Wide working range comprehensive optimization method based on ANPC-DAB converter

Abstract

The invention relates to the field of ANPC-DAB type converters, in particular to a wide working range comprehensive optimization method based on an ANPC-DAB converter. According to the method, the voltage conversion ratio is calculated through the input voltage and the output voltage, and the external phase shift angle ratio of a primary side H bridge and a secondary side H bridge of the converter is determined according to the relation between the output voltage and a set value. And judging the working mode of the converter according to the maximum transmission power and the current transmission power, calculating a current effective value according to a voltage conversion ratio and an external phase shift angle ratio, and optimizing the current effective value and a current peak value by taking the current effective value as an optimization target and combining a complete differential optimization function with the working mode to obtain an optimal modulation scheme. According to the invention, the soft switching range can be expanded, and the switching loss of a switching tube in the ANPC-DAB type converter is effectively reduced, so that the overall efficiency of the converter is improved.

Description

Technical Field

[0001] The invention relates to the technical field of ANPC-DAB converters, and in particular to a comprehensive optimization method based on a wide working range of an ANPC-DAB converter. Background Art

[0002] With the rapid development and continuous expansion of DC distribution networks and distributed DC generation systems, efficient power transmission has become increasingly important. In order to maintain the stability of the DC bus voltage, an interface circuit needs to be selected. DAB-type DC converters have attracted widespread attention from scholars due to their many advantages such as wide voltage regulation capability, bidirectional power transmission capability, current isolation and high power density. However, the requirements for the voltage withstand capability and production cost of the prototype are also getting higher and higher. A common method to improve the voltage withstand capability is to connect the input sides of multiple DAB modules in series. However, the serial DAB structure always requires a large number of different DAB modules. Therefore, the complexity of the control system, power flow adjustment, the total number of switches and the total cost of prototype production will be greatly increased. Therefore, neutral point clamped DC-DC converters are becoming more and more important in practical applications, including three-level diode neutral point clamped (DNPC) DAB-type DC-DC converters and three-level ANPC-DAB-type DC-DC converters. Similar to the DAB converter, bidirectional power transmission can also be achieved. By adjusting the relative phase relationship of the AC output equivalent voltage across the inductor, the inductor current characteristics of the three-level ANPC-DAB are adjusted. However, there is still a lack of methods for optimizing the best modulation scheme of ANPC-DAB in the prior art. Summary of the invention

[0003] In view of this, the object of the present invention is to propose a comprehensive optimization method based on a wide operating range of an ANPC-DAB converter to optimize the best modulation scheme of ANPC-DAB.

[0004] Based on the above purpose, the present invention provides a comprehensive optimization method for a wide operating range of an ANPC-DAB converter, comprising the following steps:

[0005] S1, determining the input voltage, output voltage and output voltage reference value of the ANPC-DAB converter;

[0006] S2, calculating the voltage matching ratio through the input voltage, the output voltage and the transformer ratio, and obtaining the external phase shift angle ratio between the primary full bridge and the secondary full bridge of the ANPC-DAB converter according to the output voltage and the output voltage reference value;

[0007] S3, obtaining the duty cycle of the primary full bridge and the internal phase shift angle ratio of the primary full bridge according to the voltage matching ratio and the external phase shift angle ratio;

[0008] S4, obtaining the maximum transmission power of the ANPC-DAB converter and the power per unit value currently required to be transmitted, and determining the working mode of the ANPC-DAB converter according to the power per unit value required to be transmitted and the voltage matching ratio requirement;

[0009] S5. Analyze the duty cycle of the DVDM according to the different working modes of the ANPC-DAB converter, and obtain the operating limit of the system soft switching range by analyzing each power tube switching process;

[0010] S6. Establish a loss model for the entire system, splitting it into conduction loss, switching loss, and magnetic loss;

[0011] S7. According to the voltage conversion ratio and different modulation degrees of freedom, the effective current value and the peak-to-peak current are obtained. The effective current value and the peak-to-peak current are taken as optimization targets. Based on the loss model, the optimal modulation scheme is solved by combining the working mode boundary and the soft switching working boundary through the fully differential optimization function.

[0012] Preferably, the formula for calculating the voltage matching ratio is:

[0013]

[0014] Among them, k is the voltage matching ratio; V1 is the input voltage, V2 is the output voltage, and n is the high-frequency transformer ratio.

