A method for adaptive start-stop control of a storage side converter of a light storage system

Abstract

The application discloses an adaptive start-stop control method for an energy storage side converter of a light storage system, and relates to the technical field of light storage system control. The method aims to solve the problems of large standby loss and shortened service life of an energy storage device caused by the continuous operation of an energy storage side converter for maintaining the voltage of a direct-current bus in a direct-current coupling type light storage system. The method is applied to a light storage system in which an energy storage device is connected to a direct-current bus through a converter. A multi-dimensional joint criterion including a direct-current bus voltage stability criterion, an energy storage state of charge (SOC) safety constraint criterion and an optional supplementary criterion is constructed. In combination with hysteresis control logic, the converter is turned off when all the criteria meet the steady-state condition, and the converter is started when any criterion does not meet the condition. The adaptive start-stop of the converter is realized, the stability of the system is ensured, the loss is reduced, and the service life of the energy storage device is prolonged.

Description

Technical Field

[0001] This application belongs to the field of photovoltaic-storage system control technology, and relates to an adaptive start-stop control method for the energy storage-side converter of a photovoltaic-storage system. Background Technology

[0002] As the proportion and installed capacity of new energy sources such as wind and solar power connected to the grid via inverters continue to expand, the future power system will be a "dual-high" system characterized by a high proportion of renewable energy and a high proportion of power electronic equipment. When voltage and frequency disturbances occur in the grid, inverters used in solar and other new energy applications may experience a mismatch between the system's required output power and the output power of the new energy sources. Therefore, energy storage devices are needed to buffer this power imbalance.

[0003] When configuring energy storage in a photovoltaic (PV) system, a suitable coupling method needs to be selected based on the structure of the PV power generation unit. Firstly, the energy storage device can be connected to the AC side of the PV system via an inverter, known as AC coupling. Besides AC coupling, the energy storage device can also be connected to the DC bus, known as DC coupling. DC coupling can be further divided into two types: direct connection of the energy storage to the DC bus and connection via an inverter.

[0004] To ensure normal system operation, photovoltaic (PV) power generation systems with a DC bus require DC bus voltage stability control. Currently, DC bus control methods can be broadly categorized into three types: the first maintains DC bus voltage by adjusting PV power to match the output power of the grid-side converter; the second maintains DC bus voltage by adjusting the output power of the grid-side converter to match the PV power; and the third maintains DC bus voltage by controlling the charging / discharging of energy storage devices to buffer the power imbalance between PV power and grid-side converter output power. The PV power adjustment method is primarily used in PV systems without energy storage; the grid-side power adjustment method relies on grid-side response speed and is suitable for applications where grid-side control with a fast response time is used; the energy storage method offers fast response speed and is suitable for applications where grid-side control with a slower response time is used, and is also applicable to applications where grid-side control is used.

[0005] However, this method currently has certain problems: in order to maintain a stable DC bus voltage, the energy storage-side converter has to operate continuously, and the current of the energy storage device fluctuates around 0. The continuously fluctuating current will generate significant losses in the energy storage-side converter, and frequent charging / discharging may affect the service life of the energy storage device. Summary of the Invention

[0006] This application provides an adaptive start-stop control method for the energy storage-side converter in a photovoltaic-energy storage system. It aims to solve the technical problem in DC-coupled photovoltaic-energy storage systems where the energy storage-side converter needs to continue operating even in steady state to maintain the DC bus voltage stability, resulting in fluctuations in the output current of the energy storage device, significant standby losses of the converter, and a shortened service life of the energy storage device.

[0007] To achieve the above objectives, this application employs the following technical means: This application provides an adaptive start-stop control method for the energy storage-side converter of a photovoltaic-energy storage system, including: The adaptive start-stop of the energy storage-side converter is controlled by constructing a multi-dimensional joint criterion, which includes the DC bus voltage stability criterion and the SOC safety constraint of the energy storage device in sequence. When both the DC bus voltage stability criterion and the energy storage device state of charge (SOC) safety constraint criterion are met simultaneously, the final determination is that the energy storage side converter can be shut down; when the two criteria cannot be met simultaneously, the final determination is that the energy storage side converter can be turned on.

[0008] As a further improvement of this application, the DC bus voltage stability criterion is as follows: determining whether the DC bus voltage is within the allowable range; when the DC bus voltage is lower than the preset value, the energy storage device discharges to increase the DC bus voltage; when the DC bus voltage is higher than the preset value, the energy storage device charges to decrease the DC bus voltage; when the DC bus voltage is within the allowable range, the energy storage device does not need to charge / discharge to adjust the DC bus voltage.

