Medium voltage regulating circuit, system and method

Abstract

The invention discloses a medium-voltage voltage regulating circuit, system and method, and belongs to the technical field of medium-voltage power distribution. The medium-voltage voltage regulating circuit comprises a tapped voltage regulating transformer Tr1 connected in series with a medium-voltage main line, a voltage compensation unit connected in series with the input side of the Tr1, a current compensation unit connected in parallel with the medium-voltage main line, and a DC support unit. And the direct current sides of the power modules of the voltage compensation unit and the current compensation unit can be connected with the direct current support unit together or separately. The millisecond-level response power module preferentially processes voltage fluctuation and electric energy quality problems, mechanical tap switching is started only when deviation continuously exceeds the capacity of the power module, the service life of key mechanical parts is greatly prolonged while wide-range and high-precision continuous voltage regulation and reactive power and harmonic comprehensive treatment are achieved, and the cost is reduced. And the comprehensive cost and the maintenance requirement are reduced. The scheme is particularly suitable for medium-voltage power distribution network scenes such as data centers sensitive to electric energy quality, precision manufacturing, medical equipment and the like.

Description

Technical Field

[0001] This invention relates to the field of medium-voltage power distribution technology, and more specifically, to a medium-voltage voltage regulating circuit, system, and method. Background Technology

[0002] In actual operation of three-phase medium-voltage (6kV to 35kV) distribution networks, voltage fluctuations and drops are common due to factors such as changes in line impedance, load fluctuations, and the integration of distributed power sources. These fluctuations are accompanied by power quality issues such as three-phase imbalance and harmonic pollution. For sensitive loads such as data centers, precision manufacturing facilities, and medical equipment, even minor voltage fluctuations or shocks can lead to serious consequences such as equipment failure and data loss.

[0003] Existing medium-voltage voltage regulation technologies mostly use tapped voltage regulating transformers for wide-range voltage regulation, which has the advantages of large capacity and low cost. However, voltage step impacts are inevitably generated during tap switching, and the voltage regulation accuracy is low, which cannot meet the high-precision voltage stabilization requirements of sensitive loads. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides a medium-voltage voltage regulation system and method. Through innovative topology and control strategies, it achieves deep synergy between mechanical on-load voltage regulation and power electronic series / parallel compensation, which can provide high-quality voltage comparable to pure power electronic solutions, while significantly reducing system costs and losses.

[0005] According to one aspect of the present invention, a medium-voltage regulating circuit is provided, applied to a three-phase medium-voltage distribution network main line, comprising: a tapped voltage regulating transformer Tr1, whose autotransformer winding is connected in series in the medium-voltage main line, and having multiple taps and a tap switching mechanism for switching the multiple taps; a voltage compensation unit, comprising a series transformer Tr3 and a voltage compensation power module having an AC side and a DC side; the primary side of the series transformer Tr3 is connected in series to the input side of the tapped voltage regulating transformer Tr1, and its secondary side is connected to the AC side of the voltage compensation power module; a current compensation unit, comprising a parallel transformer Tr2 and a current compensation power module having an AC side and a DC side; the primary side of the parallel transformer Tr2 is connected in parallel to the medium-voltage main line, and its secondary side is connected to the AC side of the current compensation power module; and a DC support unit; wherein the DC sides of the voltage compensation power module and the current compensation power module are connected to the same DC support unit, or are respectively connected to different DC support units.

[0006] Preferably, both the voltage compensation power module and the current compensation power module use fully controlled power semiconductor switching devices as switching devices.

[0007] Preferably, the fully controllable power semiconductor switching device is an IGBT.

[0008] Preferably, the current compensation power module and the voltage compensation power module are each a multi-level converter or a two-level converter.

[0009] As a more specific implementation, the primary side of the parallel transformer Tr2 is connected in parallel to one of the following locations: the medium-voltage main line on the output side of the tapped voltage regulating transformer Tr1; the medium-voltage main line connected to the primary input terminal of the series transformer Tr3; or the medium-voltage main line between the primary output terminal of the series transformer Tr3 and the input terminal of the tapped voltage regulating transformer Tr1.

[0010] Preferably, the DC side of the voltage compensation power module and the DC side of the current compensation power module are interconnected through the same DC support unit to form a shared DC bus.

[0011] Preferably, the medium-voltage regulating circuit further includes a DC port connected to the DC bus for connecting to an external DC source or load.

[0012] Specifically, the DC support unit includes a DC support capacitor.

