A system and method for improving power supply reliability and power quality of low-voltage distribution network

Abstract

The application relates to the field of power grid stabilization, in particular to a system and method for improving the power supply reliability and power quality of a low-voltage distribution network, which comprises a first fast switching switch connected in series to a low-voltage power supply line and located upstream of a load, a battery energy storage device and a power generation device connected in parallel to the low-voltage power supply line downstream of the first fast switching switch. The first fast switching switch and a second fast switching switch can realize the rapid connection and disconnection of the power supply, the battery energy storage device can realize the short-term power supply of the power grid and the balance of the reactive current, three-phase unbalanced current and harmonic current, and the power generation device can realize the long-term power supply of the power grid, so that the entire circuit can stably operate whether the power supply is short-term or long-term.

Description

Technical Field

[0001] This invention relates to the field of power grid stability, and more specifically to a system and method for improving the reliability and power quality of low-voltage distribution networks. Background Technology

[0002] With economic development, the reliability and power quality of low-voltage distribution networks have become increasingly important. In recent years, the rapid growth of electricity load has placed higher demands on the power supply capacity and quality of distribution systems. Among the rapidly growing industrial loads, nonlinear industrial loads, such as those from metallurgy, electrified railways, and chemicals, generally exhibit characteristics such as strong power surges, large voltage and current distortions, low power factors at grid connection points, and three-phase imbalances, adversely affecting the power quality of low-voltage distribution systems. Taking the power load of electric arc furnaces and rolling mills in the metallurgical industry as an example, the load of a 100-ton electric arc furnace can fluctuate drastically between 10-100 MVA during the smelting oxidation period, including a large amount of harmonics, negative sequence currents, and reactive currents, causing severe fluctuations and distortions in the power supply bus voltage. Simultaneously, the poor power supply conditions extend the smelting cycle of electric arc furnaces, increase energy consumption, and cause uneven rolling thickness and reduced quality in rolling mills, severely polluting the power quality of other users and even jeopardizing the normal operation of nearby substations and generator units. Electrified railway loads also exhibit characteristics such as impact, distortion, and three-phase imbalance. During the operation of electric locomotives, these loads cause a series of adverse effects on other industrial and residential power users along the line, including harmonics, voltage fluctuations, and three-phase voltage imbalances. With the development of new energy technologies, wind and solar power generators are being connected to the grid on a large scale. In particular, distributed wind and solar power generation is widely integrated into low-voltage distribution networks. The inherent volatility and unpredictability of new energy power also cause voltage fluctuations, voltage drops, and short-term power outages to the power load of the distribution network, posing challenges to power supply reliability. On the other hand, with the continuous expansion of the power system, short-term or long-term grid failures are inevitable. Power supply reliability generally permeates from high-voltage levels to low-voltage levels, and voltage drops or short-term voltage outages are very common in low-voltage distribution networks. Grid failures caused by natural disasters such as rainstorms and floods, or by force majeure events such as war, can also cause long-term power outages of several days or even weeks in localized or remote areas. Therefore, the power supply reliability of low-voltage distribution networks still needs improvement.

[0003] With the rise of high-tech industries, such as IT, integrated circuit production lines, and LCD production lines, the demands on power supply reliability and power quality are extremely high. Short-term power outages, voltage fluctuations, and voltage distortions can have a fatal impact on product quality, while prolonged power outages can cause huge economic losses or even catastrophic consequences for power users. As people's living standards improve, the reliability and quality of low-voltage power distribution also affect countless households. Pollution of power quality from large industrial loads is transmitted and permeates into the low-voltage system through the distribution network. In ordinary residential low-voltage electricity use, harmonics, voltage deviations, and voltage fluctuations also harm household appliances. Studies show that harmonics can increase the energy consumption of household appliances, affect electricity meter readings, and even damage sensitive appliances, while voltage deviations and fluctuations can affect the use of lighting and television, impacting the vital interests of the general public. Prolonged power outages will cause economic losses to residents and directly lead to complaints and claims against the power supply department.

