Two-stage cascade energy storage system power control strategy based on active instruction sharing

Abstract

The invention relates to a cascade energy storage control technology, and aims to provide a two-stage cascade energy storage system power control strategy based on active instruction sharing. Comprising the steps that a module controller of each energy storage module adopts a unified double-closed-loop control method, and the capacitor voltage and the battery current of the energy storage module are respectively controlled by an outer loop and an inner loop; a main controller of the energy storage system adopts active and reactive decoupling control, and the active power output and the reactive power output of the cascaded energy storage system are respectively managed by controlling active current and reactive current; the main controller and each module controller of the cascade energy storage system respectively undertake the tasks of integral calculation and group control. By introducing an active instruction sharing mechanism, complex parameter coordination in a traditional two-stage control system is avoided, and it is ensured that each module can independently and accurately execute the distributed power instruction; the problem of current impact caused by inconsistent dynamic performance of alternating current and direct current can be effectively avoided, and the dynamic performance and the operation stability of the cascade energy storage system are improved.

Description

Technical Field

[0001] The invention relates to a two-stage cascade energy storage system power control strategy based on active power instruction sharing, belonging to the technical field of cascade energy storage system control. Background Art

[0002] With the increase in the penetration rate of new energy, the stability of the power system faces increasingly severe challenges, so battery energy storage systems based on power electronics technology have been widely used. Among them, the cascade energy storage system based on the cascade H-bridge multi-level converter has great potential in future large-capacity energy storage systems due to its significant advantages such as modular design and high efficiency.

[0003] In cascade energy storage systems, the two-stage topology is used as an optimized topology solution. By configuring a DC / DC converter between the module and the battery, more sophisticated and flexible battery management can be achieved. However, this solution involves a complex two-stage control structure on the AC side and the DC side, which makes the overall control parameter coordination challenging. Especially during dynamic regulation, such as when switching between charge and discharge power, improperly designed control parameters may cause battery current shocks, thereby damaging the battery and energy storage module components. This current shock not only affects the reliability of the system, but may also shorten the battery life.

[0004] Therefore, how to implement a reasonable system power control strategy to ensure smooth regulation of battery side current during the power regulation process of the cascade energy storage system is the key to ensuring safe and stable operation of the system. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art and provide a power control strategy for a two-stage cascade energy storage system based on active power instruction sharing.

[0006] In order to solve the above technical problems, the solution of the present invention is:

[0007] A two-stage cascade energy storage system power control strategy based on active power command sharing is provided, which specifically includes:

[0008] (1) The module controller of each energy storage module adopts a unified dual closed-loop control method, with the outer loop and inner loop controlling the capacitor voltage and battery current of the energy storage module respectively; the main controller of the energy storage system adopts active and reactive power decoupling control, and manages the active power and reactive power output of the cascaded energy storage system respectively by controlling the active current and reactive current;

[0009] (2) After receiving the external active power command, the main controller of the cascade energy storage system calculates the active power of each module according to the number of energy storage modules and distributes it to each module controller to realize the sharing of the active power command; each module controller further calculates the total reference value of the battery current according to the received active power command value and the current battery voltage of each energy storage module, and provides it to the inner loop, and at the same time feeds back the signal of the active power command sharing to the main controller;

[0010] (3) After receiving the feedback signals from all module controllers, the main controller calculates the active current reference value of the entire cascade energy storage system and then inputs it into the active current control loop for power regulation.

[0011] As a preferred solution of the present invention, the cascade energy storage system has a three-phase star topology and a two-stage structure, each phase of which is composed of a filter reactor L f It is composed of N energy storage modules connected in series; each energy storage module has the same structure, including a module controller, and an H-bridge, a DC capacitor, a DC / DC converter and a series battery cluster arranged in sequence.

[0012] As a preferred embodiment of the present invention, the module controller calculates the total reference value of the battery current of each energy storage module according to the following formula: total reference value of battery current = first reference value of battery current + second reference value of battery current; wherein, the first reference value of battery current is calculated by the module controller as the output value of the capacitor voltage outer loop; the second reference value of battery current is obtained by calculating according to the following formula: second reference value of battery current = module active power instruction value / module battery voltage.

[0013] As a preferred solution of the present invention, a module controller is respectively provided in each energy storage module, and in its control strategy, capacitor voltage control is used as an outer loop and battery current control is used as an inner loop.

[0014] As a preferred embodiment of the present invention, the capacitor voltage control is used to adjust the capacitor voltage in the energy storage module to ensure that it remains within the rated voltage range; its specific implementation steps include: detecting the output voltage through a voltage sensor, and comparing it with the capacitor voltage reference value to obtain a voltage error value; inputting the voltage error value into the voltage loop PI controller to generate a first current reference value.

