Island operation coordination control method and system for photovoltaic micro-grid hybrid energy storage system

Abstract

The invention provides an island operation control method and system for a photovoltaic micro-grid hybrid energy storage system, and the method comprises the steps: determining an operation mode of the hybrid energy storage system according to the charge state of an energy storage unit during the island operation of the photovoltaic micro-grid hybrid energy storage system, and then carrying out the island operation control of the hybrid energy storage system based on the operation mode of the hybrid energy storage system. And determining a corresponding operation control strategy in combination with the output power of the photovoltaic system and the load demand power. According to the invention, factors such as photovoltaic output power, load consumption power, SOC information of a storage battery and a super capacitor and the like are comprehensively considered, four operation modes and corresponding energy coordination control strategies are designed, and the system can stably operate under various complex conditions.

Description

Technical Field

[0001] The present invention belongs to the technical field of photovoltaic microgrids, and in particular relates to a method and system for coordinated control of isolated island operation of a photovoltaic microgrid hybrid energy storage system. Background Art

[0002] With the growth of global energy demand and the emphasis on renewable energy, photovoltaic microgrids have been widely used as an efficient and clean energy supply system. However, when photovoltaic microgrids are operating in an isolated island, they are disconnected from the main power grid and face problems such as large power fluctuations and unstable bus voltage. These problems seriously affect the power supply reliability and power quality of photovoltaic microgrids.

[0003] At present, there are still deficiencies in the research on control strategies for photovoltaic microgrid hybrid energy storage systems under isolated island operation. For example, traditional control strategies are difficult to flexibly adjust according to the actual operation of the system, resulting in a shortened service life of energy storage components and poor system stability. Therefore, there is an urgent need for a control strategy that can effectively coordinate the operation of photovoltaic cells, batteries and supercapacitors to improve the stability and reliability of photovoltaic microgrids under isolated island operation. Summary of the invention

[0004] The purpose of the present invention is to provide a method and system for coordinated control of island operation of a photovoltaic microgrid hybrid energy storage system in view of the above-mentioned problems existing in the prior art.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] In a first aspect, the present invention proposes a method for coordinated control of island operation of a photovoltaic microgrid hybrid energy storage system, comprising:

[0007] S1. When the photovoltaic microgrid hybrid energy storage system is operating in an isolated mode, the operating mode of the hybrid energy storage system is determined according to the charge state of the energy storage unit, including:

[0008] If the charge states of the supercapacitor and the battery are both within the normal range, the hybrid energy storage system is in operation mode 1;

[0009] If the state of charge of the supercapacitor exceeds the limit and the state of charge of the battery is within the normal range, the hybrid energy storage system is in operation mode 2;

[0010] If the state of charge of the supercapacitor is within the normal range and the state of charge of the battery is off the line, the hybrid energy storage system is in operation mode 3;

[0011] If the state of charge of both the supercapacitor and the battery exceeds the limit, the hybrid energy storage system is in operation mode 4;

[0012] S2. Based on the operating mode of the hybrid energy storage system, the corresponding energy coordination control strategy is determined in combination with the output power of the photovoltaic system and the load demand power.

[0013] The S2 includes:

[0014] In operation mode 1, the hybrid energy storage system is not adjusted, and the photovoltaic system operates in MPPT control mode;

[0015] In operation mode 2,

[0016] If SOC sc <SOC sc_min And PV>PL, no adjustment is made to the hybrid energy storage system;

[0017] If SOC sc <SOC sc_min And P V <P L , the output of the battery is increased, allowing the supercapacitor to absorb excess power;

[0018] If SOC sc >SOC sc_max And P V <P L , then the hybrid energy storage system will not be adjusted;

[0019] If SOC sc >SOC sc_max And PV>PL, the battery is used to absorb the remaining power and discharge the supercapacitor;

[0020] In operation mode 3,

[0021] If SOC bat <SOC bat_min And PV>PL, no adjustment is made to the hybrid energy storage system;

[0022] If SOC bat <SOC bat_min And P V <P L , the power balance of the system is maintained by cutting off unnecessary loads;

[0023] If SOC bat >SOC bat_max And P V <P L , then the hybrid energy storage system will not be adjusted;

[0024] If SOC bat >SOC bat_max If PV>PL, the working mode of the photovoltaic system is adjusted to the constant voltage output control mode;

[0025] In operation mode 4,

[0026] If SOC bat >SOC bat_max , SOC sc >SOC sc_max And P V <P L , then the hybrid energy storage system will not be adjusted;

[0027] If SOC bat >SOC bat_max , SOC sc >SOC sc_max If PV>PL, the working mode of the photovoltaic system is adjusted to the constant voltage output control mode;

[0028] If SOC bat <SOC bat_min , SOC sc <SOC sc_min And PV>PL, no adjustment is made to the hybrid energy storage system;

[0029] If SOC bat <SOC bat_min , SOC sc <SOC sc_min And P V <P L , the power balance of the system is maintained by cutting off unnecessary loads;

[0030] If SOC bat >SOC bat_max , SOC sc <SOC sc_min And P V <P L , the output of the battery is increased, allowing the supercapacitor to absorb excess power;

[0031] If SOC bat >SOC bat_max , SOC sc <SOC sc_min If PV>PL, the working mode of the photovoltaic system is adjusted to the constant voltage output control mode;

[0032] If SOC bat <SOC bat_min , SOC sc >SOC sc_max And PV>PL, the battery is used to absorb the remaining power and discharge the supercapacitor;

[0033] If SOC bat <SOCbat_min , SOC sc >SOC sc_max If PV < PL, the power balance of the system is maintained by removing unnecessary loads;

[0034] Among them, SOC sc , SOC bat They are the state of charge of supercapacitor and battery, SOC sc_min , SOC sc_max They are the minimum and maximum state of charge allowed by the supercapacitor, SOC bat_min , SOC bat_max are the minimum and maximum state of charge allowed for the battery, PV and PL are the output power of the photovoltaic system and the load demand power, respectively.

