Frequency response control method of network following type energy storage converter

Abstract

The invention discloses a frequency response control method of a grid-following type energy storage converter, and relates to the technical field of new energy grid-connected power generation. The method comprises the following steps: step 1, detecting to obtain an active output pin and a power grid frequency frq of the following grid type energy storage converter; 2, according to the power grid frequency frq, judging whether the following grid type energy storage converter operates in a frequency modulation stage or not and enters a frequency response control mode or not; step 3, if the following network type energy storage converter operates in a frequency modulation stage, entering a frequency response control mode; 4, the frequency response control mode comprises an inertia response mode and a primary frequency modulation mode, and 5, whether the frequency response control mode exits or not is judged according to the power grid frequency frq, and if the frequency response mode exits, the following grid type energy storage converter continues to operate in the constant power control mode. According to the method, huge stock energy storage assets can be effectively activated, huge investment is delayed, and the frequency stability of the power grid can be rapidly and economically improved.

Description

Technical Field

[0001] This invention relates to the field of new energy grid-connected power generation technology, specifically to a frequency response control method for a grid-connected energy storage converter based on inertial response and primary frequency regulation. Background Technology

[0002] Most new energy power generation units are connected to the grid via power electronic converters. Their inherent low inertia and weak damping characteristics are gradually replacing the high inertia and strong damping characteristics of traditional synchronous generator sets, leading to a continuous decay of the grid's equivalent rotational inertia and increasingly prominent frequency stability issues. The core requirement for grid frequency stability is that when subjected to power disturbances, the system's inherent inertia can prevent sudden frequency changes and stabilize the frequency at a new level through measures such as primary frequency regulation. Traditional power systems rely on the enormous kinetic energy stored in the rotors of synchronous generators to naturally provide inertial response, but modern power grids are gradually losing this crucial support.

[0003] Against this backdrop, electrochemical energy storage systems are widely regarded as a key means to improve grid stability due to their advantages of rapid power regulation and flexible deployment. The core of an energy storage system is the energy storage converter, and its grid-connected control technology is mainly divided into two categories: grid-following control and grid-connected control.

[0004] Currently, the vast majority of large-scale energy storage power stations in operation adopt a grid-tracking control strategy. A grid-tracking energy storage converter can essentially be considered a controlled current source, whose normal operation depends on strict tracking of the grid voltage phase and frequency. It synchronizes with the grid in real time through a phase-locked loop and adjusts the active and reactive power injected into the grid according to dispatch commands or local frequency measurements. However, as the penetration rate of new energy sources increases, the technical limitations of existing grid-tracking energy storage converters are becoming increasingly apparent, mainly in their insufficient support for grid frequency stability, especially their inability to provide inertial response functionality similar to that of a synchronous machine. Their inherent disadvantages are as follows:

[0005] 1. Lack of inertia support: The grid itself has no inertia; it merely passively responds to the grid's commands. When the grid frequency changes suddenly (such as when a large load is added or removed), it cannot naturally "resist" the frequency change using rotor kinetic energy like a synchronous generator. It needs to wait for instructions from the grid dispatch center before it can act, resulting in a delay. This leads to a decrease in the "equivalent inertia" of modern power grids and a deterioration in frequency stability.

[0006] 2. Unable to adjust active power autonomously: Grid-connected systems typically operate in constant power factor mode and cannot, like grid-connected systems, rapidly increase active power to support grid frequency when the grid requires it.

[0007] 3. High Upgrade Costs: To address the above issues, the industry has proposed grid-based control technology. Grid-based converters can autonomously construct grid voltage and frequency, exhibiting voltage source characteristics and simulating the inertia and damping of synchronous machines, fundamentally improving grid stability. However, upgrading the vast number of existing grid-connected energy storage power stations to grid-based systems requires a complete replacement or deep modification of the core converter hardware and control system, resulting in huge investment costs, poor economic efficiency, and a long modification cycle.

[0008] In summary, while existing energy storage systems primarily based on grid-connected control can meet basic power regulation needs, they cannot satisfy the higher-order frequency stability requirements of a high proportion of renewable energy grids. Directly adopting grid-connected technologies, however, faces barriers of high cost and significant retrofitting challenges. Summary of the Invention

[0009] The technical problem to be solved by this invention is to provide a frequency response control method for grid-connected energy storage converters. This method can endow existing grid-connected energy storage converters with inertial response capabilities and primary frequency regulation capabilities similar to synchronous generators by optimizing control strategies without replacing or minimizing modifications to the existing hardware. This can effectively revitalize the huge existing energy storage assets, delay huge investments, and quickly and economically improve the frequency stability of the power grid. This has significant practical implications for ensuring the safe and reliable operation of new power systems.