[0009] As a further improvement of this application, the safety constraint criterion for the state of charge (SOC) of the energy storage device is as follows: it is determined whether the state of charge of the energy storage device is within the allowable range; if the SOC deviates from the preset value, it needs to be actively charged / discharged for adjustment; if the SOC of the energy storage device is within the allowable range, the energy storage device does not need to perform any charging / discharging.

[0010] As a further improvement to this application, when executing the multi-dimensional joint criterion, the adaptive start-up and shutdown of the energy storage-side converter is performed according to hysteresis control logic. The hysteresis control logic sets corresponding upper and lower hysteresis thresholds for DC bus voltage deviation and energy storage device state of charge deviation, respectively. When the absolute value of the DC bus voltage deviation is less than or equal to its hysteresis threshold and the absolute value of the energy storage device's state of charge deviation is less than or equal to its hysteresis threshold, the photovoltaic-storage system is determined to be in a steady state, and the energy storage-side converter is shut down. When the absolute value of the DC bus voltage deviation is greater than its hysteresis threshold or the absolute value of the energy storage device's state of charge deviation is greater than its hysteresis threshold, the photovoltaic-storage system is determined to be in an unsteady state. The energy storage-side converter is then started and kept in operation until the system returns to a steady state.

[0011] As a further improvement of this application, the DC bus voltage deviation is the difference between the actual DC bus voltage and the preset voltage reference value, and the allowable range of the DC bus voltage is limited by the hysteresis upper and lower limit thresholds.

[0012] As a further improvement of this application, the state of charge deviation of the energy storage device is the difference between the actual SOC value of the energy storage device and the preset SOC reference value, and the allowable range of the SOC is limited by the upper and lower hysteresis thresholds.

[0013] As a further improvement to this application, the multi-dimensional joint criterion also includes supplementary criteria added based on the grid-side control type or working scenario of the photovoltaic-storage system; The supplementary criteria are executed after the DC bus voltage stability criterion and the energy storage device state of charge (SOC) safety constraint criterion are applied.

[0014] As a further improvement of this application, when the grid side is grid-following control, the supplementary criterion is the new energy power change rate criterion. When the absolute value of the photovoltaic power change rate is less than or equal to the threshold, the supplementary criterion is determined to be satisfied. When the grid side is a grid-type control, the supplementary criteria include grid frequency criteria and grid voltage criteria. When both grid frequency and voltage are within their respective allowable ranges, the supplementary criteria are deemed to be satisfied.

[0015] As a further improvement to this application, The supplementary criteria also include a photovoltaic operating mode criterion. When the photovoltaic power generation unit is in constant power generation mode, the supplementary criterion is deemed to be satisfied; when the photovoltaic power generation unit is in maximum power point tracking mode, the supplementary criterion is deemed not satisfied, and the energy storage side converter continues to operate. The photovoltaic power generation unit adopts power reserve control. In each control cycle, the maximum output power is first obtained by the maximum power point tracking method and maintained until the next cycle, and then the actual output power is controlled. The determination of the supplementary criterion is synchronized with the power reserve control cycle.

[0016] As a further improvement of this application, when the photovoltaic-storage system includes multiple parallel energy storage devices and corresponding energy storage-side converters, the converters corresponding to the energy storage devices with smaller SOC deviations are prioritized to be shut down, and the converters corresponding to the energy storage devices with larger SOC deviations are prioritized to be started.

[0017] Compared with the prior art, this application has the following advantages: This application accurately identifies the steady state of the system through multi-dimensional joint criteria, preventing the energy storage-side converter from continuously operating when not in use. This significantly reduces unnecessary switching actions in standby mode, substantially lowering the converter's switching and conduction losses, and improving the energy utilization efficiency of the photovoltaic-energy storage system. Simultaneously, the hysteresis control logic effectively prevents the converter from frequently starting and stopping at criterion boundaries, reducing the number of charge-discharge cycles of the energy storage device, slowing down the aging of the energy storage cells, and extending the overall lifespan of the energy storage device. This technical solution is implemented solely through software algorithm optimization, requiring no additional hardware or circuit topology modifications. It is low-cost and highly compatible, adaptable to different grid-side control types, energy storage device types, and photovoltaic operating modes. While ensuring DC bus voltage stability and system operational safety, it significantly improves the economy and reliability of the photovoltaic-energy storage system. Attached Figure Description

