Distributed cooperative control method for ac microgrid with optical storage

Abstract

This invention discloses a distributed collaborative control method for photovoltaic and energy storage systems suitable for AC microgrids. This method addresses the collaboration problem between photovoltaic and energy storage systems on a short timescale by introducing distributed collaborative control based on frequency information, achieving efficient collaborative control between photovoltaic and energy storage systems on a short timescale. Compared with existing methods, this method: (1) enables photovoltaic and energy storage systems to passively and collaboratively respond to power changes on a short timescale. (2) enables photovoltaic systems to achieve seamless switching and withdraw some power when the bus frequency is high, achieving power sharing among photovoltaic systems. (3) prevents overcharging and over-discharging of energy storage systems, and allows power sharing among energy storage systems based on their respective SOC status and capacity.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology, specifically relating to a distributed collaborative control method for photovoltaic and energy storage in AC microgrids. Background Technology

[0002] Photovoltaic technology, with its clean and renewable advantages, has become a key component of new power systems. Photovoltaic power generation does not rely on fuel and requires no material consumption; it simply utilizes sunlight to convert light energy into electrical energy. Furthermore, photovoltaic power generation systems have low maintenance costs, long lifespans, and can operate stably in various environments, thus possessing broad application prospects in AC microgrids, especially in remote areas where the main grid cannot provide a stable power supply.

[0003] Solar-powered microgrids operate in both islanded and grid-connected modes. In grid-connected mode, solar power typically operates at maximum power, with the grid absorbing power fluctuations to stabilize the microgrid's frequency and voltage. In islanded mode, the microgrid needs independent power supply and no longer relies on the grid for frequency and voltage regulation. In this case, the instability and unpredictability of solar power generation become problematic. Therefore, energy storage is needed to smooth out solar power fluctuations, charging when solar power generation is abundant and discharging when solar power generation is insufficient, thus balancing supply and demand. Compared to the grid, the capacity and rated power of energy storage are generally fixed, so coordinated control between solar power and energy storage is required to improve energy storage utilization and the microgrid's power quality.

[0004] Traditional photovoltaic (PV) and energy storage synergy typically prioritizes economic efficiency, utilizing a centralized controller to adjust the status and output power of individual PV systems and energy storage over a longer timescale. This approach neglects the underlying short-term control needs, particularly in the event of sudden changes in sunlight or load, potentially failing to respond promptly to power fluctuations. Therefore, finding a PV-energy storage synergy strategy that considers short-term response requirements has become a pressing issue. Summary of the Invention

[0005] The purpose of this invention is to provide a fast-response distributed photovoltaic-storage coordinated control method. This invention proposes a photovoltaic-storage coordinated control method suitable for AC microgrids. This method employs a distributed droop control approach using frequency information as the transmission signal. The photovoltaic system uses f-dp / dv droop control, and the energy storage system uses a SOC-based droop control method. This allows for passive response to power changes on a short timescale, while preventing overcharging and over-protection of the energy storage system, and avoiding photovoltaic mode switching.

[0006] To achieve the above-mentioned objectives, this method adopts the following technical solution:

[0007] A distributed collaborative control method for photovoltaic and energy storage includes: an f-dp / dv droop control method for the photovoltaic system and a SOC-based droop control method for the energy storage system. The specific steps are as follows:

[0008] S1: The energy storage system acquires key data from the export side and the current SOC of the energy storage battery;

[0009] S2: The energy storage system generates an output reference frequency and reference voltage according to the proposed droop control method, and the system inner loop realizes frequency tracking;

[0010] S3: The photovoltaic system obtains the voltage and current of the photovoltaic panel and the output-side frequency;

[0011] S4: The photovoltaic system generates dp / dv reference values ​​according to the proposed droop control method, and the inner loop of the system achieves power point tracking.

[0012] Furthermore, in step S1, the key data on the output side includes three-phase voltage and three-phase current.

[0013] Frequency is used to calculate active and reactive power.

