Release type direct current power distribution system and operation method thereof

Abstract

The invention provides a novel direct-current power distribution system, which combines the advantages of single-pole and double-pole hybrid power distribution and is applied to a medium-low voltage power distribution scene. Through the innovative system architecture design and droop control strategy, the fault current is effectively reduced, the reliability of the system is improved, the possibility of element damage is reduced, in addition, after the fault occurs, the release DC power distribution strategy can effectively isolate the fault area, reduce the fault influence range and improve the stability of the system. And the strategy can also reduce the use of cables and save the system cost. Simulation verification shows that compared with a traditional bipolar system, the direct current power distribution system is better in the aspects of fault current control, post-fault voltage stability and power loss.

Description

Technical Field

[0001] This invention relates to the technical field of DC power distribution networks and power electronic system control, specifically to bipolar DC power distribution systems and their operation modes, as well as the function and application of voltage equalizers. Background Technology

[0002] In recent years, with the rapid development of new energy technologies and the widespread application of distributed power systems, power system architecture is facing unprecedented challenges and opportunities. While traditional AC systems are widely used, they have many limitations when handling distributed power source integration and DC load supply, such as low conversion efficiency and poor power quality. DC distribution systems, due to their high efficiency, low loss, and ease of integrating renewable energy, have gradually become a research hotspot.

[0003] In DC power distribution systems, grounding faults are one of the most common types of faults. Once a fault occurs, it can generate a large fault current, severely impacting system stability. Furthermore, while traditional bipolar DC power distribution systems can address voltage balance issues to some extent, they suffer from drawbacks such as high system complexity and high construction costs.

[0004] Therefore, a new technical solution is needed to improve the above-mentioned technical problems. Summary of the Invention

[0005] This invention proposes a novel control strategy based on traditional bipolar DC transmission system control strategies. This paper describes the architecture and operation method of a novel bipolar DC power distribution system. The technical solution analyzes the droop control and potential grounding faults of this new power distribution system, and elaborates on the multi-voltage equalizer converter-level and system-level control strategies to maintain voltage balance between the positive and negative poles. Furthermore, it compares the new system with a traditional bipolar system, analyzing its functions and advantages: achieving voltage balance between the positive and negative poles of the bipolar DC system; reducing fault current and power loss, thus improving system stability and reliability; and reducing cable usage, saving system costs.

[0006] Demonstrated by the invention Taking a typical application scenario of a bipolar DC power distribution system as an example, this invention will explain the principle of the operation scheme and control strategy, and compare the fault current magnitude and system power loss of the new scheme with those of the traditional bipolar DC system. The effectiveness of the system and the efficiency of the new scheme will be verified through simulation and experimental implementation cases.

[0007] The technical solution claimed in this invention is This paper introduces the architecture and operation method of a hybrid single-pole and bipolar DC power distribution system. Based on the power distribution requirements of distributed power systems and combining the power supply advantages of single-pole and bipolar systems, this invention proposes a single-pole and bipolar hybrid DC power distribution system suitable for medium and low voltage power distribution scenarios. This paper presents a hybrid power distribution system. The feasibility of this system will be explained through an introduction to its architecture. A detailed analysis of its steady-state operation and transient fault characteristics will be conducted, comparing it with a traditional two-stage system to illustrate its innovations and advantages.

[0008] This type of DC power distribution system architecture can be well applied to distributed power systems. For example... Figure 1 As shown, typical The architecture of a DC power distribution system can be roughly considered as consisting of energy storage units, photovoltaic units, wind power units, DC load units, and several asymmetrical loads. Due to the parallel connection, the energy storage, loads, and renewable energy sources in other locations can be equivalently represented by the same units shown in the diagram.

[0009] Based on the different wiring methods, this architecture can be divided into three zones: T-zone, M-zone, and I-zone. Zone T is a traditional true bipolar architecture, with the voltage equalizer on the left using a capacitor-neutral-grounded grounding method. Zone M is a pseudo-bipolar architecture, which, compared to Zone T, reduces the Z bus and provides two distribution buses and one distribution voltage. Zone I is similar to Zone T, except that the voltage equalizer on the right is not grounded. In the model, the voltage equalizer balances the voltage between the positive and negative terminals by transferring power between them.

