Micro-grid oriented to extreme climate in cold region and off-grid seamless switching control method
Patent Information
- Application Number
- CN202611244498.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-08-17
- Publication Date
- 2026-09-22
AI Technical Summary
[0004]本申请提供面向寒地极端气候的微电网并离网无缝切换控制方法，以解决基于固定参数的PI算法的PLL锁相环技术无法适应寒地极端气候下间歇性电弧带来的动态强干扰，无法实现寒地微电网并离网无缝切换的精准控制的问题，所采用的技术方案具体如下：
[0025]本申请根据起弧、融冰、熄弧、电压恢复的过程持续高频往复，使公共连接点电压呈现出间歇性、随机性的跌落与恢复波动特性，评价微电网和电网的公共连接点的目标相电压在寒地极端天气下的采集周期内受到间歇性电弧现象影响时，电压的波动程度，获取采集周期的电弧显著度；由于在寒地极端气候环境中，输电及绝缘设备覆冰引发的间歇性电弧干扰作用显著，公共连接点电压相位剧烈波动，导致传统锁相环相位跟踪精度大幅降低，解析微电网和电网的公共连接点的三相电压的相位特征，获取采集周期的相位误差显著度，并结合电弧显著度，分别计算采集周期的增益比例系数和增益积分系数，并确定锁相环输出的采集周期的实时相位；最后，对公共连接点开展孤岛运行状态检测，若公共连接点进入孤岛运行状态，进行微电网由并网向离网的无缝切换，解决基于固定参数的PI算法的PLL锁相环技术无法适应寒地极端气候下间歇性电弧带来的动态强干扰，无法实现寒地微电网并离网无缝切换的精准控制的问题。
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Figure CN122801418A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of microgrid grid-connected / off-grid switching technology, specifically to a seamless grid-connected / off-grid switching control method for microgrids in cold and extreme climate regions. Background Technology
[0002] A microgrid is a controllable small-scale power distribution system composed of wind power, photovoltaics, electrical loads, and energy storage devices. It has both grid-connected and off-grid operating modes and can interact with the main grid through a point of common coupling (PCC). Seamless switching between grid-connected and off-grid operation primarily relies on the mode switching of the energy storage converter. In grid-connected operation, the energy storage converter operates in PQ mode, while in off-grid operation, it switches to VF mode. In the microgrid grid-connected / off-grid control process, islanding detection is the core step in determining the system's grid-connected / off-grid state transition and a crucial prerequisite for ensuring smooth switching and stable power supply. Extreme low temperatures and blizzards in cold regions can easily cause severe icing on transmission lines, leading to intermittent arcing and random fluctuations in the voltage amplitude and phase at the PCC point. This abnormal electrical characteristic is highly similar to the electrical characteristics of a microgrid in islanded operation, easily causing misjudgment by the islanding detection device and incorrect triggering of the microgrid's off-grid operation. This results in drastic voltage and frequency jumps at the PCC point during grid-connected / off-grid switching, making seamless switching impossible and reducing the reliability and power quality of the microgrid's power supply.
[0003] Currently, PLL (Phase-Locked Loop) technology based on a fixed-parameter PI algorithm is widely used to stabilize the voltage at the PCC (Power Control Center) point by tracking the grid phase and correcting phase errors. However, fixed parameters cannot adapt to the strong dynamic interference caused by intermittent electric arcs in cold climates. When the phase fluctuates significantly and randomly, the tracking accuracy of PLL technology will drop sharply, making it impossible to avoid islanding misjudgment and failing to meet the high-precision control requirements for seamless on-grid and off-grid switching in cold microgrids. Summary of the Invention
[0004] This application provides a seamless on-grid / off-grid switching control method for microgrids in cold and extreme climates. It addresses the problem that PLL phase-locked loop technology based on fixed-parameter PI algorithms cannot adapt to the strong dynamic interference caused by intermittent electric arcs in cold and extreme climates, thus failing to achieve precise control for seamless on-grid / off-grid switching in cold and extreme climates. The specific technical solution adopted is as follows:
[0005] One embodiment of this application provides a seamless on-grid / off-grid switching control method for microgrids in cold and extreme climates, the method comprising the following steps:
[0006] Collect the three-phase voltages of the common connection point of the microgrid and the power grid at each collection time within the collection period;
[0007] Based on the values of all phase voltages within the acquisition period and the differences between adjacent phase voltages, the voltage fluctuation of each phase within the acquisition period is calculated, and the arc significance of the acquisition period is obtained. Based on the three-phase voltages within the acquisition period, the voltage quadrature components are determined. Based on the voltage quadrature components, the phase error significance of the acquisition period is calculated. Combined with the arc significance, the gain proportional coefficient and gain integral coefficient of the acquisition period are calculated, and the real-time phase of the acquisition period output by the phase-locked loop is determined.