[0015] Preferably, obtaining the external phase shift angle ratio between the primary full bridge and the secondary full bridge of the ANPC-DAB converter according to the output voltage and the output voltage reference value includes:

[0016] The output voltage of the secondary full-bridge is collected, and the output voltage is subtracted from the output voltage reference value. According to the difference between the output voltage and the output voltage reference value, the external phase shift angle ratio between the primary full-bridge power switch tube drive signal and the secondary full-bridge power switch tube drive signal is obtained through a proportional-integral controller.

[0017] Preferably, obtaining the duty cycle of the primary full bridge and the internal phase shift angle ratio of the primary full bridge includes:

[0018] According to the values ​​of the external phase shift angle ratio and the voltage matching ratio, the duty cycle of the primary full bridge and the internal phase shift angle ratio of the primary full bridge are obtained according to the offline lookup table.

[0019] Preferably, step S5 specifically includes:

[0020] According to the working mode division of the ANPC-DAB converter and the basic characteristics of the power switch tube, the basic conditions for the switch tube to achieve soft turning-on are analyzed, and the minimum boundary current value that can achieve soft turning-on of the switch tube is calculated according to the law of conservation of energy. According to the different working states of the ANPC-DAB converter, the duty cycle of the DVDM is analyzed. By analyzing the switching process of each power tube, the operating limit of the system soft switching range is obtained.

[0021] Preferably, the loss model includes:

[0022] Conduction loss model:

[0023]

[0024] Where P cond represents the conduction loss, R ds(on) Indicates the on-resistance of the corresponding switch Si when it is in the on state, I RMS represents the root mean square current;

[0025] Switching loss model:

[0026] The switching loss is defined as P sw , including conduction loss P turn-on and turn-off loss P turn-off ;

[0027]

[0028] where f sw represents the switching frequency, t on and t off Represents the time interval between the conduction process and the shutdown process, V ce(t) is the on-state voltage, i L(t) is the inductor current, E turn-on and E turn-off are the turn-on energy and turn-off energy respectively;

[0029] Magnetic loss model:

[0030] The magnetic loss of the transformer is defined as P trans , the magnetic loss is composed of copper loss P copper and iron loss P iron Composition, of which:

[0031]

[0032] P iron =C m f s α B β

[0033] Among them IRMS is the root mean square current, R Cu is the equivalent resistance of the high-frequency transformer, f s represents the switching frequency, B is the peak magnetic flux density, C is m , α and β are empirical parameters;

[0034] B=V2 / (4Nf s ×A core )

[0035] Where N is the turns ratio of the transformer, A Core is the cross-sectional area of ​​the core, and V2 is the secondary output voltage.

[0036] Preferably, the formula for the peak-to-peak current is:

[0037] i peak =i peak (D1,D2,D3,k)

[0038] where i peak represents the peak-to-peak value of the current, k is the voltage matching ratio, D1 is the inner phase shift angle ratio between the driving signal of the primary full-bridge switch tube S1 and the driving signal of the switch tube S4, D2 is the outer phase shift angle ratio between the primary full-bridge switch tube S1 and the secondary full-bridge switch tube Q1 of the ANPC-DAB converter, D3 is the duty cycle of the driving signal of the primary full-bridge switch tube S1 in the primary full-bridge, S1, S4 and Q1 are the numbers of the primary full-bridge switch tube and the secondary full-bridge switch tube respectively.

[0039] Preferably, the fully differential optimization function is:

[0040]

[0041] Among them, P copper Represents copper loss, P cond represents the conduction loss, I RMS Represents the root mean square current, I swi is the transient current value of the corresponding switch tube at the time of shutdown, P swi is the turn-off loss of the corresponding switch tube at the turn-off moment.

[0042] Preferably, the fully differential optimization function includes inequality constraints and equality constraints;

[0043] The inequality constraints include the minimum current value that can achieve soft turn-on of the switch and the boundary conditions of different working modes:

[0044] The minimum current value that can achieve soft turn-on of the switch is:

[0045]

[0046] The boundary conditions of different working modes are:

[0047]

[0048] The equality constraint formula is:

[0049] P=P ref

[0050] Among them, D1 is the internal phase shift angle ratio between the driving signal of the primary full-bridge switch tube S1 and the driving signal of the switch tube S4, D2 is the external phase shift angle ratio between the primary full-bridge switch tube S1 and the secondary full-bridge switch tube Q1 of the ANPC-DAB converter, D3 is the duty cycle of the driving signal of the primary full-bridge switch tube S1 in the primary full-bridge, k is the voltage matching ratio, V2 is the output voltage, n is the high-frequency transformer ratio, f s represents the switching frequency, i L (t) is the inductor current, L is the inductance, P is the per-unit value of the transmitted power, and P* is the per-unit reference value of the transmitted power.

