Two-stage electrochemical energy storage primary frequency modulation self-adaptive tracking method

Abstract

The invention relates to a two-stage electrochemical energy storage primary frequency modulation self-adaptive tracking method, which adopts a method that a DC / DC converter responds to a power grid frequency deviation direction and combines energy storage battery charge state dynamic evaluation to carry out power distribution, and a grid-connected converter operates in a mode of stabilizing direct current bus voltage to realize self-adaptive adjustment of power. The system has the advantages that the frequency modulation effect is good, safe and stable operation of the power station is facilitated, and the influence on the service life of the related energy storage battery in the frequency modulation process is small.

Description

Technical Field

[0001] This invention relates to the field of energy storage frequency regulation technology, and in particular to a two-stage electrochemical energy storage primary frequency regulation adaptive tracking method. Background Technology

[0002] As the proportion of renewable energy in the power system continues to increase, grid connection points face the risk of frequency oscillations. Electrochemical energy storage units (ESLs) assisting primary frequency regulation can effectively improve the stability of the power system. On the one hand, by rapidly responding to frequency changes, they suppress large frequency fluctuations, reducing the risk of cascading failures caused by frequency instability. On the other hand, ESLs operate in synergy with renewable energy generation and traditional generator sets, optimizing the power distribution and regulation mechanisms of the power system and enhancing overall system stability and anti-interference capabilities. Simultaneously, ESLs are also crucial for improving the absorption capacity of renewable energy. Due to the intermittency and volatility of renewable energy generation, large-scale grid connection can easily lead to wind and solar power curtailment. ESLs not only play a role in peak shaving and valley filling but also rapidly support grid frequency stability, helping the grid better accommodate renewable energy generation, improving the utilization efficiency of renewable energy in the power system, and promoting the green and low-carbon transformation of the energy structure.

[0003] While electrochemical energy storage has demonstrated significant advantages in primary frequency regulation, several technical challenges remain to be addressed. Regarding control mode switching, virtual inertial control and virtual droop control are currently the two main modes employed. The former is highly effective in suppressing the rate of change of frequency deviation during the initial stages of load disturbances, while the latter is particularly effective in reducing steady-state frequency deviation. However, in actual grid operation scenarios, seamless switching between these two control modes presents complex challenges. Due to the dynamic and variable nature of grid operating conditions, a series of key parameters are difficult to accurately aggregate. If the critical value is not properly selected, the active power output of the energy storage unit will experience discontinuous jumps during mode switching. This sudden change in output not only causes additional power surges to the grid, triggering secondary frequency fluctuations and increasing the difficulty of system frequency control, but also causes the energy storage battery to endure drastic changes in charging and discharging current in a short period, accelerating the aging of internal electrode materials and the loss of active materials, thereby significantly shortening the cycle life and overall service life of the energy storage battery.

[0004] With the rapid iteration of energy storage battery technology, large-capacity energy storage power stations are continuously being connected to the grid, significantly improving the frequency regulation capability of energy storage. However, while capacity increases, the differences in remaining battery state of charge (SOC) are also widening, even affecting overall frequency regulation performance. Currently, newly built energy storage power stations can typically only output at maximum power for 2 hours at full charge. When the SOC is too high or too low, the energy storage battery is prone to overcharging and over-discharging, which not only shortens the battery's cycle life but also causes significant negative impacts on grid operation due to the instability of its output. Existing control strategies are relatively effective in regulating frequencies when dealing with short-term load disturbances and a good SOC state; however, prolonged disturbances may cause the SOC state to deteriorate rapidly, threatening the safe and stable operation of the power station. Summary of the Invention

[0005] The purpose of this invention is to provide a two-stage electrochemical energy storage primary frequency regulation adaptive tracking method to solve one or more of the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A two-stage electrochemical energy storage primary frequency regulation adaptive tracking method is proposed. This method employs a DC / DC converter response to the grid frequency deviation direction, combined with dynamic assessment of the energy storage battery's state of charge (SOC) for power allocation. The grid-connected converter operates to maintain a stable DC bus voltage, thus achieving adaptive power regulation. The control method for the DC / DC converter's response to the grid frequency deviation direction is as follows: the grid frequency deviation signal is filtered through the DC / DC converter's dead-time stage to obtain a new frequency deviation signal Δf. c The system then enters the droop control and virtual inertial control stages, generating droop control commands and virtual inertial control commands respectively. These two commands are then added together and combined with the energy storage power adjustment coefficient K obtained from the dynamic assessment of the energy storage battery's state of charge. soc Multiplication is performed to construct a dynamic power regulation model; the power command is further modified by a limiting stage to obtain the power control command P. B This enables the energy storage unit's output power to be dynamically optimized and adjusted based on the energy storage battery's state of charge. Attached Figure Description

[0008] Figure 1 This is a diagram illustrating the overall control strategy of a two-stage electrochemical energy storage primary frequency modulation adaptive tracking method provided in some embodiments of the present invention.

