Zero-crossing distortion processing method, harmonic optimization method, storage medium and variable frequency drive

Abstract

The invention discloses a zero-crossing distortion processing method, a harmonic optimization method, a storage medium and a variable frequency drive; the zero-crossing distortion processing method comprises: detecting three-phase current; determining a target large sector where a three-phase input current vector is located in a voltage vector space according to the direction information of the three-phase current; wherein the voltage vector space comprises six large sectors, and the six large sectors are adjacently distributed in a counterclockwise order; if any phase current in the three-phase current passes through the phase current zero point, the voltage vector in the target large sector is used to synthesize a voltage reference vector. The invention detects the three-phase current, and when any phase current passes through the current zero point, the direction information of the three-phase current is used to determine the basic voltage vector in the target large sector to synthesize the voltage reference vector, thereby avoiding the situation of forced vector replacement in the original SVPWM algorithm and solving the problem of current distortion in the Vienna circuit when the current passes through the zero point.

Description

Technical Field

[0001] The invention relates to the technical field of three-level rectifier modulation, and in particular to a zero-crossing distortion processing method, a harmonic optimization method, a storage medium and a variable frequency driver. Background Art

[0002] With the continuous popularization and application of new energy vehicles, power inverter and rectification technology is increasingly widely used in the field of new energy vehicle charging piles and on-board converters, and the demand is also growing. At the same time, as the global energy crisis becomes increasingly serious, how to achieve energy recovery and efficient utilization has become a key issue that needs to be solved urgently; Vienna rectifiers can achieve unidirectional energy flow, low voltage stress of switching devices, fewer switching devices compared to other three-level rectifiers, and no need to set dead zones. Therefore, they are widely used in various electronic equipment and communication systems, including radio station power supplies and monitoring equipment, electric vehicle charging pile pre-rectifier and other circuit equipment; as a grid-connected pre-stage device, its power input and output quality is particularly important, mainly manifested in the input power harmonic content, output power harmonic content, output power density, etc. The quality of the above parameters is affected by the modulation strategy of the VIENNA rectifier.

[0003] Due to the existence of filter inductance in the Vienna rectifier, the three-phase current leads the three-phase voltage by a certain angle, causing current distortion when the Vienna rectifier passes through zero point, thus affecting the current quality. Summary of the invention

[0004] The main purpose of the present invention is to provide a zero-crossing distortion processing method, aiming to solve the current distortion problem that occurs when the current crosses the zero point of the Vienna circuit.

[0005] To achieve the above object, the present invention proposes a zero-crossing distortion processing method, which is applied to a three-phase Vienna circuit; the zero-crossing distortion processing method comprises: Detect three-phase current; Determine a target large sector where the three-phase input current vector is located in the voltage vector space according to the direction information of the three-phase current; wherein the voltage vector space includes six large sectors, and the six large sectors are adjacently distributed in a counterclockwise order; If any phase current among the three-phase currents passes through the phase current zero point, the voltage vector in the target large sector is used to synthesize the voltage reference vector.

[0006] Optionally, if any phase current of the three-phase current passes through the phase current zero point, the preceding steps include: Input the three-phase current into the phase-locked loop to obtain the angle of the three-phase input current vector; Subtract the three-phase input current vector angle from the set angle value, and determine whether the difference is less than the preset difference; If the difference is less than the preset difference, the step of synthesizing a voltage reference vector using a voltage vector in a target large sector is performed if any phase current among the three-phase currents passes through a phase current zero point.

[0007] Optionally, the step of determining a target large sector in a voltage vector space where a three-phase input current vector is located according to the direction information of the three-phase current may then include: Record the name of the target large sector where the three-phase input current vector is located at different times; If the target large sector is switched in a positive sequence cycle from sector I to sector VI, the step of inputting the three-phase current to the phase-locked loop to obtain the angle of the three-phase input current vector is performed.

[0008] The present invention also proposes a harmonic optimization method, which is applied to a three-phase Vienna circuit and includes: Detect DC bus voltage, three-phase current and three-phase voltage; The three-phase current is converted into the d-axis current and the q-axis current by using the clark transformation and the park transformation, and the target DC bus voltage value is subtracted from the DC bus voltage value, and the d-axis reference current value and the q-axis reference current value are obtained according to the difference; Obtaining a d-axis reference voltage value and a q-axis reference voltage value according to the d-axis current value, the q-axis current value, the d-axis reference current value, the q-axis reference current value, the q-axis voltage value, and the d-axis voltage value; The d-axis reference voltage value and the q-axis reference voltage value are converted into three-phase reference voltages in a three-phase stationary coordinate system by inverse Clark transformation and inverse Park transformation; Obtaining the third harmonic component of the fundamental wave of the three-phase reference voltage, and superimposing it with the three-phase reference voltage to obtain a three-phase modulated voltage; The on / off of the power switch in the three-phase Vienna topology circuit is controlled by the space vector pulse width modulation method to generate the three-phase modulated voltage; wherein the target large sector where the three-phase input current vector is located in the voltage vector space is determined according to the direction information of the three-phase current.

[0009] Optionally, the d-axis reference voltage value and the q-axis reference voltage value are obtained according to the d-axis current value, the q-axis current value, the d-axis reference current value, the q-axis reference current value, the q-axis voltage value and the d-axis voltage value, and the calculation is performed using the following formula:

[0010] in, is the d-axis reference voltage value, is the q-axis reference voltage value, is the proportional gain coefficient, is the integral gain coefficient, is the d-axis reference current value, is the q-axis reference current value, is the angular frequency, is the inductance value, is the q-axis current value, is the d-axis current value, is the d-axis voltage value, is the q-axis voltage value.

[0011] Optionally, obtaining the third harmonic component of the three-phase reference voltage fundamental wave includes: A filter is used to filter each phase voltage in the three-phase reference voltage to obtain its third harmonic component.

[0012] Optionally, controlling the on / off of a power switch in a three-phase Vienna topology circuit to generate the three-phase modulated voltage by a space vector pulse width modulation method includes: According to the polarity of the three-phase voltage, a positive carrier voltage and a negative carrier voltage required for space vector pulse width modulation are obtained; By comparing the three-phase modulation voltage with the positive carrier voltage and the negative carrier voltage, the driving signal of the power switch is determined.

