An optimal current effective value control method and system based on DAB converter

Abstract

The present invention discloses an optimal current effective value control method and system based on a DAB converter, which is specifically as follows: the values of the inner phase shift angle D1, the outer phase shift angle D2 of the DAB topology at the primary input end, and the variable pulse duty cycle D3 on the secondary side are adjusted to achieve stable power transmission. Compared with the traditional single phase shift control, the present invention increases the control quantities D1 and D3 so that the ZVS opening of all switching tubes can be achieved under low current effective values. The switching loss is greatly reduced, the reliability of the components in the topology is guaranteed, and the power transmission efficiency is improved. At the same time, most of the working modes under the optimal current effective value control strategy can achieve ZVS opening of all switching tubes. Therefore, in actual applications, soft switching within the full power and voltage regulation range can be achieved through fewer mode conversions, which significantly reduces the control complexity.

Description

Technical Field

[0001] The present invention belongs to the technical field of isolated DC-DC converter topology control, and in particular to an optimal current effective value control method and system based on a DAB converter. Background Art

[0002] With the development of the economy and technology, the large-scale development of new energy is imperative. The application of renewable energy sources such as wind, solar, hydro, and geothermal energy is an important path to environmental protection and sustainable development. For this type of sustainable distributed energy, DC distribution systems can better capture and absorb electrical energy.

[0003] Therefore, DC power distribution systems and DC power conversion technology have become one of the key research focuses in the industry. Due to its advantages such as high power density, low loss, bidirectional power flow, modularization and voltage regulation, DAB converters have attracted much attention from industry and academia.

[0004] Phase-shift control is the most basic control method for DAB converters. This strategy controls the power transfer characteristics of the DAB circuit by shifting the square wave voltage between the full-bridges on both sides of the circuit. Traditional phase-shift control strategies can be categorized as single-, double-, and triple-phase-shift, depending on the number of phase shift angles.

[0005] Among these strategies, the single-phase-shift control strategy is relatively simple to implement and has been widely used in industrial DAB converter control. However, single-phase-shift control suffers from limited controllable degrees of freedom and poor performance, particularly when the input and output voltages of the isolation transformer are significantly unequal, leading to severe power backflow and high current stress. The dual-phase-shift control strategy can eliminate reactive power and reduce current stress by increasing variable degrees of freedom. However, for most voltage conversion ratios under most operating conditions, this strategy has a narrow soft-switching region, making it unsuitable for wide-range voltage regulation. For the three-phase-shift control strategy, achieving a wider soft-switching region results in larger current peaks and RMS values, increasing conduction losses and reducing operational reliability. Therefore, research on optimized control strategies for DAB converters is highly significant. Summary of the Invention

[0006] In order to solve the problems existing in the prior art, the present invention provides an optimal current effective value control method and system based on a DAB converter, which can realize power transmission from the medium-voltage DC side to the low-voltage DC side, increase the control amount while improving control flexibility. At the same time, it can enable ZVS (zero voltage switching) of all switching tubes to be turned on at a low current effective value, reduce the losses generated during operation, ensure the reliability of the components in the topology, realize stable power transmission, reduce the backflow power generated during power transmission, and improve overall efficiency.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for optimal current effective value control based on a DAB converter. The DAB converter includes a primary full bridge and a secondary full bridge connected via an inductor L and a high-frequency isolation transformer. The primary full bridge includes switches S1-S4, and the secondary full bridge includes switches Q1-Q4. The primary full bridge circuit is connected to the primary winding of the high-frequency isolation transformer via the inductor L. The input end of the primary full bridge is V1, which is equivalent to the output end of the connected medium-voltage DC distribution network. The output end V2 of the secondary full bridge is equivalent to the input end of the connected low-voltage DC distribution network. An inner phase shift angle D1 between the drive signals of each switch in the primary full bridge of the DAB converter, an outer phase shift angle D2 between the drive signals of each switch in the secondary full bridge and the primary full bridge, and a variable pulse duty cycle D3 of switches Q1 and Q3 in the secondary full bridge are used as control variables. These control variables are used to adjust the required transmission power to achieve optimal current effective value control and enable low-current ZVS switching of the switches in the DAB converter.

