Grid-connected control method for energy storage converter

Abstract

The invention discloses an energy storage converter grid-connected control method, which relates to the technical field of energy storage management, and comprises the following steps: S1, determining the capacity and the type of an energy storage system and the rated power of a converter, and setting control parameters of a grid-connected converter; and S2, checking the battery state of the energy storage system, ensuring that the charging state of the battery is good, and carrying out normal work self-inspection on hardware and software of the converter. The output voltage and the power grid voltage are sampled before grid connection, and the phase and the frequency of the output voltage are quickly adjusted after the synchronization control strategy is performed when the phase difference is too large, so that the output voltage is synchronized with the power grid, the impact of current and voltage during grid connection is reduced, smooth grid connection switching is realized, obvious oscillation is avoided, and the grid connection reliability is improved. And the frequency change is kept in an allowable range, so that the problem of grid connection failure caused by power grid fluctuation can be avoided, and the power grid and equipment are protected.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage management, and in particular to a grid-connected control method for an energy storage converter. Background Art

[0002] With the development of high-tech in recent years, precision manufacturing, information industry, Internet servers and other related industries have accounted for an increasingly higher proportion in national life and the economy. The electrical equipment in these industries is extremely sensitive to interference in the system and requires a continuous and stable high-quality power supply. Any power quality problems such as voltage sag may cause sensitive electrical equipment to fail to work properly, or even cause engineering operations to stop, and the economic losses caused are difficult to estimate.

[0003] At present, when the power quality of the traditional energy storage inverter meets the grid connection conditions, if the energy storage inverter is directly connected to the grid, the voltage amplitude, frequency and phase of the load will be different from the grid voltage, which makes the phase difference after grid connection too large, resulting in a large current shock when connected to the grid, increasing the risk of system failure, and the phase difference may cause the system to oscillate, affecting the stability of the grid and even causing large-scale power outages. Summary of the invention

[0004] The purpose of the present invention is to provide a grid-connected control method for an energy storage inverter to solve the problem raised in the above background technology that when the energy storage inverter is directly connected to the grid, the voltage amplitude, frequency and phase of the load are different from the grid voltage, so that the phase difference after grid connection is too large, resulting in a large current shock when connected to the grid, increasing the risk of system failure, and the phase difference may cause oscillation in the system, affecting the stability of the grid and even causing large-scale power outages.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for controlling a grid-connected energy storage converter, comprising the following steps:

[0006] S1. Determine the capacity and type of the energy storage system and the rated power of the converter, and set the control parameters of the grid-connected converter;

[0007] S2. Check the battery status of the energy storage system to ensure that the battery is in good charging condition and perform a self-check on the normal operation of the converter hardware and software;

[0008] S3. After the self-check is completed, the control system of the converter is used to check whether the voltage, frequency and phase of the grid are synchronized with the energy storage converter before the grid connection;

[0009] S4. If the output voltage is not in the same frequency but in the same phase as the grid voltage, the energy storage converter voltage is synchronized with the main grid voltage through a pre-synchronization control strategy to reduce the impact current when connected to the grid;

[0010] S5, using the phase-locked PLL to achieve phase-locked judgment with the phase of the power grid. After the phase lock is successful, the output power of the energy storage converter is set through the microgrid instruction. After closed-loop control, the PWM module comparison register value is updated to achieve grid-connected power output;

[0011] S6. Monitor the changes in current, voltage and frequency during the grid connection process, and monitor the operating status of the energy storage system in real time after grid connection.

[0012] Preferably, in step S1, the capacity calculation of the energy storage system calculates the required energy storage capacity according to the load demand and the usage time, and the calculation formula is as follows:

[0013] Q(kWh)=(1+30%)(P×T);

[0014] Where: Q is the energy storage capacity, P is the load power, and T is the usage time.

[0015] Preferably, in step S3, the detecting whether the voltage, frequency and phase of the power grid are the same as those of the energy storage converter comprises the following steps:

[0016] S31, voltage detection: use the built-in voltage sensor of the energy storage converter to monitor the voltage value of the power grid in real time;

[0017] S32, frequency detection: monitor the frequency of the power grid through the frequency detection module of the energy storage converter;

[0018] S33, phase detection: Utilize the phase-locked loop function of the energy storage converter to detect the phase of the power grid in real time.

