UPS System Electrical State Quantity Prediction Method, Control Method, System

Abstract

The present invention discloses a method for predicting electrical state quantities, a control method, and a system for a UPS system. In terms of the control strategy of the UPS system, first, the relationship between the predicted values of the dynamic variables of the UPS system and the switching variables of the switching tubes is obtained through the discrete model of the UPS system. Then, an objective optimization control function is constructed based on MPC (Model Predictive Control). Finally, the optimal switching variables at each moment are obtained by traversing the cost values Q of the objective optimization control function under various switching states. The method proposed by the present invention solves the problems of complex cooperative control and difficult control optimization of multi-converter combined systems, and improves the working efficiency of high-power UPS systems and the stability of the control system.

Description

Technical Field

[0001] The present invention relates to the technical field of UPS control, and particularly to a method for predicting electrical state quantities, a control method, and a system of a UPS system. Background Art

[0002] For example Figure 1 , the topology of a high-power UPS system is a T-type three-level rectifier, a T-type three-level inverter, and a three-level three-phase DC converter with a common DC bus structure. There are two voltage-stabilizing capacitors C1 and C2 on the DC bus, and an electromagnetic bypass switch (composed of thyristors) is equipped. The T-type three-level rectifier is connected to the AC grid, and two DC buses are led out from the DC side capacitors; the T-type three-level inverter is connected to the load, and the three-level bidirectional DC converter is connected to the energy storage battery, and the battery is connected to the DC bus through the three-level bidirectional DC converter. The T-type three-level inverter takes power from the DC bus and inversely converts it into alternating current to supply power to the electrical load. The electromagnetic bypass switch is connected between the commercial power and the load. The UPS system has a total of 4 working modes: bypass working mode, UPS power supply mode, battery power supply mode, and battery power feeding mode.

[0003] Figure 2 is a working mode diagram of the power UPS. The high-power UPS has 4 working modes: bypass working mode, UPS power supply mode, battery power supply mode, and battery power feeding mode.

[0004] Bypass working mode: At this time, the UPS fails, or the manual bypass switch is disabled, and the grid directly supplies power to the load, and the UPS is locked.

[0005] UPS power supply mode: When the commercial power and the UPS are both normal, the bypass switch is disconnected at this time. The T-type three-level rectifier works in the PWM rectification state, and the T-type three-level inverter works in the PWM inversion state. The grid supplies power to the load through the rectifier and the inverter. At the same time, the three-level bidirectional DC converter obtains electrical energy from the DC bus to charge the battery.

[0006] Battery power supply mode: When the commercial power is abnormal and the UPS is normal, the electromagnetic bypass switch is disconnected, the T-type three-level rectification module is locked, and the battery can directly supply power to the load through the bidirectional DC converter and the T-type three-level inversion module to ensure continuous power supply.

[0007] Battery power supply mode: When the mains power and the UPS are both normal, the load does not require power supply and the battery SOC (State of Charge) > 0.8, the electromagnetic bypass switch is disconnected, the T-type three-level inverter module is locked, and the battery feeds electrical energy back to the power grid through the bidirectional DC converter and the T-type three-level rectifier (operating in the inverter mode). In recent years, UPS has been continuously developing towards large-scale and modularization, and system integration and central monitoring have also been continuously improved. However, with the continuous expansion of the market, the application scenarios of UPS have also increased accordingly, the load has become more and more complex, and the number of harsh conditions that need to be adapted to has become more and more, which has put forward many adjustment requirements for UPS. How to achieve high-power application of UPS and improve the operation efficiency and control stability of the UPS system is an important research topic in the current development of UPS technology and industry. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a method, a control method, and a system for predicting electrical state quantities of a UPS system, aiming at the deficiencies of the existing technology, and solving the problems of complex control and low reliability of multiple converters in the existing UPS system.

