Dual active bridge converter device with even number of modules, zero common mode modulation method, device and system

Abstract

The invention discloses a dual-active-bridge converter device with even modules and a zero common-mode modulation method, device and system, and belongs to the technical field of common-mode interference rejection, the device comprises 2N dual-active-bridge converters, and a primary side dual-active bridge in each dual-active-bridge converter is connected with an isolation transformer through a symmetrical coupling phase-shifting inductor; the zero common mode modulation method comprises the following steps: equally dividing the dual-active converter into N groups, for each group, under the condition that the output power requirement is met, controlling switch driving signals of bridge arms A1 and A2 to be complementary, and controlling the internal shift ratio between A1 and B1 to be equal to the internal shift ratio between A2 and B2; and under the condition that the switch driving signals of the C1 and the D1 are complementary and the switch driving signals of the C2 and the D2 are complementary, the external shift ratio between the A1 and the C1 and the external shift ratio between the A2 and the C2 are adjusted, so that the power of the two converters is equal. According to the invention, the problem of common-mode interference suppression of a multi-module dual-active bridge converter device can be effectively solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of common mode interference suppression, and more specifically, relates to a dual active bridge converter device of an even-numbered module, a zero common mode modulation method, a device and a system. Background Art

[0002] The dual active bridge converter is widely used in energy storage systems, DC microgrids, electric vehicles and many other fields due to its high efficiency, high power density, electrical isolation, bidirectional energy transmission, and easy zero voltage switching. The dual active bridge converter has modular characteristics. According to different application scenarios, different series-parallel forms are adopted: the series input and series output system is suitable for occasions with high input voltage and output voltage; the series input and parallel output system is suitable for occasions with high input voltage and low output voltage; the parallel input and parallel output system is suitable for occasions with low output voltage and large current; the parallel input and series output system is suitable for occasions with low input voltage and high output voltage. By rationally designing the series-parallel form of the dual active bridge converter, the device stress can be effectively reduced, the electrothermal design can be simplified, and the system reliability can be improved.

[0003] However, with the improvement of power density and efficiency, the electromagnetic interference problem of dual active bridge converters has become more serious. On the one hand, with the development of wide bandgap semiconductors, silicon carbide devices have gradually replaced silicon devices, and the switching frequency has become higher and higher, resulting in the deterioration of the noise source of electromagnetic interference. On the other hand, the dual active bridge converter uses a high-frequency transformer to achieve electrical isolation. The compact winding structure of the high-frequency transformer leads to large parasitic capacitance between the windings, which deteriorates the interference conduction path and produces serious common-mode interference. Common-mode interference will propagate along the cable and deteriorate system reliability.

[0004] In order to improve electromagnetic compatibility and meet relevant standards (such as DO160 or MIL-STD-461G), the common-mode interference of the dual active bridge converter must be suppressed. The common-mode interference suppression methods are mainly divided into interference path optimization and interference source optimization. Interference path optimization is divided into three categories: electromagnetic interference filter, shielding, and leakage current path optimization. Passive filter is the most widely used technology in practical applications. However, passive filter is large in size and heavy in weight, which reduces the power density of the whole system; active filter uses integrated amplifier circuit to sample interference signal for active compensation, which can effectively improve power density, but its high-frequency suppression effect is not good. Shielding is a common technology to reduce transformer common-mode interference, but shielding will inevitably increase transformer loss and cost. In addition, common-mode interference can also be improved by optimizing the topology. Zero common mode can be achieved by coupling symmetrical inductors, but this method is only applicable to single phase shift modulation, which limits the modulation freedom. Interference source optimization is mainly divided into spread spectrum modulation and pulse cancellation modulation. Spread spectrum modulation disperses narrowband harmonic energy into a wider spectrum range by periodically adjusting the switching frequency, thereby reducing electromagnetic interference spikes. However, power fluctuations caused by switching frequency changes make the control algorithm more complicated. Pulse cancellation achieves common-mode voltage cancellation by optimizing the switching pulse timing. However, pulse cancellation places higher requirements on circuit topology and is only applicable to multi-module systems. In addition, pulse cancellation requires the switching signals of the corresponding bridge arms to be complementary, which leads to power coupling between different modules, making power balance difficult to achieve. Power imbalance will cause overvoltage and overcurrent in some periods, affecting the safe and stable operation of the system. Summary of the invention

[0005] In view of the defects and improvement needs of the prior art, the present invention provides a dual active bridge converter device of an even-numbered module, a zero common-mode modulation method, device and system, the purpose of which is to effectively solve the common-mode interference suppression problem of a multi-module dual active bridge converter device.

[0006] To achieve the above object, according to one aspect of the present invention, there is provided a dual active bridge converter device of an even number of modules, comprising: 2N dual active bridge converters;

[0007] In the dual active bridge converter, a symmetrically coupled phase-shifting inductor is arranged between the primary dual active bridge and the isolation transformer;

[0008] The symmetrical coupled phase-shift inductor includes two inductors, which are respectively arranged between the midpoints of the two bridge arms of the primary dual active bridge and the isolation transformer; the winding ends of the two inductors are opposite, the self-inductance of the two inductors is equal, and the series equivalent inductance is L ph ;

[0009] Where N is a positive integer, L ph It is the preset primary and secondary side phase shift inductance value.

[0010] According to another aspect of the present invention, there is provided a zero common mode modulation method of the dual active bridge converter device of the even-numbered modules, comprising:

[0011] 2N dual active bridge converters in the dual active bridge converter device of the even-numbered modules are evenly divided into N groups of converters; in each group of converters, two dual active bridge converters are respectively recorded as a first converter and a second converter, two bridge arms of the primary side of the first converter are respectively recorded as A1 and B1, and two bridge arms of the secondary side are respectively recorded as C1 and D1, and two bridge arms of the primary side of the second converter are respectively recorded as A2 and B2, and two bridge arms of the secondary side are respectively recorded as C2 and D2;

[0012] For each group of converters, respectively performing power balanced zero common mode modulation to achieve zero common mode modulation of a dual active bridge converter device of an even number of modules;

[0013] Power-balanced zero common-mode modulation includes:

[0014] Under the condition that the output power requirement is met, the switch drive signals of bridge arms A1 and A2 are controlled to be complementary, and the internal shift ratio D between bridge arms A1 and B1 is controlled. 1_1 Compared with the inward movement between bridge arms A2 and B2, D 1_2 equal; when the switch drive signals of bridge arms C1 and D1 are complementary, and the switch drive signals of bridge arms C2 and D2 are complementary, the outward shift ratio D between bridge arms A1 and C1 is adjusted. 0_1 Compared with the outward shift between bridge arms A2 and C2, D 0_2 , so that the power of the first converter and the second converter are equal.

