Current sharing control method and ac-DC conversion system

Abstract

A current sharing control method and an AC-DC conversion system, which are applied to a current sharing controller. The current sharing controller (2002) is used for controlling the operating state of an AC-DC converter (2001), the AC-DC converter (2001) comprises at least two rectifier units, and each of the at least two rectifier units uses a combination of a bridge topology and an LLC resonant tank. The method comprises: on the basis of the absolute values of instantaneous values of three-phase input voltages of at least two rectifier units, determining target adjustment phases (304); on the basis of current sampling values of the at least two rectifier units, determining a target duty cycle of a target adjustment phase in each rectifier unit, wherein the target duty cycle is used for indicating the adjustment of voltage gain of an LLC resonant tank (306); and on the basis of the target duty cycle of the target adjustment phase in each rectifier unit, adjusting the duty cycle of control signals for switch transistors in each rectifier unit (308). The pulse width of control signals for switch transistors in a rectifier unit is adjusted to adjust amplitude distribution of an input voltage of a resonant tank, so as to change the gain of an LLC, thereby controlling an output current of the LLC, and thus achieving the aim of current sharing.

Description

Current sharing control method and AC-DC conversion system

[0001] The present application claims priority to the Chinese patent application No. 202411323309.4, filed on September 20, 2024, and entitled "Current sharing control method and AC-DC conversion system", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the field of electric energy conversion, and in particular, to a current sharing control method and an AC-DC conversion system. BACKGROUND

[0003] The conventional AC-DC converter usually adopts a two-stage topology of PFC+DCDC. The front-stage PFC is used to control the input current to achieve high power factor and low total harmonic distortion; and the rear-stage DC-DC converter is used to control the output voltage and current to ensure the stability of the output voltage and current under different working conditions. The two-stage topology needs two-stage switching devices and an intermediate bus capacitor, which limits the optimization of efficiency, power density and cost to a certain extent. On the basis of the two-stage topology, the intermediate bus capacitor is removed, and only a one-stage switching network is needed, which derives a three-phase single-stage topology, has higher efficiency and higher power density, and has a broad application prospect in the fields of communication power supply, electric vehicle charging and other high-power power supplies.

[0004] In the application scenarios of high power and low voltage and large current, the current of the three-phase single-stage topology is large, and higher current-resistant switching devices are needed. Moreover, the ripple current on the output capacitor is also large, which affects the indicators such as efficiency, heat and reliability. Usually, the method of parallel connection of multiple switching devices and parallel connection of multiple output capacitors is used to share the current and reduce the current flowing through each switching device and output capacitor.

[0005] In actual applications, devices are non-ideal devices, and the parameters of devices will differ due to reasons such as process and batch, so it is impossible to make the parameters of each component consistent. For example, the precision of the inductance and the capacitance is 5%-10%. The output gain of each rectification unit is greatly affected by the parameters of the resonant tank components. The difference in gain caused by the difference in the parameters of the components will cause the problem of uneven output current, which further limits the development of the three-phase single-stage topology in the application scenarios of larger power and low voltage and large current. SUMMARY

[0006] The present application provides a current sharing control method and an AC-DC conversion system to solve the technical problem of uneven output current of the converter in the prior art.

[0007] In a first aspect, the embodiments of the present application provide a current sharing control method, applied to a current sharing controller, the current sharing controller being configured to control an operating state of an AC-DC converter, the AC-DC converter comprising at least two rectifier units, each of the at least two rectifier units being in a bridge topology combined with an LLC resonant tank; the method comprising:

[0008] obtaining current sampling values of the at least two rectifier units and absolute values of three-phase input voltage instantaneous values of the at least two rectifier units;

[0009] determining a target adjustment phase according to the absolute values of the three-phase input voltage instantaneous values of the at least two rectifier units;

[0010] determining a target duty cycle of the target adjustment phase in each rectifier unit according to the current sampling values of the at least two rectifier units, the target duty cycle being configured to indicate an adjustment of a voltage gain of the LLC resonant tank;

[0011] adjusting a duty cycle of a control signal of a switch tube corresponding to the target adjustment phase in each rectifier unit according to the target duty cycle of the target adjustment phase in each rectifier unit.

[0012] In a possible implementation, the determining of the target adjustment phase according to the absolute values of the three-phase input voltage instantaneous values of the at least two rectifier units comprises:

[0013] determining, according to the absolute values of the three-phase input voltage instantaneous values of each of the at least two rectifier units, a first input phase with the largest absolute value of the three-phase input voltage instantaneous values, a second input phase with the second largest absolute value of the three-phase input voltage instantaneous values, and a third input phase with the smallest absolute value of the three-phase input voltage instantaneous values in each rectifier unit;

[0014] the target adjustment phase is any one of the following combinations, the combinations comprising the first input phase, the second input phase, and the third input phase all being the target adjustment phase, and the second input phase and the third input phase being the target adjustment phase.

[0015] In a possible implementation, the determining of the target duty cycle of the target adjustment phase in each rectifier unit according to the current sampling values of the at least two rectifier units comprises:

[0016] comparing the current sampling values of the at least two rectifier units to determine relative sizes of the current sampling values of each rectifier unit;

[0017] determining, according to the relative sizes of the current sampling values of each rectifier unit, an adjustment amount of the duty cycle of the target adjustment phase in each rectifier unit;

[0018] determining the target duty cycle of the target adjustment phase in each rectifier unit according to the adjustment amount of the duty cycle of the target adjustment phase in each rectifier unit and an initial value of the duty cycle.

[0019] In a possible implementation, the at least two rectifier units include a first rectifier unit and a second rectifier unit; the target adjustment phase includes a second input phase and a third input phase; and the duty cycle adjustment amount of the target adjustment phase in each rectifier unit is determined according to the relative size of the current sampling value of each rectifier unit, including:

[0020] the difference between the first current sampling value and the second current sampling value is input into the first preset current sharing loop;

[0021] in a case where the first current sampling value is greater than the second current sampling value, the duty cycle adjustment amount of the second input phase and the third input phase in the first rectifier unit is obtained;

[0022] in a case where the first current sampling value is less than the second current sampling value, the duty cycle adjustment amount of the second input phase and the third input phase in the second rectifier unit is obtained.

