Control method, control device and electronic equipment of three-level converter

Abstract

The application provides a control method and device of a three-level converter and electronic equipment, the three-level converter comprising a three-level conversion circuit and a half-bridge circuit, the direct current side of the three-level conversion circuit being connected with the half-bridge circuit; the half-bridge circuit comprising a first switch tube, a second switch tube, a first inductor, an upper split capacitor and a lower split capacitor, the capacitance of the upper split capacitor and the lower split capacitor being different; the control method comprising the following steps: obtaining a first current flowing from the three-level conversion circuit to the connection midpoint of the upper split capacitor and the lower split capacitor; obtaining a first reference current based on the reference voltage and the actual voltage of the direct current bus; obtaining a second reference current based on the voltage average of the lower split capacitor and the reference voltage of the direct current bus; generating a modulation wave based on the first reference current, the second reference current, the current of the first inductor and the first current; and comparing the modulation wave with a triangular wave to generate the driving signal of the first switch tube and the second switch tube.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and more specifically, to a control method, control device, and electronic device for a three-level converter. Background Technology

[0002] In the field of power electronics, three-level converters, as devices for converting DC to AC power, are crucial for improving energy efficiency and ensuring reliable system operation. However, when a three-level converter operates in a single-phase system, in a grid-connected mode with unbalanced three-phase voltage, or in an off-grid mode with an unbalanced load, low-frequency ripple will appear on the DC bus voltage. This low-frequency ripple not only increases the harmonic distortion rate of the grid current or load voltage but also leads to increased device stress. Furthermore, when a three-level converter operates off-grid with a half-wave load, a half-bridge circuit is required to achieve midpoint voltage balance. Therefore, for three-level converters with half-bridge circuits, effectively suppressing various low-frequency ripples on the DC side while maintaining midpoint voltage balance is a pressing issue that needs to be addressed.

[0003] In related technologies, the main methods for suppressing low-frequency ripple on the DC side are as follows:

[0004] First, based on the principle of conservation of instantaneous pulsating power on the DC and AC sides, the reference voltage is calculated in an open loop, and then DC side ripple suppression is achieved through closed-loop control. However, this method relies on accurate system parameters and has poor robustness. When the system parameters change, the ripple suppression effect is not good.

[0005] Secondly, by extracting the second harmonic ripple information from the DC-side bus voltage in real time and obtaining the fundamental frequency information through synchronous coordinate transformation, closed-loop suppression is performed. However, this coordinate transformation requires knowledge of the phase information of the AC-side voltage, making it difficult to apply to multiphase converters. Furthermore, this method cannot eliminate other secondary ripples in the DC-side bus voltage.

[0006] Third, suppression can be achieved by actively controlling the second harmonic ripple in the voltage of the upper and lower split capacitors. However, this method requires that the average voltages of the upper and lower split capacitors be unequal, which will lead to an increase in the maximum stress of the device. Since the midpoint voltage balance needs to be maintained in a three-level converter to reduce AC side voltage and current distortion and avoid excessive stress, this method is not suitable for three-level converters. Summary of the Invention

[0007] The present invention aims to solve the technical problems existing in the prior art and provide a control method, control device and electronic device for a three-level converter, which can effectively suppress low-frequency ripple on the DC side while satisfying the neutral point voltage balance.

[0008] In a first aspect, the present invention provides a control method for a three-level converter, the three-level converter including a three-level conversion circuit and a half-bridge circuit, wherein the DC side of the three-level conversion circuit is connected to the half-bridge circuit; the half-bridge circuit includes a first switch, a second switch, a first inductor, an upper split capacitor, and a lower split capacitor, the first switch and the second switch being connected in series between the positive and negative terminals of a DC bus, the upper split capacitor and the lower split capacitor being connected in series between the positive and negative terminals of the DC bus, the two ends of the first inductor being respectively connected to the midpoint of the connection of the first switch and the second switch and the midpoint of the connection of the upper split capacitor and the lower split capacitor, wherein the capacitance values ​​of the upper split capacitor and the lower split capacitor are unequal; the control method includes the following steps:

[0009] Obtain the first current flowing from the three-level conversion circuit to the connection midpoint of the upper and lower split capacitors;

[0010] Based on the reference voltage and actual voltage of the DC bus, a first reference current is obtained;

[0011] A second reference current is obtained based on the average voltage of the lower split capacitor and the reference voltage of the DC bus;

[0012] A modulated wave is generated based on the first reference current, the second reference current, the current of the first inductor, and the first current;

[0013] The modulated wave is compared with a triangular wave to generate drive signals for the first and second switching transistors.

