JPH0444510B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an inverter, and more particularly to an inverter in which a converter for converting direct current to alternating current is composed of switching elements.

[Conventional technology]

Conventionally, switching elements such as gate turn-off thyristors (hereinafter referred to as GTO) have been used as converters for converting direct current into alternating current in inverters. When configuring an inverter using this GTO, a snubber circuit is provided to absorb the voltage when the GTO is turned on and turned off.

FIG. 1 shows a configuration diagram of a single-phase inverter using GTO. In the figure, a single-phase inverter can convert direct current supplied from a direct current power source E into alternating current and supply the alternating current to a load. GTO is used as a converter to convert this DC to AC.
1, 2, 3, and 4 are the DC power supply E and the AC output terminal T ₁ ,
Located between _T2 . Diode D ₁ and resistance connected between the anode and cathode of GTO1
R ₁ and capacitor C ₁ constitute a snubber circuit.
A snubber circuit capacitor C ₁ (hereinafter referred to as a snubber capacitor) is provided to absorb the voltage when the GTO 1 is turned off and to reduce the switching power when the GTO 1 is turned off. Diode _D1 is
Snubber capacitor when GTO1 turns on
Provided to block discharge current from _C1 . That is, when the snubber capacitor C ₁ discharges, the current flows through the snubber circuit resistor R ₁ (hereinafter referred to as snubber resistor). A snubber resistor _R1 is provided to consume the discharge energy of the snubber capacitor _C1 .

In addition, a current limiting reactor L ₁ is used to suppress the rise rate di/dt of the current when GTO 1 turns on, and to limit the current when the arm is short-circuited.
is provided. A diode D ₂ and a resistor R ₂ are connected in parallel to the current limiting reactor L ₁ . This diode D ₂ is provided to prevent overvoltage from being applied to GTO 1 when it is turned on and off, and the resistor R ₂ is provided to prevent overvoltage from being applied to GTO 1 when it is turned on and turned off.
It is provided in order to consume the energy generated in the current limiting reactor L ₁ and to increase the suppression of the rise rate di/dt of the current when the GTO 1 is turned off.

In addition, snubber resistors R ₃ , R ₅ , R ₇ provided in GTO2, 3, 4, snubber capacitors C ₂ , C ₃ ,
C ₄ , diode D ₃ , D ₄ , D ₅ , D ₆ , D ₇ , D ₈ , resistance
R ₄ , R ₆ , R ₈ and current limiting reactors L ₂ , L ₃ , L ₄ each have the same functions as those used in GTO1.

Furthermore, freewheel diodes D ₉ , D ₁₀ , D ₁₁ ,
D ₁₂ is connected.

With the above configuration, in the inverter shown in Fig. 1, by controlling GTO1, 2, 3, and 4 by switching, DC is converted to AC and connected between AC output terminals T ₁ and T ₂ . can be supplied to the load. And by the snubber circuit
The switching power during turn-off of GTOs 1, 2, 3, and 4 can be reduced, and good switching operation can be ensured.

[Problem to be solved by the invention]

However, when GTO1, _{2, 3, and 4 are turned on, the discharge energy of snubber capacitors C 1} , C ₂ , C ₃ , and C ₄ is transferred to snubber resistors R ₁ , R ₃ , R ₅ , and
Since the power is consumed by _R7 , there is a drawback that power is consumed by the snubber circuit. Furthermore, as the operating frequency of the GTO switching operation increases, losses increase.

Further, in the power supply lines of the DC power supply E and the GTOs 1, 2, 3, and 4, inductance occurs due to the wiring, as shown by the symbol _L5 in FIG. Therefore,
At both ends of this inductance _L5 , GTO1, 2,
When 3 and 4 turn off, a back electromotive force is generated.
Then, the energy of this inductance L ₅ is added to the DC voltage V _D and the snubber capacitor C ₁ ,
Since the voltage is applied to C ₂ , C ₃ , and C ₄ , the snubber capacitors C ₁ , C ₂ , C ₃ , and C ₄ are overcharged. In particular, in a large capacity inverter, each component constituting the inverter becomes large, the distance between the DC power source E and the GTO becomes long, and the value of the inductance _L5 becomes large. Therefore, in such a case, as shown in FIG. 2, the leading value of the voltage V _C applied to the snubber capacitor becomes more than twice the DC voltage V _D.
And the overcharged snubber capacitors C ₁ , C ₂ ,
The charges of C ₃ and C ₄ are GTO1, 2, 3, and 4, respectively.
When turns off, the snubber resistors R ₁ , R ₃ , R ₅ ,
Since it is discharged through _R7 , there is a disadvantage that the loss due to the snubber circuit further increases.

