All-silicon carbide voltage sag treatment device and control method

Abstract

The invention discloses a full silicon carbide voltage sag treatment device and a control method. The device comprises a first silicon carbide static change-over switch K1, a second silicon carbide static change-over switch K2, a third silicon carbide static change-over switch K1, a third silicon carbide static change-over switch K3, an energy storage converter, an energy storage battery and three ports I, II and III, by utilizing the device, a fault source of voltage sag is positioned and treated by detecting the voltage state of a port, and grid connection / grid disconnection / removal is carried out on the energy storage converter according to actual requirements through an off-grid control algorithm and a grid connection control algorithm, so that rectification / inversion mode conversion is realized, and the reliability of the energy storage converter is improved. Input and output power is adaptively adjusted according to the change of power grid frequency, and bidirectional energy flow and peak load shifting are realized. According to the invention, the cost is low, rapid voltage sag treatment with millisecond-level response time can be realized, power supply of a sensitive load can be effectively guaranteed when a power grid fails, and the energy storage converter has a self-adaptive peak regulation function and has a certain practical value.

Description

Technical Field

[0001] The present invention relates to the technical field of voltage sag control, and in particular to a full silicon carbide voltage sag control device and a control method. Background Art

[0002] Voltage sag refers to the phenomenon that the RMS value of the power frequency voltage at a certain point in the power system suddenly drops to 0.1pu~0.9pu and returns to normal after a short duration of 10ms~1min. Voltage sag is a common type of power quality problem and will have a negative impact on sensitive loads. Voltage sag includes single-phase sag, two-phase sag and three-phase sag. When a voltage sag occurs, the phenomenon may trigger the undervoltage protection of the equipment or directly cause the equipment to stop operating, resulting in direct or indirect economic losses.

[0003] The causes of voltage sag can be divided into the following three categories:

[0004] (1) Short circuit fault in the power grid: When a fault occurs, the system impedance changes, causing a sudden drop in voltage.

[0005] (2) Starting of large loads: When large motors, transformers and other high-power equipment are started, the grid current will increase sharply, causing a temporary drop in voltage at the common node.

[0006] (3) Natural factors such as lightning strikes: Disturbances to the power system caused by lightning or severe weather conditions can also cause voltage sags. Lightning can cause voltage surges on overhead lines, which in turn affects the voltage level in the system.

[0007] There are three main types of existing power electronic devices for managing voltage sags: UPS (Uninterruptible Power Supply), UPQC (Unified Power Quality Conditioner) and DVR (Dynamic Voltage Restorer). All three types of devices can cope with voltage sags well, but each has its own shortcomings. The inverter in the UPS is always in operation, which can ensure that the power supply quality on the load side will not be affected by the grid voltage sag, but it reduces the efficiency of the system, and long-term operation requires high reliability of the inverter. UPQC adjusts the output voltage of the series converter to compensate for the grid voltage sag and maintain the stability of the load side voltage. However, UPQC can not only manage voltage sags, but also manage grid harmonic currents. Its control method is complex and costly, and its performance is excessive for scenarios where only voltage sag management is required. The DVR device is connected in series between the grid and the load through passive devices such as transformers or filter capacitors. By compensating for the difference between the actual grid voltage and the ideal grid voltage, the load is guaranteed to operate reliably. However, DVR requires a high-power transformer, which increases the cost of the device. Summary of the invention

[0008] The purpose of the present invention is to provide a full silicon carbide voltage sag control device and a control method. The device uses a full silicon carbide MOSFET as a static switching switch, which is low in cost and fast in speed, and can achieve rapid voltage sag control with a response time of milliseconds; the energy storage converter has an adaptive peak-shaving function, which can achieve bidirectional energy flow and peak shaving and valley filling.

[0009] The present invention adopts the following technical solution:

[0010] A full silicon carbide voltage sag control device, comprising:

[0011] The first to third silicon carbide static transfer switches K1 to K3, an energy storage converter, an energy storage battery and three ports Ⅰ to Ⅲ.

[0012] The first end of the first silicon carbide static transfer switch K1 and the first end of the second silicon carbide static transfer switch K2 are both connected to one side of port I, the contact end of the first silicon carbide static transfer switch K1 and the contact end of the third silicon carbide static transfer switch K3 are both connected to one side of port II, the contact end of the second silicon carbide static transfer switch K2, the first end of the third silicon carbide static transfer switch K3 and one side of the energy storage inverter are all connected to port III, the other side of the energy storage inverter is connected to the energy storage battery, the other side of port I is connected to the three-phase power grid, and the other side of port II is connected to the load.

[0013] The silicon carbide static transfer switch includes phase A, phase B and phase C, each phase includes 4 parallel branches, and each branch includes an N-channel silicon carbide MOSFET and a P-channel silicon carbide MOSFET connected in series back to back.

[0014] Furthermore, the SiC static transfer switch K x , x=1,2,3; In phase A, the first N-channel SiC MOSFETQ Ax1 The source of the second P-channel SiC MOSFETQ Ax2 The drain of the third N-channel silicon carbide MOSFETQ Ax3 The source of the fourth P-channel SiC MOSFETQ Ax4 The drain of the fifth N-channel silicon carbide MOSFETQ Ax5 The source of the sixth P-channel SiC MOSFETQ Ax6 The drain of the seventh N-channel silicon carbide MOSFETQ Ax7 The source of the eighth P-channel SiC MOSFETQ Ax8 The drain of the first N-channel silicon carbide MOSFETQ Ax1 The drain of the third N-channel silicon carbide MOSFETQ Ax3 The drain of the fifth N-channel silicon carbide MOSFETQ Ax5 The drain of the seventh N-channel SiC MOSFET Q Ax7 The drain of the A phase is connected to the A phase input terminal i ; Second P-channel SiC MOSFETQ Ax2 The source of the fourth P-channel silicon carbide MOSFETQ Ax4 The source of the sixth P-channel silicon carbide MOSFETQ Ax6 The source of the eighth P-channel SiC MOSFETQ Ax8 The source of is connected to the A phase output terminal A0.

