Asymmetric LLC resonant medium voltage DC conversion circuit, device and control method

Abstract

The present invention relates to an asymmetric LLC resonant medium voltage DC conversion circuit, device and control method, wherein the circuit comprises a first bridge arm, a second bridge arm, a third bridge arm, a third bridge arm inductor, a fourth bridge arm, a fourth bridge arm inductor, an LC resonant unit and a transformer T; when the first bridge arm is turned on and the second bridge arm is turned off, the LC resonant unit and the fourth bridge arm inductor form an LLC resonant cavity, so that the low voltage side of the transformer T outputs a positive half-wave low voltage AC voltage, and when the first bridge arm is turned off and the second bridge arm is turned on, the LC resonant unit and the third bridge arm inductor form an LLC resonant cavity, so that the low voltage side of the transformer T outputs a negative half-wave low voltage AC voltage. The implementation of the present invention can reduce the circuit construction cost, and the high voltage side of the transformer in the present invention does not need to be directly connected to a large capacitor, which reduces the fault capacity requirements of the transformer T and the DC circuit breaker, and helps to improve the construction economy of the DC power supply system of the submarine monitoring station.

Description

Technical Field

[0001] The present invention relates to a direct current power supply technology for a seabed observation station, and in particular to an asymmetric LLC resonant medium voltage direct current conversion circuit and device and a control method. Background Art

[0002] As environmental and energy problems become increasingly severe, the ocean, which accounts for more than 70% of the earth's area, has gradually become the focus of human attention. Further exploration and observation of the ocean has become a key means for the development of marine science and technology. At the same time, in order to obtain a large amount of reliable observation data, building an observation station on the seabed is an important way to conduct continuous long-term in-situ underwater measurements. Considering the limitations of transmission distance and transmission capacity, onshore DC power is usually transmitted to the seabed observation station through a submarine cable at high or medium voltage. Therefore, a medium-voltage-low-voltage DC transformer is required in the seabed observation station to convert the voltage into low-voltage DC to achieve power supply. Since the DC transformer is in the seabed observation station, it is usually far away from the onshore DC bus, up to hundreds of kilometers. Therefore, the resistance of the submarine cable will affect the voltage on the medium-voltage side when the power changes. For example, for a 100km long submarine cable, its parasitic resistance is 150 ohms. When the input current changes from 0 to 10 amperes, the voltage drop on the cable fluctuates by 1.5 kilovolts. Therefore, the medium-voltage-low-voltage DC transformer used in the seabed observation station needs to adjust the output within a wider input voltage range.

[0003] In the related art, the non-resonant multi-level medium voltage DC transformer based on phase-shift control technology is the basic solution for realizing medium-low voltage DC interconnection. However, due to the adoption of phase-shift control technology, the non-resonant multi-level medium voltage DC transformer is prone to lose zero voltage switching (ZVS) when the voltage gain is not unity, similar to the traditional dual active full bridge converter (DAB), resulting in a significant reduction in the overall conversion efficiency. Therefore, the non-resonant multi-level medium voltage DC transformer is not suitable for constructing a DC transformer with a wide input voltage variation range in the seabed observatory. At the same time, in the non-resonant multi-level medium voltage DC transformer, since the upper and lower bridge arms are always electrically connected to the medium voltage DC bus, there will be a bridge arm circulation between the four bridge arms, further reducing the operating efficiency of the entire converter system. In addition, in the non-resonant multi-level medium voltage DC transformer, the high-frequency transformer in the AC link is usually subjected to square wave or quasi-square wave voltage. When the power changes, it will cause DC bias in the transformer core, affecting the safe and stable operation of the DC transformer. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide an asymmetric LLC resonant medium voltage DC conversion circuit and device and a control method.

[0005] The technical solution adopted by the present invention to solve the technical problem is: constructing an asymmetric LLC resonant medium voltage DC conversion circuit, including a first bridge arm, a second bridge arm, a third bridge arm, a third bridge arm inductor, a fourth bridge arm, a fourth bridge arm inductor, an LC resonant unit and a transformer T;

[0006] The input end of the first bridge arm is used to connect to the positive pole of the medium voltage DC voltage, the output end of the second bridge arm is used to connect to the negative pole of the medium voltage DC voltage, the first end of the LC resonance unit is connected to the output end of the first bridge arm and the input end of the second bridge arm at the same time, the second end of the LC resonance unit is connected to the input end of the first bridge arm through the third bridge arm inductor and the third bridge arm, and is connected to the output end of the second bridge arm through the fourth bridge arm inductor and the fourth bridge arm;

[0007] The high voltage side of the transformer T is connected to the LC resonance unit. When the first bridge arm is turned on and the second bridge arm is turned off, the LC resonance unit and the fourth bridge arm inductor form an LLC resonance cavity, so that the low voltage side of the transformer T outputs a positive half-wave low voltage AC voltage. When the first bridge arm is turned off and the second bridge arm is turned on, the LC resonance unit and the third bridge arm inductor form an LLC resonance cavity, so that the low voltage side of the transformer T outputs a negative half-wave low voltage AC voltage.

[0008] Preferably, the third bridge arm and the fourth bridge arm respectively include a plurality of sub-switch modules;

[0009] The plurality of sub-switch modules included in the third bridge arm are sequentially connected in series, and the plurality of sub-switch modules included in the fourth bridge arm are sequentially connected in series;

[0010] Each of the sub-switch modules is used to form a short-circuit conduction loop or a capacitive conduction loop according to a control signal.

[0011] Preferably, each of the sub-switch modules includes a first switch tube S1j1, a first diode D1j1, a second switch tube S1j2, a second diode D1j2 and a first capacitor VC1j;

[0012] The first end of the first switch tube S1j1 is connected as the input end of the sub-switch module to the output end of the sub-switch module at the previous stage or to the input end of the first bridge arm or to the inductor of the fourth bridge arm. The first diode D1j1 and the first end and the second end of the first switch tube S1j1 are connected in parallel. The control end of the first switch tube S1j1 is used to access the first sub-control signal.