[0051] Beneficial effects of the present invention: The method of the present invention first calculates the voltage matching ratio by obtaining the input voltage, output voltage and output voltage reference value of the ANPC-DAB converter. Then, according to the relationship between the output voltage and the output voltage reference value, the external phase shift angle ratio between the primary full bridge and the secondary full bridge is determined. Then, the duty cycle of the primary full bridge and its internal phase shift angle ratio are obtained by using an offline lookup table according to the voltage matching ratio and the external phase shift angle ratio reference value. In addition, the present invention also calculates the maximum transmission power of the ANPC-DAB converter and the per-unit value of the currently required transmission power, and determines the working mode of the converter according to the power demand and the voltage matching ratio. With the goal of achieving soft opening of the power switch tube, the duty cycle of the DVDM is analyzed, and the operation limit of the soft switching range of the system is obtained by analyzing each power tube switching process. Finally, according to the voltage conversion ratio and different modulation degrees of freedom, the effective value and peak-to-peak value of the current are calculated and used as the optimization target. Through the complete differential optimization function, the working mode boundary and the soft switch working boundary are combined to solve the optimal modulation scheme. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only for the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0053] Figure 1 is a flow chart of an optimization method according to an embodiment of the present invention;

[0054] Figure 2 A flowchart of an optimization using a complete differential function according to an embodiment of the present invention;

[0055] Figure 3 A schematic diagram of the topological structure of an ANPC-DAB converter according to an embodiment of the present invention;

[0056] Figure 4 Schematic diagram of ZVS analysis at each switch state switching moment under double-sided variable duty cycle modulation according to an embodiment of the present invention, wherein: Figure 4 (a) is the zero state where the inductor current is negative. Figure 4 (b) is the zero state where the inductor current is negative. Figure 4 (c) is the positive state where the inductor current is positive. Figure 4 (d) is the positive state where the inductor current is negative. Figure 4 (e) is the negative state where the inductor current is positive. Figure 4 (f) is the negative state where the inductor current is negative;

[0057] Figure 5 is a typical working waveform of an embodiment of the present invention, wherein: Figure 5 (a) is working mode 1, Figure 5 (b) is working mode 2, Figure 5 (c) is working mode 3, Figure 5 (d) is working mode 4, Figure 5 (e) is working mode 5, Figure 5 (f) is working mode 6;

[0058] Figure 6 A control execution block diagram of an embodiment of the present invention;

[0059] Figure 7 A comparison diagram of the effective current values ​​of the present invention and other modulation strategies under different voltage matching ratios of an embodiment of the present invention;

[0060] Figure 8 A comparison diagram of current peak values ​​of the present invention and other modulation strategies under different voltage matching ratios of an embodiment of the present invention;

[0061] Fig. 9 This is a comparison chart of the efficiency of the embodiment of the present invention and other modulation strategies. DETAILED DESCRIPTION

[0062] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments.

[0063] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0064] like Figure 1 As shown, the present invention discloses a method and system for comprehensive optimization of a wide operating range under double-sided variable duty cycle modulation based on an ANPC-DAB converter, comprising the following steps:

[0065] S1. Determine the input voltage, output voltage and output voltage reference value of the ANPC-DAB converter;

[0066] S2. Calculate the voltage matching ratio by input voltage, output voltage and transformer ratio;

[0067] The voltage matching ratio formula is as follows:

[0068]

[0069] Among them, k is the voltage matching ratio; V1 is the input voltage, V2 is the output voltage, and n is the high-frequency transformer ratio.

[0070] The external phase shift angle ratio between the primary and secondary full bridges of the ANPC-DAB converter is obtained according to the output voltage and the output voltage reference value, as follows:

[0071] The output voltage of the secondary full-bridge is collected, and the output voltage is subtracted from the output voltage reference value. Based on this difference, the external phase shift angle ratio between the primary full-bridge power switch tube drive signal and the secondary full-bridge power switch tube drive signal is calculated through a proportional-integral controller.

