CN104009626A - A Feedback Circuit for Current Feedback DC-DC Converter - Google Patents

Abstract

The invention relates to an electronic circuit technology, in particular to a feedback circuit for a current feedback type DC-DC converter. The feedback circuit for the current feedback type DC-DC converter is characterized by comprising a first comparator COMP1, a second comparator COMP2, a subtractor and an RS trigger, the positive input end of the first comparator COMP1 is connected with feedback currents, the negative phase input end of the first comparator COMP1 is connected with first reference currents Iref1, the output end of the first comparator COMP1 is connected with the R end of the RS trigger, the positive input end of the subtractor is connected with the first reference currents Iref1, the negative input end of the subtractor is connected with second reference currents Iref1, the positive input end of the second comparator COMP2 is connected with the output end of the subtractor, the negative phase input end of the second comparator COMP2 is connected with the feedback currents, and the output end of the second comparator COMP2 is connected with the S end of the RS trigger. The feedback circuit has the advantages that the peak value and the valley value of the feedback currents in each period are limited, and therefore generation of the non-linear phenomena such as diverging and chaos is limited. The feedback circuit is particularly suitable for the current feedback type DC-DC converter.

Description

A Feedback Circuit for Current Feedback DC-DC Converter

technical field

The invention belongs to the electronic circuit technology, and in particular relates to a feedback circuit for a current feedback type DC-DC converter.

Background technique

Due to the existence of inductance, capacitance and switching, switching power supply itself is a strong nonlinear system. At the same time, these nonlinear properties make power system analysis and control methods very unreliable, and there are various nonlinear phenomena, and these Non-linear phenomena will affect the overall performance of the DC-DC converter. In actual engineering, these bifurcations and chaotic phenomena should be avoided as much as possible.

Peak current feedback and valley current feedback are two feedback control modes that are widely used at present. They both feed back the inductor current sampling to the comparator for comparison with the reference current and then input it to the logic unit to generate a driving signal with a certain duty ratio. Drive the switch of the switching tube, as shown in Figure 2. The difference is that in the peak current feedback, the sampled inductor current value is input to the positive input terminal of the comparator to compare with the reference peak current value, while in the valley current feedback, the sampled inductor current value is input to the '-' end of the comparator and compared with the reference valley Value current value comparison. The on-time control unit, that is, the pulse square wave CLK, is used in both feedback methods to limit the operating frequency of the system.

The switching converter with peak current feedback and valley current feedback mode is a nonlinear variable structure control system. The power switch tube is turned on or off to make the system switch periodically in different structures, which leads to the switching converter with complex non-linear structure. Linear behavior, such as period-doubling bifurcation, Hopf bifurcation, Flip bifurcation, boundary collision bifurcation and other bifurcation roads leading to chaos, sub-harmonic oscillation, frequency drop and low-frequency fluctuation phenomena, etc.

The Chinese patent with the application number: CN201210351869.1 mentions that the feedback current value is compared and output by the comparator and connected to the RS flip-flop for logical operation, and then combined with the pulse width control module and the inverter to achieve a fixed cut-off time. But this feedback method fails to control the chaos to improve the stability of the converter system.

The Chinese patent with the application number CN201210288345.2 mentions the method of using the feedback voltage value instead of the CLK signal to input the RS flip-flop logic unit to avoid sub-harmonic oscillation, that is, the purpose of bifurcation chaos phenomenon. However, it can only directly adjust the peak value of the current, and the adjustment of the valley value needs to be indirectly controlled by changes in other parts of the system, so the corresponding speed is relatively slow.

In peak current feedback, since the state switching time is when the feedback current value is equal to the reference current value, the current peak value remains unchanged in each cycle, but there is no limit to the current valley value. With the change of circuit parameters, the current valley value The values may not be equal, which leads to nonlinear phenomena such as bifurcation and chaos. In contrast, in the valley value current feedback, the current valley value is constant in each cycle, but the current peak value is indeed not limited. As the circuit parameters change, the current peak value may not be equal, which also leads to a split The generation of nonlinear phenomena such as bifurcation and chaos.

Contents of the invention

The object of the present invention is to solve the problems in the above-mentioned conventional technology, and propose a feedback circuit for a current feedback DC-DC converter that combines a peak current feedback loop and a valley current feedback loop to enhance the stability of the converter system.

