WO2019205368A1

WO2019205368A1 - Method and device for starting half bridge-full bridge hybrid modular multilevel converter

Info

Publication number: WO2019205368A1
Application number: PCT/CN2018/101987
Authority: WO
Inventors: 熊文; 王莉; 赵宏伟; 尚慧玉
Original assignee: 广州供电局有限公司
Priority date: 2018-04-27
Filing date: 2018-08-23
Publication date: 2019-10-31
Also published as: CN108471251B; JP2021516946A; KR20200125988A; JP7125504B2; KR102440726B1; CN108471251A

Abstract

A method for starting a half bridge-full bridge hybrid modular multilevel converter. The method comprises: controlling a plurality of half bridge submodules and a plurality of full bridge submodules to remain latched, such that all of the half bridge submodules and all of the full bridge submodules reach respective initial voltages thereof; controlling the plurality of half bridge submodules to remain latched, and reducing the total voltage increase speed of all of the full bridge submodules by means of controlling operating states of at least a portion of the full bridge submodules; separately controlling operating states of each full bridge submodule and each half bridge submodule, such that the voltages of all of the half bridge submodules and the voltages of all of the full bridge submodules all reach a rated voltage. And a device for starting a half bridge-full bridge hybrid modular multilevel converter. The described method and device may avoid causing a large impact current at the moment a system is unlatched, thereby improving the safety of the system.

Description

Method and device for starting modular multilevel converter with half bridge and full bridge

Technical field

The invention relates to the technical field of power supply, in particular to a method and a device for starting a modular multilevel converter with a half bridge and a full bridge.

Background technique

Modular Multilevel Converter (MMC) realizes high voltage output by cascading several converter valve submodule units. MMC does not require direct cascading of switching devices, has low requirements for consistent triggering of the device, and has many advantages such as good scalability, low switching frequency, low operating loss, and high output voltage waveform quality.

However, when the AC power grid supplies power to the flexible DC transmission network through the MMC, due to the low damping characteristic of the flexible DC transmission network, when the MMC has a short-circuit fault, the current rise rate of the fault reaches several thousand amps per millisecond, and the AC circuit breaker only has The breaking speed of tens of milliseconds, which will make the critical equipment such as MMC in the DC network with severe electrical stress and reduce the safety of equipment operation in the power grid. Therefore, when a short circuit fault occurs in the MMC, the safety of the power grid system is not good.

Summary of the invention

Based on this, it is necessary to provide a method and a device for starting a modular multilevel converter with a half bridge and a full bridge in combination with the problem that the safety of the power grid system is not good when the short circuit fault occurs in the current MMC.

A method of starting a modular multilevel converter with a half bridge and a full bridge, the modular multilevel converter comprising a plurality of half bridge submodules and a plurality of full bridge submodules. The method includes:

Controlling the plurality of half bridge submodules and the plurality of full bridge submodules to remain latched such that all half bridge submodules and all full bridge submodules reach respective initial voltages;

Controlling the plurality of half bridge submodules to remain latched, and reducing a total voltage increase speed of all full bridge submodules by controlling an operating state of at least a portion of the full bridge submodules; wherein an operating state of the full bridge submodule includes One of a latching, semi-latching or bypassing;

Controlling the working states of the full bridge submodules and the half bridge submodules respectively, so that the voltages of all the half bridge submodules and the voltages of all the full bridge submodules reach the rated voltage; wherein the working state of the half bridge submodule Includes bypass or blocking.

In one of these embodiments, the modular multilevel converter is connected to the AC grid by a series charging resistor.

In one of the embodiments, the step of keeping all of the half bridge submodules latched, and reducing the total voltage increase speed of the full bridge submodule by controlling the operating state of at least a portion of the full bridge submodules includes:

The charging resistor is bypassed when the current of the charging resistor is less than a preset current value.

The charging resistor is bypassed when the voltage of the charging resistor is greater than a preset voltage value.