[0015] In phase B, the ninth N-channel SiC MOSFET Q Bx1 The source of the tenth P-channel SiC MOSFETQ Bx2 The drain of the eleventh N-channel silicon carbide MOSFETQ Bx3 The source of the twelfth P-channel SiC MOSFETQ Bx4 The drain of the thirteenth N-channel silicon carbide MOSFETQ Bx5 The source of the fourteenth P-channel SiC MOSFETQ Bx6 The drain of the fifteenth N-channel silicon carbide MOSFETQ Bx7 The source of the sixteenth P-channel SiC MOSFETQ Bx8The drain of the ninth N-channel silicon carbide MOSFETQ Bx1 The drain of the eleventh N-channel SiC MOSFET Q Bx3 The drain of the thirteenth N-channel silicon carbide MOSFETQ Bx5 The drain of the fifteenth N-channel SiC MOSFETQ Bx7 The drain of the B phase is connected to the B phase input terminal i ; Tenth P-channel SiC MOSFETQ Bx2 The source of the twelfth P-channel silicon carbide MOSFETQ Bx4 The source of the fourteenth P-channel silicon carbide MOSFETQ Bx6 The source of the sixteenth P-channel SiC MOSFETQ Bx8 The source of is connected and led out as the B-phase output terminal B0.

[0016] In phase C, the seventeenth N-channel SiC MOSFET Q Cx1 The source of the eighteenth P-channel SiC MOSFETQ Cx2 The drain of the nineteenth N-channel silicon carbide MOSFETQ Cx3 The source of the 20th P-channel SiC MOSFETQ Cx4 The drain of the twenty-first N-channel silicon carbide MOSFETQ Cx5 The source of the twenty-second P-channel SiC MOSFET Q Cx6 The drain of the twenty-third N-channel silicon carbide MOSFETQ Cx7 The source of the twenty-fourth P-channel silicon carbide MOSFETQ Cx8 The drain of the seventeenth N-channel silicon carbide MOSFETQ Cx1 The drain of the nineteenth N-channel silicon carbide MOSFETQ Cx3 The drain of the twenty-first N-channel SiC MOSFETQ Cx5 The drain of the twenty-third N-channel silicon carbide MOSFETQ Cx7 The drain of the C phase is connected to the C phase input terminal i ; Eighteenth P-channel silicon carbide MOSFETQ Cx2 The source of the 20th P-channel SiC MOSFETQ Cx4 The source of the twenty-second P-channel silicon carbide MOSFETQ Cx6 The source of the twenty-fourth P-channel silicon carbide MOSFETQ Cx8 The source of is connected to the C phase output terminal C0.

[0017] Furthermore, the energy storage converter includes a three-phase DC / AC bidirectional converter, a control unit and a human-machine interaction interface, wherein the topology of the three-phase DC / AC bidirectional converter is an LC-type three-phase two-level converter, the control unit includes a main control DSP, a drive circuit, a sampling circuit and a protection circuit, and the human-machine interaction interface is used to display the current parameters and operating conditions of the energy storage converter.

[0018] Furthermore, the present invention also proposes a control method for a full silicon carbide voltage sag control device, comprising:

[0019] S1. Initially, the first to third silicon carbide static transfer switches K1 to K3 are all disconnected, and the voltages of ports I and III are detected. If the voltages of ports I and III are the set rated values, the first and second silicon carbide static transfer switches K1 and K2 are closed, and the third silicon carbide static transfer switch K3 is disconnected, and the normal working mode is entered; if the voltage of port I is not the rated value, indicating that a power grid failure occurs, the first and second silicon carbide static transfer switches K1 and K2 are disconnected, and the third silicon carbide static transfer switch K3 is closed; if the voltage of port III is not the rated value, It indicates that the energy storage converter fails, the first silicon carbide static transfer switch K1 is closed, the second and third silicon carbide static transfer switches K2 and K3 are disconnected, and the load is powered by the power grid; if the voltages of port I and port III are both non-rated values, it indicates that both the power grid and the energy storage converter fail, the first to third silicon carbide static transfer switches K1 to K3 maintain the status quo and are all disconnected; when the voltages of port I and port III are restored to the set rated values, the first and second silicon carbide static transfer switches K1 and K2 are closed again, the third silicon carbide static transfer switch K3 is disconnected, and the normal working mode is entered.

[0020] S2. After entering the normal working mode, when a voltage drop at port I is detected, the second silicon carbide static transfer switch K2 is disconnected. If the voltage at port I returns to normal at this time, it means that the energy storage converter has failed and it should be cut off; if the voltage at port I still drops temporarily at this time, the first silicon carbide static transfer switch K1 is disconnected. If the voltage at port I returns to normal, it means that the load has failed and it should be cut off; if the voltage at port I still drops temporarily, it means that the grid has a voltage drop. The third silicon carbide static transfer switch K3 is closed, and the energy storage converter switches from the grid-connected mode to the off-grid mode to supply power to the load alone.

[0021] S3. According to the result of locating the fault source in step S1, the corresponding component fault is eliminated, the first and second silicon carbide static transfer switches K1 and K2 are closed, the third silicon carbide static transfer switch K3 is opened, and the normal working mode is re-entered.

[0022] S4. According to the result of fault source location in step S1, the operation mode of the energy storage converter is switched to realize grid connection / off-grid connection / removal, and switch between grid connection inverter mode and grid connection rectification mode.

[0023] Further, in step S2, determining whether a voltage sag occurs at port I includes the following:

[0024] Set the three-phase voltage u of port I A 、u B 、u C The expressions are:

[0025] u A =k1U m cosωt

[0026] u B =k2U m cos(ωt-120°)

[0027] u C =k3U m cos(ωt+120°)

[0028] Wherein, k1 represents the coefficient of the A phase voltage deviation from the rated value, k2 represents the coefficient of the B phase voltage deviation from the rated value, k3 represents the coefficient of the C phase voltage deviation from the rated value, k1,k2,k3∈[0,1]; U m represents the rated value of the phase voltage amplitude; ω represents the rated value of the grid voltage angular frequency; t represents time.

[0029] The expression of the sum of the squares of the three-phase voltages is:

[0030]

[0031] Among them, K, η, and C are all constants.

[0032] When the sum of the squares of the three-phase voltages is less than the set minimum sum of the squares of the three-phase voltages, a voltage sag occurs.

[0033] Calculate the effective values ​​of all phase voltages. When the effective values ​​of the three-phase voltages reach the set threshold and remain for the set fundamental wave period, it indicates that the voltage sag has ended and the voltage has returned to normal.

[0034] Furthermore, the calculation formula of the effective value of the phase voltage is:

[0035]

[0036] Where N represents the total number of sampled voltage values, u i Indicates the voltage value of the ith sample, URMS Indicates the effective value of the phase voltage.

