Control method for isolated dc / dc converter

Abstract

The application provides a control method of an isolated DC / DC converter, and relates to the field of power supplies, and comprises the following steps: in a first time interval of a first switching period, controlling the original side switching unit to work in a first mode, so that the voltage applied to the original side winding is a first level; in a second time interval of the first switching period, controlling the original side switching unit to work in a second mode, so that the voltage applied to the original side winding is a second level; in a third time interval of the first switching period, controlling the original side switching unit to work in a third mode, so that the voltage applied to the original side winding is a third level, wherein the first time interval is adjacent to the second time interval, the sum of the first time interval and the second time interval is half of the first switching period, and the third time interval is also half of the first switching period.

Description

Technical Field

[0001] This application relates to the field of power supplies, and in particular to control methods for isolated DC / DC converters. Background Technology

[0002] Isolated DC / DC converters are used in many applications because they can achieve isolation between the output and input terminals and can utilize the high turns ratio of the transformer T to achieve a large transformation ratio between the output voltage Vout and the input voltage Vin.

[0003] Especially when the isolated DC / DC converter is implemented as a resonant converter, it can achieve soft switching across the entire load range, thereby reducing switching losses, improving converter efficiency, reducing size, and increasing power density, thus gaining wider applications.

[0004] With the development of technology and the diversification of market product demands, a wide input voltage Vin range or a wide output voltage Vout range is needed and expected. For example, in the field of new energy vehicles, the requirements for the input voltage Vin range of the vehicle's isolated DC / DC converter are becoming increasingly wider, such as between 200V and 500V, or between 500V and 1000V, while the output voltage Vout is usually between 12V and 16V. In other words, the vehicle-mounted isolated DC / DC converter has the problem of a wide input voltage Vin range.

[0005] We know that for isolated DC / DC converters (such as resonant converters), frequency conversion control can be used, that is, controlling the operating frequency of the switching transistors in the isolated DC / DC converter, or duty cycle control under fixed frequency can be used.

[0006] To meet the wide input voltage Vin range, existing control methods suffer from abrupt switching between modes, resulting in poor reliability of isolated DC / DC converters. Summary of the Invention

[0007] This application provides a control method for an isolated DC / DC converter, wherein the isolated DC / DC converter includes a primary-side switching unit, a transformer, and a secondary-side switching unit. The primary-side switching unit is connected between the input terminal of the isolated DC / DC converter and the primary winding of the transformer, and the secondary-side switching unit is connected between the secondary winding of the transformer and the output terminal of the isolated DC / DC converter, comprising:

[0008] During a first time interval of a first switching cycle, the primary-side switching unit is controlled to operate in a first mode, such that the voltage applied to the primary-side winding is at a first level; during a second time interval of the first switching cycle, the primary-side switching unit is controlled to operate in a second mode, such that the voltage applied to the primary-side winding is at a second level; during a third time interval of the first switching cycle, the primary-side switching unit is controlled to operate in a third mode, such that the voltage applied to the primary-side winding is at a third level, wherein the first time interval is adjacent to the second time interval, and the sum of the first time interval and the second time interval and the third time interval each occupy half of the first switching cycle.

[0009] Furthermore, the first duty cycle of the first time interval during the first switching cycle is between 0 and... The values ​​can be adjusted.

[0010] Furthermore, the input voltage at the input terminal and the output voltage at the output terminal are detected, and the first duty cycle of the first time interval in the first switching cycle is adjusted according to the input voltage and the output voltage.

[0011] Furthermore, the first duty cycle increases as the gain between the output voltage and the input voltage increases.

[0012] Furthermore, it also includes: controlling the primary-side switching unit to operate in a first mode during the fourth time interval of the second switching cycle, such that the voltage applied to the primary-side winding is a first level; controlling the primary-side switching unit to operate in a fourth mode during the fifth time interval of the second switching cycle, such that the voltage applied to the primary-side winding is a second level; and controlling the primary-side switching unit to operate in a third mode during the sixth time interval of the second switching cycle, such that the voltage applied to the primary-side winding is a third level, wherein the fourth time interval is adjacent to the fifth time interval, and the sum of the fourth time interval and the fifth time interval and the sixth time interval each occupy half of the second switching cycle.

[0013] Furthermore, the fourth time interval occupies a second duty cycle of the second switching cycle between 0 and... The values ​​can be adjusted.