[0019] Preferably, in step S4, the synchronization of the energy storage converter voltage with the main grid voltage through the pre-synchronization control strategy includes the following steps:

[0020] S41, respectively sample the grid voltage and the output voltage of the energy storage converter, and obtain the phase θ of the grid voltage and the output voltage after passing through the phase-locked loop. g and θ, frequency f g with f;

[0021] S42, obtain the phase and frequency adjustment value θ through the PI regulator c With f c , the calculation formula is as follows:

[0022]

[0023]

[0024] Where: k θp , k θi is the phase regulator PI parameter, kfp , k fi is the frequency regulator PI parameter;

[0025] S43, before performing inner loop control, convert the phase output value to obtain the frequency reference value f ref , the calculation formula is as follows:

[0026]

[0027] S44, frequency output adjustment value f c The frequency reference value is used as the control inner loop given value, and the final output is adjusted by the inner loop PI controller after the difference is made. The calculation formula is:

[0028]

[0029] In the formula, k p , k i It is the PI parameter of the inner loop regulator. The voltage frequency and phase are adjusted simultaneously through the phase and frequency double closed loops. After a short closed loop adjustment, the output voltage can be made to have the same frequency and phase as the grid voltage.

[0030] Preferably, in step S5, the use of phase-locked PLL to achieve phase synchronization determination with the power grid includes the following steps:

[0031] S51, using a phase comparator to detect the phase difference between the grid signal and the local oscillator signal, and determining whether the phase difference is within a set tolerance range to confirm whether the phase lock is successful;

[0032] S52, after the phase lock is successful, the output power of the energy storage converter is set through the microgrid instruction, and after closed-loop control, the comparison register value of the PWM module is updated to achieve grid-connected power output;

[0033] S53, if the phase locking fails, the number of phase locking attempts is counted and judged in the program, and when the number of failures is less than 3, the phase locking will be re-performed and the cycle will be continued;

[0034] S54. When the number of phase-lock failures is greater than three times, the system will delay for a period of time to wait for the grid voltage to stabilize, and at the same time clear the number of phase-lock failures and perform phase-lock detection again until the output voltage is successfully synchronized with the grid voltage to achieve grid-connected switching.

[0035] Preferably, in step S6, monitoring the current, voltage and frequency changes during the grid connection process includes the following steps:

[0036] S61, Current monitoring: Regularly collect current data, record instantaneous current value and average current value, monitor current waveform, and ensure it is within the safe range;

[0037] S62, voltage monitoring: real-time monitoring of grid voltage, recording instantaneous voltage value and average voltage value, checking voltage fluctuation, and ensuring that the voltage is within the allowable range;

[0038] S63, Frequency monitoring: Monitor the grid frequency to ensure it is within the standard range, record frequency changes, and analyze the impact of frequency fluctuations on the system;

[0039] S64. Perform trend analysis on historical data, identify the change patterns of current, voltage and frequency, and output visual data changes.

[0040] Preferably, in step S6, the process of real-time monitoring of the operating status of the energy storage system after grid connection is: collecting energy storage inverter data in real time through sensors, transmitting the collected data to the monitoring platform through a wired or wireless network, processing the collected data, monitoring the data in real time, setting thresholds for various parameters according to safety standards of the equipment and system, and automatically issuing an alarm and processing when the monitored parameters exceed the set thresholds.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] 1. In this method, the output voltage and the grid voltage are sampled before grid connection. When the phase difference is too large, the phase and frequency of the output voltage are quickly adjusted through the synchronous control strategy to synchronize the output voltage with the grid, thereby reducing the impact of current and voltage during grid connection, achieving smooth grid connection switching without obvious oscillation, and keeping the frequency change within the allowable range. This can avoid the problem of grid connection failure caused by grid fluctuations and protect the grid and equipment.