[0015] Furthermore, the inward shift is compared to D 1_1 and D 1_2 , and outward displacement compared to D 0_1 and D 0_2 Methods of determination include:

[0016] Determine the output power per unit value P * , and calculate the voltage conversion ratio k;

[0017] Find P from the pre-established optimal phase shift lookup table * , k corresponding to the outer phase shift ratio D0 and the inner phase shift ratio D1; the optimal phase shift lookup table records all the inner phase shift ratio and outer phase shift ratio combinations that can meet the preset conditions under each output power per unit value and voltage conversion ratio combination; the preset conditions include: the size relationship between the output power per unit value and the inner phase shift ratio and the outer phase shift ratio, the soft switching boundary conditions, and the setting of the inner phase shift ratio D1 can suppress the DC side ripple;

[0018] Compare the inward shift to D 1_1 and D 1_2 All are assigned the value of D1;

[0019] Determine the control error ΔD0 of the external shift phase and obtain the output power per unit value P * The sign of the partial derivative relative to the current outward shift of the first converter, and the output power per unit value P * The signs of the partial derivatives relative to the current outward shift of the second transformer are recorded as the first sign and the second sign respectively;

[0020] Assign the first sign to ΔD0 to get ΔD0', and compare the outward shift to D 0_1 Assign a value of D0-ΔD0'; assign a second sign to ΔD0 to get ΔD0", compare the outward shift to D 0_2 Assign value to D0+ΔD0".

[0021] Furthermore, the optimal phase shift lookup table is established in the following manner:

[0022] Select the output power per unit value P in the range of (0,1) * , and select the voltage conversion ratio k in the range of (0,1.5) to obtain multiple operating points; each operating point corresponds to a combination of output power per unit value and voltage conversion ratio;

[0023] For each working point (P * ,k), solve the output power per unit value P * Compared with the size relationship between the inner shift and the outer shift, D1 and D0, the working point (P * ,k) The corresponding shift ratio set U1;

[0024] From the working point (P * , k) The corresponding shift phase set U1 is selected to select the inner shift phase and outer shift phase combinations that meet the soft switching boundary conditions, and the working point (P * ,k) The corresponding shift ratio set U2;

[0025] From the working point (P * , k) from the corresponding shift ratio set U2, select the inner shift ratio and outer shift ratio combination that satisfies D1 = l / m, and get the working point (P * ,k) corresponds to the optimal shift ratio set;

[0026] The optimal phase shift ratio set corresponding to each working point is recorded in the optimal phase shift ratio lookup table to complete the establishment of the optimal phase shift ratio lookup table;

[0027] Wherein, l is a positive odd number, and m is a multiple or order of the target harmonic frequency relative to the switching frequency.

[0028] Furthermore, before recording the optimal shift ratio set corresponding to each working point into the optimal shift ratio lookup table, the method further includes:

[0029] For each working point, determine the inner shift ratio and outer shift ratio combination with the smallest inner shift ratio value in the corresponding optimal shift ratio set, and delete the remaining inner shift ratio and outer shift ratio combinations from the optimal shift ratio set.

[0030] Further, determine the output power per unit value P * ,include:

[0031] The output voltage command value U o * The output voltage U of the first converter or the second converter o After making the difference, PI control is performed to obtain the output power per unit value P * .

[0032] Further, determining the control error ΔD0 of the outward phase shift includes:

[0033] If the input of the first converter is connected in series with the input of the second converter, the input voltage command value U i_ave The first converter input voltage U i1 After making the difference, PI control is performed to obtain the control error ΔD0 compared with the outward shift.

[0034] If the inputs of the first converter and the outputs of the second converter are connected in parallel, the average input current I i_ave The input current I i1 After making the difference, PI control is performed to obtain the control error ΔD0 of the external shift phase, or the output current average value I o_ave The output current I of the first converter o1 After making the difference, PI control is performed to obtain the control error ΔD0 compared with the outward shift.

[0035] If the inputs of the first converter and the second converter are connected in parallel and their outputs are connected in series, the average input current I i_ave The input current I i1 After making the difference, PI control is performed to obtain the control error ΔD0 of the external shift, or the output voltage average value U o_ave The output voltage U of the first converter o1 After making the difference, PI control is performed to obtain the control error ΔD0 of the outward shift phase.

[0036] According to another aspect of the present invention, there is provided a zero common mode modulation device of the above-mentioned dual active bridge converter device of even modules, comprising: a control module and N modulation modules;

[0037] A control module, used for evenly dividing 2N dual active bridge converters in the dual active bridge converter device of the even-numbered modules into N groups of converters; in each group of converters, two dual active bridge converters are respectively recorded as a first converter and a second converter, two bridge arms of the primary side of the first converter are respectively recorded as A1 and B1, and two bridge arms of the secondary side are respectively recorded as C1 and D1, and two bridge arms of the primary side of the second converter are respectively recorded as A2 and B2, and two bridge arms of the secondary side are respectively recorded as C2 and D2;

[0038] N modulation modules are respectively used to perform power-balanced zero common mode modulation on N groups of converters, so as to realize zero common mode modulation of a dual active bridge converter device of an even number of modules;

[0039] The modulation module includes:

[0040] The first control loop is used to determine the output power per unit value P * , and calculate the voltage conversion ratio k;

[0041] A table lookup unit, whose input terminal is connected to the output terminal of the first control loop, is used to look up P from a pre-established optimal phase shift lookup table. * , k corresponding to the outer phase shift D0 and the inner phase shift D1; the optimal phase shift lookup table records all the inner phase shift and outer phase shift combinations that can meet the preset conditions under each output power per unit value and voltage conversion ratio combination; the preset conditions include: the size relationship between the output power per unit value and the inner phase shift and outer phase shift, the soft switching boundary conditions, and the ability to suppress DC side ripple;

