Fixed-frequency minimum inductance peak current control converter and method based on mode switching

Abstract

The invention discloses a mode switching-based fixed-frequency minimum inductance peak current control converter and method, and aims to solve the problems of high two-stage topology loss, difficulty in magnetic element design caused by frequency conversion control and narrow soft switching ZVS (zero voltage switching) range of the existing bidirectional AC / DC (alternating current / direct current) converter. The converter comprises a direct-current side parallel MOS tube H bridge, an alternating-current side matrix bidirectional half bridge, an inductor and a high-frequency transformer, a control module drives a switching tube at a fixed frequency, a target mode is selected from three expansion phase-shifting modes according to voltage gain and power grid reference current, power transmission and a ZVS condition equation are combined, and a zero voltage switching mode is selected from three expansion phase-shifting modes. And solving the phase shift ratio enabling the inductance peak current to be minimum. According to the invention, the power conversion loss is reduced, the design difficulty and cost volume of magnetic elements are reduced, wide-working-condition ZVS is realized, and the method 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 direct current scene.

Description

Technical Field

[0001] This invention relates to the field of power electronic conversion technology, and in particular to a fixed-frequency minimum inductance peak current control converter and method based on mode switching. Background Technology

[0002] The global energy system is undergoing profound changes, with traditional centralized fossil fuels rapidly giving way to distributed renewable energy. By the end of 2024, global installed capacity of photovoltaic and wind power had exceeded 3.6 TW, accounting for 19% of total power generation, and this figure is expected to exceed 35% by 2030. However, there is an inherent contradiction between the strong intermittency of wind and solar power output and the high stability requirements of the power grid, which can only be alleviated through the synergy of distributed grids, energy storage units, and intelligent dispatch.

[0003] Microgrids are considered a key vehicle for resolving the aforementioned contradictions. Their modular and spatially distributed layout can shorten energy transmission paths, reduce line losses, increase the proportion of local renewable energy consumption, and enrich power supply forms. Current mainstream AC / DC hybrid microgrids integrate renewable power generation, distributed energy storage, and power electronic conversion devices into a single port, with the bidirectional AC / DC converter (commonly known as a micro-inverter) serving as the crucial link between the microgrid and the main grid. It not only performs DC-AC power conversion but also needs to achieve grid synchronization, power factor correction, and harmonic mitigation; its operational quality directly determines the stability boundary of the microgrid.

[0004] Constrained by size, cost, and efficiency, micro-inverters generally adopt a two-stage architecture of DC-DC boost + DC-AC inversion. While this topology is mature, the cascading of multiple power stages leads to accumulated losses, increasing both heat dissipation and installation costs. To pursue higher efficiency, the industry has turned its attention to single-stage dual active bridge (DAB) structures, coupled with frequency conversion modulation strategies such as extended phase shift (EPS), dual phase shift (DPS), and triple phase shift (TPS), aiming to achieve zero-voltage turn-on (ZVS) and reduce the effective value of inductor current over a wide voltage gain and full load range. Unfortunately, frequency conversion significantly widens the operating bandwidth of transformers and magnetic components, forcing designers to reserve saturation margins based on worst-case low frequencies. This results in low core utilization, large size, and high cost in commonly used frequency bands, ultimately limiting power density. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of the prior art by proposing a fixed-frequency minimum inductance peak current control converter and method based on mode switching, thereby achieving efficient and reliable bidirectional power transmission between distributed energy resources and the power grid.