In one embodiment, the step of keeping all of the half bridge submodules latched, and reducing the total voltage increase speed of the full bridge submodules by controlling the operating state of at least a portion of the full bridge submodules includes:

Controlling all half bridge modules to remain locked when the voltage of each full bridge submodule reaches the operating threshold of the self-powered power supply;

a full bridge submodule bypass with a control voltage not less than the first threshold voltage;

a full bridge sub-module half-locking of the control voltage between the second threshold voltage and the first threshold voltage; wherein the second threshold voltage is less than the first threshold voltage;

The full bridge submodule whose control voltage is less than the second threshold voltage is blocked.

In one of the embodiments, the step of keeping all of the half bridge submodules latched, and reducing the total voltage increase speed of the full bridge submodules by controlling the operating state of at least part of the full bridge submodules includes:

When the ratio of the average voltage of all half bridge modules to the average voltage of all full bridge submodules is greater than the preset multiple, all full bridge submodules are controlled to be semi-latched, and all half bridge submodules are controlled to be blocked.

In one of the embodiments, the predetermined multiple is in the range of 0.6 to 1.4.

In one embodiment, the steps of respectively controlling the operating states of the respective full bridge submodules and the respective half bridge submodules such that the total voltage of all the half bridge submodules and all the full bridge submodules reach the rated voltage include:

The full bridge sub-module bypass of the control voltage not less than the third threshold voltage, and the half bridge sub-module bypass of the control voltage not less than the third threshold voltage.

A starting device for a modular multi-level inverter with a half bridge and a full bridge, the modular multilevel converter comprising a plurality of half bridge submodules and a plurality of full bridge submodules, the modular The multilevel converter is connected to the AC grid via a series charging resistor. The device includes:

The control module is not controlled, and all the half bridge modules and all the full bridge submodules are kept locked so that all the half bridge modules and all the full bridge submodules reach the initial voltage;

a semi-control start module for controlling all half-bridge sub-modules to remain locked, and reducing a total voltage increase speed of the full-bridge sub-module by controlling an operating state of at least part of the full-bridge sub-modules; wherein, the full-bridge sub-module The working state includes one of a latching, a semi-latching or a bypass;

The full control startup module is configured to respectively control the working states of the full bridge submodules and the half bridge submodules, so that the voltages of all the half bridge submodules reach the rated voltage, and the voltages of all the full bridge submodules are up to the rated a voltage; wherein the operating state of the half bridge submodule includes bypass or blocking.

In one embodiment, the half-control starting module is configured to control all half-bridge modules to remain locked when the voltage of each full-bridge sub-module reaches a working threshold of the self-receiving power supply;

The half-control starting module is further configured to control a full bridge sub-module bypass with a voltage not less than a first threshold voltage;

The half-control starting module is further configured to control a full bridge sub-module half-locking voltage between a second threshold voltage and the first threshold voltage; wherein the second threshold voltage is less than the first threshold voltage;

The half-control starting module is further configured to control a full bridge submodule latching whose voltage is less than the second threshold voltage.

The method and device for starting the above-mentioned half-bridge and full-bridge hybrid modular multi-level converter, firstly, all half-bridge modules and all full-bridge sub-modules are kept locked, that is, all half-bridge modules and all full bridges The submodules are subjected to a charging process so that all half bridge modules and all full bridge submodules reach the initial voltage. Secondly, all half-bridge modules are controlled to remain locked, and the total voltage increase speed of the full bridge sub-module is decreased by controlling the operating state of at least part of the full-bridge sub-modules. In this way, the average voltage of all the half bridge modules gradually increases, and the average voltage of all the full bridge submodules gradually increases, and the two gradually approach, and the voltages of all the submodules are equalized at this time. Then, the working states of each full bridge submodule and each half bridge submodule are respectively controlled so that the voltages of all the half bridge submodules reach the rated voltage, and the voltages of all the full bridge submodules reach the rated voltage. Thus, during the startup of the modular multilevel converter, the voltages of all full bridge submodules and all half bridge submodules increase slowly, and the voltages of all submodules remain in a more balanced state. Therefore, the output voltage of the modular multilevel converter is slowly increased to the rated voltage, which can avoid a large inrush current at the moment of system unlocking, thereby improving the safety factor of the grid system.

