JPH1014097A - Power converter capacitor capacity judging device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] In a power converter for converting a single-phase alternating current into a direct current and converting the direct current into an alternating current, a stable and highly accurate reduction in the capacitance of the capacitor is not affected by external circuit conditions. Is to judge. SOLUTION: First power converters 3a and 3b for converting single-phase AC 1 to DC, second power converters 5a, 5b and 5c for converting DC to AC, and first and second powers In a power converter provided with a DC intermediate circuit consisting of a capacitor 4 connected in parallel to the DC side of the converter, the magnitude of the AC voltage fluctuation of the capacitor, the AC input current and the AC input voltage of the first power converter, or a combination thereof. Means 82 for estimating the capacitance value of the capacitor based on the command value is provided. When the estimated value of the capacitance becomes equal to or less than the reference value of the comparator 83, it is determined that the capacitance has decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter for converting a single-phase alternating current into a direct current, and further converting the direct current into an alternating current. About.

[0002]

2. Description of the Related Art Conventionally, as a technique for detecting the capacitance of a DC-side capacitor provided in a power converter, a time constant circuit comprising a charging resistor is used by utilizing a waveform at the time of initial charging of a DC intermediate circuit. (Japanese Patent Laid-Open No. 5-308701) for estimating a capacitance value based on the measured value.

[0003]

In the above prior art, since the charging time of the capacitor is influenced by the power supply voltage, the charging resistance, and the like, the accurate detection of the capacitance of the capacitor requires the accurate detection of the external circuit condition. Becomes An object of the present invention is to convert a single-phase alternating current into a direct current, and in a power converter that converts the direct current into an alternating current, stably and accurately determine a decrease in the capacitance of the capacitor without being affected by external circuit conditions. It is in.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a power converter for converting a single-phase alternating current to a direct current and converting the direct current to an alternating current. A means for estimating the capacitor capacity based on the input voltage, input current or their command values on the single-phase AC side is provided, and when the estimated value of the capacitor capacity becomes equal to or less than a predetermined reference value, the capacitor capacity is reduced. It is solved by the judgment. Further, the magnitude of the AC voltage fluctuation of the capacitor of the DC intermediate circuit is compared with a predetermined reference voltage set based on the input voltage, input current or their command values on the single-phase AC side of the power converter, and the AC This is solved by determining that the capacitance of the capacitor has decreased when the magnitude of the voltage fluctuation exceeds the reference voltage.

In the present invention, the capacitance C of the capacitor is estimated from the following (Equation 3). According to this (Equation 3), once the magnitude of the AC voltage fluctuation ΔE of the capacitor is obtained, the capacitor capacitance C can be obtained without depending on the external circuit constants other than the power supply voltage and the capacitor capacitance. The decrease is determined from the magnitude of C. In addition, from the following (Equation 2), the magnitude of the AC voltage fluctuation ΔE
Ask for. According to (Equation 2), the value of ΔE changes due to the change in the capacitance C of the capacitor. Then, similarly, this ΔE can be obtained without depending on the external circuit constants other than the power supply voltage and the capacitance of the capacitor, and the decrease of the capacitance C of the capacitor is determined from the magnitude of ΔE. Therefore, according to the present invention, the capacitance of the capacitor can be determined stably and accurately without being affected by the external circuit conditions.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of a device for judging the capacity of a capacitor of a power converter according to the present invention, which is an example applied to a PWM converter / inverter system for driving an electric vehicle. In FIG. 1, reference numeral 1 denotes an overhead wire that is a single-phase AC voltage source, 2 denotes a single-phase transformer that transforms the overhead wire voltage into an input voltage suitable for the converter, and 3a and 3b configure a converter that is a first converter. Switching arm,
4 is a capacitor installed in the DC intermediate circuit, 5a to 5c are switching arms constituting an inverter as a second converter, and 6 is an induction motor as a load device. Here, reference numerals 31 and 32 in 3a denote self-extinguishing switching elements provided with a rectifying element for freewheel, and pulse width modulation (P) of the AC voltage by on / off control.
WM) control. In this example, IGBT is used, but GT
O or a transistor may be used. 3a, 3b and 5
a to 5c have the same configuration.