[0042] The second control loop is used to determine the control error ΔD0 of the outward shift phase and obtain the output power per unit value P * The sign of the partial derivative relative to the current outward shift of the first converter, and the output power per unit value P * The signs of the partial derivatives relative to the current outward shift of the second transformer are recorded as the first sign and the second sign respectively;

[0043] and a shift ratio determination unit, whose first input terminal is connected to the output terminal of the table lookup unit, and whose second input terminal is connected to the output terminal of the second control loop, and which is used to perform the following operations:

[0044] Compare the inward shift between bridge arms A1 and B1 to D 1_1 Compared with the inward shift between bridge arms A2 and B2, D 1_2 All are assigned the value of D1;

[0045] Assign the first sign to ΔD0 to get ΔD0', and compare the outward displacement between bridge arms A1 and C1 to D 0_1 Assign the value to D0-ΔD0';

[0046] Assign the second sign to ΔD0, and get ΔD0", and compare the outward displacement between bridge arms A2 and C2 to D 0_2 Assign value to D0+ΔD0".

[0047] According to another aspect of the present invention, there is provided a dual active bridge converter system of an even number of modules, comprising: the dual active bridge converter device of the even number of modules provided by the present invention, the zero common mode modulation device provided by the present invention, and a driver;

[0048] The driver is used to generate a switch driving signal for each converter according to the inner shift phase ratio and the outer shift phase ratio determined by the zero common mode modulation device, and apply the switch driving signal to the corresponding converter.

[0049] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0050] (1) The dual active bridge converter device of the even-numbered modules provided by the present invention, wherein the primary full bridge in each dual active bridge converter is connected between a symmetrically coupled phase-shifting inductor and an isolation transformer, and the two inductor windings in the symmetrically coupled phase-shifting inductor are respectively arranged between the midpoints of the two bridge arms of the primary dual active bridge and the isolation transformer, and the winding self-inductance of the two inductors is equal and the series equivalent inductance is L ph , so that the inductance value of the coupled phase-shift inductor is equal to the preset phase-shift inductance value, and does not affect the power output; and because the same-name ends of the windings of the two inductors are opposite, the equivalent voltage sources of the two inductor windings are complementary, and for the common-mode loop, the common-mode excitations generated by the two inductor windings cancel each other out, so that the excitation of the inductor to the common-mode voltage is eliminated, effectively reducing the common-mode interference of the dual-active bridge converter. At the same time, the number of dual-active bridge converters in the present invention is an even number, and modulation can be performed by grouping two by two, so as to achieve zero common-mode modulation while ensuring power balance.

[0051] (2) The zero common mode modulation method provided by the present invention divides the dual active bridge converters in the dual active bridge converter device of the even number of modules into a group of two. For each group of converters, under the condition of meeting the output power requirement, the switch drive signals of the bridge arms A1 and A2 are controlled to be complementary, and the internal shift ratio D between the bridge arms A1 and B1 is controlled to be 1_1 Compared with the inward shift between bridge arms A2 and B2, D 1_2 The switch drive signals of bridge arms C1 and D1 are controlled to be complementary, and the switch drive signals of bridge arms C2 and D2 are controlled to be complementary, so that both converters in the group can achieve zero common mode modulation. On this basis, the external shift ratio D between bridge arms A1 and C1 is adjusted. 0_1 Compared with the outward shift between bridge arms A2 and C2, D 0_2 , making the power of the first converter and the second converter equal, thereby achieving power balance while realizing zero common mode modulation.

[0052] (3) In the preferred embodiment of the zero common mode modulation method provided by the present invention, a method for recording each working point, i.e., an inner shift ratio and an outer shift ratio combination corresponding to the output power per unit value and the voltage conversion ratio combination, is pre-established. These inner shift ratio and outer shift ratio combinations simultaneously satisfy the magnitude relationship between the output power per unit value and the inner shift ratio and the outer shift ratio, and the soft switching boundary condition. The setting of the inner shift ratio D1 can suppress the DC side ripple. In the actual modulation process, the output power per unit value P is determined. * After calculating the voltage conversion ratio k, the optimal combination of inner shift phase ratio and outer shift phase ratio is determined by table lookup, and based on this, the inner shift phase ratio and outer shift phase ratio of each converter in the group are determined, thereby achieving power balance while realizing zero common mode modulation and effectively suppressing DC side ripple.

[0053] (4) In the preferred embodiment of the zero common mode modulation method provided by the present invention, when establishing the optimal phase shift lookup table, only the inner phase shift ratio and the outer phase shift ratio combination with the most obvious DC side ripple suppression effect are retained, thereby suppressing the DC side ripple to the greatest extent during the phase shift modulation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 is a schematic diagram of the existing dual active bridge converter topology;

[0055] Figure 2 A schematic diagram of a topology of a dual active bridge converter provided in an embodiment of the present invention;

[0056] Figure 3 It is a schematic diagram of the extended phase shift modulation of the existing dual active bridge converter;

[0057] Figure 4 A schematic diagram of cooperative modulation of a group of converters formed by two dual active bridge converters according to an embodiment of the present invention;

[0058] Figure 5 A schematic diagram of a zero common mode modulation method and device provided in this embodiment;

[0059] Figure 6 A topological schematic diagram of a dual active bridge converter provided by the present invention. DETAILED DESCRIPTION

[0060] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain 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 can be combined with each other as long as they do not conflict with each other.

[0061] In the present invention, the terms "first", "second", etc. (if any) in the present invention and the accompanying drawings are used to distinguish similar objects but not necessarily to describe a specific order or sequence.

[0062] Before introducing the technical solution of the present invention in detail, the topological structure of the dual active bridge converter is briefly described first. Figure 1 The figure shows a traditional dual active bridge converter, which consists of two full bridges connected by a single-sided phase-shifting inductor Lph and a high-frequency isolation transformer T. Each full bridge includes two bridge arms, a total of four bridge arms, which are respectively recorded as bridge arm A, bridge arm B, bridge arm C and bridge arm D. The transformation ratio of the secondary voltage to the primary voltage of the transformer is n = N s / N p Each bridge arm contains two switch tubes. The driving signals of the upper and lower switch tubes of bridge arm A are respectively denoted as S A1 , S A2 The driving signals of the upper and lower switch tubes of bridge arm B are respectively denoted as S B1 and S B2 , and so on. i and U o They represent the DC bus voltage on the primary and secondary sides respectively, that is, the input voltage and the output voltage.

