Phase-shift frequency conversion control method, controller and system for three-level dual active bridge converter

Abstract

The present invention discloses a three-level dual active bridge converter phase shift frequency conversion control method, controller and system, which belongs to the technical field of converter control. The method includes: obtaining the equivalent load impedance Z eq and voltage ratio m, combined with the phase shift inductance value L, fixed switching frequency value f c Calculate the switching frequency update value f that changes with time during the current switching cycle s , so that when the primary and secondary soft switching boundary conditions are met at the same time, the actual average switching frequency is lower than f c ; Get the duty cycle D used to describe the internal phase shift ps1 , external phase shift duty cycle D ps2 And the frequency update value f s The coupling relationship between the primary and secondary sides is solved under the constraints of the soft switching boundary conditions to obtain D ps1 and D ps2 ; Based on f s 、D ps1 and D ps2 Generates driving signals for each switching device and acts on each switching device. The present invention can effectively suppress EMI noise peaks and solve the problem of transmission power fluctuation when the switching frequency changes without adding additional hardware.

Description

Technical Field

[0001] The present invention belongs to the technical field of converter control, and more specifically, relates to a phase-shift frequency conversion control method, a controller and a system for a three-level dual-active bridge converter. Background Art

[0002] The three-level dual-active-bridge (DAB) converter consists of two three-level active full-bridge circuits connected via a phase-shifting inductor and a high-frequency transformer. It has the advantages of low voltage stress, bidirectional power transmission, electrical isolation, voltage matching, and flexible control. As a key component of medium-voltage energy interconnection, it has been widely used in smart distribution networks, integrated ship power systems, distributed power generation systems, and other occasions.

[0003] Three-level DAB converters inherently suffer from electromagnetic interference (EMI). The continuous switching of the converter's power devices emits EMI noise, severely impacting the safe and stable operation of electronic information and power systems. It also generates significant switching losses, impacting the converter's transmission efficiency. Conventionally, the converter operates at a fixed switching frequency, generating significant EMI noise spikes at that frequency and its multiples. To address this issue, existing methods often incorporate additional passive EMI filters to suppress EMI noise, but this significantly increases the cost, size, and weight of the three-level DAB converter system.

[0004] Therefore, economically and effectively suppressing EMI without adding additional hardware is of great significance to the cost, power density, safety and reliability of three-level DAB converters. Summary of the Invention

[0005] In response to the shortcomings of the existing technology and the need for improvement, the present invention provides a phase-shifted frequency conversion control method, controller, and system for a three-level dual-active bridge converter. The purpose is to effectively suppress EMI noise peaks and solve the problem of transmission power fluctuations when the switching frequency changes, based on a method of real-time control of switching frequency changes and synchronous matching of phase-shift duty cycles, without adding additional hardware.

[0006] To achieve the above object, according to one aspect of the present invention, a phase-shift frequency conversion control method for a three-level dual active bridge converter is provided, comprising:

[0007] Step S1: According to the transmission power command value P of the three-level dual active bridge converter in the current switching cycle ref , output voltage command value V ref And the input voltage sampling value V obtains the equivalent load impedance Z eq and voltage transformation ratio m;

[0008] Step S2: According to the equivalent load impedance Z eq And voltage ratio m, as well as phase shift inductance value L, fixed switching frequency value f c Calculate the switching frequency update value f that changes with time during the current switching cycle s , so that when the primary and secondary soft switching boundary conditions are met at the same time, the actual average switching frequency is lower than the fixed switching frequency value f c ;

[0009] Step S3: Derivation of the internal phase shift duty ratio D used to describe the three-level dual active bridge converter based on the relationship between the primary and secondary side powers during power transmission ps1 , external phase shift duty cycle D ps2 And the frequency update value f s The coupling relationship between the two sides is solved under the constraints of the primary and secondary soft switching boundary conditions to obtain the internal phase shift duty cycle D of the three-level dual active bridge converter in the current switching cycle. ps1 and the external phase shift duty cycle D ps2 ;

[0010] Step S4: Based on the switching frequency change value f in the current switching cycle s , internal phase shift duty cycle D ps1 and the external phase shift duty cycle D ps2 A driving signal for each switching device is generated and acts on each switching device to realize phase-shift frequency conversion control of a three-level dual active bridge converter.

