Common-mode voltage suppression method, multi-level four-leg inverter motor system, equipment and medium

Abstract

The invention relates to a common-mode voltage suppression method, a multi-level four-bridge-arm inverter motor system, equipment and a medium. The method comprises the following steps: acquiring switching states of three bridge arms in a current three-phase inverter; according to the sum of the on-off states of the three bridge arms, determining the influence condition of the current on-off states of the three bridge arms on the common-mode voltage; determining the on-off state of a fourth bridge arm according to the influence of the current on-off state on the common-mode voltage; and simultaneously outputting the on-off states of the four bridge arms to an inverter to drive a motor system to operate. Compared with the prior art, the method has the advantages of small influence on the bridge arm structure of the inverter, small calculation overhead, good common-mode voltage suppression effect and the like.

Description

Technical Field

[0001] The present invention relates to the field of inverters, and in particular to a common-mode voltage suppression method, a multi-level four-bridge-arm inverter motor system, equipment and a medium. Background Art

[0002] As an energy conversion device, the inverter usually adopts pulse width modulation technology to achieve drive control by changing pulse information during the process of converting DC power into AC power. Inverters have been widely used in AC motor traction systems as drive and variable frequency speed regulation equipment. There are common-mode stray circuits in the inverter-motor system, which generate common-mode interference. The shaft current generated by the common-mode voltage will corrode the motor bearing surface and affect the service life of the motor.

[0003] The multi-level inverter has higher output power quality, lower harmonic content, and drives the motor to run more smoothly and reliably. It is widely used in motor drive systems, but the control index requirements of multi-level inverters are also higher. Taking the three-level inverter as an example, in addition to the output voltage and current indicators, it is also necessary to control the midpoint potential of the two constant voltage capacitors on the DC side to maintain balance. At the same time, the number of voltage vectors under the four-leg inverter structure increases exponentially. Especially when facing multi-level inverters, if the model predictive control strategy is adopted, the amount of traversal optimization calculation is too large, which is easy to cause problems such as system delay.

[0004] Currently, there are three ways to suppress common-mode interference: the first is to add an external common-mode filter, in which the inductor is large and has a greater impact on the overall system; the second is to optimize the modulation strategy, which suppresses the common-mode voltage by changing the switching state and frequency of the inverter output. The current optimization strategy will increase switching losses, reduce DC voltage utilization, or reduce the modulation ratio while suppressing the common-mode voltage; the third means is to change the topology of the inverter, such as adding an auxiliary switch isolator on the DC side. This method has a high modification cost and is difficult to standardize for production and use. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a common-mode voltage suppression method, a multi-level four-bridge-arm inverter motor system, a device and a medium. The method sets the common-mode voltage suppression according to the switching quantity of the fourth bridge arm determined according to the switching state of the first three bridge arms, decouples the switching control of the three bridge arms and the common-mode voltage suppression of the fourth bridge arm, is suitable for different multi-level three-phase inverter topologies and various optimization control strategies, is easy to modify, and the calculation overhead of the optimization control process is low.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] According to a first aspect of the present invention, a common mode voltage suppression method for a multi-level four-bridge-arm inverter motor system is provided, comprising:

[0008] Get the switch status of the three bridge arms in the current three-phase inverter;

[0009] Determine the influence of the current switching states of the three bridge arms on the common mode voltage according to the sum of the switching states of the three bridge arms;

[0010] Determine the switch state of the fourth bridge arm according to the influence of the current switch state on the common mode voltage;

[0011] The switching states of the four bridge arms are output to the inverter at the same time to drive the motor system to operate.

