JPH0318274A - Current resonance type converter - Google Patents

Abstract

PURPOSE:To control output voltage to a fixed value in a current resonance type converter in a discontinuous mode by changing an inductance value of a variable inductor with the control current to cause resonance frequency variations. CONSTITUTION:When input voltage Vin is reduced, the resonance frequency is reduced due to the increase of inductance of a variable inductor 9 and it is stabilized at a point when the output voltage before the fluctuation becomes equal to the output voltage after the fluctuation. By controlling the variable inductance in this way, the output voltage can be kept constant against the input fluctuation. In a physical circuit the output voltage changes against the load fluctuation. It is, however, far less than the influence of input fluctuation and by changing the resonance frequency and controlling the ratio of input voltage to output one, it can be well matched off.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to improving the control characteristics of a discontinuous mode current resonant converter having a period in which no current flows.

Conventional technology〉 Conventional electric current fi! A type converter uses LC resonance to change the current of a switching element such as a MOSFET into a smoothly changing sinusoidal waveform for switching, and the current waveform during switching is sinusoidal (resonant). waveform) and can switch when the resonant current becomes zero, so it has the characteristics of low noise and switching loss during switching. Therefore, this current resonant converter is considered to be an effective method for reducing the noise and increasing the frequency of a switching power supply (related to miniaturization of the device).

Note that the current resonance type has a discontinuous mode in which the current does not flow, and a continuous mode in which the current does not flow.The discontinuous mode is roughly divided into two types: half waveform and full waveform, and in both cases, the resonant current is , is a current resonant converter in a discontinuous mode where the current flows only in the switching or on state.

The output voltage of this current resonant converter is controlled by the ratio of the switching frequency fs to the resonant frequency fn (fs/f
This is done by changing n). In particular, in the case of the full waveform current resonance type, if circuit losses are ignored, the output voltage has no load dependence and is affected only by input voltage fluctuations, and the relationship between input and output voltages is as shown in the following equation: Determined by the ratio of switching frequency and resonant frequency.

Vout/Vin=fs/fn
−・・■However, Vin: Input voltage (DC
) Vout: Output voltage (DC).

Problems to be Solved by the Invention> However, the current resonant converter shown in the above-mentioned prior art
Since a fixed inductor or fixed capacitor is used as a resonant element in a motor, the resonant frequency fn shown in equation (2) above is constant, and in order to control the output voltage Vout, the switching frequency fS must be changed. There was a need. Therefore, since the switching frequency fluctuates, beats occur when operating in parallel. Further, noise countermeasures are complicated. Furthermore, capacitors, choke coils,
There were problems such as hindering the miniaturization of transformers and the like.

The present invention has been made based on the above-mentioned problems of the prior art, and aims to provide a current resonant converter that can control the output voltage while keeping the switching frequency fixed. It is.

<Means for Solving the Problems> The structure of the present invention for solving the above problems is a discontinuous mode current resonant converter that controls the output voltage to a constant value in response to input fluctuations and load fluctuations. An LC resonant circuit consisting of a variable inductor and a capacitor, and a power voltage control circuit that increases or decreases the control current of the variable inductor based on the difference between the output voltage and a reference voltage are provided, and the inductance value of the variable inductor is changed by the control current. The present invention is characterized in that the output voltage is controlled to a constant value by changing the resonance frequency.

According to the present invention, the control current is increased or decreased depending on the level of the output voltage, and the inductance value of the variable inductor is changed to change the resonance frequency, thereby keeping the output voltage constant while the switching frequency remains constant. It is possible to control the value.

<Example> Hereinafter, the present invention will be explained based on the drawings.

FIG. 1 is a block diagram showing an embodiment of a current resonant converter according to the present invention, and shows all waveforms of a half-bridge circuit type converter.