[0037] Furthermore, in step S4, the operation mode switching of the energy storage converter includes the following contents:

[0038] When the full silicon carbide voltage sag control device is connected to the power grid, energy storage converter and load, if the voltage of port I and port III is the set rated value, the energy storage converter operates in the grid-connected rectification mode to charge the energy storage battery, and when the state of charge of the energy storage battery is above 80%, the energy storage converter can also operate in the grid-connected inverter mode to transmit energy to the power grid; if the voltage of port I is not the rated value, the energy storage converter operates in the off-grid inverter mode to supply power to the load; if the voltage of port III is not the rated value or the voltages of port I and port III are both non-rated values, the drive signal of the switch tube inside the energy storage converter is blocked.

[0039] When the device enters the normal working mode, the energy storage converter works in the grid-connected rectification mode; when the grid voltage sags, the energy storage converter works in the off-grid inverter mode to supply power to the load; when the grid voltage sag ends, the energy storage converter resumes the set working mode; when the energy storage converter fails or is under maintenance, the energy storage converter is cut off, and the drive signal of its internal switch tube is blocked. When the energy storage converter returns to normal, the set working mode is resumed; when the load fails, the first to third silicon carbide static transfer switches K1 to K3 are disconnected, and the energy storage converter is cut off. When the load fault is eliminated, the energy storage converter resumes the set working mode; when the load is not working, the first and third silicon carbide static transfer switches K1 and K3 are disconnected, and the second silicon carbide static transfer switch K2 is closed. According to the frequency of the grid, the energy storage converter adaptively changes the input and output power, switches between the grid-connected inverter mode and the grid-connected rectification mode, and cuts the peak and fills the valley.

[0040] Furthermore, the energy storage converter adaptively changes the input and output power including the following:

[0041] The frequency of the power grid is detected through a frequency-locked loop, and the error between the frequency and the reference frequency is calculated and input into the adaptive controller. When the power grid frequency is higher than the rated frequency, the extended state observer embedded inside it observes and adjusts the parameters according to the adaptive control law to generate an input active current reference value, and the energy storage converter switches to the grid-connected rectification mode to absorb power from the power grid; when the power grid frequency is lower than the rated frequency, the extended state observer embedded inside it observes and adjusts the parameters according to the adaptive control law to generate an output active current reference value, and the energy storage converter switches to the grid-connected inverter mode to emit power to the power grid.

[0042] Among them, the parameter vector θ(t) of the adaptive controller is:

[0043] θ(t)=[k0(t)c T(t)d T (t)d0(t)] T

[0044] Among them, k0(t), c T (t), d T (t) and d0(t) both represent the adjustable parameters of the adaptive controller.

[0045] Signal Vectors in Adaptive Controllers for:

[0046]

[0047] Among them, ω ref (t) represents the reference frequency of the input controller, u v1 (t) and u v2 (t) represents the output signal of the signal generators A1 and A2 in the controller, i p (t) represents the active current reference value.

[0048] The error between the grid frequency and the reference frequency is u (t) is:

[0049]

[0050] Among them, G m (t) represents the transfer function of the energy storage converter, and λ(t) represents the difference between each element in the parameter vector and the reference value.

[0051] Therefore, the adaptive control law is expressed as:

[0052]

[0053] Wherein, I represents the identity matrix, τ represents the τth moment, and 0≤τ≤t.

[0054] Furthermore, the mode switching includes the following:

[0055] The outer loop adopts PI control, and the desired output voltage is used as the reference value of the outer loop. It is input into the PI controller after subtracting it from the actual voltage value obtained by sampling. The output of the PI controller is used as the reference value of the inner loop state feedback control; the inner loop adopts state feedback control, and the actual values ​​of the inductor current and capacitor voltage are multiplied by the corresponding feedback coefficient and then added, and then subtracted from the output of the PI controller to obtain the modulation signal of the switch tube; the state space model of the energy storage converter is:

[0056]

[0057] Where A represents the system matrix, B represents the input matrix, D represents the perturbation matrix, E represents the output matrix, j represents the imaginary unit, and Rf Represents the equivalent series resistance of the filter inductor, L f Represents the filter inductance, C f Represents the filter capacitor, x=[i f u f ] T represents the state matrix, i f represents the inductor current, u f represents the capacitor voltage, u o Indicates the voltage of the inverter bridge output to the midpoint of the DC side capacitor, i L Indicates the grid-side current.

[0058] The control law is:

[0059] u o_ref =k p (u f_ref -u sampling )+k i ∫(u f_ref -u sampling )dt-K f x(t)

[0060] Among them, u o_ref represents the modulation signal of the switch tube, k p and k i Respectively represent the proportional coefficient and integral coefficient of the PI controller, u f_ref Indicates the output voltage reference value, u sampling Indicates the actual sampling value of the output voltage, K f represents the state feedback coefficient matrix.

[0061] When the energy storage converter is off-grid, the voltage reference value u of the grid-connected control algorithm f_ref_active is the actual sampled voltage value u sampling , the grid-connected control algorithm outputs u active 0; when connected to the grid, the voltage reference value u of the off-grid control algorithm f_ref_passive is the actual sampled voltage value u sampling , the off-grid control algorithm outputs u passive is 0; the specific expression is:

[0062]

[0063] The operation mode of the energy storage converter is switched by changing the reference values ​​of the grid-connected control algorithm and the off-grid control algorithm.

[0064] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0065] 1. The present invention can achieve millisecond-level rapid voltage sag control and effectively ensure the power supply of sensitive loads.

[0066] 2. The present invention adopts full silicon carbide MOSFET as a static switching switch, which has high voltage resistance, high speed and low cost.

[0067] 3. When any of the power grid, load or energy storage converter fails, the device proposed by the present invention can quickly cut off the fault source to prevent crosstalk.

[0068] 4. The energy storage converter contained in the present invention can adaptively adjust the peak value, reduce the peak value and fill the valley value, so as to ensure the stable operation of the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 It is the overall structural diagram of the present invention.

[0070] Figure 2 It is the actual structural diagram of the static transfer switch of the present invention.

[0071] Figure 3 It is an overall implementation flow chart of the present invention.

[0072] Figure 4 This is an example diagram of sliding window effective value calculation according to an embodiment of the present invention.

[0073] Figure 5 It is a control block diagram of an energy storage converter according to an embodiment of the present invention.

