JPH0759148B2 - Resonance type DC-DC converter control method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC-DC converter which is widely used as a power source for electronic devices and the like, and more particularly to a so-called resonance type DC-DC converter which reduces switching loss of a switching element by utilizing an LC resonance circuit. It relates to a control method.

[0002]

2. Description of the Related Art Resonant DC-DC converters have been used in a wide range of fields as a power source for electronic devices such as industrial controllers, communication devices, computer devices, office devices and household electric appliances.

The resonance type DC-DC converter is intended to reduce the switching loss by opening and closing the switching element at the time when the voltage or current of the resonance circuit becomes zero. A voltage type that uses zero voltage, a current type that uses zero current, a half waveform in which the voltage or current of the switching element is unidirectional, a bidirectional full waveform, a boost type with different input / output voltage conversion ratios, There are various types such as step-down type and buck-boost type. The present invention can be applied to any of them, but the following description will be given taking the voltage half-wave step-up / down type shown in FIG. 5 as an example.

In FIG. 5, 1 is a direct current power source having an input voltage E _I , 2 is a resonance capacitor, 3 is a switching element using a transistor, a thyristor or the like, and 4 is a reverse voltage of the switching element 3. , 5 is a resonance reactor, 6 is a transformer that insulates the input / output voltage and adjusts the voltage ratio, 7 is a diode that rectifies the output voltage, 8 is a voltage smoothing capacitor,
Reference numeral 9 is a load device.

Although this type of circuit configuration and its operation are known, the operation will be briefly described with reference to FIG. When the switching element 3 is closed at time T ₀ , a loop of DC power supply 1 → switching element 3 → reactor 5 → transformer 6 primary winding → DC power supply 1 is formed, and the exciting inductance of the reactor 5 and the transformer 6 from the DC power supply 1 is formed. Power is supplied and the primary current I _L1 increases linearly.

When the switching element 3 is opened at time T ₁ , the primary current I _L1 commutates to the capacitor 2. Therefore, a series resonance circuit of the exciting inductances of the capacitor 2, the reactor 5, and the transformer 6 is formed, and the primary current I
_L1 and the voltage V _C have a sinusoidal vibration waveform as shown.

At time T ₂ , the secondary winding voltage of the transformer 6 exceeds the voltage of the capacitor 8, that is, the output voltage E _O , and the secondary current I _L2 starts to flow. Assuming that the capacitance of the capacitor 8 is sufficiently large and that the voltage E _O is constant during the resonance cycle period, the series resonance circuit is formed by the capacitor 1, the reactor 5, and the transformer 6 as well as all the primary inductances after the time T _{2. Therefore} , although the primary current I _L1 , the voltage V _C , and the secondary current I _L2 have different angular frequencies from those before time T _2, they still have a sinusoidal vibration waveform.

When the voltage V _C falls from positive to zero at time T ₃ , the primary current I _L1 flowing through the capacitor 2 is _rectified to the diode 4 and the voltage V _C is clamped to zero volt. When the time T ₄ is reached and the secondary current I _L2 also becomes zero, the negative primary current I _L1 continues to flow in the diode 4, and the surplus power stored in the exciting inductances of the reactor 5 and the transformer 6 is regenerated in the DC power supply 1. .

At time T ₅ , the switching element 3 is closed again when the primary current I _L1 becomes positive,
Thereafter, the same operation as that after time T ₀ is repeated. In this way, the voltage E _I of the input DC power supply 1 is converted into the voltage E _O , and the power is transmitted to the secondary side in the form of (I _L2 · E _O ).
If the average value of the secondary current I _L2 is I _O , (I _O ·
E _O ) is the average output power.

[0010]

In the converter circuit of FIG. 5, the time T _{5 at which the} switching element 3 normally closes.
In FIG. 6, the voltage V _C, that is, the voltage of the switching element 3 is zero, and no switching loss occurs when the circuit is closed, and the advantage of the resonance type is exhibited. However, the configuration of FIG. 5 takes various forms of operation depending on the circuit constants and the input / output voltage / current conditions, and the switching element 3 as shown by the chain line in FIG.
There is a case where the voltage V _C does not drop to zero even at time T ₅ when the circuit is closed.