[0010] by Figure 1 The function of each unit is illustrated using an example. The photovoltaic unit is connected between the PZ buses via a two-level DC / DC converter to provide power to the system; the wind power unit is connected between the PZ buses via a two-level DC / AC converter to provide power to the system; the energy storage unit is connected to the PN and ZN buses via a two-level DC / DC converter to maintain voltage stability on the PN bus in region M and the ZN bus in region T; the DC load unit is connected to the bus via a two-level DC / DC converter, allowing the system to provide two voltages to the load. The bipolar DC system includes several asymmetrical loads, which are connected to the DC bus via DC / DC converters.

[0011] To address the shortcomings of existing technologies, the purpose of this invention is to provide a... The study investigates the operation methods of a DC power distribution system.

[0012] The DC power distribution system includes: energy storage unit, power supply, DC load unit, load, and voltage equalizer; the power supply in this patent is exemplified by photovoltaic unit and wind power unit.

[0013] The system is divided into three zones: T, M, and I. T represents TT, indicating that the neutral point of this zone is grounded; I represents IT, indicating that the neutral point of this zone is not grounded; and M represents Middle, representing the intermediate region. Zones T and I employ a true bipolar architecture, while zone M employs a pseudo bipolar architecture. The system balances the positive and negative voltages through a droop compensation control strategy.

[0014] The energy storage unit, photovoltaic unit, and wind power unit are connected to the DC bus via a DC / DC converter to provide power to the system.

[0015] The DC load unit and the load are connected to the DC bus via an interface, consuming the electrical energy provided by the system.

[0016] The voltage equalizer is installed on both sides of zone T and zone I, maintaining voltage balance between the positive and negative busbars by transmitting power, and independently controlling the voltages of zone T and zone I. The voltage equalizer is grounded with the neutral point ungrounded.

[0017] Preferably, the M region is a pseudo-bipolar architecture, with only two distribution buses and one distribution voltage provided within the M region, and no Z bus provided.

[0018] After completing the system setup, this invention will next discuss the system's operation mode and droop control when two typical faults occur. The operation mode is as follows:

[0019] During normal system operation, the voltage balance between the positive and negative terminals is maintained by a voltage equalizer;

[0020] When a ground fault occurs, voltage equalizers and droop compensation control strategies are used to reduce the fault current.

[0021] Preferably, when a ground fault occurs in the system, the fault current is reduced and the voltage of the non-faulty pole is stabilized by adjusting the control parameters of the voltage equalizer.

[0022] Preferably, during the system design and implementation phase, the parameter settings of the voltage equalizer and the droop compensation control strategy are optimized through simulation and experimental verification.

[0023] Preferably, during system operation, the voltage, current, and power parameters of the system are monitored in real time, and the control strategy is dynamically adjusted based on the monitoring results to adapt to different operating conditions and load changes.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. When a grounding fault and an inter-electrode short circuit occur in the system, this invention... The DC power distribution system architecture can significantly reduce the total fault current at the fault point. Compared with traditional bipolar systems, the peak fault current is significantly reduced, thus minimizing the impact of faults on the system and improving system stability and reliability. In the event of a single-pole grounding fault or an inter-pole short-circuit fault, This type of DC power distribution system can effectively isolate faults and reduce their impact range. Depending on the location of the fault point, it can guarantee reliable power supply to at least one area of ​​the system, either zone T or zone I, rather than causing a partial power outage in a bipolar system; thus ensuring the continuity and stability of the system.

[0026] 2. The M-zone design of this invention eliminates the Z-line, which saves busbar materials, reduces system construction costs, and improves economic efficiency. By introducing a voltage equalizer and a droop compensation control strategy, effective voltage balance between the positive and negative poles of the bipolar DC system is achieved, ensuring the power supply quality of the system and reducing system problems caused by voltage imbalance.

[0027] 3. The simulation model built using the MATLAB-Simulink-PLECS Blocket environment in this invention verifies... The feasibility and efficiency of the DC power distribution system architecture show significant advantages over traditional bipolar systems in terms of fault current and bus voltage stability. Attached Figure Description

[0028] 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:

[0029] Figure 1 for Schematic diagram of a DC transmission system architecture;

[0030] Figure 2 for Simplified circuit diagram of a DC transmission system architecture;

[0031] Figure 3 This is the overall circuit diagram for a single-phase ground fault system.

