High efficiency and low noise isolated bridgeless pfc converter and operating method thereof

Abstract

A Power Factor Correction (PFC) converter includes an input terminal that receives an AC voltage, an isolated bridgeless Power Factor Correction stage connected to the input terminal, an isolated DC-DC stage connected to the PFC stage where the control input and output voltages have a linear relationship, and an output terminal connected to the DC-DC stage that outputs a DC voltage.

Description

Technology Field

[0001] A high-efficiency and low-noise isolated bridgeless Power Factor Correction (PFC) converter and a method of operation thereof are provided. Background Technology

[0003] Conventional two-stage AC-DC converters have a structure combining a bridge diode, a boost PFC converter, and a DC-DC converter. While the boost PFC converter provides high performance in terms of power factor control, it increases switching losses due to hard-switching operation, which reduces power conversion efficiency and acts as a constraint on power density improvement. Furthermore, the boost PFC converter generates high electromagnetic interference (EMI) noise due to hard-switching operation while directly connected to the input AC system, causing adverse effects on the system.

[0004] Furthermore, DC-DC converters have widely utilized topologies such as LLC resonant converters to improve overall system efficiency and provide galvanic isolation between the input and the load. In this case, the LLC resonant converter provides soft-switching, which can improve power conversion efficiency and power density while minimizing switching losses.

[0005] However, resonant converters, such as LLC resonant converters, have operating points that vary depending on the load size, making control difficult under light loads. This acts as a critical disadvantage in systems that require a wide output range and high output voltage control performance, such as on-board chargers for electric vehicles, programmable power sources, and power supplies for measuring instruments.

[0006] To address the aforementioned problems, a three-stage AC-DC converter has been introduced in recent research. In a three-stage AC-DC converter, the DC-DC stages consist of isolated DC-DC converters and non-isolated DC-DC converters. Like conventional DC-DC converters, the isolated DC-DC converter is designed with high efficiency and electrical isolation as priorities. On the other hand, the non-isolated DC-DC converter utilizes a converter, such as a Buck converter, in which the control input value versus the output voltage has a linear relationship. Due to this functional separation of the DC-DC stages, design optimization is possible for each power conversion stage, and output control performance can be significantly improved. However, increased switching losses and reduced power conversion efficiency caused by the hard switching operation of the PFC converter still occur, and power conversion efficiency and power density may decrease due to the addition of separate power conversion stages.

[0007] Accordingly, in order to improve power conversion efficiency in the aforementioned 3-stage AC-DC converter system, a bridgeless PFC converter combining a PFC stage and a rectifier has recently been introduced. While this can improve power conversion efficiency by minimizing losses in the diodes within the rectifier, large common-mode noise and leakage current from parasitic capacitors present in the input AC system can cause electronic device failure and damage to users. Prior art literature

[0009] Korean Registered Patent 10-2306880, Korean Registered Patent 10-2473161, Korean Published Patent 2022-0033739 The problem to be solved

[0010] One embodiment was completed based on the idea that if high efficiency and electrical insulation, which are priority considerations in the design of conventional DC-DC stages, can be applied to the PFC stage, the design burden of the DC-DC stage can be reduced.

[0011] One embodiment is intended to block the generation of common mode noise and leakage current while having high efficiency.

[0012] In addition to the above-mentioned tasks, embodiments according to the present invention may be used to achieve other tasks not specifically mentioned. means of solving the problem

[0014] A Power Factor Correction (PFC) converter according to one embodiment includes an input terminal receiving an AC voltage, an isolated bridgeless Power Factor Correction stage connected to the input terminal, an isolated DC-DC stage connected to the PFC stage where the control input and output voltages have a linear relationship, and an output terminal connected to the DC-DC stage that outputs a DC voltage.

[0015] A PFC converter according to one embodiment includes an input terminal that receives an AC voltage, an isolated bridgeless Power Factor Correction Stage connected to the input terminal, an isolated DC-DC stage connected to the PFC stage where the control input and output voltage have a linear relationship, and an output terminal connected to the DC-DC stage that outputs a DC voltage. Effects of the invention

[0017] According to one embodiment, while selecting a bridgeless structure to apply high-efficiency characteristics of the PFC stage, by applying the circuit structure and operation according to one embodiment, common mode noise, leakage current, etc. that occur when using a bridgeless structure can be fundamentally blocked.

[0018] In addition, according to one embodiment, by applying a soft switching technology such as ZCS (Zero-current switching), losses caused by the high-speed switching operation of the converter can be minimized.

