Power conversion device with wide load adaptability and capable of parallel operation of multiple devices and control method of power conversion device

Abstract

The invention discloses a power supply conversion device with wide load adaptability and capable of parallel operation of multiple devices and a control method of the power supply conversion device. The power supply conversion device comprises an input LCL filtering unit, a three-phase Vienna conversion unit, an LLC isolation conversion unit, an H-bridge inversion output unit and an output LCL filtering unit which are connected in sequence. The three-phase Vienna conversion unit, the LLC isolation conversion unit and the H-bridge inversion output unit are respectively connected with a control unit; the H-bridge inverter output unit can measure the resistance-inductance value of an output load, so that a loop suitable for the load is selected for control, and the wide-range load adaptability is met by using an interleaving parallel control strategy with a current-sharing ring, a front-back voltage-sharing voltage loop parallel operation strategy and a single-pole frequency doubling driving method; flexible parallel operation is realized, the output efficiency is improved, the output current ripple is greatly reduced, and the use scene of the power supply conversion device is greatly expanded.

Description

Technical Field

[0001] The invention relates to a switching power supply, and in particular to a power conversion device with wide load adaptability and capable of connecting multiple units in parallel, and a control method thereof. Background Art

[0002] In the modern marine environment, the magnetic characteristics of the hull will generate a magnetic field around the ship. This magnetic field will not only increase the probability of magnetic detection, but also interfere with electronic equipment, affect the structural stress of the hull, and even affect the health of personnel. By using power equipment for demagnetization, these risks can be effectively reduced to ensure the safety and normal operation of the ship. The demagnetization of the ship is to use the power supply equipment to provide the required current to the demagnetization coil to generate a reverse magnetic field to eliminate or reduce the magnetism of the hull, thereby reducing the magnetic field strength of the ship. However, due to the influence of many factors such as the magnetic characteristics of the hull, the environmental magnetic field, the demagnetization system design, the navigation conditions, and the mission requirements, the demagnetization amount required for different hulls is different. Therefore, it is necessary to design a power conversion device with wide load adaptability that can be connected in parallel with multiple units to adapt to different hull conditions and various operating environments to the greatest extent. Summary of the invention

[0003] Purpose of the invention: The first purpose of the present invention is to provide a power conversion device that can adapt to different hull conditions and different operating environments, has wide load adaptability and can be used in parallel with multiple units; the second purpose of the present invention is to provide a control method for the power conversion device.

[0004] Technical solution: The present invention discloses a power conversion device with wide load adaptability and capable of connecting multiple units in parallel, comprising a control unit, a first communication unit, and an input LCL filter unit, a three-phase Vienna conversion unit, an LLC isolation conversion unit, an H-bridge inverter output unit, and an output LCL filter unit connected in sequence; the input LCL filter unit is connected to a three-phase AC source, and the output LCL filter unit is connected to a required output load; the three-phase Vienna conversion unit, the LLC isolation conversion unit, and the H-bridge inverter output unit are each connected to a control unit, and each control unit is connected in series with each other through an internal second communication unit, and is connected to the first communication unit at the same time; the three-phase Vienna conversion unit adopts a classic three-phase Vienna conversion topology, and the LLC isolation conversion unit and the H-bridge inverter output unit both adopt a two-way full-bridge topology, wherein an output relay is provided at the output end of the H-bridge inverter output unit;

[0005] When N power conversion devices are used in parallel, the three-phase Vienna conversion units can be connected in parallel or powered separately; the output ends of the H-bridge inverter output units are connected in parallel, and at the same time, the first communication units of the N power conversion devices are also connected in parallel to communicate with the external host computer; the magnitude and direction of the current output by each power conversion device are independent, and it will only control its own current output magnitude and direction according to instructions, and will not be affected by other power conversion devices in parallel.

[0006] Furthermore, the control unit also includes an operation processing unit, a sampling unit, an auxiliary power supply, a drive unit and an RTC unit. The operation processing unit is connected to other units respectively, and the auxiliary power supply supplies power to each unit; the three-phase Vienna conversion unit, the LLC isolation conversion unit, and the H-bridge inverter output unit are respectively connected to the sampling unit and the drive unit of the corresponding control unit, and the RTC unit is used to realize information recording in the event of power failure.

