Low-voltage single-phase power supply method suitable for high-proportion distributed source load access

Abstract

The invention discloses a low-voltage single-phase power supply method suitable for high-proportion distributed source load access, and the method comprises the steps: monitoring three-phase current in real time, and controlling a three-phase converter to transfer unbalanced current among three phases when unbalance occurs, so as to enable the three-phase current to tend to be balanced; monitoring power grid harmonics in real time, and controlling the converter to generate reverse harmonic current for counteracting; the output of the converter is dynamically adjusted according to network voltage and reactive power requirements, reactive power compensation is realized, and voltage stability is maintained; an optimization model is established, energy coordinated optimization scheduling is achieved, and the energy utilization efficiency is improved; operation parameters are monitored in real time, the power grid is optimized and controlled, the stability and the capacity of the power grid are improved, and better flexible access conditions are provided for high-proportion distributed source loads; the problems of low-voltage three-phase imbalance, voltage fluctuation and flicker, harmonic waves, voltage out-of-limit and the like can be solved on site, the power supply quality and reliability of rural areas are improved, more stable power supply is provided for residents in the rural areas, and therefore the living quality is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of AC and DC power distribution networks, and in particular relates to a low-voltage single-phase power supply method suitable for access of high-proportion distributed sources and loads. Background Art

[0002] The current power supply and grid regulation capabilities are limited. There are problems such as low voltage qualification rate, large line loss, serious three-phase imbalance, limited access capacity of distributed photovoltaic power generation and AC charging piles for electric vehicles. In addition, a large number of distributed power sources are connected to the low-voltage single-phase distribution network, making power quality problems such as three-phase imbalance, voltage over-limit, harmonics, voltage fluctuation and flicker more prominent, seriously affecting the safe and high-quality power supply of the low-voltage distribution network. It is urgent to further break through the low-voltage safe and high-quality power supply technology and distributed power consumption technology. The three-phase imbalance of the existing low-voltage distribution network is mainly solved by phase-changing switches, but phase-changing switches can only partially solve the three-phase imbalance problem, and there are risks such as phase-to-phase short circuit and short-term power supply interruption. In order to solve the above problems, it is necessary to develop a low-voltage single-phase power supply method that is suitable for high-proportion distributed source-load access. Summary of the invention

[0003] The purpose of the present invention is to overcome the shortcomings of the prior art and to provide a low-voltage single-phase power supply method that is suitable for access to a high proportion of distributed sources and loads. The method can solve the problems of low-voltage three-phase imbalance, voltage fluctuation and flicker, harmonics, voltage over-limit, etc. on-site, improve the power supply quality and reliability in rural areas, and provide a more stable power supply for residents in rural areas, thereby improving the quality of life.

[0004] The object of the present invention is achieved as follows: a low-voltage single-phase power supply method adapted to high-proportion distributed source-load access comprises the following steps:

[0005] (1) Real-time detection of the three-phase current in the low-voltage single-phase power supply area, and the use of advanced control algorithms to monitor and analyze the collected three-phase current in real time. When an imbalance occurs, the unbalanced current is transferred between the three phases by controlling the three-phase converter, so that the three-phase current tends to be balanced, so that the low-voltage single-phase distribution network is always maintained in a three-phase balanced state;

[0006] (2) Real-time detection of harmonic components in the power grid, identification of harmonic components using harmonic detection algorithms, and control of the converter to generate reverse harmonic currents to offset them, thereby reducing the impact of harmonics on the power grid;

[0007] (3) Using reactive power compensation algorithm, dynamically adjust the output of the converter according to the voltage and reactive power demand of the power grid to achieve reactive power compensation and maintain voltage stability;

[0008] (4) Establish a coordinated optimization model for source, grid, load and storage in low-voltage single-phase power supply substations, communicate with distributed power sources, energy storage systems and loads in the substations, realize coordinated optimization scheduling among different energy sources in the substations, and improve energy utilization efficiency;

[0009] (5) Real-time detection of low-voltage grid operating parameters, adoption of flexible power supply quality control technology, and optimization and control of the grid to improve grid stability and capacity, providing better flexible access conditions for high-proportion distributed sources and loads.

[0010] Preferably, high-performance power electronic devices are used to construct the three-phase converter, wherein the power electronic devices include IGBT and MOSFET.

[0011] Preferably, the advanced control algorithm includes a fuzzy control algorithm and a neural network control algorithm.

[0012] Preferably, the harmonic detection algorithm is a fast Fourier transform algorithm.