DRAWINGS

1 is a schematic diagram of a modular multilevel converter of an embodiment;

2 is a schematic diagram of a half bridge sub-module of an embodiment;

3 is a schematic diagram of a half bridge sub-module bypass of an embodiment;

4 is a schematic diagram of a full bridge submodule of an embodiment;

5 is a schematic diagram of a half-blocking of a full bridge sub-module according to an embodiment;

6 is a schematic diagram of a full bridge submodule bypass of an embodiment;

7 is a schematic diagram showing the connection of a modular multilevel converter and an AC power grid according to an embodiment;

8 is a schematic flow chart showing a method for starting a half-bridge and full-bridge hybrid modular multilevel converter according to the first embodiment;

9 is a schematic flow chart of a method for starting a half-bridge and full-bridge hybrid modular multi-level converter according to a second embodiment;

10 is a schematic flow chart showing a method for starting a half-bridge and full-bridge hybrid modular multilevel converter according to a third embodiment;

11 is a block diagram showing the structure of a starting device of a modular multilevel converter in which a half bridge and a full bridge are mixed according to an embodiment.

detailed description

The above described objects, features and advantages of the present invention will become more apparent from the aspects of the appended claims.

1 is a schematic diagram of a modular multilevel converter of an embodiment. As shown in FIG. 1, the modular multilevel converter includes a plurality of half bridge submodules and a plurality of full bridge submodules. The half bridge submodule and the full bridge submodule are collectively referred to as submodules. A modular multi-level inverter (referred to as an inverter) that is a hybrid of a half bridge and a full bridge contains at least one phase unit. In this embodiment, the inverter includes three phase units, which are an A phase unit, a B phase unit, and a C phase unit, respectively. Each phase unit includes an upper arm and a lower arm. The upper arm and the lower arm have the same structure. The upper arm and the lower arm each include at least one half bridge module, at least one full bridge submodule, and a reactor connected in series. In this embodiment, the upper bridge arm and the lower bridge arm each include a half bridge submodule, a full bridge submodule, and a reactor connected in series. In this embodiment, the inverter further includes a control device (not shown).

The half bridge submodule and the full bridge submodule are described in detail below.

2 is a schematic diagram of a half bridge sub-module of an embodiment. The half bridge submodule includes a capacitor and a first switching unit in parallel with the capacitor. In this embodiment, the first switching unit includes a first turn-off device and a second turn-off device. The negative electrode of the first turn-off device is connected in series with the positive electrode of the second turn-off device to form a first switching unit. The positive terminal of the first turn-off device serves as the positive electrode of the first switching unit, and the negative electrode of the second turn-off device serves as the negative electrode of the first switching unit. A connection point of the first switchable device and the second turn-off device serves as a first end point, and a negative terminal of the first switch unit serves as a second end point. The half bridge sub-module accesses the corresponding circuit through the first end point and the second end point. The operating state of the half bridge submodule includes bypass or blocking.

The working state of the half bridge submodule latching can be referred to FIG. 2. The half-bridge sub-module latching means that the first switch-off device of the half-bridge sub-module is turned off, and the second turn-off device is turned off.

3 is a schematic diagram of a half bridge sub-module bypass of an embodiment. As shown in FIG. 3, the half bridge sub-module bypass refers to the first shutdown device of the half bridge sub-module being turned off, and the second shutdown device is turned on.

