A direct-mounted energy storage slow-start control method and system

Abstract

The present invention discloses a direct-mounted energy storage slow start control method and system, the system includes an overvoltage judgment module, an overcurrent judgment module, an overvoltage limit module, an overcurrent limit module, a voltage control module, a current control module and a PWM modulation module. The method includes: collecting the grid voltage signal V abc , calculate V abc The amplitude V p ; Collect line current signal I abc , calculate I abc The amplitude I p The virtual impedance coefficient is set according to the voltage amplitude; the current reference slope coefficient is set according to the current amplitude; the voltage control module performs closed-loop control on the grid connection point voltage, generates a current reference instruction to the current control module, obtains a voltage modulation signal, and sends it to the PWM modulation module to generate the converter switch drive signal. This invention can effectively solve the overvoltage and overcurrent problems that occur at the moment of startup of the direct-mounted energy storage system, improving the safety and reliability of the direct-mounted energy storage connected to the power system.

Description

Technical Field

[0001] The present invention belongs to the field of power electronics and power systems, and particularly relates to a direct-mounted energy storage soft start control method and system, which can be applied to high-power power electronic converter applications. Background Art

[0002] In recent years, the importance of energy storage technology has gradually become apparent. Energy storage is considered a crucial component of the six-step process of power generation: procurement, generation, transmission, distribution, utilization, and storage. It is also a key component of future smart grid development. Currently, low-voltage energy storage systems are the most widely used, but they suffer from isolation transformers, large footprints, high losses, and low system efficiency. Furthermore, the low switching frequency of energy storage converters affects the output power quality of the energy storage system.

[0003] Compared to low-voltage energy storage systems, direct-mounted energy storage systems respond faster and more consistently to grid dispatch commands, making them more aligned with future grid requirements for high-power, high-capacity, high-efficiency, high-utilization, and high-dynamic electrochemical energy storage. However, high-power, high-capacity direct-mounted energy storage systems are prone to overcurrent during startup, which can cause magnetizing inrush current in transformers. Furthermore, when an unloaded line is closed and connected to the grid, overvoltage can occur on the line at the moment of closing, impacting the safe and stable operation of the system.

[0004] Existing technical solutions do not effectively solve the overvoltage and overcurrent problems of direct-mounted energy storage systems, reducing the safety and reliability of direct-mounted energy storage systems in new power systems. Summary of the Invention

[0005] The purpose of the present invention is to solve the problem of overvoltage and overcurrent at the startup moment of a large-capacity direct-mounted energy storage system, and to propose a direct-mounted energy storage slow-start control method and system, which can be applied to high-power power electronic converter applications.

[0006] The present invention specifically provides a direct-mounted energy storage slow-start control method, the steps of which are as follows:

[0007] Step 1: The overvoltage judgment module collects the grid connection point voltage signal Vabc, calculates the amplitude Vp of Vabc and determines whether it exceeds the first overvoltage threshold Vo1 or the second overvoltage threshold Vo2;

[0008] Step 2: The overcurrent judgment module collects the line current signal Iabc, calculates the amplitude Ip of Iabc and determines whether it exceeds the first overcurrent threshold Io1 or the second overcurrent threshold Io2;

[0009] Step 3: If the voltage amplitude Vp is less than the first overvoltage threshold Vo1, the overvoltage limiting module sets the virtual impedance value coefficient to m1; if the voltage amplitude Vp is between Vo1 and Vo2, the overvoltage limiting module sets the virtual impedance value coefficient to m2; if the voltage amplitude Vp is greater than the second overvoltage threshold Vo2, the overvoltage limiting module sets the virtual impedance value coefficient to m3;

[0010] Step 4: If the current amplitude Ip is less than the first overcurrent threshold Io1, the overcurrent limiting module sets the current given slope coefficient to n1; if the current amplitude Ip is between Io1 and Io2, the overcurrent limiting module sets the current given slope coefficient to n2; if the current amplitude Ip is greater than the second overcurrent threshold Io2, the overcurrent limiting module sets the current given slope coefficient to n3;

[0011] Step 5: The voltage control module performs closed-loop control on the grid connection point voltage, generates a current setting instruction to the current control module, obtains a voltage modulation signal to the PWM modulation module, and generates a converter switch tube drive signal.

