Abstract: Introduced 10kW entire bridge phase shifting ZVSPWM cocurrent rectification module main circuit and control circuit’s design, has given the main transformer and the resonant inductance parameter computation, finally has given the experiment profile.
Key word: Entire bridge phase shifting; Zero potential switch; Falls the frequency
Introduction
In large-scale power plant, because needs the direct-current load is quite big, accumulator cell’s capacity usually above 2000A · h. If uses conventional 10A or the 20A switch rectification module, generally needs 20 or 10 above modules is parallel, counts parallel excessively many, is inoperable for lack to the module between brings certain influence, moreover the reliability does not increase along with the module parallel number increases, generally the parallel number should better below 10. At present, the large capacity direct-current charging power source uses in the power plant controls the power source to be quite many, therefore, has the essential development very much in view of the power plant user’s large capacity switch rectification charging source. This article introduced 10kW the entire bridge phase shifting ZVSPWM rectification module was precisely had considered this kind of request, it used added the clamp diode’s ZVS-FBPWM cocurrent converter technique, the control circuit uses the UC3879 special-purpose entire bridge phase shifting control chip, simultaneously when underloading used cut technologies and so on turn-on frequency, had the weight to be light, efficiency higher merit.
Figure 1
1 rectification module main circuit design and parameter computation
Rectification module’s main circuit functional block diagram as shown in Figure 1, by inputs the EMI filter, the rectification filter, the ZVS entire bridge converter, the output rectification filter and outputs the EMI filter and so on to be composed.
In Figure 1 by switching valve S1~S4, clamp diode D1 and D2, resonant inductance Lr, separates straight electric capacity Cb, main transformer T1 as well as the dead resistance and the electric capacity and so on is composed the entire bridge phase shifting ZVS converter, S1 and S3 are manage in advance, S2 and S4 are lag the tube. S1 (S3) in advance S4(S2) certain angle, namely phase shifting angle. S1~S4 uses the IGBT single-valve to compose parallel, the turn-on frequency is about 25kHz.
Figure 2
1.1 transformer parameter design
Because designs entire bridge phase shifting ZVSPWM rectification module peak power output close 10kW, if uses conventional the ferrites magnetic core, because the power is quite big, the magnetic core not too good chooses, in the actual design the magnetic core has used the ultracrystallite magnetism link. Compares with the ferrites, the ultracrystallite material quality has the high saturated magnetism dense (to be possible to reach 1.2~1.6T) and low merits and so on loss and fine temperature stability, is suitable serves as the high efficiency switching power supply’s main transformer’s magnetic core.
This module’s input output target to input 304~456V, outputs 198~286V/35A.
1) directs current bus bar most low voltage Vdmin
Vdmin≈Vinmin×1.35=410.4V (1)
In the formula: Vinmin is three-phase input voltage minimum value 304V.
2) transformer vice-side most low voltage V2min
V2min=(Vomax VD Vr)/Dmax=(286 3 2)/0.95=306.3V (2)
In the formula: Vomax is the module output voltage maximum, takes is 286V;
VD is the rectification diode’s pressure drop, takes is 3V;
Vr is the transformer vice-side winding potential drop of internal resistance and the line pressure drop, takes is 2V;
Dmax is the biggest dutyfactor, takes is 0.95.
3) the transformer changes compares n
n=Vdmin/V2min=410.4/306.3=1.33
The actual transformer primary side takes is 21 circles, vice-side is 16 circles, changes the ratio is 21/16=1.3125.
1.2 resonant inductance Lr parameter design
In the entire bridge phase shifting ZVS converter, in manages in advance S1(S3) switching process, because output filter inductance L1 and resonant inductance Lr is series connected, but L1 and the resonant inductance compares is quite generally big, therefore manages very easily in advance to realize ZVS; But in lag tube S2(S4) switching process, because the transformer vice-side is the short circuit, this time depends upon resonant inductance Lr the energy to realize ZVS, therefore the lag tube realizes ZVS to be quite difficult, the general layout realizes the zero potential switch above 1/3 full load load.