[0019] According to one embodiment, by having high efficiency and electrical isolation handled at the PFC stage, a converter having a linear relationship between the control input and output voltage, such as a buck converter, can be applied to the DC-DC converter stage, so a system can be configured that has high efficiency and simultaneously provides improved control performance.

[0020] According to one embodiment, by providing high efficiency and electrical isolation at the PFC converter stage, the design burden of the DC-DC stage can be reduced.

[0021] According to one embodiment, high output control performance can be provided by having a linear relationship between the control input and the output voltage, and accordingly, high power conversion efficiency and improved control performance can be provided for applications with a large output voltage range, such as electric vehicle chargers. Brief explanation of the drawing

[0023] FIG. 1 is a schematic diagram showing a high-efficiency and low-noise isolated bridgeless PFC converter according to one embodiment. FIG. 2 is a circuit diagram of a high-efficiency and low-noise isolated bridgeless PFC converter according to one embodiment. FIG. 3 is a circuit diagram showing an equivalent circuit according to a mode of a high-efficiency and low-noise isolated bridgeless PFC converter according to one embodiment. FIG. 4 is a diagram showing the main operation waveforms according to the mode of a high-efficiency and low-noise isolated bridgeless PFC converter according to one embodiment. FIG. 5 is a diagram showing a control algorithm of a high-efficiency and low-noise isolated bridgeless PFC converter according to one embodiment. Specific details for implementing the invention

[0024] Embodiments of the present invention are described in detail with reference to the attached drawings so that those skilled in the art can easily implement the invention. The present invention may be embodied in various different forms and is not limited to the embodiments described herein. In the drawings, parts unrelated to the explanation have been omitted to clearly explain the invention, and the same reference numerals are used for identical or similar components throughout the specification. Furthermore, specific descriptions of widely known prior art are omitted.

[0025] Throughout the specification, when a part is described as "including" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0026] Throughout the specification, expressions written in the singular form may be interpreted as singular or plural unless explicit expressions such as "one" or "singular" are used.

[0027] Throughout the specification, terms including ordinal numbers, such as first, second, etc., may be used to describe various components, but these components are not limited by terms including ordinal numbers. Terms including ordinal numbers are used solely for the purpose of distinguishing one component from another. For example, without departing from the scope of the present disclosure, the first component may be named the second component, and similarly, the second component may be named the first component.

[0028] Throughout the specification, "transmission or provision" may include not only direct transmission or provision but also indirect transmission or provision through other devices or by using an alternative route.

[0029] Throughout the specification and in the flowcharts described with reference to the drawings, the order of operations may be changed, multiple operations may be merged, some operations may be divided, and certain operations may not be performed.

[0030] Then, a high-efficiency and low-noise isolated bridgeless PFC converter and its operation method according to one embodiment will be described in detail.

[0031] FIG. 1 is a schematic diagram showing a high-efficiency and low-noise isolated bridgeless PFC converter according to one embodiment, and FIG. 2 is a circuit diagram of a high-efficiency and low-noise isolated bridgeless PFC converter according to one embodiment.

[0032] Referring to Fig. 1, the PFC stage utilizes a bridgeless structure and has the circuit structure and operation of Fig. 2, thereby enabling high efficiency while fundamentally blocking common-mode noise and leakage current. Furthermore, since electrical isolation is applied to the PFC stage, a converter can be applied to the DC-DC stage that is non-isolated while having a linear relationship between the control input and output voltages, thus enabling the configuration of a system with high power conversion efficiency and improved control performance. Additionally, by applying soft switching technologies such as ZCS (Zero-current switching), losses caused by the high-speed switching operation of the converter can be minimized.

[0033] Referring to Fig. 2, the PFC converter is an AC voltage (v g Input terminal receiving ), DC voltage (V dc It includes a transformer (T) comprising an output terminal that outputs ), a primary side connected to an input terminal, and a secondary side connected to an output terminal.

[0034] The steady-state operation of an isolated bridgeless PFC converter is the input AC voltage v g It is distinguished according to the backing track, and the switch period T s It has three operation modes.

[0035] During the positive half-cycle of the AC voltage, inductor L1, switch S1, diode D a , and D c Only conducts and participates in the operation of the circuit of Fig. 3. On the other hand, during the negative half-cycle of the AC voltage, inductor L2, switch S2, and diode D b , and D d Only when it conducts does it participate in the operation of the circuit. For example, during the positive half-cycle of the alternating voltage, when switch S1 is turned on, inductor L1 is charged by the alternating voltage, and during the negative half-cycle of the alternating voltage, when switch S2 is turned on, inductor L2 is charged by the alternating voltage.