[0013] According to another aspect of the present invention, a medium-voltage voltage regulating system is provided, comprising the aforementioned medium-voltage voltage regulating circuit, and further comprising a voltage acquisition unit, a current acquisition unit, a signal processing unit, a communication unit, and a central controller. The voltage acquisition unit is used to acquire the three-phase voltage signal of the medium-voltage main line and the phase synchronous voltage signal of each phase of the autotransformer of the tapped voltage regulating transformer Tr1, and transmits the acquired signals to the signal processing unit. The current acquisition unit is used to acquire the current signal of the medium-voltage main line and transmit the acquired signal to the signal processing unit. The signal processing unit is used to receive the signals transmitted by the voltage acquisition unit and the current acquisition unit, preprocess the signals, and send them to the central controller. The communication unit is used to receive external control commands from external devices and transmit the received external control commands to the central controller. The central controller is used to generate control commands based on the voltage and current signals from the signal processing unit, and / or based on the external control commands from the communication unit, and send the control commands to at least one of the tap switching mechanism of the tapped voltage regulating transformer Tr1, the voltage compensation power module, and the current compensation power module.

[0014] Preferably, the voltage acquisition unit is a medium-voltage voltage transformer; the current acquisition unit is a Rogowski coil; the communication unit supports wired or wireless communication; and the signal processing unit is an embedded microprocessor integrating signal filtering and analog-to-digital conversion modules.

[0015] According to another aspect of the present invention, a voltage regulation method for the aforementioned medium-voltage voltage regulation system is provided. The voltage regulation method is executed by the central controller and includes the following steps: S1, monitoring the three-phase voltage of the medium-voltage main line and the synchronous phase voltage signals of each phase of the autotransformer Tr1 of the tapped voltage regulating transformer, and calculating a first voltage deviation value of the monitored three-phase voltage relative to the target voltage; S2, determining whether the first voltage deviation value is greater than a preset second threshold; if so, calculating the required fine voltage compensation amount and / or voltage imbalance compensation amount based on the synchronous phase voltage signals of each phase, and generating control commands to drive the voltage compensation power module through... The series transformer Tr3 injects a corresponding compensation voltage into the medium-voltage main line; if not, no adjustment is made and the execution is terminated; S3, continue to monitor the three-phase voltage of the medium-voltage main line and the phase synchronous voltage signal of each phase of the autotransformer winding of the tapped voltage regulating transformer Tr1, and calculate the second voltage deviation value of the monitored three-phase voltage relative to the target voltage, and determine whether the second voltage deviation value is greater than the preset first threshold. If not, the adjustment ends and the execution is terminated; if so, a control command is generated to drive the tap switching mechanism of the tapped voltage regulating transformer Tr1 to switch taps and perform wide-range coarse voltage adjustment; wherein the first threshold is greater than the second threshold.

[0016] Furthermore, the current of the medium-voltage main line is monitored simultaneously, and based on the synchronous phase voltage signals of each phase, the required reactive power compensation current, unbalanced current mitigation amount, and harmonic compensation current are calculated, and control commands are generated to drive the current compensation power module to inject the corresponding compensation current into the medium-voltage main line through the parallel transformer Tr2.

[0017] Furthermore, the active power exchange between the current compensation power module and the medium-voltage main line is adjusted to maintain the DC-side voltage stability of the current compensation power module.

[0018] The beneficial effects of this invention are as follows: 1. The voltage regulating circuit of this invention sets the fast-response series transformer Tr3 on the input side of the tapped voltage regulating transformer Tr1. This allows the power electronic device to "preprocess" grid voltage disturbances in the first instance, preventing grid voltage fluctuations from being transmitted to the output side of Tr1. The mechanical tap switching of Tr1 is only activated when the voltage deviation continuously exceeds the capacity of the power electronic device. While achieving wide-range, high-precision continuous voltage regulation and comprehensive management of reactive power and harmonics, it greatly extends the life of key mechanical components, reduces overall costs and maintenance requirements, and can precisely control the output load voltage. The compensation path is short and the efficiency is high, which can maximize the high-precision advantage of fine adjustment of the power electronic device. It is particularly suitable for medium-voltage distribution network scenarios such as data centers, precision manufacturing, and medical equipment that are sensitive to power quality.

[0019] 2. The voltage compensation power module and current compensation power module of the present invention adopt fully controlled power switching devices, which can achieve optimal compensation waveform quality and dynamic response speed, and are suitable for high-end power quality management scenarios.

[0020] 3. The voltage compensation power module and the current compensation power module of the present invention share a DC support unit, forming a back-to-back structure; the current compensation power module not only provides reactive power and harmonic compensation, but also provides an active power path for the voltage compensation power module, maintaining the stability of the DC bus voltage, and realizing internal energy circulation and efficient coordination.