[0074] Figure 6 2 is a schematic diagram of voltage sag detection according to an embodiment of the present invention. DETAILED DESCRIPTION

[0075] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0076] To achieve the above object, the present invention proposes a full silicon carbide voltage sag control device, such as Figure 1 As shown, including:

[0077] The first to third silicon carbide static transfer switches K1 to K3, an energy storage converter, an energy storage battery and three ports Ⅰ to Ⅲ.

[0078] The first end of the first silicon carbide static transfer switch K1 and the first end of the second silicon carbide static transfer switch K2 are both connected to one side of port I, the contact end of the first silicon carbide static transfer switch K1 and the contact end of the third silicon carbide static transfer switch K3 are both connected to one side of port II, the contact end of the second silicon carbide static transfer switch K2, the first end of the third silicon carbide static transfer switch K3 and one side of the energy storage inverter are all connected to port III, the other side of the energy storage inverter is connected to the energy storage battery, the other side of port I is connected to the three-phase power grid, and the other side of port II is connected to the load.

[0079] The silicon carbide static transfer switch includes phase A, phase B and phase C, each phase includes 4 parallel branches, and each branch includes an N-channel silicon carbide MOSFET and a P-channel silicon carbide MOSFET connected in series back to back.

[0080] like Figure 2 As shown, the silicon carbide static transfer switch K x , x=1,2,3; In phase A, the first N-channel SiC MOSFETQ Ax1 The source of the second P-channel SiC MOSFETQ Ax2 The drain of the third N-channel silicon carbide MOSFETQ Ax3 The source of the fourth P-channel SiC MOSFETQ Ax4 The drain of the fifth N-channel silicon carbide MOSFETQ Ax5 The source of the sixth P-channel SiC MOSFETQ Ax6 The drain of the seventh N-channel silicon carbide MOSFETQ Ax7 The source of the eighth P-channel SiC MOSFETQ Ax8 The drain of the first N-channel silicon carbide MOSFETQ Ax1 The drain of the third N-channel silicon carbide MOSFETQ Ax3 The drain of the fifth N-channel silicon carbide MOSFETQ Ax5 The drain of the seventh N-channel SiC MOSFET Q Ax7 The drain of the A phase is connected to the A phase input terminal i ; Second P-channel SiC MOSFETQ Ax2 The source of the fourth P-channel silicon carbide MOSFETQ Ax4 The source of the sixth P-channel silicon carbide MOSFETQ Ax6 The source of the eighth P-channel SiC MOSFETQ Ax8 The source of is connected to the A phase output terminal A0.

[0081] In phase B, the ninth N-channel SiC MOSFET Q Bx1 The source of the tenth P-channel SiC MOSFETQ Bx2 The drain of the eleventh N-channel silicon carbide MOSFETQ Bx3 The source of the twelfth P-channel SiC MOSFETQ Bx4 The drain of the thirteenth N-channel silicon carbide MOSFETQ Bx5 The source of the fourteenth P-channel SiC MOSFETQ Bx6 The drain of the fifteenth N-channel silicon carbide MOSFETQBx7 The source of the sixteenth P-channel SiC MOSFETQ Bx8 The drain of the ninth N-channel silicon carbide MOSFETQ Bx1 The drain of the eleventh N-channel SiC MOSFET Q Bx3 The drain of the thirteenth N-channel silicon carbide MOSFETQ Bx5 The drain of the fifteenth N-channel SiC MOSFETQ Bx7 The drain of the B phase is connected to the B phase input terminal i ; Tenth P-channel SiC MOSFETQ Bx2 The source of the twelfth P-channel silicon carbide MOSFETQ Bx4 The source of the fourteenth P-channel silicon carbide MOSFETQ Bx6 The source of the sixteenth P-channel SiC MOSFETQ Bx8 The source of is connected and led out as the B-phase output terminal B0.

[0082] In phase C, the seventeenth N-channel SiC MOSFET Q Cx1 The source of the eighteenth P-channel SiC MOSFETQ Cx2 The drain of the nineteenth N-channel silicon carbide MOSFETQ Cx3 The source of the 20th P-channel SiC MOSFETQ Cx4 The drain of the twenty-first N-channel silicon carbide MOSFETQ Cx5 The source of the twenty-second P-channel SiC MOSFET Q Cx6 The drain of the twenty-third N-channel silicon carbide MOSFETQ Cx7 The source of the twenty-fourth P-channel silicon carbide MOSFETQ Cx8 The drain of the seventeenth N-channel silicon carbide MOSFETQ Cx1 The drain of the nineteenth N-channel silicon carbide MOSFETQ Cx3 The drain of the twenty-first N-channel SiC MOSFETQ Cx5 The drain of the twenty-third N-channel silicon carbide MOSFETQ Cx7 The drain of the C phase is connected to the C phase input terminal i ; Eighteenth P-channel silicon carbide MOSFETQ Cx2 The source of the 20th P-channel SiC MOSFETQ Cx4 The source of the twenty-second P-channel silicon carbide MOSFETQ Cx6 The source of the twenty-fourth P-channel silicon carbide MOSFETQ Cx8 The source of is connected to the C phase output terminal C0.

[0083] The energy storage converter includes a three-phase DC / AC bidirectional converter, a control unit and a human-machine interface. The topology of the three-phase DC / AC bidirectional converter is an LC-type three-phase two-level converter. The control unit includes a main control DSP, a drive circuit, a sampling circuit and a protection circuit. The human-machine interface is used to display the current parameters and working conditions of the energy storage converter.

[0084] The present invention also proposes a control method for a full silicon carbide voltage sag control device, such as Figure 3 As shown, including:

[0085] S1. Initially, the first to third silicon carbide static transfer switches K1 to K3 are all disconnected, and the voltages of ports I and III are detected. If the voltages of ports I and III are the set rated values, the first and second silicon carbide static transfer switches K1 and K2 are closed, and the third silicon carbide static transfer switch K3 is disconnected, and the normal working mode is entered; if the voltage of port I is not the rated value, indicating that a power grid failure occurs, the first and second silicon carbide static transfer switches K1 and K2 are disconnected, and the third silicon carbide static transfer switch K3 is closed; if the voltage of port III is not the rated value, It indicates that the energy storage converter fails, the first silicon carbide static transfer switch K1 is closed, the second and third silicon carbide static transfer switches K2 and K3 are disconnected, and the load is powered by the power grid; if the voltages of port I and port III are both non-rated values, it indicates that both the power grid and the energy storage converter fail, the first to third silicon carbide static transfer switches K1 to K3 maintain the status quo and are all disconnected; when the voltages of port I and port III are restored to the set rated values, the first and second silicon carbide static transfer switches K1 and K2 are closed again, the third silicon carbide static transfer switch K3 is disconnected, and the normal working mode is entered.

