Hybrid modular multilevel converter and charging method, controller, system thereof

Abstract

The application provides a hybrid modular multilevel converter and a charging method, a controller and a system thereof, and relates to the technical field of converter control. The hybrid modular multilevel converter comprises a three-phase circuit and a controller. Each phase circuit comprises a series connection of an upper bridge arm and a lower bridge arm. Each bridge arm in the upper bridge arm and the lower bridge arm comprises a series connection of N sub-modules. The N sub-modules comprise h half-bridge sub-modules and f full-bridge sub-modules, and N = h + f. Each sub-module comprises a capacitor. The controller is configured to charge the capacitor in each sub-module until the capacitor voltage is stable, control the capacitor bypass in each full-bridge sub-module, charge the capacitor in each half-bridge sub-module until the capacitor voltage in each sub-module is equal, and control constant current charging of each sub-module until the capacitor voltage in each sub-module is equal to a rated voltage. The application can reduce current impact in the charging process of the hybrid modular multilevel converter.

Description

Technical Field

[0001] This application relates to the field of converter control technology, and in particular to a hybrid modular multilevel converter and its charging method, controller, and system. Background Technology

[0002] Modular multilevel converters (MMCs) are a well-developed type of high-power multilevel converter, widely used in flexible DC transmission, flexible DC distribution, and motor drives. Compared with traditional converters, MMCs offer advantages such as modular hardware, low output voltage harmonic content, low switching frequency, low losses, and easy capacity expansion.

[0003] A single bridge arm of a Hybrid Modular Multilevel Converter (HMMC) includes a half-bridge submodule and a full-bridge submodule. During the charging process of the HMMC, a large current surge is generated, causing large fluctuations in capacitor voltage and reducing the normal service life of the capacitor.

[0004] Therefore, how to reduce the current surge during the charging process of hybrid modular multilevel converters is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] This application provides a hybrid modular multilevel converter and its charging method, controller, and system to reduce current surges during the charging process of the hybrid modular multilevel converter.

[0006] According to a first aspect of the embodiments of this application, a hybrid modular multilevel converter is provided, including a three-phase circuit and a controller. Each phase circuit includes an upper bridge arm and a lower bridge arm connected in series. Each of the upper bridge arm and the lower bridge arm includes N sub-modules connected in series. The N sub-modules include h half-bridge sub-modules and f full-bridge sub-modules, where N = h + f, and N, h, and f are positive integers. Each sub-module includes a capacitor. The controller is configured to: Charge the capacitors in each of the sub-modules until the capacitor voltage stabilizes; By controlling the bypass of capacitors in each of the full-bridge submodules, the capacitors in each of the half-bridge submodules are charged until the voltages of the capacitors in each of the submodules are equal. Each of the sub-modules is controlled to perform constant current charging until the voltage of the capacitor in each sub-module is equal to the rated voltage.

[0007] According to a second aspect of the embodiments of this application, a charging method for a hybrid modular multilevel converter is provided. The hybrid modular multilevel converter includes a three-phase circuit, each phase circuit including an upper bridge arm and a lower bridge arm connected in series. Each of the upper bridge arm and the lower bridge arm includes N sub-modules connected in series. The N sub-modules include h half-bridge sub-modules and f full-bridge sub-modules, where N = h + f, and N, h, and f are positive integers. Each sub-module includes a capacitor. The charging method includes: Charge the capacitors in each of the sub-modules until the capacitor voltage stabilizes; By controlling the bypass of capacitors in each of the full-bridge submodules, the capacitors in each of the half-bridge submodules are charged until the voltages of the capacitors in each of the submodules are equal. Each of the sub-modules is controlled to perform constant current charging until the voltage of the capacitor in each sub-module is equal to the rated voltage.

[0008] According to a third aspect of the embodiments of this application, a controller is provided for implementing a charging method for a hybrid modular multilevel converter as described in the second aspect.

[0009] According to a fourth aspect of the embodiments of this application, a power conversion system is provided, including a hybrid modular multilevel converter as described in the first aspect.

[0010] In this application, the hybrid modular multilevel converter includes a three-phase circuit and a controller. Each phase circuit includes an upper bridge arm and a lower bridge arm connected in series. Each bridge arm includes N sub-modules connected in series. The N sub-modules include h half-bridge sub-modules and f full-bridge sub-modules, where N = h + f, and N, h, and f are positive integers. Each sub-module includes a capacitor. The controller is configured to charge the capacitors in each sub-module until the capacitor voltage stabilizes. Uncontrolled charging is performed initially. Once the capacitor voltage stabilizes, the full-bridge sub-module can draw power from the capacitor to supply power to the drive circuit, thereby controlling the switching of the transistors in the full-bridge sub-module. During uncontrolled charging, since the capacitors in the full-bridge sub-modules are charging at all times, while the capacitors in the half-bridge sub-modules are charging only for half the time, the capacitor voltage of the full-bridge sub-modules is greater than that of the half-bridge sub-modules at the end of the uncontrolled charging phase. Then, the controller bypasses the capacitors in each full-bridge submodule, charging the capacitors in each half-bridge submodule until the voltages of the capacitors in each submodule are equal. The controller then activates the switches in each full-bridge submodule, bypassing the capacitors in each full-bridge submodule and charging only the capacitors in each half-bridge submodule, thus increasing the capacitor voltages in each half-bridge submodule and decreasing the voltage difference between the capacitor voltages in the full-bridge and half-bridge submodules. This charging phase ends when the capacitor voltages in the half-bridge submodules equal those in the full-bridge submodules. Finally, the controller controls each submodule to perform constant current charging until the capacitor voltages in each submodule equal their rated voltages. Because the capacitor voltages in the half-bridge submodules equal the capacitor voltages in the full-bridge submodules at the end of the constant current charging phase controlled by the controller, the voltage difference between the capacitor voltages in the full-bridge and half-bridge submodules is small, thereby reducing the current surge during the charging process of the hybrid modular multilevel converter. In addition, constant current charging can make the charging process more stable and reduce the current surge during the charging process of hybrid modular multilevel converters. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0012] Figure 1 This is a schematic diagram of a hybrid modular multilevel converter provided in an embodiment of this application.

[0013] Figure 2This is a schematic diagram of a full-bridge submodule provided in an embodiment of this application.

[0014] Figure 3 This is a schematic diagram of the structure of a half-bridge submodule provided in an embodiment of this application.

[0015] Figure 4 This is a schematic diagram of a current path in the first stage of a hybrid modular multilevel converter provided in an embodiment of this application.

[0016] Figure 5 This is a schematic diagram of a current path in the full-bridge submodule of the hybrid modular multilevel converter provided in the embodiments of this application.

[0017] Figure 6 This is a schematic diagram of a current path in the full-bridge submodule of the hybrid modular multilevel converter provided in the embodiments of this application.

[0018] Figure 7 This is a schematic diagram of another current path for the full-bridge submodule in the third stage of the hybrid modular multilevel converter provided in the embodiments of this application.

[0019] Figure 8 This is a control block diagram for the fourth stage of a hybrid modular multilevel converter provided in an embodiment of this application.

[0020] Figure 9 This is a schematic flowchart illustrating a charging method for a hybrid modular multilevel converter provided in an embodiment of this application. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] Exemplary hybrid modular multilevel converter Please see Figure 1 In one exemplary embodiment, a hybrid modular multilevel converter is provided. For example... Figure 1 As shown, the hybrid modular multilevel converter includes a three-phase circuit and a controller. Each phase circuit includes an upper bridge arm and a lower bridge arm connected in series. Each bridge arm in the upper and lower bridge arms includes N sub-modules connected in series. The N sub-modules include h half-bridge sub-modules and f full-bridge sub-modules, where N = h + f, and N, h, and f are positive integers. Each sub-module includes a capacitor. The controller is configured as follows: Charge the capacitors in each submodule until the capacitor voltage stabilizes; By controlling the bypass of capacitors in each full-bridge submodule, the capacitors in each half-bridge submodule are charged until the voltage of the capacitors in each submodule is equal. Control each submodule to perform constant current charging until the voltage of the capacitor in each submodule is equal to the rated voltage.