[0012] Preferably, determining the influence of the current switching states of the three bridge arms on the common mode voltage according to the sum of the switching states of the three bridge arms specifically includes:

[0013] When the sum of the switch states of the three bridge arms is less than 0, it is determined that the influence of the current switch states of the three bridge arms on the common mode voltage is to reduce the common mode voltage;

[0014] When the sum of the switch states of the three bridge arms is equal to 0, it is determined that the influence of the current switch states of the three bridge arms on the common mode voltage is that the common mode voltage is not affected;

[0015] When the sum of the switch states of the three bridge arms is greater than 0, it is determined that the influence of the current switch states of the three bridge arms on the common mode voltage is to increase the common mode voltage.

[0016] Preferably, the determining of the switch state of the fourth bridge arm according to the influence of the current switch state on the common mode voltage is specifically:

[0017] If the switching states of the three bridge arms currently affect the common mode voltage by reducing the common mode voltage, the fourth bridge arm selects a switching state that increases the common mode voltage;

[0018] The influence of the switch states of the current three bridge arms on the common mode voltage is to increase the common mode voltage, and the fourth bridge arm selects a switch state that reduces the common mode voltage.

[0019] Preferably, when the switch states of the current three bridge arms have no effect on the common mode voltage, the switch state of the fourth bridge arm is 0.

[0020] Preferably, the switching state of the three bridge arms in the current three-phase inverter is obtained by the process including: collecting the current current value and the speed value, optimizing using the model predictive control model, and outputting the switching state of the three bridge arms corresponding to the voltage vector with the smallest error between the control quantity and the expected value at the next moment; wherein a midpoint potential fluctuation term is provided in the cost function of the model predictive control model.

[0021] Preferably, the switching state of the three bridge arms in the current three-phase inverter is obtained by the process including: collecting the current current value and speed value, optimizing using the space vector control model, and outputting the switching state of the three bridge arms corresponding to the voltage vector with the smallest error between the control quantity and the expected value at the next moment; wherein a midpoint potential fluctuation term is set in the cost function of the model predictive control model.

[0022] Preferably, the determining of the influence of the current switch states of the three bridge arms on the common mode voltage and the determining of the switch state of the fourth bridge arm both adopt a table lookup method.

[0023] According to a second aspect of the present invention, a multi-level four-arm inverter motor system is provided, the system comprising a motor, a multi-level four-arm inverter and a controller, the controller adopts the above-mentioned method to control the multi-level four-arm inverter, and drives the motor through the multi-level four-arm inverter.

[0024] According to a third aspect of the present invention, there is provided an electronic device, comprising a memory and a processor, wherein a computer program is stored in the memory, and when the processor executes the program, any one of the methods described above is implemented.

[0025] According to a fourth aspect of the present invention, there is provided a computer-readable storage medium having a computer program stored thereon, wherein when the program is executed by a processor, any one of the methods described above is implemented.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The multi-level inverter of the present invention determines the switching state of the fourth bridge arm by the switching state of the first three bridge arms, decouples the third bridge arm and the fourth bridge arm and controls them in steps, which does not affect the working state of the three bridge arms of the original inverter, does not increase the additional switching loss or reduce the DC voltage utilization rate and modulation ratio, is suitable for different three-phase inverter topologies and various optimization control strategies, and is easy to transform. By controlling the switching state of the four-bridge-arm inverter, the common-mode voltage is suppressed, the influence of common-mode interference on the motor system is reduced, the motor safety is improved, and the service life is extended.

[0028] (2) The present invention suppresses the common-mode voltage by selecting the switch state through a table lookup of the fourth bridge arm, and uses a model predictive control model to perform three-level multi-objective control, that is, the cost function does not need to include a common-mode voltage suppression term, which reduces the amount of calculation and has fewer control targets, which is conducive to the adjustment of the weight coefficient of the cost function. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a flow chart of the method of the present invention;

[0030] Figure 2 It is a schematic diagram of the correspondence between each voltage vector outputted by the three-level inverter and the switch state;

[0031] Figure 3 Grouping the effects of the switching states of the three-level inverter on the common-mode voltage;

[0032] Figure 4 A flow chart of a fourth bridge arm switch state selection strategy algorithm for suppressing common mode voltage;

[0033] Figure 5 4 is a motor system control block diagram of a multi-level four-arm inverter motor system in an embodiment. DETAILED DESCRIPTION

[0034] 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 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 should fall within the scope of protection of the present invention.

