An energy storage system and control method

Abstract

The application relates to energy-saving control technology and discloses an energy storage system and a control method, wherein the energy storage unit comprises a battery module, a power conversion unit, a system control unit, an energy-saving control unit and a load identification unit; the battery module is used for realizing the caching of electric energy; the power conversion unit realizes direct-current alternating-current conversion, charge-discharge control and output electric energy voltage control; the system control unit is the control center of the whole energy storage system, and corresponding strategy control is carried out on the energy flow of the system based on different working conditions and control targets; the load identification unit identifies different types of loads based on software algorithm through voltage and current information of the load, so that the energy-saving control strategy is matched based on the load type. The application automatically identifies the type of the load through the software algorithm, adapts the corresponding energy-saving strategy based on the load type, and thus solves the problem that the load cannot normally work due to improper energy-saving strategies.

Description

Technical Field

[0001] This invention relates to energy-saving control technology, and more particularly to an energy storage system and control method. Background Technology

[0002] As societal energy consumption increases, the whole society is striving to reduce energy consumption through energy conservation measures, such as energy-saving light bulbs in homes and on the streets, and by promoting the timely disconnection of power to unused equipment. These energy-saving methods require replacing specialized energy-saving equipment or disconnecting power, but equipment replacement can lead to a series of complex and intertwined costs.

[0003] With the increasing use of energy storage devices in homes and shopping malls, these devices address emergency power needs and reduce electricity costs through peak-valley arbitrage. Because energy storage devices have energy buffers, they can achieve energy redistribution across time and space. Based on this principle, and by combining energy storage buffers with system control strategies, a novel energy control strategy based on new energy storage devices is proposed at the system-wide level, thereby achieving both energy savings and cost reduction. Summary of the Invention

[0004] This invention addresses the problem that existing energy-saving methods involve replacing loads with special energy-saving loads, which incurs additional costs. As energy storage systems become increasingly common in homes and shopping malls, this invention provides an energy storage system and control method.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0006] An energy storage system includes an energy storage unit and a branch control unit. The energy storage unit controls the branch control unit. The energy storage unit is used for energy storage and conversion, and for isolating the power grid and load. The branch control unit is used to connect the power grid, energy storage, and load. The energy storage unit comprises a battery module, a power conversion unit, a system control unit, an energy-saving control unit, and a load identification unit. The battery module is used for energy buffering. The power conversion unit performs DC-AC conversion, charge / discharge control, and output voltage control. The system control unit is the control center of the entire energy storage system, performing corresponding strategy control on the system's energy flow based on different operating conditions and control objectives. The load identification unit identifies different types of loads based on the load's voltage and current information using software algorithms, thereby implementing a matching energy-saving control strategy based on the load type.

[0007] Preferably, the branch control unit includes a first branch control unit, a second branch control unit, and a third branch control unit; the first branch control unit is used to control the power grid and the load branch A; the second branch control unit is used to control the power grid and the energy storage branch B; and the third branch control unit is used to control the energy storage and the load branch C.

[0008] To address the aforementioned technical problems, the present invention also provides a control method for an energy storage system, wherein the control method implemented through the energy storage system includes:

[0009] The energy storage system is charged and discharged based on the peak and off-peak electricity of the power grid. The energy storage system is charged during off-peak hours and discharged during peak hours.

[0010] The operating mode selection of the energy storage system includes normal power supply mode and energy-saving power supply mode.

[0011] In normal power supply mode, the power flow is controlled by the branch control unit to provide normal power load; in energy-saving power supply mode, the power flow is controlled by the branch control unit and the power load is determined by the energy storage unit.

[0012] As a preferred option, the energy-saving power supply mode includes: storing the electricity in the working area; identifying different types of loads through a load identification unit; determining the energy-saving control method based on the load type; the energy-saving control unit performing energy-saving control for different energy-saving control strategies; and realizing the power supply of the energy-saving mode through a power conversion unit.