[0014] Furthermore, the second duty cycle of the fourth time interval during the second switching cycle is adjusted according to the input voltage and the output voltage.

[0015] Furthermore, the second duty cycle increases as the gain between the output voltage and the input voltage increases.

[0016] Furthermore, the primary-side switching unit is a full-bridge topology, including a first switching bridge arm formed by a first upper switching transistor and a second lower switching transistor connected in series, and a second switching bridge arm formed by a third upper switching transistor and a fourth lower switching transistor connected in series. The first and second switching bridge arms are connected in parallel. The common node of the first and second switching bridge arms are respectively connected to the two ends of the primary winding. In the first mode, the first upper switching transistor and the fourth lower switching transistor are controlled to be on, and the second lower switching transistor and the third upper switching transistor are controlled to be off. In the second mode, the second lower switching transistor and the fourth lower switching transistor are controlled to be on, and the first upper switching transistor and the third upper switching transistor are controlled to be off. In the third mode, the second lower switching transistor and the third upper switching transistor are controlled to be on, and the first upper switching transistor and the fourth lower switching transistor are controlled to be off. In the fourth mode, the first upper switching transistor and the third upper switching transistor are controlled to be on, and the second lower switching transistor and the fourth lower switching transistor are controlled to be off.

[0017] Furthermore, it includes: determining a first duty cycle and a second duty cycle based on the input voltage and the output voltage, wherein the first duty cycle is equal to the second duty cycle; determining the time lengths of a second time interval and a fifth time interval based on the first duty cycle and the second duty cycle, wherein the time lengths of the second time interval and the fifth time interval are equal.

[0018] Furthermore, the primary-side switching unit is a stacked half-bridge topology, including an upper bus capacitor, a lower bus capacitor, an upper switching branch, and a lower switching branch. The upper bus capacitor and the lower bus capacitor are connected in series. The upper switching branch includes a first and a second switching transistor connected in series. The lower switching branch includes a third and a fourth switching transistor connected in series. The upper bus capacitor is connected in parallel with the upper switching branch, and the lower bus capacitor is connected in parallel with the lower switching branch. The common node of the upper switching branch and the common node of the lower switching branch are respectively connected to the two ends of the primary-side winding. A switching cycle is adjacent to the second switching cycle, and in the first mode, the first and fourth switches are controlled to be turned on, and the second and third switches are controlled to be turned off; in the second mode, the first and third switches are controlled to be turned on, and the second and fourth switches are controlled to be turned off; in the third mode, the second and third switches are controlled to be turned on, and the first and fourth switches are controlled to be turned off; in the fourth mode, the second and fourth switches are controlled to be turned on, and the first and third switches are controlled to be turned off.

[0019] Furthermore, the method includes: determining a preset duty cycle based on the input voltage and the output voltage; detecting and obtaining the upper bus capacitor voltage on the upper bus capacitor and the lower bus capacitor voltage on the lower bus capacitor, and determining the difference in time length between the second time interval and the fifth time interval based on the voltage difference between the upper bus capacitor voltage and the lower bus capacitor voltage; and determining the first duty cycle and the second duty cycle based on the difference in time length between the preset duty cycle and the preset duty cycle.

[0020] The features and technical advantages of this disclosure have been outlined quite extensively above to facilitate a better understanding of the detailed description that follows. Additional features and advantages of this disclosure, which form the subject matter of the claims, will be described below. Those skilled in the art will understand that the disclosed concepts and specific embodiments can be readily used as the basis for modifying or designing other structures or processes to achieve the same purpose as this disclosure. Those skilled in the art will also recognize that such equivalent structures do not depart from the spirit and scope of this disclosure as set forth in the appended claims. Attached Figure Description

[0021] To gain a more complete understanding of this disclosure and its advantages, the following description is provided in conjunction with the accompanying drawings, wherein:

[0022] Figure 1 A schematic diagram of a typical isolated DC / DC converter with a full-bridge topology and primary-side switching units is shown.

[0023] Figure 2 An embodiment of this application is shown applying to... Figure 1 A schematic diagram of the voltage across the primary winding of an isolated DC / DC converter.