[0018] Figure 1 This is a structural diagram of a photovoltaic-storage system; Figure 2 For control flowchart; Figure 3 This is the DC bus voltage hysteresis control logic; Figure 4 For the hysteresis control logic of the energy storage device's state of charge; Figure 5 The control block diagram of an existing grid-type photovoltaic converter based on supercapacitor energy storage is shown. Figure 6 The diagram shows the outer loop control block diagram for the supercapacitor voltage; where (a) maximum power sampling, (b) maximum power hold, and (c) photovoltaic power standby. Figure 7 Workflow for photovoltaic power backup control; Figure 8 This is a control block diagram of the supercapacitor-side converter; Figure 9 Waveform diagram of hysteresis control experiment of supercapacitor-side converter; Figure 10 The waveform diagram of DC bus voltage under real meteorological conditions is shown. In the picture: Photovoltaic voltage; Photovoltaic current; Photovoltaic power; Boost chopper duty cycle; Supercapacitor voltage; Reference value for supercapacitor voltage; Supercapacitor discharge current; Duty cycle of the bidirectional chopper; DC bus voltage; DC bus voltage reference value; Reference value for supercapacitor current; Three-phase output voltage; Three-phase output current; Output active power; No reactive power output; Active power reference value; Virtual rotor input power; Modulation voltage. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of this application.

[0020] This application proposes an adaptive start-stop control method for the energy storage-side converter in a photovoltaic-energy storage system. This scheme intelligently starts and stops the energy storage-side converter by applying hysteresis control to the DC bus voltage and the state of charge of the energy storage device. While ensuring system stability, it reduces the operating time of the energy storage-side converter during standby, thereby reducing standby losses and extending the service life of the energy storage device. This application is applicable to photovoltaic-energy storage systems where the energy storage device is connected to a DC bus structure via a converter, such as… Figure 1 The diagram shown is a structural diagram of a photovoltaic-energy storage system.

[0021] In DC-coupled photovoltaic-energy storage systems where the energy storage device is connected to the DC bus via a converter, the energy storage-side converter continues to operate even when the DC bus voltage is stable. This causes continuous fluctuations in the output current of the energy storage device, resulting in significant losses in the converter and potentially impacting the device's lifespan due to frequent charging and discharging. Therefore, this application proposes an adaptive start-stop control method for the energy storage-side converter in a photovoltaic-energy storage system. This method avoids unnecessary switching operations of the converter in standby mode while ensuring system stability, thereby reducing standby losses and extending the lifespan of the energy storage device.

[0022] Specifically, this application provides an adaptive start-stop control method for a photovoltaic-storage system's energy storage-side converter, applied to a DC-coupled photovoltaic-storage system where the energy storage device is connected to a DC bus via a converter. The photovoltaic-storage system includes a photovoltaic power generation unit, an energy storage device, an energy storage-side converter, a grid-side converter, and a DC bus. The energy storage-side converter is used to control the DC bus voltage stability, including: Adaptive start-stop of the energy storage-side converter is achieved by constructing multi-dimensional joint criteria and hysteresis control logic. The multi-dimensional joint criteria include sequentially performed DC bus voltage stability criteria and energy storage device SOC safety constraint criteria. Supplementary criteria can also be added according to the grid-side control type or working scenario of the photovoltaic-storage system. The hysteresis control logic sets corresponding upper and lower hysteresis thresholds for the DC bus voltage deviation and the energy storage device state of charge deviation, respectively. When the absolute value of the DC bus voltage deviation is less than its lower hysteresis threshold and the absolute value of the energy storage device state of charge deviation is less than its lower hysteresis threshold, and the supplementary criterion (if any) meets the preset conditions, the photovoltaic-energy storage system is determined to be in a steady state, and the energy storage side converter is shut down. When the absolute value of the DC bus voltage deviation is greater than its upper hysteresis threshold or the absolute value of the energy storage device state of charge deviation is greater than its upper hysteresis threshold, or the supplementary criterion (if any) does not meet the preset conditions, the photovoltaic-energy storage system is determined to be in a non-steady state, and the energy storage side converter is started and maintained until the system returns to a steady state.

[0023] The control principle of this application is as follows: when the energy storage-side converter is not required to operate, it is shut down. By reducing unnecessary switching operations of the energy storage-side converter and the number of charge / discharge cycles of the energy storage device in standby mode, the standby loss on the energy storage side is reduced, and the service life of the energy storage device is extended. Since the system loses control over the DC bus voltage and the energy storage device during the shutdown period of the energy storage-side converter, in order to ensure the stability of the DC bus voltage and the state of charge of the energy storage device, a joint criterion is established by detecting multiple variables. When the DC bus voltage and the state of charge of the energy storage device are within the allowable range, the energy storage-side converter is shut down.

