Power conversion system and backflow constraint control method for smart microgrid

Abstract

The present invention discloses an electric energy conversion system for an intelligent microgrid and a backflow constraint control method, comprising a power generation unit, a rectifier unit, a high-frequency inverter full bridge, a resonant network, a high-frequency transformer, a double-circuit high-frequency rectifier module and a DC power grid connected in sequence; the double-circuit high-frequency rectifier module comprises a switch tube S 5 ~ S 8 Form a full-bridge circuit, voltage-equalizing capacitor C 1 , C 2 The high-frequency transformer is composed of two transformers, one connected in series with the switch tube at the secondary side. S 5 S 6 The middle point of the bridge arm and the connecting switch tube S 7 S 8 The full-bridge transformer at the middle point of the bridge arm and the switch tube connected to the secondary side S 5 S 6 The half-bridge transformer with the middle point of the bridge arm and the middle point of the voltage-equalizing capacitor has expanded the soft switch conduction range of the converter, optimized the problem of excessive reflux power on the output side and low converter operating efficiency, achieved zero reflux power, and greatly improved the operating efficiency of the system.

Description

Technical Field

[0001] The present invention relates to the technical field of electric energy conversion systems, and in particular to an electric energy conversion system for an intelligent microgrid and a backflow constraint control method. Background Art

[0002] Smart microgrid technology is flexible and decentralized. It can not only meet small-scale energy needs, but also improve energy efficiency through connection and complementarity with the power grid. However, the smart microgrid system has reflux power in the power conversion process, which reduces the conversion efficiency and causes unnecessary waste in the power conversion system. Therefore, the research on zero reflux power and soft switching technology will become the focus. Summary of the invention

[0003] The purpose of the present invention is to provide an electric energy conversion system and a reflux constraint control method for an intelligent microgrid. A dual transformer is used to form a high-frequency transformer part. By introducing two transformers, the voltage stress on the components is greatly reduced. By controlling the turns ratio of the two transformers, an additional controllable degree of freedom k is added, a wide voltage input range is achieved, the soft switch conduction range of the converter is expanded, the problems of excessive reflux power on the output side and low converter operating efficiency are optimized, zero reflux power is achieved, and the operating efficiency of the system is greatly improved.

[0004] The technical solution to achieve the purpose of the present invention is:

[0005] An electric energy conversion system for an intelligent microgrid comprises a power generation unit, a rectifier unit, a high-frequency inverter full bridge, a resonant network, a high-frequency transformer, a double-circuit high-frequency rectifier module and a DC power grid connected in sequence; the double-circuit high-frequency rectifier module comprises a switch tube S 5 ~ S 8 , the switch tube S 5 ~ S 8 Form a full-bridge circuit, voltage-equalizing capacitor C 1 , C 2 After being connected in series as the output end, the high-frequency transformer is composed of two transformers, one of which is connected to the secondary side of the switch tube. S 5 S 6 The middle point of the bridge arm and the connecting switch tube S 7 S 8 The turns ratio of the full-bridge transformer at the midpoint of the bridge arm is n 1 :1 and the secondary side connected to the switch tubeS 5 S 6 The bridge arm midpoint and the voltage-equalizing capacitor C 1 C 2 The half-bridge transformer at the midpoint has a turns ratio of n 2 :1.

[0006] In the preferred technical solution, the high-frequency inverter full bridge includes a switch tube S 1 ~S 4 , the switch tube S 1 ~S 4 A full-bridge circuit is formed, and the input end of the full-bridge circuit is connected to a filter capacitor C H , switch tube S 1 ~S 4 With body diode d S1 ~ d S4 And parasitic capacitance C S1 ~ C S4 .

[0007] In the preferred technical solution, the switch tube controlling the high-frequency inverter bridge S 1 The pulse width is 0 to π, the switch tube S 2 The pulse width is π to 2π, the switch tube S 3 The pulse width is from α to π+α, and the switch tube S 4 The pulse width is π+α to 2π+α, which generates an AC voltage Contains three voltage levels: +V1, -V1, and 0. V1 is the input voltage. α is the pulse width.

[0008] In the preferred technical solution, the switch tube of the dual-loop high-frequency rectifier module is controlled S 5 The pulse width is β to π+β, the switch tube S 6 The pulse width is π+β to 2π+β, and the switch tube S 7 The pulse width is π+β+γ to 2π+β+γ, and the switch tube S8 The pulse width is β+γ to π+β+γ, and the switch tube S 5 Hysteresis switch S 1 The angle is β, which generates an AC voltage Contains three voltage levels: +V2, -V2, and 0, generating AC voltage Contains two voltage levels: +0.5V2 and -0.5V2, V2 is the output voltage, β, γ is the pulse width.

