JPH10210759A - 3-level inverter device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To protect switching devices from breakdown when excessive voltages are applied to the devices, by a method wherein the switching devices are connected so as to have the leakage current of the 2nd switching device larger than the leakage current of the 1st switching device and have the leakage current of the 3rd switching device larger than the leakage current of the 4th switching device. SOLUTION: 1st and 2nd switching devices 21 and 22 are connected in series in a forward direction between the (+) side terminal and the output terminal of a DC voltage source 1, and 3rd and 4th switching devices 23 and 24 are connected in series in a forward direction between the (-) side terminal and the output terminal of the DC voltage source 1. A device whose leakage current is larger than the leakage current of the 1st switching device 21 is selected as the 2nd switching device 22, and a device whose leakage current is larger than the leakage current of the 4th switching device 24 is selected as the 3rd switching device 23. When an output voltage is -E, a voltage higher than a potential difference between a neutral point and the (+) side is not applied to the 1st switching device 21. In the same way, when the output voltage is +E, a voltage higher than a potential difference between the neutral point and the (-) side is not applied to the 4th switching device 24.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a three-level inverter device for suppressing a voltage applied to a switching element.

[0002]

2. Description of the Related Art In recent years, inverters using high-speed switching elements such as IGBTs have been widely used in railway vehicles and the like. By using this kind of high-speed switching element, the operating frequency of the inverter can be increased, and there are many advantages such as reduction of noise and high-speed response. On the other hand, the high-speed switching element has a disadvantage that it is difficult to increase the breakdown voltage as compared with the low-speed element such as GTO. In addition, there is a problem that the price of the element becomes expensive even if the withstand voltage can be increased. For this reason, in a railway vehicle or the like, by connecting two groups of capacitors in series and connecting them in parallel to a DC power supply, it becomes possible to use the connection point of the capacitors divided into two groups as a neutral point. , Only a half of the DC power supply voltage is applied to the high-speed switching element.

[0003]

However, since the leakage current of the high-speed switching element varies, the voltage applied to the element may be larger than half the DC voltage, and the variation of the leakage current is extremely large. In such a case, the entire voltage of the DC voltage power supply is applied to the element, and the element may be broken by an overvoltage. The present invention has been made in view of the above points, and an object of the present invention is to prevent an element from being damaged by an overvoltage applied to the element even when the leakage current of the element has a large variation. .

[0004]

In order to solve such a problem, a switching element having first to fourth four antiparallel diodes connected in series to both terminals of a DC voltage power supply having a neutral point. And a first switching element and a second switching element.
A first diode connected to a polarity where the neutral side is an anode, and a third switching element and a fourth switching element between an interconnection point of the switching elements and a neutral point of the DC voltage power supply. Between the interconnection point and the neutral point of the DC voltage power supply, a second diode connected to the polarity where the neutral side is a cathode, and a connection point between the second switching element and the third switching element are output. In a three-level inverter device including a unit inverter configured to be connected to an end, a leakage current of a second switching element is larger than a leakage current of a first switching element, and a leakage of a fourth switching element. Third than current
Are connected so as to increase the leakage current of the switching element.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of a three-level inverter according to the present invention. Reference numeral 1 denotes a DC voltage power supply having a neutral point. For example, two capacitors (not shown) are connected in series and connected in parallel with the DC power supply. The connection can be realized by using the connection point of the capacitors divided into two groups as a neutral point. 21 is a first switching element, 22 is a second switching element, 23 is a third switching element, 24 is a fourth switching element, and all of the switching elements 21 to 24 have antiparallel diodes. . 3 is the first diode,
4 is a second diode, and 5 is a unit inverter.

A first switching element 21 and a second switching element 22 are connected in series in a forward direction between the positive terminal of the DC voltage power supply 1 and the output terminal, and the output terminal and the negative side of the DC voltage power supply 1 are connected. A third switching element 23 and a fourth switching element 24 are connected in series between the terminals in the forward direction. In addition, the first switching element 21 and the second
And the DC voltage power supply 1
The first diode 3 is connected between the neutral point and the neutral point so that the neutral point side becomes the anode, and the interconnection point between the third switching element 23 and the fourth switching element 24 is connected to the DC voltage power supply 1. The second inverter 4 is connected between the neutral point and the neutral point so as to have a polarity where the neutral point side is a cathode, thereby forming a unit inverter 5.