In Figure 1, vin is the input voltage, 1 and 2 are dividing capacitors that divide the input voltage Vin into two, 3 and 4 are switching elements such as HOS "ET" connected in series across the input voltage Vin, and 5 and 6 are switching elements such as HOS "ET". A gate drive circuit connects between the gate and source terminals of MOSFETs 3 and 4 to drive MOSFETs T3 and 4. 7 and 8 are parasitic diodes of 140srETs 3 and 4. 9 is an intactor Kawamaki at the connection point of split capacitors 1 and 2. A variable inductor for resonance to which one end of the wire is connected; 10 is a lance to which both ends of the primary winding are connected to the connection point of the semiconductor switches 3 and 4 and the other end of the inductor winding of the variable inductor 9; 11 is a lance; A resonance capacitor is connected to both ends of the primary winding of the transformer 10, 12 and 13 are rectifier diodes whose anodes are connected to both ends of the secondary windings of the transformer 10, and 14 is a rectifier diode 12. ,
The choke coils 15 and 16 have one end connected to the cathode 4 of 13, and the other end of the choke coil 14 and 1
- A filter capacitor and a load resistor connected between the middle point of the lance 10, and 14 and 15 are output filters. v out is the output voltage applied across the load resistor. Further, 17 and 18 are voltage detection resistors for detecting the voltage across the load resistor 16, and 19 is a voltage reference voltage value.
20 is an operational amplifier that takes and amplifies the difference between the divided output voltage by the output voltage detection resistors 17 and 18 and the output reference voltage value 20, 21 is a base drive circuit driven by the voltage across the load resistor 16, and 22 is a base drive This is a current control transistor that amplifies the current of the output of the circuit 21 and drives the control winding of the variable inductor 9, and the output voltage control circuit is controlled by 17 to 22. In the above diagram, 140slrT is used as the switching element, but it is not limited to this.

Further, FIG. 2 is a principle diagram of the variable intactor 9 used in FIG. 1.

In FIG. 2, two cores 23, 2 with the same material shape and
4, and connect the intactor measurement to the resonant circuit and the control side to the control circuit. That is, the resonance current 1 flows through the inductor winding 25, and the control current Ict flows through the control winding 26.
flows.

Next, I will explain the operating principle of this variable intactor. Note that FIG. 3 is a diagram showing the movement of magnetic flux on the magnetization (B-I) curve, and FIG. 4 is a characteristic diagram of the variable intactor.

In Fig. 2, when the DC control current I ct1 is flowing, the resonant current I1 is flowing, and the ampere turn of the control field is larger than the ampere turn of the inductor 4, the magnetization characteristic of the core 23 is as shown in Fig. 3. As in the first quadrant, a minor loop is drawn by the resonance current I1 around the operating point determined by the control current Ict1 on the initial magnetization curve. Note that the slope of the minor loop is called incremental permeability.

This deviation in control current 1 ct1 causes the minor loop caused by the resonance current IL to move on the initial magnetization curve, so that the incremental magnetic permeability changes. On the other hand, regarding core 24,
The direction of the control current Ict is opposite, and the characteristic is symmetrical to that of the core 23, as shown in the third quadrant of FIG. The inductance Lr of the variable inductor at this time is expressed by the following equation.

Lr = 2 μ o H jtd −
N 2 - A/ 1 --- ■
However, μ0: Magnetic permeability of vacuum μd: Incremental magnetic permeability of core N: Number of turns measured by intactor A: Cross-sectional area 1: Magnetic path length. Therefore, by changing the control current 1ct, the inductance Lr of the variable inductor can be changed,
As shown in FIG. 4, when the control current ICt is small, the inductance Lr becomes large.

FIG. 5 is an operation waveform diagram for explaining the operation of FIG. 1. Note that it is assumed that the output filter on the secondary side is sufficiently large and that the load current 10 is always constant.

7 8 In Fig. 5, immediately before time TO, both NOSFETs 3 and 4 are off, and on the secondary side, through the rectifier diodes 12 and 13, the load current is 0. is flowing back. MOS at time '1゛0
When the FE 3 is turned on, the drain-source current Ids1 increases linearly through the primary winding of the transformer 10 and the variable inductor 9 until the rectifier diode 13 is turned off.

(Period of 'r1≦t≦1゛2) When the rectifier diode 13 is turned off at time T1, resonance by the resonance capacitor 11 and the variable inductor 9 starts. The resonant current (1) of the variable intactor 9 and the voltage Vc across the resonant capacitor 11 are expressed by the following equation.

IL (t) = IO /N0 (Vin/2/Zn)
− sin ω(t −TI ) Idsl−}−1dl ・・・■
Vc (t)=Vin/2 − (Vin/2>−
cos b:> (t-TI) ・- ■
However, N: 1. Turns ratio of lance 10 Zn: Characteristic impedance (Zn = 1''Lr /Cr) (J): 1/7 Lr Cr I di: Parasitic diode (7) current, (T 2 ≦t≦T3) The resonant current ■L becomes negative, and a current flows through the parasitic diode 7 of the HOSrlET3 to the input open in the direction of regenerating power.If the MOSFET 3 is turned off during this period (time 'l''a ) Since NOSFET 3 can be turned off when no current flows (zero current switching), no switching loss occurs.

{Period of 1゛3≦and≦'r4} At time T3, the resonant current It stops flowing, so
The resonance capacitor 11 continues discharging linearly until the rectifier diode 13 is turned on, and the V of the resonance capacitor 11 decreases.
As shown in the waveform diagram c, the discharge ends at time 'I'4.

