CN111900866A - Control circuit and control method of switching circuit and switching circuit - Google Patents

Abstract

The invention discloses a control circuit of a switch circuit, a control method and a switch circuit, wherein a reference voltage is used to compensate an output voltage through feedback; a characteristic voltage of an inductor current of the switch circuit is obtained, and the characteristic voltage is adjusted according to an adjustment parameter Perform proportional adjustment to output the adjusted voltage; obtain the compensation voltage and the adjusted voltage, and after making a difference between the two, output the corrected compensation voltage, which is used to control the conduction time of the main power tube of the switching circuit. According to the present invention, the waveform of the input current can be improved to effectively reduce the THD.

Description

Switch circuit control circuit, control method and switch circuit

technical field

The invention relates to the technical field of power electronics, in particular to a control circuit, a control method and a switch circuit of a switch circuit.

Background technique

Switching conversion circuits are widely used in the field of power electronics technology. In order to prevent the input current of the converter from polluting the power grid, it is generally required that the THD (total harmonic distortion, total harmonic distortion) generated by the converter should be reduced as much as possible and meet the specific standards of the country or industry. Constant on-time (COT) control is a common way to control switching circuits, especially suitable for high power factor (HPF) and inductive voltage near-continuous (BCM) applications, simple control, no need to sample the input voltage, there are Better efficiency and EMI effect, widely used. The constant on-time control block diagram is shown in Figure 1. After the difference between the reference voltage Vref and the feedback voltage V _FB , the error signal e passes through the compensator to obtain the compensation voltage Vc. After comparing with the sawtooth wave, the on-time T _ON of the MOS is obtained. , For high PF applications, the system bandwidth is low, and the Vc voltage is basically unchanged in the power frequency period, so the T _ON time is also unchanged in the power frequency period.

In the boost circuit, theoretically, the input current and the input voltage have a proportional relationship, and the THD of the input current will be very small. However, in practical applications, due to the influence of MOS drive delay and zero-crossing detection delay, the actual inductor current I _in works in a discontinuous state, and the inductor and various parasitic capacitances and RC snubber circuit capacitors may resonate. The peak inductor current is no longer proportional to the input voltage, as shown in Figure 2(a); in addition, near the zero-crossing of the grid voltage V _in , the existence of negative current makes the average value of the inductor current I _in advance to 0, that is, A "dead zone" phenomenon occurs, as shown in Figure 2(b). Therefore, the current waveform distortion generated in the practical application of the Boost circuit, especially the more serious "dead zone" phenomenon, will cause the input current to generate a large THD.

SUMMARY OF THE INVENTION

In view of this, the purpose of the present invention is to provide a control method and control circuit of a switch circuit, which can effectively reduce the THD of the input current of the switch circuit.

Based on the above purpose, the present invention proposes a control circuit for a switch circuit, the control circuit comprising:

Compensation voltage generating circuit, the compensation voltage is output by the reference voltage through feedback compensation;

Characterizing the voltage adjustment circuit, obtaining the characteristic voltage of the inductor current of the switching circuit, and performing proportional adjustment on the characteristic voltage according to an adjustment parameter, and outputting the adjusted voltage;

The correction circuit obtains the compensation voltage and the adjustment voltage, and after making a difference between the two, outputs the corrected compensation voltage, which is used to control the conduction time of the main power tube of the switch circuit.

Optionally, the adjustment parameter is positively correlated with the compensation voltage.

Optionally, the control circuit further includes:

The conduction time arithmetic circuit compares the modified compensation voltage with a sawtooth wave signal to obtain a first conduction control signal. When the sawtooth wave signal does not reach the modified compensation voltage, the first control signal controls the main The power tube is normally turned on;

a delay logic circuit, when the sawtooth wave signal reaches the correction compensation voltage, if the characteristic voltage is less than the threshold voltage, the delay logic circuit controls the conduction time of the main power tube to extend, and when the main power tube extends the conduction time When the time reaches the threshold time, the delay logic circuit controls the main power tube to turn off; or, when the characteristic voltage is greater than or equal to the threshold voltage, the delay logic circuit controls the main power tube to turn off, so The extended conduction time of the main power tube is less than or equal to the threshold time.