[0024] Figure 3 An embodiment of this application is shown. Figure 1 A schematic diagram of the isolated DC / DC converter operating in the first mode;

[0025] Figure 4 An embodiment of this application is shown. Figure 1 A schematic diagram of the isolated DC / DC converter operating in the second mode;

[0026] Figure 5 An embodiment of this application is shown. Figure 1 A schematic diagram of the isolated DC / DC converter operating in the third mode;

[0027] Figure 6 An embodiment of this application is shown. Figure 1 A schematic diagram of the isolated DC / DC converter operating in the fourth mode;

[0028] Figure 7This diagram illustrates a typical isolated DC / DC converter with a stacked half-bridge topology as the primary-side switching unit.

[0029] Figure 8 An embodiment of this application is shown. Figure 7 A schematic diagram of the isolated DC / DC converter operating in the first mode;

[0030] Figure 9 An embodiment of this application is shown. Figure 7 A schematic diagram of the isolated DC / DC converter operating in the second mode;

[0031] Figure 10 An embodiment of this application is shown. Figure 7 A schematic diagram of the isolated DC / DC converter operating in the third mode;

[0032] Figure 11 An embodiment of this application is shown. Figure 7 A schematic diagram of the isolated DC / DC converter operating in the fourth mode;

[0033] Figure 12 An embodiment of this application is shown applying to... Figure 7 A schematic diagram of the voltage across the primary winding of an isolated DC / DC converter.

[0034] Unless otherwise stated, correspondences and symbols in the different figures generally refer to corresponding parts. These figures are drawn to clearly illustrate relevant aspects of the various embodiments and are not necessarily drawn to scale. Detailed Implementation

[0035] The technical solutions of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0036] One embodiment of this application provides a control method for an isolated DC / DC converter. Please refer to... Figure 1 The diagram shown is a typical primary-side switching unit for a full-bridge topology isolated DC / DC converter. The isolated DC / DC converter includes a primary-side switching unit 110, a first transformer T, and a secondary-side switching unit 120. The primary-side switching unit 110 is connected between the input terminal of the isolated DC / DC converter and the primary winding Pr of the first transformer T. The secondary-side switching unit 120 is connected between the secondary winding Sr of the first transformer T and the output terminal of the isolated DC / DC converter.

[0037] Specifically, the primary-side switching unit 110 of the full-bridge topology includes a first switching bridge arm formed by connecting the first upper switching transistor S1 and the second lower switching transistor S2 in series, and a second switching bridge arm formed by connecting the third upper switching transistor S3 and the fourth lower switching transistor S4 in series. The first switching bridge arm and the second switching bridge arm are connected in parallel. The common node C of the first switching bridge arm and the common node D of the second switching bridge arm are respectively connected to the two ends of the primary winding Pr.

[0038] And, input to Figure 1 The input voltage Vin at the input terminal of the isolated DC / DC converter or the output voltage Vout at its output terminal has a wide range. For example, when the isolated DC / DC converter is implemented as an on-board DC / DC converter in a new energy vehicle, its input voltage Vin is 200V to 500V, or 500V to 1000V; the output voltage Vout is used to power the load in the new energy vehicle, and it can be between 12V and 16V, that is, the input voltage Vin has a wide range.

[0039] This application does not limit the isolation DC / DC converter to frequency conversion control or duty cycle control under fixed frequency; this can be determined according to the actual control requirements.

[0040] Please combine Figure 2 The application of an embodiment of this application shown is applied to Figure 1 A schematic diagram of the voltage across the primary winding of the isolated DC / DC converter. The control method for the isolated DC / DC converter provided in this application includes:

[0041] During the first time interval t1 of the first switching cycle T1, the primary-side switching unit 110 is controlled to operate in the first mode, so that the voltage applied to the primary-side winding Pr is the first level V1;

[0042] During the second time interval t2 of the first switching cycle T1, the primary-side switching unit 110 is controlled to operate in the second mode, such that the voltage applied to the primary-side winding Pr is the second level V2.

[0043] During the third time interval t3 of the first switching cycle T1, the primary-side switching unit 110 is controlled to operate in the third mode, such that the voltage applied to the primary-side winding Pr is the third level V3, wherein the first time interval t1 is adjacent to the second time interval t2, and the sum of the first time interval t1 and the second time interval t2 and the third time interval t3 each occupy half of the first switching cycle T1.

[0044] like Figure 2As shown, the first level V1 is the input voltage Vin at the input terminal of the isolated DC / DC converter, the second level V2 is zero voltage, and the third level V3 is the negative input voltage Vin.

