A resonant converter and a resonant converter control method

Abstract

The application discloses a resonant converter and a resonant converter control method. The resonant converter comprises a resonant cavity, a first circuit electrically connected with a first end of the resonant cavity, and a second circuit electrically connected with a second end of the resonant cavity. The resonant cavity comprises a transformer, and the transformer is electrically connected with the resonant cavity. The first circuit comprises at least one primary side switch, and the second circuit comprises at least one controllable switch. An initial secondary side switching frequency is set, the at least one controllable switch is controlled according to the initial secondary side switching frequency, so that the second circuit generates power. The secondary side switching frequency of the at least one controllable switch is adjusted according to the set initial secondary side switching frequency and a signal reflecting the power of the second circuit, so that the secondary side switching frequency of the second circuit tracks the primary side switching frequency of the first circuit. The application realizes the communication control between the primary side and the secondary side of the resonant converter through sampling the output voltage for switching frequency tracking and output voltage control.

Description

Technical Field

[0001] This invention relates to the field of power electronic converter technology, and more specifically to a resonant converter and a resonant converter control method. Background Technology

[0002] Resonant converters (LLCs) are applied to solid-state transformers (SSTs) and have broad application prospects in DC power consumption or generation fields such as data centers, electric vehicle charging and swapping stations, photovoltaics, and energy storage. In these applications, the input of an SST is medium-voltage AC (MVAC), and the output is low-voltage DC (LVDC), generally requiring a wide output voltage range. Furthermore, an SST can include multiple phases, each phase including multiple cascaded power modules. Each power module can include a front-end AC-DC converter and a back-end DC-DC converter. In the DC-DC converter of an SST, the primary side (medium voltage side) and the secondary side (low voltage side) are isolated by a high-frequency transformer insulation plate. However, existing primary and secondary fiber optic communication connections are complex and inconvenient to operate. Moreover, as the number of power modules per phase increases, the number of optical fibers required in the back-end increases. Since existing product solutions have extremely high reliability requirements for fiber optic communication, a communication failure can easily cause system downtime. In addition, LLCs rely solely on frequency and voltage modulation, making voltage boosting difficult, and the large switching frequency adjustment range affects efficiency.

[0003] To address the aforementioned issues, the first approach in existing technologies involves delaying the turn-on or turn-off of the secondary-side switch in the resonant converter to reduce the frequency regulation range of the frequency modulation boost converter. This approach is characterized by: the primary side adjusting the primary-side switching frequency through a closed-loop sampling of the output voltage; and the secondary side obtaining primary-side switching frequency synchronization information by sampling the zero-crossing point of the primary-side resonant current, and calculating the delay time of the secondary-side switch in an open-loop manner, thereby reducing the frequency regulation range to some extent. It is evident that this approach requires sampling the output voltage for primary-side frequency modulation and sampling the zero-crossing point of the primary-side resonant cavity current for secondary-side switch control, both relying on communication between the primary and secondary sides. When the system operates under light load, the requirements for current zero-crossing sampling are even higher, which is not conducive to control under full load variations. Furthermore, this approach only allows the secondary side to operate in a continuous current state; the delayed turn-off of the switch with current flowing will affect system efficiency. The second method uses an inductive power converter. This method is characterized by: semi-controlled rectification at the receiver; no communication between the transmitter and receiver; a fixed carrier frequency at the receiver (i.e., a fixed switching frequency); and closed-loop control of the output voltage to adjust the phase shift angle of the output-side switch. At the transmitter, phase shift control is achieved by locking the phase difference between the resonant cavity voltage and current, indirectly controlling the output voltage. As can be seen, the second method is similar to the first, requiring sampling the resonant cavity current to obtain switching frequency synchronization information. Furthermore, the receiver can only operate in a continuous current state, and the delayed turn-off of the switch with current will affect efficiency. Meanwhile, in the second method, the receiver's switching frequency is fixed, and output voltage control is achieved by adjusting the phase shift angle of the primary and secondary sides.

[0004] Existing technologies require sampling the current in the resonant cavity to obtain primary and secondary switching frequency synchronization information. When resonant cavity sampling is not required, only the output voltage is sampled on the secondary side, enabling communication-free operation between the primary and secondary sides of the LLC, which is of great significance for improving the reliability of the SST. Summary of the Invention

[0005] This invention provides a resonant converter and a resonant converter control method. By controlling the secondary-side switching frequency and phase shift angle through a closed-loop control of the output voltage of the resonant converter, the resonant converter can achieve efficient operation without communication between the primary and secondary sides.

[0006] To achieve the above objectives, the present invention discloses the following technical solution:

[0007] The present invention provides a resonant converter, the resonant converter including a resonant cavity, a first circuit electrically connected to a first end of the resonant cavity, and a second circuit electrically connected to a second end of the resonant cavity; the resonant cavity includes at least one transformer, the primary winding of the transformer being electrically connected to the first end of the resonant cavity, and the secondary winding of the transformer being electrically connected to the second end of the resonant cavity;

[0008] The first circuit includes at least one primary-side switch, and the second circuit includes at least one controllable switch. An initial secondary-side switching frequency is set, and at least one controllable switch is controlled according to the initial secondary-side switching frequency to generate power in the second circuit. The secondary-side switching frequency of the at least one controllable switch is adjusted according to the set initial secondary-side switching frequency and a signal reflecting the power of the second circuit to make the secondary-side switching frequency of the second circuit track the primary-side switching frequency of the first circuit.

[0009] The aforementioned resonant converter also includes a primary-side control module, which generates a drive signal for the primary-side switch based on the frequency signal of the primary-side switch.

[0010] In the aforementioned resonant converter, the primary-side control module includes a first carrier generation unit and a first PWM generation unit;

[0011] The first carrier generation unit generates a primary side triangular carrier according to the set primary side initial switching frequency;

[0012] The first PWM generation unit compares the primary-side triangular carrier generated by the first carrier generation unit with a set duty cycle to generate a drive signal for the primary-side switch. The frequency of the drive signal for the primary-side switch is the primary-side switch frequency.

[0013] The aforementioned resonant converter also includes a secondary-side control module, which includes a voltage comparison module, a regulator, a frequency comparison module, a limiter, and a second carrier generation module.