[0011] Furthermore, in step S2, the switching frequency update value f that changes with time in the current switching cycle is s The expression is as follows:

[0012]

[0013] Among them, f p is the frequency of the given switching frequency change, t is the time in the current switching cycle; f u 、f l They represent the upper and lower limits of the switching frequency range, and f s ∈[f l ,f u ], the soft switching boundary conditions of the primary and secondary sides are met at the same time.

[0014] Furthermore, the upper limit frequency f of the switching frequency variation range is u The expression is:

[0015]

[0016] Furthermore, the lower limit frequency f of the switching frequency variation range isl Satisfaction: 20f p ≤f l ≤0.5f u ;

[0017] in, n represents the transformation ratio of the isolation transformer in the three-level dual active bridge converter.

[0018] Furthermore, when forward power transmission is performed, in step S3, the coupling relationship is as follows:

[0019]

[0020] Furthermore, the inner phase shift duty ratio D obtained by step S3 is ps1 and the external phase shift duty cycle D ps2 The expression is as follows:

[0021] If Δ=(3m 2 +2m+1)(1-4kfs)-2 is greater than or equal to 0, then:

[0022]

[0023] If Δ=(3m 2 +2m+1)(1-4kfs)-2 is less than 0, then:

[0024]

[0025] According to another aspect of the present invention, a three-level dual active bridge converter phase-shift frequency controller is provided, comprising:

[0026] The pre-processing module is used to calculate the transmission power command value P of the three-level dual active bridge converter in the current switching cycle. ref , output voltage command value V ref And the input voltage sampling value V obtains the equivalent load impedance Z eq and voltage transformation ratio m;

[0027] Switching frequency update module is used to update the switching frequency according to the equivalent load impedance Z eq And voltage ratio m, as well as phase shift inductance value L, fixed switching frequency value f c Calculate the switching frequency update value f that changes with time during the current switching cycle s , so that when the primary and secondary soft switching boundary conditions are met at the same time, the actual average switching frequency is lower than the fixed switching frequency value f c ;

[0028] The phase shift duty cycle calculation module is used to derive the internal phase shift duty cycle D used to describe the three-level dual active bridge converter based on the relationship between the primary and secondary side powers during power transmission.ps1 , external phase shift duty cycle D ps2 And the frequency update value f s The coupling relationship between the two sides is solved under the constraints of the primary and secondary soft switching boundary conditions to obtain the internal phase shift duty cycle D of the three-level dual active bridge converter in the current switching cycle. ps1 and the external phase shift duty cycle D ps2 ;

[0029] And the driving signal wave module is used to change the switching frequency value f based on the current switching cycle s , internal phase shift duty cycle D ps1 and the external phase shift duty cycle D ps2 A driving signal for each switching device is generated and acts on each switching device to realize phase-shift frequency conversion control of a three-level dual active bridge converter.

[0030] Furthermore, the switching frequency update value f that changes with time in the current switching cycle s The expression is as follows:

[0031]

[0032] Among them, f p is the frequency of the given switching frequency change, t is the time in the current switching cycle; f u 、f l They represent the upper and lower limits of the switching frequency range, and f s ∈[f l ,f u ], the soft switching boundary conditions of the primary and secondary sides are met at the same time.

[0033] Furthermore, the upper limit frequency f of the switching frequency variation range is u The expression is:

[0034]

[0035] Furthermore, the lower limit frequency f of the switching frequency variation range is l Satisfaction: 20f p ≤f l ≤0.5f u ;

[0036] in, n represents the transformation ratio of the isolation transformer in the three-level dual active bridge converter.

[0037] Furthermore, when forward power transmission is performed, the coupling relationship is as follows:

[0038]

[0039] Furthermore, the internal phase shift duty ratio D obtained by the phase shift duty ratio calculation module is ps1 and the external phase shift duty cycle D ps2 The expression is as follows:

[0040] If Δ=(3m 2 +2m+1)(1-4kfs)-2 is greater than or equal to 0, then:

[0041]

[0042] If Δ=(3m 2 +2m+1)(1-4kfs)-2 is less than 0, then:

[0043]

[0044] According to another aspect of the present invention, a three-level dual active bridge converter system is provided, comprising: a three-level dual active bridge converter, and the three-level dual active bridge converter phase-shift frequency conversion controller provided by the present invention.

