Pulse generation method and system of intelligent optimization cascaded multilevel inverter

Abstract

The invention relates to the technical field of inversion control, in particular to an intelligent optimization cascade multilevel inverter pulse generation method and system, and the method comprises the steps: obtaining a voltage control quantity of a motor in a period, calculating a control quantity prediction value through employing a Lagrange extrapolation method, and obtaining a control quantity prediction value; performing coordinate transformation on the control quantity predicted value to obtain a three-phase voltage instruction; traversing unit output voltages generated by the N inversion units cascaded in the mth phase based on the control set, and counting an mth phase switching function and an mth phase output voltage; finding out the closest mth-phase output voltage, and taking the mth-phase switching function corresponding to the mth-phase output voltage as a switching state control signal of the N inversion units of the mth phase; the appropriate switching state is selected according to the calculated voltage control quantity and directly acts on the switching tube, the PWM modulation link is omitted, the system response speed can be increased, controller resources can be released, and the method is more adaptive to an intelligent operation and maintenance system.

Description

Technical Field

[0001] The present invention relates to the technical field of inverter control, and in particular to a pulse generation method and system for a multi-level inverter. Background Art

[0002] At present, cascaded multi-level inverters mostly use linear controllers such as PI control to calculate the voltage control quantity through double closed-loop control, and then send the control quantity to the PWM modulation module to generate pulses through carrier stacking and other methods. The application of intelligent technology in the operation and maintenance of frequency converters has significantly improved the operating efficiency and reliability of motor speed control systems. Through real-time monitoring by the intelligent operation and maintenance system, potential risks in the operation of frequency converter equipment can be discovered in time, and intelligent decisions and instructions can be provided in time. In order to further improve the reliability and stability of system operation, the frequency converter needs to respond more quickly to the instructions issued by the intelligent operation and maintenance system and optimize the output according to the instructions. The inertia link in the controller calculation process and the control delay introduced by the PWM modulation module will affect the rapidity of the system.

[0003] The existing PWM modulation technology is mature and the implementation method is simple, but there are the following problems: (1) The PWM modulation module will introduce delays, reduce the speed of the system, and it is difficult to respond quickly when the upper-level operation and maintenance system issues new instructions, affecting the work efficiency of the operation and maintenance system; (2) Multiple carriers are prone to carrier desynchronization when external disturbances occur, requiring additional carrier synchronization technology, which will increase the calculation amount of the control system and occupy controller resources. This reduces the resources of the variable frequency equipment to support the operation and maintenance system and increases the difficulty of development. Summary of the invention

[0004] The purpose of the present invention is to provide a pulse generation method of a cascaded multi-level inverter with intelligent optimization to solve the above technical problems;

[0005] The present invention also aims to provide a pulse generation system for cascaded multi-level inverters with intelligent optimization to solve the above technical problems.

[0006] The technical problem solved by the present invention can be achieved by adopting the following technical solutions:

[0007] A pulse generation method for a cascaded multi-level inverter with intelligent optimization, comprising:

[0008] Step S1, obtaining the voltage control amount of the motor in one cycle, calculating the control amount prediction value by using the Lagrange extrapolation method, and obtaining the three-phase voltage command by subjecting the control amount prediction value to coordinate transformation;

[0009] Step S2, constructing a control set for controlling the switching state of the switch tube in the inverter unit, traversing the unit output voltages generated by each of the N inverter units cascaded in the mth phase based on the control set, and counting the mth phase switching function and the corresponding mth phase output voltage formed by the N inverter units in various switching states;

[0010] Step S3, finding the m-th phase output voltage closest to the m-th phase voltage instruction in the three-phase voltage instruction, and using the m-th phase switching function corresponding to the m-th phase output voltage as the switching state control signal of the N inverter units of the m-th phase;

[0011] Wherein, N is a positive integer greater than 1, and m is the phase sequence u, v, w of the three-phase electricity.

[0012] Preferably, in step S1, a speed feedback value and a flux feedback value of the motor are obtained through a sensor or an observer, a q-axis voltage control instruction is calculated through a closed-loop controller based on a difference between the speed feedback value and a preset speed reference value, and a d-axis voltage control instruction is calculated through the closed-loop controller based on a difference between the flux feedback value and a preset flux reference value, and the q-axis voltage control instruction and the d-axis voltage control instruction are transformed from dq axis to αβ axis to obtain the voltage control amount u(k), wherein the voltage control amount includes the α-axis voltage control amount u α (k) and β-axis voltage control quantity u β (k).