[0015] As a preferred embodiment of the present invention, the specific implementation steps of the battery current control include: detecting the battery current through a current sensor, and comparing it with the total reference value of the battery current to obtain a current error value; inputting the current error value into a current loop PI controller to generate a pulse width modulation signal, and using the pulse width modulation signal to control the switching state of the switching device in the DC / DC converter.

[0016] As a preferred solution of the present invention, the main controller adopts an active and reactive power decoupling control strategy, which specifically includes:

[0017] (1) Detect the three-phase AC voltage and current output by the cascade energy storage system through voltage sensors and current sensors respectively; calculate the phase angle in real time according to the phase-locked loop, and convert the three-phase AC voltage and current into the dq coordinate system; set the command values ​​of active power and reactive power respectively according to the grid demand and the state of the energy storage system;

[0018] (2) Controlling the active current: calculating the active current reference value according to the active power command value, comparing the d-axis current with the active current reference value to obtain a d-axis current error value; inputting the d-axis current error value into the voltage loop PI controller to generate a d-axis modulation signal reference value;

[0019] (3) Controlling reactive current: Calculating reactive current reference value according to reactive power command value, comparing q-axis current with reactive current reference value to obtain q-axis current error value; inputting q-axis current error value into voltage loop PI controller to generate q-axis modulation signal reference value;

[0020] (4) Convert the d-axis and q-axis modulation signal reference values ​​to a three-phase coordinate system to obtain a three-phase modulation signal reference value; and use the three-phase modulation signal reference value to control the switching state of the switching devices in the H bridge of each energy storage module.

[0021] As a preferred solution of the present invention, the calculation formula of the active current reference value is: active current reference value=active power command value / (1.5×rated phase voltage amplitude of the power grid).

[0022] As a preferred solution of the present invention, the calculation formula of the reactive current reference value is: reactive current reference value=-reactive power command value / (1.5×rated phase voltage amplitude of the power grid).

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The present invention avoids the complex parameter coordination in the traditional two-level control system by introducing an active power instruction sharing mechanism, ensuring that each module can independently and accurately execute the allocated power instruction;

[0025] 2. The present invention can effectively avoid the current shock problem caused by the inconsistency of AC and DC dynamic performance, and improve the dynamic performance and operation stability of the cascade energy storage system. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a topological diagram of the main circuit of the cascade energy storage system in the present invention.

[0027] Figure 2This is a power control block diagram of a two-stage cascade energy storage system based on active power command sharing.

[0028] Figure 3 The diagram is a waveform diagram of AC and DC currents during power regulation of a cascade energy storage system using the method of the present invention. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are 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.

[0030] Part I Implementation of the Invention

[0031] First, the two-stage cascade energy storage system described in the present invention is as follows Figure 1 As shown, it has a three-phase star topology and a two-stage structure, and each phase is filtered by a filter reactor L f It is composed of N energy storage modules connected in series; each energy storage module has the same structure, including a module controller, and an H-bridge, a DC capacitor, a DC / DC converter and a series battery cluster arranged in sequence.

[0032] Secondly, for the above two-stage cascade energy storage system, the present invention proposes a power control strategy based on active power command sharing, which specifically includes:

[0033] 1. The module controller of each energy storage module adopts a unified dual closed-loop control method, and controls the capacitor voltage and battery current of the energy storage module with the outer loop and inner loop respectively; the main controller of the energy storage system adopts active and reactive decoupling control, and manages the active power and reactive power output of the cascade energy storage system by controlling the active current and reactive current respectively.

[0034] Specifically, the active and reactive power decoupling control strategy adopted by the main controller includes:

[0035] (1) Detect the three-phase AC voltage and current output by the cascade energy storage system through voltage sensors and current sensors respectively; calculate the phase angle in real time according to the phase-locked loop, and convert the three-phase AC voltage and current into the dq coordinate system; set the command values ​​of active power and reactive power respectively according to the grid demand and the state of the energy storage system;

[0036] (2) Control the active current: Calculate the active current reference value according to the active power command value, and the calculation formula is: Active current reference value = active power command value / (1.5 × grid rated phase voltage amplitude). Compare the d-axis current with the active current reference value to obtain the d-axis current error value, and then input it into the voltage loop PI controller to generate the d-axis modulation signal reference value;

[0037] (3) Control the reactive current: Calculate the reactive current reference value according to the reactive power command value, and the calculation formula is: reactive current reference value = - reactive power command value / (1.5 × grid rated phase voltage amplitude). Compare the q-axis current with the reactive current reference value to obtain the q-axis current error value, and then input it into the voltage loop PI controller to generate the q-axis modulation signal reference value;

[0038] (4) Convert the d-axis and q-axis modulation signal reference values ​​to a three-phase coordinate system to obtain a three-phase modulation signal reference value; and use the three-phase modulation signal reference value to control the switching state of the switching devices in the H bridge of each energy storage module.

