Electrochemical energy storage low-voltage ride-through model considering multi-target cooperation and modeling method

Abstract

The invention provides an electrochemical energy storage low-voltage ride-through model considering multi-target cooperation. The electrochemical energy storage low-voltage ride-through model comprises a main circuit model and a control circuit model, the main circuit model comprises a battery module and a converter module; the control circuit model comprises a constant voltage control module and a converter control module; the battery module comprises a battery and a converter; the constant voltage module is used for providing a first control signal for the converter, the first control signal is used for controlling the converter to convert a first direct current into a second direct current in a working mode, and the second direct current is a constant-voltage direct current voltage; and the converter control module is used for providing a second control signal for the converter, and the second control signal is used for controlling the converter module to convert the second direct current into the alternating current in the running state. According to the model, the technical limitation of electrochemical energy storage fault ride-through research is broken through, and after the electrochemical energy storage system is connected to the grid, the system is ensured to continuously operate without being disconnected from the grid in a grid-connected point voltage drop state within a certain range.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical energy storage, and in particular to an electrochemical energy storage low voltage ride-through model and a modeling method taking multi-objective coordination into consideration. Background Art

[0002] As the global demand for clean energy grows, the proportion of renewable energy such as wind and solar energy in the power system continues to rise. Although this trend helps reduce greenhouse gas emissions and promote energy transformation, it also brings unprecedented challenges to the stability and control of the power grid. Energy storage technology has the characteristics of rapid response and controllability. It can store and release power and energy, enhance the power grid's ability to absorb a large proportion of new energy, reduce the impact on the power grid, and achieve peak shaving and valley filling. Compared with traditional thermal power generation, the intermittent and volatile characteristics of new energy power generation pose severe challenges to the stable operation of the power grid. Therefore, many places have introduced new energy distribution and storage related solutions, and the traditional "source, grid, load" structure consisting of the power generation side, the grid side and the power consumption side has gradually changed to a "source, grid, load, storage" structure. However, the transient operating conditions of the "source, grid, load, storage" structure system during failure have changed significantly compared with the traditional structure. At present, many scholars have conducted energy storage system modeling and simulation, but because the manufacturer only provides a black box model, further research on the transient process of energy storage is hindered. It is urgent to establish a structured electromagnetic simulation model of energy storage to verify the accuracy of the control strategy. Summary of the invention

[0003] In order to ensure that the electrochemical energy storage system can operate without disconnecting from the grid when the voltage drops or rises within a certain range due to various situations such as instantaneous faults and unstable output, and in order to design the needs of relay protection for the electrochemical energy storage system, the present invention proposes a fault ride-through control strategy and a fault current calculation method that are adapted to the structure of the electrochemical energy storage system, and builds an electrochemical energy storage low voltage ride-through model considering multi-objective collaboration in simulink to simulate various faults causing voltage drops at the grid connection point, ensuring that the electrochemical energy storage system can operate continuously without disconnecting from the grid within a specific range.

[0004] To achieve the above object, the technical solution adopted by the present invention is as follows: a low voltage ride-through model of electrochemical energy storage considering multi-objective coordination, including a main circuit model and a control circuit model; the main circuit model includes a battery module and a converter module; the control circuit model includes a constant voltage control module and a converter control module;

[0005] The battery module includes a battery and a converter;

[0006] The battery is used to output a first direct current to the converter;

[0007] The converter is used to switch the working mode, to convert the first direct current into the second direct current in the working mode, and to transmit the second direct current to the converter module; the second direct current is a constant voltage direct current voltage, and the working mode includes a step-down working mode and a step-up working mode;

[0008] The converter module is used to convert the second direct current into alternating current in an operating state; the operating state includes a normal operating state and a low voltage fault state;

[0009] The constant voltage module is used to provide a first control signal to the converter, and the first control signal is used to control the converter to convert the first direct current into the second direct current in the working mode;

[0010] The converter control module is used to provide a second control signal to the converter, and the second control signal is used to control the converter module to convert the second direct current into alternating current in a running state.

[0011] Furthermore, the battery includes a controlled voltage source and a controlled resistor, and the controlled voltage source is connected in series with the controlled resistor.

[0012] Further, the converter includes a first capacitor, a second capacitor, a first inductor, a first controllable device and a second controllable device;

[0013] The first capacitor is connected in parallel across the output terminals of the battery;

[0014] The second capacitor is connected in parallel across the input end of the converter module;

[0015] The emitter of the first controllable device and the collector of the second controllable device are connected to the positive electrode of the first capacitor through the first inductor respectively;

[0016] The collector of the first controllable device is connected to the positive electrode of the second capacitor;

[0017] The emitter of the second controllable device is connected to the negative electrode of the first capacitor and the negative electrode of the second capacitor respectively;

[0018] The gate of the first controllable device and the gate of the second controllable device are respectively controlled by the first control signal.