[0009] In the preferred technical solution, the resonant current The zero-crossing point adjustment is in the switch tube S 5 The opening point of the switch makes the resonant current S 5 In phase, eliminating the reactive power of the high-frequency rectifier full bridge.

[0010] The present invention also discloses a backflow constraint control method for an electric energy conversion system for a smart microgrid, which is applied to the electric energy conversion system for the smart microgrid. The backflow constraint control method comprises the following steps:

[0011] S01: Controls the switch tube of the high-frequency inverter bridge S 1 The pulse width is 0 to π, the switch tube S 2 The pulse width is π to 2π, the switch tube S 3 The pulse width is from α to π+α, and the switch tube S 4 The pulse width is π+α to 2π+α, which generates an AC voltage Contains three voltage levels: +V1, -V1, and 0, V1 is the input voltage;

[0012] S02: Controls the switch tube of the dual-loop high-frequency rectifier module S 5 The pulse width is β to π+β, the switch tube S 6 The pulse width is π+β to 2π+β, and the switch tube S 7 The pulse width is π+β+γ to 2π+β+γ, and the switch tube S 8 The pulse width is β+γ to π+β+γ, and the switch tube S 5 Hysteresis switch S 1 The angle is β, which generates an AC voltage Contains three voltage levels: +V2, -V2, and 0, generating AC voltage Contains two voltage levels of +0.5V2 and -0.5V2, V2 is the output voltage;

[0013] S03: Obtain a reflux constraint control relationship according to a steady-state model of the resonant current and the output power, and obtain a minimum reflux power.

[0014] In the preferred technical solution, the calculation method of the resonant current includes:

[0015] Using the fundamental wave approximation analysis method to perform steady-state analysis, we get , and The fundamental phasors of the three voltages are , and After normalization, the normalized phasor expression is as follows:

[0016]

[0017] In the formula, yes The normalized vector of ; yes The normalized vector of ; yes The normalized vector of ; M is the voltage gain, k is the turns ratio of the two transformers, defined as ;

[0018] Will and The two are combined into , simplify to get the equivalent circuit diagram:

[0019]

[0020] According to the equivalent circuit diagram, the normalized resonant current expression is:

[0021]

[0022] in, Q is the quality factor, , is the normalized switching frequency, is the switching angular frequency, For time, .

[0023] The preferred technical solution also includes:

[0024] Calculate the normalized power :

[0025] .

[0026] In the preferred technical solution, the calculation method of the backflow constraint control relationship includes:

[0027] Get the minimum resonant current:

[0028]

[0029] According to the obtained steady-state model of resonant current and output power, a The Lagrange equation is:

[0030]

[0031] Among them, λ is the Lagrange multiplier, C is a constant;

[0032] Will L Taking partial derivatives with respect to α we get:

[0033]

[0034] Will L Taking partial derivatives of β we get:

[0035]

[0036] Will L Taking the partial derivative of γ we get:

[0037]

[0038] Will L right λ Taking partial derivatives we get:

[0039]

[0040] Simplifying the above four equations, we can get the reflux constraint control equation:

[0041]

[0042] Substitute the reflux constraint control relation into Simplified return current constraint power :

[0043]

[0044] control The V1 pulse width α and transformer turns ratio k, to control the size.

[0045] The present invention further discloses a backflow constraint control system for an electric energy conversion system for a smart microgrid, which is applied to the above-mentioned electric energy conversion system for a smart microgrid. The backflow constraint control system adopts the above-mentioned backflow constraint control method for an electric energy conversion system for a smart microgrid for control.

[0046] Compared with the prior art, the present invention has the following significant advantages:

[0047] (1) The present invention proposes an electric energy conversion system suitable for a smart microgrid. The secondary side adopts a full-bridge and half-bridge connection mode to form a dual-loop topology structure, realizing four voltage levels. The voltage level of the secondary side can reach up to 1.5 times. This effectively reduces the secondary side current stress and prolongs the service life of active devices.

[0048] (2) The present invention adopts a dual transformer to form the high-frequency transformer part. By introducing two transformers, the voltage stress on the components is greatly reduced. By controlling the turns ratio of the two transformers, an additional controllable degree of freedom k is added, thereby achieving a wide voltage input range and expanding the soft switching conduction range of the converter.

