JPH104686A - Power converter, using auxiliary resonance commutation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the optimum zero-voltage switching by selecting the values of the equivalent inductances of positive- and negative-side routes, connecting the first connecting point between main switch elements and the second connecting point between smoothing capacitors, so that the voltage of a discharge-side resonance capacitor can become zero or negative at the time of commutation. SOLUTION: The values of equivalent inductances of positive- and negative- inductances Lf' connecting points P1 and P2 are selected so that the voltage of a discharge-side resonance capacitor can become zero or negative at the time of commutation. The inductances Lc in smoothing capacitors CD1 and CD2 and inductances around main switch elements S1 and S2 are not able to change freely, even when they exist, and the values of the equivalent inductances Lf' are decided within such a range that the optimum values of the positive- and negative-side equivalent inductances Lf are large than (Lc+Ls). More specifically, a conductor having the inductance value of [Lf-(Lc+Ls)] is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an auxiliary resonance comprising a series circuit of a bidirectional auxiliary switch element and a resonance reactor disposed between a connection point between main switch elements and a connection point between voltage dividing smoothing capacitors. The present invention relates to a power converter using an auxiliary resonance commutation circuit.

[0002]

2. Description of the Related Art In general, in a power conversion device including a power semiconductor switching element, a loss called a switching loss occurs when a switch is turned on and off, and this loss increases in proportion to the operating frequency when operated at a high frequency. , Will be a serious problem. Recently, various soft switching systems based on zero voltage switching (ZVS) or zero current switching (ZCS) have been proposed, but no system that can be used for a large-capacity power converter has been found.

However, in 1989, (USA) IEEE-I
AS Conference Record, pp. 829-834, RESONANT SNUBBERS WITH AUXILIARY SWITCHES, William McM.
The circuit based on urray is a practical method. As a method for controlling this type of circuit, Japanese Patent Publication No. 5-502365 discloses a method of controlling a power converter using an auxiliary resonant commutation circuit. The details of such a method are based on literatures, and will be briefly described here with reference to FIGS.

FIG. 6 shows an example in which an auxiliary switch element having a reverse blocking ability is used, that is, F
ig1, E denotes a DC power source, CD1 and CD2 denote smoothing capacitors connected in series to divide the DC power source E, and S1 and S
2 is a main switch element, D1 and D2 are main switch elements S1
, S2 are diodes connected in anti-parallel, CR1 and CR2 are resonance capacitors connected in parallel to the main switch elements S1 and S2, Lr is a resonance reactor, and SA1 and SA2 are auxiliary switch elements. Here, the auxiliary switching elements SA1 and SA2 are thyristors having reverse blocking capability, and both are connected in anti-parallel to have bidirectionality.

FIG. 7 shows another example in which an auxiliary switch element having a series connection diode is used, that is, FIG. 1 described in the above-mentioned publication, where SA3 and SA4 are auxiliary switch elements. Here, the auxiliary switch elements SA3 and SA4 are
A switch element having a low reverse blocking capability and a diode having a large reverse element capability connected in series are used, and have a bidirectional property by their anti-parallel connection configuration. In practice, the switch element and the diode are often integrated into a single module, in which case they are connected as shown by the dotted lines in FIG.

[0006]

FIG. 6 and FIG.
Will be described with reference to the circuit diagram of FIG. 8 and the waveform diagram of FIG. Io is a load current, Ip is a positive current, In is a negative current, and VC1 is the voltage of the resonance capacitor CR1. FIG.
At this point, the gate is being applied to the main switch element S2. However, if the load current Io flows in the direction shown in the figure, it does not flow to the main switch element S2 but to the diode D2. From this state, when the gate-off of the main switching element S2 and the turning-on of the auxiliary switching element SA1 are performed simultaneously at time T0, a current flows through a path shown by a dashed line and a straight line is obtained until the current of the resonant reactor Lr becomes the load current Io. The diode D2 is conducting until time T. Here, when the resonance reactor current becomes the load current Io, the diode D2 becomes non-conductive, and the resonance reactor L
The resonance operation by r and the resonance capacitors CR1 and CR2 (the capacitance of CR1 and CR2 is assumed to be (1 / 2C)) starts, and a current flows through a path shown by a solid line. Thereby, as shown by the dotted line in FIG. 9, the voltage VC1 of the resonance capacitor CR1 is discharged and becomes zero at time T. When a gate is applied to the main switch element S1 at this time, ZVS
Therefore, no switching loss occurs.

