A DC transformer and its high frequency link voltage matching phase shift modulation method

Abstract

The present invention discloses a DC transformer and a high-frequency link voltage matching phase-shift modulation method thereof, wherein the DC transformer comprises one or more bridge modules, wherein the bridge module comprises a first transmission unit, a second transmission unit and a high-frequency isolation transformer connected between the first transmission unit and the second transmission unit, wherein the first switch device, the second switch device, the third switch device and the fourth switch device in the first transmission unit form a first full-bridge circuit; the fifth switch device is connected in series with the first capacitor, and the fifth switch device and the first capacitor in series are connected in parallel with the first switch device; the sixth switch device is connected in series with the second capacitor, and the sixth switch device and the second capacitor in series are connected in parallel with the third switch device. The DC transformer has a bidirectional fault current blocking capability, and the above-mentioned phase-shift modulation method is used to improve the power supply reliability of the entire power grid.

Description

Technical Field

[0001] The invention belongs to the field of power electronics, and in particular relates to a direct current transformer and a high-frequency link voltage matching phase-shift modulation method thereof. Background Art

[0002] In the process of networking medium and high voltage DC power grid, DC transformer is an important link to promote its development. Since traditional DC transformer has no or only has the ability to block unidirectional fault current, when it is applied to DC power grid, it will be damaged by the impact of DC fault current from DC power grid, affecting the safe operation and reliable power supply of DC transformer itself and DC power grid. Therefore, how to make DC transformer have bidirectional fault current blocking function is an urgent problem to be solved. Summary of the invention

[0003] In view of the above problems, the present invention provides a DC transformer and a high-frequency link voltage matching phase-shift modulation method thereof. The DC transformer has fast fault recovery and high power supply reliability.

[0004] The object of the present invention is to provide a DC transformer, comprising one or more bridge modules, wherein the bridge module comprises a first transmission unit, a second transmission unit and a high-frequency isolation transformer connected between the first transmission unit and the second transmission unit, wherein:

[0005] The first transmission unit is composed of a first switch device, a second switch device, a third switch device, a fourth switch device, a fifth switch device, a sixth switch device, a first capacitor and a second capacitor, wherein:

[0006] The first switch device, the second switch device, the third switch device, and the fourth switch device form a first full-bridge circuit;

[0007] The fifth switch device is connected in series with the first capacitor, and the fifth switch device, the first capacitor and the first switch device are connected in series in parallel;

[0008] The sixth switch device is connected in series with the second capacitor, and the series-connected sixth switch device, the second capacitor and the third switch device are connected in parallel.

[0009] Furthermore, the first to sixth switching devices include power electronic switches and anti-parallel diodes.

[0010] Further, the second transmission unit is composed of a seventh switch device, an eighth switch device, a ninth switch device, a tenth switch device, an eleventh switch device, a twelfth switch device, a third capacitor and a fourth capacitor, wherein the seventh switch device, the eighth switch device, the ninth switch device and the tenth switch device form a second full-bridge circuit, the eleventh switch device is connected in series with the third capacitor, and the eleventh switch device and the third capacitor in series are connected in parallel with the seventh switch device, the twelfth switch device is connected in series with the fourth capacitor, the twelfth switch device and the fourth capacitor in series are connected in parallel with the ninth switch device, and the seventh to twelfth switch devices are power electronic switches and anti-parallel diodes;

[0011] or,

[0012] The second transmission unit is composed of a seventh switch device, an eighth switch device, a ninth switch device, a tenth switch device and a third capacitor, wherein the seven switch devices, the eighth switch device, the ninth switch device and the tenth switch device form a second full-bridge circuit, the third capacitor is connected in parallel with the second full-bridge circuit, and the seventh to tenth switch devices are all diodes or include power electronic switches and anti-parallel diodes.

[0013] Furthermore, the DC transformer and the one or more bridge modules include one or more of the following connection relationships:

[0014] The medium voltage and / or high voltage interface side of the DC transformer is connected in series with the one or more bridge modules, and the low voltage interface side thereof is connected in parallel with the one or more bridge modules.

[0015] The medium voltage and / or high voltage interface side of the DC transformer is connected in series with the one or more bridge modules, and the low voltage interface side of the DC transformer is connected in series with the one or more bridge modules.

[0016] The medium voltage and / or high voltage interface side of the DC transformer is connected in parallel with the one or more bridge modules, and the low voltage interface side of the DC transformer is connected in parallel with the one or more bridge modules.

[0017] The medium voltage and / or high voltage interface side of the DC transformer is connected in parallel with the one or more bridge modules, and the low voltage interface side of the DC transformer is connected in series with the one or more bridge modules.

[0018] Furthermore, when the DC transformer includes a plurality of bridge modules, one or more bridge modules among the plurality of bridge modules are redundantly arranged with other bridge modules.

