Mode-switching based fixed-frequency minimum-inductor peak-current-controlled converter and method

Abstract

The application discloses a mode-switching-based fixed-frequency minimum-inductance peak-current control converter and method, aiming at solving the problems of high loss of a two-stage topology of an existing bidirectional AC / DC converter, difficulty in magnetic element design caused by frequency conversion control, and narrow soft-switching ZVS range. The converter comprises a DC side parallel MOS tube H bridge, an AC side matrix bidirectional half bridge, an inductor and a high-frequency transformer, a control module drives a switching tube at a fixed frequency, selects a target mode among three extended phase-shift modes according to a voltage gain and a grid reference current, and solves a phase-shift ratio that minimizes the inductance peak current by simultaneously solving power transmission and ZVS condition equations. The application reduces power conversion loss, reduces the difficulty and cost and volume of magnetic element design, realizes wide-working-condition ZVS, is suitable for bidirectional power transmission of distributed new energy and a power grid in a micro grid, and can also be applied to a multi-path DC scene.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power electronic conversion technology, and in particular to a fixed-frequency minimum-inductor peak current control converter and method based on mode switching. BACKGROUND

[0002] The global energy system is undergoing profound changes. Under the drive of carbon neutralization goals, traditional centralized fossil energy is accelerating its replacement by "distributed renewable energy". By the end of 2024, global photovoltaic and wind power installations have exceeded 3.6TW, accounting for 19% of total power generation, and it is expected that the proportion will exceed 35% by 2030. However, there is a natural contradiction between the strong intermittency of wind and light output and the high stability requirements of the power grid, which must rely on the coordination of distributed power grids, energy storage units and intelligent scheduling to alleviate.

[0003] Microgrids are considered a key carrier to resolve the above-mentioned contradictions. Their modular, spatially dispersed layout can shorten the energy transmission path, reduce line losses, increase local renewable energy consumption, and diversify power supply. The current mainstream AC / DC hybrid microgrid integrates renewable power generation, distributed energy storage and power electronic conversion devices at the same port, among which the bidirectional AC / DC converter (commonly known as a micro-inverter) is the throat connecting the microgrid and the main grid. It not only completes the conversion of direct current to alternating current, but also needs to achieve grid synchronization, power factor correction and harmonic control, and its operating quality directly determines the stability boundary of the microgrid.

[0004] Constrained by volume, cost and efficiency, micro-inverters generally adopt a two-stage architecture of DC-DC boost + DC-AC inversion. Although this topology is mature, the cascading of multiple power stages results in cumulative losses, and the cost of heat dissipation and installation increases simultaneously. In pursuit of higher efficiency, the industry has turned its attention to single-stage dual active bridge (DAB) structures, and has combined extended phase shift (EPS), double phase shift (DPS), triple phase shift (TPS) and other frequency modulation strategies, in order to achieve zero voltage switching (ZVS) and reduce inductor current effective value in a wide voltage gain and full load range. Unfortunately, frequency conversion operation significantly widens the operating frequency band of transformers and magnetic components, and designers have to reserve saturation margins at the worst low frequency point, resulting in low utilization rate, large volume and high cost of magnetic cores in the commonly used frequency band, and the power density is actually limited. SUMMARY

[0005] The present application aims to address the shortcomings of the prior art. The present application proposes a fixed-frequency minimum-inductor peak current control converter and method based on mode switching, achieving efficient and reliable bidirectional power transmission between distributed energy and the grid.

