WO2018117058A1

WO2018117058A1 - Power conversion device with discharge function

Info

Publication number: WO2018117058A1
Application number: PCT/JP2017/045400
Authority: WO
Inventors: 公徳清水; 英人高田; 淳之介井村
Original assignee: 株式会社日立産機システム
Priority date: 2016-12-20
Filing date: 2017-12-18
Publication date: 2018-06-28
Also published as: KR20190009829A; CN109463034B; CN109463034A; JP2018102042A; KR102089915B1; JP6626431B2

Abstract

Provided is a power conversion device with various discharge functions with different capacitances and discharge resistor values, wherein discharge abnormality is detected using the same procedure without setting an abnormality determination value on a per-device basis. The power conversion device with the discharge functions has: a converter unit for converting an input alternating current to a direct current; a smoothing capacitor for smoothing the direct current; an inverter unit for converting the direct current to an alternating current and outputting the alternating current to a motor; and a discharge circuit which, when the device is stopped, discharges the smoothing capacitor that has been charged. The power conversion device is provided with a voltage detector for detecting the voltage across the smoothing capacitor, and a discharge abnormality detection unit for detecting discharge abnormality on the basis of the detection voltage detected by the voltage detector. The discharge abnormality detection unit is provided with a voltage change ratio detection unit for obtaining a voltage change ratio that is the ratio of the detection voltages detected before and after a predetermined time, and an abnormality determination unit for performing abnormality determination by comparing the obtained voltage change ratio with a reference value.

Description

Power conversion device having discharge function

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

In power converters such as large-capacity inverters and servo drivers, it is necessary to discharge the charged power immediately for safety after operation is stopped. Therefore, although a discharge circuit is provided, it is necessary to perform a protective operation when there is an abnormality in the discharge circuit or the like.

As a background art for solving this problem, Patent Document 1 describes that “a converter that converts a DC voltage output from a capacitor into a DC voltage of a different level, and a DC voltage that is output from the converter is converted into an AC voltage and applied to a load. A discharge circuit having an inverter to be applied, a smoothing capacitor provided in parallel with the converter and the inverter, a resistance through which a discharge current from the smoothing capacitor flows, and a switching element for opening and closing a current path through which the discharge current flows, and a smoothing capacitor A discharge circuit failure detection device for detecting a failure in a discharge circuit in a system including a voltage sensor for detecting a voltage across both ends of the current circuit opens and closes a current path by a switching element by PWM control with two different duty ratios The rate of change of the voltage across the terminals obtained at the PWM control stage with a low duty ratio Based on the rate of change of voltage across obtained at the stage of the PWM control in a high 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, in large-capacity inverters and servo drivers, a large-capacity capacitor has been added to the DC bus for peak cuts during the operation cycle, and a common converter system has been adopted to save energy. The capacitor capacity on the DC bus varies depending on the equipment, such as providing a plurality of inverters. In addition, since the discharge resistance is selected in accordance with the capacitor capacity, the state of discharge varies 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 Document 1, the discharge circuit abnormality is determined by comparing the voltage change rate of the voltage across the smoothing capacitor in a predetermined discharge circuit and two predetermined different discharge operations with a normal value. As described above, when the capacitor capacity and the discharge resistance value are various and are not determined uniformly depending on the equipment, normal values cannot be determined for each system. Further, it is considered that the voltage used as a reference for the protective operation due to the change in the capacitance of the capacitor may not be appropriate for the apparatus with 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 apparatus in a power conversion apparatus having various discharge functions with different capacitor capacities and discharge resistance values. To do.

In order to solve the above problems, in the present invention, the voltage change rate of the DC bus for a certain period of time during the discharge operation is obtained to create a value corresponding to a circuit time constant, and an abnormality of the circuit is detected by the fluctuation of the value.