[0013] Preferably, the reactive power compensation algorithm includes a power factor-based algorithm, an instantaneous reactive power theory algorithm and a fuzzy logic-based reactive power compensation algorithm.

[0014] Preferably, the low-voltage single-phase power supply station area source-grid-load-storage coordination optimization model consists of an objective function and constraints for minimizing the total operating cost.

[0015] Preferably, the flexible power supply quality control technology specifically includes: real-time monitoring of low-voltage power grid operating parameters, and use of power electronic devices to accurately control the transmission and conversion of electric energy.

[0016] Preferably, the low-voltage power grid operating parameters include voltage, current, power and phase.

[0017] Preferably, the power electronic device is a flexible AC transmission system device and a power electronic transformer, wherein the flexible AC transmission system device is a static VAR compensator, a static VAR generator and a thyristor-controlled series capacitor.

[0018] Due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0019] (1) The present invention adopts real-time detection of three-phase current, advanced control algorithm and three-phase converter to effectively solve the three-phase imbalance problem of low-voltage distribution network, reduce line loss rate and improve the reliability and stability of the power grid;

[0020] (2) The present invention adopts real-time harmonic detection, harmonic detection algorithm and reactive power compensation algorithm to achieve harmonic control and voltage reactive power control, thereby improving the power quality of the power grid;

[0021] (3) The present invention adopts real-time detection of grid operation parameters and flexible power supply quality control technology to improve the access capacity of distributed power sources and loads and promote the development and popularization of renewable energy;

[0022] (4) The present invention adopts a source-grid-load-storage coordinated optimization model to improve energy utilization efficiency and achieve sustainable development;

[0023] (5) The present invention adopts a new type of low-voltage single-phase safe and high-quality power supply technology with a high proportion of distributed sources and loads that are flexibly connected, which solves the problems of low-voltage three-phase imbalance, voltage fluctuation and flicker, harmonics, voltage over-limit, etc. on the spot, improves the power supply quality and reliability in rural areas, and provides more stable power supply for residents in rural areas, thereby improving the quality of life. DETAILED DESCRIPTION

[0024] The technical solution of the present invention is further specifically described below through embodiments.

[0025] The present invention provides a low-voltage single-phase power supply method suitable for high-proportion distributed source-load access, which is specifically implemented through the following five method steps.

[0026] The first step is to detect the three-phase current of the low-voltage single-phase power supply station in real time, and use advanced control algorithms to monitor and analyze the collected three-phase current in real time. When an imbalance occurs, the unbalanced current is transferred between the three phases by controlling the three-phase converter to balance the three-phase current, so that the low-voltage single-phase distribution network is always maintained in a three-phase balanced state.

[0027] Among them, it is critical to use high-performance power electronic devices (such as IGBT, MOSFET, etc.) to build a three-phase converter. A three-phase converter with good performance is related to the accuracy of three-phase parameter detection and the stability of three-phase regulation.

[0028] The advanced control algorithm can adopt the fuzzy control algorithm and neural network control algorithm of the existing technology.

[0029] The second step is to detect the harmonic components in the power grid in real time, use the most commonly used harmonic detection algorithms such as fast Fourier transform to identify the harmonic components, and control the converter to generate reverse harmonic current to offset them, thereby reducing the impact of harmonics on the power grid.

[0030] The third step is to use a reactive power compensation algorithm to dynamically adjust the output of the converter according to the voltage and reactive power requirements of the power grid to achieve reactive power compensation and maintain voltage stability.

[0031] The reactive power compensation algorithm includes a power factor-based algorithm, an instantaneous reactive power theory algorithm and a fuzzy logic-based reactive power compensation algorithm, and the instantaneous reactive power theory algorithm is preferred.

[0032] The instantaneous reactive power theoretical algorithm (taking a three-phase circuit as an example) to achieve reactive power compensation is explained below.

[0033] First, the three-phase voltage u a 、u b 、u c and three-phase current i a 、i b 、i c The coordinate system is converted into the α-β coordinate system or the dq coordinate system through coordinate transformation (such as Clarke transformation and Park transformation).

[0034] Then, in the α-β coordinate system, the instantaneous reactive power Instantaneous active power

[0035] Finally, according to the calculation result of instantaneous reactive power, the reactive power compensation device (such as static VAR compensator SVC or static VAR generator SVG) is controlled to generate or absorb corresponding reactive power to achieve reactive power compensation.

