A ripple absorbing device

Abstract

The application discloses a ripple absorbing device applied to an AC / DC conversion circuit and connected in parallel with an output end of the AC / DC conversion circuit, comprising a first inductor, a first capacitor, a first switch and a second switch, wherein the output end of the AC / DC conversion circuit is connected in parallel with a series branch of the first inductor and the second switch, and two ends of the second switch are connected in parallel with a series branch of the first capacitor and the first switch. The ripple absorbing device of the application actively absorbs the output ripple of the AC / DC conversion circuit, and has small volume and low cost.

Description

Technical Field

[0001] This invention relates to circuit filtering techniques, and more particularly to a method for filtering out circuit output ripple. Background Technology

[0002] AC / DC converter circuits contain ripple at the output, especially single-stage PFC AC / DC converter circuits where the output current exhibits significant power frequency ripple. Known technologies typically filter out this ripple by adding an output filter capacitor. However, this output filter capacitor increases the circuit size and cost. Summary of the Invention

[0003] This invention provides an active capacitor technology that is connected in parallel with the output capacitor to absorb the AC component output by the AC / DC conversion circuit and reduce the output ripple current.

[0004] The technical solution of the present invention is: a ripple absorption device, wherein the ripple absorption device is connected in parallel to the output terminal of an AC / DC conversion circuit, the ripple absorption device includes a first inductor, a first capacitor, a first switch, and a second switch, the output terminal of the AC / DC conversion circuit is connected in parallel with the series branch of the first inductor and the second switch, and the two ends of the second switch are connected in parallel with the series branch of the first capacitor and the first switch.

[0005] The aforementioned ripple absorption device samples the current and voltage values ​​at its input terminal and controls the ratio of the voltage and current sample values ​​at the input terminal of the ripple absorption device to be equal to the equivalent impedance.

[0006] The aforementioned ripple absorption device absorbs the ripple within the bandwidth of the AC / DC conversion circuit.

[0007] The aforementioned ripple absorption device further includes a first operational amplifier, a first capacitor, a first resistor, and a second resistor. The first input terminal of the first operational amplifier is connected to the second resistor. The second resistor samples the current at the input terminal of the ripple absorption device. The second input terminal of the first operational amplifier is connected to the positive input terminal of the ripple absorption device through the first capacitor and is also connected to ground through the second resistor.

[0008] The output of the first operational amplifier is connected to the second switch after passing through the second driving circuit, thereby controlling the switching of the second switch.

[0009] The switching state of the first switch is complementary to that of the second switch.

[0010] The aforementioned ripple absorption device samples the current at its input terminal and the current at the output terminal of the AC / DC conversion circuit, and controls the current at the input terminal of the ripple absorption device to be equal to the AC component of the current at the output terminal of the AC / DC conversion circuit.

[0011] The aforementioned ripple absorption device further includes a comparator. The first input terminal of the comparator receives the current from the input terminal of the ripple absorption device, and the second input terminal of the comparator receives the current from the output terminal of the AC / DC conversion circuit after passing through a fourth capacitor.

[0012] The output of the comparator is connected to the second switch via a driver circuit to control the switching of the second switch.

[0013] The switching state of the first switch is complementary to that of the second switch.

[0014] To make the above-mentioned features and advantages of the invention more apparent and understandable, specific embodiments are described below, and detailed descriptions are provided in conjunction with the accompanying drawings. Attached Figure Description

[0015] Figure 1 This is the first specific embodiment of the ripple absorption device of the present invention.

[0016] Figure 2 This is a second specific embodiment of the ripple absorption device of the present invention.

[0017] Figure 3 for Figure 1 The first specific embodiment of the control scheme for the medium ripple absorption device.

[0018] Figure 4 for Figure 3 An implementation circuit of the control scheme.

[0019] Figure 5 for Figure 1 A second specific embodiment of the control scheme for the medium ripple absorption device. Detailed Implementation

[0020] The technical solutions of the present invention will now be clearly and completely described with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] like Figure 1As shown, in the first embodiment of the present invention, a ripple absorption device 13 is connected in parallel to the output terminal of the AC / DC converter circuit 11 and in parallel with the load 12. The ripple absorption device 13 absorbs the ripple current in the output current I1 of the AC / DC converter circuit 11. The AC / DC converter circuit 11 accepts AC input vAC and converts it into DC output Vo, which is then supplied to the load 12. The AC / DC converter circuit 11 is, for example, a single-stage PFC, more specifically, a single-stage flyback PFC. Its output current I1 contains ripple current, and the input terminal of the ripple absorption device generates current I2, thereby filtering out specific ripple in the current I1, so that the current I0 in the load is a DC current.

[0022] The ripple absorption device 13 of the present invention includes an inductor L1, a switch Q2, a switch Q1, and a capacitor C1. The inductor L1 and the switch Q2 are connected in series and then connected in parallel with the output terminal of the AC / DC conversion circuit. The two ends of the switch Q2 are connected in parallel with the series branch of the switch Q1 and the capacitor C1. The switching states of the switch Q2 and the switch Q1 are complementary. The inductor L1 and the capacitor C1 form an equivalent impedance Zi under the control of the switch Q1 and the switch Q2. The equivalent impedance Zi can absorb the ripple component in the current I1.

[0023] like Figure 2 As shown, with Figure 1 The difference is that in this embodiment, the ripple absorption device 23 and the DC / DC conversion circuit 24 are connected in parallel after the AC / DC conversion circuit 21. In this embodiment, the ripple absorption device 23 is connected in parallel to the intermediate DC bus and in parallel with the DC / DC conversion circuit 24. The ripple absorption device 23 absorbs the ripple current in the output current I1 of the AC / DC conversion circuit 21.