[0021] 4. The medium-voltage voltage regulation system of the present invention is equipped with a DC port, which can be flexibly connected to DC distributed energy sources such as photovoltaics and energy storage, or DC loads such as electric vehicle charging piles. This makes the medium-voltage voltage regulation system of the present invention not only able to improve power quality, but also able to act as an energy router, promoting the local consumption of new energy sources and system interaction, which is in line with the development direction of new power systems.

[0022] 5. The voltage regulation method of the present invention divides the adjustment range by dual thresholds, avoids frequent operation of the tap switching mechanism, extends the service life of the equipment, reduces maintenance costs, and improves the long-term operational stability of the system. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of one topology of the medium-voltage regulating system of the present invention.

[0024] Figure 2 This is a schematic diagram of another topology of the medium-pressure regulating system of the present invention.

[0025] Figure 3 This is a schematic diagram of another topology of the medium-voltage regulating system of the present invention.

[0026] Figure 4 This is a flowchart of the voltage regulation method of the present invention. Detailed Implementation

[0027] First, let's explain the terminology used in this invention: Tapped voltage regulating transformer Tr1: This transformer employs an autotransformer structure, with its autotransformer winding connected in series in the medium-voltage main line. Multiple voltage adjustment taps are installed on the winding, and a tap switching mechanism is used to change the effective number of turns of the winding by switching different taps, achieving a wide range of output voltage adjustment. This is the core coarse adjustment device of this invention. The tap switching mechanism can, for example, use a vacuum on-load tap changer to achieve arc-free switching.

[0028] The voltage compensation unit consists of a series transformer Tr3 and a voltage compensation power module. The primary side of the series transformer Tr3 is connected in series with the output side of Tr1, serving as electrical isolation and voltage matching. The voltage compensation power module is a power electronic converter with both AC and DC sides. By outputting a controllable AC compensation voltage, it achieves fine voltage adjustment and three-phase imbalance compensation, and is the core fine-tuning device of this invention.

[0029] The current compensation unit consists of a parallel transformer Tr2 and a current compensation power module. The primary side of the parallel transformer Tr2 is connected in parallel to the medium-voltage main line to achieve electrical isolation and voltage level matching. The current compensation power module is a power electronic converter that injects controllable compensation current into the main line to achieve reactive power compensation, harmonic suppression, and three-phase unbalanced current management. It is the core device for power quality management in this invention.

[0030] DC support unit: A device or combination of devices that provides voltage support and energy buffering on the DC side of voltage-compensated power modules and current-compensated power modules. It includes two connection forms: ① The DC sides of two power modules are connected to a common DC support unit to achieve shared DC support; ② The DC sides of two power modules are each connected to an independent DC support unit to achieve independent DC support.

[0031] Fully controlled power semiconductor switching devices: power electronic switching devices that can be actively controlled to turn on and off via control signals, including but not limited to insulated gate bipolar transistors (IGBTs) and silicon carbide metal oxide semiconductor field-effect transistors (SiC-MOSFETs). Unlike semi-controlled devices, they feature high switching frequency and flexible control.

[0032] Shared DC bus: A common DC transmission line formed by connecting the DC side of the voltage-compensated power module and the DC side of the current-compensated power module, which enables energy exchange between the two power modules.

[0033] Central Controller: As the core control unit of the medium-voltage voltage regulation system, it possesses functions such as operating parameter monitoring, deviation calculation, hierarchical voltage regulation control, power quality management control, DC voltage stabilization control, collaborative scheduling, and remote communication interaction. The central controller acquires the three-phase voltage and three-phase current of the medium-voltage main line in real time, as well as the synchronous phase voltage signal of the autotransformer winding of the tapped voltage regulating transformer Tr1, through voltage acquisition, current acquisition, and signal processing units. It calculates the voltage deviation value and judges it according to preset thresholds, realizing the drive control of the tap switching mechanism to complete wide-range coarse voltage adjustment. Simultaneously, the central controller calculates the fine voltage compensation and voltage imbalance compensation amounts, and drives the voltage compensation power module through duty cycle control to inject compensation voltage into the main line via the series transformer Tr3, achieving high-precision fine voltage adjustment and imbalance correction. For the reactive power component, harmonic component, and imbalance component in the line current, the central controller calculates the corresponding compensation current command, drives the current compensation power module to inject compensation current through the parallel transformer Tr2, and completes reactive power compensation, harmonic suppression, and imbalance management. Furthermore, the central controller maintains DC-side voltage stability by adjusting the active power exchange between the current compensation power module and the main line, providing a stable DC operating voltage for both the voltage compensation power module and the current compensation power module. The central controller also interacts with external devices through a communication unit, receiving remote control commands and uploading system operating parameters, enabling remote monitoring and intelligent scheduling of the system.

