Power lever mechanism of energy storage type direct current power flow controller and application

Abstract

The invention provides a power lever mechanism of an energy storage type direct current power flow controller and application. The power lever mechanism comprises the following steps: constructing the energy storage type direct current power flow controller; designing a power coordination control strategy; in a hybrid AC / DC power distribution network, an energy storage type DC power flow controller is connected to each line in series, and controllable voltage sources in the lines are connected in series through energy exchange and constant capacitor voltage values between capacitors on the controller and an energy storage system and between the capacitors; and according to the droop characteristic of the hybrid AC / DC power distribution network, a power coordination control strategy is formulated, and power equalization between DC power grids and regulation and control of AC power grid output power are carried out. The energy storage system is integrated on the basis of a traditional direct current power flow controller, the application mode of the energy storage system in a novel electric power system is enriched, the function and efficiency of the electric power system are remarkably improved, the system can be connected into a power grid in a more flexible and efficient mode, and the energy storage system is suitable for popularization and application. And powerful support is provided for realizing active power coordination control of the hybrid AC / DC power distribution network.

Description

Technical Field

[0001] This invention relates to the technical field of electrical engineering, specifically to the power lever mechanism and application of energy storage DC power flow controllers, and more particularly to the power lever mechanism of energy storage DC power flow controllers and their application in active power coordination control of hybrid AC / DC distribution networks. Background Technology

[0002] The efficient and reliable utilization of renewable energy in power distribution networks is a crucial research area in electrical engineering and a key component of next-generation power systems. Hybrid AC / DC distribution networks, as a novel power grid structure, combine the advantages of DC and AC grids. By connecting AC and DC sources and loads via busbars, they aim to minimize power conversion stages, thereby improving overall efficiency and reducing system costs. This grid structure demonstrates significant potential for enhancing the efficiency and reliability of power systems.

[0003] However, efficient coordinated control and power exchange in hybrid AC / DC distribution networks still face many challenges. Currently, research on active power coordination control in hybrid AC / DC distribution networks mainly relies on multiple interconnected converters to achieve power control. These studies have made some progress in the framework of coordinated power control, but their working mechanism is based on the principle of full power processing, meaning that the rated capacity of the interconnected converters is limited to the maximum transmission power. This method has been widely proven to be less efficient compared to partial power processing mechanisms. The main idea of ​​partial power processing is to embed an equivalent voltage source in series with the original power source into the system, so that only a portion of the total power is processed through the converter. This not only reduces power loss but also improves power transmission efficiency.

[0004] Patent document CN115149592A discloses a control method for a power control-based energy storage AC / DC hybrid microgrid system. This method controls a microgrid system comprising: a central controller, converters, AC loads, DC loads, and distributed energy units. The method includes the following steps: acquiring basic equipment information of each distributed energy unit within the microgrid system and performing control for the first control cycle; in each control cycle, collecting operating information of each distributed energy unit; and based on this operating information, determining the active power reference values ​​of all energy storage units, the reactive power reference values ​​of all distributed energy units, and the scalar coefficients of each distributed energy unit for the next control cycle.

[0005] Although partial power processing (PPP) theoretically offers numerous advantages, its benefits have not been fully realized in practical applications of hybrid AC / DC distribution networks. Current research has not yet identified corresponding control strategies to reveal how PPP works synergistically with power coordination control in AC / DC distribution networks. Therefore, how to effectively implement PPP in hybrid AC / DC distribution networks to further improve system efficiency and reliability has become an urgent problem to be solved.

[0006] Therefore, a new technical solution is needed to improve the above-mentioned technical problems. Summary of the Invention

[0007] In view of the deficiencies in the prior art, the purpose of this invention is to provide a power lever mechanism and application of an energy storage type DC power flow controller.

[0008] The power lever mechanism of the energy storage DC power flow controller provided by the present invention includes the following steps:

[0009] Step S1: Construct an energy storage DC power flow controller, which integrates an energy storage system on the basis of the original DC power flow controller and connects to the power grid through power electronic devices;

[0010] Step S2: Design a power coordination control strategy, utilize a partial power processing mechanism, and use an energy storage DC power flow controller to implement a power lever mechanism to quantitatively adjust the power of the entire system;

[0011] Step S3: In the hybrid AC / DC distribution network, the energy storage DC power flow controller is connected in series to each line, and the energy exchange between the capacitor on the controller and the energy storage system and between each capacitor is constant to connect the controllable voltage source in the line in series.

