Mixed-mode operation method applied to direct-current power converter

Abstract

According to the mixed mode operation method applied to the DC power converter, the DC power converter receives an input voltage, and the size of the input voltage is between a minimum voltage and a maximum voltage. The mixed-mode operation method comprises the steps that when the input voltage is larger than the lower critical voltage and smaller than the upper critical voltage, the direct-current power converter operates in a series resonance conversion mode; when the input voltage is smaller than the lower critical voltage, the DC power converter operates in an inductance-inductance-capacitance conversion mode. When the input voltage is greater than the upper critical voltage, the DC power converter operates in an inductance-inductance-capacitance conversion mode.

Description

Technical Field

[0001] The present invention relates to a mixed-mode operation method, and in particular to a mixed-mode operation method applied to a DC power converter. Background Art

[0002] A resonant converter can shape the waveform of the switching voltage and / or switching current using a resonant tank to minimize switching losses and operate at high frequencies. Due to the advantages of the resonant converter, such as high efficiency, a simple structure that can be realized by integrating magnetic components, soft switching on the primary and secondary switches, and applicability to applications with a wide voltage range, it is widely used as an isolated DC-DC converter.

[0003] However, how to balance efficiency, selection of low withstand voltage rated components, and better hold-up time is a development direction that technicians in this field pay attention to and seek to achieve through technical means.

[0004] Therefore, how to design a mixed-mode operation method for a DC power converter to solve the problems and technical bottlenecks in the prior art is an important topic studied by the inventors of this case. Summary of the invention

[0005] In order to solve the above problem, a mixed-mode operation method is applied to a DC power converter, wherein the DC power converter receives an input voltage, and the magnitude of the input voltage is between a minimum voltage and a maximum voltage. The mixed-mode operation method includes: When the input voltage is greater than a lower threshold voltage and less than an upper threshold voltage, the DC power converter operates in a series resonant conversion mode, wherein the lower threshold voltage is greater than the minimum voltage and the upper threshold voltage is less than the maximum voltage; When the input voltage is less than the lower threshold voltage, the DC power converter operates in an inductor-inductor-capacitor conversion mode; and When the input voltage is greater than the upper threshold voltage, the DC power converter operates in the inductor-inductor-capacitor conversion mode.

[0006] Furthermore, the mixed mode operation method also includes: When the input voltage is equal to the lower threshold voltage, the DC power converter operates in the series resonant conversion mode or the inductor-inductor-capacitor conversion mode; and When the input voltage is equal to the upper threshold voltage, the DC power converter operates in the series resonant conversion mode or the inductor-inductor-capacitor conversion mode.

[0007] Furthermore, when the DC power converter operates in the series resonant conversion mode, the switching frequency of the DC power converter is substantially fixed.

[0008] Furthermore, when the DC power converter operates in the series resonant conversion mode, the ratio of the output voltage of the DC power converter to the input voltage is substantially fixed.

[0009] Furthermore, the switching frequency is the first resonant frequency of the DC power converter at the highest efficiency.

[0010] Further, the DC power converter includes a resonant tank, which includes a resonant inductor and a resonant capacitor connected in series and a magnetizing inductor of a transformer; The first resonant frequency: fr1=, wherein fr1 is the size of the first resonant frequency, Lr is the size of the resonant inductance, and Cr is the size of the resonant capacitance.

[0011] Furthermore, when the DC power converter operates in the LC conversion mode, the ratio of the switching frequency of the DC power converter to the input voltage is substantially fixed.

[0012] Furthermore, when the DC power converter operates in the LC conversion mode, the output voltage of the DC power converter is substantially fixed.

[0013] Furthermore, when the input voltage reaches the upper threshold voltage, the output voltage is correspondingly an output upper limit voltage, and the output upper limit voltage is an upper limit voltage of a buck converter connected to a downstream secondary of the DC power converter.

[0014] Furthermore, when the input voltage reaches the lower critical voltage, the output voltage is correspondingly an output lower limit voltage, and the output lower limit voltage is a lower limit voltage of a buck converter connected to a downstream secondary of the DC power converter.

[0015] The beneficial effect of the present invention is that the method has the characteristics and advantages of achieving the technical effects of taking into account efficiency, the selection of low withstand voltage rated components, and better holding time. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A block diagram of a two-stage DC-DC power conversion architecture.

[0017] Figure 2 The waveform diagram is a diagram showing the relationship between the switching frequency and the input voltage when the DC power converter operates in the SRC mode and the LLC mode.