[0013] The second end of the first switch tube S1j1 is connected to the first end of the second switch tube S1j2, the second diode D1j2 and the first end and the second end of the second switch tube S1j2 are connected in parallel, the control end of the second switch tube S1j2 is used to access the second sub-control signal, the second end of the second switch tube S1j2 is connected as the output end of the sub-switch module to the input end of the sub-switch module located at the subsequent stage or to the third bridge arm inductor or to the output end of the second bridge arm, and the two ends of the first capacitor VC1j are respectively connected to the first end of the first switch tube S1j1 and the second end of the second switch tube S1j2.

[0014] Preferably, the LC resonance unit includes a resonant capacitor Cr; the first end of the resonant capacitor Cr is the first end of the LC resonance unit, the second end of the resonant capacitor Cr is connected to the first end of the resonant inductor Lm, the second end of the resonant inductor Lm is connected to the first end of the high-voltage side of the transformer T, the second end of the high-voltage side of the transformer T is connected to the third bridge arm inductor and the fourth bridge arm inductor, and the resonant capacitor Cr can form the LLC resonant cavity with the leakage inductance of the transformer T and one of the bridge arm inductors.

[0015] Preferably, the LC resonance unit also includes a resonant inductor Lm; the first end and the second end of the resonant inductor Lm are respectively connected to the first end and the second end of the high voltage side of the transformer T, and the LLC resonant cavity is composed of the resonant capacitor Cr, the resonant inductor Lm and one of the bridge arm inductors, or is composed of the resonant capacitor Cr, one of the bridge arm inductors and an equivalent inductance formed by connecting the leakage inductance of the transformer T in parallel with the resonant inductor Lm.

[0016] Preferably, the first bridge arm includes a plurality of third switch tubes Q3; the third switch tubes Q3 are connected in series in sequence, and the control end of each third switch tube Q3 is used to simultaneously access the first on-off control signal;

[0017] The second bridge arm includes a plurality of fourth switch tubes Q4 ; the fourth switch tubes Q4 are connected in series in sequence, and the control end of each fourth switch tube Q4 is used to simultaneously access the second on-off control signal.

[0018] The present invention also constructs a control method for controlling the above-mentioned asymmetric LLC resonant medium voltage DC conversion circuit, the method comprising:

[0019] The first half-cycle control step: according to the preset positive half-wave low-voltage AC voltage amplitude, respectively controlling the number of capacitive conduction loops formed by the multiple sub-switch modules included in the third bridge arm and the number of capacitive conduction loops formed by the multiple sub-switch modules included in the fourth bridge arm, and controlling the first bridge arm to be turned on and the second bridge arm to be turned off, and continuing for a first preset time;

[0020] The second half-cycle control step: according to the preset negative half-wave low-voltage AC voltage amplitude, respectively control the number of capacitive conduction loops formed by the multiple sub-switch modules included in the third bridge arm and the number of capacitive conduction loops formed by the multiple sub-switch modules included in the fourth bridge arm, and control the first bridge arm to be closed and the second bridge arm to be turned on, and last for a second preset time.

[0021] Preferably, the expression of the preset positive half-wave low-voltage AC voltage amplitude is:

[0022] ;

[0023] Represents the preset positive half-wave low-voltage AC voltage amplitude; represents the transformation ratio of the transformer T; represents the number of capacitive conduction loops formed by the multiple sub-switch modules included in the third bridge arm in the first half-cycle control step; Represents medium voltage DC voltage; represents the number of capacitive conduction loops formed by the multiple sub-switch modules included in the fourth bridge arm in the first half-cycle control step;

[0024] The expression of the preset negative half-wave low-voltage AC voltage amplitude is:

[0025] ;

[0026] Represents the preset negative half-wave low-voltage AC voltage amplitude; represents the number of capacitive conduction loops formed by the multiple sub-switch modules included in the fourth bridge arm in the second half-cycle control step; represents the number of capacitive conduction loops formed by the multiple sub-switch modules included in the third bridge arm in the second half-cycle control step;

[0027] in, equal , equal .

[0028] Preferably, the number of sub-switch modules included in the third bridge arm and the fourth bridge arm is N, where N is a natural number greater than 3;

[0029] In the first half-cycle control step, it also includes: limiting the and The setting value of

[0030] Wherein, the first preset function is expressed as:

[0031] ;

[0032] In the second half-cycle control step, it also includes: limiting the and The setting value of

[0033] Wherein, the second preset function is expressed as:

[0034] ;

[0035] represents the minimum permissible voltage value across the capacitive conduction loop; Represents the maximum allowable voltage value across the capacitive conduction loop.

[0036] The present invention also constructs a control circuit, including a processor, and the processor implements the steps of the above-mentioned control method when executing the stored computer program.

[0037] The present invention also constructs an asymmetric LLC resonant medium-voltage DC conversion device, comprising the asymmetric LLC resonant medium-voltage DC conversion circuit described above, and the control circuit described above.

[0038] The implementation of the present invention has the following beneficial effects: the entire bridge arm is constituted by the third bridge arm and the fourth bridge arm to form an asymmetric structure, thereby reducing the circuit construction cost, and compared with the traditional LLC resonant DC transformer, the high-voltage side of the transformer T in the asymmetric LLC resonant medium-voltage DC conversion circuit does not need to be directly connected to a large capacitor, and can quickly isolate the discharge behavior of the transformer T itself during a medium-voltage DC fault, reduce the fault capacity requirements of the transformer T and the DC circuit breaker, help improve the construction economy of the DC power supply system of the submarine monitoring station, and can also eliminate the DC bias phenomenon of the transformer T when the power changes, effectively improving the operating reliability, safety and efficiency of the DC conversion circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0040] Figure 1 is a circuit schematic diagram of an asymmetric LLC resonant medium voltage DC conversion circuit in some embodiments of the present invention;

[0041] Figure 2 is a circuit schematic diagram of an asymmetric LLC resonant medium voltage DC conversion circuit in some other embodiments of the present invention;

[0042] Figure 3 is a circuit schematic diagram of a sub-switch module in some embodiments of the present invention;

[0043] Figure 4 is a circuit schematic diagram of the first bridge arm and the second bridge arm in some embodiments of the present invention;

[0044] Figure 5 is a program flow chart of the control method in some embodiments of the present invention. DETAILED DESCRIPTION

[0045] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0046] It should be noted that the flowcharts shown in the accompanying drawings are only exemplary and do not necessarily include all the contents and operations / steps, nor do they have to be executed in the order described. For example, some operations / steps can be decomposed, while some operations / steps can be combined or partially combined, so the actual execution order may change according to actual conditions.

