Micro-grid stability control method and system of self-adaptive droop coefficient

Abstract

The invention belongs to the technical field of micro-grid droop control, and particularly relates to a micro-grid stability control method and system of a self-adaptive droop coefficient. Through a mode of performing frequency and voltage droop coefficient adaptive control on a micro source in a micro-grid, the problem of unstable frequency and voltage caused by load fluctuation during isolated island operation of the micro-grid is solved, and frequency fluctuation caused by active power change is coped with by adjusting a frequency droop coefficient in real time. And voltage fluctuation caused by reactive power change is coped with by adjusting the voltage droop coefficient in real time. According to the invention, in practical application, microgrid voltage and frequency fluctuation caused by load fluctuation can be effectively suppressed, and microgrid voltage and frequency are controlled to be stabilized at rated values; meanwhile, the algorithm has better dynamic response speed and steady-state control precision, is simple, does not need to add an additional hardware circuit, and is easy for engineering realization.

Description

Technical Field

[0001] The present invention belongs to the technical field of microgrid droop control, and in particular relates to a microgrid stability control method and system with an adaptive droop coefficient. Background Art

[0002] Since the droop control strategy simulates the external characteristics of the grid-connected operation of synchronous generator sets, multiple micro-sources based on this strategy can automatically realize power distribution and form a peer-to-peer microgrid without communication. The microgrid has high reliability and can operate in both grid-connected and island modes. However, when the microgrid operates in island mode, due to the inherent characteristics of droop control, when the load fluctuation causes the output power of the micro-source (such as new energy grid-connected inverter, energy storage grid-connected inverter, etc.) to deviate from the rated power, the frequency and amplitude of the micro-source output voltage will deviate from the rated value, thereby affecting the stable operation of the microgrid and reducing the power supply quality of the microgrid.

[0003] In view of the above problems, the existing technologies mainly include:

[0004] One method is to use a voltage control scheme based on a virtual excitation controller and its derivative methods, adding reactive power deviation integral control to the traditional droop control to form a two-level control. This method is equivalent to a droop controller with a first-order filter link, which causes a delay in the voltage dynamic response;

[0005] The other is to adjust the voltage and frequency by changing the droop control parameters. This method replaces the frequency and voltage droop coefficients with a simple function related to active and reactive power. When the power change is detected, the droop amount (i.e., the droop coefficient) is dynamically adjusted according to the actual output power to reduce the fluctuations in the amplitude and frequency of the microgrid caused by the sudden change of load. This method cannot accurately achieve stable control of the voltage amplitude and frequency of the microgrid, and will affect the power distribution accuracy and dynamic response speed between multiple micro sources.

[0006] Patent announcement number CN106712027B is an improved droop control strategy for low-voltage microgrids based on dynamic references. The value of the frequency reference in PU droop control is constructed according to the change of active load to compensate for the frequency fluctuation of the microgrid. The principle of the voltage reference value in Qf droop control is constructed based on the change of reactive load, the reactive droop coefficient is improved, and the reactive sharing of microsources is improved. Among them, the dynamic frequency reference in Qf droop control is the frequency deviation caused by load changes on the basis of its rated value, which adapts to the frequency adjustment when the reactive power demand of different load sides is almost not affected by the reactive output of the microsource, realizes the frequency error adjustment, and then improves the frequency stability; the dynamic voltage reference in PU droop control is the voltage drop value of each microsource line on the machine based on its rated value, which simplifies the control. The above patent cannot accurately realize the stable control of the voltage amplitude and frequency of the microgrid, and will affect the power distribution accuracy and dynamic response speed between multiple microsources. Therefore, it is urgent for technicians in this field to solve the above technical problems. Summary of the invention