[0006] The technical solution to achieve the purpose of this invention is: A mode-switching-based fixed-frequency minimum inductance peak current control converter is applied to bidirectional power transmission between distributed energy resources and the AC grid, including: The DC-side H-bridge module consists of the first to fourth switching transistors. Q 1 to Q 4 They are 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. S 1 to S 4 The system is composed of components that enable the conversion of high-frequency AC power into power frequency AC power to adapt to the power grid and the reception of power frequency AC power from the power grid and its conversion into high-frequency AC power. 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 to the DC-side H-bridge module, and the secondary side is connected to 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-DC conversion stage. Power transmission is directly achieved through 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. I ref Calculate the voltage gain: k=V ac / V dc ,in V dc The turns ratio of the DC side voltage after passing through the high-frequency transformer n The converted equivalent voltage, V ac The equivalent voltage of the AC side voltage, and based on the voltage gain k With grid reference current I ref Select the target mode from the three preset extended phase-shifting operating modes; 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. D 1 Compared to relocation D 2 Furthermore, the peak inductor current is minimized during the solution process; the ZVS condition equation is specifically: the inductor current before the DC-side switch is turned on. i 0 ≥0, Inductor current before DC-side switch is turned off i2 ≤0, Inductor current before the AC-side switch is turned on. i 1 ≤0, where i 0 This represents the inductor current at the rising edge of the square wave of the DC-side equivalent voltage. i 1 The inductor current at the rising edge of the square wave of the AC side equivalent voltage is given. i 2 This represents the inductor current at the falling edge of the square wave equivalent voltage on the DC side.

[0007] Furthermore, the three working modes include: Mode 1: Inward Shift Compared D 1 >0 and outward shift compared to D 2 >0, the D 1 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 half a switching period. D 2 It is the ratio of the time when the rising edge of the AC side equivalent voltage square wave leads the falling edge of the DC side equivalent voltage square wave to half a switching period, and the DC side equivalent voltage square wave intersects with the AC side equivalent voltage square wave. Mode 2: Inward shift compared to D 1 <0 and outward shift compared to D 2 >0, the DC side equivalent voltage square wave is included in the AC side equivalent voltage square wave; Furthermore, the first to fourth switching transistors of the DC-side H-bridge module are MOSFETs, and the current stress of a single MOSFET is reduced by configuring them in parallel.

[0008] Furthermore, 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 D 1 Compared to relocation D 2 If the solution satisfies the constraints of Mode 1: D 1 >0、 D 2 If the voltage gain is greater than 0 and meets the zero-voltage switching condition, then mode 1 is selected; if not, then mode 2 is switched to solve again based on the compatibility between the voltage gain and the grid reference current.

[0009] Furthermore, the specific logic of the control module to minimize the inductor peak current is as follows: Enter mode 1, and voltage gaink 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. i 2 By adjusting the inward shift compared to D 1 Compared to relocation D 2 make i 2 Take the minimum value; Enter mode 1, and voltage gain k 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. i 1 By adjusting the inward shift compared to D 1 Compared to relocation D 2 make i 2 Take the minimum value; Enter mode 2, and voltage gain k 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. i 2 By adjusting the inward shift compared to D 1 Compared to relocation D 2 make i 2 Take the minimum value; Enter mode 2, and voltage gain k 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. i 1 By adjusting the inward shift compared to D 1 Compared to relocation D 2 make i 2 Take the smallest value.

[0010] Furthermore, 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 (meeting the requirements for saturation current, iron loss, and copper loss).

[0011] A mode-switching-based fixed-frequency minimum inductor peak current control method, applied to the aforementioned mode-switching-based fixed-frequency minimum inductor peak current control converter, is characterized by comprising the following steps: Step S1: Set the switching frequency to a fixed value and initialize the inner shift ratio. D 1 Compared to relocationD 2 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. D 1 Compared to relocation D 2 ; Step S5: Based on the obtained inward shift ratio D 1 Compared to relocation D 2 A PWM drive signal is generated to control the switching action of the DC-side H-bridge module and the AC-side matrix bidirectional half-bridge module, thereby achieving power transfer.

[0012] Furthermore, 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.

[0013] Furthermore, in step S4, the solution for the inward shift is compared to... D 1 Compared to relocation D 2 If the target pattern is pattern 1, solve using a simultaneous equation: , If the target mode is mode 2, solve using a simultaneous equation: , Furthermore, the method only involves a small range of hard switching at the mode switching transition 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.

