High-power modular LLC resonant converter interleaving parallel control system and method

Abstract

The invention discloses a high-power modular LLC resonant converter interleaving parallel control system and method, and belongs to the technical field of power control. The system comprises a gain control unit, a voltage regulation unit and a stagger angle control unit which are arranged on the input side of an inverter, the gain control unit is used for calculating the difference of gains among phases according to the unbalance degree of output current of each phase and adjusting the conduction time of a switching tube of each phase by using phase shift control, and an output switching signal is input to a lower half bridge arm of the inverter after being subjected to phase shift of the interlacing angle control unit; the voltage regulation unit compares the difference value between the actual output voltage and the set output voltage as the input of the voltage-controlled oscillator, and the output switching signal is input to the upper half bridge arm of the inverter after being subjected to phase shift of the interleaving angle control unit; and the interlacing angle control unit calculates the interlacing angle of each phase during parallel connection according to the phase number of the parallel module and the operation mode of each phase, and adjusts the interlacing angle according to the amplitude of the output current ripple to realize the minimum output current ripple.

Description

Technical Field

[0001] The present invention belongs to the technical field of power control, and in particular relates to a high-power modular LLC resonant converter staggered parallel control system and method. Background Art

[0002] In the decades since its invention, LLC resonant converter has been widely used due to its high efficiency, high power density, and easy soft switching within the full load range. It is considered to be the simplest topology that can achieve zero voltage turn-on on the primary side and zero current turn-off on the secondary side, and is one of the most effective DC-DC topologies at present. However, due to the limitations of power semiconductor devices in terms of voltage resistance, current carrying capacity, and switching speed, the power range of single-phase LLC resonant converters is generally limited to 100W-1kW, which limits the application of LLC in high-power energy transmission occasions. For this reason, LLC parallel technology came into being. By evenly distributing power to each phase of LLC running in parallel, it can be applied to higher power occasions. However, in actual applications, the difference in device parameters will lead to differences in LLC voltage gain of each phase, which will lead to serious imbalance in output current, increase the current stress of power devices, and seriously reduce the service life and reliability of the device. Therefore, current sharing technology must be used for LLC parallel operation. The current sharing methods for multi-phase LLC parallel can be mainly divided into two categories: passive current sharing and active current sharing. Passive current sharing is to achieve current sharing of the circuit only through the design of circuit topology without adding any detection links and power device switches to the circuit, and the current sharing effect is not good. Active current sharing is to add detection links and control links to the original circuit and achieve current sharing through additional control. Controllable capacitors and controllable inductors are the most direct technologies for compensating the parameter differences of components. Although the idea is simple, the addition of additional active devices increases the operating cost and control difficulty. Another widely used current sharing technology is to use phase shift control to adjust the gain of each phase. This method does not require additional devices and can achieve gain control by adjusting the gate signal of the switch tube. However, due to the complex influence of phase shift control on gain, the control process often relies on actual debugging rather than theoretical calculation. In addition, the increase of the phase shift angle will also reduce the duty cycle of the output current, and present a larger current amplitude when the average value of the output current is the same, which will cause the output current ripple to increase further after the system is connected in parallel. Summary of the invention

[0003] In view of the deficiencies in the prior art, an object of the present invention is to provide a high-power modular LLC resonant converter staggered parallel control system and method, which solves the problems in the prior art.

[0004] The purpose of the present invention can be achieved through the following technical solutions:

[0005] A high-power modular LLC resonant converter interleaved parallel control system, comprising: a gain control unit, a voltage adjustment unit and an interleaving angle control unit arranged at the input side of an inverter;

[0006] The gain control unit calculates the gain difference between the phases according to the imbalance of the output current of each phase, and uses phase shift control to adjust the conduction time of the switch tube of each phase to obtain the same voltage gain. The output switching signal is input to the lower half bridge arm of the inverter after phase shifting by the staggered angle control unit;

[0007] The voltage regulating unit compares the difference between the actual output voltage and the set output voltage as the input of the voltage controlled oscillator. The switching signal output by the voltage controlled oscillator is input to the upper half bridge arm of the inverter after being phase-shifted by the staggered angle control unit.