[0013] As a preferred option

[0014] Load type identification is achieved by calculating the load impedance angle from the load current. The load category is determined based on the range of the load impedance angle. For a single-phase system, the load impedance angle is... For a three-phase system, its load impedance angle

[0015]

[0016]

[0017] Among them, i1 d i1 is the effective value of the active current in a single-phase system. q This represents the effective value of the reactive current in a single-phase system. When the value is zero, it is a purely resistive load; α It is the load current, i β It is the load current i α The virtual value for hysteresis rotation of 90 degrees, where θ is the angle of voltage. It is an inductive load; It is a resistive-capacitive load; when the distortion rate THD is greater than a threshold, it is defined as a nonlinear load; THD represents the THD value of the load current, that is, the distortion of the sine wave of the load current. THD is equal to the ratio of the root square of the sum of squares of each harmonic current obtained by Fourier decomposition to the effective value of the fundamental wave (50Hz).

[0018]

[0019]

[0020] Among them, i2 d i2 is the effective value of the active current in the three-phase system. q This represents the effective value of the reactive current in a three-phase system. When the value is zero, it is a purely resistive load; a It is the line current of phase A in a three-phase system, i b It is the line current of phase B in a three-phase system, i c It is the line current of phase C in a three-phase system, where θ is the voltage angle. It is an inductive load; It is a resistive-capacitive load; when the distortion rate THD is greater than a threshold, it is defined as a nonlinear load. THD represents the THD value of the load current, that is, the distortion of the sine wave of the load current. THD is equal to the ratio of the root square of the sum of squares of each harmonic current obtained by Fourier decomposition to the effective value of the fundamental wave (50Hz).

[0021] Preferably, the energy-saving control unit performs energy-saving control for different energy-saving control strategies, including voltage reduction energy-saving strategy, zero-crossing time energy-saving strategy, and voltage reduction and zero-crossing time energy-saving strategy. When the load type is a purely resistive load, a resistive-capacitive load, or a nonlinear load, energy-saving control is performed through the voltage reduction energy-saving strategy. When the load type is a resistive-inductive load, energy-saving control is performed through the voltage reduction energy-saving strategy, the zero-crossing time energy-saving strategy, and the voltage reduction and zero-crossing time energy-saving strategy.

[0022] As a preferred option, voltage reduction and energy-saving strategies include:

[0023] Initialization of target voltage U ac_out Through the stepped-down voltage U nL Perform the calculation of the target voltage;

[0024] Among them, U ac_out =U nL *kn; kn is the proportional adjustment coefficient for voltage reduction, and kn<1;

[0025] The first load current is determined. If the load current exceeds the current threshold, a sudden change occurs. When a sudden change occurs, the target voltage is adjusted, and the adjusted target voltage is U1. ac_out U1 ac_out =U ac_out -Δu; otherwise, if no sudden change occurs, adjust the target voltage, and the adjusted target voltage is U2. ac_out U2 ac_out =U ac_out+Δu; Δu is the step size for adjusting the target voltage, and Δu>0;

[0026] The second load current determination involves assessing the load current against the adjusted target voltage. The load current I_L is determined when it falls within the rated current range I. n _L*k1 <I_L<I n When I_L*k2, the target voltage is stable; otherwise, the process returns to the initial load current determination, where I_L is the load current. n _L represents the rated current of the load under rated voltage, k1 and k2 are current target coefficients, and 0 <k1<k2<1。

[0027] Preferred energy-saving strategies during the zero-crossing period include:

[0028] Voltage duration initialization, the voltage duration includes the duration T(U) of the energy storage device's output load rated voltage. ac_nL_out ) and the duration T(U) of zero voltage output by the energy storage device ac_0_out );

[0029] The initial load current assessment involves a sudden change if the load current exceeds the current threshold. Upon this sudden change, the duration of the energy storage device's output load-rated voltage and the duration of its zero-voltage output are adjusted. The adjusted duration of the energy storage device's output load-rated voltage is denoted as T1(U). ac_nL_out ); T1(U ac_nL_out )=T(U ac_nL_out -Δt; The duration of zero voltage output by the adjusted energy storage device is T1(U ac_0_out ); T1(U ac_0_out )=T(U ac_0_out )+Δt;

[0030] Otherwise, if no sudden change occurs, the duration of the rated voltage output by the energy storage device and the duration of zero voltage output by the energy storage device are adjusted. The adjusted duration of the rated voltage output by the energy storage device is T2(U ac_nL_out ); T2(U ac_nL_out )=T(U ac_nL_out The duration of zero voltage output by the adjusted energy storage device is T2(U) + Δt; ac_0_out ); T2(U ac_0_out )=T(U ac_0_out )-Δt;