[0014] The output of the voltage comparison module is connected to the input of the frequency comparison module via the regulator, so as to compare the output voltage of the second circuit with the set reference output voltage, and the output first signal is transmitted to the frequency comparison module after adjustment.

[0015] The output of the frequency comparison module is connected to the input of the second carrier generation module via the limiter, so as to compare the signal frequency output by the regulator with the set initial switching frequency of the secondary side, and the output second signal is transmitted to the second carrier generation module after being limited.

[0016] The second carrier generation module is used to generate a drive signal for the controllable switch based on the signal output by the limiter. The frequency of the drive signal is the secondary-side switching frequency, which tracks the primary-side switching frequency.

[0017] In the aforementioned resonant converter, the second carrier generation module includes a second carrier generation unit and a second PWM generation unit;

[0018] The second carrier generation unit generates a secondary triangular carrier based on the signal frequency output by the limiter;

[0019] The second PWM generation unit compares the secondary triangular carrier generated by the second carrier generation unit with the set duty cycle to generate the drive signal for the controllable switch.

[0020] In the aforementioned resonant converter, the regulator is a proportional-integral regulator.

[0021] In the aforementioned resonant converter, the secondary-side control module is configured to: when the primary-side switching frequency is the same as the initial secondary-side switching frequency, the primary-side switch and the controllable switch operate synchronously; when the primary-side switching frequency is different from the controllable switch frequency, the output voltage of the secondary-side control module is used to adjust the secondary-side switching frequency of the controllable switch in a closed-loop manner, so that the secondary-side switching frequency automatically tracks the primary-side switching frequency, and the phase difference between at least one controllable switch and at least one primary-side switch is controlled to achieve output voltage stability.

[0022] In the aforementioned resonant converter, the primary-side switch includes a first switch, a second switch, a third switch, and a fourth switch. The first switch and the second switch are connected in series to form a first primary-side bridge arm, and the third switch and the fourth switch are connected in series to form a second primary-side bridge arm. The first primary-side bridge arm and the second primary-side bridge arm are connected in parallel, and the midpoints of the first primary-side bridge arm and the second primary-side bridge arm are respectively electrically connected to the first end of the resonant cavity.

[0023] In the aforementioned resonant converter, the first switch, the second switch, the third switch, and the fourth switch are all metal-oxide-semiconductor field-effect transistors.

[0024] In the aforementioned resonant converter, the controllable switch includes a first controllable switch transistor, a second controllable switch transistor, a third controllable switch transistor, and a fourth controllable switch transistor. The first and second controllable switch transistors are connected in series to form a first secondary side bridge arm, and the third and fourth controllable switch transistors are connected in series to form a second secondary side bridge arm. The first and second secondary side bridge arms are connected in parallel, and the midpoints of the first and second secondary side bridge arms are electrically connected to the second end of the resonant cavity, respectively.

[0025] In the aforementioned resonant converter, the first and third controllable switches are diodes, and the second and fourth controllable switches are metal-oxide-semiconductor field-effect transistors.

[0026] In the aforementioned resonant converter, the first and second controllable switching transistors are diodes, and the third and fourth controllable switching transistors are metal-oxide-semiconductor field-effect transistors.

[0027] In the aforementioned resonant converter, the controllable switch includes a fifth controllable switch transistor, a sixth controllable switch transistor, a seventh controllable switch transistor, and an eighth controllable switch transistor. The fifth, sixth, seventh, and eighth controllable switch transistors are connected in series to form a third secondary side bridge arm. The second circuit also includes a capacitor bridge arm formed by a first capacitor and a second capacitor connected in series. The third secondary side bridge arm is connected in parallel with the capacitor bridge arm. The midpoint of the third secondary side bridge arm is electrically connected to the midpoint of the capacitor bridge arm. The second end of the resonant cavity is electrically connected between the electrical connection points of the fifth and sixth controllable switch transistors and the electrical connection points of the seventh and eighth controllable switch transistors.

[0028] The resonant converter described above further includes a resonant capacitor, a resonant inductor, and a magnetizing inductor connected in series with the converter.

[0029] In the aforementioned resonant converter, the second circuit operates in discontinuous current mode.

[0030] Another aspect of the present invention provides a cascaded system comprising at least two cascaded power modules, each power module comprising an AC-DC converter and a DC-DC converter, wherein the DC-DC converter comprises the aforementioned resonant converter.

[0031] To better achieve the purpose of the invention, the present invention also provides a resonant converter control method. The control method is used in a resonant converter, which includes a resonant cavity, a first circuit electrically connected to a first end of the resonant cavity, and a second circuit electrically connected to a second end of the resonant cavity. The resonant cavity includes at least one transformer, the primary winding of which is electrically connected to the first end of the resonant cavity, and the secondary winding of which is electrically connected to the second end of the resonant cavity. The first circuit includes at least one primary-side switch, and the second circuit includes at least one controllable switch. The control method includes the following steps:

[0032] Set an initial switching frequency for the primary and secondary sides, and control at least one of the controllable switches according to the initial switching frequency for the secondary sides, so that the second circuit generates power;

[0033] The secondary-side switching frequency of at least one of the controllable switches is adjusted according to the set initial secondary-side switching frequency and the signal reflecting the power of the second circuit, so that the secondary-side switching frequency of the second circuit tracks the primary-side switching frequency of the first circuit.

[0034] The above-mentioned resonant converter control method further includes the following steps:

[0035] Set an initial switching frequency for the primary side, and generate a primary side triangular carrier through the first carrier generation unit;

[0036] The first PWM generation unit compares the primary-side triangular carrier wave with a set duty cycle to generate a drive signal for the primary-side switch. The frequency of the drive signal for the primary-side switch is the frequency of the primary-side switch.

[0037] The above-described resonant converter control method, wherein setting an initial switching frequency on the primary and secondary sides, and controlling at least one controllable switch according to the initial switching frequency on the secondary side to enable the second circuit to generate power, includes the following steps:

[0038] Set the initial switching frequency of the primary and secondary sides, and generate a secondary side triangular carrier through the second carrier generation unit;

[0039] The second PWM generation unit compares the secondary side triangular carrier with a set duty cycle to generate a drive signal for the controllable switch, thereby enabling the second circuit to generate power.