[0049] (3) The present invention uses the backflow constraint control method to optimize the problem of excessive backflow power on the output side and low converter operating efficiency, achieving zero backflow power and greatly improving the operating efficiency of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 This is a schematic diagram of an electric energy conversion system suitable for a smart microgrid in this embodiment;

[0051] Figure 2 This is a circuit structure diagram of an electric energy conversion system suitable for a smart microgrid in this embodiment;

[0052] Figure 3 This embodiment controls the switch tube S 1 ~ S 4 And switch tube S 5 ~ S 8 The generated AC voltage waveform and resonant current waveform;

[0053] Figure 4 This embodiment is applicable to the electric energy conversion system of the smart microgrid, and the equivalent circuit in the phasor domain is established by using FHA;

[0054] Figure 5 This embodiment M =0.5, k=1, V1=168V, V2=84V, P =200W, , 、 、 , And the current waveform of each switch tube;

[0055] Figure 6 This embodiment M =0.5, k=1, V1=168V, V2=84V, P =400W, , 、 、 , And the current waveform of each switch tube. DETAILED DESCRIPTION

[0056] The principle of the present invention is as follows: the present invention adopts a dual transformer to form a high-frequency transformer part. By introducing two transformers, the voltage stress on the components is greatly reduced; by controlling the turns ratio of the two transformers, an additional controllable degree of freedom k is added, a wide voltage input range is achieved, and the soft switch conduction range of the converter is expanded. The secondary side adopts a full-bridge and half-bridge connection mode to form a dual-loop topology structure, realizing four voltage levels, and the voltage level of the secondary side can reach up to 1.5 times. Thereby effectively reducing the secondary side current stress and extending the service life of the active device.

[0057] Example 1

[0058] like Figure 1 As shown, an electric energy conversion system for a smart microgrid includes a primary connected distributed generator, a rectifier unit, a high-frequency inverter full bridge, a resonant network, a high-frequency transformer, a double-circuit high-frequency rectifier module and a DC power grid. The problem of excessive output side reflux power and low converter operating efficiency is optimized through a reflux constraint control method.

[0059] Distributed generators or power generation units convert renewable energy into electrical energy, which is converted into high-frequency DC voltage through a low-frequency rectifier bridge, and then converted into high-frequency AC voltage through a high-frequency inverter bridge. The high-frequency AC voltage is converted into high-frequency DC voltage through a resonant network, a high-frequency transformer and a dual-circuit rectifier module, and then transmitted to the DC grid.

[0060] The high-frequency transformer adopts a dual transformer to form the high-frequency transformer part. By introducing two transformers, the voltage stress on the components is greatly reduced; by controlling the turns ratio of the two transformers, an additional controllable degree of freedom k is added, achieving a wide voltage input range and expanding the soft switching conduction range of the converter.

[0061] The secondary side uses full-bridge and half-bridge connection modes to form a dual-loop topology structure, achieving four voltage levels, and the voltage level of the secondary side can reach up to 1.5 times, thereby effectively reducing the current stress on the secondary side.

[0062] Specifically, Figure 2 As shown, the rectifier unit is composed of four diodes connected end to end in sequence.

[0063] The high-frequency inverter full bridge consists of input voltage V1, filter capacitor C H , switch tube S 1 ~ S 4 , Body diode d S1 ~ d S4 And parasitic capacitance C S1 ~ C S4 Composition, switch tube S 1 ~S 4 A full-bridge circuit is formed, and the input end of the full-bridge circuit is connected to a filter capacitor C H .

[0064] The resonant network consists of a resonant capacitor C r , resonant inductor L r Connect in sequence.

[0065] The dual-circuit high-frequency rectifier module consists of a switch tube S 5 ~ S 8 , Body diode d S5 ~ d S8 , parasitic capacitance C S5 ~ C S8 , voltage balancing capacitor C 1 , C 2 And the output voltage V2, the switch tube S 5 ~ S 8 Form a full-bridge circuit, voltage-equalizing capacitor C 1 , C 2 Connect in series as the output terminal.

[0066] The high-frequency transformer consists of two transformers, the secondary side of which is connected to S 5 S 6 Bridge arm midpoint and connection S 7 S 8 Full-bridge transformer at the midpoint of the bridge arm (turn ratio is n 1 :1) Secondary side connection S 5 S 6 The midpoint of the bridge arm and C 1 C 2 Half-bridge transformer (turns ratio is n 2 :1), and the turns ratio of the two transformers n 2 : n 1 Defined as k.

[0067] like Figure 3 As shown, the switch tube controlling the high-frequency inverter bridge S 1 The pulse width is 0 to π, the switch tube S 2 The pulse width is π to 2π, the switch tube S 3 The pulse width is from α to π+α, and the switch tube S 4 The pulse width is π+α to 2π+α; thus, an AC voltage is generated. Contains three voltage levels: +V1, -V1, and 0.

[0068] Control the switch tube of the dual-loop high-frequency rectifier module S 5 The pulse width is β to π+β, the switch tube S 6 The pulse width is π+β to 2π+β, and the switch tube S 7 The pulse width is π+β+γ to 2π+β+γ, and the switch tube S 8 The pulse width is β+γ to π+β+γ; and the switch tube S 5 Hysteresis switch S 1 The angle is β; this produces an AC voltage Contains three voltage levels: +V2, -V2, and 0, generating AC voltage Contains two voltage levels: +0.5V2 and -0.5V2. for and The superposition contains four voltage levels: +1.5V2, -1.5V2, +0.5V2, and -0.5V2.

[0069] Specifically, the resonant current The zero-crossing point adjustment is in the switch tube S 5 The opening point of the switch makes the resonant current S 5 The in-phase cancellation eliminates the reactive power of the high-frequency rectifier full bridge.

[0070] In another embodiment, a backflow constraint control method for an electric energy conversion system for a smart microgrid is applied to the above-mentioned electric energy conversion system for a smart microgrid, and the backflow constraint control method includes the following steps:

[0071] S01: Controls the switch tube of the high-frequency inverter bridge S 1 The pulse width is 0 to π, the switch tube S 2 The pulse width is π to 2π, the switch tube S 3 The pulse width is from α to π+α, and the switch tube S 4 The pulse width is π+α to 2π+α, which generates an AC voltage Contains three voltage levels: +V1, -V1, and 0, V1 is the input voltage;

[0072] S02: Controls the switch tube of the dual-loop high-frequency rectifier module S 5 The pulse width is β to π+β, the switch tube S 6 The pulse width is π+β to 2π+β, and the switch tube S 7 The pulse width is π+β+γ to 2π+β+γ, and the switch tube S 8 The pulse width is β+γ to π+β+γ, and the switch tube S 5 Hysteresis switch S 1 The angle is β, which generates an AC voltage Contains three voltage levels: +V2, -V2, and 0, generating AC voltage Contains two voltage levels of +0.5V2 and -0.5V2, V2 is the output voltage;

[0073] S03: Obtain a reflux constraint control relationship according to a steady-state model of the resonant current and the output power, and obtain a minimum reflux power.

[0074] Specifically, using the Fundamental Harmonic Approximation (FHA) analysis method for steady-state analysis, we can get , and The fundamental phasors of the three voltages are expressed as right , and After normalization, the normalized phasor expression is as follows:

[0075]

[0076] In the formula, yes The normalized vector of ; yes The normalized vector of ; yes The normalized vector of ; is the basic value, defined as ; is the voltage gain, defined as ; is the turns ratio of the two transformers, defined as ( is the number of turns of the full-bridge transformer, is the number of turns of the half-bridge transformer).

[0077] Will and The two are combined into , simplify the circuit, such as Figure 4 shown.

[0078]

[0079] According to the normalized switching frequency , Quality Factor The normalized impedance of the capacitor can be obtained: .

[0080] in, is the switching angular frequency, is the normalized resonant angular frequency, is the resonant capacitor, is the resonant inductor.

[0081] in, is the normalized impedance, is the load resistance and n is the number of transformer turns.

[0082] According to the equivalent circuit diagram, the normalized resonant current expression is:

[0083]

[0084] in, t For time, , .

[0085] According to the formula The normalized power can be calculated :

[0086]

[0087] Specifically, the reflux constraint control method includes the following processes:

[0088] Get the minimum resonant current:

[0089]

[0090] According to the obtained steady-state model of resonant current and output power, a The Lagrange equation is:

[0091]

[0092] Among them, λ is the Lagrange multiplier, C is a constant;

[0093] Will L Taking partial derivatives with respect to α we get:

[0094]

[0095] Will L Taking partial derivatives of β we get:

[0096]

[0097] Will L Taking the partial derivative of γ we get:

[0098]

[0099] Will L Taking partial derivatives with respect to λ we get:

[0100]

[0101] Simplifying the above four equations, we can get the relationship of the reflux constraint control method:

[0102]

[0103] Substitute the reflux constraint control method into Simplified, the return current constraint power can be obtained P M :

[0104]

[0105] By formula It can be seen that only control The V1 pulse width α and the transformer turns ratio k can be to control the size.

[0106] Another embodiment, a backflow constraint control system for an electric energy conversion system for a smart microgrid, is applied to the above-mentioned electric energy conversion system for a smart microgrid, and the backflow constraint control system adopts the above-mentioned backflow constraint control method for an electric energy conversion system for a smart microgrid for control.

[0107] The specific reflux constraint control method is the same as above and will not be repeated here.

[0108] In order for the converter to operate efficiently, appropriate parameter design is required:

[0109] choose Q =1, F =1.4, ω S =200πkHz, L r =88.44μH, C r =56.14nF.

[0110] The designed input voltage V1 is 168V, the output voltage V2 is 84V, and the rated power is 400W.

[0111] By simulating according to the designed input, output voltage and power, all switches can achieve soft switching.

[0112] To verify the correctness of the theory, simulation tests were carried out in PSIM.

[0113] when M =0.5, k=1, V1=168V, V2=84V, P =200W, , 、 、 , And the current waveform of each switch tube is as follows Figure 5 shown.

[0114] when M =0.5, k=1, V1=168V, V2=84V, P =400W, , 、 、 , And the current waveform of each switch tube is as follows Figure 6 shown.

[0115] After verification with the simulation waveform, it is found that the theory is consistent with the practice, proving that the present invention is feasible.

[0116] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principles of the present invention shall be equivalent replacement modes and shall be included in the protection scope of the present invention.

Claims

1. An electric energy conversion system for a smart microgrid, characterized in that: The invention comprises a power generation unit, a rectifier unit, a high-frequency inverter full bridge, a resonant network, a high-frequency transformer, a double-circuit high-frequency rectifier module and a DC power grid which are connected in sequence; the double-circuit high-frequency rectifier module comprises a switch tube S 5 ~ S 8 , the switch tube S 5 ~ S 8 Form a full-bridge circuit, voltage-equalizing capacitor C 1 , C 2 After being connected in series as the output end, the high-frequency transformer is composed of two transformers, one of which is connected to the secondary side of the switch tube. S 5 S 6 The middle point of the bridge arm and the connecting switch tube S 7 S 8 The turns ratio of the full-bridge transformer at the midpoint of the bridge arm is n 1 :1 and the secondary side connected to the switch tube S 5 S 6 The bridge arm midpoint and the voltage-equalizing capacitor C 1 C 2 The half-bridge transformer at the midpoint has a turns ratio of n 2 :1; The high frequency inverter full bridge includes a switch tube S 1 ~S 4 , the switch tube S 1 ~S 4 A full-bridge circuit is formed, and the input end of the full-bridge circuit is connected to a filter capacitor C H ; Control the switch tube of the high-frequency inverter bridge S 1 The pulse width is 0 to π, the switch tube S 2 The pulse width is π to 2π, the switch tube S 3 The pulse width is from α to π+α, and the switch tube S 4 The pulse width is π+α to 2π+α, which generates an AC voltage Contains three voltage levels: +V1, -V1, and 0. V1 is the input voltage. α is the pulse width; Control the switch tube of the dual-loop high-frequency rectifier module S 5 The pulse width is β to π+β, the switch tube S 6 The pulse width is π+β to 2π+β, and the switch tube S 7 The pulse width is π+β+γ to 2π+β+γ, and the switch tube S 8 The pulse width is β+γ to π+β+γ, and the switch tube S 5 Hysteresis switch S 1 The angle is β, which generates an AC voltage Contains three voltage levels: +V2, -V2, and 0, generating AC voltage Contains two voltage levels: +0.5V2 and -0.5V2, V2 is the output voltage, β, γ is the pulse width; The reflux constraint control relationship is obtained based on the resonant current and output power steady-state model, and the minimum reflux power is obtained; Calculate the normalized power : ， in, M is the voltage gain, k is the turns ratio of the two transformers, Q is the quality factor, is the normalized switching frequency; The reflux constraint control relationship is obtained: ， Substitute the reflux constraint control relation into Simplified return current constraint power : ， control The V1 pulse width α and transformer turns ratio k, to control the size.

