Flying capacitor voltage balance control method of flying capacitor multi-level inverter and related equipment

Abstract

The invention relates to the technical field of multi-level inverter control, in particular to a flying capacitor voltage balance control method of a flying capacitor multi-level inverter and related equipment. The method comprises the following steps of: sampling an output alternating current voltage of the flying capacitor multi-level inverter and sampling an output alternating current iL; obtaining an output duty ratio signal according to the output AC voltage sampling value and the output AC current sampling value; according to the current direction of the output alternating current, the nth flying capacitor voltage reference voltage and the sampling voltage, the driving signal final adjustment amount of the nth pair of switching tubes and the (n + 1) th pair of switching tubes is obtained; according to the output duty ratio signal and the final adjustment amount of the driving signals of the nth pair and the (n + 1) th pair of the switching tubes, driving duty ratio signals of the nth pair and the (n + 1) th pair of the switching tubes are obtained; and the working states of the nth pair of switching tubes and the (n + 1) th pair of switching tubes are further controlled. According to the invention, output voltage and inductive current double-loop control is combined, and the dynamic response of the system is accelerated.

Description

Technical Field

[0001] The present invention relates to the technical field of multi-level inverter control, and in particular to a flying capacitor voltage balance control method of a flying capacitor multi-level inverter and related equipment. Background Art

[0002] Multilevel circuits can reduce the size of filter inductors by minimizing the voltage variation across them. Traditionally, multilevel circuits have been primarily used in medium- and high-voltage applications, primarily addressing issues such as insufficient voltage ratings for power devices and high electromagnetic interference. Meanwhile, multilevel technology is increasingly being applied in low-voltage applications to improve inverter efficiency and power density. Increasing the number of levels reduces device voltage stress, enabling the use of higher-performance low-voltage power devices and thus reducing device losses. Furthermore, multilevel circuits can increase the equivalent switching frequency and reduce the volt-second product of magnetic components, further reducing the demand for filter inductors.

[0003] Flying capacitor multilevel inverters are currently the most promising solution for increasing inverter power density. Compared to two-level circuits, multilevel circuits can increase the number of voltage levels at the bridge arm switching nodes, reducing the voltage swing across the filter inductor. Furthermore, modulation strategies can be used to increase the converter's equivalent operating frequency. This maintains the switching frequency of individual power devices, and switching losses do not increase significantly. However, the volt-second product of the filter inductor is significantly reduced, reducing its inductance and volume accordingly, significantly improving the inverter's power density. Among the commonly used multilevel circuit topologies, flying capacitor multilevel circuits are characterized by their simple structure, ease of scalability, and the small number of power devices required.

[0004] Figure 1 This is a seven-level flying capacitor inverter circuit topology, including high-frequency bridge arm, low-frequency bridge arm, flying capacitor, and output filter components. The advantages of using a flying capacitor multi-level inverter are:

[0005] (1) Due to the existence of flying capacitors, the voltage stress of the high-frequency bridge arm switch tube is significantly reduced; the voltage change during each switch switching is small, which reduces the impact of dv / dt and has good electromagnetic compatibility.

[0006] (2) Carrier phase-shift modulation can increase the equivalent operating frequency of the circuit without increasing the switching frequency of the device. Therefore, the volume of the filter inductor can be significantly reduced, and the loss of the power device will not increase significantly.

[0007] (3) The existence of the low-frequency bridge arm can further expand the number of output levels and improve the DC side voltage utilization.

[0008] However, multi-level inverters require more power devices, making the corresponding drive and control circuits more complex. Furthermore, stable flying capacitor voltage is a prerequisite for normal circuit operation, requiring corresponding dynamic voltage balancing control. Summary of the Invention

[0009] In response to the problems in the prior art, the present invention provides a flying capacitor voltage balance control method and related equipment for a flying capacitor multi-level inverter. Unlike traditional control methods, the present invention has the characteristics of simple control, fast dynamic response and high stability, which is more conducive to flying capacitor voltage control. The method of the present invention is applicable to the flying capacitor voltage balance control of a flying capacitor multi-level inverter with all levels. The specific technical solution is as follows:

[0010] A flying capacitor voltage balance control method for a flying capacitor multi-level inverter comprises the following steps:

[0011] Step S1: the output AC voltage v of the flying capacitor multi-level inverter is o Sampling is performed and recorded as the output AC voltage sampling value v o_adc ; Output AC current i of flying capacitor multilevel inverter L Sampling is performed and recorded as the output AC current sampling value i L_adc ; Step S2, according to the output AC voltage sampling value v o_adc And the output AC current sampling value i L_adc Get the output duty cycle signal D; Step S3, according to the output AC current i L The current direction, and the nth flying capacitor voltage reference voltage V cn_ref The nth flying capacitor sampling voltage V cn Get the nth pair of switch tubes S connected to the nth flying capacitor na,b The final adjustment of the driving signal Δd' n and the n+1th pair of switch tubes S connected to the nth flying capacitor n+1a,b The final adjustment of the driving signal Δd' n+1 ; Among them, the nth pair of switch tubes S na,b Including switch tube S na and switch tube S nb , the n+1th pair of switch tubes S n+1a,b Including switch tube S n+1a and switch tube S n+1b ;