[0063] However, with the improvement of power density and efficiency, the electromagnetic interference problem of dual active bridge converters has become more serious. On the one hand, with the development of wide bandgap semiconductors, silicon carbide devices have gradually replaced silicon devices, and the switching frequency has become higher and higher, resulting in the deterioration of the noise source of electromagnetic interference. On the other hand, the dual active bridge converter uses a high-frequency transformer to achieve electrical isolation. The compact winding structure of the high-frequency transformer leads to large parasitic capacitance between the windings, which deteriorates the interference conduction path and produces serious common-mode interference. Common-mode interference will propagate along the cable and deteriorate system reliability.

[0064] The conventional dual active bridge converter is only provided with a single-side phase-shift inductor, which will generate excitation to the common-mode voltage and further deteriorate the common-mode interference of the dual active bridge converter.

[0065] In view of the above problems, the present invention improves the topological structure of the dual active bridge converter, adopts symmetrical coupled inductors instead of conventional unilateral asymmetrical phase-shifting inductors, eliminates the excitation of the inductors on the common-mode voltage without affecting the power transmission of the dual active bridge converter, and improves the zero common-mode interference of the dual active bridge converter.

[0066] Multiple modules can effectively reduce the electrical stress of the device, simplify the electrical design and heat dissipation design, improve reliability, and can be flexibly applied to various occasions by adopting different series and parallel forms, including DC power grids, multi-electric aircraft, rail transportation, etc. In view of the problem that the multi-module dual active bridge converter device achieves common mode voltage cancellation through pulse cancellation, it will cause the problem that it is difficult to achieve power balance between different modules. In the device provided by the present invention, the number of dual active bridge converters is an even number, and modulation can be performed by grouping two by two to achieve zero common mode modulation while ensuring power balance.

[0067] On the basis of the above topology optimization, the present invention further optimizes the phase shift modulation of the dual active bridge converter, and retains the ability of power balance control while achieving zero common mode modulation. On this basis, the present invention further optimizes the phase shift ratio to further achieve the effect of suppressing DC side ripple.

[0068] The following are examples.

[0069] Embodiment 1:

[0070] A dual active bridge converter device of an even number of modules, comprising: 2N dual active bridge converters;

[0071] like Figure 2 As shown, in this embodiment, a symmetrically coupled phase-shifting inductor is provided between the primary dual active bridge and the isolation transformer in the dual active bridge converter;

[0072] The symmetrical coupled phase-shift inductor includes two inductors, which are respectively arranged between the midpoints of the two bridge arms of the primary dual active bridge and the isolation transformer; the winding ends of the two inductors are opposite, the self-inductance of the two inductors is equal, and the series equivalent inductance of the two inductors is equal to L ph ;

[0073] Among them, L ph is the preset primary and secondary side phase shift inductance value; N is a positive integer and in practical applications, it can be set accordingly according to the actual application occasion.

[0074] In this embodiment, the unilateral asymmetric phase-shift inductor in the traditional dual-active bridge converter is replaced by a symmetrical coupled phase-shift inductor, which includes two inductors, which are respectively arranged between the midpoints of the two bridge arms of the primary dual-active bridge and the isolation transformer; the winding ends of the two inductors are opposite, the winding self-inductances of the two inductors are equal, and the series equivalent inductance of the two inductors is equal to L phTherefore, the inductance value of the symmetrically coupled phase-shift inductor is the same as the inductance value of the unilateral asymmetrical phase-shift inductor, which does not affect the power transmission of the dual active bridge converter. At the same time, the equivalent voltage sources of the two inductor windings are complementary. For the common-mode loop, the common-mode excitations generated by the two inductor windings cancel each other out, so that the excitation of the inductor on the common-mode voltage is eliminated, effectively reducing the common-mode interference of the dual active bridge converter.

[0075] The even number (2N) dual active bridge converters in this embodiment can adopt different series-parallel forms according to different application scenarios. Since the common-mode interference of each dual active bridge converter is improved, the zero common-mode interference of the entire device is also improved.

[0076] Embodiment 2:

[0077] A zero common mode modulation method is used to implement zero common mode modulation of the dual active bridge converter device of the even-numbered modules provided in the above-mentioned embodiment 1.

[0078] According to the traditional phase-shift modulation method of the dual-active bridge converter, for the two bridge arms A and B included in the primary dual-active bridge and the two bridge arms C and D included in the secondary dual-active bridge, the switch drive signal of each bridge arm is a pulse signal with a 50% duty cycle. The switch drive signal of bridge arm A is used as the reference signal. The phase shift between the switch drive signals of bridge arms A and B is defined as the inner phase shift D1, and the phase shift between the switch drive signals of bridge arms A and C is defined as the outer phase shift D0. The drive signals of bridge arms D and C are complementary. Based on the different relationship between the inner phase shift D1 and the outer phase shift D0, the dual-active bridge converter has two working modes. In the two working modes, the drive signal S of the upper switch tube of bridge arms A, B, C, and D is A1 , S B1 , S C1 and S D1 , the voltage between the midpoints of bridge arms A and B is V AB , the voltage between the midpoints of bridge arms C and D is V CD , and the inductor current I L like Figure 3 shown.

[0079] Through such a phase-shift modulation method, zero common-mode modulation of a single dual-active bridge converter can be achieved. However, for a topology including multiple dual-active bridge converters, since the phase-shift modulation method requires the switching signals of the corresponding bridge arms to be complementary, this will lead to power coupling between different modules, making power balance difficult to achieve.