[0014] In some embodiments, the formula for calculating the first current is:

[0015] ;

[0016] In the formula, Indicates the external load current; Indicates the load voltage; This indicates the actual voltage of the DC bus.

[0017] In some embodiments, the step of obtaining the first reference current based on the reference voltage and the actual voltage of the DC bus includes:

[0018] The low-frequency ripple component of the DC bus is obtained by subtracting the reference voltage and the actual voltage of the DC bus; the difference between zero and the low-frequency ripple component is then input into the ripple suppression controller to obtain the first reference current.

[0019] In some embodiments, the ripple suppression controller is a controller with low-frequency sinusoidal signal tracking capability, and is one of a multi-resonant controller, a repetitive controller, a sliding mode controller, a backstepping controller, or a Lyapunov controller.

[0020] In some embodiments, the step of obtaining a second reference current based on the average voltage of the lower split capacitor and the reference voltage of the DC bus includes: subtracting half of the reference voltage of the DC bus from the average voltage of the lower split capacitor and inputting the difference into a midpoint voltage balance controller to obtain the second reference current.

[0021] In some embodiments, the midpoint voltage balance controller is a controller with DC signal tracking capability, and is one of a proportional-integral controller, a proportional-integral-derivative controller, a sliding mode controller, a backstepping controller, or a Lyapunov controller.

[0022] In some embodiments, the step of generating a modulated wave based on the first reference current, the second reference current, the current in the first inductor, and the first current includes:

[0023] The sum of the first reference current and the second reference current is used as the total reference current; the difference between the total reference current and the current of the first inductor and the first current is input into the current loop controller to generate the modulation wave.

[0024] In some embodiments, the current loop controller is a controller with AC / DC signal tracking capability, and is one of a proportional-integral multivibrator controller, a repetitive controller, a sliding mode controller, a backstepping controller, and a Lyapunov controller.

[0025] Secondly, the present invention provides a control device for a three-level converter, applied to a three-level converter, the three-level converter including a three-level conversion circuit and a half-bridge circuit, the DC side of the three-level conversion circuit being connected to the half-bridge circuit; the half-bridge circuit including a first switching transistor, a second switching transistor, a first inductor, an upper split capacitor, and a lower split capacitor, the first switching transistor and the second switching transistor being connected in series between the positive and negative terminals of a DC bus, the upper split capacitor and the lower split capacitor being connected in series between the positive and negative terminals of the DC bus, the two ends of the first inductor being respectively connected to the midpoint of the connection of the first switching transistor and the second switching transistor and the midpoint of the connection of the upper split capacitor and the lower split capacitor, the capacitance values ​​of the upper split capacitor and the lower split capacitor being unequal; the control device includes:

[0026] The first current acquisition module is used to acquire the first current flowing from the three-level conversion circuit to the connection midpoint of the upper split capacitor and the lower split capacitor.

[0027] The first reference current acquisition module is used to acquire a first reference current based on the reference voltage and the actual voltage of the DC bus;

[0028] The second reference current acquisition module is used to acquire a second reference current based on the average voltage of the lower split capacitor and the reference voltage of the DC bus.

[0029] A modulation wave generation module is used to generate a modulation wave based on the first reference current, the second reference current, the current of the first inductor, and the first current;

[0030] The drive signal generation module is used to compare the modulated wave with the triangular wave to generate drive signals for the first switch and the second switch.

[0031] Thirdly, the present invention provides an electronic device, comprising:

[0032] At least one processor; and

[0033] A memory communicatively connected to the at least one processor; wherein,

[0034] The memory stores one or more computer programs that can be executed by the at least one processor, the one or more computer programs being executed by the at least one processor to enable the at least one processor to perform the control method of the three-level converter as described in any one aspect embodiment.