Note that iA is the anode current and V _AK is the GTO
is the voltage between the anode and cathode of .

In addition, in conventional inverters, in order to increase the capacity of the inverter and increase the operating frequency, the snubber resistor must have a large capacity, which has the disadvantage of increasing the size and cost of the inverter. .

The present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to provide an inverter that can suppress energy absorbed when turning off a switching element from being consumed as thermal energy when turning on a switching element. There is a particular thing.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a switching element, a freewheel rectifier connected in antiparallel to the switching element, a reactor connected in series to the switching element, and a capacitor and a rectifier connected in series. It has four sets of arms each having a snubber circuit connected at both ends to the switching element in parallel, and these arms are divided into pairs every two sets, and each pair of arms connects the switching element. They are connected in series with each other as a reference, and both ends are connected to a DC power supply, and the series connection point of each pair of arms is connected to a load as an output end, and by controlling the switching elements of each arm, DC power is converted to AC power. In an inverter that converts into electric power and supplies it to a load, an auxiliary capacitor and an auxiliary rectifying element are connected in series and inserted between the series connection point of the snubber circuit capacitor and rectifying element of each arm and the output end of each arm. One end of each auxiliary capacitor is connected to each output terminal, the cathode side of each auxiliary rectifying element is connected to a snubber circuit, and a connection point between the auxiliary capacitor and auxiliary rectifying element of each arm and the DC power supply is connected. A fourth rectifying element is inserted, and among these fourth rectifying elements, the fourth rectifying element used for the arm connected to the positive polarity side of the DC power supply has its anode side connected to the negative polarity side of the DC power supply, and the fourth rectifying element is used for the arm connected to the positive polarity side of the DC power supply. The fourth rectifying element used in the arm connected to the negative polarity side of the inverter is characterized in that the cathode side is connected to the positive polarity side of the DC power source.

[Effect]

According to the above-described means, the charge accumulated in the snubber capacitor when the switching element is turned off is transferred to the auxiliary capacitor when the switching element is turned on. The charge stored in the auxiliary capacitor is discharged through the load when the switching element is turned off.

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described based on the drawings.

FIG. 3 shows a preferred embodiment of the invention. Incidentally, members that are the same as or correspond to those in FIG. 1 are given the same reference numerals.

In this embodiment, unlike the case shown in FIG. 1, GTO1,
Current limiting reactor L ₁ connected in series with 2, 3, 4,
L ₂ , L ₃ , and L ₄ are connected to AC output terminals T ₁ and T ₂ , snubber capacitors C ₁ and C ₃ are connected to the anode sides of GTO 1 and 3, and snubber capacitors C ₂ and C ₄ are connected to the GTO
They are connected to the cathode sides of Nos. 2 and 4, respectively.
And snubber capacitors C ₁ , C ₂ , C ₃ , C ₄ are connected to GTO via diodes D ₁ , D ₃ , D ₅ , D ₇ respectively.
It is connected to the cathode side of 1, 2, 3, and 4.

Also, snubber capacitors C ₁ , C ₂ and diodes D ₁ ,
The connecting portion of D ₃ is connected to the AC output terminal T ₁ via diodes D ₁₃ and D ₁₄ and auxiliary capacitors C ₅ and C ₆ for storing the charges of snubber capacitors C ₁ and C ₂ , respectively. The connections between snubber capacitors C ₃ and C ₄ and diodes D ₅ and D ₇ are each connected to a diode.
It is connected to the AC output terminal T ₂ via D ₁₅ , D ₁₆ and auxiliary capacitors C ₇ , C ₈ for storing the charges of the snubber capacitors C ₃ , C ₄ .

Diodes D ₁₃ , D ₁₄ and auxiliary capacitors C ₅ , C ₇
The connecting portions are connected to the negative polarity side of the DC power source E via diodes D ₁₇ and D ₁₈ , respectively.