[0080] This embodiment aims to achieve zero common mode modulation while retaining the control capability of power balancing. This embodiment is proposed based on the following findings:

[0081] For a topology consisting of two dual-active converters, the two bridge arms of the primary side in one of the converters are respectively denoted as A1 and B1, and the two bridge arms of the secondary side are respectively denoted as C1 and D1. The two bridge arms of the primary side in the other converter are respectively denoted as A2 and B2, and the two bridge arms of the secondary side are respectively denoted as C2 and D2. When the switch drive signal and the shift ratio inside a single dual-active bridge meet the above requirements, the switch drive signals of the control bridge arms A1 and A2 are complementary, and the internal shift ratio D between the bridge arms A1 and B1 is 1_1 Compared with the outward shift between bridge arms A2 and B2, D 1_2 Equal to achieve common mode voltage cancellation, such as Figure 4 As shown, where S A1_1 and S A1_2 They represent the driving signals of the upper switch tubes of bridge arms A1 and A2, respectively. B1_1 and S B1_2 They represent the driving signals of the upper switch tubes of bridge arms B1 and B2, respectively. C1_1 and S C1_2 Respectively represent the driving signals of the upper switch tubes of bridge arms C1 and C2, S D1_1 and S D1_2 Respectively represent the driving signals of the upper switch tubes of bridge arms D1 and D2, T hs Represents half of the switching period, T hs =1 / 2 / f s (f s Indicates the switching frequency). At this time, by adjusting the external shift phase D between the shift phase bridge arms A1 and C1, 0_1 Compared with the outward shift between bridge arms A2 and C2, D 0_2 The power of the two converters can still be adjusted freely, retaining the ability of power balance control.

[0082] Based on the above findings, the zero common mode modulation method provided in this embodiment specifically includes:

[0083] 2N dual active bridge converters in the dual active bridge converter device of the even-numbered modules are evenly divided into N groups of converters; in each group of converters, two dual active bridge converters are respectively recorded as a first converter and a second converter, two bridge arms of the primary side of the first converter are respectively recorded as A1 and B1, and two bridge arms of the secondary side are respectively recorded as C1 and D1, and two bridge arms of the primary side of the second converter are respectively recorded as A2 and B2, and two bridge arms of the secondary side are respectively recorded as C2 and D2;

[0084] For each group of converters, power-balanced zero common-mode modulation is performed respectively to achieve zero common-mode modulation of the dual active bridge converter of the even-numbered modules;

[0085] Power-balanced zero common-mode modulation includes:

[0086] When the output power requirement is met, the switching drive signals of bridge arms A1 and A2 are complementary, and the internal shift between bridge arms A1 and B1 is controlled to be equal to D 1_1 compared with the internal shift between bridge arms A2 and B2 1_2 equal; when the switching drive signals of bridge arms C1 and D1 are complementary and the switching drive signals of bridge arms C2 and D2 are complementary, the external shift between bridge arms A1 and C1 is adjusted compared with D 0_1 and the external shift between bridge arms A2 and C2 compared with D 0_2 to make the power of the first converter and the second converter equal.

[0087] In this embodiment, through the above modulation method, the dual-active converters in the device are divided into groups of two. For each group of converters, the zero-common-mode modulation for power balance is performed respectively, so as to achieve the zero-common-mode modulation of each converter and make the power of the converters within the known group equal. Thus, while achieving zero-common-mode modulation, it can ensure that the power of each converter in the dual-active bridge converter device of the entire even module is equal.

[0088] For each dual-active bridge converter, according to the different relationships between the internal shift ratio D1 and the external shift ratio D0, the dual-active bridge converter has two operating modes. When D1 < D0, it is denoted as mode 1; when D0 ≤ D1 ≤ 2D0, it is denoted as mode 2. In the two operating modes, the per-unit value of the output power P * and the internal shift ratio D1, the external shift ratio D2 satisfy:

[0089]

[0090] The soft-switching boundary conditions in the two operating modes are as follows:

[0091] Mode 1:

[0092]

[0093] Mode 2:

[0094]

[0095] Among them, f s represents the switching frequency; k represents the voltage conversion ratio, that is, the ratio of the output voltage to the input voltage. By calculating through the input voltage command, the influence of input voltage fluctuation on control can be reduced, and its calculation expression is:

[0096]

[0097] It is easy to understand that when performing the above-mentioned power balanced zero common mode modulation, the above-mentioned conditions must be met simultaneously. Usually, there are often multiple combinations of the inner shift phase ratio D1 and the outer shift phase ratio D2 that meet the above-mentioned conditions at the same time. The DC side ripple suppression can be further achieved by optimizing the inner shift phase ratio D1. Specifically, setting D1 = l / m can suppress the DC side ripple, where m is the multiple or order of the target harmonic frequency relative to the switching frequency, which can be obtained through modeling or measurement in practical applications, and its value is an odd number; l is an odd number, that is, l = 1, 3, 5, 7….

[0098] In order to further suppress the DC side ripple and optimize the performance of the dual active bridge converter on the basis of achieving zero common mode modulation and power balance, as a preferred implementation, this embodiment further optimizes the setting of the inner shift ratio and the outer shift ratio. Specifically, this embodiment takes the above-mentioned output power per unit value and the size relationship between the inner shift ratio and the outer shift ratio, the soft switching boundary condition, and the setting of the inner shift ratio D1 to suppress the DC side ripple as the preset conditions, and pre-establishes an optimal shift ratio lookup table for recording all the inner shift ratio and outer shift ratio combinations that can meet the preset conditions under each output power per unit value and voltage conversion ratio combination; so that in actual applications, after determining the output power per unit value and the voltage conversion ratio, the corresponding optimal inner shift ratio and outer shift ratio combination can be found from the optimal shift ratio lookup table, and based on the search result, adjustments can be made between the converters in the group to achieve power balance.