4 is a schematic diagram of a full bridge sub-module of an embodiment. The full bridge submodule includes a capacitor and a second switching unit and a third switching unit in parallel with the capacitor. The second switching unit includes a third turn-off device and a fourth turn-off device. The negative electrode of the third turn-off device is formed in series with the positive electrode of the fourth turn-off device. The positive terminal of the third turn-off device serves as the positive electrode of the second switching unit, and the negative electrode of the fourth turn-off device serves as the negative electrode of the second switching unit. The connection point of the third turn-off device and the fourth turn-off device serves as a third terminal. The third switching unit includes a fifth turn-off device and a sixth turn-off device. The negative terminal of the fifth turn-off device is connected in series with the positive electrode of the sixth turn-off device. The positive terminal of the fifth turn-off device serves as the positive electrode of the third switching unit, and the negative electrode of the sixth turn-off device serves as the negative terminal of the third switching unit. The connection point of the fifth turn-off device and the sixth turn-off device serves as a fourth terminal. The full bridge submodule is connected to the corresponding circuit through the third end point and the fourth end point. The working state of the full bridge submodule includes one of blocking, semi-latching or bypassing.

Full-bridge sub-module latching means that the third, fourth, fifth, and sixth turn-off devices of the full-bridge sub-module are all turned off. See Figure 4 for a schematic diagram of the full bridge submodule latching.

FIG. 5 is a schematic diagram of a half-blocking of a full bridge sub-module according to an embodiment. As shown in FIG. 5, the full-bridge sub-module half-locking means that the third switchable device of the full-bridge sub-module is turned on, and the fourth, fifth, and sixth-off devices are turned off. In other embodiments, the third, fourth, and fifth turn-off devices may be turned off, and the sixth turn-off device may be turned on.

6 is a schematic diagram of a full bridge sub-module bypass of an embodiment. As shown in FIG. 6, the full bridge submodule bypass means that the third and fifth switchable devices of the full bridge submodule are turned off, and the fourth and sixth turnable devices are turned on. Or in other embodiments, the third and fifth turn-off devices are turned on, and the fourth and sixth turn-off devices are turned off.

Figure 7 is a schematic diagram showing the connection of a modular multilevel converter to an AC grid in accordance with an embodiment. The modular multilevel converter is connected to the AC grid via a series charging resistor. In this embodiment, the inverter is connected to the AC grid through the charging resistor R and its bypass switch QA and the incoming line switch QF. The charging resistor R is connected in series with the line switch QF. The charging resistor R is connected in parallel with the bypass switch QA.

8 is a flow chart showing a method of starting a half-bridge and full-bridge hybrid modular multilevel converter of the first embodiment. The method includes:

In step S120, all half-bridge modules and all full-bridge sub-modules are controlled to be latched so that all half-bridge modules and all full-bridge sub-modules reach an initial voltage.

Specifically, this step is an uncontrolled start-up phase. That is, at this stage, the control device controls all sub-modules to be latched, closes the incoming switch QF, and all sub-modules are charged so that all sub-modules have an initial voltage that can be operated. In this way, each sub-module can be put into preparation. The charging resistor R prevents overcurrent from being generated during the initial phase of charging of the AC system and damaging the system components. When the current of the charging resistor is less than the preset current value, the control device controls the charging resistor bypass. Alternatively, the control device controls the charging resistor bypass when the voltage of the charging resistor is greater than a preset voltage value. Since one full bridge submodule can be continuously charged during one cycle of alternating current, one half bridge module can only be charged in half a cycle. Therefore, after the same charging time, the voltage of one full bridge submodule is about twice the voltage of one half bridge module, and the voltages of both are lower. In this way, the converter can be prepared for the next working phase. Further, the preset current value may be 0.1 pu. The preset voltage value can be zero.

Step S140, controlling all the half bridge submodules to remain locked, and reducing the total voltage increase speed of the full bridge submodules by controlling the working state of at least part of the full bridge submodules.

Specifically, this phase is a semi-control start phase, that is, the control device only controls the full bridge submodule, and does not need to control the half bridge submodule. The control device can control a portion of the full bridge sub-module to be semi-latched such that the full bridge sub-modules are charged during the half cycle of the alternating current. Or the control device controls part of the full bridge submodule bypass so that the full bridge submodules stop charging. In this way, on the one hand, the charging speed of all the full bridge sub-modules can be reduced, so that the total voltage increase speed is lowered; on the other hand, the charging speed of all the half bridge sub modules can be increased, so that the voltage increasing speed is increased. Therefore, the average voltage of all half-bridge modules gradually increases, and the average voltage of all full-bridge sub-modules gradually increases, but the two gradually approach. Eventually the voltages of all submodules are equalized. Therefore, this causes the output voltage of the converter to rise steadily, reducing the probability of inrush current.

