Method and system for eliminating common-mode voltage of motor driver based on four-quadrant frequency converter

Abstract

This invention discloses a common-mode voltage elimination method and system for motor drivers based on a four-quadrant frequency converter, belonging to the field of motor drive technology. The method includes: obtaining the three-phase PWM waves of the rectifier and inverter in the four-quadrant frequency converter, thereby obtaining the duration of the three-phase voltage of the rectifier and the three-phase voltage of the inverter; comparing the sum of the durations of the three-phase voltages of the rectifier and the inverter, shrinking each phase voltage of the larger voltage by the same amount on both sides, and stretching each phase voltage of the smaller voltage by the same amount on both sides, so that after the stretching, the sum of the durations of the three-phase voltages of the two are equal; after the stretching, aligning the three rising edges of the three-phase voltage of the rectifier with the three rising edges of the three-phase voltage of the inverter, and aligning the three falling edges of the three-phase voltage of the rectifier with the three falling edges of the three-phase voltage of the inverter. This invention completely eliminates common-mode voltage without changing the control performance of the motor driver.

Description

Technical Field

[0001] This invention belongs to the field of motor drive technology, and more specifically, relates to a method and system for eliminating common-mode voltage in motor drivers based on four-quadrant frequency converters. Background Technology

[0002] With socio-economic development and increasing environmental pressure, people are paying more and more attention to environmental protection and energy issues. Traditional rectifiers can no longer meet the needs of modern power grids. To ensure the safe and economical operation of the power grid and electrical equipment, the most direct approach is to replace traditional converters with a converter that operates with a sinusoidal grid-side current and a unity power factor. After years of research and practice, pulse width modulation (PWM) technology has been introduced into rectifier control. It not only solves the pollution to the power grid caused by traditional uncontrolled rectifiers, but also achieves sinusoidal current control with a unity power factor and bidirectional energy transmission. However, the switching frequency of the power switching devices in a three-phase PWM rectifier is generally 2–15 kHz, which generates high-order harmonics that interfere with the power grid. These harmonics, once they enter the power grid, can affect loads sensitive to electromagnetic interference and also cause losses. Usually, inductors are used for filtering to reduce high-order harmonics. By increasing the value of the grid-side filter inductor, harmonics can be reduced. However, when the rectifier power is relatively large, the losses of the AC-side reactor increase. In addition, the reactor is large in size and weight, and its cost is also relatively high. Applying an LCL filter on the AC side can reduce the high-order harmonic content in the current, and under the same harmonic requirements, it can reduce the inductance value compared to a purely inductive filter, thereby improving the dynamic response of the system.

[0003] In the field of AC drives, three-phase two-level power supply motor control systems are widely used. Four-quadrant frequency converters used to drive motors primarily employ Space Vector Pulse Width Modulation (SVPWM). However, conventional SVPWM suffers from problems such as high common-mode voltage and high frequency. The common-mode voltage amplitude is equal to Udc / 2, and the frequency is equal to the inverter switching frequency, ranging from several kHz to tens of kHz. Large amplitude and high frequency common-mode voltage can induce motor shaft current, causing damage to motor bearings and winding insulation, and generating electromagnetic interference, affecting the normal operation of nearby electronic equipment.

[0004] For safety reasons, motor drive systems often require grounding, inevitably resulting in common-mode loops. Although the impedance of these common-mode loops is primarily capacitive, they still generate significant common-mode currents under high-frequency common-mode voltage excitation. In the field of variable frequency speed control, shaft currents caused by common-mode voltage in PWM inverter systems severely impact motor lifespan. Related research indicates that bearing failure accounts for approximately 40% of all motor failures, with 25% of bearing failures caused by shaft currents induced by inverter power supply. With the further increase in switching frequency and speed of semiconductor devices, and the increasing prevalence of high-power, high-capacity equipment, common-mode problems are becoming increasingly severe. The existence of common-mode issues reduces the overall system performance, lowers reliability, and increases the failure rate, hindering the long-term stable operation of inverter systems. To meet the common-mode suppression requirements of PWM inverter systems, external common-mode filters are typically used. However, the magnetic components of these filters—common-mode inductors—generally occupy about 25% of the system's volume. Therefore, the addition of filters significantly affects the size and weight of PWM inverter systems, limiting the improvement of power density.