[0012] Step S4: adjust the output duty cycle signal D and the final drive signal value Δd' n , the final adjustment amount of the driving signal Δd' n+1 Get the nth pair of switch tubes S connected to the nth flying capacitor na,b The driving duty cycle signal dn and the n+1th pair of switch tubes S connected to the nth flying capacitor n+1a,b The driving duty cycle signal d n+1 ;

[0013] Step S5, according to the nth pair of switch tubes S connected to the nth flying capacitor na,b The driving duty cycle signal d n , the n+1th pair of switch tubes S connected to the nth flying capacitor n+1a,b The driving duty cycle signal d n+1 Control the nth pair of switch tubes S connected to the nth flying capacitor in the flying capacitor multi-level inverter na,b The working state of the flying capacitor multi-level inverter and the n+1th pair of switch tubes S connected to the nth flying capacitor n+1a,b working status.

[0014] Preferably, step S2 specifically includes the following steps:

[0015] Step S21: Output voltage reference value v o_ref And the output AC voltage sampling value v o_adc The output AC voltage error ε is obtained by subtracting v ; Step S22, the output AC voltage error ε v The input voltage controller generates the output current reference signal i L_ref ;

[0016] Step S23: Output current reference signal i L_ref and the output AC current sampling value i L_adc The output AC current error ε is obtained by subtracting i ;

[0017] Step S24: Output AC current error ε i The input current controller generates an output duty cycle signal D.

[0018] Preferably, the current reference signal i in step S22 L_ref is calculated as follows:

[0019] i L_ref =ε v G v (s);

[0020]

[0021] Among them, G v (s) is the transfer function of the voltage controller, K pv is the proportional coefficient of the voltage controller, Krv is the resonance coefficient of the voltage controller, ω cvis the cutoff frequency of the voltage controller, ω ov is the fundamental angular frequency of the voltage controller.

[0022] Preferably, the output duty cycle signal D is calculated as follows:

[0023] D=ε i G i (s);

[0024]

[0025] Among them, G i (s) is the transfer function of the current controller, K pi is the proportional coefficient of the current controller, Kri is the resonance coefficient of the current controller, ω ci is the cutoff frequency of the current controller, ω oi is the fundamental angular frequency of the current controller.

[0026] Preferably, the step S3 specifically includes the following steps:

[0027] Step S31: The nth flying capacitor voltage reference voltage V cn_ref The nth flying capacitor sampling voltage V cn The nth flying capacitor voltage error ε is obtained by subtracting cn ;

[0028] Step S32: The nth flying capacitor voltage error ε cn The voltage error signals of the two flying capacitors are respectively cn-1 , ε cn+1 The difference between the two adjacent flying capacitors of the nth flying capacitor generates the error signal ε cn_n-1 and ε cn_n+1 ;

[0029] Step S33: The error signals ε of two adjacent flying capacitors of the nth flying capacitor are converted to cn_n-1 and ε cn_n+1 After inputting the proportional controller respectively, the nth pair of switch tubes S connected to the nth flying capacitor are obtained. na,b The driving duty cycle adjusts the amplitude signal Δd n , the n+1th pair of switch tubes S connected to the nth flying capacitor n+1a,b The driving duty cycle adjusts the amplitude signal Δd n+1 ;

[0030] Step S34: According to the output AC current i L The current direction and driving duty cycle adjustment amplitude signal Δd n , drive duty cycle adjustment amplitude signal Δd n+1Get the nth pair of switch tubes S connected to the nth flying capacitor na,b The final adjustment of the driving signal Δd' n and the n+1th pair of switch tubes S connected to the nth flying capacitor n+1a,b The final adjustment of the driving signal Δd' n+1 .

[0031] Preferably, the error signal ε between two adjacent flying capacitors of the nth flying capacitor in step S32 is cn_n-1 and ε cn_n+1 is calculated as follows:

[0032] ε cn_n-1 =ε cn -ε cn-1 ;

[0033] ε cn_n+1 =ε cn -ε cn+1 .

[0034] Preferably, in step S33, the nth pair of switch tubes S connected to the nth flying capacitor na,b The driving duty cycle adjusts the amplitude signal Δd n , the n+1th pair of switch tubes S connected to the nth flying capacitor n+1a,b The driving duty cycle adjusts the amplitude signal Δd n+1 is calculated as follows:

[0035] Δd n =K p ε cn_n-1 ;

[0036] Δd n+1 =K p ε cn_n+1 ;

[0037] Among them, K p is the proportional coefficient of the proportional controller.