[0043] 2. In this method, the voltage, frequency and phase of the power grid are monitored in real time to ensure that the energy storage inverter can respond to power grid changes in a timely manner. After grid connection, the current, voltage and frequency changes are monitored in real time to ensure that the system operates within a safe range. Thresholds are set and automatic alarms are issued to deal with potential problems in a timely manner and reduce the risk of failure. Through historical data analysis, change patterns are identified, system operation strategies are optimized, and overall efficiency is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 The present invention is a flow chart of a method for controlling a grid-connected energy storage converter. DETAILED DESCRIPTION

[0045] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the implementation regulations described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] See also Figure 1 The present invention provides a technical solution: a method for controlling a grid-connected energy storage converter, comprising the following steps:

[0047] Step 1: Determine the capacity and type of the energy storage system and the rated power of the converter, and set the control parameters of the grid-connected converter;

[0048] The capacity calculation of the energy storage system is based on the load demand and usage time to calculate the required energy storage capacity. The calculation formula is as follows:

[0049] Q(kWh)=(1+30%)(P×T);

[0050] In the formula: Q is the energy storage capacity, P is the load power, and T is the usage time;

[0051] Step 2: Check the battery status of the energy storage system to ensure that the battery is in good charging condition and perform a self-check of the hardware and software of the converter to ensure that the battery is in good condition and reduce the risk of system downtime due to battery failure;

[0052] Step 3: After the self-check is completed, the voltage, frequency and phase of the power grid are detected by the control system of the converter before the grid connection. The voltage, frequency and phase of the power grid are monitored in real time to ensure that the energy storage converter can respond to grid changes in a timely manner and can be connected smoothly when connected to the grid. The specific steps include:

[0053] 31) Voltage detection: Use the built-in voltage sensor of the energy storage converter to monitor the voltage value of the power grid in real time;

[0054] 32) Frequency detection: Monitor the frequency of the power grid through the frequency detection module of the energy storage converter;

[0055] 33) Phase detection: Utilize the phase-locked loop function of the energy storage converter to detect the phase of the power grid in real time

[0056] Step 4: If the output voltage is not in the same frequency but in the same phase as the grid voltage, the energy storage converter voltage is synchronized with the main grid voltage through a pre-synchronization control strategy to reduce the impact current when connected to the grid. The pre-synchronization control strategy can be used to reduce the impact current when the energy storage converter is connected to the grid, protect the grid and equipment, and avoid the problem of grid connection failure caused by grid fluctuations.

[0057] The following steps are used to synchronize the voltage of the energy storage converter with the main grid voltage through the pre-synchronization control strategy:

[0058] 41) Sample the grid voltage and the output voltage of the energy storage converter respectively, and obtain the phase θ of the grid voltage and the output voltage respectively after passing through the phase-locked loop g and θ, frequency f gwith f;

[0059] 42) The phase and frequency adjustment values ​​θ are obtained through the PI regulator c With f c , the calculation formula is as follows:

[0060]

[0061]

[0062] Where: k θp , k θi is the phase regulator PI parameter, k fp , k fi is the frequency regulator PI parameter;

[0063] 43) Before the inner loop control is performed, the phase output value is converted to obtain the frequency reference value f ref , the calculation formula is as follows:

[0064]

[0065] 44) Frequency output adjustment value f c The frequency reference value is used as the control inner loop given value, and the final output is adjusted by the inner loop PI controller after the difference is made. The calculation formula is:

[0066]

[0067] In the formula, k p , k i It is the PI parameter of the inner loop regulator. The voltage frequency and phase are adjusted simultaneously through the phase and frequency double closed loop. After a short closed loop adjustment, the output voltage can be made to have the same frequency and phase as the grid voltage.

[0068] Step 5: Use phase-locked PLL to achieve phase synchronization with the power grid and phase lock judgment. After the phase lock is successful, the output power of the energy storage converter is set through the microgrid instruction. After closed-loop control, the PWM module comparison register value is updated to achieve grid-connected power output. The phase synchronization with the power grid is achieved through PLL to ensure that the output power of the energy storage converter matches the power grid. After the phase lock is successful, the output power of the energy storage converter can be accurately controlled to improve energy utilization efficiency.