[0008] The interleaving angle control unit calculates the interleaving angle of each phase in parallel according to the phase number of the parallel modules and the operating mode of each phase, and adjusts the interleaving angle according to the output current ripple amplitude to obtain the minimum output current ripple.

[0009] Furthermore, in the gain control unit, the parallel current sharing mechanism is analyzed based on the state plane method, and the state of multi-phase LLC parallel operation is decomposed into the operation state of single-phase LLC secondary sideband voltage source type load, and the state equations corresponding to the P, O, and N modes are respectively:

[0010]

[0011]

[0012]

[0013] In the formula, the subscript N represents the normalized value, the subscript 0 represents the state quantity of the system when it is running in steady state, and C r is the resonant capacitor value, v Cr Refers to the resonant capacitor voltage, L r is the resonant inductance, i Lr Refers to the resonant inductor current, L m is the magnetizing inductance, L n Refers to the excitation inductance L m With the resonant inductor L r The ratio of L n =L m / L r .

[0014] Furthermore, in the gain control unit, the modeling of the phase shift angle and the voltage gain is obtained based on the modal analysis method, and the function Mag(α) of the phase shift angle with respect to the voltage gain is:

[0015]

[0016] Where n is the transformer primary-to-secondary ratio, T c is the switching period, αT c is the duration of the P phase, M is the duration of the phase shift phase, and I o (α), V o (α) represents the function of the average output current and the average output voltage with respect to the phase shift angle; Δi L (t) is the current flowing to the transformer, which is numerically equal to the difference between the resonant inductor current and the magnetizing inductor current.

[0017] Furthermore, in the staggered angle control unit, the frequency condition for the output current to reduce the ripple by staggering is that all phase frequencies are exactly the same, and the staggered phases of each phase are determined by the total number of parallel phases in the system and the mode of operation of each phase; N-phase LLC parallel connection is staggered, and the ripple reduction effect is best when the output current has no O mode. When the staggered angle of each phase is π / N, the ripple is reduced to times, α is a constant related to the number of parallel phases N; the staggered angle corresponding to the minimum ripple of the output current in the O mode decreases from the reference phase until the minimum output current ripple is obtained.

[0018] Furthermore, the calculation formula of the constant α related to the number of parallel phases N is:

[0019]

[0020] A high-power modular LLC resonant converter interleaved parallel control method, using the above-mentioned high-power modular LLC resonant converter interleaved parallel control system, comprises the following steps:

[0021] S1, collect the output voltage value and compare it with the set output voltage value, and transmit the value to the voltage-controlled oscillator through the controller, and the voltage-controlled oscillator outputs a switching signal of a certain frequency to the staggered angle control unit;

[0022] S2 collects the output current of each phase and calculates the average output current based on the switching frequency; after the output current is compared, the phase shift angle of each phase is adjusted by the phase shift control and output to the staggered angle control unit;

[0023] S3, the interleaving angle control unit sets the size of the interleaving angle according to the mode of each phase output current in steady state. When the output current does not have O mode, the interleaving angle is maintained at π / N. When O mode appears in a certain phase, starting from the second phase, the interleaving angle of each phase needs to be gradually reduced until the minimum output current ripple is obtained. This interleaving angle is used as the interleaving angle of the system when it is finally in steady state operation.

[0024] A computer storage medium stores a readable program, and when the program is running, it can execute the above-mentioned high-power modular LLC resonant converter interleaving parallel control method.

[0025] An electronic device, comprising: a processor, a memory, a communication interface and a communication bus, wherein the processor, the memory and the communication interface communicate with each other through the communication bus;

[0026] The memory is used to store at least one executable instruction, and the executable instruction enables the processor to perform operations corresponding to the above-mentioned high-power modular LLC resonant converter interleaved parallel control method.

[0027] A computer program product includes computer instructions, wherein the computer instructions instruct a computing device to execute operations corresponding to the above-mentioned high-power modular LLC resonant converter interleaving parallel control method.