[0047] The block diagrams shown in the accompanying drawings are merely functional entities and do not necessarily correspond to physically independent entities. That is, these functional entities may be implemented in software form, or in one or more hardware modules or integrated circuits, or in different networks and / or processor devices and / or microcontroller devices.

[0048] See also Figure 1 , is a circuit schematic diagram of an asymmetric LLC resonant medium-voltage DC conversion circuit in some embodiments of the present invention. The asymmetric LLC resonant medium-voltage DC conversion circuit is suitable for a seabed observation station, and includes a first bridge arm 1, a second bridge arm 2, a third bridge arm 3, a third bridge arm inductor 4, a fourth bridge arm 5, a fourth bridge arm inductor 6, an LC resonance unit 7 and a transformer T.

[0049] The input end of the first bridge arm 1 is used to connect the positive pole of the medium voltage DC voltage, the output end of the second bridge arm 2 is used to connect the negative pole of the medium voltage DC voltage, the first end of the LC resonance unit 7 is connected to the output end of the first bridge arm 1 and the input end of the second bridge arm 2 at the same time, the second end of the LC resonance unit 7 is connected to the input end of the first bridge arm 1 through the third bridge arm inductor 4 and the third bridge arm 3, and is connected to the output end of the second bridge arm 2 through the fourth bridge arm inductor 6 and the fourth bridge arm 5. The high voltage side of the transformer T is connected to the LC resonance unit 7. When the first bridge arm 1 is turned on and the second bridge arm 2 is turned off, the LC resonance unit 7 and the fourth bridge arm inductor 6 form an LLC resonance cavity, so that the low voltage side of the transformer T outputs a positive half-wave low voltage AC voltage. When the first bridge arm 1 is turned off and the second bridge arm 2 is turned on, the LC resonance unit 7 and the third bridge arm inductor 4 form an LLC resonance cavity, so that the low voltage side of the transformer T outputs a negative half-wave low voltage AC voltage. The transformer T can be an existing DC transformer.

[0050] This embodiment uses the third bridge arm 3 and the fourth bridge arm 5 as two half-bridge arms to form the entire bridge arm, forming an asymmetric structure, which helps to reduce construction costs and improve operating efficiency. Compared with the traditional LLC resonant DC transformer, the high-voltage side of the transformer T in the asymmetric LLC resonant medium-voltage DC conversion circuit does not need to be directly connected to a large capacitor. When a medium-voltage DC fault occurs, the discharge behavior of the transformer T itself can be quickly isolated by shutting down the first and second bridge arms, reducing the fault capacity requirements of the transformer T and the DC circuit breaker, which helps to improve the construction economy of the DC power supply system of the submarine monitoring station; furthermore, the waveform of the transformer T in the AC link is a sine wave, which eliminates the DC bias phenomenon of the transformer T when the power changes, and effectively improves the operating reliability, safety and efficiency of the DC conversion circuit.

[0051] In some embodiments, Figure 1 or Figure 2 As shown, the third bridge arm 3 and the fourth bridge arm 5 include a plurality of sub-switch modules 35 respectively. The plurality of sub-switch modules 35 included in the third bridge arm 3 are connected in series in sequence, and the plurality of sub-switch modules 35 included in the fourth bridge arm 5 are connected in series in sequence, and each sub-switch module 35 is used to form a short-circuit conduction loop or a capacitive conduction loop according to a control signal. It should be noted that the short-circuit conduction loop can be equivalent to a short-circuit wire, and the capacitive conduction loop can be equivalent to a "capacitor". If the sub-switch module 35 forms a capacitive conduction loop, the sub-switch module 35 can be equivalent to a capacitor. If the sub-switch module 35 forms a short-circuit conduction loop, it can be equivalent to a wire. Since each sub-switch module 35 is equivalent to a "capacitor" when forming a capacitive conduction loop, the voltage across the sub-switch module 35 can be regarded as a fixed value for the input AC voltage with a stable frequency at this time. Therefore, by analyzing Figure 1 or Figure 2 It can be seen that the number of capacitive conduction loops formed on the third bridge arm 3 and the fourth bridge arm 5 respectively and the medium voltage DC voltage have the following relationship: , represents the voltage across the “capacitor” when each sub-switch module 35 forms a capacitive conduction loop and is connected to an AC voltage. Represents medium voltage DC voltage; ( ) represents the total number of capacitive conduction loops formed by the sub-switch modules 35 in the third bridge arm 3 and the fourth bridge arm 5. Further analysis shows that when the first bridge arm 1 is turned on and the second bridge arm 2 is turned off, the voltage amplitude on the high-voltage side of the transformer T is: , represents the AC voltage on the high voltage side of transformer T, represents the number of capacitive conduction loops formed by the plurality of sub-switch modules 35 included in the third bridge arm 3 when the first bridge arm 1 is turned on; represents the number of capacitive conduction loops formed by the multiple sub-switch modules 35 included in the fourth bridge arm 5 when the first bridge arm 1 is turned on; when the first bridge arm 1 is turned off and the second bridge arm 2 is turned on, the voltage amplitude on the high-voltage side of the transformer T is: ; represents the number of capacitive conduction loops formed by the multiple sub-switch modules 35 included in the fourth bridge arm 5 when the second bridge arm 2 is turned on; It represents the number of capacitive conduction loops formed by the multiple sub-switch modules 35 included in the third bridge arm 3 when the second bridge arm 2 is turned on.

