A grid-connected inverter control method for energy storage system and a grid control system

Abstract

The present disclosure relates to a grid-connected inverter control method for an energy storage system and a grid control system, the control method comprising: acquiring grid voltage and current; judging the working mode of the energy storage system; when the working mode of the energy storage system is a non-operating mode, comparing the grid voltage with a preset voltage, obtaining a first target reactive power according to the comparison result, and obtaining an inverter control signal according to the first target reactive power; when the working mode of the energy storage system is an operating mode, calculating the grid active power according to the grid voltage and the grid current, comparing the grid active power with a preset power value, obtaining a second target reactive power according to the comparison result, and obtaining an inverter control signal according to the second target reactive power and the target active power.

Description

Technical Field

[0001] The embodiments of the present disclosure relate to the field of power grid control technology, and more specifically, to a grid-connected inverter control method for an energy storage system and a power grid control system. Background Art

[0002] The power conversion system (PCS) of battery energy storage is a unit that realizes the interaction between energy storage batteries and grid power. It is a key component of the energy storage system. The main function of the PCS system is to charge and discharge the energy storage battery system in the grid-connected mode; and to control the four-quadrant operation function of active and reactive power, thereby realizing the regulation of bidirectional active power and reactive power.

[0003] However, during the grid-connected operation of the PCS system, there are often a large number of inductive loads, which gradually increase the reactive power and thus lead to increasing energy losses, directly affecting the power supply quality of the power grid and ultimately affecting the economic benefits of the power companies. Therefore, it is necessary to improve the control methods of the PCS system and the power grid. Summary of the invention

[0004] An objective of the embodiments of the present disclosure is to provide a new technical solution for a grid-connected inverter control method of an energy storage system.

[0005] According to a first aspect of the present disclosure, a method for controlling grid-connected inverter of an energy storage system is provided, the method comprising:

[0006] Obtain grid voltage and current;

[0007] Determine the working mode of the energy storage system;

[0008] When the working mode of the energy storage system is a non-operating mode, comparing the grid voltage with a preset voltage, obtaining a first target reactive power according to the comparison result, and obtaining an inverter control signal according to the first target reactive power;

[0009] When the working mode of the energy storage system is the operation mode, the grid active power is calculated according to the grid voltage and the grid current, the grid active power is compared with a preset power value, a second target reactive power is obtained according to the comparison result, and an inverter control signal is obtained according to the second target reactive power and the target active power.

[0010] Optionally, when the working mode of the energy storage system is a non-operating mode, comparing the grid voltage with a preset voltage, obtaining a first target reactive power according to the comparison result, and obtaining an inverter control signal according to the first target reactive power, comprises:

[0011] The preset voltage includes: a first preset voltage, a second preset voltage, a third preset voltage and a fourth preset voltage, the fourth preset voltage is greater than the third preset voltage, the third preset voltage is greater than the second preset voltage, and the second preset voltage is greater than the first preset voltage;

[0012] When the grid voltage is greater than the fourth preset voltage, the first target reactive power is a first power value;

[0013] When the grid voltage is greater than the third preset voltage and less than or equal to the fourth preset voltage, the first target reactive power is a second power value;

[0014] When the grid voltage is greater than the second preset voltage and less than or equal to a third preset voltage, the first target reactive power is a third power value;

[0015] When the grid voltage is greater than the first preset voltage and less than or equal to the second preset voltage, the first target reactive power is a fourth power value.

[0016] Optionally, the first power value is -Qmax, where Qmax is the maximum reactive power allowed to be output;

[0017] The second power value is Qmax*(V3-V) / (V4-V3), V3 is the third preset voltage, V4 is the fourth preset voltage, V is the grid voltage, and Qmax is the maximum reactive power allowed to be output;

[0018] The third power value is Qmax*(V2-V) / (V2-V1), V2 is the second preset voltage, V1 is the first preset voltage, and Qmax is the maximum reactive power allowed to be output;

[0019] The fourth power value is Qmax, where Qmax is the maximum reactive power allowed to be output.

[0020] Optionally, the grid voltage is an average value of multiple grid voltages collected within a certain time period.

[0021] Optionally, when the working mode of the energy storage system is the operation mode, the grid active power is calculated according to the grid voltage and the grid current, the grid active power is compared with a preset power value, a second target reactive power is obtained according to the comparison result, and an inverter control signal is obtained according to the second target reactive power and the target active power, including:

[0022] The preset power value includes a first preset power value, a second preset power value and a third preset power value, the first preset power value is greater than the second preset power value, and the second preset power value is greater than the third preset power value;

[0023] When the active power of the power grid is greater than the first preset power value, the second target reactive power is the first target value;

[0024] When the grid active power is greater than the second preset power value and less than the first preset power value, the second target reactive power is the second target value;

[0025] When the grid active power is greater than the third preset power value and less than the second preset power value, the second target reactive power is the third target value.

[0026] Optionally, the first target value is -Qmax, where Qmax is the maximum reactive power allowed to be output;

[0027] The second target value is Qmax*(P2-P) / (P1-P2), Qmax is the maximum reactive power allowed to be output, P1 is the first preset power value, P2 is the second preset power value, and P is the active power of the power grid;

[0028] The third target value is Qmax, where Qmax is the maximum reactive power allowed to be output.