[0014] Compared with the prior art, the present invention, employing the above technical solution, has the following beneficial effects: (1) The fixed-frequency minimum inductor peak current control converter and method proposed in this invention reduces losses and improves efficiency by optimizing the minimum inductor peak current. Taking the minimum inductor peak current as the core of the derivation, and combining voltage gain and load requirements, the DC side current is optimized when the voltage is low and the AC side current is optimized when the voltage is high, which directly reduces inductor conduction losses and improves power transmission efficiency. This not only improves the utilization rate of clean energy such as photovoltaic and wind power, but also reduces the heat dissipation pressure of equipment and adapts to the needs of miniaturized deployment.

[0015] (2) By using a fixed switching frequency, the magnetic components do not need to be adapted to a wide frequency range. Only the parameters need to be optimized for a single frequency, which greatly simplifies the design process. At the same time, it avoids excessive redundancy design, reduces the size of components, reduces costs, and ensures that the components operate in the optimal range under all operating conditions, thus making full use of the resources.

[0016] (3) The algorithm derivation incorporates soft-switching ZVS conditions. By optimizing the shift ratio, it can still meet the soft-switching requirements under conditions such as voltage mismatch and light load, greatly expanding the ZVS coverage, reducing switching losses, reducing voltage spikes and device failure risks, and improving system stability and power quality.

[0017] (4) The fixed-frequency minimum inductance peak current control converter and method based on mode switching proposed in this invention, when applied to a multi-channel DC scenario, only needs to calculate the external phase shift and internal phase shift of each full bridge relative to the AC half bridge due to its fixed-frequency characteristics. The control is simple, and the inductance current obtained by the multi-channel DC control is finally superimposed on the AC measurement, which will make it easier for the AC measurement switch to achieve soft switching. Attached Figure Description

[0018] Figure 1 This is a topology diagram of a single-stage DC / AC dual active bridge converter based on the mode-switching fixed-frequency minimum inductor peak current control converter and method of the present invention. Figure 2 This is an equivalent circuit diagram of the voltage across the inductor in an embodiment of the present invention; Figure 3 The diagram shows the equivalent voltage waveform and inductor current waveform across the inductor in mode 1 of this invention. Figure 4 The diagram shows the equivalent voltage waveform and inductor current waveform across the inductor in mode 2 of this invention. Figure 5 The diagram shows the equivalent voltage waveform and inductor current waveform across the inductor in mode 3 of this invention. Figure 6 This is a system control block diagram of the present invention; Figure 7 This is a topology diagram of a mode-switching fixed-frequency minimum inductance peak current control converter with two DC inputs in an embodiment of the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] A fixed-frequency minimum inductance peak current control converter and method based on mode switching, including: A mode-switching-based fixed-frequency minimum inductance peak current control converter is applied to bidirectional power transmission between distributed energy resources and the AC grid, such as... Figure 1 As shown, it includes: The DC-side H-bridge module consists of the first to fourth switching transistors. Q 1 to Q 4 They are 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. S 1 to S 4 The system is composed of components that enable the conversion of high-frequency AC power into power frequency AC power to adapt to the power grid and the reception of power frequency AC power from the power grid and its conversion into high-frequency AC power. 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 to the DC-side H-bridge module, and the secondary side is connected to 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-DC conversion stage. Power transmission is directly achieved through high-frequency conversion between the DC-side H-bridge module and the AC-side matrix bidirectional half-bridge module. For ease of analysis, the voltages on both sides are equivalent to the voltages directly applied across the bridge arms of the inductor by the switching devices, such as... Figure 2 The equivalent circuit is shown. Figure 2 of V ac for Figure 1 of V cd , Figure 2 of V dc for Figure 1 of n times V ab Inductor current I L The flow direction is from the ac side to the dc side.

