 10 ... OR circuit, 11 ... edge detection Circuit and delay gate circuit, 12 DSP, A ...
Intermediate point (current detection point), Q1 to Q6: switching element, R: resistance

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Claims (3)

[Claims] An inverter circuit having a plurality of switching elements, a current detection circuit for detecting a current of the inverter circuit, and a current detection value are calculated excluding a detection value during a period corresponding to switching on and off of the switching element. A current detection device for an inverter, comprising: a calculation means. 2. The inverter current detecting device according to claim 1, further comprising fixing means for fixing the detected value of the current detecting circuit to a constant value during a period corresponding to the time when the switching element is switched on and off. 3. An inverter circuit having a plurality of switching elements, a fixing means driving circuit for receiving a driving signal for switching the switching elements, a current detection circuit for detecting a current of the inverter circuit, and switching on / off of the switching elements. And a fixing means for fixing the detection value of the current detection circuit to a constant value during a period corresponding to the time when the switching element is turned on and off, excluding a detection value during a period corresponding to the time. The inverter current detection device according to claim 1, wherein the fixing unit driving circuit outputs an operation signal to the fixing unit for a predetermined time from a rise and / or a fall of the drive signal.