[0035] The working mode of the photovoltaic system is realized by the Boost converter, which specifically includes:

[0036] In MPPT control mode, the Boost converter collects the current i from the photovoltaic system. pv and voltage U pv , the reference current i is calculated by using the improved perturbation observation method mppt , and i mppt with i pv By comparison, the duty cycle D is obtained through the PI controller and the pulse width modulation circuit;

[0037] In the constant voltage output control mode, the Boost converter uses a dual closed-loop control method to maintain the stability of the bus voltage.

[0038] The reference current i is calculated by using the improved perturbation observation method. mppt include:

[0039] A1. Based on i pv Calculate P(k) and P(k-1) from the voltage Upv respectively, and calculate the difference ΔP between them;

[0040] A2, determine whether |ΔP| is greater than or equal to the set threshold. If so, proceed to A3; if not, proceed to A6;

[0041] A3, determine whether ΔP is greater than 0, if it is, go to A4; if not, go to A5;

[0042] A4. Determine whether U(k) is greater than U(k-1). If so, set U(k+1)=U(k)+ΔU1; if not, set U(k+1)=U(k)-ΔU1.

[0043] A5. Determine whether U(k) is greater than U(k-1). If so, set U(k+1)=U(k)-ΔU1; if not, set U(k+1)=U(k)+ΔU1;

[0044] A6, determine whether ΔP is greater than 0, if it is, go to A7; if not, go to A8;

[0045] A7. Determine whether U(k) is greater than U(k-1). If so, set U(k+1)=U(k)+ΔU2; if not, set U(k+1)=U(k)-ΔU2;

[0046] A8. Determine whether U(k) is greater than U(k-1). If so, set U(k+1)=U(k)-ΔU2; if not, set U(k+1)=U(k)+ΔU2;

[0047] Wherein, P(k) and P(k-1) are the powers at time k and time k-1 respectively, U(k) and U(k-1) are the voltages at time k and time k-1 respectively, ΔU1 and ΔU2 are two different voltage change steps, and ΔU1>ΔU2;

[0048] Continue the disturbance adjustment process of A1-A8 and continuously measure the current and voltage values ​​of the photovoltaic system. The current measured when the photovoltaic system is operating in the maximum power point area is i mppt .

[0049] The method further comprises:

[0050] In each working mode, when the bus voltage changes, the following energy storage element control strategy is adopted:

[0051] First, the net power fluctuation of the microgrid is determined according to the change of the bus voltage, and then the current reference values ​​of the supercapacitor and the battery are allocated using the first-order low-pass filtering method. Finally, the charging and discharging of the supercapacitor and the battery are adjusted according to the actual charge state of the supercapacitor and the battery and the energy coordination control strategy determined by S2.

[0052] In a second aspect, the present invention proposes a photovoltaic microgrid hybrid energy storage system island operation coordination control system, including an operation mode determination module and an energy coordination control strategy determination module;

[0053] The operation mode determination module is used to determine the operation mode of the hybrid energy storage system according to the charge state of the energy storage unit when the photovoltaic microgrid hybrid energy storage system is islanded, including:

[0054] If the charge states of the supercapacitor and the battery are both within the normal range, the hybrid energy storage system is in operation mode 1;

[0055] If the state of charge of the supercapacitor exceeds the limit and the state of charge of the battery is within the normal range, the hybrid energy storage system is in operation mode 2;

[0056] If the state of charge of the supercapacitor is within the normal range and the state of charge of the battery is off the line, the hybrid energy storage system is in operation mode 3;

[0057] If the state of charge of both the supercapacitor and the battery exceeds the limit, the hybrid energy storage system is in operation mode 4;

[0058] The energy coordination control strategy determination module is used to determine the corresponding energy coordination control strategy based on the operation mode of the hybrid energy storage system, combined with the output power of the photovoltaic system and the load demand power.

[0059] The energy coordination control strategy includes:

[0060] In operation mode 1, the hybrid energy storage system is not adjusted, and the photovoltaic system operates in MPPT control mode;

[0061] In operation mode 2,

[0062] If SOC sc <SOC sc_min And PV>PL, no adjustment is made to the hybrid energy storage system;

[0063] If SOC sc <SOC sc_min And P V <P L , the output of the battery is increased, allowing the supercapacitor to absorb excess power;

[0064] If SOC sc >SOC sc_max And P V <P L , then the hybrid energy storage system will not be adjusted;

[0065] If SOC sc >SOC sc_max And PV>PL, the battery is used to absorb the remaining power and discharge the supercapacitor;

[0066] In operation mode 3,

[0067] If SOC bat <SOC bat_min And PV>PL, no adjustment is made to the hybrid energy storage system;

[0068] If SOC bat <SOC bat_min And P V <P L, the power balance of the system is maintained by cutting off unnecessary loads;

[0069] If SOC bat >SOC bat_max And P V <P L , then the hybrid energy storage system will not be adjusted;

[0070] If SOC bat >SOC bat_max If PV>PL, the working mode of the photovoltaic system is adjusted to the constant voltage output control mode;

[0071] In operation mode 4,

[0072] If SOC bat >SOC bat_max , SOC sc >SOC sc_max And P V <P L , then the hybrid energy storage system will not be adjusted;

[0073] If SOC bat >SOC bat_max , SOC sc >SOC sc_max If PV>PL, the working mode of the photovoltaic system is adjusted to the constant voltage output control mode;

[0074] If SOC bat <SOC bat_min , SOC sc <SOC sc_min And PV>PL, no adjustment is made to the hybrid energy storage system;

[0075] If SOC bat <SOC bat_min , SOC sc <SOC sc_min And P V <P L , the power balance of the system is maintained by cutting off unnecessary loads;

[0076] If SOC bat >SOC bat_max , SOC sc <SOC sc_min And P V <P L , the output of the battery is increased, allowing the supercapacitor to absorb excess power;

[0077] If SOC bat >SOC bat_max , SOC sc<SOC sc_min If PV>PL, the working mode of the photovoltaic system is adjusted to the constant voltage output control mode;

[0078] If SOC bat <SOC bat_min , SOC sc >SOC sc_max And PV>PL, the battery is used to absorb the remaining power and discharge the supercapacitor;

[0079] If SOC bat <SOC bat_min , SOC sc >SOC sc_max If PV < PL, the power balance of the system is maintained by removing unnecessary loads;

[0080] Among them, SOC sc , SOC bat They are the state of charge of supercapacitor and battery, SOC sc_min , SOC sc_max They are the minimum and maximum state of charge allowed by the supercapacitor, SOC bat min , SOC bat max are the minimum and maximum state of charge allowed for the battery, PV and PL are the output power of the photovoltaic system and the load demand power, respectively.