[0021] Figure 3 It extends the equivalent voltage waveform across the inductor and the inductor current waveform under phase-shift modulation, with the DC side being a three-level voltage with adjustable duty cycle. V dc The AC side uses an AC matrix half-bridge to chop the grid voltage and generate a quasi-two-level voltage. V ac .in V dcThe amplitude is the DC input voltage multiplied by the transformer turns ratio. n , V ac The amplitude is equal to half of the instantaneous grid voltage. By adjusting... V dc Duty cycle and V ac and V dc Power transfer is achieved through the phase difference between the phases. Therefore, the DAB microinverter has two control degrees of freedom: inward shift relative to the phase difference. D 1. Compared to relocation D 2, for example Figure 3 As shown, D 1 is defined as V dc Positive voltage square wave rising edge leads V ac The ratio of the rise time of the positive voltage square wave to half a switching period. D 2 is defined as V ac Positive voltage square wave rising edge leads V dc The ratio of the falling edge time of the positive voltage square wave to half a switching period. After neglecting the effect of dead time on the dual active bridge converter, the inductor current will exhibit a linear change during the high-frequency period. (Definition of corresponding...) V dc The inductor current at the rising edge of the positive voltage square wave is i 0 ,correspond V dc The inductor current at the falling edge of the positive voltage square wave is i 2 ,correspond V ac The inductor current at the rising edge of the positive voltage square wave is i 1 Due to the symmetry of the inductor current, t 0 time and t At time 3, the currents are opposite. t 1 moment and t The currents are opposite at time 4. t 2 moments and t The currents are reversed at time 5. (Continued) V ac and V dc They are also used to represent the amplitude of the square wave voltage across the inductor.

[0022] For extended phase-shift modulation, there are three modes, among which mode 1 is as follows: Figure 3 As shown, D 1 and D2 are all greater than 0. V dc Positive voltage square wave and V ac Positive voltage square waves intersect, mode 2 as follows Figure 4 As shown, D 1 is less than 0, D 2 is greater than 0, V dc A positive voltage square wave is included V ac Within a positive voltage square wave, mode 3 is as follows Figure 5 As shown, D 1 is greater than 0, D 2 is less than 0, V dc Positive voltage square wave in V ac Outside the positive voltage square wave.

[0023] In the extended phase-shifting operating mode, the duty cycle D 1 and D 2. The outward phase angle of the two bridge arms can be obtained. That is, the angle by which the fundamental wave of the DC voltage square wave leads the fundamental wave of the AC voltage square wave: (1), Define voltage ratio: (2), Considering that the dead time accounts for a very small proportion of the entire switching cycle, and that waveform analysis of half a cycle is generally applicable to the analysis of the entire mode; and considering that the MOSFET's turn-on and turn-off times account for a very small proportion of the entire high-frequency cycle, it can be considered as a linear switch, thus allowing us to formulate the inductor current formula. Below, we only derive the formulas for modes 1 and 2 (related to the algorithm): Mode 1: (3), Due to the symmetry of the inductor current t 0 time and t The currents are opposite at time 3: (4), By combining the equations, we obtain the instantaneous value expression of the inductor current when power is transferred from the DC side to the AC side in the mode 1 operating state, as shown in equation (5) (when power is transferred from the AC side to the DC side, the voltage square wave reversal analysis can be performed): (5), Then the average AC side current (i.e., the reference current value) during this switching cycle I ref ) can be represented as: (6), in I ref The absolute value of the power transfer multiplied by the absolute value of the grid voltage at that moment represents the power transmitted at that time. The direction of power flow is determined by the phase lead or lag relationship between the fundamental DC voltage wave and the fundamental AC voltage wave. If the fundamental DC voltage wave leads the fundamental AC voltage wave, power is transmitted from DC to AC; if the fundamental DC voltage wave lags the fundamental AC voltage wave, power is transmitted from AC to DC. The algorithm derivation in this paper is based on... Figure 3 and Figure 4 The control quantities are all derived by converting DC power to AC power. D 1 and D 2, obtained D 1 and D 2. After that, it is a fixed frequency, the frequency is determined, therefore the amount of transmitted power and i 0 、i 1 、i 2 The quantities have been determined, and the phase-shifting module processes them according to the power flow direction. D 1 and D 2. The corresponding PWM wave of the control switch can be obtained, so the algorithm part is mainly quantitative analysis.

