Coordinated control method for energy consumption of direct current energy consumption device in stages

Abstract

The application provides a coordinated control method for stage-by-stage elastic energy consumption adjustment of a direct current energy consumption device. The coordinated control method for stage-by-stage elastic energy consumption adjustment of the direct current energy consumption device comprises at least three direct current voltage thresholds, and specifically comprises the following steps: obtaining a direct current bus voltage; obtaining a capacitor voltage and an input state of an energy consumption device sub-module; detecting the direct current bus voltage in real time, and generating different energy consumption device operation instructions by comparison with the direct current voltage thresholds to control the direct current energy consumption device to enter a corresponding state. The coordinated control strategy for stage-by-stage elastic energy consumption adjustment of the direct current energy consumption device effectively realizes fast and accurate input of the energy consumption of the direct current energy consumption device by controlling the jump of the operation state of the direct current energy consumption device, prevents overvoltage, and does not cause the phenomenon of large fluctuation of the direct current voltage of an access point caused by repeated switching of the energy consumption device in the energy consumption process, thereby improving the transient stability and fault ride-through capability of the direct current system.

Description

Technical Field

[0001] This application relates to the field of high-power power electronic converter technology. Specifically, it relates to a method for coordinated energy consumption control between a DC energy-consuming device and a DC system. Background Technology

[0002] In practical engineering fields such as grid connection of new energy via flexible DC transmission and transmission of offshore wind power via flexible DC transmission, if the AC system at the receiving end fails and the power capacity decreases, but the power transmitted at the sending end cannot be reduced rapidly in a short period of time, energy will accumulate in the DC line and the converter stations at both ends, causing the DC line voltage to rise rapidly in a short period of time. In severe cases, it may cause insulation problems in the DC line, damage to the converter devices and related supporting equipment in the converter stations at both ends, and cause huge economic losses.

[0003] Currently, a relatively effective solution both domestically and internationally is to install DC power dissipation devices between the positive and negative poles of the DC side at the receiving end of the flexible DC transmission line. These devices absorb surplus power during AC system faults at the receiving end to suppress DC overvoltage, thereby achieving power balance and maintaining the DC voltage within the equipment's tolerance range, thus achieving fault ride-through. Currently, DC power dissipation devices are mainly classified into two categories: distributed and centralized. Both types of distributed power dissipation submodules and centralized power dissipation submodules with voltage divider functions contain power capacitors and power semiconductor devices. Therefore, a high voltage spike occurs at the moment the DC power dissipation device is switched on. Regarding the coordinated control methods between the DC power dissipation device and the DC system, one approach is to use the technically mature voltage hysteresis control. During periods when the system requires energy consumption, the DC power dissipation device is repeatedly switched on and off. Although some methods use auxiliary calculations to convert surplus power into the duty cycle of the DC power dissipation device, repeated switching is still necessary. Furthermore, this coordinated control strategy requires a large amount of computation, thus necessitating a certain reaction time. Based on a coordinated control strategy that calculates the power difference between the DC and AC systems at the receiving end without repeated switching, the DC energy-consuming device has a slow response speed, and the control effect of the DC voltage always lags behind the calculation results. Furthermore, the control system needs to collect relevant electrical quantities of the DC and AC systems at the receiving end, resulting in higher costs and a more complex control system.

[0004] Therefore, a coordinated control strategy between DC energy-consuming devices and DC systems that is effective, reliable, and cost-efficient is needed to effectively solve the problem of DC voltage spikes caused by repeated switching of DC energy-consuming devices during periods of energy consumption. Summary of the Invention

[0005] This application provides a coordinated control method for staged flexible adjustment of energy consumption in DC energy-consuming devices, which can achieve high-performance control of energy-consuming devices and avoid the phenomenon of repeated switching of DC energy-consuming devices during periods when the system needs to consume energy.