[0029] Optionally, obtaining an inverter control signal according to the first target reactive power includes:

[0030] Performing a Park transformation on the grid current to obtain a first current and a second current corresponding to the grid current;

[0031] Performing a Park transformation on the grid voltage to obtain a first voltage and a second voltage corresponding to the grid voltage;

[0032] Obtaining a first target reactive current according to the first target reactive power;

[0033] Performing proportional-integral control on the difference between the first target reactive current and the first current to obtain a first error signal, adding the first error signal to a first voltage to obtain a first control amount; performing proportional-integral control on the second current to obtain a second error signal, adding the second error signal to the second voltage to obtain a second control amount;

[0034] Performing Park inverse transformation on the first control quantity and the second control quantity to obtain the inverter control signal.

[0035] Optionally, obtaining an inverter control signal according to the second target reactive power and the target active power includes:

[0036] Acquire a second target reactive current according to the second target reactive power;

[0037] According to the preset target active power, a target active current is obtained;

[0038] Performing a Park transformation on the grid current to obtain a first current and a second current corresponding to the grid current;

[0039] Performing a Park transformation on the grid voltage to obtain a first voltage and a second voltage corresponding to the grid voltage;

[0040] Performing proportional-integral control on the difference between the second target reactive current and the first current to obtain a first error signal, and adding the first error signal to the first voltage to obtain a first control amount; performing proportional-integral control on the difference between the target active current and the second current to obtain a second error signal, and adding the second error signal to the second voltage to obtain a second control amount;

[0041] Performing a Park inverse transformation on the first control amount and the second control amount to obtain the target control signal, where the target control signal is a PWM duty cycle.

[0042] Optionally, the method further comprises:

[0043] The actual voltage of the power grid is phase-locked to obtain a phase-locked angle, and the actual current and actual voltage are subjected to Parker transformation using the phase-locked angle so that the phase of the current and voltage in the AC signal output by the inverter circuit is the same as the phase of the actual voltage of the power grid.

[0044] According to a second aspect of the present disclosure, there is also provided a power grid control system, the system comprising: a controller and a battery energy storage system, the battery energy storage system comprising a battery, and an inverter circuit connected between the battery and the power grid, the controller comprising a memory and a processor, the memory being used to store a computer program, the processor being used to execute any one of the methods of the first aspect under the control of the computer program.

[0045] According to a third aspect of the present disclosure, a computer-readable storage medium is provided, characterized in that a program or instruction is stored on the readable storage medium, and when the program or instruction is executed by a processor, any method in the first aspect is implemented.

[0046] One beneficial effect of the embodiments of the present disclosure is that a target current is obtained according to the operating state of the energy storage system and the actual voltage and actual current of the power grid; the conditions when the system is operating and not operating are controlled respectively, and the target current is output, and a current control signal is obtained according to the target current to drive the inverter circuit to output an AC signal to the power grid according to the DC signal provided by the battery, and the current of the power grid when it is operating and not operating can be controlled respectively according to the operating state of the energy storage system, so that the output current is close to the target current, thereby stably operating the power grid and improving the efficiency of active power.

[0047] Other features and advantages of the embodiments of the present disclosure will become apparent from the following detailed description of exemplary embodiments of the present disclosure with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the present disclosure and, together with the description, serve to explain the principles of the embodiments of the present disclosure.

[0049] Figure 1 is a schematic diagram of the structure of a power grid control system according to an embodiment of the present disclosure;

[0050] Figure 2 is a flow chart of a control method of a battery energy storage system according to an embodiment;

[0051] Figure 3 is a schematic diagram of a control method of a battery energy storage system when the operating state of the energy storage system is not operating according to an embodiment;

[0052] Figure 4 The present invention is a control method for a battery energy storage system when the operating state of the energy storage system is in operation according to an embodiment. DETAILED DESCRIPTION

[0053] Various exemplary embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. It should be noted that the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present invention unless otherwise specifically stated.

[0054] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses.

[0055] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered as part of the specification.

[0056] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0057] It should be noted that like reference numerals and letters refer to similar items in the following figures, and therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0058] <System Embodiment>

[0059] Figure 1 FIG. 1 is a schematic diagram of a structure of a power grid control system that can be applied according to an embodiment. Figure 1 As shown, the system includes a control module 107 and a battery energy storage system, the battery energy storage system includes a battery 100, and an inverter circuit 101 connected between the battery 100 and the power grid 103. The system can be applied to a grid-connected operation scenario in which a transmission line in a power system is connected to a transmission grid.

[0060] In this embodiment, the control module 107 is used to execute a control method of a battery energy storage system disclosed in this embodiment. For example, the control module 107 in this embodiment can be a digital signal processing chip and a field programmable gate array (FPGA) of a power conversion system (Power Conversion System, PCS).

[0061] In this embodiment, the inverter circuit 101 can receive charging and discharging from the power grid, convert the AC signal provided by the power grid 103 into a DC signal and provide it to the battery 100, and charge the battery 100. The battery of the battery energy storage system is an energy storage battery, which can be used to store the electric energy of the DC signal output by the inverter circuit 101 and provide electric energy for the load device.