[0019] Furthermore, a first inductor is connected in series between the medium voltage and / or high voltage interface side of the DC transformer and the medium voltage and / or high voltage DC bus side of the DC power transmission grid.

[0020] Another object of the present invention is to provide a high-frequency link voltage matching phase-shift modulation method for a DC transformer as described above, comprising:

[0021] Determine one or more of the following modulation parameters:

[0022] The number of one or more bridge modules in the DC transformer N, the DC voltage V across the DC transformer dc1 、V dc2 ;

[0023] Based on the modulation parameters determined above, calculating the matching shift ratio D0 of the first transmission unit in the DC transformer;

[0024] According to the calculated matching phase shift value D0, phase shift modulation is performed on the first transmission unit and the second transmission unit in the DC transformer respectively.

[0025] Further, the performing phase shift modulation on the first transmission unit and the second transmission unit in the DC transformer respectively comprises:

[0026] In one switching cycle, the power electronic switches in each switching device in the first transmission unit of the DC transformer are controlled to operate respectively, so that the power electronic switches in the first switching device and the fourth switching device form completely identical first modulation waves, the modulation wave formed in the power electronic switch in the fifth switching device is opposite to the first modulation wave, the power electronic switches in the second switching device and the third switching device form completely identical second modulation waves, and the modulation wave formed in the power electronic switch in the sixth switching device is opposite to the second modulation wave; wherein the duty ratios of the first modulation wave and the second modulation wave are both 50%+D0, and the phase shift angle between the first modulation wave and the second modulation wave is 180 degrees;

[0027] In one switching cycle, each switch device in the second transmission unit in the DC transformer is controlled to operate, wherein:

[0028] When the second transmission unit includes the seventh to twelfth switching devices, and the seventh to twelfth switching devices are all power electronic switches and anti-parallel diodes:

[0029] The seventh switch device and the tenth switch device form completely identical third modulation waves, and the modulation wave formed in the power electronic switch in the eleventh switch device is opposite to the third modulation wave; the eighth switch device and the ninth switch device form completely identical fourth modulation waves, and the modulation wave formed in the power electronic switch in the twelfth switch device is opposite to the fourth modulation wave; wherein the phase shift angle between the third modulation wave and the fourth modulation wave is 180 degrees;

[0030] or,

[0031] When the second transmission unit includes the seventh to the tenth switching devices, and the seventh to the tenth switching devices are all diodes, the seventh switching device and the tenth switching device form a completely identical third modulation wave; the eighth switching device and the ninth switching device form a completely identical fourth modulation wave; wherein the phase shift angle between the third modulation wave and the fourth modulation wave is 180 degrees;

[0032] or,

[0033] When the second transmission unit includes seventh to tenth switching devices, and the seventh to tenth switching devices are all power electronic switches and anti-parallel diodes, a completely identical third modulation wave is formed in the power electronic switches in the seventh switching device and the tenth switching device, and a completely identical fourth modulation wave is formed in the power electronic switches in the eighth switching device and the ninth switching device; wherein the phase shift angle between the third modulation wave and the fourth modulation wave is 180 degrees.

[0034] Further, the one switching cycle includes t0, t1, t2, t3, t4, t5 and t6, and the lengths of the time periods from t0 to t1 and t3 to t4 are both the product of the matching shift ratio D0 and half the switching cycle, and the lengths of the time periods from t0 to t2 and t3 to t5 are both the product of the shift ratio D between the first transmission unit and the second transmission unit and half the switching cycle;

[0035] Then, in the one switching cycle, controlling the power electronic switches in the first transmission unit in the DC transformer to perform actions specifically includes:

[0036] At time t0, the first to fourth power electronic switches are turned on, and the fifth to sixth power electronic switches are turned off;

[0037] At time t1, the power electronic switch in the sixth switch device is turned on, and the power electronic switches in the second to third switch devices are turned off;

[0038] At time t3, the power electronic switches in the second to third switch devices are turned on; the power electronic switch in the sixth switch device is turned off;

[0039] At time t4, the power electronic switch in the fifth switch device is turned on, and the power electronic switches in the first and fourth switch devices are turned off;

[0040] At time t6, the power electronic switches in the first, fourth and sixth switch devices are turned on, and the power electronic switches in the second to third and fifth switch devices are turned off;

[0041] Respectively controlling each switch device in the second transmission unit in the DC transformer to perform an action includes:

[0042] When the second transmission unit includes the seventh to twelfth switching devices, and the seventh to twelfth switching devices are all power electronic switches and anti-parallel diodes:

[0043] At time t0, the power electronic switches in the eighth to ninth and twelfth switch devices are turned on, and the power electronic switches in the seventh and tenth switch devices are turned off;

[0044] At time t2, the power electronic switches in the seventh, tenth to eleventh switch devices are turned on, and the power electronic switches in the eighth to ninth and eleventh switch devices are turned off;