[0012] Step S4: Based on the droop characteristics of the hybrid AC / DC distribution network, including the frequency-power droop characteristics of the AC network and the voltage-power droop characteristics of the DC network, formulate a power coordination control strategy to perform power sharing among DC networks and regulate the output power of the AC network.

[0013] Preferably, the topology of the energy storage DC power flow controller in step S1 includes multiple units and an energy storage system. The switching duty cycle of each unit is adjusted according to the control strategy to coordinate the power control.

[0014] Preferably, the power coordination control strategy in step S2 includes controlling the average value of the DC grid bus voltage, equally distributing the power among the DC grids, and obtaining the steady state of the system by adjusting the output power of the AC grid to a given value and using the capacitor voltage as the inner loop control.

[0015] Preferably, the hybrid AC / DC distribution network in step S3 includes multiple DC grids, one AC grid, and an energy storage DC power flow controller. The DC grids and AC grids are connected by a bus to form a hybrid AC / DC system.

[0016] Preferably, the frequency-power droop characteristic of the AC power grid in step S4 is characterized by fP droop, and the frequency-power droop characteristic is expressed as follows:

[0017] f ac =f acmax -k ac P ac (1)

[0018] Among them, f ac P represents the frequency of the AC power grid. ac f represents the output power of the AC power grid. acmax k represents the maximum frequency of the AC power grid. ac The droop factor of an AC power grid is defined as follows:

[0019] k ac =(f acmax -f acmin ) / P acmax (2)

[0020] The voltage-power droop characteristic of the DC grid is characterized by VP droop, as shown below:

[0021] V dci =V dcmax -k dci P dci i = 1, 2, 3(3)

[0022] Among them, V dci P represents the bus voltage of the i-th DC grid. dci V represents the output power of the i-th DC grid. dcmax k represents the maximum output voltage of the DC power grid. i The droop factor of a DC power grid is defined as follows:

[0023] k dci =(V dcmax -V dc min ) / P dcimax (4)

[0024] Among them, V dcmin P represents the minimum output voltage of a DC power grid. dcimax This indicates the maximum output power of the DC power grid.

[0025] This invention also provides a power lever application for an energy storage type DC power flow controller, comprising the following modules:

[0026] Module M1: Constructs an energy storage DC power flow controller, which integrates an energy storage system on the basis of the original DC power flow controller and connects to the power grid through power electronic devices;

[0027] Module M2: Design a power coordination control strategy, utilize a partial power processing mechanism, and use an energy storage DC power flow controller to implement a power lever mechanism to quantitatively adjust the power of the entire system;

[0028] Module M3: In a hybrid AC / DC distribution network, an energy storage DC power flow controller is connected in series to each line. Through the energy exchange between the capacitor on the controller and the energy storage system and between each capacitor, the voltage value of the capacitor is kept constant, and a controllable voltage source is connected in series in the line.

[0029] Module M4: Based on the droop characteristics of the hybrid AC / DC distribution network, including the frequency-power droop characteristics of the AC network and the voltage-power droop characteristics of the DC network, formulate a power coordination control strategy to perform power sharing among DC networks and regulate the output power of the AC network.

[0030] Preferably, the topology of the energy storage DC power flow controller in module M1 includes multiple units and an energy storage system. The switching duty cycle of each unit is adjusted according to the control strategy to coordinate and control the power.

[0031] Preferably, the power coordination control strategy in module M2 includes controlling the average value of the DC grid bus voltage, equally distributing the power among the DC grids, and obtaining the steady state of the system by adjusting the output power of the AC grid to a given value and using the capacitor voltage as the inner loop control.

[0032] Preferably, the hybrid AC / DC distribution network in module M3 includes multiple DC grids, one AC grid, and an energy storage DC power flow controller. The DC grids and AC grids are connected by a bus to form a hybrid AC / DC system.