[0038] Preferably, in step S34, the nth pair of switch tubes S connected to the nth flying capacitor na,b The final adjustment of the driving signal Δd' n is calculated as follows:

[0039] Δd' n =Δd n sign(i L );

[0040] The n+1th pair of switch tubes S connected to the nth flying capacitor n+1a,b The final adjustment of the driving signal Δd' n+1 The calculation method of Δd' is as follows:n+1 =Δd n+1 sign(i L );

[0041]

[0042] Among them, sign(i L ) is the current sign function. The output AC current i of the flying capacitor multilevel inverter L The sign function of .

[0043] Preferably, in step S4, the nth pair of switch tubes S connected to the nth flying capacitor na,b The driving duty cycle signal d n and the n+1th pair of switch tubes S connected to the nth flying capacitor n+1a,b The driving duty cycle signal d n+1 The calculation method of d is as follows: n =D+Δd' n ;

[0044] d n+1 =D+Δd' n+1 .

[0045] An electronic device includes a memory and a processor, wherein the memory is used to store a computer program, and the processor runs the computer program to enable the electronic device to perform the flying capacitor voltage balancing control method of a flying capacitor multi-level inverter.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] The present invention combines dual-loop control of output voltage and inductor current. The voltage outer loop is used to control the output voltage waveform; the current inner loop is used to improve the output impedance and accelerate the dynamic response of the system.

[0048] In the present invention, there is no limit on the number of levels of the flying capacitor multi-level inverter, that is, for a flying capacitor multi-level inverter with any number of levels, the control strategy of the present invention can be used to achieve voltage control of the flying capacitor. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly describes the drawings required for the specific embodiments or the description of the prior art. Similar elements or parts are generally identified by similar reference numerals throughout the drawings. Elements or parts in the drawings are not necessarily drawn to scale.

[0050] Figure 1 This is a topological structure diagram of a flying capacitor multi-level inverter of the present invention, which has 7 levels.

[0051] Figure 2 This is a schematic diagram of the high-frequency bridge arm modulation signal used by the flying capacitor multi-level inverter to output an ideal sinusoidal voltage and to offset the influence of voltage bias.

[0052] Figure 3 It is a schematic diagram of the principle of obtaining the final adjustment amount of the driving signal in the present invention.

[0053] Figure 4 It is a schematic diagram of the principle of the control method of the present invention.

[0054] Figure 5 It is a schematic diagram of the PWM control signal of the switch tube in the control method of the present invention.

[0055] Figure 6 This is a simulated waveform of the flying capacitor voltage when the bus voltage changes when the control method of the present invention is not adopted.

[0056] Figure 7 This is a simulated waveform of the flying capacitor voltage when the bus voltage changes when the control method of the present invention is adopted.

[0057] Figure 8 This is an experimental waveform of the flying capacitor voltage when the bus voltage changes using the control method of the present invention. DETAILED DESCRIPTION

[0058] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0059] It will be understood that when used in this specification and the appended claims, the terms “comprises” and “comprising” indicate the presence of described features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof.

[0060] It should also be understood that the terms used in the present specification are only for the purpose of describing particular embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms unless the context clearly indicates otherwise.

[0061] It should be further understood that the term "and / or" used in the present description and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

[0062] Example 1:

[0063] This embodiment provides a flying capacitor voltage balance control method for a flying capacitor multi-level inverter. The method of the present invention is applicable to the flying capacitor voltage balance control of a flying capacitor multi-level inverter with all levels. The following is an example of a flying capacitor multi-level inverter with 7 levels. The topology circuit is as follows: Figure 1 shown.

[0064] The high frequency bridge arm is composed of the switch tube S 1a -S 6b are connected in series, where S na,b The nth pair of switches connected to the nth flying capacitor are driven by a pair of complementary signals. These switches are turned on or off according to the corresponding drive signals, thereby generating the required multi-level waveform. The low-frequency bridge arm includes the switch S a , switch tube S b The low-frequency bridge arm and the high-frequency bridge arm form a full-bridge circuit, which improves the DC side voltage utilization. When the output voltage polarity is positive, the switch tube S b Always on, the circuit is equivalent to a seven-level circuit connected to the low-voltage side. Conversely, when the output voltage polarity is negative, the switch tube S a Conducting, switching tube S b Turn off, low frequency bridge arm midpoint potential V d It is pulled up to the DC side voltage to provide a DC bias for the output voltage. At this time, the circuit is equivalent to a seven-level circuit connected to the high-voltage side. It can be seen that the action of the low-frequency bridge arm further expands the number of output voltage levels. In addition, the switch tube S a , switch tube S b With low-frequency periodic switching, switching losses and reverse recovery losses can be ignored. To balance the voltage stress of the power devices, the 1st to 5th flying capacitors C1-C5 need to provide a step voltage reference. The sampling voltage of the nth flying capacitor is:

[0065]

[0066] Where V cn is the nth flying capacitor sampling voltage, N is the number of levels, which is 7 in this example. s1 、L s2 They are the output filter inductors of the high-voltage side and the low-voltage side, C s It is an output filter capacitor used to filter out high-frequency current ripple; Figure 1 Medium V g is the single-phase grid voltage. Vdc is the DC power supply voltage.

