A control method and control circuit for a bidirectional resonant DC-DC converter

Abstract

This application provides a control method and control circuit for a bidirectional resonant DC-DC converter. After detecting commutation of the secondary-side resonant current, the control method controls the corresponding switches in each arm of the secondary circuit to delay for a specified time before turning them off. Since the current commutates to the anti-parallel diode or body diode of the complementary switch in the same arm after turn-off, the complementary switches in each arm of the secondary circuit are turned on after a corresponding dead time. This ensures that each switch in the secondary circuit only experiences reverse current flow during the dead time, thus reducing conduction losses. Furthermore, each delay time is determined based on the input and / or output electrical parameters of the bidirectional resonant DC-DC converter and the required gain. Therefore, even when the switching frequency is set higher than the resonant frequency, the required gain can still be achieved. This reduces the frequency adjustment range in wide-voltage output applications and significantly improves the switching frequency.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, and in particular to a control method and control circuit for a bidirectional resonant DC-DC converter. Background Technology

[0002] With the development trend of energy interconnection, energy interaction between different energy storage systems has become commonplace. Among these, the demand for bidirectional DC-DC power conversion is gradually being met by users and the market. To ensure safety, isolation systems are typically used between different energy systems, such as bidirectional vehicle power supplies and bidirectional charging stations. Commonly used bidirectional DC-DC converters are mostly DAB (Dual Active Bridge) and CLLC topologies. The DAB topology controls gain and power through phase shifting, but its soft-switching range is limited, resulting in high switching losses when the battery voltage range is wide. The CLLC topology, on the other hand, is a resonant topology that achieves gain and power control through frequency modulation, resulting in higher efficiency.

[0003] However, in existing CLLC resonant converters, the secondary-side switches operate in synchronous rectification mode. If a wide range of voltage gain is required, this results in a large adjustment range for the switching frequency. In addition, with the development of devices, the application of SiC (silicon carbide) and GaN (gallium nitride) devices is gradually increasing. When these devices are reverse-flowing current, if the drive is not turned on, a turn-on voltage of 3V or even higher will be generated. At the same time, as the switching frequency increases, the proportion of reverse current flow time in the entire switching cycle increases, which will generate greater conduction losses in synchronous rectification applications, increase the difficulty of device heat dissipation, and lead to a decrease in system power.

[0004] Therefore, developing a control scheme to improve the above-mentioned technical problems has become an urgent need. Summary of the Invention

[0005] In view of this, this application provides a control method and control circuit for a bidirectional resonant DC-DC converter, which reduces the adjustment range of the switching frequency and reduces conduction losses while achieving a wide range of voltage gain.

[0006] To achieve the above objectives, this application provides the following technical solution:

[0007] The first aspect of this application provides a control method for a bidirectional resonant DC-DC converter. The bidirectional resonant DC-DC converter includes: a transformer, a primary circuit, a secondary circuit, and a resonant cavity disposed between the transformer and the primary circuit and / or the secondary circuit; both the primary circuit and the secondary circuit are single-phase full-bridge circuits, and each switch in the single-phase full-bridge circuit has an anti-parallel diode or a body diode; the control method includes:

[0008] Obtain the input electrical parameters and / or output electrical parameters of the bidirectional resonant DC-DC converter;

[0009] The delay time of each bridge arm in the secondary circuit is determined based on the input electrical parameters and / or output electrical parameters and the required gain of the bidirectional resonant DC-DC converter.

[0010] Based on the input electrical parameters and / or output electrical parameters and a preset reference signal, the switching frequencies of the primary circuit and the secondary circuit are set to be greater than the resonant frequency of the resonant cavity;

[0011] When the secondary resonant current of the bidirectional resonant DC-DC converter crosses zero, starting from the zero-crossing moment, the corresponding switching transistors in the secondary circuit are turned off after each of the aforementioned delay times; then, after the dead time, the complementary switching transistors in the secondary circuit are turned on.

[0012] Optionally, all the aforementioned delay times are equal and less than a preset value, so that each switch in the corresponding bridge arm of the secondary circuit remains turned on with zero voltage; or,

[0013] When the required gain of the bidirectional resonant DC-DC converter is greater than 1, the delay times are not equal.

[0014] Optionally, when the delay times are not equal, there exists a delay time that varies in the same direction as the required gain of the bidirectional resonant DC-DC converter.

[0015] Optionally, after setting the switching frequencies of the primary-side circuit and the secondary-side circuit to be greater than the resonant frequency of the resonant cavity, the method further includes:

[0016] The drive control signal for the primary circuit is generated and output according to the switching frequency.

[0017] Optionally, in the single-phase full-bridge circuit, the switching transistors of the two halves of the same bridge arm are complementary in conduction.

[0018] In the primary circuit, the switching transistors of different half-bridge arms in different bridge arms operate in the same way.