[0008] Furthermore, the internal phase shift angle D1 of the switch tubes S1 and S4 in the primary side full bridge is equal to the internal phase shift angle D1 of the switch tubes S2 and S3;

[0009] The external phase shift angle D2 between the switch tubes Q1 and S1 in the secondary side full bridge and the primary side full bridge, the external phase shift angle D2 between the switch tubes Q2 and S2, the external phase shift angle D2 between the switch tubes Q3 and S3, and the external phase shift angle D2 between the switch tubes Q4 and S4 are all equal;

[0010] The variable pulse duty ratio D3 of the switch tubes Q1 and Q3 in the secondary side full bridge is equal.

[0011] Furthermore, the variable pulse duty ratio of the switch tube Q2 and the switch tube Q4 in the secondary side full bridge is (1-D3).

[0012] Furthermore, the optimal current effective value control method has six control modes, specifically including control modes A to F:

[0013] The boundary conditions for the values of the primary side inner phase shift angle D1, outer phase shift angle D2 and secondary side variable pulse duty cycle D3 of control modes A, D, E, and F are as follows:

[0014] (2)

[0015] The boundary conditions for the values of the primary side inner phase shift angle D1, outer phase shift angle D2 and secondary side variable pulse duty cycle D3 of control modes B and C are:

[0016] (5).

[0017] Furthermore, in the control mode A, the switch tube S1, the switch tube S2, the switch tube Q1, the switch tube Q2, the switch tube Q3 and the switch tube Q4 all achieve ZVS turn-on;

[0018] In the control modes B, D, and E, all switches are turned on in ZVS.

[0019] In the control mode F, the switch tubes S1 , S2 , S4 , Q1 , Q2 , Q3 and Q4 all achieve ZVS turn-on.

[0020] Furthermore, the output power range of control mode A is [0, MV1 / 4]. The steady-state inductor current stress value at each moment of control mode A is calculated using the DAB converter's primary-side inner phase shift angle D1, outer phase shift angle D2, and secondary-side variable pulse duty cycle D3. Based on the positive and negative current values of the steady-state current at each moment of control mode A, the boundary conditions for the values of the DAB converter's primary-side inner phase shift angle D1, outer phase shift angle D2, and secondary-side variable pulse duty cycle D3 in control mode A are obtained.

[0021] in, , k is the voltage matching ratio of the converter, the number ratio n is the high frequency transformer turns, fs is the switching frequency, V 1 is the input voltage, V2 is the output voltage, L For inductance.

[0022] Furthermore, the output power expression of control mode A is obtained based on the voltage and the steady-state current of control mode A at each moment:

[0023] (1)

[0024] Where, the number ratio n is the high frequency transformer turns, fs is the switching frequency, V 1 is the input voltage, V2 is the output voltage, L is the inductor;

[0025] By taking the partial derivative of formula (1), the maximum output power of control mode A is obtained as ,make , the output power range of control mode A is [0,MV1 / 4].

[0026] Furthermore, the output power range of the control mode B is [0, MV1(k-1) / k 2 ], the output power range of the control mode C is [0, MV1(k-1) / k 2], the output power range of control mode D is [0, 0.25MV1], the output power range of control mode E is [0,MV1(k+3) / (k+2)], and the output power range of control mode F is [0,MV1(k+3) / (k+2)], where , k is the voltage matching ratio of the converter, the number ratio n is the high frequency transformer turns, fs is the switching frequency, V 1 is the input voltage, V2 is the output voltage, L For inductance.

