JP3375255B2 - Inverter circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an inverter circuit in which switching elements connected in parallel are connected to a bridge.

[0002]

2. Description of the Related Art Generally, when the power capacity required by a single power switching semiconductor element cannot be obtained,
Switching elements such as two or more IGBTs or MOSFETs are connected in parallel and used. An example of a bridge inverter circuit using switching elements connected in parallel in this way is shown in FIG.

In FIG. 5, a first arm A1 to a fourth arm A4 employing two parallel-connected IGBTs 1A and 1B, 2A and 2B, 3A and 3B, and 4A and 4B as switching elements are shown. A bridge inverter formed by full bridge connection is connected between the positive and negative DC input power supply terminals 5 and 6. Between the connection point between the first arm A1 and the second arm A2 and the connection point between the third arm A3 and the fourth arm A4, the load side circuit 7 includes the AC lines 8A, 8B and 9A. And 9B, and current balancers 10, 11
Connected through. The current balancers 10 and 11 have two windings 10A and 10B, 1 on a ferrite core, respectively.
1A and 11B are usual ones, and two IGBTs 1A and 1B connected in parallel, 2A and 2B, 3A and 3 are connected in parallel.
B and serves to balance the current between 4A and 4B respectively.

Next, the drive circuit will be described.
Reference numerals A and 12B are drive circuits exclusively provided for driving the IGBTs 1A and 1B of the first arm A1 and have the same circuit configuration. Therefore, the drive circuit 12A
The circuit configuration will be described. A bias power supply is made up of the first secondary winding 14A of the isolation transformer 13, the diode 15A and the capacitor 16A, and a DC bias voltage is applied to the gate amplifier 17A. The gate amplifier 17A has a built-in photocoupler P for signal insulation transmission, is driven by a control signal from the control circuit 18, and gives a drive signal to the IGBT 1A. Similarly, the gate amplifier 17B outputs the drive signal to the IGB.
It is applied to T1B and the IGBT1B is driven in phase with the IGBT1A.

On the other hand, the IG of the second arm A2
The BTs 2A and 2B are driven by the same drive signal from the common drive circuit 12C. This drive circuit 12C is also the drive circuit 1
The circuit configuration is the same as 2 A, and the third transformer of the isolation transformer 13 is used.
Secondary winding 14C, diode 15C and capacitor 1
6C, and a gate amplifier 17C that receives the DC bias voltage. The gate amplifier 17C also has a built-in photocoupler P for signal insulation transmission, is driven by the control signal from the control circuit 18, and outputs a drive signal having a phase opposite to that of the drive signal given to the IGBTs 1A and 1B.
Give to T2A and 2B. As a result, the IGBTs 1A and 1B and the IGBTs 2A and 2B alternately switch each other.

Since the switching circuit 19 ′ including the arms A3 and A4 has the same circuit configuration as the switching circuit 19 including the arms A1 and A2, illustration of the drive circuit and the like is omitted. IGBT1A, 1B of arm A1 and IGBT4 of arm A4
A and 4B perform switching in pairs, and I of arm A2
The GBTs 2A and 2B and the IGBTs 3A and 3B of the arm A3 perform switching in pairs.

[0007]

However, in such a conventional bridge inverter, the I of the arm A1 is
The drive circuits of the GBTs 1A and 1B are connected to the IGBT of the arm A2.
When the drive circuits of 2A and 2B are made common, the current balancer 10 is short-circuited because the emitter electrode, that is, a part of the drive signal line to the AC side terminal (shown by the chain line 20) short-circuits the AC lines 8A and 8B. As a result, as shown in the figure, the drive circuits for the IGBTs 1A and 1B of the arm A1 have to be separated, which increases the cost. Further, if the drive circuits are separated, if there is a difference in the operation time of the drive circuits, the switching of the IGBTs 1A and 1B will be different, and one of the IGBTs will bear a load, which is likely to cause a failure.

The present invention has been made by paying attention to such a conventional problem, and an object thereof is to solve the above problems by sharing a driving circuit of switching elements connected in parallel.

[0009]

In order to solve the above-mentioned problems, the invention according to claim 1 includes a first arm A1 to a fourth arm A4 each having a plurality of switching elements connected in parallel with each other. The connection point between the first arm A1 and the second arm A2, which is connected to the bridge, is located on one side above and below, and the third point is located above and below the other side.
In the full bridge inverter in which the load side circuit is connected through the current balancer between the connection point between the arm A3 and the fourth arm A4, the first arm A1 and the third arm A3 located on the upper side, respectively. In common with the driving circuit of the plurality of switching elements connected in parallel, the current balancer is prevented from being short-circuited between the driving circuit and each AC side terminal of the switching elements connected in parallel. , An inverter circuit characterized by connecting interference preventing resistors of substantially the same value.

