Modular bidirectional conversion system and zero-crossing control method

Abstract

The embodiment of the present disclosure discloses a modular bidirectional current conversion system and a zero-crossing control method. The control method comprises: in response to at least part of the first module in the level conversion module switching from processing the first half cycle of the modulation signal to processing the second half cycle of the modulation signal in the first cycle, and at least part of the second module switching from processing the first half cycle of the modulation signal to processing the second half cycle of the modulation signal in the second cycle, outputting a compensation control pulse to at least one target switch in the plurality of switches of the second module in the second cycle to turn on the target switch in the corresponding time length of the compensation control pulse; wherein the second cycle is a modulation cycle located after the first cycle; the positive and negative polarities of the first half cycle and the second half cycle are different; the compensation control pulse at least partially overlaps with the control pulse of the target switch corresponding to the first module in the second cycle; the processing of the modulation signal by the level conversion module comprises: inverter processing and / or rectifier processing.

Description

TECHNICAL FIELD

[0001] The embodiment of the present disclosure relates to the technical field of electric power, and particularly relates to a modular bidirectional conversion system and a zero-crossing point control method. BACKGROUND

[0002] ANPC (Advanced Neutral-Point-Clamped) is an advanced power electronic topology widely used in the field of power conversion. ANPC is an improved Neutral-Point Clamped (NPC) technology mainly used in three-level inverters. Compared with traditional NPC inverters, ANPC improves the efficiency and performance of inverters by adding active control elements. The working principle of ANPC is based on accurate control of the switching state in each switching cycle to reduce the switching times and stress of power switching devices, thereby realizing more efficient power conversion. However, in a parallel system composed of multiple ANPC modules, it is difficult to achieve complete precision synchronization of each module, and the different switching states of different modules will cause the phenomenon of midpoint circulating current between modules, affecting the conversion efficiency and stability of the circuit. SUMMARY

[0003] Therefore, the embodiment of the present disclosure provides a modular bidirectional conversion system and a zero-crossing point control method.

[0004] In one aspect, the embodiment of the present disclosure provides a zero-crossing point control method of a modular bidirectional conversion system, wherein the modular bidirectional conversion system is a parallel system; the parallel system comprises multiple level conversion modules connected in parallel, and each level conversion module comprises one or more bridge arm units composed of multiple switches; each bridge arm unit comprises an upper bridge arm composed of a first switch, a second switch and a fifth switch, and a lower bridge arm composed of a third switch, a fourth switch and a sixth switch; the first switch and the fourth switch are connected to the positive terminal and the negative terminal of a direct current network respectively, the connection point of the fifth switch and the sixth switch is connected to the neutral terminal of the direct current network, and the connection point of the second switch and the third switch is connected to an alternating current network.

[0005] The control method comprises:

[0006] In response to the fact that at least part of the first modules in the level conversion modules switch from processing a modulation signal of a first half cycle to processing a modulation signal of a second half cycle in a first cycle, and at least part of the second modules switch from processing the modulation signal of the first half cycle to processing the modulation signal of the second half cycle in a second cycle, a compensation control pulse is output to at least one target switch in the multiple switches of the second modules in the second cycle to turn on the target switch in the corresponding time length of the compensation control pulse.

[0007] The second period is a modulation period after the first period; the first half period and the second half period have different polarities; the compensation control pulse at least partially overlaps with a control pulse of a target switch corresponding to the first module in the second period; and the level conversion module processes the modulation signal by means of inversion and / or rectification.

[0008] In some embodiments, the target switch is in an off state during a period in which the first half period of the modulation signal is processed, and the target switch is in a high-frequency switching state during a plurality of periods in which the second half period of the modulation signal is processed.

[0009] In some embodiments, the target switch is the first switch and / or the fourth switch, and the second period is a next period of the first period.

[0010] In some embodiments, the outputting of the compensation control pulse to at least one target switch of the plurality of switches of the second module in the second period comprises:

[0011] At a switching time of the first period and the second period, a first input signal input to a control device is switched from a first level to a second level, and the control device is configured to control states of at least some of the plurality of switches.