[0013] Preferably, in step S1, the expression for calculating the predicted value of the control amount using the Lagrange extrapolation method is:

[0014] u(k+1)=3u(k)-3u(k-1)+u(k-2)

[0015] Wherein, u(k+1) is the control amount prediction value, k represents the current moment, u(k) represents the voltage control amount at the current moment, u(k-1) represents the voltage control amount at the previous moment, and u(k-2) represents the voltage control amount at the previous two moments;

[0016] The control quantity prediction value is converted from the αβ two-phase coordinate system to the uvw three-phase coordinate system to obtain the three-phase voltage command u u 、u v 、u w .

[0017] Preferably, in step S2, each of the inverter units is provided with an H-shaped inverter bridge composed of the switch tubes, and the switch tubes include:

[0018] A first switch tube, wherein the collector of the first switch tube is connected to the positive electrode of the power supply;

[0019] A second switch tube, wherein the collector of the second switch tube is connected to the emitter of the first switch tube to form a first output end of the inverter unit;

[0020] A third switch tube, wherein the collector of the third switch tube is connected to the positive electrode of the power supply;

[0021] A fourth switch tube, wherein the collector of the fourth switch tube is connected to the emitter of the first switch tube to form a second output end of the inverter unit.

[0022] Preferably, in step S2, the switch state of the inverter unit in the control center includes:

[0023] When the first switch tube is turned on, the second switch tube is turned off, the third switch tube is turned off, and the fourth switch tube is turned on, the inverter unit outputs a first DC voltage;

[0024] When the first switch tube is turned on, the second switch tube is turned off, the third switch tube is turned on, and the fourth switch tube is turned off, the inverter unit outputs a second DC voltage;

[0025] When the first switch tube is turned off, the second switch tube is turned on, the third switch tube is turned on, and the fourth switch tube is turned off, the inverter unit outputs a third DC voltage;

[0026] When the first switch tube is turned off, the second switch tube is turned on, the third switch tube is turned off, and the fourth switch tube is turned on, the inverter unit outputs a fourth DC voltage;

[0027] The unit output voltage includes the first DC voltage, the second DC voltage, the third DC voltage, and the fourth DC voltage.

[0028] Preferably, in step S2, the m-th phase switching function is a set of switching states of the N inverter units, expressed as:

[0029] S m =[S 1 S 2 … S n … S N ] T

[0030] Where S n Indicates the switching state of the nth inverter unit among the N inverter units cascaded in the mth phase.

[0031] Preferably,

[0032] The m-th phase output voltage u im The calculation formula is,

[0033] u im =U o1 +U o2 +…+U on +…+U oN

[0034] Among them U on Represents the unit output voltage of the nth inverter unit among the N inverter units cascaded in the mth phase.

[0035] Preferably, in step S3, the m-th phase output voltage closest to the m-th phase voltage instruction is found by constructing a cost function, and the m-th phase switching function corresponding to the minimum value of the cost function is used as the switching state control signal of the m-th phase. The formula of the cost function is:

[0036] G m =(u m -u im ) 2

[0037] Among them, G m represents the calculated value of the cost function in the mth phase, u m represents the m-th phase voltage command, u im represents the m-th phase output voltage.

[0038] Preferably, step S3 comprises,

[0039] Step S31, constructing the cost function, initializing the calculated value of the cost function, and using the initialization result as an intermediate variable;

[0040] Step S32, starting from the first m-th phase output voltage, substituting the currently retrieved m-th phase output voltage into the cost function, and determining whether the calculated value of the cost function of the current m-th phase output voltage is less than the intermediate variable, if so, executing step S33; if not, directly executing step S34;

[0041] Step S33, updating the calculated value of the cost function of the current m-th phase output voltage to the intermediate variable, and updating the m-th phase switching function corresponding to the current m-th phase output voltage to the switching state control signal, and executing step S34;

[0042] Step S34, determine whether all of the m-th phase output voltages have been retrieved. If not, retrieve the next m-th phase output voltage as the currently retrieved m-th phase output voltage, and return to execute step S32; if all of them have been retrieved, output the finally obtained switch state control signal.

[0043] A pulse generation system of a cascade multi-level inverter with intelligent optimization includes an inverter control module, each phase of which is cascaded with N inverter units that can controllably output unit output voltages, and further includes:

[0044] A closed-loop controller, connected to the motor, for obtaining a voltage control amount of the motor;

[0045] A voltage command calculation module, connected to the closed-loop controller, is used to calculate the control quantity prediction value by Lagrange extrapolation method, and to perform coordinate transformation on the control quantity prediction value to obtain a three-phase voltage command;

[0046] an optimization module connected to the voltage instruction calculation module, the optimization module being used to traverse the m-th phase switching function and the corresponding m-th phase output voltage formed by combining the N inverter units in various switching states according to the control set, and output the m-th phase switching function corresponding to the m-th phase output voltage closest to the m-th phase voltage instruction in the three-phase voltage instruction as the switch state control signal of the N inverter units of the m-th phase;

[0047] Wherein, N is a positive integer greater than 1, and m is the phase sequence u, v, w of the three-phase electricity.