[0045] At time t5, the power electronic switches in the eighth to ninth and twelfth switch devices are turned on, and the power electronic switches in the seventh and tenth to eleventh switch devices are turned off;

[0046] or,

[0047] When the second transmission unit includes seventh to tenth switching devices, and the seventh to tenth switching devices are all diodes,

[0048] At time t0, the eighth to ninth switching devices are turned on, and the seventh and tenth switching devices are turned off;

[0049] At time t2, the seventh and tenth switch devices are turned on, and the eighth to ninth switch devices are turned off;

[0050] At time t5, the eighth to ninth switch devices are turned on, and the seventh and tenth switch devices are turned off;

[0051] or,

[0052] When the second transmission unit includes the seventh to tenth switching devices, and the seventh to tenth switching devices are all power electronic switches and anti-parallel diodes,

[0053] At time t0, the power electronic switches in the eighth to ninth switch devices are turned on, and the power electronic switches in the seventh and tenth switch devices are turned off;

[0054] At time t2, the power electronic switches in the seventh and tenth switch devices are turned on, and the power electronic switches in the eighth to ninth switch devices are turned off;

[0055] At time t5, the power electronic switches in the eighth to ninth switching devices are turned on, and the power electronic switches in the seventh and tenth switching devices are turned off.

[0056] Furthermore, the matching shift ratio D0 of the first transmission unit in the DC transformer satisfies:

[0057]

[0058] Wherein, N is the number of one or more bridge modules in the DC transformer, N>0, and N is an integer.

[0059] The DC transformer of the present invention has the following beneficial effects:

[0060] (1) The DC transformer includes one or more bridge modules, that is, the DC transformer adopts a modular design, which avoids the use of large-capacity centralized high-frequency transformers, reduces the loss of the high-frequency link of the transformer, and facilitates installation, debugging and transportation.

[0061] (2) The DC transformer integrates bidirectional fault current blocking capability. When a medium (high) voltage DC grid fails, the various switch devices on the medium and high voltage sides can be locked, so that the DC transformer can block the discharge fault current from the first capacitor and the second capacitor in the DC transformer to the DC grid. Due to the unidirectional current flow function of the diode, the charging fault current from the DC grid to the DC transformer can be blocked, thereby minimizing the damage of the fault current to the DC transformer and achieving complete isolation of the DC transformer when the DC grid fails. At the same time, it reduces the use of medium (high) voltage DC circuit breakers in the external power grid and reduces the operating loss and construction cost of the DC grid.

[0062] (3) Some of the bridge modules in one or more bridge modules are in online redundant state and have online switching function, which can realize online switching of bridge modules in online redundant state and non-stop switching of faulty bridge modules, thereby improving overall reliability;

[0063] (4) By adopting high-frequency link voltage matching phase-shift modulation, the proposed DC transformer can achieve high-frequency link voltage matching operation with switching devices within its entire operating range, thereby improving the overall operating efficiency of the DC transformer and the current stress characteristics of the switching devices.

[0064] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0066] Figure 1 A schematic structural diagram of a DC transformer in an embodiment of the present invention is shown;

[0067] Figure 2 A schematic structural diagram of another DC transformer in an embodiment of the present invention is shown;

[0068] Figure 3 A schematic structural diagram of a third DC transformer in an embodiment of the present invention is shown;

[0069] Figure 4 , Figure 5 A schematic diagram of waveforms formed by a high-frequency link voltage matching phase-shift modulation method based on a DC transformer in an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0070] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0071] The embodiment of the present invention introduces a DC transformer, such as Figure 1-3 As shown, they are three preferred embodiments of the present invention, and the same thing about these three preferred embodiments is that the DC transformers all include N improved dual active full-bridge modules MDAB (Modified Dual Active Bridge Integrated with Bidirectional DC Fault Current Isolating Function) with integrated bidirectional fault current blocking function, wherein N is an integer, N>0, in the embodiment of the present invention, taking the i-th improved dual active full-bridge module MDAB with integrated bidirectional fault current blocking function as an example, the structure of the MDAB is introduced, wherein i∈N, N is an integer, and the improved dual active full-bridge module MDAB with integrated bidirectional fault current blocking function is referred to as the MDAB, the MDAB includes a first transmission unit CB-Hi, a second transmission unit Hi, and a high-frequency isolation transformer HFL-T connected between the first transmission unit CB-Hi and the second transmission unit Hi, wherein the first transmission unit CB-Hi is composed of a first switch device, a second switch device, a third switch device, a fourth switch device, a fifth switch device, a sixth switch device, a first capacitor C 11i And the second capacitor C 12iwherein the first switch device, the second switch device, the third switch device, and the fourth switch device form a first full-bridge circuit; the fifth switch device and the first capacitor C 11i The fifth switch device and the first capacitor C connected in series 11i The sixth switch device is connected in parallel with the second capacitor C 12i The sixth switch device and the second capacitor C connected in series 12i The DC transformer is connected in parallel with the third switch device. 11i , the second capacitor C 12i Under the action of the switch device connected in series, the DC transformer is regularly cut out or put in. Exemplary: When the fifth switch device is in the on state, the first capacitor C 11i When the fifth switch device is in the off state, the first capacitor C 11i Similarly, when the sixth switch device is in the on state, the second capacitor C 12i When the sixth switch device is in the off state, the second capacitor C 12i In the cut-out state. When the DC transformer fails, the fifth switch device and the sixth switch device are both in the locked off state, and the first capacitor and the second capacitor are both in the energized cut-out state, so as to quickly resume operation after the DC transformer works normally.