Diodes D ₁₄ , D ₁₆ and auxiliary capacitors C ₆ , C ₈
The connecting portions are connected to the positive polarity side of the DC power source E via diodes D ₁₉ and D ₂₀ , respectively.

The reason why each GTO is provided with a current limiting reactor is to strengthen the current limiting effect when an arm short circuit occurs. Also, the auxiliary capacitor C ₅ ,
C ₆ , C ₇ , C ₈ are snubber capacitors C ₁ , C ₂ , C ₃ , C ₄
Larger capacity is used.

With the above configuration, in this embodiment, as in the case of FIG. 1 described above, DC power can be converted into AC power and supplied to the load.

This embodiment differs from the case in which the snubber resistor consumes the electric charge charged in the snubber capacitor when the GTO turns on in FIG. 1, when the GTO turns on.
The charge on the snubber capacitor is transferred to the auxiliary capacitor.

That is, when GTO1 turns on, the discharge current of snubber capacitor _C1 flows through the loop of GTO1, current limiting reactor _L1 , auxiliary capacitor _C5 , and diode _D13 , and the charge of snubber capacitor _C1 is charged to auxiliary capacitor _C5 . Ru. At this time, since GTO2 is turned off, a DC voltage is applied to GTO2.

Next, when GTO1 turns off, the circulating current continues to flow through the closed loop of GTO4, freewheel diode _D10 , and current limiting reactor _L2 due to the energy of the load, so the terminal voltage of GTO2 is approximately
Become an OV. Therefore, the charge accumulated in the auxiliary capacitor _C5 is discharged through the load and the diode _D17 . That is, the diode _D17 is connected to the auxiliary capacitor _C5 as a circuit that releases the energy stored in the auxiliary capacitor _C5 through the load.

Furthermore, when the charge in the auxiliary capacitor C ₅ is discharged, the charge in the snubber capacitor C ₂ of the GTO 2 is discharged via the diode D ₁₄ , the auxiliary capacitor C ₆ , and the load. This discharge causes the charge in the snubber capacitor C ₂ to be stored in the auxiliary capacitor C ₆ .
The charge stored on the auxiliary capacitor is then transferred to the GTO
1 turns on when the load and diode D ₁₉
is discharged through. i.e. auxiliary capacitor C ₆
The charges accumulated in the GTO1 are released through the loop of the diode D ₁₉ , the GTO1, and the current limiting reactor L ₁ when the GTO1 is turned on. However, since there is almost no loss in this loop, the charge discharged from the auxiliary capacitor C ₆ has its polarity reversed and is charged again to the auxiliary capacitor C ₆ . Moreover,
At this time, the snubber capacitor _C2 has already been charged to the power supply voltage, so the auxiliary capacitor
The charge on C ₆ will be discharged via the load connected between terminals T ₁ and T ₂ .

Note that the same operation as described above is repeated when GTO2 is turned on while GTO1 is turned off. Also, GTO3 and 4 are each turned on,
When turning off, the operation is similar to that described above.

According to this embodiment, when the GTO is turned on, the electric charge stored in the snubber capacitor can be stored in the auxiliary capacitor, so there is no need for a conventional snubber resistor. Therefore, the device can be made smaller and losses can be reduced.

Moreover, since the charge stored when the GTO is turned on can be supplied as energy to the load when the GTO is turned off, loss can be reduced and power can be used effectively.

Further, in this embodiment, the charge of the snubber capacitor that is overcharged by the energy of the inductance _L5 due to the wiring can be regenerated into the power source.

That is, if the snubber capacitor C ₁ is overcharged, this charge is transferred to the diodes D ₁₇ , D ₁₈ ,
It is regenerated to the power source through a loop of the snubber capacitor C ₁ and the DC power source E, and when the snubber capacitor C ₂ is overcharged, it is regenerated to the power source via the diodes D ₁₄ and D ₁₅ . In addition, the snubber capacitor C ₃ ,
Even if C ₄ is overcharged, the charging charge is similarly regenerated to the power supply.

As described above, according to this embodiment, even if the inductance value due to the wiring is large, the charge overcharged in the snubber capacitor is regenerated to the power supply, so that it is possible to reduce loss and protect the GTO.

