Master-slave type three-level energy storage converter system

Abstract

The invention discloses a master-slave three-level energy storage converter system which is characterized in that + Udc / 2 and-Udc / 2 of an input direct current side of a three-level energy storage converter are connected with two end points of a support capacitor C1 and a support capacitor C2 which are connected in series, and a connection point of the capacitor C1 and the capacitor C2 is a reference point O; the two switching tubes Sa2 and Sa3 are connected in series reversely, an emitting electrode of the switching tube Sa3 is connected with a point O, an emitting electrode of the switching tube Sa2 is connected with an emitting electrode of the switching tube Sa1 and a collecting electrode of the switching tube Sa4 to form A-phase output, a collecting electrode of the switching tube Sa1 is connected with an input direct current side + Udc / 2, and an emitting electrode of the switching tube Sa4 is connected with an input direct current side-Udc / 2; wherein the B-phase circuit, the C-phase circuit and the A-phase circuit have the same structure. The beneficial effects of the invention are that the system is fast in dynamic response, is simple to realize, and solves the problems that the reliability of centralized control is lower and the distributed control is more complex after the parallel capacity expansion through a PCS in the prior art; voltage margin control is added in the slave, so that the problems of host overload and parallel system voltage collapse caused by load disturbance during communication failure are avoided.

Description

Technical Field

[0001] The present application relates to the field of electric energy storage, and in particular to a master-slave three-level energy storage converter system. Background Art

[0002] In order to ensure the green and sustainable development of my country's economy, new energy power generation technology has made rapid progress. However, wind power, photovoltaic power generation and other power generation methods are affected by climate. Their intermittent, volatile and random nature have a great impact on the stability, power quality and economy of the power grid when they are connected to the grid on a large scale. At the same time, due to the continuous increase in loads, the pressure on power dispatching of the power grid is huge during peak power consumption, which has also had a certain negative impact on the stability of the power grid. The emergence of energy storage technology has provided a series of solutions to the above problems. After applying energy storage technology to the field of new energy power generation, it has effectively improved the power fluctuation problem of wind power, photovoltaic power generation and other power generation methods. When the energy storage system is connected to the grid, it can smooth the load and reduce the peak and fill the valley; when it is off the grid, it can independently supply power to the load, improving the stability and economy of the power grid.

[0003] The power conversion system (PCS) is a hub device that connects the energy storage system to the power grid or load end. Its main function is to perform bidirectional conversion of energy. In order to meet the requirements of large capacity and high efficiency of new energy power generation systems, multiple PCSs can be operated in parallel to improve system capacity and reliability. The use of appropriate parallel control strategies can improve the power density of the parallel system, enhance the robustness of the system, and facilitate equipment maintenance and reduce costs. The circuit topology of PCS is diverse, which is the basis for its power conversion. The topology selected by PCS in different occasions is also different. The two-level converter topology has the disadvantages of large harmonics, low efficiency, and low withstand voltage level. Therefore, the more common converter topologies in high-power occasions are mainly cascaded H-bridge (CHB) and three-level types. Although the H-bridge cascade topology can theoretically be expanded to a very high level and reduce the THD of the output voltage, it also adds many independent DC sources and switching devices, which greatly increases the cost and volume, and the difficulty of control and design will also become greater due to the complexity of the structure. Traditional PCS communication methods include centralized control and distributed control. The centralized control structure is simple, but its control stability depends on the working status of the public control unit. Therefore, its control reliability is low and it is rarely used in actual projects. Compared with centralized control, distributed control has higher reliability, better scalability and more flexible control strategies, but the control is more complicated.

[0004] In summary, firstly, the traditional energy storage converter, due to the limited power of a single machine, often expands the capacity by parallel connection of PCS in high-power applications, but the reliability of centralized control is low and the distributed control is more complicated after parallel connection; secondly, the traditional master-slave control has the phenomenon of communication packet loss and disconnection, and the dynamic response is slow and the communication requirements are relatively high. Therefore, in order to improve the efficiency and reliability of energy storage converters, it is necessary to conduct a systematic study on energy storage converters. Summary of the invention

[0005] The present application is a master-slave three-level energy storage converter system designed to solve the above technical problems.

[0006] The technical solution adopted by this application to solve its technical problem is:

[0007] A master-slave three-level energy storage converter system, wherein the three-level energy storage converter inputs a DC side +U dc / 2 and -U dc / 2 connects the two endpoints of the supporting capacitors C1 and C2 in series, and the connection point of the capacitors C1 and C2 is the reference point O; the two switch tubes S a2 , S a3 Reverse series connection, switch tube S a3 The emitter of the switch is connected to point O, and the switch S a2 The emitter of the switch tube S a1 The emitter and switch tube S a4 The collector of the switch tube S a1 The collector of the input DC side +U dc / 2 connected, switch tube S a4 The emitter and input DC side -U dc / 2 connected;

[0008] Two switch tubes S b2 , S b3 Reverse series connection, switch tube S b3 The emitter of the switch is connected to point O, and the switch S b2 The emitter of the switch tube S b1 The emitter and switch tube S b4 The collector of the switch tube S b1 The collector of the input DC side +U dc / 2 connected, switch tube S b4 The emitter and input DC side -U dc / 2 connected;

[0009] Two switch tubes S c2 , S c3 Reverse series connection, switch tube S c3 The emitter of the switch is connected to point O, and the switch S c2The emitter of the switch tube S c1 The emitter and switch tube S c4 The collector of the switch tube S c1 The collector of the input DC side +U dc / 2 connected, switch tube S c4 The emitter and input DC side -U dc / 2 is connected.

[0010] The master-slave three-level energy storage converter system adopts the sine pulse width modulation SPWM technology to generate the switch tube drive signal, U c1 and U c2 are two high-frequency carriers with the same amplitude, phase, and frequency, U r is a sinusoidal modulated wave;

[0011] For phase A: When U r Greater than U c1 When S a1 When U r Less than U c2 When S a4 The bridge arm outputs N state, and the rest are O state.

[0012] For phase B: When U r Greater than U c1 When S b1 When U r Less than U c2 When S b4 The bridge arm outputs N state, and the rest are O state.

[0013] For phase C: When U r Greater than U c1 When S c1 When U r Less than U c2 When S c4 The bridge arm outputs N state, while the rest are O state.

[0014] The master-slave three-level energy storage converter system, the S a3 and S a2 As S a1 and S a4 The complementary tube is turned on; the S b3 and S b2 As S b1 and S b4 The complementary tube is turned on; the S c3 and S c2 As S c1 and Sc4 The complementary tube is turned on.

[0015] The master-slave three-level energy storage converter system adopts a grid-connected power voltage control structure based on master-slave control, including a three-level energy storage converter host 0 and multiple three-level energy storage converter slaves; the host 0 and the slave have the same circuit structure, and the converter provides active power and reactive power to the grid when connected to the grid; wherein the host 0 is dominant and is responsible for managing and regulating the power flow of the energy storage system, and at the same time sends instructions to the slave, monitors the status and collects data; the specific structure is:

[0016] The three-level energy storage converter host 0 collects the three-phase AC frequency signal f through the host 0PLL0 module g With the phase signal θ g , and output phase-lock information pll 00 、pll 01 ; Park conversion module 00 collects three-phase AC current i 0a 、i 0b 、i 0c , Park transformation module 01 collects three-phase AC voltage u a 、u b 、u c Park transformation module 00 and Park transformation module 01 transform the variables under the three-phase stationary coordinate system abc to the two-phase rotating coordinate system dq through Park transformation, and obtain the voltage e of the host 0 of the three-level energy storage converter under the dq coordinate axis 0d 、e 0q With current i 0d 、i 0q , thereby achieving power decoupling; the host 0 power outer loop module is based on the power setting value P ref , Q ref The voltage e of the host 0 of the three-level energy storage converter under the dq coordinate axis 0d 、e 0q Perform calculations to obtain the direct axis component i of the current dref and the quadrature axis component i qref The host 0 current inner loop module receives the transmission information of the Park conversion module 00, the Park conversion module 01 and the host 0 power outer loop module to perform calculations, generate a duty cycle signal d0, and control the host 0SPWM0 module to drive the switch tube action of the three-level energy storage converter host 0 to achieve the grid-connected control of the three-level energy storage converter host 0;

[0017] The three-level energy storage converter host 0 and the three-level energy storage converter slave exchange information through a communication network, and the slave obtains the current direct axis component i generated by the power outer ring module of the host 0. dref and the quadrature axis component iqref ; Slave n collects three-phase AC frequency signal f through its own slave n PLLn module g With the phase signal θ g , and output respective phase-locked information pll n0 、pll n1 , and the voltage e of the slave n of the three-level energy storage converter under the dq coordinate axis is obtained through the respective Park transformation modules n0 and Park transformation modules n1 nd 、e nq With current i nd 、i nq The slave n current inner loop module receives the transmission information from the Park conversion module n0, Park conversion module n1 and the host 0 power outer loop module for calculation and generates a duty cycle signal d n , and controls the slave n SPWM module to drive the switch tube action of the three-level energy storage converter slave n, thereby realizing the grid-connected control of the three-level energy storage converter slave n.