[0072] The first to sixth switching devices all include power electronic switches and anti-parallel diodes. Each switching device includes an anti-parallel diode to achieve bidirectional fault current blocking on the medium (high) voltage side of the DC transformer, so that when a fault occurs in the DC power grid, it can block the capacitor discharge in the DC transformer and block the impact current of the power grid from entering the DC transformer. Especially for external transient faults, there is no physical breakpoint between the DC transformer and the DC power grid. When the fault is cleared, the system can be quickly restored to improve the power supply reliability of the entire power grid.

[0073] Specifically, Figure 1-3 As shown in FIG. 1 , the structure of the medium (high) voltage side of the i-th improved dual active full-bridge module MDAB with integrated bidirectional fault current blocking capability is specifically as follows: the first switch device is composed of a power electronic switch S 11i With anti-parallel diode D 11i The second switch device is composed of a power electronic switch S 12i With anti-parallel diode D 12i The third switch device is composed of a power electronic switch S 13i With anti-parallel diode D 13i The fourth switch device is composed of a power electronic switch S 14iWith anti-parallel diode D 14i The fifth switch device is composed of a power electronic switch Q 1i With anti-parallel diode R 1i The sixth switch device is composed of a power electronic switch Q 2i With anti-parallel diode R 2i The first capacitor C 11i And the second capacitor C 12i Both are discrete switched capacitors, diode R 1i With D 12i , R 2i With D 14i Therefore, when a short circuit occurs in the medium voltage DC grid, the DC transformer is controlled by the protection strategy, and each switch device in the DC transformer is locked. Then, the two discrete capacitors C in each MDAB 11i , C 12i Since the reverse diode R 1i ~R 2i The unidirectional current flow function will not be able to discharge to the external fault point, thereby reducing the total fault current at the fault point and maintaining the first capacitor C 11i With the second capacitor C 12i The capacitor voltage is convenient for the fault handling of the DC fault point and the restart of the DC transformer. 11i ~D 14i The unidirectional current flow function is realized. At this time, the external power grid cannot inject fault current into the DC transformer. At the same time, the safety of the discrete capacitors in the DC transformer is guaranteed and the service life of the DC transformer is improved.

[0074] Figure 1-3 The difference between the illustrated embodiments is that the structure of the second transmission unit Hi is set differently according to the power transmission direction and fault handling requirements of different application scenarios of the DC transformer.

[0075] Figure 1 In the embodiment, the second transmission unit Hi includes a seventh switch device, an eighth switch device, a ninth switch device, a tenth switch device and a third capacitor C 21i , wherein the seventh to tenth switching devices form a full-bridge circuit, and the full-bridge circuit and the third capacitor C 21i Further, the seventh switch device is composed of a power electronic switch S 21i With anti-parallel diode D 21i The eighth switching device is composed of a power electronic switch S 22i With anti-parallel diode D 22i The ninth switch device is composed of a power electronic switch S 23i With anti-parallel diode D 23iThe tenth switch device is composed of a power electronic switch S 24i With anti-parallel diode D 24i Composition. Figure 1 When the DC transformer shown transmits power, bidirectional transmission can be achieved. However, since no blocking capacitor is provided in the second transmission unit Hi, the low-voltage side of the DC transformer does not have a fault current blocking capability.

[0076] Figure 2 In the structure of the second transmission unit Hi Figure 1 The structures are the same, but the seventh to tenth switching devices are all diodes. Figure 2 The DC transformer shown in does not have a bidirectional transmission function, and when transmitting power, it can only transmit power from the medium voltage side or the high voltage side to the low voltage side. Similarly, since no blocking capacitor is provided in the second transmission unit Hi, the low voltage side of the DC transformer does not have a fault current blocking capability.

[0077] Figure 3 In the structure of the second transmission unit Hi Figure 1 The structure of the first transmission unit CB-Hi is the same, in which the settings of each switch device and capacitor are the same, so that the DC transformer has a bidirectional transmission function, and the (high) voltage side and the low voltage side have a bidirectional fault current blocking capability, which will not be repeated here.

