Constant common-mode voltage modulation method and system suitable for multiphase series-wound topology

Abstract

The application discloses a constant common-mode voltage modulation method and system suitable for a multi-phase series winding topology, and belongs to the field of AC transmission and common-mode suppression. The method comprises the following steps: determining the available bridge arm switch states of the multi-phase series winding topology; calculating the average value of the voltages at each end of the winding under all available switch states to obtain the common-mode voltages corresponding to different switch states; and selecting the switch states that satisfy the same common-mode voltage amplitude and the minimum absolute value to combine and complete vector synthesis and modulation. The application solves the problem of large system common-mode voltage amplitude (±V dc / 2) and non-constant voltage under the modulation scheme of the ordinary multi-phase series winding topology, can reduce the system common-mode voltage amplitude to 1 / N of the existing level, can avoid the damage of the excessive common-mode voltage to the insulation of the inverter system, can maintain the constant common-mode voltage amplitude, and can solve the problem of the damage of the common-mode current generated by the high-frequency change of the common-mode voltage amplitude to the motor bearing under the existing modulation method.

Description

Technical Field

[0001] This invention belongs to the field of AC drives and their common-mode suppression, and more specifically, relates to a constant common-mode voltage modulation method and system suitable for multiphase series winding topologies. Background Technology

[0002] In recent years, with the rapid development of power electronics technology, voltage source inverters based on pulse width modulation (PWM) technology have been widely used in AC drive applications. Their high-frequency switching characteristics give the inverter system advantages such as low harmonic content and fast dynamic response. However, due to the binary nature of the switching voltage, the output phase voltage is momentarily unbalanced. This generates a high-amplitude, high-frequency common-mode voltage (CMV) applied to the motor side, threatening the motor's insulation and causing common-mode electromagnetic interference (EMI) problems. The common-mode current (CMC) generated by the high-frequency changing common-mode voltage can cause electrolytic corrosion of the bearings, affecting the reliable operation of the system.

[0003] Therefore, common-mode rejection methods for PWM inverter systems have become a research hotspot in recent years, mainly divided into hardware and software solutions. Hardware solutions typically require the addition of passive or active common-mode filters to the system, but this inevitably increases the system's cost and size. Software solutions reduce common-mode voltage and achieve common-mode electromagnetic interference suppression by optimizing the switching vector combination, but are mainly applicable to traditional half-bridge topologies.

[0004] Chinese invention patent CN109039207A discloses an N-phase N+1 bridge arm inverter topology and its modulation method, such as Figure 1 As shown, this N-phase N+1 bridge arm topology is also known as the series winding topology. Its voltage utilization is twice that of the half-bridge topology, while only requiring the addition of one bridge arm. Therefore, it can significantly improve drive capability, maintain the number of power devices in the inverter topology, reduce drive system cost, and increase power density.

[0005] However, the common-mode voltage of the series winding topology cannot be determined by existing methods, which affects the implementation of the software suppression scheme for the common-mode voltage of this topology. This results in an excessively large output common-mode voltage of the series winding topology under the existing modulation method, and the amplitude changes frequently. Summary of the Invention

[0006] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a constant common-mode voltage modulation method and system suitable for multi-phase series winding topology. Its purpose is to solve the technical problem that the output common-mode voltage of series winding topology is too large and the amplitude changes frequently under the existing modulation method.

[0007] To achieve the above objectives, according to one aspect of the present invention, a constant common-mode voltage modulation method suitable for multiphase series winding topologies is provided, comprising:

[0008] S1. Determine the available bridge arm switch states for the multiphase series winding topology;

[0009] S2. Calculate the average value of the voltage at each terminal of the winding under all available switching states to obtain the common-mode voltage corresponding to different switching states;

[0010] S3. Select the switching states that have the same common-mode voltage amplitude and the smallest absolute value, and combine them for vector synthesis and modulation.

[0011] Furthermore, the formula for calculating the common-mode voltage is as follows:

[0012]

[0013] N is the number of phases in the series winding, and N is an odd number; V Leg1 ~V Leg(N+1) This represents the voltage at the midpoint of each bridge arm.