[0072] S3. According to the voltage matching ratio and the external phase shift angle ratio reference value, the corresponding duty cycle of the primary full bridge and the internal phase shift angle ratio of the primary full bridge are obtained by an offline lookup table, as follows:

[0073] According to the values ​​of the external phase shift angle ratio and the voltage matching ratio, the corresponding duty cycle of the primary full bridge and the internal phase shift angle ratio of the primary full bridge are found in the offline lookup table.

[0074] S4. Calculate the maximum transmission power required by the ANPC-DAB converter under different working conditions, determine the working mode of the ANPC-DAB converter according to the required transmission power and voltage matching ratio, and the phase relationship of the AC equivalent voltage waveform on both sides of the primary and secondary sides and the working characteristics of the inductor current under different working modes. Figure 5 Down:

[0075] The ANPC-DAB converter has six operating modes under the new asymmetric modulation strategy, and the transmission power of each operating mode is shown in the table.

[0076] Table 1

[0077]

[0078]

[0079] S5. According to the different working modes of the selected ANPC-DAB converter, the boundary conditions under different switching states are analyzed in order to realize the soft switching of the power switch tube. The details are as follows:

[0080] According to the different working states of the ANPC-DAB converter, the duty cycle of the DVDM is analyzed, and the switching process of each power tube is analyzed to obtain the operating limit of the system soft switching range.

[0081] S6. The loss optimization targets are selected as conduction loss, switching loss and magnetic loss, and the corresponding energy loss models are established respectively. The details are as follows:

[0082] Conduction loss model establishment:

[0083]

[0084] Conduction loss is denoted as P cond , the on-resistance of the corresponding switch Si in the on state is recorded as R ds(on) , the root mean square current is recorded as I RMS ;

[0085] Switching loss model establishment:

[0086] The switching loss can be defined as P sw , which can be divided into conduction loss P turn-on and turn-off loss P turn-off .

[0087]

[0088] Where fsw is the switching frequency, t on and t offRepresents the time interval between the conduction process and the shutdown process, V ce (t) is the on-state voltage, i L (t) is the inductor current, E turn-on and E turn-off are the turn-on energy and turn-off energy respectively.

[0089] Magnetic loss model establishment:

[0090] The conduction loss of the transformer can be defined as P trans The power loss of the transformer is composed of copper loss P copper and iron loss P iron The copper loss of the transformer can be calculated by

[0091]

[0092] Transformer iron loss P iron It is relatively complex and depends mainly on the switching frequency fs and the variation principle of the hysteresis curve. Subsequently, the amount of iron loss can be estimated using the Steinmetz equation.

[0093] P iron =C m f s α B β

[0094] Where B is the peak magnetic flux density, C m , α and β are empirical parameters

[0095] B=V2 / (4Nf s ×A core )

[0096] Where N is the turns ratio of the transformer, A Core is the cross-sectional area of ​​the core.

[0097] S7. Based on the power loss model proposed above, a comprehensive optimization strategy for a large operating range is proposed, which optimizes the peak current, effective current and soft switching range at the same time. Based on the genetic algorithm, the peak-to-peak current is selected as the optimization target. A mathematical framework based on the complete differential algorithm is designed to reduce the RMS current and expand the ZVS range. The peak-to-peak current formula is as follows, see Figure 2 Graph optimized using fully differential functions for the present invention:

[0098] Table 2

[0099]

[0100]

[0101]

[0102] The optimization objectives can be divided into the main optimization objectives and sub-optimization objectives. The purpose of the complete differential algorithm proposed in this paper is to set corresponding optimization boundaries for the sub-optimization objectives. For example, if the optimization result of the peak current leads to an increase in the RMS current value or a decrease in the soft switching range, the designed algorithm will discard this set of optimization results.

[0103] There are two different ways to set up the detailed mathematical framework of the complete differentiation algorithm.

[0104]

[0105] The first method to achieve integrated optimization is to set ΔI RMS and ΔI swi The sign of (i=1,2…n) is less than 0. Therefore, the peak current can be minimized and other sub-optimization objectives can also be reduced.

[0106]

[0107] The second method to achieve integrated optimization is to set ΔI RMS and ΔI swi The sign of (i=1,2…n) is greater than a certain value ΔI set Therefore, the peak current can be minimized and other sub-optimization objectives can also be optimized through further optimization.