[0048] Beneficial effects of the present invention: Due to the adoption of the above technical scheme, the present invention designs the control set of the switch state offline according to the number of cascade units per phase, and each switch state corresponds to a voltage vector; in each control cycle, the appropriate switch state is selected according to the calculated voltage control amount, and directly acts on the switch tube, eliminating the PWM modulation link, which can improve the system response speed, release controller resources, and be more suitable for intelligent operation and maintenance systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 Schematic diagram of the steps of a pulse generating method for a multi-level inverter according to an embodiment of the present invention;

[0050] Figure 2 is a flow chart of a pulse generating method of a multi-level inverter in an embodiment of the present invention;

[0051] Figure 3 This is a schematic diagram of step S3 in an embodiment of the present invention;

[0052] Figure 4 is a topological diagram of a pulse generating system of a multi-level inverter in an embodiment of the present invention;

[0053] Figure 5 A topological diagram of an inverter subsystem in an embodiment of the present invention;

[0054] Figure 6 is a topological diagram of an inverter unit in an embodiment of the present invention;

[0055] Figure 7 4 is a logic block diagram of a pulse generation method for a multi-level inverter in an embodiment of the present invention.

[0056] In the attached figure: 1. inverter unit; 2. voltage command calculation module; 3. optimization module; 4. motor; 5. phase-shifting transformer; 6. closed-loop controller; Q1. first switch tube; Q2. second switch tube; Q3. third switch tube; 4. fourth switch tube. DETAILED DESCRIPTION

[0057] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0058] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0059] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0060] An intelligent optimization method for pulse generation of cascaded multilevel inverters, such as Figures 1 to 6 As shown, including

[0061] Step S1, obtaining the voltage control amount of the motor 4 in one cycle, calculating the control amount prediction value by using the Lagrange extrapolation method, and obtaining the three-phase voltage command after the control amount prediction value is subjected to coordinate transformation;

[0062] Step S2, constructing a control set for controlling the switching state of the switch tube in the inverter unit 1, traversing the unit output voltages generated by each of the N inverter units 1 cascaded in the mth phase based on the control set, and counting the mth phase switching function and the corresponding mth phase output voltage formed by the N inverter units 1 in various switching states;

[0063] Step S3, finding an m-th phase output voltage that is closest to the m-th phase voltage instruction in the three-phase voltage instruction, and using the m-th phase switching function corresponding to the m-th phase output voltage as the switching state control signal of the N inverter units 1 of the m-th phase;

[0064] Wherein, N is a positive integer greater than 1, and m is the phase sequence u, v, w of the three-phase electricity.

[0065] Specifically, the present invention designs a switch state control set offline according to the number of cascade units per phase, and each switch state corresponds to a voltage vector; in each control cycle, a suitable switch state is selected according to the voltage control amount calculated by the controller, and acts directly on the switch tube, eliminating the PWM modulation link. The switch tube in the present invention is an IGBT tube.

[0066] The present invention can improve the system response speed, release controller resources, and be more suitable for intelligent operation and maintenance systems.

[0067] In a preferred embodiment, in step S1, the speed feedback value and the flux feedback value of the motor 4 are obtained by a sensor or an observer, and the q-axis voltage control instruction is calculated through a closed-loop controller 6 based on the difference between the speed feedback value and the preset speed reference value, and the d-axis voltage control instruction is calculated through a closed-loop controller 6 based on the difference between the flux feedback value and the preset flux reference value, and the q-axis voltage control instruction and the d-axis voltage control instruction are transformed from the dq axis to the αβ axis to obtain the voltage control amount u(k), and the voltage control amount includes the α-axis voltage control amount u α (k) and β-axis voltage control quantity u β (k).

[0068] In a preferred embodiment, in step S1, the expression for calculating the control amount prediction value using the Lagrange extrapolation method is:

[0069] u(k+1)=3u(k)-3u(k-1)+u(k-2)

[0070] Among them, u(k+1) is the control amount prediction value, k represents the current moment, u(k) represents the voltage control amount at the current moment, u(k-1) represents the voltage control amount at the previous moment, and u(k-2) represents the voltage control amount at the previous two moments;

[0071] The control quantity prediction value is converted from the αβ two-phase coordinate system to the uvw three-phase coordinate system to obtain the three-phase voltage command u u 、u v 、u w .

