Hybrid direct-current energy consumption device and control method thereof

Abstract

The invention discloses a hybrid direct-current energy consumption device and a control method thereof.The device comprises a plurality of sub-modules and a centralized energy consumption resistor connected with the sub-modules in series, each sub-module has the independent on-off capacity, and the centralized energy consumption resistor is connected with the sub-modules in series according to the change of system direct-current voltage and a set threshold value; the number of the conducted sub-modules is adjusted in real time in an alternate conduction control mode, and accurate control over energy consumption power is achieved; the concentrated energy consumption resistor is used for dissipating surplus power and is a key energy consumption element in the device; the device is connected to the two ends of a system direct current side bus in parallel, when a main grid side alternating current breaks down, the device is started and absorbs surplus power, and the device comprises a no-load mode, a full-load mode and a power adjustable mode; according to the device and the control method, flexible adjustment of energy consumption power is realized through a submodule alternate conduction mode, and the energy efficiency and the operation stability of the device are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of direct current (DC) power transmission, and in particular to a hybrid DC energy consumption device and a control method thereof. Background Art

[0002] Flexible DC transmission technology based on modular multi-level converters (MMCs) is currently the primary method for connecting large-scale, long-distance offshore wind power to onshore AC grids. The most common topology for offshore wind power flexible DC grid-connected systems is AC aggregation and point-to-point flexible DC centralized transmission. This has been applied in numerous offshore wind power grid-connected projects both domestically and internationally. In recent years, offshore wind power installed capacity has increased annually, and DC transmission voltage levels have continued to rise, posing a significant challenge to the system's ability to cope with AC faults. When an onshore AC fault occurs, the AC power output capacity of the onshore converter station decreases, and the active power generated by the wind farm is injected into the DC system from the offshore converter station. The resulting large excess power will cause a rapid rise in DC voltage. If uncontrolled, this will trigger overvoltage protection, causing the DC system to shut down. To address the problem of excess power during AC faults, offshore wind power flexible DC grid-connected systems primarily employ DC energy dissipation devices on the DC side of the onshore converter station. Currently, the main topologies for DC energy dissipation devices include centralized, distributed, and hybrid.

[0003] Centralized DC energy dissipation devices have a simple topology and use relatively few components. However, during fault ride-through, the need to simultaneously control the switching on and off of all IGBTs in the entire bridge arm places high demands on device manufacturing, involves specialized device driving methods, and presents significant technical challenges. Distributed DC energy dissipation devices offer reduced voltage and current fluctuations, improved EMC performance, and, thanks to their modular design, eliminate the need for series and parallel connection of components and offer good scalability. However, these devices require more power components and complex water cooling, leading to high equipment costs. Therefore, developing a hybrid DC energy dissipation device with adjustable power consumption and efficient regulation capabilities is of great practical significance and application value. Summary of the Invention

[0004] The purpose of the present invention is to provide a hybrid DC energy consumption device and a control method thereof, which realizes flexible adjustment of energy consumption power by alternately turning on submodules, thereby improving the energy efficiency and operation stability of the device.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] A hybrid DC energy dissipation device, comprising a plurality of submodules and a centralized energy dissipation resistor connected in series with the submodules, wherein:

[0007] Each submodule has the ability to be turned on and off independently. Based on the changes in the system DC voltage and the set threshold, the number of submodules turned on is adjusted in real time through a rotation control method to achieve precise control of energy consumption.

[0008] The concentrated energy dissipation resistor is used to dissipate excess power and is a key energy dissipation component in the device;

[0009] The device is connected in parallel to both ends of the DC busbar of the system. When a fault occurs in the AC side of the main grid, the device starts and absorbs the surplus power. The device includes no-load mode, full-load mode and power adjustable mode.

[0010] In no-load mode, the insulated gate bipolar transistor (IGBT) units in all submodules are turned off, the submodule capacitors are connected in series to support the DC side voltage, and the device current and absorbed power are zero;

[0011] In full load mode, the IGBT units of all submodules are turned on, the DC side voltage is fully applied to both ends of the centralized energy dissipation resistor, and the branch current of the device reaches the maximum value;

[0012] In the power adjustable mode, by changing the sum of the output voltages of the submodules, the voltage across the centralized energy dissipation resistor is adjusted, thereby adjusting the current and power of the device branch. At this time, the device absorbs power between 0 and the system rated transmission power P rated The absorbed power of the device is composed of two parts, including the power consumed by the centralized energy-consuming resistor and the capacitor charging power of all sub-modules put into use.