[0014] Furthermore, the multiphase series winding topology includes: N+1 bridge arms, each bridge arm including: an upper bridge arm power switching device and a lower bridge arm power switching device, the upper node of the upper bridge arm power switching device in each bridge arm is connected to the DC bus voltage, the lower node of the lower bridge arm power switching device is connected to the power supply ground, and the lower node of the upper bridge arm power switching device is connected to the upper node of the lower bridge arm power switching device as the output node of the bridge arm.

[0015] Furthermore, for a series winding topology where N>3, step S3 includes;

[0016] Determine the distribution of the vector combination corresponding to the selected switch state in the fundamental plane and the kth harmonic plane; k = 3, 5, ..., N-2;

[0017] A combination of relatively long switching vectors on the fundamental plane is selected for vector synthesis;

[0018] The effective time of the selected switching vector is calculated based on the reference vector. The effective time of each switching vector satisfies the following conditions: In the fundamental plane, the sum of the scalar multiplications of each switching vector and its effective time is equal to the scalar multiplication of the reference vector and the unit period time, so as to synthesize the reference vector; In the k-th harmonic plane, within a unit period, the sum of the scalar multiplications of each switching vector and its effective time is equal to zero, so as to suppress the k-th harmonic; The sum of the effective times of each switching vector is equal to the unit period.

[0019] Within a unit cycle, each switching vector operates according to the calculated switching vector action time, synthesizes a reference vector, and maintains a constant common-mode voltage of the inverter system.

[0020] Furthermore, for a three-phase series winding topology, step S3 includes;

[0021] The duration of action of the selected switching vector is calculated based on the reference vector; the duration of action of each switching vector satisfies the following: in the fundamental plane, the sum of the scalar multiplications of each switching vector and its duration equals the scalar multiplication of the reference vector and the unit period time; the sum of the durations of action of each switching vector equals the unit period.

[0022] Within a unit cycle, each switching vector operates according to the calculated switching vector action time, synthesizes a reference vector, and maintains a constant common-mode voltage of the inverter system.

[0023] According to another aspect of the present invention, a constant common-mode voltage modulator suitable for a multiphase series winding topology is provided, comprising:

[0024] A switch state selection module is used to determine the available bridge arm switch states of the multiphase series winding topology;

[0025] The common-mode voltage calculation module is used to calculate the average value of the voltage at each terminal of the winding under all available switching states, so as to obtain the common-mode voltage corresponding to different switching states.

[0026] The common-mode voltage modulation module is used to select and combine switching states that have the same common-mode voltage amplitude and the smallest absolute value for vector synthesis and modulation.

[0027] According to another aspect of the present invention, an inverter system with constant common-mode voltage is provided, comprising: the modulator described above and a multiphase series winding topology; the multiphase series winding topology outputs a constant common-mode voltage under the control of the modulator.

[0028] Overall, the above-described technical solutions conceived by this invention can achieve the following beneficial effects compared with the prior art.

[0029] This invention can calculate the common-mode voltage amplitude corresponding to the switching state of each arm of a multiphase series winding topology. It selects vector combinations with small common-mode voltages and the same amplitude for reference vector synthesis and provides a specific switching modulation scheme. This solves the problem of large common-mode voltage amplitudes (±V) in ordinary multiphase series winding topology modulation schemes. dc This addresses the issue of inconsistent voltage ( / 2), reducing the system's common-mode voltage amplitude to 1 / N of the current level, thus preventing excessive common-mode voltage from damaging the inverter system's insulation. Simultaneously, it maintains a constant common-mode voltage amplitude, thereby resolving the problem of common-mode current damage to motor bearings caused by high-frequency changes in the common-mode voltage amplitude under existing modulation methods. Furthermore, the system's common-mode electromagnetic interference is significantly reduced. Attached Figure Description

[0030] Figure 1 It is a typical topology of an N-phase N+1 bridge arm series winding circuit;

[0031] Figure 2 It is the equivalent impedance network of an N-phase permanent magnet synchronous motor driven by a multiphase series winding topology;

[0032] Figure 3 It is a typical topology of existing three-phase four-bridge-arm series winding circuits;

[0033] Figure 4 It shows the distribution of each switch vector in the αβ plane of a three-phase series winding topology;

[0034] Figure 5 It is a combination of three-phase series winding topology reference vector and switching vector (V7, V 12 V 14 The vector composition relationship of );