[0086] S2. After entering the normal working mode, when a voltage drop at port I is detected, the second silicon carbide static transfer switch K2 is disconnected. If the voltage at port I returns to normal at this time, it means that the energy storage converter has failed and it should be cut off; if the voltage at port I still drops temporarily at this time, the first silicon carbide static transfer switch K1 is disconnected. If the voltage at port I returns to normal, it means that the load has failed and it should be cut off; if the voltage at port I still drops temporarily, it means that the grid has a voltage drop. The third silicon carbide static transfer switch K3 is closed, and the energy storage converter switches from the grid-connected mode to the off-grid mode to supply power to the load alone.

[0087] Among them, judging whether a voltage sag occurs at port I includes the following contents:

[0088] Set the three-phase voltage u of port I A 、u B 、u C The expressions are:

[0089]

[0090] Wherein, k1 represents the coefficient of the A phase voltage deviation from the rated value, k2 represents the coefficient of the B phase voltage deviation from the rated value, k3 represents the coefficient of the C phase voltage deviation from the rated value, k1,k2,k3∈[0,1]; U m represents the rated value of the phase voltage amplitude; ω represents the rated value of the grid voltage angular frequency; t represents time.

[0091] The expression of the sum of the squares of the three-phase voltages is:

[0092]

[0093] Among them, K, η, and C are all constants.

[0094] From formula (2), we can see that the sum of the squares of the three-phase voltages is composed of a sinusoidal component of twice the fundamental frequency and a DC component. When the single-phase voltage drops to 90% of the normal value (single-phase voltage drops account for about 70% of all voltage drops), for example, k1 = 0.9, k2 = k3 = 1, and the sinusoidal component is -1, the sum of the squares of the three-phase voltages can achieve the minimum value, which is 1.31U m 2 Therefore, as long as the sum of the squares of the three-phase voltages is less than 1.31U m 2 The sum of the squares of the three-phase voltages is calculated once in each sampling cycle of the DSP. To avoid false operation, the values ​​calculated for 10 consecutive sampling cycles are all less than 1.31U. m 2 At the same time, the effective values ​​of all phase voltages are calculated. When the effective values ​​of the three-phase voltages reach the rated values ​​and remain at this value for 10 fundamental wave cycles, the voltage sag is considered to have ended, indicating that the voltage has returned to normal.

[0095] The traditional effective value calculation method needs one cycle to reflect the change of voltage amplitude. The present invention adopts the sliding window effective value calculation method, such as Figure 4 As shown, Figure 4 (a) shows the actual waveform of phase A power grid. Figure 4(b) shows the calculation result of the sliding window effective value of phase A voltage. It can be seen from the figure that the response speed obtained by the sliding window effective value calculation method is faster than that of the traditional effective value calculation method, and the waveform changes continuously. The specific method is as follows: define an array A of size 1000 to store voltage sampling values. Since the sampling frequency is 50kHz, there are exactly 1000 sampling data for sampling the voltage of one fundamental wave cycle (taking 50Hz as an example). When array A is full, the latest sampled voltage value will overwrite the earliest data, that is, A[0], and then the next voltage sampling value will overwrite A[1]... and so on. At the same time, the effective value U of the voltage is calculated in each sampling cycle. RMS , the specific formula is:

[0096]

[0097] Where N represents the total number of sampled voltage values, u i Indicates the voltage value of the ith sample, U RMS Indicates the effective value of the phase voltage.

[0098] S3. According to the result of locating the fault source in step S1, the corresponding component fault is eliminated, the first and second silicon carbide static transfer switches K1 and K2 are closed, the third silicon carbide static transfer switch K3 is opened, and the normal working mode is re-entered.

[0099] S4. According to the result of fault source location in step S1, the operation mode of the energy storage converter is switched to realize grid connection / off-grid connection / removal, and switch between grid connection inverter mode and grid connection rectification mode.

[0100] The operation mode switching of the energy storage converter includes the following:

[0101] When the full silicon carbide voltage sag control device is connected to the power grid, energy storage converter and load, if the voltage of port I and port III is the set rated value, the energy storage converter operates in the grid-connected rectification mode to charge the energy storage battery, and when the state of charge of the energy storage battery is above 80%, the energy storage converter can also operate in the grid-connected inverter mode to transmit energy to the power grid; if the voltage of port I is not the rated value, the energy storage converter operates in the off-grid inverter mode to supply power to the load; if the voltage of port III is not the rated value or the voltages of port I and port III are both non-rated values, the drive signal of the switch tube inside the energy storage converter is blocked.

[0102] When the device enters the normal working mode, the energy storage converter works in the grid-connected rectification mode; when the grid voltage sags, the energy storage converter works in the off-grid inverter mode to supply power to the load; when the grid voltage sag ends, the energy storage converter resumes the set working mode; when the energy storage converter fails or is under maintenance, the energy storage converter is cut off, and the drive signal of its internal switch tube is blocked. When the energy storage converter returns to normal, the set working mode is resumed; when the load fails, the first to third silicon carbide static transfer switches K1 to K3 are disconnected, and the energy storage converter is cut off. When the load fault is eliminated, the energy storage converter resumes the set working mode; when the load is not working, the first and third silicon carbide static transfer switches K1 and K3 are disconnected, and the second silicon carbide static transfer switch K2 is closed. According to the frequency of the grid, the energy storage converter adaptively changes the input and output power, switches between the grid-connected inverter mode and the grid-connected rectification mode, and cuts the peak and fills the valley.

[0103] The energy storage converter adaptively changes the input and output power including the following:

[0104] The frequency of the power grid is detected through a frequency-locked loop, and the error between the frequency and the reference frequency is calculated and input into the adaptive controller. When the power grid frequency is higher than the rated frequency, the embedded extended state observer observes and adjusts the parameters according to the adaptive control law to generate the input active current reference value, and the energy storage converter switches to the grid-connected rectification mode to absorb power from the power grid; when the power grid frequency is lower than the rated frequency, the embedded extended state observer observes and adjusts the parameters according to the adaptive control law to generate the output active current reference value, and the energy storage converter switches to the grid-connected inverter mode to send power to the power grid. The control goal is to reduce the frequency error so that the power grid frequency tends to be consistent with the reference frequency.