[0009] To solve the above technical problems, the technical solution adopted by the present invention is: A method for predicting electrical state quantities of a UPS system, including:

[0010] The calculation formula for the predicted value i g (k + 1) of the alternating current output by the T-type three-level rectifier of the UPS system is:

[0011]

[0012] The calculation formula for the reference value u r_ref (k) of the alternating voltage output by the T-type three-level rectifier of the UPS system is:

[0013]

[0014] The calculation formula for the reference value u i_ref (k) of the alternating voltage output by the T-type three-level inverter of the UPS system is:

[0015] u i_ref (k) = u n (k);

[0016] The calculation formula for the predicted value u(k + 1) of the alternating voltage of the UPS system is:

[0017]

[0018] The calculation formula for the predicted value U cn (k + 1) of the regulated voltage capacitor on the DC side of the UPS system is:

[0019]

[0020] Predicted value i of the inductor current of the three-level three-phase DC converter in the UPS system L The calculation formula for (k + 1) is as follows:

[0021]

[0022] Among them, u(k) is the AC voltage output by the T-type three-level rectifier, and L s is the value of the output filter inductor of the T-type three-level rectifier, and T s is the sampling interval time, and R S is the output line resistance of the UPS system, and i g (k) is the grid-side current at the k sampling moment, and u g (k) is the grid voltage at the k sampling moment; u r_ref (k) is the command voltage output by the AC side of the T-type three-level rectifier at the k sampling moment, and i rg_ref (k) is the command value of the grid-side current at the k sampling moment; u n (k) is the sampled value of the rated load voltage at the k sampling moment; ω is the grid angular frequency; U cn (k + 1) is the voltage value of the DC-side capacitor C of the T-type three-level rectifier at the (k + 1) sampling moment, and U n (k) is the voltage value of C at the k sampling moment, and i cn (k) is the voltage value of C n at the k sampling moment, and i cn (k) is the current value flowing through C n at the k sampling moment; U ES is the voltage of the energy storage battery, L is the inductor value of the three-level three-phase DC converter of the UPS system, T1 to T4 are the output states of the switching tubes of the three-level three-phase DC converter, and i L (k) is the inductor current value of the three-level bidirectional DC converter at the k moment; n = 1, 2; || represents the logical OR operation.

[0023] The present invention can predict the electrical states corresponding to each switching quantity, which is convenient for overall optimizing the control of the UPS system during the control process of the UPS system, thereby solving the problems of complex control and low reliability of multiple converters in the existing UPS system.

[0024] The present invention also provides a prediction system for electrical state quantities of a UPS system, which includes a computer device; the computer device is configured or programmed to execute the steps of the method for predicting electrical state quantities of the UPS system of the present invention.

[0025] The present invention also provides a control method for a UPS system, including:

[0026] When the UPS system operates in the UPS power supply mode, if the battery SOC ≥ 0.8, then construct the optimization function Q = J1 + J2;

[0027] When the UPS system operates in the UPS power supply mode, if the battery SOC < 0.8, then construct the optimization function Q = J1 + J2 + J3;

[0028] When the UPS system operates in the battery power supply mode or the battery power feeding mode, if the battery SOC > 0.2, then construct the optimization function Q = J2 + J4;

[0029] Among them,

[0030] J1 = |u rα_ref (k + 1) - u rα (k + 1)| + |u rβ_ref (k + 1) - u rβ (k + 1)| + λ1|U c1 (k + 1) - U c2 (k + 1)|;

[0031] J2 = |u iα_ref (k + 1) - u iα (k + 1)| + |u iβ_ref (k + 1) - u iβ (k + 1)|;

[0032] J3 = |U dc_ref - U dc (k + 1)| + |i L_ref - i L (k + 1)|;

[0033] J4 = |U dc_ref - U dc (k + 1)| + |i L_ref - i L (k + 1)| + λ2|U c1 (k + 1) - U c2 (k + 1)|;

