Two-stage single-phase three-level boost inverter control method and system

Abstract

The invention discloses a method and a system for controlling a two-stage single-phase three-level boost inverter. The method comprises the following steps of: controlling an input current by using a first proportional integral controller according to an actual value and a reference value of the input current of the two-stage single-phase three-level boost inverter; using a second proportional integral controller to control the flying capacitor voltage according to the actual value and the reference value of the flying capacitor voltage of the two-stage single-phase three-level boost inverter; using a third proportional-integral controller to control the average value of the DC bus voltage according to the average value of the DC bus voltage of the two-stage single-phase three-level boost inverter and the reference average value to obtain a grid-connected current amplitude; controlling the grid-connected current by using a proportional resonance controller according to the grid-connected current amplitude and the grid-connected current of the two-stage single-phase three-level boost inverter; and calculating the duty ratio of each switch according to the input current control result, the flying capacitor voltage control result and the grid-connected current control result. The method does not need a complex algorithm or extra hardware support, and is easy for engineering realization.

Description

Technical Field

[0001] The present invention relates to inverter control technology, and in particular to a two-stage single-phase three-level boost inverter control method and system. Background Art

[0002] With the rapid development of renewable energy generation and energy storage technologies, the performance optimization of single-phase inverters, as core devices for energy conversion, has attracted considerable industry attention. Two-stage inverters, with their wide input voltage range and flexible controllability, are widely used in distributed energy generation and storage systems.

[0003] The two-stage single-phase three-level boost inverter integrates a two-stage power conversion structure, boost conversion technology and a three-level topology. It has the characteristics of a wide input voltage range, high energy conversion efficiency, low power device voltage stress and compact filter design. It can be widely used in new energy power generation (such as photovoltaics, energy storage), electric vehicles and other fields.

[0004] The safe and efficient operation of this system requires achieving four control objectives: balancing the flying capacitor voltage to achieve three-level functionality, balancing the bus voltage to provide stable input to the inverter, eliminating input current ripple at twice the power frequency to minimize impact on the DC power supply system (such as photovoltaic panels and batteries), and ensuring that the grid-connected current quality meets grid standards. Due to the multivariable nonlinear coupling characteristics of this system, existing control methods struggle to simultaneously address these performance objectives. Summary of the Invention

[0005] The technical problem to be solved by the present invention is as follows: In response to the above-mentioned problems of the prior art, a two-stage single-phase three-level boost inverter control method and system are provided, which can simultaneously achieve multiple control objectives such as pulsation-free input current, constant flying capacitor voltage and bus voltage, and high-quality grid-connected current, without the need for complex algorithms or additional hardware support, and is easy to implement in engineering.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: A two-stage single-phase three-level boost inverter control method comprises the following steps: S101) Using a first proportional-integral controller to control the input current of the two-stage single-phase three-level boost inverter according to the actual input current value and the reference value, to obtain an input current control result ; S102) Using a second proportional-integral controller to control the flying capacitor voltage according to the actual value and reference value of the flying capacitor voltage of the two-stage single-phase three-level boost inverter, to obtain a flying capacitor voltage control result ; S103) Using a third proportional-integral controller to control the average DC bus voltage according to the average DC bus voltage of the two-stage single-phase three-level boost inverter and the reference average, to obtain a grid-connected current amplitude. ; S104) uses a proportional resonant controller to adjust the grid current amplitude The grid-connected current of the two-stage single-phase three-level boost inverter is used to control the grid-connected current and obtain the grid-connected current control result. ; S105) Considering the bus voltage feedforward, according to the input current control result , flying capacitor voltage control results and grid-connected current control results Calculate the duty cycle of each switch.

[0007] Furthermore, before step S101, the method further includes: constructing a mathematical model of a two-stage single-phase three-level boost inverter, determining a corresponding relationship between each control input and a control object in the mathematical model according to a control target, and constructing a controller corresponding to each control object, wherein the two-stage single-phase three-level boost inverter inputs a DC source. u in , input boost inductor L b ,switch T 3 and T 4 Connect in sequence to form a loop and input DC source u in The positive electrode passes through the input boost inductor L b ,switch T 2 and T 1. Connect the switches in parallel T 5 and T 6 input terminal, switch T 5 and T 6 respectively through the switch T 7 and T 8. Connect the input DC source u in Negative pole, switch and Complementary, switch and Complementary, switch 、 and 、 The mathematical model expression of the complementary, two-stage single-phase three-level boost inverter is as follows:

[0008] in, 、 、 and are the values of boost inductor, flying capacitor, bus capacitor and filter inductor respectively. and are the input voltage and input current respectively, and are the flying capacitor voltage and DC bus voltage respectively, and are the grid voltage and grid current respectively, and The switches to be solved are and switch The duty cycle, Is the switch to be solved and switch duty cycle.