[0013] The present invention also proposes a storage medium, which is a computer-readable storage medium. A computer program is stored on the storage medium. When the computer program is executed by a processor, the zero-crossing distortion processing method and / or the harmonic optimization method are implemented.

[0014] The present invention further provides a variable frequency driver, which includes a processor and the storage medium.

[0015] The present invention discloses a zero-crossing distortion processing circuit, a harmonic optimization method, a storage medium and a variable frequency drive. The zero-crossing distortion processing method is applied to a three-phase Vienna circuit; the zero-crossing distortion processing method includes: detecting three-phase current; determining the target large sector where the three-phase input current vector is located in the voltage vector space according to the direction information of the three-phase current; the voltage vector space includes six large sectors, and the six large sectors are adjacently distributed in a counterclockwise order; if any phase current in the three-phase current passes through the phase current zero point, the voltage vector in the target large sector is used to synthesize the voltage reference vector. The present invention detects the three-phase current, and when any phase current passes through the current zero point, the direction information of the three-phase current is used to determine the basic voltage vector in the target large sector to synthesize the voltage reference vector, thereby avoiding the situation of forced vector replacement in the original SVPWM algorithm and solving the problem of current distortion in the Vienna circuit when the current passes through the zero point. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0017] Figure 1 This is a schematic diagram of the topological structure of the Vienna circuit; Figure 2 It is a schematic diagram of the current partition of the Vienna circuit within the fundamental wave period; Figure 3 Space vector diagram for Vienna Circuit; Figure 4 It is the equivalent circuit diagram of Vienna circuit; Figure 5 Schematic diagram of the reference voltage vector and current resultant vector of the Vienna circuit in different sectors; Figure 6 It is the voltage synthesis vector process diagram; Figure 7 Schematic diagram of the Vienna circuit reference voltage vector and current resultant vector in the same sector; Figure 8 This is a schematic diagram of the current zero-crossing distortion area of ​​the Vienna circuit; Fig. 9 Schematic diagram of the vector hexagons in each sector; Fig.10 is an overall block diagram of the harmonic optimization method of the present invention; Fig.11 This is the input starting current peak waveform under traditional SPWM modulation control; Fig.12 It is the input starting current peak waveform under equivalent SVPWM modulation control; Fig.13 It is the waveform diagram of the A-phase modulation voltage and the injected A-phase third harmonic compensation under the equivalent SVPWM modulation control; Fig.14 To increase the modulation signal and carrier signal waveform of phase A after auxiliary judgment of input current; Fig.15 To increase the input current auxiliary judgment, the input power is 3.5KW, and the output voltage waveform diagram; Fig.16 This is the input current THD diagram with an input power of 3.5KW under SVPWM modulation; Fig.17 It is a flow chart of an embodiment of a method for processing zero-crossing distortion of the present invention.

[0018] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0019] 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.

[0020] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0021] In the present invention, unless otherwise clearly specified and limited, the terms "connection", "fixation", etc. should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0022] In addition, in the present invention, descriptions such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0023] The topological structure of the three-phase Vienna circuit in the present invention is as follows: Figure 1 shown. , , is the three-phase voltage of the power grid, , , is the three-phase filter inductor, and is the DC side capacitance. Figure 1In the topology shown, each bridge arm consists of two fast recovery diodes and a bidirectional power flow unit. Each bidirectional power flow unit consists of two switch tubes with anti-parallel diodes connected in reverse series, and the two switch tubes share a driving signal. On the AC side, the power grid is connected to the midpoint of the diode of each bridge arm through the filter inductor and its parasitic resistance. On the DC side, two filter capacitors are connected in series to the positive and negative busbars on the DC side; the midpoints of the two filter capacitors are connected to the three-phase bidirectional power flow unit.

[0024] Since the Vienna rectifier is three-phase symmetrical, the current flow path and output voltage of the Vienna rectifier are analyzed by taking phase A as an example. Among them, the DC side midpoint O is taken as the voltage reference point.

[0025] Each phase of the three-phase Vienna rectifier has three states: N state, O state and P state. Vienna rectifier is a three-level rectifier with an output voltage of have ,0, There are three situations, corresponding to the three states of P, O, and N. Among them, in the P state, the corresponding phase switch is turned off, and the current flows from this phase through the capacitor In the O state, the corresponding phase switch is turned on, and the current flows directly from this phase to the midpoint O. In the N state, the corresponding phase switch is turned off, and the current flows from the midpoint O through the capacitor Each three-phase power flow unit There are two states: on and off, with on defined as 1 and off defined as 0. The three bidirectional power flow units can be combined to produce a total of 8 switch states, as shown in Table 1.

[0026]

[0027] Table 1 Under different polarities of three-phase current, the above 8 switch states correspond to different working modes of Vienna circuit. In one fundamental wave cycle, the three-phase current is divided into 6 regions, each region is 60° apart and has two phases with the same polarity. Figure 2 When the three-phase current is in region I, >0, <0, <0. The output state combinations of region I (defined as basic voltage vectors) are: OOO, OON, ONO, ONN, POO, PON, PNO, PNN. Considering the symmetry of the three phases, the analysis principles of other regions are the same and will not be repeated.

[0028] From Table 1 and Figure 2 , we can get the space vector diagram formed by 25 basic voltage vectors of Vienna circuit, as Figure 3 shown. Figure 3The relationship between the basic voltage vector and the current direction is given. According to the direction of the current, the space vector diagram is divided into six sectors. Figure 3 The middle sector has a corresponding switch sequence. To avoid redundancy, the switch sequence in each sector is not described here.

[0029] Figure 4 Is the equivalent circuit of the three-phase Vienna circuit. is the x-phase grid voltage, is the x-phase AC input current, is the reference voltage amplitude of phase x. When operating at unity power factor, due to the voltage drop of the input filter inductor, the rectifier AC input current will lead the reference voltage angle In some areas, there is a phenomenon that the polarity of the AC input current is inconsistent with the reference voltage, which leads to the problem of current zero-crossing distortion.