[0040] The above-described resonant converter control method, wherein adjusting the secondary-side switching frequency of at least one controllable switch according to a set initial secondary-side switching frequency and a signal reflecting the power of the second circuit, such that the secondary-side switching frequency of the second circuit tracks the primary-side switching frequency of the first circuit, includes the following steps:

[0041] The output voltage of the second sampling circuit is compared with the set reference output voltage, and the resulting first comparison signal is adjusted by the regulator and then output to the frequency comparison module.

[0042] The frequency comparison module compares the signal frequency output by the regulator with the set initial switching frequency of the secondary side, and the resulting second comparison signal is limited by the limiter and then output to the second carrier generation unit.

[0043] The second carrier generation unit generates a secondary triangular carrier from the signal output by the limiter, and the second PWM generation unit generates a drive signal for the controllable switch. The frequency of the drive signal is the secondary switching frequency, which tracks the primary switching frequency of the first circuit.

[0044] In the above-described resonant converter control method, when the primary-side switching frequency is the same as the initial secondary-side switching frequency, the primary-side switch and the controllable switch operate synchronously; when the primary-side switching frequency is different from the controllable switch frequency, the output voltage of the second circuit is used to adjust the secondary-side switching frequency of the controllable switch in a closed-loop manner, so that the secondary-side switching frequency automatically tracks the primary-side switching frequency, and the phase difference between at least one controllable switch and at least one primary-side switch is controlled to achieve output voltage stability.

[0045] Compared with the prior art, the embodiments of the present invention have all or part of the following beneficial technical effects:

[0046] The technical solution disclosed in this invention achieves communication-free control between the primary and secondary sides of the resonant converter by sampling the output voltage for switching frequency tracking and output voltage control. This solution eliminates the need for resonant cavity sampling, reducing sampling costs, and allows the secondary side to operate in a discontinuous current state, reducing secondary side turn-off losses. Even when there is no communication between the primary and secondary sides of the resonant converter and the primary side cannot obtain output voltage information, the system can still operate stably. Furthermore, by controlling the secondary side switching transistors, output voltage boosting is achieved, the frequency modulation range is reduced, and efficiency is improved.

[0047] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the present invention. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of a first implementation of the resonant converter of the present invention;

[0049] Figure 2 This is a schematic diagram illustrating the process of generating drive signals for the primary and secondary switches.

[0050] Figure 3 is Figure 1 The schematic diagram illustrates the synchronization principle between the primary and secondary switching frequencies. Figure 3a This is a schematic diagram illustrating the synchronization principle when the primary-side switching frequency is the same as the initial secondary-side switching frequency. Figure 3b This is a schematic diagram illustrating the synchronization principle when the primary-side switching frequency and the secondary-side switching frequency are different.

[0051] Figure 4 This is a schematic diagram of a second implementation of the resonant converter of the present invention;

[0052] Figure 5 This is a schematic diagram of a third implementation of the resonant converter of the present invention;

[0053] Figure 6 This is a typical operating waveform diagram of the resonant converter of the present invention;

[0054] Figure 7 for Figure 6 V when the excitation current is ignored CrN with i LrN The trajectory diagram;

[0055] Figure 8 This is a diagram illustrating the control effect of a single resonant converter during load addition and subtraction according to the present invention.

[0056] Figure 9 This diagram illustrates the control effect of the resonant converter of the present invention when the input voltage drops by 10%.

[0057] Figure 10 This is a diagram showing the control effect of the resonant converter of the present invention when the input voltage increases by 10%.

[0058] Figure 11 This is a control effect diagram of the resonant converter of the present invention when the primary-side switching frequency is increased by 30Hz;

[0059] Figure 12 This is a topology diagram of one implementation of the cascaded system of the present invention;

[0060] Figure 13 for Figure 12 Control block diagram of the A2D part of the SST non-communication distributed control system;

[0061] Figure 14 for Figure 12 Control block diagram of the D2D part of the SST non-communication distributed control system;

[0062] Figure 15 for Figure 12 Diagram showing the control effect of a cascaded system when the input voltage increases by 10%.

[0063] Figure 16 for Figure 12 Diagram showing the control effect of a cascaded system when the input voltage drops by 10%.

[0064] Figure 17 This is a flowchart of the steps of the resonant converter control method of the present invention. Detailed Implementation

[0065] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments to further understand the purpose, solution and effect of the present invention, but it is not intended to limit the scope of protection of the appended claims.

[0066] Certain terms are used in this specification and the following claims to refer to specific components or parts. Those skilled in the art will understand that users or manufacturers may use different names or terms to refer to the same component or part. This specification and the following claims do not distinguish components or parts by differences in name, but rather by differences in function. The terms "comprising" and "including" used throughout this specification and the following claims are open-ended and should be interpreted as "including but not limited to". Furthermore, the term "connection" here includes any direct and indirect electrical connection means. Indirect electrical connection means include connections made through other means.

[0067] It should be noted that in the description of this invention, the terms "lateral", "longitudinal", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and "about", or "approximately", "substantially", "left and right", etc., indicating the orientation or positional relationship or parameters, are all based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, a specific size, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0068] The principle of this invention lies in achieving zero-communication control between the primary and secondary sides of the resonant converter and stable output voltage by tracking the secondary-side switching frequency and phase shift angle through closed-loop control of the output voltage of the resonant converter. Specifically, the resonant converter includes a resonant cavity, a first end of which is connected to a first circuit, which includes at least one primary-side switch, and a second end of which is connected to a second circuit, which includes at least one controllable switch. In this invention, by setting an initial switching frequency between the primary and secondary sides, and controlling at least one controllable switch according to the initial switching frequency, the second circuit can generate power. Furthermore, the secondary-side switching frequency of the at least one controllable switch can be adjusted according to the set initial switching frequency and a signal reflecting the power of the second circuit, so that the secondary-side switching frequency of the second circuit tracks the primary-side switching frequency of the first circuit, thereby achieving zero-communication control between the primary and secondary sides of the resonant converter. Moreover, by controlling the phase difference between at least one controllable switch and at least one primary-side switch, stable output voltage can be achieved.