[0067] The driving signal of the low-frequency bridge arm is determined by the output voltage polarity and is switched with the power frequency as the cycle. a When conducting, the midpoint potential of the low-frequency bridge arm V d It will be pulled up to the DC side voltage, so the output voltage of the low-frequency bridge arm is a power frequency square wave. In order to obtain an ideal sinusoidal output voltage, the modulation signal of the high-frequency bridge arm also needs to be processed accordingly in the negative half cycle to offset the influence of the voltage bias. At this time, the modulation wave signal of the flying capacitor inverter is as follows Figure 2 shown.

[0068] The high-frequency bridge arm adopts carrier phase shift modulation, that is, the above-mentioned flying capacitor inverter modulation wave signal is compared with (N-1) groups of carrier signals, thereby obtaining (N-1) pairs of high-frequency switch tube drive signals. In this embodiment, a total of six groups of carrier signals are used, namely u c1 -u c6 , corresponding to the switch tube S 1a,b -S 6a,b When the flying capacitor inverter modulates the wave signal u m Greater than carrier u cx When the signal is on, the corresponding switch tube S xa On, on the contrary, the switch tube S xb Conductive, where x = 1, 2, 3, 4, 5, 6.

[0069] Flying-capacitor multilevel inverters use power devices connected in series to reduce voltage stress on individual devices. Flying capacitors ensure equal voltage distribution across the series switches. If the capacitor voltage deviates from its balanced value, it increases the voltage stress on the switches, potentially causing overvoltage breakdown. Furthermore, since the switches are connected in series, failure of even one can damage all of them. Therefore, capacitor voltage balance is essential for the normal and reliable operation of the inverter, and appropriate measures must be taken to maintain capacitor voltage stability.

[0070] Although carrier phase-shift modulation can achieve automatic capacitor voltage balancing, this natural voltage balancing effect depends on load conditions. When the bus voltage or load experiences sudden changes, it is difficult to quickly and accurately achieve voltage regulation. Therefore, an active voltage control method is needed to speed up the voltage response and improve the system's dynamic performance.

[0071] From the above analysis, we can see that the current flowing through the flying capacitor will be affected by the duty cycle of the two adjacent pairs of switch tubes. n+1a,b The driving duty cycle signal d n+1When the input current of the nth flying capacitor increases, the capacitor voltage of the nth flying capacitor will also increase; when the nth pair of switch tubes S connected to the nth flying capacitor is increased, na,b The driving duty cycle signal d n The effect is the opposite.

[0072] If the nth flying capacitor C n Capacitor voltage V Cn If the voltage is less than the reference voltage, a positive current should be applied to the nth flying capacitor, that is, to increase d n+1 and reduce d n Similarly, if the n-1th flying capacitor C n-1 Capacitor voltage V Cn-1 If it is less than the reference value, d should be increased n , it can be seen that d n It will be affected by the voltage deviation of two adjacent capacitors at the same time. In addition, the direction of the load current should also be considered. When the current is reversed, the control logic is opposite.

[0073] Therefore, the flying capacitor voltage balance control method of the flying capacitor multi-level inverter provided in this embodiment includes the following steps:

[0074] Step S1: the output AC voltage v of the flying capacitor multi-level inverter is o Sampling is performed and recorded as the output AC voltage sampling value v o_adc ; Output AC current i of flying capacitor multilevel inverter L Sampling is performed and recorded as the output AC current sampling value i L_adc .v o_adc =v o *H v (s);

[0075] i L_adc =i L *H i (s);

[0076] Among them, H v (s) Transfer function of the voltage sampling circuit, H i (s) is the transfer function of the current sampling circuit.

[0077] Step S2: According to the output AC voltage sampling value v o_adc And the output AC current sampling value i L_adc The output duty cycle signal D is obtained. Specifically, the following steps are included:

[0078] Step S21: Output voltage reference value v o_ref And the output AC voltage sampling value v o_adc The output AC voltage error ε is obtained by subtracting v. Specifically, ε v =v o_ref -v o_adc .

[0079] Step S22: Output AC voltage error ε v The input voltage controller generates the output current reference signal i L_ref . Current reference signal i L_ref is calculated as follows:

[0080] i L_ref =ε v G v (s);

[0081]

[0082] Among them, G v (s) is the transfer function of the voltage controller, K pv is the proportional coefficient of the voltage controller, Krv is the resonance coefficient of the voltage controller, ω cv is the cutoff frequency of the voltage controller, ω ov is the fundamental angular frequency of the voltage controller.

[0083] Step S23: Output current reference signal i L_ref and the output AC current sampling value i L_adc The output AC current error ε is obtained by subtracting i . Specifically, ε i =i L_ref -i L_adc .