Reference numeral 7 denotes a control circuit for the power converter.
The power converter control circuit 7 includes a main controller 71, a converter PWM controller 72, and an inverter PWM controller 73.
Consists of The main control unit 71 inputs a DC voltage command Ed * and a gate start / stop signal GS1 * and the like to the converter PWM control unit 72, and inputs an inverter frequency command Fi *, an output voltage command E * and a gate start signal to the inverter PWM control unit 73. / Stop signal GS2 * and the like. Converter PWM control unit 72 and inverter PWM control unit 73 output gate signals (ON / OFF signals).
Here, the voltage ed is the voltage of the capacitor 4 of the DC intermediate circuit, the average voltage of which is used as a feedback signal for controlling the output voltage of the converter, and the DC intermediate circuit voltage specific to the converter connected to the single-phase AC power supply. It is also used as a signal for suppressing the beat of the inverter output current generated due to the AC fluctuation of the inverter. Here, the voltage and current detecting means used for normal control is omitted.

On the other hand, reference numeral 8 denotes a capacitor capacitance judging circuit corresponding to a characteristic portion of the present invention. The capacitor capacitance judging circuit 8 comprises an AC component detector 81 for detecting an AC fluctuation component from a capacitor voltage of a DC intermediate circuit, and an AC component detector 81. The capacitor AC voltage output from the detector 81 and the converter input current command value Is * given from the converter PWM control unit 72
And a capacity estimator 82 for estimating the capacitor capacity from the modulation factor a, a first comparator 83, a second comparator 84, and a memory for recording the capacitor capacity estimated value and the history of control variables or feedback signals related thereto. 85. Reference numeral 91 denotes an external display for warning a decrease in the capacitance of the capacitor determined by the first comparator. Reference numeral 92 denotes a monitor for reading data recorded in the memory 85. As a matter of course, the display 91 and the monitor 92 may be provided inside the capacitor capacity determination circuit 8, the power converter control circuit 7, and the like.

The operation of the present embodiment will be described below with reference to FIGS. FIG. 2 shows a main circuit configuration. In a PWM converter using a single-phase AC as a power supply, an AC fluctuation of twice the frequency of the single-phase power supply occurs in the capacitor of the DC intermediate circuit during operation. FIG. 3 shows an example of the operation waveform.
FIG. 3 shows the converter input current is with respect to the power supply voltage es.
This is an example in which (equivalent to the power supply current) is controlled to the same phase (power supply power factor 1). Here, the converter input voltage ec is
As shown in FIG. 3A, the operation is performed at the control angle θs with respect to the power supply voltage es. Actually, the converter input voltage ec
Is an AC voltage composed of voltage pulses subjected to PWM control, but here, a fundamental wave is shown. Assuming that the converter input voltage ec is a sine wave, the converter output current id at this time is the sum of the average current Id and the twice frequency component of the power supply voltage, as shown in FIG. AC component ΔId
Is

(Equation 1) Here, a: converter modulation ratio Is: converter input current (fundamental wave effective value), which is approximately obtained. On the other hand, the inverter input current iin
v is negligible if harmonic components caused by switching are ignored and beatless control of the inverter is performed.
It can be regarded as almost a direct current. Therefore, the capacitor voltage ed has a waveform as shown in FIG. 3 (c). If the amplitude of the voltage fluctuation at this time is ΔE, it is given by the following equation.

(Equation 2) Here, ω: power supply angular frequency C: capacitor capacitance Amplitude of voltage fluctuation ΔE is a converter modulation rate a (a value obtained by standardizing the amplitude of a converter input voltage fundamental wave by an average capacitor voltage), and an effective value of a converter input current Is (is ) And the capacitor capacitance C, and does not depend on external circuit constants other than the power supply voltage or the capacitor capacitance. Therefore, if ΔE is obtained, the capacitor capacitance C can be estimated from (Equation 3) without being affected by external circuit conditions.

(Equation 3) As a matter of course, the converter input current Is may be a detected value, and there is no problem if the converter input voltage is used instead of a variable variable in the converter, for example, the converter modulation factor a.