[0010] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0011] A frequency response control method for a grid-connected energy storage converter includes the following steps:

[0012] Step 1: Detect the active power output pin and grid frequency frq of the grid-connected energy storage converter;

[0013] Step 2: Based on the grid frequency frq, determine whether the grid-connected energy storage converter is operating in the frequency regulation stage and whether it has entered the frequency response control mode.

[0014] Step 3: If the grid-connected energy storage converter is operating in the frequency regulation stage, then enter the frequency response control mode.

[0015] Step 4: The frequency response control modes include inertia response mode and primary frequency modulation mode. The formula for frequency response control is as follows:

[0016] (1)

[0017] The formula for the inertial response mode is as follows:

[0018] (2)

[0019] The formula for the primary frequency modulation mode is as follows:

[0020] (3)

[0021] In formulas (1), (2) and (3), Represents the Laplace operator. This represents the difference between the actual frequency of the power grid and the standard frequency. This represents the difference between mechanical power and electromagnetic power. This indicates the inertial response power output of the grid-type energy storage converter. This indicates the primary frequency regulation power output of the grid-type energy storage converter. This represents the virtual inertia of the grid-type energy storage converter. This indicates the damping provided by the grid-type energy storage converter and frequency-dependent loads. This represents the reciprocal of the droop coefficient of the grid-type energy storage converter. This represents the time constant of a grid-connected energy storage converter;

[0022] In this step, frequency control is performed according to formula (1);

[0023] Step 5: Determine whether the frequency response control mode has been exited based on the grid frequency frq. If the frequency response mode has been exited, the grid-connected energy storage converter will continue to operate in constant power control mode.

[0024] Furthermore, in step 2, the condition for entering the frequency response control mode is that both the grid frequency frq and the frequency change rate are greater than the set dead zone; in step 5, the condition for exiting the frequency response control mode is that both the grid frequency frq and the frequency change rate are less than the set dead zone; the dead zone value for the grid frequency frq deviation is 0.05Hz, and the dead zone value for the frequency change rate is 1Hz / s. The frequency change rate refers to the grid frequency change rate, which is an important characteristic parameter reflecting the frequency stability of the power system, representing the amount of change in the grid frequency per unit time.

[0025] The beneficial effects of this invention are:

[0026] The frequency response control method for grid-connected energy storage converters provided by this invention, compared with the prior art, not only enables the grid-connected energy storage converter to have the inertia and damping characteristics of a synchronous generator during operation, but also has the primary frequency regulation characteristics of a synchronous generator. When the grid-connected active power or grid frequency is disturbed, frequency fluctuations can be suppressed, thereby enhancing the stability of the grid-connected energy storage converter during grid-connected operation. Attached Figure Description

[0027] Figure 1 This is a block diagram of the PWM control according to an embodiment of the present invention;

[0028] Figure 2This is a block diagram illustrating the frequency response of an embodiment of the present invention;

[0029] Figure 3 This is a block diagram of active power control according to an embodiment of the present invention;

[0030] Figure 4 This is a primary wiring diagram of the power grid according to an embodiment of the present invention;

[0031] Figure 5 This is a diagram of the PWM active power output with no inertia response according to an embodiment of the present invention;

[0032] Figure 6 This is a diagram of the PWM active power output after the inertia response in an embodiment of the present invention.

[0033] Figure 7 This is a power grid frequency diagram with no inertia response according to an embodiment of the present invention;

[0034] Figure 8 This is a diagram of the power grid frequency after the inertia response according to an embodiment of the present invention. Detailed Implementation

[0035] The present invention will now be described in conjunction with the accompanying drawings. The specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the present invention. Various modifications and improvements to the technical solutions of the present invention made by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope of the present invention.

[0036] To verify the effectiveness of the proposed inertia response control and primary frequency regulation control for system frequency stability, this invention uses PowerFactory software to build a grid-connected simulation model of a grid-connected energy storage converter.