[0005] Therefore, in high-power, high-frequency inverter systems, common-mode voltage must be suppressed to ensure system safety. Simultaneously, to reduce costs, software-based common-mode voltage suppression methods are needed. However, existing software-based common-mode voltage suppression methods can only weaken the common-mode voltage to a certain extent, but cannot completely eliminate it. Furthermore, while weakening the common-mode voltage, they may affect the system's control performance and may also cause excessive harmonic currents. Summary of the Invention

[0006] To address the shortcomings and improvement needs of existing technologies, this invention provides a method and system for eliminating common-mode voltage in motor drives based on four-quadrant frequency converters. The purpose is to completely eliminate common-mode voltage without changing the control performance of the motor drive.

[0007] To achieve the above objectives, according to one aspect of the present invention, a method for eliminating common-mode voltage in a motor driver based on a four-quadrant frequency converter is provided, comprising:

[0008] (S1) Obtain the three-phase PWM waves of the rectifier and inverter in the four-quadrant frequency converter, and thus obtain the action time t of the three-phase voltage vector of the rectifier. A t B and t C And the duration t of the three-phase voltage vector of the inverter. U t V and t W ;

[0009] (S2) Compare the sum of the action times of the three-phase voltage vectors of the rectifier and the inverter. Contract each phase voltage vector of the larger one to both sides by the same amount, and extend each phase voltage vector of the smaller one to both sides by the same amount, so that after the contraction and extension, the sum of the action times of the three-phase voltage vectors of the rectifier and the inverter are equal.

[0010] (S3) Align the three-phase PWM wave of the rectifier with the three-phase PWM wave of the inverter after the expansion and contraction, so that the three rising edges of the three-phase PWM wave of the rectifier are aligned with the three rising edges of the three-phase PWM wave of the inverter, and the three falling edges of the three-phase PWM wave of the rectifier are aligned with the three falling edges of the three-phase PWM wave of the inverter, thereby eliminating the common-mode voltage of the motor driver.

[0011] Furthermore, in step (S3), when aligning the three-phase PWM wave of the rectifier with the three-phase PWM wave of the inverter after the expansion and contraction, the alignment method that minimizes the area of ​​the image enclosed by the three-phase voltage vector and the reference voltage vector after alignment is selected.

[0012] Furthermore, in step (S2), the amount Δt that unilaterally contracts or expands the voltage vector of each phase of the rectifier is... AFE And the amount Δt that contracts or expands one side of the voltage vector of each phase of the inverter. INV The calculation method is as follows:

[0013] Δt=t A +t B +t C -(t U +t V +t W )

[0014]

[0015]

[0016]

[0017]

[0018] in, This indicates the duration of the zero vector of the rectifier. This indicates the duration of the zero vector of the inverter.

[0019] According to another aspect of the present invention, a motor drive controller based on a four-quadrant frequency converter is provided, comprising:

[0020] The PWM module is used to obtain the three-phase PWM waves of the rectifier and inverter in the four-quadrant frequency converter, thereby obtaining the duration t of the three-phase voltage of the rectifier.A t B and t C And the duration t of the three-phase voltage of the inverter U t V and t W ;

[0021] The telescopic module is used to compare the sum of the durations of the three-phase voltages of the rectifier and the inverter. It contracts each phase voltage of the larger voltage by the same amount on both sides and stretches each phase voltage of the smaller voltage by the same amount on both sides, so that after the telescopic module is stretched, the sum of the durations of the three-phase voltages of the rectifier and the inverter are equal.

[0022] And an alignment module, used to align the three-phase PWM wave of the rectifier and the three-phase PWM wave of the inverter after the expansion and contraction, so that the three rising edges of the three-phase voltage of the rectifier are aligned with the three rising edges of the three-phase voltage of the inverter, and the three falling edges of the three-phase voltage of the rectifier are aligned with the three falling edges of the three-phase voltage of the inverter, thereby eliminating the common-mode voltage of the motor driver.

[0023] Furthermore, when aligning the three-phase PWM wave of the rectifier with the three-phase PWM wave of the inverter after the alignment module is stretched, it selects the alignment method that minimizes the area of ​​the image enclosed by the voltage vector and the reference voltage vector after alignment.

