JP3259319B2 - Inverter abnormality detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter composed of two unit inverters which are used by connecting the DC side in series, in which an abnormality occurs and the DC voltage sharing becomes unbalanced between the unit inverters. The present invention relates to an inverter abnormality detection device for detecting such imbalance and taking measures such as stopping the operation of the inverter.

[0002]

2. Description of the Related Art The allowable value of the DC voltage of an inverter is determined by the rated voltage of a switching element such as a power transistor used in the inverter. When there is a product line that has been used, 2
When an inverter device that generates a desired AC power source from a double DC power source is configured, the device may be configured by diverting a product having the above-described results. In such a case, a method may be adopted in which the DC sides of two unit inverters are connected in series and half of the voltage value of the DC power supply is applied to the unit inverter.

FIG. 2 is a circuit diagram showing a conventional inverter composed of two unit inverters whose DC side is connected in series and an abnormality detecting device therefor. In this figure, a DC power supply 100 that rectifies an AC power supply 1 with a rectifier 2 to obtain DC power, and a unit inverter 5 connected in series to the DC power supply 100
DC power is supplied to the load 8 by transformers 61 and 62 and rectifiers 71 and 72 connected to the AC sides thereof. The inverters 51 and 52 using power transistors can perform high-frequency PWM control with a carrier frequency of 10 kHz level.
The DC applied to the load 8 can be controlled with high accuracy and high speed, and since the frequency of the pulsating flow contained in the DC is high, it is easy to remove the pulsating flow. The feature is that high quality DC power can be obtained.

Since the DC sides of the unit inverters 51 and 52 are connected in series, when both unit inverters 51 and 52 are in equilibrium, the voltage sharing is also equilibrium, and each half of the voltage of the DC power supply 100 is mutually equal. Is shared. For some reason, for example, when an abnormality such as a control pulse for controlling the turn-on or turn-off of the switching element is disturbed or any of the switching elements is broken, the voltage between the two unit inverters 51 and 52 is changed. An unbalance appears, and this unbalance appears as an unbalance of the voltage sharing on the DC side. If such a situation occurs and the unbalance ratio is large, one of the unit inverters 51 or 52 will share a large voltage, and there is a possibility that an accident may occur in which the element is destroyed.

[0005] To detect such an abnormal situation and take appropriate measures such as stopping the operation of the inverter, an abnormality detecting device 4 as shown in the figure is provided. The abnormality detection device 4 includes two detectors 41 and 4 each including a resistor voltage divider connected in parallel to the DC side of the unit inverters 51 and 52.
2, isolation amplifiers 43 and 44 for insulating the outputs of these detectors 41 and 42, an adder 45 for adding the output signals thereof,
An absolute value converter 46 for taking the absolute value of the output signal, a setter 47 for determining a threshold value for determining whether or not the detected value is regarded as abnormal, an output signal of the absolute value converter 46 and an output signal of the setter 47 And a comparator 48 that outputs a High signal when the output signal of the absolute value converter 46 is larger and outputs a Low signal otherwise. In the figure, the output signal of the comparator 48 is input to a control device included in the inverters 51 and 52 and used as information for stopping the inverters 51 and 52.

[0006] From the detectors 41 and 42 to the isolation amplifiers 43 and 4
4 are both signals based on the connection lines on the DC side of the inverters 51 and 52, so that when the voltage sharing is balanced, the detection voltages are in the opposite directions to each other. The result of the addition is zero. Actually, since the characteristics do not completely become zero due to variations in element characteristics, the threshold value set by the setting unit 47 is set to a value that does not cause a malfunction.

The adder 45 is often used as an analog arithmetic unit, and the absolute value converter 46 outputs a positive input as it is and a negative input inverts the output to the positive. It may be paraphrased. Therefore, a diode bridge using four diodes can be used as the absolute value converter 46. However, since the diode has a dead zone of about 0.5 to 1 V as is well known, it is not appropriate to set a threshold value close to or below this value. In such a case, an ideal full-wave rectifier circuit using two operational amplifiers (for example, transistor technology SPECIAL No. 17 page 65, CQ Publishing Company) is used.

[0008]

As apparent from FIG. 2, the detecting device 4 uses many electronic components such as two detectors 41 and 42, two insulating amplifiers 43 and 44, and an adder 45. The device becomes complicated, which causes a problem of reduced reliability and high price. An object of the present invention is to solve such a problem and to provide an inverter abnormality detection device having a small number of components.

[0009]

According to the present invention, there is provided, in accordance with the present invention, an imbalance in DC voltage sharing of an inverter in which the DC sides of two unit inverters are connected in series and connected to a DC power supply. A series circuit of two resistors having the same resistance value connected in parallel to the DC power supply, and inserted between a connection point of the two resistances and a connection point of the unit inverter. And a detection signal insulated from the DC side circuit of the inverter by insulating and amplifying a voltage between terminals of the detection resistor by an insulating amplifier.

