JP6626431B2 - Power converter with discharge function - Google Patents

Description

  The present invention relates to a power conversion device having a discharge function, and particularly to a discharge abnormality detection technique for the power conversion device.

  In a power conversion device such as a large-capacity inverter or servo driver, it is necessary to immediately discharge the charged power for safety after the operation is stopped. Therefore, although a discharge circuit is provided, it is necessary to perform a protection operation when the discharge circuit or the like has an abnormality.

  As a background art for solving this problem, Patent Document 1 discloses “a converter that converts a DC voltage output from a battery to a DC voltage of a different level, and a DC voltage that is output from the converter to an AC voltage and is applied to a load. A discharge circuit including: an inverter to be applied; a smoothing capacitor provided in parallel with the converter and the inverter; a resistor through which a discharge current flows from the smoothing capacitor; and a switching element that opens and closes a current path through which the discharge current flows. Circuit failure detection device for detecting a failure of a discharge circuit in a system including a voltage sensor for detecting a voltage across the terminals of the circuit, performs switching operation of a current path by a switching element by PWM control at two different duty ratios. And the rate of change of the voltage between both ends obtained at the stage of PWM control at a low duty ratio and Based on the rate of change of voltage across obtained in step a PWM control at a duty ratio, it detects the presence or absence of a failure of the discharge circuit. "Is described as (see Abstract).

JP 2015-116097 A

  In recent years, large-capacity inverters and servo drivers have added a large-capacity capacitor to the DC bus for peak cutting during the operation cycle, and have adopted a common converter system for energy saving. The capacity of the capacitor on the DC bus takes various values depending on the equipment, such as having a plurality of inverter units. Further, since the discharge resistance is selected according to the capacitance of the capacitor, the state of the discharge differs depending on the equipment, and it becomes difficult to detect the discharge operation and the abnormality of the discharge circuit.

  In the method described in Patent Literature 1, a discharge circuit is determined in advance by comparing a voltage change rate of a voltage between both ends of a smoothing capacitor during a predetermined two different discharge operations with a normal value in a predetermined discharge circuit. As described above, when the capacitor capacity and the discharge resistance value are various and cannot be determined uniformly depending on the equipment, a normal value cannot be determined for each system. Further, it is considered that the voltage serving as a reference for the protection operation due to a change in the capacitance of the capacitor may not be appropriate for the device at a predetermined value.

  An object of the present invention is to detect a discharge abnormality in the same procedure without setting an abnormality determination value for each device in a power conversion device having various discharge functions having different capacitor capacities and discharge resistance values. I do.

  In order to solve the above-mentioned problem, in the present invention, a voltage change rate of a DC bus during a certain period of time during a discharging operation is obtained to generate a value corresponding to a circuit time constant, and a change in the value is used to detect a circuit abnormality.

  To give an example of the power conversion device of the present invention, a converter for converting an input alternating current into a direct current, a smoothing capacitor for smoothing the direct current, and an inverter for converting the direct current into an alternating current and outputting it to a motor, A power conversion device having a discharge function having a discharge circuit that discharges the charge of the smoothing capacitor when the device is stopped, a voltage detector that detects a voltage of the smoothing capacitor, and a voltage detector that detects the voltage of the smoothing capacitor. A discharge abnormality detection unit that detects a discharge abnormality based on the detection voltage, wherein the discharge abnormality detection unit calculates a voltage change rate that is a ratio of the detection voltages before and after a predetermined time, and a voltage change rate detection unit that calculates the voltage change rate. An abnormality determination unit that performs an abnormality determination by comparing the voltage change rate with a reference value.

  According to the present invention, in a power conversion device having various discharge functions having different capacitor capacities and discharge resistance values, it is possible to detect a discharge abnormality in the same procedure without setting an abnormality determination value for each device. it can. In addition, the calculation cost can be reduced by not calculating the circuit time constant itself.