[0045] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0046] The present invention is based on the transmission power instruction value P ref , output voltage command value V ref And the input voltage sampling value V obtains the equivalent load impedance Z eq After the voltage ratio m, combined with the phase shift inductance value L, fixed switching frequency value f c Calculate the switching frequency update value f that changes with time during the current switching cycle s , the switching frequency update value f determined by the present invention s In the current cycle, the soft switching boundary conditions of the primary and secondary sides are met while changing in real time with time, ensuring the effectiveness of the phase shift control. s Real-time changes eliminate the need for EMI noise to be concentrated at a fixed frequency, resulting in a wider spectrum distribution and effectively reducing EMI noise peaks. Furthermore, because the actual average switching frequency is lower than the original fixed switching frequency, the switching losses of the three-level dual active bridge converter are effectively reduced. Furthermore, the present invention controls the phase-shift duty cycle in real time during operation to match the switching frequency changes, effectively suppressing output voltage and power fluctuations when the switching frequency changes.

[0047] In general, the present invention is based on a method for real-time control of switching frequency changes and synchronous matching of phase-shift duty cycles. It can effectively suppress EMI noise peaks and reduce switching losses of the three-level dual-active bridge converter without adding additional hardware, while effectively suppressing output voltage and output power fluctuations when the switching frequency changes. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 Schematic diagram of an existing three-level dual active bridge converter;

[0049] Figure 2 A schematic diagram of a phase-shift frequency conversion control method for a three-level dual active bridge converter provided by an embodiment of the present invention;

[0050] Figure 3 The soft switching boundary and D ps1 、D ps2 Schematic diagram of the relationship curve;

[0051] Figure 4 A block diagram of a phase-shifted frequency conversion controller for a three-level dual active bridge converter provided by an embodiment of the present invention;

[0052] Figure 5 A schematic diagram comparing the switching frequencies of the three-level dual active bridge converter phase-shift frequency conversion control method provided by an embodiment of the present invention and the traditional phase-shift control method;

[0053] Figure 6 1 is a waveform diagram of a phase-shift duty cycle that matches a switching frequency change value in an embodiment of the present invention;

[0054] Figure 7 A schematic diagram comparing the output voltage and output power of the phase-shift frequency conversion control method for a three-level dual active bridge converter provided by an embodiment of the present invention and the traditional phase-shift control method;

[0055] Figure 8 Schematic diagram of EMI noise of a three-level dual active bridge converter phase-shift frequency conversion control method provided by an embodiment of the present invention and a traditional phase-shift control method. DETAILED DESCRIPTION

[0056] 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 with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0057] In the present invention, the terms "first", "second", etc. (if any) in the present invention and the drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0058] Before explaining the technical solution of the present invention in detail, the topology and basic operating principle of a three-level dual-active-bridge (DAB) converter are briefly described. Figure 1 The figure shows an existing three-level dual active bridge converter, which consists of a primary three-level full bridge and a secondary three-level full bridge connected through a phase-shifting inductor L and a high-frequency isolation transformer (with a transformation ratio of n:1). The two bridge arms of the primary three-level full bridge are marked as a and b, and the two bridge arms of the secondary three-level full bridge are marked as c and d. Each bridge arm contains four switching tubes (S x1 -S x4 , x=a,b,c,d), 2 clamping diodes (such as D c1 and D c2 ) and a flying capacitor (e.g. C ss1 ). V1 and V2 represent the DC bus voltage of the primary and secondary sides. In each bridge arm, S x1 -S x4 The driving signals are all square waves, and S x1 With S x4 The driving signal of S x2 -S x3 The driving signal of S is complementary; x2 Compared to S x1 The time t of the driving signal phase shift ps1 By the internal phase shift duty ratio D ps1 and the switching frequency f, specifically t ps1 =D ps1 / (2f); between the two bridge arms of the primary side, S a1 With S b1 The driving signals of the two bridge arms on the secondary side are complementary, S c1 With S d1 The driving signals of the primary and secondary sides are complementary, and the same applies to the other signals; the phase shift time t ps2 (For example, S a1 With S c1 Between) by the external phase shift duty cycle D ps2 and the switching frequency f, specifically t ps2 =D ps2 / (2f).