[0006] Based on the characteristics of the coordinated control method of this application, the method is applicable to DC energy-consuming devices with adjustable power consumption, which are connected in series in the same direction across the positive and negative DC lines of a flexible DC system and consist of multiple sub-modules and energy-consuming resistors. The coordinated control method for staged flexible adjustment of energy consumption of DC energy-consuming devices includes:

[0007] Obtain the DC bus voltage;

[0008] Obtain the current operating status of the DC power consumption device;

[0009] Compare the DC bus voltage with a preset voltage action threshold to generate a control command;

[0010] According to the control command, the DC energy-consuming device operates in the corresponding preset energy-consuming state.

[0011] Furthermore, before acquiring the DC bus voltage, the method also includes preset DC voltage thresholds, which include at least two upper limit action thresholds and one lower limit action threshold. The upper limit action thresholds are greater than the rated voltage of the DC system, and the number of upper limit action thresholds is selected according to the actual DC system project and the type of DC energy-consuming device used.

[0012] Furthermore, the operation of the DC energy-consuming device in the corresponding preset energy-consuming state according to the control command specifically includes: when the measured DC bus voltage amplitude reaches different upper limit action thresholds, controlling the energy-consuming device to be in different energy-consuming states; when the measured DC bus voltage is less than the lower limit action threshold, the energy-consuming device executes a cut-off command, the energy-consuming device is cut off from the system, and the DC voltage is controlled within the allowable range.

[0013] Furthermore, if the DC voltage amplitude reaches the first upper limit action threshold, it is determined that the system has entered the transient process stage. The energy-consuming device enters the first energy-consuming state controlled by the first upper limit action threshold from the zero energy-consuming state of the bypass state. If the DC voltage amplitude drops to the lower limit action threshold, it is determined that the DC system transient process has ended or the fault is minor and the DC voltage is within the allowable range. The DC energy-consuming device starts to execute the cut-off control command, and then the DC energy-consuming device is cut off from the system and no longer participates in energy consumption.

[0014] Furthermore, the first upper limit action threshold is selected based on the fluctuation limit of the DC voltage amplitude slightly greater than that of the DC system during normal operation. The power consumed by the DC energy-consuming device corresponding to the first upper limit action threshold is determined when the DC voltage just rises to the first upper limit voltage action threshold and no longer fluctuates significantly. At this time, the DC energy-consuming device is activated, and the power consumed by the DC energy-consuming device is adjusted so that the DC voltage drops to just slightly greater than the lower limit action threshold. At this time, the power consumed by the energy-consuming device is recorded as P11. When the system is operating normally, the DC energy-consuming device is activated until the DC voltage just drops to the lower limit action threshold. At this time, the power consumed by the energy-consuming device is recorded as P12. The larger value between P11 and P12 is taken as the power value consumed by the DC energy-consuming device corresponding to the first upper limit action threshold, and the working state of the corresponding DC energy-consuming device is recorded as the first energy-consuming state.

[0015] Furthermore, after the determination system enters the transient process, the DC energy-consuming device first enters the first energy-consuming state. If the DC voltage continues to rise uncontrollably, when the measured DC voltage reaches the second upper limit action threshold, the energy-consuming state of the DC energy-consuming device is changed by control to increase energy consumption, and the DC energy-consuming device is converted from the first energy-consuming state to the second energy-consuming state.

[0016] Furthermore, the second upper limit action threshold is numerically greater than the first upper limit action threshold but less than the highest voltage the system can withstand. The power consumed by the DC energy-consuming device in the second energy-consuming state corresponding to the second upper limit action threshold can be preset as follows: when the DC energy-consuming device enters the first energy-consuming state, the measured DC voltage continues to rise and its amplitude reaches the second upper limit action threshold and then stops rising. At this time, the power consumed by the energy-consuming device is adjusted so that the DC voltage drops to slightly greater than the lower limit action threshold. At this time, the state of the DC energy-consuming device is taken as the second energy-consuming state corresponding to the second upper limit action threshold.

[0017] Furthermore, the plurality of upper limit action thresholds include a maximum upper limit threshold, which is selected as the maximum transient DC voltage amplitude that the DC system can allow. The corresponding DC energy-consuming device operates in the mode of maximum energy consumption, and its state is recorded as the maximum energy consumption state.