[0007] Furthermore, the output bus voltage of the three-phase Vienna conversion unit is directly connected to the LLC isolation conversion unit, and the output of the three-phase Vienna conversion unit is not connected to the LLC isolation conversion unit in the middle.

[0008] Furthermore, the output bus voltage of the LLC isolation conversion unit is adjustable over a wide range; the LLC isolation conversion unit can operate in a frequency modulation closed-loop regulation mode or in a fixed frequency open-loop mode.

[0009] A control method for a power conversion device, wherein a three-phase Vienna conversion unit uses a space vector algorithm to control the output voltage;

[0010] The LLC isolation conversion unit and the H-bridge inverter output unit both use a two-way full-bridge staggered parallel control strategy with a current-sharing loop, including: in the staggered parallel control method, the driving phases of the two full-bridge circuits are staggered by 180 degrees; a current-sharing loop is added on the basis of the staggered parallel control method, and the current error is calculated by detecting and comparing the output currents of the two full-bridge circuits, and then the frequency or duty cycle of the driving signal is adjusted according to the current error to make the output currents of the two full-bridge circuits tend to be consistent;

[0011] The LLC isolation conversion unit uses variable frequency control to adjust the switching frequency according to the load conditions to stabilize the output voltage;

[0012] The H-bridge inverter output unit uses a unipolar frequency multiplication driving method, including: at a fixed driving frequency, by changing the driving duty cycle, controlling the two diagonal MOS tubes to conduct twice in each switching cycle, and generating a signal at twice the switching frequency at the output end to achieve high-frequency output;

[0013] When parallel operation is used, the H-bridge inverter output unit adopts a voltage loop control strategy with front and rear voltage equalization.

[0014] Furthermore, when the control unit of the three-phase Vienna conversion unit detects that the three-phase voltage passing through the input LCL filter unit is normal and has no phase loss, the three-phase Vienna conversion unit operates normally, and the output voltage enters the LLC isolation conversion unit, which then transforms and isolates the voltage and inputs it into the H-bridge inverter output unit; the H-bridge inverter output unit first measures the output load size according to the instruction of the first communication unit, selects appropriate loop control parameters, and then, after receiving the external current size instruction obtained by the first communication unit, preferentially determines whether the voltages before and after its output relay are consistent. If they are consistent, the output relay is closed normally to output the current and output the required current; if they are inconsistent, the voltage loop of the H-bridge inverter output unit is entered, the duty cycle is controlled to raise the voltage before the output relay, and after the voltage before the output relay is consistent with the output voltage after the output relay, the output relay is closed again, and the voltage is converted to the corresponding current loop to output the required current, so as to protect the H-bridge inverter output unit from damage during parallel startup delay or hot plugging;

[0015] When the control unit of the three-phase Vienna conversion unit detects that any phase of the three-phase voltage input through the LCL filter unit is missing, the three-phase Vienna conversion unit performs uncontrolled rectification and inputs the voltage to the LLC isolation conversion unit, which performs control and voltage conversion and then outputs it through the H-bridge inverter output unit.

[0016] Furthermore, the phase loss detection method is to sample the input three-phase electricity through the control unit of the three-phase Vienna conversion unit, and perform vector superposition on the sampled voltage to determine whether there is a phase loss. If the vector superposition result is within the set value range, the three-phase voltage is determined to be normal; if the deviation between the addition result and 0 is greater than the set value, it is determined to be a phase loss.

[0017] Furthermore, when any phase of the three-phase input is missing, the three-phase Vienna conversion unit performs uncontrolled rectification, and the output voltage is only related to the voltages of the remaining two phases. At this time, the power conversion device can only guarantee stable half-power output; secondly, if during normal operation, the three-phase input changes from normal to missing phase, if the output power at this time is greater than half of the rated power, the output current of the H-bridge inverter output unit is forced to be reduced until the output power becomes half of the rated power; if the output power at this time is less than or equal to half of the rated power, normal operation is maintained.