[0084] Step S24: Output AC current error ε i The input current controller generates the output duty cycle signal D. The output duty cycle signal D is calculated as follows:

[0085] D=ε i G i (s);

[0086]

[0087] Among them, G i (s) is the transfer function of the current controller, K pi is the proportional coefficient of the current controller, Kri is the resonance coefficient of the current controller, ω ci is the cutoff frequency of the current controller, ω oi is the fundamental angular frequency of the current controller.

[0088] Step S3, according to the output AC current i L The current direction, and the nth flying capacitor voltage reference voltage Vcn_ref The nth flying capacitor sampling voltage V cn Get the nth pair of switch tubes S connected to the nth flying capacitor na,b The final adjustment of the driving signal Δd' n and the n+1th pair of switch tubes S connected to the nth flying capacitor n+1a,b The final adjustment of the driving signal Δd' n+1 ; Among them, the nth pair of switch tubes S na,b Including switch tube S na and switch tube S nb , the n+1th pair of switch tubes S n+1a,b Including switch tube S n+1a and switch tube S n+1b The specific steps include:

[0089] Step S31: The nth flying capacitor voltage reference voltage V cn_ref The nth flying capacitor sampling voltage V cn The nth flying capacitor voltage error ε is obtained by subtracting cn . Specifically, ε cn =V cn_ref -V cn .

[0090] In step S32, except for the first and last complementary bridge arms, i.e., the first complementary bridge arm and the sixth complementary bridge arm, the duty cycle change of any complementary bridge arm affects the voltages of two adjacent flying capacitors. cn The voltage error signals of the two flying capacitors are respectively cn-1 , ε cn+1 The difference between the two adjacent flying capacitors of the nth flying capacitor generates the error signal ε cn_n-1 and ε cn_n+1 The error signal ε between two adjacent flying capacitors of the nth flying capacitor cn_n-1 and ε cn_n+1 The calculation method of ε is as follows: cn_n-1 =ε cn -ε cn-1 ;

[0091] ε cn_n+1 =ε cn -ε cn+1 .

[0092] For the first flying capacitor C1, its voltage is only affected by the first complementary bridge arm and the second complementary bridge arm. Therefore, for the first flying capacitor C1, the above expression needs to make ε cn-1 =0, that is, the above expression degenerates into:

[0093] ε cn_n-1 =ε cnn=1.

[0094] Similarly, for the fifth flying capacitor C5, its voltage is only affected by the fifth complementary bridge arm and the sixth complementary bridge arm. Let ε cn+1 =0, that is, the above expression degenerates into:

[0095] ε cn_n+1 =ε cn n=5.

[0096] Step S33, based on the relationship between the flying capacitor voltage value and the duty cycle of the two complementary bridge arms connected, that is, if the flying capacitor C n If the voltage is less than the reference voltage, a positive current should be applied to the capacitor, which means increasing Δd n+1 and reduce Δd n Similarly, if the capacitor C n-1 If the voltage is less than the reference value, Δd should be increased n The error signals ε of the two adjacent flying capacitors of the nth flying capacitor are cn_n-1 and ε cn_n+1 After inputting the proportional controller respectively, the nth pair of switch tubes S connected to the nth flying capacitor are obtained. na,b The driving duty cycle adjusts the amplitude signal Δd n , the n+1th pair of switch tubes S connected to the nth flying capacitor n+1a,b The driving duty cycle adjusts the amplitude signal Δd n+1 The nth pair of switch tubes S connected to the nth flying capacitor na,b The driving duty cycle adjusts the amplitude signal Δd n , the n+1th pair of switch tubes S connected to the nth flying capacitor n+1a,b The driving duty cycle adjusts the amplitude signal Δd n+1 The calculation method of Δd is as follows: n =K p ε cn_n-1 ;

[0097] Δd n+1 =K p ε cn_n+1 ;

[0098] Among them, K p is the proportional coefficient of the proportional controller.

[0099] Step S34, considering the direction of the output current, the adjustment direction given in step S34 is when the output current is positive. When the output current is negative, the above adjustment direction should be opposite, so according to the output AC current i L The current direction and driving duty cycle adjustment amplitude signal Δd n , drive duty cycle adjustment amplitude signal Δd n+1Get the nth pair of switch tubes S connected to the nth flying capacitor na,b The final adjustment of the driving signal Δd' n and the n+1th pair of switch tubes S connected to the nth flying capacitor n+1a,b The final adjustment of the driving signal Δd' n+1 .

[0100] The nth pair of switch tubes S connected to the nth flying capacitor na,b The final adjustment of the driving signal Δd' n The calculation method of Δd' is as follows: n =Δd n sign(i L );

[0101] The n+1th pair of switch tubes S connected to the nth flying capacitor n+1a,b The final adjustment of the driving signal Δd' n+1 The calculation method of Δd' is as follows: n+1 =Δd n+1 sign(i L );

[0102]

[0103] Among them, sign(i L ) is the current sign function. The output AC current i of the flying capacitor multilevel inverter L The sign function of .