[0033] Preferably, the frequency-power droop characteristic of the AC power grid in module M4 exhibits an fP droop, which is expressed as follows:

[0034] f ac =f acmax -k ac P ac (1)

[0035] Among them, f ac P represents the frequency of the AC power grid. ac f represents the output power of the AC power grid.acmax k represents the maximum frequency of the AC power grid. ac The droop factor of an AC power grid is defined as follows:

[0036] k ac =(f acmax -f acmin ) / P acmax (2)

[0037] The voltage-power droop characteristic of the DC grid is characterized by VP droop, as shown below:

[0038] V dci =V dcmax -k dci P dci i = 1, 2, 3(3)

[0039] Among them, V dci P represents the bus voltage of the i-th DC grid. dci V represents the output power of the i-th DC grid. dcmax k represents the maximum output voltage of the DC power grid. i The droop factor of a DC power grid is defined as follows:

[0040] k dci =(V dcmax -V dc min ) / P dcimax (4)

[0041] Among them, V dcmin P represents the minimum output voltage of a DC power grid. dcimax This indicates the maximum output power of the DC power grid.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] 1. This invention, by integrating an energy storage system into a traditional DC power flow controller, not only enriches the application methods of energy storage systems in new power systems, but also significantly improves the functionality and efficiency of power systems. It can connect to the grid in a more flexible and efficient manner, providing strong support for realizing active power coordination control of hybrid AC / DC distribution networks.

[0044] 2. The power coordination control strategy of the present invention can accurately regulate the output power of the distribution network over a wide range, thereby significantly improving the system's flexibility and response speed. This is of great significance for coping with complex and ever-changing power demands and ensuring the stable operation of the power system.

[0045] 3. This invention reveals the power lever mechanism of the energy storage DC power flow controller in a hybrid AC / DC distribution network, and achieves the purpose of regulating the large power of the entire system with a small part of the power through a partial power processing mechanism, thereby reducing the capacity requirements of the equipment and effectively reducing engineering costs, providing a strong guarantee for the economic and sustainable development of the power system.

[0046] 4. The active power coordination control strategy proposed in this invention can maintain a balanced distribution of loads among DC grids while quantitatively regulating the power of AC grids, thereby improving capacity utilization and significantly enhancing system stability and reliability, laying a solid foundation for the efficient and reliable operation of hybrid AC / DC distribution networks.

[0047] 5. This invention will further promote the continuous development and improvement of hybrid AC / DC distribution network technology. By achieving more precise and efficient power coordination control, this invention will provide strong support for the widespread application and popularization of hybrid AC / DC distribution networks, thereby promoting the upgrading and transformation of the entire power system. Attached Figure Description

[0048] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0049] Figure 1 This is a schematic diagram of the hybrid AC / DC distribution network of the present invention;

[0050] Figure 2 This is a schematic diagram of the droop characteristics of the DC power grid and AC power grid of the present invention;

[0051] Figure 3 This is a topology diagram of the energy storage type DC power flow controller of the present invention;

[0052] Figure 4 This is a control block diagram of the DC power flow controller of the present invention;

[0053] Figure 5 This is a logic block diagram of the DC power flow controller drive signal generation according to the present invention;

[0054] Figure 6 This is a schematic diagram of the DC grid voltage of the present invention;

[0055] Figure 7 This is a schematic diagram of the output power of the DC grid and AC grid of the present invention. Detailed Implementation

[0056] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0057] Example 1:

[0058] Reference Figure 1 and Figure 2 According to the present invention, a power lever mechanism for an energy storage type DC power flow controller includes the following steps:

[0059] Step S1: Construct an energy storage DC power flow controller. The energy storage DC power flow controller integrates an energy storage system on the basis of the original DC power flow controller and is connected to the power grid through power electronic devices. The topology of the energy storage DC power flow controller includes multiple units and an energy storage system. The switching duty cycle of each unit is adjusted according to the control strategy to coordinate and control the power.

[0060] Step S2: Design a power coordination control strategy, utilize a partial power processing mechanism, and use an energy storage DC power flow controller to implement a power lever mechanism to quantitatively adjust the power of the entire system. The power coordination control strategy includes controlling the average value of the DC grid bus voltage, distributing the power among the DC grids equally, and obtaining the steady state of the system by adjusting the output power of the AC grid to a given value and using the capacitor voltage as the inner loop control.