[0010]

In the configuration according to the present invention, a series circuit of two resistors having the same resistance value is connected in parallel to a DC power supply, and between each connection point between the two resistors and two unit inverters connected in series. If the voltage across the terminals of the detection resistor is used as the detection voltage and the unbalance of the DC voltage sharing between the unit inverters occurs, the voltage at the connection point of the unit inverter changes and the terminal of the detection resistor A potential difference occurs between them. By inputting this potential difference to the isolation amplifier and isolating it from the DC side circuit of the inverter and using the output signal as a detection voltage to determine abnormality, only one detector and one isolation amplifier are required, and the adder can be used. It becomes unnecessary.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.
FIG. 1 is a circuit diagram of an inverter and an abnormality detection device therefor according to an embodiment of the present invention. The same circuit elements as those in FIG. In this figure, the abnormality detection device 9 includes a series circuit of two resistors 91 and 92 connected in parallel to a DC power supply 100 and having the same resistance value.
A detection resistor 93 inserted between the connection point of the series circuit and the connection point of the series connection of the unit inverters 51 and 52 is insulated from the DC circuit of the inverter that inputs a voltage between terminals of the detection resistor 93 and outputs a detection signal. An isolating amplifier 94, an absolute value converter 46 for obtaining the absolute value of the detection signal, and a comparator 48 for comparing the output signal thereof with the threshold value set by the setting unit 47. If it is determined that is larger than the threshold value, a High signal is output; otherwise, a Low signal is output. This signal is input to a control device (not shown) of the unit inverters 51 and 52 to stop the operation. It is also possible to adopt a configuration for simply issuing an alarm or a configuration for juxtaposing them.

Since the voltage at the connection point between the resistors 91 and 92 is one half of the voltage of the DC power supply 100, the unit inverter 51,
When there is no abnormality in 52 and the voltage sharing on the DC side is shared by half, the voltage between the terminals of the detection resistor 93 is zero. Actually, the voltage between the terminals of the detection resistor 93 is not always completely zero due to variations in the resistance values of the resistors 91 and 92 and variations in the characteristics of various semiconductor elements in the unit inverters 51 and 52. By setting the threshold value set by the setting unit 47 to an appropriate value for a detection voltage that does not need to be determined to be abnormal, it is possible to avoid erroneous determination to be determined to be abnormal.

When an imbalance occurs in the DC voltage sharing of the unit inverters 51 and 52, a voltage is generated between the detection resistors 93.
The polarity of the voltage of the detection resistor 93 is determined depending on which of the unit inverters 51 and 52 has the larger shared voltage. In this determination, it is not necessary to specify which of the unit inverters 51 and 52 has become abnormal. Therefore, in either case, the absolute value converter 46 calculates the absolute value of the detection signal so that the abnormality can be detected in both cases. Is used as a determination signal for the presence or absence of an abnormality.

If the resistances of the resistors 91 and 92 are small, the flowing current increases and the power consumption increases. Therefore, it is desirable that the resistance is as high as possible within a range that does not affect the detection sensitivity. The setting of the threshold value by the setting device 47 is different from the setting value of FIG. That is, in FIG.
Since the voltage is divided by 2, the detection voltage differs depending on the division ratio even at the same unbalance ratio. Therefore, the setting of the threshold value is determined in consideration of the partial pressure ratio. On the other hand, the voltage between terminals of the detection resistor 93 in FIG. 1 is different in that a difference in DC voltage due to unbalance appears as it is. If this value is too large, a configuration may be adopted in which the detection resistor 93 is used as a voltage divider and the detection terminal is pulled out from a tap in the middle.

[0015]

As described above, according to the present invention, a series circuit of two resistors having the same resistance value is connected in parallel to a DC power supply, and each of the two resistors and two unit inverters connected in series are connected to each other. If a detection resistor is inserted between the connection points and the voltage between the terminals of the detection resistance is used as the detection voltage, the voltage at the connection point of the unit inverter changes when the unbalance of the DC voltage sharing occurs between the unit inverters. A potential difference occurs between the terminals of the detection resistor. Therefore, an abnormality can be detected with only one detection voltage from the DC circuit, and only one insulation amplifier is required to insulate it from the DC circuit, and an adder can be eliminated, and the number of circuit components can be reduced. Thus, the effect of improving reliability and lowering the price can be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an inverter and an abnormality detection device thereof according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional inverter and its abnormality detection device.

[Explanation of symbols]

 Reference Signs List 100 DC power supply 51 Unit inverter 52 Unit inverter 91 Detector 92 Detector 93 Insulation amplifier 94 Insulation amplifier 95 Adder 96 Absolute value converter 97 Setting device 98 Comparator

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02H 7/122 H02M 7/48

Claims (1)

(57) [Claims] An abnormality detecting device (4) for detecting an imbalance in DC voltage sharing of inverters, wherein the DC sides of two unit inverters (51, 52) are connected in series and connected to a DC power supply (100). And two resistors (91, 92) of the same resistance connected in parallel to the DC power supply (100).
And a detection resistor (93) inserted between a connection point of these two resistors (91, 92) and a connection point of the unit inverters (51, 52). An inverter abnormality detection device characterized in that a voltage between the terminals is insulated and amplified by an insulation amplifier (46) to obtain a detection signal insulated from a DC side circuit of the inverter.