[0034] See Figures 1 to 3 In one embodiment of the present invention, a medium-voltage voltage regulation system is proposed for use in a three-phase medium-voltage distribution network main line. The system includes: a tapped voltage regulating transformer Tr1, whose autotransformer winding is connected in series in the medium-voltage main line, and has multiple taps and a tap switching mechanism for switching the multiple taps; a voltage compensation unit, including a series transformer Tr3 and a voltage compensation power module having AC and DC sides; the primary side of the series transformer Tr3 is connected in series to the input side of the tapped voltage regulating transformer Tr1, and its secondary side is connected to the AC side of the voltage compensation power module; a current compensation unit, including a parallel transformer Tr2 and a current compensation power module having AC and DC sides; the primary side of the parallel transformer Tr2 is connected in parallel to the medium-voltage main line, and its secondary side is connected to the AC side of the current compensation power module; and a DC support unit; wherein the DC sides of the voltage compensation power module and the current compensation power module are connected to the same DC support unit, or are connected to different DC support units respectively.

[0035] It is worth mentioning that this invention uses an autotransformer as the tapped voltage regulating transformer Tr1 for the following reasons: The series winding of an autotransformer is naturally suitable for setting multiple taps, and with the tap switching mechanism, the effective number of turns in the winding can be flexibly changed, achieving a wide range of step-like coarse adjustment of the medium voltage; unlike ordinary two-winding transformers, autotransformers do not require separate full-capacity windings for the primary and secondary sides, only a common winding and a series winding are needed. The amount of wire used in the windings is far less than that of a two-winding transformer of the same capacity, directly reducing copper losses and improving overall operating efficiency; the transmission capacity of an autotransformer consists of two parts: electromagnetic induction transmission and direct electrical conduction, wherein… Direct electrical conduction eliminates the need for electromagnetic conversion through a magnetic core, resulting in no magnetic conversion losses. Therefore, autotransformers of the same capacity are far more efficient than ordinary two-winding transformers. For the same volume and weight, autotransformers offer a larger effective output capacity, making them suitable for the high-capacity voltage regulation and power transmission needs of medium-voltage distribution networks. Medium-voltage distribution networks are a crucial link connecting high-voltage grids and low-voltage users, characterized by long lines, large load fluctuations, and wide voltage regulation range requirements. The wide-range voltage regulation, large capacity, high efficiency, and small size of autotransformers perfectly suit this scenario. Furthermore, their series connection to the main line eliminates the need to alter the existing topology of the medium-voltage distribution network, resulting in low engineering modification costs and easy promotion.

[0036] According to the above embodiments, the voltage compensation unit is connected in series with the input side of the tapped voltage regulating transformer Tr1, which allows for precise compensation of the input voltage in advance. This enables the power electronic devices in the voltage compensation unit to "preprocess" grid voltage disturbances in real time, preventing grid voltage fluctuations from being transmitted to the output side of Tr1. Mechanical tap switching is only initiated when the voltage deviation continuously exceeds the capacity of the power electronic devices. This achieves wide-range, high-precision continuous voltage regulation and comprehensive management of reactive power and harmonics, while greatly extending the life of key mechanical components, reducing overall costs and maintenance requirements. Moreover, it can precisely control the output load voltage, with a short compensation path and high efficiency, maximizing the high-precision advantages of fine-tuning by the power electronic devices. It is particularly suitable for medium-voltage distribution network scenarios such as data centers, precision manufacturing, and medical equipment that are sensitive to power quality. The current compensation unit is connected in parallel with the main line, which can simultaneously achieve reactive power compensation, harmonic suppression, and other functions without the need for additional independent equipment, reducing system deployment costs and improving the power supply quality of the medium-voltage distribution network. In addition, the DC side of the two power modules is connected to the DC support unit, which can suppress DC side voltage fluctuations and provide stable voltage support for the switching devices of the power modules in the voltage compensation unit and current compensation unit to turn on and off, avoiding the decrease in compensation accuracy or device damage caused by DC voltage fluctuations.