[0081] The system further includes a Boost converter, which is used to control the working mode of the photovoltaic system. The specific control strategy includes:

[0082] In MPPT control mode, the Boost converter collects the current i from the photovoltaic system. pv and voltage U pv , the reference current i is calculated by using the improved perturbation observation method mppt , and i mppt with i pv By comparison, the duty cycle D is obtained through the PI controller and the pulse width modulation circuit;

[0083] In the constant voltage output control mode, the Boost converter uses a dual closed-loop control method to maintain the stability of the bus voltage.

[0084] The reference current i is calculated by using the improved perturbation observation method. mppt include:

[0085] A1. Based on i pv Calculate P(k) and P(k-1) from the voltage Upv respectively, and calculate the difference ΔP between them;

[0086] A2, determine whether |ΔP| is greater than or equal to the set threshold. If so, proceed to A3; if not, proceed to A6;

[0087] A3, determine whether ΔP is greater than 0, if it is, go to A4; if not, go to A5;

[0088] A4. Determine whether U(k) is greater than U(k-1). If so, set U(k+1)=U(k)+ΔU1; if not, set U(k+1)=U(k)-ΔU1.

[0089] A5. Determine whether U(k) is greater than U(k-1). If so, set U(k+1)=U(k)-ΔU1; if not, set U(k+1)=U(k)+ΔU1;

[0090] A6, determine whether ΔP is greater than 0, if it is, go to A7; if not, go to A8;

[0091] A7. Determine whether U(k) is greater than U(k-1). If so, set U(k+1)=U(k)+ΔU2; if not, set U(k+1)=U(k)-ΔU2;

[0092] A8. Determine whether U(k) is greater than U(k-1). If so, set U(k+1)=U(k)-ΔU2; if not, set U(k+1)=U(k)+ΔU2;

[0093] Wherein, P(k) and P(k-1) are the powers at time k and time k-1 respectively, U(k) and U(k-1) are the voltages at time k and time k-1 respectively, ΔU1 and ΔU2 are two different voltage change steps, and ΔU1>ΔU2;

[0094] Continue the disturbance adjustment process of A1-A8 and continuously measure the current and voltage values ​​of the photovoltaic system. The current measured when the photovoltaic system is operating in the maximum power point area is i mppt .

[0095] The system also includes an energy storage element control module;

[0096] The energy storage element control module is used to execute the following energy storage element control strategy in each working mode when the bus voltage changes:

[0097] First, the net power fluctuation of the microgrid is determined according to the change of the bus voltage, and then the current reference values ​​of the supercapacitor and the battery are allocated using the first-order low-pass filtering method. Finally, the charging and discharging of the supercapacitor and the battery are adjusted according to the actual charge state of the supercapacitor and the battery and the energy coordination control strategy determined by S2.

[0098] Compared with the prior art, the present invention has the following beneficial effects:

[0099] 1. The present invention provides a method for controlling the isolated operation of a photovoltaic microgrid hybrid energy storage system. When the photovoltaic microgrid hybrid energy storage system is in isolated operation, the operation mode of the hybrid energy storage system is determined according to the charge state of the energy storage unit. Then, based on the operation mode of the hybrid energy storage system, the corresponding operation control strategy is determined in combination with the output power of the photovoltaic system and the load demand power. The method comprehensively considers multiple factors such as photovoltaic output power, load consumption power, SOC information of batteries and supercapacitors, and designs 4 operation modes and their corresponding energy coordination control strategies, so that the system can automatically adjust according to different operating conditions to ensure that the system can operate stably under various complex situations.

[0100] 2. The present invention provides a photovoltaic microgrid hybrid energy storage system island operation control method, which adopts an improved disturbance observation method to calculate the reference current under the MPPT control mode. The method formulates different tracking strategies according to the change in the output power of the photovoltaic system, thereby obtaining a more ideal maximum power point tracking effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0101] Figure 1 This is a flow chart of the method described in Example 1.

[0102] Figure 2 This is the power flow diagram of the PV microgrid under island operation.

[0103] Figure 3 This is the conversion circuit schematic of the Boost converter.

[0104] Figure 4 This is the control strategy diagram of the Boost converter.

[0105] Figure 5 Flowchart of the improved perturbation and observation method.

[0106] Figure 6 This is the control strategy diagram of the energy storage element under island operation.

[0107] Figure 7 This is a structural diagram of the system described in Example 2.

[0108] Figure 8 This is a structural diagram of the system described in Example 3. DETAILED DESCRIPTION

[0109] The present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0110] Embodiment 1:

[0111] A coordinated control method for island operation of a photovoltaic microgrid hybrid energy storage system, such as Figure 1 As shown, the specific steps are as follows:

[0112] 1. Analyze the power flow when the PV microgrid is operating in an isolated island.

[0113] The power flow diagram of the photovoltaic microgrid under island operation is as follows: Figure 2 As shown, the photovoltaic cell outputs power to the load through the Boost converter, where the output power PV of the photovoltaic system and the load demand power PV are both unidirectional flows, and the power P of the battery bat 、Supercapacitor power P sc , busbar capacitance P dc Both are bidirectional and satisfy:

[0114] P V =P bat +P sc +P L +P dc

[0115] If the DC bus voltage changes, the DC bus capacitor energy satisfies the following equation:

[0116]

[0117] ΔE C =T(P V -P L -P sc -P bat )

[0118] In the above formula, Udc_ref is the reference value of DC bus voltage, T is the running time, C dc , U dc are bus capacitance and voltage respectively.