[0028] Beneficial effects of the present invention:

[0029] 1. The present invention can realize the current sharing of multi-phase LLC resonant converters in staggered parallel connection, and is particularly suitable for current sharing control of any phase system with more than two phases. When the parallel system causes uneven current sharing due to changes in the resonant cavity gain caused by component parameter errors, the gain of the phase with higher gain is reduced through phase shift control, so that the gain of all phases is adjusted to the same level to achieve output current sharing.

[0030] 2. The interleaving angle control in the present invention adjusts the interleaving angle according to the number of phases of the parallel system and the mode of system operation to reduce the output current ripple as much as possible, giving full play to the advantage of load sharing of the parallel system and improving the efficiency and reliability of the system during parallel operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 It is a schematic diagram of the structure of the converter interleaved parallel control system of the present invention;

[0033] Figure 2 It is a state plane trajectory diagram of the output voltage after the output voltage changes under the control of the parallel system of the present invention;

[0034] Figure 3 It is a phase shift control waveform diagram used in the present invention;

[0035] Figure 4It is a schematic diagram of modal decomposition for phase shift control of the present invention;

[0036] Figure 5 It is a comparison diagram of the theoretical gain and actual gain of phase shift control obtained based on modal decomposition of the present invention;

[0037] Figure 6 It is a schematic diagram of the present invention for reducing the sinusoidal output current ripple by staggered parallel connection. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] Example 1

[0040] like Figure 1 As shown, a high-power modular LLC resonant converter interleaved parallel control system includes: a gain control unit, a voltage adjustment unit and an interleaving angle control unit arranged at the input side of the inverter,

[0041] The input port of the DC voltage and the output port of the rectifier circuit are both in parallel. The diode bridge on the secondary side prevents the reverse flow of current, so there is no need to consider the circulation problem. The voltage regulation unit compares the difference between the actual output voltage and the expected output voltage as the input of the voltage-controlled oscillator. The voltage-controlled oscillator outputs a switching signal of a specific frequency to adjust the gain of each phase resonant cavity. The output switching signal is input to the upper half bridge arm Q of the inverter after the phase shift angle is controlled by the staggered angle control unit. i1 With Q i2 The gain control unit calculates the gain difference between each phase according to the imbalance of the output current of each phase, and uses phase shift control to adjust the conduction time of each phase switch to obtain the same voltage gain. The gain reduction effect is achieved by increasing the phase difference between the lower half bridge arm and the upper half bridge arm. The output switching signal is input to the lower half bridge arm Q of the inverter after the staggered angle control unit performs staggered angle control. i3 With Q i4 .

[0042] In the gain control unit, the parallel current sharing mechanism is analyzed based on the state plane method. The state of multi-phase LLC parallel operation is decomposed into the operation state of single-phase LLC secondary sideband voltage source type load; the state equations corresponding to the P, O, and N modes are:

[0043]

[0044]

[0045]

[0046] In the formula, the subscript N represents the normalized value, the subscript 0 represents a set of state quantities corresponding to the steady state, and C r is the resonant capacitor value, v Cr is the resonant capacitor voltage, L r is the resonant inductance, i Lr Refers to the resonant inductor current, L m is the magnetizing inductance, L n Refers to the excitation inductance L m With the resonant inductor L r The ratio of L n =L m / L r . Figure 2 It is the state plane trajectory after the parallel output voltage changes when the switching frequency is fixed.

[0047] In the gain control unit, the modeling of the phase shift angle and voltage gain of the phase shift control is based on the modal analysis method; the key waveforms of the phase shift control are as follows: Figure 3 As shown, the resonant inductor current i Lr2 Compared with the current i when phase shift control is not used Lr1 It is not a simple truncated relationship. The output current amplitude of phase-shift control is large but the conduction time is short, while the output current amplitude of non-phase-shift control is small but the conduction time is long.