[0024] The control proposed in this application consists of three steps: The first step is to determine whether the DC bus voltage is within the allowable range. When the DC bus voltage is lower than the preset value, the energy storage device discharges to increase the DC bus voltage; when the DC bus voltage is higher than the preset value, the energy storage device charges to decrease the DC bus voltage. Therefore, when the DC bus voltage is within the allowable range, the energy storage device does not need to adjust the DC bus voltage for charging / discharging.

[0025] The second step is to determine whether the State of Charge (SOC) of the energy storage device is within the allowable range. SOC is a crucial indicator of the remaining capacity of the energy storage device, representing the ratio of its current remaining capacity to its fully charged capacity, usually expressed as a percentage, with a range of 0-100%. Since the energy storage device needs to charge / discharge according to different operating conditions, its SOC should be maintained near a preset value between 0-100% during stable system operation, allowing for sufficient margin for both charging and discharging. If the SOC deviates from the preset value, active charging / discharging is required for adjustment. Therefore, if the SOC of the energy storage device is also within the allowable range, no charging / discharging is necessary. If both the first and second steps are satisfied, and there are no additional conditions for the third step, the energy storage-side converter is directly shut down; if there are additional conditions for the third step, the third step is initiated.

[0026] Third, additional criteria can be added based on the functions and usage scenarios of the photovoltaic-storage system. To ensure that shutting down the energy storage-side converter does not affect the specific functions of certain photovoltaic-storage systems, other necessary criteria can be added according to the usage scenarios. For example, when the grid side of the photovoltaic-storage system is grid-following control, the energy storage device may need to smooth out fluctuations in renewable energy power; the magnitude of the renewable energy power change rate can be used as an additional criterion.

[0027] After the first and second steps are passed, if the grid side of the photovoltaic and energy storage system is controlled by following the grid, the rate of change of renewable energy power should be within the allowable range, and the rate of change of renewable energy power can be used as an additional criterion; if the grid side of the photovoltaic and energy storage system is controlled by connecting the grid, the energy storage device may need to provide the transient energy required for active support, and the grid frequency and voltage can be used as additional criterions.

[0028] After the first and second steps are passed, the energy storage-side converter can be shut down if the additional criteria are within the allowable range. The introduction of additional criteria can more accurately control the start and stop of the energy storage-side converter, but it is only a supplementary criterion for the DC bus voltage and the state of charge of the energy storage device, and is not mandatory.

[0029] Optionally, the DC bus voltage deviation is the difference between the actual DC bus voltage and a preset voltage reference value, and the allowable range of the DC bus voltage is limited by the hysteresis upper and lower threshold values. For example, the hysteresis lower threshold value ( The value range is 0.5%~2% × preset voltage reference value, and the upper limit threshold of hysteresis ( The value range is 3%~5% × preset voltage reference value.

[0030] Optionally, the state of charge (SOC) deviation of the energy storage device is the difference between the actual SOC value of the energy storage device and the preset SOC reference value. The allowable range of the SOC is limited by the upper and lower hysteresis thresholds. For example, the lower hysteresis threshold ( The value range is 1% to 3%, and the upper limit threshold of hysteresis ( The value ranges from 5% to 8%.

[0031] Optionally, the supplementary criteria are based on the grid-side control type selection setting of the photovoltaic-storage system. The grid-side control type includes grid-following control and grid-building control. The supplementary criteria, together with the DC bus voltage criteria and the SOC criteria, constitute further limitations.

[0032] Optionally, the start-stop control of the energy storage-side converter is equipped with a delay logic. When the system is determined to meet the steady-state conditions, the converter is shut down after a delay of 0.5s to 2s; when the system is determined to meet the non-steady-state conditions, the converter is started immediately.

[0033] Optionally, when the grid side is grid-following control, the supplementary criterion is the new energy power change rate criterion. For example, the power change rate threshold is set to 0.05kW / (s·kW)~0.1kW / (s·kW). When the absolute value of the photovoltaic power change rate is less than this threshold, the supplementary criterion is determined to be satisfied.

[0034] When the grid side is a grid-type control, the supplementary criteria include grid frequency criteria and grid voltage criteria. For example, the allowable range of grid frequency is 49.5Hz~50.5Hz, and the allowable range of grid voltage is 0.9pu~1.1pu. When both grid frequency and voltage are within the corresponding allowable range, the supplementary criteria are deemed to be satisfied.

[0035] For example, when the energy storage device is a supercapacitor, the preset reference value of SOC is 50%~60%, and the lower limit threshold of hysteresis ( Take 1%~2%, upper limit threshold of hysteresis ( The SOC is set at 5% to 6%; when the energy storage device is a battery, the preset reference value is 40% to 80%, and the lower hysteresis threshold is ( Take 2%~3%, upper limit threshold of hysteresis ( Take 7%~8%.