[0006] The technical solution to achieve the purpose of the present application is:

[0007] The application discloses a mode-switching-based fixed-frequency minimum-inductance peak-current control converter, which is applied to bidirectional power transmission between distributed energy and an AC power grid, and comprises the following parts:

[0008] a DC side H bridge module composed of first to fourth switch tubes to parallel connection, which converts input DC power into high-frequency AC power;

[0009] an AC side matrix bidirectional half-bridge module composed of fifth to eighth switch tubes to which can convert high-frequency AC power into power-frequency AC power to adapt to a power grid and receive power-frequency AC power of the power grid and convert the power-frequency AC power into high-frequency AC power;

[0010] an energy transmission module comprising an inductor L and a high-frequency transformer T, wherein a primary side of the high-frequency transformer T is connected with the DC side H bridge module, a secondary side of the high-frequency transformer T is connected with the AC side matrix bidirectional half-bridge module, the inductor L is connected with the high-frequency transformer T in series, and the converter has no intermediate DC conversion link, and power transmission is directly realized through high-frequency conversion of the DC side H bridge module and the AC side matrix bidirectional half-bridge module;

[0011] a control module configured to:

[0012] drive the switch tubes of the DC side H bridge module and the AC side matrix bidirectional half-bridge module at a fixed switching frequency;

[0013] collect DC side voltage, AC side voltage and grid reference current in real time , calculate voltage gain: wherein is an equivalent voltage of the DC side voltage after conversion through a high-frequency transformer transformation ratio , is an equivalent voltage of the AC side voltage, and target mode is selected from three preset extended phase-shift working modes according to the voltage gain and the grid reference current ;

[0014] based on the target mode, internal phase-shift ratio and external phase-shift ratio are solved by simultaneously solving a power transmission equation and a zero-voltage switching (ZVS) condition equation, and the inductance peak current is minimized in the solving process; the ZVS condition equation is specifically: inductance current before the DC side switch tube is turned on , inductance current before the DC side switch tube is turned off , and inductance current before the AC side switch tube is turned on , wherein is the inductance current at the rising edge of the DC side equivalent voltage square wave, the inductor current at the rising edge of the equivalent voltage square wave on the AC side, the inductor current at the falling edge of the equivalent voltage square wave on the DC side.

[0015] Further, the three working modes include:

[0016] Mode 1: the inner phase shift ratio and the outer phase shift ratio , the is the ratio of the time that the rising edge of the equivalent voltage square wave on the AC side leads the rising edge of the equivalent voltage square wave on the DC side to the half switching period, and the is the ratio of the time that the rising edge of the equivalent voltage square wave on the AC side leads the falling edge of the equivalent voltage square wave on the DC side to the half switching period, and the equivalent voltage square wave on the DC side is partially intersected with the equivalent voltage square wave on the AC side;

[0017] Mode 2: the inner phase shift ratio and the outer phase shift ratio , the equivalent voltage square wave on the DC side is contained in the equivalent voltage square wave on the AC side;

[0018] Further, the first to fourth switching tubes of the DC side H-bridge module are MOS tubes, and the current stress of a single MOS tube is reduced by parallel configuration.

[0019] Further, the specific logic of the control module selecting the target mode is:

[0020] the inner phase shift ratio is solved in priority according to Mode 1 and the outer phase shift ratio , if the solving result meets the constraint condition of Mode 1: , and meets the zero voltage switching condition, Mode 1 is selected; if not, according to the adaptability of the voltage gain and the grid reference current, Mode 2 is switched to for re-solution.

[0021] Further, the specific logic of the control module minimizing the inductor peak current is:

[0022] when the voltage gain is less than 1, the inductor peak current is the inductor current at the falling edge of the equivalent voltage square wave on the DC side , the inner phase shift ratio and the outer phase shift ratio are adjusted to make take the minimum value;

[0023] when the voltage gain is greater than 1, the inductor peak current is the inductor current at the rising edge of the equivalent voltage square wave on the AC side , the inner phase shift ratio Compared with the outer shift Make The value is minimum

[0024] Enter mode 2, and the voltage gain When less than 1, the inductance peak current is the inductance current at the falling edge of the equivalent voltage square wave on the DC side By adjusting the inner shift ratio Compared with the outer shift Make The value is minimum

[0025] Enter mode 2, and the voltage gain When greater than 1, the inductance peak current is the inductance current at the rising edge of the equivalent voltage square wave on the AC side By adjusting the inner shift ratio Compared with the outer shift Make The value is minimum

[0026] Further, the fixed switching frequency is matched with the design parameters of the high-frequency transformer and the inductor, so that the high-frequency transformer and the inductor work in the optimal parameter state under a single frequency (satisfying the requirements of saturation current, iron loss and copper loss).