[0105] The design of the adaptive control law is based on the MRAC characteristics.

[0106] Among them, the parameter vector θ(t) of the adaptive controller is:

[0107] θ(t)=[k0(t)c T (t)d T (t)d0(t)] T

[0108] Among them, k0(t), c T (t), d T (t) and d0(t) both represent the adjustable parameters of the adaptive controller.

[0109] Signal Vectors in Adaptive Controllers for:

[0110]

[0111] Among them, ω ref(t) represents the reference frequency of the input controller, u v1 (t) and u v2 (t) represents the output signal of the signal generators A1 and A2 in the controller, i p (t) represents the active current reference value.

[0112] The error between the grid frequency and the reference frequency is u (t) is:

[0113]

[0114] Among them, G m (t) represents the transfer function of the energy storage converter, and λ(t) represents the difference between each element in the parameter vector and the reference value.

[0115] Therefore, the adaptive control law is expressed as:

[0116]

[0117] Wherein, I represents the identity matrix, τ represents the τth moment, and 0≤τ≤t.

[0118] Mode switching includes the following:

[0119] Take into account both steady-state accuracy and dynamic response. On the one hand, the energy storage inverter has a high output voltage steady-state accuracy, which can effectively support the grid voltage when connected to the grid, and ensure that the load works at the rated value when off the grid. On the other hand, the energy storage inverter has a fast output voltage dynamic response, which can reduce the impact current when connected to the grid, and ensure the continuity of power supply to sensitive loads when off the grid.

[0120] Control block diagram Figure 5 As shown in the figure, in order to reduce the static error in steady state, the outer loop adopts PI control, and the desired output voltage is used as the reference value of the outer loop. It is input into the PI controller after subtracting it from the actual voltage value obtained by sampling. The output of the PI controller is used as the reference value of the inner loop state feedback control; in order to achieve fast response speed in dynamic state, the inner loop adopts state feedback control, and the actual values ​​of the inductor current and capacitor voltage are multiplied by the corresponding feedback coefficient and then added, and then subtracted from the output of the PI controller to obtain the modulation signal of the switch tube; the state space model of the energy storage converter is:

[0121]

[0122] Where A represents the system matrix, B represents the input matrix, D represents the perturbation matrix, E represents the output matrix, j represents the imaginary unit, and R f Represents the equivalent series resistance of the filter inductor, L f Represents the filter inductance, C f Represents the filter capacitor, x=[i f uf ] T represents the state matrix, i f represents the inductor current, u f represents the capacitor voltage, u o Indicates the voltage of the inverter bridge output to the midpoint of the DC side capacitor, i L Indicates the grid-side current.

[0123] The control law is:

[0124] u o_ref =k p (u f_ref -u sampling )+k i ∫(u f_ref -u sampling )dt-K f x(t)(5)

[0125] Among them, u o_ref represents the modulation signal of the switch tube, k p and k i Respectively represent the proportional coefficient and integral coefficient of the PI controller, u f_ref Indicates the output voltage reference value, u sampling Indicates the actual sampling value of the output voltage, K f represents the state feedback coefficient matrix.

[0126] The off-grid control algorithm and the grid-connected control algorithm of the energy storage converter are executed simultaneously, and the sum of the outputs of the two algorithms is used as the modulation signal u. When the energy storage converter is off-grid, the voltage reference value u of the grid-connected control algorithm is f_ref_active is the actual sampled voltage value u sampling , the grid-connected control algorithm outputs u active 0; when connected to the grid, the voltage reference value u of the off-grid control algorithm f_ref_passive is the actual sampled voltage value u sampling , the off-grid control algorithm outputs u passive is 0; the specific expression is:

[0127]

[0128] The operation mode of the energy storage converter is switched by changing the reference values ​​of the grid-connected control algorithm and the off-grid control algorithm.

[0129] Figure 6 The voltage sag detection MATLAB / Simulink simulation diagram is given, where: Figure 6 (a) shows the three-phase voltage waveform of the power grid. Figure 6 (b) shows the three-phase voltage square sum waveform, Figure 6(c) shows the voltage sag detection waveform. Take the grid B phase voltage sag to 85% of the rated value as an example. When the sag occurs, the value of the sum of the squares of the three-phase voltages quickly drops to 1.31U m 2 Next, after the DSP detects it, it will set the signal to 1 and start calculating the effective value of the three-phase voltage. Therefore, the first and second silicon carbide static transfer switches K1 and K2 are disconnected, the third silicon carbide static transfer switch K3 is closed, the power grid is cut off, and the energy storage converter switches to the passive inverter mode to supply power to the load. When the effective value of the three-phase voltage returns to the rated value after 10 fundamental cycles, the signal is set to 0. Therefore, the first and second silicon carbide static transfer switches K1 and K2 are closed, the third silicon carbide static transfer switch K3 is disconnected, the energy storage converter stops supplying power to the load, and the power grid resumes supplying power to the load.

[0130] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A full silicon carbide voltage sag control device, characterized in that: include: The first to third silicon carbide static transfer switches K1 to K3, an energy storage converter, an energy storage battery and three ports Ⅰ to Ⅲ; The first end of the first silicon carbide static transfer switch K1 and the first end of the second silicon carbide static transfer switch K2 are both connected to one side of port I, the contact end of the first silicon carbide static transfer switch K1 and the contact end of the third silicon carbide static transfer switch K3 are both connected to one side of port II, the contact end of the second silicon carbide static transfer switch K2, the first end of the third silicon carbide static transfer switch K3 and one side of the energy storage converter are all connected to port III, the other side of the energy storage converter is connected to the energy storage battery, the other side of port I is connected to the three-phase power grid, and the other side of port II is connected to the load; The silicon carbide static transfer switch includes phase A, phase B and phase C, each phase includes 4 parallel branches, and each branch includes an N-channel silicon carbide MOSFET and a P-channel silicon carbide MOSFET connected in series back to back.