[0072] Specifically, the present invention calculates the voltage control quantity u through the traditional closed-loop controller 6 α (k) and u β (k), and calculate the control quantity prediction value u by Lagrangian extrapolation method α (k+1),u β (k+1), and then through Clark inverse transformation to obtain the three-phase voltage command u u 、u v 、u w ; The Lagrange extrapolation expression is:

[0073] u(k+1)=3u(k)-3u(k-1)+u(k-2)

[0074] Among them, u(k+1) is the predicted value of the control quantity, including u α (k+1),u β (k+1), k represents the current moment, u(k) represents the voltage control amount at the current moment, u(k-1) represents the voltage control amount at the previous moment, and u(k-2) represents the voltage control amount at the previous two moments.

[0075] The pulse generation process of the present invention is as follows Figure 2 As shown, the speed feedback value ω and the flux feedback value Φ of the motor 4 are received through the closed-loop controller 6;

[0076] The motor 4 speed feedback value ω and the speed reference value ω ref The angular velocity error is obtained by subtracting the angular velocity error through a subtractor, and the angular velocity error is passed through the first proportional integral (PI) controller to output the q-axis current reference value i qref , the q-axis current reference value i qref The actual q-axis current i q Subtract the q-axis current error and input the q-axis current error into the second PI controller to output the q-axis voltage control command u q ;

[0077] Set the flux reference value Φ ref Subtract the flux feedback value Φ to get the flux error value, and then input the flux error value into the third PI controller to output the d-axis voltage control command u d .

[0078] q-axis voltage control command u q and d-axis voltage control command u d After the coordinate transformation from dq axis to αβ axis, the voltage control amount u at the current moment is obtained. α (k) and u β (k).

[0079] Furthermore, we can obtain u through Z transform. α (k) Voltage control value u at the previous moment α (k-1) and the voltage control quantity u at the first two moments α (k-2) and u β (k) Voltage control quantity u at the previous moment β (k-1) and the voltage control quantity u at the first two moments β (k-2).

[0080] Calculate the control quantity prediction value u through the Lagrange extrapolation formula α (k+1),u β(k+1), and then through Clark inverse transformation to obtain the three-phase voltage command u u 、u v 、u w .

[0081] Specifically, Clark inverse transform is mainly used to convert u in the two-phase stationary coordinate system α (k),u β (k) The quantity is converted to u in the three-phase stationary coordinate system u 、u v 、u w In the pulse generation method of the cascade multilevel inverter, the voltage control quantity in the two-phase stationary coordinate system is calculated by the traditional controller in the early stage, and the predicted value is further obtained by the Lagrange extrapolation method. However, the actual inverter output is three-phase (u, v, w phase), so Clark inverse transformation is required to convert the information in the two-phase coordinate system into the three-phase voltage command u u 、u v 、u w , in order to achieve the correspondence with the actual three-phase circuit, thereby controlling the output of the inverter.

[0082] In further details, the present invention traverses the m-th phase switching function and the corresponding m-th phase output voltage formed by combining N inverter units 1 in various switching states according to the control set, and outputs the m-th phase switching function corresponding to the m-th phase output voltage closest to the m-th phase voltage instruction in the three-phase voltage instruction as the switch state control signal of the N inverter units 1 of the m-th phase by setting the optimization module 3 of the cost function;

[0083] The switching function of the mth phase is

[0084] S m =[S 1 S 2 … S n … S N ] T

[0085] m represents the phase sequence, and the switching function of phase u is S u , the switching function of phase v is S v , the switching function of phase w is S w , the switching function of each phase controls the N inverter units cascaded in the corresponding phase 1, S n Indicates the switching state of the nth inverter unit 1 among the N inverter units 1 cascaded in the mth phase.

[0086] The mth phase output voltage u im The calculation formula is,

[0087] u im =Uo1 +U o2 +…+U on +…+U oN

[0088] Among them U on It represents the unit output voltage of the nth inverter unit 1 among the N inverter units 1 cascaded in the mth phase, and m represents the phase sequence u, v, w of the three-phase electricity.