[0027] The mode switching based fixed frequency minimum inductance peak current control method is applied to the mode switching based fixed frequency minimum inductance peak current control converter, and is characterized in that it comprises the following steps:

[0028] Step S1, set the switching frequency to a fixed value, and initialize the initial values of the inner shift ratio Compared with the outer shift ;

[0029] Step S2, real-time acquisition of DC side voltage, AC side voltage and grid reference current, calculation of DC side equivalent voltage, AC side equivalent voltage, and calculation of voltage gain;

[0030] Step S3, according to the voltage gain and the grid reference current, select the target extended shift mode;

[0031] Step S4, based on the target working mode, simultaneously solve the power transmission equation and the zero voltage switch condition equation, and solve the inner shift ratio Compared with the outer shift ;

[0032] Step S5, according to the inner shift ratio Compared with the outer shift The PWM driving signal is generated to control the switching tube action of the DC side H bridge module and the AC side matrix bidirectional half bridge module, and the power transmission is realized.

[0033] Further, the power transfer equation in step S4 is derived based on the linear variation characteristic of the inductance current, and the influence of the dead time and the switching time of the switch tube on the inductance current is ignored.

[0034] Further, when the inner phase shift is solved in step S4 and the outer phase shift is compared When the target mode is mode 1, the formula is solved simultaneously:

[0035]

[0036] When the target mode is mode 2, the formula is solved simultaneously:

[0037]

[0038] Further, the method only has a small range of hard switching at the mode switching transition and near the zero point of the grid current, and soft switching is realized by satisfying the zero voltage switching condition under the rest working conditions.

[0039] Compared with the prior art, the above technical scheme has the following beneficial effects:

[0040] (1) The minimum inductance peak current control converter and method based on mode switching are proposed, which optimizes the minimum inductance peak current, reduces the loss and improves the efficiency; taking the minimum inductance peak current as the core, combining the voltage gain and the load demand, the direct current side current is optimized when the voltage is low, and the alternating current side current is optimized when the voltage is high, which directly reduces the inductance conduction loss and improves the power transmission efficiency. It not only improves the utilization rate of clean energy such as photovoltaic and wind power, but also reduces the equipment heat dissipation pressure and adapts to the small size deployment demand.

[0041] (2) The fixed switching frequency is adopted, the magnetic element does not need to adapt to a wide frequency range, only needs to optimize the parameters for a single frequency, and the design process is greatly simplified. At the same time, excessive redundant design is avoided, the element volume is reduced, the cost is reduced, and the element works in the optimal interval under all working conditions, and full utilization is realized.

[0042] (3) The algorithm derivation integrates the soft switching ZVS condition, the phase shift ratio is optimized, the soft switching demand can still be met under the working conditions such as voltage mismatch and light load, the ZVS coverage range is greatly widened, the switching loss is reduced, the voltage peak and the device failure risk are reduced, and the system stability and the power quality are improved.

[0043] (4) The frequency-fixed minimum inductance peak current control converter and method based on mode switching provided by the application, when applied to a multi-path DC scenario, due to its frequency-fixed characteristics, only the outer and inner moving phases of the respective full-bridge relative to the AC measurement half-bridge need to be calculated, the control is simple, and the inductance current obtained by multi-path DC control is finally superimposed on the AC measurement, which makes the AC measurement switch tube more easily achieve soft switching. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 The topological structure diagram of the single-stage DC / AC dual active bridge converter of the frequency-fixed minimum inductance peak current control converter and method based on mode switching of the application;

[0045] Figure 2 The equivalent circuit diagram of the inductance voltage in the embodiment of the application;

[0046] Figure 3 The equivalent voltage waveform and inductance current waveform diagram of the inductance in mode 1 in the embodiment of the application;

[0047] Figure 4 The equivalent voltage waveform and inductance current waveform diagram of the inductance in mode 2 in the embodiment of the application;