[0078] In this embodiment, the power electronic switch is a thyristor device, including an insulated gate bipolar transistor (IGBT), an integrated gate-commutated thyristor (IGCT), a gate turn-off thyristor (GTO), etc.

[0079] The medium voltage and / or high voltage interface side of the DC transformer is connected in series with the one or more MDABs, and the low voltage interface side is connected in parallel with the one or more MDABs; a plurality of bridge modules are connected in series on the medium (high) voltage interface side to improve the withstand voltage level of the DC transformer, and a plurality of bridge modules are connected in parallel on the low voltage interface side to improve the power level of the DC transformer. However, the DC transformer and the MDAB are not limited to the above connection relationship. According to the different application scenarios and power requirements of the MDAB, the connection relationship between the DC transformer and the one or more MDABs also includes: the medium (high) voltage interface side of the DC transformer is connected in series with the one or more MDABs, the low voltage interface side is connected in series with the one or more MDABs, the medium (high) voltage interface side of the DC transformer is connected in parallel with the one or more MDABs, the low voltage interface side is connected in parallel with the one or more MDABs, the medium (high) voltage interface side of the DC transformer is connected in parallel with the one or more MDABs, and the low voltage interface side is connected in series with the one or more MDABs.

[0080] In this embodiment, since the DC transformer includes N MDABs, when N>1, there is a redundant setting between the N MDABs, and a part of the N MDABs are running in an online redundant state, and the other part of the MDABs are in an operational state, that is, the MDABs in the DC transformer include one or more main bridge modules MDAB and one or more backup bridge modules MDAB. Wherein, when the MDAB is in an online redundant state, its terminal voltage is 0, and the DC capacitor in the first transmission unit CB-Hi maintains a certain voltage, so that when some of the MDABs in operation fail, they can be quickly replaced, thereby improving the operational reliability of the DC transformer. For example, with Figure 1 Take the DC transformer in the figure as an example, if the i-th MDAB operates in the online redundant state, then Q 1i ~Q 2i , S 21i ~S 24i In the locked state, at the same time, S 11i ~S 14i In the unlocked state, the high-voltage side current flows through S 11i ~S 14i , S 11i ~S 12i With S 13i ~S 14i Two sets of parallel circuits are formed to reduce the conduction loss of the redundant module in the online redundant state. At the same time, when the MDAB in operation fails, the MDAB module in the online redundant state is used to realize the online removal of the faulty module of the DC transformer without stopping, thereby improving the power supply reliability.

[0081] In this embodiment, a first inductor is further connected in series between the medium voltage and / or high voltage interface side of the DC transformer and the medium voltage and / or high voltage DC bus side of the DC transmission grid to reduce DC current ripple and achieve flexibility in control and modulation.

[0082] The embodiment of the present invention also introduces a high-frequency link voltage matching phase shift modulation method of a DC transformer, comprising: first determining one or more of the following modulation parameters: the number N of one or more MDABs in the DC transformer, the DC voltage V at both ends of the DC transformer, dc1 、V dc2; Secondly, based on the modulation parameters determined above, the matching phase shift ratio D0 of the first transmission unit in the DC transformer is calculated; then, according to the calculated matching phase shift ratio D0, the first transmission unit and the second transmission unit in the DC transformer are phase-shift modulated respectively. In the present application, the first transmission unit and the second transmission unit in all MDABs in the DC transformer are phase-shift modulated. By adopting high-frequency link voltage matching phase shift modulation, the DC transformer can achieve voltage matching soft switching operation of the high-frequency link within its entire operating range, thereby improving the overall operating efficiency of the DC transformer and the current stress characteristics of the switching device.

[0083] Specifically, Figure 1 Take the i-th MDAB in the DC transformer as an example for phase shift modulation, as Figure 1 As shown, the voltages of CB-H1 and H1 (not shown in full) of MDAB1 are V 1p1 、V 2p1 , the voltages of CB-Hi and Hi of MDABi are V 1pi 、V 2pi , the voltage of the first transmission unit CB-HN (not shown in full) of MDABN is V 1pN 、V 2pN The total voltages of CB-H and H (not all shown) of 1-N MDABs are V 1p 、V 2p Taking MDABi as an example, the currents passing through the first to tenth switching devices in MDABi are i 11i 、i 12i 、i 13i 、i 14i 、i C11i 、i C12i 、i 21i 、i 22i 、i 23i 、i 24i , the voltage of the first capacitor and the second capacitor is V C11i 、V C12i , the input and output currents of CB-Hi of MDABi are i 1id 、i 1i , the input and output currents of Hi of MDABi are i 2i 、i 2id , the voltage ratio of the high frequency isolation transformer HFL-T is k T : 1, and the voltage on both sides is v 1i 、v 2i , the first inductor L dc The voltage is V Ldc , the DC voltage V across the DC transformer dc1 、V dc2; The current across the DC transformer is I dc1 ,I dc2 .