Step S160: Control the working states of the full bridge submodules and the half bridge submodules respectively, so that the voltages of all the half bridge submodules reach the rated voltage, and the voltages of all the full bridge submodules reach the rated voltage.

Specifically, this phase is a full control startup phase, that is, the control device can simultaneously control the full bridge submodule and the half bridge submodule. The working state of each full bridge submodule and each half bridge submodule can be dynamically controlled to slowly adjust the voltage of all submodules to the rated voltage to complete the startup process.

The starting method of the above-mentioned half-bridge and full-bridge hybrid modular multi-level converter, firstly, all half-bridge sub-modules and all full-bridge sub-modules are kept locked, that is, all half-bridge sub-modules and all full-bridge sub-modules The charging process is performed so that all half bridge modules and all full bridge submodules reach the initial voltage. Secondly, all half-bridge modules are controlled to remain locked, and the total voltage increase speed of the full bridge sub-module is decreased by controlling the operating state of at least part of the full-bridge sub-modules. In this way, the average voltage of all the half-bridge modules gradually increases, and the average voltage of all the full-bridge sub-modules gradually increases, and the two gradually approach, and the voltages of all the sub-modules are equalized at this time. Then, the working states of each full bridge submodule and each half bridge submodule are respectively controlled so that the voltages of all the half bridge submodules reach the rated voltage, and the voltages of all the full bridge submodules reach the rated voltage. Thus, during the startup of the modular multilevel converter, the voltages of all full bridge submodules and all half bridge submodules increase slowly, and the voltages of all submodules remain in a more balanced state. Therefore, the output voltage of the modular multilevel converter is slowly increased to the rated voltage, which can avoid a large inrush current at the moment of system unlocking, thereby improving the safety factor of the grid system.

9 is a flow chart showing a method of starting a half-bridge and full-bridge hybrid modular multilevel converter of the second embodiment. Controlling that all of the half bridge submodules remain latched, and before the step of controlling the operating state of at least a portion of the full bridge submodules to decrease the total voltage increase rate of the full bridge submodules, ie, before step S140, includes:

Step S130, detecting whether the voltage of each full bridge submodule reaches the working threshold of the self-powered power supply. If the voltage of each full bridge submodule reaches the operating threshold of the self-powered power supply, step S140 is performed. If the voltage of each full bridge submodule does not reach the operating threshold of the self-powered power supply, step S130 is continued.

Specifically, whether the voltage of each full bridge sub-module reaches the working threshold of the self-powered power source means whether each full bridge sub-module can work normally. When the voltage of each full bridge sub-module reaches the working threshold of the self-receiving power supply, it means that each full bridge sub-module can trigger the work by itself. Otherwise, the full bridge submodule whose voltage does not reach the operating threshold needs to continue charging.

Controlling that all of the half bridge submodules remain latched, and before the step of controlling the operating state of at least part of the full bridge submodules to decrease the total voltage increase speed of the full bridge submodules, step S140 includes:

When the voltage of each full bridge sub-module reaches the working threshold of the self-receiving power supply, step S141 is executed to control all half-bridge sub-modules to remain locked.

Specifically, at this time, the voltage of each half bridge submodule is smaller than the voltage of any full bridge submodule. This step controls the device to cause the half bridge submodule to continue charging.

Step S142, the control bridge voltage is not less than the full threshold sub-module bypass of the first threshold voltage.

Specifically, the full bridge sub-module bypass that controls the device control voltage not less than the first threshold voltage may cause the full bridge sub-modules to neither charge nor discharge. In this way, under the same AC power grid, the number of full-bridge sub-modules that are simultaneously charged can be reduced, and the number of charged half-bridge sub-modules is unchanged, so that the voltage rise speed of each half-bridge sub-module is accelerated, that is, each half-bridge The submodule is charged faster.