[0119] From the above analysis, we can get:

[0120]

[0121] Changes in the output power of photovoltaic cells and the power consumed by the load will cause fluctuations in the DC bus voltage. The change of the former is uncertain, so it is necessary to adjust the charging and discharging power of the battery and supercapacitor at the same time to achieve the purpose of stabilizing the DC bus voltage.

[0122] 2. Monitor the output power of the photovoltaic system and the load demand power in real time to determine the charge state of the energy storage unit at this time.

[0123] 3. Determine the operating mode of the hybrid energy storage system according to the charge state of the energy storage unit, including:

[0124] If the charge states of the supercapacitor and the battery are both within the normal range, the hybrid energy storage system is in operation mode 1;

[0125] If the state of charge of the supercapacitor exceeds the limit and the state of charge of the battery is within the normal range, the hybrid energy storage system is in operation mode 2;

[0126] If the state of charge of the supercapacitor is within the normal range and the state of charge of the battery is off the line, the hybrid energy storage system is in operation mode 3;

[0127] If the charge state of both the supercapacitor and the battery exceeds the limit, the hybrid energy storage system is in operation mode 4.

[0128] 4. Based on the operating mode of the hybrid energy storage system, the corresponding energy coordination control strategy is determined in combination with the output power of the photovoltaic system and the load demand power, including:

[0129] Operation Mode 1:

[0130] This mode is the normal working mode. At this time, the energy storage element can effectively smooth out power fluctuations. The photovoltaic system works in the MPPT control mode, so the hybrid energy storage system is not adjusted.

[0131] Operation Mode 2:

[0132] Since the supercapacitor processes the high-frequency part of the power fluctuation, the supercapacitor's deactivation will reduce the energy storage system's ability to suppress high-frequency power fluctuations, so it needs to be restored to a safe range. According to the balance relationship of the output power, the energy coordination control strategy of this mode can be divided into the following four cases:

[0133] (1)SOC sc <SOC sc_min And PV>PL, at this time, the hybrid energy storage system is not adjusted;

[0134] (2)SOC sc <SOC sc_min And P V <P L , the output of the battery is increased, allowing the supercapacitor to absorb excess power;

[0135] (3)SOC sc >SOC sc_max And P V <P L , then the hybrid energy storage system will not be adjusted;

[0136] (4)SOC sc >SOC sc_max If PV>PL, the battery is used to absorb the remaining power and discharge the supercapacitor.

[0137] Operation Mode 3:

[0138] Since the battery processes the low-frequency part of the power fluctuation, if the battery stops working, the energy storage system's ability to suppress power fluctuations will be weakened for a long time. And because the battery capacity is much larger than the supercapacitor, it is difficult to control the output of the supercapacitor to meet the overall needs of the system. At this time, it can also be divided into the following four situations:

[0139] If SOC bat <SOC bat_min And PV>PL, no adjustment is made to the hybrid energy storage system;

[0140] If SOC bat <SOC bat_min And P V <P L , the power balance of the system is maintained by cutting off unnecessary loads;

[0141] If SOC bat >SOC bat_max And P V <P L , then the hybrid energy storage system will not be adjusted;

[0142] If SOC bat >SOC bat_max If PV>PL, the working mode of the photovoltaic system is adjusted to the constant voltage output control mode;

[0143] Operation Mode 4:

[0144] The energy coordination control strategy in this working mode is divided into the following 8 cases:

[0145] If SOC bat >SOC bat_max , SOC sc >SOC sc_max And P V <P L , then the hybrid energy storage system will not be adjusted;

[0146] If SOC bat >SOC bat_max , SOC sc >SOC sc_max If PV>PL, the working mode of the photovoltaic system is adjusted to the constant voltage output control mode;

[0147] If SOC bat <SOC bat_min , SOC sc <SOC sc_minAnd PV>PL, no adjustment is made to the hybrid energy storage system;

[0148] If SOC bat <SOC bat_min , SOC sc <SOC sc_min And P V <P L , the power balance of the system is maintained by cutting off unnecessary loads;

[0149] If SOC bat >SOC bat_max , SOC sc <SOC sc_min And P V <P L , the output of the battery is increased, allowing the supercapacitor to absorb excess power;

[0150] If SOC bat >SOC bat_max , SOC sc <SOC sc_min If PV>PL, the working mode of the photovoltaic system is adjusted to the constant voltage output control mode;

[0151] If SOC bat <SOC bat_min , SOC sc >SOC sc_max And PV>PL, the battery is used to absorb the remaining power and discharge the supercapacitor;

[0152] If SOC bat <SOC bat_min , SOC sc >SOC sc_max If PV < PL, the power balance of the system is maintained by removing unnecessary loads;

[0153] Among them, SOC sc , SOC bat They are the state of charge of supercapacitor and battery, SOC sc_min , SOC sc_max They are the minimum and maximum state of charge allowed by the supercapacitor, SOC bat_min , SOC bat_max They are the minimum and maximum state of charge allowed for the battery.

[0154] 5. Coordinate and control the system based on the determined energy coordination control strategy.

[0155] The working mode of the photovoltaic system is controlled by the Boost converter through switching. The conversion circuit schematic of the Boost converter is shown in Figure 3 As shown, U in is the input voltage, L is the inductance on the photovoltaic power generation side, R is the equivalent resistance on the DC bus side, C is the equivalent inductance on the DC bus side, UL is the inductance voltage, and U0 is the output voltage. When the switch tube S is turned on, S is equivalent to a short circuit. At this time, the inductor L absorbs energy from the power supply and plays an energy storage role. At this time, U L =U in ; However, when the switch tube is disconnected, S is equivalent to a short circuit, and the inductance cannot change suddenly, so the energy is released outward.

[0156] According to the duty cycle D, we can get:

[0157]

[0158] If there is excess energy in the microgrid and the energy storage element has reached a point where it cannot stabilize power due to its own SOC characteristics, it is necessary to adjust the working mode of the photovoltaic power generation system. The working mode of the photovoltaic system can be adjusted to a constant voltage mode to stabilize the output power of the photovoltaic cell at a non-maximum power point value to achieve the purpose of stabilizing the bus voltage. The control strategy of the Boost converter is as follows Figure 4 shown.