[0030] Vienna circuit output voltage per phase It can be expressed as: This formula shows that the working state of the Vienna circuit is not only determined by the state of the bidirectional power flow unit, but also affected by the current polarity. When the current sign is positive, the output voltage can only be or 0; when the current sign is negative, the output voltage can only be or 0.

[0031] Since the space vector diagram is symmetrical, the following takes sector I as an example to analyze the cause of current zero-crossing distortion. In sector I, the three-phase current satisfies >0, <0, <0. Phase A can output P state and O state, and phase B and phase C can output O state and N state. When the reference voltage vector uref is in sector I, the basic voltage vector for synthesizing uref can form a small hexagon, such as Figure 5 As shown in the yellow part. When uref is in the small area 3 in sector I, regardless of the influence of the current direction on the output voltage state, the basic voltage vector , , For synthesizing uref, the switching sequence is ONN→OON→PON→POO→PON→OON→ONN. Figure 5 (a). However, due to the voltage drop on the filter inductor, the current synthesis vector iref leads the reference voltage vector uref by an angle in actual operation. When iref is in the second sector, the current polarities projected by iref on the three phases A, B, and C are >0, >0, <0. At this time, due to >0, phase B can only output P or O state, so the basic voltage vector ONN cannot appear in the switching sequence. Since the bidirectional power flow unit of phase B is turned on and the current of phase B is positive, the output voltage state of phase B is forced to be converted to P state, that is, the basic voltage vector ONN is forced to be changed to OPN. At this time, the switching sequence is OPN→OON→PON→POO→PON→OON→OPN. Figure 5 (b) shown.

[0032] Since the time corresponding to the basic voltage vector remains unchanged and the basic voltage vector ONN is forced to be changed to OPN, the ideal output reference voltage vector is modified and only the actual synthetic voltage vector can be output, such as Figure 6 As shown. Figure 4 It can be seen that since the reference voltage vector is changed, the current also changes. Current distortion occurs when the current is commutated, that is, when the current crosses zero. The distorted area is given by When the current synthesis vector iref and the reference voltage vector uref are in the same sector, the polarities of iref and uref projected onto the three phases A, B, and C are the same, and there will be no forced vector replacement. The actual switching sequence is the same as the ideal switching sequence, and there is no current zero-crossing distortion. Figure 7 shown.

[0033] Depend on Figure 4 In the figure, the equivalent circuit of the Vienna circuit can be obtained:

[0034] Solving the problem, we can get the phase angle difference as: .

[0035] When the grid frequency f is a fixed value, The size of depends on the AC input current and filter parameters. The larger the AC input current, the larger the filter inductance needs to be used to limit the ripple amplitude of the input current. The bigger. The current zero-crossing distortion range is determined. The three-phase current commutates once every 60° in one fundamental wave cycle. Each time the current commutates, the current zero-crossing distortion will occur. There are 6 distortion areas in total, such as Figure 8 It should be noted that Figure 8 The angles determined in can be freely determined, and they change according to the direction of the selected 0 angle, and are not necessarily a fixed combination of 0°, 60°, 120°, 180°, 240° and 300°. When the right direction is selected as the 0 angle direction, the angle combination changes to 30°, 90°, 150°, 210°, 270° and 330°.

[0036] The invention proposes a zero-crossing distortion processing method, aiming at processing the current distortion phenomenon occurring when the current crosses the zero point.

[0037] The zero-crossing distortion processing method is applied to a three-phase Vienna circuit; the zero-crossing distortion processing method comprises: Step S10: Detect three-phase current.

[0038] Step S20, determining a target large sector where the three-phase input current vector is located in the voltage vector space according to the direction information of the three-phase current; wherein the voltage vector space includes six large sectors, and the six large sectors are adjacently distributed in a counterclockwise order.

[0039] Step S30: If any phase current among the three-phase currents passes through the phase current zero point, the voltage vector in the target large sector is used to synthesize the voltage reference vector.

[0040] It should be noted that zero-crossing distortion occurs when the three-phase current crosses zero. Figure 3 It can be seen that the space vector diagram can be divided into six large sectors according to the current; Figure 2 and Figure 3 It can be seen that there is a phase current with a changed current direction between two adjacent large sectors. The six large sectors are adjacently distributed in a counterclockwise order, namely the I, II, III, IV, V, and VI large sectors, and each large sector is divided into 6 small sectors.

[0041] According to the above content, we can know that the direction of the three-phase current corresponding to each large sector is different, which can be referred to Figure 2 The direction of the three-phase current can be detected, and the large sector where the current synthesis vector is located can be determined by the direction of the three-phase current; Figure 2 For example, detect the current of phase A , B phase current , C phase current ; in getting >0, <0, <0, it can be obtained that the current synthesis vector of the current three-phase current is in the Ith largest sector. >0, <0, >0, the current synthesis vector of the current three-phase current is in the VI largest sector.

[0042] Because the direct cause of zero-point distortion is that the current synthesis vector and the reference voltage vector are not in the same large sector, Figure 8It can be seen that there are six distortion areas in the space vector diagram, and the distortion areas can be calculated, and each distortion area is a left-closed and right-open interval in the angle domain. After determining the direction of the 0 angle of the space vector diagram, the smaller angle value of each distortion area can be obtained. It is easy to obtain that the smaller angle value of each distortion area corresponds to the zero point of one of the three-phase currents. That is, at the smaller angle value of each distortion area, there is a zero point of one phase current, and the current direction changes.

[0043] It should be noted that when any one of the three-phase currents passes through zero, the current synthesis vector is at the junction of two large sectors. Due to the existence of the filter inductor, the voltage synthesis vector lags behind the current synthesis vector. At the next moment, the voltage reference vector and the current synthesis vector will be in different large sectors, resulting in zero-point distortion.

[0044] This scheme proposes a method of directly using the input current to judge the large sector, which avoids the sector judgment error in principle and thus can eliminate the zero-crossing distortion of the input circuit.