[0035] The present invention has the following beneficial effects:

[0036] This invention provides a control method, control device, and electronic device for a three-level converter. The three-level converter includes a three-level conversion circuit and a half-bridge circuit. The DC side of the three-level conversion circuit is connected to the half-bridge circuit. The half-bridge circuit includes a first switch, a second switch, a first inductor, an upper split capacitor, and a lower split capacitor. The first and second switches are connected in series between the positive and negative terminals of the DC bus. The upper and lower split capacitors are connected in series between the positive and negative terminals of the DC bus. The two ends of the first inductor are respectively connected to the midpoint of the connection between the first and second switches and the midpoint of the connection between the upper and lower split capacitors. The capacitance values ​​of the upper and lower split capacitors are not equal. The control method includes: acquiring a first current flowing from the three-level conversion circuit to the midpoint of the connection between the upper and lower split capacitors; acquiring a first reference current based on the reference voltage and actual voltage of the DC bus; acquiring a second reference current based on the average voltage of the lower split capacitor and the reference voltage of the DC bus; generating a modulation wave based on the first reference current, the second reference current, the current of the first inductor, and the first current; and comparing the modulation wave with a triangular wave to generate drive signals for the first and second switches.

[0037] The above control method does not rely on precise system parameters and phase information, nor does it require coordinate transformation. The control process is simple and easy to implement; it is robust and can effectively suppress low-frequency ripples on the DC side. It is applicable to single-phase, two-phase, and three-phase three-level converters, and has a wide range of applications. Attached Figure Description

[0038] Figure 1 The circuit schematic and control strategy diagram of the three-level converter provided in the embodiments of the present invention;

[0039] Figure 2 A flowchart of a control method for a three-level converter provided in an embodiment of the present invention;

[0040] Figure 3 A flowchart for obtaining the first reference current provided in an embodiment of the present invention;

[0041] Figure 4 A flowchart for generating a modulated wave is provided in an embodiment of the present invention;

[0042] Figure 5(a) is an overall waveform diagram of the three-level converter provided in the embodiment of the present invention;

[0043] Figure 5(b) shows a local waveform diagram corresponding to the control method using the relevant technology;

[0044] Figure 5(c) is a partial waveform diagram corresponding to the control method provided by the embodiment of the present invention;

[0045] Figure 6 A structural block diagram of the control device for a three-level converter provided in an embodiment of the present invention;

[0046] Figure 7 This is a structural block diagram of an electronic device provided in an embodiment of the present invention. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0048] It should be noted that although functional modules are divided in the device schematic diagram and the logical order is shown in the flowchart, in some cases, the steps shown or described may be executed in a different order than the module division in the device or the order in the flowchart. In the description of this invention, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the number itself, while "above," "below," and "within" are understood to include the number itself. The use of "first" and "second" is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features. Unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," "setting," and "arrangement," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; a mechanical connection or an electrical connection; a direct connection or an indirect connection through an intermediate medium; or a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0049] like Figure 1 As shown, the three-level converter includes a half-bridge circuit 10 and a three-level conversion circuit 20, with the DC side of the three-level conversion circuit 20 connected to the half-bridge circuit 10; the half-bridge circuit 10 includes a first switching transistor. Second switching transistor First Inductor Upper split capacitor Lower split capacitor First switching transistor Second switching transistor A split capacitor is connected in series between the positive and negative terminals of the DC bus. Lower split capacitor The first inductor is connected in series between the positive and negative terminals of the DC bus. The two ends are respectively connected to the first switching transistor Second switching transistor The connection midpoint and the upper split capacitor Lower split capacitor The connection midpoint, the upper split capacitor Lower split capacitor The capacitance values ​​are not equal.

[0050] In some specific embodiments of the present invention, the three-level converter further includes a filter circuit 30, the AC side of the three-level converter 20 is connected to the filter circuit 30, and a three-phase load is connected through the filter circuit 30. Specifically, the filter circuit 30 includes three LC filter branches, each LC filter branch including a second inductor. and filter capacitor Second inductor and filter capacitor One end of the series circuit is connected to the three-level converter circuit 20, and the second inductor and filter capacitor The other end of the series connection is connected to the upper split capacitor. Lower split capacitor The connection midpoint. One end of each phase load is connected to the second inductor. and filter capacitor The connection midpoint, the other end of each phase load is connected to the upper split capacitor. Lower split capacitor The midpoint of the connection.