[0027] The present invention also proposes an optimal current effective value control system based on a DAB converter, comprising:

[0028] Data acquisition module, used to collect instantaneous output voltage and output power;

[0029] Data processing module, used to convert the instantaneous output voltage and output power into the required output power P ref and voltage reference value V ref Make a difference and perform PI modulation according to the above optimal current effective value control method to obtain the boundary conditions of the primary side inner phase shift angle D1, outer phase shift angle D2 and secondary side variable pulse duty cycle D3;

[0030] The switch tube control module is used to obtain the boundary conditions of the primary side inner phase shift angle D1, outer phase shift angle D2 and secondary side variable pulse duty cycle D3, and use the DSP chip to generate PWM signals and output them to the switch tube driver board. The driver board generates drive signals corresponding to the primary and secondary side full-bridge switch tubes to realize the sequential switching of the switch tubes.

[0031] Compared with the prior art, the present invention has at least the following beneficial effects:

[0032] The present invention provides an optimal current effective value control method and system based on a DAB converter. Compared with traditional phase-shift control, this optimal current effective value control strategy adds a control variable, the secondary side variable pulse duty cycle D3. By adjusting the primary side inner phase shift angle D1, outer phase shift angle D2 and secondary side variable pulse duty cycle D3, the defects of large return power and current stress can be improved.

[0033] An embodiment of the present invention provides an optimal current RMS control method for a DAB converter. This method introduces an inner phase shift angle on the primary side to generate a three-level waveform, reducing backflow power. By adjusting the primary-side inner phase shift angle D1, the outer phase shift angle D2, and the secondary-side variable pulse duty cycle D3, stable power transmission is achieved through PI closed-loop modulation. Furthermore, while maintaining a constant transmission power, the RMS current can be minimized by adjusting the values of various variables to improve efficiency.

[0034] Furthermore, this optimal current RMS control strategy can avoid the contradiction between peak current stress and soft switching range. The ZVS turn-on of all switching tubes can be achieved at low current RMS, which greatly reduces switching losses, ensures the reliability of devices in the topology, and improves power transmission efficiency.

[0035] Furthermore, most operating modes under the optimal current RMS control strategy can achieve ZVS turn-on of all switching tubes. Therefore, in practical applications, soft switching within the full power and voltage regulation range can be achieved through fewer mode conversions, significantly reducing the control complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagram of the topology of a DAB converter according to an embodiment of the present invention;

[0037] Figure 2 Schematic diagram of waveform of mode A of an optimal current effective value control method based on a DAB converter according to an embodiment of the present invention;

[0038] Figure 3 Schematic diagram of waveforms of mode B of an optimal current effective value control method based on a DAB converter according to an embodiment of the present invention;

[0039] Figure 4 Schematic diagram of waveform of mode C of an optimal current effective value control method based on a DAB converter according to an embodiment of the present invention;

[0040] Figure 5 Schematic diagram of waveform of mode D of an optimal current effective value control method based on a DAB converter according to an embodiment of the present invention;

[0041] Figure 6 Schematic diagram of waveform of mode E of an optimal current effective value control method based on a DAB converter according to an embodiment of the present invention;

[0042] Figure 7 Schematic diagram of waveform of mode F of an optimal current effective value control method based on a DAB converter according to an embodiment of the present invention;

[0043] Figure 8 Schematic diagram showing how the effective current value of a DAB converter-based optimal current effective value control method according to an embodiment of the present invention compares with other strategies in terms of how the effective current value varies with transmission power. DETAILED DESCRIPTION

[0044] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0045] To make the purpose, technical effects, and technical solutions of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention are clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention; it is obvious that the described embodiments are only part of the embodiments of the present invention. Based on the embodiments disclosed in the present invention, other embodiments obtained by ordinary technicians in this field without making any creative efforts should fall within the scope of protection of the present invention.

[0046] See also Figure 1 The DAB converter topology of an embodiment of the present invention includes a primary-side full-bridge, an inductor L, a high-frequency isolation transformer, and a secondary-side full-bridge. S1-S4 represent the switches of the primary-side full-bridge; Q1-Q4 represent the switches of the secondary-side full-bridge. The input of the primary-side full-bridge is V1, which is equivalent to the output of the connected medium-voltage DC distribution network.