[0035] Example

[0036] like Figure 1 As shown, this embodiment provides a common mode voltage suppression method for a multi-level four-bridge-arm inverter motor system, including:

[0037] Get the switch status of the three bridge arms in the current three-phase inverter;

[0038] Determine the influence of the current switching states of the three bridge arms on the common mode voltage according to the sum of the switching states of the three bridge arms;

[0039] Determine the switch state of the fourth bridge arm according to the influence of the current switch state on the common mode voltage;

[0040] The switching states of the four bridge arms are output to the inverter at the same time to drive the motor system to operate.

[0041] Next, this embodiment is described in detail by taking a three-level inverter as an example.

[0042] In this embodiment, the influence of the current switching states of the three bridge arms on the common-mode voltage is determined based on the sum of the switching states of the three bridge arms, specifically including: when the sum of the switching states of the three bridge arms is less than 0, it is determined that the influence of the current switching states of the three bridge arms on the common-mode voltage is to reduce the common-mode voltage; when the sum of the switching states of the three bridge arms is equal to 0, it is determined that the influence of the current switching states of the three bridge arms on the common-mode voltage is not to affect the common-mode voltage; when the sum of the switching states of the three bridge arms is greater than 0, it is determined that the influence of the current switching states of the three bridge arms on the common-mode voltage is to increase the common-mode voltage.

[0043] like Figure 2 As shown in the figure, the voltage vector that the three-level inverter can output corresponds to the 27 switch states of the three-phase bridge arm. For each space voltage vector, considering the system stray parameters, mainly the stray capacitance, through circuit topology analysis, the influence of each vector on the common mode voltage is divided into three categories: increase, decrease and no influence, and the result is Figure 3 The grouping diagram of the influence of 27 switch states of the three-level inverter on the common-mode voltage is shown. The specific principle is: the value of the common-mode voltage is defined as the average value of the output phase voltage of each bridge arm at the current moment, and each voltage vector can be grouped accordingly. In order to suppress the common-mode voltage, a fourth bridge arm is added, so that the common-mode voltage value is changed to the average value of the output phase voltage of the four bridge arms. The common-mode voltage amplitude fluctuation caused by the first three bridge arms is balanced by the output phase voltage of the fourth bridge arm, thereby achieving common-mode voltage suppression.

[0044] like Figure 4 As shown, the fourth bridge arm switch state selection strategy for suppressing the common mode voltage includes:

[0045] First, similar to the traditional motor drive system, the closed-loop control is realized by collecting the motor running current information, speed information, etc., and using the model predictive control algorithm. For multi-level inverters, model predictive control can more conveniently realize multi-objective control by rewriting the cost function, such as controlling the DC side midpoint potential balance. For three-level inverters, the model predictive control is used to optimize 27 switch states, determine the switch state of the first three bridge arms of the inverter, and then judge this switch state to determine its Figure 3 For the group, we can look up the corresponding table to find out its influence on the common-mode voltage.

[0046] Next, in order to achieve common-mode voltage suppression, the corresponding fourth bridge arm switch state is selected and output to the inverter together with the first three bridge arm switch states to complete the control operation. For example: the current current value and speed value are sampled, and after calculation and processing, the model predictive control algorithm is used to find the optimal value. Under the premise of ensuring that the midpoint potential of the DC side capacitor is within the allowable balance range, the switch state corresponding to the voltage vector that minimizes the error between the control amount and the expected value at the next moment is obtained, such as (1,0,0). According to Figure 3It can be seen that the (1,0,0) switching state will increase the common-mode voltage, so the switching state of the fourth bridge arm should be -1, that is, the optimal switching state at the next moment is (1,0,0,-1), which is output to the inverter to drive the motor system. Among the 27 switching states of the three-level inverter, the switching state corresponding to the middle vector (divided according to the vector modulus length) and the (0,0,0) switching state have no effect on the common-mode voltage. When the current three bridge arms are optimized through model predictive control, the switching state of the fourth bridge arm is 0.