[0034] u rα (k + 1) is the projection of the AC voltage u r (k + 1) output by the T-type three-level rectifier at the (k + 1)-th sampling moment on the α-axis, and u rα_ref (k + 1) is the reference value of the AC voltage u r_ref (k + 1) output by the T-type three-level rectifier on the α-axis; u rβ (k + 1) is the projection of the AC voltage u r (k + 1) output by the T-type three-level rectifier at the (k + 1)-th sampling moment on the β-axis, and u rβ_ref(k + 1) is the reference value u of the AC voltage output by the T-type three-level rectifier at the (k + 1)-th sampling moment r_ref The projection of (k + 1) on the β-axis; U c1 (k + 1), U c2 (k + 1) respectively represent the voltage values of the DC-side capacitors C1 and C2 of the T-type three-level rectifier at the (k + 1)-th sampling moment, u iα (k + 1) is the AC voltage u output by the T-type three-level inverter at the (k + 1)-th sampling moment i The projection of (k + 1) on the α-axis, u iα_ref (k + 1) is the reference value u of the AC voltage output by the T-type three-level inverter at the (k + 1)-th sampling moment i_ref The projection of (k + 1) on the α-axis, u iβ (k + 1) is the reference value u of the AC voltage output by the T-type three-level inverter at the (k + 1)-th sampling moment i_ref The projection of (k + 1) on the β-axis, u iβ_ref (k + 1) is the reference value u of the AC voltage output by the T-type three-level inverter i_ref The projection of (k + 1) on the β-axis, λ1 is the control weight of the T-type three-level rectifier, λ2 is the control weight of the three-level three-phase DC converter; i L_ref Is the inductor current value of the three-level three-phase DC converter; U dc_ref Is the DC-side voltage command value of the T-type three-level rectifier, U dc (k + 1) is the value of the DC-side capacitor voltage at the (k + 1)-th moment;

[0035] Select the signal when the optimization function is the smallest, and correspondingly control the on and off of the switching tubes of the T-type three-level rectifier, T-type three-level inverter, and three-level three-phase DC converter;

[0036] Among them, u r_ref (k + 1), u i_ref (k + 1) are calculated according to the electrical state quantity prediction method of the UPS system of the present invention, or are calculated by using the electrical state quantity prediction system of the UPS system of the present invention u r_ref (k + 1), u i_ref (k + 1).

[0037] The UPS system control method of the present invention has significant advantages over traditional control methods (such as PI control and current tracking control) in a multi-terminal converter system. Since the control objects of traditional control methods are mostly a certain system, such as the energy storage output port, the rectifier input port, and the inverter output port in a UPS, the optimal switching control of each port may be mutually restricted, making it difficult to achieve comprehensive optimization. However, the UPS system control method of the present invention predicts in advance the electrical states corresponding to each switching quantity and uses a comprehensive optimization function to achieve the overall optimal control of the multi-port system, and there is no problem of mutual restriction between the optimal switching controls of each port.

[0038] The control method for optimizing switching quantities using the overall objective function can achieve the coordinated optimization function of multiple ports. By using the optimization function Q to find the switching combination that can quickly approach the command value, the response speed of the present invention is faster and the reliability is higher compared with traditional PI control.

[0039] In the present invention, λ1 + λ2 = 1. Since there may be a mutually restrictive phenomenon in the control of the DC side balance between the T-type three-level rectifier and the three-phase DC converter, the converter is determined to perform DC side capacitor balance control according to the power margin, and the overall balance factor of the system is 1. λ1 and λ2 are the weights of their respective controllers, which are set according to the controller margin. Setting λ1 + λ2 = 1 in the present invention can overcome the mutually restrictive problem in the control of the DC side balance between the T-type three-level rectifier and the three-phase DC converter.