[0059] During operation, the three-level dual-active bridge converter can perform both forward and reverse power transmission. During forward power transmission, terminal V1 serves as the input and terminal V2 serves as the output, connected to the load. During reverse power transmission, terminal V2 serves as the input and terminal V1 serves as the output, connected to the load. In practical applications, the three-level dual-active bridge converter often operates in forward power transmission mode. Without loss of generality, the following embodiments will be described using forward power transmission as an example.

[0060] Conventional phase-shift control methods for three-level dual-active bridge converters operate at a fixed switching frequency, generating significant EMI noise spikes at the fixed switching frequency and its multiples, and resulting in high switching losses. To address this issue, the present invention provides a phase-shifted frequency-variable control method, controller, and system for a three-level dual-active bridge converter. The overall concept is as follows: Based on the phase-shift control principle of the three-level dual-active bridge converter, a switching frequency variation range that simultaneously satisfies the primary and secondary soft switching boundary conditions is determined. Within this variation range, a real-time switching frequency update value is calculated, and the average value of the actual switching frequency is lower than the fixed switching frequency. This eliminates the EMI noise concentration at the fixed frequency, resulting in a wider spectrum distribution, effectively reducing the EMI noise peak, and effectively reducing the switching losses of the three-level dual-active bridge converter. Furthermore, during operation, the phase-shift duty cycle is controlled in real time to match the switching frequency changes, effectively suppressing output voltage and power fluctuations when the switching frequency changes.

[0061] The following are examples.

[0062] Example 1:

[0063] A phase-shift frequency conversion control method for a three-level dual active bridge converter, such as Figure 2 As shown, it includes: step S1 to step S3, each step is as follows:

[0064] Step S1: According to the transmission power command value P of the three-level dual active bridge converter in the current switching cycle ref , output voltage command value V 2ref And the input voltage sampling value V1 to obtain the equivalent load impedance Z eq And voltage transformation ratio m.

[0065] Specifically, according to the transmission power instruction value P ref and the output voltage command value V 2ref The equivalent load impedance can be calculated as:

[0066]

[0067] According to the output voltage command value V 2ref The voltage transformation ratio can be calculated as m=V1 / nV2 based on the input voltage sampling value V1, where n represents the transformation ratio of the transformer in the three-level dual active bridge converter.

[0068] Step S2: According to the equivalent load impedance Z eq And voltage ratio m, as well as phase shift inductance value L, fixed switching frequency value f c Calculate the switching frequency update value f that changes with time during the current switching cycle s, so that when the primary and secondary soft switching boundary conditions are met at the same time, the actual average switching frequency is lower than the fixed switching frequency value f c .

[0069] To ensure the effectiveness of phase-shift control, the switching frequency in the three-level dual active bridge converter should meet the soft switching boundary conditions of both the primary and secondary sides.

[0070] In the three-level dual active bridge converter, the soft switching boundary conditions of the switching devices in the primary three-level full bridge are:

[0071]

[0072] The soft switching boundary conditions of the switching devices in the secondary three-level full-bridge are:

[0073]

[0074] The internal phase shift duty cycle D ps1 As the horizontal axis, the external phase shift duty ratio D ps2 As the vertical coordinate, draw the above-mentioned primary and secondary soft switching boundary conditions in the corresponding two-dimensional plane as shown in Figure 3 As shown, ZVS boundary 1 represents the soft switching boundary condition for the switching devices in the primary three-level full-bridge, and ZVS boundary 2 represents the soft switching boundary condition for the switching devices in the secondary three-level full-bridge. The shaded area in the upper left corner of the figure represents the region where both primary and secondary soft switching boundary conditions are satisfied. It is easy to understand that to ensure that both primary and secondary switching boundary conditions are satisfied, the designed switching frequency curve should be located in the shaded area or intersect with the line corresponding to the ZVS boundary. Based on the above considerations, this embodiment first determines the upper and lower frequency limits of the switching frequency variation range based on the primary and secondary soft switching boundary conditions, and then designs a time-varying switching frequency update value within this variation range.