[0012] Furthermore, the amplitude Vp of Vabc is calculated in step 1, and the specific implementation steps are as follows:

[0013] 1) Transform the grid-connected point voltage signal Vabc from the three-phase abc coordinate system to the two-phase stationary coordinate system αβ:

[0014]

[0015] Among them, Va, Vb and Vc are the three-phase voltages at the grid connection point, Vα and Vβ are the two-phase voltages in the stationary coordinate system;

[0016] 2) Calculate the voltage amplitude Vp based on the two-phase voltages Vα and Vβ:

[0017]

[0018] Furthermore, the amplitude Ip of Iabc is calculated in step 2, and the specific implementation steps are as follows:

[0019] 1) Transform the line current signal Iabc from the three-phase abc coordinate system to the two-phase stationary coordinate system αβ:

[0020]

[0021] Among them, Ia, Ib and Ic are the three-phase currents of the line respectively, and Iα and Iβ are the two-phase currents of the stationary coordinate system respectively;

[0022] 2) Calculate the voltage amplitude Ip based on the two-phase currents Iα and Iβ:

[0023]

[0024] Furthermore, the virtual impedance coefficient in step 3 ranges from 0 to 1, and m1 <m2<m3。

[0025] Furthermore, in step 4, the value range of the current given slope coefficient is between 0 and 1, and n1>n2>n3.

[0026] Furthermore, the voltage closed-loop control and current closed-loop control in step 5 adopt a proportional-integral regulator to achieve zero-static-error command value tracking of the synchronous rotating coordinate system.

[0027] The present invention also relates to a direct-mounted energy storage soft-start control system, which includes an overvoltage judgment module, an overcurrent judgment module, an overvoltage limiting module, an overcurrent limiting module, a voltage control module, a current control module and a PWM modulation module; the overvoltage judgment module is respectively connected to the overvoltage limiting module and the voltage control module, the overcurrent judgment module is respectively connected to the overcurrent limiting module and the current control module, the output end of the voltage control module is connected to the input end of the current control module, and the output end of the current control module is connected to the PWM modulation module.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] This invention proposes a slow-start control method and system for direct-mounted energy storage systems, effectively resolving the overvoltage and overcurrent issues that occur during startup, thereby improving the safety and reliability of direct-mounted energy storage systems connected to power systems. Specifically, this solution is applicable to any energy storage converter application.

[0030] The present invention sets the virtual impedance value coefficient according to the instantaneous overvoltage value, realizes the equivalent increase of the transmission line resistance, reduces the distributed capacitance of the transmission line, reduces the impact on the system, is simple to implement, and does not reduce the transmission efficiency of the converter; sets the current given slope coefficient according to the instantaneous overcurrent value, so that the current reference value gradually increases and is limited to reduce the damage caused by the starting current to the system; it can simultaneously take into account the suppression of overvoltage and overcurrent components, realize dual closed-loop control of voltage and current, and effectively solve the overvoltage and overcurrent problems in the startup process of the direct-mounted energy storage system. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a flow chart of the direct-mounted energy storage slow-start control method;

[0032] Figure 2 This is the structural diagram of the direct-mounted energy storage slow-start control system;

[0033] Figure 3 This is the schematic diagram of the slow start control algorithm for the energy storage converter;

[0034] Figure 4 This is the topology diagram of the direct-mounted energy storage system;

[0035] Figure 5 is the voltage waveform when the soft start control method is not applied;

[0036] Figure 6 It is the voltage waveform when the slow start control method is applied;

[0037] Figure 7 is the current waveform when the soft start control method is not applied;

[0038] Figure 8 It is the current waveform when the soft start control method is applied. DETAILED DESCRIPTION

[0039] To better illustrate the technical solution provided by the present invention, the specific implementation methods of the present invention will be further introduced below with reference to the accompanying drawings.

[0040] Figure 1 A flow chart is provided for implementing a direct-mounted energy storage slow-start control method, including:

[0041] Step 1: The overvoltage judgment module collects the grid voltage signal V abc , calculate V abc The amplitude V p And determine whether it exceeds the first overvoltage threshold V o1 Or the second overvoltage threshold V o2 ;

[0042] Step 2: The overcurrent judgment module collects the line current signal I abc , calculate I abc The amplitude I p And judge whether it exceeds the first overcurrent threshold I o1 Or the second overcurrent threshold I o2 ;

[0043] Step 3: If the voltage amplitude V p Less than the first overvoltage threshold V o1 , then the overvoltage limit module sets the virtual impedance coefficient to m1. If the voltage amplitude V p At V o1 and V o2 If the voltage amplitude V p Greater than the second overvoltage threshold V o2 , then the overvoltage limit module sets the virtual impedance value coefficient to m3;

[0044] Step 4: If the current amplitude I p Less than the first overcurrent threshold I o1, then the overcurrent limit module sets the current given slope coefficient to n1. If the current amplitude I p In I o1 and I o2 If the current amplitude is I p Greater than the second overcurrent threshold I o2 , then the overcurrent limit module sets the current given slope coefficient to n3;

[0045] Step 5: The voltage control module performs closed-loop control on the grid connection point voltage, generates a current setting instruction to the current control module, obtains a voltage modulation signal to the PWM modulation module, and generates a converter switch tube drive signal.

