KR102089915B1 - Power conversion device with discharge function - Google Patents

Abstract

In a power conversion device having various discharge functions having different capacitor capacities and discharge resistance values, an abnormality detection value is detected in the same procedure without setting an abnormality determination value for each device. A converter unit that converts the input AC into DC, a smoothing capacitor that smooths the DC, an inverter unit that converts the DC into AC, and outputs it to the motor, and discharges the charge charged in the smoothing capacitor when the device stops A power conversion device having a discharge function having a discharge circuit, comprising: a voltage detector for detecting the voltage of the smoothing capacitor; and a discharge abnormality detection unit for detecting a discharge abnormality based on the detected voltage detected by the voltage detector, The discharge abnormality detection unit includes a voltage change rate detection unit for obtaining a voltage change rate that is a ratio of the detection voltage before and after a predetermined time, and an abnormality determination unit for comparing the obtained voltage change rate and a reference value to perform an abnormality determination.

Description

Power conversion device with discharge function

The present invention relates to a power conversion device having a discharge function, particularly to a discharge abnormality detection technology.

In power conversion devices such as large-capacity inverters and servo drivers, it is necessary to immediately discharge the charged power for safety after stopping operation. For this reason, although a discharge circuit is provided, it is necessary to perform a protective operation in the event of an abnormality in the discharge circuit or the like.

As a background technique for solving this problem, Patent Document 1 includes a converter that converts a DC voltage output from a capacitor into a DC voltage of a different level, an inverter that converts a DC voltage output from the converter into an AC voltage, and applies it to a load. A smoothing capacitor installed in parallel with the converter and an inverter, a discharge circuit having a resistance through which a discharge current from the smoothing capacitor flows, and a switching element that opens and closes a current path through which the discharge current flows, and a voltage sensor that detects the voltage across the smoothing capacitor. A discharge circuit failure detection device for detecting a failure of a discharge circuit in a system provided includes a step of opening / closing a current path by a switching element by PWM control at two different duty ratios, and a low duty ratio. The rate of change of the voltage across both ends obtained in the step of PWM control in and the step of PWM control in high duty ratio On the basis of the rate of change of voltage across the obtained document, and detecting the presence or absence of a failure of the discharge circuit. Is described as "(see abstract).

Japanese Patent Publication No. 2015-116097

In recent years, in a large-capacity inverter or servo driver, a large-capacity capacitor is added to the DC bus for a peak cut during an operation cycle, or a common converter method is employed to save energy, and a plurality of inverter parts are provided for one converter part. For example, the capacitor capacity on the DC bus has various values depending on the equipment. In addition, since discharge resistance is also selected in accordance with the capacitor capacity, the appearance of the discharge varies depending on the equipment, making it difficult to detect the discharge operation or abnormality of the discharge circuit.

In the method described in Patent Document 1, the discharge circuit abnormality is determined by comparing the rate of voltage change of the voltage across the smoothing capacitor during two different discharge operations in a predetermined discharge circuit and in a predetermined discharge value with a normal value. Accordingly, if the capacitor capacity and the discharge resistance value are varied and are not uniformly determined, a normal value cannot be determined for each system. In addition, it is considered that the voltage used as a reference for the protection operation may not be suitable for the device at a predetermined value due to a change in the capacitor capacity.

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

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

As an example of the power conversion device of the present invention, a converter unit for converting the input AC into DC, a smoothing capacitor for smoothing the DC, an inverter unit for converting the DC into AC, and outputting it to the motor, the smoothing capacitor A power conversion device having a discharge function having a discharge circuit for discharging charges charged at the time of stopping the device, comprising: a voltage detector for detecting the voltage of the smoothing capacitor; and a discharge based on the detected voltage detected by the voltage detector. A discharge abnormality detection unit for detecting an abnormality, the discharge abnormality detection unit, a voltage change rate detection unit for obtaining a voltage change rate that is a ratio of the detected voltage before and after a predetermined time, and an abnormality determination unit for performing abnormality determination by comparing the obtained voltage change rate and a reference value It is equipped.

ADVANTAGE OF THE INVENTION According to this invention, in the electric power conversion apparatus which has various discharge functions with different capacitor capacity and discharge resistance value, it is possible to detect discharge abnormality in the same procedure without setting an abnormality determination value for each apparatus. In addition, the cost of calculation can be reduced by not obtaining the circuit time constant itself.