[0159] If the switch is connected to b, the Boost converter operates in MPPT control mode. The Boost converter collects the current i from the photovoltaic system. pv and voltage U pv , the reference current i is calculated by using the improved perturbation observation method mppt , and i mppt with i pv By comparison, the duty cycle D is obtained through the PI controller and the pulse width modulation circuit. Among them, the process of the improved perturbation observation method is as follows Figure 5 As shown, including:

[0160] A1. Based on i pv Calculate P(k) and P(k-1) from the voltage Upv respectively, and calculate the difference ΔP between them;

[0161] A2, determine whether |ΔP| is greater than or equal to the set threshold. If so, proceed to A3; if not, proceed to A6;

[0162] A3, determine whether ΔP is greater than 0, if it is, go to A4; if not, go to A5;

[0163] A4. Determine whether U(k) is greater than U(k-1). If so, set U(k+1)=U(k)+ΔU1; if not, set U(k+1)=U(k)-ΔU1.

[0164] A5. Determine whether U(k) is greater than U(k-1). If so, set U(k+1)=U(k)-ΔU1; if not, set U(k+1)=U(k)+ΔU1;

[0165] A6, determine whether ΔP is greater than 0, if it is, go to A7; if not, go to A8;

[0166] A7. Determine whether U(k) is greater than U(k-1). If so, set U(k+1)=U(k)+ΔU2; if not, set U(k+1)=U(k)-ΔU2;

[0167] A8. Determine whether U(k) is greater than U(k-1). If so, set U(k+1)=U(k)-ΔU2; if not, set U(k+1)=U(k)+ΔU2;

[0168] Wherein, P(k) and P(k-1) are the powers at time k and time k-1 respectively, U(k) and U(k-1) are the voltages at time k and time k-1 respectively, ΔU1 and ΔU2 are two different voltage change steps, and ΔU1>ΔU2;

[0169] Continue the disturbance adjustment process of A1-A8 and continuously measure the current and voltage values ​​of the photovoltaic system. The current measured when the photovoltaic system is operating in the maximum power point area is i mppt .

[0170] If the switch is connected to a, it operates in constant voltage output control mode. The Boost converter uses a dual closed-loop control method - voltage outer loop and current inner loop to maintain the stability of the bus voltage. dc_ref and U dc By comparison, the offset is obtained through the voltage outer loop PI controller i pv_ref , i.e. i pv The reference current value is then compared with i pv_ref and i pv , obtained through the current inner loop PI controller and pulse width modulation circuit.

[0171] If the system operates in Mode 1, Mode 2, Mode 3_(1), Mode 3_(2), Mode 3_(3), Mode 4_(1), Mode 4_(3), Mode 4_(4), Mode 4_(5), Mode 4_(7) and Mode 4_(6), the photovoltaic system needs to operate in the MPPT control mode. In other modes, the power output of the photovoltaic system exceeds the regulation range of the energy storage element and the load demand. Therefore, it is necessary to adjust the photovoltaic power generation system to the constant voltage mode to reduce the regulation pressure of the energy storage element.

[0172] Embodiment 2:

[0173] The steps are the same as in Example 1, except that:

[0174] This embodiment also includes a control strategy for energy storage elements under island operation, such as Figure 6 As shown, specifically including:

[0175] In each working mode of island operation, when the bus voltage changes, the net power fluctuation of the microgrid is first determined according to the change value of the bus voltage (the photovoltaic microgrid system working in the island operation mode will cause the net power fluctuation of the microgrid due to the change of the photovoltaic system output power and the load consumption power, and the bus voltage will change at this time. If the control system finds that the bus voltage has changed, it will prompt the battery and supercapacitor to start running, and use their charging and discharging characteristics to stabilize the bus voltage. Therefore, the state of the microgrid net power fluctuation can be obtained by using the phenomenon of bus voltage drop or rise), and then the first-order low-pass filtering method is used for energy distribution, and the current reference value i of the energy storage element is obtained through the voltage outer loop. ref ,i ref The supercapacitor current reference value I is obtained through a low-pass filter sc_ref and battery current reference value I bat_ref Then, the supercapacitor and battery are charged and discharged according to their actual state of charge and the energy coordination control strategy determined by the selector. Finally, the output current signal is compared with the actual current value flowing through the energy storage element, and the bidirectional DC / DC converter of the energy storage element is controlled through the PI controller and PWM control.

[0176] Embodiment 3:

[0177] A photovoltaic microgrid hybrid energy storage system island operation coordination control system, such as Figure 7 As shown, it includes an operation mode determination module, an energy coordination control strategy determination module, and a Boost converter;

[0178] The operation mode determination module is used to determine the operation mode of the hybrid energy storage system according to the charge state of the energy storage unit when the photovoltaic microgrid hybrid energy storage system is islanded, including:

[0179] If the charge states of the supercapacitor and the battery are both within the normal range, the hybrid energy storage system is in operation mode 1;

[0180] If the state of charge of the supercapacitor exceeds the limit and the state of charge of the battery is within the normal range, the hybrid energy storage system is in operation mode 2;

[0181] If the state of charge of the supercapacitor is within the normal range and the state of charge of the battery is off the line, the hybrid energy storage system is in operation mode 3;

[0182] If the state of charge of both the supercapacitor and the battery exceeds the limit, the hybrid energy storage system is in operation mode 4;

[0183] The energy coordination control strategy determination module is used to determine the corresponding energy coordination control strategy based on the operation mode of the hybrid energy storage system, combined with the output power of the photovoltaic system and the load demand power.