[0032] Figure 4 Equivalent circuit diagram for a single-stage ground fault system;

[0033] Figure 5 This is the overall circuit diagram of the inter-pole short-circuit fault system;

[0034] Figure 6 The equivalent circuit diagram of a two-phase short-circuit fault system;

[0035] Figure 7 This is a schematic diagram of the total current at the ground fault point.

[0036] Figure 8A schematic diagram of the current fed into the fault point in zone I of the ground fault.

[0037] Figure 9 A schematic diagram of the power supply current between P and Z zones in area I of a ground fault;

[0038] Figure 10 This is a schematic diagram of the positive bus voltage in the T-zone of a ground fault.

[0039] Figure 11 A schematic diagram of the positive bus voltage in zone I of a ground fault;

[0040] Figure 12 A schematic diagram of the negative bus voltage in area T of a ground fault;

[0041] Figure 13 A schematic diagram of the negative bus voltage in zone I of a ground fault;

[0042] Figure 14 This is a schematic diagram of the total current at the two-phase short-circuit fault point.

[0043] Figure 15 A schematic diagram of the current fed into the fault point in zone I of a two-phase short circuit.

[0044] Figure 16 A schematic diagram of the power supply current between PZ in region I of a two-phase short circuit.

[0045] Figure 17 This is a schematic diagram of the positive bus voltage in region T during a two-phase short circuit.

[0046] Figure 18 A schematic diagram of the positive bus voltage in zone I of a two-phase short-circuit fault;

[0047] Figure 19 A schematic diagram of the negative bus voltage in zone T during a two-phase short-circuit fault;

[0048] Figure 20 A schematic diagram of the negative bus voltage in zone I of a two-phase short-circuit fault; Detailed Implementation

[0049] 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 protection scope of the present invention.

[0050] Example 1: (Normal operation, analysis of droop control)

[0051] During normal operation, The DC distribution system in this model is not significantly different from the traditional bipolar DC distribution system because voltage equalizers are installed on both sides of this model, which is also the case in most actual distribution systems. The voltage equalizers balance the power, so there will not be a large power flow in the actual M-region. Differences in the M-region have a relatively small impact on the system; therefore, this patent only discusses the droop control relationship for normal operation.

[0052] In order to analyze The droop control of the DC power distribution system architecture requires simplification of the system. As mentioned earlier... A typical DC power distribution system includes: an energy storage unit, a power supply, a DC load unit, a load, and a voltage equalizer. The energy storage unit can be simplified as a resistor connected to the bus via a two-level DC / DC converter; the power supply can be simplified as an independent source connected to the bus via a two-level DC / DC converter to maintain the bus voltage. These two structures can be further simplified to a voltage source and a resistor connected in series. The load and unbalanced resistor are considered current sources; the voltage equalizer's function is to balance the voltage and is considered a controlled voltage source. Therefore… All units of the DC power distribution system can be simplified to basic components such as voltage sources, current sources, resistors, and capacitors, which greatly simplifies the model and calculation analysis.

[0053] M1, M2, M3, M4, and M5 represent five simplified ESS (Energy Storage System equivalent units between two buses after simplification) (e.g., Figure 3 r1, r2, r3, r4, r5 represent the equivalent internal resistances of the five ESSs; V1, V2, V3, V4, V5 represent the equivalent voltage sources of the five ESSs; Vp1 is the voltage between P and Z of the T-zone bus; VN1 is the voltage between Z and N of the T-zone bus; Vp2 is the voltage between P and Z of the I-zone bus; VN2 is the voltage between Z and N of the I-zone bus.