[0012] After a preset time length at the switching time, the first input signal is switched from the second level to the first level to form a first compensation pulse.

[0013] A first rising edge of the first compensation pulse is delayed for a first time length to form a second compensation pulse.

[0014] The control device inverses a signal containing the second compensation pulse to output a control signal containing the compensation control pulse.

[0015] In some embodiments, the method further comprises:

[0016] In the first period, a control signal of the third switch of the first module is switched from a second level to a first level.

[0017] In the second period, a control signal of the third switch of the second module is switched from a second level to a first level.

[0018] In some embodiments, the switching of the control signal of the third switch of the second module from the second level to the first level in the second period comprises:

[0019] At a switching moment of the first period and the second period, a second input signal inputted to a control device is switched from a first level to a second level; wherein the control device is configured to control states of at least part of the plurality of switches;

[0020] The control device switches a control signal of the third switch from the second level to the first level according to the second input signal.

[0021] In some embodiments, the control device switches the control signal of the third switch from the second level to the first level according to the second input signal, comprising:

[0022] The control device delays the second input signal for a second time length;

[0023] The second input signal after the delay is inverted to output the control signal; wherein the control signal is switched from the second level to the first level at a moment after the switching moment for a second time length; the second time length is less than a first time length; wherein the first time length is a switching time difference between the fourth switch and the sixth switch and / or a switching time difference between the first switch and the fifth switch.

[0024] In another aspect, the embodiments of the present disclosure provide a control device of a modular bidirectional current conversion system, which performs part or all steps of any of the above control methods.

[0025] The control device is connected to control terminals of at least part of the switches to output control signals.

[0026] In another aspect, the embodiments of the present disclosure provide a modular bidirectional current conversion system, comprising: a plurality of level conversion modules connected in parallel;

[0027] A control device connected to control terminals of at least part of the switches to output control signals.

[0028] The control device performs part or all steps of any of the above control methods.

[0029] In some embodiments, the modular bidirectional current conversion system further comprises:

[0030] A direct current network and an alternating current network connected to the level conversion modules.

[0031] In the scheme provided by the embodiment of the present disclosure, in a parallel system with multiple level conversion modules, if a level conversion module exists that is not synchronized in switching half cycle, a compensation control pulse is added to the control signal of the target switch of the level conversion module switched later, so that it is at least partially consistent with the control signal of the corresponding switch of the level conversion module switched earlier, thereby effectively reducing the midpoint circulating current problem caused by the on-off state difference of the corresponding switches of different level conversion modules, and improving the stability of the system. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 A topology diagram of an ANPC type three-level converter provided by the embodiment of the present disclosure;

[0033] Figure 2 A structure diagram of a parallel system corresponding to the control method of the modular bidirectional current conversion system provided by the embodiment of the present disclosure;

[0034] Figure 3 A flowchart of the control method of the modular bidirectional current conversion system provided by the embodiment of the present disclosure;

[0035] Figure 4 A corresponding switch control signal waveform diagram of one level conversion module in the modular bidirectional current conversion system provided by the embodiment of the present disclosure in one carrier cycle when outputting a positive half cycle signal;

[0036] Figure 5 A corresponding switch control signal waveform diagram of one level conversion module in the modular bidirectional current conversion system provided by the embodiment of the present disclosure in one carrier cycle when outputting a negative half cycle signal;

[0037] Figure 6 A corresponding switch control signal waveform diagram of one level conversion module in the modular bidirectional current conversion system provided by the embodiment of the present disclosure in multiple carrier cycles during the output positive and negative half cycle signal switching process;

[0038] Figure 7 A corresponding switch control signal waveform diagram after adding a compensation control pulse in the control method of the modular bidirectional current conversion system provided by the embodiment of the present disclosure; Figure 6

[0039] Figure 8A A principle diagram of adding a compensation control pulse in the control method of the modular bidirectional current conversion system provided by the embodiment of the present disclosure;