[0023] In a possible implementation, the at least two rectifier units include a first rectifier unit and a second rectifier unit; the target adjustment phase includes a first input phase, a second input phase and a third input phase; and the duty cycle adjustment amount of the target adjustment phase in each rectifier unit is determined according to the relative size of the current sampling value of each rectifier unit, including:

[0024] the difference between the first current sampling value and the second current sampling value is input into the second preset current sharing loop;

[0025] in a case where the first current sampling value is greater than the second current sampling value, the duty cycle adjustment amount of the first input phase, the second input phase and the third input phase in the first rectifier unit is obtained;

[0026] in a case where the first current sampling value is less than the second current sampling value, the duty cycle adjustment amount of the first input phase, the second input phase and the third input phase in the second rectifier unit is obtained.

[0027] In a possible implementation, the target duty cycle of the target adjustment phase in each rectifier unit is determined according to the current sampling value of the at least two rectifier units, including:

[0028] the average current value of the at least two rectifier units is determined according to the current sampling value of the at least two rectifier units;

[0029] the target duty cycle of the target adjustment phase in each rectifier unit is determined according to the current sampling value of each rectifier unit and the average current value.

[0030] In a possible implementation, the current sampling value includes at least one of the following current sampling values: an input current sampling value, a rectifier output current sampling value, a resonance current sampling value, a switch tube current sampling value and a transformer secondary side current sampling value.

[0031] In a second aspect, the present application provides an AC-DC conversion system, which comprises an AC-DC converter and a current-sharing controller; the AC-DC converter comprises at least two rectifier units, each of which adopts a combination of a bridge topology and an LLC resonant tank.

[0032] The current-sharing controller is configured to control the working state of the AC-DC converter, and specifically configured to execute the method steps.

[0033] In a third aspect, the present application further provides a computer device, which comprises a processor and a memory connected to the processor in communication;

[0034] The memory stores computer execution instructions;

[0035] The processor executes the computer execution instructions stored in the memory to implement the above method.

[0036] In a fourth aspect, the present application further provides a computer readable storage medium, which stores computer execution instructions, and the computer execution instructions are executed by the processor to implement the above method.

[0037] In a fifth aspect, the present application further provides a computer program product, which comprises computer execution instructions, and the computer execution instructions are executed by the processor to implement the above method.

[0038] The embodiments of the present application provide a current-sharing control method and an AC-DC conversion system, which are applied to a current-sharing controller configured to control the working state of an AC-DC converter, and the AC-DC converter comprises at least two rectifier units, each of which adopts a combination of a bridge topology and an LLC resonant tank; the method comprises the following steps: obtaining the current sampling values of the at least two rectifier units and the absolute values of the three-phase input voltage instantaneous values of the at least two rectifier units; determining a target adjustment phase according to the absolute values of the three-phase input voltage instantaneous values of the at least two rectifier units; determining the target duty cycle of the target adjustment phase in each rectifier unit according to the current sampling values of the at least two rectifier units, and the target duty cycle is configured to indicate the adjustment of the voltage gain of the LLC resonant tank; and adjusting the duty cycle of the control signal of the switch tube corresponding to the target adjustment phase in each rectifier unit according to the target duty cycle of the target adjustment phase in each rectifier unit. The embodiments of the present application adjust the pulse width of the control signal of the switch tube in the rectifier unit to adjust the amplitude distribution of the input voltage of the resonant tank, change the gain of the LLC, and thus control the output current of the LLC, so as to achieve the purpose of current sharing. BRIEF DESCRIPTION OF DRAWINGS

[0039] The accompanying drawings, which are incorporated into and form a part of the specification, illustrate one embodiment consistent with the present application and, together with the description, serve to explain the principles of the application.

[0040] Fig. 1 is a schematic diagram of the current after the LLC rectifier bridge in one embodiment;

[0041] Fig. 2 is a schematic diagram of the current ripple cancellation effect of the three-phase single-stage two-phase interleaved in one embodiment;

[0042] Fig. 3 is a flowchart of the current sharing control method in one embodiment;

[0043] Fig. 4 is a schematic diagram of the structure of the three-phase single-stage interleaved AC-DC converter in one embodiment;

[0044] Fig. 5 is a schematic diagram of the waveform of the three-phase input AC in one embodiment;

[0045] Fig. 6 is a schematic diagram of the conduction of the rectifier unit in one embodiment;

[0046] Fig. 7 is a schematic diagram of the conduction of the rectifier unit in one embodiment;

[0047] Fig. 8 is a schematic diagram of the Upn waveform in one embodiment;

[0048] Fig. 9 is a flowchart of the current sharing control method in one embodiment;

[0049] Fig. 10 is a block diagram of the current sharing control in one embodiment;

[0050] Fig. 11 is a schematic diagram of the output current of the rectifier unit when the SM ratio is the same in one embodiment;

[0051] Fig. 12 is a schematic diagram of the output current of the rectifier unit when the SM ratio is different in one embodiment;

[0052] Fig. 13 is a block diagram of the current sharing control in one embodiment;

[0053] Fig. 14 is a block diagram of the current sharing control in one embodiment;

[0054] Fig. 15 is a comparison diagram when the resonant inductance is different by 5% in one embodiment;

[0055] Fig. 16 is a comparison diagram when the resonant capacitance is different by 5% in one embodiment;

[0056] Fig. 17 is a comparison diagram when the excitation inductance is different by 5% in one embodiment;

[0057] Fig. 18 is a schematic diagram of the input current THD before the current sharing regulation is added in one embodiment;

[0058] Fig. 19 is a schematic diagram of input current THD with current sharing regulation provided in one embodiment;

[0059] Fig. 20 is a schematic diagram of the structure of an AC-DC conversion system provided in one embodiment;

[0060] Fig. 21 is a hardware structure diagram of a computer device provided in one embodiment.