If an example of the power converter of the present invention is given, a converter unit that converts input alternating current into direct current, a smoothing capacitor that smoothes the direct current, an inverter unit that converts the direct current into alternating current and outputs the motor, A power conversion device having a discharge function having a discharge circuit that discharges the electric charge charged in the smoothing capacitor when the device is stopped, the voltage detector detecting the voltage of the smoothing capacitor, and the voltage detector A discharge abnormality detecting unit that detects a discharge abnormality based on the detected voltage, and the discharge abnormality detecting unit obtains a voltage change rate detecting unit that obtains a voltage change rate that is a ratio of a detected voltage around a predetermined time. An abnormality determination unit that compares the voltage change rate with a reference value to determine abnormality.

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

It is the schematic of the power converter device of Example 1 of this invention. FIG. 3 is a diagram illustrating an equivalent circuit of the discharge circuit according to the first embodiment. It is a figure which shows the voltage change at the time of discharge of the discharge circuit of FIG. It is a figure which shows the voltage change at the time of the discharge circuit abnormality of Example 1. FIG. FIG. 3 is a diagram illustrating a voltage change rate detection unit according to the first embodiment. It is a figure which shows the abnormality determination part of Example 1. FIG. It is a figure which shows the voltage change at the time of the discharge circuit abnormality of Example 2 of this invention. It is a figure which shows the abnormality determination part of Example 3 of this invention. It is the schematic of the power converter device of Example 4 of this invention. It is a figure which shows the abnormality determination part of Example 4.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that, in the drawings for explaining the embodiments, the same constituent elements are given the same names and symbols as much as possible, and the repeated explanation thereof is omitted.

FIG. 1 is a schematic diagram of the power conversion apparatus according to the 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 thereto. In the configuration of FIG. 1, an external capacitor 2 and an external discharge resistor 3 are connected for peak cutting. Even in the common converter system described above, the basic configuration is the same except that a plurality of inverter units 8 to motors 9 are connected in parallel. Moreover, although the symbol of a diode or a transistor is used for the discharge circuit 5, the inverter part 8, and the converter part 7 in FIG. 1, it is an example and a kind will not be ask | required if 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, since a circuit during discharge is operated after power is shut off, the circuit is represented by an equivalent circuit in which a capacitor 21, a discharge resistor 22, and a switch 23 are connected in series as shown in FIG. In this circuit, the electric charge charged in the capacitor 21 when the switch 23 is turned on is discharged through the discharge resistor 22. 2 corresponds to the 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, when the circuit can be discharged normally, when t is time, the voltage V (t) across the capacitor 21 is V (t) = V0 · exp (−t / τ) [V]
It is represented by

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

Next, the voltage across the capacitor at time t1 and t2 = t1 + dt after dt time is V (t1) = V0 · exp (−t1 / τ)
V (t2) ＝ V0 ・ exp (−t2 / τ) ＝ V0 ・ exp (− (t1 + dt) / τ)
And
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 the time t.
Therefore, as shown in FIG. 3, during the discharge time, the voltage decreases at the rate of change rate A regardless of the dt taken at any time.

Next, consider a case where an abnormality occurs on the circuit. FIG. 4 shows a graph of a change in DC voltage when an abnormality occurs in the circuit during the discharge period. For example, when several of the discharge resistors 3 connected in parallel are burned out and the resistance value is increased, that is, when R is increased and the time constant τ is increased in the above calculation, the voltage change rate B1 is obtained. With respect to the normal voltage change rate A,
B1> A
It becomes. In FIG. 4, this is the case as shown by a broken line (when an abnormality occurs (time constant is large)). In particular, when all the resistors fail in an open state or when a disconnection occurs on the circuit, the DC voltage becomes a constant value.

Conversely, when the discharge resistance is short-circuited internally and the resistance value is small, that is, when R is small and the time constant τ is small in the above calculation, the voltage change rate B2 is obtained as follows: B2 <A
It becomes. In FIG. 4, this is the case of the alternate long and short dash line (abnormal time (small time constant)).

Also, 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. Even when the motor 9 is driven by an external force and is in a power generation state even though it is later, the smoothing capacitor 4 is additionally charged. Therefore, the voltage change is a curve during normal discharge in FIG. To the curve from the broken line (abnormal time (large time constant)). The voltage change rate obtained by the above calculation method is different from the normal voltage change rate A.