[0036] One end of inductor L1 is connected to one end of the input side, and the other end of inductor L1 is connected to diode D a It is connected to. The first terminal of switch S1 is connected to the other terminal of inductor L1 and diode D a It is connected to, and the second terminal of switch S1 is diode D c It is connected to.

[0037] One end of the primary side of the transformer is diode D a It is connected to, and the other end of the primary side of the transformer is connected to the second terminal of switch S1 and diode D c It is connected to.

[0038] One end of inductor L2 is connected to one end of the input side, and the other end of inductor L2 is connected to diode D b It is connected to. The first terminal of switch S2 is connected to the other terminal of inductor L2 and diode D b It is connected to, and the second terminal of switch S2 is diode D d It is connected to.

[0039] One end of the primary side of the transformer is the second terminal of switch S2 and diode D d It is connected to, and the other end of the primary side of the transformer is diode D b It is connected to.

[0040] Capacitor C1 is connected to the primary side of the transformer, and diode D b and diode D c It is connected to.

[0041] FIG. 3 is a circuit diagram showing an equivalent circuit according to a mode of a high-efficiency and low-noise isolated bridgeless PFC converter according to one embodiment, and FIG. 4 is a diagram showing a major operation waveform according to a mode of a high-efficiency and low-noise isolated bridgeless PFC converter according to one embodiment.

[0042] Referring to FIGS. 3 and FIGS. 4, the positive half-period (v g The detailed operation mode of the isolated bridgeless PFC converter during the switching cycle in >0) is shown.

[0043] Before Mode 1, the primary current i1 and the secondary current i2 flow in the positive direction.

[0044] The operation of Mode 1 [t0-t1] is described as follows. Mode 1 begins at t0 when switch S1 is turned on. The primary inductor L1 is charged by the grid voltage. Leakage inductance L lk If is negligibly small, the average voltage V of capacitor C1 during the switching period C1 and capacitor C located on the secondary side r The average voltage V Cr It is as follows.

[0045] [Mathematical Formula 1]

[0046] V C1 = v g

[0047] [Mathematical Formula 2]

[0048] V Cr = V dc - nv g

[0049] In Equation 2, n is the turn ratio of transformer T, defined as the secondary turn ratio divided by the primary turn ratio. In Mode 1, capacitors C1 and L lk , C r In a resonant circuit composed of the above, resonance occurs, and energy is transferred from the primary side to the secondary side through transformer T. At this time, the state equation generated in the resonant circuit is as follows.

[0050] [Mathematical Formula 3]

[0051]

[0052] [Mathematical Formula 4]

[0053]

[0054] C in mathematical equation 4 eq is defined as follows.

[0055] [Mathematical Formula 5]

[0056]

[0057] Consequently, based on the above mathematical equations 2 to 4, the secondary current i2 is given as follows.

[0058] [Mathematical Formula 6]

[0059]

[0060] In mathematical equation 6, the angular frequency ω r and characteristic impedance Z r It is equal to mathematical formula 7.

[0061] [Mathematical Formula 7]

[0062]

[0063] At t1, the point at which mode 1 ends, the series resonance ends and the secondary current i2 becomes 0. Meanwhile, in this case, diodes D2 and D3 remain in a conducting state.

[0064] The operation of Mode 2 [t1-t2] is described as follows. In Mode 2, switch S1 remains in the ON state, and the secondary side is in a state where resonance is complete, so the secondary side current i2 remains at 0. When Mode 2 ends, diodes D2 and D3 are turned off. At this time, since the current flowing through the diodes is 0, Zero-current switching (ZCS) occurs. Accordingly, the reverse recovery problem of the diodes is resolved, thereby eliminating power loss caused by the high-speed operation of the diodes.

[0065] The operation of Mode 3 [t2-t3] is described as follows. At t2, switch S1 is turned off. In this mode, L1 and L m The energy stored in is transferred to the output side through diodes D1 and D4.

[0066] The operation of the circuit in Fig. 2 in the negative half-cycle is similar to the operation of the circuit in Fig. 2 in the positive half-cycle described above.

[0067] When D is the duty ratio of switches S1 and S2, the output voltage V dc and input AC voltage v g The relationship is as follows.