[0039] 2. After the main controller of the cascade energy storage system receives the external active power command, it calculates the active power of each module according to the number of energy storage modules and distributes it to each module controller to realize the sharing of the active power command; each module controller further calculates the total reference value of the battery current based on the received active power command value and the current battery voltage of each energy storage module, and provides it to the inner loop, and at the same time feeds back the signal that the active power command sharing is completed to the main controller.

[0040] The present invention proposes to respectively set a module controller in each energy storage module, and in the control strategy of the module controller, the capacitor voltage control is used as an outer loop, and the battery current control is used as an inner loop.

[0041] Among them, the capacitor voltage control is used to adjust the capacitor voltage in the energy storage module to ensure that it remains within the rated voltage range; its specific implementation steps include: detecting the output voltage through a voltage sensor, and comparing it with the capacitor voltage reference value to obtain a voltage error value; inputting the voltage error value into the voltage loop PI controller to generate a first current reference value. The specific implementation steps of the battery current control include: detecting the battery current through a current sensor, and comparing it with the total battery current reference value to obtain a current error value; inputting the current error value into the current loop PI controller to generate a pulse width modulation signal, and using the pulse width modulation signal to control the switching state of the switching device in the DC / DC converter.

[0042] On this basis, the module controller calculates the total reference value of the battery current of each energy storage module according to the following formula: total reference value of battery current = first reference value of battery current + second reference value of battery current; wherein, the first reference value of battery current is calculated by the module controller as the output value of the capacitor voltage outer loop; the second reference value of battery current is obtained by calculating according to the following formula: second reference value of battery current = module active power instruction value / module battery voltage.

[0043] 3. After receiving the feedback signals from all module controllers, the main controller calculates the active current reference value of the entire cascade energy storage system, and then inputs it into the active current control loop for power regulation.

[0044] Part II: A specific application example

[0045] This example constructs the circuit topology and control model of a cascade energy storage system in the PLECS simulation software to verify the specific feasibility and corresponding technical effects of the present invention.

[0046] Figure 1 The main circuit topology diagram of the cascade energy storage system of the embodiment of the present invention is shown in the figure. As shown in the figure, the cascade energy storage system has a three-phase star topology and a two-stage structure. Each phase of the cascade energy storage system is composed of a filter reactor L f It is composed of N energy storage modules connected in series; each energy storage module has the same structure, including a module controller, an H-bridge, a DC capacitor, a DC / DC converter and a series battery cluster.

[0047] In this embodiment, the rated line voltage of the power grid is set to 10 kV, the rated power of the energy storage system is set to 2 MW, the number of energy storage modules per phase is set to 10, and the rated voltage of the energy storage module battery cluster is set to 0.8 kV.

[0048] Based on the cascade energy storage system, a power control strategy based on active power command sharing is provided, including the following contents:

[0049] 1. By controlling the active current and reactive current of the energy storage system in the main controller, the active power and reactive power output are managed respectively, so as to ensure that the energy storage system has a higher dynamic response speed; in the initial state of the simulation, the active power of the system is set to the rated discharge power, that is, 2MW. In each energy storage module, the energy storage battery is connected to the H bridge through DC / DC. Each energy storage module adopts a unified dual closed-loop control structure, and the outer loop and inner loop control the energy storage module capacitor voltage and battery current respectively. Among them, the voltage of the DC capacitor of each module is controlled to 1kV through DC / DC.

[0050] 2. The cascade energy storage system receives an external rated charging power (-2MW) instruction, and distributes the active power instructions of each system to each module controller (-66.7kW) evenly according to the number of modules, so as to realize the sharing of active power instructions. Each module calculates the total reference value of the battery current according to the received module active power instruction value and the current module battery voltage, and the calculation formula is: total reference value of battery current = first reference value of battery current + second reference value of battery current. Among them, the first reference value of battery current is calculated by the module controller and is the output of the capacitor voltage outer loop; wherein, the calculation formula of the second reference value of battery current is: second reference value of battery current = module active power instruction value / module battery voltage. The battery current instruction value is provided to the inner loop of the DC / DC controller, and then the signal of the completion of active power instruction sharing is fed back to the main controller.

[0051] 3. After receiving the feedback signals from all module controllers, the main controller of the cascade energy storage system calculates the active current reference value of the entire system. The calculation formula is: active current reference value = active power command value / (1.5×rated phase voltage amplitude of the power grid), and inputs it into the active current control loop for power regulation, thereby ensuring the smooth operation of the system during dynamic operations such as charging and discharging power switching, and ensuring the safety and stability of the system.

[0052] Figure 2 The power control block diagram of a two-stage cascade energy storage system based on active power command sharing is shown.

