JP2006158065A - Inverter device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an overcurrent from being passed through switching elements or reflux diodes in ground fault detection. <P>SOLUTION: The inverter device includes: a converter unit 14 that rectifies an alternating current inputted from an alternating-current power source 1; a smoothing unit 9 that is charged with the rectified output of the converter unit 14 and outputs smoothed voltage obtained by smoothing the rectified output; an inverter unit 15 that has the switching elements and the reflux diodes connected in parallel with the switching elements and carries out PWM control to supply an alternating current from its output to a load; current detection units 5a to 5c that detect the value of a current flowing to the output of the inverter unit 15; a duty setting unit that sets the on/off time of the switching elements; a gate control unit 10 that turns on/off the switching elements based on a duty; and a ground fault resistance estimation unit 21 that estimates a ground fault resistance on the basis of the duty and a current value. With respect to the duty, an on-time is set so that, when the output of the inverter unit 15 is connected to the ground, an overcurrent is not passed through the switching elements. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an inverter device having a ground fault protection function.

  A conventional inverter device will be described with reference to FIG. In FIG. 5, reference numeral 1 denotes an AC power source, and usually one phase (S phase in the figure) is grounded. 13 is a switch for turning on / off the AC power source 1, 14 is a converter unit that rectifies the AC input from the AC power source 1, 9 is a smoothing capacitor that is a smoothing unit that smoothes the rectified output of the converter unit 14, and 15 is a smoothing unit. An inverter unit that PWM-controls the smoothed output of the capacitor 9 to supply AC to the load, 7 is an AC motor as a load, 2a to 2f are diodes for rectifying AC power into DC power in the converter unit 14, 4a to 4f Is a switching element for PWM modulating a DC voltage in the inverter unit 15, 3 a to 3 f are connected in parallel to the switching elements 4 a to 4 f, and a freewheeling diode for flowing reactive current, 5 a to 5 c are outputs of the inverter unit 15. A current detector 11 for detecting a three-phase current, 11 determines a ground fault based on detection signals 5a to 5c. Earth 絡判 by with command section for commanding the operation mode of the inverter device 15, 10 is a gate controller for turning on and off the switching elements 4a-4f, 6a, 6b is an equivalent inductance and equivalent resistance of the AC motor 7.

  Next, an operation when the W phase of the motor 7 is grounded in the inverter device shown in FIG. 5 will be described. When the W phase of the motor 7 is grounded, the circuit indicated by the broken line 19 in FIG. 5 is equivalently formed. 18 is a model of ground fault resistance. The ground fault detection is performed before the motor 7 is actually started after the closing switch 13 is turned on and the smoothing capacitor 9 is charged. That is, before starting the operation of the motor 7, the ground fault determination command unit 11 outputs a command signal for turning on the lower arm switching elements 4d, 4e, and 4f for a predetermined period, and the gate control unit 10 is based on this command. Then, the switching elements 4d, 4e, and 4f are turned on.

  When no ground fault occurs, no current flows through the motor 7 even when the three switching elements 4d to 4f constituting the lower arm are turned on, so that the current detected by the current detectors 5a to 5c is zero. It becomes. However, when the W phase of the motor 7 is grounded, the AC power source 1 again passes through the ground fault resistor 18, the W phase switching element 4f, the diode 2d or 2f from the grounded S phase of the AC power source 1. A circuit is formed in which a ground fault current flows to the R or T phase. This ground fault current is detected by the W-phase current detector 5c, whereby a W-phase ground fault is detected. The on-time of the three switching elements depends on the AC power supply frequency, and at least one cycle of on-time is required.

Japanese Patent Laid-Open No. 7-239359 (page 5-6, FIG. 1)

  As described above, the conventional inverter device detects the ground fault by turning on the switching elements 4a to 4f and detecting the ground fault current flowing through the switching elements with the current detectors 5a to 5c. At this time, when the resistance value of the ground fault resistor 18 is extremely small, an excessive ground fault current flows through the switching elements 4a to 4f, thereby causing thermal fatigue to the switching elements 4a to 4f, and the life of the switching elements 4a to 4f. Was shortened.