[0048] Figure 5 The equivalent voltage waveform and inductance current waveform diagram of the inductance in mode 3 in the embodiment of the application;

[0049] Figure 6 The system control block diagram of the application;

[0050] Figure 7 The topology diagram of the frequency-fixed minimum inductance peak current control converter based on mode switching of two-path DC input in the embodiment of the application. DETAILED DESCRIPTION

[0051] The technical solutions in the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0052] The frequency-fixed minimum inductance peak current control converter and method based on mode switching, comprising:

[0053] The frequency-fixed minimum inductance peak current control converter based on mode switching is applied to bidirectional power transmission between distributed energy and an AC power grid, as shown in the figure, comprising: Figure 1

[0054] ​The DC side H-bridge module is composed of first to fourth switch tubes to Parallelly connected, the input DC is converted into high-frequency AC;

[0055] The AC side matrix bidirectional half-bridge module is composed of fifth to eighth switch tubes to The AC side matrix bidirectional half-bridge module can realize conversion from high-frequency AC into power-frequency AC to adapt to the power grid and receive power-frequency AC and convert it into high-frequency AC;

[0056] The energy transmission module includes an inductor L and a high-frequency transformer T, the primary side of the high-frequency transformer T is connected with the DC side H-bridge module, the secondary side is connected with the AC side matrix bidirectional half-bridge module, the inductor L is connected in series with the high-frequency transformer T, and the converter has no intermediate DC conversion link, and power transmission is directly realized through high-frequency conversion of the DC side H-bridge module and the AC side matrix bidirectional half-bridge module;

[0057] For the convenience of analysis, the turn-on and turn-off of the switch devices are equivalent to the bridge arm voltage directly added to the inductor, as shown in the equivalent circuit of Figure 2 , wherein Figure 2 , is Figure 1 , , Figure 2 , is Figure 1 , times . The inductor current flows from the ac side to the dc side.

[0058] Figure 3 is the equivalent voltage waveform of the inductor and the inductor current waveform under the extended phase shift modulation, the DC side is a three-level voltage with adjustable duty cycle , and the AC side is a quasi-two-level voltage generated by chopping the grid voltage by the AC matrix half-bridge. The amplitude of is the input DC voltage multiplied by the transformer ratio , The amplitude of is equal to half of the instantaneous grid voltage. The power transmission is realized by adjusting the duty cycle of and the phase difference between and . Therefore, the DAB micro-inverter has two control degrees of freedom: the inner phase shift ratio , as shown in Figure 3 , is defined as the rising edge of the positive voltage square wave is ahead of the ratio of the time of the positive voltage square wave rising edge to the half switching period, is defined as the positive voltage square wave rising edge is advanced the ratio of the time of the positive voltage square wave falling edge to the half switching period. After ignoring the effect of dead time on the dual active bridge converter, the inductor current will present linear change in the high frequency period. Define the corresponding the inductor current at the positive voltage square wave rising edge time is , the corresponding the inductor current at the positive voltage square wave falling edge time is , the corresponding the inductor current at the positive voltage square wave rising edge time is . Due to the symmetry of the inductor current, the current at the time is opposite to that at the time , the current at the time is opposite to that at the time the current at the time is opposite to that at the time , the current at the time is opposite to that at the time the current at the time is opposite to that at the time , the current at the time is opposite to that at the time. The subsequent and are also used to represent the amplitude of the square wave voltage across the inductor.

[0059] For extended phase shift modulation, there are three modes in total, mode 1 is as shown in Figure 3 , both and are greater than 0, the positive voltage square wave intersects with the positive voltage square wave, mode 2 is as shown in Figure 4 , both and are less than 0, the positive voltage square wave is contained in the positive voltage square wave, mode 3 is as shown in Figure 5 , both and are greater than 0, the positive voltage square wave is outside the positive voltage square wave.