[0019] Further, the constant voltage module includes a voltage outer loop and a first current inner loop;

[0020] The voltage outer loop:

[0021] Used to obtain a capacitor voltage and a voltage reference value, wherein the capacitor voltage is the voltage across the second capacitor;

[0022] used for comparing the capacitor voltage with the voltage reference value to obtain a current reference value;

[0023] The first current inner loop:

[0024] Used to obtain an inductor current, where the inductor current is a current flowing through the first inductor;

[0025] used to compare the inductor current with the current reference value and generate a first PWM trigger signal and a second PWM trigger signal based on the comparison result, wherein the first PWM trigger signal and the second PWM trigger signal are complementary;

[0026] The first control signal includes the first PWM trigger signal and the second PWM trigger signal;

[0027] The first PWM trigger signal is used to control the gate of the second controllable device;

[0028] The second PWM trigger signal is used to control the gate of the first controllable device.

[0029] Further, the converter includes three groups of controllable components, and the three groups of controllable components correspond one-to-one to the three phases of the busbar;

[0030] The controllable device includes a third controllable device and a fourth controllable device;

[0031] The emitter of the third controllable device and the collector of the fourth controllable device are connected to the input end of the corresponding phase of the busbar respectively;

[0032] The collector of the third controllable device is connected to the positive electrode of the converter output terminal;

[0033] The emitter of the fourth controllable device is connected to the negative electrode of the converter output terminal;

[0034] The gate of the third controllable device and the gate of the fourth controllable device are respectively controlled by the second control signal.

[0035] Furthermore, the converter control module includes a power outer loop and a second current inner loop, and the power outer loop includes a grid-connected control link and a fault ride-through link;

[0036] The grid-connected control link is used to obtain a first active reference value and a first reactive reference value; the first active reference value is a positive-sequence active current reference value under normal operating conditions, and the first reactive reference value is a positive-sequence reactive current reference value under normal operating conditions;

[0037] The fault ride-through link is used to obtain a second active reference value and a second reactive reference value; the second active reference value is a positive-sequence active current reference value under a low voltage fault state, and the second reactive reference value is a positive-sequence reactive current reference value under a normal operating state;

[0038] The second current inner loop:

[0039] Used to obtain d-axis current and q-axis current;

[0040] Used to obtain a first trigger signal according to the first reactive power reference value, the second reactive power reference value and the q-axis current;

[0041] Used to obtain a second trigger signal according to the first active power reference value, the second active power reference value and the d-axis current;

[0042] The second control signal includes the first trigger signal and the second trigger signal;

[0043] The first trigger signal is used to control the gate of the third controllable device;

[0044] The second trigger signal is used to control the gate of the fourth controllable device.

[0045] Further, the low voltage fault state includes a first moment, a second moment, a third moment, a first time period and a second time period, the first moment is the moment when the low voltage fault occurs, the second moment is the moment when the voltage starts to recover after the low voltage fault occurs, the third moment is the moment when the voltage recovers to a normal range after the low voltage fault occurs, the first time period is the time period between the first moment and the second moment, and the second time period is the time period between the second moment and the third moment;

[0046] The first active reference value includes a first current reference value, a third current reference value, a fifth current reference value and a sixth current reference value; the first current reference value is a positive-sequence active current reference value of the inner current loop under normal operation of the power grid; the third current reference value is an active current reference value before a low voltage fault occurs; the fifth current reference value is a positive-sequence active current reference value for the first period; the sixth current reference value is a positive-sequence active current reference value for the second period;

[0047] The first reactive power reference value includes the second current reference value and the fourth current reference value; the second current reference value is the positive-sequence reactive current reference value of the inner current loop under normal grid operation; the fourth current reference value is the positive-sequence reactive current reference value under low voltage fault state.

[0048] Furthermore, the grid connection control link:

[0049] Used to obtain a first power, a second power, an active power reference value and a reactive power reference value; the first power is the active power under normal operating conditions, and the second power is the reactive power under normal operating conditions;

[0050] for comparing the first power and the active power reference value in the normal operating state to obtain a first current reference value;

[0051] Used to compare the second power and the reactive power reference value in the normal operating state to obtain a second current reference value.

[0052] Furthermore, the fault riding link:

[0053] Used to obtain the rated current, the maximum current limit value, the d-axis voltage positive sequence component, the third current reference value, the slope, the third power and the fourth power; the third power is the active power steady-state value before the low voltage fault occurs, and the fourth power is the active power at the second moment;

[0054] Used to obtain the effective value of the grid connection point voltage under the low voltage fault state;

[0055] Used to obtain a fourth current reference value according to the effective value of the grid connection point voltage and the rated current in the low voltage fault state;

[0056] for obtaining a fifth current reference value according to the first current reference value, the current maximum limit value and the fourth current reference value during the first time period;

[0057] and obtaining a sixth current reference value according to the slope, the fourth power, the third power, the d-axis voltage positive sequence component and the third current reference value during the second time period.