[0108] After setting the appropriate Δ sign, the RMS current and switching loss can also be reduced when the peak current is optimized. In order to avoid the direction change of the inductor current, corresponding restrictions should also be designed. In order to keep all switches in ZVS, due to the symmetry of the inductor current, the inductor current direction can be designed as

[0109]

[0110] The mathematical laws of the comprehensive optimization method are as follows:

[0111] i peak =i peak (D1,D2,D3,k)

[0112] Among them, i peak is the optimization objective, and k is a given value.

[0113] The completely differential function includes inequality constraints and equality constraints;

[0114] The inequality constraints mainly include being able to achieve ZVS operation of all switches as inequality restrictions, as shown below:

[0115]

[0116] The operating boundaries in DVDM Mode 1 should also be considered as inequality limits.

[0117]

[0118] The equality constraint formula is as follows:

[0119] P=P ref

[0120] Where P is the per-unit value of the transmission power; P ref is the per-unit reference value of the transmission power;

[0121] Embodiment 1:

[0122] Topology Figure 3 As shown, it includes two symmetrical H bridges connected to a high-frequency transformer through an inductor L, where the high-frequency transformer is referred to as HFT. The turns ratio of the transformer is n, the input voltage is denoted as V1, and the output voltage is denoted as V2. In the equivalent circuit model of ANPC-DAB, the equivalent AC output voltages on the primary and secondary sides are marked as V h1 and V h2 . Ts represents the switching period of the switch tube. Switches S1, S2, S3, S4, S5, and S6 are located on the primary H-bridge, and switches S7, S8, S9, S10, S11, and S12 are located on the secondary H-bridge. DSi and DQi are the reverse parallel diodes of the primary H-bridge and the secondary H-bridge, respectively, while CSi and CQi are the junction capacitances of the corresponding switches on the primary H-bridge and the secondary H-bridge.

[0123] By controlling the inner phase shift angle D1 between the trigger signal of the primary H-bridge switch tube S1 and the trigger signal of the switch tube S6, and the outer phase shift angle D2 between the primary H-bridge switch tube S1 and the secondary H-bridge switch tube Q1, combined with the duty cycle D3 of the primary H-bridge switch tube S1, the current stress under the same transmission power can be reduced. The new asymmetric modulation strategy helps to expand the zero voltage switching (ZVS) range of the switch tube in the ANPC-DAB converter, thereby effectively improving the efficiency of the ANPC-DAB converter and realizing the efficient operation of the ANPC-DAB controller. See Figure 4 , which shows a schematic diagram of ZVS analysis at each switch state switching moment under unilateral asymmetric modulation of the present invention.

[0124] The output obtained by the present invention through control is the switch trigger signal of the ANPC-DAB converter, wherein the trigger signals of the two switch tubes on each half bridge are complementary. Therefore, the trigger signals of all switch devices in the ANPC-DAB converter can be determined by obtaining D1, D2 and D3.

[0125] The ANPC-DAB converter of the present invention has six operating modes, which are distinguished by the inductor current waveform. Figure 5 : Figure 5 (a) is the waveform of working mode 1; see Figure 5 (b) is the waveform of working mode 2; see Figure 5 (c) is the waveform of working mode 3; see Figure 5 (d) is the waveform of working mode 4; see Figure 5 (e) is the waveform of working mode 5; see Figure 5 (f) is the waveform of working mode 6.

[0126] The ANPC-DAB converter has six operating modes under the new asymmetric modulation strategy, and the transmission power of each operating mode is shown in the table.

[0127] Table 3

[0128]

[0129] The system is modeled for power, and the loss optimization targets are selected as conduction loss, switching loss, and magnetic loss, and the corresponding energy loss models are established respectively. The details are as follows:

[0130] Conduction loss model establishment:

[0131]

[0132] Switching loss model establishment:

[0133]

[0134] Magnetic loss model establishment:

[0135]

[0136] P iron =C m f s α B β

[0137] B=V2 / (4Nf s ×A core )

[0138] According to the working mode of ANPC-DAB converter and the basic characteristics of different power switch tubes, the soft switching of the power switch tube is realized, the duty cycle of DVDM is analyzed, and the switching process of each power tube is analyzed to obtain the operating limit of the soft switching range of the system.

[0139] According to the voltage conversion ratio and different modulation degrees of freedom, the effective value and peak-to-peak value of the current are obtained. Taking these two values ​​as optimization targets, combined with the complete differential optimization function, the working mode boundary and the soft switching working boundary, the optimal modulation scheme is solved.