[0018] Furthermore, to ensure that the DC system can still transmit a certain amount of power during the transient process, the lower limit action threshold is selected as the minimum DC voltage amplitude allowed when the DC system is operating normally, and the corresponding operating state of the DC energy consumption device is a state of bypassing the DC system and not consuming power.

[0019] Furthermore, the method for determining the energy consumption state of the DC energy-consuming device corresponding to the Nth upper limit action threshold (N is a positive integer and N≠1) between the first upper limit action threshold and the highest upper limit action threshold includes the following steps:

[0020] Step 1: After the measured DC voltage amplitude reaches the upper limit action threshold of the N-1th step, the DC energy consumption device enters the N-1th energy consumption state, causing the DC voltage to continue to rise.

[0021] Step 2: When the DC voltage rises to the Nth upper limit action threshold, prevent it from rising significantly, and the DC voltage amplitude is less than the N+1th upper limit action threshold. At this time, adjust the power consumed by the DC energy-consuming device so that the DC voltage drops to a level slightly higher than the lower limit action threshold.

[0022] Step 3: Record the current state of the DC power consumption device as the Nth power consumption state of the DC power consumption device corresponding to the Nth upper limit action threshold.

[0023] The above-described technical solution of the present invention has the following beneficial technical effects:

[0024] 1. The reference quantity for the aforementioned coordinated control strategy is only the DC bus voltage, which is simple in principle and economical in cost;

[0025] 2. The coordinated control strategy requires minimal calculations, reacts rapidly, and effectively controls the DC voltage within permissible limits;

[0026] 3. Effectively realizes rapid and efficient control of DC energy-consuming devices, and solves the problem of DC voltage spikes caused by repeated switching of DC energy-consuming devices during energy consumption;

[0027] 4. Enhanced transient stability and fault ride-through capability of DC systems; Attached Figure Description

[0028] Figure 1 This is a schematic diagram of a typical flexible DC system with a DC power dissipation device used in an embodiment of the present invention.

[0029] Figure 2 This is a schematic diagram of the voltage action threshold distribution of the coordinated control strategy described in this invention;

[0030] Figure 3 This is a flowchart of the coordination control strategy described in this invention;

[0031] Figure 4 A topology diagram of a DC power consumption device applicable to the coordinated control method described in this invention; Detailed Implementation

[0032] To make the technical solution and advantages of the present invention clearer, the present invention will be further described in detail below with reference to a specific DC energy-consuming device. Furthermore, in the following description, some detailed descriptions of the structure and working principle of the DC energy-consuming device are omitted, and the focus is on the coordination and control method between the DC energy-consuming device and the DC system.

[0033] like Figure 1 As shown, this invention is mainly applied to flexible DC transmission systems with adjustable power consumption. The sending end of the flexible DC system is not limited to the AC grid; it is also applicable to offshore wind farms. When a fault occurs in the receiving end AC system of the flexible system, and the receiving end AC / DC system has a power surplus, the excess energy will accumulate in the converter station and DC line, causing overvoltage conditions in the line and converter equipment.

[0034] DC power dissipation devices can effectively suppress DC system overvoltage, but most coordinated control strategies will exhibit repeated switching during the power dissipation period of the DC power dissipation devices. The repeated switching of DC power dissipation devices will cause large peaks in DC voltage, which will have a certain impact on the DC system. If the fault lasts for a long time, it will also have a certain impact on the insulation performance of the equipment. In addition, due to the large fluctuation of DC voltage during the switching process, a certain amount of harmonic pollution will also be generated.

[0035] Therefore, a fast and effective control method to avoid repeated switching of energy-consuming devices is crucial.