[0031] The second load current determination involves assessing the load current against the adjusted target voltage. The load current I_L is determined when it falls within the rated current range I. n _L*k1 <I_L<I nWhen I_L*k2, the target voltage is stable; otherwise, the process returns to the initial load current determination, where I_L is the load current. n _L represents the rated current of the load under rated voltage, k1 and k2 are current target coefficients, and 0 <k1<k2<1。

[0032] Preferred energy-saving strategies during voltage reduction and zero-crossing periods include:

[0033] Voltage duration and voltage initialization; voltage duration includes the duration T(U) of the rated voltage output by the energy storage device to the load. ac_nL_out The duration of zero voltage output by the energy storage device, T(U) ac_0_out ) and the duration T(U) of the voltage after step-down output from the energy storage device ac_out );

[0034] The initial load current assessment involves a sudden change if the load current exceeds the current threshold. Upon this sudden change, the duration of the energy storage device's output load-rated voltage and the duration of its zero-voltage output are adjusted. The adjusted duration of the energy storage device's output load-rated voltage is denoted as T1(U). ac_nL_out ); T1(U ac_nL_out )=T(U ac_nL_out -Δt; The duration of zero voltage output by the adjusted energy storage device is T1(U ac_0_out ); T1(U ac_0_out )=T(U ac_0_out )+2Δt; The duration of the adjusted energy storage device's output voltage after step-down is T1(U ac_out ); T1(U ac_out )=T(U ac_out -Δt; The adjusted target voltage is U1 ac_out U1 ac_out =U start -Δu;

[0035] Otherwise, if no sudden change occurs, the duration of the rated voltage output by the energy storage device and the duration of zero voltage output by the energy storage device are adjusted. The adjusted duration of the rated voltage output by the energy storage device is T2(U ac_nL_out ); T2(U ac_nL_out )=T(U ac_nL_out The duration of zero voltage output by the adjusted energy storage device is T2(U) + Δt; ac_0_out ); T2(U ac_0_out )=T(U ac_0_out -2Δt; the duration of the adjusted energy storage device's output voltage after step-down, T2(U ac_out ); T2(U ac_out )=T(U ac_out +Δt; The adjusted target voltage is U2 ac_out U2ac_out =U start +Δu;

[0036] The second load current determination involves assessing the load current against the adjusted target voltage. The load current I_L is determined when it falls within the rated current range I. n _L*k1 <I_L<I n When I_L*k2, the target voltage is stable; otherwise, the process returns to the initial load current determination, where I_L is the load current. n _L represents the rated current of the load under rated voltage, k1 and k2 are current target coefficients, and 0 <k1<k2<1。

[0037] This invention, by adopting the above technical solutions, has significant technical effects:

[0038] This invention fully integrates the current trend of new energy sources with energy-saving control, and automatically adapts to the load type from the power supply head to achieve energy-saving control, rather than replacing the load equipment, in order to achieve the major goal of social energy conservation.

[0039] This invention isolates the power grid and loads during energy-saving control through an energy storage system, thereby solving the power quality problems caused to the power grid by energy-saving control of loads at the source.

[0040] This invention uses software algorithms to automatically identify the type of load and adapt the corresponding energy-saving strategy based on the load type, thereby solving the problem of loads failing to work properly due to improper energy-saving strategies. Attached Figure Description

[0041] Figure 1 This is a system diagram of the present invention;

[0042] Figure 2 This is a flowchart of the present invention;

[0043] Figure 3 This is a branch unit control architecture diagram of the present invention;

[0044] Figure 4 This is a flowchart of the energy-saving power supply process of the present invention;

[0045] Figure 5 This is an architecture diagram of energy-saving strategies for different types of loads according to the present invention;

[0046] Figure 6 These are schematic diagrams illustrating three different energy-saving strategies of the present invention;

[0047] Figure 7 This is a flowchart of the voltage reduction and energy-saving strategy of the present invention;

[0048] Figure 8This is a flowchart of the zero-crossing time-interruption energy-saving strategy of the present invention;

[0049] Figure 9 This is a flowchart of the voltage reduction and zero-crossing time-disruption energy-saving strategy of the present invention;