[0060] In the extended phase shift working mode, the outer phase shift angle of the two side full bridge arms can be obtained from the duty cycles and , that is, the angle by which the DC voltage square wave fundamental wave is advanced to the AC voltage square wave fundamental wave:

[0061] (1)

[0062] Define the voltage gain:

[0063] ​(2)

[0064] Considering that the dead time accounts for a very low proportion in the whole switching cycle, and the waveform analysis of half cycle is universal for the whole mode analysis; and considering that the time of MOSFET opening and closing accounts for a very low proportion in the whole high-frequency cycle, it can be considered that the linear switch, so the inductance current formula can be written, only mode 1 and mode 2 (related to the algorithm) are derived as follows:

[0065] Mode 1:

[0066] (3)

[0067] Due to the symmetry of inductance current, The current at time and The current at time is opposite:

[0068] (4)

[0069] The simultaneous equations are obtained. When the power is transmitted from the DC side to the AC side in the mode 1 working state, the instantaneous value expression of the inductance current is shown in equation (5) (when the power is transmitted from the AC side to the DC side, the voltage square wave reversal analysis can be performed):

[0070] (5)

[0071] The average value of the AC side current in the switching cycle (i.e. the reference current value ) can be represented as:

[0072] (6)

[0073] Where the absolute value of times the absolute value of the grid voltage at this time represents the transmission power at the current time, and the power flow direction is determined by the phase lead and lag relationship between the DC voltage square wave fundamental wave and the AC voltage square wave fundamental wave. If the DC voltage square wave fundamental wave leads the AC voltage square wave fundamental wave, the power is transmitted from DC to AC; if the DC voltage square wave fundamental wave lags the AC voltage square wave fundamental wave, the power is transmitted from AC to DC. The algorithm derivation in this paper is based on Figure 3 and Figure 4 are derived to obtain control quantities and , and and are determined, and the frequency is determined, so the amount of transmission power and is determined, and the shift phase module processes and to obtain the corresponding PWM wave of the control switch tube, so the algorithm part is mainly quantitative analysis.

[0074] When power is transferred from the AC side to the DC side, Figure 3 The image as a whole is symmetrical about the x-axis. The image as a whole is symmetrical about the x-axis.

[0075] Mode 2:

[0076] (7)

[0077] Due to the symmetry of inductance current, The moment and The moment the current is opposite:

[0078] (8)

[0079] Simultaneously, when power is transferred from the DC side to the AC side, the instantaneous value expression of the inductance current in the mode 2 working state is shown as formula (9) (voltage square wave flip analysis when power is transferred from the AC side to the DC side):

[0080] (9)

[0081] The AC side current average value (i.e. reference current value , the current direction is from the power grid) of the switching period can be represented as:

[0082] (10)

[0083] When power is transferred from the AC side to the DC side, Figure 4 The image as a whole is symmetrical about the x-axis. The image as a whole is symmetrical about the x-axis.

[0084] Figure 6 The system control block diagram of the single-stage dual active bridge DC / AC converter, the control process is to collect AC voltage, DC voltage, inductance and turns ratio and other parameters, through the optimal control algorithm proposed to calculate the relevant control parameters 、 , and the control parameters 、 and the fixed frequency are introduced into the PWM module to drive the corresponding switch. Therefore, the control algorithm is the core.

[0085] In the dual active bridge converter, due to the large number of switch tubes, the switching loss occupies the dominant position of the loss, in order to reduce the switching loss, it is necessary to make the voltage across the switch device zero before conduction, so as to realize ZVS.

[0086] In order to realize ZVS, the following current conditions need to be met:

[0087] (11)

[0088] where and are the current and voltage across the switching device in AC side and DC side respectively, is the leakage inductance, and are the AC and DC side MOSFET parallel capacitances. In ideal working condition, the voltage or current across the device first drops to zero and then slowly rises to the off-state level, thus realizing a nearly zero-loss switching process. However, the realization of soft switching depends on specific electrical conditions, resulting in limited regulation range. To overcome this limitation, the modulation strategy proposed in this paper can effectively expand the soft switching operating range under different power levels.