[0184] The energy coordination control strategy includes:

[0185] In operation mode 1, the hybrid energy storage system is not adjusted, and the photovoltaic system operates in MPPT control mode;

[0186] In operation mode 2,

[0187] If SOC sc <SOC sc_min And PV>PL, no adjustment is made to the hybrid energy storage system;

[0188] If SOC sc <SOC sc_min And P V <P L , the output of the battery is increased, allowing the supercapacitor to absorb excess power;

[0189] If SOC sc >SOC sc_max And P V <P L , then the hybrid energy storage system will not be adjusted;

[0190] If SOC sc >SOC sc_max And PV>PL, the battery is used to absorb the remaining power and discharge the supercapacitor;

[0191] In operation mode 3,

[0192] If SOC bat <SOC bat_min And PV>PL, no adjustment is made to the hybrid energy storage system;

[0193] If SOC bat <SOC bat_min And P V <P L , the power balance of the system is maintained by cutting off unnecessary loads;

[0194] If SOC bat >SOC bat_max And P V <P L , then the hybrid energy storage system will not be adjusted;

[0195] If SOC bat >SOC bat_max If PV>PL, the working mode of the photovoltaic system is adjusted to the constant voltage output control mode;

[0196] In operation mode 4,

[0197] If SOC bat >SOC bat_max , SOC sc >SOC sc_max And P V <P L , then the hybrid energy storage system will not be adjusted;

[0198] If SOC bat >SOC bat_max , SOC sc >SOC sc_max If PV>PL, the working mode of the photovoltaic system is adjusted to the constant voltage output control mode;

[0199] If SOC bat <SOC bat_min , SOC sc <SOC sc_min And PV>PL, no adjustment is made to the hybrid energy storage system;

[0200] If SOC bat <SOC bat_min , SOC sc <SOC sc_min And P V <P L , the power balance of the system is maintained by cutting off unnecessary loads;

[0201] If SOC bat >SOC bat_max , SOC sc <SOC sc_min And P V <P L , the output of the battery is increased, allowing the supercapacitor to absorb excess power;

[0202] If SOC bat >SOC bat_max , SOC sc <SOC sc_min If PV>PL, the working mode of the photovoltaic system is adjusted to the constant voltage output control mode;

[0203] If SOC bat <SOC bat_min , SOC sc >SOC sc_maxAnd PV>PL, the battery is used to absorb the remaining power and discharge the supercapacitor;

[0204] If SOC bat <SOC bat_min , SOC sc >SOC sc_max If PV < PL, the power balance of the system is maintained by removing unnecessary loads;

[0205] Among them, SOC sc , SOC bat They are the state of charge of supercapacitor and battery, SOC sc_min , SOC sc_max They are the minimum and maximum state of charge allowed by the supercapacitor, SOC bat_min , SOC bat_max are the minimum and maximum state of charge allowed for the battery, PV and PL are the output power of the photovoltaic system and the load demand power, respectively.

[0206] The Boost converter is used to control the working mode of the photovoltaic system. The specific control strategy includes:

[0207] In MPPT control mode, the Boost converter collects the current i from the photovoltaic system. pv and voltage U pv , the reference current i is calculated by using the improved perturbation observation method mppt , and i mppt with i pv By comparison, the duty cycle D is obtained by the PI controller and the pulse width modulation circuit, wherein the reference current i is calculated by the improved perturbation observation method. mppt include:

[0208] A1. Based on i pv Calculate P(k) and P(k-1) from the voltage Upv respectively, and calculate the difference ΔP between them;

[0209] A2, determine whether |ΔP| is greater than or equal to the set threshold. If so, proceed to A3; if not, proceed to A6;

[0210] A3, determine whether ΔP is greater than 0. If so, proceed to A4; if not, proceed to A5;

[0211] A4. Determine whether U(k) is greater than U(k-1). If so, set U(k+1)=U(k)+ΔU1; if not, set U(k+1)=U(k)-ΔU1.

[0212] A5. Determine whether U(k) is greater than U(k-1). If so, set U(k+1)=U(k)-ΔU1; if not, set U(k+1)=U(k)+ΔU1;

[0213] A6, determine whether ΔP is greater than 0, if it is, go to A7; if not, go to A8;

[0214] A7. Determine whether U(k) is greater than U(k-1). If so, set U(k+1)=U(k)+ΔU2; if not, set U(k+1)=U(k)-ΔU2;

[0215] A8. Determine whether U(k) is greater than U(k-1). If so, set U(k+1)=U(k)-ΔU2; if not, set U(k+1)=U(k)+ΔU2;

[0216] Wherein, P(k) and P(k-1) are the powers at time k and time k-1 respectively, U(k) and U(k-1) are the voltages at time k and time k-1 respectively, ΔU1 and ΔU2 are two different voltage change steps, and ΔU1>ΔU2;

[0217] Continue the disturbance adjustment process of A1-A8 and continuously measure the current and voltage values ​​of the photovoltaic system. The current measured when the photovoltaic system is operating in the maximum power point area is i mppt .

[0218] In the constant voltage output control mode, the Boost converter uses a dual closed-loop control method to maintain the stability of the bus voltage.

[0219] Embodiment 4:

[0220] Same as Example 3, except that:

[0221] The system also includes an energy storage element control module;

[0222] The energy storage element control module is used to execute the following energy storage element control strategy in each working mode when the bus voltage changes:

[0223] First, the net power fluctuation of the microgrid is determined according to the change of the bus voltage, and then the current reference values ​​of the supercapacitor and the battery are allocated using the first-order low-pass filtering method. Finally, the charging and discharging of the supercapacitor and the battery are adjusted according to the actual charge state of the supercapacitor and the battery and the energy coordination control strategy determined by S2.

Claims

1. A method for coordinated control of island operation of a photovoltaic microgrid hybrid energy storage system, characterized in that: The method comprises: S1. When the photovoltaic microgrid hybrid energy storage system is operating in an isolated mode, the operating mode of the hybrid energy storage system is determined according to the charge state of the energy storage unit, including: If the charge states of the supercapacitor and the battery are both within the normal range, the hybrid energy storage system is in operation mode 1; If the state of charge of the supercapacitor exceeds the limit and the state of charge of the battery is within the normal range, the hybrid energy storage system is in operation mode 2; If the state of charge of the supercapacitor is within the normal range and the state of charge of the battery is off the line, the hybrid energy storage system is in operation mode 3; If the state of charge of both the supercapacitor and the battery exceeds the limit, the hybrid energy storage system is in operation mode 4; S2. Based on the operating mode of the hybrid energy storage system, the corresponding energy coordination control strategy is determined in combination with the output power of the photovoltaic system and the load demand power.