1 is a schematic diagram of a power conversion device according to a first embodiment of the present invention. FIG. 3 is a diagram illustrating an equivalent circuit of the discharge circuit according to the first embodiment. FIG. 3 is a diagram illustrating a voltage change at the time of discharging of the discharging circuit of FIG. 2. FIG. 4 is a diagram illustrating a voltage change when a discharge circuit is abnormal in the first embodiment. FIG. 4 is a diagram illustrating a voltage change rate detection unit according to the first embodiment. FIG. 4 is a diagram illustrating an abnormality determination unit according to the first embodiment. FIG. 7 is a diagram illustrating a voltage change when a discharge circuit is abnormal in Embodiment 2 of the present invention. FIG. 11 is a diagram illustrating an abnormality determination unit according to a third embodiment of the present invention. It is a schematic diagram of a power converter of a fourth embodiment of the present invention. FIG. 14 is a diagram illustrating an abnormality determination unit according to a fourth embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings for describing the embodiments, the same constituent elements are given the same names and symbols as much as possible, and the repeated description thereof will be omitted.

  FIG. 1 is a schematic diagram of a power conversion device according to a first embodiment of the present invention. The power conversion device 1 includes a smoothing capacitor 4, a discharge circuit 5, a voltage detection circuit 6, a converter unit 7, an inverter unit 8, and a circuit control unit 10, and an external capacitor 2 and an external discharge resistor 3 are connected. In the configuration of FIG. 1, an external capacitor 2 and an external discharge resistor 3 are connected for peak cutting. Even with the above-described common converter system, the basic configuration is the same, except that only a plurality of inverter units 8 to motors 9 are connected in parallel. Further, in FIG. 1, the symbols of diodes and transistors are used for the discharge circuit 5, the inverter unit 8 and the converter unit 7, but this is an example, and any type may be used as long as it provides the same function. The circuit control unit 10 controls the switch element of the inverter unit 8, the switch element 13 of the discharge circuit 5, and the like.

First, the principle of the present invention will be described with reference to FIGS.
In general, a circuit at the time of discharging is operated after the power is cut off, and is represented by an equivalent circuit in which a capacitor 21, a discharging resistor 22, and a switch 23 are connected in series as shown in FIG. In this circuit, the switch 23 is turned on, and the electric charge charged in the capacitor 21 is discharged through the discharge resistor 22. 2 is a combination of the internal capacitor 14 and the external capacitor 2 of FIG. 1, the discharge resistor 22 corresponds to the external discharge resistor 3, and the switch 23 corresponds to the switch element 13 of the discharge circuit 5.
At this time, if the circuit can discharge normally, if t is time, the voltage V (t) across the capacitor 21 is
V (t) = V0 · exp (−t / τ) [V]
Is represented by

here,
V0: Voltage when t = 0
exp: natural exponential function τ: circuit time constant, τ = CR in the equivalent circuit of FIG.
C: capacitance of the capacitor 21
R: resistance value of the discharge resistor 22

The voltage at both ends of the capacitor at the next time t1 and t2 = t1 + dt after dt time is
V (t1) = V0exp (-t1 / τ)
V (t2) = V0 ・ exp (−t2 / τ) = V0 ・ exp (− (t1 + dt) / τ)
Becomes
The voltage change rate A during dt is A = V (t2) / V (t1) = exp (−dt / τ)
It becomes. Since τ is a circuit time constant, it is constant. When dt is constant, the rate of change A is constant regardless of time t.
Therefore, as shown in FIG. 3, the voltage decreases at the rate of the rate of change A regardless of dt at any time during the discharge time.

Next, a case where an abnormality occurs in the circuit will be considered. FIG. 4 shows a graph of a DC voltage change when an abnormality occurs in the circuit during the discharge period. For example, when some of the discharge resistors 3 connected in parallel are burned or the like and the resistance value increases, that is, when R increases and the time constant τ increases in the above calculation, the voltage change rate B1 is obtained. And the normal voltage change rate A,
B1> A
It becomes. FIG. 4 shows a case shown by a broken line (abnormality (large time constant)). In particular, when all the resistors fail in an open state or when a break occurs in the circuit, the DC voltage has a constant value.

Conversely, when the discharge resistance is short-circuited internally and the resistance value is reduced, that is, when R is reduced and the time constant τ is reduced in the above calculation, the voltage change rate B2 is calculated as B2 <A
It becomes. FIG. 4 shows a case like the one-dot chain line (abnormality (small time constant)).