[0018] The master-slave three-level energy storage converter system, the master-slave control-based grid-connected power voltage control structure also includes a master-slave control grid-connected power voltage control strategy, and the control strategy is specifically:

[0019] The three-level energy storage converter host 0 samples the three-phase AC frequency signal f g , three-phase AC phase signal θ g , three-phase AC voltage u a 、u b 、u c and the three-phase alternating current i 0a 、i 0b 、i 0c Since it is not convenient to realize closed-loop control of three-phase AC voltage and three-phase AC current, the three-phase AC frequency signal f g (should be consistent with the previous description) and the three-phase AC phase signal θ g Input the host 0PLL0 module, and the obtained phase-locking information pll00 and pll01 are used to phase-lock the Park transformation module 00 and Park transformation module 01 respectively; in order to reduce the control variables and realize power decoupling, the variables under the three-phase stationary coordinate system abc are transformed to the two-phase rotating coordinate system dq through the Park transformation module 00 and Park transformation module 01, and the voltage e of the three-level energy storage converter host 0 under the dq coordinate axis is obtained. 0d 、e 0q With current i 0d 、i 0q ; Then, the voltage e of the host 0 of the three-level energy storage converter under the dq coordinate axis is 0d 、e 0q With power setting value P ref, Q ref Enter the host 0 power outer loop module and generate the current direct axis component i dref and the quadrature axis component i qref , and the current i of the host 0 of the three-level energy storage converter under the actual conversion dq coordinate axis 0d 、i 0q After comparison, the host 0 current inner loop module generates a duty cycle signal d0; finally, the host 0 SPWM0 module modulates the output drive signal to control the three-level energy storage converter host 0;

[0020] The three-level energy storage converter slave 1 samples the three-phase AC frequency signal f g , three-phase AC phase signal θ g , three-phase AC voltage u a 、u b 、u c and the three-phase alternating current i 1a 、i 1b 、i 1c Since it is not convenient to realize closed-loop control of three-phase AC voltage and three-phase AC current, the three-phase AC frequency signal f g With the three-phase AC phase signal θ g The PLL1 module of slave 1 is input, and the phase-locked information pll10 and pll11 are obtained to phase-lock Park transformation module 10 and Park transformation module 11 respectively; in order to reduce the control variables and realize power decoupling, the variables under the three-phase stationary coordinate system abc are transformed to the two-phase rotating coordinate system dq through Park transformation module 10 and Park transformation module 11, and the voltage e of the three-level energy storage converter slave 1 under the dq coordinate axis is obtained. 1d 、e 1q With current i 1d 、i 1q ; Then, the host 0 power outer loop module generates the current direct axis component i dref and the quadrature axis component i qref , and the current i of the slave 1 of the three-level energy storage converter under the actual conversion dq coordinate axis 1d 、i 1q After comparison, the duty cycle signal d1 is generated by the current inner loop module of slave 1; finally, the SPWM1 module of slave 1 modulates the output drive signal to control the three-level energy storage converter slave 1;

[0021] The other slaves also receive the direct axis component i generated by the host 0 power outer loop module dref and the quadrature axis component i qref The specific control method is the same as slave 1.

[0022] The master-slave three-level energy storage converter system adopts an off-grid constant voltage-frequency ratio control structure based on master-slave control, including a three-level energy storage converter host 0 and multiple three-level energy storage converter slaves; when off-grid, the host 0 controls the voltage amplitude and frequency of the three-phase AC side, the host 0 issues a current instruction according to the voltage loop calculation result, and the slave obtains the current instruction and supplies power to the load together with the host; the specific structure is:

[0023] The Park conversion module 00 in the three-level energy storage converter host 0 collects the three-phase AC current i L0a 、i L0b 、i L0c , Park transformation module 01 collects three-phase AC voltage u La 、u Lb 、u Lc ; Host 0 realizes power decoupling through Park transformation module 00 and Park transformation module 01, transforms the variables under the three-phase stationary coordinate system abc to the two-phase rotating coordinate system dq through Park, and obtains the current i of the three-level energy storage converter host 0 under the dq coordinate axis L0d 、i L0q With voltage u L0d 、u L0q ; The host 0 voltage outer loop module is based on the voltage setting value V ref The voltage u of the host 0 of the three-level energy storage converter under the dq coordinate axis L0d 、u L0q Perform calculations to obtain the direct axis component i of the current Ldref and the quadrature axis component i Lqref The host 0 current inner loop module performs calculations based on the information transmitted by the Park conversion module 00 and the host 0 voltage outer loop module, and the host 0 current inner loop module generates a duty cycle signal d L0 , and control the host 0SPWM0 module to drive the switch tube action of the three-level energy storage converter host 0 to achieve off-grid control of the three-level energy storage converter host 0;

[0024] The three-level energy storage converter host 0 and the three-level energy storage converter slave exchange information through the communication network, and the slave obtains the current direct axis component i generated by the host 0 voltage outer loop module. Ldref and the quadrature axis component i Lqref The slave n obtains the current i of the three-level energy storage converter slave n under the dq coordinate axis through its own Park transformation module n0. nd 、i nq The slave n current inner loop module receives the transmission information of the Park conversion module n0 and the host 0 voltage outer loop module for calculation and generates a duty cycle signal d Ln, and controls the slave nSPWM module to drive the switch tube action of the three-level energy storage converter slave n, thereby realizing off-grid control of the three-level energy storage converter slave n.

[0025] The master-slave three-level energy storage converter system, the off-grid constant voltage-frequency ratio control structure based on master-slave control also includes an off-grid constant voltage-frequency ratio control strategy based on master-slave control, and the control strategy is specifically:

[0026] The three-level energy storage converter host 0 samples the three-phase AC voltage u La 、u Lb 、u Lc With three-phase alternating current i L0a 、i L0b 、i L0c Since it is not convenient to realize closed-loop control of three-phase AC voltage and three-phase AC current, in order to reduce the control variables and realize power decoupling, the variables under the three-phase stationary coordinate system abc are transformed to the two-phase rotating coordinate system dq through Park transformation module 00 and Park transformation module 01, and the current i of the host 0 of the three-level energy storage converter under the dq coordinate axis is obtained. L0d 、i L0q With voltage u L0d 、u L0q ; Then, the voltage u of the three-level energy storage converter host 0 under the dq coordinate axis L0d 、u L0q With the voltage setting value V ref Enter the host 0 voltage outer loop module and generate the current direct axis component i Ldref and the quadrature axis component i Lqref , and the current i of the host 0 of the three-level energy storage converter under the actual conversion dq coordinate axis L0d 、i L0q After comparison, the host 0 current inner loop module generates a duty cycle signal d L0 ; Finally, the host 0SPWM0 module modulates the output drive signal to control the three-level energy storage converter host 0;

[0027] The three-level energy storage converter samples the three-phase AC current i from the machine 1 L1a 、i L1b 、i L1c Since the three-phase AC voltage and the three-phase AC current are not convenient to realize closed-loop control, in order to reduce the control variables and realize power decoupling, the variables under the three-phase stationary coordinate system abc are transformed to the two-phase rotating coordinate system dq through the Park transformation module 10, and the current i of the slave 1 of the three-level energy storage converter under the dq coordinate axis is obtained. L1d 、i L1q ; Then, the host 0 voltage outer loop module generates the current direct axis component i Ldref and the quadrature axis component iLqref , and the current i of the slave 1 of the three-level energy storage converter under the actual conversion dq coordinate axis L1d 、i L1q After comparison, the duty cycle signal d is generated by the current inner loop module of slave 1. L1 ; Finally, the slave 1 SPWM1 module modulates the output drive signal to control the three-level energy storage converter slave 1;

[0028] The other slaves also receive the host 0 voltage and the outer loop module generates the current direct axis component i Ldref and the quadrature axis component i Lqref The specific control method is the same as slave 1.

[0029] The master-slave three-level energy storage converter system, the AC voltage margin controller, in the AC voltage margin control, each converter can control the voltage output on the AC side, and no switching instructions between the master and slave machines are required, and there are multiple voltage support points in the parallel system;

[0030] When the parallel system is running stably, the host 0 adopts dual-loop control to stabilize the AC side voltage, and the slave adopts single-loop control to provide power to the system; when the power of the host 0 exceeds the limit, it switches to the single-loop control mode, runs at maximum power and loses control of the AC voltage; at this time, when the slave detects that the AC side voltage is less than the reference set in the local voltage loop, the slave switches to dual-loop control to control the AC side voltage to maintain stable operation of the system.