[0004] For a long time, there have been many technologies and products related to improving the reliability and power quality of low-voltage distribution networks, but they only address one problem at a time. For example, Static Var Compensators (SVCs) and Static Var Generators (SVG) only solve dynamic reactive power compensation and voltage fluctuation problems; Active Power Filters (APFs) only solve harmonic suppression problems; Dynamic Voltage Restorers (DVRs) only solve voltage dips and short-term power outages. Power reliability and power quality issues often occur simultaneously in the power grid, but it's impossible to install all power quality equipment in a low-voltage distribution network. Instead, targeted equipment is installed to address specific problems and improve one or more aspects of power quality and reliability. Therefore, there is an urgent need to design a method that can comprehensively solve the problems of power reliability and power quality in low-voltage distribution networks, thereby improving the power supply level of low-voltage distribution networks and ensuring the sustainable development of industry, agriculture, and society as a whole. Summary of the Invention

[0005] To address the problems of unstable power supply on the power source side and harmonics, voltage fluctuations, three-phase power imbalance, and low power factor on the load side in existing low-voltage distribution networks, the first aspect of this invention proposes a system for improving the reliability and power quality of low-voltage distribution networks, comprising:

[0006] A first fast-change switch 100 connected in series with the low-voltage power supply line and located upstream of the load;

[0007] A battery energy storage device 200 and a power generation device 300 are located downstream of the first fast switching switch 100 and connected in parallel to the low-voltage power supply line. The battery energy storage device 200 includes a bidirectional energy storage converter 210 and a DC battery pack 220. One end of the bidirectional energy storage converter 210 is connected to the DC battery pack 220, and the other end of the bidirectional energy storage converter 210 is connected to the low-voltage power supply line. The power generation device 300 includes a generator 320 and a second fast switching switch 310. One end of the second fast switching switch 310 is connected to the low-voltage power supply line, and the other end is connected to the generator 320.

[0008] Optionally, the first fast switching switch 100 and / or the second fast switching switch 310 include:

[0009] The parallel-connected RC damping circuit 101, the anti-parallel thyristor pair 102, and the fast mechanical switch 103.

[0010] Optionally, the fast mechanical switch 103 is a permanent magnet switch.

[0011] Optionally, the fixed contacts and the contacts of the fast mechanical switch 103 are located in the same vacuum environment.

[0012] Optionally, the bidirectional energy storage converter 210 is an IGBT full-bridge converter.

[0013] Optionally, the battery energy storage device 200 further includes a DC support capacitor 240, which is connected in parallel with the DC battery pack 220.

[0014] Optionally, the generator 320 is a diesel generator.

[0015] A second aspect of this invention provides a method for improving the reliability and power quality of low-voltage distribution networks, comprising:

[0016] When the low-voltage distribution network is in operation, the vector transformation method is used to detect the instantaneous reactive current, three-phase unbalanced current and harmonic current of the load;

[0017] The battery energy storage device 200 described above is used as a current generator to generate the reverse current of the instantaneous reactive current, three-phase unbalanced current and harmonic current for reverse compensation.

[0018] or,

[0019] When the low-voltage distribution network load is abnormally interrupted for a first preset time, the first fast switching switch 100 is disconnected and the battery energy storage device 200 is started.

[0020] When the low-voltage distribution network load experiences an abnormal interruption for a second preset time, the first fast switching switch 100 is disconnected, and the aforementioned battery energy storage device 200 and power generation device 300 are started. The second preset time is longer than the first preset time.

[0021] Optionally, the detection of instantaneous reactive current, three-phase unbalanced current, and harmonic current of the load using the vector transformation method includes:

[0022] When the three-phase voltage is the fundamental positive sequence voltage, the instantaneous three-phase voltage and current are transformed by coordinate transformation to obtain the instantaneous three-phase active power and instantaneous three-phase reactive power;

[0023] The DC component in the three-phase instantaneous active power is filtered out to obtain the target three-phase instantaneous active power;

[0024] Instantaneous reactive current, three-phase unbalanced current, and harmonic current are obtained based on the target three-phase instantaneous active power, three-phase instantaneous reactive power, and three-phase instantaneous voltage.