[0009] Furthermore, when the first proportional-integral controller is used to control the input current according to the actual value of the input current of the two-stage single-phase three-level boost inverter and the reference value, the input voltage of the two-stage single-phase three-level boost inverter is obtained. , input current and the input current Reference value , the input current The corresponding reference value Input the first proportional-integral controller, which converts the input voltage Subtract the output result of the first proportional integral controller to obtain the input current control result , the expression is as follows:

[0010] in, and are the proportional gain and integral gain of the first proportional-integral controller, and s is the Laplace variable.

[0011] Furthermore, when the flying capacitor voltage of the two-stage single-phase three-level boost inverter is controlled by the second proportional-integral controller according to the actual value of the flying capacitor voltage of the two-stage single-phase three-level boost inverter and the reference value, the flying capacitor voltage of the two-stage single-phase three-level boost inverter is specifically obtained. And the flying capacitor voltage reference value , the flying capacitor voltage And the flying capacitor voltage reference value Input the second proportional integral controller to obtain the flying capacitor voltage control result , the expression is as follows:

[0012] in, and are the proportional gain and integral gain of the second proportional-integral controller respectively, and s is the Laplace variable.

[0013] Furthermore, when the third proportional-integral controller is used to control the average DC bus voltage according to the average DC bus voltage of the two-stage single-phase three-level boost inverter and the reference average, the DC bus voltage of the two-stage single-phase three-level boost inverter is obtained. With reference average , calculate the average bus voltage , the average bus voltage With reference average Input the third proportional integral controller to get the grid current amplitude , the expression is as follows:

[0014] in, and are the proportional gain and integral gain of the third proportional-integral controller respectively, and s is the Laplace variable.

[0015] Furthermore, a proportional resonant controller is used according to the grid current amplitude. When controlling the grid current of a two-stage single-phase three-level boost inverter, the grid current amplitude is calculated. Reference value , obtain the grid voltage of the two-stage single-phase three-level boost inverter and grid-connected current , the reference value and grid-connected current Input proportional resonant controller to convert grid voltage Subtract the output result from the proportional resonant controller to get the grid-connected current control result , the expression is as follows:

[0016]

[0017] in, and are the proportional gain and integral gain of the proportional resonant controller, s is the Laplace variable, is the grid voltage angular frequency, is the phase angle of the grid voltage.

[0018] Furthermore, considering the bus voltage feedforward, according to the input current control result , flying capacitor voltage control results and grid-connected current control results When calculating the duty cycle of each switch, include the calculation of the complementary switch T 1 and T 4 duty cycle steps, including: Considering the bus voltage feedforward, according to the input current control result , flying capacitor voltage control results Compute switch T The duty cycle of 1 is expressed as follows:

[0019] in, is the input current of the two-stage single-phase three-level boost inverter, is the flying capacitor voltage of the two-stage single-phase three-level boost inverter, is the DC bus voltage of the two-stage single-phase three-level boost inverter; According to the switch T The duty cycle of 1 is calculated to get the switch T The duty cycle of 4 is expressed as follows: d 4=1- d 1 in, d 4 is switch T 4 duty cycle.

[0020] Furthermore, considering the bus voltage feedforward, according to the input current control result , flying capacitor voltage control results and grid-connected current control results When calculating the duty cycle of each switch, include the calculation of the complementary switch T 2 and T 3 duty cycle steps, including: According to the flying capacitor voltage control results With switch T 1 Duty cycle calculation switch T The duty cycle of 2 is expressed as follows:

[0021] in, d 1 is switch T A duty cycle of 1, is the input current of the two-stage single-phase three-level boost inverter; According to the switch T The duty cycle of 2 is calculated to get the switch T The duty cycle of 3 is expressed as follows: d 3=1- d 2 in,d 2 is the switch T 2 duty cycle.

[0022] Furthermore, considering the bus voltage feedforward, according to the input current control result , flying capacitor voltage control results and grid-connected current control results When calculating the duty cycle of each switch, include the calculation of the complementary switch 、 Complementary switches 、 The duty cycle steps include: According to the grid current control results Compute switch or The duty cycle is expressed as follows:

[0023] in, is the DC bus voltage of the two-stage single-phase three-level boost inverter; According to the switch or The duty cycle of the switch is calculated or The duty cycle is expressed as follows: d’ =1- d in, d’ For switch or duty cycle.