[0052] In this embodiment, the sub-switch modules 35 respectively constitute the third bridge arm 3 and the fourth bridge arm 5 in a cascade form, and the number of capacitive conduction loops formed by the sub-switch modules 35 respectively included in the third bridge arm 3 and the fourth bridge arm 5 can be controlled to control the number of "capacitors" equivalently connected in series on the third bridge arm 3 and the fourth bridge arm 5, thereby controlling the voltage division obtained by the LLC resonant cavity, and then controlling the output voltage of the transformer T, that is, realizing a modular control multi-level output scheme, which has the advantages of simple control and high efficiency.

[0053] In some embodiments, Figure 3 As shown, each sub-switch module 35 includes a first switch tube S1j1, a first diode D1j1, a second switch tube S1j2, a second diode D1j2 and a first capacitor VC1j.

[0054] The first end of the first switch tube S1j1 is connected as the input end of the sub-switch module 35 to the output end of the sub-switch module 35 located at the previous stage or to the input end of the first bridge arm 1 or to the fourth bridge arm inductor 6. The cathode and anode of the first diode D1j1 are respectively connected in parallel with the first end and the second end of the first switch tube S1j1, and the control end of the first switch tube S1j1 is used to access the first sub-control signal; the second end of the first switch tube S1j1 is connected to the first end of the second switch tube S1j2, the cathode and anode of the second diode D1j2 are respectively connected in parallel with the first end and the second end of the second switch tube S1j2, and the control end of the second switch tube S1j2 is used to access the second sub-control signal. The second end of the second switch tube S1j2 is connected as the output end of the sub-switch module 35 to the input end of the sub-switch module 35 located at the subsequent stage or to the third bridge arm inductor 4 or to the output end of the second bridge arm 2. The two ends of the first capacitor VC1j are respectively connected to the first end of the first switch tube S1j1 and the second end of the second switch tube S1j2.

[0055] Specifically, the first sub-control signal and the second sub-control signal can be PWM signals, which can respectively control the on and off of the first switch tube S1j1 and the second switch tube S1j2, but the first switch tube S1j1 and the second switch tube S1j2 will not be turned on at the same time. When the first switch tube S1j1 is turned on, the sub-switch module 35 is equivalent to forming a capacitive conduction loop, and when the second switch tube S1j2 is turned on, the sub-switch module 35 is equivalent to forming a short-circuit conduction loop. In addition, for the third bridge arm 3 and the fourth bridge arm 5, as shown in FIG. Figure 1 or Figure 2 As shown, HB1, HB2, ..., HBN correspond to the 1st to Nth sub-switch modules 35 in the third bridge arm 3 or the fourth bridge arm 5 respectively; for the third bridge arm 3, the input end of HB1 is connected to the input end of the first bridge arm 1, and the output end of HB1 is connected to the third bridge arm inductor 4; for the fourth bridge arm 5, the input end of HB1 is connected to the fourth bridge arm inductor 6, and the output end of HB1 is connected to the output end of the second bridge arm 2; HB1 corresponds to the sub-switch module 35 of HB2 located in the front stage, and HBN corresponds to the sub-switch module 35 of HBN-1 located in the rear stage.

[0056] In this embodiment, the first diode D1j1 and the second diode D1j2 can, on the one hand, clamp the first end and the second end of the first switch tube S1j1 and the second switch tube S1j2, thereby protecting the first switch tube S1j1 and the second switch tube S1j2; on the other hand, provide a freewheeling path when the LLC resonant cavity and the transformer T release the stored energy, thereby preventing the circuit from being damaged by the reverse electromotive force, so that the sub-switch module 35 not only has a simple circuit structure, but also has the characteristics of high safety and reliability.

[0057] Optionally, the first switch tube S1j1 and the second switch tube S1j2 are NPN transistors or NMOS transistors. The first end of the first switch tube S1j1 and the first end of the second switch tube S1j2 correspond to the collector of the corresponding NPN transistor or the drain of the NMOS transistor, the second end of the first switch tube S1j1 and the second end of the second switch tube S1j2 correspond to the emitter of the corresponding NPN transistor or the source of the NMOS transistor, and the control end of the first switch tube S1j1 and the control end of the second switch tube S1j2 correspond to the base of the corresponding NPN transistor or the gate of the NMOS transistor.

[0058] In some embodiments, Figure 1As shown, the LC resonance unit 7 includes a resonance capacitor Cr. The first end of the resonance capacitor Cr is the first end of the LC resonance unit 7, the second end of the resonance capacitor Cr is connected to the first end of the high voltage side of the transformer T, the second end of the high voltage side of the transformer T is connected to the third bridge arm inductor 4 and the fourth bridge arm inductor 6, and the resonance capacitor Cr can form the LLC resonance cavity (recorded as embodiment A) with the leakage inductance of the transformer T and one of the bridge arm inductors (i.e., the third bridge arm inductor 4 or the fourth bridge arm inductor 6).

[0059] This embodiment uses the leakage inductance of the transformer T, the resonant capacitor Cr and the bridge arm inductance to form an LLC resonant cavity, which helps to reduce the volume and weight of the medium voltage DC conversion circuit and improve the stray parameter performance of the resonant cavity.

[0060] Since the design difficulty of the transformer T is relatively high in the technical solution of forming the LLC resonant cavity through the leakage inductance of the transformer T, in order to reduce the design difficulty, in some embodiments, such as Figure 2 As shown, the LC resonance unit 7 further includes a resonance inductor Lm. The first end and the second end of the resonance inductor Lm are respectively connected to the first end and the second end of the high voltage side of the transformer T, and the second end of the resonance inductor Lm also serves as the second end of the LC resonance unit 7.