[0031] The master-slave three-level energy storage converter system, the AC voltage margin controller in the AC voltage margin control, U dref_m is the host 0 voltage loop instruction, U dref_s1 is the low deviation limit of AC voltage of slave 1, U dref_s2 is the low deviation limit of AC voltage of slave 2, P max The maximum output active power of the master and slave, P ref Active power command for master and slave machines;

[0032] The voltage margin outer loop controller of the slave 1 and the voltage margin outer loop controller of the slave 2 are equal in status;

[0033] The voltage margin outer loop controller of slave 1 is implemented as follows: the voltage loop command value U of master 0 dref_m The actual voltage u of the host 0 d_m After the difference is made, the host 0 current low deviation limit i is obtained through the PI0 module. _m ; Slave 1 AC voltage low deviation limit U dref_s1 The actual voltage u of slave 1 d_s1 After the difference is made, the low deviation limit value i of slave 1 current is obtained through the PI1 module. _s1; Host 0 current low deviation limit i _m The current low deviation limit i of slave 1 s1 After comparison operation by the Max01 module, the low deviation limit of the AC current of slave 1 is obtained;

[0034] The voltage margin outer loop controller of the slave 2 is implemented as follows: the voltage loop command value U of the host 0 dref_m The actual voltage u of the host 0 d_m After the difference is made, the host 0 current low deviation limit i is obtained through the PI0 module. _m ; Slave 2 AC voltage low deviation limit U dref_s2 The actual voltage u of slave 2 d_s2 After the difference is made, the low deviation limit value i of slave 2 current is obtained through the PI2 module. _s2 ; Host 0 current low deviation limit i _m The current low deviation limit i of slave 2 _s2 After comparison operation by the Max02 module, the low deviation limit of the AC current of slave 2 is obtained;

[0035] When the communication is normal, the host 0 is responsible for controlling the AC side voltage; at this time, the AC side voltage is greater than the voltage low deviation limit of the two slaves, and the current low deviation limit i in the voltage margin outer loop controller of slaves 1 and 2 is _s1 with i _s2 It is always a negative limit value, which is less than the instruction issued by the master 0 communication. Slave 1 and slave 2 are responsible for providing power at this time and operate in single-loop mode. The master-slave three-level energy storage converter system operates stably at point A in the AC voltage margin control principle, that is, the power of the master 0, slave 1 and slave 2 is at the active power instruction value of the master and slave, and the voltage of the master 0, slave 1 and slave 2 is at the voltage loop instruction value of the master 0.

[0036] When a communication failure occurs and the AC side suddenly cuts into the load, the slave can only output power according to the instruction before the communication disconnection. At this time, the host 0 is very likely to be overloaded by adjusting the power alone. When the output power of the host 0 reaches the maximum, it has not yet met the load power. The AC side voltage will drop until it is lower than the low deviation limit of the AC voltage of slave 1; at this time, the output of the outer loop controller of slave 1 gradually increases and exceeds the instruction of the host 0 before the communication disconnection. Slave 1 is i _s1 The power is supplemented for the current loop command, and the AC voltage is controlled to the low deviation limit of the AC voltage of slave 1. At this time, the master-slave three-level energy storage converter system operates at point B in the AC voltage margin control principle, that is, the power of master 0 is at the maximum output active power value of master 0, the power of slave 1 is greater than the active power command value of slave 1, but does not exceed the maximum output active power value of slave 1, and the power of slave 2 is at the active power command value of slave 2; the voltages of master 0, slave 1 and slave 2 are at the low deviation limit of the AC voltage of slave 1;

[0037] When the system is running at point B in the AC voltage margin control principle and there is still load cut-in, and the output power of slave 1 is insufficient, the AC side voltage continues to drop, similar to the response of slave 1. Slave 2 detects that the voltage is less than the AC voltage low deviation limit set by itself. Master 0 and slave 1 run in single-loop mode, and slave 2 is i _s2 The current loop instruction starts to control the AC side voltage to the low deviation limit of the AC voltage of slave 2 and compensates for the remaining power. The master-slave three-level energy storage converter system now operates at point C in the AC voltage margin control principle, that is, the power of master 0 is at the maximum output active power value of master 0, the power of slave 1 is at the maximum output active power value of slave 1, and the power of slave 2 is greater than the active power instruction value of slave 2, but does not exceed the maximum output active power value of slave 2; the voltages of master 0, slave 1 and slave 2 are at the low deviation limit of the AC voltage of slave 2.

[0038] At least one of the above technical solutions adopted in the embodiments of the present application can achieve the following beneficial effects:

[0039] (1) The master-slave three-level energy storage converter system designed in the present invention has fast dynamic response and simple implementation, which solves the problems of low reliability of centralized control and complex distributed control after expansion through PCS parallel connection.

[0040] (2) The AC voltage margin control strategy proposed in the present invention avoids the problem of host 0 overload and parallel system voltage collapse caused by load disturbance during communication failure by adding voltage margin control in the slave. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0042] Figure 1 It is the topology diagram of three-level energy storage converter;

[0043] Figure 2 It is the topology diagram of the A-phase three-level energy storage converter;

[0044] Figure 3(a) is a schematic diagram of the commutation mode of a three-level converter (i A >0, open S a1 , Close S a2 , S a3 , S a4 );

[0045] Figure 3(b) is a schematic diagram of the commutation mode of a three-level converter (i A >0, open S a2 , S a3 , Close S a1 , Sa4 );

[0046] Figure 3(c) is a schematic diagram of the commutation mode of a three-level converter (i A >0, open S a4 , Close S a1 , S a2 , S a3 );

[0047] Figure 3(d) is a schematic diagram of the commutation mode of a three-level converter (i A <0, open S a1 , Close S a2 , S a3 , S a4 );

[0048] Figure 3(e) is a schematic diagram of the commutation mode of a three-level converter (i A <0, open S a2 , S a3 , Close S a1 , S a4 );

[0049] Figure 3(f) is a schematic diagram of the commutation mode of a three-level converter (i A <0, open S a4 , Close S a1 , S a2 , S a3 );

[0050] Figure 4 This is the principle diagram of co-directional carrier stacked SPWM modulation;

[0051] Figure 5 It is a schematic diagram of the PQ control structure based on master-slave control;

[0052] Figure 6 This is the block diagram of the current loop decoupling control;

[0053] Figure 7 It is the relationship diagram between the stationary coordinate system and the rotating coordinate system;

[0054] Figure 8 It is the block diagram of the current loop structure;

[0055] Fig. 9 This is a simplified structural diagram of the current loop;

[0056] Fig.10 It is a schematic diagram of the VF control structure based on master-slave control;

[0057] Fig.11 It is a schematic diagram of the decoupling structure of the converter dual-loop control system;

[0058] Fig.12It is a schematic diagram of the decoupling structure of the converter dual-loop control system;

[0059] Fig.13 It is a schematic diagram of the structure of the converter voltage loop control system;

[0060] Fig.14 It is the block diagram of off-grid VF control strategy based on master-slave control;

[0061] Fig.15 This is the AC voltage margin control principle diagram;

[0062] Fig.16 is the voltage margin outer loop controller diagram of slave 1;

[0063] Fig.17 This is the voltage margin outer loop controller diagram for slave 2. DETAILED DESCRIPTION

[0064] In order to make the purpose, technical solution and advantages of the present application clearer, the technical solution of the present application will be clearly and completely described below in combination with the specific embodiments of the present application and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application.

[0065] The technical solutions provided by various embodiments of the present application are described in detail below in conjunction with the accompanying drawings.

[0066] In order to facilitate the understanding of the embodiments of the present application, the three-level energy storage converter structure proposed in the present invention is a T-type neutral point clamped (NPC) topology structure. Figure 1 As shown, a master-slave three-level energy storage converter system, the three-level energy storage converter input DC side +U dc / 2 and -U dc / 2 connects the two endpoints of the supporting capacitors C1 and C2 in series, and the connection point of the capacitors C1 and C2 is the reference point O; the two switch tubes S a2 , S a3 Reverse series connection, switch tube S a3 The emitter of the switch is connected to point O, and the switch S a2 The emitter of the switch tube S a1 The emitter and switch tube S a4 The collector of the switch tube S a1 The collector of the input DC side +U dc / 2 connected, switch tube S a4 The emitter and input DC side -U dc / 2 are connected; the 4 switch tubes form a "T" shape.

[0067] Two switch tubes S b2 , S b3 Reverse series connection, switch tube S b3 The emitter of the switch is connected to point O, and the switch S b2 The emitter of the switch tube S b1 The emitter and switch tube S b4 The collector of the switch tube S b1 The collector of the input DC side +U dc / 2 connected, switch tube S b4 The emitter and input DC side -U dc / 2 connected;

[0068] Two switch tubes S c2 , S c3 Reverse series connection, switch tube S c3 The emitter of the switch is connected to point O, and the switch S c2 The emitter of the switch tube S c1 The emitter and switch tube S c4 The collector of the switch tube S c1 The collector of the input DC side +U dc / 2 connected, switch tube S c4 The emitter and input DC side -U dc / 2 is connected.

[0069] The master-slave three-level energy storage converter system adopts the sine pulse width modulation SPWM technology to generate the switch tube drive signal, U c1 and U c2 are two high-frequency carriers with the same amplitude, phase, and frequency, U r is a sinusoidal modulated wave;

[0070] For phase A: When U r Greater than U c1 When S a1 When U r Less than U c2 When S a4 The bridge arm outputs N state, and the rest are O state.

[0071] For phase B: When U r Greater than U c1 When S b1 When U r Less than U c2 When S b4 The bridge arm outputs N state, and the rest are O state.

[0072] For phase C: When U r Greater than U c1 When S c1 When U r Less than U c2 When S c4 The bridge arm outputs N state, while the rest are O state.