[0045] If any phase current of the three-phase current passes through the phase current zero point, the voltage reference vector is synthesized using the voltage vector in the target large sector. It should be noted that when the reference voltage vector uref is in a certain sector, the basic voltage vector used to synthesize uref can form a small hexagon. There is an overlapping area between the hexagons corresponding to two adjacent large sectors. That is, the basic voltage vector in a large sector can synthesize a reference voltage vector located in an adjacent large sector.

[0046] Take sectors I and II as an example. Fig. 9 As shown in the figure, in sector I divided by current direction, there are 7 voltage vectors: , , , , , as well as . The range of the reference voltage that can be synthesized is a regular hexagon, which includes not only the entire sector I, but also II-1 and II-2 of sector II, and VI-5 and VI-6 of sector VI. Similarly, in sector II, the range of the reference voltage vector that can be synthesized is a regular hexagon, and II-1 and II-2 overlap with I-5 and I-6 of sector I. When the reference vector falls into the overlapping area, there are voltage vectors in sectors I and II that can synthesize the reference vector, and the redundant small vectors can be used to balance the output voltage midpoint potential. If the traditional SVPWM method is used, it is impossible to synthesize the correct reference vector, such as Figure 6 When using input current to assist in determining the voltage in a large sector, a zero vector can be used in sector II. , redundant small vector and the mid vector To synthesize the reference voltage vector of sector I, so as to avoid the distortion problem of input current crossing zero. In this example, the direction of the three-phase current can be used to determine whether the input current crosses the zero point, that is, any phase current of the three-phase current passes through the phase current zero point; when the input current crosses the zero point, the current synthesis vector is in sector II. At this time, the basic voltage vector of sector II can be used to synthesize the reference voltage vectors of sectors I-5 and I-6 to avoid the above-mentioned forced replacement of the vector, which causes zero-crossing distortion.

[0047] The present invention discloses a zero-crossing distortion processing circuit, and the zero-crossing distortion processing method is applied to a three-phase Vienna circuit; the zero-crossing distortion processing method includes: detecting three-phase current; determining the target large sector where the three-phase input current vector is located in the voltage vector space according to the direction information of the three-phase current; wherein the voltage vector space includes six large sectors, and the six large sectors are adjacently distributed in a counterclockwise order; if any phase current in the three-phase current passes through the phase current zero point, the voltage vector in the target large sector is used to synthesize the voltage reference vector. The present invention detects the three-phase current, and when any phase current passes through the current zero point, the direction information of the three-phase current is used to determine the basic voltage vector in the target large sector to synthesize the voltage reference vector, thereby avoiding the situation of forced vector replacement in the original SVPWM algorithm, and solving the problem of current distortion in the Vienna circuit when the current passes through the zero point.

[0048] If any phase current among the three-phase currents passes through the phase current zero point, before that includes: Step S40, inputting the three-phase current into a phase-locked loop to obtain the angle of the three-phase input current vector; Step S50, subtracting the three-phase input current vector angle from the set angle value, and determining whether the difference is less than the preset difference; Step S60: If the difference is less than the preset difference, executing the step of synthesizing a voltage reference vector using the voltage vector in the target large sector if any phase current of the three-phase current passes through the phase current zero point.

[0049] It should be noted that the three-phase current commutates once every 60° in one fundamental wave cycle. Each time the current commutates, current zero-crossing distortion will occur, with a total of 6 distortion regions. Figure 8 It is known that after confirming After that, the size of the distortion area is determined, and after the direction of the 0 angle in the spatial vector diagram is determined, the smaller angle of each distortion area is correspondingly determined. Figure 8 As shown, the smaller angle values ​​of the six distortion areas are combinations of 0°, 60°, 120°, 180°, 240° and 300° respectively.

[0050] The three-phase phase-locked loop circuit is mainly composed of basic components such as a phase detector, a loop filter, and a voltage-controlled oscillator, and also includes some specific circuits and control logic related to the three-phase system. In a three-phase system, it is usually necessary to sample and process the three-phase voltage or current signal and convert it into a signal form suitable for the phase-locked loop input. The phase detector in the circuit compares the phase of the input three-phase current signal with the output signal of the voltage-controlled oscillator to generate a phase error signal. After the error signal is filtered by the loop filter, the output frequency and phase of the voltage-controlled oscillator are controlled to gradually track the phase change of the three-phase current signal. When the phase-locked loop reaches a locked state, the output signal of the voltage-controlled oscillator maintains a fixed phase relationship with the three-phase current signal. By measuring and processing the phase of the output signal of the voltage-controlled oscillator, the angle information of the three-phase current can be obtained. It should be noted that the three-phase input current vector is the current synthesis vector described above.

[0051] The set angle value is determined by the R&D personnel according to the smaller angle value of the distortion area in the space vector diagram. Figure 8 In the example shown, the smaller angle values ​​of the six distortion areas are 0°, 60°, 120°, 180°, 240° and 300°. That is, the set angle values ​​are 0°, 60°, 120°, 180°, 240° and 300°. The angles of the three-phase input current vectors are subtracted from the set angles to obtain six differences, and the sizes of the six differences and the preset differences are determined respectively; it is easy to understand that since the three-phase input current vector rotates counterclockwise, the angle corresponding to the three-phase input current vector increases continuously within one cycle, and combined with Figure 2 and Figure 8 It can be seen that when the angle corresponding to the three-phase input current vector is greater than the set angle value, it means that the current synthesis vector and the reference voltage vector are located in different large sectors, and zero-crossing distortion may exist, and corresponding measures need to be taken.

[0052] In addition, the three-phase input current vector angle is subtracted from the set angle value and compared with the preset difference value; the difference between the three-phase input current vector angle and the set angle value less than zero is not used. The preset difference can be specifically expressed as the current synthesis vector iref leading the reference voltage vector uref by an angle That is, Figure 8 The angle of the distortion area shown in . R&D personnel can obtain the angle of the current synthesis vector iref leading the reference voltage vector uref according to the formula mentioned above. , and use it as the preset difference; or set the preset difference yourself, and the preset difference needs to be greater than zero and less than the angle .

