Three-level power module variable mode control method of grid-connected converter

Abstract

The present disclosure relates to the technical field of power electronic converter control, and particularly relates to a three-level power module variable mode control method of a grid-connected converter. Based on an electronic circuit of an active neutral point clamped three-level power module, in the electronic circuit, according to an operation mode, switching between topologies of passive neutral point clamping and active neutral point clamping of the three-level power module is realized through controllable elements. The present disclosure flexibly switches the working topology of the power module by using a software method, without the need for locking and shutdown, and without the need for hardware changes, thereby improving the operation flexibility of the converter.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of power electronic converter control, and particularly relates to a three-level power module variable mode control method of a grid-connected converter. BACKGROUND

[0002] As the interface between new energy power generation system and power grid, the power module is one of the most important hardware modules in the converter to ensure the operation quality of the product. The control mode of the power module directly affects the operation efficiency and maintenance cost of the converter.

[0003] The demand for new energy power generation makes the unit rectifier adopt a large-capacity multi-level topology. With the increasingly stringent requirements of grid-connected guidelines and unit reliability, it is a trend for large-capacity new energy units to adopt full-power converters. The use of three-level power modules in converters can significantly increase the capacity of a single converter and improve the reliability of the unit. The maximum capacity of a full-power converter based on integrated gate-commutated thyristors (IGCT) for wind power has exceeded 10 MW. Compared with the traditional neutral point clamped three-level (NPC) power module, the active neutral point clamped (ANPC) power module used in the converter can reduce the temperature difference of power semiconductors and significantly improve the power density of the converter.

[0004] The demand for new energy grid connection makes the multi-mode switching application scenarios of unit grid-connected converter control increase. Including: grid-following control, which requires the converter to operate in maximum power tracking control (MPPT) and output active power (P) to the grid point. Under grid voltage fault, the grid-connected converter is required to continuously output reactive power (Q) to support the voltage amplitude of the grid point. Although the grid voltage fault operation mode is short, it is an essential function of new energy unit grid connection. Grid-forming control requires the grid-connected converter to stably output active and reactive power (P / Q) to the grid point. The grid-connected converter with an increased DC bus energy storage battery requires the grid-connected converter to operate in voltage and frequency control (V / f) and droop control (Droop) during black start to restore the microgrid. In summary, grid-forming control requires the grid-connected converter to flexibly output active and reactive power (P / Q) to support the grid.

[0005] New energy power generation has obvious randomness and volatility. Grid-connected converters run in medium and low load for a long time, and in full load for a small amount of time. Grid-connected converters running in maximum power tracking control (MPPT) can maximize new energy power generation and improve investment returns. At present, the number of demonstration projects of grid-connected converters running in stable output active and reactive power (P / Q) network mode is also gradually increasing. New power systems require flexible switching between maximum output active power (P) and stable output reactive power (Q) control of new energy generators.

[0006] Compared with NPC power modules, the existing technology, ANPC power modules use redundant switch states to transfer the switching loss of specific power semiconductors. ANPC topology power density can be improved. But ANPC power modules also increase switching loss, and increase the driver loss of all-controlling power semiconductors.

[0007] For example, the most common integrated gate-commutated thyristor (IGCT) in high-power converters. Because IGCT drive needs a capacitor bank to transfer large current at turn-off, and needs to continuously inject maintenance current to ensure conduction state in steady state, IGCT drive needs to input more power from the power supply side to ensure the stability of the turn-off capacitor bank voltage and the maintenance current level.

[0008] When the unit operates in maximum power tracking mode, the through-flow path of the NPC power module of the grid-connected converter is the same as that of the ANPC power module. However, the NPC power module reduces the control complexity of the converter and also reduces the driver loss of all-controlling power semiconductors. Three-phase NPC power modules reduce the driver loss of six all-controlling power semiconductors. Therefore, the efficiency of the grid-connected converter power module using the NPC topology mode is higher than that of the ANPC topology mode.