[0018] Furthermore, the method for determining the output load size is to output a known frequency f and amplitude V through the H-bridge inverter output unit. rmsThe AC signal is then sampled on the output load current waveform to calculate the zero-point phase difference θ between the voltage and current and the current amplitude I rms ; Then, the specific values ​​of the output resistance R and the inductance L are separated according to formulas (1) and (2), and finally, according to the obtained resistance and inductance values, the appropriate loop control parameters of the H-bridge inverter output unit are selected, and the parameters are fixed until the next load detection operation is continued;

[0019]

[0020] Where, impedance |Z total The magnitude of | is equal to the amplitude of the output voltage V rms Divide by the current amplitude I rms ;ω=2πf;θ is the phase difference between voltage and current.

[0021] Furthermore, after the output relay of the H-bridge inverter output unit is closed, if the voltage before and after the output relay is inconsistent again, the voltage balancing operation will not be performed again, but the device protection operation will be directly performed.

[0022] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0023] 1) Strong load adaptability. The resistance and inductance value of the output load is detected by the H-bridge inverter output unit, and the control parameters of the output loop are adjusted automatically, so that it can adapt to the use of most degaussing coils.

[0024] 2) Strong interchangeability. The output of each power conversion device is independent and is not affected by the output of other power conversion devices. It can be interchanged at will, which is convenient for installation and use.

[0025] 3) The usage scenarios are highly flexible and compatible. By connecting multiple units in parallel, the current can be superimposed arbitrarily to adapt to the different current requirements of various usage scenarios.

[0026] 4) High performance, half-power output can be achieved in the absence of any phase input; and because the LLC isolation conversion unit and the H-bridge inverter output unit both use an interleaved parallel control strategy with a current-sharing loop, the H-bridge inverter output unit also uses a unipolar frequency-doubling drive method, which improves output efficiency, greatly reduces output current ripple, and makes the current zero-crossing smooth, achieving higher performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a structural schematic diagram of a power conversion device with wide load adaptability and capable of parallel operation of multiple units provided by an embodiment of the present invention;

[0028] Figure 2 is a schematic diagram of the structure of a control unit in an embodiment of the present invention;

[0029] Figure 3 is a schematic structural diagram of a three-phase Vienna conversion unit in an embodiment of the present invention;

[0030] Figure 4 is a structural schematic diagram of an LLC isolation conversion unit in an embodiment of the present invention;

[0031] Figure 5 is a structural schematic diagram of an H-bridge inverter output unit in an embodiment of the present invention;

[0032] Figure 6 It is a schematic diagram of the structure of N power conversion devices connected in parallel in an embodiment of the present invention. DETAILED DESCRIPTION

[0033] The present invention will be further described below in conjunction with the accompanying drawings.

[0034] like Figure 1 As shown, an embodiment of the present invention provides a power conversion device with wide load adaptability and capable of connecting multiple units in parallel, comprising a control unit, a first communication unit, and an input LCL filter unit, a three-phase Vienna conversion unit, an LLC isolation conversion unit, an H-bridge inverter output unit, and an output LCL filter unit connected in sequence; the input LCL filter unit is connected to a three-phase AC source, the output LCL filter unit is connected to a required output load (resistive-inductive load), and the three-phase Vienna conversion unit, the LLC isolation conversion unit, and the H-bridge inverter output unit are each connected to a control unit.

[0035] Combination Figure 2 The control unit includes an operation processing unit, a sampling unit, an auxiliary power supply, a driving unit, a second communication unit and an RTC unit. The operation processing unit is connected to other units respectively, and the auxiliary power supply supplies power to each unit. The three-phase Vienna conversion unit, the LLC isolation conversion unit, and the H-bridge inverter output unit are respectively connected to the sampling unit and the driving unit of the corresponding control unit. The RTC unit is used to realize information recording in the case of power failure. Each control unit is connected in series with each other through the internal second communication unit and is connected to the first communication unit at the same time.

[0036] Combination Figure 3 The three-phase Vienna conversion unit of this embodiment adopts the classic three-phase Vienna conversion topology, which is a mature topology structure and will not be described in detail here. The output bus voltage of the three-phase Vienna conversion unit is directly connected to the LLC isolation conversion unit, and the output intermediate ground O of the three-phase Vienna conversion unit is not connected to the LLC isolation conversion unit.