[0024] The present invention also proposes a two-stage single-phase three-level boost inverter control system, comprising: An input current control module is used to control the input current of the two-stage single-phase three-level boost inverter according to the actual input current value and the reference value using a first proportional-integral controller to obtain an input current control result. ; The flying capacitor voltage control module is used to control the flying capacitor voltage according to the actual value and reference value of the flying capacitor voltage of the two-stage single-phase three-level boost inverter using a second proportional integral controller to obtain a flying capacitor voltage control result. ; The DC bus ground pressure average value control module is used to use the third proportional integral controller to control the DC bus voltage average value according to the DC bus voltage average value of the two-stage single-phase three-level boost inverter and the reference average value to obtain the grid-connected current amplitude. ; The grid-connected current control module is used to use a proportional resonant controller to control the grid-connected current amplitude. The grid-connected current of the two-stage single-phase three-level boost inverter is used to control the grid-connected current and obtain the grid-connected current control result. ; Duty cycle calculation module, used to control the result according to the input current , flying capacitor voltage control results and grid-connected current control results Calculate the duty cycle of each switch.

[0025] Compared with the prior art, the advantages of the present invention are: The present invention sequentially performs input current control, flying capacitor voltage control, DC bus voltage average value control, grid-connected current control, and duty cycle calculation without requiring complex algorithms or additional hardware support.

[0026] The DC bus voltage average value control, input current control, and flying capacitor voltage control of the present invention are all designed to use proportional-integral controllers, thereby achieving a precise balance between the flying capacitor voltage and the bus voltage and ensuring the stability of the input current.

[0027] The grid-connected current control design of the present invention uses a proportional resonant controller to achieve zero steady-state error tracking.

[0028] The duty cycle calculation of the present invention considers the bus voltage feedforward calculation duty cycle and the DC bus voltage, and effectively suppresses the second harmonic of the input current without adding additional devices and control complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a two-stage single-phase three-level boost inverter circuit diagram.

[0030] Figure 2 Flowchart of an embodiment of the present invention.

[0031] Figure 3 4 is a logic block diagram of each controller in an embodiment of the present invention.

[0032] Figure 4 This is the result of not adding bus voltage feedforward.

[0033] Figure 5 This is the steady-state result of the control method according to the embodiment of the present invention.

[0034] Figure 6 This is a dynamic result of switching input power under the control method of an embodiment of the present invention.

[0035] Figure 7 This is a dynamic result of a grid voltage disturbance under the control method of an embodiment of the present invention. DETAILED DESCRIPTION

[0036] The present invention will be further described below in conjunction with the accompanying drawings and specific preferred embodiments, but the scope of protection of the present invention is not limited thereby.

[0037] Example 1 like Figure 1 As shown, the two-stage single-phase three-level boost inverter includes an input DC source u in , an input boost inductor L b , a flying capacitor C f , a bus capacitor C dc , an output filter inductor L g , an AC grid and eight IGBT switches T 1 to T 8, where the input DC source u in , input boost inductor L b , switch tube T 3 and T 4 Connect in sequence to form a loop and input DC source u in The positive electrode passes through the input boost inductor L b , switch tube T 2 and T 1. Connect the switch tubes in parallel T 5 and T 6 input terminal, switch tube T 5 and T 6 respectively through the switch tube T 7 and T 8. Connect the input DC source u in Negative pole, forming another loop, flying capacitor C f Connect the switch tube at both ends T 2 and T 3 output terminal, bus capacitor C dc Connect the switch tube at both ends T 1 and T 4 output terminal, output filter inductor L g Connect the switch tube at both ends T 5 and T 6 output terminals, switches T 4 and T 1 complementary, switch T 3 and T 2 complementary, switch T6. T 7 and T 5. T 8 complementary.

[0038] against Figure 1 The two-stage single-phase three-level boost inverter shown in the figure, this embodiment proposes a two-stage single-phase three-level boost inverter control method, which achieves excellent steady-state performance and dynamic response speed. In addition, the control structure is simple, does not require complex algorithms or additional hardware support, and is easy to implement in engineering. It provides a reliable technical solution for the promotion and application of two-stage single-phase three-level boost inverters.

[0039] like Figure 2 As shown, the method of this embodiment includes the following steps: S100) A mathematical model of a two-stage single-phase three-level boost inverter is established, a corresponding relationship between each control input and a controlled object in the mathematical model is determined according to a control target, and a controller corresponding to each controlled object is constructed.

[0040] The mathematical model of the two-stage single-phase three-level boost inverter is as follows: (1) in, 、 、 and are the values of boost inductor, flying capacitor, bus capacitor and filter inductor respectively. and are the input voltage and input current respectively, and are the flying capacitor voltage and DC bus voltage respectively, and are the grid voltage and grid current respectively, and Switch and switch The duty cycle, It's a switch and switch duty cycle.

