A full silicon carbide voltage sag control device and control method

Abstract

The present invention discloses a full silicon carbide voltage sag control device and control method, the device includes the first to third silicon carbide static switching switches K1 to K3, an energy storage converter, an energy storage battery and three ports Ⅰ to Ⅲ; using the device, the voltage state of the port is detected to locate and control the fault source of the voltage sag, and the energy storage converter is connected to the grid / off the grid / removed according to actual needs through an off-grid control algorithm and a grid-connected control algorithm to achieve rectification / inversion mode conversion, and the input and output power are adaptively adjusted according to the change of the grid frequency to achieve bidirectional energy flow and peak shaving and valley filling. The present invention has low cost, can achieve rapid voltage sag control with a response time of milliseconds, can effectively guarantee the power supply of sensitive loads when the grid fails, and the energy storage converter has an adaptive peak-shaving function, which has certain practical value.

Description

Technical Field

[0001] The present invention relates to the technical field of voltage sag mitigation, and particularly to a fully silicon carbide voltage sag mitigation device and a control method therefor. Background Art

[0002] Voltage sag refers to the phenomenon that the root mean square value of the power frequency voltage at a certain point in the power system suddenly drops to 0.1 p.u. - 0.9 p.u. and returns to normal after a short duration of 10 ms - 1 min. Voltage sag is a relatively common problem in power quality, which will have a negative impact on sensitive loads. Voltage sags include single-phase sags, two-phase sags, and three-phase sags. When a voltage sag occurs, this phenomenon may trigger the under-voltage protection of the equipment or directly cause the equipment to stop running, resulting in direct or indirect economic losses.

[0003] The reasons for voltage sags can be classified into the following three categories:

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

[0005] (2) Starting of large loads: When large power equipment such as large motors and transformers starts, it will cause a sharp increase in the grid current, resulting in a voltage sag at the common node.

[0006] (3) Natural factors such as lightning strikes: Disturbances to the power system under lightning or adverse weather conditions will also trigger voltage sags. Lightning may cause voltage surges on overhead lines, thereby affecting the voltage level in the system.

[0007] There are mainly three types of power electronic devices for governing voltage sags: UPS (Uninterruptible Power Supply), UPQC (Unified Power Quality Conditioner), and DVR (Dynamic Voltage Restorer). All these three types of devices can handle voltage sags well, but each has its drawbacks. The inverter in the UPS is always in operation, which can ensure that the power supply quality on the load side is not affected by the grid voltage sag. However, it reduces the system efficiency, and the long-term operation requires high reliability of the inverter. The UPQC compensates for the grid voltage sag by adjusting the output voltage of the series converter to maintain the stability of the load-side voltage. However, the UPQC can not only govern voltage sags but also deal with grid harmonic currents. Its control method is complex and the cost is high, which is overkill for scenarios that only require voltage sag governance. The DVR device is connected in series between the grid and the load through passive devices such as transformers or filter capacitors. By compensating the difference between the actual grid voltage and the ideal grid voltage, it ensures the reliable operation of the load. However, the DVR requires a high-power transformer, increasing the cost of the device. Summary of the Invention

[0008] The object of the present invention is to provide a fully silicon carbide voltage sag governance device and control method. The device uses fully silicon carbide MOSFETs as static transfer switches, which are low-cost and fast, and can achieve fast voltage sag governance with a response time in the millisecond level; the energy storage converter has an adaptive peak shaving function and can achieve bidirectional energy flow to smooth out the power peaks and valleys.

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

[0010] A fully silicon carbide voltage sag governance device includes:

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

[0012] The first ends of the first silicon carbide static transfer switch K1 and the second silicon carbide static transfer switch K2 are both connected to one side of port Ⅰ. The contact ends of the first silicon carbide static transfer switch K1 and 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 grid, and the other side of port Ⅱ is connected to the load.

[0013] Among them, the silicon carbide static transfer switch includes three phases: phase A, phase B, and phase C. Each phase includes 4 parallel branches, and each branch includes a N-channel silicon carbide MOSFET and a P-channel silicon carbide MOSFET connected in series back-to-back.

