JPH06121547A - Inverter - Google Patents

Abstract

PURPOSE:To feed only required quantity of required resonance current by connecting a saturable reactor in series with a resonance reactor and taking out current from the joint thereof thereby suppressing unnecessary resonance current as low as possible. CONSTITUTION:A series circuit of two sets of self-extinguishing switching elements 21, 22, each comprising a diode 31 or 32 and a snubber capacitor 51 or 52, is connected forward with a DC power supply 1 while a series circuit of two sets of diodes 71, 72, each connected in parallel with a resonance capacitor 81 and 82, is connected reversely with the DC power supply 1. A resonance reactor 9 and a saturable reactor 91 are connected in series between the joint of the self-extinguishing switching elements 21, 22 and the joint of the diodes 71, 72 and load current is taken from the end of the saturable reactor 91 opposite to the joint of the diodes 71, 72.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter devised so as to sufficiently suppress switching loss which occurs when a self-turn-off switching element is turned on and off.

[0002]

2. Description of the Related Art A typical basic circuit of a conventional inverter is shown in FIG. Reference numeral 1 is a DC power supply, and 21 and 22 are self-extinguishing type switching elements, which are connected in series and connected to the DC power supply 1. Diodes 31 and 32 are connected in anti-parallel to the self-extinguishing switching elements 21 and 22, respectively, and a series connection body of snubber diodes 41 and 42 and snubber capacitors 51 and 52 is connected in parallel. Snubber resistors 61 and 62 are connected in parallel to 41 and 42, respectively. The load is taken from the series connection point of the self-extinguishing type switching elements 21 and 22. The self-extinguishing switching elements 21 and 22 alternately turn on and off to supply AC power to the load.

In this circuit, when the load current is flowing to the self-extinguishing type switching element 21, when the element is turned off, the load current is commutated to the series circuit of the snubber diode 41 and the snubber capacitor 51, and the snubber capacitor 51. By this action, no voltage is immediately applied to the self-extinguishing type switching element 21, and the switching loss can be made extremely small. The load current charges the snubber capacitor 51,
When the snubber capacitor 52 is discharged and the snubber capacitor 52 reaches zero volt, the load current starts flowing through the diode 32. In a PWM-controlled inverter, in this state, it often happens that the self-extinguishing switching element 22 is turned off and then the self-extinguishing switching element 21 is turned on again. Then,
A large current flows through the self-extinguishing switching element 21 and the diode 32 in a state close to a short circuit until the charge accumulated in the diode 32 in which the current flows is discharged. Immediately after the diode 32 reversely recovers, a large current continues to flow in the snubber diode 42 and the snubber capacitor 52 in a state close to a short circuit. Due to these large currents, large losses occur in the self-turn-off switching device 21 and the diode 32.

At this time, a self-extinguishing type switching element
When 21 is turned on, the electric charge charged to the voltage E of the DC power supply 1 in the snubber capacitor 41 is discharged via the snubber resistor 61. This causes a loss in the snubber resistor 61 and the self-extinguishing type switching element 21. If the capacitance of the snubber capacitor is C _{s and the} operating frequency is f, this loss P becomes P = (1/2) C _s E ² × f, which increases in proportion to the operating frequency, and at high frequencies (1 kHz or more) It becomes a big problem.

As described above, in the conventional inverter, the high frequency operation is difficult due to the switching loss of the self-turn-off switching element and the loss due to the consumption of the electrostatic energy accumulated in the snubber capacitor. Various proposals have been made to solve these problems. For example, various methods have been proposed in which a part or all of the electrostatic energy stored in the snubber capacitor is regenerated to a DC power source via a power conversion circuit, but all of the circuits are complicated and are in practical use. Almost never.