[0073] The master-slave three-level energy storage converter system, the S a3 and S a2 As S a1 and S a4 The complementary tube is turned on; the S b3 and S b2 As S b1 and S b4 The complementary tube is turned on; the S c3 and S c2 As S c1 and S c4 The complementary tube is turned on.

[0074] Next, we analyze the A phase. The A phase TNPC structure topology is as follows: Figure 2 shown.

[0075] Assume that point O between capacitors C1 and C2 is the reference point, the direction of the current flowing out of each phase bridge arm is defined as the positive direction, and the direction of the current flowing in is defined as the negative direction. Then, when the current is positive and negative, there are three commutation modes.

[0076] When the bridge arm current is in the positive direction:

[0077] (1) As shown in Figure 3(a), when the switch tube S a1 Open, switch tube S a2 , S a3 , S a4 When turned off, the current flows through S a1 , not through S a2 , S a3 , S a4 At this time, the voltage of the output terminal of phase A relative to point O is U dc / 2;

[0078] (2) As shown in Figure 3(b), when the switch tube S a2 , S a3 Open, switch tube S a1 , S a4 When off, the current flows through D a3 , S a2 , not through S a1 , S a4 , at this time, the voltage of the output terminal of phase A relative to point O is 0;

[0079] (3) As shown in Figure 3(c), when the switch tube S a4 Open, switch tube S a1 , S a2 , S a3 When turned off, the current flows through S a4 , not through S a1 , S a2 , S a3 At this time, the voltage of the output terminal of phase A relative to point O is -U dc / 2;

[0080] When the bridge arm current is in the negative direction:

[0081] (1) As shown in Figure 3(d), when the switch tube S a1 Open, switch tube S a2 , S a3 , S a4 When off, the current flows through D a1 , not through S a2 , S a3 , S a4 At this time, the voltage of the output terminal of phase A relative to point O is U dc / 2;

[0082] (2) As shown in Figure 3(e), when the switch tube S a2 , S a3 Open, switch tube S a1 , S a4 When turned off, the current flows through S a2 , S a3 , not through S a1 , S a4 , at this time, the voltage of the output terminal of phase A relative to point O is 0;

[0083] (3) As shown in Figure 3(f), when the switch tube S a4 Open, switch tube S a1 , S a2 , S a3 When turned off, the current flows through S a4 , not through S a1 , S a2 , S a3 At this time, the voltage of the output terminal of phase A relative to point O is -U dc / 2;

[0084] Sinusoidal Pulse Width Modulation (SPWM) is used to generate the switch drive signal. The same-direction stacked SPWM modulation has the advantages of less output harmonic content and simple control. The principle is as follows: Figure 4 shown.

[0085] Figure 4 Middle Uc1 and U c2 are two high-frequency carriers with the same amplitude, phase, and frequency, U r For a sinusoidal modulation wave, when U r Greater than U c1 When S a1 When U r Less than U c2 When S a4 The bridge arm is turned on, and the output of the bridge arm is in N state; the rest are in O state. In order to simplify the implementation in digital chips, S a3 and S a2 As S a1 and S a4 The complementary tube is turned on.

[0086] Define the output as U when the P level state is dc / 2, the output is 0 when the O level state, and -U when the N level state dc / 2. The corresponding relationship between the output and the switch state of the T-type three-level converter is shown in Table 1, where ON means the switch is turned on, and OFF means the switch is turned off.

[0087] Table 1 Relationship between T-type topology output and working status

[0088]

[0089] like Figure 5 As shown, the master-slave three-level energy storage converter system adopts a grid-connected power voltage control structure based on master-slave control, including a three-level energy storage converter host 0 and multiple three-level energy storage converter slaves; the host 0 and the slave have the same circuit structure, and the converter provides active power and reactive power to the grid when connected to the grid; wherein the host 0 is dominant and is responsible for managing and regulating the power flow of the energy storage system, and at the same time sends instructions to the slave, monitors the status and collects data; the specific structure is:

[0090] The three-level energy storage converter host 0 collects the three-phase AC frequency signal f through the host 0PLL0 module g With the phase signal θ g , and output phase-lock information pll 00 、pll 01 ; Park conversion module 00 collects three-phase AC current i 0a 、i 0b 、i 0c , Park transformation module 01 collects three-phase AC voltage u a 、u b 、u cPark transformation module 00 and Park transformation module 01 transform the variables under the three-phase stationary coordinate system abc to the two-phase rotating coordinate system dq through Park transformation, and obtain the voltage e of the host 0 of the three-level energy storage converter under the dq coordinate axis. 0d 、e 0q With current i 0d 、i 0q , thereby achieving power decoupling; the host 0 power outer loop module is based on the power setting value P ref , Q ref The voltage e of the host 0 of the three-level energy storage converter under the dq coordinate axis 0d 、e 0q Perform calculations to obtain the direct axis component i of the current dref and the quadrature axis component i qref The host 0 current inner loop module receives the transmission information of the Park conversion module 00, the Park conversion module 01 and the host 0 power outer loop module to perform calculations, generate a duty cycle signal d0, and control the host 0SPWM0 module to drive the switch tube action of the three-level energy storage converter host 0 to achieve the grid-connected control of the three-level energy storage converter host 0;

[0091] The three-level energy storage converter host 0 and the three-level energy storage converter slave exchange information through a communication network, and the slave obtains the current direct axis component i generated by the power outer ring module of the host 0. dref and the quadrature axis component i qref ; Slave n collects three-phase AC frequency signal f through its own slave n PLLn module g With the phase signal θ g , and output respective phase-locked information pll n0 、pll n1 , and the voltage e of the slave n of the three-level energy storage converter under the dq coordinate axis is obtained through the respective Park transformation modules n0 and Park transformation modules n1 nd 、e nq With current i nd 、i nq The slave n current inner loop module receives the transmission information from the Park conversion module n0, Park conversion module n1 and the host 0 power outer loop module for calculation and generates a duty cycle signal d n , and controls the slave n SPWM module to drive the switch tube action of the three-level energy storage converter slave n, thereby realizing the grid-connected control of the three-level energy storage converter slave n.

[0092] The master-slave three-level energy storage converter system, the master-slave control-based grid-connected power voltage control structure also includes a master-slave control grid-connected power voltage control strategy, and the control strategy is specifically:

[0093] The three-level energy storage converter host 0 samples the three-phase AC frequency signal f g , three-phase AC phase signal θ g , three-phase AC voltage u a 、u b 、u c and the three-phase alternating current i 0a 、i 0b 、i 0c Since it is not convenient to realize closed-loop control of three-phase AC voltage and three-phase AC current, the three-phase AC frequency signal f g (should be consistent with the previous description) and the three-phase AC phase signal θ g Input the host 0PLL0 module, and the obtained phase-locking information pll00 and pll01 are used to phase-lock the Park transformation module 00 and Park transformation module 01 respectively; in order to reduce the control variables and realize power decoupling, the variables under the three-phase stationary coordinate system abc are transformed to the two-phase rotating coordinate system dq through Park transformation modules 00 and Park transformation modules 01, and the voltage e of the three-level energy storage converter host 0 under the dq coordinate axis is obtained. 0d 、e 0q With current i 0d 、i 0q ; Then, the voltage e of the host 0 of the three-level energy storage converter under the dq coordinate axis is 0d 、e 0q With power setting value P ref , Q ref Enter the host 0 power outer loop module and generate the current direct axis component i dref and the quadrature axis component i qref , and the current i of the host 0 of the three-level energy storage converter under the actual conversion dq coordinate axis 0d 、i 0q After comparison, the host 0 current inner loop module generates a duty cycle signal d0; finally, the host 0 SPWM0 module modulates the output drive signal to control the three-level energy storage converter host 0;

[0094] The three-level energy storage converter slave 1 samples the three-phase AC frequency signal f g , three-phase AC phase signal θ g , three-phase AC voltage u a 、u b 、u c and the three-phase alternating current i 1a 、i 1b 、i 1c Since it is not convenient to realize closed-loop control of three-phase AC voltage and three-phase AC current, the three-phase AC frequency signal f g With the three-phase AC phase signal θ gThe PLL1 module of slave 1 is input, and the phase-locked information pll10 and pll11 are obtained to phase-lock Park transformation module 10 and Park transformation module 11 respectively; in order to reduce the control variables and realize power decoupling, the variables under the three-phase stationary coordinate system abc are transformed to the two-phase rotating coordinate system dq through Park transformation module 10 and Park transformation module 11, and the voltage e of the three-level energy storage converter slave 1 under the dq coordinate axis is obtained. 1d 、e 1q With current i 1d 、i 1q ; Then, the host 0 power outer loop module generates the current direct axis component i dref and the quadrature axis component i qref , and the current i of the slave 1 of the three-level energy storage converter under the actual conversion dq coordinate axis 1d 、i 1q After comparison, the duty cycle signal d1 is generated by the current inner loop module of slave 1; finally, the SPWM1 module of slave 1 modulates the output drive signal to control the three-level energy storage converter slave 1;

[0095] The other slaves also receive the direct axis component i generated by the host 0 power outer loop module dref and the quadrature axis component i qref The specific control method is the same as slave 1.