[0024] Furthermore, the amount Δt by which the telescoping module contracts or expands one side of the voltage of each phase of the rectifier is determined. AFE And the amount Δt that contracts or expands one side of the voltage of each phase of the inverter. INV The calculation method is as follows:

[0025] Δt=t A +t B +t C -(t U +t V +t W )

[0026]

[0027]

[0028]

[0029]

[0030] in, This indicates the duration of the zero vector of the rectifier. This indicates the duration of the zero vector of the inverter.

[0031] According to another aspect of the present invention, a motor drive system based on a four-quadrant frequency converter is provided, comprising:

[0032] Electric motor;

[0033] A four-quadrant frequency converter has its inverter connected to the three-phase windings of the motor.

[0034] And the motor drive controller based on a four-quadrant frequency converter provided by the present invention.

[0035] Furthermore, the motor drive system based on a four-quadrant frequency converter provided by the present invention also includes:

[0036] The LCL filter is connected to the power grid and the rectifier of the four-quadrant frequency converter, respectively.

[0037] Furthermore, the parameters of the LCL filter are designed as follows:

[0038] L all =L1+L2

[0039]

[0040]

[0041]

[0042]

[0043] Where L1 and L2 represent the bridge arm inductance and grid-side inductance of the LCL filter, respectively, ΔI ripple-max For the maximum ripple current, f sw U is the switching frequency. dc E is the DC-side output voltage. p-max I is the peak value of the grid-side phase voltage, ω is the grid angular frequency, and I is the peak value of the phase voltage. p-max C represents the peak value of the grid-side phase current. f For the filter capacitor, P N U is the rated active power of the rectifier. g For three-phase phase voltage, R d f is the resistance connected in series in the capacitor branch. res The resonant frequency, This is the inductance ratio.

[0044] In summary, the above-described technical solutions conceived in this invention can achieve the following beneficial effects:

[0045] (1) This invention suppresses the common-mode voltage of the system without adding additional common-mode voltage filters or other hardware, thus reducing hardware costs. Furthermore, based on a three-phase PWM wave, it performs scaling and alignment operations on the three-phase voltages of the rectifier and inverter, ensuring that the rectifier voltage and inverter voltage are always equal. This completely eliminates the common-mode voltage of the motor driver based on the four-quadrant inverter. Simultaneously, since this process does not change the duration of the active voltage vector, it does not affect control performance. In summary, this invention can eliminate common-mode voltage without affecting control performance, and it can also ensure the system's performance, reliability, and stability even when the motor driver switching frequency is high.

[0046] (2) In a preferred embodiment of the present invention, the alignment method that minimizes the image area enclosed by the voltage vector and the reference voltage vector after alignment is selected from a number of optional alignment methods, thereby effectively reducing the current harmonics on the motor side and the grid side. Attached Figure Description

[0047] Figure 1 A schematic diagram of the topology of a four-quadrant frequency converter with an LCL filter provided by the present invention;

[0048] Figure 2 A schematic diagram of common-mode voltage elimination provided by the present invention;

[0049] Figure 3 Examples of three-phase PWM wave alignment for rectifiers and inverters provided by the present invention; wherein (a) to (f) are 6 selectable alignment methods;

[0050] Figure 4 The present invention provides a schematic diagram of three-phase PWM wave expansion and contraction for a rectifier and an inverter; wherein, (a) is a schematic diagram of three-phase voltage contraction in the rectifier, and (b) is a schematic diagram of three-phase voltage expansion in the inverter;

[0051] Figure 5 This is a flowchart of a common-mode voltage elimination method for motor drivers based on a four-quadrant frequency converter, provided in an embodiment of the present invention.

[0052] Figure 6 This is a schematic diagram illustrating the alignment method selection provided in an embodiment of the present invention;

[0053] Figure 7 This is a schematic diagram of phase shifting of a three-phase PWM wave provided in an embodiment of the present invention. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0055] In this invention, the terms "first," "second," etc. (if present) in the invention and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0056] To address the technical problem that existing software methods can only suppress but not completely eliminate the common-mode voltage of four-quadrant frequency converters, and may affect control performance while suppressing common-mode voltage, this invention provides a common-mode voltage elimination method and system for motor drivers based on four-quadrant frequency converters. The overall idea is to fully analyze the principle of common-mode voltage generation in four-quadrant frequency converters, namely, the generation of common-mode voltage due to the unequal voltages of the rectifier and inverter. Therefore, based on the three-phase PWM waves of the rectifier and inverter, the three-phase voltages are adjusted by scaling, aligning, and other operations to make the voltages of the rectifier and inverter equal, thereby achieving the goal of completely eliminating common-mode voltage. At the same time, when adjusting the three-phase voltages, only the distribution of the zero voltage vector is changed without changing the duration of the active voltage vector, so as not to affect control performance while eliminating common-mode voltage.