[0014] Furthermore, the silicon carbide static transfer switch K x , where x = 1, 2, 3; in phase A, the source of the first N-channel silicon carbide MOSFET Q Ax1 is connected to the drain of the second P-channel silicon carbide MOSFET Q Ax2 ; the source of the third N-channel silicon carbide MOSFET Q Ax3 is connected to the drain of the fourth P-channel silicon carbide MOSFET Q Ax4 ; the source of the fifth N-channel silicon carbide MOSFET Q Ax5 is connected to the drain of the sixth P-channel silicon carbide MOSFET Q Ax6 ; the source of the seventh N-channel silicon carbide MOSFET Q Ax7 is connected to the drain of the eighth P-channel silicon carbide MOSFET Q Ax8 ; the drain of the first N-channel silicon carbide MOSFET Q Ax1 , the drain of the third N-channel silicon carbide MOSFET Q Ax3 , and the drain of the fifth N-channel silicon carbide MOSFET Q Ax5 are all connected to the drain of the seventh N-channel silicon carbide MOSFET Q Ax7 , which is led out as the input terminal A of phase A i ; the source of the second P-channel silicon carbide MOSFET Q Ax2 , the source of the fourth P-channel silicon carbide MOSFET Q Ax4 , and the source of the sixth P-channel silicon carbide MOSFET Q Ax6 are all connected to the source of the eighth P-channel silicon carbide MOSFET Q Ax8 , which is led out as the output terminal A0 of phase A.

[0015] In phase B, the source of the ninth N-channel silicon carbide MOSFET Q Bx1 is connected to the drain of the tenth P-channel silicon carbide MOSFET Q Bx2 ; the source of the eleventh N-channel silicon carbide MOSFET Q Bx3 is connected to the drain of the twelfth P-channel silicon carbide MOSFET Q Bx4 ; the source of the thirteenth N-channel silicon carbide MOSFET Q Bx5 is connected to the drain of the fourteenth P-channel silicon carbide MOSFET Q Bx6 ; the source of the fifteenth N-channel silicon carbide MOSFET Q Bx7 is connected to the drain of the sixteenth P-channel silicon carbide MOSFET Q Bx8is connected to the drain; the ninth N-channel silicon carbide MOSFET Q Bx1 the drain of, the eleventh N-channel silicon carbide MOSFET Q Bx3 the drain of, the thirteenth N-channel silicon carbide MOSFET Q Bx5 the drains of are all connected to the drain of the fifteenth N-channel silicon carbide MOSFET Q Bx7 and led out as the B-phase input terminal B i ; the tenth P-channel silicon carbide MOSFET Q Bx2 the source of, the twelfth P-channel silicon carbide MOSFET Q Bx4 the source of, the fourteenth P-channel silicon carbide MOSFET Q Bx6 the sources of are all connected to the source of the sixteenth P-channel silicon carbide MOSFET Q Bx8 and led out as the B-phase output terminal B0.

[0016] In the C phase, the source of the seventeenth N-channel silicon carbide MOSFET Q Cx1 is connected to the drain of the eighteenth P-channel silicon carbide MOSFET Q Cx2 ; the source of the nineteenth N-channel silicon carbide MOSFET Q Cx3 is connected to the drain of the twentieth P-channel silicon carbide MOSFET Q Cx4 ; the source of the twenty-first N-channel silicon carbide MOSFET Q Cx5 is connected to the drain of the twenty-second P-channel silicon carbide MOSFET Q Cx6 ; the source of the twenty-third N-channel silicon carbide MOSFET Q Cx7 is connected to the drain of the twenty-fourth P-channel silicon carbide MOSFET Q Cx8 ; the source of the seventeenth N-channel silicon carbide MOSFET Q Cx1 the drain of, the drain of the nineteenth N-channel silicon carbide MOSFET Q Cx3 the drain of, the drain of the twenty-first N-channel silicon carbide MOSFET Q Cx5 are all connected to the drain of the twenty-third N-channel silicon carbide MOSFET Q Cx7 and led out as the C-phase input terminal C i ; the source of the eighteenth P-channel silicon carbide MOSFET Q Cx2 the source of, the source of the twentieth P-channel silicon carbide MOSFET Q Cx4 the source of, the source of the twenty-second P-channel silicon carbide MOSFET Q Cx6 are all connected to the source of the twenty-fourth P-channel silicon carbide MOSFET Q Cx8 and led out as 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, switch the operation mode of the energy storage converter to achieve grid connection / off-grid / disconnection, and switch between grid-connected inverter mode and grid-connected rectifier mode.