[0058] A modeling method for constructing the electrochemical energy storage low voltage ride-through model considering multi-objective synergy includes the following steps:

[0059] A battery module is constructed based on the electrochemical energy storage system and the working mode; the battery module includes the battery and the converter, and the output end of the battery is connected to the input end of the converter;

[0060] The converter module is constructed based on the electrochemical energy storage system; the output end of the converter is connected to the input end of the converter module, and the output end of the converter module is connected to the power grid;

[0061] Based on the constant voltage control strategy, the constant voltage control module is constructed on the converter; the constant voltage control module is used to control the converter to convert the first direct current into the second direct current in the working mode;

[0062] The converter control module is constructed on the converter module based on a low voltage ride-through strategy; the converter control module is used to control the converter module to convert the second direct current into alternating current in a running state.

[0063] Compared with the prior art, the present invention has the following beneficial effects:

[0064] 1. After the electrochemical energy storage system is connected to the grid, when various faults occur and cause the voltage drop at the grid connection point, the model proposed in the present invention can ensure that the system can continue to operate without being disconnected from the grid within a certain range of the voltage drop. This provides a solution to the lack of research on fault ride-through caused by the transformation of power systems in many places from a "source, grid, load" structure to a "source, grid, load, storage" structure.

[0065] 2. The model proposed in the present invention is based on the fault response characteristics of the black box model provided by the manufacturer, and the low-voltage ride-through control strategy is proposed and compared with it, breaking the manufacturer's technical limitations on the research on electrochemical energy storage fault ride-through.

[0066] 3. The model proposed in the present invention only changes the control strategy of the converter, which is lower cost and more intelligent than achieving the above capabilities by replacing power electronic components. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 It is a schematic diagram of the main circuit model of the present invention;

[0068] Figure 2 It is a schematic diagram of the structure of the battery in the present invention;

[0069] Figure 3 A schematic diagram of the functional relationship between the converter and the constant voltage control module in the present invention;

[0070] Figure 4 is a low voltage fault ride-through requirement curve of the electrochemical energy storage system in the present invention;

[0071] Figure 5 Schematic diagram of the functional relationship between the converter module and the converter control module in the present invention;

[0072] Figure 6 A schematic diagram showing a comparison between the low voltage ride-through control of the model proposed in the embodiment of the present invention and the black box model when the voltage drops to 0.35 pu under high-power discharge conditions;

[0073] Figure 7 A schematic diagram showing a comparison between the low voltage ride-through control of the model proposed in the embodiment of the present invention and the black box model when the voltage drops to 0.50 pu under high-power discharge conditions;

[0074] Figure 8A schematic diagram showing a comparison between the low voltage ride-through control of the model proposed in the embodiment of the present invention and the black box model when the voltage drops to 0.75 pu under high-power discharge conditions;

[0075] Fig. 9 A schematic diagram showing a comparison between the low voltage ride-through control of the model proposed in the embodiment of the present invention and the black box model when the voltage drops to 0.35 pu under low-power discharge conditions;

[0076] Fig.10 A schematic diagram showing a comparison between the low voltage ride-through control of the model proposed in the embodiment of the present invention and the black box model when the voltage drops to 0.50 pu under low-power discharge conditions;

[0077] Fig.11 The figure is a schematic diagram comparing the low voltage ride-through control of the model proposed in the embodiment of the present invention and the black box model when the voltage drops to 0.75pu under low-power discharge conditions.

[0078] The reference numerals are: 11, battery; 12, converter; 13, converter module; 14, LCL filter circuit; 15, power grid; 111, controlled voltage source; 112, controlled resistor;

[0079] U bat , battery output voltage; U dc , converter output voltage; S7, first controllable device; S8, second controllable device; e a , the first PWM trigger signal; e b , second PWM trigger signal; L1, first inductor; C1, first capacitor; C dc , the second capacitor; S1, the third controllable device of phase A; S2, the fourth controllable device of phase A; S3, the third controllable device of phase B; S4, the fourth controllable device of phase B; S5, the third controllable device of phase C; S6, the fourth controllable device of phase C. DETAILED DESCRIPTION

[0080] It is worth noting that the methods used in the present invention are all conventional methods unless otherwise specified; the raw materials and devices used are all conventional commercially available products, and their sources are not specifically limited unless otherwise specified.