The present embodiment utilizes the characteristic characteristic of the single-phase converter. That is, in FIG.
The AC component detector 81 detects the AC component amplitude value ΔE of the capacitor voltage ed, and the capacity estimator 82 detects the AC component amplitude value ΔE of the capacitor voltage and the converter input current command value I
The capacitor capacitance C is estimated from s * and the modulation factor a. The first comparator 83 compares the predetermined reference capacity 1 with the estimated capacity of the capacity estimator 82, and outputs “1” to the output CC1 when the estimated capacity is smaller than the reference capacity 1 ( Normally, “0” is output). When the CC1 becomes “1”, the display 91 outputs a display indicating that the capacitance C of the capacitor has decreased. This makes it possible to stably and accurately detect a decrease in the capacitance C of the capacitor without being affected by external circuit conditions. Further, the second comparator 84
When the output of the capacity estimator 82 becomes equal to or less than the reference capacity 2 (<reference capacity 1), “1” is output to the output CC2 (normally “0” is output). As a result, the main control unit 71 fixes the gate start / stop conditions GS1 * and GS2 * to the gate stop, and stops the operation of the converter and the inverter by the functions of the converter PWM control unit 72 and the inverter PWM control unit 73. This makes it possible to prevent abnormal operation of the converter and the inverter accompanying the abnormal decrease in the capacitance C of the capacitor. On the other hand, the memory 85 records the history of the change of the capacitor C together with the related control variables and feedback values. The data recorded in the memory 85 is read out to the monitor 92 to monitor the aging of the capacitor C. Here, the control variables related to the AC voltage fluctuation of the capacitor are, for example, the modulation factor a and the converter input current Is shown in (Equation 2). This makes it possible to easily find a capacitor that may have a reduced capacity, and is particularly effective for reducing maintenance work and estimating the life.

Although the above embodiment is an example in which the present invention is applied to a PWM converter / inverter system for driving an induction motor, a similar effect can be expected even with a power supply device that outputs a constant frequency alternating current.

FIG. 4 shows another embodiment of the present invention. The main circuits 1 to 6 and the control circuit 7 of the power converter are the same as in the embodiment of FIG. Reference numeral 8 denotes a capacitor capacity determination circuit corresponding to a feature of the present invention. The capacitor capacity determination circuit 8 includes an AC component detector 81 that detects an AC fluctuation component ΔE from the capacitor voltage ed of the DC intermediate circuit, a reference voltage calculator 86 that calculates a reference voltage from the converter input current Is and the modulation factor a, It comprises a first comparator 83, a second comparator 84, and a memory 85 for recording the amplitude value ΔE of the AC voltage and the history of control variables or feedback signals related thereto. Reference numeral 91 denotes an external display for warning a decrease in the capacitance of the capacitor determined by the first comparator. Reference numeral 92 denotes a monitor for reading data recorded in the memory 85. Naturally, the display 91 and the monitor 9
2 is a capacitor capacity determination circuit 8 and a power converter control circuit 7
It may be inside such as.

In FIG. 4, an AC component detector 81 detects an AC component amplitude value ΔE of the capacitor voltage ed. (If the AC component detector 81 is provided with a maximum value detection function, the operating state changes every moment. Can also play the role of detecting the maximum voltage amplitude.) The reference voltage calculator 86 calculates reference values 1 and 2 as reference voltages from the converter input current Is and the modulation factor a from the relationship of (Equation 2). Here, the reference value 1 is set to ΔE + α1 (α1 is a predetermined value) or ΔEmax + α1
(ΔEmax is the maximum value of ΔE assumed in normal operation). The reference value 2 is set to ΔE + α2 (α2 is a predetermined value, α2> α1) or ΔEmax + α2. The first comparator 83 includes a reference value 1 and an AC component detector 8.
When ΔE is larger than the reference value 1, “1” is output to the output CC1 (normally “0” is output). When the CC1 becomes “1”, the display 91 outputs a display indicating that the capacitance of the capacitor has decreased. As a result, a decrease in the capacitance of the capacitor can be detected by monitoring the AC component of the capacitor voltage without being affected by the external circuit conditions. Further, the second comparator 8
4 outputs "1" to the output CC2 when the detection result of the AC component detector 81 exceeds the reference value 2 (normally "0").
Output). As a result, the main control unit 71 fixes the gate start / stop conditions GS1 * and GS2 * to the gate stop, and sets the converter PWM control unit 72 and the inverter P
The operation of the converter and the inverter is stopped by the operation of the WM control unit 73. Thereby, the abnormal decrease of the capacitor C is detected from the increase of the capacitor AC voltage component,
It is possible to prevent the abnormal operation of the converter and the inverter accompanying it. Other functions of the present embodiment are the same as those of the embodiment of FIG.