[0036] The fourth step method is: establish a low-voltage single-phase power supply substation source-grid-load-storage coordinated optimization model, communicate with the substation's distributed power sources, energy storage systems and loads, achieve coordinated optimization scheduling among different energy sources in the substation, and improve energy utilization efficiency.

[0037] The source-grid-load-storage coordination optimization model for low-voltage single-phase power supply stations consists of an objective function and constraints that minimize the total operating cost.

[0038] (1) Objective function: Minimize the total operating cost C total , including the distributed generation cost C DG , Cost of purchasing electricity from the main power grid C grid 、Energy storage system operating cost C ESS and the penalty cost C for unsatisfied load unmet , the calculation formula is:

[0039] C total =C DG +C grid +C ESS +C unmet

[0040] 1. Distributed power generation cost C DG :

[0041] For distributed power sources (such as photovoltaic and wind power generation), the power generation cost is usually related to the power generation and can be expressed as Where T is the total number of time periods, N DG is the number of distributed generation, C DG,iis the unit power generation cost of the ith distributed generation, P DG,i,t is the power generated by the ith distributed generation at time t.

[0042] 2. Cost of purchasing electricity from the main power grid:

[0043] Among them C grid,t is the unit cost of purchasing electricity from the main grid at time t, P grid,t is the power purchased from the main grid at time t.

[0044] 3. Energy storage system operating cost C ESS :

[0045] Including the charging and discharging loss cost and maintenance cost of the energy storage system, it can be expressed as Among them C ch is the unit cost of charging the energy storage system, P ch,t is the charging power of the energy storage system at time t, C dis is the unit cost of discharging the energy storage system, P dis,t is the discharge power of the energy storage system at time t, C maintenance is the unit maintenance cost of the energy storage system, E ESS,t is the stored energy of the energy storage system at time t.

[0046] 4. Penalty cost C for unsatisfied load unmet :

[0047] When the load demand cannot be fully met, a penalty cost will be incurred to encourage the system to meet the load demand as much as possible, expressed as Among them C unmet is the penalty cost per unit of unmet load, P unmet,t is the unmet load power at time t.

[0048] (2) Constraints:

[0049] 1. Power balance constraints:

[0050] At each moment, the total power generation of the system (including distributed power generation and main grid power supply) plus the discharge power of the energy storage system should be equal to the total load demand plus the charging power of the energy storage system, that is, Where P load,t is the total load demand at time t.

[0051] 2. Distributed power output constraints:

[0052] The power generation of distributed generation usually has upper and lower limits, namely in and Respectively, they are the minimum and maximum power generation of the i-th distributed generation.

[0053] 3. Power purchase power constraints of the main power grid:

[0054] The power purchased from the main power grid also has upper and lower limits, namely in and They are the minimum and maximum power purchased from the main grid.

[0055] 4. Energy storage system constraints:

[0056] The storage energy of the energy storage system has upper and lower limits, namely in and are the minimum and maximum storage energies of the energy storage system respectively.

[0057] The charging and discharging power of the energy storage system also has upper and lower limits, namely and in and are the minimum and maximum powers of charging and discharging of the energy storage system, respectively.

[0058] 5. Load demand constraints:

[0059] Load demand is usually known or predictable. At each moment, load demand should be within a certain range, i.e. That and are the minimum and maximum power required by the load, respectively.

[0060] By solving this optimization model, we can obtain the power generation plan of distributed power sources, the power purchase plan of the main power grid, the charging and discharging plan of the energy storage system, and the load scheduling plan, thereby achieving coordinated optimization of source, grid, load and storage and efficient utilization of energy.

[0061] The fifth step is to detect the operating parameters of the low-voltage power grid in real time, adopt flexible power supply quality control technology, and improve the stability and capacity of the power grid through optimized control of the power grid, so as to provide better flexible access conditions for high-proportion distributed sources and loads. Among them, flexible power supply quality control technology is a technology aimed at optimizing the power supply quality of the power grid and improving the adaptability of the power grid.

[0062] First, a large number of sensors are used to monitor various parameters of the low-voltage power grid in real time, including voltage, current, power and phase. That is, high-precision sensors are installed at different nodes of the power grid (such as substations, feeders, etc.) to fully obtain information on the operating status of the power grid in order to accurately grasp the current status of power supply quality.

[0063] Then, power electronic devices, such as flexible AC transmission system devices (including static VAR compensator SVC, static VAR generator SVG, thyristor controlled series capacitor TCSC, etc.) and power electronic transformers, are used to quickly and accurately control the transmission and conversion of electric energy. For example, SVG can quickly inject or absorb reactive power according to the reactive power demand of the power grid by controlling the on and off of internal power semiconductor devices, thereby completing the regulation of the low-voltage power grid voltage.