[0081] See also Figure 1The embodiment of the present invention provides an electrochemical energy storage low voltage ride-through model considering multi-objective coordination, including a main circuit model and a control circuit model; the main circuit model includes a battery module and a converter module 13; the control circuit model includes a constant voltage control module and a converter control module; the converter module is a converter (Power Conversion System, PCS), and the converter converts the second direct current output by the battery module into alternating current under the control strategy to achieve synchronous grid connection, generally adopts dq axis decoupling control to achieve independent control of active power and reactive power, and filters out harmonics through an LCL filter circuit 14, and is connected to the power grid 15 through a transformer;

[0082] The battery module includes a battery 11 and a converter 12;

[0083] Preferably, see Figure 2 , the battery includes a controlled voltage source 111 and a controlled resistor 112, and the controlled voltage source 111 and the controlled resistor 112 are connected in series. The battery module must have both load characteristics to consume electrical energy and power characteristics to release electrical energy. In order to simulate the charging and discharging process of the power supply, this embodiment selects a controlled voltage source 111 and a controlled resistor 112, and connects the two in series as a battery. At the same time, it is stipulated that the positive and negative currents flowing through the controlled resistor 112 represent the discharge and charging processes respectively. The battery does not consider the internal resistance problem caused by the battery polarization reaction, nor is it affected by external factors such as temperature. The only state variable of the battery is the state of charge SOC, so the calculation parameters are simpler, the circuit parameters are easy to obtain, and the applicability is strong;

[0084] This battery ignores the effect of the internal polarization reaction on the internal resistance of the battery, and also ignores the effect of the external environment. The expression of the battery is:

[0085] U bat =U OC -R0I;

[0086] Where U bat is the battery output voltage, U OC is the voltage of the controlled voltage source, R0 is the internal resistance of the battery, which is related to the battery state of charge, and I is the battery current, with the discharge current being positive;

[0087] The battery 11 is used to output a first direct current to the converter 12;

[0088] The converter 12 is used to switch the working mode, to convert the first direct current into the second direct current in the working mode, and to transmit the second direct current to the converter module 13; the second direct current is a constant voltage direct current voltage, and the working mode includes a buck working mode and a boost working mode; the converter 12 is a bidirectional DC / DC converter. The bidirectional DC / DC converter is a circuit that converts constant direct current into variable direct current. By switching the two working modes of the buck working mode (Buck) and the boost working mode (Boost) through the bidirectional DC / DC converter, the size of the direct current can be converted.

[0089] See also Figure 3 The converter 12 includes a first capacitor C1, a second capacitor C dc , a first inductor L1, a first controllable device S7 and a second controllable device S8;

[0090] The first capacitor C1 is connected in parallel across the output terminals of the battery 11;

[0091] The second capacitor C dc Connected in parallel at both ends of the input end of the converter module 13;

[0092] The emitter of the first controllable device S7 and the collector of the second controllable device S8 are connected to the positive electrode of the first capacitor through the first inductor respectively; preferably, the first controllable device S7 and the second controllable device S8 are both IGBTs;

[0093] The collector of the first controllable device S7 is connected to the second capacitor C dc The positive electrode;

[0094] The emitter of the second controllable device S8 is connected to the negative electrode of the first capacitor C1 and the negative electrode of the second capacitor C dc The negative electrode;

[0095] The gate of the first controllable device S7 and the gate of the second controllable device S8 are respectively controlled by the first control signal.

[0096] When the converter 12 is in the boost operation mode, the first controllable device S7 is turned on, and the converter output voltage U dc As input, the battery output voltage U bat As output, the electric energy of the DC bus is transmitted to the battery to charge the battery; when working in the step-down working mode, S8 is turned on, and the battery output voltage U bat As input, the converter output voltage U dc As output, the energy stored in the battery is transferred to the DC bus and the battery is in a discharged state.

[0097] The constant voltage module is used to provide a first control signal to the converter, and the first control signal is used to control the converter to convert the first direct current into the second direct current in the working mode;

[0098] Still see Figure 3 , the constant voltage module includes a voltage outer loop and a first current inner loop; the constant voltage control strategy of the bidirectional DC / DC converter is that the voltage loop is used as the outer loop and the current loop is used as the inner loop;

[0099] Voltage outer loop:

[0100] Used to obtain a capacitor voltage and a voltage reference value, where the capacitor voltage is the voltage across the second capacitor;

[0101] Used to compare the capacitor voltage with a voltage reference value to obtain a current reference value;

[0102] i ref =k P_DC (u ref -u dc )+k I_DC ∫(u ref -u dc )dt;

[0103] In the formula, i ref is the current reference value, u ref is the voltage reference value to be set, u dc is the capacitor voltage, k P_DC is the proportional coefficient of the voltage outer loop PI controller, k I_DC is the integral coefficient of the voltage outer loop PI controller;

[0104] First current inner loop:

[0105] Used to obtain an inductor current, where the inductor current is a current flowing through the first inductor;

[0106] Used to compare the inductor current with the current reference value, and generate a first PWM trigger signal and a second PWM trigger signal based on the comparison result, wherein the first PWM trigger signal and the second PWM trigger signal are complementary;

[0107] u PWM =k P_i (i ref -i L )+k I_i ∫(i ref -i L )dt;

[0108] In the formula, u PWM is the converter PWM voltage reference value, i L is the inductor current, k P_i is the proportional coefficient of the current inner loop PI controller, k I_i is the integral coefficient of the current inner loop PI controller.

[0109] The PWM voltage reference value generates a complementary first PWM trigger signal e through PWM a and the second PWM trigger signal e b ;

[0110] The first control signal includes a first PWM trigger signal and a second PWM trigger signal;

[0111] The first PWM trigger signal e a Used to control the gate of the second controllable device S8;

[0112] The second PWM trigger signal e b Used to control the gate of the first controllable device S7.