[0061] The specific embodiments of the present application have been shown by the above-described drawings, and will be described in more detail hereinafter. These drawings and the written description are not intended to restrict the scope of the concept of the present application by any means, but to illustrate the concept of the present application to those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0062] The exemplary embodiments will be described in detail herein with reference to the attached drawings. In the following description, the same numbers are used to indicate the same or similar components. The embodiments described in the following exemplary embodiments do not represent all the embodiments consistent with the present application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of the present application as detailed in the appended claims.

[0063] In the description of the present application, the terms "first", "second" are used only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specifically limited.

[0064] The conventional AC-DC converter usually adopts a two-stage topology of PFC+DCDC. The former PFC is used to control the input current to achieve high power factor and low total harmonic distortion; the latter DC-DC converter is used to control the output voltage and current to ensure the stability of the output voltage and current under different operating conditions. The two-stage topology requires two-stage switching devices and an intermediate bus capacitor, which limits the optimization of efficiency, power density and cost to a certain extent.

[0065] Based on the optimization of the two-stage topology, the intermediate bus capacitor is removed, and only one switching network is needed, which derives a three-phase single-stage topology with higher efficiency and higher power density, and has a broad application prospect in the fields of communication power supply, electric vehicle charging and other high-power power supplies.

[0066] In high-power and low-voltage high-current application scenarios, the current of the three-phase single-stage topology is large, and higher current-resistant switching devices are required. Moreover, the ripple current on the output capacitor is also large, which affects the efficiency, heat, and reliability, etc. of the indicators. Usually, multiple switching devices in parallel and multiple output capacitors in parallel are used to divide the current and reduce the current flowing through each switching device and output capacitor. For example, if the switching tube is changed from 1 to 2 in parallel, the current flowing through each switching tube is theoretically reduced by half, and the conduction loss of the switching tube is also reduced by half.

[0067] As the three-phase single-stage topology has only one rectifier unit, the input is 380V, 50HZ, the output is 270V, 50KW, and the output electrolytic capacitor has a capacity of 5640uF. The current ripple after the LLC rectifier bridge is very large, with a peak-to-peak value of 425.9A, as shown in FIG. 1. The ripple current shape on the output electrolytic capacitor is similar to a half-wave sine wave. The effective value of the ripple current of the output electrolytic capacitor from 0.02s to 0.18s is 83.32A. Taking an electrolytic capacitor with a rated ripple current effective value of 2A as an example, at least 42 electrolytic capacitors are needed in parallel without considering the derating. Too many electrolytic capacitors are not conducive to improving the power density of the three-phase single-stage.

[0068] Usually, multiple rectifier units are used in staggered parallel method to stagger the switching tube wave sequence of the rectifier bridge unit by an angle, such as 90 degrees for two-phase staggered parallel and 120 degrees for three-phase staggered parallel. This makes the output current of the rectifier unit produce ripple cancellation effect, thereby reducing the output current ripple of the rectifier unit and further reducing the current ripple on the output electrolytic capacitor. As shown in FIG. 2, the current ripple cancellation effect of the output current of the rectifier units U1 and U2 in the three-phase single-stage two-phase staggered parallel converter.

[0069] After using two rectifier units in staggered parallel, under the same working condition, the input is 380V, 50HZ, the output is 270V, 50KW, and the output electrolytic capacitor has a capacity of 5640uF. The effective value of the ripple current of the output electrolytic capacitor from 0.02s to 0.18s is 27.2A. Taking an electrolytic capacitor with a rated ripple current effective value of 2A as an example, only 14 electrolytic capacitors are needed in parallel without considering the derating, which is 28 fewer than the 42 needed without staggered parallel. The number of electrolytic capacitors is greatly reduced, which is conducive to improving the power density of the three-phase single-stage.

[0070] The output gain of each rectification unit is greatly affected by resonant tank component parameters, such as resonant inductance difference, resonant capacitance difference, and excitation inductance difference, which will affect the gain of LLC. When the frequency, duty cycle, and phase of each rectification unit are the same, the output current will be uneven due to the gain difference. When the uneven current exceeds a certain limit, the heat distribution of each rectification unit will be uneven, and in severe cases, the rectification unit with large current will overcurrent, which will damage the switch tube and affect the reliability of the switch tube.

[0071] In actual applications, devices are non-ideal devices, and device parameters will differ due to process, batch, etc. It is impossible to make the parameters of each component consistent. For example, the inductance and capacitance accuracy is 5%-10%. The uneven current problem of the interleaved parallel three-phase single-stage topology caused by the difference in device parameters further limits the development of the three-phase single-stage topology in larger power and low-voltage high-current application scenarios.

[0072] The embodiment of the present application provides a current sharing control method, which is applied to a current sharing controller. The current sharing controller is used to control the working state of an AC-DC converter. The AC-DC converter includes at least two rectification units. The at least two rectification units are combined with a bridge topology structure and an LLC resonant tank. As shown in FIG. 3, the method includes the following steps.

[0073] In step 302, the current sampling values of the at least two rectification units and the absolute values of the three-phase input voltage instantaneous values of the at least two rectification units are obtained.

[0074] In step 304, a target adjustment phase is determined according to the absolute values of the three-phase input voltage instantaneous values of the at least two rectification units.

[0075] In step 306, a target duty cycle of the target adjustment phase in each rectification unit is determined according to the current sampling values of the at least two rectification units. The target duty cycle is used to indicate the adjustment of the voltage gain of the LLC resonant tank.

[0076] In step 308, the duty cycle of the control signal of the switch tube corresponding to the target adjustment phase in each rectification unit is adjusted according to the target duty cycle of the target adjustment phase in each rectification unit.