[0053] If the difference is less than the preset difference, it means that the current synthesis vector and the reference voltage vector are located in different large sectors, and there may be zero-crossing distortion. If any phase current of the three-phase current passes through the phase current zero point, the step of using the voltage vector in the target large sector to synthesize the voltage reference vector is executed.

[0054] The step of determining the target large sector where the three-phase input current vector is located in the voltage vector space according to the direction information of the three-phase current comprises: Record the name of the target large sector where the three-phase input current vector is located at different times; If the target large sector is switched in a positive sequence cycle from sector I to sector VI, the step of inputting the three-phase current to the phase-locked loop to obtain the angle of the three-phase input current vector is performed.

[0055] It should be noted that this scheme is based on dividing the space vector diagram into six large sectors distributed in counterclockwise order, and dividing the large sectors according to the direction combination of the three-phase current. It is easy to see that this scheme relies on the three-phase input current vector to switch from sector I to sector VI in a positive sequence cycle. If you go directly from sector I to sector IV, this scheme cannot be applied.

[0056] Therefore, in the first cycle, the name of the target large sector where the three-phase input current vector is located at different times can be obtained, and it can be determined whether the change of the target large sector in the cycle is switched in the manner of a positive sequence cycle from sector I to sector VI. If the target large sector is switched in the manner of a positive sequence cycle from sector I to sector VI, it can be considered that the operation mode of the motor meets the application conditions of this solution. In subsequent cycles, there is no need to record the name of the target large sector where the three-phase input current vector is located at different times again and determine whether it is a positive sequence cycle from sector I to sector VI.

[0057] In addition, since the three-phase phase-locked loop is phase-locked by converting the input voltage into a DC quantity through the dq coordinates, it is very insensitive to sampling interference. The angle obtained by phase locking does not have spikes, and the zero crossing of the input current occurs within 6 specific angles. Therefore, the phase-locked loop angle can be used to filter the current sampling. When the input current sign changes, check whether the angle obtained by the phase-locked loop is near the above 6 angles, and it can be determined whether the current zero crossing has indeed occurred or is caused by sampling interference. At the same time, using the method of a unidirectional state machine, the software only allows the sector switching to be a positive sequence cyclic switching from sector I to sector VI, and does not allow reverse switching, which avoids the sector judgment error caused by sampling jitter at the current zero crossing.

[0058] The modulation strategy of Vienna rectifier is mainly space vector PWM modulation, which has the advantages of high voltage utilization, low power harmonic content and simple modulation method. However, the traditional algorithm must go through the Vienna closed-loop control quantity calculation, Park inverse transformation to obtain the α component and β component of the voltage in the two-phase stationary coordinate system, Clark inverse transformation to obtain the sinusoidal modulation wave, and then perform large-sector judgment on the modulation wave, calculation of the reference vector area, and calculation of the time occupied by the basic vector. The calculation is relatively complicated, and once the output power is increased, it will cause poor system dynamic performance.

[0059] The present invention also proposes a harmonic optimization method, which is applied to a three-phase Vienna circuit and includes: Detect DC bus voltage, three-phase current and three-phase voltage; The three-phase current is converted into the d-axis current and the q-axis current by using the clark transformation and the park transformation, and the target DC bus voltage value is subtracted from the DC bus voltage value, and the d-axis reference current value and the q-axis reference current value are obtained according to the difference; Obtaining a d-axis reference voltage value and a q-axis reference voltage value according to the d-axis current value, the q-axis current value, the d-axis reference current value, the q-axis reference current value, the q-axis voltage value, and the d-axis voltage value; The d-axis reference voltage value and the q-axis reference voltage value are converted into three-phase reference voltages in a three-phase stationary coordinate system by inverse Clark transformation and inverse Park transformation; Obtaining the third harmonic component of the fundamental wave of the three-phase reference voltage, and superimposing it with the three-phase reference voltage to obtain a three-phase modulated voltage; The on / off of the power switch in the three-phase Vienna topology circuit is controlled by the space vector pulse width modulation method to generate the three-phase modulated voltage; wherein the target large sector where the three-phase input current vector is located in the voltage vector space is determined according to the direction information of the three-phase current.

[0060] It should be noted that the Clark Transform is a space vector transformation method that converts time domain signals (such as voltage, current, magnetic flux, etc.) in a three-phase stationary coordinate system (abc) to a two-phase stationary coordinate system (αβ0). From a geometric point of view, the Clark Transform is equivalent to projecting the vectors in a three-phase system from a three-dimensional space to a two-dimensional plane. Taking the voltage vector as an example, in the three-phase stationary coordinate system, the voltage vectors are located on coordinate axes that are 120° apart from each other. Through the Clark Transform, these three vectors are projected onto a two-dimensional plane perpendicular to the body diagonal, and two mutually perpendicular vectors are obtained, thereby realizing the conversion from three phases to two phases.

[0061] Park Transformation is a coordinate transformation method widely used in fields such as motor control. It converts variables in a two-phase stationary coordinate system (αβ) into a synchronous rotating coordinate system (dq0). From a physical point of view, Park Transformation is a means of converting AC quantities in a stationary coordinate system into DC quantities in a rotating coordinate system. In a synchronous rotating coordinate system, the d-axis is usually consistent with the direction of the magnetic field. Taking the motor as an example, the current in the stator winding of the motor alternates with time in a stationary coordinate system. After Park Transformation, in a synchronous rotating coordinate system, the d-axis current component is mainly used to generate a magnetic field, and the q-axis current component is mainly used to generate torque. This makes the control of the motor more intuitive, because the two key physical quantities, torque and magnetic field, can be independently controlled by DC quantities in a rotating coordinate system.

[0062] In motor control systems, PI (proportional-integral) controllers are used to regulate the d-axis and q-axis currents of the motor. For example, when a target DC bus voltage is set , the actual measured DC bus voltage is , their difference It can be used as the input of the PI controller. According to the control strategy, the PI controller will output a regulation signal to change the d-axis and q-axis currents. Generally speaking, for a motor control system based on voltage regulation, the regulation signal output by the PI controller is and The relationship between can be expressed as ,in, is the proportionality coefficient, is the integral coefficient. This adjustment signal will further affect the reference current of the d-axis and q-axis and .