[0037] Combination Figure 4 and Figure 5In this embodiment, the LLC isolation conversion unit and the H-bridge inverter output unit both adopt a two-way full-bridge topology, wherein an output relay is provided at the output end of the H-bridge inverter output unit, and the full-bridge topology structure is also a prior art.

[0038] The output bus voltage of the LLC isolation conversion unit is adjustable over a wide range; the LLC isolation conversion unit can work in a frequency modulation closed-loop regulation mode or a fixed frequency open-loop mode. The adjustable bus voltage and the open-loop and closed-loop regulation modes are realized through software algorithms, which are existing technologies.

[0039] like Figure 6 As shown, when N power conversion devices are used in parallel, the three-phase Vienna conversion units (input AC ends) can be connected in parallel or powered separately; the output ends (load ends) of the H-bridge inverter output units are connected in parallel, and at the same time, the first communication units of the N power conversion devices are also connected in parallel to communicate with the external host computer; the magnitude and direction of the current output by each power conversion device are independent, and will only control its own current output magnitude and direction according to instructions, and will not be affected by other power conversion devices in parallel. For example, when there are two power conversion devices in parallel, machine 1 and machine 2 can output +5A at the same time, or machine 1 can output +5A and machine 2 can output 4A or even -5A, which are independent of each other.

[0040] In addition, in some cases, if the overall EMC (electromagnetic compatibility) performance of the power conversion device is good, the aforementioned power conversion device with wide load adaptability may also not have an input LCL filter unit, but only retain the input inductance required in the three-phase Vienna topology, and the function of the device remains unchanged.

[0041] An embodiment of the present invention also provides a control method for the power conversion device described in the embodiment of the present invention, which is used to control the stable output of each unit in three-phase or phase-loss conditions, detect the resistance and inductance of the output load, control the loop size of the H-bridge inverter output unit, and achieve stable current output during parallel operation.

[0042] The control method includes:

[0043] (1) The three-phase Vienna conversion unit uses a space vector algorithm to control the output voltage. This control method is a prior art and will not be described in detail here.

[0044] (2) Both the LLC isolation conversion unit and the H-bridge inverter output unit use a control strategy of two full-bridges interleaved in parallel with a current-sharing loop. Specifically:

[0045] The two full-bridge input and output are connected in parallel. In the staggered parallel control method, the overall performance is optimized by staggering the driving phases of the two full-bridges by 180 degrees to achieve a more stable output current and voltage. Figure 4 or Figure 5 , briefly exemplifying the basic control logic, the MOS tube drive signal of each full-bridge circuit is divided into two groups of complementary control signals: the first group (Q1, Q4) and (Q2, Q3): when Q1 and Q4 are turned on at the same time, Q2 and Q3 are turned off, and vice versa. The second group (Q5, Q8) and (Q6, Q7): when Q5 and Q8 are turned on at the same time, Q6 and Q7 are turned off, and vice versa. In the staggered parallel control method, in order to achieve a smoother output, the drive signals of the two full-bridge circuits are usually staggered by 180 degrees, that is, when one group of MOS tubes of the first full-bridge circuit is turned on, the corresponding group of MOS tubes of the second full-bridge circuit is in the off state. For example, the on-time of Q1 and Q4 in the first full-bridge circuit is 0-T / 2, and the off-time is T / 2-T. Q2 and Q3 are complementary to Q1 and Q4, that is, the off-time is 0-T / 2, and the on-time is T / 2-T. The waveforms of Q5 and Q8 in the second full-bridge circuit are 180 degrees out of phase with Q1 and Q4, with a off-time of 0-T / 2 and a on-time of T / 2-T. The same is true for Q6 and Q7 and Q2 and Q3, thereby achieving the effect of reducing the output voltage and current ripple.

[0046] On the basis of the above-mentioned staggered parallel control method, a current equalization loop is added to ensure that the current distribution between the two full-bridge circuits is uniform, so that the output currents of the two full-bridge circuits are consistent, and current imbalance is avoided to improve the reliability and efficiency of the system. The current equalization loop control method is to install a current sensor at the output end of each full-bridge circuit to detect the output currents I1 and I2, compare the two output currents I1 and I2, calculate the current error, and then adjust the frequency or duty cycle of the drive signal according to the calculated current error to balance the output currents of the two groups of circuits.