[0089] In a preferred embodiment, in step S2, each inverter unit 1 is provided with an H-shaped inverter bridge composed of switch tubes, such as Figure 6 As shown, the switch tube includes:

[0090] A first switch tube Q1, wherein the collector of the first switch tube Q1 is connected to the positive electrode of the power supply;

[0091] A second switch tube Q2, wherein the collector of the second switch tube Q2 is connected to the emitter of the first switch tube Q1 to form a first output end of the inverter unit 1;

[0092] A third switch tube Q3, wherein the collector of the third switch tube Q3 is connected to the positive electrode of the power supply;

[0093] The fourth switch tube Q4 , wherein the collector of the fourth switch tube Q4 is connected to the emitter of the first switch tube Q1 to form the second output end of the inverter unit 1 .

[0094] Specifically, Figure 5 , Figure 6 As shown, the present invention is mainly applied to an inverter subsystem. The inverter subsystem inputs three-phase AC power and outputs DC voltage. It mainly includes a phase-shifting transformer 5 and an inverter unit 1. The phase-shifting transformer 5 is used to decompose the three-phase AC power into N groups of three-phase power. The inverter subsystem includes 3N inverter units 1 in total, wherein each phase is cascaded with N inverter units 1 for AC / DC inversion.

[0095] Each inverter unit 1 has the same structure, including a rectifier bridge composed of diodes, a first diode D1 and a second diode D2 are connected in series in the same direction, a third diode D3 and a fourth diode D4 are connected in series in the same direction, a fifth diode D5 and a sixth diode D6 are connected in series in the same direction, anodes of the first diode D1, the third diode D3 and the fifth diode D5 are respectively connected to the three-phase AC input terminal, cathodes of the second diode D2, the fourth diode D4 and the sixth diode D6 are respectively connected to the three-phase AC input terminal, a capacitor C is connected across the output end of the rectifier bridge, a first switch tube Q1, a second switch tube Q2, a third switch tube Q3 and a fourth switch tube Q4 form an H-shaped inverter bridge, and the purpose of the present invention is to generate an optimized control signal input to the inverter subsystem, thereby optimizing the output of the inverter subsystem.

[0096] In a preferred embodiment, in step S2, controlling the switch state of the centralized inverter unit 1 includes:

[0097] When the first switch tube Q1 is turned on, the second switch tube Q2 is turned off, the third switch tube Q3 is turned off, and the fourth switch tube Q4 is turned on, the inverter unit 1 outputs a first DC voltage;

[0098] When the first switch tube Q1 is turned on, the second switch tube Q2 is turned off, the third switch tube Q3 is turned on, and the fourth switch tube Q4 is turned off, the inverter unit 1 outputs a second DC voltage;

[0099] When the first switch tube Q1 is turned off, the second switch tube Q2 is turned on, the third switch tube Q3 is turned on, and the fourth switch tube Q4 is turned off, the inverter unit 1 outputs a third DC voltage;

[0100] When the first switch tube Q1 is turned off, the second switch tube Q2 is turned on, the third switch tube Q3 is turned off, and the fourth switch tube Q4 is turned on, the inverter unit 1 outputs a fourth DC voltage;

[0101] The unit output voltage includes a first DC voltage, a second DC voltage, a third DC voltage and a fourth DC voltage.

[0102] Specifically, the present invention constructs a control set. According to the topology of the inverter unit 1, each inverter unit 1 has four valid switch states, as shown in Table 1 below.

[0103]

[0104] Table 1

[0105] in,

[0106]

[0107]

[0108] S n represents the switch state of the nth inverter unit 1 among the N inverter units 1 cascaded in the mth phase, S n =(S n1 S n2 ).

[0109] It means that when the first switch tube Q1 is turned on, the second switch tube Q2 is turned off, the third switch tube Q3 is turned off, and the fourth switch tube Q4 is turned on, the inverter unit 1 outputs a first DC voltage of positive potential;

[0110] When the first switch tube Q1 is turned on, the second switch tube Q2 is turned off, the third switch tube Q3 is turned on, and the fourth switch tube Q4 is turned off, the inverter unit 1 outputs a second DC voltage of zero potential;

[0111] When the first switch tube Q1 is turned off, the second switch tube Q2 is turned on, the third switch tube Q3 is turned on, and the fourth switch tube Q4 is turned off, the inverter unit 1 outputs a third DC voltage of a negative potential;

[0112] When the first switch tube Q1 is turned off, the second switch tube Q2 is turned on, the third switch tube Q3 is turned off, and the fourth switch tube Q4 is turned on, the inverter unit 1 outputs a fourth DC voltage of zero potential.

[0113] In a preferred embodiment, in step S2, the m-th phase switching function is a set of switching states of N inverter units 1, expressed as:

[0114] S m =[S 1 S 2 … S n … S N ] T

[0115] Where S n It represents the switching state of the nth inverter unit 1 among the N inverter units 1 cascaded in the mth phase; m represents the phase sequence u, v, w of the three-phase electricity.