2. A photovoltaic microgrid hybrid energy storage system island operation coordinated control method according to claim 1, characterized in that: The S2 includes: In operation mode 1, the hybrid energy storage system is not adjusted, and the photovoltaic system operates in MPPT control mode; In operation mode 2, If SOC sc <SOC sc_min And PV>PL, no adjustment is made to the hybrid energy storage system; If SOC sc <SOC sc_min And P V <P L , the output of the battery is increased, allowing the supercapacitor to absorb excess power; If SOC sc >SOC sc_max And P V <P L , then the hybrid energy storage system will not be adjusted; If SOC sc >SOC sc_max And PV>PL, the battery is used to absorb the remaining power and discharge the supercapacitor; In operation mode 3, If SOC bat <SOC bat_min And PV>PL, no adjustment is made to the hybrid energy storage system; If SOC bat <SOC bat_min And P V <P L , the power balance of the system is maintained by cutting off unnecessary loads; If SOC bat >SOC bat_max And P V <P L , then the hybrid energy storage system will not be adjusted; If SOC bat >SOC bat_max If PV>PL, the working mode of the photovoltaic system is adjusted to the constant voltage output control mode; In operation mode 4, If SOC bat >SOC bat_max , SOC sc >SOC sc_max And P V <P L , then the hybrid energy storage system will not be adjusted; If SOC bat >SOC bat_max , SOC sc >SOC sc_max If PV>PL, the working mode of the photovoltaic system is adjusted to the constant voltage output control mode; If SOC bat <SOC bat_min , SOC sc <SOC sc_min And PV>PL, no adjustment is made to the hybrid energy storage system; If SOC bat <SOC bat_min , SOC sc <SOC sc_min And P V <P L , the power balance of the system is maintained by cutting off unnecessary loads; If SOC bat >SOC bat_max , SOC sc <SOC sc_min And P V <P L , the output of the battery is increased, allowing the supercapacitor to absorb excess power; If SOC bat >SOC bat_max , SOC sc <SOC sc_min If PV>PL, the working mode of the photovoltaic system is adjusted to the constant voltage output control mode; If SOC bat <SOC bat_min , SOC sc >SOC sc_max And PV>PL, the battery is used to absorb the remaining power and discharge the supercapacitor; If SOC bat <SOC bat_min , SOC sc >SOC sc_max If PV<PL, the power balance of the system is maintained by removing unnecessary loads; Among them, SOC sc , SOC bat They are the state of charge of supercapacitor and battery, SOC sc_min , SOC sc_max They are the minimum and maximum state of charge allowed by the supercapacitor, SOC bat_min , SOC bat_max The minimum and maximum values ​​of the state of charge allowed by the battery, PV, P L They are the output power of the photovoltaic system and the load demand power respectively.

3. A method for coordinated control of isolated island operation of a photovoltaic microgrid hybrid energy storage system according to claim 2, characterized in that: The working mode of the photovoltaic system is realized by the Boost converter, which specifically includes: In MPPT control mode, the Boost converter collects the current i from the photovoltaic system. pv and voltage U pv , the reference current i is calculated by using the improved perturbation observation method mppt , and i mppt with i pv By comparison, the duty cycle D is obtained through the PI controller and the pulse width modulation circuit; In the constant voltage output control mode, the Boost converter uses a dual closed-loop control method to maintain the stability of the bus voltage.

4. A photovoltaic microgrid hybrid energy storage system island operation coordinated control method according to claim 3, characterized in that: The reference current i is calculated by using the improved perturbation observation method. mppt include: A1. Based on i pv Calculate P(k) and P(k-1) from the voltage Upv respectively, and calculate the difference ΔP between them; A2, determine whether |ΔP| is greater than or equal to the set threshold. If so, proceed to A3; if not, proceed to A6; A3, determine whether ΔP is greater than 0, if it is, go to A4; if not, go to A5; A4. Determine whether U(k) is greater than U(k-1). If so, set U(k+1)=U(k)+ΔU1; if not, set U(k+1)=U(k)-ΔU1. A5. Determine whether U(k) is greater than U(k-1). If so, set U(k+1)=U(k)-ΔU1; if not, set U(k+1)=U(k)+ΔU1; A6, determine whether ΔP is greater than 0, if it is, go to A7; if not, go to A8; A7. Determine whether U(k) is greater than U(k-1). If so, set U(k+1)=U(k)+ΔU2; if not, set U(k+1)=U(k)-ΔU2; A8. Determine whether U(k) is greater than U(k-1). If so, set U(k+1)=U(k)-ΔU2; if not, set U(k+1)=U(k)+ΔU2; Wherein, P(k) and P(k-1) are the powers at time k and time k-1 respectively, U(k) and U(k-1) are the voltages at time k and time k-1 respectively, ΔU1 and ΔU2 are two different voltage change steps, and ΔU1>ΔU2; Continue the disturbance adjustment process of A1-A8 and continuously measure the current and voltage values ​​of the photovoltaic system. The current measured when the photovoltaic system is running in the maximum power point area is i mppt .

5. The method for coordinated control of island operation of a photovoltaic microgrid hybrid energy storage system according to claim 1, characterized in that: The method further comprises: In each working mode, when the bus voltage changes, the following energy storage element control strategy is adopted: First, the net power fluctuation of the microgrid is determined according to the change of the bus voltage, and then the current reference values ​​of the supercapacitor and the battery are allocated using the first-order low-pass filtering method. Finally, the charging and discharging of the supercapacitor and the battery are adjusted according to the actual charge state of the supercapacitor and the battery and the energy coordination control strategy determined by S2.

6. A photovoltaic microgrid hybrid energy storage system island operation coordination control system, characterized in that: The system includes an operation mode determination module and an energy coordination control strategy determination module; The operation mode determination module is used to determine the operation mode of the hybrid energy storage system according to the charge state of the energy storage unit when the photovoltaic microgrid hybrid energy storage system is islanded, including: If the charge states of the supercapacitor and the battery are both within the normal range, the hybrid energy storage system is in operation mode 1; If the state of charge of the supercapacitor exceeds the limit and the state of charge of the battery is within the normal range, the hybrid energy storage system is in operation mode 2; If the state of charge of the supercapacitor is within the normal range and the state of charge of the battery is off the line, the hybrid energy storage system is in operation mode 3; If the state of charge of both the supercapacitor and the battery exceeds the limit, the hybrid energy storage system is in operation mode 4; The energy coordination control strategy determination module is used to determine the corresponding energy coordination control strategy based on the operation mode of the hybrid energy storage system, combined with the output power of the photovoltaic system and the load demand power.