[0063] The control block diagram may include a phase-locked loop, an output voltage outer loop, an input current inner loop, and a midpoint voltage balance loop. Among them: the phase-locked loop obtains the phase angle of the input voltage as the angle for the subsequent dq coordinate transformation; the output voltage outer loop uses PI control, and its output is used as the reference quantity of the active axis d axis of the current inner loop, which is compared with the current Id obtained by actual sampling calculation and decoupled after PI control. In order to achieve a power factor of 1, the reference value of the q-axis current can be set to 0 for PI control and then decoupled, thereby obtaining the modulation wave of the rectifier grid-side voltage, that is, the d-axis reference voltage value and the q-axis reference voltage value. and .

[0064] The d-axis reference voltage value and the q-axis reference voltage value are converted into a three-phase reference voltage in a three-phase stationary coordinate system by inverse Clark transformation and inverse Park transformation. The third harmonic component of the fundamental wave of the three-phase reference voltage is obtained and superimposed with the three-phase reference voltage to obtain a three-phase modulation voltage.

[0065] It should be noted that in the three-phase inverter circuit, the utilization rate of its DC voltage is 0.866. In order to improve the utilization rate of DC voltage, it is considered to inject three-phase harmonic components into the modulation wave signal. After adding the third harmonic, it is found that the top of the modulation wave waveform is flattened, the adjustable range is widened, and the fundamental amplitude is larger. After the original sine signal is injected with higher harmonics, the top of the wave is flattened, which increases the linear adjustable range. The SPWM modulation wave can be generated by the intersection relationship between the isosceles triangle carrier and the reference sine wave. After injecting the third harmonic, a new modulation wave (saddle wave) can be synthesized. If the maximum amplitude of the new modulation wave is kept unchanged, the fundamental amplitude needs to be increased to 1.1548 times of the original fundamental wave.

[0066] When the amplitude of the injected third harmonic is Vm1 / 6, the amplitude of the fundamental voltage based on the injection of the third harmonic increases by 15.48%. This is equivalent to improving the utilization rate of the DC voltage. Specifically, when the modulation depth is the maximum, under the conventional SPWM, the maximum amplitude of the A-phase voltage output is a specific value, and the amplitude of the fundamental voltage is a certain value. Under the same conditions, in order to achieve the maximum amplitude of the A-phase voltage, the fundamental voltage amplitude is obtained to be a higher value after injecting the third harmonic. After calculation, it can be seen that the amplitude of the fundamental voltage based on the injection of the third harmonic increases by 15.48%. The third harmonic injection SVPWM technology is a technology that optimizes the output voltage waveform by injecting the third harmonic component into the modulation wave based on the traditional SPWM technology. Injecting the third harmonic can improve the output voltage utilization of the inverter and improve the waveform quality of the output voltage without increasing the switching frequency and hardware complexity. The voltage utilization rate during SVPWM modulation is 15.5% higher than that of SPWM. During the voltage and current dual-loop PI operation, Ud and Id are not easy to saturate, thereby reducing the current THD under the condition of small boost.

[0067] After the three-phase modulation voltage is obtained, the on / off of the power switch in the three-phase Vienna topology circuit is controlled by a space vector pulse width modulation method to generate the three-phase modulation voltage.

[0068] Space-Vector Pulse-Width Modulation (SVPWM) is an advanced PWM technology based on the concept of space vector. In a three-phase inverter, the output three-phase voltage can be represented by a space vector, which rotates in space and its position and size depend on the instantaneous value of the three-phase voltage. The modulation process is divided into the following three steps: (1) sector judgment; (2) action time calculation; (3) switching time allocation.

[0069] It should be noted that, in the process of controlling the on / off of the power switch in the three-phase Vienna topology circuit to generate the three-phase modulated voltage by the space vector pulse width modulation method, the above-mentioned zero-crossing distortion processing method is applied. Specifically, in the sector judgment step, the target large sector where the three-phase input current vector is located in the voltage vector space is determined according to the direction information of the three-phase current; wherein, the target large sector where the three-phase input current vector is located in the voltage vector space is determined according to the direction information of the three-phase current.

[0070] Correspondingly, if any phase current among the three-phase currents passes through the phase current zero point, the voltage vector in the target large sector is used to synthesize the voltage reference vector.

[0071] The harmonic optimization method provided by the present invention obtains the third harmonic component of the fundamental wave of the three-phase reference voltage and superimposes it with the three-phase reference voltage to obtain a three-phase modulation voltage; and injects the three-phase harmonic component into the modulation wave signal. After adding the third harmonic, the top of the modulation wave waveform is flattened, the adjustable range is widened, and the fundamental amplitude is increased. After the original three-phase reference voltage is injected with high-order harmonics, the top of the wave is flattened, the linear adjustable range is increased, the utilization rate of the DC voltage is improved, and the current THD is reduced.

[0072] like Fig.10 As shown, Fig.10 The overall block diagram of the harmonic optimization method.

[0073] Combination Fig.10 The following processing steps are available: (1) Based on the given target DC bus voltage The actual DC bus voltage The error between them is used to design the voltage outer loop controller and calculate the corresponding reference current value of the current decoupling controller. .

[0074] (2) Obtain the grid-side voltage equations of the Vienna rectifier mathematical model, which contains the current , Exhibits coupling characteristics, which makes it difficult to control the two independently (3) Introduce feedforward decoupling to eliminate the coupling between the two current quantities and calculate the actual collected dq axis current , The output value after the nominal model is obtained, and the error between it and the voltage given value before coupling compensation is calculated. The error is then fed back to the output end of the PI link of the complex vector control through a first-order low-pass filter. Finally, the coupling compensation term is added to obtain the dq axis reference voltage value output by the controller. , .

[0075] (4) , The voltage reference value in the three-phase stationary coordinate system is obtained through inverse Park transformation and inverse Clarke transformation. ,because In , , The phase difference is 120°, and the waveform obtained through the intersection of them is the third harmonic component of the fundamental wave. , , , and then with , , The required SVPWM modulation voltage is obtained by superposition. .