[0019] Optionally, the input electrical parameters and / or output electrical parameters include at least one of the following: input current, input voltage, output current, and output voltage.

[0020] A second aspect of this application provides a control circuit for a bidirectional resonant DC-DC converter. The bidirectional resonant DC-DC converter includes: a transformer, a primary circuit, a secondary circuit, and a resonant cavity disposed between the transformer and the primary circuit and / or the secondary circuit; both the primary circuit and the secondary circuit are single-phase full-bridge circuits, and each switch in the single-phase full-bridge circuit has an anti-parallel diode or a body diode; the control circuit includes: a primary-side drive circuit, a secondary-side drive circuit, a zero-crossing detection circuit, a control module, and an input sampling circuit and / or an output sampling circuit; wherein...

[0021] The input sampling circuit is used to sample the input electrical parameters of the bidirectional resonant DC-DC converter, and the output sampling circuit is used to sample the output electrical parameters of the bidirectional resonant DC-DC converter.

[0022] The zero-crossing detection circuit is used to detect whether the current in the resonant cavity crosses zero and to generate a zero-crossing signal;

[0023] The control module is used to receive the zero-crossing signal and the input electrical parameters and / or the output electrical parameters, execute the control method of the bidirectional resonant DC-DC converter as described in any of the first aspects above, and control the operation of each switch in the primary-side circuit through the primary-side drive circuit, and control the operation of each switch in the secondary-side circuit through the secondary-side drive circuit.

[0024] Optionally, when the zero-crossing detection circuit is used to detect whether the current in the resonant cavity has crossed zero, it is specifically used for:

[0025] Detect whether the secondary resonant current and / or primary resonant current of the bidirectional resonant DC-DC converter cross zero.

[0026] Optionally, the input sampling circuit is used to sample the input current and input voltage on the DC side of the primary circuit;

[0027] The output sampling circuit is used to sample the output current and output voltage on the DC side of the secondary circuit.

[0028] Optionally, the resonant cavity includes: at least one resonant inductor module and at least one resonant capacitor module;

[0029] When the number of resonant inductor modules and resonant capacitor modules is 1, they are respectively set on the primary and secondary sides of the transformer, or both are set on the same side of the transformer.

[0030] When the number of resonant inductor modules is greater than 1, each resonant inductor module is respectively located on the primary and secondary sides of the transformer; when the number of resonant capacitor modules is greater than 1, each resonant capacitor module is respectively located on the primary and secondary sides of the transformer.

[0031] The control method for the bidirectional resonant DC-DC converter provided in this application, after detecting the commutation of the secondary resonant current, controls the corresponding switches in each arm of the secondary circuit to delay for a certain period of time before turning them off. Since the current is commutated to the anti-parallel diode or body diode of the complementary switch in the same arm after the turn-off, the complementary switches in each arm of the secondary circuit are then turned on after a corresponding dead time. This ensures that each switch in the secondary circuit only has the condition of reverse current flow during the dead time, which greatly reduces the conduction loss. Moreover, the delay time of each arm of the secondary circuit is determined based on the input electrical parameters and / or output electrical parameters of the bidirectional resonant DC-DC converter and the required gain. Therefore, even if the switching frequency of the primary and secondary circuits is set to be greater than the resonant frequency of the resonant cavity, the required gain of the bidirectional resonant DC-DC converter can still be achieved. This can further reduce the frequency adjustment range in wide voltage output applications and has a significant effect on improving the switching frequency. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0033] Figure 1 A schematic diagram of the structure of the bidirectional resonant DC-DC converter and its control circuit provided in the embodiments of this application;

[0034] Figure 2a A schematic diagram of a resonant cavity provided in an embodiment of this application;

[0035] Figure 2b A schematic diagram of another resonant cavity structure provided in an embodiment of this application;

[0036] Figure 2c A schematic diagram of another resonant cavity structure provided in an embodiment of this application;

[0037] Figure 2d A schematic diagram of another resonant cavity structure provided in an embodiment of this application;

[0038] Figure 2e A schematic diagram of another resonant cavity structure provided in an embodiment of this application;

[0039] Figure 3 A schematic diagram of a specific circuit of a bidirectional resonant DC-DC converter and a control circuit of the bidirectional resonant DC-DC converter provided in the embodiments of this application;

[0040] Figure 4 A flowchart illustrating the control method for a bidirectional resonant DC-DC converter provided in this application embodiment;

[0041] Figure 5 The signal waveform diagram is shown for the control method of the bidirectional resonant DC-DC converter provided in the embodiments of this application. Detailed Implementation

[0042] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] In this application, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0044] This application provides a control method for a bidirectional resonant DC-DC converter to reduce the adjustment range of the switching frequency and reduce conduction losses while achieving a wide range of voltage gain.