[0036] Furthermore, the supplementary criterion includes a photovoltaic operating mode criterion. The supplementary criterion is determined to be satisfied only when the photovoltaic power generation unit is in constant power generation mode; when the photovoltaic power generation unit is in maximum power point tracking (MPPT) mode, the supplementary criterion is determined not to be satisfied, and the energy storage side converter continues to operate.

[0037] The photovoltaic power generation unit employs power reserve control, and in each control cycle, the maximum output power is first obtained through the maximum power point tracking method. And maintain this until the next cycle, then control the actual output power ( The determination of the supplementary criterion is synchronized with the power reserve control cycle.

[0038] Alternatively, as an optional solution, an outer loop control of the energy storage device voltage can be added to the grid-side grid-type control. By adjusting the active power command of the grid-type control at the minute level, the SOC of the energy storage device can be kept stable near a preset reference value. The hysteresis threshold of the SOC criterion is matched with the adjustment accuracy of the outer loop control of the voltage.

[0039] When a photovoltaic-storage system includes multiple parallel energy storage devices and corresponding energy storage-side converters, the converters corresponding to the energy storage devices with smaller SOC deviations are prioritized for shutdown, while the converters corresponding to the energy storage devices with larger SOC deviations are prioritized for startup.

[0040] The determination order of the multi-dimensional joint criteria is replaced as follows: first determine the state of charge (SOC) criterion of the energy storage device, then determine the DC bus voltage criterion, and finally determine the supplementary criterion (if any). The determination logic is still an AND logic relationship.

[0041] As an optional solution, an emergency fault mechanism can also be added. For example, when a fault is detected in the energy storage-side converter, a sudden change in DC bus voltage exceeds 1.5 times the upper limit of the hysteresis threshold, or a sudden change in SOC exceeds 1.5 times the upper limit of the hysteresis threshold, all shut-down energy storage-side converters will be immediately started and an alarm signal will be triggered.

[0042] In summary, the control flow of the standby loss optimization control scheme for the energy storage-side converter of the photovoltaic-storage system proposed in this application is as follows: Figure 2 As shown. When determining the DC bus voltage and the state of charge of the energy storage device, this application also provides corresponding hysteresis control, the specific control logic of which is as follows: Figure 3 and Figure 4 As shown.

[0043] When the absolute value of the DC bus voltage deviation Less than the set hysteresis lower limit voltage When the DC bus voltage is determined to be in a steady state, the energy storage-side converter can be shut down. Subsequently, the DC bus voltage begins to deviate from the preset value due to the slight power difference between the photovoltaic power and the grid-side power, until... Voltage greater than the set upper limit of hysteresis If the DC bus voltage is determined to be in an unsteady state, the energy storage-side converter will restart operation until... Less than ,final exist and The changes between them.

[0044] Figure 3 This is the DC bus voltage hysteresis control logic; the determination of the state of charge of the energy storage device is the same as that of the DC bus voltage: when the absolute value of the deviation of the state of charge of the energy storage device... Less than the lower limit of the hysteresis loop of the energy storage device's state of charge When the energy storage device is determined to be in a steady state of charge, the energy storage-side converter can be shut down; until... Greater than the upper limit of the hysteresis loop of the energy storage device's state of charge. Subsequently, it is determined that the energy storage device is in an unsteady state of charge, and the energy storage-side converter continues to operate to restore the energy storage device's state of charge.

[0045] Figure 4 This is the state-of-charge hysteresis control logic for the energy storage device. In a DC-coupled photovoltaic-energy storage system where the energy storage device is connected to the DC bus via a converter, the energy storage-side converter needs to continue operating even when the DC bus voltage is stable. This causes continuous fluctuations in the output current of the energy storage device, resulting in significant losses in the energy storage-side converter. Frequent charging / discharging may also affect the service life of the energy storage device.

[0046] This application enables timely shutdown of the energy storage-side converter when the photovoltaic-energy storage system is in a steady state, avoiding unnecessary switching operations of the converter in standby mode, thereby reducing standby losses and extending the lifespan of the energy storage device. In DC-coupled photovoltaic-energy storage systems where the energy storage device is connected to the DC bus via a converter, a joint criterion is used to timely shut down the energy storage-side converter when it is in standby mode. This reduces unnecessary switching operations of the converter and the number of charge / discharge cycles of the energy storage device in standby mode, thus reducing standby losses and extending the lifespan of the energy storage device. Hysteresis control based on the deviation between the energy storage device's state of charge (SOC) and the DC bus voltage is employed, ensuring that the DC bus voltage and SOC are maintained within a stable range while starting and stopping the energy storage-side converter. This solution is implemented solely through software algorithms, requiring no additional hardware or circuit topology modifications, resulting in low implementation costs.