[0096] (1) Grid-connected PQ control strategy based on master-slave control

[0097] The power-voltage control (PQ) control strategy is to control the active power and reactive power generated by the converter when connected to the grid. The PQ control structure under master-slave control is as follows: Figure 5 As shown, the status of each converter is equal. Generally, the converter needs to provide active power to the power grid and operate at a unit power factor. At this time, the active reference value is set according to the capacity, and the reactive reference value is set to 0; if the converter needs to provide reactive power in addition, the reactive reference value can be set according to the need.

[0098] The grid-connected converter has the characteristics of a current source and needs to control the grid-connected current under a given instruction. The PI controller can control the DC quantity without a net error. Therefore, the control system is generally designed in a mathematical model under a rotating coordinate system. Let L s Represents the filter inductance and is equal to L1+L2. In the TNPC topology, it can be approximately considered that the voltages of the upper and lower capacitors of the DC bus are equal, that is, u dc1 =u dc2 , define u rd =S d u dc1 ,u rq =S qu dc1 , then the mathematical model expression of the system in the dq rotating coordinate system is:

[0099]

[0100] From equation (1), we can see that there is a grid voltage component in the mathematical model of the converter, and there is also a variable ωL between the dq axes. s i q 、-ωL s i d In order to decouple the dq axis and realize separate control, the controller is compensated for the corresponding coupling component, and the command voltage control equation of the converter dq axis is:

[0101]

[0102] In the formula, K iP and K iI are the current PI controller parameters, and is the dq axis grid-connected current command value.

[0103] Since the switching frequency of the PWM converter is high, it can be approximately considered that the command voltage u rd * 、u rq * The actual output voltage u rd 、u rq If they are equal, then we can substitute formula (2) into formula (1) and simplify it to get:

[0104]

[0105] As shown in equation (3), the dq axis current variables of the converter are decoupled and can be independently controlled. Therefore, the decoupling control structure shown in equation (2) is as follows: Figure 6 shown.

[0106] The mathematical model of the three-phase T-type three-level circuit in the stationary coordinate system abc is converted to the dq coordinate system through Park transformation. The transformation relationship is as follows: Figure 7 shown.

[0107] The command value given by the superior is generally the grid-connected active and reactive power P S * , Q S * , when the grid voltage vector is oriented on the d-axis in the dq rotating coordinate system, according to Figure 7 It can be deduced that u sd is the three-phase voltage amplitude, u sd =0, then the dq grid-connected current command calculation expression is as follows:

[0108]

[0109] There is a delay in the sampling and converter control of the digital chip. The inertia link is used to simulate the delay equivalently. According to formula (3), the current loop structure block diagram after decoupling control is as follows: Figure 8 shown.

[0110] Figure 8 In, e dq is the grid voltage feedforward quantity, T s is the current signal sampling period (i.e., switching period), K PWM is the converter gain, which is equal to the converter DC bus voltage U dc With the triangular carrier amplitude U c The ratio of , rewrite the PI controller into zero-pole form, that is

[0111]

[0112] Combine the small time constants of the two inertial links and ignore the small quadratic term, and we have

[0113]

[0114] Through formula (5) and formula (6), we can get Figure 8 The simplified current loop structure is as follows: Fig. 9 shown.

[0115] Depend on Fig. 9 The open-loop transfer function of the current command is:

[0116]

[0117] For the PI controller, let:

[0118]

[0119] After correction, the open-loop transfer function of the current loop is:

[0120]

[0121] From formula (9), the characteristic equation of the system is:

[0122]

[0123] The damping coefficient of the system is taken as ξ=0.707, then:

[0124]

[0125] According to equations (8) and (11), the parameters of the current loop PI controller can be obtained as follows:

[0126]

[0127] (2) Off-grid VF control strategy based on master-slave control

[0128] like Fig.10 As shown, the master-slave three-level energy storage converter system adopts an off-grid constant voltage-frequency ratio control structure based on master-slave control, including a three-level energy storage converter host 0 and multiple three-level energy storage converter slaves; when off-grid, the host 0 controls the voltage amplitude and frequency of the three-phase AC side, and the host 0 issues a current instruction according to the calculation result of the voltage loop. After the slave obtains the current instruction, it supplies power to the load together with the host; the specific structure is:

[0129] The Park conversion module 00 in the three-level energy storage converter host 0 collects the three-phase AC current i L0a 、i L0b 、i L0c , abc01 / dq01 module collects three-phase AC voltage u La 、u Lb 、u Lc ; Host 0 realizes power decoupling through Park transformation module 00 and Park transformation module 01, transforms the variables under the three-phase stationary coordinate system abc to the two-phase rotating coordinate system dq through Park, and obtains the current i of the three-level energy storage converter host 0 under the dq coordinate axis L0d 、i L0q With voltage u L0d 、u L0q ; The host 0 voltage outer loop module is based on the voltage setting value V ref The voltage u of the host 0 of the three-level energy storage converter under the dq coordinate axis L0d 、u L0q Perform calculations to obtain the direct axis component i of the current Ldref and the quadrature axis component i Lqref The host 0 current inner loop module performs calculations based on the information transmitted by the Park conversion module 00 and the host 0 voltage outer loop module, and the host 0 current inner loop module generates a duty cycle signal d L0 , and control the host 0SPWM0 module to drive the switch tube action of the three-level energy storage converter host 0 to achieve off-grid control of the three-level energy storage converter host 0;

[0130] The three-level energy storage converter host 0 and the three-level energy storage converter slave exchange information through the communication network, and the slave obtains the current direct axis component i generated by the host 0 voltage outer loop module. Ldref and the quadrature axis component i Lqref The slave n obtains the current i of the three-level energy storage converter slave n under the dq coordinate axis through its own Park transformation module n0. nd 、inq The slave n current inner loop module receives the transmission information of the Park conversion module n0 and the host 0 voltage outer loop module for calculation and generates a duty cycle signal d Ln , and controls the slave nSPWM module to drive the switch tube action of the three-level energy storage converter slave n, thereby realizing off-grid control of the three-level energy storage converter slave n.

[0131] The master-slave three-level energy storage converter system, the off-grid constant voltage-frequency ratio control structure based on master-slave control also includes an off-grid constant voltage-frequency ratio control strategy based on master-slave control, and the control strategy is specifically:

[0132] The three-level energy storage converter host 0 samples the three-phase AC voltage u La 、u Lb 、u Lc With three-phase alternating current i L0a 、i L0b 、i L0c Since it is not convenient to realize closed-loop control of three-phase AC voltage and three-phase AC current, in order to reduce the control variables and realize power decoupling, the variables under the three-phase stationary coordinate system abc are transformed to the two-phase rotating coordinate system dq through Park transformation module 00 and Park transformation module 01, and the current i of the host 0 of the three-level energy storage converter under the dq coordinate axis is obtained. L0d 、i L0q With voltage u L0d 、u L0q ; Then, the voltage u of the three-level energy storage converter host 0 under the dq coordinate axis L0d 、u L0q With the voltage setting value V ref Enter the host 0 voltage outer loop module and generate the current direct axis component i Ldref and the quadrature axis component i Lqref , and the current i of the host 0 of the three-level energy storage converter under the actual conversion dq coordinate axis L0d 、i L0q After comparison, the host 0 current inner loop module generates a duty cycle signal d L0 ; Finally, the host 0SPWM0 module modulates the output drive signal to control the three-level energy storage converter host 0;

[0133] The three-level energy storage converter samples the three-phase AC current i from the machine 1 L1a 、i L1b 、i L1cSince the three-phase AC voltage and the three-phase AC current are not convenient to realize closed-loop control, in order to reduce the control variables and realize power decoupling, the variables under the three-phase stationary coordinate system abc are transformed to the two-phase rotating coordinate system dq through the Park transformation module 10, and the current i of the slave 1 of the three-level energy storage converter under the dq coordinate axis is obtained. L1d 、i L1q ; Then, the host 0 voltage outer loop module generates the current direct axis component i Ldref and the quadrature axis component i Lqref , and the current i of the slave 1 of the three-level energy storage converter under the actual conversion dq coordinate axis L1d 、i L1q After comparison, the duty cycle signal d is generated by the current inner loop module of slave 1. L1 ; Finally, the slave 1 SPWM1 module modulates the output drive signal to control the three-level energy storage converter slave 1;

[0134] The other slaves also receive the host 0 voltage and the outer loop module generates the current direct axis component i Ldref and the quadrature axis component i Lqref The specific control method is the same as slave 1.

[0135] like Fig.10 The figure shows the variable voltage variable frequency (VF) control based on master-slave control. The host 0 adopts VF control to establish the voltage amplitude and frequency on the AC side. The slave has the same control strategy as when connected to the grid. It adopts a single-loop PQ to control the output power. The voltage amplitude and frequency established by the host 0 are obtained through a phase-locked loop. The master and slaves exchange information through a communication network. The host 0 issues a current command based on the calculation result of the voltage loop. After obtaining the current command, the slave supplies power to the load together with the host 0.