The present invention also provides a control method for a switching circuit, comprising the steps of:

Compensate output voltage by reference voltage through feedback;

obtaining the characteristic voltage of the inductor current of the switching circuit, and performing proportional adjustment on the characteristic voltage according to an adjustment parameter, and outputting the adjusted voltage;

The compensation voltage and the adjustment voltage are acquired, and after making a difference between the two, a corrected compensation voltage is output, which is used to control the conduction time of the main power tube of the switching circuit.

Optionally, when the sawtooth wave signal reaches the correction compensation voltage, when the sawtooth wave signal reaches the correction compensation voltage, if the characteristic voltage is less than the threshold voltage, the conduction time of the main power tube is prolonged, and when the main power When the extended conduction time of the power tube reaches the threshold time, the delay logic circuit controls the main power tube to be turned off; or, when the characteristic voltage is greater than or equal to the threshold voltage, the main power tube is turned off, and the The extended conduction time of the main power tube is less than or equal to the threshold time.

The present invention also provides a switch circuit, including any one of the above control circuits.

Compared with the prior art, the present invention has the following advantages: the present invention takes into account the bad influence of the inductor current existing in the actual application of the switching circuit on the waveform of the input circuit, and uses the adjustment voltage representing the inductor current to correct the compensation voltage, Furthermore, the on-off time of the switching circuit is adjusted, so as to optimize the waveform of the input circuit and reduce the THD. In some specific technical solutions, the present invention can further adjust the on-off time of the switching circuit by extending the on-time or comparing the conditions, thereby further reducing the THD.

Description of drawings

FIG. 1 schematically shows a structural block diagram of a constant control circuit based on the prior art.

Fig. 2 schematically shows the voltage and current change curves in the switching circuit based on the prior art, wherein Fig. 2(a) is the comparison between the input current Iin and the standard sine curve, and Fig. 2(b) is the input current Iin. Curve comparison of voltage Vin and input current Iin with time.

FIG. 3 schematically shows the principle diagram of the modified compensation voltage generating circuit of the present invention.

FIG. 4 schematically shows the control circuit principle diagram of the switch circuit of the present invention.

Fig. 5 schematically shows the voltage and current change curves in the switching circuit of the present invention, wherein Fig. 5(a) is a comparison between the input current Iin and the standard sinusoidal curve and the prior art according to the solution of the present invention, and Fig. 5 (b) is a comparison between the curve of the input voltage Vin and the input current Iin changing with time according to the technical solution of the present invention and the prior art.

Detailed ways

The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, but the present invention is not limited to these embodiments. The present invention covers any alternatives, modifications, equivalent methods and arrangements made within the spirit and scope of the present invention.

The invention is described in more detail by way of example in the following paragraphs with reference to the accompanying drawings. It should be noted that the accompanying drawings are all in a relatively simplified form and in an inaccurate scale, and are only used to facilitate and clearly assist in explaining the purpose of the embodiments of the present invention.