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

[0024] Set the expressions of the three-phase voltages u A 、u B 、u C to be respectively:

[0025] u A =k1U m cosωt

[0026] u B =k2U m cos(ωt - 120°)

[0027] u C =k3U m cos(ωt + 120°)

[0028] where 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, and 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] where K, η, and C all represent 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 all reach the set threshold and remain for the set number of fundamental periods, it indicates that the voltage sag ends and the voltage returns to normal.

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

[0035]

[0036] where N represents the total number of sampled voltage values, u i represents the i-th sampled voltage value, 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) all represent the adjustable parameters of the adaptive controller.

[0045] The signal vector in the adaptive controller is:

[0046]

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

[0048] The error e u (t) between the grid frequency and the reference frequency 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] Among them, I represents the identity matrix, τ represents the τ-th moment, 0 ≤ τ ≤ t.

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

[0055] The outer loop adopts PI control, takes the desired output voltage as the reference value of the outer loop, subtracts the actually sampled voltage value from it and inputs it into the PI controller, and 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, multiplies the actual values of the inductor current and the capacitor voltage by the corresponding feedback coefficients and then adds them, and then subtracts the output of the PI controller to obtain the modulation signal of the switching tube; the state space model of the energy storage converter is:

[0056]

[0057] Among them, 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, Rf Denotes the equivalent series resistance of the filtering inductor, L f Denotes the filtering inductor, C f Denotes the filtering capacitor, x = [i f u f T Denotes the state matrix, i f Denotes the inductor current, u f Denotes the capacitor voltage, u o Denotes the voltage of the output of the inverter bridge to the midpoint of the DC-side capacitor, i L Denotes 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] Wherein, u o_ref Denotes the modulation signal of the switching tube, k p And k i Respectively denote the proportional coefficient and the integral coefficient of the PI controller, u f_ref Denotes the output voltage reference value, u sampling Denotes the actual sampled value of the output voltage, K f Denotes the state feedback coefficient matrix.

[0061] When the energy storage converter operates off-grid, the voltage reference value u f_ref_active Of the grid-connection control algorithm is the actually sampled voltage value u sampling , And the output u active Of the grid-connection control algorithm is 0; when operating in grid connection, the voltage reference value u f_ref_passive Of the off-grid control algorithm is the actually sampled voltage value u sampling , And the output u passive Of the off-grid control algorithm is 0; the specific expression is:

[0062]

[0063] By changing the reference values of the grid-connection control algorithm and the off-grid control algorithm, the operation mode of the energy storage converter is switched.

[0064] Compared with the prior art by adopting the above technical solutions, the present invention has the following technical effects:

[0065] 1. The present invention can achieve fast voltage sag governance at the millisecond level and effectively guarantee 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] Among them, the silicon carbide static transfer switch includes three phases of A, B, and C. Each phase includes 4 parallel branches, and each branch includes a N-channel silicon carbide MOSFET and a P-channel silicon carbide MOSFET connected in series back-to-back.