[0037] In one embodiment of the present invention, the voltage compensation power module and the current compensation power module use fully controllable power semiconductor switching devices as switching devices. Preferably, IGBTs can be used because IGBTs combine the advantages of high input impedance of MOSFETs and low on-state voltage drop of GTRs, resulting in low switching losses and strong load-carrying capacity, thus ensuring the reliability and stability of circuit operation. Compared with traditional semi-controlled devices such as thyristors, fully controllable power semiconductor switching devices have high switching frequency and fast response speed, enabling rapid output of controllable compensation voltage and current, improving voltage regulation accuracy and power quality management, and adapting to adjustment requirements under different operating conditions. This avoids the shortcomings of semi-controlled devices such as adjustment lag and inflexible control, while reducing device losses and improving circuit operating efficiency.

[0038] In one embodiment of the present invention, the current compensation power module and the voltage compensation power module are each a multilevel converter or a two-level converter. The multilevel converter is, for example, a three-level NPC converter and a modular multilevel converter (MMC). Multilevel converters are selected for high-voltage, high-capacity scenarios to reduce voltage stress on switching devices, reduce output harmonics, and avoid the problem of severe harmonic pollution caused by two-level converters in high-voltage scenarios. Two-level converters are selected for medium- and low-voltage, small-capacity scenarios to simplify the topology, reduce the number of devices, and reduce hardware costs, thus balancing economy and practicality. The two converter types can be flexibly switched to expand the applicable range of the circuit and adapt to medium-voltage distribution networks of different voltage levels and capacities.

[0039] See again Figure 1 In one embodiment of the present invention, the primary side of the parallel transformer Tr2 is connected in parallel to the medium-voltage main line of the output side of the tapped voltage regulating transformer Tr1. This circuit topology can directly monitor the voltage and current on the load side, and can specifically address the power quality problems that still exist after voltage regulation by Tr1, ensuring that the final power quality supplied to the load meets the standards, while avoiding the power quality problems from affecting the fine and coarse adjustment effects.

[0040] See again Figure 2 In one embodiment of the present invention, the primary side of the parallel transformer Tr2 is connected in parallel to the medium-voltage main line connected to the primary input terminal of the series transformer Tr3. This circuit topology can address potential power quality issues from the grid side at the source, prevent poor power from being transmitted to the load side through Tr3 and Tr1, and ensure that fine-tuning steps can be accurately compensated based on clean voltage signals.

[0041] See again Figure 3In one embodiment of the present invention, the primary side of the parallel transformer Tr2 is connected in parallel to the medium-voltage main line between the primary output terminal of the series transformer Tr3 and the input terminal of the tapped voltage regulating transformer Tr1. This circuit topology can mitigate the harmonics that may be generated during the operation of Tr3, and at the same time correct the voltage and current deviation between the grid side and the output side of Tr3, further purify the voltage signal input to Tr1, and improve the accuracy of fine and coarse adjustment.

[0042] In one embodiment of the present invention, the DC side of the voltage-compensated power module and the DC side of the current-compensated power module are interconnected through the same DC support unit to construct a shared DC bus. This DC bus enables energy exchange between the DC sides of the two power modules, reducing the number of components in the DC support unit, simplifying the circuit structure, reducing equipment size, and lowering costs. Simultaneously, it achieves energy complementarity; when one power module experiences energy fluctuations, the shared DC bus can buffer the fluctuations, improving the stability of the DC side voltage and avoiding problems such as excessive voltage fluctuations and unstable power module operation caused by independent DC support. Specifically, the DC support unit includes a DC support capacitor. The DC support capacitor has a simple structure, low cost, and good energy buffering effect, stabilizing the DC side voltage and providing a reliable DC operating voltage for the power module. This avoids problems such as high costs and inconvenient maintenance caused by using complex components in the DC support unit, while ensuring the stability of the DC side voltage, improving the operational reliability of the power module, and indirectly extending the service life of the entire voltage regulation circuit.

[0043] In one embodiment of the present invention, the medium-voltage regulating circuit further includes a DC port connected to the DC bus for connecting to an external DC source or load. The DC port enables the system of the present invention to have AC / DC hybrid power supply capability, allowing connection to distributed DC sources such as photovoltaics and energy storage batteries, thus improving the renewable energy absorption capacity. Simultaneously, it can connect to DC loads such as DC charging piles, adapting to new power load demands and expanding the system's application scenarios. The DC port enables energy interaction between the DC source and the AC distribution network. For example, energy storage batteries can charge during off-peak hours and discharge during peak hours, helping to smooth voltage fluctuations in the distribution network and improving the flexibility and economy of energy dispatch. The external DC source can serve as a backup power source, providing temporary power to the compensation power module when the system malfunctions, improving the redundancy and reliability of system operation.