[0009] In network construction and grid voltage fault ride-through, grid-connected converters are required to output stable reactive power (Q) to support the grid point voltage. ANPC power modules can optimize the switching state to select the current path in the power module, optimize the switching and conduction loss of power semiconductors, and reduce the switching thermal stress. ANPC power modules sacrifice driver loss to optimize the switching and conduction loss of power semiconductors. In this network construction function, the efficiency of the grid-connected converter power module using the ANPC topology mode is higher than that of the NPC topology mode.

[0010] In the two most important grid-connected modes (grid following and network construction), if the new energy unit power module can achieve seamless switching between NPC and ANPC modes, it can reduce the driver loss of all-controlling power semiconductors, improve the operating efficiency of the unit, and increase the power generation of the unit.

[0011] The topology of the active neutral point clamped three-level power module includes the passive neutral point clamped three-level topology. In theory, the passive neutral point clamped three-level topology is taken as a modified selection of the active neutral point clamped three-level topology under hardware failure. However, in practice, the power module exception belongs to a serious hardware failure, and the failed power module is required to exit operation. Without a redundant power module, the entire converter needs to exit operation. SUMMARY

[0012] In view of the above problems, the disclosure provides a three-level power module mode switching control method of a grid-connected converter.

[0013] In a first aspect, a three-level power module mode switching control method of a grid-connected converter is provided, and the method comprises:

[0014] The operation modes of the grid-connected converter include a grid-following control mode, a grid-forming mode, and a voltage fault mode;

[0015] According to the operation mode, the grid-connected converter is instructed to switch between the passive neutral point clamped topology and the active neutral point clamped topology; wherein,

[0016] In the grid-following control mode, the grid-connected converter operates in the passive neutral point clamped topology; in the grid-forming mode and the voltage fault mode, the grid-connected converter operates in the active neutral point clamped topology.

[0017] Further, the grid-connected converter comprises fully controlled power semiconductor devices.

[0018] Further, the switching states of the fully controlled power semiconductor devices are controlled to switch the grid-connected converter between the passive neutral point clamped topology and the active neutral point clamped topology.

[0019] Further, the grid-connected converter is a multi-level power module.

[0020] Further, the grid-connected converter is an active neutral point clamped three-level power module.

[0021] Further, for the grid-connected converter with energy storage batteries connected in parallel on the AC bus side, in the black start process, the grid-forming mode includes a voltage and frequency control mode and a droop control mode.

[0022] Further, in the grid-following mode or the grid-forming mode, the grid-connected converter is instructed to switch between the passive neutral point clamped topology and the active neutral point clamped topology according to the proportion of active power and reactive power output to the grid.

[0023] Further, in the voltage fault mode, the grid-connected converter is instructed to switch between the passive neutral point clamped topology and the active neutral point clamped topology alternately.

[0024] Further, when the active neutral point clamped topology and the passive neutral point clamped topology are alternately switched to operate, based on the current direction at the alternating current outlet of the grid-connected converter, and the current topology mode and the switch state, it is judged whether the grid-connected converter is operated in the effective switch state.

[0025] Further, in the effective switch state, the grid-connected converter continues to operate in the current topology mode and performs the effective switch state cycle until the current direction at the alternating current outlet of the grid-connected converter changes; when it is confirmed that the current direction changes, the grid-connected converter is instructed to switch the topology mode.

[0026] Further, in the non-effective switch state, the grid-connected converter is instructed to switch the topology mode.

[0027] In a second aspect, an electronic device includes a processor, a communication interface, a memory, and a communication bus, wherein the processor, the communication interface, and the memory complete communication with each other through the communication bus.

[0028] The memory stores a computer program.

[0029] The processor is configured to execute the computer program stored in the memory to implement the three-level power module mode switching control method of the grid-connected converter.

[0030] In a third aspect, a computer readable storage medium stores a computer program, and the computer program is executed by a processor to implement the three-level power module mode switching control method of the grid-connected converter.

[0031] The present disclosure has at least the following beneficial effects:

[0032] The present disclosure uses a software method to flexibly switch the working topology of the power module, without the need to change the hardware, and can optimize the current working path, reduce semiconductor switch loss, and improve the power generation of the unit under multiple grid-connected functions of the converter. The working topology of the power module is flexibly switched, without the need for latching shutdown or hardware changes, improving the operating flexibility of the converter. The working topology of the power module is flexibly switched, and the power semiconductor is soft switched during the switching process, i.e., the turn-on and turn-off loss can be ignored, improving the operating flexibility of the converter.