[0006] In addition, "IEEE T"
RASACTION ON POWER ELECTRONICS "Vol.7 No.2 The paper" A Rugged Soft "described in p385-p392 of April 1992 issue.
"Com-mutated PWM Inverter for AC Drive" uses the minimum required number of two switching elements to compose one phase of the inverter, and also enables operation with switching loss suppressed as much as possible both on and off. An inverter circuit has been introduced.This circuit is shown in Fig. 8. The same symbols as in Fig. 7 are components having the same function. In this circuit, a snubber circuit connected to the self-extinguishing type switching elements 21 and 22. Is only the snubber capacitors 51, 52, which is a so-called lossless snubber circuit, which is simpler than that in Fig. 7. Furthermore, the capacitors 71, 72 in which the resonant capacitors 81, 82 are connected in parallel are connected in series to the power supply. 1 in the reverse direction, connect the resonance reactor 9 between the series connection point of the self-extinguishing switching elements 21, 22 and the series connection point of the diodes 71, 72, and connect the diodes 71, 72 in series. So that take out the load from the connection point.

The operation of this circuit will be briefly described. When the self-extinguishing switching element 22 is in the ON state and the load current i ₀ is flowing in the direction shown by the arrow in FIG. i ₀ all flows from the diode 72, and the current due to the residual magnetic energy of the resonance reactor 9 flows in the direction opposite to the arrow of i _L shown in FIG. 7, and the self-extinguishing switching element 22 → diode 72 → resonance reactor 9 route (Refer to the operation to be described later for such a state). In this state, when the self-extinguishing type switching element 22 is turned off by the gate signal under the PWM control, the return current (-i _L )
Is commutated to the snubber capacitors 51 and 52, and no voltage is immediately applied to the self-extinguishing type switching element 22, that is, so-called zero voltage switching (ZVS), and turn-off loss can be extremely small.
The current -i _L is discharged and charged by the snubber capacitors 51 and 52 and the resonance reactor 9 by the resonance of the snubber capacitors 51 and 52, and the resonance is stopped when the respective voltages become zero and the DC power supply voltage E. At this time, if there is residual magnetic energy in the resonance reactor 9, the current due to this is diode 31 → DC power supply 1 → diode 72 → resonance reactor 9
, And is regenerated to the DC power supply 1. If the self-extinguishing type switching element 21 is turned on while the current is flowing through the diode 31, the current does not immediately flow out, that is, so-called zero current switching (ZCS), and no turn-on loss occurs.

Next, when the electrostatic energy of the resonance reactor 9 is released and the current becomes zero, the DC power supply 1 → self-extinguishing type switching element 21 → resonance reactor 9 contrary to the conventional case.
→ diode 72 → DC power source 1 route, for the DC power supply voltage E is applied to the resonant reactor 9, current i _L is gradually increased in the direction of the arrow in FIG. 8, the load current i ₀ equal to the diode 72 It becomes non-conductive. From this moment, the resonance operation by the resonance reactor 9 and the resonance capacitors 81, 82 starts, the resonance capacitors 81, 82 are discharged and charged respectively, and become 0 and the DC power supply voltage E, respectively, and the resonance operation is stopped.
Thereafter, due to the residual magnetic energy of the resonant reactor 9, a return current flows in the route of the resonant reactor 9 → diode 71 → self-extinguishing type switching element 21. That is, the load current i ₀ and the resonance current having the peak value I _r flow in the self-extinguishing type switching element 21 and the resonance reactor 9 in a superimposed manner. I _r = E (2C _r / L) ^1/2 where C _r is the capacitance of the resonant capacitors 81 and 82, and L is the inductance of the resonant reactor 9.

Next, when the self-extinguishing type switching element 21 is turned off by the PWM signal, the current flowing in the resonance reactor 9 is commutated to the snubber capacitors 51 and 52, and the resonance operation between the capacitors and the resonance reactor starts. The self-extinguishing type switching device 21 can be turned off by the snubber capacitor 51 by ZVS described above without the occurrence of switching off loss. The resonance operation is stopped when the voltages of the snubber capacitors 51 and 52 become the DC power supply voltage E and zero. It was flowing in the resonance reactor 9 (load current +
A large current (resonance current) is regenerated to the DC power supply 1 through the route of the diode 32 → resonance reactor 9 → diode 71 → DC power supply 1. Here, if the self-extinguishing type switching element 22 is turned on while the current is flowing through the diode 32, Z
It becomes CS and no turn-on loss occurs. When the current i _L of the resonance reactor 9 decreases due to the release of the residual magnetic energy of the resonance reactor 9 and becomes equal to the load current I ₀ , the diode 71 becomes non-conducting, and the resonance reactor 9 and the resonance capacitors 81, 82 are connected. Resonance starts again.
Resonance continues until the resonant capacitors 81 and 82 are at the DC power supply voltage E and zero, respectively.