[0062] In this embodiment, the inverter circuit 101 can perform bidirectional commutation between the battery and the grid side, for example, receiving the control signal of the control module 107, converting the DC power on the battery side into AC power through the control signal and then inputting it into the grid side. The DC side of the inverter circuit is connected to the battery through the DC contactor 104, and the AC side is connected to the grid through the AC contactor 105 and the AC circuit breaker 106. The DC contactor 104 and the AC contactor 105 are used to control the on and off of the current, thereby controlling the connection of the circuit, and the AC circuit breaker 106 is used to cut off the circuit when the circuit load is too large.

[0063] In this embodiment, the energy storage system may further include a filter 102 and a sampling circuit, and the inverter circuit 101 includes a variety of power electronic devices, such as an insulated gate bipolar transistor (IGBT) and a DCAC alternating current and direct current bidirectional conversion circuit. The filter 102 is used to filter the AC output and filter out the harmonic components of the AC output. The sampling circuit may include a voltage transformer, a current transformer, a Hall sensor, and a synchronous capture circuit. For example, the sampling circuit inputs a battery voltage detection circuit and a current detection circuit through the DC side, an inverter voltage sampling circuit before and after the AC side filter, a grid voltage sampling circuit, a grid current sampling circuit, and an IO input and output signal circuit. All sampling signals and control signals collected by the sampling circuit are input into the control module 107 for control, and the control module outputs a modulation signal to drive the inverter circuit 101 to output a target current or a target voltage.

[0064] refer to Figure 1 The sampling circuit includes a DC voltage sampling circuit, an AC voltage sampling circuit, an inverter voltage sampling circuit and a grid voltage sampling circuit. The DC voltage sampling circuit is used to collect the DC voltage on the battery side to the control module, so as to monitor whether the voltage on the battery side is output normally and stably; the AC current sampling circuit and the inverter voltage sampling circuit are used to collect the current and voltage after inversion to the control module, so as to monitor whether the current and voltage after inversion are consistent with the target current and target voltage, thereby improving the control efficiency of the system.

[0065] In this embodiment, the battery energy storage system further includes an interaction module 108, which is used for interaction between the user and the battery energy storage system. The user obtains all information of the battery energy storage system through the interaction module 108, and can control the system through the interaction module 108. For example, the interaction module 108 is used to receive control instructions input by the user, and send the control instructions to the control module 107, so that the control module 107 executes the control instructions; wherein the control instructions include instructions for controlling the start or stop of the generator set;

[0066] The interaction module 108 is also used to receive control information input by the user and send the control information to the control module, so that the control module 107 executes a control method of a battery energy storage system disclosed in this embodiment according to the control information; wherein the control information includes at least one of a reference power, a preset voltage and a target active power.

[0067] A technician can design a computer program according to the solution of the embodiment of the present disclosure. How the computer program controls the processor to operate is well known in the art, so it will not be described in detail here.

[0068] <Method Example>

[0069] Figure 2 is a flowchart of a control method for a battery energy storage system according to an embodiment. The implementation subject of this embodiment is a power grid control system, for example Figure 1 Central control module.

[0070] like Figure 2 As shown, the control method of the battery energy storage system of this embodiment may include the following steps S210 to S240:

[0071] Step S210, obtaining grid voltage and current.

[0072] In this embodiment, the operating state of the energy storage system includes the operating state and the non-operating state of the energy storage system. When the energy storage system is in operation, the power grid and the energy storage system are connected to each other, and the power grid charges and discharges the energy storage system. The non-operating state of the system may be a standby, hot standby or dynamic monitoring state. Considering that the power grid side will cause power loss due to the increase of reactive power when the energy storage system is in operation and not in operation, this embodiment compensates the power grid respectively from the two states of the energy storage system in operation and not in operation to improve the efficiency of the active power on the power grid side.

[0073] In this embodiment, the grid voltage and current are the actual voltage and current of the grid, and the actual active power and reactive power of the grid can be calculated based on the actual voltage and current of the grid. The actual voltage and actual current of the grid can be obtained by a sampling circuit, for example, by using the grid voltage sampling circuit and the grid current sampling circuit in the above system embodiment.

[0074] Step S220, determining the working mode of the energy storage system.

[0075] The working modes of the energy storage system include non-operating mode and operating mode. The non-operating mode of the energy storage system means that the system is not in an off-grid state, at which time the energy storage system is disconnected from the grid. The operating mode of the energy storage system means that the system is in a grid-connected state, at which time the energy storage system and the grid are connected to each other. The working mode of the energy storage system can be obtained by manual detection or by the changes in voltage and current, judging the working mode of the energy storage system according to the changes in voltage and current, and then automatically reporting the working status.

[0076] In this embodiment, different control methods are used for different operating states of the energy storage system. When the operating state of the energy storage system is in operation, the control method has the following steps:

[0077] Step S230, when the working mode of the energy storage system is a non-operating mode, the grid voltage is compared with a preset voltage, a first target reactive power is obtained according to the comparison result, and an inverter control signal is obtained according to the first target reactive power.

[0078] In this embodiment, since the voltages at different circuit sampling points or at different times may be different, in order to improve the control accuracy, the grid voltage in this embodiment is obtained by collecting the actual voltage of the grid, calculating the average value of multiple grid voltages collected within a certain period of time, and then comparing the grid voltage with the preset voltage to determine the target reactive power. In this embodiment, the first target reactive power of the grid can be determined based on the relationship between the average value and the preset voltage.