  Furthermore, in the process in which the closing switch 13 is turned on and the smoothing capacitor 9 is charged, excessive current also flows through the free-wheeling diodes 3a to 3f, causing thermal fatigue, thereby shortening the life of the free-wheeling diodes 3a to 3f. When the W phase of the motor 7 is grounded, in the charging process of the smoothing capacitor 9, the grounding resistor 18 and the W phase free-wheeling diode 3c are passed from the ground phase (S phase) of the AC power supply 1 to the smoothing capacitor 9. Charging current will flow. When the resistance value of the ground fault resistor 18 is small, an excessive charging current flows through the freewheeling diode.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an inverter device that prevents an overcurrent from flowing through a switching element and a free-wheeling diode in detecting a ground fault.

To achieve the above object, an inverter device according to a first aspect of the present invention includes a converter unit that rectifies an alternating current input from an alternating current power source, and a smoothed voltage that is charged by the rectified output of the converter unit and smoothes the rectified output. A smoothing unit that outputs a switching element, a switching element that forms an upper arm and a lower arm, and a free-wheeling diode connected in parallel to the switching element. The smoothing voltage is input and PWM control is performed to load an alternating current from the output. An inverter unit supplied to the inverter unit, a current detection unit that detects a current value flowing through the output of the inverter unit, a duty setting unit that sets a duty of on / off time of the switching element, and the switching of the upper arm or the lower arm A gate control unit for turning on and off the element based on the duty, and based on the duty and the current value. A ground fault resistance estimation unit that estimates ground fault resistance, and the duty sets the on-time so that the output of the inverter unit is in a ground fault state and the switching element does not become an overcurrent. It is a feature.

Further, in the inverter device according to the second invention, in the first invention, when the current value detected by the current detector is smaller than the first reference current value, the current value is gradually increased until the current value becomes the first reference current value. Further, the on-time is increased.

According to a third aspect of the present invention, there is provided an inverter device comprising: a converter unit that rectifies an alternating current input from an alternating current power supply; an input interruption means that turns on and off the alternating current power supply; and a rectified output of the converter unit. A smoothing unit that is charged and outputs a smoothed voltage obtained by smoothing the rectified output; a switching element that forms an upper arm and a lower arm; and a free-wheeling diode that is connected in parallel to the switching element; The smoothing unit includes an inverter unit that performs PWM control and supplies alternating current from the output to the load, and a current detection unit that detects a current value flowing through the output of the inverter unit. A ground fault detection unit that determines that a ground fault occurs when the current value becomes larger than the second reference current value until the battery is charged. It is intended.

According to a fourth aspect of the present invention, there is provided an inverter device that rectifies an alternating current input from an alternating current power source, and is charged by a rectified output of the converter portion and outputs a smoothed voltage obtained by smoothing the rectified output. And an inverter for supplying an alternating current from the output to the load by PWM control while inputting the smoothing voltage and a switching diode that forms an upper arm and a lower arm and a free-wheeling diode connected in parallel to the switching element A current detection unit that detects a current value that flows to the output of the inverter unit, a duty setting unit that sets a duty of an on / off time of the switching element, and the upper arm or the arm based on the duty After turning on the gate control unit for turning on and off the switching element and the on / off means, the smoothing unit is charged. Until the current value becomes larger than the second reference current value, and when the ground fault detection unit determines that there is a ground fault, The ground fault resistance estimation part which estimates ground fault resistance based on the detection current is provided.

In the inverter device according to the fifth invention, in the fourth invention, when the ground fault detection unit does not determine that there is a ground fault, the duty setting unit charges the smoothing unit after turning on the shut-off means. The duty of the switching element is set based on the current value until.

Further, in the inverter device according to the sixth invention, in the fourth invention, when the ground fault detection unit does not determine that there is a ground fault, the duty setting unit charges the smoothing unit after turning on the shut-off means. Until the initial value of the duty is set based on the current value until the current value becomes the first reference current value when the current value is smaller than the first reference current value, It is characterized by this.

According to the first invention, the duty setting unit for setting the duty of the on / off time of the switching element at the time of detecting the ground fault is provided, and the on time during which the switching element is not thermally destroyed even in the ground fault state is set as the duty. I did it. Therefore, the ground fault current flowing through the switching element can be limited, and the ground fault can be detected without causing the switching element to be thermally destroyed.
At the same time, a ground fault resistance estimation unit is provided to estimate the ground fault resistance based on the duty set by the duty setting unit and the current value detected by the current detection unit. There is an effect that it is possible to predict the ground fault in advance.