[0077] The current sampling value of the rectification unit refers to the current in the rectification unit circuit, which is obtained by sampling the current or voltage in the circuit. The sampling points and sampling time of the current sampling values of the at least two rectification units need to be consistent to determine the current at the same position at the same time of the at least two rectification units.

[0078] According to different sampling points of the current sampling value, when the current in the circuit is directly collected, the current sampling value can include one or more of the input current sampling value (such as collected at point A in FIG. 4), the rectified output current sampling value (such as collected at point B in FIG. 4), the resonant current sampling value (such as collected at point C in FIG. 4), the switch tube current sampling value (such as collected at points D1-D6 in FIG. 4), and the transformer secondary side current sampling value (such as collected at point E in FIG. 4). By directly sampling the current at each point in the circuit, the current sampling value can be quickly obtained.

[0079] When the current sampling value is indirectly determined by collecting the voltage in the circuit, as shown in FIG. 4, the resonant capacitor current can be calculated by sampling the resonant capacitor differential voltage and using the following formula:

[0080] Since the resonant capacitor and the resonant inductor are in the same current loop, their currents are equal. After the resonant capacitor current is calculated, the resonant current i Lr i cr .

[0081] In addition, the current sampling value of the rectifier unit can be directly sampled and obtained inside the rectifier unit by the above method, or the total current of all rectifier units can be sampled, and the current sampling value of the rectifier unit can be determined by the sum of the total current and the current sampling values of the other rectifier units.

[0082] The instantaneous value of the three-phase input voltage can be obtained by sampling each phase of the input voltage. For an AC-DC converter including at least two rectifier units, the input end of each rectifier unit is connected to the output end of the three-phase alternating current, and the input ends of the at least two rectifier units are connected in parallel. The three-phase input voltage of each rectifier unit is equal, and only the instantaneous value of the three-phase input voltage of one of the rectifier units or the instantaneous value of the total three-phase input voltage needs to be obtained. The three-phase input voltage can be sampled for 3 phases / lines, or for 2 phases / lines, and then the other phase / line voltage can be calculated.

[0083] As shown in FIG. 4, the AC-DC converter includes two interleaved rectifier units U1 and U2. In step 304, the instantaneous values of the three-phase input voltages Ua, Ub, and Uc of the rectifier units U1 and U2 need to be obtained. The voltage sampling points of Ua, Ub, and Uc can be at the input end of one of the rectifier units U1 or U2, or at the output end of the three-phase alternating current. Ua, Ub, and Uc can be directly collected, or two of Ua, Ub, and Uc can be collected, and then the remaining voltage can be calculated.

[0084] In the rectifier unit with the combination of bridge topology and LLC resonant tank, the input voltage Upn of the resonant tank varies with the firing mode of the control signal of the switch tube in a switching cycle, as shown in the circuit structure of Fig. 4. When the input voltage satisfies |Ua|>|Ub|>|Uc|, and Ua>0, Ub<0, Uc<0 (hereinafter, if no special description, the working condition is taken as an example for description), the firing frequency of the control signal of the switch tube connected by each phase of the three-phase input AC power is the same, and the duty ratio of Ua phase is 0.5=the duty ratio of Ub phase+the duty ratio of Uc phase without considering the dead time.

[0085] When Sa1, Sa2, Sb3, Sb4 are simultaneously turned on, i.e. the upper bridge arm connected with Ua and the lower bridge arm connected with Ub are turned on, as shown in Fig. 6, the positive electrode of Upn is clamped to Ua, the negative electrode of Upn is clamped to Ub, and Upn=Ua-Ub. When Sa1, Sa2, Sc3, Sc4 are simultaneously turned on, i.e. the upper bridge arm connected with Ua and the lower bridge arm connected with Uc are turned on, as shown in Fig. 7, the positive electrode of Upn is clamped to Ua, the negative electrode of Upn is clamped to Uc, and Upn=Ua-Uc.

[0086] Since |Ua|>|Ub|>|Uc|, and Ua>0, Ub<0, Uc<0, the amplitude of Ua-Ub is greater than that of Ua-Uc, i.e. the amplitude of Upn when the lower bridge arm connected with Ub is turned on is greater than that when the lower bridge arm connected with Uc is turned on. As shown in Fig. 8, adjusting the turn-on duration of the switch tube on the lower bridge arm connected with Ub and the turn-on duration of the switch tube on the lower bridge arm connected with Uc can change the effective value of Upn in a switching cycle, the LLC gain changes, and the output current changes accordingly.

[0087] Therefore, for each rectifier unit, the current working condition of the rectifier unit is determined according to the absolute value of the instantaneous value of the three-phase input voltage of the rectifier unit, and then the duty ratio of the control signal of the switch tube of each rectifier unit is adjusted according to the current working condition and the size of the current sampling value of all rectifier units, so as to change the voltage gain of the LLC resonant tank of each rectifier unit, thereby changing the size of the output current.

[0088] In the method provided by the above embodiment, the current sampling value of at least two rectifier units and the absolute value of the three-phase input voltage instantaneous value of the at least two rectifier units are obtained; the target adjustment phase is determined according to the absolute value of the three-phase input voltage instantaneous value of the at least two rectifier units; the target duty cycle of the target adjustment phase in each rectifier unit is determined according to the current sampling value of the at least two rectifier units, and the target duty cycle is used to indicate the adjustment of the voltage gain of the LLC resonant tank; and the duty cycle of the control signal of the switch tube corresponding to the target adjustment phase in each rectifier unit is adjusted according to the target duty cycle of the target adjustment phase in each rectifier unit. The pulse width of the control signal of the switch tube in the rectifier unit is adjusted to adjust the amplitude distribution of the input voltage of the resonant tank, so as to change the gain of the LLC, thereby controlling the output current of the LLC and achieving the purpose of current sharing.