[0023] The controller is configured to charge the capacitors in each submodule until the capacitor voltage stabilizes. Initially, uncontrolled charging is performed. Once the capacitor voltage stabilizes, the full-bridge submodule draws power from the capacitors to supply power to the drive circuit, thereby controlling the switching of the transistors in the full-bridge submodule. During uncontrolled charging, because the capacitors in the full-bridge submodule are charging at all times, while the capacitors in the half-bridge submodule are charging only half the time, the capacitor voltage in the full-bridge submodule is greater than the capacitor voltage in the half-bridge submodule at the end of the uncontrolled charging phase. Then, the controller bypasses the capacitors in each full-bridge submodule, charging the capacitors in each half-bridge submodule until the voltages of the capacitors in each submodule are equal. The controller then activates the switches in each full-bridge submodule, bypassing the capacitors in each full-bridge submodule and charging only the capacitors in each half-bridge submodule, thus increasing the capacitor voltages in each half-bridge submodule and decreasing the voltage difference between the capacitor voltages in the full-bridge and half-bridge submodules. This charging phase ends when the capacitor voltages in the half-bridge submodules equal those in the full-bridge submodules. Finally, the controller controls each submodule to perform constant current charging until the capacitor voltages in each submodule equal their rated voltages. Because the capacitor voltages in the half-bridge submodules equal the capacitor voltages in the full-bridge submodules at the end of the constant current charging phase controlled by the controller, the voltage difference between the capacitor voltages in the full-bridge and half-bridge submodules is small, thereby reducing the current surge during the charging process of the hybrid modular multilevel converter. In addition, constant current charging can make the charging process more stable and reduce the current surge during the charging process of hybrid modular multilevel converters.

[0024] In an exemplary embodiment, Figure 1The hybrid modular multilevel converter consists of a three-phase six-bridge arm. Each bridge arm in the three-phase six-bridge arm is named a phase bridge arm. Each phase bridge arm includes N sub-modules (SM) connected in series. Each phase bridge arm may also include a reactor L1. The N sub-modules include h HBSMs (Half Bridge Sub-Modules) and f FBSMs (Full Bridge Sub-Modules), where N = h + f. The highest level output of the hybrid modular multilevel converter on the AC side is a stepped wave with N+1 levels. The larger N is, the closer the AC side output is to a sine wave.

[0025] In an exemplary embodiment, Figure 1 The AC voltage of phase A of the hybrid modular multilevel converter is U SA The AC voltage of phase B is U SB The AC voltage of phase C is U SC Each phase's AC terminal is connected to the upper and lower bridge arms of each phase circuit via a bypass switch KM2 and an AC contactor KM1 connected in series. The starting resistor R and bypass switch KM2 are connected in parallel. The DC voltage of the hybrid modular multilevel converter is U. DC When the hybrid modular multilevel converter starts up, the AC contactor KM1 is closed first. The AC power supply charges the capacitors in each submodule through the starting resistor R. When the DC voltage U... DC When the set value is reached, the bypass switch KM2 is closed, the bypass start resistor R is activated, and the AC power supply charges the capacitors in each submodule.

[0026] In an exemplary embodiment, Figure 1 The document does not show that every submodule includes a capacitor, but in reality, every submodule includes a capacitor. Figure 2 This is a schematic diagram of the structure of a full-bridge submodule provided in an embodiment of this application. Figure 3 This is a schematic diagram of the structure of a half-bridge submodule provided in an embodiment of this application, as shown below. Figure 2 and Figure 3 As shown, both the full-bridge submodule and the half-bridge submodule include capacitors.

[0027] In an exemplary embodiment, Figure 1 The controller is not shown in the image, but the hybrid modular multilevel converter actually includes a controller, which connects to each sub-module.

[0028] In some embodiments, such as Figure 2As shown, the full-bridge submodule includes a first bridge arm, a second bridge arm, and a first capacitor connected in parallel; the first bridge arm includes a first upper bridge arm and a first lower bridge arm connected in series, and the connection point of the first upper bridge arm and the first lower bridge arm serves as the first end of the full-bridge submodule; the second bridge arm includes a second upper bridge arm and a second lower bridge arm connected in series, and the connection point of the second upper bridge arm and the second lower bridge arm serves as the second end of the full-bridge submodule.

[0029] Figure 2 In the full-bridge submodule, there are a first bridge arm, a second bridge arm, and a first capacitor C1 connected in parallel. The first bridge arm includes a first upper bridge arm and a first lower bridge arm connected in series. The first upper bridge arm includes a switch S1 and an anti-parallel diode D1, and the first lower bridge arm includes a switch S2 and an anti-parallel diode D2. The second bridge arm includes a second upper bridge arm and a second lower bridge arm connected in series. The second upper bridge arm includes a switch S3 and an anti-parallel diode D3, and the second lower bridge arm includes a switch S4 and an anti-parallel diode D4. The connection point of switches S1 and S2 serves as the first terminal of the full-bridge submodule, and the connection point of switches S3 and S4 serves as the second terminal of the full-bridge submodule. The voltage between the first and second terminals of the full-bridge submodule is U. FBSM .

[0030] In some embodiments, such as Figure 3 As shown, the half-bridge submodule includes a third bridge arm and a second capacitor connected in parallel; the third bridge arm includes a third upper bridge arm and a third lower bridge arm connected in series, and the connection point of the third upper bridge arm and the third lower bridge arm serves as the first end of the half-bridge submodule; the connection point of the third lower bridge arm and the second capacitor serves as the second end of the half-bridge submodule.

[0031] Figure 3 In the half-bridge module, a third bridge arm and a second capacitor C2 are connected in parallel. The third bridge arm consists of a third upper bridge arm and a third lower bridge arm connected in series. The third upper bridge arm includes a switch S5 and an anti-parallel diode D5, and the third lower bridge arm includes a switch S6 and an anti-parallel diode D6. The connection point of switches S5 and S6 serves as the first terminal of the half-bridge module, and the connection point of switch S6 and the second capacitor C2 serves as the second terminal of the half-bridge module. The voltage between the first and second terminals of the half-bridge module is U. HBSM .

[0032] In some embodiments, the controller is further configured to: By bypassing the capacitors in each full-bridge submodule, the capacitors in each half-bridge submodule are charged until the voltages of the capacitors in each submodule are equal. Before controlling each submodule to perform constant current charging, the operation of each full-bridge submodule is controlled so that the full-bridge submodule is equivalent to a half-bridge submodule, charging the capacitors in each submodule until the capacitor voltage is stable.

[0033] At the end of the charging phase, which only charges the capacitors in each half-bridge submodule, the capacitor voltage of the half-bridge submodule equals the capacitor voltage of the full-bridge submodule. At this point, the operation of each full-bridge submodule is controlled to make the full-bridge submodule equivalent to a half-bridge submodule, charging the capacitors in each submodule until the capacitor voltage stabilizes. Since the full-bridge submodule is equivalent to a half-bridge submodule, the capacitor voltages of each half-bridge submodule and each full-bridge submodule are kept equal. The capacitor voltages of each half-bridge submodule and each full-bridge submodule are increased synchronously, so that when the constant current charging phase of each submodule is entered, the capacitor voltage of each submodule is closer to the rated voltage, reducing overmodulation.

