A series flexible DC comprehensive voltage regulating device based on AC-DC hybrid technology

Abstract

The application relates to the technical field of low-voltage treatment, and discloses a series flexible DC comprehensive voltage regulating device based on AC-DC mixing technology, which comprises a rectifying unit and an inverting unit. The rectifying unit is installed at the front end of a transformer station and close to the transformer side, and converts 220V AC voltage into +375V DC voltage. The inverting unit is installed at the end of the transformer station and close to the user side, and converts +375V DC voltage into 220V AC voltage to supply power to the end user. The rectifying unit and the inverting unit are connected through a DC line. The application realizes energy interconnection between the transformer side and the end user side in the transformer station, solves the voltage overrun problem at the end of the transformer station line, and reduces the line current to 1 / 3, the line voltage drop to 1 / 3 and the line loss to 1 / 9 under the condition of the same power. The DC voltage drop reaches 150V, which is 7 times of the AC voltage drop of 22V. The line power supply capacity is increased by 20 times.

Description

Technical Field

[0001] This invention relates to the field of low voltage management, and more particularly to a series-type flexible DC integrated voltage regulating device based on AC / DC hybrid technology. Background Technology

[0002] With rapid economic growth in recent years and the booming development of urban villages and peri-urban areas, rural electricity demand has surged. The contradiction between the power supply capacity of rural power distribution networks and the rapidly increasing demand has become increasingly prominent, leading to frequent low-voltage problems that severely affect users' normal electricity use and pose a serious challenge to power supply reliability. Furthermore, in remote mountainous areas, low-voltage problems are also increasing due to factors such as higher residential electricity consumption, excessively long power lines, and excessively thin power lines. With the construction of new power systems, the large-scale integration of distributed photovoltaic power has brought problems such as high voltage at the end of the low-voltage distribution network and voltage fluctuations.

[0003] Traditional solutions include transformer substation upgrades and low-voltage line voltage regulators. Transformer upgrades are time-consuming and costly. Low-voltage line voltage regulators involve connecting the phase wires of the equipment in series with the low-voltage line; the voltage rise process can lower the voltage upstream of the equipment, potentially affecting nearby users. Furthermore, there should be no users within a certain distance of the installation point. Neither solution effectively addresses the high / low voltage issues caused by long and thin power lines in remote mountainous areas.

[0004] Low-voltage distribution networks suffer from weak infrastructure and long power lines, resulting in significant power quality issues. A high proportion of new single / three-phase power sources exacerbates these problems, leading to multiple concurrent power quality issues. Limited control measures for low-voltage distribution networks result in unsatisfactory control effects, making it difficult to effectively address the increasingly severe power quality problems in distribution areas. Summary of the Invention

[0005] To address the shortcomings and defects of existing technologies, this invention provides a series-type flexible DC integrated voltage regulation device based on AC / DC hybrid distribution technology, which realizes energy mutual assistance between the transformer side and the end user side within the distribution area and solves the problem of voltage exceeding the limit at the end of the distribution line.

[0006] The objective of this invention can be achieved through the following technical solutions.

[0007] A series-type flexible DC integrated voltage regulation device based on AC / DC hybrid distribution technology includes a rectifier unit and an inverter unit. The rectifier unit is installed at the front end of the distribution area near the transformer side, rectifying 220V AC voltage into ±375V DC voltage. The inverter unit is installed at the end of the distribution area near the user side, inverting ±375V DC voltage into 220V AC voltage to supply power to the end user. The rectifier unit and the inverter unit are connected by a DC line.

[0008] A series-type flexible DC integrated voltage regulating device based on AC / DC hybrid technology includes the following steps:

[0009] In S1, the rectifier unit at the front end of the distribution area and the inverter unit at the user end are connected to the power grid in series. After the equipment is powered on, the initial state is bypassed, and the power conversion section does not operate. The rectifier unit supplies power to the inverter unit through the bypass circuit breaker, and the inverter unit supplies power to the end user through the bypass circuit breaker. During this process, the equipment actively performs self-checks, including checks on IGBTs, relays, fuses, DC bus connections, etc.

[0010] S2, when the equipment receives the power-on command, the rectifier unit actively disconnects the bypass circuit breaker, exits the bypass state, the inverter unit is powered off, and the rectifier unit starts DC startup.