[0099] Output power per unit value P * is the output power and the power reference value P N The ratio, P N It is expressed as:

[0100]

[0101] In this embodiment, the method for establishing the optimal phase shift lookup table includes:

[0102] Considering the output power per unit value P * It usually does not exceed 1, and the voltage conversion ratio k usually does not exceed 1.5. Therefore, the output power per unit value P is selected in the range of (0,1) with a step size of 0.1. * , and select the voltage conversion ratio k in the range of (0,1.5) with a step size of 0.1, and set the selected output power per unit value P * Combined with the voltage conversion ratio k, multiple operating points are obtained; in practical applications, the step size of the selected operating point can be flexibly adjusted. If a more specific output power per unit value and voltage conversion ratio range can be determined, the relevant range can be adjusted accordingly;

[0103] For each working point (P *,k), solve the output power per unit value P * Compared with the size relationship between the inner shift and the outer shift, D1 and D0, the working point (P * ,k) The corresponding shift ratio set U1;

[0104] From the working point (P * , k) The corresponding shift phase set U1 is selected to select the inner shift phase and outer shift phase combinations that meet the soft switching boundary conditions, and the working point (P * ,k) The corresponding shift ratio set U2;

[0105] From the working point (P * , k) from the corresponding shift ratio set U2, select the inner shift ratio and outer shift ratio combination that satisfies D1 = l / m, and get the working point (P * ,k) corresponds to the optimal shift ratio set;

[0106] The optimal phase shift ratio set corresponding to each working point is recorded in the optimal phase shift ratio lookup table to complete the establishment of the optimal phase shift ratio lookup table;

[0107] Wherein, l is a positive odd number, and m is a multiple or order of the target harmonic frequency relative to the switching frequency.

[0108] For the inner shift phase ratio and outer shift phase ratio combination that meets the preset conditions, the smaller the value of the inner shift phase ratio D1 is, the more obvious the suppression effect on the DC side ripple is. Therefore, before recording the optimal shift phase ratio set corresponding to each working point into the optimal shift phase ratio lookup table, this embodiment also includes:

[0109] For each working point, determine the inner shift ratio and outer shift ratio combination with the smallest inner shift ratio value in the corresponding optimal shift ratio set, and delete the remaining inner shift ratio and outer shift ratio combinations from the optimal shift ratio set.

[0110] Based on the established optimal shift ratio lookup table, such as Figure 5 As shown, in this embodiment, when each group of converters performs power balanced zero common mode modulation, the inner shift ratio D 1_1 and D 1_2 , and outward displacement compared to D 0_1 and D 0_2 Methods of determination include:

[0111] Determine the output power per unit value P * , and calculate the voltage conversion ratio k;

[0112] Find P from the pre-established optimal phase shift lookup table *, k corresponding to the outward shift ratio D0 and the inward shift ratio D1; when looking up the table, the inward shift ratio and outward shift ratio combination corresponding to any working point can be calculated by linear interpolation;

[0113] Compare the inward shift to D 1_1 and D 1_2 All are assigned the value of D1;

[0114] Determine the control error ΔD0 of the external shift phase and obtain the output power per unit value P * The sign of the partial derivative relative to the current outward shift of the first converter, and the output power per unit value P * The signs of the partial derivatives relative to the current outward shift of the second transformer are recorded as the first sign and the second sign respectively;

[0115] Assign the first sign to ΔD0 to get ΔD0', and compare the outward shift to D 0_1 Assign a value of D0-ΔD0'; assign a second sign to ΔD0 to get ΔD0", compare the outward shift to D 0_2 Assign value to D0+ΔD0".

[0116] Based on the output power per unit value P * Compared with the inward shift D1 and the outward shift D0, the output power per unit value P can be obtained. * The per-unit value of D0 relative to the outward shift is:

[0117]

[0118] Substituting the corresponding outward shift ratio value into the above expression, we can get the specific partial derivative value, and use the Sign function to extract the corresponding sign; when the input of the Sign function is positive, the output is 1; when the input is negative, the output is -1; when the input is 0, the output is 0.

[0119] It is easy to understand that when the series and parallel connection modes of two converters in a group of converters are different, the output power per unit value P * The control method of the control error ΔD0 is different from that of the outward shift. Figure 6 For example, the inputs of the two converters are connected in series and the outputs are connected in parallel. The power balance at this time is equivalent to the input voltage balance of the two converters, where S A1_1 and S A1_2 They represent the driving signals of the upper switch tubes of bridge arms A1 and A2, respectively. B1_1 and S B1_2 They represent the driving signals of the upper switch tubes of bridge arms B1 and B2, respectively. C1_1 and S C1_2 Respectively represent the driving signals of the upper switch tubes of bridge arms C1 and C2, S D1_1 and S D1_2Respectively represent the driving signals of the upper switch tubes of the bridge arms D1 and D2; S A2_1 and S A2_2 They represent the driving signals of the lower switch tubes of bridge arms A1 and A2, respectively. B2_1 and S B2_2 They represent the driving signals of the lower switch tubes of bridge arms B1 and B2, respectively. C2_1 and S C2_2 They represent the driving signals of the lower switch tubes of bridge arms C1 and C2, respectively. D2_1 and S D2_2 Respectively represent the driving signals of the lower switch tubes of the bridge arms D1 and D2. Figure 5 As shown, determine the output power per unit value P * , including: setting the output voltage command value The output voltage U of the first converter or the second converter o After making the difference, PI control is performed to obtain the output power per unit value P * ; Determine the control error ΔD0 compared with the external shift, including: the input voltage average value U i_ave The first converter input voltage U i1 After making the difference, PI control is performed to obtain the control error ΔD0 of the outward shift phase.

[0120] In other topologies, for example, if the inputs of the first converter and the outputs of the second converter are connected in parallel, the average input current I i_ave The input current I i1 After making the difference, PI control is performed to obtain the control error ΔD0 of the external shift phase, or the output current average value I o_ave The output current I of the first converter o1 After making the difference, PI control is performed to obtain the control error ΔD0 compared with the outward shift.

[0121] If the inputs of the first converter and the second converter are connected in parallel and their outputs are connected in series, the average input current I i_ave The input current I i1 After making the difference, PI control is performed to obtain the control error ΔD0 of the external shift, or the output voltage average value U o_ave The output voltage U of the first converter o1 After making the difference, PI control is performed to obtain the control error ΔD0 of the outward shift phase.

[0122] In general, this embodiment optimizes the extended phase-shift modulation, and can achieve power balance while realizing zero common-mode modulation, and optimizes the phase shift ratio, and can effectively suppress DC side ripple.

[0123] Embodiment 3:

[0124] A zero common mode modulation device is used to implement zero common mode modulation of the dual active bridge converter device of the even modules provided in the above embodiment 1.