[0041] This embodiment has the following four control objectives: (1) According to the law of conservation of power, there will be secondary pulsation power on the DC side of the single-phase inverter. If there is secondary pulsation in the input current, it will affect the performance of the DC power generation system. Therefore, it is necessary to ensure that the input current is constant; (2) The front-stage converter operates in three-level mode to reduce the voltage stress of the switching device and the volume of the input boost inductor. In order to achieve the three-level characteristics, the flying capacitor voltage must be kept constant. (3) The intermediate DC bus voltage must be stable as the input of the subsequent inverter, so the average value of the bus voltage needs to be controlled to remain constant; (4) In order to ensure the quality of the grid-connected current, it is necessary to control the grid-connected current to maintain a sinusoidal state.

[0042] According to formula (1), the mathematical model of the two-stage single-phase three-level boost inverter has three control inputs, among which the control input and It can be used to control the input current and flying capacitor voltage. However, due to the existence of four control objectives, this embodiment considers using the bus voltage differential equation to achieve average power conservation on the input and output sides of the system, so that the average value of the bus capacitor voltage is controlled by the amplitude of the grid current as the control input.

[0043] According to the corresponding relationship between the control input and the controlled object determined above, combined with formula (1), the following controller is designed in this embodiment: (1) For input current control, a PI controller (referred to as a first proportional integral controller in this embodiment for distinction) is used to control the input current. The formula is as follows: (2) In the above formula, is the input current control result, and The switches to be solved are and switch The duty cycle, and are the proportional gain and integral gain of the first proportional-integral controller, s is the Laplace variable, It is the reference value of the input current. In this embodiment, the reference value of the input current is given in an open loop. When applied to the field of photovoltaic power generation, the reference value can be calculated by the MPPT algorithm.

[0044] (2) For flying capacitor voltage control, a PI controller (referred to as a second proportional integral controller in this embodiment for distinction) is used to control the flying capacitor voltage. The formula is as follows: (3) In the above formula, is the flying capacitor voltage control result, and The switches to be solved are and switch The duty cycle, and are the proportional gain and integral gain of the second proportional-integral controller, s is the Laplace variable, It is the reference value of the flying capacitor voltage, which is usually set to half of the bus voltage.

[0045] (3) For the DC bus voltage average value control, a PI controller (referred to as the third proportional integral controller in this embodiment for distinction) is used to control the DC bus voltage average value to obtain the grid current amplitude. , the formula is as follows: (4) In the above formula, and are the proportional gain and integral gain of the third proportional-integral controller, s is the Laplace variable, is the reference average value of the bus voltage, is the average value of the bus voltage. In this embodiment, the average value of the bus voltage is the DC bus voltage It is obtained by a 100 Hz notch filter. The transfer function of the notch filter is expressed as follows: (5) in, is the grid voltage angular frequency, is the damping coefficient.

[0046] (4) For grid-connected current control, in order to achieve zero steady-state error tracking of the grid-connected current, this embodiment adopts a PR controller, i.e., a proportional resonant controller, to control the grid-connected current. The formula is as follows: (6) in, is the result of grid-connected current control, Is the switch to be solved and switch The duty cycle, and are the proportional gain and integral gain of the proportional resonant controller, s is the Laplace variable, is the reference value of the grid-connected current, and its expression is as follows: (7) in is the phase angle of the grid voltage, obtained through a phase-locked loop.

[0047] From formula (2), we can know that the control object With the first proportional-integral controller and the switch and switch There is a mathematical relationship between the duty cycle of With the second proportional-integral controller and the switch and switch There is a mathematical relationship between the duty cycle of with proportional resonant controllers and switches and switch There is a mathematical relationship between the duty cycles of the control objects and the corresponding controllers. Therefore, we consider first using the mathematical relationship between the control objects and the corresponding controllers to perform different control processes and calculate the values of the control objects. Then, we use the mathematical relationship between the control objects and the corresponding duty cycles to calculate the duty cycles of different switches according to the values of the control objects.

[0048] S102) Input current control: Using a first proportional-integral controller to control the input current according to the actual input current value and the reference value of the two-stage single-phase three-level boost inverter, an input current control result is obtained. .

[0049] Specifically, such as Figure 3 As shown, the input current control needs to obtain the input voltage of the two-stage single-phase three-level boost inverter , input current and the input current Reference value , according to the control object in formula (2) Mathematical relationship with the first proportional-integral controller , the input current The corresponding reference value Input the first proportional-integral controller, which converts the input voltage Subtract the output result of the first proportional integral controller to obtain the input current control result .

[0050] S103) Flying capacitor voltage control: Using a second proportional-integral controller to control the flying capacitor voltage according to the actual value and reference value of the flying capacitor voltage of the two-stage single-phase three-level boost inverter, a flying capacitor voltage control result is obtained. .