[0046] Step 1 calculates V abc The amplitude V p The specific implementation steps are:

[0047] 1) The grid voltage signal V abc Transform from the three-phase abc coordinate system to the two-phase stationary coordinate system αβ:

[0048]

[0049] Among them, V a 、V b and V c They are the three-phase voltage at the grid connection point, V α and V β are the two-phase voltages in the stationary coordinate system respectively;

[0050] 2) According to the two-phase voltage V α With V β Calculate the voltage amplitude V p :

[0051]

[0052] The step 2 calculates I abc The amplitude I p , the specific implementation steps are:

[0053] 1) The line current signal I abc Transform from the three-phase abc coordinate system to the two-phase stationary coordinate system αβ:

[0054]

[0055] Among them, I a , I b and I c They are the three-phase current of the line, I α and I β are the two-phase currents in the stationary coordinate system respectively;

[0056] 2) According to the two-phase current I α with I β Calculate the voltage amplitude I p :

[0057]

[0058] The virtual impedance coefficient in step 3 has a value range of 0 to 1, and m1 <m2<m3。

[0059] In step 4, the value range of the current given slope coefficient is between 0 and 1, and n1>n2>n3.

[0060] The voltage closed-loop control and current closed-loop control in step 5 adopt a proportional-integral regulator to achieve zero-static-error command value tracking of the synchronous rotating coordinate system.

[0061] Figure 2 This is a block diagram of the structure of a direct-mounted energy storage slow-start control system. The control system includes an overvoltage determination module, an overcurrent determination module, an overvoltage limiting module, an overcurrent limiting module, a voltage control module, a current control module, and a PWM modulation module. The overvoltage determination module is connected to the overvoltage limiting module and the voltage control module, respectively. The overcurrent determination module is connected to the overcurrent limiting module and the current control module, respectively. The voltage control module output is connected to the current control module input, and the current control module output is connected to the PWM modulation module.

[0062] Figure 3 The voltage control module uses a proportional-integral regulator to perform closed-loop voltage regulation, with the input being the voltage command value V ref And the collected grid voltage signal V abc The output passes through the overvoltage limit module to generate the current command value I ref The overvoltage limit module is a curve with a slope of m, and the value of m is between 0 and 1. The expression of the voltage loop proportional integral regulator is:

[0063]

[0064] Among them, K pv K is the voltage loop proportional coefficient, iv is the voltage loop integral coefficient.

[0065] The current control module uses a proportional integral regulator to perform closed-loop regulation on the current, and the input is the current command value I ref And the collected line current signal I abcThe output is passed through the PWM adjustment module to generate the converter switching signal. The overcurrent limit module is n multiplied by the virtual resistance R, and the value of n is between 0 and 1. The expression of the current loop proportional integral regulator is:

[0066]

[0067] Among them, K pi is the proportional term coefficient, K ii is the integral term coefficient.

[0068] Furthermore, the implementation method of this patent is specifically explained by taking a 2MW direct-mounted energy storage system as an example. Figure 4 The topological structure diagram of the direct-mounted energy storage system is shown in Figure 2. The output reference power P of the energy storage system is set , Q set They are set to 1MW and 0.5MVar respectively, the load power is set to 2MW and 0.5MVar, the system rated voltage is 10kV, the rated frequency is 50Hz, the number of power module cascades is 10, the battery module rated voltage is 1100V, the inverter side filter inductor is 8mH, and the battery side filter capacitor is 11mF.

[0069] Figure 5 This is the voltage waveform when the slow start control method is not applied. At t = 0.1s, S1 is closed to charge the unloaded overhead line. It can be seen that a clear line overvoltage phenomenon has occurred. The normal voltage peak of the 220kV voltage level line is: The maximum phase voltage amplitude after 0.1s closing is 381.84kV, and the overvoltage multiple is 2.024 times.