If the switching element 3 is closed under such a condition, an excessive short-circuit current of the capacitor 2 may flow through the switching element 3 and damage the element. This is hereinafter referred to as a non-zero voltage mode, and various operating modes including this are described in detail in the Institute of Electronics, Information and Communication Engineers Study Group material PE90-14.

FIG. 7 shows the control characteristics and the non-zero voltage mode region. The characteristic CH ₇₃ shows the operating range of the above-mentioned non-zero voltage mode on the characteristic surface of the output current I _O and the output voltage E _O , and is non-zero within the characteristic CH ₇₃ curve, that is, in the low output current region. The voltage mode is set.

The input voltage E _I is 50 V and the circuit constants are as follows. Capacitor 2 capacity C _R = 3 μF Reactor 5 inductance L _R1 = 2 μH Excitation inductance of transformer 6 L = 10 μH Generally, a DC-DC converter used as a power source of an electronic device usually has a constant voltage characteristic such as characteristic CH _71. However, as long as this is the case, the non-zero voltage mode does not occur in the above example.

However, in the case of an overload condition, the output voltage E _O is lowered to limit the output current I _O to a low value as shown in the characteristic CH ₇₂ , and a foldback current for preventing burnout of the equipment. Limiting, so-called current limiting of the exemplary shape, is widely practiced. In this case, when the output current I _O is 25 A or less, the non-zero voltage mode is set, and the normal current limiting operation cannot be performed.

Characteristic CH ₇₄ has a capacitance of the capacitor 2 of 3 μF.
Shows a non-zero voltage mode region in the case of changing from 0.1 μF to 0.3 μF, and again the low current side inside the characteristic CH ₇₄ curve is the non-zero voltage mode. As is clear from such an illustration, if the capacitance of the capacitor 2 is changed to 0.3 μF, a stable current limiting operation can be performed without the fallback current limiting curve of the characteristic CH ₇₂ entering the non-zero voltage mode region. Is possible. Thus, although the non-zero voltage mode can be avoided by reducing the capacitance of the capacitor 2, the angular frequency of the resonance circuit rises and the switching frequency naturally rises.

[0016] Figure 8 shows a relationship between the switching frequency F _S of the output voltage E _O and the switching device 3 when operated on characteristics CH ₇₂ in FIG. 7, the characteristics CH ₈₁ capacitor 2 capacity In case of 3μF, characteristic CH ₈₂ is 0.3μ
This is the case of F.

The applicant of the present invention has previously proposed the patent application "Resonant DC-DC Converter Control Method" filed on August 31, 1990. This shows an example in which the resonance capacitor is switched according to the operating frequency of the resonance type DC-DC converter to suppress the frequency change width.

The non-zero voltage mode region can be avoided by switching the capacitor 2 by a method similar to the above proposal. An example using this technique is shown in FIGS. 3 and 4. In FIG. 3, 10 and 11 are capacitors, and 13 is a switching element. In the figure, the same reference numerals as those in FIG. 5 indicate parts having the same functions.

Here, the capacitor 10 is a resonance capacitor used in the entire frequency range, and is 0.
Select 3 μF. The capacitor 11 is a resonance capacitor used only in the low frequency region, and is selected to be 2.7 μF, for example. Switching element 12 turns on capacitor 11.
It is a bidirectional switching element for performing disconnection.
That is, in the high frequency range, the resonance capacitor is a capacitor
Although only 10 is used and the capacitance is 0.3 μF, in the low frequency range, the switching element 12 is closed and the capacitor 11 is connected in parallel to be used as 3 μF.

FIG. 4 shows a control circuit for generating the drive signal SW ₁ for opening and closing the switching element 12, 111 is a counter for counting the operating frequency F _S of the resonance circuit, and 112 is a counter.
, 113 respectively, outputs when the count value N _{s of the} counter 111 exceeds the predetermined upper switching point N _H and outputs it, and outputs it when comparing with the predetermined lower switching point N _L. A comparator configured to produce an output when rotated, 114 is set by the comparator 112 to output C
_The switching element 3 is turned on, and the switching element 3 is driven through the drive circuit 115.
Is a flip-flop for generating the drive signal SW ₁ of Here, the flip-flop 114 is the comparator 113.
Then, the output C _ON and the drive signal SW ₁ are extinguished to open the switching element 12.