[0125] This embodiment includes: a control module and N modulation modules;

[0126] The control module is used to evenly divide 2N dual active bridge converters in the dual active bridge converter device of the even-numbered modules into N groups of converters; in each group of converters, two dual active bridge converters are respectively recorded as a first converter and a second converter, two bridge arms of the primary side of the first converter are respectively recorded as A1 and B1, and two bridge arms of the secondary side are respectively recorded as C1 and D1, and two bridge arms of the primary side of the second converter are respectively recorded as A2 and B2, and two bridge arms of the secondary side are respectively recorded as C2 and D2;

[0127] The N modulation modules are respectively used to perform power-balanced zero common mode modulation on the N groups of converters, so as to realize zero common mode modulation of the dual active bridge converter of the even number of modules;

[0128] The modulation module includes:

[0129] The first control loop is used to determine the output power per unit value P * , and calculate the voltage conversion ratio k;

[0130] A table lookup unit, whose input terminal is connected to the output terminal of the first control loop, is used to look up P from a pre-established optimal phase shift lookup table. * , k corresponding to the outer phase shift D0 and the inner phase shift D1; the optimal phase shift lookup table records all the inner phase shift and outer phase shift combinations that can meet the preset conditions under each output power per unit value and voltage conversion ratio combination; the preset conditions include: the size relationship between the output power per unit value and the inner phase shift and outer phase shift, the soft switching boundary conditions, and the ability to suppress DC side ripple;

[0131] The second control loop is used to determine the control error ΔD0 of the outward shift phase and obtain the output power per unit value P * The sign of the partial derivative relative to the current outward shift of the first converter, and the output power per unit value P * The signs of the partial derivatives relative to the current outward shift of the second transformer are recorded as the first sign and the second sign respectively;

[0132] and a shift ratio determination unit, whose first input terminal is connected to the output terminal of the table lookup unit, and whose second input terminal is connected to the output terminal of the second control loop, and which is used to perform the following operations:

[0133] Compare the inward shift between bridge arms A1 and B1 to D 1_1 Compared with the inward shift between bridge arms A2 and B2, D 1_2 All are assigned the value of D1;

[0134] Assign the first sign to ΔD0 to get ΔD0', and compare the outward displacement between bridge arms A1 and C1 to D 0_1 Assign the value to D0-ΔD0';

[0135] Assign the second sign to ΔD0, and get ΔD0", and compare the outward displacement between bridge arms A2 and C2 to D 0_2 Assign value to D0+ΔD0".

[0136] In this embodiment, the specific implementation of each module can refer to the description in the above embodiment 2 and will not be repeated here.

[0137] Embodiment 4:

[0138] A dual active bridge converter system for even-numbered modules, comprising: the dual active bridge converter device for even-numbered modules provided in the above embodiment 1, the zero common mode modulation device and the driver provided in the above embodiment 3;

[0139] The driver is used to generate switch drive signals for each converter according to the inner shift phase ratio and outer shift phase ratio determined by the zero common mode modulation device, and apply them to the corresponding converter to make the dual active bridge converter device of the even-numbered modules output the specified power.

[0140] It will be easily understood by those skilled in the art that the above description is only 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 protection scope of the present invention.

Claims

1. A dual active bridge converter device with an even number of modules, characterized in that: include: 2N dual active bridge converters; In the dual active bridge converter, a symmetrically coupled phase-shifting inductor is provided between the primary dual active bridge and the isolation transformer; The symmetrically coupled phase-shifting inductor includes two inductors, which are respectively arranged between the midpoints of the two bridge arms of the primary dual active bridge and the isolation transformer; the winding ends of the two inductors are opposite, the self-inductance of the two inductors is equal, and the series equivalent inductance is L ph ; Where N is a positive integer, L ph It is the preset primary and secondary side phase shift inductance value.

2. The zero common mode modulation method of the dual active bridge converter device of even modules as claimed in claim 1, characterized in that: include: The 2N dual active bridge converters in the dual active bridge converter device of the even-numbered modules are evenly divided into N groups of converters; in each group of converters, the two dual active bridge converters are respectively recorded as a first converter and a second converter, the two bridge arms of the primary side of the first converter are respectively recorded as A1 and B1, and the two bridge arms of the secondary side are respectively recorded as C1 and D1, and the two bridge arms of the primary side of the second converter are respectively recorded as A2 and B2, and the two bridge arms of the secondary side are respectively recorded as C2 and D2; For each group of converters, respectively performing power balanced zero common mode modulation to achieve zero common mode modulation of the dual active bridge converter device of the even modules; The power balanced zero common mode modulation includes: Under the condition that the output power requirement is met, the switch drive signals of bridge arms A1 and A2 are controlled to be complementary, and the internal shift ratio D between bridge arms A1 and B1 is controlled. 1_1 Compared with the inward shift between bridge arms A2 and B2, D 1_2 equal; when the switch drive signals of bridge arms C1 and D1 are complementary, and the switch drive signals of bridge arms C2 and D2 are complementary, the outward shift ratio D between bridge arms A1 and C1 is adjusted. 0_1 Compared with the outward shift between bridge arms A2 and C2, D 0_2 , so that the power of the first converter and the second converter are equal.

3. The zero common mode modulation method according to claim 2, characterized in that: Inward shift compared to D 1_1 and D 1_2 , and outward displacement compared to D 0_1 and D 0_2 Methods of determination include: Determine the output power per unit value P * , and calculate the voltage conversion ratio k; Find P from the pre-established optimal phase shift lookup table * , k corresponding to the outer phase shift ratio D0 and the inner phase shift ratio D1; the optimal phase shift lookup table records all the inner phase shift ratio and outer phase shift ratio combinations that can meet the preset conditions under each output power per unit value and voltage conversion ratio combination; the preset conditions include: the size relationship between the output power per unit value and the inner phase shift ratio and the outer phase shift ratio, the soft switching boundary conditions, and the setting of the inner phase shift ratio D1 can suppress the DC side ripple; Compare the inward shift to D 1_1 and D 1_2 All are assigned the value of D1; Determine the control error ΔD0 of the external shift phase and obtain the output power per unit value P * The sign of the partial derivative relative to the current outward shift of the first converter, and the output power per unit value P * The signs of the partial derivatives relative to the current outward shift of the second transformer are recorded as the first sign and the second sign respectively; Assign the first sign to ΔD0 to get ΔD0', and compare the outward shift to D 0_1 Assign a value of D0-ΔD0'; assign a second sign to ΔD0 to get ΔD0", compare the outward shift to D 0_2 Assign value to D0+ΔD0".