The technical solution adopted by the present invention to solve the above technical problems is: a feedback circuit for a current feedback DC-DC converter, including a DC-DC converter, characterized in that it also includes a first comparator COMP1, a second Comparator COMP2, subtractor and RS flip-flop; wherein, the positive input terminal of the first comparator COMP1 is connected to the feedback current output by the DC-DC converter, its negative phase input terminal is connected to the first reference current Iref1, and its output terminal is connected to The R terminal of the RS flip-flop; the positive input terminal of the subtractor is connected to the first reference current Iref1, and its negative input terminal is connected to the second reference current Iref1; the positive input terminal of the second comparator COMP2 is connected to the output terminal of the subtractor, and its negative input terminal is connected to the output terminal of the subtractor. The phase input terminal is connected to the feedback current output by the DC-DC converter, and its output terminal is connected to the S terminal of the RS flip-flop; the output terminal of the RS flip-flop is connected to the input terminal of the DC-DC converter.

The invention has the beneficial effects of combining the respective characteristics of the peak current feedback and the valley current feedback, omitting the on-time control unit used in the traditional circuit and the circuit, and dividing the state switching time into the time when the peak value of the feedback current is equal to the reference current 1 The value and the valley value of the feedback current are equal to the value of the reference current 2, which limits the peak value and valley value of the feedback current in each cycle, thereby limiting the generation of nonlinear phenomena such as bifurcation and chaos.

Description of drawings

Fig. 1 is the structure diagram of the feedback circuit used for the current feedback type DC-DC converter of the present invention;

Figure 2 is a schematic diagram of the peak feedback and valley feedback DC-DC converter topology;

Fig. 3 is the structural schematic diagram of the current feedback type buck-boost converter that the peak value feedback and the valley value feedback combination provided by the present invention;

4 is a schematic diagram of the time-domain waveform of the inductor current in a current feedback DC-DC converter that combines peak feedback and valley feedback provided by the present invention;

Fig. 5 is a bifurcation diagram of the inductor current of the buck-boost converter under peak current feedback control with the reference current Iref1 as the bifurcation parameter;

Fig. 6 is a bifurcation diagram of the inductor current of the buck-boost converter under valley current feedback control with the reference current Iref1 as the bifurcation parameter;

FIG. 7 is a bifurcation diagram of the inductor current of the buck-boost converter under the current feedback control provided by the present invention with the reference current Iref1 as the bifurcation parameter;

Fig. 8 is a comparison diagram of the waveform of the inductor current and the switching signal in the current feedback DC-DC converter provided by the present invention when the value of the reference current Iref1 is 0.1;

Fig. 9 is a comparison diagram of the waveforms of the inductor current and the switch signal in the current feedback DC-DC converter provided by the present invention when the value of the reference current Iref1 is 0.4;

Fig. 10 is a waveform comparison diagram of the peak current feedback and the current feedback DC-DC converter provided by the present invention when the value of the reference current Iref1 is 0.8;

FIG. 11 is a comparative diagram of the peak current feedback and the waveforms of the inductor current and switching signals in the current feedback DC-DC converter provided by the present invention when the value of the reference current Iref1 is 1.5.

Detailed ways

Below in conjunction with accompanying drawing, describe technical scheme of the present invention in detail

As shown in Figure 1, the feedback circuit for the current feedback type DC-DC converter of the present invention is characterized in that it includes a first comparator COMP1, a second comparator COMP2, a subtractor and an RS flip-flop; wherein, the first The positive input terminal of a comparator COMP1 is connected to the feedback current, its negative phase input terminal is connected to the first reference current Iref1, and its output terminal is connected to the R terminal of the RS flip-flop; the positive input terminal of the subtractor is connected to the first reference current Iref1, and its The negative input terminal is connected to the second reference current Iref1; the positive input terminal of the second comparator COMP2 is connected to the output terminal of the subtractor, its negative input terminal is connected to the feedback current, and its output terminal is connected to the S terminal of the RS flip-flop.

Working principle of the present invention is:

The first comparator COMP1 is a part of the peak current feedback loop, that is, the feedback current value is input to the positive input terminal of the comparator. When the feedback current value i _L1 is greater than Iref1 , the output of the first comparator COMP1 is 1; when the feedback current value i _L1 is smaller than Iref1 , the output of the comparator is 0. The second comparator COMP2 is a part of the valley current feedback loop, that is, the feedback current value is input to the negative phase input terminal of the comparator. When the feedback current value i _L1 is greater than Iref1-Iref2, the output of the second comparator COMP2 is 0; when the feedback current value i _L1 is smaller than Iref1-Iref2, the output of the second comparator COMP2 is 1. The output of the first comparator COMP1 is connected to the R terminal of the RS flip-flop; the output of the second comparator COMP2 is connected to the S terminal of the RS flip-flop. It can be seen from the logic of the RS flip-flop that when the R terminal changes from 0 to 1, the flip-flop output Q is 0, and the switch tube is turned off; when the S terminal changes from 0 to 1, the flip-flop output Q is 1, and the switch tube is turned on. Therefore, the output of the two comparators controls the switching of the switching tube. When the output of the first comparator COMP1 is 1, that is, when the feedback current value i _L1 is greater than Iref1, the switch is turned off; when the output of the second comparator COMP2 is 1, that is, when the feedback current value i _L1 is smaller than Iref1-Iref2, the switch tube open.