In order to solve the above-mentioned problems, a second aspect of the present invention includes a first arm A1 and a second arm A2 each including a plurality of switching elements connected in parallel to each other, and a capacitor A respectively. The third arm A3 and the fourth arm A4 are connected to a half bridge, and the connection points between the first arm A1 and the second arm A2 located on the upper and lower sides of one side and the upper and lower sides on the other side are located. Third
In the half-bridge inverter in which the load side circuit is connected through the current balancer between the arm A3 and the connection point of the fourth arm A4, the parallel-connected switching element of the first arm A1 located on the upper side. And a resistance for interference prevention having substantially the same resistance value, in which the current balancer is prevented from being short-circuited between the drive circuit and the AC side terminals of the switching elements connected in parallel. The present invention provides an inverter circuit characterized in that

In order to solve the above-mentioned problems, the invention according to claim 3 is the same as that of claim 1 or 2.
The interference prevention resistor has a resistance value within a range of about 50 mΩ to 10Ω or less.

[0012]

FIG. 1 is a diagram for explaining a first embodiment of the present invention, in which switching of an upper arm of a full bridge inverter circuit such as a parallel-connected IGBT or power MOSFET is performed. It is characterized in that the element drive circuit is shared and a resistor is connected between the drive circuit and each AC side terminal of the switching elements connected in parallel.

In FIG. 1, the same symbols as those shown in FIG. 5 indicate corresponding members. In this embodiment, the winding 14A of the isolation transformer 13 and the diode 15
A single drive circuit 12A composed of A, a capacitor 16A, and a gate amplifier 17A drives the switching elements 1A and 1B connected in parallel in the first arm A1. In order to eliminate the adverse effect of driving with a single drive circuit 12A, the interference prevention resistor R1 having substantially the same resistance value is provided between the drive circuit 12A and the AC side terminals a and b of the switching elements 1A and 1B. , R2 are connected to each other.

The resistors R1 and R2 are simply the current balancer 1
Not only is it possible to prevent the short circuit between the windings 10A and 10B of 0, making it difficult for the cross current i to flow, but also to disrupt the current balance between the switching elements 1A and 1B, and to prevent them from being connected to the AC terminals a and b. Even when a voltage is generated at the cross current i and the cross current i flows, the cross current i causes the resistors R1 and R2 to generate the voltages e1 and e2 having the polarities shown in the drawing. Voltage e1
Biases the switching element 1B in the OFF direction to decrease the current, and the voltage e2 acts to bias the switching element 1A in the ON direction to decrease the current. In any case, since the cross current i is reduced and the switching elements 1A and 1B cooperate to cooperate with the current balance operation, the current balance is further improved.

Here, as shown in FIG. 2, the current balancer 10 is formed by winding the ferrite core 10C through the AC wires 8A and 8B for one turn in the opposite direction to form the windings 10A and 10B. Is connected to.
The current balancer 11 also has the same configuration as the current balancer 10. When the characteristics of the switching elements 1A and 1B, 2A and 2B, 3A and 3B, and 4A and 4B in parallel are substantially the same and the currents of the AC lines 8A and 8B and the AC lines 9A and 9B are balanced, respectively. , Each AC line 8A and 8
B, the magnetic fluxes formed by the AC lines 9A and 9B cancel each other out, and no voltage is induced in the windings 10A and 10B and 11A and 11. When a current imbalance occurs due to a difference in saturation voltage of switching elements, a magnetic flux is generated according to the difference in current, and a reverse polarity voltage is generated for the one with a large current to reduce the current. For the one with a smaller current, a voltage of the same polarity is generated to increase the current and balance the current.

Next, FIG. 3 shows a first arm A1 and a second arm A2 each having switching elements 1A and 1B, 2A and 2B connected in parallel, and a third arm A3 having capacitors C1 and C2, respectively. In the same manner as described above, the resistors R1 and R2 are connected to the half-bridge inverter in which the fourth arm A4 and the fourth arm A4 are connected to each other, and the operation and effect of the portion related to the resistors R1 and R2 are described above. The description is omitted because it is similar to the example.

In any of the embodiments, the larger the resistance value of the interference prevention resistors R1 and R2 is in principle, the more effective it is. However, when the resistance value is large, the charging / discharging time of the gate capacitance of the switching element is long. Therefore, the rising and falling characteristics of the gate voltage deteriorate, which is not desirable. Generally, a resistance of 10 Ω or less is used as the gate resistance, so that the interference prevention resistance R1,
The resistance value of R2 is preferably 10Ω or less.