[0024] When power is transferred from the AC side to the DC side Figure 3 shown i L The image is symmetrical about the x-axis.

[0025] Mode 2: (7), Due to the symmetry of the inductor current t 0 time and t The currents are opposite at time 3: (8), By combining the equations, we obtain the instantaneous value expression of the inductor current when power is transferred from the DC side to the AC side in the mode 2 operating state, as shown in equation (9) (when power is transferred from the AC side to the DC side, the voltage square wave can be analyzed by reversal): (9), Then the average AC side current (i.e., the reference current value) during this switching cycle I ref (The direction of the current is from the power grid) can be represented as: (10), When power is transferred from the AC side to the DC side Figure 4 shown iL The image is symmetrical about the x-axis.

[0026] Figure 5 This is a system control block diagram for a single-stage dual active bridge DC / AC converter. The control flow involves collecting parameters such as AC voltage, DC voltage, inductance, and turns ratio, and then calculating the relevant control parameters using the proposed optimal control algorithm. D 1. D 2. Then adjust the control parameters. D 1. D 2. The predetermined frequency f is introduced into the PWM module to drive the corresponding switching transistors. Therefore, the control algorithm is the core.

[0027] In a dual active bridge converter, due to the large number of switching transistors, switching losses dominate the losses. In order to reduce switching losses, the voltage across the switching devices needs to be zero before they are turned on, so as to achieve ZVS.

[0028] To achieve ZVS, the following current condition must be met: (11), in I ac , V ac and I dc , V dc These are the current and voltage flowing through the switching device on the AC side and the current and voltage flowing through the switching device on the DC side, respectively. L It's a leakage sensation. C ac and C dc This refers to the parallel capacitor connected to the AC / DC side MOSFET. Under ideal operating conditions, when the device is turned off, the voltage or current first drops to zero, then slowly rises to the off-state level, thus achieving a near-zero-loss switching process. However, the implementation of soft switching depends on specific electrical conditions, which limits its regulation range. To address this limitation, the modulation strategy proposed in this paper can effectively extend the operating range of soft switching at different power levels.

[0029] from Figure 1 It can be seen that, in order to achieve zero-voltage turn-on on the DC side, it is necessary to ensure that... Q 1. Q 4. Q 2. Q 3. Before turn-on, the energy on the junction capacitance is completely discharged. At this time, the voltage difference across the MOSFET is zero, which means it is necessary to ensure... Q 1 and Q 4. Inductor current at turn-on time i L (t )≤0. Similarly, to achieve zero-voltage switching on AC, it is necessary to ensure that... S 1. S 2. S 3. S 4. Before switching on, the energy on the junction capacitance is completely discharged, that is... S 1. Inductor current at turn-on time i L ( t )≥0. Due to the symmetry of the full-bridge devices on both sides, the soft switching of all switches can be satisfied when the above three conditions are met.

[0030] Combining the above situations Figure 3 , Figure 4 as well as i 0 、i 1 、i 2 The necessary conditions for zero-voltage switching of all switches, as defined in Table 1, are as follows: Table 1. Conditions for Achieving ZVS by Combining Extended Shift and Shift Frequency Conversion , In a dual active bridge converter, precise control of the switching timing ensures i 0 、i 1 、i 2 Meeting the conditions in Table 1 satisfies the soft-switching conditions for zero-voltage switching (ZVS). Furthermore, due to symmetry, regardless of whether power is transferred in the forward or reverse direction, i 0 、 i 1 、i 2 The conditions for satisfying ZVS are all the same. Also, i 0 、i 1 、i 2 Under different voltage gains and different operating modes, one of them represents the peak value of the inductor current. Therefore, by finding the control quantity that minimizes this value under the same power conditions, the peak inductor current can be minimized.

[0031] The control algorithm is derived and designed below.

[0032] Firstly As the baseline value, I ref The actual grid current reference value is given externally.