[0080] As Figure 2 shown, the silicon carbide static transfer switch K x , where x = 1, 2, 3; in phase A, the source of the first N-channel silicon carbide MOSFET Q Ax1 is connected to the drain of the second P-channel silicon carbide MOSFET Q Ax2 ; the source of the third N-channel silicon carbide MOSFET Q Ax3 is connected to the drain of the fourth P-channel silicon carbide MOSFET Q Ax4 ; the source of the fifth N-channel silicon carbide MOSFET Q Ax5 is connected to the drain of the sixth P-channel silicon carbide MOSFET Q Ax6 ; the source of the seventh N-channel silicon carbide MOSFET Q Ax7 is connected to the drain of the eighth P-channel silicon carbide MOSFET Q Ax8 ; the drains of the first N-channel silicon carbide MOSFET Q Ax1 , the third N-channel silicon carbide MOSFET Q Ax3 , and the fifth N-channel silicon carbide MOSFET Q Ax5 are all connected to the drain of the seventh N-channel silicon carbide MOSFET Q Ax7 , and are led out as the input terminal A i of phase A; the sources of the second P-channel silicon carbide MOSFET Q Ax2 , the fourth P-channel silicon carbide MOSFET Q Ax4 , and the sixth P-channel silicon carbide MOSFET Q Ax6 are all connected to the source of the eighth P-channel silicon carbide MOSFET Q Ax8 , and are led out as the output terminal A0 of phase A.

[0081] In phase B, the source of the ninth N-channel silicon carbide MOSFET Q Bx1 is connected to the drain of the tenth P-channel silicon carbide MOSFET Q Bx2 ; the source of the eleventh N-channel silicon carbide MOSFET Q Bx3 is connected to the drain of the twelfth P-channel silicon carbide MOSFET Q Bx4 ; the source of the thirteenth N-channel silicon carbide MOSFET Q Bx5 is connected to the drain of the fourteenth P-channel silicon carbide MOSFET Q Bx6 ; the source of the fifteenth N-channel silicon carbide MOSFET QBx7 The source of Bx8 is connected to the drain of the sixteenth P-channel silicon carbide MOSFET Q Bx1 ; The drain of the ninth N-channel silicon carbide MOSFET Q Bx3 , the drain of the eleventh N-channel silicon carbide MOSFET Q Bx5 , and the drain of the thirteenth N-channel silicon carbide MOSFET Q Bx7 are all connected to the drain of the fifteenth N-channel silicon carbide MOSFET Q i and led out as the B-phase input terminal B Bx2 ; The source of the tenth P-channel silicon carbide MOSFET Q Bx4 , the source of the twelfth P-channel silicon carbide MOSFET Q Bx6 , and the source of the fourteenth P-channel silicon carbide MOSFET Q Bx8 are all connected to the source of the sixteenth P-channel silicon carbide MOSFET Q

[0082]

[0082] Cx1 In the C phase, the source of the seventeenth N-channel silicon carbide MOSFET Q Cx2 is connected to the drain of the eighteenth P-channel silicon carbide MOSFET Q Cx3 ; The source of the nineteenth N-channel silicon carbide MOSFET Q Cx4 is connected to the drain of the twentieth P-channel silicon carbide MOSFET Q Cx5 ; The source of the twenty-first N-channel silicon carbide MOSFET Q Cx6 is connected to the drain of the twenty-second P-channel silicon carbide MOSFET Q Cx7 ; The source of the twenty-third N-channel silicon carbide MOSFET Q Cx8 is connected to the drain of the twenty-fourth P-channel silicon carbide MOSFET Q Cx1 ; The drain of the seventeenth N-channel silicon carbide MOSFET Q Cx3 , the drain of the nineteenth N-channel silicon carbide MOSFET Q Cx5 , and the drain of the twenty-first N-channel silicon carbide MOSFET Q Cx7 are all connected to the drain of the twenty-third N-channel silicon carbide MOSFET Q i and led out as the C-phase input terminal C Cx2 ; The source of the eighteenth P-channel silicon carbide MOSFET Q Cx4 , the source of the twentieth P-channel silicon carbide MOSFET Q Cx6 , and the source of the twenty-second P-channel silicon carbide MOSFET Q Cx8 are all connected to the source of the twenty-fourth P-channel silicon carbide MOSFET Q