[0008] The common connection point is monitored for islanded operation status. If the common connection point enters the islanded operation status, the microgrid is seamlessly switched from grid-connected to off-grid.
[0009] Furthermore, the method for calculating the voltage fluctuation is as follows:
[0010] Take any one of the three phases as the target phase, and determine the intermittent arc frequency of the target phase in the acquisition period based on the value of the target phase voltage during the acquisition period.
[0011] The frequency of target phase fluctuations during the acquisition period is determined based on the difference in voltage between adjacent target phases within the acquisition period.
[0012] The product of the sum of the intermittent arc frequency of the target phase during the acquisition period and the digital 1, and the fluctuation frequency, is denoted as the voltage fluctuation of the target phase during the acquisition period.
[0013] Furthermore, the intermittent arc frequency of the target phase during the acquisition cycle is: the ratio of the number of target phase voltages exceeding the standard power supply voltage range within the acquisition cycle to the total number of target phase voltages within the acquisition cycle.
[0014] Furthermore, the fluctuation frequency of the target phase during the acquisition period is: the coefficient of variation of the absolute values of all values in the first-order difference sequence of the target phase voltage sequence during the acquisition period.
[0015] Furthermore, the arc significance of the acquisition period is: the average value of the voltage fluctuation of the three phases during the acquisition period.
[0016] Furthermore, the voltage orthogonal component is the result of converting the three-phase voltage at each acquisition moment within the acquisition cycle into a two-phase stationary coordinate system voltage, and then into a synchronous rotating coordinate system voltage.
[0017] Furthermore, the method for calculating the significance of the phase error during the acquisition period is as follows:
[0018] Obtain the absolute values of each voltage quadrature component in the acquisition period, and extract the maximum absolute value within the acquisition period, which is recorded as the extreme value of the voltage quadrature component in the acquisition period. The ratio of the difference between the extreme value of the voltage quadrature component in the acquisition period and the historical maximum voltage quadrature component in the acquisition period to the historical maximum voltage quadrature component in the acquisition period is recorded as the voltage quadrature ratio of the acquisition period. The maximum value of the voltage quadrature ratio in the acquisition period and the maximum value of the number 0 are recorded as the phase error significance of the acquisition period.
[0019] Furthermore, the method for calculating the gain ratio coefficient is as follows:
[0020] The hyperbolic tangent of the product of the arc significance and the phase error significance during the acquisition period is denoted as the gain ratio of the acquisition period; the product of the sum of the gain ratio of the acquisition period and the number 1, and the preset initial scaling factor is denoted as the gain ratio factor of the acquisition period.
[0021] Furthermore, the gain integral coefficient is the product of the sum of the gain ratio of the acquisition period and the number 1, and the preset initial integral coefficient.
[0022] Furthermore, the method for determining the real-time phase of the acquisition period output by the phase-locked loop is as follows:
[0023] Based on the gain proportional coefficient and gain integral coefficient of the acquisition period, proportional-integral calculations are performed on the voltage quadrature components corresponding to the three-phase voltage at the point of common coupling during the acquisition period to obtain the grid angular frequency estimated by the phase-locked loop; the angular frequency is then integrated to obtain the real-time phase of the acquisition period output by the phase-locked loop.