[0051] Specifically, such as Figure 3 As shown, the flying capacitor voltage control needs to obtain the flying capacitor voltage of the two-stage single-phase three-level boost inverter And the flying capacitor voltage reference value , according to the control object in formula (3) Mathematical relationship with the second proportional-integral controller , the flying capacitor voltage And the flying capacitor voltage reference value Input the second proportional integral controller to obtain the flying capacitor voltage control result .

[0052] S104) DC bus voltage average value control: Use the third proportional integral controller to control the DC bus voltage average value according to the DC bus voltage average value of the two-stage single-phase three-level boost inverter and the reference average value to obtain the grid-connected current amplitude. .

[0053] Specifically, such as Figure 3 As shown, the DC bus voltage average value control needs to obtain the DC bus voltage of the two-stage single-phase three-level boost inverter With reference average , calculate the average bus voltage According to formula (4), the average bus voltage With reference average Input the third proportional integral controller to get the grid current amplitude ; S105) Grid current control: Use proportional resonant controller according to the grid current amplitude The grid-connected current of the two-stage single-phase three-level boost inverter is used to control the grid-connected current and obtain the grid-connected current control result. .

[0054] Specifically, such as Figure 3 As shown, the grid-connected current control needs to first calculate the grid-connected current amplitude according to formula (7) Reference value , and then obtain the grid voltage of the two-stage single-phase three-level boost inverter and grid-connected current , according to the control object in formula (6) Mathematical Relationship to Proportional Resonant Controller , the reference value and grid-connected current Input proportional resonant controller to convert grid voltage Subtract the output result from the proportional resonant controller to get the grid-connected current control result .

[0055] S106) Duty cycle calculation: Consider bus voltage feedforward and control the input current according to the result. , flying capacitor voltage control results and grid-connected current control results Calculate the duty cycle of each switch.

[0056] Specifically, the control object in the above formula (2) is With switch and switch The mathematical relationship of the duty cycle , the control object in formula (3) With switch and switch The mathematical relationship of the duty cycle And the control object in formula (6) With switch and switch The mathematical relationship of the duty cycle The duty cycle can be calculated 、 and expression, which facilitates subsequent control implementation.

[0057] Duty cycle The expression is as follows: (8) The above formula considers the bus voltage feedforward, and the input current control result is , flying capacitor voltage control results Calculate the duty cycle , by Consider The calculation can achieve no secondary pulsation of input current, where is the input current control result, is the flying capacitor voltage control result, is the input current of the two-stage single-phase three-level boost inverter, is the flying capacitor voltage of the two-stage single-phase three-level boost inverter, is the DC bus voltage of the two-stage single-phase three-level boost inverter; Duty cycle The expression is as follows: (9) The above formula is based on the flying capacitor voltage control result With switch T The duty cycle of 1 is calculated to get the duty cycle ,in, is the flying capacitor voltage control result, d 1 is switch T A duty cycle of 1, is the input current of the two-stage single-phase three-level boost inverter; Duty cycle The expression is as follows: (10) The above formula is based on the grid current control result Calculate the duty cycle ,in, is the result of grid-connected current control, is the DC bus voltage of the two-stage single-phase three-level boost inverter; At the same time, due to the switch and Complementary, switch and Complementary, switch 、 and 、 Complementary, complementary switches need to satisfy the duty cycle sum is 1, therefore, according to the input current control result , flying capacitor voltage control results and grid-connected current control results When calculating the duty cycle of each switch, include: (1) Calculate complementary switches T 1 and T 4 duty cycle, the steps include: First, the input current control result , flying capacitor voltage control results Substitute into formula (8) to calculate the switch T Duty cycle of 1 d 1; Then, according to the switch T The duty cycle of 1 is calculated to get the switch T The duty cycle of 4 is expressed as follows: d 4=1- d 1 in, d 4 is switch T 4 duty cycle.

[0058] (2) Calculate complementary switches T 2 and T 3 duty cycle, the steps include: First, the flying capacitor voltage control result Substitute into formula (9) to calculate the switch T Duty cycle of 2 d 2; Then, according to the switch T The duty cycle of 2 is calculated to get the switch T The duty cycle of 3 is expressed as follows: d 3=1- d 2 in, d 2 is the switch T 2 duty cycle.

[0059] (3) Calculate complementary switches 、 Complementary switches 、 The duty cycle of the system includes: First, the grid current control result Substitute into formula (10) to calculate the switch or Duty cycle d ; Then, according to the switch or The duty cycle of the switch is calculated or The duty cycle is expressed as follows: d’ =1- d in, d’ For switch or duty cycle.