[0025] Optionally, the instantaneous reactive current, three-phase unbalanced current, and harmonic current can be obtained using the following formulas:

[0026]

[0027] Among them, i Ca For instantaneous reactive current, i Cb For three-phase unbalanced current, i Cc Harmonic current, The target is the instantaneous active power of the three phases. q represents the three-phase instantaneous reactive power, u a u b u c This refers to the instantaneous voltage of the three phases.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] This invention provides a system and method for improving the reliability and power quality of low-voltage power distribution networks. The system includes: a first fast-change switch connected in series with the low-voltage power supply line and located upstream of the load; a battery energy storage device and a power generation device located downstream of the first fast-change switch and connected in parallel with the low-voltage power supply line; wherein the battery energy storage device includes a bidirectional energy storage converter and a DC battery pack, one end of the bidirectional energy storage converter is connected to the DC battery pack, and the other end of the bidirectional energy storage converter is connected to the low-voltage power supply line; the power generation device includes a generator and a second fast-change switch, one end of the second fast-change switch is connected to the low-voltage power supply line, and the other end is connected to the generator. The first fast-change switch and the second fast-change switch of this invention can realize the rapid connection and disconnection of power supply; the battery energy storage device can realize short-term power supply to the grid and generate reactive current, three-phase unbalanced current, harmonic current, and reverse current, thereby balancing the reactive current, three-phase unbalanced current, and harmonic current; and the power generation device can realize long-term power supply to the grid, ensuring that the entire circuit can operate stably regardless of whether there is a short-term or long-term power outage. Attached Figure Description

[0030] Figure 1 This is a detailed structural diagram of the system proposed in this invention for improving the reliability and power quality of low-voltage distribution networks.

[0031] Figure 2 This is a schematic diagram of the structure of the first fast switching switch and the second fast switching switch proposed in this invention;

[0032] Figure 3 This is a schematic diagram of the battery energy storage device proposed in this invention;

[0033] Figure 4 This is a schematic diagram of some steps in the method for improving the power supply reliability and power quality of low-voltage distribution networks proposed in this invention.

[0034] Figure 5 The present invention proposes Figure 4 A detailed step diagram of step S1. Detailed Implementation

[0035] When supplying power to a low-voltage 380V distribution network, instability on the power supply side often causes voltage drops (i.e., a voltage decrease of 20%-80%, lasting 20ms-1000ms), short-term voltage interruptions (i.e., voltage dropping to 0V, lasting 1s-10s), and long-term voltage interruptions (i.e., voltage dropping to 0V, lasting 10s-10h or more). This instability is often caused by grid faults, human error, or external natural disasters, leading to a decrease in power supply reliability. While using a backup power supply to switch to the faulty source can restore power, voltage is temporarily lost during the switching process, causing voltage transients on the load. If the backup power supply also fails or is delayed in power restoration, it can cause prolonged power outages. Instability in the power supply from the source side frequently reduces the reliability of the power supply load. The use of impulsive loads (such as welding machines, electric motors, etc.) on the power supply load side can cause severe fluctuations in the supply voltage or imbalances in the three-phase voltage. The use of nonlinear loads (such as rectifiers, frequency converters, and other power electronic equipment) can lead to severe harmonic distortion of the supply voltage. To address the instability of the power supply on the power source side of low-voltage distribution networks and the problems of harmonics, voltage fluctuations, three-phase imbalances, and low power factor on the load side, a system and method integrating battery energy storage, rapid switching of diesel generator power, power electronic control, and power quality management is needed to comprehensively solve the power supply reliability problems caused by the power source side and the power quality problems caused by the load side in low-voltage distribution networks.

[0036] Example 1:

[0037] A system for improving the reliability and power quality of low-voltage distribution networks, such as Figure 1 As shown. In a 380V low-voltage power supply network, 380V mains power supplies power to the load through a power supply line controlled by a circuit breaker. A first fast-change switch 100 is connected in series downstream of the circuit breaker and upstream of the load, and a battery energy storage device 200 and a generator 300 are connected in parallel on the subsequent power supply line.

[0038] The power generation device 300 includes a generator 320 and a second fast switching switch 310. One end of the second fast switching switch 310 is connected to the low-voltage power supply line, and the other end is connected to the generator 320, thereby controlling whether the generator 320 is connected to the low-voltage power supply line.