[0040] Figure 8B A corresponding principle diagram without adding a compensation control pulse; Figure 8A

[0041] Figure 9 ​​The adjustment of the third switch and fourth switch control signals in the control method of the modular bidirectional conversion system provided by the embodiments of the present disclosure is compared in the following table;

[0042] Figure 10 A structural schematic diagram of a modular bidirectional conversion system provided by the embodiments of the present disclosure is shown in the following figure. DETAILED DESCRIPTION

[0043] In order to facilitate the understanding of the present disclosure, the present disclosure will be described more fully below with reference to the related drawings. The preferred embodiments of the present disclosure are shown in the drawings. However, the present disclosure can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present disclosure more thorough and comprehensive.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present disclosure belongs. The terms used in the specification of the present disclosure are only for the purpose of realizing the description of the specific embodiments and are not intended to limit the present disclosure. The term "and / or" used herein includes any and all combinations of one or more related listed items. In the embodiments of the present disclosure, the terms "first", "second", "third", "fourth" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second", "third", "fourth" can be explicitly or implicitly included one or more of the features.

[0045] Currently, the power supply system of rail transit mostly uses a unidirectional rectifier device to convert electrical energy from three-phase alternating current into direct current to provide a direct current power supply for rail transit vehicles. In order to realize the bidirectional flow of energy on the direct current side and the alternating current side of the rail transit power supply system and provide stable direct current overhead line voltage, a regenerative bidirectional traction power supply device is also introduced into the rail transit power supply system. The alternating current side of the regenerative bidirectional traction power supply device is connected to an alternating current power grid, and the direct current side is connected to a direct current traction network. When the rail transit vehicle is in a traction state, the power supply device works in a rectification state to convert alternating current from the alternating current power grid into direct current to power the direct current traction network. When the rail transit vehicle is in a braking state, the power supply device works in an inversion state to convert direct current from the direct current traction network into alternating current to be fed back to the alternating current power grid.

[0046] ANPC (Active Neutral-point-clamped, active neutral-point-clamped) three-level converter is an important power electronic circuit, and the main circuit topology is as follows Figure 1As shown, it can operate in both rectification and inverter modes. Specifically, the ANPC three-level topology includes an upper bridge arm composed of a first switch K1, a second switch K2, and a fifth switch K5 connected together, and a lower bridge arm composed of a third switch K3, a fourth switch K4, and a sixth switch K6 connected together. The first switch K1 and the fourth switch K4 are connected to the positive terminal (+) and the negative terminal (-) of the DC bus, respectively. The connection point of the fifth switch K5 and the sixth switch K6 is connected to the neutral terminal (N) of the DC bus, and the connection point of the second switch K2 and the third switch K3 is connected to the AC terminal (S).

[0047] This disclosure provides a control method for a modular bidirectional converter system. This modular bidirectional converter system is a parallel system; for simplicity, it will be referred to as a parallel system below. Figure 2 A schematic diagram of the parallel system 100 is shown below. Figure 2 As shown, the parallel system 100 includes: multiple level conversion modules 110 connected in parallel (such as... Figure 1 The ANPC-type three-level converter shown includes a level conversion module 110 comprising one or more bridge arm units composed of multiple switches. The bridge arm unit includes an upper bridge arm composed of a first switch K1, a second switch K2, and a fifth switch K5, and a lower bridge arm composed of a third switch K3, a fourth switch K4, and a sixth switch K6. The first switch K1 and the fourth switch K4 are respectively connected to the positive terminal + and the negative terminal - of the DC network 200 (such as the DC traction network mentioned above). The connection point of the fifth switch K5 and the sixth switch K6 is connected to the neutral terminal N of the DC network 200. The connection point of the second switch K2 and the third switch K3 is connected to the AC network 300 (such as the AC power grid mentioned above).