[0069] Figure 1 This is a schematic diagram of a first implementation of the resonant converter of the present invention. Figure 1As shown, an embodiment of the present invention provides a resonant converter, including a resonant cavity 30, a first circuit 10 electrically connected to a first end of the resonant cavity, and a second circuit 20 electrically connected to a second end of the resonant cavity. The first circuit 10 may include a primary-side switch 101. The second circuit 20 may include a controllable switch 201. The resonant cavity 30 may include a transformer 301, the primary winding of which is electrically connected to the first end of the resonant cavity 30, and the secondary winding of which is electrically connected to the second end of the resonant cavity 30. In other embodiments, the resonant cavity 30 may further include a resonant capacitor 302, a resonant inductor 303, and a magnetizing inductor 304 connected in series with the converter 301.

[0070] The aforementioned resonant converter may further include a primary-side control module 11, used to generate a drive signal for the primary-side switch 101 based on the frequency signal of the primary-side switch. In some embodiments, the primary-side control module 11 may specifically include a first carrier generation unit 111 and a first PWM generation unit 112. The first carrier generation unit 111 can generate a primary-side triangular carrier according to a set initial primary-side switching frequency. The first PWM generation unit 112 can compare the primary-side triangular carrier generated by the first carrier generation unit 111 with a set duty cycle to generate a drive signal for the primary-side switch 101, wherein the frequency of the drive signal for the primary-side switch 101 is the primary-side switching frequency.

[0071] Specifically, the process by which the primary-side control module 11 generates the drive signal for the primary-side switch 101 is as follows: Figure 2 As shown. Where, f s This represents the initial switching frequency on the primary side, mod indicates the remainder, abs indicates the absolute value, and duty indicates the duty cycle. The primary side control module uses the set initial switching frequency f. s The generation cycle is 1 / f s The primary side triangular carrier is generated and compared with the set duty cycle to generate the drive signal for the primary side switch.

[0072] The aforementioned resonant converter may further include a secondary-side control module 21. In some embodiments, the secondary-side control module 21 may specifically include a voltage comparison module 213, a regulator 214, a frequency comparison module 215, a limiter 216, and a second carrier generation module 210. Figure 1 As shown, the output of voltage comparison module 213 is connected to the input of frequency comparison module 215 via regulator 214, in order to convert the output voltage V of second circuit 20 into voltage. o With the set reference output voltage V orefThe first signal output is compared and then regulated by regulator 214 before being transmitted to frequency comparison module 215. The output of frequency comparison module 215 is connected to the input of second carrier generation module 210 via limiter 216, so as to compare the frequency of the signal output by regulator 214 with the set secondary side initial switching frequency f. sec0 The output second signal is compared and then limited by the limiter 216 before being transmitted to the second carrier generation module 210. The second carrier generation module 210 is used to generate a drive signal for the controllable switch 201 based on the signal output by the limiter 216. The frequency of the drive signal is the secondary-side switching frequency, which tracks the primary-side switching frequency. Preferably, the regulator 214 can be a proportional-integral regulator.

[0073] Similar to the drive signal generation process of the primary side switch 101, the second carrier generation module 210 may include a second carrier generation unit 211 and a second PWM generation unit 212; the second carrier generation unit 211 generates a secondary side triangular carrier based on the signal frequency output by the limiter 214; the second PWM generation unit 212 compares the secondary side triangular carrier generated by the second carrier generation unit 211 with the set duty cycle to generate the drive signal of the controllable switch 201.

[0074] Figure 1 This is a schematic diagram of a first implementation of the resonant converter of the present invention. In this embodiment, the primary-side switch 101 may specifically include a first switch Q1, a second switch Q2, a third switch Q3, and a fourth switch Q4. The first switch Q1 and the second switch Q2 are connected in series to form a first primary-side bridge arm, and the third switch Q3 and the fourth switch Q4 are connected in series to form a second primary-side bridge arm. The first primary-side bridge arm and the second primary-side bridge arm are connected in parallel. The midpoint of the first primary-side bridge arm and the midpoint of the second primary-side bridge arm are electrically connected to the first end of the resonant cavity 30, respectively. The first switch Q1, the second switch Q2, the third switch Q3, and the fourth switch Q4 are metal-oxide-semiconductor field-effect transistors. The controllable switch 201 specifically includes a first controllable switch S1, a second controllable switch S2, a third controllable switch S3, and a fourth controllable switch S4. The first and second controllable switches S1 and S2 are connected in series to form a first secondary side bridge arm, and the third and fourth controllable switches S3 and S4 are connected in series to form a second secondary side bridge arm. The first and second secondary side bridge arms are connected in parallel. The midpoints of the first and second secondary side bridge arms are electrically connected to the second end of the resonant cavity 30. In the figure, V... dc Indicates the input DC voltage, C r L r L m These represent the resonant capacitance, resonant inductance, and magnetizing inductance, respectively. o Indicates the output capacitance, V o Indicates the output voltage, voref f represents the output voltage reference value. pri f represents the primary-side switching frequency. sec0 This indicates the initial switching frequency on the secondary side.

[0075] Figure 3 is a schematic diagram illustrating the synchronization principle of the primary and secondary switching frequencies of the resonant converter in this embodiment. Taking a duty cycle of 0.5 as an example... Figure 3a As shown, when the primary-side switching frequency is the same as the initial secondary-side switching frequency, the primary-side switch and the controllable switch operate synchronously; as Figure 3b As shown, when the primary-side switching frequency is different from the controllable switching frequency, the output voltage of the secondary-side control module 21 is closed-loop adjusted to regulate the secondary-side switching frequency of the controllable switch, so that the secondary-side switching frequency automatically tracks the primary-side switching frequency, and the phase difference α between the controllable switch 201 and the primary-side switch 101 is controlled to stabilize the output voltage.