2. The full silicon carbide voltage sag control device according to claim 1, characterized in that: Silicon Carbide Static Transfer Switch K x , x=1,2,3; In phase A, the first N-channel SiC MOSFETQ Ax1 The source of the second P-channel SiC MOSFETQ Ax2 The drain of the third N-channel silicon carbide MOSFETQ Ax3 The source of the fourth P-channel SiC MOSFETQ Ax4 The drain of the fifth N-channel silicon carbide MOSFETQ Ax5 The source of the sixth P-channel SiC MOSFETQ Ax6 The drain of the seventh N-channel silicon carbide MOSFETQ Ax7 The source of the eighth P-channel SiC MOSFETQ Ax8 The drain of the first N-channel silicon carbide MOSFETQ Ax1 The drain of the third N-channel SiC MOSFETQ Ax3 The drain of the fifth N-channel silicon carbide MOSFETQ Ax5 The drain of the seventh N-channel SiC MOSFETQ Ax7 The drain of the A phase is connected to the A phase input terminal i ; Second P-channel SiC MOSFETQ Ax2 The source of the fourth P-channel silicon carbide MOSFETQ Ax4 The source of the sixth P-channel silicon carbide MOSFETQ Ax6 The source of the eighth P-channel SiC MOSFETQ Ax8 The source of is connected to the output terminal A0 of phase A; In phase B, the ninth N-channel SiC MOSFET Q Bx1 The source of the tenth P-channel SiC MOSFETQ Bx2 The drain of the eleventh N-channel silicon carbide MOSFETQ Bx3 The source of the twelfth P-channel SiC MOSFETQ Bx4 The drain of the thirteenth N-channel silicon carbide MOSFETQ Bx5 The source of the fourteenth P-channel SiC MOSFETQ Bx6 The drain of the fifteenth N-channel silicon carbide MOSFETQ Bx7 The source of the sixteenth P-channel SiC MOSFETQ Bx8 The drain of the ninth N-channel silicon carbide MOSFETQ Bx1 The drain of the eleventh N-channel SiC MOSFET Q Bx3 The drain of the thirteenth N-channel silicon carbide MOSFETQ Bx5 The drain of the fifteenth N-channel SiC MOSFETQ Bx7 The drain of the B phase is connected to the B phase input terminal i ; Tenth P-channel SiC MOSFETQ Bx2 The source of the twelfth P-channel silicon carbide MOSFETQ Bx4 The source of the fourteenth P-channel silicon carbide MOSFETQ Bx6 The source of the sixteenth P-channel SiC MOSFETQ Bx8 The source of is connected to the output terminal B0 of the B phase; In phase C, the seventeenth N-channel SiC MOSFET Q Cx1 The source of the eighteenth P-channel SiC MOSFETQ Cx2 The drain of the nineteenth N-channel silicon carbide MOSFETQ Cx3 The source of the 20th P-channel SiC MOSFETQ Cx4 The drain of the twenty-first N-channel silicon carbide MOSFETQ Cx5 The source of the twenty-second P-channel SiC MOSFET Q Cx6 The drain of the twenty-third N-channel silicon carbide MOSFETQ Cx7 The source of the twenty-fourth P-channel silicon carbide MOSFETQ Cx8 The drain of the seventeenth N-channel silicon carbide MOSFETQ Cx1 The drain of the nineteenth N-channel silicon carbide MOSFETQ Cx3 The drain of the twenty-first N-channel SiC MOSFETQ Cx5 The drain of the twenty-third N-channel silicon carbide MOSFETQ Cx7 The drain of the C phase is connected to the C phase input terminal i ; Eighteenth P-channel silicon carbide MOSFETQ Cx2 The source of the 20th P-channel SiC MOSFETQ Cx4 The source of the twenty-second P-channel silicon carbide MOSFETQ Cx6 The source of the twenty-fourth P-channel silicon carbide MOSFETQ Cx8 The source of is connected to the C phase output terminal C0.

3. The full silicon carbide voltage sag control device according to claim 1, characterized in that: The energy storage converter includes a three-phase DC / AC bidirectional converter, a control unit and a human-machine interface. The topology of the three-phase DC / AC bidirectional converter is an LC-type three-phase two-level converter. The control unit includes a main control DSP, a drive circuit, a sampling circuit and a protection circuit. The human-machine interface is used to display the current parameters and working conditions of the energy storage converter.

4. The control method applied to the full silicon carbide voltage sag control device according to claim 1, characterized in that: include: S1. Initially, the first to third silicon carbide static transfer switches K1 to K3 are all disconnected, and the voltages of ports I and III are detected. If the voltages of ports I and III are the set rated values, the first and second silicon carbide static transfer switches K1 and K2 are closed, and the third silicon carbide static transfer switch K3 is disconnected, and the normal working mode is entered; if the voltage of port I is not the rated value, indicating that a power grid failure occurs, the first and second silicon carbide static transfer switches K1 and K2 are disconnected, and the third silicon carbide static transfer switch K3 is closed; if the voltage of port III is not the rated value, It indicates that the energy storage converter fails, the first silicon carbide static transfer switch K1 is closed, the second and third silicon carbide static transfer switches K2 and K3 are disconnected, and the load is powered by the power grid; if the voltages of port I and port III are both non-rated values, it indicates that both the power grid and the energy storage converter fail, the first to third silicon carbide static transfer switches K1 to K3 maintain the status quo and are all disconnected; when the voltages of port I and port III are restored to the set rated values, the first and second silicon carbide static transfer switches K1 and K2 are closed again, the third silicon carbide static transfer switch K3 is disconnected, and the normal working mode is entered; S2, after entering the normal working mode, when the voltage of port I is detected to be temporarily reduced, the second silicon carbide static transfer switch K2 is disconnected. If the voltage of port I returns to normal at this time, it means that the energy storage converter has a fault and it is removed; If the voltage at port I still drops temporarily at this time, disconnect the first silicon carbide static transfer switch K1. If the voltage at port I returns to normal, it means that the load has failed and it should be removed. If the voltage at port I still drops temporarily, it means that the grid voltage drops temporarily. The third silicon carbide static transfer switch K3 is closed, and the energy storage converter switches from the grid-connected mode to the off-grid mode to supply power to the load alone. S3, according to the result of locating the fault source in step S1, troubleshoot the corresponding component faults, close the first and second silicon carbide static transfer switches K1 and K2, and open the third silicon carbide static transfer switch K3, and re-enter the normal working mode; S4. According to the result of fault source location in step S1, the operation mode of the energy storage converter is switched to realize grid connection / off-grid connection / removal, and switch between grid connection inverter mode and grid connection rectification mode.