[0047] The following are specific embodiments of the control strategy proposed in this application: A typical existing grid-connected photovoltaic system based on supercapacitor energy storage has the following overall control block diagram: Figure 5 As shown, the photovoltaic array of this system is connected to the DC bus via a boost-type DC / DC chopper, while the supercapacitor energy storage uses a bidirectional DC / DC chopper connected in parallel to the same DC bus. Finally, grid-connected operation is achieved through a grid-side inverter. Specifically: the boost chopper provides power reserve by adjusting the operating point of the photovoltaic array; the bidirectional chopper on the energy storage side is responsible for maintaining stable bus voltage, ensuring dynamic power balance between the power generation unit and the grid; and the inverter provides necessary active support capabilities for the system through grid-based control.

[0048] It should be noted that although the embodiments described in this application use supercapacitors as energy storage devices, the control method proposed in this application can be applied to different energy storage devices. Furthermore, the structure and control method of the photovoltaic side, energy storage side, and grid side in this embodiment are not limited to this specific embodiment; it is sufficient to ensure that the energy storage is connected to the system DC bus through an inverter and that the DC bus voltage is controlled by the energy storage.

[0049] The grid-side control strategy is divided into grid-type control and supercapacitor voltage outer loop control, which will be explained separately below.

[0050] This embodiment employs grid-based control on the grid side. The core implementation process of grid-based control includes: first, acquiring the output capacitor voltage and grid-side current signal, and obtaining the system's real-time output power through the power calculation module; second, calculating the virtual phase angle and induced electromotive force by combining the governor equation and rotor oscillation equation of the synchronous generator through electromechanical transient simulation with electromagnetic transient calculation; subsequently, introducing a virtual impedance link to generate the inverter modulation wave reference voltage; finally, driving the inverter power switching devices to transmit the power of the new energy power generation unit to the grid. The specific grid-side control strategy is unrelated to the control proposed in this application and will not be elaborated upon here.

[0051] Considering the linear relationship between the state of charge (SOC) and terminal voltage of a supercapacitor, its SOC can be controlled by controlling the terminal voltage. Therefore, to stabilize the SOC of the supercapacitor near its rated standby value, a specific embodiment adds a slower-responding (minute-level) outer loop of supercapacitor voltage to the basic grid-based control to achieve SOC management control. This is achieved by adjusting the active power command of the grid-based control. The state of charge of the supercapacitor is adjusted slowly. Simultaneously, to reduce the supercapacitor's involvement in absorbing power fluctuations on the photovoltaic side during active power command regulation, photovoltaic power feedforward is added to redirect photovoltaic power... Increased as a feedforward term to In the middle. For example Figure 6 The diagram shown is the outer loop control block diagram for the supercapacitor voltage.

[0052] In this embodiment, the photovoltaic side employs power backup control, the principle of which is similar to sample-and-hold, such as... Figure 7 The diagram illustrates the photovoltaic power reserve control workflow. In each power reserve control cycle, the maximum output power of the photovoltaic array is first obtained using the maximum power point tracking method. Record this power value unchanged until the next cycle, and calculate the actual power output of the photovoltaic array for the remaining time in this cycle. The photovoltaic array is controlled to switch between maximum power point tracking (MPPT) mode and constant power generation mode. When changes in ambient irradiance or temperature affect the photovoltaic output characteristics, the system can update its operation via MPPT. and Maintain a high level of power reserve accuracy.

[0053] In a specific embodiment, a bidirectional chopper on the supercapacitor side is used to stabilize the DC bus voltage. Figure 8 This is the control strategy for the supercapacitor side. Based on the traditional dual-loop voltage and current control, this strategy improves the DC bus voltage outer loop from conventional PI control to proportional-integral resonant control, while adding a virtual rotor kinetic energy feedforward control. The former can transfer the second harmonic power generated by the system when the three-phase load is unbalanced from the DC bus to the supercapacitor, thereby effectively suppressing the second harmonic ripple of the DC bus voltage. The resonant frequency is twice the grid frequency, which can be obtained using the virtual angular frequency of the grid-type control. This eliminates the need for a phase-locked loop (PLL). The latter can adjust the grid-type converter input power determined by the governor due to sudden changes in grid-side load. and output power By charging / discharging the supercapacitor in advance, grid-side disturbances are directly transferred to the supercapacitor side, reducing DC bus voltage fluctuations.