[0140] According to the different working modes of the selected ANPC-DAB converter, the boundary conditions under different switching states are analyzed in order to realize the soft switching of the power switch tube. The details are as follows:

[0141] The conduction status of the switch tube in different switch states:

[0142] Table 4

[0143]

[0144]

[0145] According to the different working states of the ANPC-DAB converter, the duty cycle of the DVDM is analyzed, and the switching process of each power tube is analyzed to obtain the operating limit of the system soft switching range.

[0146] Based on the power loss model proposed above, a comprehensive optimization strategy for a large operating range is proposed, which optimizes the peak current, effective current and soft switching range at the same time. Based on the genetic algorithm, the peak-to-peak current is selected as the optimization target. A mathematical framework based on the complete differential algorithm is designed to reduce the RMS current and expand the ZVS range. The peak-to-peak current formula is as follows, see Figure 2 Graph optimized using fully differential functions for the present invention:

[0147]

[0148]

[0149]

[0150] The optimization objectives can be divided into the main optimization objectives and sub-optimization objectives. The purpose of the complete differential algorithm proposed in this paper is to set corresponding optimization boundaries for the sub-optimization objectives. For example, if the optimization result of the peak current leads to an increase in the RMS current value or a decrease in the soft switching range, the designed algorithm will discard this set of optimization results.

[0151] There are two different ways to set up the detailed mathematical framework of the complete differentiation algorithm.

[0152]

[0153] The first method to achieve integrated optimization is to set ΔI RMS and ΔIswi The sign of (i=1,2…n) is less than 0. Therefore, the peak current can be minimized and other sub-optimization objectives can also be reduced.

[0154]

[0155] The second method to achieve integrated optimization is to set ΔI RMS and ΔI swi The sign of (i=1,2…n) is greater than a certain value ΔI set Therefore, the peak current can be minimized and other sub-optimization objectives can also be optimized through further optimization.

[0156] After setting the appropriate Δ sign, the RMS current and switching loss can also be reduced when the peak current is optimized. In order to avoid the direction change of the inductor current, corresponding restrictions should also be designed. In order to keep all switches in ZVS, due to the symmetry of the inductor current, the inductor current direction can be designed as

[0157]

[0158] The mathematical laws of the comprehensive optimization method are as follows:

[0159] i peak =i peak (D1,D2,D3,k)

[0160] Among them, i peak is the optimization objective, and k is a given value.

[0161] The completely differential function includes inequality constraints and equality constraints;

[0162] The inequality constraints mainly include being able to achieve ZVS operation of all switches as inequality restrictions, as shown below:

[0163]

[0164] The operating boundaries in DVDM Mode 1 should also be considered as inequality limits.

[0165]

[0166] The equality constraint formula is as follows:

[0167] P=P ref

[0168] Where P is the per-unit value of the transmission power; P ref is the per-unit reference value of the transmission power;

[0169] See also Figure 6, is a flow chart of the single-sided double-sided duty cycle modulation method of the present invention, and its specific implementation process includes the following steps:

[0170] Step 1, measuring the input voltage V1 and output voltage V2 of the ANPC-DAB converter;

[0171] Step 2: Calculate the voltage conversion ratio k based on the measured input voltage V1 and output voltage V2, and compare the output voltage V2 with the output voltage given value V 2ref , after making a difference, the external phase shift angle ratio D2 of the primary side H-bridge switch tube S1 trigger signal and the secondary side H-bridge switch tube Q1 trigger signal is obtained through the proportional integral controller, and the duty cycle D3 of the primary side full bridge and the internal phase shift angle ratio D1 of the primary side full bridge are obtained through the offline lookup table;

[0172] Step 3, determine the power that the current converter needs to transmit, and compare it with the maximum transmission power to obtain the transmission power per unit value P*, based on which the boundary constraint conditions of the current working mode are determined to select the working mode;

[0173] Step 4, taking the effective value of current and the peak-to-peak value of current as the optimization targets, the optimization solution is performed through the complete differential optimization function, where the equality constraint is determined by the per-unit value of the transmission power, and the inequality constraints are the soft switching boundary constraint and the working mode operation boundary constraint, respectively, to obtain the optimal modulation scheme (D1(opt), (D2(opt), (D3(opt));

[0174] Step 5, after obtaining the optimal modulation scheme (D1(opt), (D2(opt), (D3(opt)), according to the improved asymmetric duty cycle modulation strategy, obtain the trigger signals of all switch tubes S1, S2, S3, S4, S5, S6, S7, S8, S9, S10, S11, S12 of the ANPC-DAB converter.