[0089] From Figure 1 it can be seen that to achieve zero-voltage turn-on in the DC side, it is necessary to ensure that the energy on the junction capacitance is completely discharged before turn-on, at which time the voltage difference across the MOSFET is zero, i.e., it is necessary to ensure that and the inductor current at the turn-on moment Similarly, to achieve zero-voltage turn-on in the AC side, it is necessary to ensure that the energy on the junction capacitance is completely discharged before turn-on, i.e., the inductor current at the turn-on moment Due to the symmetry of the full-bridge devices on both sides, when the above three conditions are met, the soft switching of all switches is satisfied.

[0090] Combining the above conditions with the definitions of Figure 3 , Figure 4 and , the necessary conditions for zero-voltage switching of all switches are shown in Table 1:

[0091] Table 1 Conditions for ZVS realization by extended phase shift combined with frequency conversion

[0092]

[0093] In a dual active bridge converter, by precisely controlling the switching timing to ensure meets the conditions in Table 1, the soft switching condition of zero-voltage turn-on (ZVS) can be met. And according to the symmetry, whether it is forward power transmission or reverse power transmission, the conditions for ZVS are consistent. At the same time, under different voltage gains and different operating modes, one of them represents the peak inductor current, so solving the control quantity that makes this value minimum under the same power condition can ensure the minimum inductor peak current.

[0094] The control algorithm is derived and designed as follows.

[0095] Firstly, take as the reference value, as the external given actual grid current reference value.

[0096] 1. According to the working mode of mode1, derive

[0097] Take as the reference value, obtain , , and , and and are solved to obtain equation (12)

[0098] (12)

[0099] The condition constraint of mode1 is:

[0100] (13)

[0101] The value range of and is obtained:

[0102] (14)

[0103] In order to connect with mode2 and obtain smaller absolute value, add constraint , and finally obtain the value range of and the controllable range of :

[0104] (15)

[0105] Next, through and the calculated ZVS current standard value which may be the peak current, firstly, equation (5) and equation (12) are solved to obtain:

[0106] (16)

[0107] Discuss the value of corresponding to the peak inductance current:

[0108] (1) When is the peak value, and construct the function about to obtain:

[0109] When monotonic,

[0110] when, monotonically decreasing,

[0111] therefore take

[0112] (2) when, is the peak value, therefore take the right boundary, ;

[0113] 2, when the transition condition is met , according to mode 2 to derive

[0114] take as the reference value, obtain , , and , and with simultaneously, formula (17) is obtained

[0115] (17)

[0116] The condition constraint of mode 2 is:

[0117] (18)

[0118] obtain the value range of and :

[0119] (19)

[0120] Next, by and the calculated possible peak current ZVS current unit, first from formula (9) and formula (17) simultaneously:

[0121] (20)

[0122] Discuss the value of corresponding to the inductance current peak:

[0123] (1) when, is the peak value, therefore take the right boundary:

[0124] (2) when, according to is the peak value, three cases ( must be less than 0):

[0125] Case 1: When, With monotonous increase, so take (Here with link, is seamless)

[0126] Case 2: When,

[0127] That is , With first increase and then decrease,

[0128] When, Increase;

[0129] When, Decrease;

[0130] So take

[0131] Case 3: When, With monotonous decrease, so take

[0132] The calculated by this way Final control quantity according to the current mode , can guarantee the minimum inductance peak current on the basis of also meet ZVS conditions that is greater than 0, less than 0, less than 0.

[0133] Summary of algorithm process:

[0134] I, according to the sampling voltage and given reference current to calculate the voltage gain , current reference value And

[0135] II, first according to mode1 algorithm

[0136] When, ;

[0137] When, ;

[0138] Determine whether it needs to transition to mode2, that is, whether to meet ;

[0139] If not, the obtained is substituted into equation (12) to obtain the control variable

[0140] If yes, the mode is switched to mode 2, and the mode 2 is solved again

[0141] III. According to mode 2, the following is calculated

[0142] When

[0143] When

[0144] When

[0145] When

[0146] The obtained is substituted into equation (17) to obtain the control variable