[0048] In a parallel system, it is desirable for multiple level conversion modules 110 to convert synchronously. However, since each level conversion module 110 operates independently, it is difficult to guarantee complete synchronization. Therefore, carrier synchronization and phase synchronization functions can be added. In this case, synchronization of each module can be almost achieved, but small errors are still unavoidable.

[0049] Because the level conversion module 110 uses different switching combinations to process the positive and negative half-cycles of the AC power, the aforementioned minor error results in some of the multiple level conversion modules 110 switching from processing the positive half-cycle signal to processing the negative half-cycle signal (or vice versa) within a carrier cycle, while others do not switch during that carrier cycle, meaning the switching occurs in subsequent carrier cycles. In other words, some level conversion modules 110 output upper bridge arm control signals, while others output lower bridge arm control signals.

[0050] The output or input signal polarity of the different level conversion modules 110 is different, which can cause voltage difference between the modules, midpoint circulating current phenomenon, and thus reduce the conversion efficiency of the system, cause energy waste, and affect the stability of the system.

[0051] Therefore, the control method shown in the embodiment of the present disclosure is proposed, and the timing diagram of the control signal shown in the embodiment of the present disclosure is combined to illustrate the control method. Figure 3 Figure 4 to Figure 6 The method includes the following steps. Figure 3 to Figure 6

[0052] In step S101, it is determined that at least part of the first modules 111 in the level conversion module 110 switches from processing the first half cycle of the modulation signal to processing the second half cycle of the modulation signal in the first cycle T1, and at least part of the second modules 112 switches from processing the first half cycle of the modulation signal to processing the second half cycle of the modulation signal in the second cycle T2.

[0053] In step S102, a compensation control pulse P0 is output to at least one target switch of the plurality of switches of the second module in the second cycle T2 to turn on the target switch in the corresponding time length of the compensation control pulse.

[0054] The second cycle T2 is a modulation cycle after the first cycle T1. The positive and negative polarities of the first half cycle and the second half cycle are different. The compensation control pulse P0 at least partially overlaps the control pulse P1 of the target switch corresponding to the first module 111 in the second cycle T2. The processing of the modulation signal by the level conversion module 110 includes inverter processing and / or rectifier processing.

[0055] In the embodiment of the present disclosure, the inverter processing or rectifier processing of the AC / DC conversion of the plurality of level conversion modules 110 in the system is implemented. The inverter processing refers to the input of DC power from the DC network 200 to the level conversion module 110, and the output of AC power to the AC network 300. The rectifier processing refers to the input of AC power from the AC network 300 to the level conversion module 110, and the output of DC power to the DC network 200.

[0056] Here, the first cycle T1 refers to any carrier cycle that meets the following conditions: at least one level conversion module 110 meets the half cycle switching condition of the first module 111 described above, and at least one level conversion module meets the half cycle switching condition of the second module 112 described above.

[0057] The second cycle T2 refers to any carrier cycle that meets the following conditions: at least one level conversion module 110 meets the half cycle switching condition of the first module 111 described above, and at least one level conversion module 110 meets the half cycle switching condition of the second module 112 described above. ​​

[0058] The following describes the implementation of the inverse conversion process by the level conversion module 110, and takes the process of switching from outputting a positive half-cycle signal to outputting a negative half-cycle signal as an example:

[0059] Figure 4 The corresponding switch control signals in one carrier cycle of the level conversion module 110 outputting a positive half-cycle signal are shown.

[0060] As can be seen, in the case of outputting a positive half-cycle signal, the three switches of the lower bridge arm are in the closed state, and the second switch K2 remains in the open state as the output path. The first switch K1 and the fifth switch K5 adjust the size of the output voltage by sequentially adjusting the duty cycle in each cycle.

[0061] It is worth noting that in one cycle, the duty cycle of the first switch K1 is smaller than that of the fifth switch K5, because the switching process actually needs a period of time, and if the first switch K1 and the fifth switch K5 are switched synchronously, the first switch K1 and the fifth switch K5 will be opened at the same time for a period of time, thereby causing a circulating current in the branch where the first switch K1 and the fifth switch K5 are located. Therefore, a "dead time" is needed here, including the first dead time RED and the second dead time FED, so that there is a time difference between the two switching times, thereby avoiding circulating current in the bridge arm.