[0045] Please see Figure 3 shown Figure 1 The diagram shows the isolated DC / DC converter operating in the first mode. The first upper switch S1 and the fourth lower switch S4 are controlled to be on, while the second lower switch S2 and the third upper switch S3 are controlled to be off, thus applying the input voltage Vin to the primary winding Pr. (See also...) Figure 4 shown Figure 1 The diagram shows the isolated DC / DC converter operating in the second mode. The second lower switch S2 and the fourth lower switch S4 are controlled to be turned on, while the first upper switch S1 and the third upper switch S3 are controlled to be turned off, resulting in a zero voltage applied to the primary winding Pr. (See also...) Figure 5 shown Figure 1 The diagram shows the isolated DC / DC converter operating in the third mode. The second lower switch S2 and the third upper switch S3 are controlled to be turned on, and the first upper switch S1 and the fourth lower switch S4 are controlled to be turned off, so that a negative input voltage Vin is applied to the primary winding Pr.

[0046] In one practical embodiment, the first duty cycle of the first time interval t1 during the first switching period T1 is between 0 and... The duty cycle is adjustable between these values. When the first duty cycle in the first limiting state is... When the second time interval t2 shrinks to zero and the first time interval t1 expands to half of the first switching cycle T1, then the first time interval t1 and the third time interval t3 each occupy half of the first switching cycle T1. The primary-side switching unit 110 of the isolated DC / DC converter switches only between the first mode and the third mode, that is, the isolated DC / DC converter operates in full-voltage mode. When the first duty cycle in the second extreme state is 0, the first time interval t1 shrinks to zero and the second time interval t2 expands to half of the first switching cycle T1. Then the second time interval t2 and the third time interval t3 each occupy half of the first switching cycle T1. The primary-side switching unit 110 of the isolated DC / DC converter switches only between the second mode and the third mode, that is, the isolated DC / DC converter operates in half-voltage mode. When the first duty cycle is between 0 and... When the intervals change, such as Figure 2As shown, the primary-side switching unit 110 of the isolated DC / DC converter switches between the first mode, the second mode and the third mode. The voltage applied to the primary winding Pr varies between the half-voltage mode and the full-voltage mode of the isolated DC / DC converter, and changes smoothly and continuously with the change of the first duty cycle. In extreme conditions, it can smoothly and continuously transition to the half-voltage mode or the full-voltage mode.

[0047] In one embodiment of the actual implementation, the control method for the isolated DC / DC converter further includes: detecting and obtaining the input voltage Vin at the input terminal and the output voltage Vout at the output terminal, and adjusting the first duty cycle of the first time interval t1 to the first switching period T1 according to the input voltage Vin and the output voltage Vout.

[0048] Specifically, in one embodiment, the first duty cycle increases as the gain between the output voltage Vout and the input voltage Vin increases. As mentioned above, in a typical new energy vehicle's on-board DC / DC converter, the input voltage Vin is 200V to 500V, or 500V to 1000V; the output voltage Vout is used to power the load in the new energy vehicle, and it can be between 12V and 16V. That is, the input voltage Vin has a wide range, and the output voltage Vout can be considered basically constant. In actual implementation, the first duty cycle can be controlled to vary with the input voltage Vin, specifically decreasing as the input voltage Vin increases and increasing as the input voltage Vin decreases. That is, when the input voltage Vin is in a lower limit state, the first duty cycle can be set to a certain value. That is, the isolated DC / DC converter operates in full voltage mode. When the input voltage Vin is at a higher limit, the first duty cycle can be 0, that is, the isolated DC / DC converter operates in half voltage mode. In the intermediate input voltage Vin range between the lower limit and the higher limit, the isolated DC / DC converter operates in the first duty cycle adjustable mode, and the three modes switch smoothly and continuously.

[0049] It is evident that the control method for the isolated DC / DC converter provided in this application enables the modulation state of the isolated DC / DC converter to change continuously with the input voltage Vin. This not only meets the market demand for isolated DC / DC converters with a wide input voltage Vin range, but also allows the input voltage Vin of the isolated DC / DC converter to transition smoothly and continuously between modes when it changes over a wide range, thereby improving the reliability and efficiency of the isolated DC / DC converter.

[0050] Furthermore, control methods for isolated DC / DC converters also include:

[0051] During the fourth time interval t4 of the second switching cycle T2, the primary-side switching unit 110 is controlled to operate in the first mode, so that the voltage applied to the primary-side winding Pr is the first level V1.