[0035] Figure 6 Under a three-phase series winding topology, based on the proposed constant common-mode voltage modulation method, a switch vector combination (V7, V) is selected. 12 V 14 At time T, within a unit period s Internal switch operation modes;

[0036] Figure 7 It is a combination of three-phase series winding topology reference vector and switching vector (V3, V5, V 10 The vector composition relationship of );

[0037] Figure 8 Under a three-phase series winding topology, based on the proposed constant common-mode voltage modulation method, a switch vector combination (V3, V5, V...) is selected. 10 At time T, within a unit period s Internal switch operation modes;

[0038] Figure 9 These are experimental measurement results of the four-arm voltage and system common-mode voltage under a three-phase series winding topology and based on the existing series winding topology modulation method.

[0039] Figure 10 These are experimental measurement results of the four-arm voltage and the system common-mode voltage under a three-phase series winding topology, based on the proposed constant common-mode voltage modulation method;

[0040] Figure 11 It is a typical topology of a five-phase, six-bridge-arm series-winding circuit;

[0041] Figure 12 It shows the distribution of each switch vector in the αβ plane of a five-phase series winding topology;

[0042] Figure 13 It shows the distribution of each switch vector in the xy plane of a five-phase series winding topology;

[0043] Figure 14 It is a switching vector combination (V) of a five-phase series winding topology. 54 V 23 V 27 V 44 V 46 Vector composition relationship in the αβ plane;

[0044] Figure 15 It is a switching vector combination (V) of a five-phase series winding topology. 54 V 23 V 27 V 44 V 46 Vector composition relationship in the xy plane;

[0045] Figure 16 Under a five-phase series winding topology, based on the proposed constant common-mode voltage modulation method, a switch vector combination (V...) is selected. 54 V 23 V 27 V 44 V 46 At time T, within a unit period s Inside, the switching operation modes of the 6 bridge arms;

[0046] Figure 17 Under a five-phase series winding topology, based on existing series winding topology modulation methods, within a unit period T s Inside, the switching operation modes of the 6 bridge arms. Detailed Implementation

[0047] 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.

[0048] like Figure 1 The multiphase series winding topology shown is an N-phase N+1 bridge arm topology, where N ≥ 3 and is an odd number; there are N+1 bridge arms, defined as Leg1 to Leg(N+1). Each bridge arm has two switching states: 1. The upper switch is on, and the lower switch is off. At this time, the voltage at the midpoint of the bridge arm is... Define this switch state as S i =1 (i = 1, 2, 3, 4, ..., N+1); 2. The upper transistor is turned off and the lower transistor is turned on. At this time, the voltage at the midpoint of the bridge arm is Define this switch state as S i=0 (i=1,2,3,4,…,N+1). And define the voltage at the midpoint of each bridge arm as V. Leg1 ~V LegN+1 .

[0049] This is a multiphase series winding topology with N phases. Each winding has two terminals, positive and negative, defined as V. p(i)+ V p(i)- , i = 1, 2, 3, 4, ..., N;

[0050] To achieve the method of this invention, namely, to keep the output common-mode voltage amplitude of the control system constant, it is first necessary to realize a quantitative calculation method for the common-mode voltage of the multiphase series winding topology.

[0051] Common-mode voltage typically refers to the average phasor voltage occurring between each conductor and a specified reference point (often ground or rack). In a traditional half-bridge topology, the quantitative formula for calculating the magnitude of the common-mode voltage is:

[0052]

[0053] Therefore, the common-mode voltage of this topology can be easily obtained by calculating the average value of the voltages at the midpoints of the three half-bridge arms.

[0054] For multiphase series winding topologies, when the number of phases is N, there are N+1 bridge arms (where N≥3 and is an odd number). There is currently no available method for calculating the common-mode voltage for this topology. To address this issue, we analyze it from the perspective of circuit impedance networks.

[0055] Assuming that the impedance of the N-phase stray parameter branch remains symmetrical on the AC side of the multiphase series winding topology, an equivalent circuit model of the N-phase series winding motor drive system can be established. According to the π-type equivalent circuit of transmission line theory, the winding to other electrodes can be modeled, and the impedance between electrodes can be uniformly represented by impedance. In the equivalent circuit, the bypass impedance of the two ends of the winding to the reference electrode is equal.