Step S143, the control bridge is half-blocked by the full bridge sub-module between the second threshold voltage and the first threshold voltage.

Specifically, the second threshold voltage is less than the first threshold voltage. The full bridge submodule half-latching of the control device control voltage between the second threshold voltage and the first threshold voltage may make the full bridge submodule equal to the half bridge submodule. On the one hand, the full bridge submodule voltage is small and can continue Charging, but the charging speed is reduced. On the other hand, it is also possible to further increase the charging speed of each half bridge module.

Step S144, the full bridge submodule whose control voltage is less than the second threshold voltage is blocked.

Specifically, the voltage of the full bridge submodule that controls the device control voltage to be less than the second threshold voltage is small, such that the full bridge submodules are latched even though the full bridge submodules continue to be charged at normal speed.

Through the above steps, the control device can reduce the overall charging speed of all the full bridge sub-modules, so that the overall charging speed of all the half bridge modules is increased. The average voltage of all half-bridge modules gradually increases. The average voltage of all full bridge submodules also gradually increases. However, the average voltage of all half-bridge modules increases at a faster rate than the average voltage of all full-bridge sub-modules. The average voltage of the final half bridge submodule tends to coincide with the average voltage of the full bridge submodule, that is, the average voltage of the half bridge submodule and the average voltage of the full bridge submodule may be equal or approximately equal. In this way, the voltages of all the sub-modules in the converter gradually reach an equilibrium state, and finally the voltages of all the sub-modules reach the working threshold of the self-powered power supply, and the design difficulty of the self-powered power supply of each sub-module is reduced. In addition, the voltage of the inverter rises slowly, which can effectively avoid the inrush current.

10 is a flow chart showing a method of starting a half-bridge and full-bridge hybrid modular multi-level converter of the third embodiment. In this embodiment, after the step of controlling all the half bridge submodules to remain latched and reducing the total voltage increase speed of the full bridge submodule by controlling the working state of at least part of the full bridge submodules, step S140 includes:

In step S151, it is determined whether the ratio of the average voltage of all the half bridge submodules to the average voltage of all the full bridge submodules is greater than a preset multiple.

In step S153, when the ratio of the average voltage of all the half bridge modules to the average voltage of all the full bridge submodules is greater than a preset multiple, all the full bridge submodules are controlled to be semi-blocked, and all half bridge submodules are controlled to be locked.

In this way, the control device can make all full bridge submodules equivalent to half bridge submodules, ie all submodules in the converter are half bridge submodules. At this time, the sub-module type in the converter can be made single, which is convenient for controlling the device control. Specifically, the preset multiple may be in the range of 0.6 to 1.4. Thus, the average voltage of all half-bridge modules is approximately equal to the average voltage of all full-bridge sub-modules. That is, the voltage of the inverter reaches an equilibrium state, and the voltage of the inverter always maintains a balanced increase.

In this embodiment, the working states of the full bridge submodules and the half bridge submodules are respectively controlled so that the total voltage of all the half bridge modules and all the full bridge submodules reaches the rated voltage, that is, step S160 includes:

Step S161, the control bridge voltage is not less than the third threshold voltage of the full bridge sub-module bypass, and the control voltage is not less than the third threshold voltage of the half bridge sub-module bypass.

Specifically, when the voltage of the inverter is close to the rated voltage, the control device controls the high-bridge full-bridge module to stop charging, that is, in the bypass state. The half bridge module with higher voltage control part of the control device stops charging, that is, it is in the bypass state. In this way, continue to reduce the voltage rise rate of all sub-modules so that the total voltage of all sub-modules is slowly approaching the rated voltage. In order to avoid a large inrush current caused by the inverter at the moment of unlocking.