[0061] Step S3: In the hybrid AC / DC distribution network, the energy storage DC power flow controller is connected in series to each line, and the energy exchange between the capacitor on the controller and the energy storage system and between each capacitor is constant to connect the controllable voltage source in the line in series. The hybrid AC / DC distribution network includes multiple DC grids, one AC grid and the energy storage DC power flow controller. The DC grid and the AC grid are connected through a bus to form a hybrid AC / DC system.

[0062] Step S4: Based on the droop characteristics of the hybrid AC / DC distribution network, including the frequency-power droop characteristics of the AC network and the voltage-power droop characteristics of the DC network, a power coordination control strategy is formulated to perform power sharing among DC networks and regulation of the output power of the AC network. The frequency-power droop characteristic of the AC network is exhibited as fP droop, which is expressed as follows:

[0063] f ac =f acmax -k ac P ac (1)

[0064] Among them, f ac P represents the frequency of the AC power grid. ac f represents the output power of the AC power grid. acmax k represents the maximum frequency of the AC power grid. ac The droop factor of an AC power grid is defined as follows:

[0065] k ac =(f acmax -f acmin ) / P acmax (2)

[0066] The voltage-power droop characteristic of the DC grid is characterized by VP droop, as shown below:

[0067] V dci =V dcmax -k dci P dci i = 1, 2, 3(3)

[0068] Among them, V dci P represents the bus voltage of the i-th DC grid. dci V represents the output power of the i-th DC grid. dcmax k represents the maximum output voltage of the DC power grid. i The droop factor of a DC power grid is defined as follows:

[0069] k dci =(V dcmax -V dc min ) / P dcimax (4)

[0070] Among them, V dcmin P represents the minimum output voltage of a DC power grid. dcimax This indicates the maximum output power of the DC power grid.

[0071] The present invention also provides a power lever application of an energy storage DC power flow controller. The power lever application of the energy storage DC power flow controller can be implemented by executing the process steps of the power lever mechanism of the energy storage DC power flow controller. That is, those skilled in the art can understand the power lever mechanism of the energy storage DC power flow controller as a preferred embodiment of the power lever application of the energy storage DC power flow controller.

[0072] Example 2:

[0073] This invention also provides a power lever application for an energy storage type DC power flow controller, comprising the following modules:

[0074] Module M1: Constructs an energy storage DC power flow controller. The energy storage DC power flow controller integrates an energy storage system on the basis of the original DC power flow controller and is connected to the power grid through power electronic devices. The topology of the energy storage DC power flow controller includes multiple units and an energy storage system. The switching duty cycle of each unit is adjusted according to the control strategy to coordinate and control the power.

[0075] Module M2: Design a power coordination control strategy, utilizing a partial power processing mechanism and a power lever mechanism through an energy storage DC power flow controller to quantitatively adjust the power of the entire system; the power coordination control strategy includes controlling the average value of the DC grid bus voltage, evenly distributing the power among the DC grids, and obtaining the steady state of the system by adjusting the output power of the AC grid to a given value and using the capacitor voltage as the inner loop control.

[0076] Module M3: In a hybrid AC / DC distribution network, an energy storage DC power flow controller is connected in series to each line. Through energy exchange between the controller's capacitors and the energy storage system, as well as between the capacitors, the voltage value of the capacitors is kept constant, and a controllable voltage source is connected in series in the line. The hybrid AC / DC distribution network includes multiple DC grids, one AC grid, and an energy storage DC power flow controller. The DC grids and AC grids are connected through a bus to form a hybrid AC / DC system.

[0077] Module M4: Based on the droop characteristics of hybrid AC / DC distribution networks, including the frequency-power droop characteristics of the AC network and the voltage-power droop characteristics of the DC network, a power coordination control strategy is formulated to perform power sharing among DC networks and regulation of the output power of the AC network. The frequency-power droop characteristic of the AC network is exhibited as fP droop, which is expressed as follows:

[0078] f ac =f acmax -k ac P ac (1)

[0079] Among them, f ac P represents the frequency of the AC power grid. ac f represents the output power of the AC power grid. acmax k represents the maximum frequency of the AC power grid. ac The droop factor of an AC power grid is defined as follows:

[0080] k ac =(f acmax -f acmin ) / P acmax (2)

[0081] The voltage-power droop characteristic of the DC grid is characterized by VP droop, as shown below:

[0082] V dci =V dcmax -k dci P dci i = 1, 2, 3(4)

[0083] Among them, V dci P represents the bus voltage of the i-th DC grid. dci V represents the output power of the i-th DC grid. dcmax k represents the maximum output voltage of the DC power grid. i The droop factor of a DC power grid is defined as follows:

[0084] k dci =(V dcmax -V dc min ) / P dcimax (4)

[0085] Among them, V dcmin P represents the minimum output voltage of a DC power grid. dcimax This indicates the maximum output power of the DC power grid.

[0086] Example 3:

[0087] This invention aims to achieve active power coordination control and precise regulation of line power flow in hybrid AC / DC distribution networks. Combining the fundamental theoretical framework and practical engineering applications of hybrid AC / DC distribution networks, it proposes a power leverage mechanism for an energy storage-based DC power flow controller and its application in active power coordination control of hybrid AC / DC distribution networks. This invention constructs a new method for connecting energy storage systems to the grid, and for the first time applies a DC power flow controller to a hybrid AC / DC distribution network, expanding the application scenarios of DC power flow controllers. It reveals the power leverage mechanism of the energy storage-based DC power flow controller, and for the first time applies a partial power processing mechanism in a hybrid AC / DC distribution network. While achieving flexible regulation of AC distribution network output, it realizes a balanced distribution of unbalanced power between AC and DC distribution networks, improving the operational safety of the distribution network system.

[0088] The technical solution claimed in this invention is a power lever mechanism for an energy storage-type DC power flow controller and its application in active power coordination control of hybrid AC / DC distribution networks. This invention mainly includes the topology of the energy storage-type DC power flow controller and an active power coordination control strategy utilizing the power lever mechanism. Based on a composite DC power flow controller, the energy storage-type DC power flow controller replaces the original voltage source with an energy storage system, enabling the energy storage system to connect to the power grid via power electronic devices. The specific topology is as follows: Figure 1As shown, the energy storage-type DC power flow controller connects capacitors in series in each line using a given power coordination control strategy. The capacitors maintain a constant voltage through energy exchange with each other and with the energy storage system. This is equivalent to inserting a controllable voltage source in series in the line. Due to the characteristics of DC line power transmission, a power lever is realized, thereby controlling the power in the system by changing the low voltage across the capacitors. In other words, a small power source on the DC power flow controller controls the large power of the entire system.

[0089] The specific implementation methods are as follows:

[0090] A. Droop characteristics and power coordination control of AC / DC distribution networks

[0091] by Figure 1 Taking a given hybrid AC / DC distribution network as an example, it includes three DC grids, one AC grid, and an energy storage DC power flow controller.

[0092] In AC power grids, the active power and frequency characteristics often exhibit a drooping fP, which can be expressed as follows:

[0093] f ac =f acmax -k ac P ac (1)

[0094] Among them, f ac P represents the frequency of the AC power grid. ac f represents the output power of the AC power grid. acmax k represents the maximum frequency of the AC power grid. ac The droop factor of an AC power grid is defined as follows:

[0095] k ac =(f acmax -f acmin ) / P acmax (2)

[0096] In a DC power grid, its active power and voltage exhibit a drooping characteristic (VP), as shown below:

[0097] V dci =V dcmax -k dci P dci i = 1, 2, 3(3)

[0098] Among them, V dci P represents the bus voltage of the i-th DC grid. dci V represents the output power of the i-th DC grid. dcmax k represents the maximum output voltage of the DC power grid. i The droop factor of a DC power grid is defined as follows:

[0099] k dci =(V dcmax -V dc min ) / P dcimax (4)

[0100] Among them, V dcmin P represents the minimum output voltage of a DC power grid. dcimax This indicates the maximum output power of the DC power grid. The droop characteristics of DC and AC power grids are as follows: Figure 2 As shown.

[0101] Multiple DC power grids often face load imbalance, where some grids reach their maximum output power while others are far below it. This imbalance leads to underutilization of capacity and system instability. To achieve coordinated power control across the entire system, power sharing among DC grids is an efficient and reliable method. This approach can be derived as follows.