[0047] It should be noted that for the control strategy of the first three bridge arms, traditional proportional integral control, sliding mode control and other control strategies are also applicable, which does not affect the subsequent steps of suppressing the common mode voltage of the present invention. Especially for two-level inverters, the traditional proportional integral control strategy is more widely used in the industry. The present invention can add a fourth bridge arm on this basis, collect the switch state to be output to the first three bridge arms at the next moment, and then look up the table such as Figure 3 , obtain the switch state information of the fourth bridge arm, and uniformly output it to the inverter to achieve the common-mode voltage suppression effect. Aiming at the multi-control target requirements of the multi-level inverter, the present invention integrates the step of obtaining the switch state by looking up the table of the fourth bridge arm into the model predictive control algorithm, simplifies the multi-level inverter control algorithm, and achieves the common-mode voltage suppression effect without affecting the three-phase output performance and the optimization calculation amount of the model predictive control.

[0048] Since the switch state of the fourth bridge arm is selected and calculated separately based on the switch states of the first three bridge arms, rather than incorporating the switch state of the fourth bridge arm into the data set of the model predictive control algorithm, for a three-level inverter, there are 27 switch states for the three bridge arms, while for a three-level four-bridge inverter, the number of switch states increases to 81, which greatly increases the complexity of the optimization algorithm and the calculation cycle, and is more likely to cause delay problems.

[0049] like Figure 5 As shown, this embodiment also provides a multi-level four-bridge-arm inverter motor system, which includes a motor, a multi-level four-bridge-arm inverter and a controller, wherein the controller controls the multi-level four-bridge-arm inverter by the above method, and drives the motor through the multi-level four-bridge-arm inverter. The present invention obtains the switching state of the fourth bridge arm by a separate table lookup, and then uniformly outputs the control inverter, simplifies the control algorithm, and realizes common-mode voltage suppression.

[0050] The electronic device of the present invention includes a central processing unit (CPU), which can perform various appropriate actions and processes according to computer program instructions stored in a read-only memory (ROM) or loaded from a storage unit into a random access memory (RAM). In the RAM, various programs and data required for device operation can also be stored. The CPU, ROM and RAM are connected to each other via a bus. An input / output (I / O) interface is also connected to the bus.

[0051] Multiple components in the device are connected to the I / O interface, including: input units, such as keyboards, mice, etc.; output units, such as various types of displays, speakers, etc.; storage units, such as disks, optical disks, etc.; and communication units, such as network cards, modems, wireless communication transceivers, etc. The communication unit allows the device to exchange information / data with other devices through computer networks such as the Internet and / or various telecommunication networks.

[0052] The processing unit performs the various methods and processes described above. For example, in some embodiments, the method can be implemented as a computer software program, which is tangibly contained in a machine-readable medium, such as a storage unit. In some embodiments, part or all of the computer program can be loaded and / or installed on the device via a ROM and / or a communication unit. When the computer program is loaded into RAM and executed by the CPU, one or more steps of the method described above can be performed. Alternatively, in other embodiments, the CPU can be configured to perform the method in any other appropriate manner (e.g., by means of firmware).

[0053] The functions described above herein may be performed at least in part by one or more hardware logic components. For example, without limitation, exemplary types of hardware logic components that may be used include: field programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), application specific standard products (ASSPs), systems on chip systems (SOCs), load programmable logic devices (CPLDs), and the like.

[0054] The program code for implementing the method of the present invention can be written in any combination of one or more programming languages. These program codes can be provided to a processor or controller of a general-purpose computer, a special-purpose computer or other programmable data processing device, so that the program code, when executed by the processor or controller, enables the functions / operations specified in the flow chart and / or block diagram to be implemented. The program code can be executed entirely on the machine, partially on the machine, partially on the machine as a stand-alone software package and partially on a remote machine, or entirely on a remote machine or server.