4. The zero common mode modulation method according to claim 3, characterized in that: The optimal phase shift lookup table is established in the following manner: Select the output power per unit value P in the range of (0,1) * , and select the voltage conversion ratio k in the range of (0,1.5) to obtain multiple operating points; each operating point corresponds to a combination of output power per unit value and voltage conversion ratio; For each working point (P * ,k), solve the output power per unit value P * Compared with the size relationship between the inner shift and the outer shift, D1 and D0, the working point (P * ,k) The corresponding shift ratio set U1; From the working point (P * , k) The corresponding shift phase set U1 is selected to select the inner shift phase and outer shift phase combinations that meet the soft switching boundary conditions, and the working point (P * ,k) The corresponding shift ratio set U2; From the working point (P * , k) from the corresponding shift ratio set U2, select the inner shift ratio and outer shift ratio combination that satisfies D1 = l / m, and get the working point (P * ,k) corresponds to the optimal shift ratio set; Recording the optimal phase shift ratio set corresponding to each working point into the optimal phase shift ratio lookup table, and completing the establishment of the optimal phase shift ratio lookup table; Wherein, l is a positive odd number, and m is a multiple or order of the target harmonic frequency relative to the switching frequency.

5. The zero common mode modulation method according to claim 4, characterized in that: Before recording the optimal shift phase ratio set corresponding to each working point into the optimal shift phase ratio lookup table, the following steps are also included: For each working point, determine the inner shift ratio and outer shift ratio combination with the smallest inner shift ratio value in the corresponding optimal shift ratio set, and delete the remaining inner shift ratio and outer shift ratio combinations from the optimal shift ratio set.

6. The zero common mode modulation method according to any one of claims 3 to 5, characterized in that: Determine the output power per unit value P * ,include: The output voltage command value U o * The output voltage U of the first converter or the second converter o After making the difference, PI control is performed to obtain the output power per unit value P * .

7. The zero common mode modulation method according to claim 6, characterized in that: Determine the control error ΔD0 of the outward shift phase, including: If the input of the first converter is connected in series with the input of the second converter, the input voltage command value U i_ave The first converter input voltage U i1 After making the difference, PI control is performed to obtain the control error ΔD0 compared with the outward shift. If the inputs of the first converter and the outputs of the second converter are connected in parallel, the average input current I i_ave The input current I i1 After making the difference, PI control is performed to obtain the control error ΔD0 of the external shift phase, or the output current average value I o_ave The output current I of the first converter o1 After making the difference, PI control is performed to obtain the control error ΔD0 compared with the outward shift. If the inputs of the first converter and the second converter are connected in parallel and their outputs are connected in series, the average input current I i_ave The input current I i1 After making the difference, PI control is performed to obtain the control error ΔD0 of the external shift, or the output voltage average value U o_ave The output voltage U of the first converter o1 After making the difference, PI control is performed to obtain the control error ΔD0 of the outward shift phase.

8. The zero common mode modulation device of the dual active bridge converter device of even modules as claimed in claim 1, characterized in that: include: A control module and N modulation modules; The control module is used to evenly divide 2N dual active bridge converters in the dual active bridge converter device of the even-numbered modules into N groups of converters; in each group of converters, two dual active bridge converters are respectively recorded as a first converter and a second converter, the two bridge arms of the primary side of the first converter are respectively recorded as A1 and B1, and the two bridge arms of the secondary side are respectively recorded as C1 and D1, and the two bridge arms of the primary side of the second converter are respectively recorded as A2 and B2, and the two bridge arms of the secondary side are respectively recorded as C2 and D2; The N modulation modules are respectively used to perform power-balanced zero common mode modulation on the N groups of converters, so as to realize zero common mode modulation on the dual active bridge converter device of the even-numbered modules; The modulation module comprises: The first control loop is used to determine the output power per unit value P * , and calculate the voltage conversion ratio k; A table lookup unit, whose input end is connected to the output end of the first control loop, is used to look up P from a pre-established optimal phase shift lookup table. * , k corresponding to the outer phase shift D0 and the inner phase shift D1; the optimal phase shift lookup table records all the inner phase shift and outer phase shift combinations that can meet the preset conditions under each output power per unit value and voltage conversion ratio combination; the preset conditions include: the size relationship between the output power per unit value and the inner phase shift and the outer phase shift, the soft switching boundary conditions, and the ability to suppress DC side ripple; The second control loop is used to determine the control error ΔD0 of the outward shift phase and obtain the output power per unit value P * The sign of the partial derivative relative to the current outward shift of the first converter, and the output power per unit value P * The signs of the partial derivatives relative to the current outward shift of the second transformer are recorded as the first sign and the second sign respectively; and a shift ratio determination unit, whose first input terminal is connected to the output terminal of the table lookup unit, and whose second input terminal is connected to the output terminal of the second control loop, and which is used to perform the following operations: Compare the inward shift between bridge arms A1 and B1 to D 1_1 Compared with the inward movement between bridge arms A2 and B2, D 1_2 All are assigned the value of D1; Assign the first sign to ΔD0 to get ΔD0', and compare the outward displacement between bridge arms A1 and C1 to D 0_1 Assign the value to D0-ΔD0'; Assign the second sign to ΔD0, and get ΔD0", and compare the outward displacement between bridge arms A2 and C2 to D 0_2 Assign value to D0+ΔD0".

9. A dual active bridge converter system with an even number of modules, characterized in that: include: The dual active bridge converter device of even-numbered modules as claimed in claim 1, the zero common mode modulation device and the driver as claimed in claim 8; The driver is used to generate switch drive signals for each converter according to the inner shift phase ratio and the outer shift phase ratio determined by the zero common mode modulation device, and apply them to the corresponding converter, so that the dual active bridge converter device of the even module outputs the specified power.

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