  Further, elements that do not appear on the equivalent circuit of FIG. 2, for example, when the operation of the circuit breaker 11 provided between the power supply 12 and the converter unit 7 in FIG. 1 is insufficient, or the operation of the power converter 1 is stopped Even when the motor 9 is driven by an external force to enter a power generation state despite the later time, the smoothing capacitor 4 is additionally charged, so that the voltage change is shown in FIG. From the broken line (abnormal (large time constant)). The voltage change rate obtained by the above calculation method is different from the voltage change rate A in the normal state.

As described above, since the voltage change rate A in the normal state and the voltage change rates B1 and B2 in the abnormal state have different values, it is possible to detect the abnormality of the discharge circuit by comparing the values.
Here, the magnitude of the dt, the timing of acquiring the voltage, the frequency, and the like depend on the design of the power conversion device and the system including the power conversion device, and thus are not particularly limited.
Further, although the voltage change rate A is a reference value for abnormality determination in the above description, there is no problem even if it has a certain width due to a voltage detection error in circuit design and a design margin.

  A configuration for detecting a discharge abnormality of a circuit based on the principle described with reference to FIGS. In FIG. 1, the power converter includes a discharge abnormality detection unit 15. The discharge abnormality detection unit 15 includes a voltage change rate detection unit 16, an abnormality determination unit 17, an output unit 18, and a storage unit 19 that stores a reference value. Have.

  The voltage change rate detection unit 16 includes a sampling unit 51 and a division unit 52, for example, as shown in FIG. The DC voltage of the DC bus detected by the voltage detection circuit 6 is sampled by the sampling unit 51 every predetermined time dt. Then, the division unit 52 obtains the voltage change rate B by dividing the ratio of the DC voltage before and after the dt time, that is, the DC voltage value after the dt time.

  The abnormality determining unit 17 includes an upper limit comparing unit 61 and a lower limit comparing unit 62, for example, as shown in FIG. The voltage change rate signal B obtained by the voltage change rate detection unit 16 is applied to the upper limit comparison unit 61 and the lower limit comparison unit 62. The upper limit comparing section 61 compares the voltage change rate signal B with a reference value, and outputs an abnormality determination signal when the voltage change rate signal B exceeds the reference value. By using αA that is α times the normal value A of the voltage change rate (here, α> 1) as the reference value, it is possible to detect an abnormality in which the time constant in FIG. 4 is large. Conversely, the lower limit comparing section 62 compares the voltage change rate signal B with the reference value, and outputs an abnormality determination signal when the voltage change rate signal B falls below the reference value. By using βA that is β times the normal value A of the voltage change rate (here, β <1) as the reference value, an abnormality in which the time constant in FIG. 4 becomes small can be detected.

  The storage unit 19 stores the reference value and supplies the reference value to the abnormality determination unit 17. Further, the voltage change rate B obtained by the voltage change rate detection unit may be stored as needed.

  The output unit 18 displays or warns an abnormal state based on the abnormality determination signal obtained by the abnormality determination unit 17. Further, a communication unit may be provided to transmit the data to an external tablet terminal or the like.

As shown in FIG. 4, when an abnormality occurs in the circuit during the discharge period, the voltage change rate changes during the discharge. The voltage change rate A at the start of discharge is obtained, and the reference values αA and βA of the abnormality determination unit 17 are set based on this value. Then, the abnormality determination unit 17 can detect an abnormality of the circuit during the discharge period by sequentially comparing the voltage change rate signal B obtained thereafter.
Note that the reference value may be created from a previously determined voltage change rate during normal discharge.

  According to the present embodiment, by using the voltage change rate during normal discharge as a reference value, an abnormality determination value is set for each device in a power conversion device having various discharge functions with different capacitor capacitances and discharge resistance values. It is possible to detect a discharge abnormality in the same procedure without performing the same. In addition, the calculation cost can be reduced by not calculating the circuit time constant itself. Further, by setting the reference value based on the voltage change rate obtained at the start of the discharge, it is possible to reliably detect an abnormality during one discharge period.