[0079] Specifically, refer to Figure 3 The preset voltage includes a first preset voltage, a second preset voltage, a third preset voltage and a fourth preset voltage, wherein the fourth preset voltage is greater than the third preset voltage, the third preset voltage is greater than the second preset voltage, and the second preset voltage is greater than the first preset voltage.

[0080] When the grid voltage is greater than the fourth preset voltage, the sign of the first target reactive power is negative, and the value of the first target reactive power is the first power value;

[0081] When the grid voltage is greater than the third preset voltage and less than or equal to the fourth preset voltage, the first target reactive power is the second power value;

[0082] When the grid voltage is greater than the second preset voltage and less than or equal to the third preset voltage, the first target reactive power is the third power value;

[0083] When the grid voltage is greater than the first preset voltage and less than or equal to the second preset voltage, the first target reactive power is the first power value;

[0084] The first power value may be set manually, for example, the first power value may be set to a power value obtained through practice that enables the system to have the best working efficiency, or may be the maximum reactive power Qmax allowed to be output by the system. The maximum reactive power Qmax is the reactive power when the active power efficiency of the system is the lowest.

[0085] Therefore, when the first power value Qm is Qmax, the calculation formula of the first target reactive power of the power grid in this embodiment is:

[0086]

[0087] Among them, Qobj is the first target reactive power, Qmax is the maximum reactive power allowed to be output by the system, V4 is the fourth preset voltage, V3 is the third preset voltage, V2 is the second preset voltage, and V1 is the first preset voltage.

[0088] The first preset voltage, the second preset voltage, the third preset voltage and the fourth preset voltage of the above embodiment are respectively proportional to the rated voltage. For example, the values ​​of V4, V3, V2 and V1 are 1.3, 1.1, 0.8 and 0.6 of the rated voltage of the system respectively. When the grid voltage is greater than the fourth preset voltage, the amplitude of the grid voltage will be larger, and it is necessary to perform inductive reactive compensation on the grid to lower the grid voltage. However, the reactive power allowed to be output cannot exceed the maximum reactive power allowed to be output by the system. Therefore, in this embodiment, when the grid voltage is greater than the fourth preset voltage, the first target reactive power is -; when the grid voltage is less than the fourth preset voltage and greater than the third preset voltage, the first target reactive power is Using the difference between the fourth preset voltage and the grid voltage, and the difference between the fourth preset voltage and the third preset voltage to determine the specific value of the first target reactive power can better reflect the linear relationship between the voltage value and the first target reactive power, and has a better error control effect, thereby improving the control accuracy of the target reactive power.

[0089] Similarly, when the grid voltage is less than the third preset voltage and greater than the second preset voltage, the amplitude of the grid voltage will be large, and capacitive reactive power compensation is required to raise the grid voltage. In this embodiment, when the grid voltage is greater than the second preset voltage and less than the third preset voltage, the first target reactive power is When the grid voltage is less than the second preset voltage and greater than the first preset voltage, the target reactive power is Qmax to increase the grid voltage.

[0090] In this embodiment, since the system has a large change relative to the load power and the voltage is relatively stable, resulting in a large change range of the current, this embodiment selects the current as the control variable to calculate the size of the target reactive power. Therefore, after determining the first target reactive power, it is necessary to determine the first target reactive current. The calculation formula for the first target reactive current is: Wherein, Iobj is the first target reactive current, Qobj is the first target reactive power, and V is the actual voltage of the power grid.

[0091] In the present embodiment, after obtaining the first target reactive power and the first target reactive current, an inverter control signal is obtained according to the first target reactive power, specifically including: performing a Park transform on the grid current to obtain a first current and a second current corresponding to the grid current; performing a Park transform on the grid voltage to obtain a first voltage and a second voltage corresponding to the grid voltage; obtaining the first target reactive current according to the first target reactive power; performing proportional-integral control on the difference between the first target reactive current and the first current to obtain a first error signal, and adding the first error signal and the first voltage to obtain a first control quantity; performing proportional-integral control on the second current to obtain a second error signal, and adding the second error signal and the second voltage to obtain a second control quantity; and then performing a Park inverse transform on the first control quantity and the second control quantity to obtain an inverter control signal.

[0092] For example, refer to Figure 3 , the target control signal is obtained by using the first target reactive current, the grid current and the grid voltage, and the grid current is subjected to Park transformation to obtain the first current I corresponding to the grid current q and the second current I d ; Perform Park transformation on the grid voltage to obtain a first voltage u corresponding to the grid voltage q and the second voltage u d , for the first target reactive current and the first current I q The difference between the first error signal and the second error signal is used for PI control to obtain a first error signal, and the control amount to be output is corrected according to the first error signal. q Add together to get the first control quantity C q , thereby eliminating the static error, making the output more stable and improving the system response speed; since the system is not in operation, the active power input at this time can be zero, so the second current I d With the second voltage u d Add together to get the second control quantity C d , for the first control quantity C q and the second control quantity C d Perform an inverse Park transform to obtain the target control signal, thereby obtaining a PWM duty cycle that meets the target.