As shown in FIGS. 3 and 4, the value of the resonance capacitor is switched and operates on the characteristic CH _{81 in the} low frequency region and on the characteristic C ₈₂ in the high frequency region as indicated by the solid arrow in FIG. Thus, the operation that avoids the non-zero voltage mode is possible in all regions.

In this way, the operation not in the non-zero voltage mode is possible, but as is apparent from FIG. 8, the output voltage E _O is lowered to limit the output current I _O. In the region (2), the switching frequency F _S is unavoidably increased several times, which causes an increase in loss of the switching element and the like.

[0023]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and in particular, in the high frequency range where the capacitance of the resonance capacitor is reduced, the switching element is opened and closed every cycle of the resonance cycle. Instead, a method of opening and closing every few cycles is used.

[0024]

However, the switching element is opened and closed every plural oscillations of the current or voltage of the resonance circuit to suppress an increase in the switching frequency and thus an increase in the switching loss.

[0025]

EXAMPLES To simplify the description here, 3 in the main circuit configuration example, the circuit example of creating a driving signal SW ₁ for switching the resonant capacitor signal i.e. the switching element 12 4
I would like to refer to each. FIG. 1 shows a main part configuration of an example of a control circuit to which the present invention is applied.
Is a control circuit section, 212 and 213 are comparators, 214 is a counter, 215 is a not gate, 216 and 217 are AND gates, 218 is an OR gate, 219 is a flip-flop, 220
Is a drive circuit that gives a drive signal SW ₂ for the switching element 3.

FIG. 2 shows waveforms at various parts according to the present invention. (A) shows a primary current I _L1 and (b) shows a voltage V.
_C and (C) show the secondary current I _L2 , respectively. See also FIG.
, (D) is the output of the comparator 213, (e) is the output of the counter 214 which generates a signal when the count value is 0,
(To) is the reset signal OFF of the flip-flop 219,
(G) indicates the output of the flip-flop 219.

Next, a detailed description will be given with reference to FIGS. 1 and 2. Order to provide a current limiting characteristics of the control circuit 211 the constant voltage characteristic or characteristics CH ₇₂ shown by the characteristic CH ₇₁ in FIG. 7, the primary current I _L1 of the transformer 6 receives the output voltage E _O and the output current I _O The peak value command I _P is output. As the control circuit 211 are known any of various methods, the I _P rather, there is also used to control the closing time width and duty ratio of the switching element 3, there is no where to the gist of the present invention more I won't mention it.

[0028] The comparator 213 performs sign judgment of the primary current I _L1, where it is assumed that produces an output when the primary current I _L1 is positive. The counter 214 counts the output of the comparator 213, and is represented by a number as shown here (0 →
1 → 2 → 3 → 0 → 1 ...) is continued, and when the count value is 0, the output shown in FIG. In addition, the action of four gate circuits, knot gate
When C _ON, which is one of the input signals of 215 and AND gate 216, is at a low level, the output of the counter 214 is selected as the set signal ON of the flip-flop 219.

When C _ON is at a high level, the resonance capacitor switching signal C _ON generated in FIG. 4 is used as it is, so that the output of the comparator 213 is large in the low frequency region where the resonance capacitor capacity is large (3 μF). Is small (0.3
μF) In the high frequency range, the output of the counter 214 is selected as the set signal ON of the flip-flop 219.

The comparator 212 compares the output I _P of the control circuit unit 211 with the primary current I _L1 , and when (I _L1 > I _P ), produces the output shown in FIG. Used as 219 reset signal OFF. FIG. 2G shows a flip-flop 219 which is set by the set signal ON and reset by the reset signal OFF.
It shows an output, and eventually becomes the drive signal SW ₂ of the switching signal 3 via the drive circuit 220.

The operation of this embodiment will be further described. Time T
_{When the} switching element 3 is closed at ₀ , the operation proceeds as in FIG. 6, and the primary current I _L1 rises linearly. When (I _L1 > I _P ) at time T ₁ , the output of the comparator 212 [FIG.
9 is reset, the drive signal SW ₂ [FIG. 2 (g)] disappears, and the switching element 3 is opened. The operation after the time T ₁ proceeds almost in the same manner as in FIG. 6, and at the time T ₂ ,
The primary current I _L1 turns from negative to positive.