[0147] In addition, the proposed frequency-fixed minimum inductance peak current control converter and method based on mode switching can also be applied to a multi-path DC scenario, each path can be equivalent to the DC-AC converter shown in Figure 1 The actual total power is the sum of the power of each path, and the specific topology is taken as an example of two paths, as shown in Figure 7 The specific implementation is that the switching tube on each DC side takes the same AC side switching signal and AC voltage as a reference, and the same algorithm calculates the internal and external phase shift according to the power demand of each DC side. Finally, the same frequency and the same AC side switching signal are used to control the phase shift of each switching signal, and the calculated power and current of each path are superimposed on the AC side to obtain the power and current of the AC side.

[0148] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.​​​​​​​​​​​

Claims

1. A mode-switching-based fixed-frequency minimum inductance peak current control converter, applied to bidirectional power transmission between distributed energy resources and the AC grid, characterized in that, include: The DC-side H-bridge module consists of the first switching transistor. Second switching transistor The circuit formed in series with the third switching transistor and the fourth switching transistor A series circuit is connected in parallel to convert the input DC power into high-frequency AC power. AC side matrix bidirectional half-bridge module, consisting of the fifth to eighth switching transistors. to A circuit composed of two series capacitors connected in parallel can be used to convert high-frequency AC power into power frequency AC power to adapt to the power grid and to receive power frequency AC power from the power grid and convert it into high-frequency AC power. The energy transfer module includes an inductor L and a high-frequency transformer T. The primary side of the high-frequency transformer T is connected to the DC-side H-bridge module, and one end of the secondary side of the high-frequency transformer T is connected to the switching transistor in the AC-side matrix bidirectional half-bridge module via an inductor. and switching transistor The connection point between them is connected, and the other end of the secondary side of the high-frequency transformer T is connected to the connection point between the two capacitors in the AC side matrix bidirectional half-bridge module. The converter has no intermediate DC-DC conversion link and the power transmission is directly realized through the high-frequency conversion between the DC side H-bridge module and the AC side matrix bidirectional half-bridge module. The control module is configured as follows: The switching transistors of the DC-side H-bridge module and the AC-side matrix bidirectional half-bridge module are driven at a fixed switching frequency; Real-time acquisition of DC-side voltage, AC-side voltage, and grid reference current. Calculate the voltage gain: ,in The ratio of the number of turns in the secondary winding to the number of turns in the primary winding of the high-frequency transformer is used to determine the DC-side voltage. The converted equivalent voltage, The equivalent voltage of the AC side voltage, and based on the voltage gain With grid reference current Select the target mode in the extended phase-shifting operating mode; the DC-side voltage is the voltage at the midpoint of the two arms of the DC-side H-bridge module. The AC side voltage refers to the switching transistor in the AC side matrix bidirectional half-bridge module. and The voltage between the connection point and the two capacitor connection points Therefore ; The equivalent voltage of the AC side voltage, and ; Based on the target mode, the power transfer equations and the zero-voltage switching (ZVS) condition equations are combined to solve for the inward shift ratio. Compared to relocation The inward shift compared to The ratio of the time by which the rising edge of the DC-side equivalent voltage square wave leads the rising edge of the AC-side equivalent voltage square wave to the half-switching period, shifted outwards compared to... The ZVS condition equation is the ratio of the time during which the rising edge of the AC-side equivalent voltage square wave leads the falling edge of the DC-side equivalent voltage square wave to the half-switching period, and the peak inductor current is minimized during the solution process; the specific ZVS condition equation is: [Corresponding to...] Inductor current at the rising edge of a positive voltage square wave ,correspond Inductor current at the falling edge of a positive voltage square wave ,correspond Inductor current at the rising edge of a positive voltage square wave ,in This represents the inductor current at the rising edge of the square wave of the DC-side equivalent voltage. The inductor current at the rising edge of the square wave of the AC side equivalent voltage is given. The inductor current at the falling edge of the square wave of the DC-side equivalent voltage; The working modes include: Mode 1: Inward Shift Compared And compared to moving outward The square wave of the equivalent voltage on the DC side intersects with the square wave of the equivalent voltage on the AC side. Mode 2: Inward shift compared to And compared to moving outward The DC-side equivalent voltage square wave is included within the AC-side equivalent voltage square wave; The specific logic for the control module to select the target mode is as follows: Prioritize solving the inward shift in mode 1 compared to Compared to relocation If the solution satisfies the constraints of Mode 1: , If the zero-voltage switching condition is met, then mode 1 is selected; If the conditions are not met, switch to mode 2 and solve again based on the compatibility between voltage gain and grid reference current; The specific logic of the control module to minimize the peak inductor current is as follows: Enter mode 1, and voltage gain When the value is less than 1, the peak inductor current is the inductor current at the falling edge of the DC-side equivalent voltage square wave. By adjusting the inward shift compared to Compared to relocation make Take the minimum value; Enter mode 1, and voltage gain When the value is greater than 1, the peak inductor current is the inductor current at the rising edge of the AC side equivalent voltage square wave. By adjusting the inward shift compared to Compared to relocation make Take the minimum value; Enter mode 2, and voltage gain When the value is less than 1, the peak inductor current is the inductor current at the falling edge of the DC-side equivalent voltage square wave. By adjusting the inward shift compared to Compared to relocation make Take the minimum value; Enter mode 2, and voltage gain When the value is greater than 1, the peak inductor current is the inductor current at the rising edge of the AC side equivalent voltage square wave. By adjusting the inward shift compared to Compared to relocation make Take the smallest value.