[0093] In this embodiment, the principle of proportional-integral control is to form a control deviation based on the given value and the actual output value, and to form a control quantity by linearly combining the proportion and integral of the deviation to control the controlled object. a , I b , I cis three-phase data with phases, which has direction, and the control object of proportional integral is a specific value. Therefore, in this embodiment, the value of the three-phase current needs to be converted into a specific value without direction. The Park transformation is a coordinate transformation method that can convert the I of the three-phase current into a specific value without direction. a , I b , I c The projection of the current on the α and β axes is equivalent to the d and q axes, so that the current on the stator is equivalent to the direct axis and the quadrature axis, where the d axis is the direct axis and the q axis is the quadrature axis. Therefore, in this embodiment, the Park transformation is used to convert the three-phase current. Figure 4 In this embodiment, the current of the q-axis and the corresponding first target reactive current are used for proportional-integral control, and the current of the d-axis and the corresponding target active current are used for proportional-integral control. That is to say, the current of the q-axis is used to regulate the reactive power of the power grid, and the current of the d-axis is used to regulate the active power of the power grid.

[0094] Among them, in this embodiment, when the first target reactive current and the grid current are PI controlled, the actual voltage is phase-locked and Park transformed, which plays a role of feedforward control. After the target current is regulated, the output reactive power can be closer to the target reactive power. At the same time, the actual voltage of the grid is phase-locked to obtain the phase-locked angle, and the actual current and the actual voltage are Park transformed using the phase-locked angle to lock the projection angle of the actual current and the actual voltage during the Park transformation, that is, the phase angle of the current and voltage in the AC signal output by the inverter circuit is the same as the phase-locked angle, so that the phase of the current and voltage in the AC signal output by the inverter circuit is the same as the phase of the actual voltage of the grid.

[0095] In this embodiment, when the operating state of the energy storage system is in operation, the control method has the following steps:

[0096] Step S240, when the working mode of the energy storage system is the operation mode, the grid active power is calculated according to the grid voltage and the grid current, the grid active power is compared with the preset power value, the second target reactive power is obtained according to the comparison result, and the inverter control signal is obtained according to the second target reactive power and the target active power.

[0097] In a feasible example, the active power of the power grid can be calculated using the power formula P=Uabc*Iabc, where P is the active power of the power grid, Uabc is the power grid voltage, and Iabc is the power grid current. Then, according to the magnitude relationship between the active power of the power grid and the preset power value, the second target reactive power of the power grid is determined. Among them, since the system is in a grid-connected operation state, its voltage is relatively stable, and the current has a relatively large range of variation relative to the load power change. Therefore, this embodiment also selects the current as the control variable, determines the second target reactive current of the power grid according to the second target reactive power, and controls the system according to the second reactive current.

[0098] In this embodiment, in the grid-connected state, the active power of the power grid is much greater than the reactive power. Therefore, this embodiment uses the active power of the power grid to determine the size of the second target reactive power. According to the size relationship between the active power of the power grid and the preset power value, the second target reactive power of the power grid is determined. The preset power value includes a first preset power value, a second preset power value and a third preset power value. The first preset power value is greater than the second preset power value, and the second preset power value is greater than the third preset power value. When the active power of the power grid is greater than the first preset power value, the second target reactive power is the first target value; when the active power of the power grid is greater than the second preset power value and less than the first preset power value, the second target reactive power is the second target value; when the active power of the power grid is greater than the third preset power value and less than the second preset power value, the second target reactive power is the third target value. Among them, the size of the first target value, the second target value and the third target value can be manually set according to the actual operating conditions of the energy storage system and the power grid.

[0099] In a feasible embodiment, when the active power of the grid is greater than the first preset power value, it has a higher active power efficiency. As long as the reactive power at this time is not greater than the maximum reactive power allowed to be output by the system, the system can still operate efficiently. However, when the active power of the system is too high, it will cause a higher voltage on the grid side. Therefore, when the active power of the grid is greater than the first preset power value, the first target value is -Qmax, where Qmax is the maximum reactive power allowed to be output, thereby improving the grid voltage.

[0100] When the active power of the power grid is greater than the second preset power value and less than the first preset power value, the difference between the actual active power and the first preset power value and the difference between the first preset power value and the second preset power value are used to achieve a better error control effect, thereby improving the control accuracy of the target reactive power. Therefore, the size of the second target value is Qmax is the maximum reactive power allowed to be output, P1 is the first preset power value, P2 is the second preset power value, and P is the active power of the power grid.

[0101] When the active power of the power grid is greater than the third preset power value and less than the second preset power value, the active power efficiency of the system is relatively low. At this time, the size of the third target value can be Qmax, so as to offset the reactive power generated on the grid side, thereby improving the active power efficiency of the system. Qmax is the maximum reactive power allowed to be output.

[0102] In this embodiment, the expression of the second target reactive power can be:

[0103]

[0104] Wherein, Qobj is the second target reactive power, Qmax is the maximum reactive power allowed to be output by the system, P1 is the first preset power value, P2 is the second preset power value, P3 is the third preset power value, P is the actual active power, - is the first target value, is the second target value, and Qmax is the third target value.