[0045] This bidirectional resonant DC-DC converter, such as Figure 1 As shown, it includes: a transformer T, a primary circuit 101, a secondary circuit 102, and a resonant cavity 103 disposed between the transformer T and the primary circuit 101 and / or the secondary circuit 102; Figure 1 Taking the example of a resonant cavity 103 positioned between transformer T and primary circuit 101, in practical applications, the resonant cavity 103 can also be positioned between transformer T and secondary circuit 102, or the resonant elements in the resonant cavity 103 can be positioned on both sides of transformer T. Specifically, the resonant cavity 103 includes at least one resonant inductor module and at least one resonant capacitor module; moreover, when the number of resonant inductor modules Lr and resonant capacitor modules Cr is both 1, they are respectively positioned on the primary and secondary sides of transformer T (e.g., ...). Figure 2a (as shown), or, both are located on the same side of transformer T (e.g. Figure 2b (as shown); when the number of resonant inductor modules is greater than 1, each resonant inductor module is respectively set on the primary and secondary sides of transformer T (as shown). Figure 2c , Figure 2d and Figure 2e (as shown in Lrp and Lrs); when the number of resonant capacitor modules is greater than 1, each resonant capacitor module is respectively set on the primary and secondary sides of transformer T (e.g., Lrp and Lrs); Figure 2e and Figure 3 The cases shown (Crp and Crs) in the resonant cavity 103, which include two resonant capacitor modules Crp and Crs and a resonant inductor module Lrs located on the secondary side, are not illustrated, but are all within the scope of protection of this application. Furthermore, both the primary-side circuit 101 and the secondary-side circuit 102 are single-phase full-bridge circuits, such as... Figure 3 As shown, each switch in both single-phase full-bridge circuits is equipped with an anti-parallel diode or a body diode. That is, this bidirectional resonant DC-DC converter can be a CLLC, LLC, or SRC type single-phase resonant converter in the prior art. Its specific structure and connection relationship can be found in the prior art, and will not be described in detail here.

[0046] Regardless of the topology used in the bidirectional resonant DC-DC converter, its control method can be found in [reference needed]. Figure 4 Specifically, it includes:

[0047] S101. Obtain the input electrical parameters and / or output electrical parameters of the bidirectional resonant DC-DC converter.

[0048] The input electrical parameters and / or output electrical parameters may specifically include at least one of the following: input current, input voltage, output current, and output voltage of the bidirectional resonant DC-DC converter. In practical applications, this can be specifically achieved through… Figure 1 The input sampling circuit 203 shown samples the input current and input voltage of the DC side of the primary circuit 101, which is also the input current and input voltage of the bidirectional resonant DC-DC converter; and samples the output current and output voltage of the DC side of the secondary circuit 102 through the output sampling circuit 204, which is also the output current and output voltage of the bidirectional resonant DC-DC converter.

[0049] The input sampling circuit 203 and the output sampling circuit 204 respectively transmit the sampled signals obtained by them to the control module 201. The control module 201 can obtain the input current, input voltage, output current and output voltage of the bidirectional resonant DC-DC converter based on them.

[0050] S102. Determine the delay time of each bridge arm in the secondary circuit based on the input electrical parameters and / or output electrical parameters and the required gain of the bidirectional resonant DC-DC converter.

[0051] In practical applications, the control module 201 can determine the delay times dt1 and dt2 of the two rectifier bridge arms in the secondary circuit based on one or more signals from the input electrical parameters and / or output electrical parameters. Moreover, the two delay times dt1 and dt2 can be equal or unequal, depending on the specific application environment, and all of them are within the protection scope of this application.

[0052] S103. Based on the input electrical parameters and / or output electrical parameters and the preset reference signal, set the switching frequency of the primary circuit and the secondary circuit to be greater than the resonant frequency of the resonant cavity.

[0053] When the switching frequencies of the primary circuit 101 and the secondary circuit 102 are less than the resonant frequency of the resonant cavity 103, the gain of the bidirectional resonant DC-DC converter is greater than 1; when the switching frequency is greater than the resonant frequency, the gain of the bidirectional resonant DC-DC converter is less than 1; if a wide range of voltage gain requirements are to be met, the adjustment range of the switching frequency in the prior art is relatively large.

[0054] In this embodiment, step S103 is performed by... Figure 1 The control module 201 limits the adjustment range of the switching frequency to above the resonant frequency based on the input electrical parameters and / or output electrical parameters and the internal preset reference signal. In step S102, it sets the corresponding delay times dt1 and dt2 for the two bridge arms in the secondary circuit 102, so that the bidirectional resonant DC-DC converter can achieve its required gain, thereby achieving a wide range of voltage gain with a small switching frequency adjustment range.

[0055] In practical applications, the order of steps S102 and S103 is not limited; they can be executed sequentially or simultaneously, depending on the specific application environment, and all are within the protection scope of this application.