[0047] Furthermore, the primary-side full-bridge circuit is connected to the primary-side winding of the high-frequency isolation transformer via the inductor L.

[0048] Furthermore, the output terminal V2 of the secondary-side full bridge is equivalent to the input terminal of the connected low-voltage DC distribution network.

[0049] Furthermore, the switching device used in the DAB converter topology may be an IGBT (Insulated Gate Bipolar Transistor) or a MOSFET (Metal-Oxide Semiconductor Field Effect Transistor).

[0050] The present invention provides a control method based on a DAB converter, and the specific steps are as follows:

[0051] 1. There is an internal phase shift angle D1 between the drive signals of each switch in the primary full-bridge. That is, there is an internal phase shift angle D1 between the drive signals of switches S1 and S4, and between the drive signals of switches S2 and S3, and the two internal phase shift angles D1 are equal.

[0052] 2. There is an external phase shift angle D2 between the drive signals of each switch tube of the secondary side full bridge and the primary side full bridge. That is, there is an external phase shift angle D2 between the drive signals of switch tube Q1 and switch tube S1, switch tube Q2 and switch tube S2, switch tube Q3 and switch tube S3, and switch tube Q4 and switch tube S4, and the four external phase shift angles D2 are equal.

[0053] 3. The variable pulse duty cycle D3 of the switches Q1 and Q3 in the secondary-side full-bridge is equal, and the variable pulse duty cycle D3 of the switches Q2 and Q4 is equal to (1-D3).

[0054] 4. Adjust the primary side inner phase shift angle D1, outer phase shift angle D2 and secondary side variable pulse duty cycle D3 to adjust the power required for transmission and realize the transmission of electric energy.

[0055] A further improvement of the present invention is that, compared with the commonly used single phase shift control, a three-level voltage is generated on the primary side by introducing an inner phase shift angle D1 on the primary side.

[0056] A further improvement of the present invention includes: more flexible control, which can improve the defects of high return power and high current stress by adjusting the inner phase shift angle D1 and the outer phase shift angle D2. A further improvement of the present invention also includes: by adjusting the inner phase shift angle D1, the outer phase shift angle D2, and the secondary-side variable pulse duty cycle D3, ZVS switching of all switches can be achieved at low current RMS values. This significantly reduces switching losses and improves power transmission efficiency.

[0057] According to the multi-degree-of-freedom characteristics of the optimal current effective value control strategy, many control modes will be generated. Different magnitude relationships between the inner phase shift angle D1, the outer phase shift angle D2 and the secondary side variable pulse duty cycle D3 correspond to different working modes, such as Figure 2-Figure 7 The following are schematic diagrams of waveforms of the converter topology in the control mode AF in the optimal current effective value control of the DAB converter according to the present invention, and the driving signals of the switch tubes S1-S4 and Q1-Q4 are shown in each figure. h1 Represents the three-level electrical square wave generated on the primary side, V h2 Represents the voltage square wave generated on the secondary side, i L Represents the current flowing through the inductor L, T s Represents a switching cycle, D1T S S3 driving pulse falling edge, D2T S Q2 driving pulse falling edge, (1+D2-D3)T S Q4 driving pulse falling edge, 0.5T S The falling edge of the S1 driving pulse, (D1+0.5)T S For the falling edge of S4 drive pulse, (D2+D3)T S is the falling edge of Q1 driving pulse, T S It is the falling edge of the S2 driving pulse;

[0058] Figure 2-Figure 4 In the control modes A~C shown, D1T S Smaller than D2T S , (D1+0.5)T S Less than (D2+D3)T S , the difference between control modes A~C is (1+D2-D3)T SThe position of Q4 is the turn-off time of switch Q4, that is, the time when its drive signal ends at high level. Among them, in control mode A, Q4's high level ends between the falling edge of S1 and the rising edge of S3; in control mode B, Q4's high level ends before the falling edge of S1; and in control mode C, Q4's high level ends after the rising edge of S3.