[0018] Figure 3The waveform diagram is a diagram showing the relationship between the output voltage and the input voltage of the DC power converter operating in the SRC mode and the LLC mode.

[0019] Figure 4 FIG. 4 is a circuit diagram of a DC power converter according to an embodiment of the present invention.

[0020] Figure 5 FIG. 4 is a waveform diagram showing the relationship between the switching frequency and the input voltage of the DC power converter in mixed-mode operation of the present invention.

[0021] Figure 6 FIG. 4 is a waveform diagram showing the relationship between the output voltage and the input voltage of the DC power converter in mixed-mode operation of the present invention.

[0022] Figure 7 for Figure 2 and Figure 5 Schematic diagram of the compared waveforms.

[0023] Figure 8 for Figure 3 and Figure 6 Schematic diagram of the compared waveforms.

[0024] Fig. 9 FIG. 4 is a waveform diagram showing the relationship between the voltage gain and the switching frequency of the DC power converter of the present invention.

[0025] Fig.10 Flow chart of the mixed mode operation method of the present invention.

[0026] 100A: isolated DC power converter, 200A: non-isolated power converter, VINDC: input voltage, VMDC: relay voltage, VOUTDC: output voltage, Q1: first switch, Q2: second switch, Lr: resonant inductor, Cr: resonant capacitor, TR: transformer, Lm: magnetizing inductor, VIN, Vin: input voltage, VO: output voltage, fsw: switching frequency, fr1: first resonant frequency, fr2: second resonant frequency, G: voltage gain, Vin (min): minimum voltage, Vin (max): maximum voltage, Vin-LL: lower critical voltage, Vin-HL: upper critical voltage, Vo-L (mixmode): output lower limit voltage, Vo-H (mixmode): output upper limit voltage, D1, D2: rectifier diode. DETAILED DESCRIPTION

[0027] The technical content and detailed description of the present invention are described as follows with reference to the accompanying drawings.

[0028] See also Figure 1 As shown in FIG. , it is a block diagram of a two-stage DC-DC power conversion architecture. Figure 1As shown, it has a two-stage structure connected in series, the first stage serves as an isolation function (i.e., an isolated DC power converter 100A), and the second stage (i.e., a non-isolated power converter 200A) outputs a low voltage to the load end. The isolated DC power converter 100A receives an input voltage VINDC and converts the input voltage VINDC into a relay voltage VMDC. The non-isolated power converter 200A receives a relay voltage VMDC and converts the relay voltage VMDC into an output voltage VOUTDC.

[0029] For example, Figure 1 The first-stage isolated DC power converter 100A is an LLC converter (or conversion circuit) with a stable output function. When the input voltage VINDC changes (i.e., changes between the minimum input voltage Vin (min) and the maximum input voltage Vin (max)), it can still maintain a constant output voltage, i.e., a constant relay voltage VMDC. If the output voltage is to be changed, the purpose of changing the voltage gain is achieved by changing the frequency. However, its disadvantage is that the frequency change range is wide, so it cannot always operate at the highest efficiency point, that is, it cannot be maintained at the first resonance point.

[0030] Taking another circuit implementation as an example, for example, Figure 1 The first-stage isolated DC power converter 100A adopts a series resonant converter, also known as a bus converter. Compared with the LLC converter, the SRC converter operates at a fixed frequency, so the output voltage to the input is a constant, that is, the output voltage changes proportionally with the input voltage. In other words, the SRC converter cannot stabilize the output voltage, so the task of stabilizing the load voltage can only be accomplished by the second-stage non-isolated power converter 200A (such as a buck converter). Since the SRC converter is a fixed frequency, the highest conversion efficiency can be maintained at any operating point, which is the advantage of the SRC converter.

[0031] See also Figure 2 and Figure 3 As shown, they are waveform diagrams of the relationship between the switching frequency and the input voltage of the isolated DC power converter operating in the SRC mode and the LLC mode, and a waveform diagram of the relationship between the output voltage and the input voltage. The specific description and principle can be combined with the above description.

[0032] Although the SRC converter has a high conversion efficiency, when the input voltage is low, the output voltage of the second-stage buck converter also decreases synchronously. In this case, the energy stored in the capacitor is less, which will make the hold-up time (or maintenance time) shorter. Therefore, compared with the LLC converter, the use of the SRC converter must add more capacitors, but this also causes the problem of increased volume. On the other hand, when the input voltage is high, the output voltage of the SRC converter is high, and the input end of the second-stage buck converter must withstand the high input voltage, so more expensive high-voltage rated components are required. For the LLC converter, since its output voltage is constant, there will be no such problem.