[0052] During the fifth time interval t5 of the second switching cycle T2, the primary-side switching unit 110 is controlled to operate in the fourth mode, so that the voltage applied to the primary-side winding Pr is the second level V2.

[0053] During the sixth time interval t6 of the second switching cycle T2, the primary-side switching unit 110 is controlled to operate in the third mode, such that the voltage applied to the primary-side winding Pr is the third level V3. The fourth time interval t4 is adjacent to the fifth time interval t5, and the sum of the fourth time interval t4 and the fifth time interval t5 and the sixth time interval t6 each occupy half of the second switching cycle T2.

[0054] Please see Figure 6 shown Figure 1 The diagram shows the isolated DC / DC converter operating in the fourth mode. The first upper switch S1 and the third upper switch S3 are controlled to be turned on, and the second lower switch S2 and the fourth lower switch S4 are controlled to be turned off, so that the voltage applied to the primary winding Pr is zero.

[0055] Alternatively, in the second mode, the first upper switch S1 and the third upper switch S3 are controlled to be turned on, and the second lower switch S2 and the fourth lower switch S4 are controlled to be turned off, so that the voltage applied to the primary winding Pr is zero. In the fourth mode, the second lower switch S2 and the fourth lower switch S4 are controlled to be turned on, and the first upper switch S1 and the third upper switch S3 are controlled to be turned off, so that the voltage applied to the primary winding Pr is zero.

[0056] In the embodiment where the primary-side switching unit 110 is a full-bridge topology, the first switching cycle T1 can be adjacent to the second switching cycle T2, meaning the first switching cycle T1 and the second switching cycle T2 alternate. In this case, over a relatively long operating period, the number of the first switching cycles T1 is equal to the number of the second switching cycles T2. This allows the primary-side switching unit 110 to operate in two different modes, namely the second and fourth modes, within two adjacent switching cycles, so that the voltage applied to the primary winding Pr is at the second level V2. This achieves loss balancing of the switching transistors within the full-bridge topology, further improving the performance of the isolated DC / DC converter. Of course, the first switching cycle T1 can also be non-adjacent to the second switching cycle T2, meaning the first switching cycle T1 and the second switching cycle T2 do not alternate. In this case, over a relatively long operating period, the number of the first switching cycles T1 is not equal to the number of the second switching cycles T2.

[0057] In practical applications, for embodiments where the primary-side switching unit 110 is a full-bridge topology, whether the first switching cycle T1 and the second switching cycle T2 are adjacent, and when they are not adjacent, the number of the first switching cycles T1 and the number of the second switching cycles T2, can be determined based on whether the losses of the switching transistors used for freewheeling are balanced when the voltage applied to the primary-side winding is at the second level.

[0058] In one specific embodiment, for an embodiment where the primary-side switching unit 110 is a full-bridge topology, the control method for the isolated DC / DC converter further includes:

[0059] The first duty cycle and the second duty cycle are determined based on the input voltage Vin and the output voltage Vout, wherein the first duty cycle is equal to the second duty cycle;

[0060] The time lengths of the second time interval t2 and the fifth time interval t5 are determined based on the first duty cycle and the second duty cycle, and the time lengths of the second time interval t2 and the fifth time interval t5 are equal.

[0061] That is, for the embodiment where the primary-side switching unit 110 is a full-bridge topology, the first duty cycle and the second duty cycle are determined based on the gain of the isolated DC / DC converter.

[0062] Similar to the principle of the first adjustable duty cycle, the second duty cycle of the fourth time interval during the second switching cycle is between 0 and... The duty cycle is adjustable. Similarly, in one embodiment, the second duty cycle of the fourth time interval during the second switching cycle is adjusted according to the input voltage and the output voltage. Similarly, in one embodiment, the second duty cycle increases as the gain between the output voltage and the input voltage increases.

[0063] It can be seen that by controlling one of the two adjacent switching cycles to achieve the second level V2 through the conduction of the first upper switch S1 and the third upper switch S3, and the other to achieve the second level V2 through the conduction of the second lower switch S2 and the fourth lower switch S4, the losses of the switching transistors in the isolated DC / DC converter can be accurately balanced.