[0059] Figure 5-Figure 7 In the control modes D~F shown, D1T S Greater than D2T S , (D1+0.5)T S Less than (D2+D3)TS. The difference between control modes D~F is (1+D2-D3)T S The position of Q4 is the time when the high level of the switch tube Q4 ends. In mode D, the high level of Q4 ends between the falling edge of S1 and the falling edge of S3; in mode E, the high level of Q4 ends before the falling edge of S3; and in mode F, the high level of Q4 ends after the falling edge of S1.

[0060] like Figure 2 , control mode A: one switching cycle T s The order of switching off the switch tube at each moment is D1T S 、D2T S , 0.5T S 、(1+D2-D3)T S 、(D1+0.5)T S 、(D2+D3)T S and T S In control mode A, all switch tubes except S3 and S4 can achieve low current ZVS turn-on.

[0061] like Figure 3 , control mode B: one switching cycle T s The order of switching off the switch tubes at each moment is (D2+D3)T S 、D1T S 、D2T S 、(1+D2-D3)T S , 0.5T S 、 (D1+0.5)T S , and T S In this mode, all switches can achieve ZVS turn-on at a lower current.

[0062] like Figure 4 , control mode C: one switching cycle T s The order of switching off the switch tube at each moment is D1T S 、D2T S , 0.5T S 、(D1+0.5)TS 、(1+D2-D3)T S 、(D2+D3)T S and T S In this mode, all switches can achieve ZVS turn-on at a lower current.

[0063] like Figure 5 , control mode D: one switching cycle T s The order of switching off the switch tube at each moment is D2T S 、D1T S 、(1+D2-D3)T S , 0.5T S 、(D1+0.5)T S 、(D2+D3)T S and T S In this mode, all switches can achieve ZVS turn-on at a lower current.

[0064] like Figure 6 , control mode E: one switching cycle T s The order of switching off the switch tube at each moment is D2T S 、(1+D2-D3)T S 、D1T S , 0.5T S 、(D1+0.5)T S 、(D2+D3)T S and T S In this mode, all switches can achieve ZVS turn-on at a lower current.

[0065] like Figure 7 , control mode F: one switching cycle T s The order of switching off the switch tube at each moment is D2T S 、D1T S , 0.5T S 、(1+D2-D3)T S 、(D1+0.5)T S 、(D2+D3)T S and T S In this mode, all switches except S3 can achieve low current ZVS turn-on.

[0066] Take control mode A as an example for detailed description:

[0067] According to the voltage and the steady-state current of control mode A at each moment, the output power expression of control mode A is obtained as follows:

[0068] (1)

[0069] Where, the number ratio n is the high frequency transformer turns, fs is the switching frequency, V 1 is the input voltage, V2 is the output voltage, L For inductance.

[0070] By taking the partial derivative of formula (1), the maximum output power of control mode A is obtained as ,make , the output power range of control mode A is [0- MV1 / 4].

[0071] In the above output power range, the steady-state inductor current stress value at each moment of control mode A is calculated using the DAB converter's primary-side inner phase shift angle D1, outer phase shift angle D2, and secondary-side variable pulse duty cycle D3. According to the positive and negative current values of the steady-state current at each moment of control mode A, the boundary conditions for the values of the DAB converter's primary-side inner phase shift angle D1, outer phase shift angle D2, and secondary-side variable pulse duty cycle D3 in control mode A are obtained, specifically:

[0072] (2)

[0073] When the values of the primary side inner phase shift angle D1, outer phase shift angle D2 and the secondary side variable pulse duty cycle D3 meet the formula (2), combined with Figure 2 It can be seen that in control mode A, a switching cycle T s The switching actions of each switch tube are as follows:

[0074] At t0, the switch tube S2 is hard turned off;

[0075] At t0', the switch tube S1ZVS is turned on, the switch tube S3ZCS is turned off, and the switch tubes Q2 and Q3ZVS are turned on;