[0036] like Figure 2 , Figure 3 As shown, this embodiment of the invention provides a coordinated control method for staged flexible adjustment of energy consumption in DC energy-consuming devices. The coordinated control method includes the following steps:

[0037] Obtain the DC bus voltage;

[0038] Obtain the current status of DC power consumption devices;

[0039] Compare the DC bus voltage with a preset voltage action threshold to generate a control command;

[0040] According to the control command, the DC energy-consuming device operates in the corresponding preset energy-consuming state;

[0041] In this example, the rated voltage of the DC line is 500kV, the rated transmission power is 1000MW, and the DC energy-consuming device has 25 H-bridge sub-modules. By changing the amplitude of the capacitor charging voltage of each sub-module, the voltage across the energy-consuming valve is changed, and the voltage division on the energy-consuming resistor is changed, thereby changing the power consumed by the DC energy-consuming device. When the system is running normally, the DC voltage fluctuation range is 1.0±5%pu, and the maximum allowable transient DC voltage peak is 1.2pu.

[0042] According to this example, the preset first upper limit action threshold is selected as 1.06 pu, the highest upper limit action threshold is 1.2 pu, and the lower limit action threshold is 0.95 pu. To briefly explain the coordinated control method of the present invention, this embodiment presets four voltage upper limit action thresholds, using 1.1 pu as the second upper limit action threshold and 1.15 as the third upper limit action threshold.

[0043] The preset method for the first energy consumption state of the DC energy-consuming device corresponding to the first upper limit action threshold is as follows:

[0044] Step 1: Set a fault in the AC system at the receiving end of the flexible DC system. The DC voltage rises exactly to the first upper limit voltage action threshold of 1.06 pu and no longer fluctuates significantly.

[0045] Step 2: At this time, the DC power consumption device is activated. By changing the positive charging voltage amplitude of the capacitor of the power consumption valve submodule, the power consumed by the DC power consumption device is adjusted so that the DC voltage drops to just slightly above the lower limit action threshold. At this time, the power consumed by the power consumption device is recorded as P11.

[0046] Step 3: When the system is running normally, put the DC power consumption device into operation until the DC voltage just drops to the lower limit action threshold. At this time, record the power consumed by the power consumption device as P12.

[0047] Step 4: Take the larger value between P11 and P12 as the power consumption value of the DC power consumption device corresponding to the first upper limit action threshold, and the working state of the corresponding DC power consumption device is the first power consumption state.

[0048] The preset method for the second energy consumption state of the DC energy-consuming device corresponding to the second upper limit action threshold is as follows:

[0049] Step 1: Set a fault in the AC system at the receiving end of the flexible DC system. When the DC energy-consuming device enters the first energy-consuming state, the DC voltage continues to rise and stops rising when its amplitude reaches the second upper limit action threshold.

[0050] Step 2: By changing the positive charging voltage amplitude of the capacitor in the energy-consuming valve submodule, the power consumed by the energy-consuming device is adjusted so that the DC voltage drops to slightly above the lower limit action threshold. At this time, the state of the DC energy-consuming device is taken as the second energy-consuming state corresponding to the second upper limit action threshold.

[0051] The method for presetting the third energy consumption state of the DC energy consumption device corresponding to the third upper limit action threshold is as follows:

[0052] Step 1: Set a fault in the AC system at the receiving end of the flexible DC system. When the DC energy-consuming device enters the second energy-consuming state, the DC voltage continues to rise and stops rising when its amplitude reaches the third upper limit action threshold.

[0053] Step 2: By changing the positive charging voltage amplitude of the capacitor in the energy-consuming valve submodule, the power consumed by the energy-consuming device is adjusted so that the DC voltage drops to slightly above the lower limit action threshold. At this time, the state of the DC energy-consuming device is taken as the third energy-consuming state corresponding to the third upper limit action threshold.

[0054] After selecting the voltage action threshold and the corresponding DC energy consumption state according to the above method, the control logic flowchart of the coordinated control method in the embodiment is as follows: Figure 3 As shown.

[0055] The system detects the DC bus voltage and the status of the DC power consumption device. First, it determines whether the DC voltage is greater than 1.06 pu. If so, it determines that the system has entered a transient process and controls the DC power consumption device to change from a zero power consumption state to the first power consumption state. Otherwise, the DC power consumption device remains in the zero power consumption state.