However, such an operation can be realized under ideal circuit conditions, and is impossible with a practical circuit. For example, if the resonance reactor Lr has a resistance,
Due to the loss due to this, as shown by the solid line in FIG.
C1 does not become zero, so that ZVS cannot be realized. As a method for solving this problem, as described in JP-A-5-502365, before conducting the resonance operation, the conduction time between the auxiliary switch element SA1 and the main switch element S2 is wrapped, and After the resonance reactor current is passed, the main switch element S2 is turned off to perform an operation called boost. However, for that purpose, complicated control such as detection of the resonance reactor current is required, and there are problems such as an increase in price and a decrease in reliability.

An object of the present invention is to use a special auxiliary resonance commutation circuit capable of performing ZVS by optimally selecting the equivalent inductance value of the positive route and the negative route. To provide a power converter.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has the following structure. That is, the first between the two main switch elements
The value of the equivalent inductance of the positive side route and the negative side route connecting the connection point of (1) and the second connection point between the smoothing capacitors is determined as follows. It is a matter of choice.

[0010] Next, in a circuit component except for an auxiliary resonance commutation circuit composed of a series circuit of an auxiliary switch element and a resonance reactor, which is not found in any document including the above-mentioned published patent publication. Consider the presence of inductance. This is because the inductance of the component itself and the wiring, which are inevitably present in the circuit configuration, albeit slightly, cannot be ignored. In particular, when the output capacity of the power converter increases, it is necessary to reduce the inductance value of the resonance reactor,
Therefore, it has been found that the value approaches the value of the wiring inductance and the like, and has a great influence. This will be described with reference to FIG.

FIG. 1 is a view similar to FIG. 6 in which the internal inductance and the wiring inductance are replaced with an equivalent inductance, wherein Lf is an equivalent inductance, P1
Is a connection point between the smoothing capacitors CD1 and CD2 connected in series, and P2 is a connection point between the main switch elements S1 and S2 connected in series. Here, the equivalent inductance Lf includes the internal inductance and the wiring inductance of the smoothing capacitor, and is further divided into a positive route and a negative route between the connection points P1 and P2. This operation will be further described with reference to the equivalent circuit diagrams of FIGS.

Now, as in the case described above, the load current I
When the auxiliary switch element SA2 is turned on in a state where o is flowing through the diode D2, the circuit operates in the equivalent circuit shown in FIG. 2 until the negative side current In becomes zero, and the positive side current Ip and the resonance capacitor CR1 Of the voltage VC1 of the equation (1),
(2). Here, ω is the equation (3), and (C /
2) is the capacitance of CR1 and CR2, L is the inductance of Lr, Lf is the equivalent inductance, and E is the power supply voltage.

[0013]

(Equation 1)

When the negative current In becomes zero at time T, the diode D2 is turned off, and the operation shifts to the equivalent circuit shown in FIG. 3, where a new resonance occurs. Here, assuming that the value of the positive-side current Ip at time T is IP1 and the value of the voltage VC1 is VC1, the values IP1 and VC1 can be expressed by equations (4) and (5). Here, ω1 and ω2 are equations (6) and (7).

[0015]

(Equation 2)

Further, with respect to the equations (1) and (2) and the equations (4) and (5), the value L of the resonance reactor Lr
(L = 4 μH), the value C of the resonance capacitors CR1 and CR2 is (C = 0.5 μF), and the calculation result is shown in FIG. 3 by changing the equivalent inductance Lf. As shown in this figure, it can be seen that the minimum value of the voltage VC1 of the positive side resonance capacitor CR1 is considerably affected by the value of the equivalent inductance Lf. If the minimum value of VC1 is a positive voltage even when the main switch element S1 is turned on at the minimum value of the voltage VC1, ZVS is not performed.
Not only does the turn-on loss of the main switch element increase, but also the occurrence of electromagnetic noise due to a sharp current change poses a problem.