[0076] At time t1, the switch tube S4 is hard-turned on;

[0077] At time t2, the switch tubes Q2 and Q3 are hard-off, and the anti-parallel diodes of the switch tubes Q4 and Q1 are turned on;

[0078] At t3, the switch tube S1 is hard-off and the anti-parallel diode of the switch tube S2 is turned on;

[0079] At t3', the switch tube S2ZVS is turned on, the switch tube S4ZCS is turned off, and the switch tubes Q1 and Q4ZVS are turned on;

[0080] At time t4, the switch tube Q4 is hard-off and the anti-parallel diode of the switch tube Q3 is turned on;

[0081] At t5, the switch tube S3 is hard-turned on;

[0082] At time t6, the switch tube S4 is turned off, the switch tube Q1 is hard-off, and the anti-parallel diode of the switch tube Q2 is turned on.

[0083] It can be seen from the above working sequence of the switch tubes that in control mode A, all switch tubes except S3 and S4 can achieve low current ZVS turn-on.

[0084] Under control mode A, the specific calculation process of the boundary conditions for the primary side inner phase shift angle D1, outer phase shift angle D2 and secondary side variable pulse duty cycle D3 is as follows:

[0085] 1. Based on the voltage volt-second balance principle, the steady-state inductor current stress value at each moment of control mode A is calculated using the DAB converter's primary-side inner phase shift angle D1, outer phase shift angle D2, and secondary-side variable pulse duty cycle D3. It can be expressed as:

[0086] (3)

[0087] Where, k is the converter voltage matching ratio, n is the high frequency transformer turn, f s is the switching frequency, V 2 is the output voltage and L is the inductance.

[0088] 2. The steady-state current expression of control mode A is as follows:

[0089] (4)

[0090] Where, V 1 is the input voltage.

[0091] 3. Such as Figure 2 The positive and negative values of the steady-state current at each moment of the control mode A are obtained as shown in the figure. Combined with formula (4), it can be seen that:

[0092]

[0093] That is: 4 D 3 2 -4 D 3+4 D 2-2 kD 1+ k >0

[0094] 4 D 3 2 -4 D 3-2 kD 1+ k <0

[0095] 4D 3 2 -4 D 3-4 D 2-2( k -2) D 1- k >0

[0096] 4 D 3 2 +4(2- k ) D 3+4 kD 2-2 kD 1+3 k -4>0

[0097] 4 D 3 2 +8 D 3-2 kD 1+ k -4<0

[0098] 4 D 3 2 -( k +8) D 3- kD 2+3 kD 1-0.5 k +4<0

[0099] The boundary conditions for the values of the internal phase shift angle D1, external phase shift angle D2 on the primary side and the variable pulse duty cycle D3 on the secondary side of the DAB converter in control mode A are obtained as follows:

[0100] (2)

[0101] In practical applications, different control modes can be transformed by adjusting the boundary conditions of the primary side inner phase shift angle D1, outer phase shift angle D2 and secondary side variable pulse duty cycle D3 to achieve the desired effect, namely transmission power and soft switching conditions.

[0102] Similarly, the calculation process of the boundary conditions of the three variables of the primary side inner phase shift angle D1, the outer phase shift angle D2 and the secondary side variable pulse duty cycle D3 in the control modes B~F is the same as the calculation process of the control mode A. Specifically, the power expression of the control modes B~F is obtained according to the voltage and the steady-state current at each moment. The output power range of the control modes B~F can be obtained by performing the same partial derivative calculation. According to the positive and negative relationship of the current and the steady-state current expression, the operating boundary conditions of the control modes B~F are obtained, as shown in Table 1, where .

[0103] Table 1 Modal BF output power range and operating boundary conditions

[0104]

[0105] It can be seen that in control modes A, D, E, and F, the boundary conditions for the values of the primary side inner phase shift angle D1, outer phase shift angle D2, and secondary side variable pulse duty cycle D3 are:

[0106] (2);

[0107] In control modes B and C, the boundary conditions for the values of the primary side inner phase shift angle D1, outer phase shift angle D2, and secondary side variable pulse duty cycle D3 are:

[0108] (5).