[0034] The following examples illustrate the four stages of the charging process of a hybrid modular multilevel converter.

[0035] (1) First stage: Uncontrolled charging stage.

[0036] Figure 1 In the middle, after closing each AC contactor KM1, because the capacitor voltage of each submodule is less than the self-powered critical voltage, it is impossible to draw power from the capacitor to supply power to the drive circuit and thus control the switching transistors in the submodule. Therefore, each submodule is in a locked state.

[0037] The capacitors in each submodule are charged until the capacitor voltage stabilizes. Uncontrolled charging is performed first. Once the capacitor voltage stabilizes, the full-bridge submodule can draw power from the capacitor to supply power to the drive circuit, thereby controlling the switching transistors in the full-bridge submodule, and then the second stage of charging is performed.

[0038] With each submodule in a locked state, switches S1, S2, S3, and S4 in the full-bridge submodule are off, and switches S5 and S6 in the half-bridge submodule are off. The hybrid modular multilevel converter consists of three phases and six bridge arms. Each bridge arm is named a phase bridge arm. The direction of current in a phase bridge arm is defined as follows: current flowing from top to bottom in a phase bridge arm is defined as positive, and current flowing from bottom to top in a phase bridge arm is defined as negative.

[0039] For each phase bridge arm, the time for the current to flow positively (current flows from top to bottom in the phase bridge arm) and negatively (current flows from bottom to top in the phase bridge arm) is equal. For the FBSM in each phase bridge arm, when the current is positive, the current flows from the first end of the full bridge submodule (i.e., the connection point of switching transistors S1 and S2) through anti-parallel diode D1, first capacitor C1, and anti-parallel diode D4 to the second end of the full bridge submodule (i.e., the connection point of switching transistors S3 and S4), and the first capacitor C1 is charged; when the current is negative, the current flows from the second end of the full bridge submodule (i.e., the connection point of switching transistors S3 and S4) through anti-parallel diode D3, first capacitor C1, and anti-parallel diode D2 to the first end of the full bridge submodule (i.e., the connection point of switching transistors S1 and S2), and the first capacitor C1 is charged. Therefore, regardless of whether the current is positive or negative, the FBSM capacitor (i.e., the first capacitor C1) is charged.

[0040] For each HBSM in the bridge arm, when the current is positive, the current flows from the first end of the half-bridge submodule (i.e., the connection point of switching transistors S5 and S6) through the anti-parallel diode D5 and the second capacitor C2 to the second end of the half-bridge submodule (i.e., the connection point of switching transistors S6 and the second capacitor C2), and the second capacitor C2 is charged. When the current is negative, the current flows from the second end of the half-bridge submodule (i.e., the connection point of switching transistors S6 and the second capacitor C2) through the anti-parallel diode D6 to the first end of the half-bridge submodule (i.e., the connection point of switching transistors S5 and S6), and the second capacitor C2 is bypassed by the anti-parallel diode D6, so the second capacitor C2 is not charged. Therefore, the HBSM capacitor (i.e., the second capacitor C2) is charged only when the current is positive, and is bypassed and not charged when the current is negative.

[0041] Since the FBSM capacitor (i.e., the first capacitor C1) is charged regardless of whether the current is positive or negative, the HBSM capacitor (i.e., the second capacitor C2) is charged only when the current is positive and bypassed when the current is negative. Moreover, for each phase bridge arm, the time for the positive current (current flowing from top to bottom in the phase bridge arm) and the time for the negative current (current flowing from bottom to top in the phase bridge arm) are equal. Therefore, at the end of the first stage of charging, the voltage of the FBSM capacitor is twice the voltage of the HBSM capacitor.

[0042] For example, U SA >U SB >U SC At that time, the current path in the first stage is as follows Figure 4 As shown, the current flows from phase A into phases B and C. It can be seen that... Figure 4In the full-bridge submodule, the current in the upper arm of phase A is negative, the current in the upper arm of phase B is positive, the current in the upper arm of phase C is positive, the current in the lower arm of phase A is positive, the current in the lower arm of phase B is negative, and the current in the lower arm of phase C is negative. In the lower arm of phase A, the upper arm of phase B, and the upper arm of phase C, the current is positive. Current flows from the first end of the full-bridge submodule (i.e., the connection point of switches S1 and S2) through anti-parallel diode D1, the first capacitor C1, and anti-parallel diode D4 to the second end of the full-bridge submodule (i.e., the connection point of switches S3 and S4), where the first capacitor C1 is charged. Current flows from the first end of the half-bridge submodule (i.e., the connection point of switches S5 and S6) through anti-parallel diode D5 and the second capacitor C2 to the second end of the half-bridge submodule (i.e., the connection point of switches S6 and C2), where the second capacitor C2 is charged. In the upper arm of phase A, the lower arm of phase B, and the lower arm of phase C, the current is negative. The current flows from the second end of the full-bridge submodule (i.e., the connection point of switching transistors S3 and S4) through anti-parallel diode D3, the first capacitor C1, and anti-parallel diode D2 to the first end of the full-bridge submodule (i.e., the connection point of switching transistors S1 and S2). The first capacitor C1 is charged. The current flows from the second end of the half-bridge submodule (i.e., the connection point of switching transistor S6 and the second capacitor C2) through anti-parallel diode D6 to the first end of the half-bridge submodule (i.e., the connection point of switching transistors S5 and S6). The second capacitor C2 is bypassed by anti-parallel diode D6 and is not charged. Figure 4 Just U SA >U SB >U SC The current path in the first stage, Figure 4 For illustrative purposes only, the magnitude relationship of the three-phase voltages is not fixed throughout the entire cycle, but rather varies, and there is also a U... SA >U SC >U SB U SB >U SA >U SC U SB >U SC >U SA U SC >U SA >U SB U SC >U SB >U SA The principle behind these situations is the same: regardless of whether the current is positive or negative, the FBSM capacitor (i.e., the first capacitor C1) is charged. The HBSM capacitor (i.e., the second capacitor C2) is charged only when the current is positive. When the current is negative, the HBSM capacitor (i.e., the second capacitor C2) is bypassed and is not charged. These situations will not be listed one by one here.

[0043] and, Figure 4In the middle, the line voltage U AB The sum of the voltages of all charging capacitors in both the A-phase and B-phase upper bridge arms, which is the sum of the voltages of the two FBSM capacitors and the voltage of the one HBSM capacitor; DC voltage U DC It equals the sum of the voltages of all charging capacitors in the upper and lower arms of phase A, which is the sum of the voltages of the two FBSM capacitors and the voltage of the one HBSM capacitor. Therefore, at the end of the first stage of charging, the DC voltage U DC Equal to line voltage U AB The peak value.

[0044] The first stage of charging ends when the capacitor voltage in each submodule stabilizes.

[0045] (2) Second stage: First half-controlled charging stage.

[0046] After the first stage of charging, the capacitor voltage of each full-bridge submodule exceeds the self-charging threshold voltage, and the switches of each full-bridge submodule are in a controllable state. However, the capacitor voltage of each half-bridge submodule is below the self-charging threshold voltage, and the switches of each half-bridge submodule are in an uncontrollable state. In the second stage, only the switches in each full-bridge submodule are controlled; the switches in each half-bridge submodule are not controlled, thus it is a semi-controlled charging state. Switches S5 and S6 in each half-bridge submodule are in the off state.