[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] Among them, k1 represents the coefficient of the deviation of the phase A voltage from the rated value, k2 represents the coefficient of the deviation of the phase B voltage from the rated value, k3 represents the coefficient of the deviation of the phase C voltage from the rated value, and 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 for the sum of the squares of the three-phase voltages is:

[0092]

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

[0094] It can be seen from formula (2) that the sum of the squares of the three-phase voltages consists of a sinusoidal component and a DC component at twice the fundamental frequency. When the single-phase voltage drops to 90% of the normal value (single-phase voltage sags account for about 70% of all voltage sag events), 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 obtain the minimum value, and the minimum value 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 , it is considered that a voltage sag has occurred. Calculate the sum of the squares of the three-phase voltages once in each sampling period of the DSP. To avoid misoperation, if the values calculated in 10 consecutive sampling periods are all less than 1.31U m 2 , it is determined that a voltage sag has occurred. At the same time, start calculating the effective values of all phase voltages. Until the effective values of the three-phase voltages all reach the rated value and remain for 10 fundamental periods, it is considered that the voltage sag has ended, indicating that the voltage has returned to normal.

[0095] The traditional effective value calculation method takes one period to reflect the change in the voltage amplitude. In the present invention, a sliding window effective value calculation method is adopted. As Figure 4 shown, Figure 4 (a) of 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 contents:

[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 operates in the grid-connected rectification mode; when a voltage sag occurs in the power grid, the energy storage converter operates in the off-grid inversion mode to supply power to the load; when the voltage sag in the power grid 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 disconnected, and the drive signals of the internal switching tubes are blocked. When the energy storage converter returns to normal, the set working mode is restored; when a load fault occurs, the first to third silicon carbide static transfer switches K1 to K3 are disconnected to cut off the energy storage converter. 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. The energy storage converter adaptively changes the input and output power according to the frequency of the power grid and switches between the grid-connected inversion mode and the grid-connected rectification mode to smooth out the peaks and fill in the valleys.

[0103] The energy storage converter adaptively changing the input and output power includes the following:

[0104] The frequency of the power grid is detected by a frequency-locked loop, the error between this 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 internally embedded extended state observer in it observes and adjusts the parameters according to the adaptive control law to generate the reference value of the input active current, 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 internally embedded extended state observer in it observes and adjusts the parameters according to the adaptive control law to generate the reference value of the output active current, and the energy storage converter switches to the grid-connected inversion mode to send power to the power grid. The control objective is to reduce the frequency error and make the frequency of the power grid tend to be consistent with the reference frequency.

[0105] The design basis of the adaptive control law is the MRAC characteristic.

[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) all represent the adjustable parameters of the adaptive controller.

[0109] The signal vector in the adaptive controller is:

[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 signals of signal generators A1 and A2 in the controller, i p (t) represents the reference value of the active current.

[0112] The error e u (t) between the grid frequency and the reference frequency 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] Among them, I represents the identity matrix, τ represents the τ-th moment, 0 ≤ τ ≤ t.

[0118] The mode switching includes the following:

[0119] Taking into account both the steady-state accuracy and the dynamic response. On the one hand, the steady-state accuracy of the output voltage of the energy storage converter is relatively high. When connected to the grid, it can effectively support the grid voltage, and when off-grid, it can ensure that the load operates at the rated value. On the other hand, the dynamic response of the output voltage of the energy storage converter is fast. When connected to the grid, it can reduce the inrush current, and when off-grid, it can ensure the continuity of power supply for sensitive loads.

[0120] The control block diagram is as Figure 5 shown. In order to have a small static error in the steady state, the outer loop uses PI control. The desired output voltage is used as the reference value of the outer loop. After subtracting the actually sampled voltage value from it, the result is input into the PI controller. The output of the PI controller is used as the reference value of the inner loop state feedback control. In order to have a fast response speed in the dynamic state, the inner loop uses state feedback control. The actual values of the inductor current and the capacitor voltage are multiplied by the corresponding feedback coefficients and then added together, and then the difference is taken with the output of the PI controller to obtain the modulation signal of the switching tube. The state space model of the energy storage converter is:

[0121]

[0122] Among them, 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, R f represents the equivalent series resistance of the filter inductor, L f represents the filter inductor, 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 represents the voltage of the output of the inverter bridge with respect to the midpoint of the DC-side capacitor, i L represents 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 represents the output voltage reference value, u sampling represents the actual sampled value of the output voltage, K f represents the state feedback coefficient matrix.