[0014] Furthermore, in step S2, the specific process of the proposed droop control method is as follows:

[0015]

[0016] V i ref =V i * -n i ·Q i (11)

[0017] Among them, f i ref It is a reference frequency, limiting the range [f] min ,f max ];f i α ,δf i These are the outputs of droop control and SOC control, respectively; f i * It is the rated frequency; P i It refers to output power; SOC i It is the battery's SOC; f i soc It is a correction value;

[0018] m i ,k i These are the active power droop coefficient and the state of charge (SOC) rise coefficient, respectively; V ref This is the reference voltage, with a limited range [V]. min V max];V * It is the rated voltage; n i It is the reactive power droop coefficient; Q i It is reactive power.

[0019] According to the Coulomb counting method, SOC can be calculated using the following formula:

[0020]

[0021] Among them, SOC i | t＝0 This is the initial value of SOC, CS i It refers to battery capacity, i bat It is the battery output current.

[0022] Furthermore, in step S2, the parameters are set as follows:

[0023] Active and reactive power droop coefficients m i ,n i The settings are based on the range of active and reactive power output from the battery:

[0024]

[0025]

[0026] Among them, P max,i ,P min,i These are the battery's maximum and minimum active power outputs; Q max,i Q min,i These are the battery's maximum and minimum reactive power outputs.

[0027] The rising coefficient k i and correction value f i soc It can be set to

[0028]

[0029] f i soc =f min -f * (16)

[0030] Furthermore, in step S4, the photovoltaic system droop control method is as follows:

[0031]

[0032] Among them, dp / This is the reference value for dp / dv; η j It is the droop coefficient; f j It is the bus frequency; f HIt is a high-frequency limit.

[0033] Furthermore, in step S4, the parameters for droop control are set as follows:

[0034] droop coefficient η j The settings are as follows:

[0035]

[0036] Among them, dp / dv min It is the minimum value of dp / dv.

[0037] The beneficial effects of this invention are:

[0038] (1) This invention enables photovoltaic and energy storage systems to passively and collaboratively respond to power changes on a short time scale.

[0039] (2) The present invention enables seamless switching of photovoltaic systems and withdraws some power when the bus frequency is high, so that power sharing can be achieved among photovoltaic systems.

[0040] (3) The present invention can prevent overcharging and over-discharging of energy storage systems, and power sharing can be carried out among energy storage systems according to their respective SOC status and capacity. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of a system for energy storage droop control based on SOC.

[0042] Figure 2 This is a schematic diagram of a system based on f-dp / dv droop photovoltaic control.

[0043] Figure 3 These are photovoltaic output characteristic curves, where (a) is the voltage-power curve and (b) is the dp / dv-power curve. Detailed Implementation

[0044] To describe the present invention in more detail, the technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0045] like Figure 1 As shown, the energy storage system consists of a battery and an inverter. The inverter input is a DC constant voltage battery, which outputs a three-phase AC voltage after inversion. This voltage is then filtered and connected to the AC bus. R... f ,L f C f These are the electrical parameters of the output-side LC filter, R. line ,L line This is the line impedance parameter. The number of slashes indicates the number of signals on the line for simplified illustration. V o(a,b,c) The inverter outputs three-phase voltage, which, after dq conversion, becomes V.o(d,q) The PI module is a proportional-integral controller.

[0046] The energy storage control consists of two control loops: an inner loop and an outer loop. The inner loop is used to track the reference voltage V. ref ∠θ is given by the reference voltage from the outer loop, and then the voltage deviation is processed by the proportional-integral module to obtain the output reference current. The current deviation is fed to the pulse width modulation (PWM) module after passing through the proportional-integral module to generate a square wave signal to drive the switching transistor.

[0047] The outer loop employs the proposed SOC-based droop control algorithm. Since this invention primarily considers active power regulation, the focus is on the P / f droop component based on SOC. Additionally, Q / V droop is incorporated to ensure signal integrity. The outer loop control aims to achieve the following: 1) Balance the SOC of different energy storage systems to avoid overuse of individual systems; 2) After SOC balance, each energy storage system can share power according to its capacity; 3) If the SOC of all energy storage systems reaches a high level, the frequency is adjusted so that the photovoltaic power source reduces power output according to frequency changes. In summary, the output voltage frequency is adjusted based on the SOC of the energy storage systems and the output power, achieving decentralized collaborative control between the photovoltaic power source and the energy storage system based on frequency signal changes.