[0054] M1 output current:

[0055] M2 output current:

[0056] M3 output current:

[0057] M4 output current:

[0058] M5 output current:

[0059] System architecture: V P1 +V N1 =V P2 +V N2 =U PN=2U DC ;

[0060] Due to the existence of unbalanced loads, the bus voltage cannot be kept balanced; in order to eliminate voltage deviation, a voltage equalizer is introduced to achieve bus voltage equalization; let the goal of the voltage equalizer be to make UP = UN; The DC power distribution system has voltage equalizers on both the left and right sides, therefore: UP1 = UN1; UP2 = UN2;

[0061] When considering the droop control of voltage control, the positive and negative bus voltages are determined by the droop control relationship, and the droop control relationship of the P, N, and Z bus voltages is:

[0062]

[0063] In the formula, K1, K2, K3, K4, and K5 are the droop control coefficients of voltage control units M1, M2, M3, M4, and M5.

[0064] Example 2: (Fault operation, including single-pole ground fault and bipolar short-circuit fault)

[0065] In this implementation example The operation method of the bipolar DC power distribution system is as follows: the bus voltage of the system remains stable; the output current of the photovoltaic source is stable at IPV; there are two voltage levels at the load terminals, which are stable at VPN or 1 / 2VPN; the two-level DC / DC converters connected to the photovoltaic and the load adopt a control strategy of compensating droop control to achieve voltage balance between the positive and negative poles of the bipolar DC power distribution system.

[0066] The two-level DC / DC converters connected to the photovoltaic (PV) unit and the load unit have similar topologies, but they perform different functions. The PV-side two-level DC / DC converter stabilizes the PV source output current IPV and transfers more power to the stage with the lower voltage to maintain positive and negative voltage balance. The DC load-side two-level DC / DC converter stabilizes the voltage across the load at VPN or 1 / 2 VPN and can absorb more power from the stage with the higher voltage to maintain positive and negative voltage balance.

[0067] The main faults in a DC power distribution system are single-phase grounding faults and two-phase short-circuit faults. The following analysis will focus on two examples: a grounding fault at bus P in zone T and a two-phase short-circuit fault at bus PZ in zone I, analyzing the fault characteristics and discussing the generation principle and flow path of the fault current. The fault current and bus voltage fluctuations will differ depending on the type of fault, but all can achieve the goal of reducing the fault current and stabilizing the voltage. This analysis primarily focuses on the two most probable fault types. To analyze the fault characteristics, a fault circuit model needs to be established. The fault process can be divided into two stages: the discharge stage of the fault electrode capacitor and the charging stage of the non-fault electrode capacitor, and the fault stabilization stage.

[0068] When studying this stage, the DC / DC converter can be simplified to a capacitor. For example... Figure 3 As shown, units M1, M2, M3, M4, and M5 are all composed of a resistor, an inductor, and a capacitor connected in series. The resistor and inductor are the line resistance and inductance of the corresponding fault circuit, and the capacitor is a simplified capacitor of the DC / DC converter. EQ1 and EQ2 represent voltage equalizer 1 and voltage equalizer 2, respectively; the voltage equalizer can be simplified to two capacitors. The voltage equalizer has three grounding methods: neutral point ungrounded; neutral point directly grounded; and neutral point grounded through a resistor. This invention analyzes the fault characteristics using an ungrounded neutral point as an example.

[0069] 1. Grounding fault

[0070] When a single-phase ground fault occurs, such as Figure 4 The fault current consists of four parts.

[0071] i fault(t) =i f_PN +i f_EQ +i f_PZ +i f_I

[0072] The fault circuits for if_EQ, if_PZ, if_PN, and if_I all consist of resistors, capacitors, and inductors, and the fault current is:

[0073]

[0074] The time-domain response of the fault current and capacitor voltage is:

[0075]

[0076] Since the initial current is much smaller than the fault current, I0 can be ignored, and the expressions for the fault current and capacitor voltage can be further simplified to:

[0077]

[0078] For if_EQ and if_PZ:

[0079]

[0080] For if_PN:

[0081]

[0082] For if_I:

[0083]