[0024] The beneficial effects of this application are:
[0025] This application utilizes the continuous high-frequency repetition of the arc initiation, de-icing, arc extinction, and voltage recovery processes to cause the point of common coupling (PCC) voltage to exhibit intermittent and random fluctuations in voltage drop and recovery. It evaluates the degree of voltage fluctuation of the target phase voltage at the PCC of the microgrid and the power grid under intermittent arcing during the acquisition period in extreme cold weather conditions, and obtains the arc significance of the acquisition period. Because the intermittent arcing interference caused by icing of transmission and insulation equipment is significant in extreme cold climates, the PCC voltage phase fluctuates drastically, leading to a significant reduction in the phase tracking accuracy of traditional phase-locked loops (PLLs). This application analyzes the PCC voltage fluctuations of the microgrid and the power grid. The phase characteristics of the three-phase voltage at the common connection point are used to obtain the phase error significance of the acquisition period. Combined with the arc significance, the gain proportional coefficient and gain integral coefficient of the acquisition period are calculated respectively, and the real-time phase of the acquisition period of the phase-locked loop output is determined. Finally, islanding operation status detection is carried out on the common connection point. If the common connection point enters the islanding operation status, the microgrid is seamlessly switched from grid-connected to off-grid. This solves the problem that the PLL phase-locked loop technology based on the fixed parameter PI algorithm cannot adapt to the dynamic strong interference caused by intermittent arcs in cold extreme climates, and cannot achieve precise control of seamless switching between grid-connected and off-grid microgrids in cold regions. Attached Figure Description
[0026] Figure 1 This is a schematic flowchart of a microgrid on-grid / off-grid seamless switching control method for cold-region extreme climates provided in one embodiment of this application.
[0027] Figure 2 This is an equivalent diagram of seamless on-grid / off-grid switching control provided in one embodiment of this application. Detailed Implementation
[0028] Please see Figure 1 The diagram illustrates a flowchart of a microgrid on / off-grid seamless switching control method for extreme cold climates provided in one embodiment of this application. The method includes the following steps:
[0029] Step S001: Collect the three-phase voltage of the common connection point of the microgrid and the power grid at each collection time within the collection period.
[0030] Equivalent diagram of seamless switching control between microgrid and off-grid is shown below. Figure 2 As shown. In Figure 2In the diagram, PCC represents the point of common connection between the microgrid and the grid; a single arrow indicates the current direction between the microgrid and the grid; a double arrow pointing to the right indicates that the energy storage in the microgrid can be supplied to the grid, and a double arrow pointing to the left indicates the direction of the transmission current when the grid supplies power; the grid has two modes: grid-connected and off-grid, and the energy storage converter can switch between PQ and VF operating modes according to the grid's operating mode; 1, 2, 3, and 4 all represent switches. If the grid is in grid-connected mode, switches 1 and 2 are closed, and the energy storage converter switches to PQ operating mode; if the grid is in off-grid mode, switches 3 and 4 are closed, and the energy storage converter switches to VF operating mode.
[0031] Among them, PQ operation mode and VF operation mode are both professional terms for grid-connected and off-grid switching. VF operation mode represents voltage and frequency control mode, while PQ operation mode represents active power and reactive power control mode.
[0032] The three-phase voltage analog signal at the common coupling point (PCC) of the microgrid and the power grid is monitored in real time using a voltage transformer. An RC low-pass filter is used to suppress high-frequency noise in the three-phase voltage analog signal. The three-phase voltage analog signal after suppressing high-frequency noise is discretized by analog-to-digital conversion to obtain the three-phase voltage at each acquisition time of the PCC within the acquisition period.
[0033] In this embodiment, the acquisition period is set to 1 minute and the sampling frequency is set to 10kHz.
[0034] Thus, the three-phase voltages of the common connection point of the microgrid and the power grid at each acquisition time within the acquisition period are obtained.
[0035] Step S002: Based on the values of all phase voltages within the acquisition period and the differences between adjacent phase voltages, calculate the voltage fluctuation of each phase within the acquisition period, and obtain the arc significance of the acquisition period. Based on the three-phase voltages within the acquisition period, determine the voltage quadrature components. Based on the voltage quadrature components, calculate the phase error significance of the acquisition period. Combined with the arc significance, calculate the gain proportional coefficient and gain integral coefficient of the acquisition period, and determine the real-time phase of the acquisition period output by the phase-locked loop.
[0036] In cold, extreme climates, the interconnection lines and insulators between microgrids and the main power grid are prone to icing, leading to intermittent surface discharge arcs on insulators that have not triggered fault trips. Specifically, in extremely low-temperature environments, ice formations on the insulator surface bridge the insulation gaps, continuously triggering surface discharges and causing a momentary drop in the point of common coupling (PCC) voltage. The heat generated by the arc gradually melts the ice, restoring the insulator's insulation performance, extinguishing the arc, and restoring the PCC voltage. This process of arc initiation, ice melting, arc extinguishing, and voltage recovery repeats frequently, causing the PCC voltage to exhibit intermittent, random fluctuations in drop and recovery.