[0051] This invention uses a three-phase system with an unbalanced load in an off-grid mode as an example for illustration, namely... Figure 1 The three-level converter in the system is a three-phase four-wire three-level converter. In off-grid mode, Figure 1 The DC bus voltage in the system is usually controlled by the energy storage system.

[0052] Before describing the control method of the three-level converter in this invention, it is necessary to analyze the low-frequency ripple component of the DC side of the three-level converter circuit 20.

[0053] It should be noted that the component labels in the above text, for example... , In the formulas below, "etc." also represent their corresponding parameter values, such as capacitance and inductance values.

[0054] Figure 1 When all three phases of the three-phase four-wire three-level converter are under load, the load voltage of phase A is: The load current is The load voltage of phase B is The load current is The load voltage of phase C is The load current is .

[0055] In a three-phase four-wire three-level converter under extremely unbalanced load conditions, such as when only phase A is loaded, the load voltage of phase A is set. and load current for:

[0056] (1)

[0057] In the formula, This represents the fundamental frequency amplitude of the load voltage in phase A; This represents the fundamental frequency amplitude of the load current in phase A; This represents the third harmonic amplitude of the load current in phase A; Indicates the fundamental angular frequency; This represents the phase difference between the fundamental frequency of the load current in phase A and the AC voltage. This represents the phase difference between the third harmonic of the load current in phase A and the AC voltage.

[0058] According to formula (1), the instantaneous power on the AC side of the three-level converter can be obtained as follows:

[0059] (2)

[0060] In the formula, This indicates the active power consumed by the load. , and These represent the amplitudes of the pulsating power at harmonics 2, 4, and 6, respectively. Indicates the fundamental angular frequency; , and These represent the phase angles at 2x, 4x, and 6x harmonic frequency pulsating power, respectively. This indicates the load voltage of phase A; This indicates the load current of phase A; This represents the inductance value of the first inductor; This indicates the capacitance value of the filter capacitor.

[0061] To suppress DC voltage ripple caused by pulsating power on the AC side, the upper split capacitor of the three-level converter... Lower split capacitor The voltage should be controlled as follows:

[0062] (3)

[0063] In the formula, , These represent the voltages of the upper and lower split capacitors, respectively; This represents the average value of the DC bus voltage; , These represent the second and fourth ripple amplitudes in the voltage of the upper and lower split capacitors, respectively. Indicates the fundamental angular frequency; and This indicates the corresponding phase angle.

[0064] According to formula (3), the current flowing through the upper and lower split capacitors is:

[0065] (4)

[0066] In the formula, , These represent the voltages of the upper and lower split capacitors, respectively; , These represent the capacitance values ​​of the upper and lower split capacitors, respectively. Indicates the fundamental angular frequency; , These represent the second and fourth ripple amplitudes in the voltage of the upper and lower split capacitors, respectively. , These represent the corresponding phase angles.

[0067] Therefore, on the DC side, the instantaneous pulsating power stored in the upper and lower split capacitors is:

[0068] (5)

[0069] In the formula, , These represent the voltages of the upper and lower split capacitors, respectively; , These represent the currents in the upper and lower split capacitors, respectively; , , and These are the amplitude values ​​of the frequency pulsation power at two, four, six, and eight times the frequency, respectively. , , and These represent the phase angles for 2x, 4x, 6x, and 8x harmonic frequency pulsating power, respectively. This represents the fundamental angular frequency.

[0070] According to formulas (2) and (5), when the voltage control of the upper and lower split capacitors is as shown in formula (3), the pulsating power caused by load imbalance or load current distortion on the AC side can be effectively buffered by the upper and lower split capacitors on the DC side, thereby effectively suppressing the low-frequency ripple on the DC side. Moreover, according to formula (5), in order to achieve the same average voltage of the upper and lower split capacitors in the half-bridge circuit 10, the capacitance values ​​of the upper and lower split capacitors in the three-level converter are set to be unequal to buffer the low-frequency pulsating power.