[0007] The technical problem to be solved by the present invention is that in the above-mentioned prior art, it is impossible to accurately achieve stable control of the voltage amplitude and frequency of the microgrid, and at the same time it will affect the power distribution accuracy and dynamic response speed among multiple micro sources.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0009] A microgrid stability control method with an adaptive droop coefficient is provided, wherein an adaptive frequency droop coefficient is obtained through active power deviation and rated active power, and an adaptive voltage droop coefficient is obtained through reactive power deviation and rated reactive power, and the method comprises the following steps:

[0010] Step 1: The PI adjustment output of the deviation between the actual output voltage of the micro-grid micro-source and the rated voltage is equivalent to the micro-source output reactive power deviation ΔQ, and the PI adjustment output of the deviation between the actual output frequency of the micro-grid micro-source and the rated frequency is equivalent to the micro-source output active power deviation ΔP;

[0011] Step 2: Combine the reactive power deviation ΔQ output by the micro-source with the rated active power P * Input to the frequency droop coefficient correction, and match the active power deviation ΔP of the micro-source output with the reactive power Q * Input voltage droop coefficient correction;

[0012] Step 3: The corrected instantaneous frequency ω ref Perform integral calculation and match the corrected instantaneous voltage U ref Get the instantaneous reference value u of the micro-source output voltage ref .

[0013] By adopting the above technical solution and adjusting the droop coefficient in real time, the system can respond quickly to load changes, reduce voltage and frequency fluctuations, and improve the overall stability of the microgrid. The PI regulator can respond quickly to deviations, improve the dynamic response speed of the system, and ensure that it quickly returns to a stable state when the load changes. By maintaining the voltage and frequency near the rated values, power quality problems are reduced, power supply reliability is improved, and the user's power experience is improved. Based on mature PI regulator technology, it is easy to implement and does not require complex hardware support, which reduces the difficulty of implementation. The adaptive adjustment mechanism enables the microgrid to allocate resources more effectively and improves the overall operation efficiency of the system.

[0014] Furthermore, in step 1, the micro-source output voltage U and the rated value U are calculated. * Deviation ΔU, calculate the microgrid output frequency ω and rated value ω * Deviation Δω:

[0015]

[0016] Calculate the reactive power deviation ΔQ and active power deviation ΔP as well as the voltage droop coefficient and frequency droop coefficient:

[0017] Among them, k up , k ui and k ωp , k ωi are the proportional and integral coefficients of the voltage PI regulator and the frequency PI regulator, respectively, They are respectively the rated voltage droop coefficient and the rated frequency droop coefficient corresponding to the microgrid operating under rated conditions.

[0018] By adopting the above technical solution, real-time measurement and calculation of deviations can quickly detect voltage and frequency changes in the microgrid, and take immediate measures to adjust, thereby improving the response speed of the system. By processing deviations through the PI regulator, control signals can be accurately generated to ensure that the microgrid can quickly return to a stable state when the load changes. The proportional part can respond to deviations quickly, while the integral part can eliminate long-term deviations to ensure the stability of the system over a long period of time. By adjusting the droop coefficient in real time, the system can adaptively adjust the control parameters according to the actual measured deviations, thereby achieving more refined control. This method can effectively respond to changes under different load conditions and improve the flexibility of the system. Through continuous monitoring and adjustment, the system can effectively suppress voltage and frequency fluctuations caused by load fluctuations, ensure that the voltage and frequency of the microgrid are stable near the rated value, and improve the overall stability of the system.

[0019] Further, in step 2, according to the rated voltage droop coefficient Calculate the voltage control reference value U of the microgrid refand frequency control reference value ω ref :

[0020]

[0021] By adopting the above technical solutions, the adaptive adjustment mechanism enables the microgrid to allocate resources more efficiently and improve the overall operating efficiency of the system. By accurately controlling voltage and frequency, energy use can be optimized and energy waste can be reduced. Whether there is excess or insufficient reactive power, this method can achieve stable control of voltage and frequency by adjusting the droop coefficient, which has strong adaptability. This enables the system to maintain stable operation under different load conditions.