[0044] In one embodiment of the present invention, a medium-voltage voltage regulating system is provided, which employs the medium-voltage voltage regulating circuit described above. The medium-voltage voltage regulating system further includes a voltage acquisition unit, a current acquisition unit, a signal processing unit, a communication unit, and a central controller. The voltage acquisition unit is used to acquire the three-phase voltage signals of the medium-voltage main line and the phase synchronous voltage signals of each phase of the autotransformer of the tapped voltage regulating transformer Tr1, and transmits the acquired signals to the signal processing unit. The current acquisition unit is used to acquire the current signals of the medium-voltage main line and transmit the acquired signals to the signal processing unit. The signal processing unit is used to receive the signals transmitted by the voltage acquisition unit and the current acquisition unit, preprocess the signals, and send them to the central controller. The communication unit is used to receive external control commands from external devices and transmit the received external control commands to the central controller. The central controller is used to generate control commands based on the voltage and current signals from the signal processing unit and / or based on the external control commands from the communication unit, and sends the control commands to at least one of the tap switching mechanism, voltage compensation power module, and current compensation power module of the tapped voltage regulating transformer Tr1.

[0045] According to the medium-voltage regulating system of the present invention, the voltage acquisition unit and the current acquisition unit realize the acquisition of all electrical parameters, providing accurate data support for control decisions; the signal processing unit preprocesses the acquired signals, filters interference signals, completes analog-to-digital conversion, and improves the accuracy of control commands; the communication unit realizes the reception and forwarding of external commands, breaking the limitations of traditional local control and supporting remote monitoring and scheduling; the central controller can be an industrial-grade PLC, configured with a dedicated power algorithm module, which serves as the control core, integrating functions such as data acquisition, command generation, and execution control to achieve coordinated control of voltage regulation and compensation, while supporting both "local signal acquisition control" and "remote command control" modes, improving the system's intelligence level and flexibility.

[0046] In one embodiment of the present invention, the voltage acquisition unit is a medium-voltage voltage transformer, which features high insulation level and high precision, enabling safe and accurate acquisition of medium-voltage main line voltage signals. The current acquisition unit is a Rogowski coil, which has fast response speed and no saturation characteristics, making it suitable for acquiring large current signals of dynamic changes in medium-voltage lines, ensuring the reliability of data acquisition under medium-voltage conditions. The communication unit supports wired communication such as Ethernet or wireless communication such as 5G, and can be flexibly selected according to the communication conditions of the distribution network site (e.g., wireless communication in remote areas and wired communication in urban areas), improving the system's installation and operational adaptability. It establishes communication connections with external devices such as external distribution network dispatch centers, receives external control commands (such as target voltage setting and adjustment mode switching), and uploads system operating parameters (such as line voltage, current, DC bus voltage, and compensation). The signal processing unit is an embedded microprocessor integrating signal filtering and analog-to-digital conversion modules, possessing high-speed computing capabilities, capable of quickly completing signal filtering and analog-to-digital conversion, ensuring real-time data processing, avoiding control command lag due to data delay, and improving system response speed.

[0047] like Figure 4 As shown, the present invention also provides a voltage regulation method for the medium-voltage voltage regulation system of the present invention. This voltage regulation method is executed by a central controller and includes: S1, monitoring the three-phase voltage of the medium-voltage main line and the synchronous phase voltage signals of each phase of the autotransformer of the tapped voltage regulating transformer Tr1, and calculating a first voltage deviation value of the monitored three-phase voltage relative to the target voltage; S2, determining whether the first voltage deviation value is greater than a preset second threshold; if so, calculating the required fine voltage compensation amount and / or voltage imbalance compensation amount based on the synchronous phase voltage signals of each phase, and generating control commands to drive the voltage compensation power module to inject corresponding voltage into the medium-voltage main line through the series transformer Tr3. If the compensation voltage is not specified, no adjustment is made and execution is terminated; S3, continue monitoring the three-phase voltage of the medium-voltage main line and the synchronous phase voltage signal of each phase of the autotransformer Tr1, and calculate the second voltage deviation value of the monitored three-phase voltage relative to the target voltage. Determine whether the second voltage deviation value is greater than the preset first threshold. If not, end the adjustment and terminate execution; if so, generate a control command to drive the tap switching mechanism of the tap-type voltage regulating transformer Tr1 to switch taps and perform wide-range coarse voltage adjustment; wherein the second threshold is less than the first threshold. For example, the first threshold is, for example, 10% of the main line voltage, and the second threshold is, for example, 5% of the main line voltage. It should be noted that the operation of calculating the required fine voltage compensation amount and / or voltage imbalance compensation amount based on the synchronous phase voltage signal of each phase is not an innovation of this invention. This operation can be carried out using existing technology.