  According to the second invention, the duty control unit sets the initial value of the duty so that the on-time is sufficiently short, and the current value detected by the current detection unit is smaller than the first reference value. Since the ON time is gradually increased until the current value reaches the first reference current value, the ground fault current can be measured with high accuracy while preventing the switching element from being overcurrent. This has the effect that the ground fault resistance can be estimated with high accuracy.

  In addition, according to the third aspect of the invention, since the ground fault detection unit that detects the ground fault by monitoring the current value during the period after the AC power supply is turned on until the smoothing unit is charged is provided. There is an effect that breakage of the return diode in the process can be prevented.

  According to the fourth invention, the ground fault resistance estimation unit for estimating the ground fault resistance based on the duty set by the duty setting unit and the current value detected by the current detection unit, and the charging process of the smoothing unit A ground fault detection unit that detects a ground fault from the current value of the ground fault, and when the ground fault detection unit does not determine a ground fault, the ground fault resistance estimation unit estimates the ground fault resistance. There is an effect that the ground fault resistance can be estimated by reducing the thermal damage of the diode.

  According to a fifth aspect of the present invention, when the ground fault detection unit does not determine that there is a ground fault, the duty setting unit sets the current during a period until the smoothing unit is charged after turning on the AC power supply. Since the on / off duty of the switching element is set based on the current value detected by the detector, there is an effect that the ground fault resistance can be estimated while preventing an overcurrent of the switching element.

  According to the sixth invention, when the ground fault detection unit does not determine that a ground fault has occurred, the duty setting unit is configured to wait until the smoothing unit is charged after the AC power is turned on. The initial value of the duty is set on the basis of the current value detected at, and if the current value detected by the current detection unit is smaller than the first reference current value, gradually until the current value becomes the first reference current value The on-time has been lengthened. Thereby, it is not necessary to shorten the on time more than necessary when setting the initial value of the duty, and there is an effect that the time required to estimate the ground fault resistance can be shortened.

Example 1.
An embodiment of the present invention will be described below with reference to FIG. FIG. 1 is an overall configuration diagram of an inverter device showing an embodiment. In FIG. 1, the same parts as those in FIG.
In FIG. 1, reference numeral 20 denotes a duty setting unit for setting on / off duty of the switching elements 4a to 4f. The duty setting unit 20 prevents the switching elements 4a to 4f from thermal fatigue even in a ground fault state. The duty is set so as to have a short on-time. 21 is a ground fault resistance estimation unit that estimates the resistance value of the ground fault resistance 18 from the duty set by the duty setting unit 20 and the detected current values detected by the current detectors (current detection units) 5a to 5c. It is a ground fault determination unit that determines a ground fault when the ground fault resistance estimated by the ground fault resistance estimation means 21 is small.

Next, the operation of this embodiment will be described in the case where the W phase of the motor 7 is grounded. After the closing switch 13 serving as the closing / blocking means is turned on and the smoothing capacitor 9 serving as the smoothing unit is charged, the gate control unit 10 turns off the switching elements 4a to 4c of the upper arm and switches the switching element 4d of the lower arm. Only .about.4f is turned on / off at a constant cycle based on the duty of the on / off time set by the duty setting unit 20.
The determination after the smoothing capacitor 9 is charged is made when the closing switch 13 is turned on and a predetermined time elapses after the charging.

When no ground fault occurs, no current flows through the switching elements 4d to 4f even if the switching elements 4d to 4f are turned on, so that the current detected by the current detectors 5a to 5c is zero.
On the other hand, when the W phase of the motor 7 is grounded, the circuit indicated by the broken line 19 in FIG. 1 is equivalently formed. For this reason, when the switching elements 4d to 4f are turned on, the ground phase (S phase in FIG. 1) of the AC power source 1 is passed through the ground fault resistor 18 and the W phase switching element 4f is passed through the diode 2d or the diode 2f, A single-phase half-wave ground fault current flows to the R or T phase of the AC power supply 1. This ground fault current is detected by the W-phase current detector 5c. At this time, the ground fault current flowing through the W-phase switching element 4f is proportional to the ON time of the switching element 4f. Therefore, if the ON time is sufficiently shorter than the OFF time, the value of the current flowing through the switching element 4f is small. Can be limited to values.
Therefore, the thermal fatigue of the switching element 4f can be reduced.