[0047] In some embodiments, the process of the controller controlling the capacitor bypass in each full-bridge submodule includes: the controller controlling the first upper bridge arm and the second upper bridge arm to be turned on, and controlling the first lower bridge arm and the second lower bridge arm to be turned off; or, controlling the first upper bridge arm and the second upper bridge arm to be turned off, and controlling the first lower bridge arm and the second lower bridge arm to be turned on, so as to bypass the first capacitor.

[0048] Figure 2 In this scenario, the controller can either turn on switches S1 and S3 and turn off switches S2 and S4, or turn off switches S1 and S3 and turn on switches S2 and S4 to bypass the first capacitor C1. For example, if the controller turns on switches S1 and S3 and turns off switches S2 and S4, one current path would be as follows: Figure 5 As shown. Figure 5 In the current circuit, current flows through switching transistors S1 and S3, but not through the first capacitor C1, thus bypassing C1 and preventing it from being charged. Similarly, when the controller turns off switching transistors S1 and S3 and turns on switching transistors S2 and S4, current flows through switching transistors S2 and S4, but not through the first capacitor C1, thus bypassing C1 and preventing it from being charged.

[0049] Therefore, for each phase bridge arm, regardless of whether the current is positive or negative, the FBSM capacitor (i.e., the first capacitor C1) is bypassed and not charged. The HBSM capacitor (i.e., the second capacitor C2) is charged only when the current is positive, and bypassed and not charged when the current is negative. The state of HBSM is consistent with that in the first stage. For detailed analysis, please refer to the first stage, which will not be repeated here.

[0050] The controller controls the operation of the switching transistors in each full-bridge submodule, bypassing the capacitors in each full-bridge submodule and charging only the capacitors in each half-bridge submodule, without charging the capacitors in the full-bridge submodule. This increases the capacitor voltage of each half-bridge submodule and decreases the voltage difference between the capacitor voltages of the full-bridge submodule and the half-bridge submodule. Finally, the charging phase ends when the capacitor voltage of the half-bridge submodule equals the capacitor voltage of the full-bridge submodule.

[0051] In the exemplary embodiment, the switching states of different full-bridge submodules may be the same or different, and this application does not impose any restrictions on this.

[0052] The second stage of charging ends when the voltage of the capacitors in each submodule is equal, that is, the voltage of the capacitors in each half-bridge submodule is equal to the voltage of the capacitors in each full-bridge submodule.

[0053] (3) The third stage: the second half-control charging stage.

[0054] After the second stage of charging, the capacitor voltage of each full-bridge submodule has exceeded the self-charging threshold voltage, and the switches of each full-bridge submodule are in a controllable state. Since the capacitor voltage in each half-bridge submodule is equal to the capacitor voltage in each full-bridge submodule, the capacitor voltage in each half-bridge submodule has also exceeded the self-charging threshold voltage, and the switches of each half-bridge submodule are also in a controllable state. However, in the third stage, only the switches in each full-bridge submodule are controlled; the switches in each half-bridge submodule are not controlled, so it is a semi-controlled charging state. Switches S5 and S6 in each half-bridge submodule are in the off state.

[0055] In the third stage, the actions of each full-bridge submodule are controlled to make the full-bridge submodule equivalent to a half-bridge submodule, and the capacitors in each submodule are charged until the capacitor voltage stabilizes.

[0056] In some embodiments, the process of the controller controlling the actions of each full-bridge submodule to make the full-bridge submodule equivalent to a half-bridge submodule includes: The controller controls the first upper bridge arm to be turned on and controls the first lower bridge arm, the second upper bridge arm, and the second lower bridge arm to be turned off; or, controls the second lower bridge arm to be turned on and controls the first upper bridge arm, the first lower bridge arm, and the second upper bridge arm to be turned off, so that the full bridge submodule is equivalent to a half bridge submodule.

[0057] Figure 2 In this configuration, the controller can either turn on switch S1 and turn off switches S2, S3, and S4; or it can turn on switch S4 and turn off switches S1, S2, and S3, thus making the full-bridge submodule equivalent to a half-bridge submodule. For example, if the controller turns on switch S4 and turns off switches S1, S2, and S3, the current path when the current is in the forward direction is as follows: Figure 6 As shown, the current path when the current is negative is as follows Figure 7 As shown. Figure 6 In the process, current flows through the anti-parallel diode D1, the first capacitor C1, and the switching transistor S4, charging the first capacitor C1. Figure 7 In this configuration, current flows through switch S4 and anti-parallel diode D2, bypassing the first capacitor C1 and preventing it from charging. Turning on switch S4 is equivalent to making it a wire, while clamping it with anti-parallel diode D3 is equivalent to disconnecting it from switch S3. In this case, the full-bridge submodule is equivalent to a half-bridge submodule consisting only of switch S1, anti-parallel diode D1, switch S2, and anti-parallel diode D2. Therefore, the full-bridge submodule is equivalent to a half-bridge submodule.

[0058] Therefore, for each phase bridge arm, the FBSM capacitor (i.e., the first capacitor C1) is charged only when the current is in the forward direction (by...). Figure 6 As can be seen, when the current is negative, the FBSM capacitor (i.e., the first capacitor C1) is bypassed and not charged (due to...). Figure 7 As can be seen, the HBSM capacitor (i.e., the second capacitor C2) is charged only when the current is positive, and the HBSM capacitor (i.e., the second capacitor C2) is bypassed and not charged when the current is negative. The state of HBSM is the same as in the first stage. For detailed analysis, please refer to the first stage. It will not be repeated here.

[0059] At the end of the second stage, the capacitor voltage of the half-bridge submodule is equal to the capacitor voltage of the full-bridge submodule. In the third stage, the operation of each full-bridge submodule is controlled to make the full-bridge submodule equivalent to a half-bridge submodule, charging the capacitors in each submodule until the capacitor voltage stabilizes. Since the full-bridge submodule is equivalent to a half-bridge submodule, the capacitor voltage of each half-bridge submodule is kept equal to the capacitor voltage of each full-bridge submodule. The capacitor voltage of each half-bridge submodule and the capacitor voltage of each full-bridge submodule are increased synchronously, so that when entering the fourth stage, the capacitor voltage of each submodule is closer to the rated voltage, reducing overmodulation.

[0060] In the exemplary embodiment, the switching states of different full-bridge submodules may be the same or different, and this application does not impose any restrictions on this.

[0061] The third stage of charging ends when the capacitor voltage in each submodule stabilizes.

[0062] (4) Fourth stage: Full-control charging stage.

[0063] After the third stage of charging is completed, the switching transistors in each full-bridge submodule and each half-bridge submodule are controlled to perform constant current charging on each submodule until the voltage of the capacitor in each submodule equals the rated voltage. In the fourth stage, the switching transistors in each full-bridge submodule and each half-bridge submodule are controlled to operate, thus entering a fully controlled charging state.

[0064] In some embodiments, the process of the controller controlling each submodule to perform constant current charging until the voltage of the capacitor in each submodule equals the rated voltage includes: The controller uses current loop control to obtain the modulated voltage; The controller corrects the nearest level approximation modulation and obtains the number of sub-modules engaged in each bridge arm at each time based on the modulation voltage and the corrected nearest level approximation modulation; wherein the engaged sub-modules include at least one of the following: a half-bridge sub-module with positive capacitor engagement, a full-bridge sub-module with positive capacitor engagement, and a full-bridge sub-module with negative capacitor engagement. Based on the number of sub-modules deployed in each bridge arm at each time, the controller performs voltage equalization sorting on each sub-module in each bridge arm to obtain the target sub-modules that need to be deployed in each bridge arm at each time. The controller generates control signals based on the target sub-modules that each bridge arm needs to be engaged at each moment; The controller controls each submodule based on the control signal, causing each submodule to be charged with constant current until the voltage of the capacitor in each submodule is equal to the rated voltage.