[0033] Other features and advantages of the present disclosure will be further described in the following description, and some will become apparent from the description, or will be understood through implementation of the present disclosure. The purpose and other advantages of the present disclosure can be achieved and obtained through the structure indicated in the specification and the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the present disclosure, and other drawings can be obtained by those skilled in the art without creative labor.

[0035] Figure 1 An electrical schematic diagram of an active neutral point clamped three-level power module;

[0036] Figure 2 An electrical schematic diagram of a passive neutral point clamped three-level power module;

[0037] Figure 3 A schematic diagram of an effective switching state cycle of a three-level power module;

[0038] Figure 4 A schematic diagram of an electronic device structure. DETAILED DESCRIPTION

[0039] In order to make the objects, technical solutions and advantages of the embodiments of the present disclosure clearer, the following will combine the drawings in the embodiments of the present disclosure to clearly and completely describe the technical solutions in the embodiments of the present disclosure. Obviously, the described embodiments are some of the embodiments of the present disclosure, rather than all the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present disclosure.

[0040] The topology of the active neutral point clamped three-level power module includes the passive neutral point clamped three-level topology. Based on the effective switching states of the two topologies, according to the grid-connected function of the converter, the power module can be flexibly switched between the two topologies. This makes the grid-connected converter power module operate at low loss, and improves the power generation of the new energy unit. It is suitable for the characteristics of strong randomness and large fluctuation of new energy unit power generation.

[0041] The hardware of the active neutral point clamped three-level power module is used to realize the switching of the three-level power module between the passive neutral point clamped topology and the active neutral point clamped topology by a software method. This method makes the grid-connected converter, in the maximum power tracking mode, can take advantage of the low loss characteristics of the passive neutral point clamped three-level power module, and improves the power generation of the new energy unit. This method makes the grid-connected converter, in the grid voltage fault mode and stable output reactive power mode, can take advantage of the low loss characteristics of the active neutral point clamped three-level power module.

[0042] A three-level power module variable mode control method of a grid-connected converter, the method comprising:

[0043] As Figure 1As shown, setting the operating mode of the grid-connected converter includes: grid-following control mode, grid-forming mode, and voltage fault mode;

[0044] According to the operating mode, the grid-connected converter is instructed to switch between the passive neutral point clamped topology and the active neutral point clamped topology; wherein,

[0045] In the grid-following control mode, the grid-connected converter operates in the passive neutral point clamped topology; in the grid-forming mode and the voltage fault mode, the grid-connected converter operates in the active neutral point clamped topology.

[0046] In specific implementation, the following is introduced:

[0047] The electrical schematic diagram of the active neutral point clamped three-level power module is as shown in Figure 1 The electrical schematic diagram of the passive neutral point clamped three-level power module is as shown in Figure 2 .

[0048] The three-level power module control method proposed in the present disclosure combines the use of passive neutral point clamping and active neutral point clamping topologies to achieve flexible switching between topologies by software method. Specifically, the following steps are included:

[0049] Step 1:

[0050] The function of the grid-connected converter is determined. If it is operated in the maximum power tracking mode, the grid-connected converter power module operates in the passive neutral point clamped three-level topology. The effective switching state of the passive neutral point clamped three-level is as shown in Table 2. The effective switching state cycle is as shown in Figure 3 .

[0051] Step 2:

[0052] If it is operated in the stable output active and reactive power mode, and the reactive power is much smaller than the active power, i.e. |Q|《|P|. Then the grid-connected converter power module operates in the passive neutral point clamped three-level topology. Otherwise, the grid-connected converter power module alternately operates in the active neutral point clamped three-level topology and the passive neutral point clamped three-level topology.

[0053] The effective switching state of the active neutral point clamped three-level is as shown in Table 1. The effective switching state cycle is Figure 4 .