[0056] Therefore, for the various conductive materials within a permanent magnet synchronous motor, four types of electrodes are simplified: windings, stator, rotor, and bearings, forming an impedance network. The subscript 'w' represents winding electrodes, 'r' represents rotor electrodes, 's' represents stator electrodes, and 'b' represents bearings. For an N-phase permanent magnet synchronous motor driven by an N-phase series winding topology, its overall impedance network can be represented as follows: Figure 2 .

[0057] After the N-phase winding is equivalently converted to a π-type configuration, a total of 2N identical ground impedance loops appear. Therefore, the influence of the voltage at the midpoint of the N+1 bridge arm on the input side will ultimately be mapped onto the potentials of these 2N points, forming a common-mode loop through the stator or rotor side. Based on symmetry and the topology of the N-phase series winding circuit, the potentials at these 2N points are: V p1+ V p1- V p2+ V p2- ,…,V p(N-1)+ V p(N-1)- V p(N)+ V p(N) .

[0058] Since the impedances in the common-mode loops containing the 2N reference points are all identical, the common-mode impedance of each branch is 2N times its original value. Therefore, the common-mode current can be calculated as follows:

[0059]

[0060] Therefore, the corresponding common-mode voltage of the N-phase series winding topology is:

[0061]

[0062] According to the above formula, the common-mode voltage of a multiphase series winding topology can be defined as the average value of the voltages at all terminals of all phase windings. Based on the topology, we can obtain: V p1+ =V Leg1 V p1- =V p2+ =V Leg2 V p2- =V p3+ =V Leg3 V p3- =V p4+ =V Leg4 V p(N-1)- =V p(N)+ =V Leg(N) V p(N)- =V Leg(N+1) .

[0063] Therefore, the formula for calculating the common-mode voltage of a multi-phase series winding topology with N phases is:

[0064]

[0065] This invention provides a constant common-mode voltage modulation method suitable for multiphase series winding topologies, comprising the following steps:

[0066] S1. Determine the available bridge arm switch states of the multiphase series winding topology;

[0067] Since each bridge arm has two switching states, the series winding topology of the N-phase N+1 bridge arms includes a total of 2 N+1 There are two available switching vector states. However, to suppress the zero-sequence voltage component in the series winding topology, the switching states of bridge arm Leg1 and bridge arm LegN+1 need to be consistent. This actually includes 2... N A number of switch states are available.

[0068] S2. Calculate the average value of the voltage at each terminal of the winding under all available switching states to obtain the common-mode voltage corresponding to different switching states;

[0069] S i When = 1, the voltage at the midpoint of the bridge arm is S i When = 0, the voltage at the midpoint of the bridge arm is

[0070] Substitute the values ​​into the following formula to calculate the common-mode voltage corresponding to the switching state of each bridge arm.

[0071]

[0072] S3. Select the switching states that have the same common-mode voltage amplitude and the smallest absolute value, and combine them for vector synthesis and modulation.

[0073] Specifically, step S3 includes,

[0074] (3-1) Select a suitable vector combination;

[0075] By classifying the switching vectors according to their common-mode voltage amplitudes and selecting switching vectors with consistent common-mode voltage amplitudes for vector synthesis, constant common-mode voltage modulation can be achieved. Simultaneously, to optimize the common-mode suppression effect of the constant common-mode voltage modulation method for multiphase series-wound inverters, the output common-mode voltage amplitude of the system needs to be minimized; that is, vector combinations with smaller common-mode voltage amplitudes are selected for vector synthesis and modulation. Preferably, to optimize the phase voltage output capability of the multiphase series-wound inverter under the constant common-mode voltage modulation method, the vector length of each switching vector in the fundamental plane needs to be considered, with longer vectors preferred to improve output voltage utilization.

[0076] (3-2) Based on the selected vector combination, perform vector synthesis and modulation;

[0077] (3-2-1) Calculate the action time of each switch vector based on the reference vector.