[0076] Reference Figure 1 As shown in Figure 3, in this embodiment, the primary-side switching frequency f pri The duty cycle is 50%, and the initial switching frequency f on the secondary side is... sec0 It can be used with the primary side switching frequency f pri They can be the same or different. Secondary side sampling output voltage V o , and the output voltage reference value v oref After comparison, the carrier frequency on the secondary side is adjusted in a closed loop. Once the system stabilizes, the carrier frequencies on the primary and secondary sides are the same, with the secondary side carrier lagging behind the primary side carrier by a certain angle. This is the angle by which the fourth controllable switch S4 on the secondary side lags behind the conduction angle of the first switch Q1 or the fourth switch Q4 on the primary side. When the output voltage increases, the lag angle increases, and the second controllable switch S2 and the fourth controllable switch S4 conduct complementaryly, thus stabilizing the output voltage. Figure 1 As shown in Figure 3, the resonant converter in this embodiment does not require resonant cavity sampling. It can achieve frequency adjustment of the primary and secondary sides by sampling the secondary side output voltage for closed-loop control.

[0077] Figure 4 This is a schematic diagram of a second implementation of the resonant converter of the present invention. Figure 1Compared to the resonant converter shown, the difference lies in the connection method of the controllable switch 201 in the second circuit 20. In this embodiment, the controllable switch 201 includes a first controllable switch S1, a second controllable switch S2, a third controllable switch S3, and a fourth controllable switch S4. The first and second controllable switches S1 and S2 are connected in series to form a first secondary side bridge arm, and the third and fourth controllable switches S3 and S4 are connected in series to form a second secondary side bridge arm. The first and second secondary side bridge arms are connected in parallel. The midpoints of the first and second secondary side bridge arms are electrically connected to the second end of the resonant cavity 30. The first and second controllable switches S1 and S2 are metal-oxide-semiconductor field-effect transistors, and the third and fourth controllable switches S3 and S4 are diodes. The working principle and process of the resonant converter in this embodiment are the same as those in the first embodiment described above, and will not be repeated here. It should be noted that the first controllable switch S1, the second controllable switch S2, the third controllable switch S3 and the fourth controllable switch S4 can be any combination of diode and metal-oxide-semiconductor field-effect transistor. The present invention is not limited thereto. The first implementation and the second implementation are preferred embodiments.

[0078] Figure 5 This is a schematic diagram of a third implementation of the resonant converter of the present invention. Figure 5 The resonant converter shown and Figure 4Compared to the resonant converter shown, the difference lies in the connection method of the second circuit 20. In this embodiment, the controllable switch 201 includes a fifth controllable switch S5, a sixth controllable switch S6, a seventh controllable switch S7, and an eighth controllable switch S8. These switches are connected in series to form a first secondary side bridge arm. The second circuit 20 also includes a capacitor bridge arm formed by a first capacitor C1 and a second capacitor C2 connected in series. The first secondary side bridge arm is connected in parallel with the capacitor bridge arm, and the midpoint of the first secondary side bridge arm is electrically connected to the midpoint of the capacitor bridge arm. The second end of the resonant cavity 30 is electrically connected between the electrical connection points of the fifth and sixth controllable switches S5 and S6, and the electrical connection points of the seventh and eighth controllable switches S7 and S8. Specifically, the fifth and seventh controllable switches S5 and S7 are diodes, and the sixth and eighth controllable switches S6 and S8 are metal-oxide-semiconductor field-effect transistors. The working principle and process of the resonant converter in this embodiment are the same as those in the first and second embodiments described above, and will not be repeated here. It should be noted that the fifth controllable switch S5 and the seventh controllable switch S7 can be diodes, and the sixth controllable switch S6 and the eighth controllable switch S8 can be semiconductor field-effect transistors. Alternatively, the fifth controllable switch S5, the sixth controllable switch S6, the seventh controllable switch S7, and the eighth controllable switch S8 can be any combination of diodes and metal-oxide-semiconductor field-effect transistors. This invention is not limited to these embodiments; the third implementation is a preferred embodiment.

[0079] A typical operating waveform of the resonant converter in the above embodiments is as follows: Figure 6 As shown in the figure. v p and v s The voltages are represented as primary side bridge arm voltage and secondary side bridge arm voltage, i Lr i represents the resonant inductor current. Lm V represents the magnetizing inductor current. Cr This represents the resonant capacitor voltage. Whether the secondary current is intermittent depends on the switching frequency and the load size. Figure 6 Taking one of the modes as an example, the proposed method is explained mathematically.

[0080] When the excitation current is ignored, Figure 6 The per-unit value V of the corresponding resonant capacitor voltage CrN The per-unit value i of the resonant inductor current LrN The trajectory diagram is as follows Figure 7 As shown.

[0081] Reference Figure 6 , Figure 7 As shown, where k represents the voltage gain, f N This indicates the per-unit value of the switching frequency. X t0 -Xt1 The center of the arc is (1, 0), corresponding to Figure 6 The waveform from t0 to t1, X t1 -X t2 The center of the arc is (1-k, 0), corresponding to Figure 6 The waveforms from t1 to t2. Figure 7 The initial value of the resonant capacitor voltage can be obtained using the cosine theorem for a triangle:

[0082]

[0083] According to V CrN0 From the relationship with power, the expressions for the primary and secondary phase shift angles can be obtained:

[0084]

[0085] As shown in equation (2), when the output power, output voltage, and switching frequency are known, the phase shift angle α can be determined. Therefore, the method proposed above can directly control the phase difference α between the primary and secondary sides based on the output voltage error, thereby achieving output voltage stability.

[0086] Taking the example of a single LLC resonant converter of the present invention having no communication between its primary and secondary sides, the implementation effect is as follows:

[0087] Figure 8 Diagram showing the control effect when adding or removing load. In the diagram, f pri f represents the primary-side switching frequency. sec Indicates the secondary-side switching frequency, v p and v s i represents the primary side arm voltage and the secondary side arm voltage, respectively. s i represents the secondary side bridge arm current. Lr i represents the resonant inductor current. Lm V represents the magnetizing inductor current. Cr This represents the resonant capacitor voltage, v o This represents the output voltage. The initial frequency f of the primary-side switching... pri0 =f r +20Hz, secondary-side switching initial frequency f sec0 =f r As can be seen, the output voltage and resonant cavity waveform remain stable during load changes, and the secondary side frequency tracks the primary side frequency.