[0061] In this embodiment, if the inductance value of the leakage inductance of the transformer T is much larger than the inductance value of the resonant inductor Lm (for example, the inductance value of the leakage inductance of the transformer T is more than 9 times the inductance value of the resonant inductor Lm), the leakage inductance of the transformer T will not have much impact on the operation of the LLC resonant cavity, so the leakage inductance of the transformer T can be ignored, that is, the LLC resonant cavity at this time is equivalent to being composed of the resonant capacitor Cr, the resonant inductor Lm and one of the bridge arm inductors (recorded as embodiment B), which makes it more convenient for developers to directly adjust the performance of the LLC resonant cavity by adjusting the parameters of the resonant inductor Lm, but compared with embodiment A, there is a defect that the stray parameter performance of the resonant cavity is poor. If the inductance values ​​of the transformer T leakage inductance and the resonant inductance Lm are not significantly different, then the LLC resonant cavity is equivalent to being composed of the resonant capacitor Cr, one of the bridge arm inductors, and an equivalent inductance formed by connecting the transformer T leakage inductance and the resonant inductance Lm in parallel (recorded as embodiment C). Although this will relatively increase the difficulty of debugging the LLC resonant cavity, it has better resonant cavity stray parameter performance than embodiment B, and the resonant cavity stray parameter performance is worse than embodiment A, while the design flexibility is between embodiments B and A.

[0062] It can be understood that although the addition of the resonant inductor Lm in this embodiment will increase the volume and weight of the circuit, it can reduce the difficulty of designing the transformer T and improve the design flexibility of the characteristic parameters of the LLC resonant cavity. As for which embodiment of the LLC resonant cavity is sampled, it can be determined according to actual conditions.

[0063] Specifically, when the first bridge arm 1 is turned on and the second bridge arm 2 is turned off or the first bridge arm 1 is turned off and the second bridge arm 2 is turned on, the LC resonant unit 7 can form an LLC resonant cavity with the third bridge arm inductor 4 or the fourth bridge arm inductor 6. Further, the inductance values ​​of the third bridge arm inductor 4 and the fourth bridge arm inductor 6 can be the same, then the resonant frequency relationship of the LLC resonant cavity is as follows:

[0064] , and Represent the two resonant frequencies of the LLC resonant cavity, represents the inductance value of the third bridge arm inductor 4 or the fourth bridge arm inductor 6, represents the inductance value of the leakage inductance of the transformer T (corresponding to embodiment A) or the inductance value of the resonant inductor Lm (corresponding to embodiment B) or the equivalent inductance value after the resonant inductor Lm is connected in parallel with the leakage inductance on the high-voltage side of the transformer T (corresponding to embodiment C), Represents the capacitance value of the resonant capacitor Cr.

[0065] In addition, the working principle of the LLC resonant cavity and the transformer T can refer to the principle of the existing LLC DC transformer, which will not be repeated here.

[0066] In some embodiments, the resonant capacitor Cr may also be composed of multiple capacitors in series or in parallel, and the resonant inductor Lm may also be composed of multiple inductors in series or in parallel, which helps to improve the flexibility of adjusting the characteristic parameters of the LLC resonant cavity.

[0067] In some embodiments, Figure 4 As shown, the first bridge arm 1 includes a plurality of third switch tubes Q3. The third switch tubes Q3 are connected in series in sequence, and the control end of each third switch tube Q3 is used to simultaneously access the first on-off control signal. Specifically, Figure 4 As shown, the first end of the first third switch tube Q3 corresponds to the input end of the first bridge arm 1, the second end of the first third switch tube Q3 is connected to the first end of the second third switch tube Q3, the second end of the second third switch tube Q3 is connected to the first end of the third third switch tube Q3, ..., the second end of the Z-1 third switch tube Q3 is connected to the first end of the Z third switch tube Q3, and the second end of the Z third switch tube Q3 corresponds to the output end of the first bridge arm 1; wherein Z is the total number of the third switch tubes Q3. In this embodiment, the control end of each third switch tube Q3 can be connected to the same control pulse signal (i.e., the first on-off control signal), so that each third switch tube Q3 can be synchronously controlled to be turned on or off at the same time, and then the first bridge arm 1 is equivalent to a switch device controlled by only one control signal, which helps to simplify the circuit control method.

[0068] In some embodiments, Figure 4 As shown, the second bridge arm 2 may include a plurality of fourth switch tubes Q4. The fourth switch tubes Q4 are sequentially connected in series, and the control end of each fourth switch tube Q4 is used to simultaneously access the second on-off control signal. Specifically, Figure 4 As shown, the first end of the first fourth switch tube Q4 corresponds to the input end of the second bridge arm 2, the second end of the first fourth switch tube Q4 is connected to the first end of the second fourth switch tube Q4, the second end of the second fourth switch tube Q4 is connected to the first end of the third fourth switch tube Q4, ..., the second end of the Z-1 fourth switch tube Q4 is connected to the first end of the Z fourth switch tube Q4, and the second end of the Z fourth switch tube Q4 corresponds to the output end of the second bridge arm 2; wherein Z is the total number of the fourth switch tubes Q4. In this embodiment, the control end of each fourth switch tube Q4 can be connected to the same control pulse signal (i.e., the second on-off control signal), so that each fourth switch tube Q4 can be synchronously controlled to be turned on or off at the same time, thereby making the second bridge arm 2 equivalent to a switch device controlled by only one control signal.

[0069] Optionally, the third switch tube Q3 and the fourth switch tube Q4 are NPN transistors or NMOS tubes, the first ends of the third switch tube Q3 and the fourth switch tube Q4 correspond to the collector of the corresponding NPN transistor or the drain of the NMOS tube, the second ends of the third switch tube Q3 and the fourth switch tube Q4 correspond to the emitter of the corresponding NPN transistor or the source of the NMOS tube, and the control ends of the third switch tube Q3 and the fourth switch tube Q4 correspond to the base of the corresponding NPN transistor or the gate of the NMOS tube.