[0048] According to this voltage regulation method of the present invention, the instantaneous disturbances on the grid side are first suppressed by fine adjustment, and then the large-range voltage deviation is solved by coarse adjustment, taking into account both instantaneous stability and wide-range voltage regulation requirements. At the same time, the rationality of voltage regulation operation is ensured by two voltage deviation judgments, avoiding unnecessary coarse adjustment operations, reducing equipment losses, improving system operating efficiency and stability, and adapting to scenarios with frequent grid-side voltage disturbances and high requirements for instantaneous voltage stability.

[0049] In one embodiment of the present invention, the current of the medium-voltage main line is also monitored simultaneously. Based on the synchronous phase voltage signals of each phase, the required reactive power compensation current, unbalanced current mitigation amount, and harmonic compensation current are calculated, and control commands are generated to drive the current compensation power module to inject the corresponding compensation current into the medium-voltage main line through the parallel transformer Tr2. This power quality management step integrates voltage regulation and power quality management, solving the shortcomings of traditional voltage regulation methods that can only adjust voltage but cannot improve power quality. While regulating voltage, the line current is monitored simultaneously, and reactive power is compensated, harmonics are suppressed, and three-phase imbalance is mitigated to improve power quality. No additional independent power quality management device is required, reducing the overall system cost. It is executed synchronously with the voltage regulation step without affecting the voltage regulation efficiency, achieving the dual goals of voltage stability and high-quality power, and adapting to the needs of new distribution networks with a large number of distributed power sources and increasing nonlinear loads. It should be noted that the operation of calculating the required reactive power compensation current, unbalanced current mitigation amount, and harmonic compensation current based on the synchronous phase voltage signals of each phase is not an innovation of the present invention; this operation can be performed using existing technology.

[0050] In one embodiment of the present invention, the active power exchange between the current compensation power module and the medium-voltage main line can also be adjusted to maintain the DC-side voltage stability of the current compensation power module. It should be noted that adjusting the active power exchange between the current compensation power module and the medium-voltage main line is not an innovation of the present invention; this operation can be performed using existing technology. This DC-side voltage stabilization control step can solve the problem of DC-side voltage fluctuations during power module operation, affecting adjustment effectiveness and equipment reliability. By adjusting the active power exchange between the current compensation power module and the main line, closed-loop stabilization of the DC-side voltage is achieved, ensuring that both the voltage compensation power module and the current compensation power module obtain a stable DC operating voltage, improving adjustment accuracy and the operational reliability of the power module. According to this DC-side voltage stabilization control step, regardless of whether the DC support unit adopts a shared or independent connection form, voltage stabilization control can be achieved, adapting to different topology scenarios, while avoiding device damage caused by abnormal DC-side voltage, extending the service life of the entire system, and improving the stability and safety of system operation.

Claims

1. A medium voltage regulating circuit applied to a main line of a three-phase medium voltage distribution network, characterized in that, The medium voltage regulating circuit comprises: a tap regulating transformer Tr1, which is connected in series with the autotransformer winding in the medium voltage main line and is provided with a plurality of taps and a tap switching mechanism for switching the plurality of taps; a voltage compensation unit, which comprises a series transformer Tr3 and a voltage compensation power module having an alternating current side and a direct current side; the primary side of the series transformer Tr3 is connected in series with the input side of the tap regulating transformer Tr1, and the secondary side of the series transformer Tr3 is connected with the alternating current side of the voltage compensation power module; a current compensation unit, which comprises a parallel transformer Tr2 and a current compensation power module having an alternating current side and a direct current side; the primary side of the parallel transformer Tr2 is connected in parallel on the medium voltage main line, and the secondary side of the parallel transformer Tr2 is connected with the alternating current side of the current compensation power module; a direct current support unit; wherein the direct current sides of the voltage compensation power module and the current compensation power module are commonly connected to the same direct current support unit, or are respectively connected to different direct current support units.

2. Medium voltage regulating circuit according to claim 1, characterized in that The voltage compensation power module and the current compensation power module both use fully controlled power semiconductor switching devices as switching devices.

3. Medium voltage regulating circuit according to claim 2, characterized in that The fully controlled power semiconductor switching devices are IGBTs.

4. Medium voltage regulating circuit according to claim 2, characterized in that The current compensation power module and the voltage compensation power module are each a multi-level inverter or a two-level inverter.