[0076] (5) Using the actual collected input voltage , , The polarity of the carrier signal of the SVPWM is determined , The former is the carrier voltage used when the input voltage is positive, and the latter is the carrier voltage used when the input voltage is negative.

[0077] (6) In the three-phase Vienna rectifier, due to the influence of the input filter inductor voltage drop, there is a problem of phase shift between the actual current and the modulation waveform, which causes the actual current zero-crossing distortion and thus affects the current THD.

[0078] (7) Using the actual collected input current , , The polarity of the modulation voltage is used to assist in determining the selection of the carrier near the actual current zero point.

[0079] (8) Finally, the modulation voltage With the selected carrier signal , By comparison, the driving signal of the switch tube of the three-phase Vienna rectifier is obtained.

[0080] The grid-side voltage equations of the above Vienna rectifier mathematical model are expressed as:

[0081] In the formula, , are the grid voltages on the d and q axes respectively; , are the input currents on the d and q axes respectively; L is the filter inductance value, R is the equivalent resistance value, and ω is the angular velocity.

[0082] Fig.10 In the embodiment, the bus voltage controller, id current controller, iq current controller and midpoint voltage balance controller may all include PI (proportional-integral) controllers.

[0083] According to the d-axis current value, the q-axis current value, the d-axis reference current value, the q-axis reference current value, the q-axis voltage value and the d-axis voltage value, the d-axis reference voltage value and the q-axis reference voltage value are obtained, and the calculation is performed using the following formula:

[0084] in, is the d-axis reference voltage value, is the q-axis reference voltage value, is the proportional gain coefficient, is the integral gain coefficient, is the d-axis reference current value, is the q-axis reference current value, is the angular frequency, is the inductance value, is the q-axis current value, is the d-axis current value, is the d-axis voltage value, is the q-axis voltage value.

[0085] The step of obtaining the third harmonic component of the fundamental wave of the three-phase reference voltage comprises: A filter is used to filter each phase voltage in the three-phase reference voltage to obtain its third harmonic component.

[0086] In order to extract the third harmonic component in the three-phase reference voltage, a band-pass filter (BPF) can usually be used. The band-pass filter allows signals within a specific frequency range to pass through, while suppressing signals of other frequencies. For the third harmonic, when the grid frequency is f, its frequency is 3f. For example, in a grid with an industrial frequency of 50HZ, the third harmonic frequency is 150HZ, so a band-pass filter with a center frequency of 150HZ needs to be designed. Common filter types include Butterworth filters, Chebyshev filters, etc.

[0087] By using a space vector pulse width modulation method, the on / off of a power switch in a three-phase Vienna topology circuit is controlled to generate the three-phase modulation voltage, comprising: According to the polarity of the three-phase voltage, a positive carrier voltage and a negative carrier voltage required for space vector pulse width modulation are obtained; By comparing the three-phase modulation voltage with the positive carrier voltage and the negative carrier voltage, the driving signal of the power switch is determined.

[0088] It should be noted that in space vector pulse width modulation, it is usually necessary to generate a switching signal by comparing it with the carrier voltage. The determination of the positive carrier voltage and the negative carrier voltage is related to the polarity of the three-phase voltage and the desired modulation effect. Generally speaking, the DC bus voltage is used as the reference (assuming that the DC bus voltage is ), we divide it in a certain ratio to get the positive and negative carrier voltages. For example, set the forward carrier voltage for , negative carrier voltage for This is a relatively simple and commonly used setting method, which enables the subsequent comparison process to cover the entire voltage variation range and facilitates effective control of the power switch device. Of course, other proportional division methods can also be used according to specific circuit characteristics, power requirements, control accuracy and other factors.

[0089] For the three-phase modulated voltage, it is necessary to compare them with the positive carrier voltage and the negative carrier voltage in real time to determine the on and off states of each power switch device in the three-phase inverter, and then generate the corresponding drive signal.

[0090] Phase A: when > When the upper power switch of the A-phase bridge arm is controlled to be turned on (the lower power switch is turned off), a corresponding driving signal is generated to drive the switch device to be in the on state; when < When the lower power switch of the A-phase bridge arm is controlled to be turned on (the upper power switch is turned off), the corresponding drive signal is also generated to realize this switch state switching; when ≤ ≤ Depending on the specific control strategy or circuit requirements, the last switching state may be maintained or a specific switching action may be performed (for example, in some soft switching technology application scenarios). However, under normal circumstances, the current state is generally kept unchanged until the next comparison result changes.

[0091] For phase B and phase C, the same comparison rules and drive signal generation logic as phase A are used to compare with the positive carrier voltage and negative carrier voltage respectively, and then the conduction and shutdown of the upper and lower power switches of each bridge arm are controlled according to the comparison results to generate corresponding drive signals.

[0092] The present invention brings at least the following beneficial effects: (1) The present invention introduces input current to assist input voltage in carrier selection and judgment under the original SPWM modulation control, which can effectively eliminate the zero-crossing distortion of the input current, reduce the input harmonic current of the Vienna rectifier, and reduce the starting current peak of the Vienna rectifier. During the starting process, SVPWM can reduce the starting current peak of the Vienna rectifier by adjusting the direction and amplitude of the voltage vector, making the starting process of the Vienna rectifier smoother and more efficient.

[0093] (2) In the process of writing software, the length of software code is shortened, the amount of calculation is small, and it is easy to implement in engineering, which reflects the practicality of the new method.

[0094] Fig.11 It is the peak waveform of input starting current under traditional SPWM modulation control; Fig.12 is the input starting current peak waveform under equivalent SVPWM modulation control; Fig.13 is the A-phase modulation voltage and the injected A-phase third harmonic compensation waveform under equivalent SVPWM modulation control; Fig.14 To increase the modulation signal and carrier signal waveform of phase A after auxiliary judgment of input current; Fig.15 To increase the input current auxiliary judgment, the input power is 3.5KW, and the output voltage waveform; Fig.16 This is the input current THD when the input power is 3.5KW under SVPWM modulation.