[0065] In an exemplary embodiment, positive capacitor connection means that the positive terminal of the capacitor is connected to the positive terminal of the output port of the submodule in which the capacitor is located, and negative capacitor connection means that the negative terminal of the capacitor is connected to the positive terminal of the output port of the submodule in which the capacitor is located.

[0066] The current loop control can control the charging speed. The sub-modules to be engaged include at least one of the following: a half-bridge sub-module with positive capacitor engagement, a full-bridge sub-module with positive capacitor engagement, and a full-bridge sub-module with negative capacitor engagement. By utilizing the negative level output capability of the FBSM, the output capability of the hybrid modular multilevel converter can be expanded, overmodulation can be avoided, the current can be accurately controlled to track the current reference value, and the current surge during the charging process of the hybrid modular multilevel converter can be reduced.

[0067] In an exemplary embodiment, Figure 8 This is a control block diagram for the fourth stage of a hybrid modular multilevel converter provided in an embodiment of this application. Figure 8 in, u abc Indicates the three-phase voltage of HMMC, i abc This represents the three-phase current of the HMMC. Indicates the synchronization angle command, u abc Obtained through a phase-locked loop (PLL) ,based on For u abc Perform the abc / dq coordinate transformation (i.e., the Parker transformation) to obtain u. d and u q u d U represents the actual value of the d-axis voltage. q Represents the actual value of the q-axis voltage; based on to i abc Perform an abc / dq coordinate transformation (i.e., Parker transformation) to obtain i d and i q i d Indicates the actual value of the d-axis current, i q This represents the actual value of the q-axis current. dref Indicates the d-axis current reference value, i qref Indicates the q-axis current reference value, i dref and i qref It is a system-given value, i qref =0, ensuring a power factor of 1 during fully controlled charging. PI stands for Proportional-Integral Controller. It refers to virtual reactance. The dq / abc coordinate transformation is an inverse Parker transformation, which can obtain the modulation voltages of phase A, phase B, and phase C. NLM stands for Nearest Level Modulation.

[0068] The first three stages use the peak line voltage to charge the capacitor. When switching to fully controlled charging, due to the limitation of the peak line voltage, the capacitor voltage of the submodule is less than the rated voltage of the submodule. If traditional nearest-level approximation modulation is used, the submodule can only use either direct capacitor input or capacitor bypass, meaning the output voltage of the submodule is 0 or equal to the capacitor voltage U. C The output capability of HMMC is U ac ∈[-U LM / 2, U LM / 2],U LM The output capability of the HMMC is only the line voltage peak value U. LM Half of the phase voltage peak U m When controlled by current, the voltage may exceed [-U]. LM / 2, U LM [ / 2] Within this range, overmodulation occurs, making it impossible to accurately control the current to track the current reference value. A negative FBSM output level means the FBSM capacitor is connected in reverse, i.e., the capacitor is negatively connected. A positive FBSM output level means the FBSM capacitor is connected in forward, i.e., the capacitor is positively connected. Utilizing the negative FBSM output capability can expand the HMMC's output capability. The HMMC's output capability is U. ac ∈[-(h / 2+f)×U C (h / 2+f)×U C [, greater than the peak phase voltage U] m U C This refers to the capacitor voltage of the submodule. Each bridge arm in the upper and lower bridge arms includes N submodules connected in series. The N submodules include h half-bridge submodules and f full-bridge submodules, where h is the number of half-bridge submodules in each bridge arm and f is the number of full-bridge submodules in each bridge arm.

[0069] In the exemplary embodiment, the controller corrects the nearest-level approximation modulation. Based on the modulation voltage and the corrected nearest-level approximation modulation, the number of submodules engaged in each bridge arm at each time step is obtained. In the corrected nearest-level approximation modulation, the number of submodules engaged in the upper bridge arm is n. refu1 =round(N x -U m ×cos(θ) / U C The number of sub-modules deployed in the lower bridge arm is n. refu2 = round(N x +U m ×cos(θ) / U C ), where N xThis refers to the corrected number of submodules in each bridge arm, a value obtained by correcting N. Generally, FBSM accounts for approximately 60% of the total number of submodules in a bridge arm, and N can be calculated from this. x ∈[-0.023N, 0.423N]; round is the rounding function; U m This represents the peak value of the phase voltage. Indicates the synchronization angle command; U C This refers to the capacitor voltage of the submodule; U m ×cos(θ) refers to the modulation voltage. Before the closest level approximation modulation correction, N... x When the position is N, the output capability of HMMC is U before correction. ac ∈[-U LM / 2, U LM / 2]; Corrected to N x At that time, the output capability of HMMC is U ac ∈[-(h / 2+f)×U C (h / 2+f)×U C ], by modifying N to N x This expands the output capability of HMMC. When n refu1 When n is less than 0, the FBSM outputs a negative level, the capacitor is negatively connected, and n refu1 ∈[-f,f+h].

[0070] In the exemplary embodiment, when no negative voltage is required, voltage equalization sorting refers to the following: when the current is positive (capacitor charging), the submodule capacitor voltages of the sub-modules connected to a single bridge arm are sorted from smallest to largest, and the sub-modules with smaller capacitor voltages are connected; when the current is negative (capacitor discharging), the submodule capacitor voltages of the sub-modules connected to a single bridge arm are sorted from largest to smallest, and the sub-modules with larger capacitor voltages are connected, in order to ensure voltage balance. When negative voltage is required, voltage equalization sorting refers to the following: when the current is positive (capacitor discharging), the submodule capacitor voltages of the sub-modules connected to a single bridge arm are sorted from largest to smallest, and the sub-modules with larger capacitor voltages are connected; when the current is negative (capacitor charging), the submodule capacitor voltages of the sub-modules connected to a single bridge arm are sorted from smallest to largest, and the sub-FBSMs with smaller capacitor voltages are connected.

[0071] In some embodiments, the process by which the controller controls each submodule based on control signals includes: Based on the control signal, the controller controls the positive connection of the capacitor in the first full-bridge submodule, and / or controls the negative connection of the capacitor in the second full-bridge submodule, and / or controls the bypass of the capacitor in the third full-bridge submodule. The controller controls the capacitor input in the first half-bridge submodule and / or controls the capacitor bypass in the second half-bridge submodule based on the control signal.

[0072] In the fourth stage, the full-bridge submodule has three states: capacitor positive connection, capacitor negative connection, or capacitor bypass. In the fourth stage, the half-bridge submodule has two states: capacitor connection or capacitor bypass.

[0073] In some embodiments, the process of the controller controlling the positive connection of the capacitor in the first full-bridge submodule includes: the controller controlling the first upper bridge arm and the second lower bridge arm in the first full-bridge submodule to be turned on, and controlling the first lower bridge arm and the second upper bridge arm in the first full-bridge submodule to be turned off, so that the first capacitor in the first full-bridge submodule is positively connected. The process of the controller controlling the negative connection of the capacitor in the second full-bridge submodule includes: the controller controlling the first upper bridge arm and the second lower bridge arm in the second full-bridge submodule to turn off, and controlling the first lower bridge arm and the second upper bridge arm in the second full-bridge submodule to turn on, so that the first capacitor in the second full-bridge submodule is negatively connected.

[0074] Figure 2 In the process of the controller controlling the capacitor in the first full-bridge submodule to be connected, the controller controls the switching transistors S1 and S4 in the first full-bridge submodule to be turned on and controls the switching transistors S2 and S3 in the first full-bridge submodule to be turned off. Current flows through the switching transistor S1, the first capacitor C1 and the switching transistor S4 so that the first capacitor C1 in the first full-bridge submodule is connected.