[0088] When the input voltage or primary frequency changes, the resonant converter adopts output voltage-switching frequency closed-loop control to ensure frequency tracking and output voltage stability, and the control application is flexible. Figure 9 and Figure 10The simulated waveforms are shown for a 10% decrease in input voltage and a 10% increase in input voltage, respectively. When the input voltage decreases, the secondary-side phase shift angle automatically increases, stabilizing the output voltage and resonant cavity waveform, with the secondary-side frequency tracking the primary-side frequency. Similarly, when the input voltage increases, the secondary-side phase shift angle automatically decreases, stabilizing the output voltage and resonant cavity waveform.

[0089] Figure 11 The diagram shows the control effect when the primary-side switching frequency is increased by 30Hz. The secondary-side frequency tracks the primary-side frequency, and the output voltage and resonant cavity waveform are stable. After the output voltage stabilizes, it equals the set value.

[0090] Based on the aforementioned resonant converter, this invention also provides a cascaded system comprising at least two cascaded power modules. Each power module includes an AC-DC converter and a DC-DC converter, with the DC-DC converter including the aforementioned resonant converter, to achieve communication-free distributed control of the cascaded system. The following description uses SST distributed control as an example for further explanation.

[0091] Figure 12 This is a topology diagram of an SST non-communication distributed cascaded system. The diagram uses two power modules M1 and M2 with their inputs connected in series and their outputs in parallel as an example, but it can be extended to N power modules; this invention is not limited to this. In this embodiment, the front stage (i.e., A2D stage) of power modules M1 and M2 can be, for example, AC-DC converters M11 and M21, and the rear stage (i.e., D2D stage) can be, for example, DC-DC converters M12 and M22. The A2D stage is a cascaded H-bridge topology, V... g L is the grid-side voltage. g For the grid-side inductor, i g For grid-side current, v b For A2D level bridge arm voltage, C dc For DC-link capacitors, v dc This is the DC-link voltage, v o This is the output voltage.

[0092] The control block diagram of a single module in the above SST is as follows: Figure 13 , Figure 14 As shown, Figure 13 This is an A2D control block diagram. Figure 14 This is a D2D control block diagram. Where v bi v dci v oi i g All are the module's own sampled signals, where i = 1 and 2 represent the module serial numbers of the power module; v dcrefi This indicates the DC-link voltage reference value, v. dcset This indicates the DC-link voltage setting value, v bsetThis indicates the set value of the bridge arm voltage amplitude, v bi K represents the amplitude of the bridge arm voltage. vb K represents the anti-droop control coefficient. pVdc G represents the proportional gain of the DC-link voltage loop. Notch1 G represents a voltage loop notch filter. Notch2 Indicates a current loop notch filter, V gM Indicates the peak voltage of the power grid, i gd This represents the d-axis component of the grid-side current. This represents a low-pass filter. A2D control achieves communication-free control through the interaction of the bridge arm voltage amplitude and the DC-link voltage anti-droop control. When the amplitude of the bridge arm voltage in this module decreases, the DC-Link voltage reference value of this module decreases, thereby increasing the amplitude of the bridge arm voltage and creating a negative feedback effect. D2D control is similar to the control of the aforementioned resonant converter and will not be described further here.

[0093] Figure 15 , Figure 16 The figures show the control effect when the grid voltage rises by 10% and falls by 10% in the aforementioned SST non-communication distributed cascade system. The results indicate that although the system exhibits some steady-state error when the grid voltage changes, it remains stable and achieves completely non-communication distributed control of SST.

[0094] The resonant converter of this invention is used in solid-state transformers and can be applied to fast charging stations, photovoltaic power plants, data centers, energy storage, and microgrids. This invention includes, but is not limited to, the embodiments listed above.

[0095] Figure 17 This is a flowchart illustrating the steps of a resonant converter control method provided in an embodiment of the present invention. The resonant converter control method of the present invention is used in a resonant converter, which includes a resonant cavity, a first circuit electrically connected to a first end of the resonant cavity, and a second circuit electrically connected to a second end of the resonant cavity. The resonant cavity includes at least one transformer, with the primary winding of the transformer electrically connected to the first end of the resonant cavity and the secondary winding of the transformer electrically connected to the second end of the resonant cavity. The first circuit includes at least one primary-side switch, and the second circuit includes at least one controllable switch. The control method includes the following steps:

[0096] S1. Set the initial switching frequency of the primary and secondary sides, and control at least one controllable switch according to the initial switching frequency of the secondary side so that the second circuit generates power.

[0097] S2. Adjust the secondary-side switching frequency of at least one controllable switch according to the set initial secondary-side switching frequency and the signal reflecting the power of the second circuit, so that the secondary-side switching frequency of the second circuit tracks the primary-side switching frequency of the first circuit.

[0098] The method described in the above embodiments may further include the following steps:

[0099] Set an initial switching frequency for the primary side, and generate a primary side triangular carrier through the first carrier generation unit;

[0100] The first PWM generation unit compares the primary side triangular carrier with the set duty cycle to generate the primary side switch drive signal. The frequency of the primary side switch drive signal is the primary side switch frequency.

[0101] In the above embodiment method, step S1, which involves setting an initial switching frequency on the primary and secondary sides and controlling at least one controllable switch according to the initial switching frequency on the secondary side to generate power in the second circuit, may specifically include:

[0102] Set the initial switching frequency of the primary and secondary sides, and generate a secondary side triangular carrier through the second carrier generation unit;

[0103] The second PWM generation unit compares the secondary triangular carrier wave with the set duty cycle to generate a drive signal for a controllable switch, thereby enabling the second circuit to generate power.

[0104] In the above embodiment method, step S2, adjusting the secondary-side switching frequency of at least one controllable switch according to the set initial secondary-side switching frequency and the signal reflecting the power of the second circuit, so that the secondary-side switching frequency of the second circuit tracks the primary-side switching frequency of the first circuit, may specifically include:

[0105] The output voltage of the second sampling circuit is compared with the set reference output voltage, and the resulting first comparison signal is adjusted by the regulator and then output to the frequency comparison module.

[0106] The frequency comparison module compares the signal frequency output by the regulator with the set initial switching frequency of the secondary side, and the resulting second comparison signal is limited by the limiter and then output to the second carrier generation unit.

[0107] The signal output from the limiter is generated into a secondary triangular carrier by the second carrier generation unit, and a drive signal for the controllable switch is generated by the second PWM generation unit. The frequency of the drive signal is the secondary switching frequency, which tracks the primary switching frequency of the first circuit.