[0069] Wherein, using the phase-locked PLL to realize phase synchronization judgment with the power grid includes the following steps:

[0070] 51) Use a phase comparator to detect the phase difference between the grid signal and the local oscillator signal, and determine whether the phase difference is within the set tolerance range to confirm whether the phase lock is successful;

[0071] 52) After the phase lock is successful, the output power of the energy storage converter is set through the microgrid instruction. After closed-loop control, the PWM module comparison register value is updated to achieve grid-connected power output;

[0072] 53) If the phase lock fails, the program will count the number of phase locks and make a judgment. If the number of failures is less than 3, the program will re-lock the phase and cycle;

[0073] 54) When the number of phase-lock failures exceeds three times, the system will delay for a period of time to wait for the grid voltage to stabilize, clear the number of phase-lock failures and perform phase-lock detection again until the output voltage is successfully synchronized with the grid voltage to achieve grid-connected switching;

[0074] Step 6: Monitor the current, voltage and frequency changes during the grid connection process, and monitor the operating status of the energy storage system in real time after grid connection. Ensure that the system operates within a safe range by monitoring the current, voltage and frequency changes in real time.

[0075] Among them, monitoring the current, voltage and frequency changes during the grid connection process includes the following steps:

[0076] 61) Current monitoring: regularly collect current data, record instantaneous current value and average current value, monitor current waveform to ensure it is within the safe range;

[0077] 62) Voltage monitoring: monitor the grid voltage in real time, record the instantaneous voltage value and average voltage value, check the voltage fluctuation, and ensure that the voltage is within the allowable range;

[0078] 63) Frequency monitoring: monitor the grid frequency to ensure it is within the standard range, record frequency changes, and analyze the impact of frequency fluctuations on the system;

[0079] 64) Perform trend analysis on historical data, identify the change patterns of current, voltage and frequency, and output visual data changes;

[0080] Among them, the process of real-time monitoring of the operating status of the energy storage system after grid connection is: collect energy storage inverter data in real time through sensors, transmit the collected data to the monitoring platform through wired or wireless networks, process the collected data, monitor the data in real time, set the thresholds of various parameters according to the safety standards of equipment and systems, and automatically issue an alarm and handle it when the monitored parameters exceed the set thresholds, set thresholds and automatically alarm, deal with potential problems in a timely manner, and reduce the risk of failure.

[0081] In this method, capacity matching is used to ensure that the capacity of the energy storage system matches the load demand to avoid overload or underload. Appropriate control parameters are set to improve the response speed and stability of the converter. The self-check mechanism is used to timely discover and solve hardware or software problems and improve the overall reliability of the system. The voltage, frequency and phase of the power grid are monitored in real time to ensure that the energy storage converter can respond to power grid changes in a timely manner. The pre-synchronization control strategy is used to reduce the impact current when the energy storage converter is connected to the power grid, protect the power grid and equipment, achieve synchronization of voltage with the power grid, improve the stability of the system, and reduce the probability of failure. Real-time monitoring of current, voltage and frequency changes ensures that the system operates within a safe range. Through historical data analysis, the change pattern is identified, the system operation strategy is optimized, and the overall efficiency is improved.

[0082] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for controlling grid-connected energy storage converter, characterized in that: The following steps are involved: S1. Determine the capacity and type of the energy storage system and the rated power of the converter, and set the control parameters of the grid-connected converter; S2. Check the battery status of the energy storage system to ensure that the battery is in good charging condition and perform a self-check on the normal operation of the converter hardware and software; S3. After the self-check is completed, the control system of the converter is used to check whether the voltage, frequency and phase of the grid are synchronized with the energy storage converter before the grid connection; S4. If the output voltage is not in the same frequency but in the same phase as the grid voltage, the energy storage converter voltage is synchronized with the main grid voltage through a pre-synchronization control strategy to reduce the impact current when connected to the grid; S5, using the phase-locked PLL to achieve phase-locked judgment with the phase of the power grid. After the phase lock is successful, the output power of the energy storage converter is set through the microgrid instruction. After closed-loop control, the PWM module comparison register value is updated to achieve grid-connected power output; S6. Monitor the changes in current, voltage and frequency during the grid connection process, and monitor the operating status of the energy storage system in real time after grid connection.