If C _{ON in} FIG. 1 is at a high level and in a low frequency range, the subsequent operation is the same as that in FIG. When C _ON is at a low level, the count value of the counter 214 is 1 at the time T ₂ and no output is produced, and the flip-flop 219
Is not set and the switching element 3 is not closed. Therefore, I _L1 , V _C , and I _L2 continue free oscillation due to the action of the resonance circuit, and have the waveforms shown in FIGS. 2A, 2B, and 2C. The primary current I _L1 also shifts from negative to positive at times T ₃ and T ₄ to increase the count value to 2 and 3, but the switching element 3 is not driven.

When the primary current I _L1 becomes positive at time T ₅ , an output is generated because the count value becomes 0, the switching element 3 is closed, and thereafter, the same operation as that after time T ₀ is repeated. As is apparent from FIG. 2, at times T ₀ , T _5, etc. when the switching element 3 is closed, the voltage V _{C of the} capacitor 11 is zero, and it is understood that the non-zero voltage mode is avoided. .

In the characteristic C ₈₃ shown in FIG. 8, the resonance capacitor has a capacitance of 0.3 μF and the switching element 3 is opened and closed as shown in FIG.
It shows the frequency characteristic when it is performed every 4 cycles as shown in
The frequency is much lower than the characteristic C _{82 of} 0.3 μF. In addition, as shown by the broken line arrow in FIG.
At the same time as switching the resonance capacitor to a small capacity, the control circuit shown in FIG. 1 is effectively used to open and close every few cycles, so that the characteristic C shown in FIG.
On the curve of H ₈₁ , it is possible to operate on the curve of the characteristic CH ₈₃ in the high frequency region, avoid the non-zero voltage mode in the entire region, and suppress the rise of the switching frequency.

Although FIG. 2 shows an example of opening and closing every 4 cycles, the number of cycles should be appropriately selected according to the value of the resonant capacitor to be switched, and the frequency change width should be reduced. is there. In addition, it is not preferable that the number of cycles is increased unnecessarily because it causes a decrease in power transmission efficiency. Further, here, a voltage half-wave step-up / down type resonance type DC-
Although the DC converter is taken as an example, for example, in a current-type resonant converter, although there are differences such as becoming a non-zero current mode in a region where the output current is large, a resonance capacitor becomes a non-zero mode and the value of the resonant reactor becomes. It is possible to avoid this by switching the switch and reduce the switching frequency by opening and closing every several cycles in the same manner.

[0036]

As described above in detail, if the control method according to the present invention is applied, even in a region where the conventional non-zero voltage mode is inoperable, a circuit constant which can avoid this is selected and a switching frequency is selected. It is possible to provide an extraordinary method capable of realizing a device capable of suppressing the rise in the minimum.

[0037]

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a main configuration of an example of a control circuit to which the present invention is applied.

FIG. 2 is a waveform diagram showing waveforms of various parts according to the present invention.

FIG. 3 is a main circuit configuration diagram shown for explaining the present invention.

FIG. 4 is a circuit diagram showing an example of a control circuit that creates a capacitor switching signal.

FIG. 5 is a main circuit configuration diagram of a conventional example.

FIG. 6 is a waveform diagram showing a waveform of each part of a conventional example.

FIG. 7 is a diagram showing control characteristics of a DC-DC converter and a non-zero voltage mode region.

FIG. 8 is a diagram showing frequency characteristics of a DC-DC converter.

[0037]

[Explanation of symbols]

1 DC power supply 2 Capacitor 3 Switching element 5 Reactor 6 Transformer 7 Diode 8 Capacitor 10 Capacitor 11 Capacitor 12 Switching element 111 Counter 112 Comparator 113 Comparator 114 Flip-flop 115 Drive circuit 211 Control circuit section 212 Comparator 213 Comparator 214 Counter 219 Flip-flop 220 drive Circuit SW ₁ drive signal SW ₂ drive signal

Claims (1)

[Claims] 1. A switching element in a resonance type DC-DC converter, which supplies power from a DC power supply to a resonance circuit composed of a reactor and a capacitor through a switching element and rectifies the power of the resonance circuit and supplies the power to a load device. The method for controlling a resonance type DC-DC converter is characterized in that opening and closing are performed at every plural oscillations of the current or voltage of the resonance circuit.