[0022] Further, in step three, according to the frequency control reference value ω ref Determine the phase angle θ of the microgrid output voltage:

[0023] Further, in step 3, according to the calculated phase angle θ and instantaneous voltage U ref , generating the instantaneous reference value of the microgrid output voltage: u ref =U ref × sinθ;

[0024] According to the generated voltage control reference value, its output voltage is adjusted in real time to ensure that the output voltage always meets the rated value.

[0025] By adopting the above technical solution, the voltage and frequency droop coefficients are adjusted in real time, which can effectively suppress the voltage and frequency fluctuations caused by load changes, thereby improving the overall stability of the microgrid. By adjusting the output voltage in real time, it is ensured that the voltage always remains near the rated value, reducing the voltage fluctuations caused by load changes and enhancing the stability of the system. The real-time adjustment mechanism enables the microgrid to respond quickly to load changes, avoiding the impact of large voltage fluctuations on the system, and improving the dynamic response speed of the system. By adaptively adjusting the droop coefficient, the microgrid can allocate resources more effectively and improve the overall operation efficiency of the system. Regardless of whether the reactive power is in excess or insufficient, this method can achieve voltage stability control by adjusting the droop coefficient, and has strong adaptability.

[0026] The present invention also includes a microgrid stability control system with an adaptive droop coefficient, a microgrid stability control method based on the adaptive droop coefficient, and an operating principle of the microgrid stability control system with an adaptive droop coefficient. The microgrid micro-source monitoring system is used to monitor micro-source parameters, and the output voltage is continuously adjusted by continuously monitoring the deviation between the output voltage and the rated value to form a closed-loop feedback control mechanism to ensure voltage stability. When the system detects voltage deviation and frequency deviation, dynamic compensation is performed through a PI regulator to quickly adjust the droop coefficient to achieve the goal of voltage stability.

[0027] The present invention has the following beneficial effects:

[0028] The present invention discloses a method for stable control of a microgrid with an adaptive droop coefficient. The micro-source of the microgrid adjusts the frequency droop control coefficient in real time according to the change of load active power, and the coefficient adjustment is automatically generated based on PI adjustment of the deviation between the grid frequency and the rated frequency; similarly, the voltage droop control coefficient is adjusted in real time according to the change of load reactive power, and the coefficient adjustment is automatically generated based on PI adjustment of the deviation between the grid voltage and the rated voltage. This method can effectively suppress the voltage and frequency fluctuations of the microgrid caused by load fluctuations, and control the voltage and frequency of the microgrid to be stable at the rated value; at the same time, the algorithm has good dynamic response speed and steady-state control accuracy, and the algorithm is simple, does not require the addition of additional hardware circuits, and is easy to implement in engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a frequency droop coefficient adaptive control principle diagram of the present invention;

[0030] Figure 2 A diagram of a frequency stabilization control method for a microgrid according to the present invention;

[0031] Figure 3 This is a frequency droop coefficient adaptive control principle diagram of the present invention;

[0032] Figure 4 It is a diagram of a frequency stabilization control method of a microgrid according to the present invention;

[0033] Figure 5 It is the control principle diagram of the present invention. DETAILED DESCRIPTION

[0034] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific preferred embodiments.

[0035] In the description of the present invention, it should be understood that the terms "left side", "right side", "upper part", "lower part" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. "First", "second" and the like do not indicate the importance of the components, and therefore cannot be understood as limiting the present invention. The specific dimensions used in this embodiment are only for illustrating the technical solution, and do not limit the scope of protection of the present invention.