In the formula: Cmos is the switching valve leaks the source electric capacity (including outside and electric capacity), actual takes is 3300pF;
Vdmax is the direct-current bus bar voltage maximum value, takes is
1.35×456=615.6V;
I1 is lags the arm switching valve shuts off when the primary side electric current.
I1= (Iomax/3 ΔI1f/2) /n (4)
In the formula: Iomax is the output current maximum value, takes is 35A;
δI1f for the permission output inductance electric current’s pulsating quantity, takes for 0.2×35=7.0A.
May result in by the above data computation Lr=24.7μH.
2 control circuit design
The control circuit used special-purpose phase shifting control component UC3879, functional block diagram as shown in Figure 2.
Figure 2 ISET is the electric current current limiting setting value, VSET is the voltage setting value, produces separately by the microprocessor; IO is the output magnitude of current, VFB is the output voltage feedback value; SHT is the breakdown close-down signal, IPR is the primary side electric current sampling value.
UC3879 uses the current mode PWM control mode, introduces in the chip the transformer primary side electric current, raised the module transient response speed. UC3879 the output OA, OB, OC, OD4 road signal has composed the driving circuit again through the TLP250 light pair, actuates the S1~S4 4 cluster switch tubes separately. OA/OB, OC/OD phase supplementary, OA(OB) distinction in advance OC(OD) certain phase shifting angle.
Because this entire bridge phase shifting switching valve uses IGBT, when electric current shutdown has the trailing phenomenon, the switching valve both sides parallel electric capacity is quite big, causes the no-load loss to be quite big. Therefore, has used the module underloading when the design cuts the turn-on frequency the method, namely when output current <0.5A, causes the turn-on frequency to reduce suitably; But works as when output current >0.5A, makes the module turn-on frequency to restore the normal value. Falls the frequency actual electric circuit as shown in Figure 3, IO ‘ is the output magnitude of current, IREF is the establishment electric current threshold value. When the output current surpasses the establishment the electric current threshold value, the Q1 breakover, the UC3879 vibration resistance becomes R28 and R17 (R17 see Figure parallel 2); But when the output current is smaller than the establishment electric current threshold value, Q1 shuts off, the UC3879 vibration resistance is R17.
The actual prototype when the exchange inputs 440V, does not fall the frequency in the situation, the no-load loss have about 220W, but after using falls the frequency control technology, no-load loss only then about 130W.
3 experimental results
Has manufactured 2 experimental prototypes according to the above design concept, Table 1 for an actual efficiency data.
Table 1 actual efficiency
| Load current /A | Efficiency/% |
| 10 | 92.6 |
| 13 | 94.2 |
| 26 | 94.15 |
| 30 | 93.90 |
| 35 | 93.41 |
Input voltage 380V, output voltage 240V.
Figure 4 is when the 2A load manages S1 in advance the actuation profile (CH1) and leaks the source profile (CH2);
After Figure 5 is the 2A load time lag, manages S2 the actuation profile (CH2) and leaks the source profile (CH1), may see the lag tube from Figure 5 not to realize ZVS;
After Figure 6 is the 15A load time lag, manages S2 the actuation profile (CH2) and leaks the source profile (CH1), may see from Figure 6 the lag tube has realized ZVS;
Figure 7 is when the 35A load transformer’s primary side profile (20A/div).
Figure 4 when 2A load the S1 actuation profile with leaks the source profile
Figure 5 when 2A load the S2 actuation profile with leaks the source profile
Figure 6 when 15A load the S2 actuation profile with leaks the source profile
Figure 7 when 35A load transformer primary side current waveform
4 conclusions
This article introduced the entire bridge phase shifting ZVSPWM rectification module’s switching valve has realized ZVS, outputs when 240V, 35The efficiency achieves 93.4%; Moreover because has used the underloading frequency conversion technology, causes the no-load loss to reduce greatly, has the widespread application prospect.