[0057] Before explaining the technical solution of the present invention in detail, the principle of eliminating common-mode voltage of the present invention will be introduced as follows.

[0058] Figure 1 The diagram shows a motor drive system based on a four-quadrant frequency converter. Figure 1 As shown, a four-quadrant frequency converter has a rectifier and an inverter. When used as a motor driver, the midpoints of the three-phase bridge arms of the inverter are connected to the three-phase windings of the motor, while the rectifier is connected to the grid side. Typically, the three phases of the rectifier are represented by A, B, and C, and the three phases of the inverter are represented by U, V, and W. To suppress harmonic content and reduce pollution to the power grid, a filter is often connected between the rectifier and the grid. Compared to traditional single-L filters, LCL filters achieve the same filtering effect with smaller inductance, smaller size, and lower cost, thus gaining wider application.

[0059] The common-mode voltage V in a four-quadrant frequency converter CM The rectifier voltage V CM整流 With inverter voltage V CM逆变 The difference, i.e., V CM =V CM整流 -V CM逆变 .

[0060] This invention discovers that when the three-phase PWM waves of the rectifier and inverter are aligned—that is, when the three rising edges of the rectifier's three-phase voltage are aligned with the three rising edges of the inverter's three-phase voltage, and the three falling edges of the rectifier's three-phase voltage are aligned with the three falling edges of the inverter's three-phase voltage—the voltage of the rectifier and the voltage of the inverter are equal within the same switching cycle, and the common-mode voltage is zero. Figure 2 and Figure 3 For example, Figure 2 The diagram shows one case of alignment between the three-phase PWM waves of the rectifier and inverter, where V A V B V C These represent the three-phase voltages A, B, and C of the rectifier, respectively, V V V V V W These represent the U, V, and W phase voltages of the inverter, respectively. According to... Figure 2 The relationship between the comparison value and the PWM waveform is adopted. Figure 2 The comparison values ​​of the medium carrier, rectifier and inverter are shown in Table 1.

[0061] Table 1 Three-phase voltages of rectifier and inverter

[0062]

[0063] In Table 1, T PWM This represents one switching cycle; t1 to t6 are the times when the rising or falling edge of each phase voltage in the three-phase voltage of the rectifier and inverter occurs.

[0064] Figure 2 The results also show the rectifier voltage, inverter voltage, and common-mode voltage under this alignment, demonstrating that the common-mode voltage is zero when the three-phase PWM waves of the rectifier and inverter are aligned. This invention is based on this discovery.

[0065] It's easy to understand that there are multiple ways to align the three-phase PWM waves of the rectifier and inverter. Figure 3 The six alignment methods shown in (a) to (f) are examples of some alignment methods. More alignment examples are not shown in detail here.

[0066] Further analysis of this invention reveals that, in order to achieve alignment of the three-phase PWM waves, the sum of the durations of the three-phase voltages of the rectifier must first be equal to the sum of the durations of the three-phase voltages of the inverter, i.e., t A +t B +t C =t U +t V +t W, where t A t B and t C The durations of the three-phase voltages A, B, and C of the rectifier are represented by t. U t V and t W These represent the durations of the U, V, and W phase voltages of the inverter. To achieve the above objectives, the three-phase voltages of the rectifier and inverter need to be scaled. However, to avoid affecting control performance, the duration of the active voltage vector cannot be changed when scaling the three-phase voltages; only the duration of the zero voltage vector can be modified. Therefore, the scaling amount for each phase voltage of the rectifier must be the same, and the scaling amount for each phase voltage of the inverter must be equal. It is easy to understand that when scaling the phase voltages, those with a larger sum of the durations of the three-phase voltages need to be "shrunk," while those with a smaller sum of the durations of the three-phase voltage vectors need to be "stretched." For example... Figure 4 As shown, due to t A +t B +t C The voltage is relatively large, therefore, the three-phase voltage of the rectifier needs to be shortened, that is, the duration of the voltage of each phase needs to be shortened, such as... Figure 4 As shown in (a), the three-phase voltage of the inverter needs to be extended, that is, the duration of each phase voltage is prolonged, such as... Figure 4 As shown in (b) of the diagram.