[0075] To simplify the representation, in step S2 of this embodiment, an intermediate coefficient, i.e., coefficient k, is introduced when designing a switching frequency that changes in real time and satisfies the primary and secondary side soft switching boundary conditions. The expression is:

[0076]

[0077] Determine the fixed switching frequency f c The relationship with 1 / 4k, if f c >1 / 4k, upper limit frequency f of switching frequency change u =1 / 4k; if f c ≤1 / 4k, upper limit frequency f of switching frequency change u =f c ;

[0078] Given the switching frequency fp , the lower limit frequency f of the switching frequency change l The value is 20f p to 0.5f u between;

[0079] In order to effectively suppress EMI noise, the switching frequency update value should satisfy the differential equation:

[0080]

[0081] Among them, A is a constant;

[0082] Combined with the determined switching frequency variation range, the periodic boundary conditions for switching frequency variation can be obtained as follows:

[0083]

[0084] That is, the design is in the first half of the change cycle (0-1 / 2f p ) Switching frequency update value f s From the lower limit frequency f l Gradually increase to the upper limit frequency f u , the second half of the change cycle (1 / 2f p -1 / f p ) is reduced to f l ;

[0085] Solving the differential equation by combining the two equations can get the switching frequency update value f s The analytical expression is:

[0086]

[0087] The switching frequency update value f determined in step S2 of this embodiment is s While changing in real time with time within the current cycle, the soft switching boundary conditions of the primary and secondary sides are met, ensuring the effectiveness of the phase shift control. At the same time, the switching frequency update value f is designed based on the consideration of suppressing EMI noise. s The time-varying expression can prevent the EMI noise from being concentrated at a fixed frequency, and has a wider spectrum distribution characteristic, which can effectively reduce the EMI noise peak. At the same time, since the actual average switching frequency is lower than the original fixed switching frequency, it can effectively reduce the switching loss of the three-level dual active bridge converter.

[0088] Step S3: Derivation of the internal phase shift duty ratio D used to describe the three-level dual active bridge converter based on the relationship between the primary and secondary side powers during forward power transmission. ps1 , external phase shift duty cycle D ps2 And the frequency update value f sThe coupling relationship between the two sides is solved under the constraints of the primary and secondary soft switching boundary conditions to obtain the internal phase shift duty cycle D of the three-level dual active bridge converter in the current switching cycle. ps1 and the external phase shift duty cycle D ps2 .

[0089] In this embodiment, the three-level dual active bridge converter operates in the forward power transmission mode. During forward power transmission, the power between the primary and secondary sides satisfies the following relationship:

[0090]

[0091] Based on the above relationship, this embodiment derives the internal phase shift duty ratio D used to describe the three-level dual active bridge converter: ps1 , external phase shift duty cycle D ps2 And the frequency update value f s The coupling relationship between them is as follows:

[0092]

[0093] By combining the above coupling relations, i.e. the expressions of the primary and secondary soft switching boundary conditions, we can solve the phase shift duty cycle that can match the switching frequency change. This solution process can also be converted into Figure 3 Find the intersection of the curve corresponding to the coupling relationship and the soft switching boundary condition. If an intersection exists, directly solve for the corresponding intersection point to determine the specific values ​​of the two phase-shift duty cycles. If no intersection exists, solve for the point on the curve corresponding to the coupling relationship that is closest to the soft switching boundary condition to determine the specific values ​​of the two phase-shift duty cycles.

[0094] In the actual solution process, we can directly use Δ=(3m 2 +2m+1)(1-4kfs)-2 is greater than or equal to 0 to determine whether the curve corresponding to the decoupling relationship and the soft switching boundary condition have an intersection; if Δ≥0, it means that there is an intersection. At this time, the intersection can be solved to obtain the inner phase shift duty cycle D ps1 and the external phase shift duty cycle D ps2 The expression is as follows:

[0095]

[0096] If Δ<0, it means that there is no intersection. At this time, the point closest to the soft switching boundary condition in the curve corresponding to the coupling relationship can be solved to obtain the inner phase shift duty cycle D ps1 and the external phase shift duty cycle D ps2 The expression is as follows:

[0097]

[0098] In step S3 of this embodiment, the inner phase shift duty ratio D is calculated by the above method. ps1 and the external phase shift duty cycle D ps2 It can match the switching frequency changes and effectively suppress the output voltage fluctuation and output power fluctuation when the switching frequency changes.