[0056] After obtaining the switching frequency, the control module 201 can generate and output the drive control signal for the primary circuit 101 based on the switching frequency, and then... Figure 1 The primary-side drive circuit 205 drives the primary-side circuit 101. Simultaneously, the control module 201 can generate and output drive control signals for the secondary-side circuit 102 based on the switching frequency and two delay times dt1 and dt2, and then... Figure 1 The secondary-side drive circuit 206 drives the secondary-side circuit 102; the specific control process of the control module 201 for the secondary-side circuit 102 is also step S104.

[0057] S104. When the secondary resonant current of the bidirectional resonant DC-DC converter crosses zero, starting from the zero-crossing moment, the corresponding switching transistors in the secondary circuit are turned off after each delay time; then, after the dead time, the complementary switching transistors in the secondary circuit are turned on.

[0058] Specifically, it can be done through Figure 1 The zero-crossing detection circuit 202 shown detects the primary resonant current Ip and / or the secondary resonant current Is of the bidirectional resonant DC-DC converter. The control module 201 determines whether the secondary resonant current Is has crossed zero based on the detection result of the zero-crossing detection circuit 202. In practical applications, if the magnetizing inductance of the transformer T is very large, the zero-crossing positions of the primary and secondary resonant currents Ip and Is are very close. In this case, a corresponding detection circuit can be set on only one side of the transformer T for zero-crossing detection, saving costs. Preferably, only the secondary resonant current Is is subjected to zero-crossing detection.

[0059] For the resonant DC-DC converters of the above-mentioned topologies, as long as the secondary resonant current crosses zero, unlike the synchronous rectification control of the secondary circuit in the prior art, this embodiment sets the turn-off time of the switch transistor in the secondary circuit that is about to be turned off to: the time after the corresponding delay time starting from the zero-crossing time, and then after the dead time after the turn-off time, controls the corresponding complementary switches in the secondary circuit to turn on.

[0060] by Figure 3 Taking the CLLC-type single-phase resonant converter as an example, both the primary circuit 101 and the secondary circuit 102 are single-phase full-bridge circuits. In these two single-phase full-bridge circuits, the switches of the two halves of the same bridge arm are complementary in conduction; moreover, the switches of the halves of the bridge arms at different positions in different arms of the primary circuit 101 operate in the same way. Specifically, the primary circuit 101 includes a first bridge arm and a second bridge arm connected in parallel; the first bridge arm is composed of a first switch S1 and a second switch S2 connected in series, with complementary drives of 50%; the second bridge arm is composed of a third switch S3 and a fourth switch S4 connected in series, with complementary drives of 50%; at the same time, the drive signals of the first switch S1 and the third switch S3 are the same. There is a first node A between the first switch S1 and the second switch S2, and a second node B between the third switch S3 and the fourth switch S4. The resonant elements (Lrp and Crp) on the primary side and the primary winding of the transformer T are connected between the two nodes. The secondary circuit 102 includes a third and a fourth bridge arm connected in parallel. The third bridge arm consists of a fifth switch S5 and a sixth switch S6 connected in series, with complementary driving forces of 50%. The fourth bridge arm consists of a seventh switch S7 and an eighth switch S8 connected in series, with complementary driving forces of 50%. A third node C is located between the fifth switch S5 and the sixth switch S6, and a fourth node D is located between the seventh switch S7 and the eighth switch S8. The resonant element (Crs) on the secondary side and the secondary winding of the transformer T are connected between the two nodes.

[0061] When the zero-crossing detection circuit 202 detects that the secondary resonant current crosses zero, a zero-crossing signal is generated and transmitted to the control module 201. Then, the control module 201 uses the zero-crossing moment as the starting point of the delay, and delays for two corresponding delay times dt1 and dt2 respectively. The drive signals are sent to the third and fourth arms of the secondary circuit 102 through the secondary drive circuit 206. The delay times dt1 and dt2 can be equal or unequal.

[0062] As Figure 5 shown, the switching tubes of the two arms in the primary circuit 101 act at the moment t0, and the secondary resonant current Is is detected to cross zero at the moment t1. After delaying for a delay time dt1 to the moment t2, the seventh switching tube S7 and the eighth switching tube S8 of the fourth arm act. After delaying for a delay time dt2 to the moment t3, the fifth switching tube S5 and the sixth switching tube S6 of the third arm act. Among them, t2 - t1 = dt1, and t3 - t1 = dt2.