[0102] Assuming that power is already evenly distributed among DC power grids, based on this concept, the following expression can be obtained:

[0103]

[0104] Where K is the ratio of the output power of the DC grid to its maximum power. Substituting (5) into (4), we can obtain:

[0105] V dc1 =V dc2 =V dc3 =V dc max -(V dcmax -V dcmin )×K(6)

[0106] In other words, by controlling the voltage of the DC grid to be consistent, power can be evenly distributed among DC grids.

[0107] After achieving power sharing among DC grids, multiple DC grids can be equivalent to a single DC grid due to the consistent voltage, simplifying the analysis of overall power transmission.

[0108] B. System steady-state analysis using the power lever mechanism

[0109] For the entire system, according to the law of conservation of energy, the power expression is as follows:

[0110]

[0111] Where P dc P represents the total output power of the DC power grid.EDCPFC P is the output power of the energy storage type DC power flow controller. loadi For the local load of the i-th DC grid, P loadac For the load on the AC side, P loss This refers to the power loss of the line.

[0112] The load is determined by the operating conditions, and the line loss has a relatively small impact on the overall system. The power coordination control strategy proposed in this invention controls the output power of the AC grid to a given value while maintaining the power distribution among the DC grids.

[0113] Analysis of the energy storage type DC power flow controller, its topology is as follows: Figure 3 As shown, the switching duty cycles of units 1, 2, 3 and the energy storage system are d1, d2, d3 and d4, respectively, which satisfy the following relationship:

[0114] d1+d2+d3+d4=1(8)

[0115] Based on the volt-second balance principle of inductors, the following expression can be obtained:

[0116] V C1 d1+V C2 d2+V C3 d3-V es d4=0(9)

[0117] Where V Ci Indicates capacitance C i The voltage V of (i = 1, 2, 3) es This indicates the voltage of the energy storage system.

[0118] Similarly, by performing an ampere-second balance analysis on the capacitor, we can obtain:

[0119] I i =I L d i (10)

[0120] Where I i It is the current in line i, I L This represents the inductor current.

[0121] Analysis of the DC circuit yields the following results:

[0122] V dci -V Ci =V dc4 (11)

[0123] Where V dc4 The voltage of DC bus 4 is maintained at a constant value by the converter station to ensure the power transmission direction of the system. It is set to be slightly lower than the lower limit V of the DC grid voltage. dcminAccording to the actual engineering construction of DC power grids, their voltage fluctuations should be much smaller than the lower voltage limit. Therefore, the difference between the DC grid voltage and its lower voltage limit, which is the capacitor voltage, is also much smaller than the DC voltage.

[0124] The power of the energy storage type DC power flow controller can be expressed as follows:

[0125] P EDCPFC =d4V es I L (12)

[0126] Substituting (9) and (10), we get:

[0127]

[0128] Because the capacitor voltage is much smaller than the DC line voltage, it can be analyzed that the power of the energy storage DC power flow controller is much smaller than the system-level power, which is also the mathematical form of partial power processing and power leverage.

[0129] C. Active power coordination control strategy of energy storage DC power flow controller

[0130] The control block diagram of the power coordination control strategy of the energy storage DC power flow controller is as follows: Figure 4 As shown. The outer loop reference values ​​for loops 1 and 2 are the average values ​​of the DC grid bus voltage, expressed as follows:

[0131] V avg =(V dc1 +V dc2 +V dc3 ) / 3(14)

[0132] Through the control of the outer loop, it can be found through simple calculations that the voltage of the DC grid will be regulated to be consistent in steady state.

[0133] The control objective of loop 3 is the required AC output power, where P ac The droop relationship can be obtained by detecting the AC frequency and substituting it into the equation. Loops 1, 2, and 3 all use capacitor voltage as the inner loop control to ensure the stability and reliability of the control system.

[0134] After obtaining the duty cycles d1, d2, and d3 in the control loop, d4 can be generated through (8). Because each part of the DC power flow controller cannot be turned on simultaneously, it is necessary to process the four switching signals to generate complementary drive signals within one cycle and distribute them to the four parts. The generated logic block diagram is as follows: Figure 5 As shown.