Note that during the period 'I'1≦t≦'I'3, only the rectifier diode l2 is turned on when the secondary is open. After this, M.O.
When the SFET 4 is turned on, the operation is similar to that described above, but the direction of the resonant current {circle around (2)} flowing through the variable inductor 9 is opposite to that of the MOSFET 3.

In this way, NOSFETs 3 and 4 are turned on alternately,
It sends input energy to the secondary system.

Next, output voltage control using a variable inductor will be explained using comparison diagrams of resonance waveforms with respect to input voltage fluctuations shown in FIGS. 1 and 6.

As shown in Figure 6, when operating with input voltage Vin1 (Figure 6 (a)), if the input voltage drops to Vin2 (Figure 6 (opening)), the input/output voltage ratio is The relationship of fS/fn is given by the above formula (■): Vout /V in = f s' / f n However, since fn = 1/2πJLr Cr, the output voltage vout also decreases. When the output voltage Vout decreases,
The negative input of the operational amplifier 20 becomes smaller than the output reference voltage value 19, and the output of the operational amplifier 20 becomes positive. Since the base drive circuit 21 and the current control transistor 22 are configured so that the control current Ict becomes small when the output of the operational amplifier 20 is positive, the inductance L of the variable inductor 9
r increases.

Assuming that the inductance of the variable inductor 9 when the input voltage Vin1 is Lr1 and the inductance of the variable inductor 9 when the input voltage Vin2 is Lr2, the characteristic impedance Zn and the resonant frequency fn are respectively expressed by the following equations.

(When input voltage Vin1) Zn1=,4 Lr1/Cr...
■fn1=1/2πtLrlCr −・−■
(When input voltage Vin2) Z n2= J I. , r2/C r
−・・■１fn2=1. /2πJLr2Cr
' -...■1 However, Z n1 < Z n2, f
n1> f n2, L r1 < L r2 Furthermore, the output voltage before and after the input voltage fluctuation is expressed by the following equation.

(Before change) Vout1= (f s / f nl) V in
1 --- ■ (After variation) Vout2-( f s / f n2) V in2
-・・■゛11 1 2 However, Vinl > Vin2 + fs is constant. Therefore, when the input voltage decreases from Vinl to Vin2, the inductance of the variable inductor increases to Lr2, so the resonance frequency decreases to fn2, Output voltage is V out
It becomes stable when 1 = V out2.

By controlling the variable intactor in this manner, the output voltage can be kept constant despite input fluctuations.

Also, in actual circuits, the output voltage changes due to load fluctuations, but this is much smaller than the influence of input fluctuations, and can be handled by changing the resonance frequency and controlling the input/output voltage ratio as described above. I can do it.

In the above embodiment, the full waveform current resonance type was explained, or even in the half waveform which is a current resonance type converter in a mode where the current is discontinuous, the output voltage control is based on the ratio of the switching frequency and the resonant frequency. Since this is done by changing the method, the method of the present invention can be applied.

Effects of the Invention> As explained above in detail with actual saturation examples, according to the present invention, the switching frequency remains constant and the output voltage can be controlled to a constant value, so noise countermeasures are easy. Also, by increasing the switching frequency, it is possible to downsize capacitors, transformers, choke coils, etc.
Furthermore, it is possible to realize a current resonant converter that can eliminate the beat that occurs when operating in parallel.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 is a block diagram showing an embodiment of the current resonant converter according to the present invention, Fig. 2 is a block diagram showing an example of the variable inductor used in Fig. 1, and Fig. 3 is a block diagram showing an example of the variable inductor used in Fig. 1. is a diagram showing the movement of magnetic flux on the magnetization curve, Figure 4 is a characteristic diagram of the variable inductor, Figure 5 is an operating waveform diagram to explain the operation of Figure 1, and Figure 6 is a resonance waveform in response to input voltage fluctuation. FIG. 9... Variable inductor for resonance, 11... Capacitor for resonance, 17, 18... Output voltage detection resistor, 19.
... Output standard voltage value, 20... Operational amplifier, 21...
・Base drive circuit, 22...transistor, Vin・
...Input voltage, Vout...Output voltage. 1 5 to -431-

Claims (1)

[Claims] A discontinuous mode current resonant converter that controls the output voltage to a constant value in response to input fluctuations and load fluctuations uses an LC resonant circuit consisting of a variable inductor and a capacitor, and controls the variable inductor based on the difference between the output voltage and a reference voltage. An output voltage control circuit that increases or decreases the current is provided, and the inductance value of the variable inductor is changed by the control current to change the resonance frequency, thereby controlling the output voltage to a constant value. Current resonant converter.