[0050] Figure 10 This is a system structure diagram of Embodiment 3 of the present invention. Detailed Implementation

[0051] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0052] Example 1

[0053] An energy storage system includes an energy storage unit and a branch control unit. The energy storage unit controls the branch control unit. The energy storage unit is used for energy storage and conversion, and for isolating the power grid and load. The branch control unit is used to connect the power grid, energy storage, and load. The energy storage unit comprises a battery module, a power conversion unit, a system control unit, an energy-saving control unit, and a load identification unit. The battery module is used for energy buffering. The power conversion unit performs DC-AC conversion, charge / discharge control, and output voltage control. The system control unit is the control center of the entire energy storage system, performing corresponding strategy control on the system's energy flow based on different operating conditions and control objectives. The load identification unit identifies different types of loads based on the load's voltage and current information using software algorithms, thereby implementing a matching energy-saving control strategy based on the load type.

[0054] The branch control unit includes a first branch control unit, a second branch control unit, and a third branch control unit; the first branch control unit is used to control the power grid and the load branch A; the second branch control unit is used to control the power grid and the energy storage branch B; and the third branch control unit is used to control the energy storage and the load branch C.

[0055] Figure 2 The overall workflow of the system involves charging and discharging based on different electricity prices on the power grid. The general principle is to charge energy storage at off-peak prices and discharge energy storage at peak prices, thereby reducing the overall electricity cost of the system. The system operates in two main modes: a normal power supply mode, which does not consider energy saving and does not change the load's supply voltage; and an energy-saving mode, which focuses on effective energy-saving strategies and controls the load's supply voltage based on energy storage, thereby reducing electricity consumption.

[0056] Among them, the peak-valley charging and discharging control of energy storage is to control the charging and discharging time and duration of energy storage based on the grid electricity price and load electricity consumption, taking into account the goal of electricity efficiency.

[0057] The branch combination control of the branch control unit is to achieve effective control of energy flow, thereby achieving the overall goal of the system. There are three types of branches: branch A (grid and load), branch B (grid and energy storage), and branch C (energy storage and load). In practical applications, each type of branch can be further decomposed into sub-branches according to engineering needs to achieve more precise control. Figure 3 The control of the given branch is initiated by the system control unit, which sends control commands to the energy-saving control unit based on the system objectives. The energy-saving control unit, based on the energy-saving status, controls different combinations of branches A, B, and C and the on / off state of the branches through branch control drive.

[0058] Table 1 lists the branch combinations. For branch combinations, the following constraints apply: First, different load branches A (grid and load) and C (energy storage and load) must be connected to the same load simultaneously to avoid voltage conflicts. Second, when charging or supporting the grid, the grid and energy storage branch B must be connected. Third, in energy-saving mode, the energy storage and load branch C must be connected, and the grid and load branch A must be disconnected.

[0059] Table 1 Branch Road Combination Table

[0060] A breaks B breaks C breaks The system stops working when power is off. efficient A is open, B is closed, C is closed. Only grid-supplied loads efficient A is disconnected, B is open, C is disconnected. Energy storage and grid charging / discharging only efficient A is disconnected, B is disconnected, C is open. Energy storage power supply only (possibly in energy-saving mode) efficient A is open, B is open, C is closed. Energy storage and load are grid loads efficient A is open, B is closed, C is open. Simultaneous power supply from the grid and energy storage is not supported under the same load. invalid A is disconnected, B is open, and C is open. Energy storage charging, energy-saving mode efficient A Pass B Pass C Pass Simultaneous power supply from the grid and energy storage is not supported under the same load. invalid

[0061] Example 2

[0062] Based on Example 1, this example is a control method for an energy storage system. Figure 2 The control methods implemented through energy storage systems include:

[0063] The energy storage system is charged and discharged based on the peak and off-peak electricity of the power grid. The energy storage system is charged during off-peak hours and discharged during peak hours.

[0064] The operating mode selection of the energy storage system includes normal power supply mode and energy-saving power supply mode.

[0065] In normal power supply mode, power flow is controlled by branch control units to provide normal power supply load. In energy-saving power supply mode, power flow is controlled by branch control units, and the power supply load is determined through energy storage units. Normal power supply mode does not consider energy saving, meaning it does not change the load's supply voltage. Energy-saving mode primarily focuses on effective energy-saving strategies from a system energy-saving perspective, using energy storage to control the load's supply voltage, thereby reducing electricity consumption.