[0136] When the master-slave PCS parallel system operates in off-grid conditions, the host 0 uses VF control as a voltage source. The inner loop of the host 0 controls the inductor current to improve the dynamic response speed of the system; the outer loop controls the filter capacitor voltage to stabilize the AC side voltage. The outer loop output is limited as the inner loop instruction to achieve zero static error regulation and over-current protection for the output current. The mathematical model of the converter under off-grid conditions is:

[0137]

[0138] It can be seen from formula (13) that there is a load current component in the mathematical model of the converter, and there are also variables coupled between the dq axes. In the rotating coordinate system, PI control is used to realize the zero-static error control of the DC quantity. In order to decouple the dq axes and realize independent control, the controller is compensated for the corresponding coupling component. The command voltage control equation of the converter dq axis is:

[0139]

[0140] In formula (14), K iP and K iI is the current loop proportional coefficient and integral coefficient, K vP and K vI is the voltage loop proportional coefficient and integral coefficient; u cd * and u cq * is the dq axis voltage outer loop command value, which is determined by the load requirement; i d * and i q * is the dq axis current inner loop command value, and the current inner loop command is determined by the voltage outer loop output; u rd * and u rq * is the converter dq axis control voltage command value.

[0141] have It is also assumed that within the bandwidth of the voltage outer loop, the current inner loop can instantaneously track the command value, that is, for the voltage loop Substituting formula (14) into (13), we can calculate:

[0142]

[0143] As shown in equation (15), the dq axis state variables of the converter are no longer coupled to each other and are not affected by the load current. Therefore, the decoupling control algorithm of state feedback plus load current and capacitor voltage feedforward shown in equation (14) realizes the decoupling control of the converter state variables. Its structure is as follows: Fig.11 shown.

[0144] Considering the delay of sampling link and converter PWM control, and using inertia link to replace the delay, according to formula (15), the structure block diagram of the dual-loop control system after decoupling control is as follows: Fig.12 shown.

[0145] Fig.12 In, τ vf is the voltage signal sampling delay, τ if is the current signal sampling delay. The sampling delay of voltage and current is equal to the switching period, that is, τ vf =τ if =T s , K PWM For a dual-loop control system, the control parameters of the inner loop are usually designed first, and then the control parameters of the outer loop are designed.

[0146] For the current inner loop, the closed-loop transfer function is:

[0147]

[0148] When the switching frequency is high enough, that is, T s When it is very small, the quadratic term s in the denominator of formula (16) 2 The coefficient of is much smaller than the coefficient of the linear term s, so the quadratic term can be ignored, and equation (16) can be simplified to:

[0149]

[0150] Will Fig.12 The current inner loop transfer function in is replaced by equation (17), and the simplified voltage outer loop control block diagram can be obtained. Its structure is as follows: Fig.13 shown.

[0151] Combine the small inertia links and ignore the small quadratic term, then we have Fig.13 The open-loop transfer function of the voltage outer loop is obtained as:

[0152]

[0153] As shown in equation (18), the voltage loop is a typical type II system. In order to control the overshoot of the system, the minimum closed-loop resonance peak value M can be used. r Design method to design PI controller. According to its design method:

[0154]

[0155] In formula (19), H represents the intermediate frequency width of the voltage loop, which is generally taken as 5. Substituting it into the above formula, we can get:

[0156]

[0157] Through the above analysis, the off-grid VF control strategy block diagram based on master-slave control is as follows Fig.14 shown.

[0158] Host 0 according to the voltage reference u d_ref and u q_ref To achieve dual-loop control. u_PI_m is the host 0 voltage outer loop controller transfer function; G i_PI_m is the transfer function of the host 0 current inner loop controller. The slave obtains the current command value of the host 0 voltage loop after actual calculation and low-pass filtering through the communication network, and obtains the d-axis current reference i d_ref_s and q-axis current reference i q_ref_s , and then realize single-loop control through the current loop. Among them, G i_PI_sis the transfer function of the inner loop controller of the slave current. Both the inner and outer loops of the master and slave adopt PI control. The outer loop parameter is k pu_m , k iu_m , the inner loop parameter is k pi_m , k ii_m , the slave inner loop parameter is k pi_s , k ii_s ; G LPF_i_ref It is the transfer function of the low-pass filter link of the slave current command.

[0159] The master-slave three-level energy storage converter system, the AC voltage margin controller, in the AC voltage margin control, each converter can control the voltage output on the AC side, and no switching instructions between the master and slave machines are required, and there are multiple voltage support points in the parallel system;

[0160] When the parallel system is running stably, the host 0 adopts dual-loop control to stabilize the AC side voltage, and the slave adopts single-loop control to provide power to the system; when the power of the host 0 exceeds the limit, it switches to the single-loop control mode, runs at maximum power and loses control of the AC voltage; at this time, when the slave detects that the AC side voltage is less than the reference set in the local voltage loop, the slave switches to dual-loop control to control the AC side voltage to maintain stable operation of the system.

[0161] (3) AC voltage margin control strategy

[0162] Although traditional master-slave control has the advantages of high control accuracy and fast response speed, it may suffer from communication packet loss or disconnection, and is highly dependent on the communication system. In order to enhance the stability of the master-slave PCS parallel system, the present invention adds voltage margin control to the slave to avoid the problem of host 0 overload and parallel system voltage collapse caused by load disturbance when communication fails.

[0163] In the master-slave three-level energy storage converter system, the AC voltage margin controller can control the voltage output on the AC side in the AC voltage margin control, and there is no need for switching instructions between the master and slave machines. There are multiple voltage support points in the parallel system. When the parallel system is running stably, the host 0 adopts dual-loop control to stabilize the AC side voltage, and the slave adopts single-loop control to provide power to the system; when the power of the host 0 exceeds the limit, it switches to the single-loop control mode, runs at maximum power and loses control of the AC voltage. At this time, when the slave detects that the AC side voltage is less than the reference set in the local voltage loop, the slave switches to dual-loop control to control the AC side voltage to maintain stable operation of the system.

[0164] AC voltage margin control principle Fig.15 Shown: U dref_m is the host 0 voltage loop instruction, U dref_s1 is the low deviation limit of AC voltage of slave 1, Udref_s2 is the low deviation limit of AC voltage of slave 2, P max The maximum output active power of the master and slave, P ref Active power command for master and slave machines;

[0165] The voltage margin outer loop controller of the slave 1 and the voltage margin outer loop controller of the slave 2 are equal in status;

[0166] The voltage margin outer loop controller of slave 1 is implemented as follows: the voltage loop command value U of master 0 dref_m The actual voltage u of the host 0 d_m After the difference is made, the host 0 current low deviation limit i is obtained through the PI0 module. _m ; Slave 1 AC voltage low deviation limit U dref s1 The actual voltage u of slave 1 d s1 After the difference is made, the low deviation limit value i of slave 1 current is obtained through the PI1 module. _s1 ; Host 0 current low deviation limit i _m The current low deviation limit i of slave 1 _s1 After comparison operation by the Max01 module, the low deviation limit of the AC current of slave 1 is obtained;

[0167] The voltage margin outer loop controller of the slave 2 is implemented as follows: the voltage loop command value U of the host 0 dref_m The actual voltage u of the host 0 d_m After the difference is made, the host 0 current low deviation limit i is obtained through the PI0 module. _m ; Slave 2 AC voltage low deviation limit U dref_s2 The actual voltage u of slave 2 d_s2 After the difference is made, the low deviation limit value i of slave 2 current is obtained through the PI2 module. _s2 ; Host 0 current low deviation limit i _m The current low deviation limit i of slave 2 _s2 After comparison operation by the Max02 module, the low deviation limit of the AC current of slave 2 is obtained;

[0168] like Fig.16 and 17 The figure shows the slave voltage margin outer loop controller. When the communication is normal, the host 0 is responsible for controlling the AC side voltage. At this time, the AC side voltage is greater than the voltage low deviation limit of the two slaves, and the current low deviation limit i in the voltage margin outer loop controller of slaves 1 and 2 is _s1 with i _s2 The limit value is always negative, which is less than the instruction sent by the master 0 communication. Slave 1 and slave 2 are responsible for providing power at this time and operate in single-loop mode. The master-slave three-level energy storage converter system operates stably at point A in the AC voltage margin control principle (such as Fig.15 As shown), that is, the power of the master 0, slave 1 and slave 2 is at the active power command value of the master and slave, and the voltage of the master 0, slave 1 and slave 2 is at the voltage loop command value of the master 0;

[0169] When a communication failure occurs and the AC side suddenly cuts into the load, the slave can only output power according to the instruction before the communication disconnection. At this time, the host 0 is very likely to be overloaded by adjusting the power alone. When the output power of the host 0 reaches the maximum, it has not yet met the load power. The AC side voltage will drop until it is lower than the low deviation limit of the AC voltage of slave 1; at this time, the output of the outer loop controller of slave 1 gradually increases and exceeds the instruction of the host 0 before the communication disconnection. Slave 1 is i _s1 The power is supplemented for the current loop command, and the AC voltage is controlled to the low deviation limit of the AC voltage of slave 1. At this time, the master-slave three-level energy storage converter system operates at point B in the AC voltage margin control principle (such as Fig.15 As shown), that is, the power of host 0 is at the maximum output active power value of host 0, the power of slave 1 is greater than the active power command value of slave 1, but does not exceed the maximum output active power value of slave 1, and the power of slave 2 is at the active power command value of slave 2; the voltages of host 0, slave 1 and slave 2 are at the low deviation limit of the AC voltage of slave 1;

[0170] When the system is running at point B in the AC voltage margin control principle and there is still load cut-in, and the output power of slave 1 is insufficient, the AC side voltage continues to drop, similar to the response of slave 1. Slave 2 detects that the voltage is less than the AC voltage low deviation limit set by itself. Master 0 and slave 1 run in single-loop mode, and slave 2 is i _s2 The current loop command starts to control the AC side voltage to the low deviation limit of the AC voltage of slave 2 and compensates for the remaining power. At this time, the master-slave three-level energy storage converter system operates at point C in the AC voltage margin control principle (such as Fig.15 As shown), that is, the power of host 0 is at the maximum output active power value of host 0, the power of slave 1 is at the maximum output active power value of slave 1, the power of slave 2 is greater than the active power instruction value of slave 2, but does not exceed the maximum output active power value of slave 2; the voltages of host 0, slave 1 and slave 2 are at the low deviation limit of the AC voltage of slave 2.