[0063] When the switching frequency of the resonant cavity 103 is greater than the resonant frequency, the gain is less than 1. If the required output gain of the bidirectional resonant DC converter is less than 1, the two delay times dt1 and dt2 can be made equal. Moreover, both of the two delay times dt1 and dt2 are less than a first preset value, so that each switching tube in the corresponding arm of the secondary circuit 102 can be turned on with zero voltage. In addition, to ensure that each switching tube in the corresponding arm of the primary circuit 101 can also be turned on with zero voltage, and at the same time reduce the turn-off loss of each switching tube in the corresponding arm of the secondary circuit 102 (that is, the fourth arm), this first preset value is generally less than 1 us, and its specific value is not limited and can be determined according to its specific application environment.

[0064] If the required output gain of the bidirectional resonant DC converter is greater than 1, the two delay times dt1 and dt2 can be made unequal. Moreover, when the two delay times dt1 and dt2 are unequal, optionally, dt1 < dt2 can be set. Among them, the delay time dt2 of the third arm changes in the same direction as the gain required by the bidirectional resonant DC converter. In practical applications, to ensure that the gain of this bidirectional resonant DC converter can increase monotonically with the increase of the delay time dt2, the delay time dt2 can be set to be less than 1 / 4 of the switching period. And the delay time dt1 of the fourth arm is less than a second preset value, that is, the delay time dt1 is as small as possible, with the primary condition of realizing soft switching of the fourth arm. In addition, to ensure that each switching tube in the corresponding arm of the primary circuit 101 can be turned on with zero voltage, and at the same time reduce the turn-off loss of each switching tube in the corresponding arm (that is, the fourth arm) of the secondary circuit 102, this second preset value is generally less than 1 us, and its specific value is not limited and can be determined according to its specific application environment.

[0065] It should be noted that in practical applications, the delay time dt1 of the fourth bridge arm can be set to vary in the same direction as the required gain of the bidirectional resonant DC-DC converter; while the delay time dt2 of the third bridge arm can be as small as possible, as long as it can achieve soft switching of the third bridge arm. That is, when the two delay times dt1 and dt2 are not equal, as long as one delay time is used to meet the gain requirement, the other delay time only needs to achieve soft switching of the corresponding bridge arm; how to set the two delay times depends on the application environment, and all are within the scope of protection of this application.

[0066] pass Figure 5 As can be seen, since the switching frequency is greater than the resonant frequency, the phase of the resonant current lags behind the phase of the voltage. Therefore, when the first and second bridge arms in the primary circuit 101 are operating, the primary resonant current Ip has not yet crossed zero (at time t0). At this time, after the second switch S2 is driven to turn off, the primary resonant current Ip is switched from the second switch S2 to the first switch S1, with the current direction from the first node A to the other end of the first switch S1. At this time, the first switch S1 is driven to turn on, realizing zero-voltage turn-on of the first switch S1, that is, soft switching is achieved. The soft switching of other switches in the primary circuit 101 is implemented in the same way as the first switch S1. For the secondary circuit 102, when the fourth bridge arm operates (at time t2), the secondary resonant current Is has already completed its commutation at time t1. The direction of the secondary resonant current Is is from the other end of the eighth switch S8 to the fourth node D. At time t2, the drive of the eighth switch S8 is turned off, and the secondary resonant current Is commutates to the seventh switch S7. The current flow changes to from the other end of the seventh switch S7 to the fourth node D. At this time, the drive of the seventh switch S7 is turned on, realizing zero-voltage turn-on of the seventh switch S7, that is, realizing soft switching. The soft switching of the eighth switch S8 is the same as that of the seventh switch S7. When the third bridge arm operates (at time t3), the secondary resonant current Is is larger than that at time t2. Other than that, it is exactly the same as the fourth bridge arm, so it is easier to realize soft switching.

[0067] As can be seen from the above analysis, the reverse current flow process of the primary and secondary switching transistors only occurs during the dead time when the complementary switching transistor is turned off and the self-drive is not turned on. During other current flow times, the drive is in the on state. Therefore, the reverse current flow process when the drive is not turned on is limited to the dead time. In practical applications, by reasonably controlling the dead time, the reverse current flow time when the drive is not turned on can be controlled, thereby reducing the reverse conduction voltage drop and reducing conduction losses.

[0068] The control method for the bidirectional resonant DC-DC converter provided in this embodiment, after detecting the commutation of the secondary resonant current, controls the corresponding switches in each arm of the secondary circuit to delay for a certain period of time before turning them off. Since the current commutates to the anti-parallel diode or body diode of the complementary switch in the same arm after the turn-off, the complementary switches in each arm of the secondary circuit are then turned on after a corresponding dead time. This ensures that each switch in the secondary circuit only has the condition of reverse current flow during the dead time, which greatly reduces the conduction loss. Moreover, the delay time of each arm of the secondary circuit is determined based on the input electrical parameters and / or output electrical parameters of the bidirectional resonant DC-DC converter and the required gain. Therefore, even if the switching frequency of the primary and secondary circuits is set to be greater than the resonant frequency of the resonant cavity, the required gain of the bidirectional resonant DC-DC converter can still be achieved. This can reduce the frequency adjustment range in wide voltage output applications and has a significant effect on improving the switching frequency. In addition, since the resonance can achieve soft switching, it can effectively reduce switching losses and further improve the frequency and system efficiency.