  Since the ground fault current does not flow through the U-phase and V-phase switching elements 4d and 4e, the current values detected by the U-phase and V-phase current detectors 5b and 5c are zero.

The ground fault resistance estimation unit 21 inputs the duty set by the duty setting unit 20 and the current value detected by the current detectors 5a to 5c, and estimates the ground fault resistance Rg.
Since the line voltage Vs of the power source and the duty voltage are the average voltage Vave, the average voltage Vave is as follows.
Vave = Vs (ton / ton + toff) (1)
Here, ton: on time toff: off time On the other hand, using the maximum value Imax of the detected current value detected by the current detectors 5a to 5c within one cycle of the line voltage frequency, The tangential resistance Rg is obtained.
Rg = Vave / Imax (2)
In this embodiment, since the current values of the U phase and the V phase are zero, the ground fault resistance of these phases is infinite. On the other hand, since a large current flows through the grounded W phase, the ground resistance becomes a small value.

The ground fault determination unit 22 determines that there is a ground fault when the value of the ground fault resistance obtained by the ground fault resistance estimation unit 21 is small, and performs processing such as gate cutoff and alarm display. When the value of the ground fault resistance is infinite or extremely large, the ground fault state is not determined, and the normal operation state is entered.
If the ground fault resistance becomes an intermediate value, it is not determined that the ground fault is present, but it is determined that the motor insulation has deteriorated and a warning is displayed.

  In the above embodiment, the lower arm switching elements 4d to 4f are turned on / off. However, the lower arm switching elements 4d to 4f are turned off, and only the upper arm switching elements 4a to 4c are turned on. The same effect can be obtained even if is turned on / off.

  Moreover, in the said Example, although the duty set by the duty setting part 20 is made into the constant value, this is changed according to the electric current value detected by the current detectors 5a-5c, and ground fault resistance Can be estimated with higher accuracy. If the ground fault resistance is large, the current value detected by the current detectors 5a to 5c becomes a small value, so that it is easily affected by noise and the current detection accuracy is deteriorated. Along with this, the estimation accuracy of the ground fault resistance also deteriorates. When the current values detected by the current detectors 5a to 5c are small values less than or equal to a predetermined value, the duty ON time is lengthened and the current value flowing through the current detectors 5a to 5c is increased to reduce noise. The influence can be eliminated, the current detection accuracy can be improved, and the estimation accuracy of the ground fault resistance can be improved.

  FIG. 2 is a flowchart showing the operation of the duty setting unit when the duty is changed according to the current value detected by the current detectors 5a to 5c. First, in step S1, the duty of the on / off time is set to an initial value. The initial value of the duty is selected so that the switching elements 4a to 4f have a short on-time that does not cause an overcurrent even if they are in a ground fault state. Next, the current value detected by the current detectors 5a to 5c in step S2 is input, and in step S3, it is determined whether or not this current value is larger than the first reference current value. Here, a current value having a magnitude that is not easily affected by noise is selected in advance as the first reference current value. If it is determined that the current value detected in step S3 is smaller than the first reference current value, the duty is set to a slightly longer duty in step S4, and the process returns to step S2. If it is determined that the current value detected in step S3 is greater than or equal to the first reference current value, the duty is fixed to the value at that time, and the process ends.

  Thus, the current detection accuracy can be improved by adjusting the duty so that the current values detected by the current detectors 5a to 5c are not affected by noise. It becomes possible to estimate the leakage resistance with high accuracy.

Example 2
FIG. 3 shows the configuration of the inverter device according to the second embodiment of the present invention, and the same parts as those in FIG. In the figure, reference numeral 24 denotes a ground fault detector, which is newly provided in addition to the embodiment 1 of FIG.