[0084] After the fault occurs, the capacitor discharges, and the fault current increases rapidly. If_EQ, if_PZ, and if_PN do not flow through the non-faulty pole, thus having minimal impact on the faulty pole. If_I flows through the non-faulty pole, but because the fault current path is long, the equivalent impedance of the fault loop is much larger than in a traditional bipolar system, resulting in a significant decrease in the fault current of the non-faulty pole. This reduces the impact on the non-faulty pole. Analysis of VC(t) shows that the bus voltages in different zones are affected to some extent when a fault occurs. For the negative bus in zone I, unlike the transient overvoltage in a traditional bipolar system, a voltage drop occurs. From the perspective of power flow, due to the grounding fault on the P bus in zone T, power demand increases, and power flows out of zone I, leading to a voltage drop. For the negative bus in zone T, due to the charging process of C3 by the fault current, a transient overvoltage occurs. Since there are many power electronic converters in the system, when the transient overvoltage exceeds the equipment's withstand voltage, it will cause irreversible damage to the equipment and increase the risk of reconfiguration failure of the non-faulty pole.

[0085] Analysis shows that when a single-phase ground fault occurs... Compared to traditional bipolar power supply systems, the DC power distribution system architecture features lower fault current at the fault point, smaller fault current in non-faulty areas, and no parameter transient overvoltages in non-faulty poles. The disadvantage is that overvoltage may occur in the fault area, causing component damage. This disadvantage can be mitigated by limiting the voltage through certain measures.

[0086] when When a ground fault occurs in a DC power distribution system, the total fault current at the fault point is relatively small, and no transient overvoltage will be generated on the negative pole of Zone I, thus improving the power supply reliability of the system. However, it is necessary to limit the transient overvoltage that occurs on the negative bus of Zone T. At the same time, when a ground fault occurs in Zone T, the voltage in Zone I can remain stable, ensuring that the system still has a certain power supply capacity and improving the system reliability.

[0087] 2. Inter-pole fault

[0088] Inter-pole faults are also Common faults in DC distribution systems include the T-zone, where a two-phase short circuit due to Z-grounding is essentially the same as a single-phase grounding fault, and will not be analyzed further here. This invention takes a short circuit between busbar P and busbar Z in zone I as an example to analyze the fault characteristics of inter-pole faults. Figure 5 This is the overall circuit diagram of the inter-pole fault system.

[0089] like Figure 6 The equivalent circuit is a second-order circuit, composed of resistors, capacitors, and inductors connected in series and parallel. The initial external voltage is VP. Following the same derivation method as for single-phase ground fault current, the fault current is:

[0090]

[0091] right Figure 6 The loop is simplified and merged using RCL, with the following RCL parameters:

[0092]

[0093] During the fault occurrence phase, C5 and CZN2 are in a charging state, while C2, CPZ1, C3, CZN1, and C1 are in a discharging state. The voltage across C3 can be expressed as:

[0094]

[0095] The voltage across C5 can be expressed as:

[0096]

[0097] because Compared to traditional bipolar systems, the DC power distribution system has a longer fault loop and greater fault impedance when a bipolar short-circuit fault occurs. Therefore, the fault current is smaller, improving the system's stability and reliability.

[0098] As can be seen from the expressions for VC3 and VC5, the transient bus voltage change during an inter-electrode short-circuit fault is exactly the opposite of that during a single-pole ground fault. When an inter-electrode short circuit occurs, the voltage between ZN on the faulty bus rises, while the voltage between ZN on the non-faulty bus falls.

[0099] Meanwhile, when an inter-electrode fault occurs in region I, the voltage in region T remains stable, ensuring that the system still has a certain power supply capacity and improving the reliability of the system.

[0100] To verify The feasibility of this type of DC system architecture was demonstrated by building a system using the MATLAB-Simulink-PLECS Blocket environment. A simulation model of a DC system is used, and the advantages of the present invention are analyzed by comparing it with a traditional bipolar system.

[0101] This simulation model includes two voltage equalizers. A DC system. This system includes:

[0102] Four power supply units (voltage sources connected to two-level DC / DC converters): connected between the PN bus in zone T, the PZ bus in zone T, the ZN bus in zone T, and the PZ bus in zone I;

[0103] Unbalanced load: connected between the three busbars PZN in zone I;

[0104] Voltage equalizer: connected between the three busbars PZN in zone T and zone I respectively;

[0105] Other resistors and capacitors;

[0106] Table 1 DC system parameters

[0107]

[0108]

[0109] This simulation mainly discusses The changes in fault current and DC bus voltage during a fault in a DC system with an unbalanced load.