[0067] The following is an example.

[0068] Example 1:

[0069] A common-mode voltage elimination method for motor drivers based on a four-quadrant frequency converter, such as Figure 5 As shown, it includes:

[0070] (S1) Obtain the three-phase PWM waves of the rectifier and inverter in the four-quadrant frequency converter, and thus obtain the action time t of the three-phase voltage of the rectifier. A t B and t C And the duration t of the three-phase voltage of the inverter U t V and t W ;

[0071] (S2) Compare the sum of the three-phase voltages of the rectifier and the inverter. Shrink each phase voltage of the larger one to both sides by the same amount, and stretch each phase voltage of the smaller one to both sides by the same amount, so that after stretching and stretching, the sum of the three-phase voltages of the rectifier and the inverter are equal.

[0072] Considering that the maximum amount of voltage expansion or contraction per phase of a rectifier or inverter is 0.25t0, the maximum amount of expansion or contraction per two phases of a three-phase inverter is 1.5t0; where t0 represents the duration of the zero-voltage vector.

[0073] Considering that if the expansion or contraction exceeds the maximum expansion or contraction of the rectifier or inverter, the following two situations will occur: (1) the high-level duration of a certain phase exceeds the switching cycle, in which case the control performance of the system will be affected; (2) Figure 4 The V7 vector shown will no longer be effective, and the switching losses of the switching transistors will increase in this case. Therefore, in this embodiment, the corresponding scaling amount is allocated according to the proportion of the maximum scaling amount of the rectifier and inverter. Thus, the amount Δt that unilaterally contracts or expands the voltage of each phase of the rectifier is determined. AFE And the amount Δt that contracts or expands one side of the voltage of each phase of the inverter. INV The calculation method is as follows:

[0074] Δt=t A +t B +t C -(t U +t V +t W )

[0075]

[0076]

[0077]

[0078]

[0079] in, This indicates the duration of the zero vector of the rectifier. This indicates the duration of the zero vector of the inverter;

[0080] (S3) Align the three-phase PWM wave of the rectifier with the three-phase PWM wave of the inverter after the expansion and contraction, so that the three rising edges of the three-phase voltage of the rectifier are aligned with the three rising edges of the three-phase voltage of the inverter, and the three falling edges of the three-phase voltage of the rectifier are aligned with the three falling edges of the three-phase voltage of the inverter, thereby eliminating the common-mode voltage of the motor driver.

[0081] In a rectifier or inverter, different states of the three-phase voltage correspond to different voltage vectors, and the slopes of different voltage vectors are shown in Table 2.

[0082] Table 2 Slopes corresponding to different voltage vectors

[0083]

[0084] Among them, i a i b i c These represent the three-phase currents, d and d respectively. a d b d c V represents the three-phase duty cycle, respectively. dc The value represents the DC bus voltage, and L represents the load inductance of the rectifier or inverter. Switch state "0" indicates that the voltage of the corresponding phase is low, and switch state "1" indicates that the voltage of the corresponding phase is high.

[0085] Considering that the actual voltage vector may deviate from the reference voltage vector after scaling and aligning the three-phase voltages, in order to reduce harmonic content, as a preferred implementation, this embodiment selects the alignment method that minimizes the area enclosed by the voltage vector and the reference voltage vector when aligning the scaled three-phase PWM wave of the rectifier with the three-phase PWM wave of the inverter. For example... Figure 6 As shown.

[0086] Phase shifting of the PWM wave can be achieved by modifying the comparison value and the duration of action within each cycle, thereby achieving alignment. Figure 7 As shown.

[0087] This embodiment uses a three-phase PWM wave to perform scaling and alignment operations on the three-phase voltages of the rectifier and inverter, making the voltage of the rectifier and the voltage of the inverter equal at all times. This achieves the effect of completely eliminating the common-mode voltage of the motor driver based on the four-quadrant frequency converter using a software-based method. At the same time, since this process does not change the duration of the active voltage vector, it does not affect the control performance.