[0089] In one of the embodiments, the target adjustment phase is determined according to the absolute value of the three-phase input voltage instantaneous value of the at least two rectifier units, including:

[0090] The absolute value of the three-phase input voltage instantaneous value of each of the at least two rectifier units is determined, and the first input phase with the maximum absolute value of the three-phase input voltage instantaneous value, the second input phase with the second maximum absolute value of the three-phase input voltage instantaneous value, and the third input phase with the minimum absolute value of the three-phase input voltage instantaneous value are determined.

[0091] The target adjustment phase is any one of the following combinations, and the following combinations include that the first input phase, the second input phase and the third input phase are all target adjustment phases, and the second input phase and the third input phase are target adjustment phases.

[0092] For each rectifier unit, the first input phase L phase with the maximum absolute value of the three-phase input voltage instantaneous value is determined, the second input phase M phase with the second maximum absolute value of the three-phase input voltage instantaneous value is determined, and the third input phase S phase with the minimum absolute value of the three-phase input voltage instantaneous value is determined. Based on FIG. 8, it can be known that the duty cycle of the L phase can be kept unchanged during adjustment, and the duty cycles of the M phase and the S phase are adjusted. At this time, the duty cycle of the M phase becomes larger, the duty cycle of the S phase becomes smaller, the effective value of Upn becomes larger, the output gain of the LLC becomes larger, and the output current becomes larger; on the contrary, the output current becomes smaller. The duty cycle of the L phase can also be adjusted during adjustment, at this time, the duty cycle of the S phase and the duty cycle of the M phase change accordingly, the output gain of the LLC also changes, and the output current changes accordingly.

[0093] The embodiments of the present application provide two combinations of target adjustment phases, which are the ratio of the S phase and the M phase, and the L phase is adjusted so that the S phase and the M phase change accordingly, so as to adjust the output gain of the LLC, and then adjust the output current of the rectifier unit.

[0094] In one of the embodiments, as shown in Fig. 9, the target duty cycle of the target adjustment phase in each rectification unit is determined according to the current sampling values of the at least two rectification units, including:

[0095] In step 902, the relative sizes of the current sampling values of the at least two rectification units are determined by comparing the current sampling values of the at least two rectification units;

[0096] In step 904, the duty cycle adjustment amount of the target adjustment phase in each rectification unit is determined according to the relative sizes of the current sampling values of the at least two rectification units;

[0097] In step 906, the target duty cycle of the target adjustment phase in each rectification unit is determined according to the duty cycle adjustment amount of the target adjustment phase in each rectification unit and the initial value of the duty cycle.

[0098] The relative sizes of the current sampling values are relative to a specific current value. In the embodiment, one of the current sampling values of the at least two rectification units is taken as the specific current value, and the current sampling values of the other rectification units are compared with the specific current value to determine whether the current sampling values of the other rectification units are too large or too small. Then, based on the comparison result, the output current of the other rectification units is adjusted by adjusting the duty cycle.

[0099] Specifically, after one of the rectification units is determined as the reference, the current sampling value of each rectification unit and the current sampling value of the reference rectification unit are input into a preset current sharing loop, and the duty cycle adjustment amount of the target adjustment phase corresponding to each rectification unit is obtained through the preset current sharing loop operation and the current sharing loop output limiting. Then, the target duty cycle is determined in combination with the initial value of the duty cycle.

[0100] The number of the preset current sharing loops is at least one and at most determined based on the number of the rectification units. When there is only one preset current sharing loop, the current sampling value of each rectification unit is input into the preset current sharing loop in sequence to obtain the duty cycle adjustment amount of each rectification unit. When there are multiple preset current sharing loops, for example, one preset current sharing loop corresponds to each rectification unit, the current sampling value of each rectification unit is input into the corresponding preset current sharing loop to obtain the duty cycle adjustment amount.

[0101] In the above process, after the specific current value among the current sampling values of the at least two rectification units is set, for example, the minimum value is taken as the specific current value or the maximum value is taken as the specific current value, the current sampling values of the at least two rectification units are directly input into the preset current sharing loop to determine the duty cycle adjustment amount.

[0102] In the method provided by the above embodiment, the current sampling value of one rectifier unit can be directly used as a reference, and the output currents of other rectifier units are adjusted to approach the output current of the reference rectifier unit, so that the control process has small calculation amount and is suitable for the case where the rectifier units are multiple.

[0103] In one of the embodiments, the at least two rectifier units include a first rectifier unit and a second rectifier unit; the target adjustment phase includes a second input phase and a third input phase; and the duty cycle adjustment amount of the target adjustment phase in each rectifier unit is determined according to the relative size of the current sampling value of each rectifier unit, including:

[0104] The difference between the first current sampling value and the second current sampling value is input to the first preset current sharing loop;

[0105] In the case where the first current sampling value is greater than the second current sampling value, the duty cycle adjustment amount of the second input phase and the third input phase in the first rectifier unit is obtained;

[0106] In the case where the first current sampling value is less than the second current sampling value, the duty cycle adjustment amount of the second input phase and the third input phase in the second rectifier unit is obtained.

[0107] After the difference between the first current sampling value and the second current sampling value is input to the first preset current sharing loop, the first preset current sharing loop can adjust the duty cycle of the second input phase or the duty cycle of the third input phase, and essentially change the ratio of the S-phase duty cycle to the M-phase duty cycle.

[0108] Taking an AC-DC converter including rectifier units U1 and U2 as an example, as shown in FIG. 10: i1 is the current sampling signal of the rectifier unit U1; i2 is the current sampling signal of the rectifier unit U2; ΔDutyM2 is the M-phase duty cycle adjustment amount of the rectifier unit U2; DutyL1 is the L-phase duty cycle of the rectifier unit U1; DutyM1 is the M-phase duty cycle of the rectifier unit U1; DutyS1 is the S-phase duty cycle of the rectifier unit U1; DutyL2 is the L-phase duty cycle of the rectifier unit U2; DutyM2 is the M-phase duty cycle of the rectifier unit U2; and DutyS2 is the S-phase duty cycle of the rectifier unit U2.