In the current feedback buck-boost circuit, as shown in Figure 3, when the switch is turned on, the inductor is charged, and the inductor current rises linearly, and the rising slope is When the inductor current rises to Iref1, the switch tube is turned off, the inductor discharges to the load, the inductor current drops, and the falling slope is Therefore, the feedback inductor current has two limit values, Iref1 and Iref1-Iref2, and the system cycle is $T=\frac{I_{\mathrm{ref}1}-(I_{\mathrm{ref}1}-I_{\mathrm{ref}2})}{m_1}+\frac{I_{\mathrm{ref}1}-(I_{\mathrm{ref}1}-I_{\mathrm{ref}2})}{{-m}_2}=\frac{I_{\mathrm{ref}2}\×L}{u_{\mathrm{in}}}+\frac{I_{\mathrm{ref}2}\×L}{{-u}_0},$ Among them, Iref1 and Iref2 are the reference current value, L is the value of the inductance, Uin is the input voltage, and U0 is the output voltage, as shown in Fig. 4 .

Taking the reference current Iref1 as the bifurcation parameter, the bifurcation diagram of the DC-DC converter system under the peak current feedback, the valley current feedback, and the combined current feedback can be obtained. As shown in Figure 5, it can be seen that in the peak current feedback, when the value of the reference current Iref1 is less than 0.8, the system is in a stable state; when the value of the reference current Iref1 is greater than 0.8, the system is in an unstable bifurcation and chaotic state. In the valley current feedback, when the value of the reference current Iref1 is greater than 0.42, the system is in a stable state; when the value of the reference current Iref1 is less than 0.42, the system is in an unstable bifurcation and chaotic state. In the current feedback of the combination of the two proposed in the present invention, the reference current Iref1 is in the range of 0 to 1.5, and the system is always in a stable state. The state of the system can be further proved from the time-domain waveform diagram of the inductor current. As shown in FIG. 6 , it is a comparison diagram of the waveforms of the inductor current and the switching signal in the valley current feedback and the combined current feedback when the value of the reference current Iref1 is 0.1. It can be seen that the valley current feedback system is in a chaotic state, while the combined current feedback system is in a stable state. As shown in FIG. 7 , it is a comparison diagram of the waveforms of the inductor current and the switch signal in the valley current feedback and combined current feedback when the value of the reference current Iref1 is 0.4. It can be seen that the valley current feedback system is in a double bifurcation state, while the combined current feedback system is in a stable state. As shown in FIG. 8 , it is a comparison diagram of the waveforms of the inductor current and the switch signal in the peak current feedback and combined current feedback when the value of the reference current Iref1 is 0.8. It can be seen that the peak current feedback system is in a double bifurcation state, while the combined current feedback system is in a stable state. As shown in FIG. 9 , it is a comparison diagram of the waveforms of the inductor current and the switching signal in the peak current feedback and combined current feedback when the value of the reference current Iref1 is 1.5. It can be seen that the peak current feedback system is in a chaotic state, while the combined current feedback system is in a stable state.

Claims (1)

1. A feedback circuit for a current feedback type DC-DC converter, comprising a DC-DC converter, characterized in that it also includes a first comparator COMP1, a second comparator COMP2, a subtractor and an RS flip-flop; Wherein, the positive input terminal of the first comparator COMP1 is connected to the feedback current output by the DC-DC converter, its negative phase input terminal is connected to the first reference current Iref1, and its output terminal is connected to the R terminal of the RS flip-flop; The input terminal is connected to the first reference current Iref1, and its negative input terminal is connected to the second reference current Iref1; the positive input terminal of the second comparator COMP2 is connected to the output terminal of the subtractor, and its negative input terminal is connected to the output of the DC-DC converter. The output terminal of the feedback current is connected to the S terminal of the RS flip-flop; the output terminal of the RS flip-flop is connected to the input terminal of the DC-DC converter.