[0033] See also Figure 4 The circuit diagram of the DC power converter embodiment of the present invention is shown in FIG. The DC power converter is an isolated DC power converter, which mainly includes three parts: the first part is a switch network, the second part is a resonant tank, and the third part is a rectifier circuit. Specifically, the switch network includes a first switch Q1 and a second switch Q2, wherein the first switch Q1 and the second switch Q2 are connected in series at a common node, and the switch network in the series configuration receives an input voltage VIN.

[0034] The resonant tank includes a resonant inductor Lr, a resonant capacitor Cr and a magnetizing inductor Lm of a transformer TR, wherein the transformer TR is used as an electrical barrier and participates in resonance. The resonant inductor Lr is connected in series with the resonant capacitor Cr and is connected between the common node of the first switch Q1 and the second switch Q2 and the magnetizing inductor Lm, but this is not the present invention.

[0035] For further explanation, please cooperate Fig. 9 As shown, it is a waveform diagram of the relationship between the voltage gain and the switching frequency of the DC power converter of the present invention, and more specifically, it is a waveform diagram of the relationship between the voltage gain and the switching frequency of the resonant slot operation. As described above, the resonant slot of the isolated DC power converter of the present invention is mainly composed of a resonant inductor Lr, a resonant capacitor Cr, and an exciting inductor Lm. The first resonant frequency fr1 is determined by the resonant inductor Lr and the resonant capacitor Cr, that is, the exciting inductor Lm does not participate in the resonance effect. Therefore, the first resonant frequency: fr1=, where fr1 is the size of the first resonant frequency, Lr is the size of the resonant inductor, and Cr is the size of the resonant capacitor. In addition, the second resonant frequency fr2 is determined by the resonant inductor Lr, the resonant capacitor Cr, and the exciting inductor Lm. Therefore, the second resonant frequency: fr2=, where fr1 is the size of the first resonant frequency, Lr is the size of the resonant inductor, Lm is the size of the exciting inductor, and Cr is the size of the resonant capacitor.

[0036] Depend on Fig. 9It can be seen that the characteristics of the LLC conversion circuit architecture are that the right half plane at the maximum gain point is the inductive region, while the left half plane is the capacitive region. And when operating in the inductive region, the smaller the switching frequency (or operating frequency) fsw (i.e., the lower the frequency), the greater the voltage gain G of the LLC conversion circuit. On the contrary, the larger the switching frequency fsw (i.e., the higher the frequency), the smaller the voltage gain of the LLC conversion circuit. At the first resonant frequency fr1, it is unity gain (i.e., voltage gain G=1).

[0037] See also Figure 4 The third part of the isolated DC power converter is a rectifier circuit formed on the secondary side of the transformer TR, which is mainly composed of rectifier diodes D1 and D2. Figure 4 The rectifier circuit limits the present invention.

[0038] See also Fig.10 As shown in FIG. 1 , it is a flow chart of the mixed-mode operation method of the present invention. The so-called "mixed-mode operation" is also called "mixed-mode operation", which means that the DC power converter is controlled to operate in different modes in response to different input voltages, so that the DC power converter can achieve the advantages of taking into account efficiency, the selection of low withstand voltage rated components, and better hold-up time. Figure 5 FIG. 1 is a waveform diagram showing the relationship between the switching frequency and the input voltage of the DC power converter of the present invention in mixed mode operation; and FIG. Figure 6 , which is a waveform diagram of the relationship between the output voltage and the input voltage of the DC power converter of the present invention in mixed mode operation.

[0039] The mixed-mode operation method of the present invention is applied to a DC power converter. The DC power converter receives an input voltage Vin, and the magnitude of the input voltage Vin is between a minimum voltage Vin (min) and a maximum voltage Vin (max). Fig.10 As shown, the mixed mode operation method includes, first, determining whether the input voltage Vin is greater than the lower threshold voltage Vin-LL and less than the upper threshold voltage Vin-HL (step S11). The lower threshold voltage Vin-LL is greater than the minimum voltage Vin (min), and the upper threshold voltage Vin-HL is less than the maximum voltage Vin (max).