[0109] The current sharing adjustment rule of the first preset current sharing loop shown in FIG. 10 is:

[0110] When i2 < i1, the current sharing loop input error is positive, the current sharing loop output ΔDutyM2 is positive, DutyM2 becomes larger, and DutyS2 becomes smaller, that is, the M-phase duty cycle of the rectifier unit U2 becomes larger, the S-phase duty cycle becomes smaller, the SM ratio becomes smaller, Upn becomes larger, the LLC gain becomes larger, i2 becomes larger, i2 approaches i1, and the current sharing purpose is achieved.

[0111] When i2>i1, the input error of the current sharing loop is negative, the output ΔDutyM2 of the current sharing loop is negative, DutyM2 becomes smaller, DutyS2 becomes larger, that is, the M-phase duty cycle of the rectifier unit U2 becomes smaller, the S-phase duty cycle becomes larger, the SM ratio becomes larger, so that Upn becomes smaller, the LLC gain becomes smaller, i2 becomes smaller, and i2 approaches i1, achieving the purpose of current sharing.

[0112] In the actual application of the above embodiment, the rated three-phase input voltage is 380V 50HZ, the rated output voltage is 270V, and the rated output power is 50KW. The parameters of the two rectifier units are consistent, and the influence of the SM ratio on the output current is observed. When the SM ratios of the rectifier units U1 and U2 are the same, as shown in FIG. 11, the effective value of Upn is consistent, and the effective value of the output current is also consistent. The above data is arranged in the following table:

[0113] Table 1 Output current of rectifier unit when SM ratios are the same

[0114] When the SM ratio of the rectifier unit U1 is greater than that of the rectifier unit U2, the effective value of Upn of the rectifier unit U1 is smaller than that of the rectifier unit U2, and the effective value of the output current of the rectifier unit U1 is smaller than that of the rectifier unit U2, as shown in FIG. 12. When the SM ratios of the two rectifier units are different, the influence on the effective value of Upn and the effective value of the output current is as follows. The SM ratio is large, the effective value of Upn is small, and the effective value of the output current is small. According to this rule, the SM ratio can be adjusted to adjust the size of the output current.

[0115] Table 2 Output current of rectifier unit when SM ratios are different

[0116] In the method provided by the above embodiment, the duty cycle of the M-phase or the duty cycle of the S-phase is adjusted, so as to change the ratio of the duty cycle of the S-phase to the duty cycle of the M-phase, control the gain of the LLC, control the output current of the rectifier unit, and further achieve the purpose of current sharing.

[0117] In one of the embodiments, the at least two rectifier units include a first rectifier unit and a second rectifier unit; the target adjustment phase includes a first input phase, a second input phase, and a third input phase; and the duty cycle adjustment amount of the target adjustment phase in each rectifier unit is determined according to the relative size of the current sampling value of each rectifier unit, and includes:

[0118] The difference between the first current sampling value and the second current sampling value is input into the second preset current sharing loop;

[0119] In the case where the first current sampling value is greater than the second current sampling value, the duty cycle adjustment amount of the first input phase, the second input phase, and the third input phase in the first rectifier unit is obtained.

[0120] In the case that the first current sampling value is less than the second current sampling value, the duty cycle adjustment amount of each of the first input phase, the second input phase and the third input phase in the second rectifying unit is obtained.

[0121] The L-phase duty cycle is adjusted while the sum of the M-phase duty cycle and the S-phase duty cycle is adjusted. Taking an AC-DC converter including rectifying units U1 and U2 as an example, as shown in FIG. 13, i1 is a current sampling signal of the rectifying unit U1, i2 is a current sampling signal of the rectifying unit U2, ΔDutyL1 is an L-phase duty cycle adjustment amount of the rectifying unit U1, ΔDutyL2 is an L-phase duty cycle adjustment amount of the rectifying unit U2, DutyL1 is an L-phase duty cycle of the rectifying unit U1, DutyM1 is an M-phase duty cycle of the rectifying unit U1, DutyS1 is an S-phase duty cycle of the rectifying unit U1, DutyL2 is an L-phase duty cycle of the rectifying unit U2, DutyM2 is an M-phase duty cycle of the rectifying unit U2, and DutyS2 is an S-phase duty cycle of the rectifying unit U2.

[0122] The current sharing regulation rule of the first preset current sharing loop shown in FIG. 13 is as follows:

[0123] When i2 < i1, the current sharing loop input error is positive, the current sharing loop output is positive, ΔDutyL1 is greater than 0, and ΔDutyL2 = 0, that is, the L-phase duty cycle of the rectifying unit U1 is reduced, the LLC gain of the rectifying unit U1 is reduced, i1 is reduced, and i1 approaches i2, thereby achieving the current sharing purpose.

[0124] When i2 > i1, the current sharing loop input error is negative, the current sharing loop output is negative, ΔDutyL1 = 0, and ΔDutyL2 is less than 0, that is, the L-phase duty cycle of the rectifying unit U2 is reduced, the LLC gain of the rectifying unit U2 is reduced, i2 is reduced, and i2 approaches i1, thereby achieving the current sharing purpose.

[0125] In the method provided in the above embodiment, the L-phase duty cycle is adjusted while the sum of the M-phase duty cycle and the S-phase duty cycle is adjusted, so as to control the LLC gain, thereby controlling the output current of the rectifying unit and further achieving the current sharing purpose.

[0126] In one of the embodiments, the target duty cycle of the target adjustment phase in each rectifying unit is determined according to the current sampling values of the at least two rectifying units, and the method comprises the following steps.

[0127] The average current value of the at least two rectifying units is determined according to the current sampling values of the at least two rectifying units.

[0128] The target duty cycle of the target adjustment phase in each rectifying unit is determined according to the current sampling value and the average current value of each rectifying unit.

[0129] The average current value of the at least two rectifier units is taken as a specific current value, and the duty cycle of each rectifier unit target adjustment phase is adjusted to achieve current sharing effect. The average value of the current sampling values of the at least two rectifier units can be calculated from the current sampling values of the at least two rectifier units, or can be obtained by sampling the total output current of the at least two rectifier units and then determining the total output current and the number of rectifier units.