[0108] In this embodiment, when the primary-side switching frequency is the same as the initial secondary-side switching frequency, the primary-side switch and the controllable switch operate synchronously; when the primary-side switching frequency is different from the controllable switch frequency, the output voltage of the second circuit is closed-loop adjusted to regulate the secondary-side switching frequency of the controllable switch, so that the secondary-side switching frequency automatically tracks the primary-side switching frequency, and the phase difference between at least one controllable switch and at least one primary-side switch is controlled to stabilize the output voltage.

[0109] For details regarding the specific implementation structure and technical effects of the method in this embodiment, please refer to the description of the corresponding part of the resonant converter provided in the above embodiments, which will not be repeated here.

[0110] As can be seen from the above, the embodiments of the present invention have at least one of the following advantages:

[0111] 1. This invention achieves switching frequency tracking and output voltage control by sampling the output voltage, realizing communication-free control between the primary and secondary sides of the LLC, and meeting the requirement of efficient operation of the LLC without communication between the primary and secondary sides.

[0112] 2. This invention eliminates the need for resonant cavity sampling, reducing sampling costs, and allows the secondary side to operate in a discontinuous current state, reducing secondary side turn-off losses.

[0113] 3. This invention achieves output voltage boost and reduces the frequency modulation range by controlling the secondary-side switching transistor, solving the problems of difficult voltage boost and large switching frequency adjustment range in LLC circuits that rely solely on frequency and voltage modulation, thus improving efficiency.

[0114] 4. This invention has a wide range of applications, realizing SST communication-free distributed control, and can be widely used in charging stations, power plants, microgrids and other fields.

[0115] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments for application in other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A resonant converter, characterized in that, include: A resonant cavity, a first circuit electrically connected to a first end of the resonant cavity, and a second circuit electrically connected to a second end of the resonant cavity; The resonant cavity includes at least one transformer, the primary winding of the transformer is electrically connected to a first end of the resonant cavity, and the secondary winding of the transformer is electrically connected to a second end of the resonant cavity. The first circuit includes at least one primary-side switch, and the second circuit includes at least one controllable switch. An initial secondary-side switching frequency is set. The at least one controllable switch is controlled according to the initial secondary-side switching frequency to generate power in the second circuit. The secondary-side switching frequency of the at least one controllable switch is adjusted according to the set initial secondary-side switching frequency and a signal reflecting the power of the second circuit, so that the secondary-side switching frequency of the second circuit tracks the primary-side switching frequency of the first circuit. The adjustment of the secondary-side switching frequency of the at least one controllable switch according to the set initial secondary-side switching frequency and the signal reflecting the power of the second circuit to track the primary-side switching frequency of the first circuit includes: The output voltage of the second circuit is compared with the set reference output voltage, and the obtained first signal is adjusted by the regulator and output to the frequency comparison module. The frequency comparison module compares the frequency of the signal output by the regulator with the set initial switching frequency of the secondary side to obtain the second signal, so that the secondary side switching frequency of the second circuit tracks the primary side switching frequency of the first circuit.

2. The resonant converter according to claim 1, characterized in that, It includes a primary-side control module, which generates a drive signal for the primary-side switch based on the frequency signal of the primary-side switch.

3. The resonant converter according to claim 2, characterized in that, The primary control module includes a first carrier generation unit and a first PWM generation unit; The first carrier generation unit generates a primary-side triangular carrier according to the set primary-side initial switching frequency; The first PWM generation unit compares the primary-side triangular carrier generated by the first carrier generation unit with a set duty cycle to generate a drive signal for the primary-side switch. The frequency of the drive signal for the primary-side switch is the primary-side switch frequency.

4. The resonant converter according to claim 1, characterized in that, It also includes a secondary-side control module, which includes a voltage comparison module, a regulator, a frequency comparison module, a limiter, and a second carrier generation module; The output of the voltage comparison module is connected to the input of the frequency comparison module via the regulator, so as to compare the output voltage of the second circuit with the set reference output voltage, and the output first signal is transmitted to the frequency comparison module after adjustment. The output of the frequency comparison module is connected to the input of the second carrier generation module via the limiter, so as to compare the signal frequency of the first signal output by the regulator with the set initial switching frequency of the secondary side, and the output second signal is transmitted to the second carrier generation module after being limited. The second carrier generation module is used to generate a drive signal for the controllable switch based on the signal output by the limiter. The frequency of the drive signal is the secondary-side switching frequency, which tracks the primary-side switching frequency.

5. The resonant converter according to claim 4, characterized in that, The second carrier generation module includes a second carrier generation unit and a second PWM generation unit; The second carrier generation unit generates a secondary triangular carrier based on the signal frequency output by the limiter; The second PWM generation unit compares the secondary triangular carrier generated by the second carrier generation unit with the set duty cycle to generate the drive signal for the controllable switch.

6. The resonant converter according to claim 4, characterized in that, The regulator is a proportional-integral regulator.

7. The resonant converter according to any one of claims 4 to 6, characterized in that, The secondary-side control module is configured to: when the primary-side switching frequency is the same as the initial secondary-side switching frequency, the primary-side switch and the controllable switch operate synchronously; when the primary-side switching frequency is different from the controllable switch frequency, the output voltage of the secondary-side control module is used to adjust the secondary-side switching frequency of the controllable switch in a closed-loop manner, so that the secondary-side switching frequency automatically tracks the primary-side switching frequency, and the phase difference between at least one controllable switch and at least one primary-side switch is controlled to achieve output voltage stability.

8. The resonant converter according to claim 1, characterized in that, The primary-side switch includes a first switch, a second switch, a third switch, and a fourth switch. The first switch and the second switch are connected in series to form a first primary-side bridge arm, and the third switch and the fourth switch are connected in series to form a second primary-side bridge arm. The first primary-side bridge arm and the second primary-side bridge arm are connected in parallel. The midpoints of the first primary-side bridge arm and the second primary-side bridge arm are electrically connected to the first end of the resonant cavity, respectively.

9. The resonant converter according to claim 8, characterized in that, The first switch, the second switch, the third switch, and the fourth switch are all metal-oxide-semiconductor field-effect transistors.