[0109] The present invention also provides an optimal current effective value control system based on a DAB converter. In practical applications:

[0110] The data acquisition module collects instantaneous output voltage and output power;

[0111] The data processing module converts the instantaneous output voltage and output power into the required output power P under specific working conditions. ref and voltage reference value V ref Make a difference, perform PI modulation according to the above-mentioned optimal current effective value control method, and the output voltage control PI regulator obtains the boundary conditions of the primary side inner phase shift angle D1, outer phase shift angle D2 and secondary side variable pulse duty cycle D3 according to the global optimization control method;

[0112] The switch tube control module is used to obtain the boundary conditions of the primary side inner phase shift angle D1, outer phase shift angle D2 and secondary side variable pulse duty cycle D3, and use the DSP chip to generate PWM signals and output them to the switch tube driver board. The driver board generates drive signals corresponding to the primary and secondary side full-bridge switch tubes to realize the sequential switching of the switch tubes, thereby achieving the power transmission and voltage and power regulation of the DAB converter.

[0113] In the embodiment of the present invention, the effective current value of each control strategy under different power transmission power is calculated in MATLAB, and the comparison results are shown as follows: Figure 8 As shown in the figure, this figure is a schematic diagram of the current effective value control method based on the DAB converter of the present invention compared with other strategies of the current effective value as the transmission power changes. In the figure, SPS represents single phase shift control, EPS represents extended phase shift control, DPS represents dual phase shift control, TPS represents single phase shift control, ADM represents asymmetric duty cycle control, and VDPSS represents the optimal current effective value control strategy proposed by the present invention. Figure 8Analysis shows that, under the same power transmission power, this optimal current RMS control strategy has the lowest current RMS stress compared to other control strategies. Therefore, the optimal current RMS control method based on DAB converter proposed in this invention has significant advantages in reducing current RMS.

[0114] In summary, the optimal RMS current control method for a DAB converter according to the present invention reduces backflow power by introducing an inner phase shift angle on the primary side to generate a three-level waveform. Stable power transmission is achieved by adjusting the primary-side inner phase shift angle D1, the outer phase shift angle D2, and the secondary-side variable pulse duty cycle D3. Furthermore, while maintaining a constant transmission power, the RMS current can be minimized by adjusting the values of these variables to improve efficiency.

[0115] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the same. Although the present invention has been described in detail with reference to the above embodiments, a person skilled in the art may still modify or make equivalent substitutions to the specific implementations of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention are within the scope of protection of the claims of the present invention to be approved.