[0047] (3) The LLC isolation conversion unit uses a variable frequency control method to adjust the switching frequency according to the load conditions to stabilize the output voltage. This is a prior art and will not be described in detail here.

[0048] (4) The H-bridge inverter output unit uses a unipolar frequency doubling driving method. When paralleling, the H-bridge inverter output unit adopts a voltage loop control strategy with front and rear voltage equalization.

[0049] The unipolar frequency multiplication driving method is to control the two diagonal MOS tubes to conduct twice in each switching cycle by changing the driving duty cycle at a fixed driving frequency, and to achieve high-frequency output by generating a signal at the output end that is twice the switching frequency. Figure 5, briefly exemplifying the basic control logic, the MOS tube drive signal of the full-bridge circuit is divided into two sets of complementary control signals: initially, the drive of Q1 and Q4 is complementary, with a duty cycle of 50% each, and the drive of Q2 and Q3 is complementary, with a duty cycle of 50% each, the drive waveforms of Q1 and Q2 are the same, and the drive waveforms of Q3 and Q4 are the same. At this time, the full bridge cannot be turned on; when the duty cycle of Q1 and Q4 is increased, and the duty cycle of Q2 and Q3 is reduced accordingly, Q1 and Q4, which are complementary at the beginning, will start to turn on, and turn on once at the beginning and end of a high-level drive cycle, thereby turning on twice in one cycle to achieve frequency doubling, and vice versa for turning on Q2 and Q3.

[0050] The specific control process of the control method is as follows:

[0051] When the control unit of the three-phase Vienna conversion unit detects that the three-phase voltage after the input LCL filter unit is normal and has no phase loss, the three-phase Vienna conversion unit works normally, and the output voltage enters the LLC isolation conversion unit, which then transforms and isolates the voltage and inputs it into the H-bridge inverter output unit; the H-bridge inverter output unit first measures the output load size according to the instruction of the first communication unit, selects the appropriate loop control parameters, and then after receiving the external current size instruction obtained by the first communication unit, first determines whether the voltage before and after its output relay is consistent. If it is consistent, the output relay is normally closed to output the current and output the required current; if it is inconsistent, it enters the voltage loop of the H-bridge inverter output unit, controls the duty cycle to raise the voltage before the output relay, and after the voltage before the output relay is consistent with the output voltage after the output relay, closes the output relay, switches to the corresponding current loop, and outputs the required current, so as to protect the H-bridge inverter output unit during the parallel startup delay or hot plug, and avoid damage. After the output relay of the H-bridge inverter output unit is closed, if the voltage before and after the output relay is inconsistent again, the voltage balancing operation will not be performed again, but the device protection operation will be performed directly.

[0052] When the control unit of the three-phase Vienna conversion unit detects that any phase of the three-phase voltage input through the LCL filter unit is missing, the three-phase Vienna conversion unit performs uncontrolled rectification and inputs the voltage to the LLC isolation conversion unit, which performs control and voltage conversion and then outputs it through the H-bridge inverter output unit.

[0053] In order to determine whether there is a phase loss, this embodiment designs a phase loss detection method, that is, the control unit of the three-phase Vienna conversion unit samples the input three-phase electricity, and performs vector superposition on the sampled voltage to determine whether there is a phase loss. When calculating and processing the sampled voltage, the voltage vector is converted to a Cartesian coordinate system according to the voltage phase determined during phase locking, using the magnitude of the sampled voltage of each phase, and the voltage amplitude is added. If the addition result is within the set value range (close to 0), the three-phase voltage is determined to be normal; if the deviation between the addition result and 0 is greater than the set value, it is determined to be a phase loss.

[0054] When the three-phase input is judged to be missing any phase, the three-phase Vienna conversion unit will switch to uncontrolled rectification, and the output voltage is only related to the voltage of the remaining two phases. At this time, the power conversion device can only guarantee stable half-power output; secondly, if during normal operation, the three-phase input changes from normal to missing phase, if the output power at this time is greater than half of the rated power, the output current of the H-bridge inverter output unit will be forced to reduce until the output power becomes half of the rated power; if the output power at this time is less than or equal to half of the rated power, it will maintain normal operation.