[0054] Table 1

[0055]

[0056] Wherein: T x D x represents a fully controlled power semiconductor T x and its anti-parallel diode D x . Dx represents the turn-on of the anti-parallel diode D and the flow of current through it. T x represents the turn-on of the anti-parallel diode D and the flow of current through it. T x (0) represents the turn-on of the anti-parallel diode D and the flow of current through it. T x represents the turn-on of the anti-parallel diode D and the flow of current through it. T

[0057] Step 3:

[0058] If it is running in voltage and frequency control (V / f) and droop control (Droop) mode, and the reactive power is much smaller than the active power, i.e. |Q| « |P|. Then the grid-connected converter power module runs in passive neutral point clamped three-level topology. Otherwise, the grid-connected converter power module alternately runs in active neutral point clamped three-level topology and passive neutral point clamped three-level topology.

[0059] Step 4:

[0060] If it is running in grid voltage fault mode, then the grid-connected converter requires to stabilize the output reactive power (Q), the power module alternately runs in active neutral point clamped three-level topology and passive neutral point clamped three-level topology.

[0061] Step 5:

[0062] When the grid-connected converter power module is required to alternately run in active neutral point clamped three-level topology and passive neutral point clamped three-level topology.

[0063] The current i ac The direction, according to the current power module three-level topology mode and switch state, to determine whether the three-point power module is running in the effective switch state.

[0064] The active neutral point clamped three-level effective switch state is shown in Table 1, and the passive neutral point clamped three-level effective switch state is shown in Table 2.

[0065] The judgment result: if the power module is running in the effective switch state, then enter step 6. If the power module is not running in the effective switch state, then enter step 7.

[0066] Table 2

[0067]

[0068] Where: T x D x represents the turn-on of the anti-parallel diode D and the flow of current through it. T x and its anti-parallel diode D x . D x represents the turn-on of the anti-parallel diode D and the flow of current through it. Tx represent the turn-on of the full-controlled power semiconductor and the current flowing through it. x (0) represent the turn-on of the full-controlled power semiconductor T x turn-on, but no current flows through it. x = 1, 2, 3, 4, 5, 6.

[0069] Step 6:

[0070] The power module continues to operate in the same topology mode and according to the effective switching state cycle. Figure 3 the current i ac at the ac outlet changes its direction.

[0071] To prevent the current i ac at the ac outlet from fluctuating at the zero-crossing point, a threshold I ac is set, which is a small enough current to be considered as zero. When the condition |i ac | < I ac is met, the current i ac is considered to have changed its direction.

[0072] After confirming that the current i ac has changed its direction, the power module needs to switch the topology mode. Go to Step 8.

[0073] Step 7:

[0074] The power module needs to change the current topology mode.

[0075] If the current switching state of the power module is at zero level (0) at the ac side output. Then, in the current topology mode, wait for the power module to enter the next switching period. The ac side output is at non-zero level (U dc / 2, -U dc / 2). Go to Step 8.

[0076] Step 8:

[0077] If it is operating in the passive neutral point clamped topology, it needs to switch to the active neutral point clamped topology. If the current switching state of the power module is at high level (U dc / 2) at the ac side output, then turn on the full-controlled power semiconductor T6. The turn-on process of T6 is zero-current soft turn-on, and the turn-on loss can be ignored. The power module then enters the effective switching state.

[0078] If the current switching state of the power module is at negative level (-U dc / 2) at the ac side output, then turn on the full-controlled power semiconductor T5. The turn-on process of T5 is zero-current soft turn-on, and the turn-on loss can be ignored. The power module then enters the effective switching state.

[0079] Similarly, if it is running in an active neutral point clamped topology, it needs to be switched to a passive neutral point clamped topology. If the current switch state of the power module is high level (U dc / 2) at the AC side output, then the fully controlled power semiconductor T6 is turned off. The turn-off process of T6 is zero-current soft turn-off, and the turn-off loss can be ignored. The power module then enters the effective switch state.

[0080] If the current switch state of the power module is negative level (-U dc / 2) at the AC side output, then the fully controlled power semiconductor T5 is turned off. The turn-off process of T5 is zero-current soft turn-off, and the turn-off loss can be ignored. The power module then enters the effective switch state.

[0081] The power module has entered the expected topology mode. Return to step 5.