[0062] Similarly, Figure 5 The corresponding switch control signals in one carrier cycle of the level conversion module 110 outputting a negative half-cycle signal are shown. In the case of outputting a negative half-cycle signal, the three switches of the upper bridge arm are in the closed state, and the third switch K3 remains in the open state as the output path. The sixth switch K6 and the fourth switch K4 adjust the size of the output voltage by sequentially adjusting the duty cycle in each cycle. Similarly, there is a difference in the duty cycle between the sixth switch S6 and the fourth switch S4 due to the setting of the "dead time".

[0063] Figure 6 The corresponding control signal timing of the two level conversion modules 110 before and after switching the positive and negative half-cycle signals in five carrier cycles is shown. As shown in Figure 6 The first module 111 and the second module 112 output a positive half-cycle signal in the period T01 to the period T02, and the first switch K1 and the fifth switch K5 of the two modules are switched twice in the period T01, the control signal of the first switch K1 is a positive pulse, and the control signal of the fifth switch K5 is a negative pulse, and due to the setting of the "dead time", the pulse width of the first switch K1 is smaller than that of the fifth switch K5.

[0064] The next cycle T02 still outputs the positive half cycle signal, and the first switch K1 and the fifth switch K5 also perform two switching operations, but the pulse width of the first switch K1 and the fifth switch K5 is reduced.

[0065] In the next cycle T03 (i.e., the first cycle T1), the pulse width of the first switch K1 and the fifth switch K5 of the two modules continues to be reduced. For the first module 111, the control signal is switched to the negative half cycle at this time, and for the second module 112, the control signal is still in the positive half cycle, but due to the dead time, the control signal of the fifth switch K5 of the second module 112 has a negative pulse, and the first switch K1 is not opened, and the other switches are still in the positive half cycle control state. For the first module, the first switch K1, the second switch K2 and the fifth switch K5 are all disconnected (i.e., the control signal is switched to low), and the third switch K3 is opened (i.e., the control signal is switched to high), thereby entering the negative half cycle control state. In this cycle T03 (i.e., the first cycle), the control signal of the sixth switch K6 of the first module generates a positive pulse, and due to the dead time, the control signal of the fourth switch K4 does not generate a negative pulse (i.e., remains low). In addition, it should be noted that the switching of the third switch K3 and the second switch K2 also needs to consider the "dead time", so the opening time of the third switch K3 needs to be slightly later than the closing time of the second switch K2.

[0066] When entering the next cycle T04 (i.e., the second cycle T2), the pulse width of the control signal of the sixth switch K6 of the first module 111 is slightly smaller than that in the last cycle T03, and the fourth switch K4 also generates a negative pulse, i.e., a small positive pulse is generated at the front and back of the cycle, forming a negative pulse in the middle. In this cycle, the second module 112 is switched to the negative half cycle control state, i.e., the first switch K1, the second switch K2 and the fifth switch K5 are turned off (i.e., the control signal is switched to low), and the third switch K3 is opened. The control signal of the sixth switch K6 generates a positive pulse, and the control signal of the fourth switch K4 only jumps once at the end of the control signal under the influence of the "dead time", and compared to the state of the fourth switch K4 of the first module in the cycle T04, it lacks a pulse of the control signal, i.e., the two positions circled do not correspond.

[0067] In this case, the problem of midpoint circulating current between the first module 111 and the second module 112 is caused.

[0068] Therefore, by the above method of the embodiment of the present disclosure, a compensation control pulse P0 is added at the corresponding position of the second module 112, as shown in Figure 7 , so that it is basically consistent with the control signal of the corresponding switch of the first module 111, thereby effectively reducing the problem of midpoint circulating current.