As described above, since the voltage change rate A at normal time and the voltage change rates B1 and B2 at abnormal time are different from each other, it is possible to detect the abnormality of the discharge circuit by comparing each of them.
Here, the magnitude of dt, the timing at which the voltage is acquired, the frequency, and the like depend on the design of the power conversion device and the system including the power conversion device, and are not particularly limited here.
Although the voltage change rate A is the reference value for abnormality determination in the above, there is no problem even if it has a certain width due to a voltage detection error in circuit design and a design margin.

Based on the principle described with reference to FIGS. 2 to 4, a configuration for detecting a discharge abnormality of the circuit will be described. In FIG. 1, the power conversion apparatus 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. I have.

The voltage change rate detection unit 16 includes a sampling unit 51 and a division unit 52 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 determines 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 determination unit 17 includes an upper limit comparison unit 61 and a lower limit comparison unit 62 as shown in FIG. The voltage change rate signal B obtained by the voltage change rate detection unit 16 is added to the upper limit comparison unit 61 and the lower limit comparison unit 62. The upper limit comparison unit 61 compares the voltage change rate signal B with the 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 (where α> 1) as the reference value, an abnormality with a large time constant in FIG. 4 can be detected. Conversely, the lower limit comparison unit 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 (where β <1) as the reference value, an abnormality with a small time constant in FIG. 4 can be detected.

The storage unit 19 stores the reference value and supplies it 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 alerts an abnormal state based on the abnormality determination signal obtained by the abnormality determination unit 17. Further, a communication means may be provided and transmitted 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. And the abnormality determination part 17 can detect the abnormality of the circuit during a discharge period by sequentially comparing with the voltage change rate signal B obtained after that.
Note that the reference value may be created from the voltage change rate during normal discharge previously obtained.

According to the present embodiment, by setting the rate of voltage change during normal discharge as a reference value, an abnormality determination value is set for each device in a power converter having various discharge functions with different capacitor capacities and discharge resistance values. Therefore, the discharge abnormality can be detected by the same procedure. Further, the calculation cost can be reduced by not obtaining the circuit time constant itself. Furthermore, by setting a reference value based on the voltage change rate obtained at the start of discharge, an abnormality during one discharge period can be reliably detected.

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

In this embodiment, the abnormality determination unit 17 shown in FIGS. 1 and 6 uses the normal voltage change rate at 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 previous discharge is stored in the storage unit 19 and sent to the abnormality determination unit 17. By determining the abnormality using the normal voltage change rate A at the previous discharge, the abnormality can be determined from the start of the discharge.

In the power conversion device of FIG. 1, for example, when the ambient temperature of the internal capacitor 14 or the external capacitor 2 is higher than expected, the capacitance of the capacitor gradually increases due to secular change when used in a severe operation pattern in which acceleration and deceleration frequently occur. May decrease. The third embodiment detects such a sign of failure.

FIG. 8A shows a reference value used for the abnormality determination unit of the present embodiment, and FIG. 8B shows a reference value used for the abnormality determination unit. The upper limit comparison unit 61 uses α1A and α2A (where 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 comparison unit 62 uses β1A and β2A (where 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 greater 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 capacitance of the capacitor is reduced, the time constant of discharge is reduced, so that a sign of failure can be detected by detecting that the voltage change rate has become smaller than a predetermined reference value. In addition, by providing the reference value α2A in the upper limit comparison unit, it is possible to detect a sign of a failure that increases the time constant.

According to the present embodiment, it is possible to make a failure sign determination by providing a determination value smaller than the abnormality determination determination value, and to notify the maintenance time based on the failure sign signal.

1, when the motor 9 is forcibly rotated by an external force during a 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 FIGS. 4 and 7, the change in the DC voltage becomes 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 when the motor becomes a generator by an external force or an abnormality determination other than that.

FIG. 9 shows a schematic diagram of the power conversion apparatus of the fourth embodiment, and FIG. 10 shows the abnormality determination unit 17 of the fourth embodiment.