FIG. 4 shows a waveform diagram of the anode current iA flowing from the snubber capacitor and the anode voltage _VAK when the GTO is turned on. In the same figure, the chain line is a waveform diagram of the conventional inverter, and the solid line is a waveform diagram of the present embodiment.

Although the peak value of the anode current iA according to this embodiment is large, the value of the anode current iA at the initial turn-on of the GTO is small. This is because the rise rate di/dt of the current at the initial turn-on of the GTO is suppressed by the current limiting reactor. On the other hand, in the conventional case, the value of the anode current iA is decreasing. This is because the snubber resistor suppresses the peak value of the anode current iA. However, G.T.O.
The values of the anode current iA and the anode voltage _VAK at the initial stage of turn-on are larger than those of this embodiment. This indicates that the local concentration of current inside the GTO element is greater than in the case of this example. That is, when the GTO is turned on, a narrow region inside the device first becomes conductive, and as time passes, the on region becomes wider. Therefore, if the rise rate di/dt of the anode current iA at turn-on of the GTO is constant, the maximum value of the current density inside the GTO element decreases over time. Therefore, the anode current iA at the initial turn-on of the GTO
A small value means that local concentration of current inside the GTO element is small. This is also clear from the fact that in this example, even if the value of the anode current iA increases, the value of the anode voltage V _AK decreases.

In this way, according to this embodiment, local concentration of current inside the GTO element can be suppressed.
The reliability of the inverter can be improved.

In this embodiment, a single-phase inverter has been described, but it goes without saying that this embodiment can be applied to a three-phase inverter.

〔Effect of the invention〕

As explained above, according to the present invention, the charge accumulated in the main capacitor when the switching element is turned off is transferred to the auxiliary capacitor when the switching element is turned on, and the charge accumulated in the auxiliary capacitor is transferred when the switching element is turned off. Since the discharge is performed through the load, it is possible to suppress the energy absorbed when the switching element is turned off from being consumed as thermal energy when the switching element is turned on, and this can contribute to reducing loss in the inverter.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a conventional single-phase inverter, FIG. 2 is an operating waveform diagram of the GTO shown in FIG. 1, and FIG. 3 is a configuration diagram showing an embodiment according to the present invention. Figure 4 is for comparing the present invention and the conventional example.
FIG. 3 is an operation waveform diagram of GTO. 1, 2, 3, 4...GTO, C ₁ , C ₂ , C ₃ , C ₄ ...
... Snubber capacitor, L ₁ , L ₂ , L ₃ , L ₄ ... Current limiting reactor, E ... DC power supply, T ₁ , T ₂ ... AC output terminal, C ₅ , C ₆ , C ₇ , C ₈ ... ...auxiliary capacitor,
_D1 to _D8 , _D13 to _D20 ...Diode, _D9 , _D10 ,
_D11 , _D12 ...Freewheel diode.

Claims (1)

[Claims] 1. A switching element, a freewheel rectifier connected in antiparallel to the switching element,
It has four sets of arms each including a reactor connected in series to the switching element, and a snubber circuit in which a capacitor and a rectifying element are connected in series and both ends of which are connected in parallel to the switching element. Each pair of arms is connected in series with the switching element as a reference, both ends of which are connected to a DC power supply, and the series connection point of each pair of arms is connected to a load as an output end. In the inverter that converts DC power into AC power and supplies it to the load by switching control of the switching elements of each arm, the series connection point between the snubber circuit capacitor and rectifier of each arm and the rectifying element of each arm are connected. An auxiliary capacitor and an auxiliary rectifying element are connected in series and inserted between the output terminal, one end of each auxiliary capacitor is connected to each output terminal, and the cathode side of each auxiliary rectifying element is connected to a snubber circuit. A fourth rectifying element is inserted between the connection point between the auxiliary capacitor and the auxiliary rectifying element of the arm and the DC power supply, and among these fourth rectifying elements, the fourth rectifying element used in the arm connected to the positive polarity side of the DC power supply The four rectifying elements have their anodes connected to the negative polarity side of the DC power supply, and the fourth rectifying elements used in the arms connected to the negative polarity side of the DC power supply have their cathodes connected to the positive polarity side of the DC power supply. An inverter characterized by: