Method and device for optimizing control of effective value of inductor current of isolated three-port converter

Abstract

The present invention discloses an inductor current effective value optimization control method and device of an isolated three-port converter. By introducing a control variable to the load output side of the second port of the three-port isolated converter, the degree of freedom of converter control is increased on the basis of the traditional control strategy; the converter is modeled and analyzed by Fourier series expansion to avoid classification discussions under multiple working modes; by curve fitting the optimization solution set, the calculation requirements of the controller for online solution are reduced, and when the load is disturbed or the load is switched, the optimization control angle at this time can be quickly solved to achieve optimized control of the inductor current. The present invention can effectively reduce the current effective value and amplitude of the three power transmission inductors in the isolated three-port converter, so that when the load is disturbed or the load is switched, the overall inductor current effective value is reduced compared with the traditional phase shift control, reducing the on-state loss of the switch tube and improving the system efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of converter control strategies, and in particular relates to an inductor current effective value optimization control method and device for an isolated three-port converter. Background Art

[0002] Three-port isolated converters are widely used in important occasions such as distributed renewable energy, energy storage batteries and DC power grids due to their high power density and flexible power transmission.

[0003] Some of the prior art uses single-phase shift control for the control method of three-port isolated converters. On this basis, the dynamic tracking of converter power transmission is realized through proportional integral control. However, the effective value of the inductor current is too large when this method is used, resulting in large losses in the converter and reducing the overall working efficiency. At the same time, when the converter is modeled for small signals, it is carried out at a steady-state operating point. When the actual operating point deviates too much from the steady-state operating point, that is, when the load changes over a large range, the loss of the converter increases. Some analyze the soft-turn-on conditions of the converter and use the average current method for modeling and analysis. Since the working conditions corresponding to the inductor current are different when the converter is turned on at different times, it is necessary to classify and discuss multiple working modes, which increases the complexity of converter analysis. There are also optimization controls for the third port of the converter under zero power flow. By analyzing the relationship between the inductor current at different turn-on times, the constraints that need to be met under different working modes are solved to achieve optimal control of the converter. However, no research has been conducted on the power transmission situation during load disturbance or switching.

[0004] In addition, although the patent 202110544434.8 proposes an improved asymmetric voltage elimination modulation strategy, which realizes power transmission within the normalized gain range of 0 to 0.5, in most distributed energy applications, power transmission between multiple ports is required. If multiple resonant converters are used in parallel, there will be a current sharing problem. This method does not analyze the problem of parallel use, and the power transmission is not flexible enough.

[0005] Therefore, there is an urgent need for an inductor current effective value optimization control method for a three-port converter to solve the problem that the effective value of the inductor current is too large and the conduction loss of the switch tube is high when using a single-phase shift control method, resulting in large system losses. Summary of the invention

[0006] The present invention aims to provide a method and device for optimizing the control of the effective value of the inductor current of an isolated three-port converter, so as to solve the above technical problems.

[0007] The present invention is achieved by adopting the following technical solutions:

[0008] In a first aspect, the present invention provides an inductor current effective value optimization control method of an isolated three-port converter, wherein port one of the three-port converter is connected to a DC power supply, port two is connected to a DC load, and port three is connected to an energy storage battery, and the three ports are coupled together by a high-frequency transformer, and the method comprises:

[0009] After the square wave voltage at the midpoint of the bridge arm of the isolated three-port converter is equivalent to the equivalent circuit of the square wave voltage source, a control variable α is added to port 2;

[0010] The equivalent circuit of the square wave voltage source is converted to obtain an equivalent circuit, and an equivalent transmission model between each port of the converter is determined; the equivalent circuit includes a Y-type equivalent circuit and a triangle equivalent circuit;

[0011] After analyzing the three-level bridge arm square wave voltage by Fourier series expansion, a mathematical model of an isolated three-port converter is established in combination with an equivalent transmission model between each port; the mathematical model of the isolated three-port converter includes an expression of the effective value of the inductor current of the converter and a per-unit expression of the port transmission power;

[0012] Combined with the mathematical model of the isolated three-port converter, the effective value of the inductor current is targeted and the KKT condition is used to solve the optimal solution set under the specified output power conditions.

[0013] The optimal solution set is fitted with data, and the obtained fitting curve is written into the control strategy to achieve optimal control of the effective value of the inductor current.

[0014] In one embodiment, the equivalent circuit of the square wave voltage source is converted to obtain an equivalent circuit, including: converting the equivalent circuit of the square wave voltage source, converting the power transmission inductance and the square wave voltage source of port two and port three to port one to obtain a three-port Y-type equivalent circuit, and obtaining a three-port triangle equivalent circuit by transforming the star-delta circuit.

[0015] In one embodiment, in order to make the three ports of the converter have the same power transmission capacity, in the triangular equivalent circuit of the power transmission inductor, the transmission inductor is designed by matching the transformer ratio to meet the principle of equal inductance of each branch, that is, L Δ =L 12 =L 13 =L 23 , considering the power transmission expression between ports, the maximum value of the port transmission power is defined as the power reference P base ,

[0016]

[0017] Where V1 is the voltage of port one; ω = 2πf, f is the switching frequency of the three-port converter; L12 is the power transfer inductance between port 1 and port 2 in the triangle equivalent circuit.

[0018] In one embodiment, the control variable α is

[0019] In one implementation, the effective value expression of the inductor current and the normalized expression of the port transmission power of the converter are respectively:

[0020] The sum of the squares of the effective values ​​of the inductor currents is defined as

[0021]

[0022] Among them, the effective value square expression of port one is for:

[0023]

[0024] The square of the effective value of the inductor current at port 2 and port 3 They are:

[0025]

[0026] Where V1 is the voltage of port 1; ω = 2πf, f is the switching frequency of the three-port converter; L 12 is the power transfer inductance between port 1 and port 2 in the triangle equivalent circuit; L 13 is the power transfer inductance between port 1 and port 3 in the triangle equivalent circuit; L 23 is the power transfer inductance between port 2 and port 3 in the triangle equivalent circuit; Indicates the multiple of the voltage at port 2 and the voltage at port 1; It represents the multiple of the voltage of port 3 and the voltage of port 1; n is the order of harmonics; α is the control variable; is the phase shift angle between bridge arm 1 and bridge arm 2; is the phase shift angle between bridge arm one and bridge arm three.

[0027] The normalized expression of the port transmission power is:

[0028]

[0029] In one implementation, the mathematical model of the combined converter is targeted at the effective value of the inductor current and solved using the KKT condition to obtain the optimal solution set under the specified output power condition:

[0030]

[0031]

[0032] In the formula, α is the control variable; is the phase shift angle between bridge arm 1 and bridge arm 2; is the phase shift angle between bridge arm one and bridge arm three.

[0033] In one embodiment, the fitting curve is expressed as:

[0034]

[0035] Wherein, P1 and P2 are the transmission power values ​​of port 1 and port 2 respectively.

[0036] In a second aspect, the present invention provides an inductor current effective value optimization control device for an isolated three-port converter, the device comprising:

[0037] A control variable module is used to convert the square wave voltage at the middle point of the bridge arm of the isolated three-port converter into an equivalent circuit of a square wave voltage source, and then add a control variable α to port 2;

[0038] An equivalent transmission model module is used to convert the equivalent circuit of the square wave voltage source to obtain an equivalent circuit, and determine the equivalent transmission model between each port of the converter; the equivalent circuit includes a Y-type equivalent circuit and a triangle equivalent circuit;

[0039] The converter mathematical model module is used to analyze the three-level bridge arm square wave voltage by Fourier series expansion, and then establish a mathematical model of the isolated three-port converter in combination with the equivalent transmission model between each port; the mathematical model of the isolated three-port converter includes an expression of the effective value of the inductor current and a per-unit expression of the port transmission power;

[0040] The KKT condition solving module is used to combine the mathematical model of the converter, take the effective value of the inductor current as the target, and use the KKT condition to solve and obtain the optimal solution set under the specified output power conditions;

[0041] The control module is used to perform data fitting on the optimal solution set, and the obtained fitting curve is written into the control strategy to realize the optimal control of the effective value of the inductor current.

[0042] In the third aspect, the present invention provides an isolated three-port converter control system, the system comprising the above-mentioned isolated three-port converter inductor current effective value optimization control device, the device combines a PI control module and a matrix decoupling network module to determine the optimal control of the three-port converter by the switching state.

[0043] In a fourth aspect, a computer-readable storage medium stores computer program instructions, which, when executed by a processor, implement the method for optimizing the effective value control of the inductor current of the three-port converter.

[0044] The beneficial effects of the present invention are:

[0045] The present invention can effectively reduce the effective value and amplitude of the current of the three power transmission inductors in the isolated three-port converter. When the load changes within a certain range, the overall effective value of the inductor current is reduced compared with the traditional phase-shift control. The reduction of the effective value of the inductor current is beneficial to the reduction of the conduction loss of the switch tube and the improvement of the overall transmission efficiency. In addition, the use of an isolated three-port converter can realize power transmission under multiple ports and meet the power matching problem in most cases. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The accompanying drawings are part of the present invention and are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but do not constitute an improper limitation of the present invention. Obviously, the accompanying drawings described below are only some embodiments. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without creative work.

[0047] Figure 1 It is an isolated three-port main circuit topology;

[0048] Figure 2 A flow chart of an inductor current effective value optimization control method of an isolated three-port converter provided in one embodiment of the present invention;

[0049] Figure 3 is an isolated three-port equivalent circuit provided in one embodiment of the present invention, wherein Figure 3 (a) is the equivalent circuit before optimization control. Figure 3 (b) is the equivalent circuit after optimized control;

[0050] Figure 4 is an equivalent circuit of an isolated three-port converted circuit provided in one embodiment of the present invention, wherein Figure 4 (a) is an isolated three-port Y-type equivalent circuit. Figure 4 (b) is an isolated three-port triangle equivalent circuit;

[0051] Figure 5 is a waveform diagram of the bridge arm midpoint voltage provided in one embodiment of the present invention, wherein Figure 5 (a) is the bridge arm voltage before optimization, Figure 5 (b) is the optimized bridge arm voltage;

[0052] Figure 6 This is the port voltage waveform before optimization;

[0053] Figure 7 An optimized port voltage waveform diagram provided in one embodiment of the present invention;

[0054] Figure 8 A before-and-after comparison diagram of an inductor current waveform provided in an embodiment of the present invention;

[0055] Fig. 9 A comparison diagram of effective values ​​before and after optimization provided in one embodiment of the present invention;

[0056] Fig.10 A block diagram of optimizing control of the effective value of the inductor current of a three-port converter provided in one embodiment of the present invention.

[0057] It should be noted that these drawings and textual descriptions are not intended to limit the conceptual scope of the present invention in any way, but are intended to illustrate the concept of the present invention for those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0058] In order to deepen the knowledge and understanding of the present invention, the technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific implementation methods. The following is an embodiment of a method for improving the low-speed performance of a high-power induction motor without a speed sensor.

[0059] Isolation three-port topology such as Figure 1 As shown, port 1 is connected to the DC power supply, port 2 is connected to the DC load, and port 3 is connected to the energy storage battery. The high-frequency transformer in the middle couples the three ports together. Among them, L1, L'2, and L'3 are the sum of the inductance connected in series to each winding and the leakage inductance of each winding of the transformer itself. At the same time, assuming that the high-frequency transformer is an ideal transformer, the excitation inductance L m It is much larger than the transformer leakage inductance and can be ignored when building the mathematical model.

[0060] like Figure 2 As shown, the inductor current effective value optimization control method of the isolated three-port converter provided by the embodiment of the present disclosure specifically includes the following steps:

[0061] Step S100: After the square wave voltage at the midpoint of the bridge arm of the isolated three-port converter is equivalent to the equivalent circuit of the square wave voltage source, a control variable α is added to the second port.

[0062] Figure 3 It is the equivalent circuit after the square wave voltage at the midpoint of the isolated three-port bridge arm is equivalent to a square wave voltage source. Among them, Figure 3 (a) is the equivalent circuit before optimization control. The traditional phase shift control strategy is adopted between the three ports to generate a two-level bridge arm voltage. Figure 3(b) is the equivalent circuit after optimized control. Based on the traditional phase-shift control strategy, port 2 adds a control variable α to generate a three-level bridge arm voltage.

[0063] Step S200: converting the equivalent circuit of the square wave voltage source to obtain an equivalent circuit, and determining an equivalent transmission model between various ports of the converter.

[0064] Furthermore, the equivalent circuit of the square wave voltage source is converted to obtain an equivalent circuit, including:

[0065] The power transmission inductance and square wave voltage source of port two and port three are converted to port one to obtain a three-port Y-type equivalent circuit, and a three-port triangle equivalent circuit is obtained by transforming the star-delta circuit.

[0066] After the equivalent Figure 3 (b) The circuit is converted to convert the power transfer inductance and square wave voltage source of port 2 and port 3 to port 1, which is equivalent to Figure 4 (a) is the circuit shown. Through the transformation of the star-delta circuit, it is equivalent to Figure 4 (b) The circuit shown is used to analyze the energy transfer between ports.

[0067] In the figure, L2, L3, L 12 , L 13 , L 23 , V2, and V3 are expressed as follows.

[0068]

[0069] Furthermore, the phase shift angle is The value of the control variable is

[0070] Figure 5 is the voltage waveform of the midpoint of the bridge arm, vgS5 is the driving voltage waveform of the switch tube S5 of port 2, and vgS8 is the driving voltage waveform of the switch tube S8 of port 2. The traditional control method adopts a single-phase shift control method, through the bridge external phase shift angle The control generates a two-level bridge arm voltage, such as Figure 5 Based on the traditional single phase shift control, the present invention adds the internal control variable α of the port two full bridge to change the conduction relationship of the bridge arm switch tube and generate a three-level bridge arm voltage, as shown in FIG. Figure 5 (b) as shown.

[0071] Step S300: After analyzing the three-level bridge arm square wave voltage by means of Fourier series expansion, a mathematical model of the converter is established in combination with an equivalent transmission model between various ports.

[0072] Using Fourier series expansion, Figure 5 (b) Analyzing the square wave voltage of the bridge arm, we can get:

[0073]

[0074] Where n is the harmonic order, ω=2πf, and f is the switching frequency of the converter.

[0075] From formula (2), we can get: Figure 3 The voltage across the inductor in (b) is:

[0076]

[0077] By integrating the inductor voltage, we can get the inductor current:

[0078]

[0079] Taking the inductor current i1 of port 1 as an example, the integrated expression can be organized as:

[0080]

[0081] in,

[0082]

[0083] The effective square expression of port one for:

[0084]

[0085] Substituting formula (6) into formula (7), we can obtain:

[0086]

[0087] Similarly, the square of the effective value of the inductor current at port 2 and port 3 is:

[0088]

[0089] Furthermore, a mathematical model of the isolated three-port converter is established, including an expression for the effective value of the converter's inductor current and a normalized expression for the port transmission power.

[0090] The converter's inductor current effective value expression and port transmission power normalized expression are as follows:

[0091] The total effective value of the inductor current is defined as

[0092]

[0093] From formula (2), the harmonic vector expression of the bridge arm square wave voltage can be obtained as follows:

[0094]

[0095] Figure 4 In the triangular equivalent circuit of (b), the vector expression of the inductor current is:

[0096]

[0097] Substituting formula (12) into formula (13), we can obtain:

[0098]

[0099] In the vector analysis of sinusoidal circuits, the expression for active power is:

[0100]

[0101] Among them, P xy(n) represents the nth harmonic power flowing from port x to port y, is the inductance L xy The current flowing, yes Substituting formula (12) and formula (14) into formula (15), we can get:

[0102]

[0103] From the vector form of the power transfer expression in formula (16), the time domain form of power transfer can be obtained as:

[0104]

[0105] Figure 3 In the equivalent circuit of (b), the power transfer between ports satisfies the relationship:

[0106]

[0107] Substituting formula (17) into formula (18), the expression of the transmission power of the port is:

[0108]

[0109] Furthermore, in order to make the three ports of the converter have the same power transmission capacity, in the triangular equivalent circuit of the power transmission inductor, the transmission inductor is designed by matching the transformer ratio to meet the principle of equal inductance of each branch, that is, L Δ =L 12 =L 13 =L 23 Considering the power transmission expression between ports, the maximum value of the port transmission power is defined as the power reference Pbase ,

[0110]

[0111] At this time, the normalized expression of the port transmission power is:

[0112]

[0113] In the formula,

[0114] Finally, the mathematical model of the isolated three-port converter is established, including the effective value of the converter's inductor current as shown in equation (11) and the normalized expression of the port transmission power as shown in equation (21).

[0115] Step S400: In combination with the mathematical model of the converter, taking the effective value of the inductor current as the target, solving using the KKT condition, and obtaining the optimal solution set under the specified output power condition.

[0116] The optimization problem of the effective value of the inductor current of the three-port converter can be described as the following nonlinear mathematical optimization problem. That is, under the condition of satisfying the power constraint, find The KKT condition is used to solve the nonlinear optimization problem, and the optimal solution set under the specified output power condition is obtained as follows:

[0117]

[0118]

[0119] In the formula, α is the control variable; is the phase shift angle between bridge arm 1 and bridge arm 2; is the phase shift angle between bridge arm one and bridge arm three.

[0120] Step S500: performing data fitting on the optimal solution set, and writing the obtained fitting curve into the control strategy to achieve optimal control of the effective value of the inductor current.

[0121] According to formula (22), the corresponding power transfer operating point is calculated and Then perform data fitting on the relevant working points to obtain α(P o1 ,P o2 ) control curve.

[0122] In order to further illustrate the technical solution of the present invention, a Matlab simulation model is built. The simulation parameters are shown in Table 1. By changing the transmission power of port 2, the optimization effect of the effective value of the inductor current is verified.

[0123] Table 1 System design parameters

[0124]

[0125]

[0126] The optimal solution is obtained by using formula (22), and the solution set is fitted with data. The fitted curve is shown in formula (23). The curve is written into the control strategy to achieve the optimization effect.

[0127] Furthermore, the fitted curve is:

[0128]

[0129] Figure 6 and Figure 7 are the voltage waveforms under the two control modes. Figure 6 is the terminal voltage at the midpoint of the unoptimized bridge arm, Figure 7 It is the port voltage at the midpoint of the bridge arm after optimization of the control freedom. Figure 8 The following is a comparison of the three power transmission inductor current waveforms before and after optimization. It can be seen from the figure that the amplitude of the waveforms of the three inductor currents is reduced after optimization. Fig. 9 The transmission power of port 2 is changed by switching the load, and the effective value curve of the inductor current before and after optimization. It can be seen from the figure that under each corresponding load after optimization, the effective value of the inductor current after optimization is smaller than the effective value of the inductor current before optimization, and the optimization effect is more obvious under light load.

[0130] In one embodiment, a device for optimizing and controlling the effective value of an inductor current of an isolated three-port converter is shown, and the device includes:

[0131] A control variable module is used to convert the square wave voltage at the middle point of the bridge arm of the isolated three-port converter into an equivalent circuit of a square wave voltage source, and then add a control variable α to port 2;

[0132] An equivalent transmission model module is used to convert the equivalent circuit of the square wave voltage source to obtain an equivalent circuit, and determine the equivalent transmission model between each port of the converter; the equivalent circuit includes a Y-type equivalent circuit and a triangle equivalent circuit;

[0133] The converter mathematical model module is used to analyze the three-level bridge arm square wave voltage by Fourier series expansion, and then establish a mathematical model of the isolated three-port converter in combination with the equivalent transmission model between each port; the mathematical model of the isolated three-port converter includes an expression of the effective value of the inductor current and a per-unit expression of the port transmission power;

[0134] The KKT condition solving module is used to combine the mathematical model of the converter, take the effective value of the inductor current as the target, and use the KKT condition to solve and obtain the optimal solution set under the specified output power conditions;

[0135] The control module is used to perform data fitting on the optimal solution set, and the obtained fitting curve is written into the control strategy to realize the optimal control of the effective value of the inductor current.

[0136] It should be noted that the inductor current effective value optimization control device of an isolated three-port converter provided in the above embodiment only uses the division of the above functional modules as an example when executing an inductor current effective value optimization control method of an isolated three-port converter. In actual applications, the above functions can be assigned to different functional modules as needed, that is, the internal structure of the device is divided into different functional modules to complete all or part of the functions described above. In addition, the inductor current effective value optimization control device of an isolated three-port converter provided in the above embodiment and the inductor current effective value optimization control method embodiment of an isolated three-port converter belong to the same concept. The implementation process thereof is detailed in the inductor current effective value optimization control method embodiment of an isolated three-port converter, which will not be repeated here.

[0137] like Fig.10 As shown, an isolated three-port converter control system is shown in one embodiment, which includes the above-mentioned isolated three-port converter inductor current effective value optimization control device, which combines PI control and matrix decoupling network to determine the optimal control of the three-port converter by the switching state.

[0138] Specifically, refer to Fig.10 As shown, the input current I1 of port one and the output voltage V′2 of port two are collected and compared with the corresponding reference values, and the difference is transmitted to the decoupling network through the PI control unit to obtain the phase shift angle between the bridge arms. and The input current I1 of port one, the input voltage V1 of port one, the input current I2 of port two, and the input voltage V2 of port two are collected and sent to the inductor current effective value optimization control device of the isolated three-port converter. The control variable α is obtained by calculating the power of port one and port two. Phase shift angle The control variable α is sent to the PWM generation module to obtain the switch state.

[0139] In one embodiment, a computer-readable storage medium is provided, on which computer program instructions are stored. When the instructions are executed by a processor, the above-mentioned inductor current effective value optimization control method of the isolated three-port converter is implemented.

[0140] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0141] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for optimizing the effective value of inductor current of an isolated three-port converter, characterized in that: Port one of the three-port converter is connected to a DC power source, port two is connected to a DC load, and port three is connected to an energy storage battery. The three ports are coupled together by a high-frequency transformer. The method includes: After the square wave voltage at the midpoint of the bridge arm of the isolated three-port converter is equivalent to the equivalent circuit of the square wave voltage source, a control variable α is added to port 2; The equivalent circuit of the square wave voltage source is converted to obtain an equivalent circuit, and an equivalent transmission model between each port of the converter is determined; the equivalent circuit includes a Y-type equivalent circuit and a triangle equivalent circuit; After analyzing the three-level bridge arm square wave voltage by Fourier series expansion, a mathematical model of an isolated three-port converter is established in combination with an equivalent transmission model between each port; the mathematical model of the isolated three-port converter includes an expression of the effective value of the inductor current of the converter and a per-unit expression of the port transmission power; Combined with the mathematical model of the isolated three-port converter, the effective value of the inductor current is targeted and the KKT condition is used to solve the optimal solution set under the specified output power conditions. The mathematical model of the isolated three-port converter is combined with the effective value of the inductor current, and the KKT condition is used to solve the optimal solution set under the specified output power condition: In the formula, is the sum of the squares of the effective values ​​of the inductor currents at the three ports, They represent the normalized expression of the transmission power of port 1 and port 2 respectively, are the per-unit values ​​of the output power specified for port 1 and port 2 respectively, and α is the control variable; is the phase shift angle between bridge arm 1 and bridge arm 2; is the phase shift angle between bridge arm one and bridge arm three; The optimal solution set is fitted with data, and the obtained fitting curve is written into the control strategy to realize the optimal control of the effective value of the inductor current; the fitting curve is used to calculate the control variable α according to the transmission power values ​​of port one and port two.

2. The inductor current effective value optimization control method of the isolated three-port converter according to claim 1, characterized in that: The equivalent circuit of the square wave voltage source is converted to obtain an equivalent circuit, including: converting the equivalent circuit of the square wave voltage source, converting the power transmission inductance of port two and port three and the square wave voltage source to port one, obtaining a three-port Y-type equivalent circuit, and obtaining a three-port triangle equivalent circuit through the transformation of the star-delta circuit.