[0084] like Figure 4 As shown, Figure 4 Introduced Figure 1 The high-frequency link voltage matching phase-shift modulation principle diagram of the DC transformer is shown in FIG. A switching cycle includes t0, t1, t2, t3, t4, t5 and t6. t0 to t6 is a switching cycle. hs is half a switching cycle, D is the shift ratio between CB-Hi and Hi, and D0 is the matching shift ratio between CB-Hi. In the MDABi, CB-Hi and Hi have different modulation principles. Specifically, in one switching cycle, the power electronic switches in each switching device in the first transmission unit are controlled to act respectively, so that S 11i With S 14i The first modulation wave, Q 1i The modulated wave formed in S 11i In contrast to the first modulation wave, the S 12i With S 13i The second modulation wave is formed in the same way, the Q 2i The modulated wave formed in S 13i The second modulation wave in is opposite; wherein the duty ratio of the first modulation wave and the second modulation wave are both 50%+D0, and the phase shift angle between the first modulation wave and the second modulation wave is 180 degrees;

[0085] In a switching cycle, the power electronic switches in each switching device in the second transmission unit are controlled to operate respectively, so that the S 21i With S 24i The third modulation wave is exactly the same as S 22i With S 23i A completely identical fourth modulation wave is formed; wherein the phase shift angle between the third modulation wave and the fourth modulation wave is 180 degrees, and the third modulation wave and the fourth modulation wave are both square waves.

[0086] In this embodiment, the lengths of the time periods t0-t1 and t3-t4 are both matched with the shift phase D0 and half the switching period T hs The lengths of the time periods t0 to t2 and t3 to t5 are the shift ratio D between the first transmission unit and the second transmission unit and half the switching period T hs The product of; then in one switching cycle, respectively controlling the power electronic switches in each switching device in the first transmission unit and the second transmission unit to perform actions specifically includes,

[0087] At time t0, S 11i ~S14i , S 22i ~S 23i On, Q 1i ~Q 2i , S 21i , S 24i Shut down;

[0088] At t1, Q 2i On, S 12i ~S 13i Shut down;

[0089] At t2, S 21i , S 24i On, S 22i ~S 23i Shut down;

[0090] At t3, S 12i ~S 13i Conductivity; Q 2i Shut down;

[0091] At t4, Q 1i Conductivity; S 11i , S 14i Shut down;

[0092] At t5, S 22i ~S 23i On, S 21i , S 24i Shutdown,

[0093] At t6, S 11i , S 14i , Q 2i On, S 12i ~S 13i , Q 1i Shut down.

[0094] Based on the above phase shift modulation, V 1pi 、V 2pi 、V 1p 、V 2p 、i 11i 、i 12i 、i 13i 、i 14i 、i C11i 、i C12i 、i 21i 、i 22i 、i 23i 、i 24i 、i 1i 、v 1i 、v 2i 、V Ldc ,I dc1 Formed as Figure 4 , 5 The waveform shown in

[0095] The V 1pi The amplitude in the time periods t1 to t3 and t4 to t6 is V 1pi =V C1 ; The V 2pi The amplitude of V in one switching cycle 2pi =V C2 =V dc2 ; The V 1p The amplitude in the time periods t1 to t3 and t4 to t6 is V 1p =NV C1 ; The V 2p The amplitude of V in one switching cycle 2p =NV C2 =NV dc2 ; The V Ldc The amplitude in the time periods t0~t1 and t3~t4 is V Ldc =V dc1 , the amplitude in the time periods t1~t3 and t4~t6 is V Ldc =V dc1 -NV C1 ;v 1i The amplitude in the time periods t1 to t3 and t4 to t6 is v 1i =V C1 ;v 2i The amplitude in the time periods t0~t2 and t5~t6 is v 2i =V C2 =V dc2 , the amplitude in the time period t2 to t4 is v 2i =-V C2 =-V dc2 .

[0096] Therefore, under the above modulation method, according to the average voltage of the DC inductor is 0, it can be known that:

[0097] V dc1 D0T hs +(V dc1 -NV C1 )(1-D0)T hs =0

[0098] Therefore, we can get:

[0099]

[0100] That is to say, the capacitor voltage on the CB-Hi side can be adjusted by matching the shift phase D0. C1 =V C2 =Vdc2 , can be obtained

[0101]

[0102] Therefore, based on the above relationship, the transformation can derive the matching shift ratio D0 of the first transmission unit:

[0103]

[0104] Wherein, N is the number of one or more bridge modules in the DC transformer, N>0, and N is an integer. The matching shift ratio of the first transmission unit of any MDAB described in the present application satisfies the above relationship.

[0105] Thus, the DC voltage V at both ends of the DC transformer is determined according to the matching shift phase D0. dc1 、V dc2 This can ensure the matching operation of the high-frequency link DC voltage of the DC transformer, thereby optimizing the high-frequency link current and the current of the switching device, and improving the comprehensive performance of the DC transformer under a wide voltage operating range.