2. A method for controlling grid-connected energy storage converter according to claim 1, characterized in that: In step S1, the capacity calculation of the energy storage system calculates the required energy storage capacity according to the load demand and the usage time, and the calculation formula is as follows: Q(kWh)=(1+30%)(P×T); Where: Q is the energy storage capacity, P is the load power, and T is the usage time.

3. A method for controlling grid-connected energy storage converter according to claim 1, characterized in that: In step S3, the step of detecting whether the voltage, frequency and phase of the power grid are the same as those of the energy storage converter comprises the following steps: S31, voltage detection: use the built-in voltage sensor of the energy storage converter to monitor the voltage value of the power grid in real time; S32, frequency detection: monitor the frequency of the power grid through the frequency detection module of the energy storage converter; S33, phase detection: Utilize the phase-locked loop function of the energy storage converter to detect the phase of the power grid in real time.

4. A method for controlling grid-connected energy storage converter according to claim 1, characterized in that: In step S4, the synchronization of the energy storage converter voltage with the main grid voltage through the pre-synchronization control strategy includes the following steps: S41, respectively sample the grid voltage and the output voltage of the energy storage converter, and obtain the phase θ of the grid voltage and the output voltage after passing through the phase-locked loop. g and θ, frequency f g with f; S42, obtain the phase and frequency adjustment value θ through the PI regulator c With f c , the calculation formula is as follows: Where: k θp , k θi is the phase regulator PI parameter, k fp , k fi is the frequency regulator PI parameter; S43, before performing inner loop control, convert the phase output value to obtain the frequency reference value f ref , the calculation formula is as follows: S44, frequency output adjustment value f c The frequency reference value is used as the control inner loop given value, and the final output is adjusted by the inner loop PI controller after the difference is made. The calculation formula is: In the formula, k p , k i It is the PI parameter of the inner loop regulator. The voltage frequency and phase are adjusted simultaneously through the phase and frequency double closed loops. After a short closed loop adjustment, the output voltage can be made to have the same frequency and phase as the grid voltage.

5. A method for controlling grid-connected energy storage converter according to claim 1, characterized in that: In step S5, the use of phase-locked PLL to achieve phase synchronization determination with the power grid includes the following steps: S51, using a phase comparator to detect the phase difference between the grid signal and the local oscillator signal, and determining whether the phase difference is within a set tolerance range to confirm whether the phase lock is successful; S52, after the phase lock is successful, the output power of the energy storage converter is set through the microgrid instruction, and after closed-loop control, the comparison register value of the PWM module is updated to achieve grid-connected power output; S53, if the phase locking fails, the number of phase locking attempts is counted and judged in the program, and when the number of failures is less than 3, the phase locking will be re-performed and the cycle will be continued; S54. When the number of phase-lock failures is greater than three times, the system will delay for a period of time to wait for the grid voltage to stabilize, and at the same time clear the number of phase-lock failures and perform phase-lock detection again until the output voltage is successfully synchronized with the grid voltage to achieve grid-connected switching.

6. A method for controlling grid-connected energy storage converter according to claim 1, characterized in that: In step S6, the monitoring of current, voltage and frequency changes during the grid connection process includes the following steps: S61, Current monitoring: Regularly collect current data, record instantaneous current value and average current value, monitor current waveform, and ensure it is within the safe range; S62, voltage monitoring: real-time monitoring of grid voltage, recording instantaneous voltage value and average voltage value, checking voltage fluctuation, and ensuring that the voltage is within the allowable range; S63, Frequency monitoring: Monitor the grid frequency to ensure it is within the standard range, record frequency changes, and analyze the impact of frequency fluctuations on the system; S64. Perform trend analysis on historical data, identify the change patterns of current, voltage and frequency, and output visual data changes.

7. A method for controlling grid-connected energy storage converter according to claim 1, characterized in that: In step S6, the process of real-time monitoring of the operating status of the energy storage system after grid connection is: collecting energy storage inverter data in real time through sensors, transmitting the collected data to the monitoring platform through wired or wireless networks, processing the collected data, monitoring the data in real time, setting thresholds for various parameters according to the safety standards of the equipment and system, and automatically issuing an alarm and processing when the monitored parameters exceed the set thresholds.

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