[0105] The values ​​of P1, 2, and 3 in the above expression of target reactive power are respectively proportional to the rated power of the system. For example, the values ​​of P1, 2, and 3 are 60%, 30%, and 20% of the rated power of the system, respectively. When the actual active power is greater than 60% of the rated power, it has a higher active power efficiency. As long as the reactive power at this time is not greater than the maximum reactive power allowed to be output by the system, the system can still operate efficiently. However, when the active power of the system is too high, it will cause the voltage on the grid side to be higher. Therefore, when the actual active power is greater than the first preset power value, the first target value may be negative Qmax. At this time, the target reactive power is negative Qmax, thereby improving the grid voltage. When the actual active power is greater than 30% of the rated power and less than 60% of the rated power, it means that the active power of the system is not high. At this time, the system still needs to output a certain amount of reactive power to regulate the reactive power generated on the grid side. This embodiment adopts a proportional coefficient control method to determine the output target reactive power. The proportional coefficient is By using the difference between the actual active power and the first preset power value, and the difference between the first preset power value and the second preset power value, a better error control effect is achieved, thereby improving the control accuracy of the target reactive power. Therefore, the size of the second target value is At this time, the target reactive power is When the actual active power is greater than 20% of the rated power and less than 30% of the rated power, it means that the active power efficiency of the system is low. The third target value can be Qmax. At this time, the target reactive power is Qmax, which can offset the reactive power generated on the grid side, thereby improving the active power efficiency of the system.

[0106] In this embodiment, the current is used as the control variable. Therefore, after determining the second target reactive power, the second target reactive current needs to be determined. The calculation formula of the second target reactive current is: Among them, Iq_obj is the second target reactive current, Qobj is the second target reactive power, and Uabc is the grid voltage.

[0107] In this embodiment, since the system is in a grid-connected state, it is also necessary to obtain the active current of the grid to control it together with the second target reactive current. Therefore, it is also necessary to obtain the target active current of the grid. The target active current can be determined by obtaining the preset target active power and the target active voltage. For example, the preset target active power P sent by the client can be received. 目标 and target active voltage U 目标 , use the target active power to get the target active current Id obj = 目标 / U 目标 , where U 目标 It can be the rated voltage or the actual grid voltage obtained by system sampling, and then the target control signal is obtained according to the second target reactive current, the target active current, the grid current and the grid voltage.

[0108] In this embodiment, the target active power and the target active voltage can be obtained through the interaction module, for example, Figure 1 The interactive module in is used to receive control information input by the user and send the control information to the control module.

[0109] In this embodiment, an inverter control signal is obtained according to the second target reactive power and the target active power, including: performing a Park transformation on the grid current to obtain a first current and a second current corresponding to the grid current; performing a Park transformation on the grid voltage to obtain a first voltage and a second voltage corresponding to the grid voltage; performing proportional-integral control on the difference between the target reactive current and the first current to obtain a first error signal, and adding the first error signal and the first voltage to obtain a first control quantity; performing proportional-integral control on the difference between the target active current and the second current to obtain a second error signal, and adding the second error signal and the second voltage to obtain a second control quantity; performing an inverse Park transformation on the first control quantity and the second control quantity to obtain a target control signal, and the target control signal is a PWM duty cycle.

[0110] In a working example, refer to Figure 4 , perform Park transformation on the grid current to obtain the first current I corresponding to the grid current q and the second current I d ; Perform a Parker transformation on the grid voltage Uabc to obtain a first voltage u corresponding to the grid voltage q and the second voltage u d; For the second target reactive current and the first current I q The difference is proportionally integrated to obtain a first error signal, and the control amount to be output is corrected according to the first error signal. The first error signal and the first voltage u q Add them together to get the first control quantity C q , thereby eliminating static error, making the output more stable and improving the system response speed; for the target active current Id obj and the second current I d The difference between the proportional integral control and the second error signal is obtained, and the control amount to be output is corrected according to the second error signal. d Add them together to get the second control quantity C d , thereby eliminating the static error and making the output more stable; at this time, the first control quantity C q and the second control quantity C d It is still the projection of the three-phase signal on the d and q axes. Therefore, in this embodiment, the first control quantity C q and the second control quantity C d Perform the Parker inverse transform and convert C d and C q The target control signal is obtained by converting the target reactive current into a three-phase PWM wave to obtain a three-phase duty cycle. The target control signal can be a PWM duty cycle that satisfies the target condition. The second target reactive current and the first current I q Proportional integral control is performed, using the target reactive current and the first current I q The actual current difference is controlled by proportional integral (PI) to obtain a first error signal.

[0111] In this embodiment, when PI control is performed on the first target reactive current and the target active current, the actual voltage is phase-locked and Park transformed, which plays a role of feedforward control. After the target current is regulated, the output reactive power can be closer to the target reactive power.

[0112] It should be noted that when performing Park transformation on the actual current and the actual voltage, this embodiment obtains the phase-locking angle by performing phase-locking control on the actual voltage of the power grid, and uses the phase-locking angle to perform Park transformation on the actual current and the actual voltage to lock the projection angle of the actual current and the actual voltage during Park transformation, that is, the phase angle of the current and voltage in the AC signal output by the inverter circuit is the same as the phase-locking angle, so that the phase of the current and voltage in the AC signal output by the inverter circuit is the same as the phase of the actual voltage of the power grid.

[0113] The phase-locked control in this embodiment can be implemented by using a phase-locked loop, which is mainly used to obtain the angle of the grid voltage to ensure that the control current and voltage in the system control are synchronized with the actual grid.