[0013] A control method for a hybrid DC energy consumption device, the method comprising:

[0014] Step 1: Obtain system DC voltage data in real time to provide a basis for subsequent control;

[0015] Step 2: Dynamically adjust the number of submodules in operation based on the changes in the acquired DC voltage and the set threshold;

[0016] Step 3: After the number of sub-modules put into operation is determined, the energy consumption power is precisely regulated by controlling the alternating conduction of the sub-modules.

[0017] It can be seen from the technical solution provided by the present invention that the above-mentioned device realizes flexible adjustment of energy consumption power by alternating conduction of sub-modules, thereby improving the energy efficiency and operation stability of the device. The topology and control logic of the above-mentioned device are simple, the reliability is high, the power control accuracy is high, the system disturbance is small, the integrated resistance power inside the sub-module is low, and the switching device loss is small. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 A schematic diagram of the overall structure of a hybrid DC energy dissipation device provided in an embodiment of the present invention;

[0020] Figure 2 This is a schematic diagram of a specific control flow of the rotating conduction control method according to an example of the present invention;

[0021] Figure 3 The figure is a flow chart of a control method for a hybrid DC energy consumption device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0022] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments, and do not constitute a limitation of the present invention. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0023] like Figure 1 This is a schematic diagram of the overall structure of a hybrid DC energy dissipation device provided in an embodiment of the present invention. The device includes multiple submodules (SM1, SM2...SMN) and a centralized energy dissipation resistor connected in series with the submodules, wherein:

[0024] Each submodule has the ability to be turned on and off independently. Based on the changes in the system DC voltage and the set threshold, the number of submodules turned on is adjusted in real time through a rotation control method to achieve precise control of energy consumption.

[0025] The concentrated energy dissipation resistor is used to dissipate excess power and is a key energy dissipation component in the device;

[0026] The device is connected in parallel to the system DC side bus (U dc ) at both ends, when a fault occurs in the AC on the main grid side, the device starts and absorbs the surplus power, and the device includes a no-load mode, a full-load mode and a power adjustable mode;

[0027] In no-load mode, the insulated-gate bipolar transistor (IGBT) units in all submodules are turned off, the submodule capacitors are connected in series to support the DC side voltage, and the device current and absorbed power are zero;

[0028] In full load mode, the IGBT units of all submodules are turned on, the DC side voltage is fully applied to both ends of the centralized energy dissipation resistor, and the branch current of the device reaches the maximum value;

[0029] In the power adjustable mode, by changing the sum of the output voltages of the submodules, the voltage across the centralized energy dissipation resistor is adjusted, thereby adjusting the current and power of the device branch. At this time, the device absorbs power between 0 and the system rated transmission power P rated The absorbed power of the device is composed of two parts, including the power consumed by the centralized energy-consuming resistor and the capacitor charging power of all sub-modules put into use.

[0030] like Figure 1 As shown, each submodule consists of a storage capacitor C, a distributed resistor R, a first IGBT unit T1, a second IGBT unit T2, a first diode D1 and a second diode D2. The storage capacitor C is connected in series with the first diode D1 and then connected in parallel to both ends of the first IGBT unit T1, providing a buffer for the on and off of the IGBT; the distributed resistor R is connected in parallel with the second diode D2, and then connected in series with the second IGBT unit T2, and then connected in parallel to both ends of the first IGBT unit T1, wherein:

[0031] The first diode D1 is used to limit the direction of branch current;

[0032] The second diode D2 is used for freewheeling (taking into account the resistance and inductance);

[0033] The first IGBT unit T1 is used to control the voltage output by the submodule to switch between zero and the capacitor voltage;

[0034] The second IGBT unit T2 is used to control the charging and discharging of the capacitor to maintain the constant voltage of the submodule capacitor;

[0035] When the first IGBT unit T1 is turned on, the submodule state is defined as the "cut-off" state; when the first IGBT unit T1 is turned off, the submodule state is defined as the "on" state;

[0036] The energy storage capacitor C is used to store electrical energy to maintain a constant capacitor voltage;

[0037] The distributed resistor R is used to consume part of the electrical energy when the submodule is turned on.