[0064] In summary, the present invention mainly solves the three-phase imbalance of the low-voltage distribution network through a phase-changing switch, but the phase-changing switch can only partially solve the three-phase imbalance problem, and there are risks such as phase-to-phase short circuit and short-term power supply interruption. Under the development and application trend of power electronics technology, the three-phase imbalance flexible control technology and device can be further studied, which can reduce the three-phase imbalance rate to below 1%, and the control performance and control effect are better. At the same time, it has the functions of harmonic control, voltage reactive power control, source-grid-load-storage coordinated optimization, etc., which can reduce the total harmonic distortion rate to below 1%, and the voltage and power factor qualification rate to more than 99%. It also has a good improvement effect on the single-phase distributed photovoltaic carrying capacity and the access capacity of electric vehicle AC charging piles, and the access capacity is increased by 200%, and the comprehensive line loss rate can also be reduced, and the comprehensive line loss is reduced by 10%.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the specific implementation modes of the present invention can still be modified or replaced by equivalents, and any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A low-voltage single-phase power supply method adapted to high-proportion distributed source-load access, characterized in that: The steps include: (1) Real-time detection of the three-phase current in the low-voltage single-phase power supply area, and the use of advanced control algorithms to monitor and analyze the collected three-phase current in real time. When an imbalance occurs, the unbalanced current is transferred between the three phases by controlling the three-phase converter, so that the three-phase current tends to be balanced, so that the low-voltage single-phase distribution network is always maintained in a three-phase balanced state; (2) Real-time detection of harmonic components in the power grid, identification of harmonic components using harmonic detection algorithms, and control of the converter to generate reverse harmonic currents to offset them, thereby reducing the impact of harmonics on the power grid; (3) Using reactive power compensation algorithm, dynamically adjust the output of the converter according to the voltage and reactive power demand of the power grid to achieve reactive power compensation and maintain voltage stability; (4) Establish a coordinated optimization model for source, grid, load and storage in low-voltage single-phase power supply substations, communicate with distributed power sources, energy storage systems and loads in the substations, realize coordinated optimization scheduling among different energy sources in the substations, and improve energy utilization efficiency; (5) Real-time detection of low-voltage grid operating parameters, adoption of flexible power supply quality control technology, and optimization and control of the grid to improve grid stability and capacity, providing better flexible access conditions for high-proportion distributed sources and loads.

2. The low-voltage single-phase power supply method adapted to high-proportion distributed source-load access according to claim 1 is characterized in that: The three-phase converter is constructed using high-performance power electronic devices, including IGBT and MOSFET.

3. The low-voltage single-phase power supply method adapted to high-proportion distributed source-load access according to claim 1 is characterized in that: The advanced control algorithm includes a fuzzy control algorithm and a neural network control algorithm.

4. The low-voltage single-phase power supply method adapted to high-proportion distributed source-load access according to claim 1 is characterized in that: The harmonic detection algorithm is a fast Fourier transform algorithm.

5. The low-voltage single-phase power supply method adapted to high-proportion distributed source-load access according to claim 1 is characterized in that: The reactive power compensation algorithm includes a power factor-based algorithm, an instantaneous reactive power theory algorithm and a fuzzy logic-based reactive power compensation algorithm.

6. The low-voltage single-phase power supply method adapted to high-proportion distributed source-load access according to claim 1 is characterized in that: The low-voltage single-phase power supply area source-grid-load-storage coordination optimization model consists of an objective function and constraints that minimize the total operating cost.

7. The low-voltage single-phase power supply method adapted to high-proportion distributed source-load access according to claim 1 is characterized in that: The flexible power supply quality control technology is specifically: real-time monitoring of low-voltage power grid operating parameters, using power electronic devices to accurately control the transmission and conversion of electric energy.

8. The low-voltage single-phase power supply method adapted to high-proportion distributed source-load access according to claim 7 is characterized in that: The low voltage grid operation parameters include voltage, current, power and phase.

9. The low-voltage single-phase power supply method adapted to high-proportion distributed source-load access according to claim 7 is characterized in that: The power electronic device is a flexible AC power transmission system device and a power electronic transformer, wherein the flexible AC power transmission system device is a static VAR compensator, a static VAR generator and a thyristor-controlled series capacitor.

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