[0064] In another embodiment, the primary-side switching unit 110 is a stacked half-bridge topology, as described in [reference needed]. Figure 7 The diagram shown is a typical primary-side switching unit of an isolated DC / DC converter with a stacked half-bridge topology. The primary-side switching unit 110 includes an upper bus capacitor C1, a lower bus capacitor C2, an upper switching branch, and a lower switching branch. The upper bus capacitor C1 and the lower bus capacitor C2 are connected in series. The upper switching branch includes a first switch Q1 and a second switch Q2 connected in series. The lower switching branch includes a third switch Q3 and a fourth switch Q4 connected in series. The upper bus capacitor C1 is connected in parallel with the upper switching branch, and the lower bus capacitor C2 is connected in parallel with the lower switching branch. The common node A of the upper switching branch and the common node B of the lower switching branch are respectively connected to the two ends of the primary winding Pr.

[0065] For the primary-side switching unit 110 in a stacked half-bridge topology, in the first mode, the first switch Q1 and the fourth switch Q4 are controlled to be turned on, and the second switch Q2 and the third switch Q3 are controlled to be turned off. (See also...) Figure 8 shown Figure 7 The diagram shows the isolated DC / DC converter operating in the first mode. In the second mode, the first switch Q1 and the third switch Q3 are controlled to be turned on, and the second switch Q2 and the fourth switch Q4 are controlled to be turned off. Please refer to [link to relevant documentation]. Figure 9 shown Figure 7 The diagram shows the isolated DC / DC converter operating in the second mode. In the third mode, the second switch Q2 and the third switch Q3 are controlled to be turned on, and the first switch Q1 and the fourth switch Q4 are controlled to be turned off. Please refer to [link to relevant documentation]. Figure 10 shown Figure 7 The diagram shows the isolated DC / DC converter operating in the third mode. In the fourth mode, the second switch Q2 and the fourth switch Q4 are controlled to be turned on, and the first switch Q1 and the third switch Q3 are controlled to be turned off. Please refer to [link to relevant documentation]. Figure 11 shown Figure 7 A schematic diagram of the isolated DC / DC converter operating in the fourth mode.

[0066] Please combine Figure 12 The application of another embodiment of this application shown is applied in Figure 7 A schematic diagram of the voltage across the primary winding of the isolated DC / DC converter, and please refer to it. Figures 8 to 11 The first level V1 is the input voltage Vin at the input terminal of the isolated DC / DC converter, the second level V2 is half of the input voltage Vin, and the third level V3 is zero voltage.

[0067] Alternatively, in the second mode, the second switch Q2 and the fourth switch Q4 are controlled to be turned on, and the first switch Q1 and the third switch Q3 are controlled to be turned off, so that the voltage applied to the primary winding Pr is half of the input voltage Vin; in the fourth mode, the first switch Q1 and the third switch Q3 are controlled to be turned on, and the second switch Q2 and the fourth switch Q4 are controlled to be turned off, so that the voltage applied to the primary winding Pr is half of the input voltage Vin.

[0068] Similar to the operating principle of the primary-side switching unit 110 when it is a full-bridge topology, the first duty cycle of the first time interval t1 during the first switching period T1 is between 0 and... The fourth time interval is adjustable, and the second duty cycle of the second switching cycle is between 0 and... The range is adjustable, and its principles and advantages will not be elaborated here.

[0069] More specifically, in an embodiment where the primary-side switching unit 110 is a stacked half-bridge topology, the first switching cycle T1 and the second switching cycle T2 are adjacent, that is, the first switching cycle T1 and the second switching cycle T2 alternate. At this time, during a relatively long working period, the number of the first switching cycles T1 is equal to the number of the second switching cycles T2, so that the voltage of the upper bus capacitor is balanced with the voltage of the lower bus capacitor, and the switching losses in the primary-side switching unit are balanced.

[0070] However, for embodiments where the primary-side switching unit 110 is a stacked half-bridge topology, the control method for the isolated DC / DC converter further includes:

[0071] The preset duty cycle is determined based on the input voltage Vin and the output voltage Vout.

[0072] The voltage across the upper bus capacitor C1 and the voltage across the lower bus capacitor C2 are detected, and the difference in time length between the second time interval t2 and the fifth time interval t5 is determined based on the voltage difference between the upper bus capacitor voltage and the lower bus capacitor voltage.

[0073] The first duty cycle and the second duty cycle are determined based on the difference between the preset duty cycle and the time length.