[0069] It is worth noting that the above control method applies to the bidirectional resonant DC-DC converter when power is transferred from the primary side to the secondary side. When power is transferred from the secondary side to the primary side, the implementation method is the same as when power is transferred from the primary side to the secondary side. It can be regarded as simply swapping the names of the primary and secondary sides, that is, naming the power input side as the primary side and the power output side as the secondary side, and then using the above control method. It will not be elaborated here, and all of them are within the protection scope of this application.

[0070] Another embodiment of this application also provides a control circuit for a bidirectional resonant DC-DC converter, such as... Figure 1 and Figure 3 As shown in the figure, at this time, the bidirectional resonant DC-DC converter includes: a transformer T, a primary circuit 101, a secondary circuit 102, and a resonant cavity 103 disposed between the transformer T and the primary circuit 101 and / or the secondary circuit 102. Figure 1 The example shown is that the resonant cavity 103 is located between the transformer T and the primary circuit 101. In practical applications, the resonant cavity 103 can also be located between the transformer T and the secondary circuit 102, or each resonant element in the resonant cavity 103 can be located on both sides of the transformer T.

[0071] Specifically, the resonant cavity 103 includes at least one resonant inductor module and at least one resonant capacitor module; moreover, when the number of resonant inductor modules Lr and resonant capacitor modules Cr is both 1, they are respectively disposed on the primary and secondary sides of the transformer T (e.g., Figure 2a (as shown), or, both are located on the same side of transformer T (e.g. Figure 2b(as shown); when the number of resonant inductor modules is greater than 1, each resonant inductor module is respectively set on the primary and secondary sides of transformer T (as shown). Figure 2c , Figure 2d and Figure 2e (as shown in Lrp and Lrs); when the number of resonant capacitor modules is greater than 1, each resonant capacitor module is respectively set on the primary and secondary sides of transformer T (e.g., Lrp and Lrs); Figure 2e and Figure 3 The resonant cavity 103 includes two resonant capacitor modules (Crp and Crs) and a resonant inductor module (Lrs) located on the secondary side, but these are not shown in the illustrations; however, they are all within the scope of protection of this application. In practical applications, the number and position of the resonant inductor module and the resonant capacitor module can be varied according to circuit requirements; moreover, the resonant inductor module is generally implemented using a single inductor, but the implementation of multiple inductors connected in series and parallel is not excluded; the resonant capacitor module can be implemented using a single capacitor or multiple capacitors connected in series and parallel, depending on the specific application environment, and all are within the scope of protection of this application. Figure 2b and Figure 2e Taking the example shown, the relationship between the parameters under the two structures is as follows:

[0072] Where Np is the number of turns in the primary winding of transformer T, and Ns is the number of turns in the secondary winding of transformer T.

[0073] The formula for calculating the resonant frequency fr is:

[0074] Moreover, both the primary circuit 101 and the secondary circuit 102 are single-phase full-bridge circuits, such as Figure 3 As shown, each switch in the two single-phase full-bridge circuits is equipped with an anti-parallel diode or a body diode.

[0075] That is, the bidirectional resonant DC-DC converter can be a single-phase resonant converter of the CLLC, LLC and SRC types in the prior art. Its specific structure and connection relationship can be found in the prior art, and will not be described in detail here.

[0076] Regardless of the topology used in this bidirectional resonant DC-DC converter, see [link to relevant documentation]. Figure 1 and Figure 3 The control circuits all include: a primary-side drive circuit 205, a secondary-side drive circuit 206, a zero-crossing detection circuit 202, a control module 201, and an input sampling circuit 203 and / or an output sampling circuit 204. Figure 1 and Figure 3 (The examples shown will include both).

[0077] The input sampling circuit 203 is used to sample the input electrical parameters of the bidirectional resonant DC-DC converter; the output sampling circuit 204 is used to sample the output electrical parameters of the bidirectional resonant DC-DC converter. Specifically, the input sampling circuit 203 is located on the DC side of the primary circuit 101, and its output terminal is connected to one input terminal of the control module 201. The input sampling circuit 203 is specifically used to sample the input current and input voltage of the bidirectional resonant DC-DC converter. The output sampling circuit 204 is located on the DC side of the secondary circuit 102, and its output terminal is connected to the other input terminal of the control module 201. The output sampling circuit 204 is specifically used to sample the output current and output voltage of the bidirectional resonant DC-DC converter.