[0033] 1. First, deduce the working mode according to mode1. by Using the baseline value, obtain , , and ,Will and Combining these equations, we obtain equation (12): (12) Apply conditional constraints to mode1: (13) get and The range of values ​​for: (14) In order to connect with mode 2 and achieve a smaller size Absolute value, plus constraints Finally obtained and Controllable range: (15) Next, through k The per-unit value of the ZVS current, which may be the peak current, is obtained by combining equations (5) and (12): (16) Discuss the corresponding cases of peak inductor current. Values: (1) k<1 hour, I 2 For the peak value, and construct I 2 about The function yields: hour, monotonous, hour, Monotonically decreasing, Therefore, take ; (2) k>1 hour, I 1 It is the peak value, therefore Take the right boundary. ; 2. When the transition conditions are met At that time, according to mode2, by Using the baseline value, obtain , , and ,Will and Combining these equations, we obtain equation (17). (17) Apply conditional constraints to mode2: (18) get and The range of values ​​for: (19) Next, through k The per-unit value of the ZVS current, which may be the peak current, is obtained by combining equations (9) and (17): (20) Discuss the corresponding cases of peak inductor current. Values: (1) k When >1, I 1 It is the peak value, therefore Take the right boundary: ; (2) k When <1, according to I 2 There are three cases for the peak value ( I 2 (must be less than 0) Scenario 1: hour, I 2 Follow I 1 Monotonically increasing, therefore take (Here and) k >1. The connection is seamless. Scenario 2: hour, Right now , I 2 Follow I 1 Increase first, then decrease; hour, I 2 increase; hour, I 2 reduce; Therefore, take ; Scenario 3: hour, I 2 Follow I 1 Monotonically decreasing, therefore take ; The result calculated using this derivation method Finally, the control quantity is calculated based on the current mode. D 1 and D 2 This ensures that the ZVS condition is met while minimizing the peak inductor current. i 0 Greater than 0, i 1 Less than 0, i 2 Less than 0.

[0034] Summary of algorithm flow: I. Calculate the voltage gain based on the sampled voltage and the given reference current. k Current reference value as well as ; II. Calculate according to mode 1 first. : k <1 hour, ; k When >1, ; Determine whether a transition to mode 2 is needed, i.e., whether the condition is met. ; If not satisfied, then the obtained result... and Substitute into equation (12) to obtain the control quantity. D 1 and D 2 ; If satisfied, transition to mode 2 and solve again according to mode 2. ; III. Calculated according to mode2 : k When >1, ; hour, ; hour, ; hour, ; The obtained and Substitute into equation (17) to obtain the control quantity. D 1 and D 2 .

[0035] Furthermore, the proposed mode-switching-based fixed-frequency minimum inductance peak current control converter and method, due to its fixed frequency, can also be applied to multi-channel DC scenarios, where each channel can be equivalent to... Figure 1 The DC-AC converter shown has a total power output that is the sum of the power outputs of each channel. The specific topology is illustrated using a two-channel example. Figure 7 As shown in the figure. The specific implementation scheme is as follows: each DC-side switch uses the same AC-side switch signal and AC voltage as a reference. The same algorithm is used to calculate the internal and external phase shift ratios according to the power requirements of each DC-side switch. Finally, the phase shift control of each switch signal is performed according to the same frequency and the same AC-side switch signal. The power and current calculated by each switch are then superimposed on the AC side to obtain the power and current of the AC side.