In this embodiment, as shown in FIG. 9, the position detector 20 is connected to the motor shaft, the motor shaft angle signal D is obtained and 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 motor speed is calculated from the motor shaft angle signal D by the rotation speed calculation unit 63 and sent to the rotation speed abnormality determination unit 64. The rotation speed abnormality determination unit 64 detects motor rotation, that is, motor rotation abnormality during discharge operation by comparing the motor rotation speed with reference values γC and δC (where γ> 1, δ <−1). To do. FIG. 10B shows a reference value used in the rotation speed abnormality determination unit 64.

In the determination unit 65, the abnormality determination signal obtained by the upper limit comparison unit 61 and the lower limit comparison unit 62 is combined with the rotation abnormality signal of the motor obtained by the rotation abnormality determination unit 64, thereby determining the external discharge resistance 3. Thus, it is possible to distinguish between abnormality determination due to a change in time constant by the smoothing capacitor 4 and the external capacitor 2, and abnormality determination due to the motor becoming a generator by 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 (tacho generator) to the motor shaft. .

According to the present embodiment, the abnormality determination is performed by combining the rotation abnormality of the motor during the discharging operation, thereby determining whether the abnormality is caused by the motor becoming a generator by an external force, or the external discharge resistor 3 and the smoothing capacitor 4. It is possible to distinguish whether the abnormality determination is due to a change in the time constant due to the above.

The present invention is not limited to the embodiments described above, and includes various modifications. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.
Each of the above-described configurations, functions, processing units, processing means, and the like may be realized by hardware by designing a part or all of them with, for example, an integrated circuit. Each of the above-described configurations, functions, and the like may be realized by software by interpreting and executing a program that realizes each function by the processor. Information such as programs, tables, and files for realizing 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.
Further, the control lines and information lines indicate what is considered necessary for the explanation, and not all the control lines and information lines on the product are necessarily shown. Actually, it may be considered that almost all the components are connected to each other.

DESCRIPTION OF SYMBOLS 1 Power converter 2 External capacitor 3 External discharge resistor 4 Smoothing capacitor 5 Discharge circuit 6 Voltage detection circuit 7 Converter part 8 Inverter part 9 Motor 10 Circuit control part 11 Circuit breaker 12 AC power supply 13 Switch element 14 Internal capacitor 15 Discharge abnormality detection part 16 Voltage change rate detection unit 17 Abnormality determination unit 18 Output unit 19 Storage unit (reference value)
20 position detector 21 capacitor 22 discharge resistance 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

A converter unit that converts input AC to DC, a smoothing capacitor that smoothes the DC, an inverter that converts the DC to AC and outputs it to the motor, and discharges the electric charge charged in the smoothing capacitor when the device is stopped A power conversion device having a discharge function having a discharge circuit to perform,
A voltage detector for detecting the voltage of the smoothing capacitor;
A discharge abnormality detector for detecting 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 detected voltages around a predetermined time;
An abnormality determination unit that performs abnormality determination by comparing the obtained voltage change rate with a reference value;
A power conversion device comprising:
The power conversion device according to claim 1,
The abnormality determination unit performs abnormality determination by using a voltage change rate obtained during a certain period during a discharge period as a reference value for comparison and comparing with a voltage change rate obtained again during the same discharge period. Power conversion device.
The power conversion device according to claim 1,
The abnormality determination unit makes an abnormality determination by using a normal voltage change rate obtained in advance as a reference value for comparison and comparing the voltage change rate obtained during a discharge period.
In the power converter device according to claim 2 or 3,
The abnormality determination unit further sets a voltage change rate closer to a normal value than a reference value for comparison for performing abnormality determination as a reference value for comparison for predictive determination, and compares the voltage change rate obtained during the discharge period with an abnormality. The power converter characterized by performing the sign determination of.
In the power converter device according to claim 2 or 3,
Furthermore, a motor rotation detection means is provided,
The abnormality determination unit detects an abnormal rotation of the motor and distinguishes whether the abnormality obtained from the change in the voltage change rate is due to an abnormality in the circuit or an abnormality due to the rotation of the motor.