[0114] In this embodiment, the target control signal may be a pulse width modulation (PWM) signal, which may be implemented by using a module having a PWM signal output function, such as Figure 1 The control module in the converter converts the analog signal into the PWM signal code required by the digital circuit.

[0115] In this embodiment, the inverter circuit is used to convert the direct current on the battery side into alternating current. As in the above system embodiment, the inverter circuit includes an inverter circuit, a filter and a sampling circuit. The inverter circuit is driven by a PWM signal to generate an alternating current signal, wherein the current of the alternating current signal corresponds to the target current. The current in the alternating current signal may be consistent with the target current, or there may be an error within an allowable range with the target current.

[0116] In this embodiment, when the system is running, the target reactive power is determined by the actual power and the preset power value, and the actual current of the power grid is controlled by the target active power and the target reactive power, and a target control signal is output; when the system is not running, the target reactive power is determined by the actual voltage and the preset voltage, and the actual current of the power grid is controlled by the target reactive power, and a target control signal is output. The voltage of the power grid in operation and in non-operation can be controlled according to the operating status of the energy storage system, thereby making the power grid operate stably and improving the efficiency of active power.

[0117] The present invention may be a system, a method and / or a computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present invention.

[0118] Computer readable storage medium can be a tangible device that can hold and store instructions used by an instruction execution device. Computer readable storage medium can be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination thereof. More specific examples (non-exhaustive list) of computer readable storage medium include: a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a static random access memory (SRAM), a portable compact disk read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device, for example, a punch card or a convex structure in a groove on which instructions are stored, and any suitable combination thereof. The computer readable storage medium used here is not interpreted as a transient signal itself, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagated by a waveguide or other transmission medium (for example, a light pulse by an optical fiber cable), or an electrical signal transmitted by a wire.

[0119] The computer-readable program instructions described herein can be downloaded from a computer-readable storage medium to each computing / processing device, or downloaded to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network can include copper transmission cables, optical fiber transmissions, wireless transmissions, routers, firewalls, switches, gateway computers, and / or edge servers. The network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions for storage in the computer-readable storage medium in each computing / processing device.

[0120] The computer program instructions for performing the operation of the present invention may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-related instructions, microcode, firmware instructions, state setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages, such as Smalltalk, C++, etc., and conventional procedural programming languages, such as "C" language or similar programming languages. Computer-readable program instructions may be executed entirely on a user's computer, partially on a user's computer, as an independent software package, partially on a user's computer, partially on a remote computer, or entirely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer via any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., using an Internet service provider to connect via the Internet). In some embodiments, an electronic circuit, such as a programmable logic circuit, a field programmable gate array (FPGA), or a programmable logic array (PLA), may be personalized by utilizing the state information of the computer-readable program instructions, and the electronic circuit may execute the computer-readable program instructions, thereby realizing various aspects of the present invention.

[0121] Various aspects of the present invention are described herein with reference to the flow charts and / or block diagrams of the methods, devices (systems) and computer program products according to embodiments of the present invention. It should be understood that each box of the flow chart and / or block diagram and the combination of each box in the flow chart and / or block diagram can be implemented by computer-readable program instructions.

[0122] These computer-readable program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing device, thereby producing a machine, so that when these instructions are executed by the processor of the computer or other programmable data processing device, a device that implements the functions / actions specified in one or more boxes in the flowchart and / or block diagram is generated. These computer-readable program instructions can also be stored in a computer-readable storage medium, and these instructions cause the computer, programmable data processing device, and / or other equipment to work in a specific manner, so that the computer-readable medium storing the instructions includes a manufactured product, which includes instructions for implementing various aspects of the functions / actions specified in one or more boxes in the flowchart and / or block diagram.

[0123] Computer-readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device so that a series of operating steps are performed on the computer, other programmable data processing apparatus, or other device to produce a computer-implemented process, thereby causing the instructions executed on the computer, other programmable data processing apparatus, or other device to implement the functions / actions specified in one or more boxes in the flowchart and / or block diagram.

[0124] The flow charts and block diagrams in the accompanying drawings show the possible architecture, functions and operations of the systems, methods and computer program products according to multiple embodiments of the present invention. In this regard, each box in the flow chart or block diagram can represent a part of a module, a program segment or an instruction, and a part of the module, a program segment or an instruction contains one or more executable instructions for realizing the specified logical function. In some alternative implementations, the functions marked in the box can also occur in a different order from the order marked in the accompanying drawings. For example, two consecutive boxes can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each box in the block diagram and / or flow chart, and the combination of the boxes in the block diagram and / or flow chart can be implemented by a dedicated hardware-based system that performs the specified function or action, or can be implemented by a combination of dedicated hardware and computer instructions. It is well known to those skilled in the art that it is equivalent to implement it by hardware, implement it by software, and implement it by combining software and hardware.

[0125] Embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or technical improvements in the marketplace, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein. The scope of the present invention is defined by the appended claims.