[0069] In the above embodiment, only one possible example is proposed. In actual applications, any situation where the switching control pulses are inconsistent due to the difference in switching rate between different modules conforms to the basic concept of the embodiments of the present disclosure, and can be adjusted by the above-mentioned way of adding compensation control pulse P0, thereby reducing the influence of the midpoint circulating current. In addition, the switching control mode of the first module 111 and the second module 112, i.e., the switching control mode of opening at high level and shutting down at low level, is only an example. In actual applications, the control signal of each switch is related to the type of switch, which will not be described here.

[0070] In some embodiments, the target switch is in an off state during a period in which the first half of the modulation signal is processed; and the target switch is in a high-frequency switching state during multiple periods in which the second half of the modulation signal is processed.

[0071] Here, the type of switch that needs to add the above-mentioned compensation control pulse P0 is pointed out. That is, the target switch is in an off state, i.e., a shutdown state, before switching the half cycle, and enters a high-frequency switching state after switching, i.e., at least one switching is needed in each period. The switch in the second module 112 is easy to miss part of the jump edge in the first period after switching the half cycle, thereby the control signal of the switch at the same position in the first module 111 is different, thereby the midpoint circulating current is easy to be generated. Therefore, the switch in the second module 112 that conforms to the above-mentioned condition can be set as the target switch.

[0072] In some embodiments, the target switch is the first switch K1 and / or the fourth switch K4; and the second period T2 is the next period of the first period T1.

[0073] In the above-mentioned circuit structure provided by the embodiments of the present disclosure, the first switch K1 and the fourth switch K4 conform to the above-mentioned condition, and therefore can be regulated as the target switch. Exemplarily, in the case of switching the positive half cycle to the negative half cycle as shown in Figure 6 , the fourth switch K4 of the second module 112 conforms to the above-mentioned condition, and therefore can be added as the target switch of the compensation control pulse P0 as shown in Figure 7 . Accordingly, in the case of switching the negative half cycle to the positive half cycle, the first switch K1 of the second module 112 conforms to the above-mentioned condition, and therefore can be added as the target switch of the compensation control pulse.

[0074] In some embodiments, as shown in Figure 8A , the step S101 of outputting the compensation control pulse P0 to at least one target switch in the multiple switches of the second module 112 in the second period T2 includes:

[0075] At a switching moment of the first period T1 and the second period T2, the first input signal input to the control device is switched from the first level to the second level; wherein the control device is configured to control states of at least part of the plurality of switches;

[0076] At a preset time length after the switching moment, the first input signal is switched from the second level to the first level to form a first compensation pulse P1.

[0077] At a first time length after a first jump edge of the first compensation pulse, a second compensation pulse P2 is formed.

[0078] At a preset time length after the switching moment, the first input signal is switched from the second level to the first level to form a first compensation pulse P1.

[0079] Here, an example of a specific implementation of a compensation control pulse is provided. The control signals of the switches in the level conversion module 110 can be provided by the control device. In the embodiment of the present disclosure, the control device forms the control signals provided to the switches by performing delay and inversion processing on the received first input signal. Here, the first input signal is switched at the position where the first period T1 and the second period T2 alternate, i.e., the above-mentioned switching moment, to form a jump edge, and is switched again to form a jump edge after a preset time length, thereby forming the first compensation pulse P1. The control device can delay the first jump edge of the first input signal according to the setting of the "dead time", thereby generating the above-mentioned second compensation pulse P2. It should be noted that the first time length of the delay needs to be less than the pulse width of the first compensation pulse P1, and after inversion, the above-mentioned compensation control pulse P0 can be formed. Figure 8B A case without the compensation control pulse P0 is shown.

[0080] It can be understood that the preset time length in the above-mentioned step 12 can be determined according to the carrier amplitude corresponding to the next pulse (CMPB), i.e., in this period, a waveform symmetrical about a center axis of the period is formed.

[0081] In some embodiments, the method further comprises:

[0082] At the first period T1, the control signal of the third switch K3 of the first module 111 is switched from the second level to the first level.