[0116] In a preferred embodiment,

[0117] The mth phase output voltage u im The calculation formula is,

[0118] u im =U o1 +U o2 +…+U on +…+U oN

[0119] Among them U on represents the unit output voltage of the nth inverter unit 1 among the N inverter units 1 cascaded in the mth phase, and m represents the phase sequence u, v, w of the three-phase electricity, that is, u im u iu 、u iv 、u iw .

[0120] In a preferred embodiment, in step S3, the m-th phase output voltage closest to the m-th phase voltage instruction is found by constructing a cost function, and the m-th phase switching function corresponding to the minimum value of the cost function is used as the switch state control signal of the m-th phase. The formula of the cost function is:

[0121] G m =(u m -u im ) 2

[0122] Among them, Gm represents the calculated value of the cost function in the mth phase, u m Indicates the mth phase voltage command, u im Represents the m-th phase output voltage.

[0123] Specifically, the cost function of phase u is,

[0124] G u =(u u -u iu ) 2

[0125] The cost function of the v phase is,

[0126] G v =(u v -u iv ) 2

[0127] The cost function of phase w is,

[0128] G w =(u w -u iw ) 2

[0129] The mth phase output voltage u im u iu 、u iv 、u iw , respectively, by traversing N inverter units 1 in various switching states;

[0130] The output voltage u is u iu For example, the u-phase output voltage is the sum of the unit output voltages of the N inverter units 1 cascaded in the u-phase:

[0131] u im =U o1 +U o2 +…+U on +…+U oN

[0132] u-phase output voltage u iu Determined by the u-phase switching function

[0133] S u =[S 1 S 2 … S n … S N ] T

[0134] The unit output voltage U of the first inverter unit o1 , according to the switching state S of the first inverter unit 1Determine, based on the switch combination in Table 1 above, the unit output voltage U of the first inverter unit o1 There will be four voltage quantities, in order: +U dc ,0,-U dc , 0.

[0135] Based on the different switch combinations of N inverter units 1, the final traversed u-phase output voltage u iu And the u-phase switching function S u Existence 4 N possibilities.

[0136] More specifically, the present invention will N u-phase output voltage u iu Substitute the cost function of phase u in turn,

[0137] G u =(u u -u iu ) 2

[0138] Calculate and find the minimum G u value, the minimum G u The u-phase output voltage u iu The corresponding u-phase switching function S u As a switch state control signal of the N inverter units 1 of the u phase;

[0139] The calculation process of the other two phases v and w is consistent with that of u and will not be repeated here.

[0140] In a preferred embodiment, Figure 3 As shown, step S3 includes,

[0141] Step S31, constructing a cost function, and initializing the calculated value of the cost function, and using the initialization result as an intermediate variable;

[0142] Step S32, starting from the first m-th phase output voltage, substituting the currently retrieved m-th phase output voltage into the cost function, and determining whether the calculated value of the cost function of the current m-th phase output voltage is less than the intermediate variable, if so, executing step S33; if not, directly executing step S34;

[0143] Step S33, updating the calculated value of the cost function of the current m-th phase output voltage as an intermediate variable, and updating the m-th phase switch function corresponding to the current m-th phase output voltage as a switch state control signal, and executing step S34;

[0144] Step S34, determine whether all the m-th phase output voltages have been retrieved. If not, retrieve the next m-th phase output voltage as the currently retrieved m-th phase output voltage, and return to step S32; if all are retrieved, output the final switch state control signal.

[0145] Specifically, the logic block diagram of the present invention is as follows: Figure 7 As shown,

[0146] Step 1, first, initialize the number of inverter units 1 per phase, set the intermediate variable g_min, the initial value of g_min is theoretically infinite, and in actual applications, a large value is set according to the controller. In the figure, a 16-bit controller is taken as an example, and the initial value of g_min is set to the maximum value of the controller, 65535.

[0147] Step 2: Initialize the switch function S m Length N, determine the control set elements and capacity, set the type value Cap to 4 N .

[0148] Step 3, initializing the switch state search variable ii=1, and searching the switch function of the ii-th switch state;

[0149] Step 4: Obtain the output voltage u corresponding to the iith switch state im , into the cost function G m , and obtain the result g;

[0150] Step 5, determine whether the result g is less than the intermediate variable g_min, if so, execute step 6; if not, execute step 7;

[0151] Step 6, select the flag sel=ii, g_min=g;

[0152] Step 7, determine whether ii is greater than or equal to Cap. If so, the switch state corresponding to the output sel is the switch function and is used as the switch state control signal; otherwise, perform an add 1 operation on ii, retrieve the iith switch state, and return to execute step 4.