[0048] The modal analysis results of LLC operation are as follows: Figure 4 As shown, Figure 4 The P, phase shift, and N modes in the 0 ~t 1 ,t 1 ~t 2 ,t 2 ~t 3 The equivalent circuit of the circuit; four sets of equations about the resonant inductor current and the resonant capacitor voltage can be written from the state at the beginning and end of the P phase, and five sets of equations about the resonant inductor current, the excitation inductance and the resonant capacitor voltage can be written from the state at the beginning and end of the O phase. The two sets of equations at the end of the O phase are derived from the symmetry of the LLC, and the tenth equation can be obtained based on the numerical relationship between the secondary current and the primary current, and then the voltage gain corresponding to the phase shift angle can be solved, such as Figure 5 shown.

[0049] The ten equations mentioned above are as follows:

[0050]

[0051]

[0052]

[0053] In the formula, ω 0 represents the resonant angular frequency, V in Represents the input DC voltage value, V o represents the output voltage, n represents the transformer ratio, and K represents the resonant inductor current at t 0 The opposite value of the value at the moment, J represents the resonant capacitor voltage at t 0 The opposite of the value at the moment, X, represents the amplitude and initial phase of the resonant inductor current in the P phase, Y, Represents the amplitude and initial phase of the resonant inductor current in the phase shift stage, Z, represents the amplitude and initial phase of the resonant inductor current in the O stage, M represents the duration of the phase shift stage, αT c Represents the duration of the P phase.

[0054] Based on the original frequency control, the modal analysis method introduces the mode of primary power supply shutting down during phase shift. According to the symmetry of LLC, the two boundary states of P mode and O mode are solved to obtain the initial value of the differential equation corresponding to each mode. Then, according to the numerical relationship between the secondary current and the primary current, all state quantities are solved: three groups of resonant currents in the P phase, phase shift phase, and O phase, the amplitude and phase of the resonant inductor, the initial value and slope of the excitation inductor, and the phase shift phase time; the difference between the resonant inductor and the excitation inductor current in half a switching cycle is equal to the secondary current converted to the primary side, and the functional relationship of the phase shift angle with respect to the voltage gain is obtained:

[0055]

[0056] Where n is the transformer primary-to-secondary ratio, T c is the switching period, αT c is the duration of the P phase, M is the duration of the phase shift phase, and I o (α), V o (α) represents the function of the average output current and the average output voltage with respect to the phase shift angle; Δi L (t) is the current flowing to the transformer, which is numerically equal to the difference between the resonant inductor current and the magnetizing inductor current.

[0057] In the staggered angle control unit, the phase of the first phase is recorded as 0. If the output current does not have an O mode, it can be approximately recorded as a sine waveform. When the two phases are connected in parallel, the output currents of the two phases can be recorded as:

[0058]

[0059]

[0060] Simplified, consider the same output current amplitude A 1 =A 2 =A, only the frequency and phase change. After removing the absolute value, the output current of the parallel connection is:

[0061]

[0062] When the two-phase frequencies are different, an angular frequency of The beat frequency phenomenon, the amplitude within each beat is 2A, which cannot achieve the effect of interleaving and paralleling to reduce ripple; because interleaving and paralleling must have the same frequency between phasesω 1 =ω 2 =ω. Figure 6 As shown in (a) to (d), Figure 6 (a) is the output current waveform of one phase. Figure 6 (b) is the result of the two-phase output current being staggered at a 90° stagger angle. Figure 6 (c) is the result after the four-phase output current is staggered at a 45° stagger angle. Figure 6 (d) in the figure is the result of the three-phase output current being staggered at a 60° stagger angle. It can be seen that the minimum value of the N-phase output current is obtained when the phases between the phases differ by π / N. After this staggering method, the ripple can be reduced to the original times. Where α is defined as a constant related to the number of parallel phases:

[0063]

[0064] If the output current is in O mode, that is, the output current is intermittent, this is caused by compressing the switch conduction time when the phase shift control reduces the gain. This will weaken the effect of interleaving and parallel connection to reduce ripple. The interleaving angle in this case is a suboptimal solution that depends on the computer simulation results. Note that the duty cycle of the first phase changes from 1 to α 1 , then the staggered phase shift of the second phase to obtain the minimum ripple is located at [π / N,α 1 +π / N]. That is, starting from the second phase, each phase needs to gradually reduce the staggered angle until the minimum output current ripple is obtained.