[0071] Furthermore, according to formula (2), the low-frequency pulsating power on the AC side caused by load imbalance or harmonics includes second and fourth harmonic power components (corresponding to 2). and 4 According to formula (3), the voltage of the upper and lower split capacitors on the DC side exhibits ripple with the same frequency as the low-frequency pulsating power (2). and 4 Based on this, when setting the control method for the three-level converter, the ripple component can be directly extracted from the DC bus voltage, and the low-frequency ripple on the DC side can be effectively suppressed without coordinate transformation and AC side voltage phase information. The ripple suppression effect is good and the robustness is strong.

[0072] Based on the above-mentioned three-level converter, in a first aspect, embodiments of the present invention provide a control method for a three-level converter, such as... Figure 2 As shown, it includes the following steps:

[0073] S210. Obtain the first current flowing through the connection midpoint of the upper and lower split capacitors in the three-level conversion circuit.

[0074] S220. Obtain the first reference current based on the reference voltage and actual voltage of the DC bus;

[0075] S230. Based on the average voltage of the lower split capacitor and the reference voltage of the DC bus, obtain the second reference current;

[0076] S240. Based on the first reference current, the second reference current, the current of the first inductor, and the first current, a modulation wave is generated;

[0077] S250. Compare the modulated wave with the triangular wave to generate drive signals for the first and second switching transistors.

[0078] Based on the above-mentioned three-level converter and its control method, the three-level converter includes a three-level conversion circuit and a half-bridge circuit. The DC side of the three-level conversion circuit is connected to the half-bridge circuit. The half-bridge circuit includes a first switch, a second switch, a first inductor, an upper split capacitor, and a lower split capacitor. The first and second switches are connected in series between the positive and negative terminals of the DC bus. The upper and lower split capacitors are connected in series between the positive and negative terminals of the DC bus. The two ends of the first inductor are respectively connected to the midpoint of the connection of the first and second switches and the midpoint of the connection of the upper and lower split capacitors. The capacitance values ​​of the upper and lower split capacitors are not equal. The control method includes: obtaining a first current flowing from the three-level conversion circuit to the midpoint of the connection of the upper and lower split capacitors; obtaining a first reference current based on the reference voltage and actual voltage of the DC bus; obtaining a second reference current based on the average voltage of the lower split capacitor and the reference voltage of the DC bus; generating a modulation wave based on the first reference current, the second reference current, the current of the first inductor, and the first current; and comparing the modulation wave with a triangular wave to generate drive signals for the first and second switches.

[0079] The above control method does not rely on precise system parameters and phase information, nor does it require coordinate transformation. The control process is simple and easy to implement; it is robust and can effectively suppress low-frequency ripples on the DC side. It is applicable to single-phase, two-phase, and three-phase three-level converters, and has a wide range of applications.

[0080] In some specific embodiments of the present invention, before executing step S210, the control method further includes: establishing a large-signal switch average model of the half-bridge circuit, and based on the large-signal switch average model, obtaining the first current flowing from the connection midpoint of the upper split capacitor and the lower split capacitor of the three-level conversion circuit.

[0081] Specifically, the large-signal switching average model is expressed by the following formula:

[0082] (6)

[0083] In the formula, This indicates the capacitance value of the split capacitor; This indicates the voltage across the split capacitor. This represents the current in the first inductor of the half-bridge circuit. This represents the first current flowing through the connection midpoint between the upper and lower split capacitors in the three-level converter circuit. This represents the inductance value of the first inductor in the half-bridge circuit. Indicates the first switching transistor in the half-bridge circuit duty cycle, This indicates the actual voltage of the DC bus.

[0084] According to formula (6), the voltage of the lower split capacitor in the half-bridge circuit is... Control of the first current This is a disturbance term, used to eliminate the first current. The impact on voltage can be eliminated by calculating the average value of its switching cycle and then feeding it forward to the current loop.

[0085] Specifically, when the three-level converter is a three-phase three-level converter, the first current... The calculation formula is:

[0086] (7)

[0087] In the formula, (x = a, b, c) represents the external load current; Indicates the load voltage; This represents the actual voltage of the DC bus;

[0088] When the three-level converter is a split-phase three-level converter, the first current... The calculation formula is:

[0089] (8)

[0090] In the formula, (x = a, b) represents the external load current; Indicates the load voltage; This indicates the actual voltage of the DC bus.