[0066] Figure 4The energy-saving power supply mode includes: energy storage with a working range of power; considering the lifespan of the energy storage battery, the discharge depth (DOD) is generally less than 100%, and under normal circumstances, the DOD is 90% to 95%, meaning the remaining power SOC is 10% to 5%; charging is a normal full charge, i.e., 100%; different types of loads are identified through the load identification unit; the energy-saving control mode is determined according to the load type; the energy-saving control unit performs energy-saving control for different energy-saving control strategies, and the power supply in the energy-saving mode is realized through the power conversion unit.

[0067] Load type identification is achieved by calculating the load impedance angle from the load current. The load category is determined based on the range of the load impedance angle. For a single-phase system, the load impedance angle is... For a three-phase system, its load impedance angle

[0068]

[0069]

[0070] Among them, i1 d i1 is the effective value of the active current in a single-phase system. q This represents the effective value of the reactive current in a single-phase system. When the value is zero, it is a purely resistive load; α It is the load current, i β It is the load current i α The virtual value for hysteresis rotation of 90 degrees, where θ is the angle of voltage. It is an inductive load; It is a resistive-capacitive load; when the distortion rate THD is greater than a threshold, it is defined as a nonlinear load; THD represents the THD value of the load current, that is, the distortion of the sine wave of the load current. THD is equal to the ratio of the root square of the sum of squares of each harmonic current obtained by Fourier decomposition to the effective value of the fundamental wave (50Hz).

[0071]

[0072]

[0073] Among them, i2 d i2 is the effective value of the active current in a three-phase system. q This represents the effective value of the reactive current in a three-phase system. When the value is zero, it is a purely resistive load; a It is the line current of phase A in a three-phase system, i b It is the line current of phase B in a three-phase system, i c It is the line current of phase C in a three-phase system, where θ is the voltage angle. It is an inductive load; It is a resistive-capacitive load; when the distortion rate THD is greater than a threshold, it is defined as a nonlinear load. THD represents the THD value of the load current, that is, the distortion of the sine wave of the load current. THD is equal to the ratio of the root square of the sum of squares of each harmonic current obtained by Fourier decomposition to the effective value of the fundamental wave (50Hz).

[0074] The energy-saving control unit performs energy-saving control for different energy-saving control strategies, including voltage reduction energy-saving strategy, zero-crossing time energy-saving strategy, and voltage reduction and zero-crossing time energy-saving strategy. Figure 5 When the load type is a purely resistive load, a resistive-capacitive load, or a nonlinear load, energy-saving control is achieved through a voltage reduction energy-saving strategy. When the load type is a resistive-inductive load, energy-saving control is achieved through a voltage reduction energy-saving strategy, a zero-crossing time energy-saving strategy, and a voltage reduction and zero-crossing time energy-saving strategy.

[0075] Figure 6 In this context, the step-down energy-saving strategy achieves energy savings simply by controlling the amplitude of the AC output voltage of the energy storage device (U1 changes to U2). The zero-crossing time-interruption energy-saving strategy outputs a voltage of U1 for a period of time, and then outputs a voltage of 0 for another period of time when the voltage crosses zero. During this cycle, the duration of U1 and 0 is adjusted based on load conditions. The voltage change process of the step-down and zero-crossing time-interruption energy-saving strategies is from U1 to 0 to U3, where the durations of U1, 0, and U3 are adjusted based on load conditions.

[0076] Figure 7 Voltage reduction and energy saving strategies include,

[0077] Initialization of target voltage U ac_out Through the stepped-down voltage U nL Perform the calculation of the target voltage;

[0078] Among them, U ac_out =U nL *kn; kn is the proportional adjustment coefficient for voltage reduction, and kn<1;

[0079] The first load current is determined. If the load current exceeds the current threshold, a sudden change occurs. When a sudden change occurs, the target voltage is adjusted, and the adjusted target voltage is U1. ac_out U1 ac_out =U ac_out -Δu; otherwise, if no sudden change occurs, adjust the target voltage, and the adjusted target voltage is U2. ac_out U2 ac_out =U ac_out +Δu; Δu is the step size for adjusting the target voltage, and Δu>0;