[0130] As shown in FIG. 14, the target adjustment phase is M phase, the AC-DC converter includes N rectifier units, each rectifier unit corresponds to a current sharing loop, the given of each current sharing loop is the average value iavg of all rectifier unit current samples, the feedbacks are the current samples i1, i2, …, iN of each rectifier unit, and the outputs of each current sharing loop are ΔDutyM1, ΔDutyM2, …, ΔDutyMN, which are used to adjust DutyM1, DutyM2, …, DutyMN respectively.

[0131] It should be noted that the idea of the current sharing control method provided in the embodiments of the present application is to adjust the duty cycle of the control signal of the switch tube on each phase corresponding bridge arm, change the amplitude distribution of the resonant tank input voltage, change the gain of LLC, and thus control the output current balance of LLC. Therefore, when adjusting, the target adjustment phase, that is, the output of the current sharing loop, can be L phase or M phase or S phase; when comparing the currents, the current sampling values of the rectifier units can be compared with the minimum value or the maximum value or the average value as the input of the preset current sharing loop; the target adjustment phases of different rectifier units can be the same or different, and the initial values of the duty cycles of the target adjustment phases of different rectifier units can be the same or different; the number of preset current sharing loops is not limited. As long as the scheme follows the above idea to achieve current sharing control, it belongs to the protection scope of the embodiments of the present application.

[0132] For the current sharing control method based on adjusting the duty cycle provided in the embodiments of the present application, in order to display the current sharing effect, taking an AC-DC converter including two rectifier units U1 and U2 as an example, the following data obtained in actual operation are as follows:

[0133] The rated three-phase input voltage is 380V 50HZ, the rated output voltage is 270V, and the rated output power is 50KW. Without adding the width modulation current sharing regulation, when the resonant inductance, resonant capacitance and excitation inductance of the rectifier unit U1 are respectively 5% smaller than those of the rectifier unit U1, the current sharing effect will be produced. After using the width modulation current sharing method provided in the embodiments of the present application, the output current difference between the rectifier unit U1 and the rectifier unit U2 gradually decreases until the current sharing is completed and stabilized, as shown in the effect comparison diagram of FIGS. 15-17.

[0134] In the above schematic diagram, the output current of the rectifier unit contains high-frequency switching ripple. To facilitate observation of the average value, the output current of the rectifier unit is sampled and the instantaneous value is displayed after two-stage 100Hz low-pass filtering.

[0135] Based on the above data, it can be known that the resonant inductance has the greatest impact on the uneven current degree, the resonant capacitance has the second greatest impact, and the excitation inductance has the least impact. Table 3 shows the uneven current degree.

[0136] After the addition of the width-adjusting current-sharing control method of the application, the average value of the output current of the rectifier unit from 0.1s to 0.2s and the uneven current degree are calculated as follows: the maximum uneven current degree is 0.02%, as shown in Table 4.

[0137] Table 3 Uneven current degree without current-sharing adjustment

[0138] Table 4 Uneven current degree with SM ratio adjustment

[0139] Table 5 Uneven current degree with L-phase adjustment

[0140] The uneven current degree is calculated according to the following formula:

[0141] In the formula,

[0142] I avg is the average output current of each rectifier unit;

[0143] I max is the output current of the rectifier unit with the greatest deviation from I avg

[0144] Figures 18 and 19 are input current THD before and after the addition of current-sharing adjustment, and the difference between different resonant parameters. Before the addition of current-sharing adjustment, the input Ua phase current THD of the SM ratio adjustment scheme and the L-phase adjustment scheme of the application is as follows: all less than 3%. Among them, the scheme of changing the SM ratio by taking the S phase or the M phase as the target adjustment phase to change the voltage gain of the LLC resonant tank and thereby change the size of the output current is defined as the SM ratio adjustment scheme, and the scheme of taking the L phase as the target adjustment phase is defined as the L-phase adjustment scheme.

[0145] Table 6 Input current THD

[0146] ​It should be understood that although the steps in the flowcharts involved in the above embodiments are shown in sequence according to the arrows, the steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified herein, the execution of the steps is not strictly limited in sequence, and the steps can be executed in other sequences. Moreover, at least some of the steps in the flowcharts involved in the above embodiments can include multiple steps or multiple stages, which are not necessarily executed at the same time, but can be executed at different times, and the execution sequence of the steps or stages is not necessarily sequential, but can be executed alternately or alternately with at least part of other steps or steps or stages in other steps.

[0147] Based on the same inventive concept, the embodiment of the present application also provides an AC-DC conversion system, as shown in Figure 20, the system 2000 includes an AC-DC converter 2001 and a current sharing controller 2002; the AC-DC converter includes at least two rectifier units, and each of the at least two rectifier units adopts a combination of a bridge topology and an LLC resonant tank;

[0148] The current sharing controller is configured to control the working state of the AC-DC converter, and specifically configured to execute the method steps in any of the above embodiments.

[0149] As shown in Figure 21, the embodiment of the present application provides a computer device 2100, which includes a memory 2101 and a processor 2102.

[0150] The memory 2101 is configured to store computer executable instructions executable by the processor.

[0151] The processor 2102 implements each step in the method in the above embodiments when executing the computer executable instructions. For details, please refer to the related description in the foregoing method embodiments.

[0152] Optionally, the memory 2101 can be independent or integrated with the processor 2102. When the memory 2101 is independently provided, the computer device further includes a bus for connecting the memory 2101 and the processor 2102.

[0153] The embodiment of the present application also provides a computer readable storage medium, which stores computer executable instructions, and when the processor executes the computer executable instructions, each step in the method in the above embodiments is implemented.

[0154] The embodiment of the present application also provides a computer program product, which includes computer executable instructions, and when the processor executes the computer executable instructions, each step in the method in the above embodiments is implemented.