[0091] When the three-level converter is a single-phase three-level converter, the first current... The calculation formula is:

[0092] (9)

[0093] In the formula, Indicates the current of a single-phase external load; Indicates the load voltage; This indicates the actual voltage of the DC bus.

[0094] In some specific embodiments of the present invention, such as Figure 3 As shown, step S220 includes:

[0095] S221. Difference between the reference voltage and the actual voltage of the DC bus to obtain the low-frequency ripple component of the DC bus.

[0096] S222. The difference between zero and the low-frequency ripple component is input into the ripple suppression controller to obtain the first reference current.

[0097] Specifically, in step S221, as Figure 1 As shown, the reference voltage of the constant DC bus is... Actual voltage of DC bus After subtraction, the low-frequency ripple component of the DC bus is obtained. .

[0098] In step S222, the zero and low-frequency ripple components are... Differential input ripple suppression controller To obtain the first reference current.

[0099] In some embodiments, the ripple suppression controller is a controller with low-frequency sinusoidal signal tracking capability, and is one of a multiresonant controller, repetitive controller, sliding mode controller, backstepping controller, and Lyapunov controller. The Lyapunov controller is a controller designed based on Lyapunov stability theory.

[0100] In this invention, the ripple suppression controller is preferably a multi-resonant controller, and the transfer function of the multi-resonant controller is:

[0101] (10)

[0102] In the formula, Indicates the bandwidth of the multi-resonant controller; Indicates the fundamental angular frequency; Indicates the number of resonances; express Secondary resonant term gain.

[0103] In some specific embodiments of the present invention, step S230 includes: taking the difference between half of the reference voltage of the DC bus and the average voltage of the lower split capacitor, and inputting the difference into the midpoint voltage balance controller to obtain a second reference current.

[0104] Specifically, half of the reference voltage of the DC bus, i.e., 0.5 The average voltage of the lower split capacitor After subtraction, input to the midpoint voltage balance controller Midpoint voltage balance controller Output the second reference current. Average voltage across the lower split capacitor. It can be obtained through low-pass filters (LPF), moving average filters (MAF), etc.

[0105] In some embodiments, the midpoint voltage balance controller is a controller with DC signal tracking capability, and is one of a proportional-integral controller, a proportional-integral-derivative controller, a sliding mode controller, a backstepping controller, or a Lyapunov controller.

[0106] In some specific embodiments of the present invention, such as Figure 4 As shown, step S240 includes:

[0107] S241. Take the sum of the first reference current and the second reference current as the total reference current;

[0108] S242. The difference between the total reference current and the current of the first inductor and the first current is input into the current loop controller to generate a modulation wave.

[0109] Specifically, the first reference current and the second reference current are added together to obtain the total reference current. Then the total reference current Subtract the first current calculated in formula (7) or formula (8) or formula (9) and the current of the first inductor Then, input current loop controller Current loop controller Output modulated wave.

[0110] In some embodiments, the current loop controller is a controller with AC / DC signal tracking capability, and is one of the proportional-integral multivibrator controller, repetitive controller, sliding mode controller, backstepping controller, and Lyapunov controller.

[0111] Based on the above three-level converter and its control method, given the system parameters shown in Table 1, in the three-phase four-wire three-level converter, only phase A is fully loaded to simulate the extremely unbalanced three-phase working condition.

[0112]

[0113] The obtained simulation waveforms are shown in Figures 5(a), (b), and (c). Figure 5(a) represents the overall waveform, Figure 5(b) represents the local waveform without the above control method, and Figure 5(c) represents the local waveform after the above control method is applied.

[0114] In Figure 5(a), the above control method was not executed 1 second prior, and it began to be executed at 1 second. When the above control method was not executed, as shown in Figure 5(b), the actual voltage of the DC bus... The circuit contains a large amount of low-frequency ripple, with a peak-to-peak value of approximately 70V. This can easily cause excessive stress on components and capacitors when the DC bus voltage is high. Furthermore, the large amount of low-frequency ripple on the DC side also increases the load voltage harmonic distortion rate. After implementing the above control method, as shown in Figure 5(c), the actual voltage of the DC bus... The low- and mid-frequency ripple gradually decreases, eventually reaching a stable state with the peak-to-peak value of the ripple decreasing to 6V, effectively suppressing low-frequency ripple on the DC side. Furthermore, when the average values ​​of the upper and lower split capacitor voltages remain balanced, the ripple mainly consists of second and fourth harmonic ripple, consistent with the theoretical analysis above. Based on the above simulation waveforms, the feasibility of the control method for the three-level converter proposed in this invention can be verified.