At this time, if the circuit constant is determined so that the peak value I _r of the resonance current becomes larger than the load current I ₀ ,
The current i _L of the resonant reactor 9 can be negative and can flow in the direction opposite to the arrow shown in FIG. That is, _assuming that the inductance of the resonance reactor 9 is L and the capacitance of the resonance capacitors 81 and 82 is C _r , i _L = I _0MAX −E (2C _r / L) ^1/2 <0 ∴ (2C _r / L) ^1/2 > I _0MAX / E Here, I _0MAX is selected as a constant so as to satisfy the condition of the expected maximum value of the load current.

As a result, the current due to the residual magnetic energy of the resonant reactor 9 after resonance recirculates through the route of the self-extinguishing type switching element 22 → diode 72 → resonant reactor 9 and becomes the first state of this explanation. Is repeated. The same operation is performed when the load current has a polarity opposite to that described above, and thus the description thereof will be omitted.

The above description is based on the current i of the resonance reactor 9.
FIG. 9 shows a time chart in which _L is associated with the states of the self-extinguishing type switching elements 21 and 22. In FIG. 9, the resonance operation of the resonance reactor 9 and the snubber capacitors 51 and 52 is omitted because the period is short. As shown in FIG. 9, the peak value I _{r of the} resonance current occurring in the period T ₅ is _set to be larger than the maximum value I _{0MAX of the} load current, and the resonance reactor current i _L is set to cross the zero line. For this reason, the peak value of the resonance current occurring in the period T ₂ is also I _r, and a large current (I _0MAX + I _r ) flows through the self-arc-extinguishing type switching element 21. In the case of FIG. 9, it is necessary to flow more than twice the load current I _0MAX into the self-extinguishing type switching element 21 (2.5 times or more is optimal in the above paper).

As described above, this conventional example realizes an inverter in which the switching loss of the self-arc-extinguishing type switching element is suppressed and the loss due to the snubber resistance is eliminated. A large current flows during steady conduction, and this large current increases the conduction loss of the self-extinguishing type switching element, which hinders the realization of a large capacity inverter. Further, a large resonance current flows even when the load current i ₀ is small, which is a problem of this circuit.

[0014]

In the above-mentioned conventional inverter, it is possible to suppress the generation of switching loss when the self-arc-extinguishing switching element is switched on / off. There is a problem that the steady conduction loss increases. The present invention has been made to solve the above problems, and it suppresses unnecessary resonance current (T ₂ period in FIG. 9) as much as possible and requires necessary resonance current (T ₅ period in FIG. 9). The purpose is to let as much as possible.

[0015]

[Means for Solving the Problems] One or two saturable reactors are inserted between the resonance reactor 9 and the series connection points of the diodes 71 and 72, and the load is connected to the series connection points of the diodes 71 and 72. The saturation reactor is taken out from the terminal on the opposite side of the series connection point.

[0016]

When the saturable reactor naturally has an iron core and the magnetization characteristics of the iron core are as shown in FIG. 3, when the current flowing in the saturable reactor is between -I _s and + I _S. Indicates that the iron core is unsaturated and has a substantially constant inductance L _c (>> inductance L of the resonant reactor 9) during this period, and the iron core is saturated and the inductance becomes zero when | I _s | or more. . If this saturable reactor becomes unsaturated during the period T ₂ of FIG. 9 and has a large inductance L _c , the peak value of the resonance current during this period can be suppressed to a small value.

[0017]

1 is a circuit diagram showing an inductance according to an embodiment of the present invention. The difference from the conventional example is that a saturable reactor 91 is inserted between the series connection point of the diodes 71 and 72 and the resonance reactor 9 and the load is taken out from the connection point between the resonance reactor 9 and the saturable reactor 91. It is a point.