[0037] The frequency response control method for the grid-connected energy storage converter in this embodiment includes the following steps:

[0038] Step 1: Detect the active power output pin and grid frequency frq of the grid-connected energy storage converter, such as... Figure 1 As shown, the "P Measurement" module is responsible for measuring the active power output pin of the grid-connected energy storage converter, and the "PLL" module is responsible for measuring the grid frequency frq.

[0039] Step 2: Based on the grid frequency frq, determine whether the grid-connected energy storage converter is operating in the frequency regulation phase and whether it has entered frequency response control mode. When both the grid frequency frq and the frequency change rate are greater than the set dead zone, it enters frequency response control mode. According to relevant national standards, the dead zone value for the grid frequency frq deviation is 0.05Hz, and the dead zone value for the frequency change rate is 1Hz / s.

[0040] Step 3: If the grid-connected energy storage converter is operating in the frequency regulation stage, it enters the frequency response control mode, i.e. Figure 1 The "Frequency Response" and "Active Power Control" modules are activated.

[0041] Step 4, the "Frequency Response" module is activated, and its specific functions are as follows: Figure 2 As shown, the frequency response control modes include inertia response mode and primary frequency modulation mode. The formula for frequency response control is as follows:

[0042] (1)

[0043] The formula for the inertial response mode is as follows:

[0044] (2)

[0045] The formula for the primary frequency modulation mode is as follows:

[0046] (3)

[0047] In formulas (1), (2) and (3), Represents the Laplace operator. This represents the difference between the actual frequency of the power grid and the standard frequency. This represents the difference between mechanical power and electromagnetic power. This indicates the inertial response power output of the grid-type energy storage converter. This indicates the primary frequency regulation power output of the grid-type energy storage converter. This represents the virtual inertia of the grid-type energy storage converter. This indicates the damping provided by the grid-type energy storage converter and frequency-dependent loads. This represents the reciprocal of the droop coefficient of the grid-type energy storage converter. This represents the time constant of the grid-connected energy storage converter.

[0048] Figure 2 The correspondence between parameters and formula parameters is as follows: Figure 2 In the K / (1+sT) module, K corresponds to The value is set to 20; T corresponds to The value is set to 0.01; M in the Ks module corresponds to The value is set to 5; D in module K corresponds to Set the value to 1; then output the active power increment dpref.

[0049] In this step, frequency control is performed according to formula (1), and then the "active power control" module is activated. Figure 3The active power control block diagram shown performs active power control and finally outputs id_ref, which is used to control the active power output of the "inverter" module. The parameter K is set to 1, the parameter T is set to 0.01, the parameter K1 is set to 1, the parameter T1 is set to 0.01, the parameter y_min is set to 0.1, and the parameter y_max is set to 0.75.

[0050] Step 5: Determine whether the frequency response control mode should be exited based on the grid frequency frq. If the frequency response mode is exited, the grid-connected energy storage converter continues to operate in constant power control mode. In this step, the condition for exiting the frequency response control mode is that both the grid frequency frq and the frequency change rate are less than the set dead zone. According to relevant national standards, the dead zone value for the grid frequency frq deviation is 0.05Hz, and the dead zone value for the frequency change rate is 1Hz / s.

[0051] Figure 4 This is a primary wiring diagram of a power grid according to an embodiment of the present invention, used to simulate the phenomenon of power grid frequency fluctuations when a load step occurs in the power grid. The diagram includes a synchronous motor, a transformer, a load, and a PWM converter. As shown, the synchronous motor acts as a power source, supplying power to the load through the line; the PWM converter converts the stored DC power into AC power, which is then connected to the power grid through the transformer to supply power to the load. When the power is balanced, the grid load is 100MW. At 0s, the load experiences a step increase, rising by 5% to 105MW. Two sets of comparative simulation experiments were conducted: one set configured with the PWM converter as a traditional constant power control grid-type energy storage converter, and the other set configured with the frequency response grid-type energy storage converter proposed in this invention.

[0052] When the PWM converter is configured as a traditional grid-connected energy storage converter, after a load step change, the converter's active power output operates in constant power mode, see [link to relevant documentation]. Figure 5 At this time, as Figure 7 As shown, the lowest frequency of the power grid is 49.074Hz, which exceeds the standard requirement (the lowest frequency cannot be lower than 49.2Hz). The power grid will take a series of actions for protection.