[0070] In some embodiments, Figure 4 As shown, the first bridge arm 1 also includes a plurality of third diodes D3 having the same number as the third switch tubes Q3. The cathode and anode of each third diode D3 are connected to the first end and the second end of the corresponding third switch tube Q3 one by one in sequence. The third diode D3 plays a clamping role, which can protect the third switch tube Q3 and provide a freewheeling path when the LLC resonant cavity and the transformer T release the stored energy to prevent the reverse electromotive force from damaging the circuit.

[0071] In some embodiments, Figure 4 As shown, the second bridge arm 2 also includes a plurality of fourth diodes D4, the same number as the fourth switch tube Q4. The cathode and anode of each fourth diode D4 are connected to the first end and the second end of the corresponding fourth diode D4 one by one in sequence. The fourth diode D4 plays a clamping role, which can protect the fourth switch tube Q4 and provide a freewheeling path when the LLC resonant cavity and the transformer T release the stored energy to prevent the reverse electromotive force from damaging the circuit.

[0072] In some embodiments, Figure 1As described above, the asymmetric LLC resonant medium voltage DC conversion circuit further includes a rectifying unit 8 connected to the low voltage side of the transformer T for rectifying the low voltage AC voltage and outputting a low voltage DC voltage.

[0073] Further, the rectifying unit 8 may include a fifth switch tube S21, a fifth diode D21, a sixth switch tube S24, a sixth diode D24, a seventh switch tube S23, a seventh diode D23, an eighth switch tube S22 and an eighth diode D22. The first end of the low-voltage side of the transformer T is simultaneously connected to the second end of the fifth switch tube S21, the anode of the fifth diode D21, the first end of the eighth switch tube S22, and the cathode of the eighth diode D22; the second end of the low-voltage side of the transformer T is simultaneously connected to the first end of the sixth switch tube S24, the cathode of the sixth diode D24, the second end of the seventh switch tube S23, and the anode of the seventh diode D23; the first end of the fifth switch tube S21, the cathode of the fifth diode D21, the first end of the seventh switch tube S23, and the cathode of the seventh diode D23 are connected as the low-voltage DC voltage positive end of the rectifier unit 8; the second end of the eighth switch tube S22, the anode of the eighth diode D22, the second end of the sixth switch tube S24, and the anode of the sixth diode D24 are connected as the low-voltage DC voltage negative end of the rectifier unit 8; the fifth switch tube S21 is connected to the third on-off control signal; the sixth switch tube S24 is connected to the fourth on-off control signal; the seventh switch tube S23 is connected to the fifth on-off control signal; and the control end of the eighth switch tube S22 is connected to the sixth on-off control signal.

[0074] In this embodiment, the fifth switch tube S21 and the sixth switch tube S24 form a first rectifier half-bridge, the seventh switch tube S23 and the eighth switch tube S22 form a second rectifier half-bridge, and under the control of the third to sixth on-off control signals, the first and second rectifier half-bridges are alternately turned on in sequence, thereby converting the low-voltage AC voltage into a low-voltage DC voltage; for the fifth diode D21, the sixth diode D24, the seventh diode D23 and the eighth diode D22, a conventional rectifier bridge structure has been formed, and its function is to maintain the rectification of the low-voltage AC voltage during the dead time (dead time refers to the short time interval during which the fifth to eighth switch tubes are not turned on at the same time during the output process of the transformer T) of the fifth to eighth switch tubes in the coordination process, thereby improving the stability of the circuit. It is easy to understand that the conduction voltage drop of the diode is larger than the conduction voltage drop of the fifth to eighth switch tubes. If a large current passes for a long time, the circuit efficiency will be reduced. Therefore, this embodiment can not only ensure the basic function of the circuit through the coordination of the diode and the triode, but also effectively improve the circuit efficiency.

[0075] Optionally, the fifth switch tube S21 , the sixth switch tube S24 , the seventh switch tube S23 and the eighth switch tube S22 are all NMOS tubes.

[0076] The present invention provides a control method, which is used to control the asymmetric LLC resonant medium voltage DC conversion circuit provided in an embodiment of the present invention, such as Figure 5 As shown, the method includes a first half-cycle control step and a second half-cycle control step.

[0077] The first half-cycle control step includes: controlling the number of capacitive conduction loops formed by the multiple sub-switch modules 35 included in the third bridge arm 3 and the number of capacitive conduction loops formed by the multiple sub-switch modules 35 included in the fourth bridge arm 5 according to the preset positive half-wave low-voltage AC voltage amplitude, and controlling the first bridge arm 1 to be turned on and the second bridge arm 2 to be turned off, and continuing for a first preset time.

[0078] The second half-cycle control step includes: controlling the number of capacitive conduction loops formed by the multiple sub-switch modules 35 included in the third bridge arm 3 and the number of capacitive conduction loops formed by the multiple sub-switch modules 35 included in the fourth bridge arm 5 according to the preset negative half-wave low-voltage AC voltage amplitude, and controlling the first bridge arm 1 to be closed and the second bridge arm 2 to be turned on, and continuing for a second preset time.

[0079] It is easy to understand that as long as the first half-cycle control step and the second half-cycle control step are cyclically and alternately executed, the transformer T can be controlled to output a stable sinusoidal low-voltage AC power. In addition, the first preset time and the second preset time can be equal, and the specific time setting can refer to the existing LLC DC transformer control scheme, which is not limited here.

[0080] Further, the analysis Figure 1 It can be seen that the expression of the preset positive half-wave low-voltage AC voltage amplitude is: . Represents the preset positive half-wave low-voltage AC voltage amplitude; Represents the transformation ratio of transformer T; represents the number of capacitive conduction loops formed by the plurality of sub-switch modules 35 included in the third bridge arm 3 in the first half-cycle control step; It represents the number of capacitive conduction loops formed by the plurality of sub-switch modules 35 included in the fourth bridge arm 5 in the first half-cycle control step.

[0081] The expression of the preset negative half-wave low-voltage AC voltage amplitude is: . Represents the preset negative half-wave low-voltage AC voltage amplitude; represents the number of capacitive conduction loops formed by the plurality of sub-switch modules 35 included in the fourth bridge arm 5 in the second half-cycle control step; It represents the number of capacitive conduction loops formed by the multiple sub-switch modules 35 included in the third bridge arm 3 in the second half-cycle control step.