5. The medium voltage regulating circuit of claim 1, wherein, The primary side of the parallel transformer Tr2 is connected in parallel at one of the following positions: the output side of the tap regulating transformer Tr1 in the medium voltage main line; the medium voltage main line connected with the input end of the primary side of the series transformer Tr3; or the medium voltage main line between the input end of the primary side of the series transformer Tr3 and the input end of the tap regulating transformer Tr1.

6. Medium voltage regulating circuit according to claim 1, characterized in that The direct current sides of the voltage compensation power module and the current compensation power module are connected with each other through the same direct current support unit to construct a shared direct current bus.

7. Medium voltage regulating circuit according to claim 6, characterized in that A direct current port is further included, which is connected with the direct current bus and is used for accessing an external direct current source or load.

8. Medium voltage regulating circuit according to any of claims 1 to 7, characterized in that The direct current support unit comprises a direct current support capacitor.

9. Medium voltage pressure regulating system, characterized in that The medium voltage regulating circuit according to any one of claims 1 to 8 further comprises a voltage acquisition unit, a current acquisition unit, a signal processing unit, a communication unit and a central controller, wherein the voltage acquisition unit is used for acquiring three-phase voltage signals of the medium voltage main line and each-phase synchronous phase voltage signals of the autotransformer winding of the tap regulating transformer Tr1, and transmitting the acquired signals to the signal processing unit; the current acquisition unit is used for acquiring current signals of the medium voltage main line and transmitting the acquired signals to the signal processing unit; the signal processing unit is used for receiving the signals transmitted by the voltage acquisition unit and the current acquisition unit, and sending the preprocessed signals to the central controller; the communication unit is used for receiving external control instructions from an external device and transmitting the received external control instructions to the central controller; and the central controller is used for receiving the preprocessed signals from the signal processing unit and the external control instructions from the communication unit, and controlling the tap regulating transformer Tr1, the voltage compensation unit and the current compensation unit according to the received signals and external control instructions. The central controller is configured to generate a control instruction according to the voltage signal and the current signal from the signal processing unit, and / or according to an external control instruction from the communication unit, and send the control instruction to at least one of the tap switching mechanism of the tap voltage regulating transformer Tr1, the voltage compensation power module, and the current compensation power module.

10. Medium voltage pressure regulating system according to claim 9, characterized in that The voltage collection unit is a medium voltage level voltage transformer; the current collection unit is a Rogowski coil; the communication unit supports wired communication or wireless communication; and the signal processing unit is an embedded microprocessor integrated with a signal filtering and analog-to-digital conversion module.

11. A method for regulating the pressure of a medium voltage regulating system according to any one of claims 9-10, characterized in that, The voltage regulating method is executed by the central controller, and includes the following steps: S1, monitoring three-phase voltages of a medium voltage main line and each phase synchronous phase voltage signal of a self-coupling winding of the tap voltage regulating transformer Tr1, and calculating a first voltage deviation value of the monitored three-phase voltages relative to a target voltage; S2, judging whether the first voltage deviation value is greater than a preset second threshold value, if yes, calculating a required fine voltage compensation amount and / or voltage imbalance compensation amount based on the each phase synchronous phase voltage signal, and generating a control instruction to drive the voltage compensation power module to inject a corresponding compensation voltage into the medium voltage main line through the series transformer Tr3; if no, no adjustment is performed and the execution is terminated; S3, continuing to monitor the three-phase voltages of the medium voltage main line and the each phase synchronous phase voltage signal of the self-coupling winding of the tap voltage regulating transformer Tr1, and calculating a second voltage deviation value of the monitored three-phase voltages relative to the target voltage, judging whether the second voltage deviation value is greater than a preset first threshold value, if no, ending the adjustment and terminating the execution; if yes, generating a control instruction to drive the tap switching mechanism of the tap voltage regulating transformer Tr1 to switch the tap, and performing voltage wide-range coarse adjustment; wherein the first threshold value is greater than the second threshold value.

12. The pressure regulating method of claim 11, wherein, Further comprising: simultaneously monitoring a current of the medium voltage main line, and calculating a required reactive compensation current, imbalance current treatment amount, and harmonic compensation current based on the each phase synchronous phase voltage signal, and generating a control instruction to drive the current compensation power module to inject a corresponding compensation current into the medium voltage main line through the parallel transformer Tr2.

13. The pressure regulating method of claim 12, wherein, Further comprising: adjusting active power exchange between the current compensation power module and the medium voltage main line to maintain the stability of the direct current side voltage of the current compensation power module.

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