  FIG. 7 shows a graph of a DC voltage change when an abnormality has occurred in the circuit before the start of discharge. In the power converter shown in FIG. 1, for example, when the resistance value of the discharge resistor 3 is increased or decreased before the start of the discharge operation, the voltage change rates B1 and B2 are abnormal from the start of the discharge operation. The judgment level is reached. The second embodiment is to detect an abnormality of this circuit.

  In the present embodiment, the abnormality determination unit 17 shown in FIGS. 1 and 6 uses the normal voltage change rate at the time of the previous discharge as the voltage change rate A used for the reference values αA and βA. The normal voltage change rate A at the time of the previous discharge is stored in the storage unit 19 and sent to the abnormality determination unit 17. By performing the abnormality determination using the normal voltage change rate A at the time of the previous discharge, the abnormality can be determined from the start of the discharge.

  In the power converter of FIG. 1, for example, when the ambient temperature of the internal capacitor 14 and the external capacitor 2 is higher than expected, if the capacitor is used in a severe operation pattern in which acceleration and deceleration frequently occur, the capacity of the capacitor gradually increases due to aging. May drop. The third embodiment detects such a sign of a failure.

  FIG. 8A shows an abnormality determination unit of the present embodiment, and FIG. 8B shows a reference value used for the abnormality determination unit. The upper limit comparing unit 61 uses α1A and α2A (here, α1, α2> 1, α1> α2) as reference values for comparison. When the voltage change rate signal B exceeds the reference value α2A and is equal to or less than the reference value α1A, a failure sign signal is output. When the voltage change rate signal B exceeds the reference value α1A, an abnormality determination signal is output. Similarly, the lower limit comparing unit 62 uses β1A and β2A (here, β1, β2 <1, β1 <β2) as reference values for comparison. When the voltage change rate signal B falls below the reference value β2A and is equal to or higher than the reference value β1A, a failure sign signal is output. When the voltage change rate signal B falls below the reference value β1A, an abnormality determination signal is output.

  When the capacity of the capacitor decreases, the time constant of the discharge decreases. Therefore, by detecting that the voltage change rate has become smaller than a predetermined reference value, it is possible to detect a sign of failure. Further, by providing the reference value α2A in the upper limit comparing section, it is possible to detect a sign of a failure in which the time constant becomes large.

  According to the present embodiment, by providing a judgment value smaller than the judgment value of the abnormality judgment, a sign of failure can be determined, and the maintenance time can be notified based on the failure sign signal.

  In the power converter of FIG. 1, when the motor 9 is forcibly rotated by an external force during the discharging operation, the motor 9 becomes a generator, and the smoothing capacitor 4 and the external capacitor 2 are charged with regenerative energy. Therefore, in the diagrams showing the discharge voltage in FIG. 4 and FIG. 7, the change of the DC voltage is like a curve of the voltage change rate B1 at the time of abnormality (large time constant). In the fourth embodiment, it is possible to detect whether an abnormality is determined due to the motor becoming a generator due to an external force or other abnormality is determined.

  FIG. 9 is a schematic diagram of a power conversion device according to the fourth embodiment, and FIG. 10 illustrates an abnormality determination unit 17 according to the fourth embodiment.

  In the present embodiment, as shown in FIG. 9, the position detector 20 is connected to the motor shaft to obtain a motor shaft angle signal D, which is sent to the abnormality determination unit 17. As shown in FIG. 10A, the abnormality determination unit 17 is provided with a rotation speed calculation unit 63 and a rotation speed abnormality determination unit 64. The rotation speed calculator 63 calculates the motor rotation speed from the motor shaft angle signal D and sends it to the rotation speed abnormality determination unit 64. The rotation speed abnormality determination unit 64 detects the rotation of the motor, that is, the motor rotation abnormality during the discharging operation, by comparing the motor rotation speed with the reference values γC and δC (here, γ> 1, δ <−1). I do. FIG. 10B shows a reference value used in the rotation speed abnormality determination unit 64.

The determination unit 65 determines the abnormality of the external discharge resistor 3 by combining the abnormality determination signal obtained by the upper limit comparison unit 61 and the lower limit comparison unit 62 with the rotation abnormality signal of the motor obtained by the rotation abnormality determination unit 64. It is possible to distinguish between an abnormality determination based on a change in the time constant of the smoothing capacitor 4 and the external capacitor 2 or an abnormality determination based on the fact that the motor becomes a generator due to an external force.
In the above description, the motor rotation speed is calculated by the rotation speed calculation unit 63 from the motor shaft angle signal of the position detector 20, but may be measured by connecting a speed detector (tachogenerator) to the motor shaft. .