[0039] The first fast-change switch 100 and the second fast-change switch 310 are used for rapid isolation from the low-voltage power supply line, and their structures are as follows: Figure 2As shown, the circuit includes a parallel RC damping circuit 101, a thyristor anti-parallel pair 102, and a fast mechanical switch 103, forming a composite switch capable of rapid closing and opening. The fast mechanical switch 103 is a permanent magnet switch. The permanent magnet switch controls the switch contacts through a permanent magnet and a magnet with a control coil, increasing the control force during contact opening and closing by more than 10 times compared to switches with simple coil control. Simultaneously, the fixed contacts and the contacts of the fast mechanical switch 103 are located in the same vacuum environment, reducing the contact spacing by more than half compared to conventional air-gap switches. Therefore, the switch closing and opening time can be shortened to 3-5 ms, while the closing and opening time of conventional coil-controlled, air-gap switches is generally up to 100 ms. Due to the shortened opening and closing time, the arc extinguishing ability is weaker, requiring the thyristor anti-parallel pair 102 for auxiliary arc extinguishing. When the fast mechanical switch 103 closes, it first triggers the thyristor to conduct, and then closes the fast mechanical switch 103, reducing the closing time of the fast mechanical switch 103 to less than 1 ms. When the fast mechanical switch 103 opens, it simultaneously triggers the anti-parallel pair of thyristors 102 to conduct. While the fast mechanical switch 103 opens within 5 ms, an arc is generated at its contacts, but it is transferred to the conducting branch of the anti-parallel pair of thyristors 102. After 5 ms, the thyristor stops triggering, and within 10 ms, according to the thyristor characteristics, the three-phase current crosses zero and naturally turns off, the arc is extinguished, and the switch is completely opened, reducing the opening time of the fast mechanical switch 103 to less than 10 ms.

[0040] The battery energy storage device 200 includes a bidirectional energy storage converter 210 and a DC battery pack 220. One end of the bidirectional energy storage converter 210 is connected to the DC battery pack 220 via a DC bus 230, and the other end of the bidirectional energy storage converter 210 is connected to the low-voltage power supply line.

[0041] The DC battery pack 220 can be a series or parallel energy storage lithium battery pack, forming an 800V DC voltage on the DC bus 230.

[0042] In further optimized solutions, such as Figure 3 As shown, the battery energy storage device 200 also includes a DC support capacitor 240, which is connected in parallel with the DC battery pack 220 for storing electrical energy.

[0043] In a further preferred embodiment, the bidirectional energy storage converter 210 is an IGBT full-bridge converter. The IGBT full-bridge converter can convert DC voltage into 380V AC voltage, and can discharge or charge the grid as a current source, or provide power to the grid as a voltage source. Simultaneously, the IGBT full-bridge converter can also convert DC voltage into a current source generator, injecting current into the grid for reactive power compensation, harmonic filtering, and negative sequence current removal.

[0044] Based on the above structure, when the voltage of the 380V mains power supply in the low-voltage distribution network drops or there is a short-term power outage, the first fast switching switch 100 can disconnect the power supply line from the 380V mains power supply within 10ms. At the same time, the battery energy storage device 200 generates three-phase 380V AC voltage to support the power supply to the load. If the 380V AC mains power supply is restored within 10 seconds, it indicates that the 380V AC mains power interruption is short-term. The bidirectional energy storage converter 210 of the battery energy storage device 200 can be locked to stop its output of 380V AC voltage. Simultaneously, the first fast-change switch 100 is closed to restore the 380V AC mains power supply. If the 380V AC mains power supply is not restored within 10 seconds, it indicates that the 380V AC mains power interruption is long-term. While the battery energy storage device 200 continues to supply power to the load, the generator 320, preferably a diesel generator, is started. Generally, it takes about 60 seconds for the diesel generator to generate three-phase 380V voltage from startup. After 60 seconds, when the diesel generator is operating normally, the bidirectional energy storage converter 210 of the battery energy storage device 200 is locked to stop its output of 380V AC voltage. Simultaneously, the second fast-change switch 310 is closed, and the diesel generator generates 380V voltage to provide long-term power to the load. When the 380V AC mains power supply is restored after a period of time (5-10 hours), the connection between the power supply line and the diesel generator power supply can be quickly disconnected within 10ms via the second fast-change switch 310. After 10ms, the first fast-change switch 100 is closed to restore the 380V AC mains power supply. This scheme can ensure a continuous and long-term power supply to the load regardless of whether the 380V AC mains power supply is interrupted for a short time (0-60s) or a long time (60s-10h), with the voltage drop time not exceeding 10ms.