[0055] In the context of the present invention, a machine-readable medium may be a tangible medium that may contain or store a program for use by or in conjunction with an instruction execution system, device, or equipment. A machine-readable medium may be a machine-readable signal medium or a machine-readable storage medium. A machine-readable medium may include, but is not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, devices, or equipment, or any suitable combination of the foregoing. A more specific example of a machine-readable storage medium may include an electrical connection based on one or more lines, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0056] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A common mode voltage suppression method for a multi-level four-bridge-arm inverter motor system, characterized in that: include: Get the switch status of the three bridge arms in the current three-phase inverter; Determine the influence of the current switching states of the three bridge arms on the common mode voltage according to the sum of the switching states of the three bridge arms; Determine the switch state of the fourth bridge arm according to the influence of the current switch state on the common mode voltage; The switching states of the four bridge arms are output to the inverter at the same time to drive the motor system to operate.

2. The method according to claim 1, characterized in that The determining, according to the sum of the switch states of the three bridge arms, the influence of the current switch states of the three bridge arms on the common mode voltage specifically includes: When the sum of the switch states of the three bridge arms is less than 0, it is determined that the influence of the current switch states of the three bridge arms on the common mode voltage is to reduce the common mode voltage; When the sum of the switch states of the three bridge arms is equal to 0, it is determined that the influence of the current switch states of the three bridge arms on the common mode voltage is that the common mode voltage is not affected; When the sum of the switching states of the three bridge arms is greater than 0, it is determined that the influence of the current switching states of the three bridge arms on the common mode voltage is to increase the common mode voltage.

3. The method according to claim 2, characterized in that The switching state of the fourth bridge arm is determined according to the influence of the current switching state on the common mode voltage, specifically: If the switching states of the three bridge arms currently affect the common mode voltage by reducing the common mode voltage, the fourth bridge arm selects a switching state that increases the common mode voltage; The influence of the switch states of the current three bridge arms on the common mode voltage is to increase the common mode voltage, and the fourth bridge arm selects a switch state that reduces the common mode voltage.

4. The method according to claim 2, characterized in that: If the switch states of the current three bridge arms have no effect on the common-mode voltage, the switch state of the fourth bridge arm is 0.

5. The method according to claim 1, characterized in that The switching states of the three bridge arms in the current three-phase inverter are obtained through the process of: collecting the current current value and the speed value, optimizing using the model predictive control model, and outputting the switching states of the three bridge arms corresponding to the voltage vector with the smallest error between the control amount and the expected value at the next moment; wherein a midpoint potential fluctuation term is provided in the cost function of the model predictive control model.

6. The method according to claim 1, characterized in that The switching states of the three bridge arms in the current three-phase inverter are obtained through the process of: collecting the current current value and the speed value, optimizing using a space vector control model, and outputting the switching states of the three bridge arms corresponding to the voltage vector with the smallest error between the control amount and the expected value at the next moment; wherein a midpoint potential fluctuation term is provided in the cost function of the model predictive control model.

7. The method according to claim 1, characterized in that The determination of the influence of the current switch states of the three bridge arms on the common mode voltage and the determination of the switch state of the fourth bridge arm both adopt a table lookup method.

8. A multi-level four-bridge-arm inverter motor system, characterized in that: The system comprises a motor, a multi-level four-bridge-arm inverter and a controller. The controller controls the multi-level four-bridge-arm inverter by using the method described in any one of claims 1 to 7, and drives the motor through the multi-level four-bridge-arm inverter.

9. An electronic device comprising a memory and a processor, wherein a computer program is stored in the memory, wherein: When the processor executes the program, the method according to any one of claims 1 to 7 is implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the method according to any one of claims 1 to 7 is implemented.

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