[0104] Step S4: adjust the output duty cycle signal D and the final drive signal value Δd' n , the final adjustment amount of the driving signal Δd' n+1 Get the nth pair of switch tubes S connected to the nth flying capacitor na,b The driving duty cycle signal d n and the n+1th pair of switch tubes S connected to the nth flying capacitor n+1a,b The driving duty cycle signal d n+1 The nth pair of switch tubes S connected to the nth flying capacitor na,b The driving duty cycle signal d n and the n+1th pair of switch tubes S connected to the nth flying capacitor n+1a,b The driving duty cycle signal d n+1 is calculated as follows:

[0105] d n =D+Δd' n ;

[0106] d n+1 =D+Δd' n+1 .

[0107] Step S5, according to the nth pair of switch tubes S connected to the nth flying capacitor na,b The driving duty cycle signal d n , the n+1th pair of switch tubes S connected to the nth flying capacitor n+1a,b The driving duty cycle signal d n+1 Control the nth pair of switch tubes S connected to the nth flying capacitor in the flying capacitor multi-level inverter na,b The working state of the flying capacitor multi-level inverter and the n+1th pair of switch tubes S connected to the nth flying capacitor n+1a,b working status.

[0108] The expression of the sawtooth wave carrier signal car1 of the first bridge arm connected to the first flying capacitor is:

[0109] car1=t PWM *sawtooth(2πf*t).

[0110] For the sawtooth wave carrier signals from the 2nd to the n+1th bridge arms, there is a phase shift time Δt relative to the previous sawtooth wave carrier signal, Δt=t PWM / 6.

[0111] Then for the sawtooth wave carrier signal car of the n+1th bridge arm connected to the nth flying capacitor n+1 The expression is:

[0112] car n+1 =t PWM *sawtooth(2πf*tn*t PWM / 6)n=1,2,3,4,5.

[0113]

[0114] in Indicates S na The complementary signal of Indicates S n+1a complementary signal.

[0115] like Figure 5 As shown, in this embodiment, the first pair of switch tubes S connected to the first flying capacitor 1a,b The first complementary bridge arm and the second pair of switch tubes S connected to the first flying capacitor 2a,b Taking the second complementary bridge arm as an example, d1 and d2 are duty cycle control signals acting on the first complementary bridge arm and the second complementary bridge arm respectively.

[0116] car1 and car2 are the sawtooth wave carrier signals of the first complementary bridge arm and the second complementary bridge arm PWM generator respectively. Their expressions are:

[0117] car1=t PWM *sawtooth(2πf*t);

[0118] car2=t PWM *sawtooth(2πf*tt PWM / 6);

[0119] Where f is the switching frequency, t PWM The sawtooth function generates a sawtooth wave with an amplitude of 1 and a period of 1 / f, corresponding to Figure 5 As shown. The sawtooth function is similar to the sine function, but creates a sawtooth wave with peaks at 0 and 1. The sawtooth wave is defined as 0 at times t that are multiples of 1 / f and increases linearly with time at all other times. There is a phase shift of time Δt between car1 and car2, which is expressed as:

[0120] Δt=t PWM / 6;

[0121] By comparing d1 and d2 with car1 and car2 respectively, the switch tube S is generated. 1a With the switch tube S 1b The control signal is expressed as:

[0122]

[0123] For the switch control signal on the same complementary bridge arm, for the first complementary bridge arm, the switch S 1a With S 1b The control signal S 1a With S 1b Complementary, that is, when S 1a =1, S 1b =0; when S 1a =0, S 1b =1. For the second complementary bridge arm, the switch tube S 2a With S 2b The control signal S 2a With S 2b Also complementary. Its expression is:

[0124]

[0125] in Indicates S 1a The complementary signal of Indicates S 2a complementary signal.

[0126] The present invention adopts a method for adjusting the duty cycle of two adjacent pairs of switch tubes to realize the capacitor voltage balance control method of the flying capacitor multi-level inverter. n+1a and switch tube S nb When turned on, the load current flows into the nth flying capacitor C n , for the nth flying capacitor C n Capacitor charging, the nth flying capacitor C n The capacitor voltage increases; when the switch tube S n+1b and switch tube S na When turned on, the nth flying capacitor C n Discharge, the nth flying capacitor C n The voltage drops. In the other two modes the capacitors are bypassed.

[0127] In the present invention, for any flying capacitor C n , only the two pairs of complementary switching devices S directly connected to it need to be controlled na,b 、S n+1a,b The on-off time of the flying capacitor is controlled, thereby controlling the charging and discharging process of the flying capacitor. The implementation process is simple and efficient.

[0128] In the present invention, there is no limit on the number of levels of the flying capacitor multi-level inverter, that is, for a flying capacitor multi-level inverter with any number of levels, the control strategy of the present invention can be used to achieve voltage control of the flying capacitor.