[0040] As an inventive concept, the present invention also provides a UPS system, which includes a computer device; the computer device is configured or programmed to execute the steps of the UPS system control method of the present invention.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention constructs an objective optimization control function through MPC (Model Predictive Control) to traverse the cost value Q of the objective optimization control function in various switching states, and obtains the optimal switching variables at each moment, improving the working efficiency and operation stability of the UPS system. The present invention solves the problems of complex cooperative control and difficult control optimization in a multi-converter combined system, improves the working efficiency of the high-power UPS system and the stability of the control system, and enables the high-power UPS system to be more widely applied to various industrial application scenarios. Brief Description of the Drawings

[0042] Figure 1 It is the overall structure diagram of a high-power UPS;

[0043] Figures 2(a) to 2(d)Schematic diagrams of four working modes of high-power UPS; among them, Fig. 2(a) is the bypass power supply mode; Fig. 2(b) is the UPS power supply mode; Fig. 2(c) is the battery power supply mode; Fig. 2(d) is the battery power feed mode;

[0044] Figures 3(a) to 3(c) Schematic diagram of the switching mode of phase A of the T-type three-level converter of the present invention; among them, in Fig. 3(a), Sa1 = 1, Sa2 = 1, and the output is P; in Fig. 3(b), Sa3 = 1, Sa4 = 1, and the output is n; in Fig. 3(c), Sa2 = 1, Sa2 = 1, and the output is O;

[0045] Figure 4 Schematic diagram of the switching state vector of the T-type three-level 27 in the present invention;

[0046] Figures 5(a) to 5(h) Schematic diagrams of 8 switching modes of the bidirectional DC converter of the present invention; among them, Fig. 5(a) is the battery feeding C2; Fig. 5(b) is the battery feeding C1; Fig. 5(c) is the battery feeding the inductor L; Fig. 5(d) is the battery feeding the capacitors C1 and C2; Fig. 5(e) is C1 charging the battery; Fig. 5(f) is C2 charging the battery; Fig. 5(g) is the inductor L discharging to the battery; Fig. 5(h) is C1 and C2 charging the battery;

[0047] Figure 6 Schematic diagram of the model predictive control of the high-power UPS of the present invention;

[0048] Figures 7(a) to 7(d) UPS simulation result diagram using the control method of the present invention; Fig. 7(a) is the DC-side capacitor simulation diagram; Fig. 7(b) is the system output power command diagram; Fig. 7(c) is the current waveform diagram during mode switching, and Fig. 7(d) is the voltage waveform diagram of the system during mode switching. Detailed implementation manners

[0049] Referring to Fig. 3, for the T-type three-level output mode of the present invention, taking phase A as an example for analysis, when Sa1 = 1, Sa2 = 1, the T-type three-level output is denoted as P at this time; when Sa3 = 1, Sa4 = 1, the T-type three-level output is denoted as N at this time; when Sa2 = 1, Sa3 = 1, the T-type three-level output is denoted as O (where 1 means the switch tube is closed, and not mentioned means the switch tube is open).

[0050] Since the power grid is a three-phase system, each phase has three output modes (P, N, 0), and there are 3 3 = 27 possible switching combination vectors that may appear in the three-phase combination (such as NPN, 0P0, N0N, etc.). Figure 4 Fig. 5 shows the 8 possible modes of the T-type three-level converter and the bidirectional DC converter, which are divided into two working modes: charging and energy feeding.

[0051] Power feeding mode: When T2 = 1, the storage battery charges the DC-side voltage stabilizing capacitor C2. When T3 = 1, the storage battery charges the DC-side voltage stabilizing capacitor C1. When T2 = T3 = 1, the storage battery charges the energy storage inductor at this time. When all the switching tubes are turned off, the energy storage battery charges the two voltage stabilizing capacitors.

[0052] Charging mode: When T1 = 1, the voltage stabilizing capacitor C1 charges the storage battery. When T4 = 1, the voltage stabilizing capacitor C2 charges the storage battery. When all the switching tubes are turned off, the storage battery charges the energy storage inductor at this time. When T1 = T4 = 1, the voltage stabilizing capacitors C1 and C2 supply power to the storage battery together at this time.