[0053] Figure 3 The waveforms of the AC current and battery current of the cascade energy storage system during the step change from the rated power discharge state (2MW) to the rated power charging state (-2MW) when the active power command sharing control is adopted are shown. The results show that through the control strategy based on active power command sharing, the system has a rapid state response, the adjustment time is less than 50ms, the power switching process is smooth, and there is no impact on the system AC current and module battery current.

[0054] Therefore, the power control strategy of the two-stage cascade energy storage system based on active power command sharing proposed in the present invention avoids the complex parameter coordination in the traditional two-stage control system by introducing the active power command sharing mechanism, effectively avoids the current shock problem caused by the inconsistency of AC and DC dynamic performance, and ensures the dynamic performance and operation stability of the cascade energy storage system.

Claims

1. A two-stage cascade energy storage system power control strategy based on active power instruction sharing, characterized in that: Specifically include: (1) The module controller of each energy storage module adopts a unified dual closed-loop control method, with the outer loop and inner loop controlling the capacitor voltage and battery current of the energy storage module respectively; the main controller of the energy storage system adopts active and reactive power decoupling control, and manages the active power and reactive power output of the cascaded energy storage system respectively by controlling the active current and reactive current; (2) After receiving the external active power command, the main controller of the cascade energy storage system calculates the active power of each module according to the number of energy storage modules and distributes it to each module controller to realize the sharing of the active power command; each module controller further calculates the total reference value of the battery current according to the received active power command value and the current battery voltage of each energy storage module, and provides it to the inner loop, and at the same time feeds back the signal of the active power command sharing to the main controller; (3) After receiving the feedback signals from all module controllers, the main controller calculates the active current reference value of the entire cascade energy storage system and then inputs it into the active current control loop for power regulation.

2. The control strategy according to claim 1, characterized in that: The cascade energy storage system has a three-phase star topology and a two-stage structure, each phase of which is composed of a filter reactor L f It is composed of N energy storage modules connected in series; each energy storage module has the same structure, including a module controller, and an H-bridge, a DC capacitor, a DC / DC converter and a series battery cluster arranged in sequence.

3. The control strategy according to claim 1, characterized in that: The module controller calculates the total reference value of the battery current of each energy storage module according to the following formula: total reference value of battery current = first reference value of battery current + second reference value of battery current; wherein, the first reference value of battery current is calculated by the module controller as the output value of the capacitor voltage outer loop; the second reference value of battery current is obtained by calculating according to the following formula: second reference value of battery current = module active power instruction value / module battery voltage.

4. The control strategy according to claim 1, characterized in that: A module controller is provided in each energy storage module, and in its control strategy, capacitor voltage control is used as an outer loop and battery current control is used as an inner loop.

5. The control strategy according to claim 4, characterized in that: The capacitor voltage control is used to adjust the capacitor voltage in the energy storage module to ensure that it remains within the rated voltage range; its specific implementation steps include: detecting the output voltage through a voltage sensor and comparing it with the capacitor voltage reference value to obtain a voltage error value; inputting the voltage error value into the voltage loop PI controller to generate a first current reference value.

6. The control strategy according to claim 4, characterized in that: The specific implementation steps of the battery current control include: detecting the battery current through a current sensor and comparing it with the total reference value of the battery current to obtain a current error value; inputting the current error value into a current loop PI controller to generate a pulse width modulation signal, and using the pulse width modulation signal to control the switching state of the switching device in the DC / DC converter.

7. The control strategy according to claim 1, characterized in that: The main controller adopts an active and reactive decoupling control strategy, which specifically includes: (1) Detect the three-phase AC voltage and current output by the cascade energy storage system through voltage sensors and current sensors respectively; calculate the phase angle in real time according to the phase-locked loop, and convert the three-phase AC voltage and current into the dq coordinate system; set the command values ​​of active power and reactive power respectively according to the grid demand and the state of the energy storage system; (2) Controlling the active current: calculating the active current reference value according to the active power command value, comparing the d-axis current with the active current reference value to obtain a d-axis current error value; inputting the d-axis current error value into the voltage loop PI controller to generate a d-axis modulation signal reference value; (3) Controlling reactive current: Calculating reactive current reference value according to reactive power command value, comparing q-axis current with reactive current reference value to obtain q-axis current error value; inputting q-axis current error value into voltage loop PI controller to generate q-axis modulation signal reference value; (4) Convert the d-axis and q-axis modulation signal reference values ​​to a three-phase coordinate system to obtain a three-phase modulation signal reference value; and use the three-phase modulation signal reference value to control the switching state of the switching devices in the H bridge of each energy storage module.

8. The control strategy according to claim 7, characterized in that: The calculation formula of the active current reference value is: active current reference value=active power command value / (1.5×rated phase voltage amplitude of the power grid).

9. The control strategy according to claim 7, characterized in that: The calculation formula of the reactive current reference value is: reactive current reference value=-reactive power command value / (1.5×rated phase voltage amplitude of the power grid).

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