5. The control method of the full silicon carbide voltage sag control device according to claim 4, characterized in that: In step S2, determining whether a voltage sag occurs at port I includes the following: Set the three-phase voltage u of port I A 、u B 、u C The expressions are: u A =k1U m cosωt u B =k2U m cos(ωt−120°) you C =k3U m cos(ωt+120°) Wherein, k1 represents the coefficient of the A phase voltage deviation from the rated value, k2 represents the coefficient of the B phase voltage deviation from the rated value, k3 represents the coefficient of the C phase voltage deviation from the rated value, k1,k2,k3∈[0,1]; U m represents the rated value of the phase voltage amplitude; ω represents the rated value of the grid voltage angular frequency; t represents time; The expression of the sum of the squares of the three-phase voltages is: Among them, K, η, and C are all constants. When the sum of the squares of the three-phase voltages is less than the set minimum sum of the squares of the three-phase voltages, a voltage sag occurs; Calculate the effective values ​​of all phase voltages. When the effective values ​​of the three-phase voltages reach the set threshold and remain for the set fundamental wave period, it indicates that the voltage sag has ended and the voltage has returned to normal.

6. The control method of the full silicon carbide voltage sag control device according to claim 5, characterized in that: The calculation formula for the effective value of the phase voltage is: Where N represents the total number of sampled voltage values, u i Indicates the voltage value of the ith sample, U RMS Indicates the effective value of the phase voltage.

7. The control method of the full silicon carbide voltage sag control device according to claim 4, characterized in that: In step S4, the operation mode switching of the energy storage converter includes the following contents: When the full silicon carbide voltage sag control device is connected to the power grid, energy storage converter and load, if the voltage of port I and port III is the set rated value, the energy storage converter works in the grid-connected rectification mode to charge the energy storage battery, and when the state of charge of the energy storage battery is above 80%, the energy storage converter can also work in the grid-connected inverter mode to transmit energy to the power grid; if the voltage of port I is not the rated value, the energy storage converter works in the off-grid inverter mode to supply power to the load; if the voltage of port III is not the rated value or the voltages of port I and port III are both not the rated value, the drive signal of the switch tube inside the energy storage converter is blocked; When the device enters the normal working mode, the energy storage converter works in the grid-connected rectification mode; when the grid voltage sags, the energy storage converter works in the off-grid inverter mode to supply power to the load; when the grid voltage sag ends, the energy storage converter resumes the set working mode; when the energy storage converter fails or is under maintenance, the energy storage converter is cut off, and the drive signal of its internal switch tube is blocked. When the energy storage converter returns to normal, the set working mode is resumed; when the load fails, the first to third silicon carbide static transfer switches K1 to K3 are disconnected, and the energy storage converter is cut off. When the load fault is eliminated, the energy storage converter resumes the set working mode; when the load is not working, the first and third silicon carbide static transfer switches K1 and K3 are disconnected, and the second silicon carbide static transfer switch K2 is closed. According to the frequency of the grid, the energy storage converter adaptively changes the input and output power, switches between the grid-connected inverter mode and the grid-connected rectification mode, and cuts the peak and fills the valley.

8. The control method of the full silicon carbide voltage sag control device according to claim 7, characterized in that: The energy storage converter adaptively changes the input and output power including the following: The frequency of the power grid is detected through a frequency-locked loop, and the error between the frequency and the reference frequency is calculated and input into the adaptive controller. When the power grid frequency is higher than the rated frequency, the extended state observer embedded inside it observes and adjusts the parameters according to the adaptive control law to generate the input active current reference value, and the energy storage converter switches to the grid-connected rectification mode to absorb power from the power grid; when the power grid frequency is lower than the rated frequency, the extended state observer embedded inside it observes and adjusts the parameters according to the adaptive control law to generate the output active current reference value, and the energy storage converter switches to the grid-connected inverter mode to send power to the power grid; Among them, the parameter vector θ(t) of the adaptive controller is: θ(t)=[k0(t)c T (t)d T (t)d0(t)] T Among them, k0(t), c T (t), d T (t) and d0(t) both represent the adjustable parameters of the adaptive controller; Signal Vectors in Adaptive Controllers for: Among them, ω ref (t) represents the reference frequency of the input controller, u v1 (t) and u v2 (t) represents the output signal of the signal generators A1 and A2 in the controller, i p (t) represents the active current reference value; The error between the grid frequency and the reference frequency is u (t) is: Among them, G m (t) represents the transfer function of the energy storage converter, λ(t) represents the difference between each element in the parameter vector and the reference value; Therefore, the adaptive control law is expressed as: Wherein, I represents the identity matrix, τ represents the τth moment, and 0≤τ≤t.

9. The control method of the full silicon carbide voltage sag control device according to claim 7, characterized in that: Mode switching includes the following: The outer loop adopts PI control, and the desired output voltage is used as the reference value of the outer loop. It is input into the PI controller after subtracting it from the actual voltage value obtained by sampling. The output of the PI controller is used as the reference value of the inner loop state feedback control; the inner loop adopts state feedback control, and the actual values ​​of the inductor current and capacitor voltage are multiplied by the corresponding feedback coefficient and then added, and then subtracted from the output of the PI controller to obtain the modulation signal of the switch tube; the state space model of the energy storage converter is: Where A represents the system matrix, B represents the input matrix, D represents the disturbance matrix, E represents the output matrix, j represents the imaginary unit, ω represents the rated value of the grid voltage angular frequency, and R f Represents the equivalent series resistance of the filter inductor, L f Represents the filter inductance, C f Represents the filter capacitor, x=[i f u f ] T represents the state matrix, i f represents the inductor current, u f represents the capacitor voltage, u o Indicates the voltage of the inverter bridge output to the midpoint of the DC side capacitor, i L represents the grid-side current, and t represents the time; The control law is: u o_ref =k p (u f_ref -u sampling )+k i ∫(u f_ref -u sampling )dt-K f x(t) Among them, u o_ref represents the modulation signal of the switch tube, k p and k i Respectively represent the proportional coefficient and integral coefficient of the PI controller, u f_ref Indicates the output voltage reference value, u sampling Indicates the actual sampling value of the output voltage, K f represents the state feedback coefficient matrix; When the energy storage converter is off-grid, the voltage reference value u of the grid-connected control algorithm f_ref_active is the actual sampled voltage value u sampling , the grid-connected control algorithm outputs u active 0; when connected to the grid, the voltage reference value u of the off-grid control algorithm f_ref_passive is the actual sampled voltage value u sampling , the off-grid control algorithm outputs u passive is 0; the specific expression is: The operation mode of the energy storage converter is switched by changing the reference values ​​of the grid-connected control algorithm and the off-grid control algorithm.

Images