Therefore, the value of the equivalent inductance on the positive and negative sides is selected so that the minimum value of the voltage of the resonance capacitor CR1 is zero or negative (in an actual circuit, it does not become negative due to the anti-parallel diode). By selecting the optimum value of the equivalent inductance as described above, the minimum value of the resonance capacitor voltage is set to zero or negative, and the main switch element is turned on near the minimum value. From this, Z
As a result, the turn-on loss is significantly reduced by the VS, and the generation of electromagnetic noise can be suppressed because no sharp current change occurs.

[0018]

FIG. 5 shows an embodiment to which the present invention is applied in a manner similar to FIG. 1, where Lf 'is an equivalent inductance,
Lc and Ls are inductances. Here, the equivalent inductance Lf ′ is (Lf ′ = Lf−Ls−Lc). That is, in FIG. 1, the auxiliary switching elements SA1 and SA2 between the connection points P1 and P2 and the resonance reactor Lr
Connection points P1 and P
2 can be selected so that the value of the equivalent inductance Lf 'at the positive side route and the negative side route connecting to the discharge side resonance capacitor becomes zero or negative during commutation. is there. Here, the inductance Lc inside the smoothing capacitors CD1 and CD2 and the main switch elements S1 and S2
Even if the surrounding inductance Ls always exists, it cannot be changed freely, and the value of the equivalent inductance Lf ′ is
As described above, the optimum value of the positive and negative side equivalent inductances Lf is determined in a range larger than (Lc + Ls). Specifically, the value of the inductance is [Lf- (Lc + Ls)]
May be used to connect between the smoothing capacitors CD1, CD2 and the main switch elements S1, S2 (diodes and resonant capacitors are connected in parallel). Note that the main switch element S1 to the main switch element S
The commutation to S2 has been described, but if the direction of the load current is reversed, the commutation to S2 to S1 is of course the same.

[0019]

As described above in detail, according to the present invention, the turn-on of the main switch element is performed at zero voltage, and the efficiency of the power converter can be improved and the generation of electromagnetic noise can be suppressed. A power converter using a resonant commutation circuit can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram in which internal inductance, wiring inductance, and the like are replaced with equivalent inductance.

FIG. 2 is a first equivalent circuit diagram shown for explaining the operation of FIG. 1;

FIG. 3 is a second equivalent circuit diagram shown for explaining the operation of FIG. 1;

FIG. 4 is a waveform chart showing an example of selecting an equivalent inductance value.

FIG. 5 is a circuit diagram showing one embodiment to which the present invention is applied.

FIG. 6 is a circuit diagram showing a conventional example using an auxiliary switch element having a reverse blocking ability.

FIG. 7 is a circuit diagram showing another conventional example using an auxiliary switching element having a series connection diode.

FIG. 8 is a circuit diagram shown for explaining the operation of FIGS. 6 and 7;

FIG. 9 is a waveform chart shown for explaining the operation of FIGS. 6 and 7;

[Explanation of symbols]

 E DC power supply CD1 Smoothing capacitor S1 Main switch element D1 Diode CR1 Resonant capacitor Lr Resonance reactor SA1 Auxiliary switch element Lf Equivalent inductance Lf 'Equivalent inductance Io Load current Ip Positive current In Negative current VC1 Voltage P1 Connection point P2 Connection point Lc inductance Ls inductance

Claims (1)

[Claims] 1. A first connection point between two main switch elements connected in series between a positive electrode and a negative electrode of a DC power supply and having an anti-parallel diode and a resonance capacitor connected in parallel, and connected in series to the DC power supply. A power conversion device comprising an auxiliary resonance commutation circuit including a series circuit of a bidirectional auxiliary switch element and a resonance reactor between the smoothing capacitor for the voltage division and a second connection point between the smoothing capacitors. The value of the equivalent inductance of the positive side route and the negative side route connecting the first connection point and the second connection point is determined by determining whether the voltage of the discharge side resonance capacitor becomes zero or negative during commutation. A power converter using an auxiliary resonance commutation circuit, which is selected as described above.