[0129] The present invention combines dual-loop control of output voltage and inductor current. The voltage outer loop is used to control the output voltage waveform; the current inner loop is used to improve the output impedance and accelerate the dynamic response of the system.

[0130] On the other hand, except for the first and last flying capacitors of the inverter, any duty cycle change of any pair of complementary switching tubes affects two different flying capacitor voltages. For the carrier phase-shift modulation used in the example of the present invention, the duty cycle of the driving signal of each power device is the same within a single switching cycle, so the average current flowing through the flying capacitor is zero, and its voltage will also remain unchanged. Although carrier phase-shift modulation can achieve automatic balancing of capacitor voltages, this natural voltage balancing effect depends on the load conditions. When there is a sudden change in the bus voltage or load, it is difficult to quickly and accurately achieve voltage regulation. Figure 6 The figure shows the simulated waveform of the flying capacitor voltage when the bus voltage suddenly increases. It can be seen that it takes nearly 30ms for the capacitor voltage to stabilize again.

[0131] After the control method of the present invention is implemented, when the bus voltage changes, the voltage of each flying capacitor responds quickly and can reach a stable value again within a short adjustment time. Figure 7The simulation results of the present invention are given. Figure 6 The simulation results shown without the control method of the present invention show that the flying capacitor settling time is shortened from 30ms to 5ms, demonstrating the rapidity of the control method proposed in the present invention. Furthermore, the simulation results show that after applying the present invention, the overshoot of the flying capacitor voltage in each capacitance change process after bus voltage fluctuations is significantly reduced, demonstrating the good dynamic performance of the proposed control method.

[0132] Table 1 Prototype parameters

[0133] Switching devices Switch device model parameter value High-frequency bridge arm SiR668ADP filter inductors 47mH Low-frequency bridge arm STB33N65 filter capacitors 200nF driver chip Si8271 Flying capacitor 6mF

[0134] Finally, a prototype of the Qidian flying capacitor inverter was built, with parameters shown in Table 1, and the control method of the present invention was applied. Figure 8 The simulation results of the flying capacitor voltage under load fluctuations using the control method of the present invention are presented. The experimental results show that the voltage of the flying capacitors C1-C4 can be quickly stabilized within 8ms when the load fluctuates, indicating that the control method proposed in the present invention can effectively and quickly stabilize the flying capacitor voltage.

[0135] Example 2:

[0136] Based on the same inventive concept as Example 1, this embodiment provides an electronic device, including a memory and a processor, wherein the memory is used to store a computer program, and the processor runs the computer program to enable the electronic device to execute the flying capacitor voltage balancing control method of the flying capacitor multi-level inverter.

[0137] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and description of the present invention.

Claims

1. A flying capacitor voltage balance control method for a flying capacitor multi-level inverter, characterized in that: The following steps are involved: Step S1: the output AC voltage v of the flying capacitor multi-level inverter is o Sampling is performed and recorded as the output AC voltage sampling value v o_adc ; Output AC current i of flying capacitor multilevel inverter L Sampling is performed and recorded as the output AC current sampling value i L_adc ; Step S2: According to the output AC voltage sampling value v o_adc And the output AC current sampling value i L_adc Obtaining an output duty cycle signal D; Step S3, according to the output AC current i L The current direction, and the nth flying capacitor voltage reference voltage V cn_ref The nth flying capacitor sampling voltage V cn Get the nth pair of switch tubes S connected to the nth flying capacitor na,b The final adjustment of the driving signal Δd' n and the n+1th pair of switch tubes S connected to the nth flying capacitor n+1a,b The final adjustment of the driving signal Δd' n+1 ; Among them, the nth pair of switch tubes S na,b Including switch tube S na and switch tube S nb , the n+1th pair of switch tubes S n+1a,b Including switch tube S n+1a and switch tube S n+1b ; Step S4: adjust the output duty cycle signal D and the final drive signal value Δd' n , the final adjustment amount of the driving signal Δd' n+1 Get the nth pair of switch tubes S connected to the nth flying capacitor na,b The driving duty cycle signal d n and the n+1th pair of switch tubes S connected to the nth flying capacitor n+1a,b The driving duty cycle signal d n+1 ; Step S5, according to the nth pair of switch tubes S connected to the nth flying capacitor na,b The driving duty cycle signal d n , the n+1th pair of switch tubes S connected to the nth flying capacitor n+1a,b The driving duty cycle signal d n+1 Control the nth pair of switch tubes S connected to the nth flying capacitor in the flying capacitor multi-level inverter na,b The working state of the flying capacitor multi-level inverter and the n+1th pair of switch tubes S connected to the nth flying capacitor n+1a,b working status.

2. The flying capacitor voltage balance control method of a flying capacitor multi-level inverter according to claim 1, wherein: The step S2 specifically includes the following steps: Step S21: Output voltage reference value v o_ref And the output AC voltage sampling value v o_adc The output AC voltage error ε is obtained by subtracting v ; Step S22: Output AC voltage error ε v The input voltage controller generates the output current reference signal i L_ref ; Step S23: Output current reference signal i L_ref and the output AC current sampling value i L_adc The output AC current error ε is obtained by subtracting i ; Step S24: Output AC current error ε i The input current controller generates an output duty cycle signal D.