[0055] In order to achieve wide load adaptability, this embodiment designs a method for detecting and calculating the output load after startup for the H-bridge inverter output unit, that is, when the power conversion device is installed and used for the first time or the use scenario is changed, a detection instruction is input through the first communication unit to make the H-bridge inverter output unit output a known frequency f and amplitude V rms The AC power is then sampled by the sampling unit in the control unit 3 to sample the current waveform on the output load, and the phase difference θ between the voltage and current and the amplitude I of the current are calculated. rms , then separate the specific values ​​of the output resistance R and inductance L according to formulas (1) and (2), and finally select the appropriate loop control parameters of the H-bridge inverter output unit according to the obtained resistance and inductance values, and fix the parameters until the next time the load detection operation is continued;

[0056]

[0057] Where, impedance |Z total The magnitude of | is equal to the amplitude of the output voltage V rms Divide by the current amplitude I rms ;ω=2πf.

[0058] The voltage of the H-bridge inverter output unit is adaptive according to the load size and output current. Within the protection range, as long as the output current is correct, the voltage is adaptive according to the impedance.

[0059] In summary, the power conversion device realizes the wide load adaptability of the device from the hardware system principle and control method, and realizes flexible parallel operation and hot plugging through the unipolar frequency doubling strategy of the H-bridge inverter output unit and the voltage loop control strategy of front and rear voltage equalization during parallel operation, which greatly expands the use scenarios of the power conversion device, improves the use stability, and realizes the improvement of output efficiency and the significant reduction of output current ripple.

Claims

1. A power conversion device with wide load adaptability and capable of connecting multiple units in parallel, characterized in that: It includes a control unit, a first communication unit, and an input LCL filter unit, a three-phase Vienna conversion unit, an LLC isolation conversion unit, an H-bridge inverter output unit, and an output LCL filter unit connected in sequence; the input LCL filter unit is connected to a three-phase AC source, and the output LCL filter unit is connected to a required output load; the three-phase Vienna conversion unit, the LLC isolation conversion unit, and the H-bridge inverter output unit are each connected to a control unit, and each control unit is connected in series with each other through an internal second communication unit, and is connected to the first communication unit at the same time; the three-phase Vienna conversion unit adopts a classic three-phase Vienna conversion topology, and the LLC isolation conversion unit and the H-bridge inverter output unit both adopt a two-way full-bridge topology, wherein an output relay is provided at the output end of the H-bridge inverter output unit; When N power conversion devices are used in parallel, the three-phase Vienna conversion units can be connected in parallel or powered separately; the output ends of the H-bridge inverter output units are connected in parallel, and at the same time, the first communication units of the N power conversion devices are also connected in parallel to communicate with the external host computer; the magnitude and direction of the current output by each power conversion device are independent, and it will only control its own current output magnitude and direction according to instructions, and will not be affected by other power conversion devices in parallel.

2. The power conversion device according to claim 1, characterized in that: The control unit also includes an operation processing unit, a sampling unit, an auxiliary power supply, a drive unit and an RTC unit. The operation processing unit is connected to other units respectively, and the auxiliary power supply supplies power to each unit; the three-phase Vienna conversion unit, the LLC isolation conversion unit, and the H-bridge inverter output unit are respectively connected to the sampling unit and the drive unit of the corresponding control unit, and the RTC unit is used to realize information recording in the event of power failure.

3. The power conversion device according to claim 1, characterized in that: The output bus voltage of the three-phase Vienna conversion unit is directly connected to the LLC isolation conversion unit, and the output intermediate ground of the three-phase Vienna conversion unit is not connected to the LLC isolation conversion unit.

4. The power conversion device according to claim 1, characterized in that: The output bus voltage of the LLC isolation conversion unit is adjustable over a wide range; the LLC isolation conversion unit can operate in a frequency modulation closed-loop regulation mode or in a fixed frequency open-loop mode.