The operation of the three-level inverter will be described. Table 1 shows the relationship between the switching state of the first to fourth switching elements and the output voltage. However, the total voltage of the DC voltage power supply is 2E, the neutral point potential is 0 (V) based on the neutral point, the positive terminal potential is E (V), and the negative terminal potential is -E (V ). First switching element 21
And the second switching element 22 is ON and the third switching element 23 and the fourth switching element 24 are OFF, the output terminal is at the potential E (V), and the first switching element 21 and the fourth Switching element 24 is OF
F, when the second switching element 22 and the third switching element 23 are ON, the output terminal is at potential 0 (V), the first switching element 21 and the second switching element 22 are OFF, and the third switching element 22 is OFF. Switching element 23 and fourth
When the switching element 24 is ON, the output terminal is at the potential -E (V), and three levels of voltages appear at the output terminal.

[0008]

[Table 1]

Conventionally, the switching elements 21 to 24 have been used without particular selection. For this reason, there were the following problems. For example, the first switching element 2
When the leakage current of the first switching element 22 is larger than the leakage current of the second switching element 22, when the output voltage is −E, the voltage applied to the second switching element 22 from the first switching element 21 increases. Similarly, when the leakage current of the fourth switching element 24 is larger than the leakage current of the third switching element 23, when the output voltage is E, the third
The switching element has a higher applied voltage than the fourth switching element. That is, the applied voltage of the second or third switching element may be higher than the half voltage (E) of the input DC voltage due to the variation of the leakage current of the element. When the entire voltage of the DC voltage power supply is applied to the second or third switching element, the switching element may be broken by an overvoltage.

In order to solve such a problem, conventionally, a parallel resistor has been added to the first to fourth switching elements in order to balance the applied voltage, or an element having a large withstand voltage has been used. For this reason, the apparatus has been increased in size and cost has been increased. In the present invention, the first to fourth switching elements, a total of four leakage currents are measured in advance, and the second switching element 22 uses an element having a larger leakage current than the first switching element 21. The third switching element 23 selects and uses an element having a larger leakage current than the fourth switching element 24.

With this connection, when the output voltage is -E, the applied voltage of the first switching element tends to be higher than that of the second switching element.
The connection point between the switching element and the second switching element is connected to the neutral point of the DC voltage power supply via the first diode, so that the first switching element is connected to the neutral point and the positive side of the DC voltage power supply. Is not applied, and a half voltage (E) of the DC voltage power supply is applied to the first and second switching elements.

Similarly, when the output voltage is + E, the applied voltage of the fourth switching element tends to be higher than that of the third switching element.
Is connected to the neutral point of the DC voltage power supply via the second diode, the fourth switching element has a potential difference (E) between the neutral point and the negative side of the DC voltage power supply. The above voltages are not applied, and the third and fourth voltages are not applied.
Of the DC voltage power supply are applied to each of the switching elements. As described above, according to the present invention, a voltage higher than the half voltage (E) is not applied to all the switching elements.

[0013]

According to the present invention, it is possible to use an element having a smaller withstand voltage than before without using a parallel resistor for balancing the applied voltage of the element, and the element is destroyed by an overvoltage. That can be prevented.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a three-level inverter to which the present invention is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC voltage power supply 21 1st switching element 22 2nd switching element 23 3rd switching element 24 4th switching element 3 diode 4 diode 5 unit inverter

Claims (1)

[Claims] 1. A switching element having first to fourth four anti-parallel diodes connected in series to both terminals of a DC voltage power supply having a neutral point, said first switching element and said second switching element. A first diode connected to a polarity where the neutral side serves as an anode, between the interconnection point of the switching elements and the neutral point of the DC voltage power supply, and the third switching element and the fourth switching element. A second diode connected between the interconnection point of the elements and a neutral point of the DC voltage power supply with a neutral side serving as a cathode, and the second switching element and the third switching element. In a three-level inverter device including a unit inverter configured to be connected to an output terminal, a connection point is higher than a leakage current of the first switching element. A switching element selected so that a leakage current of the element is large and a leakage current of the third switching element is larger than a leakage current of the fourth switching element. apparatus.