[0078] The zero-crossing detection circuit 202 is used to detect whether the current in the resonant cavity 103 has crossed zero. When the zero-crossing information indicates that the secondary resonant current Is of the bidirectional resonant DC-DC converter has crossed zero, it generates a zero-crossing signal and outputs it to the corresponding input terminal of the control module 201. Since both the primary resonant current Ip and the secondary resonant current Is can indicate that the secondary resonant current Is has crossed zero, the zero-crossing detection circuit 202 can specifically detect whether the current in the resonant cavity 103 has crossed zero by detecting whether the secondary resonant current Is and / or the primary resonant current Ip of the bidirectional resonant DC-DC converter has crossed zero. That is, in practical applications, the zero-crossing detection circuit 202 can determine the delay start point of each bridge arm in the secondary circuit 102 by detecting the zero-crossing status of the primary resonant current Ip and / or the secondary resonant current Is. Moreover, if the magnetizing inductance of the transformer T is very large and the difference between the zero-crossing positions of the primary and secondary resonant currents is very small, the corresponding detection circuit can be set on only one side of the transformer T for zero-crossing detection, saving costs. It is preferable to perform zero-crossing detection on the secondary resonant current Is. When the control module 201 adopts the control method provided in the above embodiment, the switching frequency is greater than the resonant frequency under various output gain requirements. That is, the bidirectional resonant DC converter is working in the over-resonance state. The magnetizing inductance of its converter T does not participate in the work, so the magnetizing inductance can be very large, which makes it convenient for the zero-crossing detection circuit 202 to realize the above-mentioned zero-crossing detection at low cost.

[0079] The control module 201 receives the zero-crossing signal and the input electrical parameters and / or output electrical parameters, executes the control method for the bidirectional resonant DC-DC converter as described in any of the above embodiments, and controls the operation of each switch in the primary-side circuit 101 through the primary-side drive circuit 205, and controls the operation of each switch in the secondary-side circuit 102 through the secondary-side drive circuit 206. The specific process and principle of this control method can be found in the above embodiments, and will not be repeated here.

[0080] To implement this control method, the functions of each module in the control circuit are as follows:

[0081] (1) The input sampling circuit 203 and the output sampling circuit 204 sample the input and output voltage and current of the bidirectional resonant DC-DC converter, and transmit the sampled signals to the control module 201 so that the control module 201 can obtain the above-mentioned input electrical parameters and / or output electrical parameters.

[0082] (2) The control module 201 determines the delay times dt1 and dt2 of the two bridge arms on the secondary side according to one or more signals of the above input electrical parameters and / or output electrical parameters.

[0083] (3) The control module 201 generates the switching frequency of the primary and secondary circuits based on the above-mentioned input electrical parameters and / or output electrical parameters and the internal preset reference signal. Each switch of the primary circuit 101 will operate directly according to the switching frequency generated by the control module 201.

[0084] (4) The zero-crossing detection circuit 202 detects the primary resonant current Ip and / or the secondary resonant current Is, preferably the secondary rectified current (i.e. the secondary resonant current Is). When it detects that the secondary resonant current is crossing zero, the zero-crossing detection circuit 202 outputs a zero-crossing signal to the control module 201, so that the control module 201 can determine that the secondary resonant current Is has crossed zero and obtain its zero-crossing time.

[0085] (5) After receiving the zero-crossing signal, the control module 201 delays for two time intervals dt1 and dt2 respectively, and outputs the drive control signal to control the movement of the fourth and third bridge arms.

[0086] (6) The control module 201 generates drive control signals for the primary circuit 101 and the secondary circuit 102 respectively. The drive control signal of the primary circuit 101 is generated into a drive signal of the primary circuit 101 by the primary drive circuit 205, which is used to control the operation of each switch of the primary circuit 101. The drive control signal of the secondary circuit 102 is generated into a drive signal of the secondary circuit 102 by the secondary drive circuit 206, which is used to control the operation of each switch of the secondary circuit 102.

[0087] The control circuit provided in this embodiment achieves soft switching of the secondary-side switching transistor by performing resonance zero-crossing detection on the bidirectional resonant DC-DC converter and combining it with delay time control. Compared with traditional synchronous rectification control, it effectively reduces the duration of reverse current flow when the drive is not turned on, and has a significant efficiency advantage in synchronous rectification applications of SiC and GaN devices. At the same time, by controlling the delay time, the output voltage gain is changed, thereby reducing the frequency adjustment range in wide voltage output applications, which has a significant effect on improving the switching frequency.