[0036] Embodiment 1: When the microgrid is operating in an isolated island, the voltage of the microgrid will fluctuate with the fluctuation of the load, which greatly reduces the stability and reliability of the microgrid operation. In order to solve the problem that the output power of the micro-source deviates from the rated power due to load fluctuation, refer to Figure 1 , Figure 2 and Figure 5 ,A microgrid stability control method with adaptive droop coefficient,The characteristic equation of the traditional QU (reactive voltage) droop control is shown in equation (1):

[0037] U=U * +k u ×(Q * -Q) (1)

[0038] Among them, k u is the voltage droop coefficient, U, U * are the output voltage and command value of the microgrid microsource (the microsource can be a new energy grid-connected inverter or an energy storage grid-connected inverter, etc.), Q, Q * They are the corresponding output reactive power and its command value, when the voltage droop coefficient is at the rated value k u =k u * In this case, when the micro-source output reactive power Q is equal to the command value Q * When U=U * , that is, the voltage of the microgrid operates stably at the rated value U * ,like Figure 1 At the operating point 0, when the microgrid load changes, that is, Q deviates from Q * When U≠U * , causing voltage fluctuations in the microgrid. Here the focus is on Q>Q * Take the problem as an example.

[0039] When the micro-source output power Q=Q1>Q * When , the voltage deviates from the rated value, at this time U=U1, and the microgrid operates at point 1.

[0040] In order to stabilize the microgrid voltage at the rated value U * , and keep the micro-source output power Q1 to meet the load demand, the present invention adjusts the voltage droop coefficient in real time so that k u =k u1 . Reference Figure 1 , it can be seen that the microgrid is running at point 2, and the system voltage U=U * , achieving stable control of the microgrid. The specific analysis is as follows:

[0041] According to formula (1), let Q = 0, we can obtain:

[0042]

[0043] according to Figure 1 , the droop coefficient can be obtained as k u1 The characteristic equation of QU droop control:

[0044] U=U0-k u1 ×Q (3)

[0045] Combined with equation (2), the QU droop control characteristic equation shown in equation (3) can be transformed into:

[0046]

[0047] From the above analysis, it can be seen that when the droop coefficient is k u1 On the QU droop control line, when Q=Q1, there exists U=U * , then:

[0048]

[0049] Substituting equation (5) into equation (4), we can obtain the voltage droop coefficient after adjustment (k u1 )’s QU droop control characteristic equation:

[0050]

[0051] It can be seen that when the reactive power change of the load causes the reactive power output of the micro-source to deviate from the rated value, the system voltage can be stabilized at the rated value by simply changing the voltage droop coefficient according to formula (5).

[0052] Based on the voltage droop coefficient adaptive control principle shown in formula (6), the implementation method of microgrid voltage stability control is analyzed in detail below.

[0053] In formula (6), let the micro-source output reactive power deviation ΔQ = Q1-Q * Due to the existence of reactive power deviation ΔQ, the microgrid voltage deviation ΔU=U * -U. Therefore, the voltage deviation PI can be used to adjust the output equivalent power deviation. When the voltage deviation ΔU is eliminated to zero, ΔQ=Q1-Q * ,Right now:

[0054]

[0055] Substituting equation (7) into equation (6), the voltage stability control method of the microgrid with adaptive droop coefficient according to the present invention can be obtained. Figure 2 :

[0056]

[0057] Figure 2 U ref The voltage reference value U output by the micro-source voltage stabilization controller ref , U ref It is used to generate and track the instantaneous value of the micro-source output voltage. Similarly, when the micro-source output power Q=Q2(Q <Q* ), the voltage deviates from the rated value, at this time U=U2, and the microgrid operates at point 3. By adjusting the voltage droop coefficient in real time so that ku=ku2, the microgrid operates at point 4, and the system voltage U=U * , realizing the stable control of microgrid. The specific principle is the same as above (Q * The voltage droop coefficient is adjusted in real time to effectively suppress voltage fluctuations caused by load changes. When the reactive power of the microgrid deviates, the voltage droop coefficient is adjusted to enable the microgrid to quickly return to a stable state, avoiding large voltage fluctuations and improving the reliability of microgrid operation.