[0082] It is easy to understand that this embodiment can be controlled by , , , The number of low voltage AC voltage amplitude can be effectively controlled, so that even if the medium voltage DC voltage There are large fluctuations, as long as you adjust the settings , , , By adjusting the size of , the amplitude of the low-voltage AC voltage can be controlled at a stable value, that is, the transformer T is guaranteed to operate in a wide range of high efficiency and soft switching under a wide input voltage, which plays a positive role in maintaining the stability of electrical equipment in the seabed observation station. This method also has the advantages of simple control and high efficiency.

[0083] Optionally, equal , equal , so that the amplitudes of the positive proportional wave and the negative half-wave low-voltage AC voltage are equal or nearly equal, which helps to improve the stability of the low-voltage DC voltage obtained after rectification of the low-voltage AC voltage.

[0084] In some embodiments, the number of sub-switch modules 35 included in the third bridge arm 3 and the fourth bridge arm 5 is N, where N is a natural number greater than 3.

[0085] Accordingly, in the first half-cycle control step, it also includes: limiting according to the first preset function and The setting value of; wherein the first preset function is expressed as: .

[0086] Furthermore, in the second half-cycle control step, it also includes: limiting according to the second preset function and The setting value of; wherein the second preset function is expressed as: .in, Represents the minimum allowable voltage value across the capacitive conduction loop; Represents the maximum allowable voltage across the capacitive conduction loop.

[0087] It should be noted that for capacitors of the same type, after the input frequency-stable AC voltage is applied, the voltage at both ends generally tends to a certain fixed value. In order to ensure that, in the embodiment provided by the present invention, the medium voltage DC voltage, the transformer T ratio, the preset positive half-wave and negative half-wave low voltage AC voltage amplitudes are determined. , , , When the size of is set, the voltage value of each sub-switch module 35 when forming a capacitive conduction loop is regarded as a fixed value. However, in fact, the voltage value of each sub-switch module 35 when forming a capacitive conduction loop may be different due to process differences, etc., even if the same type of first capacitor VC1j is used, there will be differences. However, in order to ensure the stability of the low-voltage AC voltage output by the transformer T, in this embodiment, based on , The value of , , , The size of the first capacitor VC1j can reduce the degree to which the inherent error superimposed on the stable output of the transformer T when the AC voltage is passed to the first capacitor VC1j to within the allowable range. and The size can be determined by the parameters, specifications, and manufacturing process of the first capacitor VC1j, but and The difference between them can be customized according to actual application requirements and is not limited here.

[0088] In some embodiments, the first end of the high voltage side of the transformer T and the first end of the low voltage side of the transformer T are the same end. Correspondingly, the first half-cycle control step also includes: controlling the fifth switch tube S21 and the sixth switch tube S24 to be turned on and lasting for a third preset time. The third preset time is slightly less than the first preset time.

[0089] Furthermore, the first half-cycle control step further includes: controlling the seventh switch tube S23 and the eighth switch tube S22 to be turned on and lasting for a fourth preset time. The fourth preset time is slightly less than the second preset time. In addition, when the first preset time and the second preset time are the same, the third preset time and the fourth preset time are also the same.

[0090] The present invention further provides a control circuit, comprising a processor, and when the processor executes a stored computer program, the processor implements the steps of the control method provided in the embodiment of the present invention.

[0091] The present invention further provides an asymmetric LLC resonant medium-voltage DC conversion device, comprising the asymmetric LLC resonant medium-voltage DC conversion circuit provided by an embodiment of the present invention, and the control circuit provided by an embodiment of the present invention.

[0092] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0093] Professionals may further appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described in the above description according to function. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians may use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0094] The steps of the method or algorithm described in conjunction with the embodiments disclosed herein may be implemented directly using hardware, a software module executed by a processor, or a combination of the two. The software module may be placed in a random access memory (RAM), a memory, a read-only memory (ROM), an electrically programmable ROM, an electrically erasable programmable ROM, a register, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.

[0095] It can be understood that the above embodiments only express the preferred implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the patent scope of the present invention. It should be pointed out that, for ordinary technicians in this field, the above technical features can be freely combined without departing from the concept of the present invention, and several deformations and improvements can be made, which all belong to the protection scope of the present invention. Therefore, all equivalent changes and modifications made to the scope of the claims of the present invention should belong to the coverage of the claims of the present invention.