[0088] Example 2:

[0089] A motor drive controller based on a four-quadrant frequency converter includes:

[0090] The PWM module is used to obtain the three-phase PWM waves of the rectifier and inverter in the four-quadrant frequency converter, thereby obtaining the duration t of the three-phase voltage of the rectifier. A t B and t C And the duration t of the three-phase voltage of the inverter U t V and t W ;

[0091] The telescopic module is used to compare the sum of the durations of the three-phase voltages of the rectifier and the inverter. It contracts each phase voltage of the larger voltage by the same amount on both sides and stretches each phase voltage of the smaller voltage by the same amount on both sides, so that after the telescopic module is stretched, the sum of the durations of the three-phase voltages of the rectifier and the inverter are equal.

[0092] And an alignment module, used to align the three-phase PWM wave of the rectifier and the three-phase PWM wave of the inverter after the expansion and contraction, so that the three rising edges of the three-phase voltage of the rectifier are aligned with the three rising edges of the three-phase voltage of the inverter, and the three falling edges of the three-phase voltage of the rectifier are aligned with the three falling edges of the three-phase voltage of the inverter, thereby eliminating the common-mode voltage of the motor driver.

[0093] Among them, when the alignment module aligns the three-phase PWM wave of the rectifier after expansion and contraction with the three-phase PWM wave of the inverter, it selects the alignment method that minimizes the area of ​​the image enclosed by the voltage vector and the reference voltage vector after alignment.

[0094] The amount Δt by which the telescoping module contracts or expands one side of the voltage of each phase of the rectifier is determined. AFE And the amount Δt that contracts or expands one side of the voltage of each phase of the inverter. INV The calculation method is as follows:

[0095] Δt=t A +t B +t C -(t U +t V +t W )

[0096]

[0097]

[0098]

[0099]

[0100] in, This indicates the duration of the zero vector of the rectifier. This indicates the duration of the zero vector of the inverter.

[0101] In this embodiment, the specific implementation methods of each module can also refer to the description in Embodiment 1 above.

[0102] Example 3:

[0103] A motor drive system based on a four-quadrant frequency converter. This embodiment is related to... Figure 1 The system shown is similar, including:

[0104] Electric motor;

[0105] A four-quadrant frequency converter has its inverter connected to the three-phase windings of the motor.

[0106] The LCL filter is connected to the power grid and the rectifier of the four-quadrant frequency converter, respectively.

[0107] This embodiment and Figure 1 The difference in the system shown is that this embodiment also includes the motor drive controller based on the four-quadrant frequency converter provided in embodiment 2 above.

[0108] In this embodiment, the parameters of the LCL filter are designed as follows:

[0109] L all =L1+L2

[0110]

[0111]

[0112]

[0113]

[0114] Where L1 and L2 represent the bridge arm inductance and grid-side inductance of the LCL filter, respectively, ΔI ripple-max For the maximum ripple current, f sw U is the switching frequency. dc E is the DC-side output voltage. p-max I is the peak value of the grid-side phase voltage, ω is the grid angular frequency, and I is the peak value of the phase voltage. p-max C represents the peak value of the grid-side phase current. f For the filter capacitor, P N U is the rated active power of the rectifier. g This refers to the three-phase phase voltage; R d The resistor connected in series in the capacitor branch is used to suppress resonance peaks and ensure the stability of the system operation; f res The resonant frequency, This is the inductance ratio.

[0115] The LCL filter designed based on the above parameters can effectively reduce harmonic content and avoid polluting the power grid.

[0116] In this embodiment, the input phase voltage is 380V, the DC output voltage is 620V, the grid frequency is 50Hz, the switching frequency is 6kHz, and E p-max The voltage is 540V. Considering both the system's current tracking capability and filtering effect, ΔI... ripple-maxTake 20% of the peak phase current. When the rectifier's rated power is 75kW, assume I is the rectifier's rated power at 75kW. p-max If we take 92A, then ΔI ripple-max It is 18.4A.

[0117] Based on the above parameters, in the LCL filter design, when the rectifier's rated power is 75kW, 0.811≤L all ≤6.085mH, C f ≤27.55uF. The smaller the total inductance of the LCL filter, the stronger its current tracking and system response capabilities, and the smaller its size; conversely, the larger the total inductance, the better the filtering effect. Considering the system's dynamic response speed, system size, and filtering effect, L is chosen as... all It is 0.9mH, C f Take 27uF. R d Take 1.069Ω. With k = 0.2, L2 = 0.15mH and L1 = 0.75mH.