[0053] The calculation method of the predicted values of the electrical state variables of each converter in the UPS system is as follows: Through the prediction calculation of the electrical state variables, the state variables at the existing k moment can be used, combined with the electrical switching quantity state, to predict the electrical state variables at the k + 1 moment, and then the optimal switching quantity can be determined according to the optimization function.

[0054] In the calculation formulas of the optimization functions and the calculation formulas of the electrical state prediction quantities of the present invention, the dimensions of each parameter are not considered. When substituting for calculation, only the values of each parameter are considered, where the dimension corresponding to the voltage value is V, and the dimension corresponding to the current value is A.

[0055] Predicted value of the rectifier output AC current i g (k + 1):

[0056]

[0057] where u(k) is the rectifier output AC voltage, and L s is the value of the output filter inductor of the UPS rectifier, T s is the sampling interval time, R S is the system output line resistance, and i g (k) is the grid-side current at the k sampling moment, and u g (k) is the grid voltage at the k sampling moment.

[0058] Reference value of the rectifier output AC voltage u r_ref (k):

[0059]

[0060] where u r_ref (k) is the AC-side output command voltage at the k sampling moment, and i rg_ref (k) is the grid-side current command value at the k sampling moment.

[0061] Reference value of the inverter output AC voltage u i_ref (k):

[0062] u i_ref u(k) = u n (k);

[0063] where u n (k) is the sampled value of the rated voltage of the load at time k.

[0064] Calculation of the predicted value of the AC voltage u(k + 1):

[0065]

[0066] where ω is the system angular frequency.

[0067] Predicted value of the DC-side voltage-stabilizing capacitor U cn (k + 1):

[0068]

[0069] where U cn (k + 1) is the capacitor voltage value of Cn (n = 1, 2) at the (k + 1)-th sampling time, and U cn (k) is the capacitor voltage value of Cn (n = 1, 2) at the k-th sampling time, and i cn (k) is the capacitor current value flowing through Cn (n = 1, 2) at the k-th sampling time.

[0070] Predicted value of the inductor current i L (k + 1) of the three-level bidirectional DC converter:

[0071]

[0072] where U ES is the voltage of the energy storage battery, L is the inductance value of the three-level bidirectional DC converter, T1 - T4 are the output states of the switching tubes (1 means the switching tube is closed, 0 means the switching tube is open), and U c1 (k) is the capacitor voltage value of C1 at the k-th sampling time, and U c2 (k) is the capacitor voltage value of C2 at the k-th sampling time. i L (k) is the inductor current value of the three-level bidirectional DC converter at time k.

[0073] See Figure 6 for the coordinated control flowchart of the high-power UPS system based on MPC:

[0074] When the UPS operates in the UPS power supply mode, first detect the SOC state of the battery.

[0075] 1) When the state of charge (SOC) of the battery > 0.8, the three-level bidirectional DC converter operates in the locked state at this time, and the battery is bypassed to the system. The load is powered jointly by the rectifier and the inverter, and the optimization function is constructed as follows (the rectifier performs capacitor voltage balance control); if the optimization function Q is minimized, it can not only ensure the balance of the upper and lower capacitors C1 and C2 on the DC side, but also achieve accurate tracking of the control command.

[0076] J1 = |u rα_ref (k + 1) - u rα (k + 1)| + |u rβ_ref (k + 1) - u rβ (k + 1)| + λ1|U c1 (k + 1) - U c2 (k + 1)|;

[0077] J2 = |u iα_ref (k + 1) - u iα (k + 1)| + |u iβ_ref (k + 1) - u iβ (k + 1)|;

[0078] Q = J1 + J2;