  Next, the operation will be described. When the input switch 13 of the inverter device is turned on, AC power is input to the converter unit 14, and the AC power is rectified and output to DC power by the diode bridges 2a to 2f. The DC power output from the converter unit 14 is charged in the smoothing capacitor 9. The ground fault detection unit 24 detects the ground fault by monitoring the current values detected by the current detectors 5a to 5c during the period until the charging of the smoothing capacitor is completed after the closing switch 13 is turned on.

  In the charging process until charging of the smoothing capacitor is completed after the closing switch 13 is turned on, the current detected by the current detectors 5a to 5c since no current flows through the inverter unit 15 unless it is in the ground fault state. The value is zero. However, for example, when the W phase of the motor is grounded, the circuit shown by the broken line 19 in FIG. 2 is equivalently configured, so that the ground fault resistance 18, W from the ground phase (S phase) of the AC power supply 1 is configured. A charging current flows through the smoothing capacitor 9 through the phase free-wheeling diode 3c. This current is detected by the W-phase current detector 5c, and based on this, the ground fault detector 24 detects the W-phase ground fault.

  When the current value detected by the current detectors 5a to 5c is excessive and exceeds the second predetermined current value, the ground fault detection unit 24 immediately determines that there is a ground fault and shuts off the input switch 13. This prevents the freewheeling diodes 3a to 3f from being damaged. If the current value detected by the current detectors 5a to 5c is equal to or smaller than the second predetermined current value and does not reach the overcurrent of the freewheeling diodes 3a to 3f, the ground fault detection unit 24 is connected to the ground fault. The duty setting unit 20, the gate control unit 10, and the ground fault resistance estimation unit 21 are operated. These operate in the same manner as in the first embodiment and estimate the ground fault resistance.

  When the ground fault detection unit 24 does not determine that there is a ground fault and the duty setting unit 20, the gate control unit 10, and the ground fault resistance estimation unit 21 are operated, the duty setting unit based on the current value detected in the charging process. Duty of on / off time is set. When the current value detected in the charging process is large, it can be determined that the ground fault resistance is small. Therefore, the thermal fatigue loss of the switching elements 4a to 4f can be prevented by setting the duty ON time short. Conversely, when the current value detected in the charging process is small, it can be determined that the ground fault resistance is large, so by setting the duty on time to be long, the current value flowing through the current detectors 5a to 5c can be increased, The influence of noise is reduced, and the ground fault resistance can be estimated with high accuracy.

  FIG. 4 is a flowchart showing this sequence. First, in step S10, the on switch 13 is turned on to turn on the AC power source 1. Next, in step S11, the ground fault detector 24 inputs the current value detected by the current detectors 5a to 5c, and compares the current value input in step S12 with the second predetermined current value to determine whether it is excessive. to decide. If it is determined in step S12 that it is excessive, it is determined that there is a ground fault, the process proceeds to step S13, the input switch 13 is shut off, an error is displayed in step S14, and the process ends. If it is not determined that the value is excessive in step S12, the process proceeds to step S15 to determine whether or not the charging process is completed. Whether or not the charging process is completed can be determined by detecting the voltage across the smoothing capacitor 9. Thereby, when the terminal voltage of the smoothing capacitor 9 becomes equal to or higher than a predetermined value, it is determined that the charging process is finished.

  If the charging process has not ended, the process returns to step S11 and the ground fault detection is repeated. If the charging process has been completed, the process proceeds to step S16, and ground fault resistance estimation is started. In other words, the duty setting unit 20 sets the duty based on the magnitude of the current value detected in the charging process, and starts the operation of the gate control unit in step S17, thereby enabling the switching elements 4a to 4c or 4d to 4f. Start switching. Next, in step S18, the ground fault resistance estimation unit estimates the ground fault resistance from the duty set by the duty setting unit 20 and the current values detected by the current detectors 5a to 5c.

  In step S19, the degree of motor insulation deterioration is estimated based on the ground fault resistance estimated in step S18. If the insulation deterioration is significant, a warning is displayed in step S20. On the other hand, if the degree of insulation deterioration is in an allowable range, the process proceeds to step S21 and normal operation is started.

  In the second embodiment, the duty of the on / off time set by the duty setting unit 20 is set based on the current value detected in the charging process, but based on the current value detected in the charging process. If the initial value of the duty is set and changed according to the detected current value as shown in the flowchart of FIG. 2, the ground fault resistance can be estimated with higher accuracy. Furthermore, since the initial value of the duty is set based on the current value detected in the charging process, it is not necessary to shorten the on time of the initial value more than necessary, and the time required to estimate the ground fault resistance is shortened. be able to.