[0113] The constant voltage control strategy first requires measuring the inductor current i in the converter. L and capacitor voltage u dc , the obtained capacitor voltage u dc With the preset voltage reference value u ref For comparison, the voltage outer loop PI controller is used to generate the current reference value i ref Then the inductor current i L With the current reference value i ref By comparison, the converter PWM voltage reference value is obtained through the PI controller in the current loop and the first PWM trigger signal e is further obtained. a and the second PWM trigger signal e b , respectively controlling the opening and closing of the second controllable device S8 and the first controllable device S7, so that the second controllable device S8 and the first controllable device S7 are alternately turned on, so as to control the bidirectional DC / DC converter to output a second direct current with a stable voltage, thereby achieving the goal of maintaining a stable DC bus voltage.

[0114] The converter module 13 is used to convert the second direct current into alternating current in the operating state; the operating state includes a normal operating state and a low voltage fault state;

[0115] Furthermore, the converter module 13 includes three groups of controllable devices, and the three groups of controllable devices correspond one to one to the three phases of the busbar;

[0116] See also Figure 1 , the controllable device includes a third controllable device and a fourth controllable device; the third controllable device includes a third controllable device S1 of phase A, a third controllable device S3 of phase B, and a third controllable device S5 of phase C, and the fourth controllable device includes a fourth controllable device S2 of phase A, a fourth controllable device S4 of phase B, and a fourth controllable device S6 of phase C

[0117] The emitter of the third controllable device and the collector of the fourth controllable device are connected to the input end of the corresponding phase of the busbar respectively;

[0118] The collector of the third controllable device is connected to the positive electrode of the converter output terminal;

[0119] The emitter of the fourth controllable device is connected to the negative electrode of the converter output terminal;

[0120] The gate of the third controllable device and the gate of the fourth controllable device are respectively controlled by the second control signal.

[0121] The converter control module is used to provide a second control signal to the converter, and the second control signal is used to control the converter module to convert the second direct current into alternating current in a running state.

[0122] In order to ensure that the grid can resume normal operation after a short circuit fault occurs, the grid-connected electrochemical energy storage system must have a low voltage ride-through function, that is, when the grid voltage drops, it can ensure continuous operation without disconnecting from the grid within a certain voltage drop range and time. Figure 4 At present, the relevant standards of my country's electrochemical energy storage converters describe the low voltage ride-through requirements of electrochemical energy storage systems as follows:

[0123] (1) When the grid voltage drops to 0, the battery energy storage system should be able to operate continuously for 0.15s without disconnecting from the grid;

[0124] (2) When the grid voltage drops below the voltage contour, the battery energy storage system operates off-grid.

[0125] See also Figure 5 The converter control module includes a power outer loop and a second current inner loop, that is, the converter adopts a control method in which the power loop is used as the outer loop and the current loop is used as the inner loop, and a low-voltage fault ride-through strategy is added to the converter control strategy. The power outer loop includes a grid-connected control link and a fault ride-through link; the active and reactive power are compared with the given value in the outer loop control, and the current reference value of the inner loop is generated by the PI controller; the input of the inner loop is the direct-axis current and quadrature-axis current in the dq coordinate system, and the reference value is generated by the outer loop.

[0126] The grid-connected control link is used to obtain a first active reference value and a first reactive reference value; the first active reference value is a positive-sequence active current reference value under normal operating conditions, and the first reactive reference value is a positive-sequence reactive current reference value under normal operating conditions;

[0127] The fault ride-through link is used to obtain a second active reference value and a second reactive reference value; the second active reference value is a positive-sequence active current reference value under a low voltage fault state, and the second reactive reference value is a positive-sequence reactive current reference value under a normal operating state;

[0128] The low voltage fault state includes the first moment, the second moment, the third moment, the first period and the second period. The first moment is the moment when the low voltage fault occurs, the second moment is the moment when the voltage starts to recover after the low voltage fault occurs, and the third moment is the moment when the voltage recovers to the normal range after the low voltage fault occurs. The first period is the period between the first moment and the second moment, and the second period is the period between the second moment and the third moment. When the low voltage fault occurs in the power grid at the first moment t1, the voltage starts to recover at the second moment t2, and the voltage recovers to the normal range at the third moment t3. The whole process of fault ride-through is divided into two parts, namely, the first period is the ride-through process during the fault (t1-t2) and the second period is the recovery process after the fault is cleared (t2-t3).

[0129] The first active reference value includes a first current reference value, a third current reference value, a fifth current reference value and a sixth current reference value; the first current reference value is a positive-sequence active current reference value of the current inner loop under normal operation of the power grid; the third current reference value is an active current reference value before a low voltage fault occurs; the fifth current reference value is a positive-sequence active current reference value for the first period; and the sixth current reference value is a positive-sequence active current reference value for the second period;

[0130] The first reactive power reference value includes a second current reference value and a fourth current reference value; the second current reference value is a positive-sequence reactive current reference value of the inner current loop under normal grid operation; the fourth current reference value is a positive-sequence reactive current reference value under low voltage fault state.