[0058] Example 2: When the microgrid is operating in an isolated island, the frequency and voltage of the microgrid will fluctuate with the load fluctuation, which greatly reduces the stability and reliability of the microgrid operation. In order to solve the problem that the output power of the micro-source deviates from the rated power due to load fluctuation, refer to Figure 3 and Figure 4 , analyzing the frequency droop coefficient adaptive control principle, the characteristic equation of the traditional P-ω (active power-frequency) droop control is shown in formula (9):

[0059] ω=ω * +kω×(P * -P) (9)

[0060] In the formula, k ω is the frequency droop coefficient, ω, ω * are the microgrid micro-source output frequency and its instruction value, P, P * are the corresponding output active power and its command value respectively.

[0061] Reference Figure 3 , at rated frequency droop coefficient (k ω =k ω * ), when the active power output P of the micro-source is equal to the command value P * When ω=ω * , that is, the microgrid frequency operates stably at the rated value ω * ,like Figure 3 The operating point is 0. When the microgrid load changes, that is, P deviates from P * When ω≠ω * , causing the frequency of the microgrid to fluctuate. Here we focus on P <P * Take the problem as an example.

[0062] When the micro-source output power P = P1 <P * When the frequency deviates from the rated value, ω=ω1>ω * , the microgrid operates at point 1.

[0063] ​In order to stabilize the microgrid frequency at the rated value ω * , and keep the micro-source output power P1 to meet the load demand, the present invention adjusts the frequency droop coefficient in real time so that k ω =k ω1 . Reference Figure 3 , it can be seen that the microgrid is running at point 2, and the system frequency ω=ω * , realizing the stable control of microgrid frequency. The specific analysis is as follows:

[0064] According to formula (9), let P = 0, we can obtain:

[0065]

[0066] according to Figure 3 , the droop coefficient can be obtained as k ω1 The characteristic equation of P-ω droop control is:

[0067] ω=ω0-kω1×P (11)

[0068] Combined with equation (10), the P-ω droop control characteristic equation shown in equation (11) can be transformed into:

[0069]

[0070] From the above analysis, we can see that when P=P1, there exists ω=ω * , then:

[0071]

[0072] Substituting equation (13) into equation (12), we can obtain the frequency droop coefficient after adjustment (k ω1 )’s P-ω droop control characteristic equation:

[0073]

[0074] It can be seen that when the load active power changes and causes the output active power of the micro-source to deviate from the rated value, the system frequency can be stabilized at the rated value by simply changing the voltage droop coefficient according to formula (13).

[0075] Based on the frequency droop coefficient adaptive control principle shown in formula (14), the implementation method of microgrid frequency stability control is analyzed in detail below.

[0076] In formula (14), let the output active power deviation of microgrid micro-source ΔP = P1-P * Due to the existence of active power deviation ΔP<0, the microgrid frequency deviation Δω=ω *-ω>0. Therefore, the frequency deviation can be used to adjust the output equivalent active power deviation. When the frequency deviation Δω is eliminated to zero, ΔP=P1-P * ,Right now:

[0077]

[0078] Substituting equation (15) into equation (14), the frequency stability control method of the microgrid with adaptive droop coefficient according to the present invention can be obtained. Figure 4 :

[0079]

[0080] Figure 4 ω in ref It is the frequency reference value output by the micro-source frequency stabilization controller and the generation and tracking control of the instantaneous value of the micro-source output voltage.

[0081] Embodiment 3: Using the microgrid control model, the microgrid circuit parameters are automatically calculated and the droop coefficient is automatically corrected. The microgrid monitoring system is used to collect the current output frequency ω and output voltage U of the microgrid in real time, as well as the actual output reactive power Q and active power P of the micro-source of the microgrid, and calculate the output voltage U of the microgrid and the rated voltage U * The deviation ΔU between the microgrid output frequency ω and the rated frequency ω * The deviation Δω between them.