1 is a schematic diagram of a power conversion device of Embodiment 1 of the present invention.
2 is a diagram showing an equivalent circuit of the discharge circuit of Example 1. FIG.
FIG. 3 is a diagram showing a voltage change during discharge of the discharge circuit of FIG. 2.
4 is a diagram showing a voltage change when the discharge circuit of Example 1 is abnormal.
5 is a diagram showing a voltage change rate detection unit of Example 1. FIG.
6 is a diagram showing an abnormality determining unit in Example 1. FIG.
7 is a diagram showing a voltage change in the case of an abnormality in the discharge circuit of Embodiment 2 of the present invention.
8 is a diagram showing an abnormality determining unit in Example 3 of the present invention.
9 is a schematic diagram of a power conversion device of Embodiment 4 of the present invention.
10 is a diagram showing an abnormality determining unit in Example 4. FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, in each drawing for explaining an embodiment, the same component is attached with the same name and code as possible, and repeated description is abbreviate | omitted.

Example 1

1 is a schematic diagram of a power conversion device of Embodiment 1 of the present invention. The power converter 1 incorporates a smoothing capacitor 4, a discharging circuit 5, a voltage detection circuit 6, a converter section 7, an inverter section 8, and a circuit control section 10, and external capacitors. (2), the external discharge resistor 3 is connected. In the configuration of Fig. 1, the external capacitor 2 and the external discharge resistor 3 are connected for peak cutting. Even in the above-described common converter method, only a plurality of inverter units 8 to the motor 9 are connected in parallel, and the basic configuration is the same. In Fig. 1, symbols of diodes and transistors are used for the discharge circuit 5, the inverter portion 8, and the converter portion 7, but it is an example, and any kind is provided as long as the same function is provided. Further, 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 principles of the present invention will be described with reference to FIGS. 2 and 3.

In general, since the circuit at the time of discharge is operated after the power is turned off, it is represented by an equivalent circuit in which the capacitor 21, the discharge resistor 22, and the switch 23 shown in FIG. 2 are connected in series. In this circuit, the switch 23 is turned on, and the charge charged in the capacitor 21 is discharged through the discharge resistor 22. The condenser 21 in FIG. 2 is a combination of the internal condenser 14 and the external condenser 2 in FIG. 1, the discharge resistor 22 is an external discharge resistor 3, and the switch 23 is a discharge circuit 5 Corresponds to the switch element 13.

At this time, if the circuit can be discharged normally, if t is time, the voltage across both ends of the capacitor 21 V (t) is

V (t) = V0 ㆍ exp (-t / τ) [V]

It is indicated by.

here,

V0: Voltage when t = 0

exp: natural exponential function

τ: circuit time constant, in the equivalent circuit of FIG. 2, τ = CR

C: capacitance of the condenser 21

R: resistance value of the discharge resistance 22

to be.

Next, the voltage across the capacitor at a certain time t1 and t2 = t1 + dt after the dt time is

V (t1) = V0 ㆍ exp (-t1 / τ)

V (t2) = V0 ㆍ exp (-t2 / τ) = V0 ㆍ exp (-(t1 + dt) / τ)

Become,

The rate of voltage change A during dt is

A = V (t2) / V (t1) = exp (-dt / τ)

Becomes Since τ is a circuit time constant, it is constant, and when dt is constant, the rate of change A becomes constant regardless of time t.

Therefore, as shown in Fig. 3, in the discharge time, the voltage decreases at a rate of change rate A even if dt is taken at any point in time.

Next, the case where an abnormality has occurred on the circuit is considered. 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 some of the discharge resistors 3 connected in parallel are damaged or the resistance value increases, that is, when R increases in the above calculation and the time constant τ increases, the voltage change rate B1 is obtained, and the voltage at normal For the rate of change A,

B1> A

Becomes In Fig. 4, it is the same case as the broken line (abnormal time (versus time constant)). In particular, when all the resistors fail in an open state or when a circuit break occurs, the DC voltage becomes a constant value.

Conversely, when the discharge resistance is shorted internally and the resistance value becomes small, that is, in the above calculation, when R becomes small and the time constant τ becomes small, the voltage change rate B2 is obtained.

B2 <A

Becomes In Fig. 4, it is the same as the one-dot chain line (in case of abnormality (time constant small)).

In addition, an element not shown 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 7 in FIG. 1 is insufficient, or a power conversion device ( Even after the operation of 1) is stopped, the motor 9 is driven by an external force and is in the power generation state, and the smoothing capacitor 4 is additionally charged, so the voltage change is based on the curve during normal discharge in FIG. 4. It becomes a curve of broken line (abnormal time (time constant)). The voltage change rate obtained by the above calculation method is a different value compared to the voltage change rate A at normal time.

As described above, since the voltage change rate A at the normal time and the voltage change rates B1 and B2 at the time of abnormality are different values, it is possible to detect an abnormality in the discharge circuit by comparing each.

Here, since the size of dt, the timing, frequency, etc. for acquiring the voltage depend on the design of the power converter or the system including the power converter, it does not matter here.

In addition, although the voltage change rate A is a reference value for abnormality determination in the above, there is no problem even if it has a slight difference as a voltage detection error in the circuit design or a margin in the design.