10. The resonant converter according to claim 1, characterized in that, The controllable switch includes a first controllable switch transistor, a second controllable switch transistor, a third controllable switch transistor, and a fourth controllable switch transistor. The first controllable switch transistor and the second controllable switch transistor are connected in series to form a first secondary side bridge arm, and the third controllable switch transistor and the fourth controllable switch transistor are connected in series to form a second secondary side bridge arm. The first secondary side bridge arm and the second secondary side bridge arm are connected in parallel, and the midpoints of the first secondary side bridge arm and the second secondary side bridge arm are respectively electrically connected to the second end of the resonant cavity.

11. The resonant converter according to claim 10, characterized in that, The first and third controllable switching transistors are diodes, and the second and fourth controllable switching transistors are metal-oxide-semiconductor field-effect transistors.

12. The resonant converter according to claim 10, characterized in that, The first and second controllable switching transistors are diodes, and the third and fourth controllable switching transistors are metal-oxide-semiconductor field-effect transistors.

13. The resonant converter according to claim 1, characterized in that, The controllable switch includes a fifth controllable switch transistor, a sixth controllable switch transistor, a seventh controllable switch transistor, and an eighth controllable switch transistor. The fifth, sixth, seventh, and eighth controllable switch transistors are connected in series to form a third secondary side bridge arm. The second circuit also includes a capacitor bridge arm formed by a first capacitor and a second capacitor connected in series. The third secondary side bridge arm is connected in parallel with the capacitor bridge arm. The midpoint of the third secondary side bridge arm is electrically connected to the midpoint of the capacitor bridge arm. The second end of the resonant cavity is electrically connected between the electrical connection point of the fifth and sixth controllable switch transistors and the electrical connection point of the seventh and eighth controllable switch transistors.

14. The resonant converter according to claim 1, characterized in that, The resonant cavity also includes a resonant capacitor, a resonant inductor, and a magnetizing inductor connected in series with the converter.

15. The resonant converter according to claim 1, characterized in that, The second circuit operates in discontinuous current mode.

16. A cascaded system, characterized in that, It includes at least two cascaded power modules, each of which includes an AC-DC converter and a DC-DC converter, wherein the DC-DC converter includes the resonant converter according to any one of claims 1-15.

17. A control method for a resonant converter, characterized in that, The control method is applied to the resonant converter according to any one of claims 1-15, wherein the resonant converter includes a resonant cavity, a first circuit electrically connected to a first end of the resonant cavity, and a second circuit electrically connected to a second end of the resonant cavity; the resonant cavity includes at least one transformer, the primary winding of the transformer is electrically connected to the first end of the resonant cavity, and the secondary winding of the transformer is electrically connected to the second end of the resonant cavity; the first circuit includes at least one primary-side switch, and the second circuit includes at least one controllable switch; the control method includes the following steps: Set an initial switching frequency for the primary and secondary sides, and control at least one of the controllable switches according to the initial switching frequency for the secondary sides, so that the second circuit generates power; Adjusting the secondary-side switching frequency of at least one controllable switch according to a set initial secondary-side switching frequency and a signal reflecting the power of the second circuit, such that the secondary-side switching frequency of the second circuit tracks the primary-side switching frequency of the first circuit; adjusting the secondary-side switching frequency of at least one controllable switch according to a set initial secondary-side switching frequency and a signal reflecting the power of the second circuit, such that the secondary-side switching frequency of the second circuit tracks the primary-side switching frequency of the first circuit, includes: The output voltage of the second circuit is compared with the set reference output voltage, and the first comparison signal obtained is adjusted by the regulator and output to the frequency comparison module. The frequency comparison module compares the frequency of the signal output by the regulator with the set initial switching frequency of the secondary side to obtain the second comparison signal, so that the secondary side switching frequency of the second circuit tracks the primary side switching frequency of the first circuit.

18. The resonant converter control method according to claim 17, characterized in that, It also includes the following steps: Set an initial switching frequency for the primary side, and generate a primary side triangular carrier through the first carrier generation unit; The first PWM generation unit compares the primary-side triangular carrier wave with a set duty cycle to generate a drive signal for the primary-side switch. The frequency of the drive signal for the primary-side switch is the primary-side switch frequency.

19. The resonant converter control method according to claim 18, characterized in that, The step of setting an initial switching frequency on the secondary side and controlling at least one controllable switch according to the initial switching frequency on the secondary side to enable the second circuit to generate power includes the following steps: Set the initial switching frequency of the primary and secondary sides, and generate a secondary side triangular carrier through the second carrier generation unit; The second PWM generation unit compares the secondary side triangular carrier with a set duty cycle to generate a drive signal for the controllable switch, thereby enabling the second circuit to generate power.

20. The resonant converter control method according to claim 18, characterized in that, The step of adjusting the secondary-side switching frequency of at least one controllable switch according to the set initial secondary-side switching frequency and a signal reflecting the power of the second circuit, so that the secondary-side switching frequency of the second circuit tracks the primary-side switching frequency of the first circuit, further includes the following steps: The output voltage of the second sampling circuit is compared with the set reference output voltage, and the resulting first comparison signal is adjusted by the regulator and then output to the frequency comparison module. The frequency comparison module compares the signal frequency output by the regulator with the set initial switching frequency of the secondary side, and the resulting second comparison signal is limited by the limiter and then output to the second carrier generation unit. The second carrier generation unit generates a secondary triangular carrier from the signal output by the limiter, and the second PWM generation unit generates a drive signal for the controllable switch. The frequency of the drive signal is the secondary switching frequency, which tracks the primary switching frequency of the first circuit.

21. The resonant converter control method according to any one of claims 18 to 20, characterized in that, When the primary-side switching frequency is the same as the initial secondary-side switching frequency, the primary-side switch and the controllable switch operate synchronously; when the primary-side switching frequency is different from the controllable switch frequency, the output voltage of the second circuit adjusts the secondary-side switching frequency of the controllable switch in a closed-loop manner, so that the secondary-side switching frequency automatically tracks the primary-side switching frequency, and controls the phase difference between at least one controllable switch and at least one primary-side switch to achieve output voltage stability.

Images