2. The fixed-frequency minimum inductance peak current control converter based on mode switching according to claim 1, characterized in that, The first to fourth switching transistors of the DC-side H-bridge module are MOSFETs.

3. The fixed-frequency minimum inductance peak current control converter based on mode switching according to claim 2, characterized in that, The fixed switching frequency is matched with the design parameters of the high-frequency transformer and inductor, so that the high-frequency transformer and inductor operate at the optimal parameter state at a single frequency.

4. A fixed-frequency minimum inductor peak current control method based on mode switching, applied to the fixed-frequency minimum inductor peak current control converter based on mode switching as described in any one of claims 1-3, characterized in that, Includes the following steps: Step S1: Set the switching frequency to a fixed value and initialize the inner shift ratio. Compared to relocation The initial value; Step S2: Real-time acquisition of DC-side voltage, AC-side voltage and grid reference current; calculation of DC-side equivalent voltage and AC-side equivalent voltage; and calculation of voltage gain. Step S3: Select the target extended phase-shifting operating mode based on the voltage gain and the grid reference current; Step S4: Based on the target operating mode, simultaneously solve the power transfer equations and the zero-voltage switching condition equations to find the inward shift ratio that minimizes the inductor peak current. Compared to relocation ; Step S5: Based on the obtained inward shift ratio Compared to relocation Generate PWM drive signals to control the switching action of the DC-side H-bridge module and the AC-side matrix bidirectional half-bridge module to achieve power transfer; In step S4, the inward shift ratio is calculated. Compared to relocation If the target mode is mode 1, solve using a simultaneous equation: If the target mode is mode 2, solve using a simultaneous equation: In the formula, For The per-unit value of the base value yes The per-unit value obtained by dividing by the base value, The inductor current at the rising edge of the square wave of the AC side equivalent voltage is given. yes The per-unit value obtained by dividing by the base value, This is the reference current for the power grid. For switching frequency, This represents the inductance value.

5. The fixed-frequency minimum inductor peak current control method based on mode switching according to claim 4, characterized in that, The power transfer equation in step S4 is derived based on the linear change characteristics of the inductor current, and the influence of the dead time and switching time of the switching transistor on the inductor current is ignored.

6. The fixed-frequency minimum inductor peak current control method based on mode switching according to claim 5, characterized in that, The method involves only a small range of hard switching at mode switching transitions and near the zero-crossing point of the grid current; in other operating conditions, soft switching is achieved by satisfying the zero-voltage switching condition.

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