The operation of the circuit shown in FIG. 1 will be described with reference to the time chart of FIG. In the figure, the alternate long and short dash line shows the case where the saturable reactor 92 is inserted. At time t ₀ , the self-extinguishing switching element 22 is turned off, and the current i _{L of the} resonant reactor 9 is increased.
The operation of turning on the self-extinguishing type switching element 21 and increasing the current i _{L of the} resonant reactor to the plus side before the polarity of becomes positive is exactly the same as the conventional example. That is,
During this operation, the saturable reactor 91 is saturated and the inductance is zero, so the same operation is performed. However, when the current of the resonant reactor 9 approaches the load current i ₀ (i ₀ −I _s ), the current flowing through the saturable reactor 91 becomes | I _s | or less, and the saturable reactor 91 becomes unsaturated and has a large inductance. To have L _c . Therefore, when the increase rate of the current in the resonance reactor 9 becomes small at time t ₁ ′ in FIG. 4 and becomes equal to the load current i ₀ at time t ₁ , resonance starts similarly to the conventional example, but the inductance related to the resonance is (L + L _c ), the peak value I _r ′ of the resonance current becomes I _r ′ = E [2C _r / (L + L _c )] ^1/2 , which is approximately (L) compared to the case without the saturable reactor 91.
/ L _c ) ^1/2 times. Therefore, the current flowing back to the self-extinguishing type switching element 21 also becomes small.

Resonance starts again at time t ₄ ′,
During the period T ₅ ′, the saturable reactor 91 is unsaturated and has a large inductance L _c , so that the resonance cycle is long and the current change rate is small. Saturable reactor at time t ₄
91 is saturated and the inductance becomes zero. For this reason, the resonance cycle becomes shorter, the rate of change of the resonance current sharply increases, and the peak value I _r ″ of the resonance current also increases and becomes approximately I _r ″ = E (2C _r / L) ^1/2. .

As a result, the current in the resonant reactor 9 is reversed in polarity as in the conventional example, and the self-extinguishing type switching element 22
A return current can be supplied to the device, and the device can be operated without impairing the conventional features.

FIG. 2 is a circuit diagram showing another embodiment of the present invention. In addition to the example of FIG. 1, a second saturable reactor 92 is inserted between the resonance reactor 9 and the saturable reactor 91. , The load is taken out from the connection point between the first saturable reactor 91 and the second saturable reactor 92.

In this embodiment, the peak value of the resonance current of resonance that starts at time t ₄ shown in FIG. 4 is a value that is hardly influenced by the magnitude of the load current i ₀ . That is, when the load becomes light and without the saturable reactor 92, the resonance current increases to a negative polarity, the current flowing back to the self-extinguishing switching element 22 during the period T ₆ is also large, and unnecessary loss occurs. Will occur. Therefore, saturable reactor 92
Is added, the saturable reactor becomes unsaturated before and after the current of the resonant reactor 9 reverses its polarity (that is, the current of the saturable reactor 92 becomes | I _s | or less), and has a large inductance L _c . It is possible to suppress the development of resonance and prevent a large return current from flowing through the self-extinguishing type switching element 22.

FIG. 5 is a circuit diagram showing still another embodiment of the present invention, in which the saturable reactor is biased with a current (ni ₀ ) proportional to the load current i ₀ . That is, in the embodiment of FIG. 1 or FIG.
The saturable reactor 91 during the period T ₁ ′ and the period T ₅ ′ shown in FIG.
Is unsaturated and has a large inductance, the T ₁ ′ and T ₅ ′ periods are longer than the T ₁ and T ₅ periods, which is an obstacle to increasing the operating frequency of the inverter.

Therefore, as shown in FIG. 5, a current transformer 10 is inserted in the wiring to the load, and n is proportional to the load current on the secondary side.
The current of i ₀ is extracted and the secondary current is converted to a saturable reactor.
Bias excitation is applied to 91 and 92 with the polarities shown in FIG. Here, the current ratio of the current transformer 10 is ni ₀ ≈I
If set to be _s, the saturable reactor 91 is saturated until the current through becomes the load current i _0, the resonance is started after reaching the load current i _0. That is, the period T ₁ ′ shown in FIG. 4 can be eliminated.