[0037] To evaluate the significance of the intermittent arcing affecting the three-phase voltage at the point of common coupling of the microgrid and the power grid, a standard power supply voltage range is set. Specifically, this embodiment sets the standard power supply voltage range according to the national standard GB / T 12325-2008. Since the nominal voltage of the transmission line is 10kV, the allowable deviation of the three-phase power supply voltage from the nominal voltage is [missing information]. The standard power supply voltage range of this embodiment is: .
[0038] Take any one of the three phases as the target phase, and record the ratio of the number of target phase voltages that exceed the standard power supply voltage range within the acquisition period to the total number of target phase voltages within the acquisition period as the intermittent arc frequency of the target phase during the acquisition period.
[0039] When the proportion of target phase voltages that exceed the standard power supply voltage range of the grid is larger during the acquisition period, the intermittent arc interference suffered by the target phase voltage at the common connection point of the microgrid and the grid during the acquisition period is more severe. At this time, the intermittent arc frequency of the target phase during the acquisition period is greater.
[0040] The target phase voltages within the acquisition period are arranged sequentially according to time order to establish the target phase voltage sequence of the acquisition period. The coefficient of variation of the absolute values of all values in the first-order difference sequence of the target phase voltage sequence of the acquisition period is recorded as the fluctuation frequency of the target phase in the acquisition period. The product of the intermittent arc frequency of the target phase in the acquisition period and the sum of the digital 1 and the fluctuation frequency is recorded as the voltage fluctuation of the target phase in the acquisition period.
[0041] The frequency of target phase voltage fluctuations during the acquisition period is used to evaluate the degree of voltage fluctuations in the target phase voltage at the point of common coupling between the microgrid and the grid, after being affected by intermittent arcing phenomena during the acquisition period under extreme cold weather conditions.
[0042] It is important to understand that an intermittent arc frequency of 0 only indicates that the voltage at the common coupling point of the microgrid and the grid does not exceed the standard supply voltage range of the grid after being affected by intermittent arc interference. It does not indicate that the voltage at the common coupling point of the microgrid and the grid is stable within the standard supply voltage range. Therefore, the sum of the intermittent arc frequency of the target phase and the number 1 during the acquisition period is used to avoid the calculation of the coefficient of variation being meaningless for the voltage fluctuation value when the intermittent arc frequency is equal to 0.
[0043] Thus, the voltage fluctuation of phases A, B, and C in the three-phase system during the acquisition period is obtained.
[0044] The average voltage fluctuation of the three phases during the acquisition period is denoted as the arc significance of the acquisition period.
[0045] Arc significance is used to evaluate the degree to which the three-phase voltages at the point of common coupling of the microgrid and the grid are affected by intermittent arcing interference under extreme cold weather conditions. The greater the arc significance, the more significant the impact of intermittent arcing on the target phase voltages at the point of common coupling of the microgrid and the grid during the acquisition period under extreme cold weather conditions, the more significant the voltage phase fluctuations, and the more likely it is to cause voltage phase shifts and exhibit islanding characteristics, that is, the three-phase voltages deviate significantly from the standard power supply voltage range of the grid.
[0046] Currently, phase-locked loop (PLL) technology is widely used to regulate the voltage amplitude at the point of common coupling (PCC) and correct phase errors. It tracks the grid phase in real time using a proportional-integral (PI) algorithm to maintain stable PCC voltage operation. However, traditional PLLs employ fixed control parameters in their PI algorithms, which can only accurately track the grid phase under normal, mild climate conditions. In cold, extreme climates, intermittent arcing caused by icing on transmission and insulation equipment has a significant impact, resulting in drastic fluctuations in the PCC voltage phase and a substantial decrease in the phase tracking accuracy of traditional PLLs. The PI algorithm is the key component in this process.
[0047] To accurately analyze the phase characteristics of the three-phase voltage at the point of common coupling (PCC) of the microgrid and the main grid, a Clarke transform is performed on the three-phase voltage at each acquisition time within the acquisition period. This transforms the three-phase voltage into a two-phase stationary coordinate system voltage. Then, a Park transform is used to convert the two-phase stationary coordinate system voltage into a synchronous rotating coordinate system voltage, yielding the direct-axis voltage component and the quadrature voltage component. The direct-axis voltage component represents the real-time voltage amplitude, while the quadrature voltage component represents the phase deviation between the real-time voltage and the standard grid voltage.