[0045] In summary, this application describes a control technology for 380V low-voltage distribution networks that uses battery energy storage devices and power generation devices as backup power sources to achieve seamless switching and continuous power supply during short-term or long-term power supply voltage interruptions.

[0046] When a 380V power supply fails, a switch can be used to switch the power supply to another 380V power source. However, this switching process, achieved through a mechanical switch, causes a brief interruption in power supply. A battery storage device can provide continuous power through an online uninterruptible power supply (UPS). The battery storage time within a UPS is typically between 10 minutes and 2 hours; power is lost when the battery is depleted. If a generator (e.g., a diesel generator) is used as a backup power source, the continuous power supply time can be significantly extended by adding diesel fuel, often lasting for several days. However, since a diesel generator requires a preparation time to start and generate power, the power supply to the load will be interrupted for an extended period. This invention addresses these problems by using a battery storage device as a short-term transitional power source and a diesel generator as a long-term backup power source during short-term or long-term power supply interruptions in a 380V low-voltage distribution network. A specially designed fast-switching switch allows for seamless switching between the power sources, ensuring a long-term continuous power supply to the load.

[0047] This patent enables a 380V low-voltage distribution network to quickly restore its voltage to rated level within 10ms when a short-term grid fault (20-100ms) causes a voltage drop. In the event of a prolonged grid fault (0.1s-60s) causing a voltage interruption, the battery energy storage device and fast transfer switch provide power to the low-voltage network via a DC battery pack and a bidirectional energy storage converter, maintaining continuous power supply. In the event of a long-term grid fault (60s-10h) causing a voltage interruption, the battery energy storage device, generator, and fast transfer switch provide power to the low-voltage network via a bidirectional energy storage converter (for initial transition) and a generator (for long-term) power supply, maintaining continuous power supply. This patent significantly improves the reliability of the low-voltage distribution network, ensuring a continuous and reliable power supply to the load under any long-term or short-term fault conditions.

[0048] Example 2:

[0049] Based on the same inventive concept, this invention also provides a method for improving the reliability and power quality of low-voltage distribution networks. This invention employs a vector transformation method to detect the instantaneous reactive current, three-phase unbalanced current, and harmonic current of the load. Using this detected current as a control target, when the 380V mains power supply is normal or the diesel generator is supplying power, a bidirectional energy storage converter acts as a current generator, emitting an inverse current of the instantaneous reactive current, three-phase unbalanced current, and harmonic current. This inverse current compensates for power quality disturbances in the load current, thereby filtering out reactive current, three-phase unbalanced current, and harmonic current from the load. This improves the load's power factor, balances the three phases, filters out harmonic current, and improves the power quality of the power grid. Figure 4 As shown, it includes the following steps S1 and S2.

[0050] S1: When the low-voltage distribution network is in operation, the vector transformation method is used to detect the instantaneous reactive current, three-phase unbalanced current and harmonic current of the load.

[0051] A further preferred option is, such as Figure 5 As shown, step S1 includes the following steps S11 to S13.

[0052] S11: When the three-phase voltage is the fundamental positive sequence voltage, the three-phase instantaneous voltage and current are transformed by coordinate transformation to obtain the three-phase instantaneous active power and the three-phase instantaneous reactive power.

[0053] When the three-phase voltage is the fundamental positive sequence voltage, the instantaneous active power and instantaneous reactive power of the three-phase instantaneous voltage and current are calculated by the following formula after coordinate transformation:

[0054]

[0055] Where p is the three-phase instantaneous active power, q is the three-phase instantaneous reactive power, and u a u b u c For three-phase instantaneous voltage, i a i b i c This represents the instantaneous current in the three phases.

[0056] S12: Filter out the DC component in the three-phase instantaneous active power to obtain the target three-phase instantaneous active power;

[0057] S13: Based on the target three-phase instantaneous active power, three-phase instantaneous reactive power, and three-phase instantaneous voltage, obtain the instantaneous reactive current, three-phase unbalanced current, and harmonic current.