[0099] Step S4: Based on the switching frequency change value f in the current switching cycle s , internal phase shift duty cycle D ps1 and the external phase shift duty cycle D ps2 A driving signal for each switching device is generated and acts on each switching device to realize phase-shift frequency conversion control of a three-level dual active bridge converter.

[0100] Specifically, when determining the switching frequency change value f s , internal phase shift duty cycle D ps1 and the external phase shift duty cycle D ps2 After that, in each switching cycle, the s Update the switching frequency of the driving signal of each switching device, and according to D ps1 and D ps2 By controlling the phase shift relationship between the driving signals, the phase shift frequency conversion control of the converter can be realized. After the phase shift frequency conversion control, the three-level dual active bridge converter will be controlled according to the transmission power command value P ref and the output voltage command value V 2ref Output power and voltage.

[0101] It is easy to understand that when the three-level dual active bridge converter operates in the reverse power transmission mode, the internal phase shift duty cycle D used to describe the three-level dual active bridge converter is redefined based on the relationship between the primary and secondary side powers during reverse power transmission. ps1 , external phase shift duty cycle D ps2 And the frequency update value f s After the coupling relationship between the two sides is obtained, the coupling expression and the primary and secondary side soft switching boundary conditions are combined to solve the internal phase shift duty ratio D ps1 and the external phase shift duty cycle D ps2 , and generate the switching device drive signal according to the required result.

[0102] Example 2:

[0103] A three-level dual active bridge converter phase-shift frequency conversion controller, this embodiment is used to implement the three-level dual active bridge converter phase-shift frequency conversion control method provided in the above embodiment 1; Figure 4 As shown, this embodiment includes:

[0104] The pre-processing module is used to calculate the transmission power command value P of the three-level dual active bridge converter in the current switching cycle. ref , output voltage command value V2ref And the input voltage sampling value V1 to obtain the equivalent load impedance Z eq and voltage transformation ratio m;

[0105] Switching frequency update module is used to update the switching frequency according to the equivalent load impedance Z eq And voltage ratio m, as well as phase shift inductance value L, fixed switching frequency value f c Calculate the switching frequency update value f that changes with time during the current switching cycle s , so that when the primary and secondary soft switching boundary conditions are met at the same time, the actual average switching frequency is lower than the fixed switching frequency value f c ;

[0106] The phase-shift duty cycle calculation module is used to derive the internal phase-shift duty cycle D used to describe the three-level dual active bridge converter based on the relationship between the primary and secondary side powers during forward power transmission. ps1 , external phase shift duty cycle D ps2 And the frequency update value f s The coupling relationship between the two sides is solved under the constraints of the primary and secondary soft switching boundary conditions to obtain the internal phase shift duty cycle D of the three-level dual active bridge converter in the current switching cycle. ps1 and the external phase shift duty cycle D ps2 ;

[0107] And the driving signal wave module is used to change the switching frequency value f based on the current switching cycle s , internal phase shift duty cycle D ps1 and the external phase shift duty cycle D ps2 A driving signal for each switching device is generated and acts on each switching device to realize phase-shift frequency conversion control of a three-level dual active bridge converter.

[0108] In this embodiment, the switching frequency update module calculates the switching frequency update value f that changes with time in the current switching cycle. s The expression is as follows:

[0109]

[0110] Among them, f p is the frequency of the given switching frequency change, t is the time in the current switching cycle; f u 、f l They represent the upper and lower limits of the switching frequency range, and f s ∈[f l ,f u ], the soft switching boundary conditions of the primary and secondary sides are met at the same time; the upper limit frequency f of the switching frequency variation range u The expression is:

[0111]

[0112] Furthermore, the lower limit frequency f of the switching frequency variation range is l Satisfaction: 20f p ≤f l ≤0.5f u ;

[0113] in, n represents the transformation ratio of the isolation transformer in the three-level dual active bridge converter.

[0114] In this embodiment, the phase-shift duty cycle calculation module obtains the internal phase-shift duty cycle D of the three-level dual active bridge converter. ps1 , external phase shift duty cycle D ps2 And the frequency update value f s The coupling relationship between them is as follows:

[0115]

[0116] Furthermore, the internal phase shift duty ratio D obtained by the phase shift duty ratio calculation module is ps1 and the external phase shift duty cycle D ps2 The expression is as follows:

[0117] If Δ=(3m 2 +2m+1)(1-4kfs)-2 is greater than or equal to 0, then:

[0118]

[0119] If Δ=(3m 2 +2m+1)(1-4kfs)-2 is less than 0, then:

[0120]

[0121] In this embodiment, the specific implementation of each module can refer to the description in the above embodiment 1 and will not be repeated here.