[0106] In this embodiment, when the DC transformer is Figure 2 When the structure shown in FIG. 1 is used, in the high-frequency link voltage matching phase shift modulation process of the DC transformer, due to the unidirectional conductivity of the diode, the second transmission unit is equivalent to a Wheatstone bridge composed of four diodes. Still taking the i-th MDAB as an example, D 21i , D 22i , D 23i , D 24i The turning-on and turning-off processes are respectively related to S 21i , S 22i , S 23i , S 24i The corresponding ones are consistent.

[0107] In this embodiment, when the DC transformer is Figure 3 When the structure shown in FIG. 1 is used, in the high-frequency link voltage matching phase shift modulation process of the DC transformer, the i-th MDAB is still taken as an example, and the other processes are the same as those mentioned above. Figure 1 The modulation process is consistent with that of the power electronic switch Q 3i , Q 4i Satisfaction: Q 3i Just need to 21i The trigger pulse is opposite, that is, S 21i On, Q 3i Then turn off, S 21i Shutdown, Q 3i At the same time, Q 4i Then you need to 23i The operating status can be reversed.

[0108] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high frequency link voltage matching phase shift modulation method for a DC transformer, characterized in that: include, Determine the following modulation parameters: The number of one or more bridge modules in the DC transformer N, the DC voltage V across the DC transformer dc1 、V dc2 ; The DC transformer includes one or more bridge modules, and the bridge module includes a first transmission unit, a second transmission unit, and a high-frequency isolation transformer connected between the first transmission unit and the second transmission unit, wherein the first transmission unit is composed of a first switch device, a second switch device, a third switch device, a fourth switch device, a fifth switch device, a sixth switch device, a first capacitor, and a second capacitor, wherein, The first switch device, the second switch device, the third switch device, and the fourth switch device form a first full-bridge circuit; The fifth switch device is connected in series with the first capacitor, and the fifth switch device and the first capacitor connected in series are connected in parallel with the first switch device; The sixth switch device is connected in series with the second capacitor, and the sixth switch device, the second capacitor and the third switch device are connected in series in parallel; Based on the modulation parameters determined above, calculating the matching shift ratio D0 of the first transmission unit in the DC transformer; According to the calculated matching shift phase D0, phase shift modulation is performed on the first transmission unit and the second transmission unit in the DC transformer respectively; The phase shift modulation of the first transmission unit and the second transmission unit in the DC transformer respectively comprises: In one switching cycle, the power electronic switches in each switching device in the first transmission unit of the DC transformer are controlled to operate respectively, so that the power electronic switches in the first switching device and the fourth switching device form completely identical first modulation waves, the modulation wave formed in the power electronic switch in the fifth switching device is opposite to the first modulation wave, the power electronic switches in the second switching device and the third switching device form completely identical second modulation waves, and the modulation wave formed in the power electronic switch in the sixth switching device is opposite to the second modulation wave; wherein the duty ratios of the first modulation wave and the second modulation wave are both 50%+D0, and the phase shift angle between the first modulation wave and the second modulation wave is 180 degrees; The one switching cycle includes t0, t1, t2, t3, t4, t5 and t6, and the lengths of the time periods from t0 to t1 and t3 to t4 are both the product of the matching shift ratio D0 and half the switching cycle, and the lengths of the time periods from t0 to t2 and t3 to t5 are both the product of the shift ratio D between the first transmission unit and the second transmission unit and half the switching cycle; Then, in one switching cycle, controlling the power electronic switches in the first transmission unit in the DC transformer to perform actions specifically includes: At time t0, the power electronic switches in the first to fourth switch devices are turned on, and the power electronic switches in the fifth to sixth switch devices are turned off; At time t1, the power electronic switch in the sixth switch device is turned on, and the power electronic switches in the second to third switch devices are turned off; At time t3, the power electronic switches in the second to third switch devices are turned on; the power electronic switch in the sixth switch device is turned off; At time t4, the power electronic switch in the fifth switch device is turned on, and the power electronic switches in the first and fourth switch devices are turned off; At time t6, the power electronic switches in the first, fourth and sixth switch devices are turned on, and the power electronic switches in the second to third and fifth switch devices are turned off; The second transmission unit is composed of a seventh switch device, an eighth switch device, a ninth switch device, a tenth switch device, an eleventh switch device, a twelfth switch device, a third capacitor and a fourth capacitor, wherein the connection relationship between each switch device and the capacitor is the same as the connection relationship between each switch device and the capacitor in the first transmission unit, and the seventh to twelfth switch devices include power electronic switches and anti-parallel diodes; or, The second transmission unit is composed of a seventh switch device, an eighth switch device, a ninth switch device, a tenth switch device and a third capacitor, wherein the seventh switch device, the eighth switch device, the ninth switch device and the tenth switch device form a second full-bridge circuit, the third capacitor is connected