[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

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 to fourth switching transistors. Q 1 to Q 4 They are 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. S 1 to S 4 The system is composed of components that enable the conversion of high-frequency AC power into power frequency AC power to adapt to the power grid and the reception of power frequency AC power from the power grid and its conversion into high-frequency AC power. 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 to the DC-side H-bridge module, and the secondary side is connected to 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-DC conversion stage. Power transmission is directly achieved through 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. I ref Calculate the voltage gain: k=V ac / V dc ,in V dc The turns ratio of the DC side voltage after passing through the high-frequency transformer n The converted equivalent voltage, V ac The equivalent voltage of the AC side voltage, and based on the voltage gain k With grid reference current I ref Select the target mode in the extended phase-shifting operating mode; 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. D 1 Compared to relocation D 2 Furthermore, the peak inductor current is minimized during the solution process; the ZVS condition equation is specifically: the inductor current before the DC-side switch is turned on. i 0 ≥0, Inductor current before DC-side switch is turned off i 2 ≤0, Inductor current before the AC-side switch is turned on. i 1 ≤0, where i 0 This represents the inductor current at the rising edge of the square wave of the DC-side equivalent voltage. i 1 The inductor current at the rising edge of the square wave of the AC side equivalent voltage is given. i 2 This represents the inductor current at the falling edge of the square wave equivalent voltage on the DC side.

2. The fixed-frequency minimum inductance peak current control converter based on mode switching according to claim 1, characterized in that, The working modes include: Mode 1: Inward Shift Compared D 1 >0 and outward shift compared to D 2 >0, the D 1 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 half a switching period. D 2 It is the ratio of the time when the rising edge of the AC side equivalent voltage square wave leads the falling edge of the DC side equivalent voltage square wave to half a switching period, and the DC side equivalent voltage square wave intersects with the AC side equivalent voltage square wave. Mode 2: Inward shift compared to D 1 <0 and outward shift compared to D 2 >0, the DC side equivalent voltage square wave is included in the AC side equivalent voltage square wave.

3. The fixed-frequency minimum inductance peak current control converter based on mode switching according to claim 1, characterized in that, The first to fourth switches of the DC-side H-bridge module are MOSFETs, and the current stress of a single MOSFET is reduced by configuring them in parallel.

4. The fixed-frequency minimum inductance peak current control converter based on mode switching according to claim 1, characterized in that, 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 D 1 Compared to relocation D 2 If the solution satisfies the constraints of Mode 1: D 1 >0、 D 2 If the value is greater than 0 and meets the zero-voltage switching condition, then select mode 1; If the conditions are not met, the solution will be switched to Mode 2 and resolved based on the compatibility between the voltage gain and the grid reference current.

5. The fixed-frequency minimum inductance peak current control converter based on mode switching according to claim 1, characterized in that, The specific logic of the control module to minimize the peak inductor current is as follows: Enter mode 1, and voltage gain k 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. i 2 By adjusting the inward shift compared to D 1 Compared to relocation D 2 make i 2 Take the minimum value; Enter mode 1, and voltage gain k 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. i 1 By adjusting the inward shift compared to D 1 Compared to relocation D 2 make i 2 Take the minimum value; Enter mode 2, and voltage gain k 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. i 2 By adjusting the inward shift compared to D 1 Compared to relocation D 2 make i 2 Take the minimum value; Enter mode 2, and voltage gain k 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. i 1 By adjusting the inward shift compared to D 1 Compared to relocation D 2 make i 2 Take the smallest value.

6. The fixed-frequency minimum inductance peak current control converter based on mode switching according to claim 1, 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.

7. 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 1-6, characterized in that, Includes the following steps: Step S1: Set the switching frequency to a fixed value and initialize the inner shift ratio. D 1 Compared to relocation D 2 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. D 1 Compared to relocation D 2 ; Step S5: Based on the obtained inward shift ratio D 1 Compared to relocation D 2 A PWM drive signal is generated to control the switching action of the DC-side H-bridge module and the AC-side matrix bidirectional half-bridge module, thereby achieving power transfer.

8. The fixed-frequency minimum inductor peak current control method based on mode switching according to claim 7, 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.

9. The fixed-frequency minimum inductor peak current control method based on mode switching according to claim 7, characterized in that, In step S4, the inward shift ratio is calculated. D 1 Compared to relocation D 2 If the target mode is mode 1, solve using a simultaneous equation: , If the target mode is mode 2, solve using a simultaneous equation: 。 10. The fixed-frequency minimum inductor peak current control method based on mode switching according to claim 7, 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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