[0122] Example 3:

[0123] A three-level dual-active bridge converter system includes: a three-level dual-active bridge converter and the three-level dual-active bridge converter phase-shift frequency conversion controller provided in the second embodiment.

[0124] The following takes a specific phase-shift frequency conversion control example as an example to further analyze and verify the beneficial effects that can be achieved by the present invention.

[0125] In the corresponding control example, the working conditions are that the primary DC bus voltage V1 is 250V and the output voltage command value V 2refSet to 220V, transmission power command value P ref Set to 807W, fixed switching frequency f c The frequency is 20kHz, the phase-shift inductor L is 0.4mH, and the transformer ratio is 1:1. Simulation experiments are conducted on the three-level dual active bridge converter operating under the traditional control method and the phase-shift frequency conversion control method proposed in the present invention.

[0126] Figure 5 The switching frequency update value f is changed by the phase shift frequency conversion control method provided by the present invention. s Compared with the traditional fixed switching frequency f c Compared with the fixed switching frequency, the switching frequency controlled by the phase-shifted frequency conversion control method varies between 10-20kHz, and the average switching frequency is reduced by about 25%, thereby reducing the switching loss of the three-level dual active bridge converter.

[0127] Figure 6 Shown is the matching f s Variation of D ps1 and D ps2 The phase-shift frequency conversion control method of the present invention follows f s Changes in the duty cycle of the phase shift are controlled in real time. Figure 7 The figure shows a comparison of the output voltage and output power of the phase-shift frequency conversion control method provided by the present invention and the traditional single phase-shift modulation method under the change of switching frequency. It can be seen that the phase-shift frequency conversion control method has more stable output voltage and output power.

[0128] Figure 8 The figure shows a comparison of conducted EMI noise. It can be seen from the comparison that when the switching frequency is fixed, the EMI spikes will generate spikes at multiples of the fixed switching frequency. After adopting the phase-shifted frequency conversion control method provided by the present invention, the EMI is smoothed and attenuated, effectively suppressing the peak of the EMI noise.

[0129] In general, the present invention is based on a method for real-time control of switching frequency changes and synchronous matching of phase-shift duty cycles. It can effectively suppress EMI noise peaks and reduce switching losses of the three-level dual-active bridge converter without adding additional hardware, while effectively suppressing output voltage and output power fluctuations when the switching frequency changes.

[0130] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements 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 three-level dual active bridge converter phase-shift frequency conversion control method, characterized in that: include: Step S1: According to the transmission power command value P of the three-level dual active bridge converter in the current switching cycle ref , output voltage command value V ref And the input voltage sampling value V obtains the equivalent load impedance Z eq and voltage transformation ratio m; Step S2: According to the equivalent load impedance Z eq And voltage ratio m, as well as phase shift inductance value L, fixed switching frequency value f c Calculate the switching frequency update value f that changes with time during the current switching cycle s , so that when the primary and secondary soft switching boundary conditions are met at the same time, the actual average switching frequency is lower than the fixed switching frequency value f c ; Step S3: Derivation of the internal phase shift duty ratio D used to describe the three-level dual active bridge converter based on the relationship between the primary and secondary side powers during power transmission ps1 , external phase shift duty cycle D ps2 And the frequency update value f s The coupling relationship between the two sides is solved under the constraints of the primary and secondary side soft switching boundary conditions to obtain the internal phase shift duty ratio D of the three-level dual active bridge converter in the current switching cycle. ps1 and the external phase shift duty cycle D ps2 ; Step S4: Based on the switching frequency change value f in the current switching cycle s , internal phase shift duty cycle D ps1 and the external phase shift duty cycle D ps2 A driving signal for each switching device is generated and acts on each switching device to achieve phase-shift frequency conversion control of the three-level dual active bridge converter.