Claims

1. A control method, characterized in that: Used to control an asymmetric LLC resonant medium-voltage DC conversion circuit, the asymmetric LLC resonant medium-voltage DC conversion circuit comprising a first bridge arm (1), a second bridge arm (2), a third bridge arm (3), a third bridge arm inductor (4), a fourth bridge arm (5), a fourth bridge arm inductor (6), an LC resonant unit (7) and a transformer T; The input end of the first bridge arm (1) is used to connect to the positive pole of the medium-voltage DC voltage, the output end of the second bridge arm (2) is used to connect to the negative pole of the medium-voltage DC voltage, the first end of the LC resonance unit (7) is simultaneously connected to the output end of the first bridge arm (1) and the input end of the second bridge arm (2), the second end of the LC resonance unit (7) is connected to the input end of the first bridge arm (1) via the third bridge arm inductor (4) and the third bridge arm (3), and is connected to the output end of the second bridge arm (2) via the fourth bridge arm inductor (6) and the fourth bridge arm (5); The high voltage side of the transformer T is connected to the LC resonance unit (7); when the first bridge arm (1) is turned on and the second bridge arm (2) is turned off, the LC resonance unit (7) and the fourth bridge arm inductor (6) form an LLC resonance cavity, so that the low voltage side of the transformer T outputs a positive half-wave low voltage AC voltage; when the first bridge arm (1) is turned off and the second bridge arm (2) is turned on, the LC resonance unit (7) and the third bridge arm inductor (4) form an LLC resonance cavity, so that the low voltage side of the transformer T outputs a negative half-wave low voltage AC voltage; The third bridge arm (3) and the fourth bridge arm (5) respectively comprise a plurality of sub-switch modules (35); the plurality of sub-switch modules (35) included in the third bridge arm (3) are sequentially connected in series, and the plurality of sub-switch modules (35) included in the fourth bridge arm (5) are sequentially connected in series; each of the sub-switch modules (35) is used to form a short-circuit conduction loop or a capacitive conduction loop according to a control signal; The first bridge arm (1) comprises a plurality of third switch tubes Q3; the third switch tubes Q3 are connected in series in sequence, and the control end of each third switch tube Q3 is used to simultaneously access a first on-off control signal; the second bridge arm (2) comprises a plurality of fourth switch tubes Q4; the fourth switch tubes Q4 are connected in series in sequence, and the control end of each fourth switch tube Q4 is used to simultaneously access a second on-off control signal; The method comprises: A first half-cycle control step: controlling the number of capacitive conduction loops formed by the plurality of sub-switch modules (35) included in the third bridge arm (3) and the number of capacitive conduction loops formed by the plurality of sub-switch modules (35) included in the fourth bridge arm (5) respectively according to a preset positive half-wave low-voltage AC voltage amplitude, and controlling the first bridge arm (1) to be turned on and the second bridge arm (2) to be turned off, and for a first preset time; The second half-cycle control step is: controlling the number of capacitive conduction loops formed by the plurality of sub-switch modules (35) included in the third bridge arm (3) and the number of capacitive conduction loops formed by the plurality of sub-switch modules (35) included in the fourth bridge arm (5) respectively according to a preset negative half-wave low-voltage AC voltage amplitude, and controlling the first bridge arm (1) to be turned off and the second bridge arm (2) to be turned on, and continuing for a second preset time.

2. The control method according to claim 1, characterized in that: The expression of the preset positive half-wave low-voltage AC voltage amplitude is: ； Represents the preset positive half-wave low-voltage AC voltage amplitude; represents the transformation ratio of the transformer T; represents the number of capacitive conduction loops formed by the plurality of sub-switch modules (35) included in the third bridge arm (3) in the first half-cycle control step; Represents medium voltage DC voltage; represents the number of capacitive conduction loops formed by the plurality of sub-switch modules (35) included in the fourth bridge arm (5) in the first half-cycle control step; The expression of the preset negative half-wave low-voltage AC voltage amplitude is: ； Represents the preset negative half-wave low-voltage AC voltage amplitude; represents the number of capacitive conduction loops formed by the plurality of sub-switch modules (35) included in the fourth bridge arm (5) in the second half-cycle control step; represents the number of capacitive conduction loops formed by the plurality of sub-switch modules (35) included in the third bridge arm (3) in the second half-cycle control step; in, equal , equal .

3. The control method according to claim 2, characterized in that: The number of sub-switch modules (35) included in the third bridge arm (3) and the fourth bridge arm (5) is N, where N is a natural number greater than 3; In the first half-cycle control step, it also includes: limiting the and The setting value of Wherein, the first preset function is expressed as: ； In the second half-cycle control step, it also includes: limiting the and The setting value of Wherein, the second preset function is expressed as: ； represents the minimum permissible voltage value across the capacitive conduction loop; Represents the maximum allowable voltage value across the capacitive conduction loop.

4. The control method according to claim 1, characterized in that: Each of the sub-switch modules (35) comprises a first switch tube S1j1, a first diode D1j1, a second switch tube S1j2, a second diode D1j2 and a first capacitor VC1j; The first end of the first switch tube S1j1 is connected as the input end of the sub-switch module (35) to the output end of the sub-switch module (35) at the previous stage or to the input end of the first bridge arm (1) or to the fourth bridge arm inductor (6); the first end and the second end of the first diode D1j1 and the first switch tube S1j1 are connected in parallel; and the control end of the first switch tube S1j1 is used to receive a first sub-control signal; The second end of the first switch tube S1j1 is connected to the first end of the second switch tube S1j2, the second diode D1j2 and the first end and the second end of the second switch tube S1j2 are connected in parallel, the control end of the second switch tube S1j2 is used to receive a second sub-control signal, the second end of the second switch tube S1j2 is connected as the output end of the sub-switch module (35) to the input end of the sub-switch module (35) at the subsequent stage or to the third bridge arm inductor (4) or to the output end of the second bridge arm (2), and the two ends of the first capacitor VC1j are respectively connected to the first end of the first switch tube S1j1 and the second end of the second switch tube S1j2.

5. The control method according to claim 1, characterized in that: The LC resonance unit (7) comprises a resonance capacitor Cr; the first end of the resonance capacitor Cr is the first end of the LC resonance unit (7); the second end of the resonance capacitor Cr is connected to the first end of the high-voltage side of the transformer T; the second end of the high-voltage side of the transformer T is connected to the third bridge arm inductor (4) and the fourth bridge arm inductor (6); the resonance capacitor Cr can form the LLC resonance cavity with the leakage inductance of the transformer T and one of the bridge arm inductors.

6. The control method according to claim 5, characterized in that: The LC resonance unit (7) further comprises a resonance inductor Lm; a first end and a second end of the resonance inductor Lm are respectively connected to a first end and a second end of a high voltage side of the transformer T; the LLC resonance cavity is formed by the resonance capacitor Cr, the resonance inductor Lm and one of the bridge arm inductors, or is formed by the resonance capacitor Cr, one of the bridge arm inductors and an equivalent inductance formed by connecting the leakage inductance of the transformer T and the resonance inductor Lm in parallel.

7. A control circuit, comprising a processor, characterized in that: When the processor executes the stored computer program, the processor implements the steps of the control method according to any one of claims 1 to 6.

8. An asymmetric LLC resonant medium voltage DC converter, characterized in that: It comprises an asymmetric LLC resonant medium voltage DC conversion circuit and a control circuit as claimed in claim 7.

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