[0038] In a specific implementation, the number of submodules turned on is adjusted in real time by a rotation control method according to the change of the system DC voltage and the set threshold. The specific process is as follows:

[0039] First, according to the absorption power P of the device chopper , and the total number of submodules N all,Calculate the number of sub-modules N that need to be invested. The calculation formula is: P rated is the rated transmission power of the system, round(x) is the rounding function, and the digits after the decimal point are rounded off;

[0040] The amount of energy absorbed by the capacitors in the submodules is used as the basis for sorting the submodule input priorities, and the concept of "rotating conduction" of the submodules is introduced, that is, the submodules with more capacitor energy are prioritized.

[0041] According to the energy absorption ranking results of the capacitors in the submodules and the number N of submodules that need to be put into operation, the final switching instructions are determined to achieve the alternating conduction of the submodules.

[0042] For example, two real number arrays are preset in the device. Here, taking 10 submodules as an example, one is used to store the 10 submodule numbers, and the other is used to store the switch control signal (0 is on, 1 is off). Figure 2 The figure shows a specific control flow diagram of the rotating conduction control method according to the embodiment of the present invention:

[0043] If a threshold signal is detected, the number array and the control array are initialized respectively, where each element of the number array is assigned a value from 1 to 10 in sequence, and the initial value of each element of the control array is set to 1. According to the number of sub-modules N that need to be invested, the element with the corresponding number index in the control array is set to 0 to achieve partial conduction and shutdown; at this time, each element of the number array is operated modulo 10 according to N to achieve circular shift.

[0044] If the above conditions are not met, all elements of the control array will be set to 0, indicating that all conduction paths are closed.

[0045] Finally, no matter what state it is in, the number array will be checked. If the element of the number array is 0, it will be assigned to 10 to ensure that no element is zero; then, the state of the control array is mapped to the output array to complete a round of conduction.

[0046] Based on the above device, the embodiment of the present invention also provides a control method for a hybrid DC energy consumption device, such as Figure 3 FIG. 1 is a flow chart of a control method for a hybrid DC energy consumption device according to an embodiment of the present invention. The method includes:

[0047] Step 1: Obtain system DC voltage data in real time to provide a basis for subsequent control;

[0048] Step 2: Dynamically adjust the number of submodules in operation based on the changes in the acquired DC voltage and the set threshold;

[0049] In this step, when the DC voltage exceeds the set threshold, the number of sub-modules put into operation is increased to dissipate more surplus power;

[0050] When the DC voltage is lower than the set threshold, the number of sub-modules put into operation is reduced to reduce the power consumption of the energy-consuming devices.

[0051] Step 3: After the number of sub-modules put into operation is determined, the energy consumption power is precisely regulated by controlling the alternating conduction of the sub-modules.

[0052] In this step, after determining the number of submodules to be deployed, those with higher capacitance are prioritized to achieve smooth power regulation. This approach not only improves the device's energy efficiency but also avoids damage to some submodules due to overworking.

[0053] In a specific implementation, the method further includes a fault ride-through control step. When a fault is detected in the receiving AC power grid, the device is quickly responded to and started to absorb the surplus power injected by the wind farm and maintain the DC voltage within a safe range.

[0054] Through the above control process, the present invention realizes the adjustable energy consumption power of the hybrid DC energy consumption device in the offshore wind power flexible DC transmission system, while ensuring the stability of the capacitor voltage of all sub-modules, the controllable fluctuation amplitude, and the uniform distribution of charging power to each sub-module, avoiding the problem of overheating and damage of internal integrated resistors caused by excessive work of some sub-modules.

[0055] It should be noted that the contents not described in detail in the embodiments of the present invention belong to the prior art known to those skilled in the art.

[0056] In summary, the device and control method described in the embodiment of the present invention are applicable to offshore wind power flexible direct current grid-connected systems, and can effectively solve the problem of increased DC line voltage when the receiving-end converter valve fails in DC transmission projects. The submodules of the device are smoothly put into and out of operation, and the dissipated energy is controllable, which solves the problem that traditional control strategies cannot flexibly adjust dissipated energy. Compared with the centralized topology, the new topology no longer uses two-level PWM modulation, but uses multi-level modulation, so it has the advantages of good EMC characteristics, high power control accuracy and small system fluctuations.

[0057] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims. The information disclosed in the background technology section of this article is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as an admission or any form of implication that the information constitutes prior art already known to those skilled in the art.