[0058] Subsequently, the DC component in the three-phase instantaneous active power is filtered out to obtain the target three-phase instantaneous active power. The target three-phase instantaneous active power, the three-phase instantaneous reactive power, and the three-phase voltage can be used to calculate the sum of the three-phase fundamental positive sequence reactive current, the three-phase fundamental negative sequence current, and the three-phase harmonic current using the following formula.

[0059]

[0060] Among them, i Ca i represents the three-phase fundamental positive-sequence reactive current (i.e., instantaneous reactive current). Cb For the three-phase fundamental negative sequence current (i.e., the three-phase unbalanced current), i Cc Harmonic current, To filter out the instantaneous active power of the DC component, i.e. the target three-phase instantaneous active power,

[0061] S2: The battery energy storage device described in Example 1 is used as a current generator to generate the reverse current of the instantaneous reactive current, three-phase unbalanced current and harmonic current for reverse compensation.

[0062] This method utilizes a vector transformation-based detection approach to detect the three-phase fundamental reactive current, higher harmonic current, and three-phase fundamental negative sequence current with a certain time delay, and then rapidly compensates for them, thereby improving the system power factor, filtering harmonics, and achieving three-phase balance. This vector transformation-based method for detecting instantaneous reactive current, harmonic current, and three-phase unbalanced current, when applied to bidirectional energy storage converters, can effectively solve power quality control and management problems.

[0063] The method for improving the power supply reliability and power quality of low-voltage distribution networks in this invention further includes disconnecting the first fast switching switch 100 and starting the battery energy storage device 200 when the load of the low-voltage distribution network is abnormally interrupted for a first preset time, thereby achieving short-term stable power supply to the load.

[0064] The method for improving the reliability and power quality of low-voltage distribution network power supply in this invention also includes disconnecting the first fast switching switch 100 and starting the battery energy storage device 200 and the power generation device 300 when the low-voltage distribution network load is abnormally interrupted for a second preset time. The second preset time is longer than the first preset time, so as to achieve a long-term stable power supply to the load and gain enough time for grid maintenance.

[0065] In summary, the power quality control method disclosed in this scheme for comprehensively solving power quality problems such as harmonics, voltage fluctuations, three-phase imbalance, and low power factor caused by nonlinear impulsive loads in 380V low-voltage distribution networks is as follows:

[0066] Nonlinear impulsive loads in 380V low-voltage distribution networks often induce harmonic currents, causing power supply voltage distortion. When the load is impulsive, it causes voltage fluctuations and flicker. Uneven currents in the three phases (A, B, and C) of the load lead to three-phase voltage imbalance. Furthermore, high reactive power in the load results in a low power factor in the power supply line, causing voltage drops and deviations. Existing mitigation techniques for harmonics include single-tuned filter (FC) devices or active power filter (APF) devices to filter out harmonic currents. For voltage fluctuations and flicker caused by impulsive loads, as well as low power factor issues, existing mitigation techniques include dynamic reactive power compensation (SVC) or SVG devices. For three-phase load current imbalances (A, B, and C), existing mitigation techniques include three-phase load balancing devices. However, these existing technologies and devices lack uniformity and cannot comprehensively address and suppress all the aforementioned power quality problems. Since power quality issues caused by nonlinear impulsive loads often occur simultaneously, comprehensive mitigation methods and measures are required. This invention utilizes the power electronic converter (PCS) of a battery energy storage device to absorb harmonic currents, reactive currents, and negative sequence currents in the load current when the 380V power supply is in normal operation. This effectively suppresses harmonics, voltage fluctuations and flicker, three-phase imbalance, and low power factor, thus comprehensively addressing power quality issues.

[0067] This method addresses power quality disturbances and low power factor issues in 380V low-voltage distribution networks caused by nonlinear loads, such as voltage and current distortion, voltage fluctuations, and three-phase voltage imbalance. By using a battery energy storage device, during normal power supply from the 380V grid, the method analyzes the harmonic distortion, reactive power, and negative sequence current of the load. It then injects a reverse-current into the grid to suppress the load's harmonic currents, fundamental reactive current, and negative sequence current, significantly improving the power quality indicators of the grid, including harmonic distortion, three-phase imbalance, voltage fluctuations, and low power factor, thus ensuring high-quality power supply to the load.