[0018]

EXAMPLE In the inverter circuit having the circuit configuration of FIG. 1, switching elements 1A and 1B, 2A and 2B, 3A and 3B, and 4A and 4B are 200A class IGB.
FIG. 4 shows the result of measuring the relationship between the values of the resistors R1 and R2 and the current balance using T. The resistors R1 and R2 have the same resistance value.

As shown in FIG. 2, the current balancer 10 is a balancer core 10C in which the AC lines 8A and 8B are passed through one turn in the opposite direction.
As C, H5C2 ferrite core T31-8-19 (T
DK Co., Ltd.) was used. Then, a copper wire having a diameter of 0.3 mm and a length of 100 mm is used as the control signal wire, and the resistance R
Current unbalance when 1 and R2 are not connected 12.5
%, The resistors R1 and R2 having the same resistance value were connected to the control signal line, and the resistance values were variously changed to perform the test.

As can be seen from FIG. 4, when the interference prevention resistors R1 and R2 have a resistance value of 50 mΩ or more, I
The imbalance of the currents flowing respectively in the GBTs 1A and 1B is limited to 5% or less. And the interference prevention resistor R1,
The current imbalance becomes smaller as R2 becomes larger. For example, in the case of 220 mΩ, the current imbalance becomes 2%. As a result of measuring by changing the resistance values of the interference prevention resistors R1 and R2 variously, the interference prevention resistor R
If the resistance values of R1 and R2 are selected within the range of about 50 mΩ to 10Ω, the current balance can be maintained in a good state with almost no adverse effect on the switching even when driven by a single drive circuit. The same applies to the IGBTs of the other arms.

In addition to the IGBT, other switching elements such as FETs or bipolar transistors can be similarly applied, and the case where the switching elements are arranged in two parallels has been described. However, the number of current balancers increases only when three or more parallels are used. And can be implemented in exactly the same way. Note that the driving circuit is only one example, and may have a configuration in which a switching element is driven using a pulse transformer.

[0022]

As described above, according to the present invention, it is possible to share the driving circuit of the switching elements connected in parallel on the upper arm side of the bridge inverter by adding a small capacity and low resistance. Can be lowered. Also, since two drive circuits are not required, there is no difference in the switching time of the switching element,
No imbalance in switching loss.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a first embodiment of the present invention.

FIG. 2 is a diagram for explaining a current balancer used in the present invention.

FIG. 3 is a diagram for explaining another embodiment of the present invention.

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

FIG. 5 is a diagram for explaining a conventional example.

[Explanation of symbols]

1A, 1B ... Switching elements 10, 11 ... Current balancers 2A, 2B ... Switching elements 12A, 12
B, 12C ... Driving circuits 3A, 3B ... Switching element 13 ... Insulation transformers 4A, 4B ... Switching element 14 ... Insulation transformer windings 5, 6 ... DC input power supply terminals 15A-15C
... Diode 7 ... Load side circuit 16A to 16C
... Capacitors 8A and 8B ... AC lines 17A to 17C
... Gate amplifiers 9A, 9B ... AC line 18 ... Control circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H02M 7/5387 H02M 1/08 H02M 7/48

Claims (3)

(57) [Claims] 1. A first arm A1 to a fourth arm A4 each having a plurality of switching elements connected in parallel to each other are connected to a bridge, and the first arm A1 and the first arm A1 located above and below one side. Second arm A2, and the third arm A3 and the fourth arm located above and below the other side.
In a full-bridge inverter in which a load side circuit is connected through a current balancer to the connection point with the arm A4, the plurality of parallel connections of the first arm A1 and the third arm A3 located on the upper side. A common drive circuit for the switching elements, and between the drive circuit and each AC side terminal of the switching elements connected in parallel ,
An inverter circuit characterized by connecting interference preventing resistors of substantially equal value , which prevent the current balancer from being short-circuited . 2. A first arm A1 and a second arm A2 each having a plurality of switching elements connected in parallel to each other, and a third arm A3 and a fourth arm A4 each having a capacitor are connected to a half bridge. The connection point between the first arm A1 and the second arm A2 located on the upper and lower sides of the one side, and the third point located on the upper and lower sides of the other side.
A half-bridge inverter in which a load-side circuit is connected through a current balancer between the arm A3 and the connection point of the fourth arm A4, the parallel-connected switching element of the first arm A1 located above Drive circuit is common, and the current balancer is prevented from being short-circuited between the drive circuit and each AC side terminal of the switching elements connected in parallel.
Ingredients, inverter circuit, characterized by connecting approximately equal interference prevention resistor resistance value. 3. In the description of claim 1 or 2,
The inverter circuit, wherein the interference prevention resistor has a resistance value in the range of approximately 50 mΩ to 10Ω.