[0024] Figure 1 and Figure 2 The inductor L1 should ideally have sufficient inductance to ensure that the current I2 is continuous, not discontinuous. Figure 1 The capacitance of capacitor C1 is greater than the capacitance of capacitor C0. Figure 2 The capacitance value of the intermediate capacitor C1 is greater than the equivalent capacitance value at the input of the subsequent DC / DC converter unit 212.

[0025] Figure 3The diagram shows an embodiment of the control unit 331 of the ripple absorption device 33 in this invention. It collects the voltage V0 at the output terminal of the AC / DC conversion circuit and the current I2 at its input terminal, and controls the ratio of voltage V0 to current I2 to be equivalent to the equivalent impedance Zi in the frequency domain. The control unit 331 outputs a drive signal to control the opening or closing of switch Q2. The control unit 331 can also output a drive signal to control the opening or closing of switch Q1. The opening states of switch Q1 and switch Q2 are complementary, so the output of control unit 331 essentially controls the switching states of both.

[0026] like Figure 4 As shown Figure 3 In one specific embodiment of the control unit 431, the control unit 431 includes an operational amplifier 4311, whose I2(S)*Ri=Vo(S)*SR1C2, where Ri is the sampling resistor of the current I2 (not shown in the figure), and the equivalent impedance Zi(S)=Ri / SR1C2. The output terminal of the operational amplifier 4311 is connected to a drive signal generation unit 4312, which generates a drive signal to drive switches Q1 and Q2, thereby controlling the equivalent impedance of the ripple absorption device 43 to be Zi(S), which can absorb the ripple in the current I1.

[0027] like Figure 5 The diagram illustrates another specific embodiment of the control unit 531 of the present invention. In this embodiment, the current I1 at the output terminal of the AC / DC conversion circuit 51 is sampled and, after DC blocking by capacitor C3, the AC ripple is input to one input terminal of comparator 5311. The other input terminal of comparator 5311 samples the current I2 at the input terminal of the ripple absorption device. After comparison and control, the current is input to drive signal generation unit 5312, which generates a control signal for switch Q2. The control unit 531 controls the current I2 to be equal to the AC component of the current I1 through comparator 5311. The output terminal of comparator 5311 is connected to drive signal generation unit 5312, which generates drive signals to drive switches Q1 and Q2. This allows the equivalent impedance of the ripple absorption device 53 to be controlled to Zi(S), enabling it to absorb the ripple in current I1, specifically the ripple after DC blocking by capacitor C3. From a time-domain perspective, when the current I1 is greater than I0, energy is stored in inductor L1 and capacitor C1. When the current I1 is less than I0, the electrical energy in inductor L1 and capacitor C1 is released to supply the load 52 or the subsequent DC / DC conversion unit.

[0028] The ripple absorption device in this invention can quickly and efficiently absorb ripple in a circuit, avoiding the use of excessively large filter capacitors and effectively reducing the circuit's size. It also avoids the lifespan limitations imposed by filter capacitors.

[0029] It is understood that the above specific description of the present invention is only for illustrating the present invention and is not limited to the technical solutions described in the embodiments of the present invention. Those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention to achieve the same technical effect; as long as the use needs are met, they are all within the protection scope of the present invention.

Claims

1. A ripple absorption device, characterized in that, The ripple absorption device is connected in parallel to the output of the AC / DC conversion circuit. The ripple absorption device includes a first inductor, a first capacitor, a first switch, and a second switch. The output of the AC / DC conversion circuit is connected in parallel with the series branch of the first inductor and the second switch. The two ends of the second switch are connected in parallel with the series branch of the first capacitor and the first switch. The ripple absorption device samples the voltage at the output terminal and the current at the input terminal of the AC / DC converter circuit, and controls the ratio of the voltage at the output terminal to the current at the input terminal of the ripple absorption device to be equivalent to the equivalent impedance in the frequency domain. The ripple absorption device absorbs the ripple within the bandwidth of the AC / DC conversion circuit. The switching state of the first switch is complementary to that of the second switch.

2. The ripple absorption device as described in claim 1, characterized in that, The ripple absorption device further includes a first operational amplifier, a second capacitor, a first resistor, and a second resistor. The first input terminal of the first operational amplifier is connected to the second resistor. The second resistor samples the current at the input terminal of the ripple absorption device. The second input terminal of the first operational amplifier is connected to the positive input terminal of the ripple absorption device through the second capacitor, and is also connected to the ground terminal through the second resistor.

3. The ripple absorption device as described in claim 2, characterized in that, The output of the operational amplifier is connected to the second switch after passing through the second driving circuit, thereby controlling the switching of the second switch.

4. The ripple absorption device as described in claim 1, characterized in that, The ripple absorption device samples the current at its input terminal and the current at the output terminal of the AC / DC conversion circuit, and controls the current at the input terminal of the ripple absorption device to be equal to the AC component of the current at the output terminal of the AC / DC conversion circuit.

5. The ripple absorption device as described in claim 4, characterized in that, It also includes a comparator, the first input terminal of which receives the current from the input terminal of the ripple absorption device, and the second input terminal of the comparator receives the current from the output terminal of the AC / DC conversion circuit after passing through a third capacitor.

6. The ripple absorption device as described in claim 5, characterized in that, The output of the comparator is connected to the second switch via a driving circuit to control the switching of the second switch.

7. The ripple absorption device as described in claim 6, characterized in that, The switching state of the first switch is complementary to that of the second switch.

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