[0079] In the above formula, J1, J2, and Q are the rectifier optimization cost function, the inverter target optimization quantity, and the system target optimization quantity respectively. Among them, u rα (k + 1) is the projection of the rectifier output AC voltage on the α-axis at the k + 1 sampling moment, and u rα_ref is the projection of the rectifier side output AC voltage command value on the α-axis. Among them, u rβ (k + 1) is the projection of the rectifier output AC voltage on the β-axis at the k + 1 sampling moment, and u rβ_ref is the projection of the rectifier output AC voltage command value on the β-axis. U c1 (k + 1), U c2 (k + 1) respectively represent the DC voltages of the DC capacitors C1 and C2 at the k + 1 sampling moment, and u iα (k + 1) is the projection of the inverter output AC voltage on the α-axis at the k + 1 sampling moment, and u iα (k + 1) is the projection of the inverter output AC voltage on the α-axis at the k + 1 sampling moment, and u iα_ref is the projection of the inverter output AC voltage command value on the α-axis. Among them, u iβ (k + 1) is the projection of the inverter output AC voltage on the β-axis at the k + 1 sampling moment, and u iβ_ref is the projection of the inverter output AC voltage command value on the β-axis. λ is the weight coefficient, and its value determines the priority of the controlled variable in the global optimization (λ1 is the rectifier control weight, and λ2 is the DC converter control weight).

[0080] Among them, the α-axis and the β-axis are the two coordinate axes of the two-phase coordinate system respectively. The expression for transforming the three-phase AC voltage from the static coordinate abc-axis vector to the perpendicular two-phase coordinate axes is as follows:

[0081]

[0082] The controller needs to traverse and optimize the rectifier and inverter switch states m = (27) 2 times within one sampling period, and select the switch digital signal S that forms the minimum cost function Q op .

[0083] 2) When the battery SOC < 0.8, the three-level bidirectional DC converter operates in the charging mode at this time, and the battery is charged. The rectifier supplies power to the load and the battery. The following optimization function is constructed (the rectifier performs capacitor voltage balance control): If the optimization function Q is minimized, it can not only ensure the balance of the upper and lower capacitors C1 and C2 on the DC side, but also achieve accurate tracking of the UPS output command and the battery output current command.

[0084] J1 = |u rα_ref (k + 1) - u rα (k + 1)| + |u rβ_ref (k + 1) - u rβ (k + 1)| + λ1|U c1 (k + 1) - U c2 (k + 1)|;

[0085] J2 = |u iα_ref (k + 1) - u iα (k + 1)| + |u iβ_ref (k + 1) - u iβ (k + 1)|;

[0086] J3 = |U dc_ref - U dc (k + 1)| + |i L_ref - i L (k + 1)|;

[0087] Q = J1 + J2 + J3;

[0088] Among them, i L_ref is the inductor current value of the three-level bidirectional DC converter. U dc_ref is the DC side voltage command value, and U dc (k + 1) is the value of the DC side capacitor voltage at the k + 1 moment, and the calculation method is U c1 (k + 1) + U c2 (k + 1).

[0089] At this time, the three-level bidirectional DC converter has two operating modes: S2 = 1, [S2, S3] = 1. The controller needs to traverse and optimize the rectifier, inverter, and DC converter switch states m = 2*(27) 2 times within one sampling period, and select the switch digital signal S that forms the minimum cost function Q op .

[0090] When the UPS operates in the battery power supply mode, first detect the SOC state of the battery.

[0091] If SOC < 0.2, the UPS operates in the locked state at this time;

[0092] If 0.2 < SOC, the battery enters the independent power supply mode at this time. The battery supplies power to the load through the DC converter and the inverter. The optimization function is constructed as follows: If the optimization function Q is minimized (the corresponding value when Q is the smallest is Qon), then the accurate tracking of the UPS output command can be achieved.