[0175] The present invention compares and analyzes the current effective value and efficiency of several traditional symmetrical phase shift modulation strategies and the single-sided double-sided duty cycle modulation strategy proposed in the present invention under the same transmission power conditions. Figure 7 As shown, under different voltage conversion ratios k, the double-sided duty cycle modulation strategy and its optimization method proposed in the present invention show the lowest current effective value. Figure 8 It shows that under different voltage conversion ratios k, the strategy and optimization method of the present invention also have the lowest current peak value. Fig. 9In the efficiency comparison, the double-sided duty cycle modulation strategy and its optimization method of the present invention show the highest efficiency, which indirectly verifies that the optimization method can realize the soft switching of the switch tube to the greatest extent. In summary, the unilateral asymmetric duty cycle modulation strategy of the present invention can effectively reduce current stress, expand the working range of soft switching, and thus significantly reduce the switching loss of the switch tube in the ANPC-DAB converter, and improve the overall efficiency of the converter.

[0176] In summary, the method and system of the present invention are intended to optimize switching losses. After comprehensive analysis, a method for accurately establishing the boundary of zero voltage switching and optimizing the dead time is proposed. On this basis, the peak current and the root mean square current are optimized using the fully differential optimization function, and a lower peak current and root mean square current under double-sided variable duty cycle modulation are successfully achieved. By comparing with the existing modulation scheme, the proposed optimization method can achieve the lowest peak current, the lowest effective current and the widest ZVS range.

[0177] Those skilled in the art should understand that the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of the present invention is limited to these examples; under the concept of the present invention, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other changes in different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity. Any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A comprehensive optimization method for wide operating range of ANPC-DAB converter, characterized in that: The following steps are involved: S1, determining the input voltage, output voltage and output voltage reference value of the ANPC-DAB converter; S2, calculating the voltage matching ratio through the input voltage, the output voltage and the transformer ratio, and obtaining the external phase shift angle ratio between the primary full bridge and the secondary full bridge of the ANPC-DAB converter according to the output voltage and the output voltage reference value; S3, obtaining the duty cycle of the primary full bridge and the internal phase shift angle ratio of the primary full bridge according to the voltage matching ratio and the external phase shift angle ratio; S4, obtaining the maximum transmission power of the ANPC-DAB converter and the power per unit value currently required to be transmitted, and determining the working mode of the ANPC-DAB converter according to the power per unit value required to be transmitted and the voltage matching ratio requirement; S5. Analyze the duty cycle of the DVDM according to the different working modes of the ANPC-DAB converter, and analyze the switching process of each power tube to obtain the operating limit of the system soft switching range; S6. Establish a loss model for the entire system, splitting it into conduction loss, switching loss, and magnetic loss; S7. According to the voltage conversion ratio and different modulation degrees of freedom, the effective current value and the peak-to-peak current are obtained. The effective current value and the peak-to-peak current are taken as optimization targets. Based on the loss model, the optimal modulation scheme is solved by combining the working mode boundary and the soft switching working boundary through the fully differential optimization function.

2. The wide operating range comprehensive optimization method based on ANPC-DAB converter according to claim 1 is characterized in that: The formula for calculating the voltage matching ratio is: Among them, k is the voltage matching ratio; V1 is the input voltage, V2 is the output voltage, and n is the high-frequency transformer ratio.

3. The wide operating range comprehensive optimization method based on ANPC-DAB converter according to claim 1 is characterized in that: The method of obtaining the external phase shift angle ratio between the primary full bridge and the secondary full bridge of the ANPC-DAB converter according to the output voltage and the output voltage reference value comprises: The output voltage of the secondary full-bridge is collected, and the output voltage is subtracted from the output voltage reference value. According to the difference between the output voltage and the output voltage reference value, the external phase shift angle ratio between the primary full-bridge power switch tube drive signal and the secondary full-bridge power switch tube drive signal is obtained through a proportional-integral controller.

4. The wide operating range comprehensive optimization method based on ANPC-DAB converter according to claim 1 is characterized in that: The step of obtaining the duty cycle of the primary full bridge and the internal phase shift angle ratio of the primary full bridge includes: According to the values ​​of the external phase shift angle ratio and the voltage matching ratio, the duty cycle of the primary full bridge and the internal phase shift angle ratio of the primary full bridge are obtained according to the offline lookup table.