Claims

1. A method for controlling grid-connected inverter of an energy storage system, characterized in that: The method comprises: Obtain grid voltage and current; Determine the working mode of the energy storage system; When the working mode of the energy storage system is a non-operating mode, comparing the grid voltage with a preset voltage, obtaining a first target reactive power according to the comparison result, and obtaining an inverter control signal according to the first target reactive power; When the working mode of the energy storage system is the operation mode, the grid active power is calculated according to the grid voltage and the grid current, the grid active power is compared with a preset power value, a second target reactive power is obtained according to the comparison result, and an inverter control signal is obtained according to the second target reactive power and the target active power; When the working mode of the energy storage system is a non-operating mode, comparing the grid voltage with a preset voltage, obtaining a first target reactive power according to a comparison result, and obtaining an inverter control signal according to the first target reactive power, including: The preset voltage includes: a first preset voltage, a second preset voltage, a third preset voltage and a fourth preset voltage, the fourth preset voltage is greater than the third preset voltage, the third preset voltage is greater than the second preset voltage, and the second preset voltage is greater than the first preset voltage; When the grid voltage is greater than the fourth preset voltage, the first target reactive power is a first power value, the first power value is -Qmax, and Qmax is the maximum reactive power allowed to be output; When the grid voltage is greater than the third preset voltage and less than or equal to the fourth preset voltage, the first target reactive power is the second power value, the second power value is Qmax*(V3-V) / (V4-V3), V3 is the third preset voltage, V4 is the fourth preset voltage, V is the grid voltage, and Qmax is the maximum reactive power allowed to be output; When the grid voltage is greater than the second preset voltage and less than or equal to the third preset voltage, the first target reactive power is a third power value, and the third power value is Qmax*(V2-V) / (V2-V1), V2 is the second preset voltage, V1 is the first preset voltage, and Qmax is the maximum reactive power allowed to be output; When the grid voltage is greater than the first preset voltage and less than or equal to the second preset voltage, the first target reactive power is a fourth power value, the fourth power value is Qmax, and Qmax is the maximum reactive power allowed to be output; When the working mode of the energy storage system is the operation mode, the grid active power is calculated according to the grid voltage and the grid current, the grid active power is compared with a preset power value, a second target reactive power is obtained according to the comparison result, and an inverter control signal is obtained according to the second target reactive power and the target active power, including: The preset power value includes a first preset power value, a second preset power value and a third preset power value, the first preset power value is greater than the second preset power value, and the second preset power value is greater than the third preset power value; When the active power of the power grid is greater than the first preset power value, the second target reactive power is the first target value, the first target value is -Qmax, and Qmax is the maximum reactive power allowed to be output; When the grid active power is greater than the second preset power value and less than the first preset power value, the second target reactive power is a second target value, the second target value is Qmax*(P2-P) / (P1-P2), Qmax is the maximum reactive power allowed to be output, P1 is the first preset power value, P2 is the second preset power value, and P is the grid active power; When the grid active power is greater than the third preset power value and less than the second preset power value, the second target reactive power is a third target value, the third target value is Qmax, and Qmax is the maximum reactive power allowed to be output.

2. The method according to claim 1, characterized in that The grid voltage is an average value of a plurality of grid voltages collected within a certain period of time.

3. The method according to claim 1, characterized in that Obtaining an inverter control signal according to the first target reactive power includes: Performing a Park transformation on the grid current to obtain a first current and a second current corresponding to the grid current; Performing a Park transformation on the grid voltage to obtain a first voltage and a second voltage corresponding to the grid voltage; Obtaining a first target reactive current according to the first target reactive power; Performing proportional-integral control on the difference between the first target reactive current and the first current to obtain a first error signal, adding the first error signal to a first voltage to obtain a first control amount; performing proportional-integral control on the second current to obtain a second error signal, adding the second error signal to the second voltage to obtain a second control amount; Performing Park inverse transformation on the first control quantity and the second control quantity to obtain the inverter control signal.

4. The method according to claim 1, characterized in that: Obtaining an inverter control signal according to the second target reactive power and the target active power, comprising: Acquire a second target reactive current according to the second target reactive power; According to the preset target active power, a target active current is obtained; Performing a Park transformation on the grid current to obtain a first current and a second current corresponding to the grid current; Performing a Park transformation on the grid voltage to obtain a first voltage and a second voltage corresponding to the grid voltage; Performing proportional-integral control on the difference between the second target reactive current and the first current to obtain a first error signal, and adding the first error signal to the first voltage to obtain a first control amount; performing proportional-integral control on the difference between the target active current and the second current to obtain a second error signal, and adding the second error signal to the second voltage to obtain a second control amount; Performing a Park inverse transformation on the first control amount and the second control amount to obtain a target control signal, wherein the target control signal is a PWM duty cycle.

5. The method according to claim 3 or 4, characterized in that: The method further comprises: The actual voltage of the power grid is phase-locked to obtain a phase-locked angle, and the actual current and actual voltage are subjected to Parker transformation using the phase-locked angle so that the phase of the current and voltage in the AC signal output by the inverter circuit is the same as the phase of the actual voltage of the power grid.

6. A power grid control system, characterized in that: The system comprises: a controller and a battery energy storage system, wherein the battery energy storage system comprises a battery and an inverter circuit connected between the battery and a power grid, wherein the controller comprises a memory and a processor, wherein the memory is used to store a computer program, and the processor is used to execute the method according to any one of claims 1 to 5 under the control of the computer program.

7. A computer-readable storage medium, characterized in that: The readable storage medium stores a program or an instruction, and when the program or the instruction is executed by a processor, the method according to any one of claims 1 to 5 is implemented.

Images