[0155] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a non-volatile computer readable storage medium. The computer execution instructions in the computer program can include the processes of the above-mentioned embodiments of the method when executed. Any reference to memory, database or other medium used in the embodiments provided in the present application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical storage, high-density embedded non-volatile memory, resistive memory (ReRAM), magnetoresistive random access memory (MRAM), ferroelectric memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. As an illustration but not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc. The database involved in the embodiments provided in the present application can include at least one of a relational database and a non-relational database. The non-relational database can include a distributed database based on a block chain, etc., without being limited thereto. The processor involved in the embodiments provided in the present application can be a general-purpose processor, a central processing unit, a graphics processing unit, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, etc., without being limited thereto.

[0156] Any combination of the technical features of the above embodiments can be made. In order to make the description simple, all possible combinations of the technical features in the above embodiments are not described, however, as long as the combination of the technical features does not exist, it should be considered as the scope of the present application.

[0157] The above embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent of the present application. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of protection of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A current sharing control method, characterized by, The application is applied to a current sharing controller used for controlling the working state of an AC-DC converter, the AC-DC converter comprising at least two rectification units, each of which adopts a combination of a bridge topology and an LLC resonant tank; the method comprises: obtaining current sampling values of the at least two rectification units and absolute values of three-phase input voltage instantaneous values of the at least two rectification units; determining a target adjustment phase according to the absolute values of the three-phase input voltage instantaneous values of the at least two rectification units; determining a target duty cycle of the target adjustment phase in each rectification unit according to the current sampling values of the at least two rectification units, the target duty cycle being used for indicating adjustment of a voltage gain of the LLC resonant tank; adjusting a duty cycle of a control signal of a switch tube corresponding to the target adjustment phase in each rectification unit according to the target duty cycle of the target adjustment phase in each rectification unit.

2. The method of claim 1, wherein, The method of determining the target adjustment phase according to the absolute values of the three-phase input voltage instantaneous values of the at least two rectification units comprises: determining a first input phase with the largest absolute value of instantaneous value, a second input phase with the second largest absolute value of instantaneous value and a third input phase with the smallest absolute value of instantaneous value in the three-phase input voltage of each rectification unit according to the absolute values of the three-phase input voltage instantaneous values of each of the at least two rectification units; the target adjustment phase is any one of the following combinations, the combinations comprising the first input phase, the second input phase and the third input phase all being the target adjustment phase, the second input phase and the third input phase being the target adjustment phase.

3. The method of claim 2, wherein, The method of determining the target duty cycle of the target adjustment phase in each rectification unit according to the current sampling values of the at least two rectification units comprises: comparing the current sampling values of the at least two rectification units to determine the relative sizes of the current sampling values of each rectification unit; determining a duty cycle adjustment amount of the target adjustment phase in each rectification unit according to the relative sizes of the current sampling values of each rectification unit; determining the target duty cycle of the target adjustment phase in each rectification unit according to the duty cycle adjustment amount of the target adjustment phase in each rectification unit and an initial value of the duty cycle.

4. The method of claim 3, wherein, The at least two rectification units comprise a first rectification unit and a second rectification unit; the target adjustment phase comprises the second input phase and the third input phase; The method of determining the duty cycle adjustment amount of the target adjustment phase in each rectification unit according to the relative sizes of the current sampling values of each rectification unit comprises: inputting a difference value between the first current sampling value and the second current sampling value into a first preset current sharing loop; in the case that the first current sampling value is greater than the second current sampling value, obtaining the duty cycle adjustment amount of the second input phase and the third input phase in the first rectification unit respectively; in the case that the first current sampling value is less than the second current sampling value, obtaining the duty cycle adjustment amount of the second input phase and the third input phase in the second rectification unit respectively.

5. The method of claim 3, wherein, The at least two rectifier units include a first rectifier unit and a second rectifier unit; the target adjustment phase includes a first input phase, a second input phase, and a third input phase; the determining of the duty cycle adjustment amount of the target adjustment phase in each rectifier unit according to the relative size of the current sampling value of each rectifier unit includes: inputting the difference between the first current sampling value and the second current sampling value into a second preset current sharing loop; in the case that the first current sampling value is greater than the second current sampling value, obtaining the duty cycle adjustment amount of the first input phase, the second input phase, and the third input phase in the first rectifier unit respectively; in the case that the first current sampling value is less than the second current sampling value, obtaining the duty cycle adjustment amount of the first input phase, the second input phase, and the third input phase in the second rectifier unit respectively.

6. The method of claim 1, wherein, The determining of the target duty cycle of the target adjustment phase in each rectifier unit according to the current sampling value of the at least two rectifier units includes: determining the average current value of the at least two rectifier units according to the current sampling value of the at least two rectifier units; determining the target duty cycle of the target adjustment phase in each rectifier unit according to the current sampling value of each rectifier unit and the average current value.

7. The method according to any one of claims 1 to 6, characterized in that, The current sampling value includes at least one of the following current sampling values: input current sampling value, rectified output current sampling value, resonant current sampling value, switch tube current sampling value, and transformer secondary side current sampling value.

8. An AC-DC conversion system, characterized by, The system includes an AC-DC converter and a current sharing controller; the AC-DC converter includes at least two rectifier units, and each of the at least two rectifier units adopts a combination of bridge topology and LLC resonant tank; The current sharing controller is configured to control the working state of the AC-DC converter, and specifically configured to execute the method steps of any one of claims 1-7.

9. A computer device, comprising: including: a processor, and a memory connected to the processor in communication; the memory stores computer execution instructions; the processor executes the computer execution instructions stored in the memory to realize the method of any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that, The computer readable storage medium stores computer execution instructions, and the computer execution instructions are executed by the processor to realize the method of any one of claims 1 to 7.

11. A computer program product, characterised in that, including computer execution instructions, the computer execution instructions are executed by the processor to realize the method of any one of claims 1 to 7.

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