2. The electric energy conversion system for a smart microgrid according to claim 1, characterized in that: The resonant current The zero-crossing point adjustment is in the switch tube S 5 The opening point of the switch makes the resonant current S 5 In phase, eliminating the reactive power of the high-frequency rectifier full bridge.

3. A backflow constraint control method for an electric energy conversion system of a smart microgrid, characterized in that: The electric energy conversion system for the smart microgrid includes a power generation unit, a rectifier unit, a high-frequency inverter full bridge, a resonant network, a high-frequency transformer, a double-circuit high-frequency rectifier module and a DC power grid connected in sequence; the double-circuit high-frequency rectifier module includes a switch tube S 5 ~ S 8 , the switch tube S 5 ~ S 8 Form a full-bridge circuit, voltage-equalizing capacitor C 1 , C 2 After being connected in series as the output end, the high-frequency transformer is composed of two transformers, one of which is connected to the secondary side of the switch tube. S 5 S 6 The middle point of the bridge arm and the connecting switch tube S 7 S 8 The turns ratio of the full-bridge transformer at the midpoint of the bridge arm is n 1 :1 and the secondary side connected to the switch tube S 5 S 6 The bridge arm midpoint and the voltage-equalizing capacitor C 1 C 2 The half-bridge transformer at the midpoint has a turns ratio of n 2 :1; The reflux constraint control method comprises the following steps: S01: Controls the switch tube of the high-frequency inverter bridge S 1 The pulse width is 0 to π, the switch tube S 2 The pulse width is π to 2π, the switch tube S 3 The pulse width is from α to π+α, and the switch tube S 4 The pulse width is π+α to 2π+α, which generates an AC voltage Contains three voltage levels: +V1, -V1, and 0, V1 is the input voltage; S02: Controls the switch tube of the dual-loop high-frequency rectifier module S 5 The pulse width is β to π+β, the switch tube S 6 The pulse width is π+β to 2π+β, and the switch tube S 7 The pulse width is π+β+γ to 2π+β+γ, and the switch tube S 8 The pulse width is β+γ to π+β+γ, γ is the pulse width, and the switch tube S 5 Hysteresis switch S 1 The angle is β, which generates an AC voltage Contains three voltage levels: +V2, -V2, and 0, generating AC voltage Contains two voltage levels of +0.5V2 and -0.5V2, V2 is the output voltage; S03: Obtain the reflux constraint control relationship according to the resonant current and output power steady-state model to obtain the minimum reflux power; Calculate the normalized power : ， in, M is the voltage gain, k is the turns ratio of the two transformers, Q is the quality factor, is the normalized switching frequency; The reflux constraint control relationship is obtained: ， Substitute the reflux constraint control relation into Simplified return current constraint power : ， control The V1 pulse width α and transformer turns ratio k, to control the size.

4. The backflow constraint control method for the electric energy conversion system of the smart microgrid according to claim 3 is characterized in that: The calculation method of resonant current includes: Using the fundamental wave approximation analysis method to perform steady-state analysis, we get , and The fundamental phasors of the three voltages are , and After normalization, the normalized phasor expression is as follows: ； In the formula, yes The normalized vector of ; yes The normalized vector of ; yes The normalized vector of ; M is the voltage gain, k is the turns ratio of the two transformers, defined as ; Will and The two are combined into , simplify to get the equivalent circuit diagram: ； According to the equivalent circuit diagram, the normalized resonant current expression is: ； in, Q is the quality factor, , is the normalized switching frequency, is the switching angular frequency, For time, .

5. The backflow constraint control method for the electric energy conversion system of the smart microgrid according to claim 3 is characterized in that: The calculation method of the backflow constraint control relationship includes: Get the minimum resonant current: ； According to the obtained resonant current and output power steady-state model, a The Lagrange equation is: ； Among them, λ is the Lagrange multiplier, C is a constant; Will L Taking partial derivatives with respect to α we get: ； Will L Taking partial derivatives of β we get: ； Will L Taking the partial derivative of γ we get: ； Will L right λ Taking partial derivatives we get: ； Simplifying the above four equations, we can get the reflux constraint control equation: 。 6. A backflow constraint control system for an electric energy conversion system of an intelligent microgrid, characterized in that: The backflow constraint control system is controlled by the backflow constraint control method for the electric energy conversion system of the smart microgrid described in any one of claims 3-5.

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