[0048] The Clark transform and the Park transform are well-known techniques and will not be elaborated further.
[0049] When the voltage quadrature component is zero, the voltage phase at the point of common coupling (PCC) is perfectly synchronized with the grid phase, and the phase-locked loop (PLL) can achieve precise phase tracking. When the voltage quadrature component is not zero, the voltage phase at PCC deviates from the grid phase, and the voltage phase needs to be corrected by closed-loop adjustment of the PLL to stabilize the electrical parameters of PCC, avoid islanding misjudgment, and ensure power supply quality.
[0050] Icing on power transmission equipment occurs when the ambient temperature is below 0°C, while extreme low temperatures in cold regions can reach -20°C to -50°C. Severe icing on equipment exacerbates the intermittent arcing interference at the point of common coupling (PCC), making voltage phase shift issues more pronounced. Traditional proportional-integral (PI) algorithms are inadequate for handling such strong dynamic interference. Therefore, it is necessary to dynamically adjust the PLC control parameters under these conditions to improve the phase tracking accuracy of the phase-locked loop (PLL) and achieve correction and updating of the PCC voltage phase.
[0051] The maximum value of the voltage quadrature component at the common connection point of the microgrid and the grid within the acquisition period and the year prior to the acquisition period, when the temperature is greater than or equal to 0℃ and the microgrid is connected to the grid, is recorded as the historical maximum voltage quadrature component of the acquisition period. The absolute values of each voltage quadrature component in the acquisition period are obtained, and the maximum absolute value within the acquisition period is extracted and recorded as the voltage quadrature component extremum of the acquisition period. The ratio of the difference between the voltage quadrature component extremum of the acquisition period and the historical maximum voltage quadrature component of the acquisition period to the historical maximum voltage quadrature component of the acquisition period is recorded as the voltage quadrature ratio of the acquisition period. The maximum value of the voltage quadrature ratio of the acquisition period and the number 0 is recorded as the phase error significance of the acquisition period.
[0052] When the historical duration before the acquisition period is less than one year and the historical maximum voltage quadrature component cannot be determined, the historical maximum voltage quadrature component of the power system with the nearest point of common coupling in the acquisition period is taken as the value of the historical maximum voltage quadrature component of the acquisition period.
[0053] In extreme cold climates, the voltage phase deviation at the point of common coupling (PCC) exhibits a significant vicious cycle with intermittent arcing interference from insulators. Specifically, intermittent arcing directly causes irregular fluctuations in the PCC voltage, resulting in a continuous increase in phase deviation. This large phase deviation further leads to the failure of phase-locked loop (PLL) power grid phase tracking, which in turn exacerbates the voltage fluctuation distortion at the PCC. When this situation occurs, it is necessary to dynamically adjust the proportional-integral (PI) control parameters and optimize the control loop gain to adapt to the severe random fluctuations in the PCC voltage, accurately correct the PCC voltage phase, suppress phase deviation, and break the vicious cycle of disturbance and control failure.
[0054] The proportional and integral coefficients preset within the phase-locked loop (PLL) can achieve relatively accurate phase tracking under normal, mild operating conditions. However, under prolonged extreme climate conditions ranging from -20°C to -50°C, the PLL's phase tracking accuracy significantly decreases, and the voltage phase at the point of common coupling (PCC) deviates substantially from the grid phase. Simultaneously, accompanied by voltage frequency fluctuations, these electrical characteristics can easily lead to misjudgments of the microgrid entering islanded operation. If microgrid switching operations are performed based on distorted phase tracking results, it will cause PCC voltage jumps, resulting in deteriorated power quality. Therefore, when the PCC voltage phase fluctuates drastically, it is necessary to appropriately adjust the PLL's loop bandwidth to mitigate phase tracking lag and reduce the deviation between the PCC voltage phase and the grid phase.
[0055] The hyperbolic tangent of the product of the arc significance and the phase error significance during the acquisition period is denoted as the gain ratio of the acquisition period; the product of the sum of the gain ratio of the acquisition period and the number 1, and the preset initial scaling factor, is denoted as the gain ratio coefficient of the acquisition period; the product of the sum of the gain ratio of the acquisition period and the number 1, and the preset initial integral coefficient, is denoted as the gain integral coefficient of the acquisition period.