[0131] Grid-connected control link:

[0132] Used to obtain a first power, a second power, an active power reference value, and a reactive power reference value; the first power is the active power under normal operating conditions, and the second power is the reactive power under normal operating conditions;

[0133] Used to compare the first power and the active power reference value to obtain the first current reference value under normal operating conditions; the positive sequence active current reference value in the second current inner loop is generated by the active power outer loop in the power outer loop:

[0134]

[0135] In the formula, is the positive sequence active current reference value of the inner loop under normal grid operation, that is, the first current reference value, k P_P is the proportional coefficient of the active power PI controller, P ref is the active power reference value, k I_P is the integral coefficient of the active power PI controller, P is the active power under normal operating conditions, that is, the first power;

[0136] Used to compare the second power and reactive power reference values ​​to obtain a second current reference value under normal operating conditions; the positive sequence reactive current reference value in the second current inner loop is generated by the reactive power outer loop in the power outer loop:

[0137]

[0138] In the formula, is the positive sequence reactive current reference value of the inner loop under normal grid operation, that is, the second current reference value, k P_Q is the proportional coefficient of the reactive power PI controller, Q ref is the reactive power reference value, k I_Q is the integral coefficient of the reactive power PI controller, Q is the reactive power under normal operating conditions, that is, the second power.

[0139] Fault ride-through stage:

[0140] Used to obtain the rated current, the maximum current limit value, the d-axis voltage positive sequence component, the third current reference value, the slope, the third power and the fourth power; the third power is the active power steady-state value before the low voltage fault occurs, and the fourth power is the active power at the second moment;

[0141] Used to obtain the effective value of the grid connection point voltage under low voltage fault conditions;

[0142] It is used to obtain the fourth current reference value according to the effective value of the grid connection point voltage and the rated current under the low voltage fault state; the electrochemical energy storage system puts forward requirements for reactive power support during the low voltage fault ride-through period, that is, the positive sequence reactive current reference value under the low voltage fault state is generated by the fault ride-through link:

[0143]

[0144] In the formula, is the positive sequence reactive current reference value under low voltage fault condition, that is, the fourth current reference value, k is a constant coefficient, usually greater than 1.5, i n is the rated current, V T is the effective value of the grid connection point voltage;

[0145] It is used to obtain the fifth current reference value according to the first current reference value, the current maximum limit value and the fourth current reference value in the first time period; during the fault ride-through period, that is, in the first time period, the output of reactive current is controlled first to ensure the grid voltage recovery, but due to the limitation of the converter capacity, the active current will also be affected to a certain extent:

[0146]

[0147] In the formula, is the positive sequence active current reference value of the first period, that is, the fifth current reference value, min is the minimization function, For max is the maximum current limit value, usually i max =1.1, 1.1 means that the PCS can withstand 1.1 times the overload current;

[0148] The sixth current reference value is obtained according to the slope, the fourth power, the third power, the d-axis voltage positive sequence component and the third current reference value in the second period. In the recovery process after the fault is cleared, that is, in the second period, the active power of the electrochemical energy storage system is calculated with the slope r id Restore to the active power steady-state value P0 before the low voltage fault occurs:

[0149]

[0150] In the formula, is the positive sequence active current reference value of the second period, that is, the sixth current reference value, r id is the slope, t is the time, t2 is the second moment, P(t2) is the active power at the second moment, that is, the fourth power, is the positive sequence component of the d-axis voltage, i dref0 is the active current reference value before the low voltage fault occurs, that is, the third current reference value, and P0 is the active power steady-state value before the low voltage fault occurs, that is, the third power;

[0151] Second current inner loop:

[0152] Used to obtain d-axis current and q-axis current;

[0153] Used to obtain a first trigger signal according to a first reactive power reference value, a second reactive power reference value and a q-axis current;

[0154] Used to obtain a second trigger signal according to the first active reference value, the second active reference value and the d-axis current;

[0155] The second control signal includes a first trigger signal and a second trigger signal;

[0156] The first trigger signal is used to control the gate of the third controllable device;

[0157] The second trigger signal is used to control the gate of the fourth controllable device.

[0158] See also Figure 5, the fault ride-through control is implemented in the following manner: when the voltage drops, the PCS emits reactive power and absorbs active power. The switching of the first reactive reference value in the normal operating state (corresponding to the second current reference value) and the low voltage fault state (corresponding to the fourth current reference value) is implemented by the third controllable device of the switch, and the switching of the first active reference value in the normal operating state (corresponding to the first current reference value), the first time period (corresponding to the fifth current reference value), and the second time period (corresponding to the sixth current reference value) is implemented by the fourth controllable device.