[0115] It should be noted that the control method of the three-level converter in this invention is not only applicable to single-phase three-level systems, but also to grid-connected modes of three-level systems connected to three-phase unbalanced grid voltages, and off-grid modes of two-phase or three-phase systems with unbalanced loads.

[0116] In a second aspect, the control device for a three-level converter provided in the embodiments of the present invention is applied to a three-level converter, which includes a half-bridge circuit 10 and a three-level conversion circuit 20, wherein the DC side of the three-level conversion circuit 20 is connected to the half-bridge circuit 10; the half-bridge circuit 10 includes a first switching transistor. Second switching transistor First Inductor Upper split capacitor Lower split capacitor First switching transistor Second switching transistor A split capacitor is connected in series between the positive and negative terminals of the DC bus. Lower split capacitor The first inductor is connected in series between the positive and negative terminals of the DC bus. The two ends are respectively connected to the first switching transistor Second switching transistor The connection midpoint and the upper split capacitor Lower split capacitor The connection midpoint, the upper split capacitor Lower split capacitor The capacitance values ​​are not equal. For example... Figure 6 As shown, the control device includes a first current acquisition module 61, a first reference current acquisition module 62, a second reference current acquisition module 63, a modulation wave generation module 64, and a drive signal generation module 65. Among them,

[0117] The first current acquisition module 61 is used to acquire the first current flowing into the connection midpoint of the upper and lower split capacitors of the three-level conversion circuit.

[0118] The first reference current acquisition module 62 is used to acquire the first reference current based on the reference voltage and the actual voltage of the DC bus.

[0119] The second reference current acquisition module 63 is used to acquire a second reference current based on the average voltage of the lower split capacitor and the reference voltage of the DC bus.

[0120] The modulation wave generation module 64 is used to generate a modulation wave based on the first reference current, the second reference current, the current of the first inductor, and the first current.

[0121] The drive signal generation module 65 is used to compare the modulated wave with the triangular wave to generate drive signals for the first switch and the second switch.

[0122] In a third aspect, an electronic device provided by an embodiment of the present invention, such as... Figure 7 As shown, the device includes a processor 71, a memory 72, an input device 73, and an output device 74; the number of processors 71 in this electronic device can be one or more. Figure 7 Taking a processor 71 as an example; the processor 71, memory 72, input device 73, and output device 74 in this electronic device can be connected via a bus or other means. Figure 7Taking a bus connection as an example, the memory 72, as a computer-readable storage medium, can be used to store software programs, computer-executable programs, and modules, such as the program instructions / modules corresponding to the decoupling control method of the converter in this embodiment. The processor 71 executes various functional applications and data processing of the device by running the software programs, instructions, and modules stored in the memory 72, thereby realizing the aforementioned decoupling control method of the converter. The input device 73 can be used to receive input digital or character information and generate key signal inputs related to user settings and function control of the device. The output device 74 may include a display screen or other display device.

[0123] The above is a detailed description of the preferred embodiments of the present invention. However, this application is not limited to the above embodiments. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of this application. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.

Claims

1. A control method for a three-level converter, characterized in that, The three-level converter includes a three-level conversion circuit and a half-bridge circuit. The DC side of the three-level conversion circuit is connected to the half-bridge circuit. The half-bridge circuit includes a first switch, a second switch, a first inductor, an upper split capacitor, and a lower split capacitor. The first and second switches are connected in series between the positive and negative terminals of the DC bus. The upper and lower split capacitors are connected in series between the positive and negative terminals of the DC bus. The two ends of the first inductor are respectively connected to the midpoint of the connection between the first and second switches and the midpoint of the connection between the upper and lower split capacitors. The capacitance values ​​of the upper and lower split capacitors are unequal. The control method includes the following steps: Obtain the first current flowing from the three-level conversion circuit to the connection midpoint of the upper and lower split capacitors; Based on the reference voltage and actual voltage of the DC bus, a first reference current is obtained; A second reference current is obtained based on the average voltage of the lower split capacitor and the reference voltage of the DC bus; A modulated wave is generated based on the first reference current, the second reference current, the current of the first inductor, and the first current; The modulated wave is compared with a triangular wave to generate drive signals for the first and second switching transistors.