[0075] Figure 2 In the process of the controller controlling the negative connection of the capacitor in the second full-bridge submodule, the controller controls the switching transistors S1 and S4 in the second full-bridge submodule to turn off, and controls the switching transistors S2 and S3 in the second full-bridge submodule to turn on, so that the current flows through the switching transistor S2, the first capacitor C1 and the switching transistor S3, so that the first capacitor C1 in the second full-bridge submodule is negatively connected.

[0076] The process of the controller controlling the capacitor bypass in the third full-bridge submodule is described in the second stage. Figure 5 This will not be elaborated upon here.

[0077] In some embodiments, the process of the controller controlling the capacitor input in the first half-bridge submodule includes: the controller controlling the third upper bridge arm in the first half-bridge submodule to be turned on, and controlling the third lower bridge arm in the first half-bridge submodule to be turned off, so that the second capacitor in the first half-bridge submodule is input. The process of the controller controlling the bypass of the capacitor in the second half-bridge submodule includes: the controller controlling the third upper bridge arm in the second half-bridge submodule to turn off and controlling the third lower bridge arm in the second half-bridge submodule to turn on, so as to bypass the second capacitor in the second half-bridge submodule.

[0078] Figure 3In the process of the controller controlling the capacitor in the first half-bridge sub-module to be connected, the controller controls the switching transistor S5 in the first half-bridge module to be turned on and controls the switching transistor S6 in the first half-bridge module to be turned off, and the current flows through the switching transistor S5 and the second capacitor C2, so that the second capacitor C2 in the first half-bridge module is connected.

[0079] Figure 3 In the process of the controller controlling the bypass of the capacitor in the second half-bridge submodule, the controller controls the switch S5 in the second half-bridge module to turn off and controls the switch S6 in the second half-bridge module to turn on, so that the current flows through the switch S6, thereby bypassing the second capacitor C2 in the second half-bridge module.

[0080] The fourth stage of charging ends when the voltage of the capacitors in each submodule equals the rated voltage. After the fourth stage of charging is completed, the entire charging process ends, and the hybrid modular multilevel converter can be switched to normal operation.

[0081] Exemplary methods In one exemplary embodiment, a charging method for a hybrid modular multilevel converter is provided, applicable to the hybrid modular multilevel converter provided in any of the above embodiments of this application.

[0082] The hybrid modular multilevel converter includes a three-phase circuit. Each phase circuit includes an upper bridge arm and a lower bridge arm connected in series. Each bridge arm in the upper and lower bridge arms includes N sub-modules connected in series. The N sub-modules include h half-bridge sub-modules and f full-bridge sub-modules, where N = h + f, and N, h, and f are positive integers. Each sub-module includes a capacitor. like Figure 9 As shown, the charging method for the hybrid modular multilevel converter includes: Step S101: Charge the capacitors in each submodule until the capacitor voltage stabilizes.

[0083] Step S102: Control the bypass of capacitors in each full-bridge submodule to charge capacitors in each half-bridge submodule until the voltage of capacitors in each submodule is equal.

[0084] Step S103: Control each submodule to perform constant current charging until the voltage of the capacitor in each submodule is equal to the rated voltage.

[0085] The capacitors in each submodule are charged until their voltages stabilize. Initially, uncontrolled charging is performed. Once the capacitor voltages stabilize, the full-bridge submodule draws power from the capacitors to supply power to the drive circuit, thereby controlling the switching of the transistors in the full-bridge submodule. During uncontrolled charging, since the capacitors in the full-bridge submodule are charging at all times, while the capacitors in the half-bridge submodule are charging only half the time, the capacitor voltage in the full-bridge submodule is greater than that in the half-bridge submodule at the end of the uncontrolled charging phase. Then, the capacitors in each full-bridge submodule are bypassed, allowing the capacitors in each half-bridge submodule to charge until their voltages are equal. The transistors in each full-bridge submodule are then activated, bypassing the capacitors in the full-bridge submodule and charging only the capacitors in the half-bridge submodules. This increases the capacitor voltage in the half-bridge submodules and decreases the voltage difference between the full-bridge and half-bridge capacitor voltages. Finally, this charging phase ends when the capacitor voltage in the half-bridge submodule equals that in the full-bridge submodule. Finally, each submodule is controlled to undergo constant current charging until the voltage of the capacitor in each submodule equals its rated voltage. Since the capacitor voltage of the half-bridge submodule equals the capacitor voltage of the full-bridge submodule at the end of the charging phase that only charges the capacitors in each half-bridge submodule, the voltage difference between the capacitor voltages of the full-bridge and half-bridge submodules is small during the constant current charging phase, thus reducing the current surge during the charging process of the hybrid modular multilevel converter. Furthermore, constant current charging ensures a smoother charging process, further reducing the current surge during the charging process of the hybrid modular multilevel converter.

[0086] In some embodiments, the full-bridge submodule includes a first bridge arm, a second bridge arm, and a first capacitor connected in parallel; the first bridge arm includes a first upper bridge arm and a first lower bridge arm connected in series, and the connection point of the first upper bridge arm and the first lower bridge arm serves as the first end of the full-bridge submodule; the second bridge arm includes a second upper bridge arm and a second lower bridge arm connected in series, and the connection point of the second upper bridge arm and the second lower bridge arm serves as the second end of the full-bridge submodule. The process of controlling capacitor bypass in each full-bridge submodule includes: Control the first upper bridge arm and the second upper bridge arm to be turned on, and control the first lower bridge arm and the second lower bridge arm to be turned off; or, control the first upper bridge arm and the second upper bridge arm to be turned off, and control the first lower bridge arm and the second lower bridge arm to be turned on, so as to bypass the first capacitor.

[0087] The switching transistors in each full-bridge submodule are controlled to bypass the capacitors in each full-bridge submodule, charging only the capacitors in each half-bridge submodule and not the capacitors in the full-bridge submodule. This increases the capacitor voltage of each half-bridge submodule and decreases the voltage difference between the capacitor voltages of the full-bridge submodule and the half-bridge submodule. Finally, the charging phase ends when the capacitor voltage of the half-bridge submodule equals the capacitor voltage of the full-bridge submodule.

[0088] In some embodiments, after step S102 and before step S103, the charging method for the hybrid modular multilevel converter further includes: controlling the operation of each full-bridge submodule to make the full-bridge submodule equivalent to a half-bridge submodule, and charging the capacitors in each submodule until the capacitor voltage is stable.

[0089] At the end of the charging phase, which only charges the capacitors in each half-bridge submodule, the capacitor voltage of the half-bridge submodule equals the capacitor voltage of the full-bridge submodule. At this point, the operation of each full-bridge submodule is controlled to make the full-bridge submodule equivalent to a half-bridge submodule, charging the capacitors in each submodule until the capacitor voltage stabilizes. Since the full-bridge submodule is equivalent to a half-bridge submodule, the capacitor voltages of each half-bridge submodule and each full-bridge submodule are kept equal. The capacitor voltages of each half-bridge submodule and each full-bridge submodule are increased synchronously, so that when the constant current charging phase of each submodule is entered, the capacitor voltage of each submodule is closer to the rated voltage, reducing overmodulation.