In this embodiment, a control signal for beatless control can be used instead of detecting the capacitor voltage. In this case, the same effect as that of the present embodiment can be realized with a simpler configuration.

The present invention is naturally applicable irrespective of the number of AC-side voltage levels (two levels, three levels, or more) of the power converter.

[0016]

As described above, according to the present invention,
In a power converter that converts a single-phase alternating current into a direct current and converts the direct current into an alternating current, it is possible to stably and accurately determine the capacitance of the capacitor without being affected by external circuit conditions. Further, when the capacitance of the capacitor is abnormally reduced, it is possible to prevent abnormal operation of the converter and the inverter accompanying the abnormal decrease. In addition, a capacitor that may cause a reduction in capacity can be easily found, and this is particularly effective for reducing maintenance work and estimating the life.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of an apparatus for determining the capacity of a capacitor of a power converter according to the present invention.

FIG. 2 illustrates a main circuit configuration.

FIG. 3 is a diagram illustrating an operation waveform.

FIG. 4 is a diagram showing another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Overhead wire which is a single-phase AC voltage source 3a, 3b, 5a-5c Switching arm 30-33 Switching element 4 Capacitor 7 Control circuit 71 Main control part 72 Converter control part 73 Inverter control part 8 Capacitor capacity judgment circuit 81 AC component detector 82 Capacity estimator 83, 84 Comparator 85 Memory 86 Reference voltage calculator 91 Display 92 Monitor

Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical indication location H02M 7/48 9181-5H H02M 7/48 M

Claims (7)

[Claims] 1. A first power converter for converting a single-phase alternating current to a direct current, a second power converter for converting a direct current to an alternating current, and a parallel connection on the DC side of the first and second power converters. Power converter with a DC intermediate circuit consisting of
A power converter provided with means for estimating a capacitor capacitance value based on the magnitude of the AC voltage fluctuation of the capacitor and the AC input current and the AC input voltage of the first power converter or their command values. Capacitor capacity determination device. 2. The device according to claim 1, wherein the means for estimating the capacitance value of the capacitor determines that the capacitance of the capacitor has decreased when the estimated value of the capacitance of the capacitor is equal to or less than a first reference value. An apparatus for determining the capacitance of a power converter, wherein the first and second power converters are stopped when the power becomes equal to or less than a second reference value smaller than the first reference value. 3. The apparatus according to claim 1, further comprising means for storing the estimated value of the capacitor capacity as a history of changes in the capacitor capacity. 4. A first power converter for converting a single-phase alternating current to a direct current, a second power converter for converting a direct current to an alternating current, and a parallel connection to the DC side of the first and second power converters. Power converter with a DC intermediate circuit consisting of
An apparatus for determining a capacitor capacity of a power converter, comprising means for comparing the magnitude of the AC voltage fluctuation of the capacitor with a predetermined reference value to determine a decrease in the capacitor capacity. 5. The capacitor of claim 4, wherein the reference value is set based on an AC input current and an AC input voltage of the first power converter or a command value thereof. Capacity determination device. 6. The device according to claim 4, wherein the means for determining a decrease in the capacitance of the capacitor is configured to reduce the capacitance of the capacitor when the magnitude of the AC voltage fluctuation of the capacitor exceeds a first reference value. And the first
Wherein the first and second power converters are stopped when a second reference value larger than the reference value is exceeded. 7. A capacitor for a power converter according to claim 4, further comprising means for storing a magnitude of a change in the AC voltage of the capacitor as a history of a change in the capacitance of the capacitor. Capacity determination device.