[0093] J2 = |u iα_ref (k + 1) - u iα (k + 1)| + |u iβ_ref (k + 1) - u iβ (k + 1)|;

[0094] J4 = |U dc_ref - U dc (k + 1)| + |i L_ref - i L (k + 1)| + λ2|U c1 (k + 1) - U c2 (k + 1)|;

[0095] Q = J2 + J4;

[0096] At this time, the three-level bidirectional DC converter needs to control the DC side voltage stability and the balance of capacitors C1\C2 due to the presence of voltage. There are 8 operating modes: S1 = 1, S2 = 1, S3 = 1, S4 = 1, [S1, S4] = 1, [S2, S3] = 1, 0(+,-)

[0097] The controller needs to traverse and optimize the inverter and DC converter switch states m = 8*27 times within one sampling period, and select the switch digital signal S that forms the minimum cost function Q op .

[0098] When the UPS operates in the battery feeding mode, first detect the SOC state of the battery.

[0099] If SOC < 0.2, the UPS operates in the locked state at this time.

[0100] If 0.2 <SOC,此时蓄电池进入独立供电模态,由蓄电池通过直流变换器和整流器(工作于逆变模式)向电网馈电,构造优化函数如下:若满足优化函数优化函数Q最小,则能实现控制UPS馈电指令的精准跟踪。

[0101] J1=|u rα_ref (k+1)-u rα (k+1)|+|u rβ_ref (k+1)-u rβ (k+1)|;

[0102] J4=|U dc_ref -U dc (k+1)|+|i L_ref -i L (k+1)|+λ2|U c1 (k+1)-U c2 (k+1)|

[0103] Q = J2 + J4;

[0104] At this time, the three-level bidirectional DC converter needs to control the DC side voltage stability and the balance of capacitors C1\C2. There are 8 working modes of voltage S1=1, S2=1, S3=1, S4=1, [S1, S4]=1, [S2, S3]=1, 0(+,-).

[0105] 0(+,-): Indicates that the converter output is 0, + indicates that the battery is forward charged through the inductor L to store energy in the inductor L, and - indicates that the battery is reversely charged through the inductor L to store energy in the inductor L.

[0106] The controller needs to traverse the optimal inverter and DC converter switch states m = 8 * 27 times in one sampling cycle, and select the switch digital signal Q that minimizes the cost function Q op .

[0107] The effectiveness and advancement of the control method proposed in this invention are verified through PSim simulation.

[0108] Figs. 7(a), 7(b), 7(c) and 7(d) are UPS simulations using the topology and control method proposed in the present invention, and the overall system capacity is 200 KVA. Among them, Fig. 7(a) is the simulation diagram of the DC-side capacitor, where udc1 and udc2 respectively represent the upper and lower DC-side capacitor voltages of the three-level. It can be seen that through the voltage balance control of the present invention, the system quickly realizes the voltage equalization of the upper and lower capacitors within 10 ms. Fig. 7(b) is the system output power command diagram, where the power command output is 100 kw. It can be seen that through the system control of the present invention, the output power can quickly track the command within 20 ms (within one power grid cycle), and the error < 1%. Figs. 7(c) and 7(d) are the current and voltage diagrams of the system during mode switching. It can be seen that when the system switches from the grid-connected mode to the island mode, the system current and voltage respond quickly and complete the output adjustment within 10 ms. It can be seen that the device of the present invention has a rapid response and can quickly realize the UPS function.