[0054] Since the grid-side control in this specific embodiment is a grid-based control, changes in grid frequency or voltage alter the power supplied by the photovoltaic-storage system to the grid to provide frequency and voltage support. These power changes change the DC bus voltage and the state of charge of the energy storage. Therefore, step three of the control proposed in this application adds grid frequency and voltage as additional criteria; the energy storage-side converter can only be shut down when both are within permissible ranges.

[0055] Meanwhile, the photovoltaic power reserve control in this case will cause the photovoltaic array to alternately operate in maximum power point tracking mode and constant power generation mode. During constant power generation mode, the difference between photovoltaic power and grid-side power is small, which is less likely to cause drastic changes in DC bus voltage and energy storage state of charge. Therefore, step three of the control proposed in this application adds the photovoltaic operating mode as an additional criterion. The energy storage-side converter can only be shut down when the photovoltaic array is in constant power generation mode.

[0056] The final implementation process of the control strategy proposed in this application on this system is as follows: First step, according to Figure 3 The hysteresis logic shown determines whether the DC bus voltage is in a steady state. If it is in a non-steady state, the energy storage-side converter continues to operate; if it is in a steady state, it proceeds to the second step of condition judgment.

[0057] The second step, according to Figure 4 The hysteresis logic shown determines whether the state of charge is in a steady state. If it is in a non-steady state, the energy storage-side converter continues to operate; if it is in a steady state, it proceeds to the third step of condition judgment.

[0058] The third step is to determine the grid frequency, grid voltage status, and photovoltaic operating mode. If the grid frequency and grid voltage are both within the allowable range, the photovoltaic array is in constant power generation mode, and the energy storage-side converter is turned off; otherwise, the energy storage-side converter continues to operate.

[0059] When the system is in steady state, the DC bus voltage, grid-side output power, and grid frequency are as follows: Figure 9 As shown. Figure 9 The waveforms for the hysteresis control experiment of the supercapacitor-side converter are shown. From 1.8s to 2.8s, the photovoltaic array is in maximum power point tracking mode to measure maximum power; the remaining time is in constant power generation mode for power reserve. Figure 9 As can be seen, when the photovoltaic array is in constant power generation mode, the supercapacitor-side converter starts and stops periodically, causing the DC bus voltage to fluctuate within a preset hysteresis range. Calculations show that within one photovoltaic power reserve control cycle, the operating time of the supercapacitor-side converter is reduced by 84%.

[0060] Meanwhile, to verify the engineering applicability of the proposed control strategy, a photovoltaic simulated power supply was tested using actual meteorological data. A short-term test of 400 seconds was conducted on a cloudy day, and the changes in light intensity, temperature, and DC bus voltage were recorded as follows: Figure 10 As shown. Figure 10 The experimental waveform of DC bus voltage under real meteorological conditions; from Figure 10 As can be seen, even if the meteorological conditions change significantly, the supercapacitor-side converter remains in a disconnected state for a long time. Calculations show that within one photovoltaic power standby control cycle, the operating time of the supercapacitor-side converter is reduced by 72%, which greatly reduces the standby loss of the system.

[0061] A second objective of this application is to provide an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the aforementioned adaptive start-stop control method for the energy storage-side converter in a photovoltaic-energy storage system. The device also includes a communication interface and a bus.

[0062] The third objective of this application is to provide a computer-readable storage medium storing a computer program that, when executed by a processor, implements the aforementioned adaptive start-stop control method for the energy storage-side converter in a photovoltaic-storage system.

[0063] A fourth objective of this application is to provide a computer program product, which includes computer instructions that instruct a computer to execute the above-described adaptive start-stop control method for the energy storage-side converter of a photovoltaic energy storage system.

[0064] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0065] These computer program instructions can also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0066] This application may take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application may take the form of a computer program product implemented on one or more computer-usable storage media (including, but not limited to, disk storage, readable storage media, optical storage, etc.) containing computer-usable program code.

[0067] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0068] Obviously, the described embodiments are only some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort should fall within the scope of protection of this application.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and not to limit them. Although this application has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation methods of this application. Any modifications or equivalent substitutions that do not depart from the spirit and scope of this application should be covered within the protection scope of this application.

Claims

1. An adaptive start-stop control method for a power converter on the energy storage side of a photovoltaic-energy storage system, characterized in that, include: The adaptive start-stop of the energy storage-side converter is controlled by constructing a multi-dimensional joint criterion, which includes a DC bus voltage stability criterion and an energy storage device state of charge (SOC) safety constraint criterion. When both the DC bus voltage stability criterion and the energy storage device state of charge (SOC) safety constraint criterion are met simultaneously, the final determination is that the energy storage side converter can be shut down; when the two criteria cannot be met simultaneously, the final determination is that the energy storage side converter can be turned on.