[0126] The off-grid control algorithm and 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 operates off-grid, the voltage reference value u f_ref_active of the grid-connected control algorithm is the actually sampled voltage value u sampling , and the output u active of the grid-connected control algorithm is 0; when operating grid-connected, the voltage reference value u f_ref_passive of the off-grid control algorithm is the actually sampled voltage value u sampling , and the output u passive of the off-grid control algorithm is 0; the specific expression is:

[0127]

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

[0129] Figure 6 The MATLAB / Simulink simulation diagram of voltage sag detection is given, where Figure 6 (a) shows the three-phase grid voltage waveform, Figure 6 (b) shows the waveform of the sum of the squares of the three-phase voltages, Figure 6 ​(c) shows the voltage sag detection waveform. Taking the voltage of phase B of the power grid sagging to 85% of the rated value as an example. After the sag occurs, the value of the sum of the squares of the three-phase voltages drops rapidly to 1.31U m 2 Hereinafter, after the DSP detects it, it sets the occurrence signal to 1 and simultaneously starts to calculate the effective values of the three-phase voltages. Therefore, 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. The power grid is cut off, and the energy storage converter is switched to the passive inverter mode to supply power to the load. When the effective values of the three-phase voltages recover to the rated value after 10 fundamental wave periods, the occurrence signal is set to 0. Therefore, 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. The energy storage converter stops supplying power to the load, and the power grid resumes supplying power to the load.

[0130] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and deformations can still be made, and these improvements and deformations should also be regarded as the protection scope of the present invention.