[0056] The higher the gain ratio of the acquisition cycle, the stronger the interference of intermittent arc fluctuations on the three-phase voltage of the microgrid and the grid common connection point under the influence of cold extreme climate, and the greater the phase deviation between the real-time voltage and the standard grid voltage.
[0057] The preset initial proportional coefficient and preset initial integral coefficient are determined according to the Ziegler-Nichols tuning method. In this embodiment, the preset initial proportional coefficient and preset initial integral coefficient are set to 1000 and 100, respectively. The function of determining the gain ratio based on the hyperbolic tangent is normalization. Normalization can avoid excessive adjustment of the coefficients of the proportional-integral algorithm, which could cause high-frequency jitter in the output phase of the PLL.
[0058] The gain proportional coefficient and gain integral coefficient of the acquisition cycle are the adaptive values of the proportional coefficient and integral coefficient in the phase-locked loop.
[0059] Based on the gain proportional coefficient and gain integral coefficient of the acquisition period, proportional-integral calculations are performed on the voltage quadrature components corresponding to the three-phase voltage at the point of common connection during the acquisition period to obtain the grid angular frequency estimated by the phase-locked loop (PLL). The angular frequency is then integrated to obtain the real-time phase of the acquisition period output by the PLL. The real-time phase output by the PLL is fed back to the next iteration of the PLL and used as the reference phase for the next iteration.
[0060] The proportional-integral adjustment calculation inside the phase-locked loop is a well-known technique and will not be described in detail here.
[0061] Even in extreme cold climates and subject to intermittent arcing, the phase-locked loop (PLL) optimized as described above can still maintain the amplitude, phase, and frequency stability of the voltage at the point of common coupling (PCC), reduce the islanding electrical characteristics of the PCC voltage, avoid misjudgment of islanding caused by intermittent arcing disturbances, prevent the microgrid from repeatedly performing off-grid switching in a short period of time, eliminate frequent voltage jumps, and ensure the quality of power supply.
[0062] At this point, the real-time phase of the acquisition cycle of the phase-locked loop output is determined.
[0063] Step S003: Conduct islanded operation status detection on the common connection point. If the common connection point enters the islanded operation status, perform a seamless switch of the microgrid from grid-connected to off-grid.
[0064] An active frequency offset method is used to detect the islanding status of the point of common coupling (PCC). In this embodiment, the frequency disturbance of the active frequency offset method is set to 0.5 Hz. If no islanding status is detected at the PCC, the microgrid continues to operate in grid-connected mode. If the PCC enters islanding mode, an energy storage converter is used to seamlessly switch the grid-connected constant power operation mode to the off-grid constant voltage and constant frequency operation mode, completing the seamless transition of the microgrid from grid-connected to off-grid.
[0065] Among them, the active frequency offset method and the mode switching of the energy storage converter are well-known technologies and will not be described in detail.
[0066] When a microgrid needs to be reconnected to the grid, pre-synchronization processing using a phase-locked loop (PLL) is required before seamless grid connection to ensure voltage stability at the point of common coupling (PCC) before and after grid connection. Specifically, upon receiving the grid connection command, the phase of the grid voltage is first extracted using the PLL, and this phase is used as the orientation angle for coordinate transformation. Clarke and Parker transformations are then performed sequentially on the grid voltage and the output voltage of the energy storage converter to obtain the direct-axis and quadrature components of the grid-side voltage, as well as the direct-axis and quadrature components of the converter output voltage. The differences between the quadrature and direct-axis components of the voltage on the grid side and the converter output side are calculated, and these differences are used as inputs for proportional-integral (PI) regulation to obtain the required angular frequency and voltage amplitude for grid connection of the energy storage converter. Once the angular frequency and voltage amplitude at the output of the energy storage converter reach the calculated target values, the grid connection switch is closed, completing the pre-synchronization control and achieving seamless grid connection of the microgrid.
[0067] Among them, the phase-locked loop extraction of grid voltage phase is a well-known technology and will not be described in detail; the situation in which the microgrid needs to be reconnected to the grid is, for example, when the grid fault has been repaired or the microgrid's energy storage capacity is insufficient.
[0068] This achieves seamless switching between microgrid and off-grid operation.