[0074] In other words, in actual implementation, the first duty cycle and the second duty cycle are determined by comprehensively considering the gain of the isolated DC / DC converter, the voltage loss of the upper bus capacitor, and the voltage loss of the lower bus capacitor.

[0075] The difference in time length between the second time interval t2 and the fifth time interval t5 is determined based on the voltage difference between the upper bus capacitor voltage and the lower bus capacitor voltage. Specifically, when the upper bus capacitor voltage and the lower bus capacitor voltage are unbalanced, if the upper bus capacitor voltage is greater than the lower bus capacitor voltage, the operating time of the second mode needs to be increased and the operating time of the fourth mode needs to be decreased to balance the upper bus capacitor voltage and the lower bus capacitor voltage, and to balance the switching losses of the switching transistors in the primary-side switching unit. In fact, when the additional operating time of the second mode occupies a duty cycle of ΔDf in one switching cycle, and the preset duty cycle determined by the input voltage Vin and the output voltage Vout is Df, then the first duty cycle is set to Df+ΔDf and the second duty cycle is set to Df-ΔDf. It can be seen that by fine-tuning the value of ΔDf, a more accurate balance can be achieved between the upper bus capacitor voltage and the lower bus capacitor voltage, as well as the switching losses of the switching transistors in the primary-side switching unit 110. In practice, the value of ΔDf is usually very small, and as described above, it can be positive or negative.

[0076] Of course, when the voltage of the upper bus capacitor and the voltage of the lower bus capacitor are balanced, the time of the second mode can be equal to the time of the fourth mode, that is, ΔDf is zero. At this time, the first duty cycle is equal to the second duty cycle.

[0077] Please see Figure 1 and Figure 7 The isolated DC / DC converter can also be a resonant converter. Therefore, the isolated DC / DC converter may further include a resonant cavity connected between the primary-side switching unit 110 and the transformer T, such as... Figure 1 and Figure 7 As shown, the resonant cavity includes a resonant capacitor Cr and a resonant inductor Lr connected in series.

[0078] In practice, this application does not limit... Figure 1 and Figure 7 The specific structure of the secondary rectifier unit 120 is applicable to any available rectifier switch unit.

[0079] Although embodiments of the present disclosure and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations may be made herein without departing from the spirit and scope of the present disclosure as defined by the appended claims.

[0080] Furthermore, the processes, machines, manufactures, compositions of matter, apparatuses, methods, and steps described in this application are merely specific embodiments. As will be readily understood by those skilled in the art from the disclosure of this application, processes, machines, manufactures, compositions of matter, means, methods, or steps that perform substantially the same function, currently exist or will be developed or implemented thereafter, will yield substantially the same results as the corresponding embodiments described herein that are available according to this disclosure. Therefore, the appended claims are intended to include such processes, machines, manufactures, compositions of matter, apparatuses, methods, or steps within their scope.

Claims

1. A control method for an isolated DC / DC converter, the isolated DC / DC converter comprising a primary-side switching unit, a transformer, and a secondary-side switching unit, wherein the primary-side switching unit is connected between the input terminal of the isolated DC / DC converter and the primary winding of the transformer, and the secondary-side switching unit is connected between the secondary winding of the transformer and the output terminal of the isolated DC / DC converter, characterized in that, include: During the first time interval of the first switching cycle, the primary-side switching unit is controlled to operate in the first mode, such that the voltage applied to the primary-side winding is at the first level. During the second time interval of the first switching cycle, the primary-side switching unit is controlled to operate in the second mode, such that the voltage applied to the primary-side winding is at the second level; During the third time interval of the first switching cycle, the primary-side switching unit is controlled to operate in the third mode, such that the voltage applied to the primary-side winding is at the third level, wherein the first time interval is adjacent to the second time interval, and the sum of the first time interval and the second time interval and the third time interval each occupy half of the first switching cycle.

2. The control method for an isolated DC / DC converter according to claim 1, characterized in that, The first duty cycle of the first time interval during the first switching cycle is between 0 and... The values ​​can be adjusted.

3. The control method for an isolated DC / DC converter according to claim 2, characterized in that, The input voltage at the input terminal and the output voltage at the output terminal are detected, and the first duty cycle of the first time interval in the first switching cycle is adjusted according to the input voltage and the output voltage.