[0118] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for common-mode voltage elimination in a motor drive based on a four-quadrant converter, characterized by, include: (S1) obtaining three-phase PWM waves of the rectifier and the inverter in the four-quadrant frequency converter, thereby obtaining the action time of three-phase voltages of the rectifier , and , and the action time of three-phase voltages of the inverter , and ; (S2) Compare the sum of the durations of the three-phase voltages of the rectifier and the inverter, and contract each phase voltage of the larger one to both sides by the same amount, and extend each phase voltage of the smaller one to both sides by the same amount, so that after contraction and extension, the sum of the durations of the three-phase voltages of the rectifier and the inverter are equal. (S3) Align the three-phase PWM wave of the rectifier with the three-phase PWM wave of the inverter after the expansion and contraction, so that the three rising edges of the three-phase voltage of the rectifier are aligned with the three rising edges of the three-phase voltage of the inverter, and the three falling edges of the three-phase voltage of the rectifier are aligned with the three falling edges of the three-phase voltage of the inverter, thereby eliminating the common-mode voltage of the motor driver. In step (S3), when aligning the three-phase PWM wave of the rectifier after expansion and contraction with the three-phase PWM wave of the inverter, the alignment method that minimizes the area of ​​the image enclosed by the voltage vector and the reference voltage vector after alignment is selected. the amount of contraction or expansion of each phase voltage of the rectifier unilaterally and the amount of contraction or expansion of each phase voltage of the inverter unilaterally is calculated as follows: in, This indicates the duration of the zero vector of the rectifier. This indicates the duration of the zero vector of the inverter.

2. A motor drive controller based on a four-quadrant frequency converter, characterized in that, include: The PWM module is used to obtain the three-phase PWM waves of the rectifier and inverter in the four-quadrant frequency converter, thereby obtaining the duration of the three-phase voltage of the rectifier. , and and the duration of the three-phase voltage of the inverter. , and ; The telescopic module is used to compare the sum of the durations of the three-phase voltages of the rectifier and the inverter, shrink each phase voltage of the larger one to both sides by the same amount, and stretch each phase voltage of the smaller one to both sides by the same amount, so that after the telescopic module is stretched, the sum of the durations of the three-phase voltages of the rectifier and the inverter are equal. And an alignment module, used to align the three-phase PWM wave of the extended rectifier with the three-phase PWM wave of the inverter, so that the three rising edges of the three-phase voltage of the rectifier are aligned with the three rising edges of the three-phase voltage of the inverter, and the three falling edges of the three-phase voltage of the rectifier are aligned with the three falling edges of the three-phase voltage of the inverter, thereby eliminating the common-mode voltage of the motor driver. When aligning the three-phase PWM wave of the rectifier with the three-phase PWM wave of the inverter after the alignment module is stretched, it selects the alignment method that minimizes the area of ​​the image enclosed by the voltage vector and the reference voltage vector after alignment. The telescopic module unilaterally contracts or expands the voltage of each phase of the rectifier. And the amount by which each phase voltage of the inverter is contracted or stretched on one side. The calculation method is as follows: in, This indicates the duration of the zero vector of the rectifier. This indicates the duration of the zero vector of the inverter.

3. A motor drive system based on a four-quadrant frequency converter, characterized in that, include: Electric motor; A four-quadrant frequency converter, wherein the inverter is connected to the three-phase windings of the motor; And the motor drive controller based on a four-quadrant frequency converter as described in claim 2.

4. The motor drive system based on a four-quadrant frequency converter as described in claim 3, characterized in that, Also includes: The LCL filter is connected to the power grid and the rectifier of the four-quadrant frequency converter, respectively.

5. The motor drive system based on a four-quadrant frequency converter as described in claim 4, characterized in that, The parameters of the LCL filter are designed as follows: in, and These represent the bridge arm-side inductance and the grid-side inductance of the LCL filter, respectively. For the maximum ripple current, For switching frequency, This is the DC-side output voltage. This represents the peak value of the grid-side phase voltage. The angular frequency of the power grid. This represents the peak value of the grid-side phase current. For filtering capacitors, The rated active power of the rectifier, For three-phase phase voltage, The resistor is connected in series in the capacitor branch. The resonant frequency, This is the inductance ratio.

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