[0159] The waveforms of the electrochemical energy storage low voltage ride-through model (structured model) constructed to consider multi-objective coordination are compared with the black box model to verify the effectiveness and reliability of the control strategy.

[0160] It is necessary to compare the low-voltage ride-through characteristics under high-power output state and low-power output state, set the structured model and the black box model to output active power 1p.u. in high-power state and 0.2pu in low-power state, and simulate the working conditions with different voltage drop depths. The electrochemical energy storage is simulated under high-power and low-power conditions, and the fault ride-through response characteristics of the structured model and the black box model are obtained respectively. The low voltage ride-through selects three cases where the voltage drops to 0.35pu, 0.50pu and 0.75pu, and the fault durations are 0.92s, 1.21s and 1.705s respectively.

[0161] Waveform comparison under different working conditions Figure 6-11 As shown;

[0162] By comparison, it is found that when the voltage drops, the energy storage generates a large reactive current under both high-power and low-power conditions and transmits reactive power to the grid, while the active current generated by the energy storage will decrease during the fault period under high-power conditions, and the active current under low-power conditions will decrease slightly or even increase, but the active power generated will decrease. By comparing with the black box model, the effectiveness of the constructed structured model and control strategy is verified.

[0163] A modeling method for constructing an electrochemical energy storage low voltage ride-through model considering multi-objective coordination includes the following steps: preferably, constructing an electrochemical energy storage low voltage ride-through model considering multi-objective coordination in simulink;

[0164] A battery module is constructed based on an electrochemical energy storage system and an operating mode; the battery module includes a battery and a converter, and the output end of the battery is connected to the input end of the converter;

[0165] A converter module is constructed based on an electrochemical energy storage system; the output end of the converter is connected to the input end of the converter module, and the output end of the converter module is connected to the power grid;

[0166] Based on the constant voltage control strategy, a constant voltage control module is constructed on the converter; the constant voltage control module is used to control the converter to convert the first direct current into the second direct current in the working mode;

[0167] A converter control module is constructed on the converter module based on the low voltage ride-through strategy; the converter control module is used to control the converter module to convert the second direct current into alternating current in a running state.

[0168] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A low voltage ride-through model for electrochemical energy storage considering multi-objective coordination, characterized by: It includes a main circuit model and a control circuit model; the main circuit model includes a battery module and a converter module; the control circuit model includes a constant voltage control module and a converter control module; The battery module includes a battery and a converter; The battery is used to output a first direct current to the converter; The converter is used to switch the working mode, to convert the first direct current into the second direct current in the working mode, and to transmit the second direct current to the converter module; the second direct current is a constant voltage direct current voltage, and the working mode includes a step-down working mode and a step-up working mode; The converter module is used to convert the second direct current into alternating current in an operating state; the operating state includes a normal operating state and a low voltage fault state; The constant voltage module is used to provide a first control signal to the converter, and the first control signal is used to control the converter to convert the first direct current into the second direct current in the working mode; The converter control module is used to provide a second control signal to the converter, and the second control signal is used to control the converter module to convert the second direct current into alternating current in a running state.

2. The electrochemical energy storage low voltage ride-through model considering multi-objective coordination according to claim 1 is characterized in that: The battery includes a controlled voltage source and a controlled resistor, wherein the controlled voltage source is connected in series with the controlled resistor.

3. The electrochemical energy storage low voltage ride-through model considering multi-objective coordination according to claim 1 is characterized in that: The converter comprises a first capacitor, a second capacitor, a first inductor, a first controllable device and a second controllable device; The first capacitor is connected in parallel across the output terminals of the battery; The second capacitor is connected in parallel across the input end of the converter module; The emitter of the first controllable device and the collector of the second controllable device are connected to the positive electrode of the first capacitor through the first inductor respectively; The collector of the first controllable device is connected to the positive electrode of the second capacitor; The emitter of the second controllable device is connected to the negative electrode of the first capacitor and the negative electrode of the second capacitor respectively; The gate of the first controllable device and the gate of the second controllable device are respectively controlled by the first control signal.

4. The electrochemical energy storage low voltage ride-through model considering multi-objective coordination according to claim 3 is characterized by: The constant voltage module comprises a voltage outer loop and a first current inner loop; The voltage outer loop: Used to obtain a capacitor voltage and a voltage reference value, wherein the capacitor voltage is the voltage across the second capacitor; used for comparing the capacitor voltage with a voltage reference value to obtain a current reference value; The first current inner loop: Used to obtain an inductor current, where the inductor current is a current flowing through the first inductor; used to compare the inductor current with the current reference value and generate a first PWM trigger signal and a second PWM trigger signal based on the comparison result, wherein the first PWM trigger signal and the second PWM trigger signal are complementary; The first control signal includes the first PWM trigger signal and the second PWM trigger signal; The first PWM trigger signal is used to control the gate of the second controllable device; The second PWM trigger signal is used to control the gate of the first controllable device.