FIG. 3 schematically shows a structural block diagram of a control circuit according to an embodiment of the present invention. The control circuit includes: a compensation voltage generating circuit 110, which is compensated by the reference voltage Vref to output a compensation voltage Vc through feedback; a characterizing voltage adjusting circuit 120, which obtains the characterizing voltage Vcs of the inductor current of the switching circuit, and performs the characterizing voltage Vcs according to An adjustment parameter k is proportionally adjusted, and the adjustment voltage k*Vcs is output; the correction circuit 130 obtains the compensation voltage Vc and the adjustment voltage k*Vcs, and after making a difference between the two, outputs the correction compensation voltage Vc1, which is used for The on-time Ton of the switch circuit is controlled. The compensation voltage generating circuit 110 is a common part in the constant control circuit, that is, after the difference between the reference voltage Vref and the feedback voltage V _FB , the error signal is passed through the compensator to obtain the compensation voltage Vc. In the prior art, the compensation voltage Vc is used to control the on-time Ton of the MOS. According to the present invention, however, the compensation voltage Vc is not directly used to control the on-off of the MOS, but undergoes some correction. The characterizing voltage adjustment circuit 120 first obtains a voltage Vcs that can characterize the inductor current in the switching circuit, but generally, Vcs cannot be directly used to correct the compensation voltage Vc. According to the present invention, an adjustment parameter k is set, and the voltage Vcs can be used to correct the compensation voltage Vc after the adjustment of the adjustment parameter k. The correction circuit obtains the compensation voltage Vc and the adjustment voltage k*Vcs, and outputs the correction compensation voltage Vc1 after processing the difference between the two. The relationship between the three is Vc1=Vc-k*Vcs. broken control. The adjustment parameter k is a constant. The value of k determines the compensation degree of the Vcs voltage. If it is too small, the compensation effect will not be achieved. If it is too large, the THD will become worse. Parasitic capacitance, etc. In the control loop, the inductor current negative feedback is introduced, Vc1=Vc-kVcs, so that the MOS conduction time near the valley bottom of the grid is longer, and the MOS conduction time near the peak is short, compensating the influence of the negative inductor current on the input current THD.

4 schematically shows a schematic diagram of a control circuit according to the present invention, including a first comparator U01, a second comparator U03, a delay logic circuit U04, a first flip-flop U02, a second flip-flop U05 and a zero-cross comparison (ZCD) U06, the zero-crossing comparator U06 controls the main power tube of the switch circuit to conduct when the inductor current crosses zero, and the first comparator U01 compares the corrected compensation voltage Vc1 with the ramp signal, and when the ramp signal does not reach the corrected compensation voltage At Vc1, the first comparator U01 outputs a low-level signal, the flip-flop U02 outputs a low-level signal, and the main power tube is normally turned on; when the ramp signal reaches the corrected compensation voltage Vc1, the first comparator U01 outputs a signal from a low-level signal The flip-flop is turned to a high level, and the output signal of the first flip-flop U02 is turned from a low level to a high level; it is judged by the second comparator U03 whether the characteristic voltage VCS of the inductor current reaches the threshold voltage VREF1, if the voltage VCS does not reach the threshold voltage VREF1, the delay logic control circuit outputs a low-level signal, and the main power tube is normally turned on and then extends the on-time until the characteristic voltage VCS reaches the threshold voltage VREF1, and the extended on-time is less than or equal to the threshold time. In addition, the delay logic circuit itself sets a threshold time. When the characteristic voltage VCS has not yet reached the threshold voltage VREF1, but the extended conduction time has reached the threshold time, the delay logic circuit outputs a high level and the main power tube is turned off.

Fig. 5 schematically shows the voltage and current change curves in the switching circuit according to the present invention, wherein Fig. 5(a) is a comparison between the input current Iin and the standard sinusoidal curve and the prior art according to the solution of the present invention. 5(b) is a comparison between the curve of the input voltage V _in and the input current I _in changing with time according to the technical solution of the present invention and the prior art. As shown in Figure 5(a), according to the technical solution of the present invention, since the Vcs signal basically follows the input voltage, the Vc1 signal is relatively high when the input voltage is low, and is relatively low when the input voltage is high, that is, the TON time of the MOS is The input voltage peak is smaller near the peak point and larger near the valley bottom. Compared with the traditional scheme, the inductor current peak value of the improved scheme is smaller at the input voltage peak and larger at the valley bottom; therefore, the improved scheme compensates for the input current caused by the negative inductor current. distortion, thereby improving THD. As shown in Figure 5(b), where V _in is the input voltage change curve, I _in-1 is the input current curve according to the prior art, I _in is the input current change curve according to the technical solution of the present invention, according to the solution of the present invention , due to the larger inductor current near the grid voltage valley, more energy can be transferred per switching cycle, the filter capacitor voltage is lower, and the input current dead time is smaller, compensating for the filter capacitor's influence on the input current THD.

