JPH1062470A - Open-phase detection system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an open-phase detection system for detecting open-phase of the input power supply for a power converter comprising a three-phase AC power supply surely at low cost by providing a rectifier circuit and a smoothing capacitoar. SOLUTION: A rectifier circuit 2, a smoothing capacitor 3 and an inverting section 4 constitute a voltage type inverter and variable speed control of an induction motor 5 is performed using three-phase AC input power supply. In such a system, a DC voltage detection circuit 7 is provided and a voltage detection amount is inputted to a fast Fourier transform(FFT) processing section 8 where FFT is performed. 2f and 6f (f: power supply frequency) are then extracted from the processing results and open-phase of input power supply is determined based on the increase/decrease of level (6f component decreases and 2f component increases in case of open-phase).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an open-phase detection system which includes a rectifier circuit and a smoothing capacitor, and which is applied to open-phase detection of an input power supply of a power converter (such as a general-purpose inverter) using three-phase alternating current as a power supply.

[0002]

2. Description of the Related Art A voltage-type inverter device is an example of a power conversion device having a three-phase alternating current input and having a rectifier circuit of a diode bridge and a smoothing capacitor. The necessity of phase loss detection when this is used for variable speed control of an induction motor will be described. FIG. 9 is a circuit diagram, and FIG. 10 is a waveform diagram. In the drawing, 1 is a three-phase AC power supply, 2 is a rectifier circuit of a diode bridge, 3 is a smoothing capacitor, and 4 is an inverse converter (for example, I
GBT bridge) and 5 are induction motors.

In a normal case, as shown in FIG. 10A, a current of 120 ° section (representing a current i _R ) flows through each line, and a DC voltage _Vdc is also 60 ° (the power supply frequency is f. In this case, a flat waveform having a ripple of 6f) is obtained.

If a break occurs at the point F on the input side of the rectifier circuit 2 and the S-phase is out of phase, the remaining R, R
The DC current _idc is supplied to the inverse converter 4 through T. At this time, the line current (for example, the current i _R ) is as shown in FIG.
As shown in (b), the current flows only once at 180 ° (2f), and the ripple (V _PK1 ) of the DC voltage V _dc also increases.

[0005] With continues to supply the same direct current i _dc and normal in such a phase loss condition, which up to six diodes _{(D u, D v, D} w, D x, D y, D z) the current that has passed through the four diodes _{(D u, D w, D} x, D z) will pass through the peak value of the current increases to I _PK1 from I _PK0, it is about 1.6 times .

Normally, the diode is selected under the condition of a three-phase input state. Therefore, in the open phase state, the diode is overloaded, and the peak value I _PK1 may repeatedly exceed the maximum value of the peak current and be damaged. Therefore, open-phase detection is required for device protection.

FIG. 11 shows a conventional example. In the figure, 1 is 3
2 is a rectifier circuit of a diode bridge, 3 is a smoothing capacitor, 4 is an inverse converter (for example, an IGBT bridge), 5 is an induction motor, 6 is an inverter controller, 10
Is a protection circuit for the purpose of overvoltage or overcurrent protection, and 11 is an output of the protection circuit 10 and an open-phase detection signal (described later).
An OR circuit 12 which takes the output of the OR circuit 11 to stop the supply of the inverter gate signal when protection is required, such as when detecting an open phase, and 31 for detecting the state of the input voltage Is an open phase detection circuit for determining an input voltage state based on the output of the transformer 31. There is also a configuration in which a photocoupler 33 is provided to detect the state of the input voltage, and the phase loss detection circuit 32 determines the input voltage state based on the output.

FIG. 12 shows another conventional example. In the figure, 1 is a three-phase AC power supply, 2 is a rectifier circuit of a diode bridge, 3
Is a smoothing capacitor, 4 is an inverse converter (for example, an IGBT bridge), 5 is an induction motor, 6 is an inverter controller, 7
Is a DC voltage detection circuit, 10 is another protection circuit for overvoltage or overcurrent protection, etc., 11 is an OR circuit which takes the logical sum of the output of the protection circuit 10 and the output of a ripple detection circuit (described later), and 12 is A gate circuit that receives the output of the OR circuit 11 and stops the supply of the inverter gate signal when protection is required, such as when phase loss is detected. A gate circuit 34 detects a ripple in the detection output (DC voltage) of the DC voltage detection circuit 7. When the ripple of the DC voltage increases by a certain level or more in the ripple detection circuit, it is determined that there is no phase.

[0009]

In the example shown in FIG.
Since a dedicated sensor such as the transformer 31 (or the photocoupler 33) and the open-phase detection circuit 32 is required, the cost increases. Further, the phase sequence of the input voltage and the like are determined by the open phase detection circuit 32.
, Detection is performed in a very short time of about one cycle, and a malfunction is likely to occur due to a response speed (a response of several seconds is sufficient for this kind of protection target) or disturbance such as noise. Lack of stability.