in parallel with the second full-bridge circuit, and the seventh to tenth switch devices are all diodes or include power electronic switches and anti-parallel diodes. The first to sixth switch devices include power electronic switches and anti-parallel diodes; In one switching cycle, each switch device in the second transmission unit in the DC transformer is controlled to operate, wherein: When the second transmission unit includes the seventh to twelfth switching devices, and the seventh to twelfth switching devices are all power electronic switches and anti-parallel diodes: The seventh switch device and the tenth switch device form completely identical third modulation waves, and the modulation wave formed in the power electronic switch in the eleventh switch device is opposite to the third modulation wave; the eighth switch device and the ninth switch device form completely identical fourth modulation waves, and the modulation wave formed in the power electronic switch in the twelfth switch device is opposite to the fourth modulation wave; wherein the phase shift angle between the third modulation wave and the fourth modulation wave is 180 degrees; or, When the second transmission unit includes the seventh to the tenth switching devices, and the seventh to the tenth switching devices are all diodes, the seventh switching device and the tenth switching device form a completely identical third modulation wave; the eighth switching device and the ninth switching device form a completely identical fourth modulation wave; wherein the phase shift angle between the third modulation wave and the fourth modulation wave is 180 degrees; or, When the second transmission unit includes the seventh to the tenth switching devices, and the seventh to the tenth switching devices are all power electronic switches and anti-parallel diodes, the power electronic switches in the seventh switching device and the tenth switching device form completely identical third modulation waves, and the power electronic switches in the eighth switching device and the ninth switching device form completely identical fourth modulation waves; wherein the phase shift angle between the third modulation wave and the fourth modulation wave is 180 degrees; Respectively controlling each switch device in the second transmission unit in the DC transformer to perform an action includes: When the second transmission unit includes the seventh to twelfth switching devices, and the seventh to twelfth switching devices are all power electronic switches and anti-parallel diodes: At time t0, the power electronic switches in the eighth to ninth and twelfth switch devices are turned on, and the power electronic switches in the seventh and tenth switch devices are turned off; At time t2, the power electronic switches in the seventh, tenth to eleventh switching devices are turned on, and the power electronic switches in the eighth to ninth and eleventh switching devices are turned off; At time t5, the power electronic switches in the eighth to ninth and twelfth switch devices are turned on, and the power electronic switches in the seventh and tenth to eleventh switch devices are turned off; or, When the second transmission unit includes the seventh to tenth switching devices, and the seventh to tenth switching devices are all diodes, At time t0, the eighth to ninth switching devices are turned on, and the seventh and tenth switching devices are turned off; At time t2, the seventh and tenth switch devices are turned on, and the eighth to ninth switch devices are turned off; At time t5, the eighth to ninth switching devices are turned on, and the seventh and tenth switching devices are turned off; or, When the second transmission unit includes the seventh to tenth switching devices, and the seventh to tenth switching devices are all power electronic switches and anti-parallel diodes, At time t0, the power electronic switches in the eighth to ninth switching devices are turned on, and the power electronic switches in the seventh and tenth switching devices are turned off; At time t2, the power electronic switches in the seventh and tenth switch devices are turned on, and the power electronic switches in the eighth to ninth switch devices are turned off; At time t5, the power electronic switches in the eighth to ninth switching devices are turned on, and the power electronic switches in the seventh and tenth switching devices are turned off; The DC transformer and the one or more bridge modules include one or more of the following connection relationships: The medium voltage and / or high voltage interface side of the DC transformer is connected in series with the one or more bridge modules, and the low voltage interface side thereof is connected in parallel with the one or more bridge modules. The medium voltage and / or high voltage interface side of the DC transformer is connected in series with the one or more bridge modules, and the low voltage interface side of the DC transformer is connected in series with the one or more bridge modules. The medium voltage and / or high voltage interface side of the DC transformer is connected in parallel with the one or more bridge modules, and the low voltage interface side of the DC transformer is connected in parallel with the one or more bridge modules. The medium voltage and / or high voltage interface side of the DC transformer is connected in parallel with the one or more bridge modules, and the low voltage interface side thereof is connected in series with the one or more bridge modules; When the DC transformer includes a plurality of bridge modules, one or more bridge modules among the plurality of bridge modules are redundantly arranged with other bridge modules; A first inductor is further connected in series between the medium voltage and / or high voltage interface side of the DC transformer and the medium voltage and / or high voltage DC bus side of the DC power transmission grid.

2. The phase shift modulation method according to claim 1, characterized in that: The matching shift ratio D0 of the first transmission unit in the DC transformer satisfies: Wherein, N is the number of one or more bridge modules in the DC transformer, N>0, and N is an integer.

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