[0048] like Figure 2 As shown, a single-stage photovoltaic power generation system consists of photovoltaic panels and an inverter. Capacitors are connected in parallel across the photovoltaic panels and then connected to the input side of the inverter. The output side of the inverter is connected to the AC bus after LC filtering. R... p ,L p C p These are the electrical parameters of the output-side LC filter, including the three-phase voltage V. g(a,b,c) The AC bus voltage frequency is obtained through a phase-locked loop (PLL).

[0049] The invented photovoltaic control algorithm consists of two parts: an inner loop and an outer loop. The inner loop is used to track the reference values ​​dp / dv. ref The outer loop provides a reference dp / dv value, and the control deviation is processed by a proportional-integral module to obtain the output current reference value. Then the current reference value The deviation from the actual output current is then processed by a proportional-integral module to obtain the reference voltage. Finally, a square wave signal is generated by PWM to drive the switching transistor.

[0050] The outer loop represents the proposed photovoltaic f-dp / dv droop control algorithm. This algorithm utilizes the dp / dv characteristics of photovoltaics to establish an f-dp / dv droop control method. The outer loop control achieves the following objectives: 1) When the bus frequency is too high, the photovoltaic power supply limits its power output according to its capacity; 2) When the bus frequency is low, the photovoltaic power supply operates at its maximum power point. Furthermore, the photovoltaic power supply can seamlessly switch between maximum power mode and power hot standby mode.

[0051] like Figure 3 The image shows the characteristic curves of an array composed of KC200GT photovoltaic panels. Figure 3 (a) is the voltage-power curve, which can be divided into two parts, the rising segment and the falling segment, with the maximum power point as the boundary. Correspondingly... Figure 3 (b) The dp / dv-power curve can also be divided into two parts—dp / dv>0 and dp / dv<0. The rising segment on the left side of the voltage-power curve corresponds to the dp / dv>0 segment on the right side of the dp / dv-power curve, and vice versa. Furthermore, by comparing the two regions on each curve, it can be seen that the same voltage change results in a larger power change in the falling segment, and the dp / dv value range corresponding to the falling segment is wider. Therefore, to obtain better dynamic and steady-state response performance, the falling segment (dp / dv<0) is used as the operating range. This invention is based on this principle, achieving mode switching by controlling the dp / dv value of the photovoltaic power source.

[0052] Based on the photovoltaic panel voltage and current collected by the sampling module, and the output port voltage, the control formula of this invention is as follows:

[0053]

[0054] Where: V ref This is the reference value for the output voltage of the photovoltaic power supply, V. * This is the voltage rating, and R is the droop factor. It is obtained based on the real-time output voltage and current of the photovoltaic panel, and k is the correction ratio coefficient.

[0055] The scaling factor is related to the dp / dv value, and the specific settings are as follows:

[0056]

[0057] Where: V max and V min These represent the maximum and minimum values ​​of the DC bus voltage, dp / dv. max It is the maximum value of dp / dv.

[0058] To describe the present invention in more detail, the technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0059] A photovoltaic-storage coordinated control method includes: an f-dp / dv droop control method for the photovoltaic system and a SOC-based droop control method for the energy storage system. The specific steps are as follows:

[0060] S1: The energy storage system obtains the active and reactive power on the output side and the current SOC of the energy storage battery;

[0061] S2: The energy storage system generates an output reference frequency and reference voltage based on the proposed droop control method. The system's inner loop achieves frequency tracking, such as... Figure 1 As shown;

[0062] S3: The photovoltaic system obtains the voltage and current of the photovoltaic panel and the output-side frequency;

[0063] S4: The photovoltaic system generates dp / dv reference values ​​based on the proposed droop control method, and the inner loop of the system achieves power point tracking, such as... Figure 2 As shown.