[0153] In a specific embodiment, specifically:

[0154] Take 3 units cascaded per phase as an example, that is, N = 3;

[0155] The control quantity u is calculated by the traditional controller α (k) and u β (k), and calculate the control quantity prediction value u by Lagrangian extrapolation method α (k+1),u β (k+1), and then through Clark inverse transformation to obtain the three-phase voltage command u u、u v 、u w ;

[0156] Traverse the voltage corresponding to the switch function in the control set and calculate the output voltage u im =U o1 +U o2 +U o3 ;

[0157] Design the cost function G, and transform u im Substitute it into the cost function to find the minimum value of the cost function, and the switching function corresponding to the minimum value is output as the switching state in this cycle.

[0158] After the switch status of each phase is determined, it is loaded to the output of the drive module.

[0159] An intelligent optimization pulse generation system for cascaded multilevel inverters, such as Figure 4 , Figure 5 , Figure 6 As shown, it includes an inverter subsystem, each phase of the inverter subsystem is cascaded with N inverter units 1 that can controllably output the output voltage of the unit, and also includes:

[0160] A closed-loop controller 6 is connected to the motor 4 and is used to obtain a voltage control value of the motor 4;

[0161] The voltage command calculation module 2 is connected to the closed-loop controller 6 and is used to calculate the control quantity prediction value by Lagrange extrapolation method, and to perform coordinate transformation on the control quantity prediction value to obtain the three-phase voltage command;

[0162] The optimization module 3 is connected to the voltage command calculation module 2. The optimization module 3 is used to traverse the m-th phase switching function and the corresponding m-th phase output voltage formed by combining the N inverter units 1 in various switching states according to the control set, and output the m-th phase switching function corresponding to the m-th phase output voltage closest to the m-th phase voltage command in the three-phase voltage command as the switch state control signal of the N inverter units 1 of the m-th phase;

[0163] Wherein, N is a positive integer greater than 1, and m is the phase sequence u, v, w of the three-phase electricity.

[0164] The above description is only a preferred embodiment of the present invention, and does not limit the implementation mode and protection scope of the present invention. For those skilled in the art, it should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the description and illustrations of the present invention should be included in the protection scope of the present invention.

Claims

1. A pulse generation method for a cascaded multi-level inverter with intelligent optimization, characterized in that: include, Step S1, obtaining the voltage control amount of the motor in one cycle, calculating the control amount prediction value by using the Lagrange extrapolation method, and obtaining the three-phase voltage command by subjecting the control amount prediction value to coordinate transformation; Step S2, constructing a control set for controlling the switching state of the switch tube in the inverter unit, traversing the unit output voltages generated by each of the N inverter units cascaded in the mth phase based on the control set, and counting the mth phase switching function and the corresponding mth phase output voltage formed by the N inverter units in various switching states; Step S3, finding the m-th phase output voltage closest to the m-th phase voltage instruction in the three-phase voltage instruction, and using the m-th phase switching function corresponding to the m-th phase output voltage as the switching state control signal of the N inverter units of the m-th phase; Wherein, N is a positive integer greater than 1, and m is the phase sequence u, v, w of the three-phase electricity.

2. The pulse generation method of the cascade multi-level inverter according to claim 1 is characterized in that: In step S1, the speed feedback value and the flux feedback value of the motor are obtained through a sensor or an observer, and a q-axis voltage control instruction is calculated through a closed-loop controller based on the difference between the speed feedback value and a preset speed reference value. A d-axis voltage control instruction is calculated through the closed-loop controller based on the difference between the flux feedback value and a preset flux reference value. The q-axis voltage control instruction and the d-axis voltage control instruction are transformed from the dq axis to the αβ axis coordinates to obtain the voltage control amount u(k), and the voltage control amount includes the α-axis voltage control amount u α (k) and β-axis voltage control quantity u β (k).

3. The pulse generation method of the cascade multi-level inverter according to claim 1, characterized in that: In step S1, the expression for calculating the predicted value of the control amount using the Lagrange extrapolation method is: u(k+1)=3u(k)-3u(k-1)+u(k-2) Wherein, u(k+1) is the control amount prediction value, k represents the current moment, u(k) represents the voltage control amount at the current moment, u(k-1) represents the voltage control amount at the previous moment, and u(k-2) represents the voltage control amount at the previous two moments; The control quantity prediction value is converted from the αβ two-phase coordinate system to the uvw three-phase coordinate system to obtain the three-phase voltage command u u 、u v 、u w .