[0068] The above are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of the claims of the present invention pending approval.

Claims

1. A system for improving the reliability and power quality of low-voltage distribution networks, characterized in that, include: A first fast-change switch (100) connected in series with the low-voltage power supply line and located upstream of the load; A battery energy storage device (200) and a power generation device (300) are located downstream of the first fast switching switch (100) and connected in parallel to the low-voltage power supply line. The battery energy storage device (200) includes a bidirectional energy storage converter (210) and a DC battery pack (220). One end of the bidirectional energy storage converter (210) is connected to the DC battery pack (220), and the other end of the bidirectional energy storage converter (210) is connected to the low-voltage power supply line. The power generation device (300) includes a generator (320) and a second fast switching switch (310). One end of the second fast switching switch (310) is connected to the low-voltage power supply line, and the other end is connected to the generator (320).

2. The system for improving the reliability and power quality of low-voltage distribution networks according to claim 1, characterized in that, The first fast switching switch (100) and / or the second fast switching switch (310) include: The circuit consists of a parallel RC damping circuit (101), an anti-parallel pair of thyristors (102), and a fast mechanical switch (103).

3. The system for improving the reliability and power quality of low-voltage distribution networks according to claim 2, characterized in that, The fast mechanical switch (103) is a permanent magnet switch.

4. The system for improving the reliability and power quality of low-voltage distribution networks according to claim 3, characterized in that, The fixed contacts and contacts of the fast mechanical switch (103) are located in the same vacuum environment.

5. The system for improving the reliability and power quality of low-voltage distribution networks according to claim 1, characterized in that, The bidirectional energy storage converter (210) is an IGBT full-bridge converter.

6. The system for improving the reliability and power quality of low-voltage distribution networks according to claim 1 or 5, characterized in that, The battery energy storage device (200) further includes a DC support capacitor (240), which is connected in parallel with the DC battery pack (220).

7. The system for improving the reliability and power quality of low-voltage distribution networks according to claim 1, characterized in that, The generator (320) is a diesel generator.

8. A method for improving the reliability and power quality of low-voltage distribution networks, characterized in that, include: When the low-voltage distribution network is in operation, the vector transformation method is used to detect the instantaneous reactive current, three-phase unbalanced current and harmonic current of the load; The battery energy storage device (200) according to any one of claims 1 to 7 is used as a current generator to generate the reverse current of the instantaneous reactive current, three-phase unbalanced current and harmonic current for reverse compensation. or, When the low-voltage distribution network load is abnormally interrupted for a first preset time, the first fast switching switch (100) is disconnected and the battery energy storage device (200) according to any one of claims 1 to 7 is started; When the low-voltage distribution network load is abnormally interrupted for a second preset time, the first fast switching switch (100) is disconnected, and the battery energy storage device (200) and the power generation device (300) as described in any one of claims 1 to 7 are started, wherein the second preset time is longer than the first preset time.

9. The method for improving the power supply reliability and power quality of low-voltage distribution networks according to claim 8, characterized in that, The method of using vector transformation to detect instantaneous reactive current, three-phase unbalanced current, and harmonic current of the load includes: When the three-phase voltage is the fundamental positive sequence voltage, the instantaneous three-phase voltage and current are transformed by coordinate transformation to obtain the instantaneous three-phase active power and instantaneous three-phase reactive power; The DC component in the three-phase instantaneous active power is filtered out to obtain the target three-phase instantaneous active power; Instantaneous reactive current, three-phase unbalanced current, and harmonic current are obtained based on the target three-phase instantaneous active power, three-phase instantaneous reactive power, and three-phase instantaneous voltage.

10. The method for improving the power supply reliability and power quality of a low-voltage distribution network according to claim 9, characterized in that, The instantaneous reactive current, three-phase unbalanced current, and harmonic current are obtained using the following formulas: Among them, i Ca For instantaneous reactive current, i Cb For three-phase unbalanced current, i Cc Harmonic current, The target is the instantaneous active power of the three phases. q represents the three-phase instantaneous reactive power, u a u b u c This refers to the instantaneous voltage of the three phases.

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