Claims
1. A seamless on-grid / off-grid switching control method for microgrids in cold, extreme climate regions, characterized in that: The method includes the following steps: Collect the three-phase voltages of the common connection point of the microgrid and the power grid at each collection time within the collection period; Based on the values of all phase voltages within the acquisition period and the differences between adjacent phase voltages, the voltage fluctuation of each phase within the acquisition period is calculated, and the arc significance of the acquisition period is obtained. Based on the three-phase voltages within the acquisition period, the voltage quadrature components are determined. Based on the voltage quadrature components, the phase error significance of the acquisition period is calculated. Combined with the arc significance, the gain proportional coefficient and gain integral coefficient of the acquisition period are calculated, and the real-time phase of the acquisition period output by the phase-locked loop is determined. The common connection point is monitored for islanded operation status. If the common connection point enters the islanded operation status, the microgrid is seamlessly switched from grid-connected to off-grid.
2. The seamless on-grid / off-grid switching control method for microgrids in cold-region extreme climates according to claim 1, characterized in that, The method for calculating the voltage fluctuation is as follows: Take any one of the three phases as the target phase, and determine the intermittent arc frequency of the target phase in the acquisition period based on the value of the target phase voltage during the acquisition period. The frequency of target phase fluctuations during the acquisition period is determined based on the difference in voltage between adjacent target phases within the acquisition period. The product of the sum of the intermittent arc frequency of the target phase during the acquisition period and the digital 1, and the fluctuation frequency, is denoted as the voltage fluctuation of the target phase during the acquisition period.
3. The microgrid on-grid / off-grid seamless switching control method for cold-region extreme climates according to claim 2, characterized in that, The intermittent arc frequency of the target phase during the acquisition cycle is the ratio of the number of target phase voltages exceeding the standard power supply voltage range during the acquisition cycle to the total number of target phase voltages during the acquisition cycle.
4. The seamless on-grid / off-grid switching control method for microgrids in cold-region extreme climates according to claim 2, characterized in that, The fluctuation frequency of the target phase during the acquisition period is: the coefficient of variation of the absolute values of all values in the first-order difference sequence of the target phase voltage sequence during the acquisition period.
5. The microgrid on-grid / off-grid seamless switching control method for cold-region extreme climates according to claim 1, characterized in that, The arc significance of the acquisition period is the average voltage fluctuation of the three phases during the acquisition period.
6. The microgrid on-grid / off-grid seamless switching control method for cold-region extreme climates according to claim 1, characterized in that, The voltage orthogonal component is the result of converting the three-phase voltage at each acquisition moment within the acquisition cycle into a two-phase stationary coordinate system voltage, and then into a synchronous rotating coordinate system voltage.
7. The seamless on-grid / off-grid switching control method for microgrids in cold-region extreme climates according to claim 1, characterized in that, The method for calculating the significance of the phase error during the acquisition period is as follows: Obtain the absolute values of each voltage quadrature component in the acquisition period, and extract the maximum absolute value within the acquisition period, which is recorded as the extreme value of the voltage quadrature component in the acquisition period. The ratio of the difference between the extreme value of the voltage quadrature component in the acquisition period and the historical maximum voltage quadrature component in the acquisition period to the historical maximum voltage quadrature component in the acquisition period is recorded as the voltage quadrature ratio of the acquisition period. The maximum value of the voltage quadrature ratio in the acquisition period and the maximum value of the number 0 are recorded as the phase error significance of the acquisition period.
8. The seamless on-grid / off-grid switching control method for microgrids in cold-region extreme climates according to claim 1, characterized in that, The method for calculating the gain ratio coefficient is as follows: The hyperbolic tangent of the product of the arc significance and the phase error significance during the acquisition period is denoted as the gain ratio of the acquisition period; the product of the sum of the gain ratio of the acquisition period and the number 1, and the preset initial scaling factor is denoted as the gain ratio factor of the acquisition period.
9. The microgrid on-grid / off-grid seamless switching control method for cold-region extreme climates according to claim 8, characterized in that, The gain integral coefficient is the product of the sum of the gain ratio of the acquisition period and the number 1, and the preset initial integral coefficient.
10. The microgrid on-grid / off-grid seamless switching control method for cold-region extreme climates according to claim 1, characterized in that, The method for determining the real-time phase of the acquisition period output by the phase-locked loop is as follows: Based on the gain proportional coefficient and gain integral coefficient of the acquisition period, proportional-integral calculations are performed on the voltage quadrature components corresponding to the three-phase voltage at the point of common coupling during the acquisition period to obtain the grid angular frequency estimated by the phase-locked loop; the angular frequency is then integrated to obtain the real-time phase of the acquisition period output by the phase-locked loop.