[0090] In some embodiments, the full-bridge submodule includes a first bridge arm, a second bridge arm, and a first capacitor connected in parallel; the first bridge arm includes a first upper bridge arm and a first lower bridge arm connected in series, and the connection point of the first upper bridge arm and the first lower bridge arm serves as the first end of the full-bridge submodule; the second bridge arm includes a second upper bridge arm and a second lower bridge arm connected in series, and the connection point of the second upper bridge arm and the second lower bridge arm serves as the second end of the full-bridge submodule. The process of controlling the actions of each full-bridge submodule to make the full-bridge submodule equivalent to a half-bridge submodule includes: Control the first upper bridge arm to be turned on, and control the first lower bridge arm, the second upper bridge arm, and the second lower bridge arm to be turned off; or, control the second lower bridge arm to be turned on, and control the first upper bridge arm, the first lower bridge arm, and the second upper bridge arm to be turned off, so that the full bridge submodule is equivalent to a half bridge submodule.

[0091] At the end of the second stage, the capacitor voltage of the half-bridge submodule is equal to the capacitor voltage of the full-bridge submodule. In the third stage, the operation of each full-bridge submodule is controlled to make the full-bridge submodule equivalent to a half-bridge submodule, charging the capacitors in each submodule until the capacitor voltage stabilizes. Since the full-bridge submodule is equivalent to a half-bridge submodule, the capacitor voltage of each half-bridge submodule is kept equal to the capacitor voltage of each full-bridge submodule. The capacitor voltage of each half-bridge submodule and the capacitor voltage of each full-bridge submodule are increased synchronously, so that when entering the fourth stage, the capacitor voltage of each submodule is closer to the rated voltage, reducing overmodulation.

[0092] In some embodiments, controlling each submodule to perform constant current charging until the voltage of the capacitor in each submodule equals the rated voltage includes: The modulation voltage is obtained by using current loop control; The nearest-level approximation modulation is corrected, and based on the modulation voltage and the corrected nearest-level approximation modulation, the number of sub-modules put into each bridge arm at each time is obtained; wherein, the put-in sub-modules include at least one of the following: a half-bridge sub-module with positive capacitor input, a full-bridge sub-module with positive capacitor input, and a full-bridge sub-module with negative capacitor input. Based on the number of sub-modules deployed in each bridge arm at each time, the sub-modules in each bridge arm are sorted by voltage equalization to obtain the target sub-modules that need to be deployed in each bridge arm at each time. Based on the target sub-modules that need to be deployed for each bridge arm at each moment, control signals are generated. Based on the control signal, each submodule is controlled to perform constant current charging until the voltage of the capacitor in each submodule is equal to the rated voltage.

[0093] The current loop control can control the charging speed. The sub-modules to be engaged include at least one of the following: a half-bridge sub-module with positive capacitor engagement, a full-bridge sub-module with positive capacitor engagement, and a full-bridge sub-module with negative capacitor engagement. By utilizing the negative level output capability of the FBSM, the output capability of the hybrid modular multilevel converter can be expanded, overmodulation can be avoided, the current can be accurately controlled to track the current reference value, and the current surge during the charging process of the hybrid modular multilevel converter can be reduced.

[0094] For technical details not described in detail in this embodiment, please refer to the specific processing content of the hybrid modular multilevel converter provided in the above embodiments of this application, which will not be repeated here.

[0095] Exemplary controller Accordingly, this application also provides a controller for executing the charging method of the hybrid modular multilevel converter provided in any of the above embodiments of this application.

[0096] For technical details not described in detail in this embodiment, please refer to the specific processing content of the charging method of the hybrid modular multilevel converter provided in the above embodiments of this application, which will not be repeated here.

[0097] Exemplary power conversion system Accordingly, embodiments of this application also provide a power conversion system, including the hybrid modular multilevel converter provided in any of the above embodiments of this application.

[0098] For technical details not described in detail in this embodiment, please refer to the specific processing content of the hybrid modular multilevel converter provided in the above embodiments of this application, which will not be repeated here.

[0099] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0100] The modules and circuits in the various embodiments of this application can be merged, divided, and deleted according to actual needs.

[0101] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0102] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A hybrid modular multilevel converter, characterized in that, It includes a three-phase circuit and a controller. Each phase circuit includes an upper bridge arm and a lower bridge arm connected in series. Each of the upper and lower bridge arms includes N sub-modules connected in series. The N sub-modules include h half-bridge sub-modules and f full-bridge sub-modules, where N = h + f, and N, h, and f are positive integers. Each sub-module includes a capacitor. The controller is configured to: Charge the capacitors in each of the sub-modules until the capacitor voltage stabilizes; By controlling the bypass of capacitors in each of the full-bridge submodules, the capacitors in each of the half-bridge submodules are charged until the voltages of the capacitors in each of the submodules are equal. Each of the sub-modules is controlled to perform constant current charging until the voltage of the capacitor in each sub-module is equal to the rated voltage.

2. The hybrid modular multilevel converter according to claim 1, characterized in that, The full-bridge submodule includes a first bridge arm, a second bridge arm, and a first capacitor connected in parallel; the first bridge arm includes a first upper bridge arm and a first lower bridge arm connected in series, and the connection point of the first upper bridge arm and the first lower bridge arm serves as the first end of the full-bridge submodule; the second bridge arm includes a second upper bridge arm and a second lower bridge arm connected in series, and the connection point of the second upper bridge arm and the second lower bridge arm serves as the second end of the full-bridge submodule. The process of the controller controlling the capacitor bypass in each of the full-bridge submodules includes: The controller controls the first upper bridge arm and the second upper bridge arm to be turned on, and controls the first lower bridge arm and the second lower bridge arm to be turned off. Alternatively, the first upper bridge arm and the second upper bridge arm can be turned off, and the first lower bridge arm and the second lower bridge arm can be turned on, so as to bypass the first capacitor.

3. The hybrid modular multilevel converter according to claim 1, characterized in that, The controller is also configured to: By controlling the bypass of capacitors in each of the full-bridge submodules, the capacitors in each of the half-bridge submodules are charged until the voltages of the capacitors in each of the submodules are equal. Before controlling each of the submodules to perform constant current charging, the operation of each of the full-bridge submodules is controlled so that the full-bridge submodule is equivalent to the half-bridge submodule, and the capacitors in each of the submodules are charged until the capacitor voltage is stable.

4. The hybrid modular multilevel converter according to claim 3, characterized in that, The full-bridge submodule includes a first bridge arm, a second bridge arm, and a first capacitor connected in parallel; the first bridge arm includes a first upper bridge arm and a first lower bridge arm connected in series, and the connection point of the first upper bridge arm and the first lower bridge arm serves as the first end of the full-bridge submodule; the second bridge arm includes a second upper bridge arm and a second lower bridge arm connected in series, and the connection point of the second upper bridge arm and the second lower bridge arm serves as the second end of the full-bridge submodule. The process by which the controller controls the actions of each full-bridge submodule to make the full-bridge submodule equivalent to the half-bridge submodule includes: The controller controls the first upper bridge arm to be turned on, and controls the first lower bridge arm, the second upper bridge arm, and the second lower bridge arm to be turned off. Alternatively, the second lower bridge arm can be turned on, and the first upper bridge arm, the first lower bridge arm, and the second upper bridge arm can be turned off, so that the full-bridge submodule is equivalent to the half-bridge submodule.

5. The hybrid modular multilevel converter according to claim 1, characterized in that, The controller controls each of the sub-modules to perform constant current charging until the voltage of the capacitor in each sub-module equals the rated voltage, including: The controller uses current loop control to obtain the modulated voltage; The controller corrects the nearest-level approximation modulation and, based on the modulation voltage and the corrected nearest-level approximation modulation, obtains the number of sub-modules engaged in each bridge arm at each moment; wherein the engaged sub-modules include at least one of a half-bridge sub-module with positive capacitor engagement, a full-bridge sub-module with positive capacitor engagement, and a full-bridge sub-module with negative capacitor engagement. Based on the number of sub-modules deployed in each bridge arm at each time moment, the controller performs voltage equalization sorting on each sub-module in each bridge arm to obtain the target sub-module that needs to be deployed in each bridge arm at each time moment. The controller generates control signals based on the target sub-modules that each bridge arm needs to be engaged at each moment; Based on the control signal, the controller controls each of the sub-modules to perform constant current charging until the voltage of the capacitor in each sub-module is equal to the rated voltage.

