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   Abstract: Has provided one kind of novel width input range, completely DCM, the clamp electric current working pattern Boost power factor compensating circuit control method. This control method does not have in the Boost electric circuit diode’s reverse restoration, thus raised the entire electric circuit’s efficiency, simultaneously, this plan has obtained the low total harmonic distortion (THD) and the high power factor (PF). This plan suits in the low power situation application. Has given the concrete theoretical analysis and a 100W electric circuit empirical datum.

    Key word: Electric current clamp pressure-rise; Power factor adjustment; Completely intermittent current pattern

Introduction

In the former active power factor compensating circuit analysis situs, a belt multiplier’s control chip is inevitable. In order to reduce the cost, one kind of electric current clamp (ClampedCurrentBoost, CCB) the control method may the simplified circuit. In this kind of electric circuit, in every a half cycle switch electric current peak value by clamp to a reference value. Input current profile followed input voltage? The type may obtain ideal THD. Because it does not need the multiplier to provide an electric current reference value, but may use any kind of summit current control the chip (for example UC3843) to complete this function, thus reduced the cost greatly, simplified the electric circuit.

    But, formerly proposed clamp electric current pattern electric circuit, when low input voltage works in intermittent current DCM, when high input voltage works in uninterrupted current pattern CCM. But the CCM working has two shortcomings: First, in electric circuit’s after flow diode’s reverse restoration, this cut electric circuit’s efficiency; Second, in electric circuit’s inductance value is quite big, this for enhanced electric circuit’s power density to bring the difficulty.

This article proposed one kind works in the general entire input voltage scope in the DCM CCBPFC electric circuit. This electric circuit eliminated the diode to restore the question reverse, thus raised electric circuit’s working efficiency; At the same time, because works is making and breaking the pattern, the inductance quantity reduces, like this may reduce the inductance the volume, enhances the power density.

This article has given this electric circuit analysis situs mathematical analysis, and has given a 100W electric circuit experimental result.

1 theoretical analysis

Electric circuit schematic diagram as shown in Figure 1. Before carrying on the analysis, the supposition following condition is tenable:

- - all primary devices are ideal;

- - converter work when stable state, turn-on frequency? Is bigger than the exchange bus bar the frequency, thus may think that in a switching period, the input voltage is constant;

- - the input voltage is ideal sine wave vac=

Vmsin (ωLt), ωL for exchange bus bar frequency;

- - the reference voltage is constant Vref for a period of time;

- - the output voltage is constant.

For ease of analysis, causes the computation the result to have nothing to do with the concrete circuit value, we use the sign Yao value, namely command

Vb=Vo;

Ib=Vo/Rt (Rt=2L/Ts, Ts is switching period);

Then inputs the voltage peak value is:

Vm=Vm/Vb    (1)

Is different with the traditional CCBPFC electric circuit, in the entire bus bar analog input cycle, this electric circuit work is making and breaking the pattern. In every a half cycle, two kind of making and breaking working pattern. As shown in Figure 1, in the switching period initial stage, in the Boost electric circuit’s switching valve is at the clear the condition, in inductance electric current iL starts from zero to increase. (RiiL) achieves the reference voltage when the sampling voltage (Vref) and the slope balancing waveform (VR) and, or achieves the biggest dutyfactor, the switching valve shuts off, the inductance electric current linearity reduces (e.g. Figure 2). These two kind of working pattern distinction definition is DCM2 and DCM1.

To one cyclical internal inductance electric current average, after may obtain under two kind of DCM working pattern electric current normalization expression respectively is:

    In the formula: Kr is the electric current pattern slope depth of compensation coefficient.

DCM1 and the DCM2 boundary condition is:

    In the formula: The slope compensates Mc=IR/(DmaxTs), IR is the slope bucking current.

Therefore, may obtain DCM1 and the DCM2 two kind of working pattern boundary point is:

ωLt=arcsin [(Iref/Dmax-IRM)/2Vm]

In the formula: For slope bucking current peak value.

States before, may obtain every a half cyclical mean current normalization transition condition value:

May obtain every half power frequency cycle by the above analysis, under different input voltage, input current profile as shown in Figure 3.

The Boost inductance value must guarantee in the entire cycle, electric circuit work in the DCM pattern.

Under the smallest input voltage’s electric current peak value is:

In the formula: Po is the output;

Eta is the lowest efficiency; Vin, rms, min is the lowest input voltage peak-to-peak value.

Therefore, the inductance value (7) decided by the type.

(Vinpmin/L)DlminTs≥2Iinp    (7)

In the formula: Vinpmin is the smallest input voltage peak value;

Dlmin is in the smallest input voltage time smallest dutyfactor, namely

Dlmin=(Vo-Vinpmin)/Vo    (8)

The output capacity must satisfy-like (9).

Co≥Po/(2πflineVoΔVo)    (9)

The sign Yao Hua power factor may (10) obtain by the type.

PF=Pin/(VinrmsIinrms)    (10)

In the formula:

Then,

2 experimental results

Establishes the following working condition:

Vm=127~311V; fline=50Hz; Vo=380V;

Po=100W; η=0.92; fs=77kHz; Dmax=0.95.

    The parameter hypothesis is:

L=370μH; Kr=0.22; C=68μF, selects 68μF/

400V aluminum electrolysis electric capacity.

Circuit diagram as shown in Figure 4.

    Obtains electric circuit profile as shown in Figure 5, may see by Figure 5, the experimental result conforms to the theoretical analysis.

    Table 1 PF which and THD and the Vin, rms relations obtains for the experiment. May see by Table 1, this electric circuit conforms to the IEC-3-2 standard.

    This electric circuit in full load (Vo=380V, Io=0.263A) efficiency test as shown in Figure 6.

Table 1 PF, THD and input voltage relations table

3 conclusions

This article realizes the DCMCCBPFC electric circuit analysis situs to one kind in the general entire input voltage scope, carried on the detailed theoretical analysis, the experimental result had proven this electric circuit might satisfy the IEC1000-3-2 standard. At the same time, because it eliminated diode’s reverse restoration, uses makes and breaks the pattern, raised electric circuit’s working efficiency and the power density. This has the very strong attraction regarding the low power’s application.