[0083] At the second period T2, the control signal of the third switch K3 of the second module 112 is switched from the second level to the first level, as shown in the above-mentioned Figure 6

[0084] ​Specifically, in some embodiments, the control signal for controlling the third switch K3 of the second module 112 is switched from the second level to the first level by the second level of the second input signal of the control device at the switching moment of the first period T1 and the second period T2, comprising:

[0085] The second input signal input to the control device is switched from the first level to the second level at the switching moment of the first period T1 and the second period T2; wherein the control device is used to control the state of at least part of the plurality of switches;

[0086] The control device switches the control signal of the third switch K3 from the second level to the first level according to the second input signal.

[0087] Here, a specific implementation of switching the state of the third switch K3 is provided, that is, the control of the third switch K3 is realized by switching the level of the input signal of the control device and outputting the control signal of the third switch K3.

[0088] Since the switching moment of the third switch K3 also needs to set a "dead time", therefore, the control device also needs to delay when outputting the control signal of the third switch K3.

[0089] In some embodiments, the control device switches the control signal of the third switch from the second level to the first level according to the second input signal, comprising:

[0090] The control device delays the second input signal for a second duration;

[0091] The delayed second input signal is inverted and outputted as a control signal; wherein the control signal is switched from the second level to the first level at the moment of the second duration after the switching moment; the second duration is less than the first duration; wherein the first duration is the switching time difference of the fourth switch and the sixth switch and / or the switching time difference of the first switch and the fifth switch, as shown in Figure 9 .

[0092] It can be understood that if the "dead time" of the third switch K3 switching is set to be the same as the "dead time" of the fourth switch K4, a circulating current will be generated between the third switch K3 and the fourth switch K4, therefore, the "dead time" of the third switch K3, i.e. the second duration, is adjusted to be less than the first duration corresponding to the "dead time" of the fourth switch K4, so as to reduce the circulating current problem inside the bridge arm.

[0093] Based on the same inventive concept, the disclosure embodiments also provide a control device of a parallel system, which performs part or all steps of any control method in the disclosure embodiments;

[0094] The control device is connected to the control end of at least part of the switches to output a control signal.

[0095] Based on the same inventive concept, the disclosure also provides a parallel system, which comprises Figure 10 a plurality of level conversion modules 110 connected in parallel, as shown in the figure.

[0096] a control device 120 connected to at least part of the control terminals of the switches to output control signals.

[0097] The control device 120 executes part or all of the steps in any of the control methods provided by the embodiments of the disclosure.

[0098] In some embodiments, the parallel system further comprises a direct current network 200 and an alternating current network 300 connected to the level conversion modules. The alternating current network can comprise a network of capacitors, inductors, etc., and can also comprise transformers, power grids, etc.

[0099] It should be understood that the terms "some embodiments", "one embodiment" or "an embodiment" mentioned throughout the specification mean that the specific features, structures or characteristics related to the embodiments are included in at least one embodiment of the disclosure. Therefore, "in one embodiment" or "in an embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. In addition, these specific features, structures or characteristics can be combined in one or more embodiments in any suitable manner. It should be understood that in various embodiments of the disclosure, the size of the sequence number of each process does not mean the order of execution, and the execution order of each process should be determined by its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the disclosure. The sequence number of the above embodiments of the disclosure is only for description, not representing the advantages or disadvantages of the embodiments.

[0100] It should be noted that in this document, the term "comprise", "include" or any other variant thereof is intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or device. Without more limitations, the element defined by the statement "comprises a" does not exclude the presence of another identical element in the process, method, article or device comprising the element.

[0101] The above is only an embodiment of the disclosure, but the protection scope of the disclosure is not limited thereto, and any skilled person in the art can easily think of changes or replacements within the technical range disclosed by the disclosure, which should be covered by the protection scope of the disclosure.