[0056] If the DC bus voltage exceeds the first upper limit action threshold, the DC energy-consuming device switches to the first energy-consuming state and continues to monitor the DC bus voltage. If the DC voltage continues to rise uncontrolled, it is determined whether it exceeds the second upper limit action threshold. If so, the DC energy-consuming device is controlled to switch to the second energy-consuming state. Otherwise, it is determined whether the DC voltage is less than the lower limit action threshold. If so, the DC energy-consuming device performs cut-off control and switches to the zero energy-consuming state. Otherwise, the first energy-consuming state is maintained.

[0057] If, according to preset conditions, the DC energy-consuming device enters the second energy-consuming state, it is determined whether the voltage is greater than the third upper limit action threshold. If so, the DC energy-consuming device is controlled to switch to the third energy-consuming state. Otherwise, it is determined whether the DC voltage is less than the lower limit action threshold. If so, the DC energy-consuming device performs cut-off control and switches to the zero energy-consuming state. Otherwise, it continues to maintain the second energy-consuming state.

[0058] If, according to preset conditions, the DC energy-consuming device enters the third energy-consuming state, it is determined whether the voltage is greater than the maximum upper limit action threshold. If so, the DC energy-consuming device is controlled to switch to the maximum energy-consuming state. Otherwise, it is determined whether the DC voltage is less than the lower limit action threshold. If so, the DC energy-consuming device performs cut-off control and switches to the zero energy-consuming state. Otherwise, the third energy-consuming state is maintained.

[0059] If, according to preset conditions, the DC energy-consuming device enters the maximum energy-consuming state, it is determined whether the DC voltage is less than the lower limit action threshold. If so, the DC energy-consuming device performs cut-off control and switches to the zero energy-consuming state; otherwise, it continues to maintain the maximum energy-consuming state.

[0060] After controlling the DC power consumption device according to the method and control strategy described above, the DC voltage can be effectively controlled within the range of 0.95pu to 1.12pu, while solving the problem of repeated switching during the power consumption period of the power consumption device.

[0061] This invention aims to propose a coordinated control method for phased flexible adjustment of energy consumption of DC energy-consuming devices. The control method determines the energy consumption state of the DC energy-consuming device by judging the relationship between the DC bus voltage and multiple preset voltage action thresholds. This avoids the problem of repeated switching of the DC energy-consuming device during energy consumption from the perspective of coordinated control strategy, reduces the negative impact of energy consumption of the energy-consuming device on the system, and improves the transient stability and fault ride-through capability of the system.

[0062] The DC power-consuming devices described in the above-described specific embodiments and examples of the present invention are merely illustrative or explanatory of the coordinated control principle of the present invention and do not constitute a limitation thereof. It should also be noted that the present invention is applicable to all DC power-consuming devices with adjustable power consumption. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the principles and scope of the present invention should be included within the protection scope of the present invention.

[0063] The above examples are only used to illustrate the technical solution of the centralized arrangement of energy-consuming resistors of the present invention. This technical solution is also applicable to the form of distributed arrangement of energy-consuming resistors, and is not intended to limit it. Various modifications or changes made with reference to the above examples are within the protection scope of the present invention.

[0064] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of those different embodiments or examples.