2. The phase-shift frequency conversion control method for a three-level dual active bridge converter according to claim 1, wherein: In step S2, the switching frequency update value f that changes with time in the current switching cycle s The expression is as follows: Among them, f p is the frequency of the given switching frequency change, t is the time in the current switching cycle; f u 、f l They represent the upper and lower limits of the switching frequency range, and f s ∈[f l ,f u ], the soft switching boundary conditions of the primary and secondary sides are met at the same time.

3. The phase-shift frequency conversion control method for a three-level dual active bridge converter according to claim 2, wherein: The upper limit frequency f of the switching frequency variation range u The expression is: Furthermore, the lower limit frequency f of the switching frequency variation range is l Satisfaction: 20f p ≤f l ≤0.5f u ; in, n represents the transformation ratio of the isolation transformer in the three-level dual active bridge converter.

4. The phase-shift frequency conversion control method for a three-level dual active bridge converter according to claim 3, wherein: When performing forward power transmission, in step S3, the coupling relationship is as follows: Furthermore, the inner phase shift duty ratio D obtained by step S3 is ps1 and the external phase shift duty cycle D ps2 The expression is as follows: If Δ=(3m 2 +2m+1)(1-4kfs)-2 is greater than or equal to 0, then: If Δ=(3m 2 +2m+1)(1-4kfs)-2 is less than 0, then:

5. A three-level dual active bridge converter phase-shift frequency controller, characterized in that: include: The pre-processing module is used to calculate the transmission power command value P of the three-level dual active bridge converter in the current switching cycle. ref , output voltage command value V ref And the input voltage sampling value V obtains the equivalent load impedance Z eq and voltage transformation ratio m; The switching frequency updating module is used to update the equivalent load impedance Z eq And voltage ratio m, as well as phase shift inductance value L, fixed switching frequency value f c Calculate the switching frequency update value f that changes with time during the current switching cycle s , so that when the primary and secondary soft switching boundary conditions are met at the same time, the actual average switching frequency is lower than the fixed switching frequency value f c ; The phase shift duty cycle calculation module is used to derive the internal phase shift duty cycle D used to describe the three-level dual active bridge converter based on the relationship between the primary and secondary side powers during power transmission. ps1 , external phase shift duty cycle D ps2 And the frequency update value f s The coupling relationship between the two sides is solved under the constraints of the primary and secondary side soft switching boundary conditions to obtain the internal phase shift duty ratio D of the three-level dual active bridge converter in the current switching cycle. ps1 and the external phase shift duty cycle D ps2 ; And the driving signal wave module is used to change the switching frequency value f based on the current switching cycle s , internal phase shift duty cycle D ps1 and the external phase shift duty cycle D ps2 A driving signal for each switching device is generated and acts on each switching device to achieve phase-shift frequency conversion control of the three-level dual active bridge converter.

6. The three-level dual active bridge converter phase-shift frequency controller according to claim 5, characterized in that: The updated switching frequency value f that changes with time during the current switching cycle s The expression is as follows: Among them, f p is the frequency of the given switching frequency change, t is the time in the current switching cycle; f u 、f l They represent the upper and lower limits of the switching frequency range, and f s ∈[f l ,f u ], the soft switching boundary conditions of the primary and secondary sides are met at the same time.

7. The three-level dual active bridge converter phase-shift frequency controller according to claim 6, characterized in that: The upper limit frequency f of the switching frequency variation range u The expression is: Furthermore, the lower limit frequency f of the switching frequency variation range is l Satisfaction: 20f p ≤f l ≤0.5f u ; in, n represents the transformation ratio of the isolation transformer in the three-level dual active bridge converter.

8. The three-level dual active bridge converter phase-shift frequency controller according to claim 7, characterized in that: When forward power transmission is performed, the coupling relationship is as follows: Furthermore, the inner phase shift duty ratio D obtained by the phase shift duty ratio calculation module is ps1 and the external phase shift duty cycle D ps2 The expression is as follows: If Δ=(3m 2 +2m+1)(1-4kfs)-2 is greater than or equal to 0, then: If Δ=(3m 2 +2m+1)(1-4kfs)-2 is less than 0, then:

9. A three-level dual active bridge converter system, characterized in that: include: A three-level dual active bridge converter, and a three-level dual active bridge converter phase-shift frequency controller according to any one of claims 5 to 8.

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