According to an embodiment, the present invention also provides a switching circuit control method, comprising the steps of: outputting a compensation voltage through feedback compensation from a reference voltage; acquiring a characteristic voltage of the inductor current of the switching circuit, and adjusting the characteristic voltage according to a The parameters are proportionally adjusted, and the adjusted voltage is output; the compensation voltage and the adjustment voltage are obtained, and after making a difference between the two, the corrected compensation voltage is output, which is used to control the conduction time of the switching circuit.

Compared with the prior art, the present invention has the following advantages: the present invention takes into account the bad influence of the inductor current existing in the practical application of the switching circuit on the waveform of the input circuit, and uses the adjustment voltage representing the inductor current to correct the compensation voltage, and then The on-off time of the switching circuit is adjusted to optimize the waveform of the input current and reduce the THD. In some specific technical solutions, the present invention can further adjust the on-off time of the switch circuit by increasing the delay condition or the comparison condition, thereby further reducing the THD.

As used in this specification and the claims, "a" or "an" should be construed to mean "at least one" unless expressly stated otherwise or the context precludes this interpretation. Unless expressly stated to the contrary, in any method described and claimed herein that includes more than one step or act, the individual steps or acts of the method are not limited to the order in which the method is recited.

The above-mentioned embodiments do not constitute a limitation on the protection scope of the technical solution. Any modifications, equivalent replacements and improvements made within the spirit and principles of the above-mentioned embodiments shall be included within the protection scope of this technical solution.

Claims (6)

1. A control circuit for a switch circuit, characterized in that the control circuit comprises: Compensation voltage generating circuit, the compensation voltage is output by the reference voltage through feedback compensation; Characterizing the voltage adjustment circuit, obtaining the characteristic voltage of the inductor current of the switching circuit, and performing proportional adjustment on the characteristic voltage according to an adjustment parameter, and outputting the adjusted voltage; The correction circuit obtains the compensation voltage and the adjustment voltage, and after making a difference between the two, outputs the corrected compensation voltage, which is used to control the conduction time of the main power tube of the switch circuit. 2 . The control circuit of claim 1 , wherein the adjustment parameter is positively correlated with the compensation voltage. 3 . 3. The control circuit of claim 1, further comprising: The conduction time arithmetic circuit compares the modified compensation voltage with a sawtooth wave signal to obtain a first conduction control signal. When the sawtooth wave signal does not reach the modified compensation voltage, the first control signal controls the main The power tube is normally turned on; a delay logic circuit, when the sawtooth wave signal reaches the correction compensation voltage, if the characteristic voltage is less than the threshold voltage, the delay logic circuit controls the conduction time of the main power tube to extend, and when the main power tube extends the conduction time When the time reaches the threshold time, the delay logic circuit controls the main power tube to turn off; or, when the characteristic voltage is greater than or equal to the threshold voltage, the delay logic circuit controls the main power tube to turn off, so The extended conduction time of the main power tube is less than or equal to the threshold time. 4. A control method for switching circuit, characterized in that, comprising the steps: Compensate output voltage by reference voltage through feedback; obtaining the characteristic voltage of the inductor current of the switching circuit, and performing proportional adjustment on the characteristic voltage according to an adjustment parameter, and outputting the adjusted voltage; The compensation voltage and the adjustment voltage are acquired, and after making a difference between the two, a corrected compensation voltage is output, which is used to control the conduction time of the main power tube of the switching circuit. 5 . The control method of the switching circuit according to claim 4 , wherein when the sawtooth wave signal reaches the correction compensation voltage, when the sawtooth wave signal reaches the correction compensation voltage, if the characteristic voltage is less than a threshold value. 6 . voltage, the conduction time of the main power tube is prolonged, and when the extended conduction time of the main power tube reaches the threshold time, the delay logic circuit controls the main power tube to turn off; or, when the characteristic voltage is greater than When it is equal to the threshold voltage, the main power tube is turned off, and the extended conduction time of the main power tube is less than or equal to the threshold time. 6. A switch circuit, characterized by comprising the control circuit according to any one of claims 1-3.

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