[0082] The present disclosure provides a variable mode switching method for a grid-connected converter three-level power module, which can make the power module run in a higher efficiency mode according to the grid-connected function of the converter, reduce the operating loss of the converter, and improve the power generation of the new energy unit.

[0083] The present disclosure provides a variable mode switching condition criterion for a grid-connected converter three-level power module, which can make the power module run in an NPC topology mode in the maximum power tracking mode, improve the working efficiency and power generation of the converter.

[0084] The present disclosure provides a variable mode switching condition criterion for a grid-connected converter three-level power module, which can make the power module run in an ANPC topology mode in the grid voltage fault mode, improve the working efficiency and power generation of the converter.

[0085] The present disclosure provides a variable mode switching condition criterion for a grid-connected converter three-level power module, which can make the power module run in an ANPC topology mode in the grid voltage fault mode, improve the working efficiency and power generation of the converter.

[0086] The present disclosure provides a variable mode switching method for a grid-connected converter three-level power module, which can make the power module switch between the ANPC and NPC modes, and the power semiconductor is soft switched during the switching process, i.e., the turn-on and turn-off losses can be ignored, thereby improving the operating flexibility of the converter.

[0087] The present disclosure relates to a topology variable mode switching algorithm for a three-level converter power module, and provides a correlation algorithm between the topology mode of the three-level power module and the unit grid-connected function. The generation mode and algorithm of the power semiconductor switch signal in the module (such as the sine pulse width modulation method, the space vector pulse width modulation, and the device protection) do not affect the variable mode switching algorithm and the correlation algorithm between the mode and the grid-connected mode.

[0088] Full control power semiconductor devices such as IGCT, Insulate-Gate Bipolar Transistor (IGBT) and the like do not affect the variable mode switching algorithm, the correlation algorithm of mode and grid connection mode.

[0089] The present disclosure provides a variable topology mode switching algorithm for a three-level converter power module, and the variable mode switching algorithm is not affected by multi-level designs such as five-level and seven-level, and the correlation algorithm of mode and grid connection mode.

[0090] The variable mode switching algorithm is not affected by renewable energy forms such as wind power generation and photovoltaic power generation, and the correlation algorithm of mode and grid connection mode.

[0091] The variable mode switching algorithm is not affected by the grid connection mode of energy storage elements such as electrochemical cells and flywheels, and the correlation algorithm of mode and grid connection mode.

[0092] The variable mode switching algorithm is not affected by the number of bridge arms of the grid-connected converter, such as single-phase, two-phase, three-phase, four-phase, five-phase and the like, and the correlation algorithm of mode and grid connection mode.

[0093] The variable mode switching algorithm is not affected by the active and reactive power control algorithm of the unit-side rectifier converter, and the correlation algorithm of mode and grid connection mode.

[0094] The variable mode switching algorithm is not affected by the number of mode switching times in one power frequency cycle, and the correlation algorithm of mode and grid connection mode.

[0095] During operation, the switching frequency and number of times of the grid-connected function of the converter do not affect the variable mode switching algorithm, and the correlation algorithm of mode and grid connection mode.

[0096] The grid-connected converter can work in a rectification state to absorb active power from the grid connection, such as charging a battery or other energy storage device on a DC bus, and the variable mode switching algorithm is not affected, and the correlation algorithm of mode and grid connection mode.

[0097] In the grid voltage fault mode, the working state of the energy consumption device on the DC bus does not affect the variable mode switching algorithm, and the correlation algorithm of mode and grid connection mode.

[0098] As shown in Figure 4 The present disclosure provides an electronic device, which includes a processor 401, a communication interface 402, a memory 403 and a communication bus 404, wherein the processor 401, the communication interface 402 and the memory 403 complete communication with each other through the communication bus 404;

[0099] The memory 403 stores a computer program.

[0100] The processor 401 is configured to implement the above-described method when executing the computer program stored in the memory 403.

[0101] The present disclosure provides a computer readable storage medium storing a computer program, and the computer program is configured to implement the above-described method when executed by a processor.