Similarly, after turning off the self-extinguishing type switching element 21, the current of the saturable reactor 91 is changed to the load current i.
_Although it decreases to ₀ and resonance starts, in this embodiment, the saturable reactor 91 is saturated at this point, and the period T ₅ ′ shown in FIG. 4 can be eliminated, as shown in FIG. Become. This makes it possible to increase the inverter operating frequency. Similarly for saturable reactor 92,
It is clear that the effect on the saturable reactor 91 is the same as that of the saturable reactor 91, which is not shown, because the current flowing through the saturable reactor 92 can maintain saturation up to around 0 ampere.

The self-extinguishing switching element in each of the above-described embodiments has the same effect as long as it is a self-extinguishing switching element. Also,
The saturable reactor may have a characteristic that the transition from unsaturated to saturated is performed gradually instead of the characteristic shown in Fig. 3. Further, the saturable reactors 91 and 92 have different characteristics and inductances. Anything is fine. It goes without saying that the resonance reactor 9 and the saturable reactor 92 do not affect the operation even if they have a positional relationship opposite to that shown in FIG.

In the embodiment of FIG. 5, the bias exciting current (ni ₀ ) of the saturable reactor is explained to be substantially equal to I _s , but this is not an absolute condition and may be changed as necessary.

[0028]

As described above, according to the present invention, the number of self-extinguishing switching elements constitutes an inverter and the switching loss generated when the self-extinguishing switching elements are turned on / off is suppressed. It is possible to provide a very excellent inverter that has a small amount of loss even if it is operated at a high frequency because the current that is slightly higher than the load current only needs to flow through the self-turn-off switching element.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of an inverter according to the present invention.

FIG. 2 is a circuit diagram of another embodiment of the inverter according to the present invention.

FIG. 3 is a diagram showing a characteristic example of a saturable reactor used in the inverter of the present invention.

FIG. 4 is a time chart for explaining the operation of the embodiment of FIGS. 1 and 2.

FIG. 5 is a circuit diagram of still another embodiment of the inverter according to the present invention.

FIG. 6 is a time chart for explaining the operation of the embodiment of FIG.

FIG. 7 is a circuit diagram showing a conventional typical inverter.

FIG. 8 is a circuit diagram of a conventional inverter that minimizes switching loss.

9 is a time chart for explaining the operation of the inverter of FIG.

[Explanation of symbols]

 1 DC power supply 21, 22 Self-extinguishing type switching element 31, 32 Diode 41, 42 Snubber diode 51, 52 Snubber capacitor 61, 62 Snubber resistance 71, 72 Diode 81, 82 Resonant capacitor 9 Resonant reactor 91, 92 Saturable reactor 10 Current transformer

Claims (4)

[Claims] 1. A diode in which two sets of self-extinguishing type switching elements in which a diode and a snubber capacitor are respectively connected in parallel are connected in series to a DC power source in the forward direction and a resonance capacitor is connected in parallel. In the inverter circuit in which two sets of two are connected in the reverse direction, and a resonance reactor is connected between the series connection point of the self-extinguishing type switching element and the series connection point of the diode, An inverter characterized in that a first saturable reactor is inserted between a connection point and the resonance reactor, and a load is taken out from a connection point between the first saturable reactor and the resonance reactor. . 2. A diode in which two sets of self-extinguishing type switching elements in which a diode and a snubber capacitor are respectively connected in parallel are connected in series to a DC power source in the forward direction and a resonance capacitor is connected in parallel. Are connected in series in the opposite direction, and a resonance reactor is connected between the series connection point of the self-extinguishing switching element and the series connection point of the diode, and the series connection point of the diode is connected. An inverter circuit in which a first saturable reactor is inserted between the resonance reactor and a second saturable reactor is further inserted between the resonance reactor and the first saturable reactor. An inverter characterized in that a load is taken out from a connection point between the second saturable reactor and the first saturable reactor. 3. The inverter according to claim 1, wherein the first saturable reactor is biased with a current proportional to a load current. 4. The inverter according to claim 1, wherein the second saturable reactor is biased with a current proportional to a load current.