[0171] The above is only an embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

Claims

1. A master-slave three-level energy storage converter system, Features: The three-level energy storage converter input DC side +U dc / 2 and -U dc / 2 connect the supporting capacitor C in series 1 and C 2 The two terminals of the capacitor C 1 and C 2 The connection point is the reference point O; the two switch tubes S a2 , S a3 Reverse series connection, switch tube S a3 The emitter of the switch is connected to point O, and the switch S a2 The emitter of the switch tube S a1 The emitter and switch tube S a4 The collector of the switch tube S a1 The collector of the input DC side +U dc / 2 connected, switch tube S a4 The emitter and input DC side -U dc / 2 connected; Two switch tubes S b2 , S b3 Reverse series connection, switch tube S b3 The emitter of the switch is connected to point O, and the switch S b2 The emitter of the switch tube S b1 The emitter and switch tube S b4 The collector of the switch tube S b1 The collector of the input DC side +U dc / 2 connected, switch tube S b4 The emitter and input DC side -U dc / 2 connected; Two switch tubes S c2 , S c3 Reverse series connection, switch tube S c3 The emitter of the switch is connected to point O, and the switch S c2 The emitter of the switch tube S c1 The emitter and switch tube S c4 The collector of the switch tube S c1 The collector of the input DC side +U dc / 2 connected, switch tube S c4 The emitter and input DC side -U dc / 2 is connected.

2. The master-slave three-level energy storage converter system according to claim 1, Features: The converter system adopts the sine pulse width modulation SPWM technology to generate the switch tube drive signal, U c1 and U c2 are two high-frequency carriers with the same amplitude, phase, and frequency, U r is a sinusoidal modulated wave; For phase A: When U r Greater than U c1 When S a1 When U r Less than U c2 When S a4 The bridge arm outputs N state, and the rest are O state. For phase B: When U r Greater than U c1 When S b1 When U r Less than U c2 When S b4 The bridge arm outputs N state, and the rest are O state. For phase C: When U r Greater than U c1 When S c1 When U r Less than U c2 When S c4 The bridge arm outputs N state, while the rest are O state.

3. The master-slave three-level energy storage converter system according to claim 2, Features: The S a3 and S a2 As S a1 and S a4 The complementary tube is turned on; the S b3 and S b2 As S b1 and S b4 The complementary tube is turned on; the S c3 and S c2 As S c1 and S c4 The complementary tube is turned on.

4. The master-slave three-level energy storage converter system according to claim 1, Features: The converter system adopts a grid-connected power and voltage control structure based on master-slave control, including a three-level energy storage converter host 0 and multiple three-level energy storage converter slaves; the host 0 and the slaves have the same circuit structure, and the converter provides active power and reactive power to the grid when connected to the grid; among them, the host 0 is dominant and is responsible for managing and regulating the power flow of the energy storage system, while sending instructions to the slaves, monitoring the status and collecting data; the specific structure is: The three-level energy storage converter host 0 collects the three-phase AC frequency signal f through the host 0PLL0 module g With the phase signal θ g , and output phase-lock information pll 00 、pll 01 ; Park conversion module 00 collects three-phase AC current i 0a 、i 0b 、i 0c ,Park transformation module 01 collects three-phase AC voltage u a 、u b 、u c Park transformation module 00 and Park transformation module 01 transform the variables under the three-phase stationary coordinate system abc to the two-phase rotating coordinate system dq through Park transformation, and obtain the voltage e of the host 0 of the three-level energy storage converter under the dq coordinate axis 0d 、e 0q With current i 0d 、i 0q , thereby achieving power decoupling; the host 0 power outer loop module is based on the power setting value P ref , Q ref The voltage e of the host 0 of the three-level energy storage converter under the dq coordinate axis 0d 、e 0q Perform calculations to obtain the direct axis component i of the current dref and the quadrature axis component i qref The host 0 current inner loop module receives the transmission information from the Park conversion module 00, Park conversion module 01 and the host 0 power outer loop module to perform calculations and generate a duty cycle signal d 0 , and control the host 0SPWM0 module to drive the switch tube action of the three-level energy storage converter host 0 to achieve grid-connected control of the three-level energy storage converter host 0; The three-level energy storage converter host 0 and the three-level energy storage converter slave exchange information through a communication network, and the slave obtains the current direct axis component i generated by the power outer ring module of the host 0. dref and the quadrature axis component i qref ; Slave n collects three-phase AC frequency signal f through its own slave n PLLn module g With the phase signal θ g , and output respective phase-locked information pll n0 、pll n1 , and the voltage e of the slave n of the three-level energy storage converter under the dq coordinate axis is obtained through the respective Park transformation modules n0 and Park transformation modules n1 nd 、e nq With current i nd 、i nq The slave n current inner loop module receives the transmission information from the Park conversion module n0, Park conversion module n1 and the host 0 power outer loop module for calculation and generates a duty cycle signal d n , and controls the slave n SPWMn module to drive the switch tube action of the three-level energy storage converter slave n, thereby realizing the grid-connected control of the three-level energy storage converter slave n.

5. The master-slave three-level energy storage converter system according to claim 4, Features: The master-slave control-based grid-connected power voltage control structure also includes a master-slave control-based grid-connected power voltage control strategy, and the control strategy is specifically: The three-level energy storage converter host 0 samples the three-phase AC frequency signal f g , three-phase AC phase signal θ g , three-phase AC voltage u a 、u b 、u c and the three-phase alternating current i 0a 、i 0b 、i 0c , the three-phase AC frequency signal f g With the three-phase AC phase signal θ g Input the host 0PLL0 module, and the obtained phase-locking information pll00 and pll01 are used to phase-lock the Park transformation module 00 and the Park transformation module 01 respectively; the variables under the three-phase stationary coordinate system abc are transformed to the two-phase rotating coordinate system dq through the Park transformation module 00 and the Park transformation module 01, and the voltage e of the three-level energy storage converter host 0 under the dq coordinate axis is obtained. 0d 、e 0q With current i 0d 、i 0q ; Then, the voltage e of the three-level energy storage converter host 0 under the dq coordinate axis 0d 、e 0q With power setting value P ref , Q ref Enter the host 0 power outer loop module and generate the current direct axis component i dref and the quadrature axis component i qref , and the current i of the host 0 of the three-level energy storage converter under the actual conversion dq coordinate axis 0d 、i 0q After comparison, the host 0 current inner loop module generates a duty cycle signal d 0 ; Finally, the host 0SPWM0 module modulates the output drive signal to control the three-level energy storage converter host 0; The three-level energy storage converter slave 1 samples the three-phase AC frequency signal f g , three-phase AC phase signal θ g , three-phase AC voltage u a 、u b 、u c and the three-phase alternating current i 1a 、i 1b 、i 1c , the three-phase AC frequency signal f g With the three-phase AC phase signal θ g Input slave 1 PLL1 module, the obtained phase-locking information pll10, pll11 respectively phase-locks Park transformation module 10 and Park transformation module 11; the variables under the three-phase stationary coordinate system abc are transformed to the two-phase rotating coordinate system dq through Park transformation module 10 and Park transformation module 11, and the voltage e of the three-level energy storage converter slave 1 under the dq coordinate axis is obtained. 1d 、e 1q With current i 1d 、i 1q ; Then, the host 0 power outer loop module generates the current direct axis component i dref and the quadrature axis component i qref , and the current i of the slave 1 of the three-level energy storage converter under the actual conversion dq coordinate axis 1d 、i 1q After comparison, the duty cycle signal d is generated by the current inner loop module of slave 1. 1 ; Finally, the slave 1 SPWM1 module modulates the output drive signal to control the three-level energy storage converter slave 1; The other slaves also receive the direct axis component i generated by the host 0 power outer loop module dref and the quadrature axis component i qref The specific control method is the same as slave 1.