[0135] This invention proposes an energy storage-type DC power flow controller, enabling energy storage systems to connect to the power grid in a novel way, thus enriching the application of energy storage in new power systems. The power coordination control strategy proposed in this invention can regulate the output power of the distribution network over a wide range, greatly improving system flexibility. This invention reveals a power lever mechanism in the DC power flow controller that utilizes a partial power processing mechanism to regulate the power of the entire system, effectively reducing equipment capacity and thus lowering engineering costs. The active power coordination control strategy proposed in this invention, while quantitatively regulating the power of the AC grid, can maintain the even distribution of load across the DC grid, improving capacity utilization and system stability. Quantitatively regulated power of the AC distribution network is an important condition for the efficient and reliable operation of hybrid AC / DC distribution networks, and this invention can promote the continuous development of hybrid AC / DC distribution networks.

[0136] like Figure 1 The energy storage-based DC power flow controller and power coordination control strategy for the power lever of the hybrid AC / DC distribution network system shown are verified. The parameters of the DC and AC grids are shown in Tables 1 and 2, and the line impedance of the system is shown in Table 3.

[0137] Table 1: DC power grid parameters

[0138]

[0139]

[0140] Table 2: AC Power Grid Parameters

[0141]

[0142] Table 3 System Line Parameters

[0143]

[0144] The energy storage-type DC power flow controller is activated within 1 second, and the voltage of the DC grid is as follows: Figure 6 As shown, the output power of the DC grid and the AC grid is as follows: Figure 7 As shown in the figure, the control objective is to control the output power of the AC grid to 7kW. It can be seen from the figure that before the DC power flow controller was put into use, the output power of the DC grid was uneven, with the AC grid output power around 2kW, far below the AC grid's capacity. After the energy storage-type DC power flow controller was put into use, the voltage of the DC grid was quickly regulated to be uniform, from... Figure 7 It can be observed that the ratio is the ratio of maximum power, achieving an even distribution of load across the DC distribution network. The power of the AC grid was also quickly adjusted to 7kW, and the system operated stably.

[0145] Those skilled in the art can understand this embodiment as a more specific description of Embodiment 1 and Embodiment 2.

[0146] Those skilled in the art will understand that, besides implementing the system and its various devices, modules, and units provided by this invention in the form of purely computer-readable program code, the same functions can be achieved entirely through logical programming of the method steps, making the system and its various devices, modules, and units of this invention function in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers. Therefore, the system and its various devices, modules, and units provided by this invention can be considered as a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; alternatively, the devices, modules, and units for implementing various functions can be considered as both software modules implementing the method and structures within the hardware component.

[0147] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A power lever mechanism for an energy storage type DC power flow controller, characterized in that, Includes the following steps: Step S1: Construct an energy storage DC power flow controller, which integrates an energy storage system on the basis of the original DC power flow controller and connects to the power grid through power electronic devices; Step S2: Design a power coordination control strategy, utilize a partial power processing mechanism, and use an energy storage DC power flow controller to implement a power lever mechanism to quantitatively adjust the power of the entire system; Step S3: In the hybrid AC / DC distribution network, the energy storage DC power flow controller is connected in series to each line, and the energy exchange between the capacitor on the controller and the energy storage system and between each capacitor is constant to connect the controllable voltage source in the line in series. Step S4: Based on the droop characteristics of the hybrid AC / DC distribution network, including the frequency-power droop characteristics of the AC network and the voltage-power droop characteristics of the DC network, formulate a power coordination control strategy to perform power sharing among DC networks and regulate the output power of the AC network.

2. The power lever mechanism of the energy storage DC power flow controller according to claim 1, characterized in that, The topology of the energy storage DC power flow controller in step S1 includes multiple units and an energy storage system. The switching duty cycle of each unit is adjusted according to the control strategy to coordinate the power control.

3. The power lever mechanism of the energy storage DC power flow controller according to claim 1, characterized in that, The power coordination control strategy in step S2 includes controlling the average value of the DC grid bus voltage, equally distributing the power among the DC grids, and obtaining the steady state of the system by adjusting the output power of the AC grid to a given value and using the capacitor voltage as the inner loop control.