[0011] S3, the rectifier unit precharges the DC bus using a dual half-wave rectification scheme. It controls the AC precharge circuit to precharge the DC bus, so that the DC bus voltage reaches twice the AC peak voltage.

[0012] S4, the rectifier unit pre-charge is completed, the power conversion unit is started, and the DC bus voltage is raised from the AC peak voltage to ±375V. The overall power conversion unit adopts the type I NPC three-level topology design. Each bridge arm of this topology has 4 switching elements and 2 clamping diodes. The midpoint of the two series switching elements is connected to the midpoint of the DC bus through the clamping diodes.

[0013] S5, after the DC bus of the rectifier unit is boosted to ±375V, it supplies power to the inverter unit through the DC pre-charge circuit. After the inverter unit detects the DC voltage input, it charges the DC bus through the DC pre-charge circuit, and the DC bus voltage of the inverter unit is consistent with that of the rectifier unit.

[0014] S6. After the inverter unit finishes pre-charging, the power conversion unit is started to convert the DC bus voltage into 220V AC power to supply power to the end users. The power conversion topology of the inverter unit is the same as that of the rectifier unit. Each bridge arm has 4 switching elements and 2 clamping diodes. The midpoint of the two series switching elements is connected to the midpoint of the DC bus through the clamping diodes.

[0015] S7, the rectifier unit and inverter unit in this solution have the same function and can be installed interchangeably. At the same time, it supports bidirectional energy flow, allowing energy to flow from the inverter side unit to the rectifier unit, thus achieving the effect of controlling high voltage at the end.

[0016] S8: When the equipment malfunctions, it actively exits the DC operating state and supplies power to the end users through the bypass circuit breaker to ensure reliable power supply for users.

[0017] Beneficial technical effects of the present invention:

[0018] A rectifier unit is installed at the front end of the transformer to convert 220V AC power to ±375V DC power. An inverter unit is installed at the user end to convert ±375V DC power back to 220V AC power, with ±375V DC transmission used in between. 750V DC is three times the voltage of 220V AC. Under the same power conditions, the line current is reduced to 1 / 3, the line voltage drop is reduced to 1 / 3, and the line loss is reduced to 1 / 9. The allowable DC voltage drop reaches 150V, which is 7 times the allowable voltage drop of 22V AC, increasing the line power supply capacity by 20 times.

[0019] This invention applies AC / DC hybrid distribution technology to low-voltage distribution areas, effectively solving the problems of low voltage caused by long power supply radius and thin wire diameter, as well as high voltage caused by photovoltaic terminal connection. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall working principle of the rectifier and inverter modules of the device under three-phase AC power supply conditions.

[0021] Figure 2 This is a schematic diagram of the overall working principle of the rectifier and inverter modules of the device in the case of single-phase AC power supply of the present invention.

[0022] Figure 3 This is the design of the Type I NPC three-level topology corresponding to step S6 of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and do not limit the scope of the invention.

[0024] Example:

[0025] like Figure 1 , Figure 2 As shown, a series flexible DC integrated voltage regulation technology for low voltage management of low-voltage distribution network users is divided into two modules: rectification and inversion, and includes the following steps:

[0026] S1: The rectifier unit at the front end of the distribution area and the inverter unit at the user end are connected to the power grid in series. After the equipment is powered on, the initial state is bypassed, and the power conversion section does not operate. The rectifier unit supplies power to the inverter unit through a bypass circuit breaker (P5 in the diagram), and the inverter unit supplies power to the end user through a bypass circuit breaker. During this process, the equipment actively performs self-checks, including IGBTs, relays (P2 in the diagram), fuses (P1 in the diagram), DC bus connections (P6 in the diagram), etc.

[0027] S2, when the equipment receives the power-on command, the rectifier unit actively disconnects the bypass circuit breaker, exits the bypass state, the inverter unit is powered off, and the rectifier unit starts DC startup.

[0028] S3, the rectifier unit precharges the DC bus using a dual half-wave rectification scheme. It controls the AC precharge circuit (P3 in the figure) to precharge the DC bus, so that the DC bus voltage reaches twice the AC peak voltage.