[0080] The second load current determination involves assessing the load current against the adjusted target voltage. The load current I_L is determined when it falls within the rated current range I. n _L*k1 <I_L<I n When I_L*k2, the target voltage is stable; otherwise, the process returns to the initial load current determination, where I_L is the load current. n _L represents the rated current of the load under rated voltage, k1 and k2 are current target coefficients, and 0 <k1<k2<1。

[0081] Figure 8 Energy-saving strategies during the zero-crossing period include:

[0082] Voltage duration initialization, the voltage duration includes the duration T(U) of the energy storage device's output load rated voltage. ac_nL_out ) for T n The duration T(U) of zero voltage output by the energy storage device ac_0_out ) is T0; T n And T0 is a specific time duration, and T n >0, T0>0; The first load current judgment: when the load current exceeds the current threshold, a sudden change occurs. When a sudden change occurs, the duration of the energy storage device's output load-rated voltage and the duration of the energy storage device's zero-voltage output are adjusted. The adjusted duration of the energy storage device's output load-rated voltage is T1(U ac_nL_out ); T1(U ac_nL_out )=T(U ac_nL_out -Δt; The duration of zero voltage output by the adjusted energy storage device is T1(U ac_o_out ); T1(U ac_0_out )=T(U ac_0_out )+Δt; ​​where Δt is the adjustment step size of the duration;

[0083] Otherwise, if no sudden change occurs, the duration of the rated voltage output by the energy storage device and the duration of zero voltage output by the energy storage device are adjusted. The adjusted duration of the rated voltage output by the energy storage device is T2(U ac_nL_out ); T2(U ac_nL_out )=T(U ac_nL_out The duration of zero voltage output by the adjusted energy storage device is T2(U) + Δt; ac_0_out ); T2(U ac_0_out )=T(U ac_0_out )-Δt;

[0084] The second load current determination involves assessing the load current against the adjusted target voltage. The load current I_L is determined when it falls within the rated current range I. n _L*k1 <I_L<I nWhen I_L*k2, the target voltage is stable; otherwise, the process returns to the initial load current determination, where I_L is the load current. n _L represents the rated current of the load under rated voltage, k1 and k2 are current target coefficients, and 0 <k1<k2<1。

[0085] Figure 9 Voltage reduction and zero-crossing time energy-saving strategies include:

[0086] Voltage duration and voltage initialization; voltage duration includes the duration T(U) of the rated voltage output by the energy storage device to the load. ac_nL_out The duration of zero voltage output by the energy storage device, T(U) ac_0_out ) and the duration T(U) of the voltage after step-down output from the energy storage device ac_out ); where T(U ac_nL_out Initialize to T n ;T(U ac_0_out Initialize T(U) to T0; ac_out Initialize to T n ;

[0087] The initial load current assessment involves a sudden change if the load current exceeds the current threshold. Upon this sudden change, the duration of the energy storage device's output load-rated voltage and the duration of its zero-voltage output are adjusted. The adjusted duration of the energy storage device's output load-rated voltage is denoted as T1(U). ac_nL_out ); T1(U ac_nL_out )=T(U ac_nL_out -Δt; The duration of zero voltage output by the adjusted energy storage device is T1(U ac_0_out ); T1(U ac_0_out )=T(U ac_0_out )+2Δt; The duration of the adjusted energy storage device's output voltage after step-down is T1(U ac_out ); T1(U ac_out )=T(U ac_out -Δt; The adjusted target voltage is U1 ac_out U1 ac_out =U start -Δu;

[0088] Otherwise, if no sudden change occurs, the duration of the rated voltage output by the energy storage device and the duration of zero voltage output by the energy storage device are adjusted. The adjusted duration of the rated voltage output by the energy storage device is T2(U ac_nL_out ); T2(U ac_nL_out )=T(U ac_nL_out The duration of zero voltage output by the adjusted energy storage device is T2(U) + Δt; ac_0_out ); T2(U ac_0_out )=T(U ac_0_out-2Δt; the duration of the adjusted energy storage device's output voltage after step-down, T2(U ac_out ); T2(U ac_out )=T(U ac_out +Δt; The adjusted target voltage is U2 ac_out U2 ac_out =U start +Δu;