Based on the principle described in Figs. 2 to 4, a configuration for detecting an abnormality in the discharge of the circuit will be described. In Fig. 1, the power conversion device includes a discharge abnormality detection unit 15, and 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 reference value. A memory unit 19 for storing is provided.

The voltage change rate detection unit 16 includes, for example, a sampling unit 51 and a division unit 52, as shown in FIG. 5. The DC voltage of the DC bus detected by the voltage detection circuit 6 is sampled by the sampling section 51 every predetermined time dt. Then, in the dividing unit 52, the voltage change rate B is obtained by dividing the ratio of the DC voltage before and after dt time, that is, the DC voltage value after dt time.

The abnormality determination unit 17 includes, for example, an upper limit comparison unit 61 and a lower limit comparison unit 62, as shown in FIG. 6. 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 comparator 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. As the reference value, an abnormality in which the time constant in Fig. 4 is increased can be detected by using αA, which is α times (here, α> 1) of the normal value A of the voltage change rate. Conversely, the lower limit comparison unit 62 compares the voltage change rate signal B with a reference value, and outputs an abnormality determination signal when the voltage change rate signal B falls below the reference value. As a reference value, an abnormality in which the time constant in Fig. 4 is small can be detected by using βA, which is β times (here, β <1) of the normal value A of the voltage change rate.

The storage unit 19 stores the reference value and supplies it to the abnormality determination unit 17. In addition, the voltage change rate B obtained by the voltage change rate detection unit may be stored at any time.

The output section 18 displays or alerts an abnormal state based on the abnormality determination signal obtained from the abnormality determination section 17. In addition, a communication means may be provided and transmitted to an external tablet terminal or the like.

As shown in Fig. 4, if an abnormality occurs in the circuit during the discharge period, the rate of voltage change during discharge. The voltage change rate A at the start of discharge is determined, 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 sequentially detect the abnormality of the circuit during the discharge period by sequentially comparing with the voltage change rate signal B obtained.

In addition, the reference value may be prepared from the rate of change in voltage during the previous normal discharge obtained in advance.

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

Example 2

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 is increased or decreased before the discharge operation starts, the voltage change rates B1 and B2 are abnormally determined from the start of the discharge operation. Level. Embodiment 2 detects an abnormality in this circuit.

In this embodiment, in the abnormality determination unit 17 shown in Figs. 1 and 6, the normal voltage change rate at the time of the previous discharge is used 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 determining abnormality using the normal voltage change rate A at the time of the previous discharge, it is possible to determine the abnormality from the start of discharge.

Example 3

In the power conversion device of FIG. 1, for example, when the ambient temperature of the internal condenser 14 or the external condenser 2 is higher than the phase information, when used in a strict operation pattern in which acceleration and deceleration frequently occur, the condenser may change over time. The capacity of may gradually decrease. Example 3 detects such a failure.

Fig. 8 (a) shows the abnormality determining unit of this embodiment, and Fig. 8 (b) shows a reference value used in the abnormality determining unit. In the upper limit comparison section 61, α1A and α2A (where α1, α2> 1, α1> α2) are used as reference values for comparison. Then, 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 preliminary signal is output. Further, when the voltage change rate signal B exceeds the reference value α1A, an abnormality determination signal is output. Similarly, in the lower limit comparison section 62, β1A and β2A (where β1, β2 <1, and β1 <β2) are used as reference values for comparison. Then, when the voltage change rate signal B is lower than the reference value β2A and is greater than or equal to the reference value β1A, a failure preliminary signal is output. In addition, 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 discharge becomes small, and thus, it is possible to detect the occurrence of a failure by detecting that the voltage change rate is smaller than a predetermined reference value. In addition, by setting the reference value α2A in the upper limit comparison section, it is possible to detect the occurrence of a failure in which the time constant increases.

According to this embodiment, it is possible to make a preliminary judgment of a failure by setting a judgment value smaller than the judgment value of the abnormality judgment, and to notify the maintenance timing based on the failure preliminary signal.

Example 4

In the power conversion device of FIG. 1, when the motor 9 is forcibly rotated by an external force during discharge operation, the motor 9 becomes a generator, and regenerates to the smoothing capacitor 4 or the external capacitor 2 Energy is charged. Therefore, in the drawing showing the discharge voltages in Figs. 4 and 7, the change in the DC voltage is the same as the curve of the voltage change rate B1 at abnormal times (time constant vs.). The fourth embodiment enables the motor to detect whether it is an abnormality determination by the motor being a generator or other abnormality determination.