[0102] The computer readable storage medium can be included in the device / apparatus described in the above embodiments, or can exist separately and not be assembled into the device / apparatus. The computer readable storage medium stores one or more programs, and the one or more programs are configured to implement the method according to the embodiments of the present disclosure when executed.

[0103] According to the embodiments of the present disclosure, the computer readable storage medium can be a non-volatile computer readable storage medium, which can include but is not limited to: a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any appropriate combination thereof. In the present disclosure, the computer readable storage medium can be any tangible medium that contains or stores a program, which can be used by or in connection with an instruction execution system, apparatus or device.

[0104] Although the present disclosure is explained in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that the technical solutions recorded in the foregoing embodiments can be modified, or some of the technical features can be replaced by equivalent features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present disclosure.

Claims

1. A three-level power module variable mode control method of a grid-connected converter, characterized by, The method comprises: Setting the operation mode of the grid-connected converter includes: grid-following control mode, grid-forming mode, and voltage fault mode; According to the operation mode, the grid-connected converter is instructed to switch between passive neutral point clamped topology and active neutral point clamped topology; wherein, In the grid-following control mode, the grid-connected converter operates in passive neutral point clamped topology; in the grid-forming mode and voltage fault mode, the grid-connected converter operates in active neutral point clamped topology; In the grid-following mode or grid-forming mode, according to the proportion of active power and reactive power output to the grid, the grid-connected converter is instructed to switch between passive neutral point clamped topology and active neutral point clamped topology.

2. The three-level power module variable mode control method of the grid-connected converter according to claim 1, characterized in that, The grid-connected converter includes fully controlled power semiconductor devices.

3. The three-level power module variable mode control method of the grid-connected converter according to claim 2, characterized in that, The switching state of the fully controlled power semiconductor devices is controlled to realize switching between passive neutral point clamped topology and active neutral point clamped topology of the grid-connected converter.

4. The three-level power module variable mode control method of the grid-connected converter according to any one of claims 1-3, characterized in that, The grid-connected converter is a multi-level power module.

5. The three-level power module variable mode control method of the grid-connected converter according to claim 4, characterized in that, The grid-connected converter is an active neutral point clamped three-level power module.

6. The three-level power module variable mode control method of the grid-connected converter according to claim 5, characterized in that, The grid-connected converter with parallel energy storage batteries on the AC bus side, in the black start process, the grid-forming mode includes voltage and frequency control mode and droop control mode.

7. The three-level power module variable mode control method of the grid-connected converter according to claim 6, characterized in that, In the voltage fault mode, the grid-connected converter is instructed to switch between passive neutral point clamped topology and active neutral point clamped topology alternately.

8. The three-level power module variable mode control method of the grid-connected converter according to any one of claims 1-3, characterized in that, When the active neutral point clamped topology and the passive neutral point clamped topology are alternately switched, based on the current direction at the AC outlet of the grid-connected converter and the current topology mode and switching state, it is judged whether the grid-connected converter is running in an effective switching state; the active neutral point clamped three-level effective switching state and the passive neutral point clamped three-level effective switching state are recorded in a table, and the effective switching state is determined by looking up the table.

9. The three-level power module variable mode control method of the grid-connected converter according to claim 8, characterized in that, In the effective switching state, the grid-connected converter continues to operate in the current topology mode and performs effective switching state cycle until the current direction at the AC outlet of the grid-connected converter changes; when it is confirmed that the current direction has changed, the grid-connected converter is instructed to switch the topology mode.

10. The three-level power module variable mode control method of a grid-connected converter according to claim 8, characterized in that, in the non-active switching state, instructing the grid-connected converter to switch the topology mode.

11. An electronic device, comprising: comprising a processor, a communication interface, a memory and a communication bus, wherein the processor, the communication interface and the memory complete mutual communication through the communication bus; the memory stores a computer program; the processor is used to execute the computer program stored on the memory, and realizes the three-level power module variable mode control method of a grid-connected converter according to any one of claims 1-10.

12. A computer readable storage medium storing a computer program, wherein the computer program comprises program instructions configured to cause a processor to perform the method according to any one of claims 1 to 11. the computer program is executed by the processor to realize the three-level power module variable mode control method of a grid-connected converter according to any one of claims 1-10.

Images