  According to the present embodiment, the abnormality determination is performed in accordance with the rotation abnormality of the motor during the discharging operation, so that the abnormality determination is performed by the motor becoming a generator due to an external force, or the external discharge resistor 3 and the smoothing capacitor 4 are used. For example, it is possible to determine whether the abnormality is determined by a change in the time constant due to the above-described operation.

The present invention is not limited to the above embodiments, but includes various modifications. For example, the above-described embodiments have been described in detail in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the described configurations. In addition, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of one embodiment can be added to the configuration of another embodiment. Further, for a part of the configuration of each embodiment, it is possible to add / delete / replace another configuration.
Further, each of the above-described configurations, functions, processing units, processing means, and the like may be partially or entirely realized by hardware, for example, by designing an integrated circuit. In addition, the above-described configurations, functions, and the like may be implemented by software by a processor interpreting and executing a program that implements each function. Information such as a program, a table, and a file that realize each function can be stored in a memory, a hard disk, a recording device such as an SSD (Solid State Drive), or a recording medium such as an IC card, an SD card, or a DVD.
In addition, control lines and information lines indicate those which are considered necessary for explanation, and do not necessarily indicate all control lines and information lines on a product. In fact, it may be considered that almost all components are interconnected.

REFERENCE SIGNS LIST 1 Power conversion device 2 External capacitor 3 External discharge resistor 4 Smoothing capacitor 5 Discharge circuit 6 Voltage detection circuit 7 Converter unit 8 Inverter unit 9 Motor 10 Circuit control unit 11 Circuit breaker 12 AC power supply 13 Switch element 14 Internal capacitor 15 Discharge abnormality detection unit 16 Voltage change rate detection unit 17 Abnormality judgment unit 18 Output unit 19 Storage unit (reference value)
Reference Signs List 20 position detector 21 capacitor 22 discharge resistor 23 switch 51 sampling unit 52 division unit 61 upper limit comparison unit 62 lower limit comparison unit 63 rotation speed calculation unit 64 rotation speed abnormality determination unit 65 determination unit

Claims (5)

A converter for converting the input alternating current into direct current, a smoothing capacitor for smoothing the direct current, an inverter for converting the direct current to alternating current and outputting to the motor, and discharging the electric charge charged in the smoothing capacitor when the apparatus is stopped. A power conversion device having a discharge function having a discharge circuit,
A voltage detector for detecting the voltage of the smoothing capacitor;
A discharge abnormality detection unit that detects a discharge abnormality based on a detection voltage detected by the voltage detector,
With
The discharge abnormality detection unit,
A voltage change rate detection unit that obtains a voltage change rate that is a ratio of detection voltages before and after a predetermined time,
An abnormality determination unit that performs an abnormality determination by comparing the obtained voltage change rate with a reference value;
A power conversion device comprising: The power converter according to claim 1,
The abnormality determination unit performs an abnormality determination by comparing a voltage change rate obtained during a certain period during a discharge period with a reference value for comparison and comparing the voltage change rate again obtained during the same discharge period. Power converter. The power converter according to claim 1,
The power converter according to claim 1, wherein the abnormality determination unit performs abnormality determination by using a previously obtained normal voltage change rate as a reference value for comparison and comparing the voltage change rate obtained during a discharge period. The power converter according to claim 2 or 3,
The abnormality determination unit further sets a voltage change rate that is closer to a normal value than a reference value for comparison for performing abnormality determination as a reference value for comparison of the sign determination, compares the voltage change rate with a voltage change rate obtained during the discharge period, and A power conversion apparatus characterized by performing a sign determination of the power conversion. The power converter according to claim 2 or 3,
Furthermore, a motor rotation detecting means is provided,
The power converter according to claim 1, wherein the abnormality determination unit detects a rotation abnormality of the motor and distinguishes whether the abnormality obtained from the change in the voltage change rate is due to a circuit abnormality or an abnormality due to motor rotation.

Images