[0082] Calculate the reactive power deviation ΔQ and active power deviation ΔP. The reactive power deviation ΔQ is obtained by the voltage deviation ΔU through the PI regulator, and the active power deviation ΔP is obtained by the frequency deviation Δω through the PI regulator. According to the calculated reactive power deviation ΔQ, adjust the voltage droop coefficient k u , according to the calculated active power deviation ΔP, adjust the frequency droop coefficient k ω , using the adjusted droop factor k u and k ω , calculate the new voltage control reference value U ref and frequency control reference value ω ref , the phase angle θ of the output voltage of the micro source is calculated by integral control, and according to the calculated phase angle θ and voltage amplitude U ref , generate an instantaneous reference value for the micro-source output voltage, and adjust the output voltage of the micro-source in real time according to the generated voltage control reference value to ensure that the output voltage always meets the rated value U * ,Through the above steps, the voltage and frequency fluctuations of the microgrid caused by load fluctuations can be effectively suppressed, and the voltage and frequency of the microgrid can be controlled to be stable at the rated value.

[0083] The preferred embodiments of the present invention are described in detail above; however, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various equivalent transformations can be made to the technical solutions of the present invention, and these equivalent transformations all belong to the protection scope of the present invention.

Claims

1. A microgrid stability control method with adaptive droop coefficient, characterized by: The adaptive frequency droop coefficient is obtained by the active power deviation and the rated active power, and the adaptive voltage droop coefficient is obtained by the reactive power deviation and the rated reactive power, including the following steps: Step 1: The PI adjustment output of the deviation between the actual output voltage of the micro-grid micro-source and the rated voltage is equivalent to the micro-source output reactive power deviation ΔQ, and the PI adjustment output of the deviation between the actual output frequency of the micro-grid micro-source and the rated frequency is equivalent to the micro-source output active power deviation ΔP; Step 2: Combine the reactive power deviation ΔQ output by the micro-source with the rated active power P * Input to the frequency droop coefficient correction, and match the active power deviation ΔP of the micro-source output with the reactive power Q * Input voltage droop coefficient correction; Step 3: The corrected instantaneous frequency ω ref Perform integral calculation and match the corrected instantaneous voltage U ref Get the instantaneous reference value u of the micro-source output voltage ref .

2. The microgrid stability control method with adaptive droop coefficient according to claim 1 is characterized in that: In step 1, calculate the output voltage U and the rated value U of the micro-source * Deviation ΔU, calculate the microgrid output frequency ω and rated value ω * Deviation Δω: Calculate the reactive power deviation ΔQ and active power deviation ΔP as well as the voltage droop coefficient and frequency droop coefficient: Among them, k up , k ui and k ωp , k ωi are the proportional and integral coefficients of the voltage PI regulator and the frequency PI regulator, respectively, They are respectively the rated voltage droop coefficient and the rated frequency droop coefficient corresponding to the microgrid operating under rated conditions.

3. The microgrid stability control method with adaptive droop coefficient according to claim 1 is characterized in that: In step 2, according to the rated voltage droop factor Calculate the voltage control reference value U of the microgrid ref and frequency control reference value ω ref :

4. The microgrid stability control method with adaptive droop coefficient according to claim 1 is characterized in that: In step 3, according to the frequency control reference value ω ref Determine the phase angle θ of the microgrid output voltage:

5. The microgrid stability control method with adaptive droop coefficient according to claim 4 is characterized in that: In step 3, according to the calculated phase angle θ and instantaneous voltage U ref , generating the instantaneous reference value of the microgrid output voltage: u ref =U ref × sinθ; According to the generated voltage control reference value, its output voltage is adjusted in real time to ensure that the output voltage always meets the rated value.

6. A microgrid stability control system with an adaptive droop coefficient, comprising the microgrid stability control method with an adaptive droop coefficient according to any one of claims 1 to 5, characterized in that: The microgrid micro-source monitoring system is used to monitor micro-source parameters. By continuously monitoring the deviation between the output voltage and the rated value, the output voltage is continuously adjusted to form a closed-loop feedback control mechanism to ensure voltage stability. When the system detects voltage deviation and frequency deviation, it dynamically compensates through the PI regulator and quickly adjusts the droop coefficient to achieve the goal of voltage stability.

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