[0060] Through the above steps, the method proposed in this embodiment can completely suppress the second harmonic of the input DC current without adding additional hardware devices or increasing computational complexity, while controlling the flying capacitor voltage and bus voltage to remain stable and output high-quality grid-connected current. The entire controller design process does not rely on any circuit parameters or power level information, has a certain degree of robustness, and achieves good steady-state and dynamic performance. The above method is completely implemented within the controller, does not require additional hardware, and is simple to implement, with significant practical value in engineering applications.

[0061] The effect of the method of this embodiment is described below through relevant experimental results.

[0062] Figure 4 The control results of the two-stage single-phase three-level boost inverter without bus voltage feedforward are shown in the figure. u f 、 u dc 、 u g 、 i g and i dc The figures represent the flying capacitor voltage, DC bus voltage, grid voltage, grid-connected current, and input current, respectively. The figure shows that when bus voltage feedforward is not used, there is a large secondary ripple in the input current, with a current pulsation amplitude of approximately 7.6 A.

[0063] Figure 5The steady-state results using the control method of this embodiment are shown in the figure. As can be seen from the figure, the second harmonic in the input current is almost completely suppressed using the control method of this embodiment, and the current ripple is approximately 1.8 A. Furthermore, the flying capacitor voltage is stabilized at 275 V, the average bus voltage is constant at 350 V, and the grid-connected current remains synchronized with the grid voltage, demonstrating that the control method of this embodiment has good steady-state performance.

[0064] Figure 6 This is the dynamic result of switching the input current under the control method of this embodiment. It can be seen from the figure that at different power levels, the control method of this embodiment can achieve the aforementioned control objectives. During dynamic switching, the flying capacitor voltage, input current and grid-connected current did not produce any impact, and the bus capacitor voltage had a slight overshoot, but after about 70 ms, the average bus voltage stabilized at 350 V. In the new steady state, the secondary pulsation of the bus voltage becomes larger. This is because the power level of the system is increased, and the inherent secondary pulsation power of the single-phase inverter becomes larger. This shows that the control method of this embodiment has good dynamic performance when switching power levels.

[0065] Figure 7 The following figure shows the dynamic results of the control method of this embodiment when a grid voltage disturbance occurs. As can be seen from the figure, when the grid voltage drops, the flying capacitor voltage, bus voltage, and input current are barely affected. The grid-connected current increases in amplitude after the grid voltage drops, but does not produce any overshoot. This demonstrates that the control method of this embodiment has good dynamic performance when a grid disturbance occurs.

[0066] Example 2 This embodiment provides a two-stage single-phase three-level boost inverter control system, including: An input current control module is used to control the input current of the two-stage single-phase three-level boost inverter according to the actual input current value and the reference value using a first proportional-integral controller to obtain an input current control result. Specifically, the input voltage of the two-stage single-phase three-level boost inverter is obtained. , input current and the input current Reference value , according to the control object in formula (2) of embodiment 1 The mathematical relationship with the first proportional-integral controller converts the input current The corresponding reference value Input the first proportional-integral controller, which converts the input voltage Subtract the output result of the first proportional integral controller to obtain the input current control result ; The flying capacitor voltage control module is used to control the flying capacitor voltage according to the actual value and reference value of the flying capacitor voltage of the two-stage single-phase three-level boost inverter using a second proportional integral controller to obtain a flying capacitor voltage control result. Specifically, the flying capacitor voltage of the two-stage single-phase three-level boost inverter is obtained. And the flying capacitor voltage reference value , according to the control object in formula (3) of embodiment 1 The mathematical relationship with the second proportional-integral controller converts the flying capacitor voltage And the flying capacitor voltage reference value Input the second proportional integral controller to obtain the flying capacitor voltage control result ; The DC bus ground pressure average value control module is used to use the third proportional integral controller to control the DC bus voltage average value according to the DC bus voltage average value of the two-stage single-phase three-level boost inverter and the reference average value to obtain the grid-connected current amplitude. Specifically, the DC bus voltage of the two-stage single-phase three-level boost inverter is obtained. With reference average , calculate the average bus voltage According to the formula (4) of the first embodiment, the average bus voltage With reference average Input the third proportional integral controller to get the grid current amplitude ; The grid-connected current control module is used to use a proportional resonant controller to control the grid-connected current amplitude. The grid-connected current of the two-stage single-phase three-level boost inverter is used to control the grid-connected current and obtain the grid-connected current control result. Specifically, the grid-connected current amplitude is calculated according to formula (7) of embodiment 1. Reference value , obtain the grid voltage of the two-stage single-phase three-level boost inverter and grid-connected current , according to the control object in formula (6) of embodiment 1 The mathematical relationship with the proportional resonant controller converts the reference value and grid-connected current Input proportional resonant controller, the grid voltage Subtract the output result from the proportional resonant controller to get the grid-connected current control result ; Duty cycle calculation module, used to consider bus voltage feedforward, according to the input current control result , flying capacitor voltage control results and grid-connected current control results Calculate the duty cycle of each switch. Specifically, the input current control result , flying capacitor voltage control results and grid-connected current control results Substituting into formula (8), formula (9) and formula (10) of embodiment 1, we get switch and switch Duty cycle and , and switches and switch Duty cycle , and then use this to calculate the duty cycle of the corresponding complementary switch.