[0040] If the judgment result of step S11 is "yes", that is, when the input voltage Vin is greater than the lower threshold voltage Vin-LL and less than the upper threshold voltage Vin-HL, the DC power converter operates in the series resonant conversion (SRC) mode (step S12). In the series resonant conversion (SRC) mode, the switching frequency fsw of the DC power converter is substantially fixed. Figure 5As shown, the switching frequency fsw is a horizontal fixed value when the input voltage Vin is between the lower threshold voltage Vin-LL and the upper threshold voltage Vin-HL, and the switching frequency is the first resonant frequency at the highest efficiency. For example, the DC power converter includes a resonance tank, and the resonance tank includes a series-connected resonant inductor Lr and a resonant capacitor Cr and a transformer excitation inductor Lm. Therefore, the first resonant frequency: fr1=, where fr1 is the size of the first resonant frequency, Lr is the size of the resonant inductor, and Cr is the size of the resonant capacitor.

[0041] In addition, when the DC power converter operates in the series resonant conversion (SRC) mode, the ratio of the output voltage Vo of the DC power converter to the input voltage Vin is substantially fixed. Figure 6 As shown, when the input voltage Vin is between the lower threshold voltage Vin-LL and the upper threshold voltage Vin-HL, when the input voltage Vin increases, the output voltage Vo also increases proportionally; conversely, when the input voltage Vin decreases, the output voltage Vo also decreases proportionally. Incidentally, the so-called "substantially fixed" mentioned above means that under ideal conditions, the switching frequency is fixed, or the ratio of the output voltage to the input voltage is fixed. However, if actual non-ideal conditions are considered, the switching frequency can be considered to be almost fixed, or the ratio of the output voltage to the input voltage can be considered to be almost fixed.

[0042] When the input voltage Vin reaches the upper threshold voltage Vin-HL, the output voltage Vo reaches the upper limit of the second-stage buck converter, that is, the output upper limit voltage Vo-H (mixmode), and is maintained at this voltage. Therefore, even if the input voltage Vin continues to increase, the output voltage Vo can be stabilized to be constant at Vo-H (mixmode), which helps to select low withstand voltage rated components for the second-stage buck converter. Similarly, when the input voltage Vin reaches the lower threshold voltage Vin-LL, the output voltage Vo reaches the lower limit of the second-stage buck converter, that is, the output lower limit voltage Vo-L (mixmode), and is maintained at this voltage. Therefore, even if the input voltage Vin continues to decrease, the output voltage Vo can be stabilized to be constant at Vo-L (mixmode), which helps to extend the hold-up time of the second-stage buck converter.

[0043] However, if the judgment result of step S11 is no, that is, when the input voltage Vin is less than or equal to the lower threshold voltage Vin-LL or greater than or equal to the upper threshold voltage Vin-HL, then it is determined whether the input voltage Vin is equal to the lower threshold voltage Vin-LL or equal to the upper threshold voltage Vin-HL (step S13). If the judgment result of step S13 is no, that is, when the input voltage Vin is less than the lower threshold voltage Vin-LL or greater than the upper threshold voltage Vin-HL, the DC power converter operates in the inductor-inductor-capacitor conversion (LLC) mode (step S14). In the inductor-inductor-capacitor conversion (LLC) mode, the ratio of the switching frequency of the DC power converter operation to the input voltage Vin is substantially fixed. Figure 5 As shown, when the input voltage Vin is less than the lower threshold voltage Vin-LL, when the input voltage Vin increases, the switching frequency fsw also increases proportionally; conversely, when the input voltage Vin decreases, the switching frequency fsw also decreases proportionally. Similarly, when the input voltage Vin is greater than the upper threshold voltage Vin-HL, when the input voltage Vin increases, the switching frequency fsw also increases proportionally; conversely, when the input voltage Vin decreases, the switching frequency fsw also decreases proportionally.

[0044] In addition, when the DC power converter operates in the inductor-inductor-capacitor conversion (LLC) mode, the output voltage Vo of the DC power converter is substantially fixed. Figure 6 As shown, when the input voltage Vin is less than the lower threshold voltage Vin-LL, the output voltage Vo is a horizontal fixed value. Similarly, when the input voltage Vin is greater than the upper threshold voltage Vin-HL, the output voltage Vo is a horizontal fixed value.

[0045] Incidentally, if the result of the judgment in step S13 is yes, that is, when the input voltage Vin is equal to the lower threshold voltage Vin-LL or equal to the upper threshold voltage Vin-HL, the DC power converter can be operated in the series resonant conversion mode (step S12) or the inductor-inductor-capacitor conversion mode (step S14). In other words, when the magnitude of the input voltage Vin is just the voltage for the transition (transfer) of the operation mode, both conversion modes can be used.