7. A photovoltaic microgrid hybrid energy storage system island operation coordination control system according to claim 6, characterized in that: The energy coordination control strategy includes: In operation mode 1, the hybrid energy storage system is not adjusted, and the photovoltaic system operates in MPPT control mode; In operation mode 2, If SOC sc <SOC sc_min And PV>PL, no adjustment is made to the hybrid energy storage system; If SOC sc <SOC sc_min And P V <P L , the output of the battery is increased, allowing the supercapacitor to absorb excess power; If SOC sc >SOC sc_max And P V <P L , then the hybrid energy storage system will not be adjusted; If SOC sc >SOC sc_max And PV>PL, the battery is used to absorb the remaining power and discharge the supercapacitor; In operation mode 3, If SOC bat <SOC bat_min And PV>PL, no adjustment is made to the hybrid energy storage system; If SOC bat <SOC bat_min And P V <P L , the power balance of the system is maintained by cutting off unnecessary loads; If SOC bat >SOC bat_max And P V <P L , then the hybrid energy storage system will not be adjusted; If SOC bat >SOC bat_max If PV>PL, the working mode of the photovoltaic system is adjusted to the constant voltage output control mode; In operation mode 4, If SOC bat >SOC bat_max , SOC sc >SOC sc_max And P V <P L , then the hybrid energy storage system will not be adjusted; If SOC bat >SOC bat_max , SOC sc >SOC sc_max If PV>PL, the working mode of the photovoltaic system is adjusted to the constant voltage output control mode; If SOC bat <SOC bat_min , SOC sc <SOC sc_min And PV>PL, no adjustment is made to the hybrid energy storage system; If SOC bat <SOC bat_min , SOC sc <SOC sc_min And P V <P L , the power balance of the system is maintained by cutting off unnecessary loads; If SOC bat >SOC bat_max , SOC sc <SOC sc_min And P V <P L , the output of the battery is increased, allowing the supercapacitor to absorb excess power; If SOC bat >SOC bat_max , SOC sc <SOC sc_min If PV>PL, the working mode of the photovoltaic system is adjusted to the constant voltage output control mode; If SOC bat <SOC bat_min , SOC sc >SOC sc_max And PV>PL, the battery is used to absorb the remaining power and discharge the supercapacitor; If SOC bat <SOC bat_min , SOC sc >SOC sc_max If PV<PL, the power balance of the system is maintained by removing unnecessary loads; Among them, SOC sc , SOC bat They are the state of charge of supercapacitor and battery, SOC sc_min , SOC sc_max They are the minimum and maximum state of charge allowed by the supercapacitor, SOC bat_min , SOC bat_max are the minimum and maximum state of charge allowed for the battery, PV and PL are the output power of the photovoltaic system and the load demand power, respectively.

8. A photovoltaic microgrid hybrid energy storage system island operation coordination control system according to claim 7, characterized in that: The system further includes a Boost converter, which is used to control the working mode of the photovoltaic system. The specific control strategy includes: In MPPT control mode, the Boost converter collects the current i from the photovoltaic system. pv and voltage U pv , the reference current i is calculated by using the improved perturbation observation method mppt , and i mppt with i pv By comparison, the duty cycle D is obtained through the PI controller and the pulse width modulation circuit; In the constant voltage output control mode, the Boost converter uses a dual closed-loop control method to maintain the stability of the bus voltage.

9. A photovoltaic microgrid hybrid energy storage system island operation coordination control system according to claim 8, characterized in that: The reference current i is calculated by using the improved perturbation observation method. mppt include: A1. Based on i pv Calculate P(k) and P(k-1) from the voltage Upv respectively, and calculate the difference ΔP between them; A2, determine whether |ΔP| is greater than or equal to the set threshold. If so, proceed to A3; if not, proceed to A6; A3, determine whether ΔP is greater than 0, if it is, go to A4; if not, go to A5; A4. Determine whether U(k) is greater than U(k-1). If so, set U(k+1)=U(k)+ΔU1; if not, set U(k+1)=U(k)-ΔU1. A5. Determine whether U(k) is greater than U(k-1). If so, set U(k+1)=U(k)-ΔU1; if not, set U(k+1)=U(k)+ΔU1; A6, determine whether ΔP is greater than 0, if it is, go to A7; if not, go to A8; A7. Determine whether U(k) is greater than U(k-1). If so, set U(k+1)=U(k)+ΔU2; if not, set U(k+1)=U(k)-ΔU2; A8. Determine whether U(k) is greater than U(k-1). If so, set U(k+1)=U(k)-ΔU2; if not, set U(k+1)=U(k)+ΔU2; Wherein, P(k) and P(k-1) are the powers at time k and time k-1 respectively, U(k) and U(k-1) are the voltages at time k and time k-1 respectively, ΔU1 and ΔU2 are two different voltage change steps, and ΔU1>ΔU2; Continue the disturbance adjustment process of A1-A8 and continuously measure the current and voltage values ​​of the photovoltaic system. The current measured when the photovoltaic system is running in the maximum power point area is i mppt .

10. A photovoltaic microgrid hybrid energy storage system island operation coordination control system according to claim 6, characterized in that: The system also includes an energy storage element control module; The energy storage element control module is used to execute the following energy storage element control strategy in each working mode when the bus voltage changes: First, the net power fluctuation of the microgrid is determined according to the change of the bus voltage, and then the current reference values ​​of the supercapacitor and the battery are allocated using the first-order low-pass filtering method. Finally, the charging and discharging of the supercapacitor and the battery are adjusted according to the actual charge state of the supercapacitor and the battery and the energy coordination control strategy determined by S2.

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