5. A control method for a power conversion device according to claim 1, characterized in that: The three-phase Vienna conversion unit uses a space vector algorithm to control the output voltage; The LLC isolation conversion unit and the H-bridge inverter output unit both use a two-way full-bridge staggered parallel control strategy with a current-sharing loop, including: in the staggered parallel control method, the driving phases of the two full-bridge circuits are staggered by 180 degrees; a current-sharing loop is added on the basis of the staggered parallel control method, and the current error is calculated by detecting and comparing the output currents of the two full-bridge circuits, and then the frequency or duty cycle of the driving signal is adjusted according to the current error to make the output currents of the two full-bridge circuits tend to be consistent; The LLC isolation conversion unit uses variable frequency control to adjust the switching frequency according to the load conditions to stabilize the output voltage; The H-bridge inverter output unit uses a unipolar frequency multiplication driving method, including: at a fixed driving frequency, by changing the driving duty cycle, controlling the two diagonal MOS tubes to conduct twice in each switching cycle, and generating a signal at twice the switching frequency at the output end to achieve high-frequency output; When parallel operation is used, the H-bridge inverter output unit adopts a voltage loop control strategy with front and rear voltage equalization.

6. The control method according to claim 5, characterized in that: When the control unit of the three-phase Vienna conversion unit detects that the three-phase voltage after the input LCL filter unit is normal and has no phase loss, the three-phase Vienna conversion unit works normally, and the output voltage enters the LLC isolation conversion unit, which then transforms and isolates the voltage and inputs it into the H-bridge inverter output unit; the H-bridge inverter output unit first measures the output load size according to the instruction of the first communication unit, selects appropriate loop control parameters, and then after receiving the external current size instruction obtained by the first communication unit, preferentially determines whether the voltages before and after its output relay are consistent. If they are consistent, the output relay is closed normally to output the current and output the required current; if they are inconsistent, the voltage loop of the H-bridge inverter output unit is entered, the duty cycle is controlled to raise the voltage before the output relay, and after the voltage before the output relay is consistent with the output voltage after the output relay, the output relay is closed again, and the voltage is converted to the corresponding current loop to output the required current, so as to protect the H-bridge inverter output unit from damage during parallel startup delay or hot plugging; When the control unit of the three-phase Vienna conversion unit detects that any phase of the three-phase voltage input through the LCL filter unit is missing, the three-phase Vienna conversion unit performs uncontrolled rectification and inputs the voltage to the LLC isolation conversion unit, which performs control and voltage conversion and then outputs it through the H-bridge inverter output unit.

7. The control method according to claim 6, characterized in that: The phase loss detection method is to sample the input three-phase electricity through the control unit of the three-phase Vienna conversion unit, and perform vector superposition on the sampled voltage to determine whether there is a phase loss. If the vector superposition result is within the set value range, the three-phase voltage is determined to be normal; if the deviation between the addition result and 0 is greater than the set value, it is determined to be a phase loss.

8. The control method according to claim 6, characterized in that: When any phase of the three-phase input is missing, the three-phase Vienna conversion unit performs uncontrolled rectification, and the output voltage is only related to the voltages of the remaining two phases. At this time, the power conversion device can only guarantee stable half-power output; secondly, if during normal operation, the three-phase input changes from normal to missing phase, if the output power at this time is greater than half of the rated power, the output current of the H-bridge inverter output unit is forced to be reduced until the output power becomes half of the rated power; if the output power at this time is less than or equal to half of the rated power, normal operation is maintained.

9. The control method according to claim 6, characterized in that: The method for determining the output load size is to output a known frequency f and amplitude V through the H-bridge inverter output unit. rms The AC signal is then sampled on the output load current waveform to calculate the zero-point phase difference θ between the voltage and current and the current amplitude I rms ; Then, the specific values ​​of the output resistance R and the inductance L are separated according to formulas (1) and (2), and finally, according to the obtained resistance and inductance values, the appropriate loop control parameters of the H-bridge inverter output unit are selected, and the parameters are fixed until the next load detection operation is continued; Where, impedance |Z total The magnitude of | is equal to the amplitude of the output voltage V rms Divide by the current amplitude I rms ;ω=2πf;θ is the phase difference between voltage and current.

10. The control method according to claim 6, characterized in that: After closing the output relay of the H-bridge inverter output unit, if the voltage before and after the output relay is inconsistent again, the voltage balancing operation will not be performed again, but the device protection operation will be performed directly.

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