Claims

1. A full silicon carbide voltage sag control device, characterized in that: Comprising: 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 ends of the first silicon carbide static transfer switch K1 and the second silicon carbide static transfer switch K2 are both connected to one side of port I. The contact ends of the first silicon carbide static transfer switch K1 and 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. The other side of port II is connected to the load; Wherein, the silicon carbide static transfer switch includes a phase A, a phase B, and a phase C. Each phase includes 4 parallel branches. Each branch includes a back-to-back series connection of an N-channel silicon carbide MOSFET and a P-channel silicon carbide MOSFET. Specifically: Silicon carbide static transfer switch K x , x = 1, 2, 3; in phase A, the source of the first N-channel silicon carbide MOSFET Q Ax1 is connected to the drain of the second P-channel silicon carbide MOSFET Q Ax2 ; the source of the third N-channel silicon carbide MOSFET Q Ax3 is connected to the drain of the fourth P-channel silicon carbide MOSFET Q Ax4 ; the source of the fifth N-channel silicon carbide MOSFET Q Ax5 is connected to the drain of the sixth P-channel silicon carbide MOSFET Q Ax6 ; the source of the seventh N-channel silicon carbide MOSFET Q Ax7 is connected to the drain of the eighth P-channel silicon carbide MOSFET Q Ax8 ; the drain of the first N-channel silicon carbide MOSFET Q Ax1 , the drain of the third N-channel silicon carbide MOSFET Q Ax3 , the drain of the fifth N-channel silicon carbide MOSFET Q Ax5 are all connected to the drain of the seventh N-channel silicon carbide MOSFET Q Ax7 , and led out as the in-phase A input terminal A i ; the source of the second P-channel silicon carbide MOSFET Q Ax2 , the source of the fourth P-channel silicon carbide MOSFET Q Ax4 , the source of the sixth P-channel silicon carbide MOSFET Q Ax6 are all connected to the source of the eighth P-channel silicon carbide MOSFET Q Ax8 , and led out as the in-phase A output terminal A0; In phase B, the source of the ninth N-channel silicon carbide MOSFET Q Bx1 is connected to the drain of the tenth P-channel silicon carbide MOSFET Q Bx2 ; the source of the eleventh N-channel silicon carbide MOSFET Q Bx3 is connected to the drain of the twelfth P-channel silicon carbide MOSFET Q Bx4 ; the source of the thirteenth N-channel silicon carbide MOSFET Q Bx5 is connected to the drain of the fourteenth P-channel silicon carbide MOSFET Q Bx6 ; the source of the fifteenth N-channel silicon carbide MOSFET Q Bx7 is connected to the drain of the sixteenth P-channel silicon carbide MOSFET Q Bx8 ; the drains of the ninth N-channel silicon carbide MOSFET Q Bx1 , the eleventh N-channel silicon carbide MOSFET Q Bx3 , and the thirteenth N-channel silicon carbide MOSFET Q Bx5 are all connected to the drain of the fifteenth N-channel silicon carbide MOSFET Q Bx7 , and are led out as the B-phase input terminal B i ; the sources of the tenth P-channel silicon carbide MOSFET Q Bx2 , the twelfth P-channel silicon carbide MOSFET Q Bx4 , and the fourteenth P-channel silicon carbide MOSFET Q Bx6 are all connected to the source of the sixteenth P-channel silicon carbide MOSFET Q Bx8 , and are led out as the B-phase output terminal B0; In phase C, the source of the seventeenth N-channel silicon carbide MOSFET Q Cx1 is connected to the drain of the eighteenth P-channel silicon carbide MOSFET Q Cx2 ; the source of the nineteenth N-channel silicon carbide MOSFET Q Cx3 is connected to the drain of the twentieth P-channel silicon carbide MOSFET Q Cx4 ; the source of the twenty-first N-channel silicon carbide MOSFET Q Cx5 is connected to the drain of the twenty-second P-channel silicon carbide MOSFET Q Cx6 ; the source of the twenty-third N-channel silicon carbide MOSFET Q Cx7 is connected to the drain of the twenty-fourth P-channel silicon carbide MOSFET Q Cx8 ; the drains of the seventeenth N-channel silicon carbide MOSFET Q Cx1 , the nineteenth N-channel silicon carbide MOSFET Q Cx3 , and the twenty-first N-channel silicon carbide MOSFET Q Cx5 are all connected to the drain of the twenty-third N-channel silicon carbide MOSFET Q Cx7 , and the connection is led out as the C-phase input terminal C i ; the sources of the eighteenth P-channel silicon carbide MOSFET Q Cx2 , the twentieth P-channel silicon carbide MOSFET Q Cx4 , and the twenty-second P-channel silicon carbide MOSFET Q Cx6 are all connected to the source of the twenty-fourth P-channel silicon carbide MOSFET Q Cx8 , and the connection is led out as the C-phase output terminal C0.

2. 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. Among them, the topological structure 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.

3. The control method applied to the full silicon carbide voltage sag control device according to claim 1, characterized in that: Comprising: S1. Initially, the first to third silicon carbide static transfer switches K1 to K3 are all disconnected. Detect the voltages of port I and port III. If the voltages of port I and port III are the set rated values, then close the first and second silicon carbide static transfer switches K1 and K2, and disconnect the third silicon carbide static transfer switch K3 to enter the normal working mode. If the voltage of port I is non-rated, it indicates that a power grid fault has occurred. Disconnect the first and second silicon carbide static transfer switches K1 and K2, and close the third silicon carbide static transfer switch K3. If the voltage of port III is non-rated, it indicates that a fault has occurred in the energy storage converter. Close the first silicon carbide static transfer switch K1, and disconnect the second and third silicon carbide static transfer switches K2 and K3. The power grid supplies power to the load. If the voltages of both port I and port III are non-rated, it indicates that both the power grid and the energy storage converter have failed. The first to third silicon carbide static transfer switches K1 to K3 remain as they are and are all disconnected. After the voltages of both port I and port III return to the set rated values, close the first and second silicon carbide static transfer switches K1 and K2 again, and disconnect the third silicon carbide static transfer switch K3 to enter the normal working mode; S2. After entering the normal working mode, when it is detected that the voltage of port I drops temporarily, then disconnect the second silicon carbide static transfer switch K2. If the voltage of port I returns to normal at this time, it indicates that a fault has occurred in the energy storage converter and it is cut off; If the voltage of port I still drops temporarily at this time, disconnect the first silicon carbide static transfer switch K1. If the voltage of port I returns to normal, it indicates that a fault has occurred in the load and it is cut off; 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.