3. The inductor current effective value optimization control method of the isolated three-port converter according to claim 2, characterized in that: In order to make the three ports of the converter have the same power transmission capacity, in the triangular equivalent circuit of the power transmission inductor, the transmission inductor is designed by matching the ratio of the isolation transformer to meet the principle of equal inductance of each branch, that is, L Δ =L 12 =L 13 =L 23 , considering the power transmission expression between ports, the maximum value of the port transmission power is defined as the power reference P base , Where V1 is the voltage of port one; ω = 2πf, f is the switching frequency of the three-port converter; L 12 is the power transfer inductance between port 1 and port 2 in the triangle equivalent circuit.

4. The inductor current effective value optimization control method of the isolated three-port converter according to claim 1, characterized in that: The effective value expression of the inductor current and the normalized expression of the port transmission power of the converter are: The sum of the squares of the effective values ​​of the inductor currents is defined as Among them, the effective value square expression of port one is for: The square of the effective value of the inductor current at port 2 and port 3 They are: Where V1 is the voltage of port 1; ω = 2πf, f is the switching frequency of the three-port converter; L 12 is the power transfer inductance between port 1 and port 2 in the triangle equivalent circuit; L 13 is the power transfer inductance between port 1 and port 3 in the triangle equivalent circuit; L 23 is the power transfer inductance between port 2 and port 3 in the triangle equivalent circuit; Indicates the multiple of the voltage at port 2 and the voltage at port 1; It represents the multiple of the voltage of port 3 and the voltage of port 1; n is the order of harmonics; α is the control variable; is the phase shift angle between bridge arm 1 and bridge arm 2; is the phase shift angle between bridge arm one and bridge arm three; The normalized expression of the port transmission power is:

5. The inductor current effective value optimization control method of the isolated three-port converter according to claim 1 or 4, characterized in that: The fitting curve is expressed as: Wherein, P1 and P2 are the transmission power values ​​of port 1 and port 2 respectively.

6. An inductor current effective value optimization control device for an isolated three-port converter, characterized in that: The device comprises: A control variable module is used to convert the square wave voltage at the middle point of the bridge arm of the isolated three-port converter into an equivalent circuit of a square wave voltage source, and then add a control variable α to port 2; An equivalent transmission model module is used to convert the equivalent circuit of the square wave voltage source to obtain an equivalent circuit, and determine the equivalent transmission model between each port of the converter; the equivalent circuit includes a Y-type equivalent circuit and a triangle equivalent circuit; The converter mathematical model module is used to analyze the three-level bridge arm square wave voltage by Fourier series expansion, and then establish a mathematical model of the isolated three-port converter in combination with the equivalent transmission model between each port; the mathematical model of the isolated three-port converter includes an expression of the effective value of the inductor current and a per-unit expression of the port transmission power; The KKT condition solving module is used to combine the mathematical model of the isolated three-port converter, take the effective value of the inductor current as the target, and use the KKT condition to solve and obtain the optimal solution set under the specified output power conditions; The mathematical model of the isolated three-port converter is combined with the effective value of the inductor current, and the KKT condition is used to solve the optimal solution set under the specified output power condition: In the formula, is the sum of the squares of the effective values ​​of the inductor currents at the three ports, They represent the normalized expression of the transmission power of port 1 and port 2 respectively, are the per-unit values ​​of the output power specified for port 1 and port 2 respectively, and α is the control variable; is the phase shift angle between bridge arm 1 and bridge arm 2; is the phase shift angle between bridge arm one and bridge arm three; The control module is used to perform data fitting on the optimal solution set, and the obtained fitting curve is written into the control strategy to realize the optimal control of the effective value of the inductor current; the fitting curve is used to calculate the control variable α according to the transmission power values ​​of port one and port two.

7. An isolated three-port converter control system, characterized in that: The system includes the inductor current effective value optimization control device of the isolated three-port converter according to claim 6, which is combined with a PI control module and a matrix decoupling network module to determine the optimal control of the three-port converter by the switch state.

8. A computer-readable storage medium having computer program instructions stored thereon, wherein when the instructions are executed by a processor, the inductor current effective value optimization control method of the isolated three-port converter according to any one of claims 1 to 5 is implemented.

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