2. The adaptive start-stop control method for the energy storage-side converter of a photovoltaic-energy storage system according to claim 1, characterized in that, The DC bus voltage stability criterion is as follows: Determine whether the DC bus voltage is within the allowable range; when the DC bus voltage is lower than the preset value, the energy storage device discharges to increase the DC bus voltage; when the DC bus voltage is higher than the preset value, the energy storage device charges to decrease the DC bus voltage; when the DC bus voltage is within the allowable range, the energy storage device does not need to charge / discharge by adjusting the DC bus voltage.

3. The adaptive start-stop control method for the energy storage-side converter of a photovoltaic-energy storage system according to claim 1, characterized in that, The safety constraint criterion for the state of charge (SOC) of the energy storage device is as follows: Determine whether the state of charge (SOC) of the energy storage device is within the allowable range; if the SOC deviates from the preset value, it needs to be actively charged / discharged for adjustment; if the SOC of the energy storage device is within the allowable range, the energy storage device does not need to be charged / discharged.

4. The adaptive start-stop control method for the energy storage-side converter of a photovoltaic-energy storage system according to claim 1, characterized in that, When executing the multi-dimensional joint criteria, the adaptive start-up and shutdown of the energy storage-side converter are performed according to the hysteresis control logic. The hysteresis control logic sets corresponding upper and lower hysteresis thresholds for the DC bus voltage deviation and the energy storage device state of charge deviation, respectively. When the absolute value of the DC bus voltage deviation is less than or equal to its hysteresis threshold and the absolute value of the energy storage device's state of charge deviation is less than or equal to its hysteresis threshold, the photovoltaic-storage system is determined to be in a steady state, and the energy storage-side converter is shut down. When the absolute value of the DC bus voltage deviation is greater than its hysteresis threshold or the absolute value of the energy storage device's state of charge deviation is greater than its hysteresis threshold, the photovoltaic-storage system is determined to be in an unsteady state. The energy storage-side converter is then started and kept in operation until the system returns to a steady state.

5. The adaptive start-stop control method for the energy storage-side converter of a photovoltaic-energy storage system according to claim 4, characterized in that: The DC bus voltage deviation is the difference between the actual DC bus voltage and the preset voltage reference value, and the allowable range of the DC bus voltage is limited by the hysteresis upper and lower limit thresholds.

6. The adaptive start-stop control method for the energy storage-side converter of a photovoltaic-energy storage system according to claim 4, characterized in that: The state of charge deviation of the energy storage device is the difference between the actual SOC value of the energy storage device and the preset SOC reference value. The allowable range of the SOC is limited by the upper and lower hysteresis thresholds.

7. The adaptive start-stop control method for the energy storage-side converter of a photovoltaic-energy storage system according to claim 1, characterized in that, The multi-dimensional joint criteria also include supplementary criteria added based on the grid-side control type or working scenario of the photovoltaic-storage system; The supplementary criteria are executed after the DC bus voltage stability criterion and the energy storage device state of charge (SOC) safety constraint criterion are applied.

8. The adaptive start-stop control method for the energy storage-side converter of a photovoltaic-energy storage system according to claim 7, characterized in that: When the grid side is grid-following control, the supplementary criterion is the new energy power change rate criterion. When the absolute value of the photovoltaic power change rate is less than or equal to the threshold, the supplementary criterion is determined to be satisfied. When the grid side is a grid-type control, the supplementary criteria include grid frequency criteria and grid voltage criteria. When both grid frequency and voltage are within their respective allowable ranges, the supplementary criteria are deemed to be satisfied.

9. The adaptive start-stop control method for the energy storage-side converter of a photovoltaic-energy storage system according to claim 7, characterized in that: The supplementary criteria also include a photovoltaic operating mode criterion. When the photovoltaic power generation unit is in constant power generation mode, the supplementary criterion is deemed to be satisfied; when the photovoltaic power generation unit is in maximum power point tracking mode, the supplementary criterion is deemed not satisfied, and the energy storage side converter continues to operate. The photovoltaic power generation unit adopts power reserve control. In each control cycle, the maximum output power is first obtained by the maximum power point tracking method and maintained until the next cycle, and then the actual output power is controlled. The determination of the supplementary criterion is synchronized with the power reserve control cycle.

10. The adaptive start-stop control method for the energy storage-side converter of a photovoltaic-energy storage system according to any one of claims 1 to 9, characterized in that: When a photovoltaic-storage system includes multiple parallel energy storage devices and corresponding energy storage-side converters, the converters corresponding to the energy storage devices with smaller SOC deviations are prioritized for shutdown, while the converters corresponding to the energy storage devices with larger SOC deviations are prioritized for startup.

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