[0110] In the first 0.1 seconds, the entire The DC transmission system operates under unbalanced load conditions. At this time, the system can meet the load-side power requirements, the bus voltage is at the simulation setpoint, and the system operates normally.

[0111] At t = 0.1s, When a fault occurs in a system, depending on the type and location of the fault, the direction of power flow will vary, causing sudden changes in voltage between certain buses and the generation of fault current.

[0112] Figures 7-9 for A comparison of fault currents in a single-stage ground fault between a novel DC system architecture and a traditional bipolar DC system architecture. Figure 7 This represents the total fault current at the fault point. Figure 8 For the fault point current fed into region I, Figure 9 This represents the power supply current between zones I and PZ. Before 0.1s, the system operates normally with no fault current. At 0.1s, a single-stage ground fault occurs in the system. Figure 7 show Compared to bipolar DC systems, the peak fault current and subsequent stability values ​​of the linear DC system are significantly smaller. (Analysis) Figure 8 The feed current in region I is the main reason for the difference in total fault current. The feed current in region I of the bipolar DC system is significantly larger. Analysis Figure 9 The main source of the difference in feed current is the current of the power supply between regions I and PZ.

[0113] Analysis of the fault circuit reveals that the difference lies in the bipolar DC system compared to... The bipolar DC system has an additional fault loop. This fault loop is powered by the power supply between the PZ sections of the I-zone bus. This also explains why the power supply current difference between the PZ sections of the I-zone bus is so large. From a power flow perspective, when a ground fault occurs in zone T, the bipolar DC system is powered by all distributed power sources on the PZ bus, while... The DC system is powered solely by the power supply between the PZ buses in zone T. The reduction in fault current effectively decreases losses to system components.

[0114] Figures 10-13 for A comparison of bus voltages under single-stage grounding faults in a DC system architecture and a traditional bipolar DC system architecture. Figure 10 This refers to the voltage between PZ on the T-zone busbar. Figure 11 The voltage between Z and N of the T-zone busbar. Figure 12 This refers to the voltage between PZ on the I-zone busbar. Figure 13 This represents the voltage between Z and N on the I-zone busbar. Before 0.1 seconds, the system was operating normally with the same voltage. At 0.1 seconds, a single-stage ground fault occurred, and the voltage changed. Figure 10 show After a fault in the DC system and the bipolar DC system, the voltage between PZ on the T-zone bus drops significantly. Figure 11 show After a fault in the DC system and the bipolar DC system, the voltage between the ZN and T-zone buses both increased significantly. Figure 12 This indicates that the voltage between PZ buses in zone I of the bipolar DC system could not be maintained after the fault. The DC system stabilizes again after fluctuations. Figure 13 This indicates that the voltage between PZ buses in zone I of the bipolar DC system increased significantly after the fault, while The DC system stabilizes again after fluctuations.

[0115] Analyze the above results. Compared to a bipolar DC system, a conventional DC system eliminates the fault loop in zone I. Due to the larger fault current and the presence of resistance, the voltage between buses P and Z in zone I of a bipolar DC system will be lowered, while the voltage between buses Z and N will be raised. Since the DC system does not have this fault circuit, the voltage tends to stabilize, which is consistent with the model analysis.

[0116] Figures 14-16 for A comparison of fault currents in Zone I of a conventional bipolar DC system architecture and a traditional bipolar DC system architecture when a two-phase short circuit occurs. Figure 14 This represents the total fault current at the fault point. Figure 15 The fault point current is fed into area T. Figure 16 This represents the power supply current between zones T and PZ. Before 0.1s, the system operates normally with no fault current. At 0.1s, a two-phase ground fault occurs. Figure 14 show Compared to bipolar DC systems, the peak fault current and subsequent stability values ​​of the linear DC system are significantly smaller. (Analysis) Figure 15 The feed current in region T is the main reason for the difference in total fault current. The feed current in region T of the bipolar DC system is significantly larger. Analysis Figure 16 The main source of the difference in feed current is the current of the power supply between T and PZ zones.