6. The hybrid modular multilevel converter according to claim 5, characterized in that, The process by which the controller controls each of the sub-modules based on the control signal includes: Based on the control signal, the controller controls the capacitor in the first full-bridge submodule to be positively connected, and / or controls the capacitor in the second full-bridge submodule to be negatively connected, and / or controls the capacitor in the third full-bridge submodule to be bypassed. Based on the control signal, the controller controls the capacitor input in the first half-bridge submodule and / or controls the capacitor bypass in the second half-bridge submodule.

7. The hybrid modular multilevel converter according to claim 6, characterized in that, The full-bridge submodule includes a first bridge arm, a second bridge arm, and a first capacitor connected in parallel; the first bridge arm includes a first upper bridge arm and a first lower bridge arm connected in series, and the connection point of the first upper bridge arm and the first lower bridge arm serves as the first end of the full-bridge submodule; the second bridge arm includes a second upper bridge arm and a second lower bridge arm connected in series, and the connection point of the second upper bridge arm and the second lower bridge arm serves as the second end of the full-bridge submodule. The process of the controller controlling the positive connection of the capacitor in the first full-bridge submodule includes: The controller controls the first upper bridge arm and the second lower bridge arm in the first full-bridge submodule to be turned on, and controls the first lower bridge arm and the second upper bridge arm in the first full-bridge submodule to be turned off, so that the first capacitor in the first full-bridge submodule is positively connected. The controller controls the negative connection process of the capacitor in the second full-bridge submodule, including: The controller controls the first upper bridge arm and the second lower bridge arm in the second full-bridge submodule to turn off, and controls the first lower bridge arm and the second upper bridge arm in the second full-bridge submodule to turn on, so that the first capacitor in the second full-bridge submodule is negatively connected.

8. The hybrid modular multilevel converter according to claim 6, characterized in that, The half-bridge submodule includes a third bridge arm and a second capacitor connected in parallel; the third bridge arm includes a third upper bridge arm and a third lower bridge arm connected in series, the connection point of the third upper bridge arm and the third lower bridge arm serves as the first end of the half-bridge submodule; the connection point of the third lower bridge arm and the second capacitor serves as the second end of the half-bridge submodule. The process of the controller controlling the capacitor input in the first half-bridge submodule includes: The controller controls the third upper bridge arm in the first half-bridge submodule to be turned on and controls the third lower bridge arm in the first half-bridge submodule to be turned off, so that the second capacitor in the first half-bridge submodule is engaged. The process of the controller controlling the capacitor bypass in the second half-bridge submodule includes: The controller controls the third upper bridge arm in the second half-bridge submodule to turn off and controls the third lower bridge arm in the second half-bridge submodule to turn on, so that the second capacitor in the second half-bridge submodule is bypassed.

9. A charging method for a hybrid modular multilevel converter, characterized in that, The hybrid modular multilevel converter includes a three-phase circuit, each phase circuit including an upper bridge arm and a lower bridge arm connected in series. Each of the upper and lower bridge arms includes N sub-modules connected in series. The N sub-modules include h half-bridge sub-modules and f full-bridge sub-modules, where N = h + f, and N, h, and f are positive integers. Each sub-module includes a capacitor. The charging method includes: Charge the capacitors in each of the sub-modules until the capacitor voltage stabilizes; By controlling the bypass of capacitors in each of the full-bridge submodules, the capacitors in each of the half-bridge submodules are charged until the voltages of the capacitors in each of the submodules are equal. Each of the sub-modules is controlled to perform constant current charging until the voltage of the capacitor in each sub-module is equal to the rated voltage.

10. The charging method for the hybrid modular multilevel converter according to claim 9, characterized in that, The full-bridge submodule includes a first bridge arm, a second bridge arm, and a first capacitor connected in parallel; the first bridge arm includes a first upper bridge arm and a first lower bridge arm connected in series, and the connection point of the first upper bridge arm and the first lower bridge arm serves as the first end of the full-bridge submodule; the second bridge arm includes a second upper bridge arm and a second lower bridge arm connected in series, and the connection point of the second upper bridge arm and the second lower bridge arm serves as the second end of the full-bridge submodule. The process of controlling the capacitor bypass in each of the full-bridge submodules includes: Control the first upper bridge arm and the second upper bridge arm to be turned on, and control the first lower bridge arm and the second lower bridge arm to be turned off; Alternatively, the first upper bridge arm and the second upper bridge arm can be turned off, and the first lower bridge arm and the second lower bridge arm can be turned on, so as to bypass the first capacitor.

11. The charging method for the hybrid modular multilevel converter according to claim 9, characterized in that, The method further includes, after bypassing the capacitors in each of the full-bridge submodules to charge the capacitors in each of the half-bridge submodules until the voltages of the capacitors in each submodule are equal, and before controlling each submodule to perform constant current charging: Control the operation of each full-bridge submodule to make the full-bridge submodule equivalent to the half-bridge submodule, and charge the capacitors in each submodule until the capacitor voltage stabilizes.

12. The charging method for the hybrid modular multilevel converter according to claim 11, characterized in that, The full-bridge submodule includes a first bridge arm, a second bridge arm, and a first capacitor connected in parallel; the first bridge arm includes a first upper bridge arm and a first lower bridge arm connected in series, and the connection point of the first upper bridge arm and the first lower bridge arm serves as the first end of the full-bridge submodule; the second bridge arm includes a second upper bridge arm and a second lower bridge arm connected in series, and the connection point of the second upper bridge arm and the second lower bridge arm serves as the second end of the full-bridge submodule. The process of controlling the actions of each of the full-bridge submodules to make the full-bridge submodules equivalent to the half-bridge submodules includes: Control the first upper bridge arm to be turned on, and control the first lower bridge arm, the second upper bridge arm, and the second lower bridge arm to be turned off; Alternatively, the second lower bridge arm can be turned on, and the first upper bridge arm, the first lower bridge arm, and the second upper bridge arm can be turned off, so that the full-bridge submodule is equivalent to the half-bridge submodule.

13. The charging method for the hybrid modular multilevel converter according to claim 9, characterized in that, The control of each submodule to perform constant current charging until the voltage of the capacitor in each submodule equals the rated voltage includes: The modulation voltage is obtained by using current loop control; The nearest-level approximation modulation is corrected, and based on the modulation voltage and the corrected nearest-level approximation modulation, the number of sub-modules engaged in each bridge arm at each time moment is obtained; wherein, the engaged sub-modules include at least one of the following: a half-bridge sub-module with positive capacitor engagement, a full-bridge sub-module with positive capacitor engagement, and a full-bridge sub-module with negative capacitor engagement. Based on the number of sub-modules deployed in each bridge arm at each time, the sub-modules in each bridge arm are sorted by voltage equalization to obtain the target sub-modules that need to be deployed in each bridge arm at each time. Based on the target sub-modules that need to be deployed for each bridge arm at each moment, control signals are generated. Based on the control signal, each of the sub-modules is controlled to perform constant current charging until the voltage of the capacitor in each sub-module is equal to the rated voltage.

14. A controller, characterized in that, A charging method for implementing the hybrid modular multilevel converter as described in any one of claims 9 to 13.

15. A power conversion system, characterized in that, Includes the hybrid modular multilevel converter as described in any one of claims 1 to 8.

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