[0065] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0066] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A coordinated control method for the phased elastic regulation of energy consumption of a direct current energy consumer, characterized in that, The method comprises the following steps: obtaining a DC bus voltage; obtaining a current working state of a DC energy consumption device; comparing the DC bus voltage with a preset voltage action threshold to generate a control instruction; according to the control instruction, the DC energy consumption device operates in a corresponding preset energy consumption state, wherein, before obtaining the DC bus voltage, a preset DC voltage threshold is further included, the DC voltage threshold comprises at least two upper limit action thresholds and one lower limit action threshold, the upper limit action threshold is greater than the DC system rated voltage, and the number of the upper limit action threshold is selected according to the actual DC system engineering and the type of the DC energy consumption device adopted, wherein, according to the control instruction, the DC energy consumption device operates in the corresponding preset energy consumption state specifically comprises: when the measured DC bus voltage amplitude reaches different upper limit action thresholds, the energy consumption device is controlled to be in different energy consumption states, when the measured DC bus voltage is less than the lower limit action threshold, the energy consumption device executes a cut-off instruction, the energy consumption device is cut off from the system, and the DC voltage is controlled within the allowable range, wherein, if the amplitude of the DC voltage reaches the first upper limit action threshold, it is determined that the system enters a transient process stage, the energy consumption device enters a first energy consumption state controlled by the first upper limit action threshold from a bypass state of zero energy consumption state, if the DC voltage amplitude drops to the lower limit action threshold, it is determined that the transient process of the DC system ends or the fault degree is slight, the DC voltage is within the allowable range, the DC energy consumption device starts to execute the cut-off control instruction, and then the DC energy consumption device is cut off from the system and no longer participates in energy consumption, the first upper limit action threshold is selected according to a fluctuation upper limit slightly greater than the amplitude of the DC voltage in the normal operation of the DC system, the power consumed by the DC energy consumption device corresponding to the first upper limit action threshold is selected according to that the DC voltage just rises to the first upper limit voltage action threshold and no longer fluctuates greatly, at this time, the DC energy consumption device is put into operation, the power consumed by the DC energy consumption device is adjusted, and the DC voltage drops to just slightly greater than the lower limit action threshold, at this time, the power consumed by the energy consumption device is recorded as P11, when the system operates normally, the DC energy consumption device is put into energy consumption until the DC voltage just drops to the lower limit action threshold, at this time, the power consumed by the energy consumption device is recorded as P12, the larger one of P11 and P12 is taken as the power value consumed by the DC energy consumption device corresponding to the first upper limit action threshold, and the working state of the corresponding DC energy consumption device is recorded as the first energy consumption state.

2. The method of claim 1, wherein, After it is determined that the system enters the transient process, the DC energy consumption device first enters the first energy consumption state, if the DC voltage cannot be controlled and continues to rise, when the measured DC voltage reaches the second upper limit action threshold, the energy consumption state of the DC energy consumption device is changed by control to increase energy consumption, and the DC energy consumption device is switched from the first energy consumption state to the second energy consumption state.

3. The method of claim 2, wherein, The second upper action threshold is greater than the first upper action threshold in value and less than the maximum voltage that the system can bear, and the power consumed by the DC energy consumption device in a second energy consumption state corresponding to the second upper action threshold can be preset as follows: when the DC energy consumption device enters the first energy consumption state, the measured DC voltage continues to rise and its amplitude reaches the second upper action threshold and no longer rises, at which time the power consumed by the energy consumption device is adjusted to make the DC voltage drop to slightly greater than the lower action threshold, at which time the state of the DC energy consumption device is taken as the second energy consumption state corresponding to the second upper action threshold.

4. The method according to any one of claims 1 to 3, characterized in that, The at least two upper action thresholds include a highest upper action threshold, which is selected as the maximum transient DC voltage amplitude that the DC system can allow, and the DC energy consumption device operates in a maximum energy consumption mode corresponding to the highest upper action threshold, and the state of the DC energy consumption device is taken as a maximum energy consumption state.

5. The method according to any one of claims 1 to 3, wherein To ensure that the DC system can still transmit a certain power during a transient process, the lower action threshold is selected as the minimum DC voltage amplitude that the DC system allows during normal operation, and the working state of the DC energy consumption device is a state of being bypassed from the DC system and not consuming power.

6. The method of claim 4, wherein, An Nth upper action threshold between the first upper action threshold and the highest upper action threshold, N being a positive integer and N≠1, and the determination method of the energy consumption state of the DC energy consumption device corresponding to the Nth upper action threshold includes the following steps: Step one: after the measured DC voltage amplitude reaches the (N-1)th upper action threshold, the DC energy consumption device enters an (N-1)th energy consumption state, and the DC voltage continues to rise, Step two: when the DC voltage rises to the Nth upper action threshold and no longer rises greatly, and the DC voltage amplitude is less than the (N+1)th upper action threshold, at which time the power consumed by the DC energy consumption device is adjusted to make the DC voltage drop to greater than the lower action threshold level, Step three: the state of the DC energy consumption device at this time is taken as an Nth energy consumption state of the DC energy consumption device corresponding to the Nth upper action threshold.

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