[0089] The second load current determination involves assessing the load current against the adjusted target voltage. The load current I_L is determined when it falls within the rated current range I. n _L*k1 <I_L<I n When I_L*k2, the target voltage is stable; otherwise, the process returns to the initial load current determination, where I_L is the load current. n _L represents the rated current of the load under rated voltage, k1 and k2 are current target coefficients, and 0 <k1<k2<1。

[0090] Example 3

[0091] Based on the above embodiments, this embodiment, for example Figure 10 As shown, it includes a photovoltaic system and a charging pile system. For Figure 7 , Figure 8 , Figure 9 The parameters in the actual engineering application will be determined according to the standard requirements of different countries and regions. For example, in China, the initial value of the step-down regulation coefficient kn will be 0.8, and the voltage regulation step size Δu will be UnL*0.01; the target coefficient of load current k1 is 0.65, k2 is 0.8, and the duration of the zero-crossing interruption Tn will be 20ms, T0 will be 20ms, and its Δt will be 10ms.

Claims

1. A control method for an energy storage system, characterized in that, The control method implemented through an energy storage system comprises energy storage units and branch control units. The energy storage units control the branch control units. The energy storage units are used for energy storage and conversion, and for isolating the power grid and loads. The branch control units are used to connect the power grid, energy storage, and loads. Each energy storage unit includes battery modules, a power conversion unit, a system control unit, an energy-saving control unit, and a load identification unit. The battery modules are used for energy buffering. The power conversion unit performs DC-AC conversion, charge / discharge control, and output voltage control. The system control unit is the control center of the entire energy storage system, implementing corresponding strategic control of the system's energy flow based on different operating conditions and control objectives. The load identification unit identifies different types of loads based on the load's voltage and current information using software algorithms, and then implements an energy-saving control strategy based on the load type. The methods include: The energy storage system is charged and discharged based on the peak and off-peak electricity of the power grid. The energy storage system is charged during off-peak hours and discharged during peak hours. The operating mode selection of the energy storage system includes normal power supply mode and energy-saving power supply mode. In normal power supply mode, the power flow is controlled by the branch control unit to provide normal power load; in energy-saving power supply mode, the power flow is controlled by the branch control unit and the power load is determined by the energy storage unit. The energy-saving control unit implements energy-saving control using different energy-saving control strategies, including voltage reduction energy-saving strategy, zero-crossing time energy-saving strategy, and voltage reduction and zero-crossing time energy-saving strategy. When the load type is a purely resistive load, a resistive-capacitive load, or a nonlinear load, energy-saving control is implemented through the voltage reduction energy-saving strategy. When the load type is a resistive-inductive load, energy-saving control is implemented through the voltage reduction energy-saving strategy, the zero-crossing time energy-saving strategy, and the voltage reduction and zero-crossing time energy-saving strategy.

2. The control method for an energy storage system according to claim 1, characterized in that, The energy-saving power supply mode includes: storing the electricity in the working area; identifying different types of loads through the load identification unit; determining the energy-saving control method according to the load type; the energy-saving control unit performs energy-saving control for different energy-saving control strategies, and realizes the power supply of the energy-saving mode through the power conversion unit.

3. The control method for an energy storage system according to claim 1, characterized in that, Load type identification is achieved by calculating the load impedance angle from the load current. The load category is determined based on the range of the load impedance angle. For a single-phase system, the load impedance angle is... For a three-phase system, its load impedance angle Official 1; ； in, This represents the effective value of the active current in a single-phase system. This represents the effective value of the reactive current in a single-phase system. When 1 is zero, it is a purely resistive load; It is the load current. It is the load current. The virtual value that lags behind the 90-degree rotation. It's the angle of voltage. It is an inductive load; It is a resistive-capacitive load; when the distortion rate THD is greater than a threshold, it is defined as a nonlinear load; THD represents the THD value of the load current, that is, the distortion of the sine wave of the load current. THD is equal to the ratio of the root square of the sum of squares of each harmonic current obtained by Fourier decomposition to the effective value of the fundamental wave at 50Hz. Official 2; ； in, This represents the effective value of the active current in a three-phase system. This represents the effective value of the reactive current in a three-phase system. When 2 is zero, it is a purely resistive load; It is the line current of phase A in a three-phase system. It is the line current of phase B in a three-phase system. It is the line current of phase C in a three-phase system. It's the angle of voltage. It is an inductive load; It is a resistive-capacitive load; when the distortion rate THD is greater than a threshold, it is defined as a nonlinear load. THD represents the THD value of the load current, that is, the distortion of the sine wave of the load current. THD is equal to the ratio of the root square of the sum of squares of each harmonic current obtained by Fourier decomposition to the effective value of the fundamental 50Hz frequency.