[0067] In summary, the present invention proposes a two-stage single-phase three-level boost inverter control method and a corresponding control system. The present invention first establishes an average mathematical model of the two-stage single-phase three-level boost inverter. According to the differential equations of the capacitor voltage and the input inductor current, a simple proportional-integral controller is designed to achieve a precise balance between the flying capacitor voltage and the bus voltage, and ensure the stability of the input current. Considering the bus voltage feedforward, the second harmonic of the input current is effectively suppressed without adding additional devices and control complexity. The grid-connected current is tracked with zero steady-state error through a common proportional resonant controller. The disclosed two-stage single-phase three-level boost inverter control strategy achieves excellent steady-state performance and dynamic response speed, and the control structure is simple, does not require complex algorithms or additional hardware support, and is easy to implement in engineering, providing a reliable technical solution for the promotion and application of two-stage single-phase three-level boost inverters.

[0068] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiment. All technical solutions based on the concept of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A two-stage single-phase three-level boost inverter control method, characterized in that: The following steps are involved: S101) Using a first proportional-integral controller to control the input current of the two-stage single-phase three-level boost inverter according to the actual input current value and the reference value, to obtain an input current control result ; S102) Using a second proportional-integral controller to control the flying capacitor voltage according to the actual value and reference value of the flying capacitor voltage of the two-stage single-phase three-level boost inverter, to obtain a flying capacitor voltage control result ; S103) Using a third proportional-integral controller to control the average DC bus voltage according to the average DC bus voltage of the two-stage single-phase three-level boost inverter and the reference average, to obtain a grid-connected current amplitude. ; S104) uses a proportional resonant controller to adjust the grid current amplitude The grid-connected current of the two-stage single-phase three-level boost inverter is used to control the grid-connected current and obtain the grid-connected current control result. ; S105) Considering the bus voltage feedforward, according to the input current control result , flying capacitor voltage control results and grid-connected current control results Calculate the duty cycle of each switch.

2. The two-stage single-phase three-level boost inverter control method according to claim 1, characterized in that: Before step S101, the method further includes: constructing a mathematical model of a two-stage single-phase three-level boost inverter, determining a corresponding relationship between each control input and a control object in the mathematical model according to a control target, and constructing a controller corresponding to each control object, wherein the two-stage single-phase three-level boost inverter inputs a DC source. u in , input boost inductor L b ,switch T 3 and T 4 Connect in sequence to form a loop and input DC source u in The positive electrode passes through the input boost inductor L b ,switch T 2 and T 1. Connect the switches in parallel T 5 and T 6 input terminal, switch T 5 and T 6 respectively through the switch T 7 and T 8. Connect the input DC source u in Negative pole, switch and Complementary, switch and Complementary, switch 、 and 、 The mathematical model expression of the complementary, two-stage single-phase three-level boost inverter is as follows: in, 、 、 and are the values of boost inductor, flying capacitor, bus capacitor and filter inductor respectively. and are the input voltage and input current respectively, and are the flying capacitor voltage and DC bus voltage respectively, and are the grid voltage and grid current respectively, and The switches to be solved are and switch The duty cycle, Is the switch to be solved and switch duty cycle.

3. The two-stage single-phase three-level boost inverter control method according to claim 1, characterized in that: When the first proportional integral controller is used to control the input current according to the actual value of the input current of the two-stage single-phase three-level boost inverter and the reference value, the input voltage of the two-stage single-phase three-level boost inverter is obtained. , input current and the input current Reference value , the input current The corresponding reference value Input the first proportional-integral controller, which converts the input voltage Subtract the output result of the first proportional integral controller to obtain the input current control result , the expression is as follows: in, and are the proportional gain and integral gain of the first proportional-integral controller, and s is the Laplace variable.

4. The two-stage single-phase three-level boost inverter control method according to claim 1, characterized in that: When the flying capacitor voltage of the two-stage single-phase three-level boost inverter is controlled by using the second proportional-integral controller according to the actual value and reference value of the flying capacitor voltage of the two-stage single-phase three-level boost inverter, the flying capacitor voltage of the two-stage single-phase three-level boost inverter is specifically obtained. And the flying capacitor voltage reference value , the flying capacitor voltage And the flying capacitor voltage reference value Input the second proportional integral controller to obtain the flying capacitor voltage control result , the expression is as follows: in, and are the proportional gain and integral gain of the second proportional-integral controller respectively, and s is the Laplace variable.