5. The wide operating range comprehensive optimization method based on ANPC-DAB converter according to claim 1 is characterized in that: Step S5 specifically includes: According to the working mode division of the ANPC-DAB converter and the basic characteristics of the power switch tube, the basic conditions for the switch tube to achieve soft turning-on are analyzed, and the minimum boundary current value that can achieve soft turning-on of the switch tube is calculated according to the law of conservation of energy. According to the different working states of the ANPC-DAB converter, the duty cycle of the DVDM is analyzed. By analyzing the switching process of each power tube, the operating limit of the system soft switching range is obtained.

6. The wide operating range comprehensive optimization method based on ANPC-DAB converter according to claim 1 is characterized in that: The loss model includes: Conduction loss model: Where P cond represents the conduction loss, R ds(on) Indicates the on-resistance of the corresponding switch Si when it is in the on state, I RMS represents the root mean square current; Switching loss model: The switching loss is defined as P sw , including conduction loss P turn-on and turn-off loss P turn-off ; where f sw represents the switching frequency, t on and t off Represents the time interval between the conduction process and the shutdown process, V ce(t) is the on-state voltage, i L(t) is the inductor current, E turn-on and E turn-off are the turn-on energy and turn-off energy respectively; Magnetic loss model: The magnetic loss of the transformer is defined as P trans , the magnetic loss is composed of copper loss P copper and iron loss P iron Composition, of which: P iron =C m f s α B β Among them I RMS is the root mean square current, R Cu is the equivalent resistance of the high-frequency transformer, f s represents the switching frequency, B is the peak magnetic flux density, C is m , α and β are empirical parameters; <h2 style=";text-align:left;direction:ltr">B = V2 / (4Nf<h2 style=";text-align:left;direction:ltr"> s <h2 style=";text-align:left;direction:ltr"> ×A<h2 style=";text-align:left;direction:ltr"> core <h2 style=";text-align:left;direction:ltr"> ) Where N is the turns ratio of the transformer, A Core is the cross-sectional area of ​​the core, and V2 is the secondary output voltage.

7. The wide operating range comprehensive optimization method based on ANPC-DAB converter according to claim 1 is characterized in that: The formula for the peak-to-peak current is: i peak =i peak (D1,D2,D3,k) where i peak represents the peak-to-peak value of the current, k is the voltage matching ratio, D1 is the inner phase shift angle ratio between the driving signal of the primary full-bridge switch tube S1 and the driving signal of the switch tube S4, D2 is the outer phase shift angle ratio between the primary full-bridge switch tube S1 and the secondary full-bridge switch tube Q1 of the ANPC-DAB converter, D3 is the duty cycle of the driving signal of the primary full-bridge switch tube S1 in the primary full-bridge, S1, S4 and Q1 are the numbers of the primary full-bridge switch tube and the secondary full-bridge switch tube respectively.

8. The wide operating range comprehensive optimization method based on ANPC-DAB converter according to claim 1 is characterized in that: The fully differential optimization function is: Among them, P copper Represents copper loss, P cond represents the conduction loss, I RMS Represents the root mean square current, I swi is the transient current value of the corresponding switch tube at the time of shutdown, P swi is the turn-off loss of the corresponding switch tube at the turn-off moment.

9. The wide operating range comprehensive optimization method based on ANPC-DAB converter according to claim 9 is characterized in that: The complete differential optimization function includes inequality constraints and equality constraints; The inequality constraints include the minimum current value that can achieve soft turn-on of the switch and the boundary conditions of different working modes: The minimum current value that can achieve soft turn-on of the switch is: The boundary conditions of different working modes are: The equality constraint formula is: P=P ref Among them, D1 is the internal phase shift angle ratio between the driving signal of the primary full-bridge switch tube S1 and the driving signal of the switch tube S4, D2 is the external phase shift angle ratio between the primary full-bridge switch tube S1 and the secondary full-bridge switch tube Q1 of the ANPC-DAB converter, D3 is the duty cycle of the driving signal of the primary full-bridge switch tube S1 in the primary full-bridge, k is the voltage matching ratio, V2 is the output voltage, n is the high-frequency transformer ratio, f s represents the switching frequency, i L (t) is the inductor current, L is the inductance, P is the per-unit value of the transmitted power, and P* is the per-unit reference value of the transmitted power.

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