4. The control method of the full silicon carbide voltage sag control device according to claim 3 is characterized in that: In step S2, determining whether a voltage sag occurs at port I includes the following: Set the three-phase voltages u A , u B , u C The expressions are respectively: u A = k1U m cosωt u B = k2U m cos(ωt - 120°) u C = k3U m cos(ωt + 120°) Among them, k1 represents the coefficient of the deviation of the phase A voltage from the rated value, k2 represents the coefficient of the deviation of the phase B voltage from the rated value, k3 represents the coefficient of the deviation of the phase C voltage from the rated value, and 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: where K, η, and C all represent 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.

5. The control method of the full silicon carbide voltage sag control device according to claim 4, characterized in that: The calculation formula for the effective value of the phase voltage is: Among them, N represents the total number of sampled voltage values, u i represents the i-th sampled voltage value, U RMS represents the effective value of the phase voltage.

6. The control method of the full silicon carbide voltage sag control device according to claim 3, 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.

7. The control method of the full silicon carbide voltage sag control device according to claim 6, 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 by a phase-locked loop, the error between this frequency and the reference frequency is calculated, and it is input into the adaptive controller. When the power grid frequency is higher than the rated frequency, the extended state observer embedded inside observes and adjusts the parameters according to the adaptive control law to generate the reference value of the input active current, 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 observes and adjusts the parameters according to the adaptive control law to generate the reference value of the output active current, and the energy storage converter switches to the grid-connected inversion mode to send out 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) all represent adjustable parameters of the adaptive controller; Signal vectors in the adaptive controller are as follows: where, ω ref (t) represents the reference frequency input to the controller, u v1 (t) and u v2 (t) represent the output signals of signal generators A1 and A2 in the controller, i p (t) represents the reference value of the active current; The error e between the power grid frequency and the reference frequency u (t) is as follows: 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; Therefore, the adaptive control law is expressed as: Among them, I represents the identity matrix, τ represents the τ-th moment, 0 ≤ τ ≤ t.

8. The control method of the full silicon carbide voltage sag control device according to claim 6, characterized in that: The mode switching includes the following: The outer loop adopts PI control. The desired output voltage is used as the reference value of the outer loop. After taking the difference between it and the actually sampled voltage value, it is input into the PI controller. 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. The actual values of the inductor current and capacitor voltage are multiplied by the corresponding feedback coefficients and then added together, and then the difference is taken with the output of the PI controller to obtain the modulation signal of the switching tube; the state space model of the energy storage converter is: Among them, 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, R f represents the equivalent series resistance of the filter inductor, L f represents the filter inductor, 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 represents the voltage of the output of the inverter bridge to the midpoint of the DC-side capacitor, i L represents the grid-side current, t represents 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 switching tube, k p and k i respectively represent the proportional coefficient and the integral coefficient of the PI controller, u f_ref represents the output voltage reference value, u sampling represents the actual sampled value of the output voltage, K f represents the state feedback coefficient matrix; When the energy storage converter operates off-grid, the voltage reference value u of the grid connection control algorithm f_ref_active is the actually sampled voltage value u sampling , and the output u of the grid connection control algorithm active is 0; when operating on-grid, the voltage reference value u of the off-grid control algorithm f_ref_passive is the actually sampled voltage value u sampling , and the output u of the off-grid control algorithm passive is 0; the specific expression is: By changing the reference values of the grid-connected control algorithm and the off-grid control algorithm, the operating mode of the energy storage converter is switched.

Images