11 is a block diagram showing the structure of a starting device of a modular multilevel converter in which a half bridge and a full bridge are mixed according to an embodiment. A starter for a modular multilevel converter with a half bridge and a full bridge, the modular multilevel converter comprising a plurality of half bridge submodules and a plurality of full bridge submodules, modular multilevel switching The flow device is connected to the AC grid through a series charging resistor. The device includes:

The control module 120 is configured to control all half bridge modules and all full bridge submodules to remain latched so that all half bridge modules and all full bridge submodules reach an initial voltage;

The semi-control start module 140 is configured to control all half-bridge sub-modules to remain locked, and reduce the total voltage increase speed of the full-bridge sub-module by controlling the working state of at least part of the full-bridge sub-modules; wherein, the operation of the full-bridge sub-module The state includes one of a latching, a semi-latching or a bypass;

The full control startup module 160 is configured to respectively control the working states of the full bridge submodules and the half bridge submodules, so that the voltages of all the half bridge submodules reach the rated voltage, and the voltages of all the full bridge submodules are reached. Rated voltage; wherein the operating state of the half bridge submodule includes bypass or blocking.

The starting device of the above-mentioned half-bridge and full-bridge hybrid modular multi-level converter, firstly, all half-bridge sub-modules and all full-bridge sub-modules are kept locked, that is, all half-bridge sub-modules and all full-bridge sub-modules The charging process is performed so that all half bridge modules and all full bridge submodules reach the initial voltage. Secondly, all half-bridge modules are controlled to remain locked, and the total voltage increase speed of the full bridge sub-module is decreased by controlling the operating state of at least part of the full-bridge sub-modules. Thus, the average voltage of all half-bridge modules gradually increases, and the average voltage of all full-bridge sub-modules gradually increases, and the two gradually approach, and the voltages of all the sub-modules are equalized at this time. Then, the working states of each full bridge submodule and each half bridge submodule are respectively controlled so that the voltages of all the half bridge submodules reach the rated voltage, and the voltages of all the full bridge submodules reach the rated voltage. Thus, during the startup of the modular multilevel converter, the voltages of all full bridge submodules and all half bridge submodules increase slowly, and the voltages of all submodules remain in a more balanced state. Therefore, the output voltage of the modular multilevel converter is slowly increased to the rated voltage, which can avoid a large inrush current at the moment of system unlocking, thereby improving the safety factor of the grid system.

In one embodiment, the half-control module 140 is configured to control all half-bridge modules to remain latched when the voltage of each full-bridge sub-module reaches a working threshold of the self-powered power source;

The semi-control start module 140 is further configured to control a full bridge sub-module bypass with a voltage not less than a first threshold voltage;

The half-control starting module 140 is further configured to control the full bridge sub-module half-locking voltage between the second threshold voltage and the first threshold voltage; wherein the second threshold voltage is less than the first threshold voltage;

The half-control starting module 140 is further configured to control the full bridge submodule latching of the voltage less than the second threshold voltage.

The technical features of the above-described embodiments may be arbitrarily combined. For the sake of brevity of description, all possible combinations of the technical features in the above embodiments are not described. However, as long as there is no contradiction between the combinations of these technical features, All should be considered as the scope of this manual.

The above-described embodiments are merely illustrative of several embodiments of the present invention, and the description thereof is more specific and detailed, but is not to be construed as limiting the scope of the invention. It should be noted that a number of variations and modifications may be made by those skilled in the art without departing from the spirit and scope of the invention. Therefore, the scope of the invention should be determined by the appended claims.

Claims

A method for starting a modular multilevel converter with a half bridge and a full bridge, characterized in that the modular multilevel converter comprises a plurality of half bridge submodules and a plurality of full bridge submodules, The method includes:

Controlling the plurality of half bridge submodules and the plurality of full bridge submodules to remain latched such that all half bridge submodules and all full bridge submodules reach respective initial voltages;

Controlling the plurality of half bridge submodules to remain latched, and reducing a total voltage increase speed of all full bridge submodules by controlling an operating state of at least a portion of the full bridge submodules; wherein an operating state of the full bridge submodule includes One of a latching, semi-latching or bypassing;