On the other hand, in the example shown in FIG. 12, the ripple of the DC voltage is detected, and the phase loss is judged from the increase or decrease of the level. It is not uniformly determined by the relationship of the current, and skill is required to determine the determination level of the ripple (V _PK ). The ripple of the DC voltage is the DC output current i
There is a problem that it tends to increase or decrease according to the magnitude of _dc , and the detection sensitivity is low.

The present invention has been made in view of the above circumstances, and an FFT (Fast) is used for frequency analysis of a rectified / smoothed waveform.
An object of the present invention is to provide an open-phase detection method capable of performing open-phase detection reliably and at low cost by applying the Fourier Transform (Fourier Transform).

[0012]

SUMMARY OF THE INVENTION The present invention provides a power conversion device having a rectifier circuit and a smoothing capacitor, which has a three-phase alternating current input, and which is equipped with an FFT operation function to analyze the frequency of a rectified / smoothed waveform. An arithmetic operation is performed to detect an open phase of the input power supply from an increase or decrease in the level of a specific frequency component, for example, a frequency component 2f or 6f twice or six times the power supply frequency f.

According to the present invention, in a power converter having a rectifier circuit and a smoothing capacitor and having a three-phase AC input, an FFT operation function is added to the frequency analysis of a DC voltage, a rectified DC current or a smoothed DC current. An open phase of the input power supply is detected from an increase or decrease in the level of a specific frequency component, for example, a frequency component 2f or 6f twice or six times the power supply frequency f.

According to the present invention, in a power converter having a rectifier circuit, a smoothing capacitor, and an inverse converter, an FFT operation function is added to a frequency analysis of an input current of the inverse converter in a three-phase AC input. It is characterized in that a frequency component proportional to the output frequency of the conversion unit is extracted, and a phase loss on the output side is detected from an increase or decrease in the level.

[0015]

FIG. 1 shows a first embodiment of the present invention. In the figure, 1 is a three-phase AC power supply, 2 is a rectifier circuit of a diode bridge, 3 is a smoothing capacitor, 4 is an inverter (for example, an IGBT bridge), 5 is an induction motor, 6 is an inverter controller, and 7 is a DC voltage. A detection circuit 8 is an FFT processing unit for performing FFT on the detected voltage of the detection circuit 7, and a component 9 extracts a component 2f twice and a component 6f six times as large as the input power frequency f. 2f, 6f detectors for judging the open phase of the power supply, 10 is another protection circuit for overvoltage or overcurrent protection, and 11 is the 2nd protection circuit.
an OR circuit 12 which takes the logical sum of the open phase detection signal of the f, 6f detection section 9 and the output of another protection circuit 10; This is a gate circuit for stopping supply of a signal.

FIG. 2 shows the relationship between the input and output of the FFT.
(A) shows the case of FFT operation, (b) shows the case of three-phase input (normal), and (c) shows the case of missing phase. For example, using the sampled signals x ₀ ~x _127, the output X ₀ to X by FFT calculation
_Ask for ₁₂₇ . The 2f and 6f components are extracted from this output. In a normal state, a large amount of the 6f component is detected as shown in FIG. The 2f component is sufficiently smaller than the 6f component. During the phase loss, the 6f component decreases and the 2f component increases as shown in FIG. An open phase is determined from the relationship between the level increase and decrease of the 2f and 6f components. The determination flow is shown in FIG.
As shown in FIG.

In the case of FIG. 3, a _Vdc data sample is input (step S1), an FFT operation is performed (S2), and it is determined whether or not 2f ≧ LEVEL1 for a 2f component of the result (S3). The judgment value LE in which the 2f component is set in advance
When it is larger than VEL1 (Yes), it is determined that the phase is missing (S4). If No, the process returns to step 1. Judgment value LEV
EL1 is a value small enough to remove disturbance and noise appearing in the 2f component, and can be detected more reliably than the other conventional example (FIG. 12) even when the current _idc is small.

In the case of FIG. 4, an open-phase counter for counting the number of consecutive detections of the 2f component equal to or higher than LEVEL 1 is provided so as to perform more accurate detection. As in FIG. 3, a _Vdc data sample is input (S11), an FFT operation is performed (S12), and the 2f component of the result is 2f.
It is determined whether or not LEVEL1 (S13). If this determination is Yes, the count of the phase loss counter is increased (S14), and it is determined whether or not the phase loss counter ≧ LEVEL2 (S15). LEVEL2 is the number of times, and is set to, for example, three times. Yes, ie, LEVEL 1 or more 2
When the f component is detected three or more times consecutively, it is determined that the phase is missing (S16). Judgment of 2f ≧ LEVEL1 (S1
If No in 3), the phase loss counter is cleared (S1).
7) Return to step 11. Phase loss counter ≥ LEVEL
When the determination of No. 2 (S15) is No, the process also returns to step 11.