[0070] Figure 6 Figure 2 shows the voltage waveform when the soft start control method is applied. It can be seen that the closing voltage control based on virtual resistance can significantly suppress line charging overvoltage. The maximum phase voltage amplitude after 0.1s closing is 230.44 kV, and the overvoltage multiple is 1.222 times, which is a significant reduction in overvoltage multiple. Furthermore, after applying the closing voltage control strategy, the system oscillation time is significantly shortened, and stabilization is more rapid.

[0071] Figure 7 This is the current waveform when the soft start control method is not applied. At t = 0.2s, S1 is closed, and it can be seen that the inrush current is large and the current distortion is serious.

[0072] Figure 8 Figure 2 shows the current waveform when applying the soft-start control method. At t = 0.2s, S1 is closed. At that instant, the PWM signal to the switch is reduced. Over the following cycles, it is gradually increased, achieving a soft start after closing the switch. This shows that soft-start control significantly suppresses the energy storage system's startup inrush current.

[0073] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply the existence of any such actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or device comprising the element.

[0074] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A direct-mounted energy storage slow start control method, characterized in that: The steps of the control method are: Step 1: The overvoltage judgment module collects the grid voltage signal V abc , calculate V abc The voltage amplitude V p And determine whether it exceeds the first overvoltage threshold V o1 Or the second overvoltage threshold V o2 ; Calculate V abc The voltage amplitude V p The specific implementation steps are: 1) The grid voltage signal V abc Transform from the three-phase abc coordinate system to the two-phase stationary coordinate system αβ: Among them, V a 、V b and V c They are the three-phase voltage at the grid connection point, V α and V β are the two-phase voltages in the stationary coordinate system respectively; 2) According to the two-phase voltage V α With V β Calculate the voltage amplitude V p : Step 2: The overcurrent judgment module collects the line current signal I abc , calculate I abc The current amplitude I p And judge whether it exceeds the first overcurrent threshold I o1 Or the second overcurrent threshold I o2 ; Computation I abc The current amplitude I p The specific implementation steps are: 1) The line current signal I abc Transform from the three-phase abc coordinate system to the two-phase stationary coordinate system αβ: Among them, I a , I b and I c They are the three-phase current of the line, I α and I β are the two-phase currents in the stationary coordinate system respectively; 2) According to the two-phase current I α with I β Calculate the current amplitude I p : Step 3: If the voltage amplitude V p Less than the first overvoltage threshold V o1 , then the overvoltage limit module sets the virtual impedance coefficient to m1. If the voltage amplitude V p At V o1 and V o2 If the voltage amplitude V p Greater than the second overvoltage threshold V o2 , then the overvoltage limit module sets the virtual impedance value coefficient to m3; Step 4: If the current amplitude I p Less than the first overcurrent threshold I o1 , then the overcurrent limit module sets the current given slope coefficient to n1. If the current amplitude I p In I o1 and I o2 If the current amplitude is I p Greater than the second overcurrent threshold I o2 , then the overcurrent limit module sets the current given slope coefficient to n3; Step 5: The voltage control module performs closed-loop control on the grid connection point voltage, generates a current setting instruction to the current control module, obtains a voltage modulation signal to the PWM modulation module, and generates a converter switch tube drive signal.

2. A direct-mounted energy storage slow start control method according to claim 1, characterized in that: The virtual impedance coefficient in step 3 has a value range of 0 to 1, and m1 <m2<m3。 3. A direct-mounted energy storage slow start control method according to claim 1, characterized in that: In step 4, the value range of the current given slope coefficient is between 0 and 1, and n1>n2>n3.

4. A direct-mounted energy storage slow start control method according to claim 1, characterized in that: The voltage closed-loop control and current closed-loop control in step 5 adopt a proportional-integral regulator to achieve zero-static-error command value tracking of the synchronous rotating coordinate system.

5. A control system based on the direct-mounted energy storage slow start control method according to claim 1, characterized in that: The system includes an overvoltage judgment module, an overcurrent judgment module, an overvoltage limiting module, an overcurrent limiting module, a voltage control module, a current control module and a PWM modulation module; the overvoltage judgment module is connected to the overvoltage limiting module and the voltage control module respectively, the overcurrent judgment module is connected to the overcurrent limiting module and the current control module respectively, the output end of the voltage control module is connected to the input end of the current control module, and the output end of the current control module is connected to the PWM modulation module.

Images