3. The flying capacitor voltage balance control method of a flying capacitor multi-level inverter according to claim 2, wherein: In step S22, the current reference signal i L_ref is calculated as follows: I L_ref =e v G v (s); Among them, G v (s) is the transfer function of the voltage controller, K pv is the proportional coefficient of the voltage controller, K rv is the resonance coefficient of the voltage controller, ω cv is the cutoff frequency of the voltage controller, ω ov is the fundamental angular frequency of the voltage controller.

4. The flying capacitor voltage balance control method of a flying capacitor multi-level inverter according to claim 2, wherein: The output duty cycle signal D is calculated as follows: D=e i G i (s); Among them, G i (s) is the transfer function of the current controller, Kpi is the proportional coefficient of the current controller, K ri is the resonance coefficient of the current controller, ω ci is the cutoff frequency of the current controller, ω oi is the fundamental angular frequency of the current controller.

5. The flying capacitor voltage balance control method of a flying capacitor multi-level inverter according to claim 1, wherein: The step S3 specifically includes the following steps: Step S31: The nth flying capacitor voltage reference voltage V cn_ref The nth flying capacitor sampling voltage V cn The nth flying capacitor voltage error ε is obtained by subtracting cn ; Step S32: The nth flying capacitor voltage error ε cn The voltage error signals of the two flying capacitors are respectively cn-1 , ε cn+1 The difference between the two adjacent flying capacitors of the nth flying capacitor generates the error signal ε cn_n-1 and ε cn_n+1 ; Step S33: The error signals ε of two adjacent flying capacitors of the nth flying capacitor are converted to cn_n-1 and ε cn_n+1 After inputting the proportional controller respectively, the nth pair of switch tubes S connected to the nth flying capacitor are obtained. na,b The driving duty cycle adjusts the amplitude signal Δd n , the n+1th pair of switch tubes S connected to the nth flying capacitor n+1a,b The driving duty cycle adjusts the amplitude signal Δd n+1 ; Step S34: According to the output AC current i L The current direction and driving duty cycle adjustment amplitude signal Δd n , drive duty cycle adjustment amplitude signal Δd n+1 Get the nth pair of switch tubes S connected to the nth flying capacitor na,b The final adjustment of the driving signal Δd' n and the n+1th pair of switch tubes S connected to the nth flying capacitor n+1a,b The final adjustment of the driving signal Δd' n+1 .

6. The flying capacitor voltage balance control method of a flying capacitor multi-level inverter according to claim 5, characterized in that: The error signal ε of the two adjacent flying capacitors of the nth flying capacitor in step S32 is cn_n-1 and ε cn_n+1 is calculated as follows: e cn_n-1 =e cn -e cn-1 ; e cn_n+1 =e cn -e cn+1 。 7. The flying capacitor voltage balance control method of a flying capacitor multi-level inverter according to claim 5, characterized in that: In step S33, the nth pair of switch tubes S connected to the nth flying capacitor na,b The driving duty cycle adjusts the amplitude signal Δd n , the n+1th pair of switch tubes S connected to the nth flying capacitor n+1a,b The driving duty cycle adjusts the amplitude signal Δd n+1 is calculated as follows: Δd n =K p e cn_n-1 ; Δd n+1 =K p e cn_n+1 ; Among them, K p is the proportional coefficient of the proportional controller.

8. The flying capacitor voltage balance control method of a flying capacitor multi-level inverter according to claim 5, characterized in that: In step S34, the nth pair of switch tubes S connected to the nth flying capacitor na,b The final adjustment of the driving signal Δd' n is calculated as follows: Δd' n =Δd n sign(i L ); The n+1th pair of switch tubes S connected to the nth flying capacitor n+1a,b The final adjustment of the driving signal Δd' n+1 The calculation method of Δd' is as follows: n+1 =Δd n+1 sign(i L ); Among them, sign(i L ) is the current sign function. The output AC current i of the flying capacitor multilevel inverter L The sign function of .

9. The flying capacitor voltage balance control method of a flying capacitor multi-level inverter according to claim 1, characterized in that: In step S4, the nth pair of switch tubes S connected to the nth flying capacitor na,b The driving duty cycle signal d n and the n+1th pair of switch tubes S connected to the nth flying capacitor n+1a,b The driving duty cycle signal d n+1 is calculated as follows: d n =D+Δd' n ; d n+1 =D+Δd' n+1 。 10. An electronic device, characterized in that: The electronic device comprises a memory and a processor, wherein the memory is used to store a computer program, and the processor runs the computer program to enable the electronic device to perform the flying capacitor voltage balancing control method of a flying capacitor multi-level inverter according to any one of claims 1 to 9.

Images