[0065] Example 2

[0066] Based on the high-power modular LLC resonant converter interleaved parallel control system mentioned in Example 1, in this embodiment, a high-power modular LLC resonant converter interleaved parallel control method is proposed, which specifically includes the following steps:

[0067] S1, first collects the output voltage value and compares it with the set output voltage value, and transmits the value to the voltage-controlled oscillator through the controller. The voltage-controlled oscillator outputs a switching signal of a certain frequency to the staggered angle control unit.

[0068] S2, collects the output current of each phase and calculates the average output current based on the switching frequency. After the output current is compared, the phase shift angle of each phase is adjusted by the phase shift control and output to the staggered angle control unit.

[0069] S3, the interleaving angle control unit sets the size of the interleaving angle according to the mode of the output current of each phase in steady state, and maintains the interleaving angle at π / N when the output current is not discontinuous. When the output current of a phase is discontinuous, starting from the second phase, the interleaving angle of each phase needs to be gradually reduced until the minimum output current ripple is obtained. This interleaving angle is used as the interleaving angle of the system when it is finally in steady state operation.

[0070] Based on similar inventive concepts, an embodiment of the present invention further provides a computer storage medium storing a readable program, which can execute the above-mentioned high-power modular LLC resonant converter interleaved parallel control method when the program is running.

[0071] Based on similar inventive concepts, an embodiment of the present invention provides an electronic device, comprising: a processor, a memory, a communication interface and a communication bus, wherein the processor, the memory and the communication interface communicate with each other through the communication bus;

[0072] The memory is used to store at least one executable instruction, and the executable instruction enables the processor to perform operations corresponding to the above-mentioned high-power modular LLC resonant converter interleaved parallel control method.

[0073] Based on similar inventive concepts, an embodiment of the present invention further provides a computer program product, including computer instructions, which instruct a computing device to execute operations corresponding to the above-mentioned high-power modular LLC resonant converter interleaved parallel control method.

[0074] The method in embodiment 2 can be implemented in hardware, firmware, or implemented as software or computer code that can be stored in a recording medium (such as CD ROM, RAM, floppy disk, hard disk or magneto-optical disk), or implemented as computer code that is originally stored in a remote recording medium or a non-temporary machine-readable medium downloaded through a network and will be stored in a local recording medium, so that the method described herein can be stored in such software processing on a recording medium using a general-purpose computer, a special-purpose processor or programmable or special-purpose hardware (such as ASIC or FPGA). It can be understood that a computer, a processor, a microprocessor controller or programmable hardware includes a storage component (e.g., RAM, ROM, flash memory, etc.) that can store or receive software or computer code, and when the software or computer code is accessed and executed by a computer, a processor or hardware, the method described herein is implemented. In addition, when a general-purpose computer accesses a code for implementing the method shown here, the execution of the code converts the general-purpose computer into a special-purpose computer for executing the method shown here.

[0075] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A high-power modular LLC resonant converter interleaved parallel control system, characterized in that: include: Set at the input side of the inverter: a gain control unit, a voltage adjustment unit and an interleaving angle control unit; The gain control unit calculates the gain difference between the phases according to the imbalance of the output current of each phase, and uses the phase shift control to adjust the conduction time of the switch tube of each phase to obtain the same voltage gain. The output switching signal is input to the lower half bridge arm of the inverter after the phase shift of the staggered angle control unit; The voltage regulating unit compares the difference between the actual output voltage and the set output voltage as the input of the voltage controlled oscillator. The switching signal output by the voltage controlled oscillator is phase-shifted by the staggered angle control unit and then input to the upper half bridge arm of the inverter. The interleaving angle control unit calculates the interleaving angle of each phase in parallel according to the phase number of the parallel modules and the operating mode of each phase, and adjusts the interleaving angle according to the output current ripple amplitude to obtain the minimum output current ripple.