6. The master-slave three-level energy storage converter system according to claim 1, Features: The converter system adopts an off-grid constant voltage-frequency ratio control structure based on master-slave control, including a three-level energy storage converter host 0 and multiple three-level energy storage converter slaves; when off-grid, the host 0 controls the voltage amplitude and frequency of the three-phase AC side, and the host 0 issues a current instruction according to the calculation result of the voltage loop. After the slave obtains the current instruction, it supplies power to the load together with the host; the specific structure is: The Park conversion module 00 in the three-level energy storage converter host 0 collects the three-phase AC current i L0a 、i L0b 、i L0c , Park transformation module 01 collects three-phase AC voltage u La 、u Lb 、u Lc ; Host 0 realizes power decoupling through Park transformation module 00 and Park transformation module 01, transforms the variables under the three-phase stationary coordinate system abc to the two-phase rotating coordinate system dq through Park, and obtains the current i of the three-level energy storage converter host 0 under the dq coordinate axis L0d 、i L0q With voltage u L0d 、u L0q ; The host 0 voltage outer loop module is based on the voltage setting value V ref The voltage u of the host 0 of the three-level energy storage converter under the dq coordinate axis L0d 、u L0q Perform calculations to obtain the direct axis component i of the current Ldref and the quadrature axis component i Lqref The host 0 current inner loop module performs calculations based on the information transmitted by the Park conversion module 00 and the host 0 voltage outer loop module, and the host 0 current inner loop module generates a duty cycle signal d L0 , and control the host 0SPWM0 module to drive the switch tube action of the three-level energy storage converter host 0 to achieve off-grid control of the three-level energy storage converter host 0; The three-level energy storage converter host 0 and the three-level energy storage converter slave exchange information through the communication network, and the slave obtains the current direct axis component i generated by the host 0 voltage outer loop module. Ldref and the quadrature axis component i Lqref ; Slave n obtains the current i of the three-level energy storage converter slave n under the dq coordinate axis through its own Park conversion module n0 nd 、i nq The slave n current inner loop module receives the transmission information of the Park conversion module n0 and the host 0 voltage outer loop module for calculation and generates a duty cycle signal d Ln , and controls the slave nSPWM module to drive the switch tube action of the three-level energy storage converter slave n, thereby realizing off-grid control of the three-level energy storage converter slave n.

7. The master-slave three-level energy storage converter system according to claim 6, Features: The off-grid constant voltage-frequency ratio control structure based on master-slave control also includes an off-grid constant voltage-frequency ratio control strategy based on master-slave control, and the control strategy is specifically: The three-level energy storage converter host 0 samples the three-phase AC voltage u La 、u Lb 、u Lc With three-phase alternating current i L0a 、i L0b 、i L0c , the variables under the three-phase stationary coordinate system abc are transformed to the two-phase rotating coordinate system dq through Park transformation module 00 and Park transformation module 01, and the current i of the three-level energy storage converter host 0 under the dq coordinate axis is obtained. L0d 、i L0q With voltage u L0d 、u L0q ; Then, the voltage u of the three-level energy storage converter host 0 under the dq coordinate axis L0d 、u L0q With the voltage setting value V ref Enter the host 0 voltage outer loop module and generate the current direct axis component i Ldref and the quadrature axis component i Lqref , and the current i of the host 0 of the three-level energy storage converter under the actual conversion dq coordinate axis L0d 、i L0q After comparison, the host 0 current inner loop module generates a duty cycle signal d L0 ; Finally, the host 0SPWM0 module modulates the output drive signal to control the three-level energy storage converter host 0; The three-level energy storage converter samples the three-phase AC current i from the slave 1 L1a 、i L1b 、i L1c , the Park transformation module 10 transforms the variables in the three-phase stationary coordinate system abc to the two-phase rotating coordinate system dq through Park, and obtains the current i of the slave 1 of the three-level energy storage converter in the dq coordinate axis L1d 、i L1q ; Then, the host 0 voltage outer loop module generates the current direct axis component i Ldref and the quadrature axis component i Lqref , and the current i of the slave 1 of the three-level energy storage converter under the actual conversion dq coordinate axis L1d 、i L1q After comparison, the duty cycle signal d is generated by the current inner loop module of slave 1. L1 ; Finally, the slave 1 SPWM1 module modulates the output drive signal to control the three-level energy storage converter slave 1; The other slaves also receive the host 0 voltage and the outer loop module generates the current direct axis component i Ldref and the quadrature axis component i Lqref The specific control method is the same as slave 1.

8. The master-slave three-level energy storage converter system according to claim 1, Features: In the AC voltage margin control, each converter can control the voltage output on the AC side without the need for switching instructions between the master and slave machines, and there are multiple voltage support points in the parallel system; When the parallel system is running stably, the host 0 adopts dual-loop control to stabilize the AC side voltage, and the slave adopts single-loop control to provide power to the system; when the power of the host 0 exceeds the limit, it switches to the single-loop control mode, runs at maximum power and loses control of the AC voltage; at this time, when the slave detects that the AC side voltage is less than the reference set in the local voltage loop, the slave switches to dual-loop control to control the AC side voltage to maintain stable operation of the system.

9. The master-slave three-level energy storage converter system according to claim 1, Features: In the AC voltage margin control, U dref_m is the host 0 voltage loop instruction, U dref_s1 is the low deviation limit of AC voltage of slave 1, U dref_s2 is the low deviation limit of AC voltage of slave 2, P max The maximum output active power of the master and slave, P ref Active power command for master and slave machines; The voltage margin outer loop controller of the slave 1 and the voltage margin outer loop controller of the slave 2 are equal in status; The voltage margin outer loop controller of slave 1 is implemented as follows: the voltage loop command value U of master 0 dref_m The actual voltage u of the host 0 d_m After the difference is made, the host 0 current low deviation limit i is obtained through the PI0 module. _m ; Slave 1 AC voltage low deviation limit U dref_s1 The actual voltage u of slave 1 d_s1 After the difference is made, the low deviation limit value i of slave 1 current is obtained through the PI1 module. s1 ; Host 0 current low deviation limit i m The current low deviation limit i of slave 1 _s1 After comparison operation by the Max01 module, the low deviation limit of the AC current of slave 1 is obtained; The voltage margin outer loop controller of the slave 2 is implemented as follows: the voltage loop command value U of the host 0 dref_m The actual voltage u of the host 0 d_m After the difference is made, the host 0 current low deviation limit i is obtained through the PI0 module. _m ; Slave 2 AC voltage low deviation limit U dref_s2 The actual voltage u of slave 2 d_s2 After the difference is made, the low deviation limit value i of slave 2 current is obtained through the PI2 module. _s2 ; Host 0 current low deviation limit i _m The current low deviation limit i with slave 2 _s2 After comparison operation by the Max02 module, the low deviation limit of the AC current of slave 2 is obtained; When the communication is normal, the host 0 is responsible for controlling the AC side voltage; at this time, the AC side voltage is greater than the voltage low deviation limit of the two slaves, and the current low deviation limit i in the voltage margin outer loop controller of slaves 1 and 2 is _s1 with i _s2 It is always a negative limit value, which is less than the instruction issued by the master 0 communication. Slave 1 and slave 2 are responsible for providing power at this time and operate in single-loop mode. The master-slave three-level energy storage converter system operates stably at point A in the AC voltage margin control principle, that is, the power of the master 0, slave 1 and slave 2 is at the active power instruction value of the master and slave, and the voltage of the master 0, slave 1 and slave 2 is at the voltage loop instruction value of the master 0. When a communication failure occurs and the AC side suddenly cuts into the load, the slave can only output power according to the instruction before the communication disconnection. At this time, the host 0 is very likely to be overloaded by adjusting the power alone. When the output power of the host 0 reaches the maximum, it has not yet met the load power. The AC side voltage will drop until it is lower than the low deviation limit of the AC voltage of slave 1; at this time, the output of the outer loop controller of slave 1 gradually increases and exceeds the instruction of the host 0 before the communication disconnection. Slave 1 is i _s1 The power is supplemented for the current loop command, and the AC voltage is controlled to the low deviation limit of the AC voltage of slave 1. At this time, the master-slave three-level energy storage converter system operates at point B in the AC voltage margin control principle, that is, the power of master 0 is at the maximum output active power value of master 0, the power of slave 1 is greater than the active power command value of slave 1, but does not exceed the maximum output active power value of slave 1, and the power of slave 2 is at the active power command value of slave 2; the voltages of master 0, slave 1 and slave 2 are at the low deviation limit of the AC voltage of slave 1; When the system is running at point B in the AC voltage margin control principle and there is still load cut-in, and the output power of slave 1 is insufficient, the AC side voltage continues to drop, similar to the response of slave 1. Slave 2 detects that the voltage is less than the AC voltage low deviation limit set by itself. Master 0 and slave 1 run in single-loop mode, and slave 2 is i _s2 The current loop instruction starts to control the AC side voltage to the low deviation limit of the AC voltage of slave 2 and compensates for the remaining power. The master-slave three-level energy storage converter system now operates at point C in the AC voltage margin control principle, that is, the power of master 0 is at the maximum output active power value of master 0, the power of slave 1 is at the maximum output active power value of slave 1, and the power of slave 2 is greater than the active power instruction value of slave 2, but does not exceed the maximum output active power value of slave 2; the voltages of master 0, slave 1 and slave 2 are at the low deviation limit of the AC voltage of slave 2.

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