Claims

1. A zero-crossing control method for a modular bidirectional converter system, characterized in that, The modular bidirectional current conversion system is a parallel system; the parallel system comprises a plurality of level conversion modules connected in parallel, the level conversion module comprises one or more bridge arm units composed of a plurality of switches; the bridge arm unit comprises an upper bridge arm composed of a first switch, a second switch and a fifth switch, and a lower bridge arm composed of a third switch, a fourth switch and a sixth switch; the first switch and the fourth switch are connected to the positive terminal and the negative terminal of a direct current network respectively, the connection point of the fifth switch and the sixth switch is connected to the neutral terminal of the direct current network, and the connection point of the second switch and the third switch is connected to an alternating current network; The control method comprises: In response to the fact that at least part of the first modules in the level conversion module switch from processing the modulation signal of the first half cycle to processing the modulation signal of the second half cycle in the first cycle, and at least part of the second modules switch from processing the modulation signal of the first half cycle to processing the modulation signal of the second half cycle in the second cycle, a compensation control pulse is output to at least one target switch in the plurality of switches of the second module in the second cycle to turn on the target switch in the corresponding time length of the compensation control pulse; wherein the first module and the second module are level conversion modules different in half cycle switching in the plurality of level conversion modules; Wherein, the second cycle is a modulation cycle located after the first cycle; the first half cycle and the second half cycle are different in positive and negative polarity; the compensation control pulse at least partially overlaps with the control pulse of the target switch corresponding to the first module in the second cycle; the processing of the level conversion module on the modulation signal comprises inversion processing and / or rectification processing.

2. The control method according to claim 1, characterized by, In the cycle of processing the modulation signal of the first half cycle, the target switch is in an off state; and in a plurality of cycles of processing the modulation signal of the second half cycle, the target switch is in a high-frequency switching state.

3. The control method according to claim 2, characterized by, The target switch is the first switch and / or the fourth switch; the second cycle is the next cycle of the first cycle.

4. The control method according to claim 1, characterized by, The output of the compensation control pulse to at least one target switch in the plurality of switches of the second module in the second cycle comprises: At the switching time of the first cycle and the second cycle, the first input signal input to the control device is switched from a first level to a second level; wherein the control device is used to control the state of at least part of the plurality of switches; After a preset time length at the switching time, the first input signal is switched from the second level to the first level to form a first compensation pulse; The first jump edge of the first compensation pulse is delayed for a first time length to form a second compensation pulse; The control device inversely processes the signal containing the second compensation pulse to output a control signal containing the compensation control pulse.

5. The control method according to any one of claims 1 to 4, characterized by, The method further comprises: In the first cycle, the control signal of the third switch of the first module is switched from a second level to a first level; In the second cycle, the control signal of the third switch of the second module is switched from a second level to a first level.

6. The control method according to claim 5, characterized by The control signal of the third switch of the second module is switched from the second level to the first level in the second period, and the control signal of the third switch of the second module is switched from the second level to the first level in the second period, comprising: At the switching moment of the first period and the second period, the second input signal input to the control device is switched from the first level to the second level; wherein the control device is used to control the state of at least part of the plurality of switches; The control device switches the control signal of the third switch from the second level to the first level according to the second input signal.

7. The control method according to claim 6, characterized by The control device switches the control signal of the third switch from the second level to the first level according to the second input signal, comprising: The control device delays the second input signal for a second time length; The delayed second input signal is inverted and output as the control signal; wherein the control signal is switched from the second level to the first level at the moment of the second time length after the switching moment; the second time length is less than the first time length; wherein the first time length is the switching time difference of the fourth switch and the sixth switch and / or the switching time difference of the first switch and the fifth switch.

8. A control device for a modular bidirectional converter system, characterized in that The control device executes the control method of any one of claims 1 to 7; The control device is connected to the control end of at least part of the switches to output the control signal.

9. A modular bidirectional current conversion system, characterized by Comprising: A plurality of level conversion modules in parallel; The control device is connected to the control end of at least part of the switches to output the control signal; The control device executes the control method of any one of claims 1 to 7.

10. The modular bidirectional current conversion system of claim 9, wherein, Also comprising: A direct current network and an alternating current network connected to the level conversion module.

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