Claims

1. A hybrid DC energy consumption device, characterized in that: The device includes a plurality of submodules and a concentrated energy-consuming resistor connected in series with the submodules, wherein: Each submodule has the ability to be turned on and off independently. Based on the changes in the system DC voltage and the set threshold, the number of submodules turned on is adjusted in real time through a rotation control method to achieve precise control of energy consumption. The concentrated energy dissipation resistor is used to dissipate excess power and is a key energy dissipation component in the device; The device is connected in parallel to both ends of the DC busbar of the system. When a fault occurs in the AC side of the main grid, the device starts and absorbs the surplus power. The device includes no-load mode, full-load mode and power adjustable mode. In no-load mode, the insulated gate bipolar transistor (IGBT) units in all submodules are turned off, the submodule capacitors are connected in series to support the DC side voltage, and the device current and absorbed power are zero; In full load mode, the IGBT units of all submodules are turned on, the DC side voltage is fully applied to both ends of the centralized energy dissipation resistor, and the branch current of the device reaches the maximum value; In the power adjustable mode, by changing the sum of the output voltages of the submodules, the voltage across the centralized energy dissipation resistor is adjusted, thereby adjusting the current and power of the device branch. At this time, the device absorbs power between 0 and the system rated transmission power P rated The absorbed power of the device is composed of two parts, including the power consumed by the centralized energy-consuming resistor and the capacitor charging power of all sub-modules put into use.

2. The hybrid DC energy dissipation device according to claim 1, characterized in that: Each submodule consists of a storage capacitor C, a distributed resistor R, a first IGBT unit T1, a second IGBT unit T2, a first diode D1, and a second diode D2. The storage capacitor C is connected in series with the first diode D1 and then connected in parallel to both ends of the first IGBT unit T1, providing a buffer for the on and off of the IGBT. The distributed resistor R is connected in parallel with the second diode D2, and then connected in series with the second IGBT unit T2, and then connected in parallel to both ends of the first IGBT unit T1. The first diode D1 is used to limit the direction of branch current; The second diode D2 is used for freewheeling; The first IGBT unit T1 is used to control the voltage output by the submodule to switch between zero and the capacitor voltage; The second IGBT unit T2 is used to control the charging and discharging of the capacitor to maintain the constant voltage of the submodule capacitor; When the first IGBT unit T1 is turned on, the submodule state is defined as the "cut-off" state; when the first IGBT unit T1 is turned off, the submodule state is defined as the "on" state; The energy storage capacitor C is used to store electrical energy to maintain a constant capacitor voltage; The distributed resistor R is used to consume part of the electrical energy when the submodule is turned on.

3. The hybrid DC energy dissipation device according to claim 1, characterized in that: According to the change of the system DC voltage and the set threshold, the number of submodules turned on is adjusted in real time through the control method of alternating conduction. The specific process is as follows: First, according to the absorption power P of the device chopper , and the total number of submodules N all ,Calculate the number of sub-modules N that need to be invested. The calculation formula is: P rated is the rated transmission power of the system, round(x) is the rounding function, and the digits after the decimal point are rounded off; The amount of energy absorbed by the capacitors in the submodules is used as the basis for sorting the submodule input priorities. The concept of "rotating conduction" of the submodules is introduced, that is, the submodules with more capacitor energy are prioritized. According to the energy absorption ranking results of the capacitors in the submodules and the number N of submodules that need to be put into operation, the final switching instructions are determined to achieve the alternating conduction of the submodules.

4. A control method for a hybrid DC energy consumption device, characterized in that: The method comprises: Step 1: Obtain system DC voltage data in real time to provide a basis for subsequent control; Step 2: Dynamically adjust the number of submodules in operation based on the changes in the acquired DC voltage and the set threshold; Step 3: After the number of sub-modules put into operation is determined, the energy consumption power is precisely regulated by controlling the alternating conduction of the sub-modules.

5. The control method of the hybrid DC energy consumption device according to claim 4, characterized in that: In step 2, When the DC voltage exceeds the set threshold, the number of sub-modules put into operation is increased to dissipate more surplus power; When the DC voltage is lower than the set threshold, the number of sub-modules put into operation is reduced to reduce the power consumption of the energy-consuming devices.

6. The control method of the hybrid DC energy consumption device according to claim 4, characterized in that: In step 3, After the number of sub-modules to be put into use is determined, sub-modules with more capacitor energy are put into use first to achieve smooth regulation of energy consumption and power.

7. The control method of the hybrid DC energy consumption device according to claim 4, characterized in that: The method further comprises a fault ride-through control step, wherein when a fault is detected in the receiving-end AC power grid, the device is quickly responded to and started to absorb the surplus power injected by the wind farm and maintain the DC voltage within a safe range.

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