[0046] See also Figure 7 and Figure 8 , which are Figure 2 and Figure 5 The waveform diagram and Figure 3 and Figure 6 The mixed mode operation method (i.e. Figure 5 and Figure 6The MIX-MODE curve shown in FIG. 1 can combine the advantages of the LLC mode and the SRC mode, that is, when the input voltage Vin is between the lower threshold voltage Vin-LL and the upper threshold voltage Vin-HL, the DC power converter is operated in the series resonant conversion (SRC) mode, and when the input voltage Vin is not between the lower threshold voltage Vin-LL and the upper threshold voltage Vin-HL (that is, the input voltage Vin is less than the lower threshold voltage Vin-LL or the input voltage Vin is greater than the upper threshold voltage Vin-HL), the DC power converter is operated in the inductor-inductor-capacitor conversion (LLC) mode, so that the technical effects of taking into account efficiency, the selection of low withstand voltage rated components, and a better hold-up time can be achieved.

[0047] The above description is only a detailed description and drawings of the preferred specific embodiments of the present invention, but the features of the present invention are not limited thereto, and are not intended to limit the present invention. The entire scope of the present invention shall be subject to the following patent application scope. All embodiments that conform to the spirit of the patent application scope of the present invention and similar variations thereof shall be included in the scope of the present invention. Any changes or modifications that can be easily thought of by anyone familiar with the art within the field of the present invention shall be covered by the following patent scope of this case.

Claims

1. A mixed mode operation method, applied to a DC power converter, characterized in that: The DC power converter receives an input voltage, and the magnitude of the input voltage is between a minimum voltage and a maximum voltage. The mixed-mode operation method includes: When the input voltage is greater than a lower threshold voltage and less than an upper threshold voltage, the DC power converter operates in a series resonant conversion mode, wherein the lower threshold voltage is greater than the minimum voltage and the upper threshold voltage is less than the maximum voltage; When the input voltage is less than the lower threshold voltage, the DC power converter operates in an inductor-inductor-capacitor conversion mode; and When the input voltage is greater than the upper threshold voltage, the DC power converter operates in the inductor-inductor-capacitor conversion mode.

2. The mixed-mode operation method for a DC power converter according to claim 1, characterized in that: The mixed mode operation method also includes: When the input voltage is equal to the lower threshold voltage, the DC power converter operates in the series resonant conversion mode or the inductor-inductor-capacitor conversion mode; and When the input voltage is equal to the upper threshold voltage, the DC power converter operates in the series resonant conversion mode or the inductor-inductor-capacitor conversion mode.

3. The mixed-mode operation method for a DC power converter according to claim 1, characterized in that: When the DC power converter operates in the series resonant conversion mode, the switching frequency of the DC power converter is substantially fixed.

4. The mixed-mode operation method for a DC power converter according to claim 1, characterized in that: When the DC power converter operates in the series resonant conversion mode, the ratio of the output voltage of the DC power converter to the input voltage is substantially fixed.

5. The mixed-mode operation method for a DC power converter according to claim 3, characterized in that: The switching frequency is the first resonant frequency of the DC power converter at the highest efficiency.

6. The mixed-mode operation method for a DC power converter according to claim 5, characterized in that: The DC power converter includes a resonant tank, which includes a resonant inductor and a resonant capacitor connected in series and a magnetizing inductor of a transformer; The first resonant frequency: fr1=, wherein fr1 is the size of the first resonant frequency, Lr is the size of the resonant inductance, and Cr is the size of the resonant capacitance.

7. The mixed-mode operation method for a DC power converter according to claim 1, characterized in that: When the DC power converter operates in the LC conversion mode, the ratio of the switching frequency of the DC power converter to the input voltage is substantially fixed.

8. The mixed-mode operation method for a DC power converter according to claim 1, characterized in that: When the DC power converter operates in the LC conversion mode, the output voltage of the DC power converter is substantially fixed.

9. The mixed-mode operation method for a DC power converter according to claim 4, characterized in that: When the input voltage reaches the upper threshold voltage, the output voltage is correspondingly an output upper limit voltage, and the output upper limit voltage is an upper limit voltage of a buck converter connected to a downstream secondary of the DC power converter.

10. The mixed-mode operation method for a DC power converter according to claim 4, characterized in that: When the input voltage reaches the lower critical voltage, the output voltage is correspondingly an output lower limit voltage, and the output lower limit voltage is a lower limit voltage of a buck converter connected to a downstream secondary of the DC power converter.

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