4. The control method for an isolated DC / DC converter according to claim 3, characterized in that, The first duty cycle increases as the gain between the output voltage and the input voltage increases.

5. The control method for an isolated DC / DC converter according to claim 4, characterized in that, Also includes: During the fourth time interval of the second switching cycle, the primary-side switching unit is controlled to operate in the first mode, such that the voltage applied to the primary-side winding is at the first level. During the fifth time interval of the second switching cycle, the primary-side switching unit is controlled to operate in the fourth mode, so that the voltage applied to the primary-side winding is the second level; During the sixth time interval of the second switching cycle, the primary-side switching unit is controlled to operate in the third mode, such that the voltage applied to the primary-side winding is at the third level, wherein the fourth time interval is adjacent to the fifth time interval, and the sum of the fourth time interval and the fifth time interval and the sixth time interval each occupy half of the second switching cycle.

6. The control method for an isolated DC / DC converter according to claim 5, characterized in that, The fourth time interval occupies the second duty cycle of the second switching cycle from 0 to... The values ​​can be adjusted.

7. The control method for an isolated DC / DC converter according to claim 6, characterized in that, The fourth time interval is adjusted according to the input voltage and the output voltage, which constitutes the second duty cycle of the second switching cycle.

8. The control method for an isolated DC / DC converter according to claim 7, characterized in that, The second duty cycle increases as the gain between the output voltage and the input voltage increases.

9. The control method for an isolated DC / DC converter according to claim 8, characterized in that, The primary-side switching unit is a full-bridge topology, comprising a first switching bridge arm formed by a first upper switching transistor and a second lower switching transistor connected in series, and a second switching bridge arm formed by a third upper switching transistor and a fourth lower switching transistor connected in series. The first and second switching bridge arms are connected in parallel. The common node of the first and second switching bridge arms is connected to both ends of the primary winding, respectively. In the first mode, the first upper switch and the fourth lower switch are controlled to be turned on, and the second lower switch and the third upper switch are controlled to be turned off. In the second mode, the second and fourth lower switches are controlled to be turned on, and the first and third upper switches are controlled to be turned off. In the third mode, the second lower switch and the third upper switch are controlled to be turned on, and the first upper switch and the fourth lower switch are controlled to be turned off. In the fourth mode, the first and third upper switches are controlled to be turned on, and the second and fourth lower switches are controlled to be turned off.

10. The control method for an isolated DC / DC converter according to claim 9, characterized in that, include: The first duty cycle and the second duty cycle are determined based on the input voltage and the output voltage, wherein the first duty cycle is equal to the second duty cycle; The time lengths of the second time interval and the fifth time interval are determined based on the first duty cycle and the second duty cycle, and the time lengths of the second time interval and the fifth time interval are equal.

11. The control method for an isolated DC / DC converter according to claim 8, characterized in that, The primary-side switching unit is a stacked half-bridge topology, including an upper bus capacitor, a lower bus capacitor, an upper switching branch, and a lower switching branch. The upper bus capacitor and the lower bus capacitor are connected in series. The upper switching branch includes a first switch and a second switch connected in series. The lower switching branch includes a third switch and a fourth switch connected in series. The upper bus capacitor and the upper switching branch are connected in parallel, and the lower bus capacitor and the lower switching branch are connected in parallel. The common node of the upper switching branch and the common node of the lower switching branch are respectively connected to the two ends of the primary-side winding. The first switching cycle is adjacent to the second switching cycle. In the first mode, the first and fourth switches are controlled to be turned on, and the second and third switches are controlled to be turned off; In the second mode, the first and third switches are controlled to be turned on, and the second and fourth switches are controlled to be turned off. In the third mode, the second and third switches are controlled to be turned on, and the first and fourth switches are controlled to be turned off. In the fourth mode, the second and fourth switches are controlled to be turned on, while the first and third switches are controlled to be turned off.

12. The control method for an isolated DC / DC converter according to claim 11, characterized in that, include: The preset duty cycle is determined based on the input voltage and the output voltage; The voltage of the upper bus capacitor on the upper bus capacitor and the voltage of the lower bus capacitor on the lower bus capacitor are detected and obtained. The difference in time length between the second time interval and the fifth time interval is determined based on the voltage difference between the upper bus capacitor voltage and the lower bus capacitor voltage. The first duty cycle and the second duty cycle are determined based on the difference between the preset duty cycle and the time length.

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