[0053] When the PWM converter is configured as the frequency response grid-type energy storage converter proposed in this invention, after a load step, the active power output of the converter responds to the frequency according to formula (1), see Figure 6 The lower the frequency, the greater the active power output, and the faster the active power deficit in the power grid is compensated, thus making the power grid frequency more stable. At this time, if... Figure 8 As shown, the lowest frequency of the power grid is 49.519Hz, which is within the standard requirements, and the power grid is operating safely.

[0054] pass Figure 7 and Figure 8Compared with the lowest point of the power grid frequency, the frequency response control and grid-type energy storage converter of this invention ensures that the power grid frequency does not exceed the limit. Compared with the traditional constant power control and grid-type energy storage converter, the power grid frequency is more stable and the power grid operation is safer.

[0055] The frequency response control method for grid-connected energy storage converters of the present invention has the following characteristics:

[0056] 1. Intelligent switching mechanism for control modes: This invention designs a set of discrimination logic based on the real-time grid frequency frq, enabling the converter to switch autonomously and seamlessly between constant power control mode and frequency response control mode. This is the foundation for realizing "plug-and-play" functional upgrades.

[0057] 2. Composite Frequency Response Architecture: In addition to the frequency response control mode, this architecture innovatively integrates inertial response mode and primary frequency regulation mode. Inertial response simulates the rotor inertia of a synchronous generator, suppressing the rate of frequency change (RoCoF); primary frequency regulation simulates governor characteristics, reducing steady-state frequency deviation. The coordinated operation of these two modes is key to achieving rapid and effective frequency support.

[0058] 3. Clear exit mechanism: An exit mechanism is set up based on whether the grid frequency and frequency change rate return to the dead zone range. This ensures that the converter can exit the frequency regulation state in a timely manner after the grid returns to normal and return to the constant power mode of normal operation, avoiding over-discharge or over-charging and ensuring its own operational safety.

[0059] The frequency response control method for grid-connected energy storage converters of the present invention has the following beneficial effects:

[0060] Compared with existing technologies, this technology not only enables grid-connected energy storage converters to have the inertia and damping characteristics of synchronous generators during operation, but also the primary frequency regulation characteristics of synchronous generators. When disturbances occur in the grid-connected active power or grid frequency, frequency fluctuations can be suppressed, thus enhancing the stability of grid-connected energy storage converters during grid-connected operation.

[0061] This invention builds a grid-connected simulation model of a grid-connected energy storage converter based on PowerFactory software, and verifies the supporting role of inertial response control and primary frequency regulation control in system frequency stability through system simulation research.

Claims

1. A frequency response control method for a grid-connected energy storage converter, characterized in that, Includes the following steps: Step 1: Detect the active power output pin and grid frequency frq of the grid-connected energy storage converter; Step 2: Based on the grid frequency frq, determine whether the grid-connected energy storage converter is operating in the frequency regulation stage and whether it has entered the frequency response control mode. Step 3: If the grid-connected energy storage converter is operating in the frequency regulation stage, then enter the frequency response control mode. Step 4: The frequency response control modes include inertia response mode and primary frequency modulation mode. The formula for frequency response control is as follows: (1) The formula for the inertial response mode is as follows: (2) The formula for the primary frequency modulation mode is as follows: (3) In formulas (1), (2) and (3), Represents the Laplace operator. This represents the difference between the actual frequency of the power grid and the standard frequency. This represents the difference between mechanical power and electromagnetic power. This indicates the inertial response power output of the grid-type energy storage converter. This indicates the primary frequency regulation power output of the grid-type energy storage converter. This represents the virtual inertia of the grid-type energy storage converter. This indicates the damping provided by the grid-type energy storage converter and frequency-dependent loads. This represents the reciprocal of the droop coefficient of the grid-type energy storage converter. This represents the time constant of a grid-connected energy storage converter; In this step, frequency control is performed according to formula (1); Step 5: Determine whether the frequency response control mode has been exited based on the grid frequency frq. If the frequency response mode has been exited, the grid-connected energy storage converter will continue to operate in constant power control mode.

2. The frequency response control method for a grid-connected energy storage converter according to claim 1, characterized in that, In step 2, the condition for entering the frequency response control mode is that both the grid frequency frq and the frequency change rate are greater than the set dead zone; in step 5, the condition for exiting the frequency response control mode is that both the grid frequency frq and the frequency change rate are less than the set dead zone; the grid frequency frq deviation dead zone value is 0.05Hz, and the frequency change rate dead zone value is 1Hz / s.

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