5. The two-stage single-phase three-level boost inverter control method according to claim 1, characterized in that: When the third proportional-integral controller is used to control the average value of the DC bus voltage according to the average value of the DC bus voltage of the two-stage single-phase three-level boost inverter and the reference average value, the DC bus voltage of the two-stage single-phase three-level boost inverter is obtained. With reference average , calculate the average bus voltage , the average bus voltage With reference average Input the third proportional integral controller to get the grid current amplitude , the expression is as follows: in, and are the proportional gain and integral gain of the third proportional-integral controller respectively, and s is the Laplace variable.

6. The two-stage single-phase three-level boost inverter control method according to claim 1, characterized in that: Use proportional resonant controller according to the grid current amplitude When controlling the grid current of a two-stage single-phase three-level boost inverter, the grid current amplitude is calculated. Reference value , obtain the grid voltage of the two-stage single-phase three-level boost inverter and grid current , the reference value and grid-connected current Input proportional resonant controller to convert grid voltage Subtract the output result from the proportional resonant controller to get the grid-connected current control result , the expression is as follows: in, and are the proportional gain and integral gain of the proportional resonant controller, s is the Laplace variable, is the grid voltage angular frequency, is the phase angle of the grid voltage.

7. The two-stage single-phase three-level boost inverter control method according to claim 2, characterized in that: Considering the bus voltage feedforward, according to the input current control result , flying capacitor voltage control results and grid-connected current control results When calculating the duty cycle of each switch, include the calculation of the complementary switch T 1 and T 4 duty cycle steps, including: Considering the bus voltage feedforward, according to the input current control result , flying capacitor voltage control results Compute switch T The duty cycle of 1 is expressed as follows: in, is the input current of the two-stage single-phase three-level boost inverter, is the flying capacitor voltage of the two-stage single-phase three-level boost inverter, is the DC bus voltage of the two-stage single-phase three-level boost inverter; According to the switch T The duty cycle of 1 is calculated to get the switch T The duty cycle of 4 is expressed as follows: d 4=1- d 1 in, d 4 is switch T 4 duty cycle.

8. The two-stage single-phase three-level boost inverter control method according to claim 2, characterized in that: Considering the bus voltage feedforward, according to the input current control result , flying capacitor voltage control results and grid-connected current control results When calculating the duty cycle of each switch, include the calculation of the complementary switch T 2 and T 3 duty cycle steps, including: According to the flying capacitor voltage control results With switch T 1 Duty cycle calculation switch T The duty cycle of 2 is expressed as follows: in, d 1 is switch T A duty cycle of 1, is the input current of the two-stage single-phase three-level boost inverter; According to the switch T The duty cycle of 2 is calculated to get the switch T The duty cycle of 3 is expressed as follows: d 3=1- d 2 in, d 2 is the switch T 2 duty cycle.

9. The two-stage single-phase three-level boost inverter control method according to claim 2, characterized in that: Considering the bus voltage feedforward, according to the input current control result , flying capacitor voltage control results and grid-connected current control results When calculating the duty cycle of each switch, include the calculation of the complementary switch 、 Complementary switches 、 The duty cycle steps include: According to the grid current control results Compute switch or The duty cycle is expressed as follows: in, is the DC bus voltage of the two-stage single-phase three-level boost inverter; According to the switch or The duty cycle of the switch is calculated or The duty cycle is expressed as follows: d’ =1- d in, d’ For switch or duty cycle.

10. A two-stage single-phase three-level boost inverter control system, characterized in that: include: An input current control module is used to control the input current of the two-stage single-phase three-level boost inverter according to the actual input current value and the reference value using a first proportional-integral controller to obtain an input current control result. ; The flying capacitor voltage control module is used to control the flying capacitor voltage according to the actual value and reference value of the flying capacitor voltage of the two-stage single-phase three-level boost inverter using a second proportional integral controller to obtain a flying capacitor voltage control result. ; The DC bus ground pressure average value control module is used to use the third proportional integral controller to control the DC bus voltage average value according to the DC bus voltage average value of the two-stage single-phase three-level boost inverter and the reference average value to obtain the grid-connected current amplitude. ; The grid-connected current control module is used to use a proportional resonant controller to control the grid-connected current amplitude. The grid-connected current of the two-stage single-phase three-level boost inverter is used to control the grid-connected current and obtain the grid-connected current control result. ; Duty cycle calculation module, used to control the result according to the input current , flying capacitor voltage control results and grid-connected current control results Calculate the duty cycle of each switch.

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