2. A high-power modular LLC resonant converter interleaved parallel control system according to claim 1, characterized in that: In the gain control unit, the parallel current sharing mechanism is analyzed based on the state plane method. The state of multi-phase LLC parallel operation is decomposed into the operation state of single-phase LLC secondary sideband voltage source type load. The state equations corresponding to the P, O, and N modes are: In the formula, the subscript N represents the normalized value, the subscript 0 represents the state quantity of the system when it is running in steady state, and C r is the resonant capacitor value, v Cr Refers to the resonant capacitor voltage, L r is the resonant inductance, i Lr Refers to the resonant inductor current, L m is the magnetizing inductance, L n Refers to the excitation inductance L m With the resonant inductor L r The ratio of L n =L m / L r .

3. A high-power modular LLC resonant converter interleaved parallel control system according to claim 2, characterized in that: In the gain control unit, the modeling of the phase shift angle and the voltage gain is obtained based on the modal analysis method, and the function Mag(α) of the phase shift angle with respect to the voltage gain is: Where n is the transformer primary-to-secondary ratio, T c is the switching period, αT c is the duration of the P phase, M is the duration of the phase shift phase, and I o (α), V o (α) represents the function of the average output current and the average output voltage with respect to the phase shift angle; Δi L (t) is the current flowing to the transformer, which is numerically equal to the difference between the resonant inductor current and the magnetizing inductor current.

4. A high-power modular LLC resonant converter interleaved parallel control system according to claim 1, characterized in that: In the staggered angle control unit, the frequency condition for the output current to reduce the ripple by staggering is that all phase frequencies are exactly the same, and the staggered phases of each phase are determined by the total number of parallel phases in the system and the mode of operation of each phase; N-phase LLC parallel connection is staggered, and the ripple reduction effect is best when the output current has no O mode. When the staggered angle of each phase is π / N, the ripple is reduced to the level of pure parallel connection. times, α is a constant related to the number of parallel phases N; The staggered angle corresponding to the minimum ripple of the output current in the O mode decreases from the reference phase until the minimum output current ripple is obtained.

5. A high-power modular LLC resonant converter interleaved parallel control system according to claim 4, characterized in that: The calculation formula of the constant α related to the number of parallel phases N is:

6. A high-power modular LLC resonant converter interleaved parallel control method, using a high-power modular LLC resonant converter interleaved parallel control system according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1, collect the output voltage value and compare it with the set output voltage value, and transmit the value to the voltage-controlled oscillator through the controller, and the voltage-controlled oscillator outputs a switching signal of a certain frequency to the staggered angle control unit; S2, collects the output current of each phase and calculates the average output current based on the switching frequency; After comparison, the output current is adjusted by the phase shift control to adjust the phase shift angle of each phase and output to the staggered angle control unit; S3, the interleaving angle control unit sets the size of the interleaving angle according to the mode of each phase output current in steady state. When the output current does not have O mode, the interleaving angle is maintained at π / N. When O mode appears in a certain phase, starting from the second phase, the interleaving angle of each phase needs to be gradually reduced until the minimum output current ripple is obtained. This interleaving angle is used as the interleaving angle of the system when it is finally in steady state operation.

7. A computer storage medium storing a readable program, characterized in that: When the program is running, it can execute the high-power modular LLC resonant converter interleaving parallel control method described in any one of claims 1 to 6.

8. An electronic device, characterized in that: include: A processor, a memory, a communication interface and a communication bus, wherein the processor, the memory and the communication interface communicate with each other via the communication bus; The memory is used to store at least one executable instruction, and the executable instruction enables the processor to perform operations corresponding to the high-power modular LLC resonant converter interleaved parallel control method according to any one of claims 1-6.

9. A computer program product comprising computer instructions, characterized in that The computer instructions instruct the computing device to execute operations corresponding to the high-power modular LLC resonant converter interleaved parallel control method as described in any one of claims 1-6.

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