  The inverter device according to the present invention is suitable for use in ground fault detection.

It is a block diagram which shows the whole structure of the inverter apparatus which concerns on one Example of this invention. It is a flowchart which shows an example of operation | movement of the duty setting part shown in FIG. It is a block diagram which shows the whole structure of the inverter apparatus which concerns on the other Example of this invention. It is a flowchart which shows operation | movement of the inverter apparatus shown in FIG. It is a block diagram which shows the whole structure of the conventional inverter apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 AC power supply, 5a, 5b, 5c Current detector (current detection part), 9 Smoothing capacitor (smoothing part), 10 Gate control part, 13 Input switch (input interruption | blocking means), 14 Converter part, 15 Inverter part, 20 Duty Setting unit, 21 Ground fault detection unit, 24 Ground fault detection unit.

Claims (6)

A converter for rectifying the alternating current input from the alternating current power supply;
A smoothing unit that is charged by the rectified output of the converter unit and outputs a smoothed voltage obtained by smoothing the rectified output;
An inverter unit having a switching element that forms an upper arm and a lower arm and a free wheeling diode connected in parallel to the switching element, inputs the smoothed voltage, and performs PWM control to supply alternating current from the output to a load;
A current detection unit for detecting a current value flowing through the output of the inverter unit;
A duty setting unit for setting a duty of an on / off time of the switching element;
A gate control unit for turning on and off the switching element of the upper arm or the lower arm based on the duty;
A ground fault resistance estimation unit that estimates ground fault resistance based on the duty and the current value;
The duty is set to the on-time so that the output of the inverter unit is in a ground fault state and the switching element does not become overcurrent.
An inverter device characterized by that. When the current value is smaller than the first reference current value, the ON time is gradually lengthened until the current value becomes the first reference current value.
The inverter device according to claim 1. A converter for rectifying the alternating current input from the alternating current power supply;
On / off means for turning on and off the AC power to the converter unit;
A smoothing unit that is charged by the rectified output of the converter unit and outputs a smoothed voltage obtained by smoothing the rectified output;
An inverter unit having a switching element that forms an upper arm and a lower arm and a free wheeling diode connected in parallel to the switching element, inputs the smoothed voltage, and performs PWM control to supply alternating current from the output to a load;
A current detection unit for detecting a current value flowing to the output of the inverter unit;
A ground fault detection unit that determines a ground fault when the current value is greater than a second reference current value after the turning-off means is turned on and before the smoothing unit is charged;
An inverter device characterized by that. A converter for rectifying the alternating current input from the alternating current power supply;
A smoothing unit that is charged by the rectified output of the converter unit and outputs a smoothed voltage obtained by smoothing the rectified output;
An inverter unit having a switching element that forms an upper arm and a lower arm and a free wheeling diode connected in parallel to the switching element, inputs the smoothed voltage, and performs PWM control to supply alternating current from the output to a load;
A current detection unit for detecting a current value flowing through the output of the inverter unit;
A duty setting unit for setting a duty of an on / off time of the switching element;
Based on the duty, a gate control unit for turning on or off the switching element of the upper arm or the arm,
A ground fault detection unit that determines a ground fault when the current value is greater than a second reference current value after charging the blocking unit and before the smoothing unit is charged;
If the ground fault is not determined in the ground fault detection unit, the ground fault resistance estimation unit for estimating the ground fault resistance based on the duty and the detected current,
An inverter device characterized by that. If the ground fault detection unit does not determine that there is a ground fault, the duty setting unit may turn on the switching element based on the current value before the smoothing unit is charged after the input cutoff unit is turned on. Set the duty,
5. The inverter device according to claim 4, wherein: If the ground fault detection unit does not determine that there is a ground fault, the duty setting unit sets the initial duty based on the current value between the time when the charging / shut-off unit is turned on and the time when the smoothing unit is charged. A value is set, and when the current value is smaller than the first reference current value, the ON time is gradually increased until the current value becomes the first reference current value.
The inverter device according to claim 4.

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