FIG. 5 shows a second embodiment of the present invention. In the second embodiment, the output current i _RP (or i _RN ) of the rectifier circuit 2 is detected by the current detector 21 and used as an input to the FFT processing unit 8. In other words, FFT is used for the frequency analysis of the current waveform.
Apply The 2f and 6f detectors 9 extract the 2f and 6f components and determine the missing phase from the level increase / decrease relationship in the same manner as in the first embodiment, and the same reference numerals are assigned to the same components (partially omitted). The description is omitted here. The current waveform is as shown in FIG. (A) is for normal operation, and (b) is for open phase operation.

FIG. 7 shows a third embodiment of the present invention. In the third embodiment, the input current i _dc (or i
_dcN ) is detected by the current detector 22 and used as an input to the FFT processing unit 8. That is, the FFT is applied to the frequency analysis of the current waveform as in the second embodiment. The 2f and 6f detectors 9 extract the 2f and 6f components and determine the missing phase from the level increase / decrease relationship in the same manner as in the first embodiment, and the same reference numerals are assigned to the same components (partially omitted). The description is omitted here.

In the case of Embodiment 3, FIGS. 8A and 8B
As shown in (c), 2f, 6 with respect to the input power frequency f
The f component is detected and used to determine the phase loss of the input power, and 2f 'and 6f with respect to the output frequency f' of the inverter.
The 'component is extracted, and the phase loss of the output is determined from the increase or decrease in the level of the 2f' (or 6f ') component. 8A shows a normal state, FIG. 8B shows an input phase loss, and FIG. 8C shows an output phase loss.
At the time of input phase loss, the 2f component increases (at the same time, the 6f component decreases), and at the time of output phase loss, the 2f ′ component increases.

[0022]

As described above, according to the present invention, the frequency component of the rectified / smoothed DC voltage or DC current clearly changes between the normal state and the open phase, so that the frequency analysis of the rectified / smoothed waveform can be performed. By using the FFT, an open phase can be reliably detected. In addition, since the detector for DC voltage and DC current may be used in common for other purposes, it can be realized at low cost. Further, by detecting the input current of the inverting unit, there is an advantage that an open phase on the output side can be detected.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIGS. 2A and 2B show input / output relations of the FFT of the first embodiment, wherein FIG. 2A shows input / output signals of an FFT operation, FIG. 2B shows a voltage waveform and spectrum in the case of three-phase input, and FIG. The voltage waveform and spectrum in the case of.

FIG. 3 is a flowchart illustrating an example of a phase loss determination according to the first embodiment.

FIG. 4 is a flowchart showing another example of the phase loss determination according to the first embodiment.

FIG. 5 is a block diagram showing a second embodiment of the present invention.

FIGS. 6A and 6B show a current waveform according to the second embodiment, wherein FIG. 6A shows a normal state and FIG.

FIG. 7 is a block diagram showing a third embodiment of the present invention.

8A and 8B show spectra of 2f, 2f ', 6f, and 6f' components of the third embodiment, where FIG. 8A shows a normal state, FIG. 8B shows an input phase loss, and FIG.

FIG. 9 is a circuit diagram showing a main circuit configuration of a variable speed control device for an induction motor using a voltage type inverter device.

FIGS. 10A and 10B are waveform diagrams for explaining the necessity of phase loss detection. FIG. 10A shows a case of three-phase input (normal), and FIG. 10B shows a case of phase loss.

FIG. 11 is a block diagram showing an example of the related art.

FIG. 12 is a block diagram showing another conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Three-phase alternating current power supply 2 ... Rectifier circuit 3 ... Smoothing capacitor 4 ... Inverse conversion unit 5 ... Induction motor 6 ... Inverter control unit 7 ... DC voltage detection circuit 8 ... FFT processing unit 9 ... 2f, 6f detection unit 10 ... Other Protection circuit 11: OR circuit 12: Gate circuit 21, 22: Current detector

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location H02P 7/63 302 H02P 7/63 302D

Claims (3)

[Claims] 1. A power converter having a rectifier circuit and a smoothing capacitor, which has a three-phase AC input, implements an FFT operation function, performs an FFT operation on frequency analysis of a rectified / smoothed waveform, and executes a specific frequency component. An open phase detection method characterized by detecting an open phase of an input power supply from an increase or decrease in a level of the input power. 2. The open-phase detection method according to claim 1, wherein a DC voltage, a rectified DC current or a smoothed DC current is analyzed. 3. A power converter having a rectifier circuit, a smoothing capacitor, and an inverter, and an FFT operation function added to a frequency analysis of an input current of the inverter in the three-phase AC input. An open-phase detection method characterized by extracting a frequency component proportional to an output frequency and detecting an open-phase on the output side from an increase or decrease in the level.