2. The control method for the three-level converter according to claim 1, characterized in that, The formula for calculating the first current is: ； In the formula, Indicates the external load current; Indicates the load voltage; This indicates the actual voltage of the DC bus.

3. The control method for the three-level converter according to claim 1, characterized in that, The step of obtaining the first reference current based on the reference voltage and the actual voltage of the DC bus includes: The low-frequency ripple component of the DC bus is obtained by subtracting the reference voltage and the actual voltage of the DC bus. The difference between zero and the low-frequency ripple component is input into the ripple suppression controller to obtain the first reference current.

4. The control method for the three-level converter according to claim 3, characterized in that, The ripple suppression controller is a controller with low-frequency sinusoidal signal tracking capability, and is one of the following: multi-resonant controller, repetitive controller, sliding mode controller, backstepping controller, and Lyapunov controller.

5. The control method for the three-level converter according to claim 1, characterized in that, The step of obtaining the second reference current based on the average voltage of the lower split capacitor and the reference voltage of the DC bus includes: The difference between half of the reference voltage of the DC bus and the average voltage of the lower split capacitor is input to the midpoint voltage balance controller to obtain the second reference current.

6. The control method for the three-level converter according to claim 5, characterized in that, The midpoint voltage balance controller is a controller with DC signal tracking capability, and is one of the following: proportional-integral controller, proportional-integral-derivative controller, sliding mode controller, backstepping controller, and Lyapunov controller.

7. The control method for the three-level converter according to claim 1, characterized in that, The step of generating a modulated wave based on the first reference current, the second reference current, the current of the first inductor, and the first current includes: The sum of the first reference current and the second reference current is taken as the total reference current; The difference between the total reference current and the current of the first inductor and the first current is input into the current loop controller to generate the modulation wave.

8. The control method for the three-level converter according to claim 7, characterized in that, The current loop controller is a controller with AC / DC signal tracking capability, and is one of the following: proportional-integral multivibrator controller, repetitive controller, sliding mode controller, backstepping controller, and Lyapunov controller.

9. A control device for a three-level converter, applied to a three-level converter, characterized in that, The three-level converter includes a three-level conversion circuit and a half-bridge circuit. The DC side of the three-level conversion circuit is connected to the half-bridge circuit. The half-bridge circuit includes a first switching transistor, a second switching transistor, a first inductor, an upper split capacitor, and a lower split capacitor. The first and second switching transistors are connected in series between the positive and negative terminals of the DC bus. The upper and lower split capacitors are connected in series between the positive and negative terminals of the DC bus. The two ends of the first inductor are respectively connected to the midpoint of the connection between the first and second switching transistors and the midpoint of the connection between the upper and lower split capacitors. The capacitance values ​​of the upper and lower split capacitors are unequal. The control device includes: The first current acquisition module is used to acquire the first current flowing from the three-level conversion circuit to the connection midpoint of the upper split capacitor and the lower split capacitor. The first reference current acquisition module is used to acquire a first reference current based on the reference voltage and the actual voltage of the DC bus; The second reference current acquisition module is used to acquire a second reference current based on the average voltage of the lower split capacitor and the reference voltage of the DC bus. A modulation wave generation module is used to generate a modulation wave based on the first reference current, the second reference current, the current of the first inductor, and the first current; The drive signal generation module is used to compare the modulated wave with the triangular wave to generate drive signals for the first switch and the second switch.

10. An electronic device, characterized in that, include: At least one processor; as well as A memory communicatively connected to the at least one processor; wherein, The memory stores one or more computer programs that can be executed by the at least one processor, the one or more computer programs being executed by the at least one processor to enable the at least one processor to perform the control method of the three-level converter as described in any one of claims 1 to 8.

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