[0009] Figure 2 The waveform change curves during the frequency modulation process of the two-stage electrochemical energy storage primary frequency modulation adaptive tracking method are shown in some embodiments of the present invention. Detailed Implementation

[0010] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0011] This embodiment provides a two-stage electrochemical energy storage primary frequency regulation adaptive tracking method. It employs a DC / DC converter response to the grid frequency deviation direction, combined with dynamic assessment of the energy storage battery's state of charge (SOC) for power allocation. The grid-connected converter operates in a stable DC bus voltage mode, achieving adaptive power regulation. The control method for the DC / DC converter's response to the grid frequency deviation direction is as follows: the grid frequency deviation signal is filtered through the DC / DC converter's dead-time stage to obtain a new frequency deviation signal Δf. c The system then enters the droop control and virtual inertial control stages, generating droop control commands and virtual inertial control commands respectively. These two commands are then added together and combined with the energy storage power adjustment coefficient K obtained from the dynamic assessment of the energy storage battery's state of charge. soc Multiplication is performed to construct a dynamic power regulation model; the power command is further modified by a limiting stage to obtain the power control command P. B The output power of the grid-connected energy storage unit is optimized and adjusted according to the State of Charge (SOC). The overall control block diagram is as follows: Figure 1 As shown.

[0012] This two-stage electrochemical energy storage primary frequency regulation adaptive tracking method can be applied to a grid with high penetration of new energy sources, in which wind power / photovoltaic accounts for more than or equal to 30%. When the method is running, it needs to coordinate frequency regulation with thermal power / hydropower units. This method can be applied to load abrupt changes (step disturbance less than or equal to 2% of system load) and continuous fluctuations (minute-level fluctuations in wind power / photovoltaic output).

[0013] Combination Figure 1 The two-stage electrochemical energy storage primary frequency regulation adaptive tracking method described herein employs a two-stage topology, including a front-end DC / DC converter, a rear-end VSC, a high-precision frequency detection unit (e.g., a PLL phase-locked loop), and a SOC estimation unit. The front-end DC / DC converter is a bidirectional Buck / Boost converter with a response time <50ms; the rear-end VSC has a THD <3% and supports low-voltage ride-through; the SOC estimation unit performs voltage correction. This execution circuit is connected to the 10kV / 35kV bus and integrated into the power grid via a step-up substation; undervoltage and overvoltage protection is ≥850V, with a time difference ≥0.3s with grid protection.

[0014] The DC / DC converter employs virtual droop control to simulate the droop characteristics of a synchronous generator participating in primary frequency regulation, increasing power generation and suppressing frequency fluctuations. This results in good primary frequency regulation when the power system experiences short-term load fluctuations or when energy storage is sufficient. Virtual inertial control, on the other hand, simulates the inertial response characteristics of the generator set to control energy storage participation in the grid's primary frequency regulation. This reduces the rate of frequency change and the maximum frequency deviation, but cannot change the steady-state frequency deviation. The formulas for calculating droop response and inertial response are:

[0015]

[0016] The formula for calculating the output power of energy storage is:

[0017]

[0018] In the formula, K B M regulates the power of the energy storage unit. B f is the virtual inertia coefficient for energy storage. c For frequency deviation, K soc The energy storage power regulation coefficient is taken into account for SOC feedback.

[0019] To avoid unnecessary frequent charging and discharging operations that could shorten the lifespan of energy storage, a primary frequency regulation dead zone is implemented. When the frequency difference is within the range of -0.033Hz to 0.033Hz, the energy storage unit does not participate in primary frequency regulation. Beyond the dead zone, it coordinates with distributed generation (DG) for joint frequency regulation. The frequency difference can be obtained using existing technologies such as PLLs (phase-locked loops). When the dead zone is exceeded, DG (such as wind and solar power) is connected to the grid for joint frequency regulation. The relevant parameters for this DG connection can be...

[0020] Voltage range: ±10% of rated voltage;

[0021] Frequency response range: 49.8-50.2Hz continuous operation;

[0022] Harmonic control: THD < 3% (IEEE 519 standard);

[0023] Virtual inertial control is required (response time < 2s);

[0024] Droop control needs to be implemented (adjustment accuracy 0.01Hz).