[0068] [Mathematical Formula 8]

[0069]

[0070] During the positive half-cycle, diode D c , and during the negative half-cycle, diode D d The voltage applied to the floating capacitor on the input system side is defined as constant by this. Accordingly, leakage current is limited, and common-mode noise generated in conventional bridgeless PFC converters is minimized.

[0071] FIG. 5 is a diagram illustrating a control algorithm of a high-efficiency and low-noise isolated bridgeless PFC converter according to one embodiment. Referring to FIG. 5, the duty cycle D is power factor correction and the output voltage V dcIt is used to control the positive accompaniment cycle, and is the duty cycle of switch S1 for the positive accompaniment cycle and switch S2 for the negative accompaniment cycle.

[0072] The duty cycle D is expressed as in Equation 9. In Equation 9, L is the inductance value of input inductors L1 and L2.

[0073] [Mathematical Formula 9]

[0074]

[0075] To secure an ideal power factor, input current i g Reference value i g is the input voltage v g Obtained through.

[0076] The nominal duty cycle Dn functions as a type of feedforward controller, controlling the input voltage and output voltage V dc Reduces the burden on the feedback controller by eliminating disturbances caused by fluctuations.

[0077] In addition, Dn is the final duty cycle D and Δi from the nonlinear system expressed in Equation 9. g By making it a first-order linear system, more effective power factor control is possible.

[0078] Although preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims also fall within the scope of the present invention.

Claims

Claim 1 A transformer comprising an input terminal receiving an AC voltage, an output terminal outputting a DC voltage, a primary side connected to the input terminal, and a secondary side connected to the output terminal; a first inductor, a first switch, a first diode, and a second diode that conduct during the positive half-cycle of the AC voltage; a second inductor, a second switch, a third diode, and a fourth diode that conduct during the negative half-cycle of the AC voltage; one end of the first inductor is connected to one end of the input terminal, and the other end of the first inductor is connected to the first diode; the first terminal of the first switch is connected to the other end of the first inductor and the first diode; the second terminal of the first switch is connected to the second diode; one end of the second inductor is connected to one end of the input terminal, and the other end of the second inductor is connected to the third diode; and the first terminal of the second switch is connected to the other end of the second inductor and the third diode A Power Factor Correction (PFC) converter that is connected, wherein the second terminal of the second switch is connected to the fourth diode, and has a duty cycle expressed by the following mathematical formula, wherein the duty cycle is the operating duty cycle of the first switch during the positive half-cycle and the duty cycle of the second switch during the negative half-cycle.[Mathematical Formula] (L is the inductance value of the first inductor L1 and the second inductor L2, n is the turn ratio of the transformer, v g is the AC voltage at the input terminal, V dc is the DC voltage at the output terminal, i g is the input current, V dc,ref is the reference DC voltage, T s θ is the switching period of the first and second switches, Δi g is the change in input current) Claim 2 delete Claim 3 A PFC converter according to claim 1, wherein one end of the primary side of the transformer is connected to the first diode, and the other end of the primary side of the transformer is connected to the second terminal of the first switch and the second diode. Claim 4 delete Claim 5 A PFC converter according to claim 1, wherein one end of the primary side of the transformer is connected to the second terminal of the second switch and the fourth diode, and the other end of the primary side of the transformer is connected to the third diode. Claim 6 A PFC converter according to claim 1, further comprising a first capacitor connected to the primary side of the transformer and the second diode. Claim 7 A PFC converter comprising: an input terminal receiving an AC voltage; an isolated bridgeless Power Factor Correction Stage connected to the input terminal; an isolated DC-DC stage connected to the PFC stage, wherein the control input and output voltages have a linear relationship; and an output terminal connected to the DC-DC stage and outputting a DC voltage; comprising a first inductor and a first switch that conduct during the positive half-cycle of the AC voltage, wherein when the first switch is turned on, the first inductor is charged by the AC voltage; and comprising a second inductor and a second switch that conduct during the negative half-cycle of the AC voltage, wherein when the second switch is turned on, the second inductor is charged by the AC voltage, and having a duty cycle expressed by the following mathematical formula, wherein the duty cycle is the operating duty cycle of the first switch during the positive half-cycle and the duty cycle of the second switch during the negative half-cycle. [Mathematical Formula] (L is the inductance value of the first inductor L1 and the second inductor L2, n is the turn ratio of the transformer, v g is the AC voltage at the input terminal, V dc is the DC voltage at the output terminal, i g is the input current, V dc,ref is the reference DC voltage, T s θ is the switching period of the first and second switches, Δi g is the change in input current) Claim 8 delete Claim 9 delete

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