Fig. 9 shows a schematic diagram of the power conversion device 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 to obtain the motor shaft angle signal D and sends it to the abnormality determination unit 17. As shown in Fig. 10A, the abnormality determination unit 17 is provided with a rotational speed calculation unit 63 and a rotational speed abnormality determination unit 64. The motor rotational speed is calculated by the rotational speed calculation unit 63 from the motor shaft angle signal D, and sent to the rotational 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 discharge operation by comparing the motor rotation speed with the reference values γC and δC (here, γ> 1, δ <-1). 10B shows a reference value used by the rotational speed abnormality determining unit 64.

The external discharge resistance () is determined by summing and determining the abnormality determination signal obtained by the upper limit comparison unit 61 and the lower limit comparison unit 62 and the rotation abnormality signal of the motor obtained by the rotation abnormality determination unit 64 by the determination unit 65. 3) It is possible to distinguish whether the abnormality is determined by a change in the time constant caused by the smoothing capacitor 4, the external capacitor 2, or the like, or the abnormality is determined by the motor being a generator by external force.

In addition, in the above, the motor rotational speed was calculated by the rotational speed calculation unit 63 from the motor shaft angle signal of the position detector 20, but it may be measured by connecting a speed detector (taco generator) to the motor shaft.

According to this embodiment, the abnormality is determined by summing the abnormality of the rotation of the motor during the discharge operation and determining whether the abnormality is caused by the motor becoming a generator by external force, the external discharge resistance 3, the smoothing capacitor 4, or the like. It is possible to distinguish whether the abnormality is determined by the change in the time constant.

The present invention is not limited to each of the above-described embodiments, and various modifications are included. For example, the above-described embodiment has been described in detail to explain the present invention in an easy-to-understand manner, and is not necessarily limited to having all the configurations described. Further, it is possible to replace a part of the structure of one embodiment with the structure of another embodiment, and it is also possible to add the structure of another embodiment to the structure of one embodiment. In addition, it is possible to add, delete, or replace other components for some of the components of each embodiment.

In addition, each of the above structures, functions, processing units, processing means, etc. may be realized in hardware by designing some or all of them with an integrated circuit, for example. In addition, each of the above-described structures, functions, and the like may be realized by software by analyzing and executing a program that the processor realizes each function. Information such as programs, tables, and files for realizing each function may be stored in a memory, a recording device such as a hard disk, a solid state drive (SSD), or a recording medium such as an IC card, SD card, or DVD.

In addition, the control line and the information line indicate what is considered necessary for explanation, and it is not always possible to indicate all control lines and information lines in the product. In practice, almost all configurations may be considered to be connected to each other.

1: Power conversion device
2: External capacitor
3: External discharge resistance
4: Smoothing condenser
5: discharge circuit
6: Voltage detection circuit
7: converter part
8: Inverter unit
9: motor
10: circuit control
11: breaker
12: AC power
13: switch element
14: internal condenser
15: discharge abnormality detection unit
16: voltage change rate detection unit
17: abnormality determination unit
18: output
19: storage unit (reference value)
20: position detector
21: condenser
22: discharge resistance
23: switch
51: sampling unit
52: antacid
61: upper limit comparison unit
62: lower limit comparison unit
63: rotation speed calculation unit
64: rotation speed abnormality determination unit
65: judgment unit

Claims (5)

A converter unit that converts the input AC into DC, a smoothing capacitor that smooths the DC, an inverter unit that converts the DC into AC, and discharges the charge charged in the smoothing capacitor when the device stops A power conversion device having a discharge function having a discharge circuit,
And a voltage detector for detecting the voltage of the smoothing capacitor,
And a discharge abnormality detection unit which detects a discharge abnormality based on the detection voltage detected by the voltage detector,
The discharge anomaly detection unit,
A voltage change rate detector for obtaining a voltage change rate that is a ratio of the detected voltage before and after a predetermined time;
And an abnormality determining unit that compares the obtained voltage change rate with a reference value to perform abnormality determination. According to claim 1,
The abnormality judging unit is characterized in that the abnormality determination is performed by comparing the rate of change of voltage obtained in a certain period during the discharge period as a reference value for comparison, and comparing with the rate of change of voltage obtained again during the same discharge period. According to claim 1,
The abnormality determining unit performs an abnormality determination by comparing the voltage change rate at normal time determined in advance as a reference value for comparison, and comparing it with the voltage change rate obtained during the discharge period. The method of claim 2 or 3,
The abnormality judging unit is further characterized in that an abnormality preliminary determination is made by comparing the rate of voltage change closer to a normal value than the reference value of the comparison for performing an abnormality determination as a reference value for comparison of the preliminary determination and comparing it with the voltage change rate determined during the discharge period. Power converter. The method of claim 2 or 3,
It further comprises a means for detecting the rotation of the motor,
The abnormality determination unit detects an abnormality in rotation of the motor, and distinguishes whether an abnormality obtained from a change in the voltage change rate is due to an abnormality in the circuit or an abnormality due to the rotation of the motor.

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