5. The electrochemical energy storage low voltage ride-through model considering multi-objective coordination according to claim 1 is characterized in that: The converter includes three groups of controllable components, and the three groups of controllable components correspond one to one to the three phases of the busbar; The controllable device includes a third controllable device and a fourth controllable device; The emitter of the third controllable device and the collector of the fourth controllable device are connected to the input end of the corresponding phase of the busbar respectively; The collector of the third controllable device is connected to the positive electrode of the converter output terminal; The emitter of the fourth controllable device is connected to the negative electrode of the converter output terminal; The gate of the third controllable device and the gate of the fourth controllable device are respectively controlled by the second control signal.

6. The electrochemical energy storage low voltage ride-through model considering multi-objective coordination according to claim 5 is characterized in that: The converter control module includes a power outer loop and a second current inner loop, and the power outer loop includes a grid-connected control link and a fault ride-through link; The grid connection control link is used to obtain a first active reference value and a first reactive reference value; The first active reference value is a positive-sequence active current reference value under normal operating conditions, and the first reactive reference value is a positive-sequence reactive current reference value under normal operating conditions; The fault ride-through link is used to obtain a second active reference value and a second reactive reference value; The second active current reference value is a positive-sequence active current reference value under a low voltage fault state, and the second reactive current reference value is a positive-sequence reactive current reference value under a normal operating state; The second current inner loop: Used to obtain d-axis current and q-axis current; Used to obtain a first trigger signal according to the first reactive power reference value, the second reactive power reference value and the q-axis current; Used to obtain a second trigger signal according to the first active power reference value, the second active power reference value and the d-axis current; The second control signal includes the first trigger signal and the second trigger signal; The first trigger signal is used to control the gate of the third controllable device; The second trigger signal is used to control the gate of the fourth controllable device.

7. The electrochemical energy storage low voltage ride-through model considering multi-objective coordination according to claim 6 is characterized by: The low voltage fault state includes a first moment, a second moment, a third moment, a first time period and a second time period, wherein the first moment is the moment when the low voltage fault occurs, the second moment is the moment when the voltage starts to recover after the low voltage fault occurs, the third moment is the moment when the voltage recovers to a normal range after the low voltage fault occurs, the first time period is the time period between the first moment and the second moment, and the second time period is the time period between the second moment and the third moment; The first active reference value includes a first current reference value, a third current reference value, a fifth current reference value and a sixth current reference value; The first current reference value is a positive-sequence active current reference value of the current inner loop under normal grid operation; The third current reference value is an active current reference value before a low voltage fault occurs; The fifth current reference value is the positive sequence active current reference value of the first time period; The sixth current reference value is a positive-sequence active current reference value in the second period; The first reactive power reference value includes the second current reference value and the fourth current reference value; The second current reference value is a positive sequence reactive current reference value of the current inner loop under normal operation of the power grid; The fourth current reference value is a positive-sequence reactive current reference value in a low voltage fault state.

8. The electrochemical energy storage low voltage ride-through model considering multi-objective coordination according to claim 7 is characterized in that: The grid-connected control link: Used to obtain a first power, a second power, an active power reference value and a reactive power reference value; the first power is the active power under normal operating conditions, and the second power is the reactive power under normal operating conditions; for comparing the first power and the active power reference value in the normal operating state to obtain a first current reference value; Used to compare the second power and the reactive power reference value in the normal operating state to obtain a second current reference value.

9. The electrochemical energy storage low voltage ride-through model considering multi-objective coordination according to claim 7 is characterized in that: The fault ride-through link: Used to obtain the rated current, the maximum current limit value, the d-axis voltage positive sequence component, the third current reference value, the slope, the third power and the fourth power; the third power is the active power steady-state value before the low voltage fault occurs, and the fourth power is the active power at the second moment; Used to obtain the effective value of the grid connection point voltage under the low voltage fault state; Used to obtain a fourth current reference value according to the effective value of the grid connection point voltage and the rated current in the low voltage fault state; for obtaining a fifth current reference value according to the first current reference value, the current maximum limit value and the fourth current reference value during the first time period; and obtaining a sixth current reference value according to the slope, the fourth power, the third power, the d-axis voltage positive sequence component and the third current reference value during the second time period.

10. A modeling method for constructing an electrochemical energy storage low voltage ride-through model considering multi-objective coordination as described in any one of claims 1 to 9, characterized in that: The following steps are involved: A battery module is constructed based on the electrochemical energy storage system and the working mode; the battery module includes the battery and the converter, and the output end of the battery is connected to the input end of the converter; The converter module is constructed based on the electrochemical energy storage system; the output end of the converter is connected to the input end of the converter module, and the output end of the converter module is connected to the power grid; Based on the constant voltage control strategy, constructing the constant voltage control module on the converter; The constant voltage control module is used to control the converter to convert the first direct current into the second direct current in the working mode; The converter control module is constructed on the converter module based on a low voltage ride-through strategy; the converter control module is used to control the converter module to convert the second direct current into alternating current in a running state.

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