Claims

1. A control method for a UPS system, characterized in that Including: When the UPS system operates in the UPS power supply mode, if the battery SOC ≥ 0.8, then construct the optimization function Q = J1 + J2; When the UPS system operates in the UPS power supply mode, if the battery SOC < 0.8, then construct the optimization function Q = J1 + J2 + J3; When the UPS system operates in the battery power supply mode or the UPS system operates in the battery feeding mode, if the battery SOC > 0.2, then construct the optimization function Q = J2 + J4; Wherein, J1 = |u rα_ref (k + 1) - u rα (k + 1)| + |u rβ_ref (k + 1) - u rβ (k + 1)| + λ1|U c1 (k + 1) - U c2 (k + 1)|; J2 = |u iα_ref (k + 1) - u iα (k + 1)| + |u iβ_ref (k + 1) - u iβ (k + 1)|; J3 = |U dc_ref -U dc (k + 1)| + |i L_ref -i L (k + 1)|; J4 = |U dc_ref -U dc (k + 1)| + |i L_ref -i L (k + 1)| + λ2|U c1 (k + 1)-U c2 (k + 1)|; u rα u is the AC output voltage of the T-type three-level rectifier at the (k + 1)-th sampling instant r Its projection on the α-axis, u rα _ ref u* is the reference value of the AC output voltage of the T-type three-level rectifier r_ref Its projection on the α-axis; u* rβ u is the AC output voltage of the T-type three-level rectifier at the (k + 1)-th sampling instant r Its projection on the β-axis, u rβ _ ref u* is the reference value of the AC output voltage of the T-type three-level rectifier at the (k + 1)-th sampling instant r_ref Its projection on the β-axis; U* c1 u(k + 1), U(k + 1) c2 u(k + 1) and U(k + 1) respectively represent the voltage values of the DC-side capacitors C1 and C2 of the T-type three-level rectifier at the (k + 1)-th sampling instant iα u is the AC output voltage of the T-type three-level inverter at the (k + 1)-th sampling instant i Its projection on the α-axis, u iα _ ref u* is the reference value of the AC output voltage of the T-type three-level inverter at the (k + 1)-th sampling instant i_ref Its projection on the α-axis, u* iβ u* is the reference value of the AC output voltage of the T-type three-level inverter at the (k + 1)-th sampling instant i_ref Its projection on the β-axis, u* iβ _ ref u* is the reference value of the AC output voltage of the T-type three-level inverter i_ref Its projection on the β-axis, λ1 is the control weight of the T-type three-level rectifier, λ2 is the control weight of the three-level three-phase DC converter; i L_ref is the inductor current value of the three-level three-phase DC converter; U dc_ref is the DC-side voltage command value of the T-type three-level rectifier, U dc u(k + 1) is the value of the DC-side capacitor voltage at the (k + 1)-th instant; i L i(k + 1) is the predicted value of the inductor current of the three-level three-phase DC converter in the UPS system; Select the signal when the optimization function is the smallest, and correspondingly control the on / off of the switching tubes of the T-type three-level rectifier, T-type three-level inverter, and three-level three-phase DC converter; where, u r_ref (k), u i_ref (k) are calculated by the following formulas respectively: u i_ref u(k) = n u(k); L s is the output filter inductance value of the T-type three-level rectifier, T s is the sampling interval time, R S is the output line resistance of the UPS system, i g (k) is the grid-side current at the k-th sampling moment, u g (k) is the grid voltage at the k-th sampling moment, i rg_ref (k) is the grid-side current command value at the k-th sampling moment, u n (k) is the sampled value of the rated load voltage at the k-th sampling moment; Predicted value i of the AC current output by the T-type three-level rectifier of the UPS system g (k + 1) is calculated by the formula: U c1 (k + 1), U c2 (k + 1) is calculated by the formula: Among them, n = 1, 2, C n is the DC-side capacitor of the T-type three-level rectifier, and i cn (k) is the current value flowing through C n at the kth sampling moment, and u(k) is the predicted value of the AC voltage at the kth sampling moment; Predicted value i of the inductor current of the three-level three-phase DC converter in the UPS system L (k + 1) is calculated by the formula: Among them, U ES is the voltage of the energy storage battery, L is the inductance value of the three-level three-phase DC converter of the UPS system, T1 to T4 are the output states of the switching tubes of the three-level three-phase DC converter, and i L (k) is the inductor current value of the three-level bidirectional DC converter at the k-th moment, and || represents the logical OR operation.

2. The UPS system control method according to claim 1, wherein λ1 + λ2 = 1.

3. A UPS system, characterized in that, Including a computer device; the computer device is configured or programmed to perform the steps of the method according to claim 1 or 2.

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