[0095] contrast Fig.11 and Fig.12,SPWM modulation, at the moment of starting, the bus voltage boost is high, the slope is steep, and there is a large input current. ,The SVPWM modulation adopted in this scheme, at the moment of starting, makes the starting process of the Vienna rectifier smoother and more efficient.

[0096] Fig.13 The modulation wave and third harmonic output by the algorithm in the program are output through DAC. The green waveform is the third harmonic voltage extracted from the A, B, and C phase voltages after Clark inverse transformation. The blue waveform is the modulation wave of the A phase voltage superimposed with the third harmonic after Clark inverse transformation, which is equivalent to the SVPWM saddle wave. Fig.14 These are the carrier and modulation waves near the zero-crossing point when phase A turns from negative to positive.

[0097] right Fig.16 By comparing the FFT analysis of the original SPWM modulation control, the introduction of the third harmonic of the three-phase modulation voltage can effectively reduce the input harmonic current of the Vienna rectifier.

[0098] The present invention also proposes a storage medium, which is a computer-readable storage medium, and a computer program is stored on the storage medium. When the computer program is executed by a processor, the zero-crossing distortion processing method and / or the harmonic optimization method as described are implemented.

[0099] The present invention further provides a variable frequency drive, comprising a processor and the storage medium. The variable frequency drive executes a computer program stored in the storage medium through the processor to implement the zero-crossing distortion processing method and / or the harmonic optimization method.

[0100] The variable frequency drive may include a variable frequency control board.

[0101] The above descriptions are only optional embodiments of the present invention, and are not intended to limit the patent scope of the present invention. All equivalent structural changes made using the contents of the present invention's specification and drawings, or directly / indirectly applied in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for processing zero-crossing distortion, characterized in that: The zero-crossing distortion processing method is applied to a three-phase Vienna circuit; the zero-crossing distortion processing method comprises: Detect three-phase current; Determine a target large sector where the three-phase input current vector is located in the voltage vector space according to the direction information of the three-phase current; wherein the voltage vector space includes six large sectors, and the six large sectors are adjacently distributed in a counterclockwise order; If any phase current among the three-phase currents passes through the phase current zero point, the voltage vector in the target large sector is used to synthesize the voltage reference vector.

2. The zero-crossing distortion processing method according to claim 1, characterized in that: If any phase current among the three-phase currents passes through the phase current zero point, before that includes: Input the three-phase current into the phase-locked loop to obtain the angle of the three-phase input current vector; Subtract the three-phase input current vector angle from the set angle value, and determine whether the difference is less than the preset difference; If the difference is less than the preset difference, the step of synthesizing a voltage reference vector using a voltage vector in a target large sector is performed if any phase current among the three-phase currents passes through a phase current zero point.

3. The zero-crossing distortion processing method according to claim 2, characterized in that: The step of determining the target large sector where the three-phase input current vector is located in the voltage vector space according to the direction information of the three-phase current comprises: Record the name of the target large sector where the three-phase input current vector is located at different times; If the target large sector is switched in a positive sequence cycle from sector I to sector VI, the step of inputting the three-phase current to the phase-locked loop to obtain the angle of the three-phase input current vector is performed.

4. A harmonic optimization method, characterized in that: The harmonic optimization method is applied to a three-phase Vienna circuit, and the harmonic optimization method comprises: Detect DC bus voltage, three-phase current and three-phase voltage; The three-phase current is converted into the d-axis current and the q-axis current by using the clark transformation and the park transformation, and the target DC bus voltage value is subtracted from the DC bus voltage value, and the d-axis reference current value and the q-axis reference current value are obtained according to the difference; Obtaining a d-axis reference voltage value and a q-axis reference voltage value according to the d-axis current value, the q-axis current value, the d-axis reference current value, the q-axis reference current value, the q-axis voltage value, and the d-axis voltage value; The d-axis reference voltage value and the q-axis reference voltage value are converted into three-phase reference voltages in a three-phase stationary coordinate system by inverse Clark transformation and inverse Park transformation; Obtaining the third harmonic component of the fundamental wave of the three-phase reference voltage, and superimposing it with the three-phase reference voltage to obtain a three-phase modulated voltage; The on / off of the power switch in the three-phase Vienna topology circuit is controlled by the space vector pulse width modulation method to generate the three-phase modulated voltage; wherein the target large sector where the three-phase input current vector is located in the voltage vector space is determined according to the direction information of the three-phase current.

5. The harmonic optimization method according to claim 4, characterized in that: According to the d-axis current value, the q-axis current value, the d-axis reference current value, the q-axis reference current value, the q-axis voltage value and the d-axis voltage value, the d-axis reference voltage value and the q-axis reference voltage value are obtained, and the calculation is performed using the following formula: in, is the d-axis reference voltage value, is the q-axis reference voltage value, is the proportional gain coefficient, is the integral gain coefficient, is the d-axis reference current value, is the q-axis reference current value, is the angular frequency, is the inductance value, is the q-axis current value, is the d-axis current value, is the d-axis voltage value, is the q-axis voltage value.

6. The harmonic optimization method according to claim 4, characterized in that: The step of obtaining the third harmonic component of the fundamental wave of the three-phase reference voltage comprises: A filter is used to filter each phase voltage in the three-phase reference voltage to obtain its third harmonic component.

7. The harmonic optimization method according to claim 4, characterized in that: By using a space vector pulse width modulation method, the on / off of a power switch in a three-phase Vienna topology circuit is controlled to generate the three-phase modulation voltage, comprising: According to the polarity of the three-phase voltage, a positive carrier voltage and a negative carrier voltage required for space vector pulse width modulation are obtained; By comparing the three-phase modulation voltage with the positive carrier voltage and the negative carrier voltage, the driving signal of the power switch is determined.

8. A storage medium, characterized in that: The storage medium is a computer-readable storage medium, and a computer program is stored on the storage medium. When the computer program is executed by the processor, it implements the zero-crossing distortion processing method as described in any one of claims 1 to 3, and / or implements the harmonic optimization method as described in any one of claims 4 to 7.

9. A variable frequency drive, characterized in that: The variable frequency drive comprises a processor and the storage medium as claimed in claim 8.

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