4. The control method for an energy storage system according to claim 1, characterized in that, Voltage reduction and energy saving strategies include, Initialization of target voltage Through the stepped-down voltage Perform the calculation of the target voltage; in, ; This is the proportional adjustment coefficient for reducing pressure, and ; The initial load current assessment determines whether a sudden change occurs if the load current exceeds the current threshold. Upon this sudden change, the target voltage is adjusted, and the adjusted target voltage is... ; Otherwise, if no sudden change occurs, the target voltage is adjusted, and the adjusted target voltage is... ; ; The step size for adjusting the target voltage, and ; The second load current determination involves assessing the load current against the adjusted target voltage. When the load current... Located within the rated current range If the target voltage is stable, then the process returns to the initial load current determination. For load current, This is the rated current of the load at rated voltage. It is the target coefficient for current, and .

5. The control method for an energy storage system according to claim 1, characterized in that, Zero-crossing time energy-saving strategies include: Voltage duration initialization, including the duration of the voltage output to the load capacity of the energy storage device. for Duration of zero voltage output by energy storage devices for ; and For a specific time period, and , The first load current assessment involves a sudden change if the load current exceeds the current threshold. When this sudden change occurs, the duration of the energy storage device's output load-rated voltage and the duration of its zero-voltage output are adjusted. The adjusted duration of the energy storage device's output load-rated voltage is as follows: ; The adjusted duration of zero voltage output from the energy storage device is: ; ;in, Adjust the duration step size; Otherwise, if no sudden change occurs, the duration of the rated voltage output by the energy storage device and the duration of zero voltage output by the energy storage device are adjusted. The adjusted duration of the rated voltage output by the energy storage device is as follows: ; The adjusted duration of zero voltage output from the energy storage device is: ; ; The second load current determination involves assessing the load current against the adjusted target voltage. When the load current... Located within the rated current range If the target voltage is stable, then the process returns to the initial load current determination. For load current, This is the rated current of the load at rated voltage. It is the target coefficient for current, and .

6. The control method for an energy storage system according to claim 1, characterized in that, Voltage reduction and zero-crossing time energy-saving strategies include: Voltage duration and voltage initialization; voltage duration includes the duration of the energy storage device's output load-rated voltage. Duration of zero voltage output by energy storage devices Duration of voltage reduction after output from energy storage device ; The initial load current assessment involves a sudden change if the load current exceeds the current threshold. During this sudden change, the duration of the energy storage device's output load-rated voltage and the duration of its zero-voltage output are adjusted. The adjusted duration of the energy storage device's output load-rated voltage is as follows: ; The adjusted duration of zero voltage output from the energy storage device is: ; The duration of the adjusted energy storage device's output voltage after step-down. ; The adjusted target voltage is ; ; Otherwise, if no sudden change occurs, the duration of the rated voltage output by the energy storage device and the duration of zero voltage output by the energy storage device are adjusted. The adjusted duration of the rated voltage output by the energy storage device is as follows: ; The adjusted duration of zero voltage output from the energy storage device is: ; The duration of the adjusted energy storage device's output voltage after step-down. ; The adjusted target voltage is ; ; The second load current determination involves assessing the load current against the adjusted target voltage. When the load current... Located within the rated current range If the target voltage is stable, then the process returns to the initial load current determination. For load current, This is the rated current of the load at rated voltage. It is the target coefficient for current, and .

7. The control method for an energy storage system according to claim 1, characterized in that, The branch control unit includes a first branch control unit, a second branch control unit, and a third branch control unit; the first branch control unit is used to control the power grid and the load branch A; the second branch control unit is used to control the power grid and the energy storage branch B; and the third branch control unit is used to control the energy storage and the load branch C.

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