Controlling the working states of the full bridge submodules and the half bridge submodules respectively, so that the voltages of all the half bridge submodules and the voltages of all the full bridge submodules reach the rated voltage; wherein the working state of the half bridge submodule Includes bypass or blocking.
The method of claim 1 wherein said modular multilevel converter is coupled to the AC grid via a series charging resistor.
The method according to claim 2, wherein said step of keeping all of the half bridge submodules latched and reducing the total voltage increase speed of the full bridge submodules by controlling the operating state of at least part of the full bridge submodules Previously included:

The charging resistor is bypassed when the current of the charging resistor is less than a preset current value.
The method according to claim 2, wherein said step of keeping all of the half bridge submodules latched and reducing the total voltage increase speed of the full bridge submodules by controlling the operating state of at least part of the full bridge submodules Previously included:

The charging resistor is bypassed when the voltage of the charging resistor is greater than a preset voltage value.
The method of claim 1 wherein said step of maintaining all of the half bridge sub-modules latched and reducing the total voltage increase rate of the full bridge sub-module by controlling an operating state of at least a portion of the full bridge sub-modules include:

Controlling all half bridge modules to remain locked when the voltage of each full bridge submodule reaches the operating threshold of the self-powered power supply;

a full bridge submodule bypass with a control voltage not less than the first threshold voltage;

a full bridge sub-module half-locking of the control voltage between the second threshold voltage and the first threshold voltage; wherein the second threshold voltage is less than the first threshold voltage;

The full bridge submodule whose control voltage is less than the second threshold voltage is blocked.
The method of claim 1 wherein said step of maintaining all of the half bridge sub-modules latched and reducing the total voltage increase rate of the full bridge sub-module by controlling an operating state of at least a portion of the full bridge sub-modules After that:

When the ratio of the average voltage of all half bridge modules to the average voltage of all full bridge submodules is greater than the preset multiple, all full bridge submodules are controlled to be semi-latched, and all half bridge submodules are controlled to be blocked.
The method of claim 6 wherein said predetermined multiple is in the range of 0.6 to 1.4.
The method according to claim 1, wherein the operating states of the respective full bridge submodules and the respective half bridge submodules are respectively controlled so that the total voltages of all the half bridge submodules and all the full bridge submodules are rated. The steps of the voltage include:

The full bridge sub-module bypass of the control voltage not less than the third threshold voltage, and the half bridge sub-module bypass of the control voltage not less than the third threshold voltage.
A starting device for a modular multilevel converter with a half bridge and a full bridge, characterized in that the modular multilevel converter comprises a plurality of half bridge submodules and a plurality of full bridge submodules, The modular multilevel converter is coupled to the AC grid via a series charging resistor, the apparatus comprising:

The control module is not controlled, and all the half bridge modules and all the full bridge submodules are kept locked so that all the half bridge modules and all the full bridge submodules reach the initial voltage;

a semi-control start module for controlling all half-bridge sub-modules to remain locked, and reducing a total voltage increase speed of the full-bridge sub-module by controlling an operating state of at least part of the full-bridge sub-modules; wherein, the full-bridge sub-module The working state includes one of a latching, a semi-latching or a bypass;

The full control startup module is configured to respectively control the working states of the full bridge submodules and the half bridge submodules, so that the voltages of all the half bridge submodules reach the rated voltage, and the voltages of all the full bridge submodules are up to the rated a voltage; wherein the operating state of the half bridge submodule includes bypass or blocking.
The device according to claim 9, wherein the half-control start module is configured to control all half-bridge modules to remain locked when the voltage of each full-bridge sub-module reaches a working threshold of the self-powered power supply;

The half-control starting module is further configured to control a full bridge sub-module bypass with a voltage not less than a first threshold voltage;

The half-control starting module is further configured to control a full bridge sub-module half-locking voltage between a second threshold voltage and the first threshold voltage; wherein the second threshold voltage is less than the first threshold voltage;

The half-control starting module is further configured to control a full bridge submodule latching whose voltage is less than the second threshold voltage.