4. The pulse generation method of the cascade multi-level inverter according to claim 1, characterized in that: In step S2, each of the inverter units is provided with an H-shaped inverter bridge composed of the switch tubes, and the switch tubes include: A first switch tube, wherein the collector of the first switch tube is connected to the positive electrode of the power supply; A second switch tube, wherein the collector of the second switch tube is connected to the emitter of the first switch tube to form a first output end of the inverter unit; A third switch tube, wherein the collector of the third switch tube is connected to the positive electrode of the power supply; A fourth switch tube, wherein the collector of the fourth switch tube is connected to the emitter of the first switch tube to form a second output end of the inverter unit.

5. The pulse generation method of the cascade multi-level inverter according to claim 4 is characterized in that: In step S2, the switch state of the inverter unit in the control center includes: When the first switch tube is turned on, the second switch tube is turned off, the third switch tube is turned off, and the fourth switch tube is turned on, the inverter unit outputs a first DC voltage; When the first switch tube is turned on, the second switch tube is turned off, the third switch tube is turned on, and the fourth switch tube is turned off, the inverter unit outputs a second DC voltage; When the first switch tube is turned off, the second switch tube is turned on, the third switch tube is turned on, and the fourth switch tube is turned off, the inverter unit outputs a third DC voltage; When the first switch tube is turned off, the second switch tube is turned on, the third switch tube is turned off, and the fourth switch tube is turned on, the inverter unit outputs a fourth DC voltage; The unit output voltage includes the first DC voltage, the second DC voltage, the third DC voltage, and the fourth DC voltage.

6. The pulse generation method of the cascade multi-level inverter according to claim 1, characterized in that: In step S2, the m-th phase switching function is a set of switching states of the N inverter units, and the expression is: S m =[S1 S2 … S n … S N ] T Where S n Indicates the switching state of the nth inverter unit among the N inverter units cascaded in the mth phase.

7. The pulse generation method of the cascade multi-level inverter according to claim 1, characterized in that: The m-th phase output voltage u im The calculation formula is, in im =U o1 +U o2 +…+U on +…+U oN Among them U on Represents the unit output voltage of the nth inverter unit among the N inverter units cascaded in the mth phase.

8. The pulse generation method of the cascade multi-level inverter according to claim 1, characterized in that: In step S3, the m-th phase output voltage closest to the m-th phase voltage instruction is found by constructing a cost function, and the m-th phase switch function corresponding to the minimum value of the cost function is used as the switch state control signal of the m-th phase. The formula of the cost function is: MR m =(in m -in im ) 2 Among them, G m represents the calculated value of the cost function in the mth phase, u m represents the m-th phase voltage command, u im represents the m-th phase output voltage.

9. The pulse generation method of the cascade multi-level inverter according to claim 8, characterized in that: Step S3 comprises, Step S31, constructing the cost function, initializing the calculated value of the cost function, and using the initialization result as an intermediate variable; Step S32, starting from the first m-th phase output voltage, substituting the currently retrieved m-th phase output voltage into the cost function, and determining whether the calculated value of the cost function of the current m-th phase output voltage is less than the intermediate variable, if so, executing step S33; if not, directly executing step S34; Step S33, updating the calculated value of the cost function of the current m-th phase output voltage to the intermediate variable, and updating the m-th phase switching function corresponding to the current m-th phase output voltage to the switching state control signal, and executing step S34; Step S34, determining whether all the m-th phase output voltages have been retrieved, if not all, retrieving the next m-th phase output voltage as the currently retrieved m-th phase output voltage, and returning to step S32; If all searches are completed, the switch state control signal finally obtained is output.

10. An intelligent optimization cascade multi-level inverter pulse generation system, comprising an inverter subsystem, wherein each phase of the inverter subsystem is cascaded with N inverter units that can controllably output unit output voltages, characterized in that: Also includes, A closed-loop controller, connected to the motor, for obtaining a voltage control amount of the motor; A voltage command calculation module, connected to the closed-loop controller, is used to calculate the control quantity prediction value by Lagrange extrapolation method, and to perform coordinate transformation on the control quantity prediction value to obtain a three-phase voltage command; an optimization module connected to the voltage instruction calculation module, the optimization module being used to traverse the m-th phase switching function and the corresponding m-th phase output voltage formed by combining the N inverter units in various switching states according to the control set, and output the m-th phase switching function corresponding to the m-th phase output voltage closest to the m-th phase voltage instruction in the three-phase voltage instruction as the switch state control signal of the N inverter units of the m-th phase; Wherein, N is a positive integer greater than 1, and m is the phase sequence u, v, w of the three-phase electricity.

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