[0025] Frequency modulation experiments were conducted using the parameters shown in Table 1, and the results were verified as follows: Figure 2As shown in the waveform, when the frequency rises from 49.8Hz to 50.2Hz, the frequency deviation signal, after one frequency modulation, is sent to the DC / DC converter to charge the energy storage unit, absorbing excess power from the grid. The current direction is from the converter to the battery (charging current). As shown in ZOOM1 of the figure, the DC current direction changes from positive to negative, and the AC current phase reverses. With the increase of df / dt, virtual inertial control plays a major role, and the current amplitude increases with the rate of change of frequency. A spike pulse appears at the initial moment, reflecting the rapid response of the energy storage unit. As the rate of change of frequency df / dt decreases, virtual droop control plays a major role, and the current rapidly decays and then quickly recovers to stability. From the droop response and inertial response calculation formulas, as well as the energy storage output power calculation formula, it can be seen that the system response time is very short, and the voltage recovers quickly after a small drop, demonstrating the supporting role of energy storage for the DC bus or grid-side voltage. The entire system quickly stabilizes at 50.2Hz after fluctuations, and the frequency support time meets the requirements.

[0026] When the frequency drops from 50.2Hz to 49.8Hz, the frequency deviation signal, after primary frequency modulation, is sent to the DC / DC converter to discharge the energy storage unit, injecting active power into the grid. At this time, the current direction is from the battery to the converter (discharge current). As shown in ZOOM1 in the figure, the current direction changes from reverse to forward. According to the droop response and inertial response calculation formulas, the system gradually switches from virtual inertial control to droop control. The current amplitude also increases with the absolute value of the frequency change rate. Subsequently, the current returns to a stable state. The voltage waveform shows local distortion at the current step point, but does not exceed the rated value ±5%, indicating that the grid still has voltage support capability. When the system operates stably at 49.8Hz, the power control command P can be obtained from the droop response, inertial response calculation formulas, and energy storage output power calculation formula. B It should gradually approach zero, and energy storage should be phased out smoothly.

[0027] Table 1

[0028] parameter numerical values parameter numerical values <![CDATA[Rated frequency f0 / Hz]]> 50 <![CDATA[Phase-locked loop (K p , K i )]]> (3，1) <![CDATA[Rated power P of energy storage system N / MW]]> 10 Control precision <![CDATA[100 μs ]]> Grid-side voltage / V 380 <![CDATA[Drooping coefficient K B > 20 <![CDATA[DC / DC converter current inner loop (K p1 , K i1 )]]> (1，5) <![CDATA[Virtual inertia coefficient M B > 6 <![CDATA[DC / DC converter current outer loop (K p2 , K i2 )]]> (1，5) DC bus voltage / V 750

[0029] All of the above-mentioned undisclosed matters can be implemented using existing technologies, so they will not be elaborated here.

[0030] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0031] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

[0032] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A two-stage electrochemical energy storage primary frequency modulation adaptive tracking method, characterized in that, The method of responding to the direction of grid frequency deviation by DC / DC converter and combining dynamic assessment of the state of charge of energy storage battery for power allocation, while the grid-connected converter operates in a way that stabilizes the DC bus voltage, thereby achieving adaptive adjustment of power.

2. The two-stage electrochemical energy storage primary frequency modulation adaptive tracking method according to claim 1, characterized in that, The DC / DC converter uses virtual droop control to simulate the droop characteristics of a synchronous generator participating in primary frequency regulation.

3. The two-stage electrochemical energy storage primary frequency modulation adaptive tracking method according to claim 2, characterized in that, The control method for the DC / DC converter to respond to the direction of grid frequency deviation is as follows: The power grid frequency deviation signal is filtered by the dead-time stage of the DC / DC converter to obtain a new frequency deviation signal Δf. c ; The system then enters the droop control and virtual inertial control stages, generating droop control commands and virtual inertial control commands respectively. The two commands are then added together and combined with the energy storage power adjustment coefficient K obtained from the dynamic assessment of the battery's state of charge. soc Multiply them to construct a dynamic power regulation model; The power command is further modified by the limiting stage to obtain the power control command P. B This enables the energy storage unit's output power to be dynamically optimized and adjusted based on the energy storage battery's state of charge.

4. The two-stage electrochemical energy storage primary frequency modulation adaptive tracking method according to claim 3, characterized in that, The calculation formula involved in the droop control command is ΔP B1 =-K B Δf.

5. The two-stage electrochemical energy storage primary frequency modulation adaptive tracking method according to claim 4, characterized in that, The calculation formula involved in the virtual inertial control command is 6. The two-stage electrochemical energy storage primary frequency modulation adaptive tracking method according to claim 5, characterized in that, The calculation formula for the dynamic power regulation model is as follows:

7. The two-stage electrochemical energy storage primary frequency modulation adaptive tracking method according to claim 6, characterized in that, The energy storage unit is set with a primary frequency regulation dead zone. When the frequency difference component is in the range of [-0.033Hz, 0.033Hz], the energy storage unit does not participate in the primary frequency regulation. When the dead zone is exceeded, it cooperates with wind power and photovoltaic power for joint frequency regulation.

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