Claims

1. A method for controlling an optimal current effective value based on a DAB converter. The DAB converter includes a primary full bridge and a secondary full bridge connected via an inductor L and a high-frequency isolation transformer. The primary full bridge includes switches S1 to S4, and the secondary full bridge includes switches Q1 to Q4. The primary full bridge circuit is connected to the primary winding of the high-frequency isolation transformer via the inductor L. The input end of the primary full bridge is V1, which is equivalent to the output end of the connected medium-voltage DC distribution network. The output end V2 of the secondary full bridge is equivalent to the input end of the connected low-voltage DC distribution network. The method is characterized in that: The inner phase shift angle D1 between the drive signals of the switch tubes in the primary-side full bridge of the DAB converter, the outer phase shift angle D2 between the drive signals of the switch tubes in the secondary-side full bridge and the primary-side full bridge, and the variable pulse duty cycle D3 of the switch tubes Q1 and Q3 in the secondary-side full bridge are used as control variables. The control variables are used to adjust the power required for transmission to achieve optimal current effective value control and enable low current ZVS opening of the switch tubes in the DAB converter; The optimal current effective value control method has six control modes, specifically including control modes A to F: The boundary conditions for the values of the primary side inner phase shift angle D1, outer phase shift angle D2 and secondary side variable pulse duty cycle D3 of control modes A, D, E, and F are as follows: The boundary conditions for the values of the primary side inner phase shift angle D1, outer phase shift angle D2 and secondary side variable pulse duty cycle D3 of control modes B and C are: The output power range of control mode A is [0, MV1 / 4]. The steady-state inductor current stress value at each moment of control mode A is calculated using the DAB converter's primary-side inner phase shift angle D1, outer phase shift angle D2, and secondary-side variable pulse duty cycle D3. Based on the positive and negative current values of the steady-state current at each moment of control mode A, the boundary conditions for the values of the DAB converter's primary-side inner phase shift angle D1, outer phase shift angle D2, and secondary-side variable pulse duty cycle D3 in control mode A are obtained. The output power range of control mode B is [0,MV1(k-1) / k 2 ]; The output power range of the control mode C is [0, MV1(k-1) / k 2 ]; The output power range of control mode D is [0,0.25MV1]; The output power range of the control mode E is [0,MV1(k+3) / (k+2)]; The output power range of the control mode F is [0,MV1(k+3) / (k+2)]; in , k is the voltage matching ratio of the converter, the number ratio n is the high frequency transformer turns, fs is the switching frequency, V 1 is the input voltage, V 2 is the output voltage, L For inductance.

2. The optimal current effective value control method based on a DAB converter according to claim 1, characterized in that: The internal phase shift angle D1 of the switch tubes S1 and S4 in the primary side full bridge is equal to the internal phase shift angle D1 of the switch tubes S2 and S3; The external phase shift angle D2 between the switch tubes Q1 and S1 in the secondary side full bridge and the primary side full bridge, the external phase shift angle D2 between the switch tubes Q2 and S2, the external phase shift angle D2 between the switch tubes Q3 and S3, and the external phase shift angle D2 between the switch tubes Q4 and S4 are all equal; The variable pulse duty ratio D3 of the switch tubes Q1 and Q3 in the secondary side full bridge is equal.

3. The optimal current effective value control method based on a DAB converter according to claim 2, characterized in that: The variable pulse duty ratio of the switch tubes Q2 and Q4 in the secondary side full bridge is (1-D3).

4. The optimal current effective value control strategy based on a DAB converter according to claim 1, characterized in that: In the control mode A, the switch tubes S1, S2, Q1, Q2, Q3 and Q4 all achieve ZVS turn-on. In the control modes B, D, and E, all switches are turned on in ZVS. In the control mode F, the switch tubes S1 , S2 , S4 , Q1 , Q2 , Q3 and Q4 all achieve ZVS turn-on.

5. The optimal current effective value control method based on a DAB converter according to claim 1, characterized in that: According to the voltage and the steady-state current of control mode A at each moment, the output power expression of control mode A is obtained as follows: (1) Where, the number ratio n is the high frequency transformer turns, fs is the switching frequency, V 1 is the input voltage, V2 is the output voltage, L is the inductor; By taking the partial derivative of formula (1), the maximum output power of control mode A is obtained as ,make , the output power range of control mode A is [0,MV1 / 4].

6. An optimal current effective value control system based on a DAB converter, characterized in that: include: Data acquisition module, used to collect instantaneous output voltage and output power; Data processing module, used to convert the instantaneous output voltage and output power into the required output power P ref and voltage reference value V ref Making a difference, performing PI modulation according to the optimal current effective value control method described in any one of claims 1 to 5, and obtaining the boundary conditions of the primary side inner phase shift angle D1, outer phase shift angle D2 and secondary side variable pulse duty cycle D3; The switch tube control module is used to obtain the boundary conditions of the primary side inner phase shift angle D1, outer phase shift angle D2 and secondary side variable pulse duty cycle D3, and use the DSP chip to generate PWM signals and output them to the switch tube driver board. The driver board generates drive signals corresponding to the primary and secondary side full-bridge switch tubes to realize the sequential switching of the switch tubes.

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