[0064] The control algorithm of the energy storage system can be expressed as follows:

[0065]

[0066] V i ref =V i * -n i ·Q i (20)

[0067] Among them, f i ref It is a reference frequency, limiting the range [f] min ,f max ];f i α ,δf i These are the outputs of droop control and SOC control, respectively; f i * It is the rated frequency; P i It refers to output power; SOC i It is the battery's SOC; f i soc It is a correction value; m i ,k i These are the active power droop coefficient and the state of charge (SOC) rise coefficient, respectively; V ref This is the reference voltage, with a limited range [V]. min V max ];V * It is the rated voltage; n i It is the reactive power droop coefficient; Q i It is reactive power.

[0068] According to the Coulomb counting method, SOC can be calculated using the following formula:

[0069]

[0070] Among them, SOC i | t＝0 This is the initial value of SOC, CS i It refers to battery capacity, i bat It is the battery output current.

[0071] Active and reactive power droop coefficients m i ,n i The settings are based on the range of active and reactive power output from the battery:

[0072]

[0073]

[0074] Among them, P max,i ,P min,i These are the battery's maximum and minimum active power outputs; Q max,i Q min,i These are the battery's maximum and minimum reactive power outputs.

[0075] The rising coefficient k i and correction value f i soc It can be set to

[0076]

[0077] f i soc =f min -f * (25)

[0078] As can be seen from (15) and (16), the rise coefficient and correction value of SOC control are the same for all batteries.

[0079] The outer loop control of a photovoltaic power source can be expressed as:

[0080]

[0081] Among them, dp / This is the reference value for dp / dv; η j It is the droop coefficient; f j It is the bus frequency; f H It is a high-frequency limit.

[0082] droop coefficient η j The settings are as follows:

[0083]

[0084] Among them, dp / dv min It is the minimum value of dp / dv.

[0085] The above description of the embodiments is provided to enable those skilled in the art to understand and apply the present invention. It will be apparent to those skilled in the art that various modifications can be made to the above embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made to the present invention by those skilled in the art based on the disclosure thereof should be within the scope of protection of the present invention.

Claims

1. A distributed collaborative control method for AC microgrid optical storage, characterized in that... The method includes an f-dp / dv droop control method for photovoltaic systems and a SOC-based droop control method for energy storage systems. The specific steps are as follows: S1: The energy storage system acquires key data from the export side and the current SOC of the energy storage battery; S2: The energy storage system generates the energy storage system output reference frequency and reference voltage according to the SOC droop control method, and the energy storage system inner loop realizes frequency tracking; S3: The photovoltaic system obtains the voltage and current of the photovoltaic panel and the output-side frequency; S4: The photovoltaic system generates the dp / dv reference value of the photovoltaic system according to the f-dp / dv droop control method, and the inner loop of the photovoltaic system realizes power point tracking; In step S2, the SOC droop control method is specifically implemented as follows: in, It is a reference frequency, limiting the range. ; These are the outputs of droop control and SOC control, respectively. It is the rated frequency; It refers to output power; It refers to the state of charge (SOC) of the energy storage system's batteries. It is a correction value; These are the active power droop coefficient and the SOC rise coefficient, respectively. This is the reference voltage, limiting the range. ; It is the rated voltage; It is the reactive power droop coefficient; It is reactive power; According to the Coulomb counting method, SOC is calculated using the following formula: in, This is the initial value of SOC. It's the battery capacity. It is the battery output current; SOC control rise coefficient and correction value Set as In step S4, the f-dp / dv droop control method is specifically implemented as follows: in, This is a reference value for dp / dv; It is the droop coefficient; It is the bus frequency; It is a high-frequency limit; In step S4, the parameters of formula (8) are set as follows: Sag coefficient The settings are as follows: in, It is the minimum value of dp / dv.

2. The distributed collaborative control method for AC microgrid optical storage as described in claim 1, characterized in that: In step S2, the parameters of formulas (1) and (2) are set as follows: Active and reactive power droop coefficients Based on the range of active and reactive power output from the battery: in, These are the maximum and minimum active power outputs of the energy storage system's batteries. These are the maximum and minimum reactive power outputs of the energy storage system's battery.

Images