[0029] S4, the rectifier unit pre-charge is completed, and the power conversion unit (P4 in the figure) is started to raise the DC bus voltage from the AC peak voltage to ±375V. The overall power conversion unit adopts the type I NPC three-level topology design. Each bridge arm of this topology has 4 switching elements and 2 clamping diodes. The midpoint of the two series switching elements is connected to the midpoint of the DC bus through the clamping diode.

[0030] S5, after the DC bus of the rectifier unit is boosted to ±375V, it supplies power to the inverter unit through the DC pre-charge circuit (P7 in the figure). After the inverter unit detects the DC voltage input, it charges the DC bus through the DC pre-charge circuit, and the DC bus voltage of the inverter unit is consistent with that of the rectifier unit.

[0031] S6. After the inverter unit pre-charge is completed, the power conversion unit is started to convert the DC bus voltage into 220V AC power to supply power to the end users. The power conversion topology of the inverter unit is the same as that of the rectifier unit. Each bridge arm has 4 switching elements (D1\D2\D3\D4) and 2 clamping diodes (D5\D6). The midpoint of the two series switching elements is connected to the midpoint of the DC bus through the clamping diode.

[0032] S7, the rectifier unit and inverter unit in this solution have the same function and can be installed interchangeably. At the same time, it supports bidirectional energy flow, allowing energy to flow from the inverter side unit to the rectifier unit, thus achieving the effect of controlling high voltage at the end.

[0033] S8: When the equipment malfunctions, the equipment actively exits the DC working state and supplies power to the end users through the bypass circuit breaker to ensure reliable power supply for users.

[0034] S9, this solution can be implemented for both three-phase AC power supply lines and single-phase AC power supply lines, depending on the local power grid conditions, and the working principle is the same.

[0035] The above embodiments are descriptions of specific implementations of the present invention, and not limitations thereof. Those skilled in the art can make various modifications and changes without departing from the spirit and scope of the present invention to obtain corresponding equivalent technical solutions. Therefore, all equivalent technical solutions should be included in the patent protection scope of the present invention.

Claims

1. A series-type flexible DC integrated voltage regulating device based on AC / DC hybrid technology, characterized in that, It includes a rectifier unit and an inverter unit. The rectifier unit is installed at the front end of the distribution area near the transformer side, which rectifies the 220V AC voltage into ±375V DC voltage. The inverter unit is installed at the end of the distribution area near the user side, which inverts the ±375V DC voltage into 220V AC voltage to supply power to the end user. The rectifier unit and the inverter unit are connected by a DC line.

2. The series-type flexible DC integrated voltage regulating device based on AC / DC hybrid technology according to claim 1, characterized in that, The rectifier unit is connected in series to the power grid. After the equipment is powered on, the initial state is a bypass state, and the power conversion section does not operate. During this process, the equipment actively performs self-checks, including IGBTs, relays, fuses, DC bus wiring, etc. When the equipment receives a start-up command, the rectifier unit actively disconnects the bypass circuit breaker, exits the bypass state, and the rectifier unit begins DC start-up, performing DC bus pre-charging. This process adopts a dual half-wave rectification scheme, controlling the AC pre-charging circuit to pre-charge the DC bus. When the DC bus voltage reaches twice the AC peak voltage, the rectifier unit finishes pre-charging and starts the power conversion unit to raise the DC bus voltage from the AC peak voltage to ±375V.

3. The series-type flexible DC integrated voltage regulating device based on AC / DC hybrid technology according to claim 1, characterized in that, The inverter unit is connected in series to the power grid. After the equipment is powered on, the initial state is a bypass state, and the power conversion section does not operate. The rectifier unit supplies power to the inverter unit through the bypass circuit breaker, and the inverter unit supplies power to the end users through the bypass circuit breaker. During this process, the equipment actively performs self-checks, including IGBTs, relays, fuses, DC bus wiring, etc. When the equipment receives a power-on command, the inverter unit is powered off. When a DC voltage input is detected, the DC bus is charged through the DC pre-charging circuit, so that the DC bus voltage of the inverter unit is consistent with that of the rectifier unit. After the inverter unit pre-charges, the power conversion unit is started to invert the DC bus voltage to 220V AC power to supply power to the end users.

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