4. The power lever mechanism of the energy storage DC power flow controller according to claim 1, characterized in that, The hybrid AC / DC distribution network in step S3 includes multiple DC grids, one AC grid, and an energy storage DC power flow controller. The DC grids and AC grids are connected by a bus to form a hybrid AC / DC system.

5. The power lever mechanism of the energy storage DC power flow controller according to claim 1, characterized in that, The frequency-power droop characteristic of the AC power grid in step S4 is characterized by fP droop, which is expressed as follows: f ac =f acmax -k ac P ac (1) Among them, f ac P represents the frequency of the AC power grid. ac f represents the output power of the AC power grid. acmax k represents the maximum frequency of the AC power grid. ac The droop factor of an AC power grid is defined as follows: k ac =(f acmax -f acmin ) / P acmax (2) The voltage-power droop characteristic of the DC grid is characterized by VP droop, as shown below: V dci =V dcmax -k dci P dci ,i=1,2,3 (3) Among them, V dci P represents the bus voltage of the i-th DC grid. dci V represents the output power of the i-th DC grid. dcmax k represents the maximum output voltage of the DC power grid. i The droop factor of a DC power grid is defined as follows: k dci =(V dcmax -V dc min ) / P dcimax (4) Among them, V dcmin P represents the minimum output voltage of a DC power grid. dcimax This indicates the maximum output power of the DC power grid.

6. A power lever application of an energy storage type DC power flow controller, characterized in that, Includes the following modules: Module M1: Constructs an energy storage DC power flow controller, which integrates an energy storage system on the basis of the original DC power flow controller and connects to the power grid through power electronic devices; Module M2: Design a power coordination control strategy, utilize a partial power processing mechanism, and use an energy storage DC power flow controller to implement a power lever mechanism to quantitatively adjust the power of the entire system; Module M3: In a hybrid AC / DC distribution network, an energy storage DC power flow controller is connected in series to each line. Through the energy exchange between the capacitor on the controller and the energy storage system and between each capacitor, the voltage value of the capacitor is kept constant, and a controllable voltage source is connected in series in the line. Module M4: Based on the droop characteristics of the hybrid AC / DC distribution network, including the frequency-power droop characteristics of the AC network and the voltage-power droop characteristics of the DC network, formulate a power coordination control strategy to perform power sharing among DC networks and regulate the output power of the AC network.

7. The power lever application of the energy storage type DC power flow controller according to claim 6, characterized in that, The topology of the energy storage DC power flow controller in module M1 includes multiple units and an energy storage system. The switching duty cycle of each unit is adjusted according to the control strategy to coordinate power control.

8. The power lever application of the energy storage type DC power flow controller according to claim 6, characterized in that, The power coordination control strategy in module M2 includes controlling the average value of the DC grid bus voltage, distributing the power equally among the DC grids, and obtaining the steady state of the system by adjusting the output power of the AC grid to a given value and using the capacitor voltage as the inner loop control.

9. The power lever application of the energy storage type DC power flow controller according to claim 6, characterized in that, The hybrid AC / DC distribution network in module M3 includes multiple DC grids, one AC grid, and an energy storage DC power flow controller. The DC grids and AC grids are connected by a bus to form a hybrid AC / DC system.

10. The power lever application of the energy storage type DC power flow controller according to claim 6, characterized in that, The frequency-power droop characteristic of the AC power grid in module M4 is exhibited as fP droop, and the frequency-power droop characteristic is expressed as follows: f ac =f acmax -k ac P ac (1) Among them, f ac P represents the frequency of the AC power grid. ac f represents the output power of the AC power grid. acmax k represents the maximum frequency of the AC power grid. ac The droop factor of an AC power grid is defined as follows: k ac =(f acmax -f acmin ) / P acmax (2) The voltage-power droop characteristic of the DC grid is characterized by VP droop, as shown below: V dci =V dcmax -k dci P dci ,i=1,2,3 (3) Among them, V dci P represents the bus voltage of the i-th DC grid. dci V represents the output power of the i-th DC grid. dcmax k represents the maximum output voltage of the DC power grid. i The droop factor of a DC power grid is defined as follows: k dci =(V dcmax -V dc min ) / P dcimax (4) Among them, V dcmin P represents the minimum output voltage of a DC power grid. dcimax This indicates the maximum output power of the DC power grid.

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