[0088] Similar or identical parts between the various embodiments in this specification can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, for system or system embodiments, since they are basically similar to method embodiments, the description is relatively simple, and relevant parts can be referred to the description of the method embodiments. The systems and system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment solution according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0089] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0090] The features described above regarding the disclosed embodiments can be substituted for or combined with each other to enable those skilled in the art to implement or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A control method for a bidirectional resonant DC-DC converter, characterized in that, A bidirectional resonant DC-DC converter includes: a transformer, a primary circuit, a secondary circuit, and a resonant cavity disposed between the transformer and the primary circuit and / or the secondary circuit; both the primary circuit and the secondary circuit are single-phase full-bridge circuits, and each switch in the single-phase full-bridge circuit has an anti-parallel diode or a body diode; the control method includes: Obtain the input electrical parameters and / or output electrical parameters of the bidirectional resonant DC-DC converter; The delay time of each bridge arm in the secondary circuit is determined based on the input electrical parameters and / or output electrical parameters and the required gain of the bidirectional resonant DC-DC converter. Based on the input electrical parameters and / or output electrical parameters and a preset reference signal, the switching frequencies of the primary circuit and the secondary circuit are set to be greater than the resonant frequency of the resonant cavity; When the secondary resonant current of the bidirectional resonant DC-DC converter crosses zero, starting from the zero-crossing moment, the corresponding switching transistors in the secondary circuit are turned off after each of the aforementioned delay times; then, after the dead time, the complementary switching transistors in the secondary circuit are turned on.

2. The control method for a bidirectional resonant DC-DC converter according to claim 1, characterized in that, All the aforementioned delay times are equal and less than a preset value, so that each switch in the corresponding bridge arm of the secondary circuit remains turned on with zero voltage; or, When the required gain of the bidirectional resonant DC-DC converter is greater than 1, the delay times are not equal.

3. The control method for a bidirectional resonant DC-DC converter according to claim 2, characterized in that, When the delay times are not equal, there exists a delay time that changes in the same direction as the required gain of the bidirectional resonant DC-DC converter.

4. The control method for a bidirectional resonant DC-DC converter according to any one of claims 1 to 3, characterized in that, After setting the switching frequencies of the primary and secondary circuits to be greater than the resonant frequency of the resonant cavity, the method further includes: The drive control signal for the primary circuit is generated and output according to the switching frequency.

5. The control method for a bidirectional resonant DC-DC converter according to any one of claims 1 to 3, characterized in that, In the single-phase full-bridge circuit, the switching transistors of the two halves of the same bridge arm conduct complementaryly. In the primary circuit, the switching transistors of different half-bridge arms in different bridge arms operate in the same way.

6. The control method for a bidirectional resonant DC-DC converter according to any one of claims 1 to 3, characterized in that, The input electrical parameters and / or output electrical parameters include at least one of the following: input current, input voltage, output current, and output voltage.

7. A control circuit for a bidirectional resonant DC-DC converter, characterized in that, A bidirectional resonant DC-DC converter includes: a transformer, a primary circuit, a secondary circuit, and a resonant cavity disposed between the transformer and the primary circuit and / or the secondary circuit; both the primary circuit and the secondary circuit are single-phase full-bridge circuits, and each switch in the single-phase full-bridge circuit has an anti-parallel diode or a body diode; the control circuit includes: a primary-side drive circuit, a secondary-side drive circuit, a zero-crossing detection circuit, a control module, and an input sampling circuit and / or an output sampling circuit; wherein... The input sampling circuit is used to sample the input electrical parameters of the bidirectional resonant DC-DC converter, and the output sampling circuit is used to sample the output electrical parameters of the bidirectional resonant DC-DC converter. The zero-crossing detection circuit is used to detect whether the current in the resonant cavity crosses zero and to generate a zero-crossing signal; The control module is used to receive the zero-crossing signal and the input electrical parameters and / or the output electrical parameters, execute the control method of the bidirectional resonant DC-DC converter as described in any one of claims 1 to 6, and control the operation of each switch in the primary-side circuit through the primary-side drive circuit, and control the operation of each switch in the secondary-side circuit through the secondary-side drive circuit.

8. The control circuit of the bidirectional resonant DC-DC converter according to claim 7, characterized in that, The zero-crossing detection circuit is used to detect whether the current in the resonant cavity has crossed zero, specifically for: Detect whether the secondary resonant current and / or primary resonant current of the bidirectional resonant DC-DC converter cross zero.

9. The control circuit of the bidirectional resonant DC-DC converter according to claim 7, characterized in that, The input sampling circuit is used to sample the input current and input voltage on the DC side of the primary circuit; The output sampling circuit is used to sample the output current and output voltage on the DC side of the secondary circuit.

10. The control circuit of the bidirectional resonant DC-DC converter according to any one of claims 7 to 9, characterized in that, The resonant cavity includes: at least one resonant inductor module and at least one resonant capacitor module; When the number of resonant inductor modules and resonant capacitor modules is 1, they are respectively set on the primary and secondary sides of the transformer, or both are set on the same side of the transformer. When the number of resonant inductor modules is greater than 1, each resonant inductor module is respectively located on the primary and secondary sides of the transformer; when the number of resonant capacitor modules is greater than 1, each resonant capacitor module is respectively located on the primary and secondary sides of the transformer.

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