[0117] Analysis of the fault circuit reveals that the difference lies in the bipolar DC system compared to... The bipolar DC system has an additional fault loop. This fault loop is powered by the power supply between PZs on the T-zone bus. This also explains why the power supply current difference between PZs is very large. From a power flow perspective, when a ground fault occurs in the T-zone, the bipolar DC system is powered by all distributed power sources on the PZ bus, and... The DC system is powered solely by the power supply between the PZ buses in Zone I. The reduction in fault current effectively reduces losses to system components.

[0118] Figures 17-20 for A comparison of bus voltages under two-phase short circuits in a DC system architecture and a traditional bipolar DC system architecture. Figure 17 This refers to the voltage between PZ on the T-zone busbar. Figure 18 This refers to the voltage between Z and N of the T-zone busbar. Figure 19 This refers to the voltage between PZ on the I-zone busbar. Figure 20 This represents the voltage between Z and N phases of busbar I. Before 0.1 seconds, the system operates normally with the same voltage. At 0.1 seconds, a two-phase short circuit occurs, causing the voltage to change. Figure 17 This indicates that the voltage between the PZ sections of the T-zone bus in the bipolar DC system could not be maintained after the fault. The DC system stabilizes again after fluctuations. Figure 18 This indicates that the voltage between PZ on the T-section bus of the bipolar DC system increased significantly after the fault, while The DC system stabilizes again after fluctuations. Figure 19 show After a fault in the DC system and the bipolar DC system, the voltage between PZ on the I-zone bus drops significantly. Figure 20 show After a fault in the DC system and the bipolar DC system, the voltage between the ZN and I buses in Zone I increases significantly.

[0119] Analyze the above results. Compared to a bipolar DC system, the T-zone fault circuit is eliminated in the T-zone DC system. Due to the larger fault current and the presence of resistance, the voltage between PZ buses in the T-zone of the bipolar DC system will be lowered, while the voltage between ZN buses will be raised. Since the DC system does not have this fault circuit, the voltage tends to stabilize, which is consistent with the model analysis.

[0120] Those skilled in the art can understand this embodiment as a more specific description of Embodiment 1.

[0121] 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.

[0122] 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. An off-grid DC power distribution system, characterized in that, include: Energy storage unit, power supply unit, DC load unit, voltage equalizer; The system is divided into region T, region M and region I, where region T and region I adopt a true bipolar architecture and region M adopts a pseudo bipolar architecture; the system balances the positive and negative voltages through a droop compensation control strategy. The energy storage unit, photovoltaic unit, and wind power unit are connected to the DC bus via a DC / DC converter to provide power to the system. The DC load unit and the load are connected to the DC bus via an interface, consuming the electrical energy provided by the system. The voltage equalizer is installed in different areas of the system to maintain the voltage balance of the positive and negative busbars by transmitting power.

2. The off-grid DC power distribution system according to claim 1, characterized in that, The voltage equalizer is grounded in a neutral point ungrounded manner. The voltage equalizers are installed on both sides of the T and I zones of the system. The voltage equalizers in the T and I zones are connected to different buses to independently control the voltage in the T and I zones.

3. The off-center DC power distribution system according to claim 1, characterized in that, The M area is a pseudo-bipolar architecture, with only two distribution buses and one distribution voltage provided within the M area, and no Z bus provided.

4. An operation method for an off-grid DC power distribution system, characterized in that, The method is applied to the off-grid DC power distribution system as described in any one of claims 1-3, and the method includes: During normal system operation, the voltage balance between the positive and negative terminals is maintained by a voltage equalizer; When a ground fault occurs, voltage equalizers and droop compensation control strategies are used to reduce the fault current.

5. The operation method of the off-center DC power distribution system according to claim 4, characterized in that, When a ground fault occurs in the system, the fault current is reduced and the voltage of the non-faulty pole is stabilized by adjusting the control parameters of the voltage equalizer.

6. The operation method of the off-center DC power distribution system according to claim 4, characterized in that, During the system design and implementation phases, the parameter settings of the voltage equalizer and droop compensation control strategy were optimized through simulation and experimental verification.

7. The operation method of the off-center DC power distribution system according to claim 4, characterized in that, During system operation, the voltage, current and power parameters of the system are monitored in real time, and the control strategy is dynamically adjusted according to the monitoring results to adapt to different operating conditions and load changes.

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