[0078] The reference vector and the switch vector combination have the following relationship:

[0079] 1. In the αβ plane (fundamental wave plane), within a unit period, the sum of the scalar products of each switching vector and its duration of action equals the sum of the reference vector and the unit period time T.s The scalar multiplication results are equal, so that a reference vector can be synthesized;

[0080] 2. For an N-phase series winding topology, in the higher harmonic plane (third, fifth, ... (N-2)th harmonic plane), within a unit period, the sum of the product of each switching vector and its operating time is equal to zero, so as to suppress higher harmonics and ensure the quality of the output current waveform.

[0081] 3. The sum of the durations of each switching vector is equal to the unit period T. s ;

[0082] Based on the above relationships, a system of equations can be listed to calculate the action time of each switch vector.

[0083] (3-2-2) Within a unit period Ts, each switching vector is operated according to the calculated switching vector action time, so as to synthesize the reference vector and maintain the common mode voltage of the inverter system constant.

[0084] Example 1

[0085] Taking a three-phase series winding topology as an example, the method of the present invention is described in detail below with reference to the accompanying drawings and specific examples:

[0086] Determine the available bridge arm switch states for a three-phase series winding topology; the three-phase series winding topology is as follows: Figure 3 As shown, there are four bridge arms, defined as Leg1 to Leg4. Since each bridge arm has two switching states, the three-phase series winding topology includes a total of 2... 4 =16 available switching vector states. However, in order to suppress the zero-sequence voltage component of the series winding topology, the switching states of bridge arm Leg1 and bridge arm Leg4 need to be consistent. In reality, there are 8 available switching states.

[0087] Based on the common-mode voltage calculation formula for a three-phase series winding topology:

[0088]

[0089] The common-mode voltage amplitude information for each switch vector state is shown in Table 1. The vector distribution in the αβ plane is as follows: Figure 4 As shown, the results indicate that under the existing series winding topology modulation method, the common-mode voltage of the inverter is within (-V dc / 2,-V dc / 6,V dc / 6,V dc The variation between / 2) has a maximum amplitude of V. dc / 2.

[0090] Table 1 Switching Vector States and CMV Amplitude of Three-Phase Series Winding Topology Inverter

[0091]

[0092] Select vector combinations with consistent common-mode voltages and the smallest absolute values ​​for vector synthesis and modulation; based on the results in Table 1: switching vectors V7, V 12 and V 14 The common-mode voltage is V. dc / 6, Switch vectors V3, V5 and V 10 The common-mode voltage is -V dc / 6. Therefore, select the switch vector combination (V7,V 12 V 14 ) or (V3,V5,V 10 ), participate in vector synthesis, and realize constant common-mode voltage modulation.

[0093] Calculate the vector action time; using the switch vector combination (V7, V 12 V 14 For example, let the reference output vector be V. ref Let each switching cycle be T. s The duration of each vector action is T7,T 12 ,T 14 .

[0094] like Figure 5 As shown, the combination of the reference vector and the switch vector has the following relationship:

[0095]

[0096] Wherein, the reference vector V ref The modulus length is |V ref |, the angle in the αβ plane is θ. Switch vector combination (V7, V 12 V 14 The modulus of ) is The angle in the αβ plane is

[0097] Substituting into the calculation, we get:

[0098]

[0099]

[0100]

[0101] Finally, based on the calculation results, during the switching modulation process, each switching transistor follows... Figure 6 Perform the action as shown. That is: in T 14 / 2, T7 / 2, T 12 T7 / 2, T 14 / 2 Within five time periods, the switching states of the four bridge arms correspond to the switching vector V respectively. 14 V7,V 12 ,V7,,V 14 .

[0102] Based on the above steps, use vector combination (V7,V) 12 V 14 During modulation, the common-mode voltage of the three-phase series winding topology inverter system will remain constant and be V. dc / 6; similarly, see reference Figure 7 , Figure 8 Using vector combination (V3,V5,V) 10 During modulation, the common-mode voltage of the three-phase series winding topology inverter system will also remain constant and be -V. dc / 6; Therefore, under the proposed modulation method, the common-mode voltage amplitude of the system is 1 / 3 of that of the existing method and remains constant.

[0103] Furthermore, experiments were conducted to compare the system common-mode voltage output of the constant common-mode voltage modulation method proposed in this application with that of existing series winding topology modulation methods under a three-phase series winding topology.

[0104] Figure 9 These are experimental measurement results of the four-bridge arm voltage and the system common-mode voltage under the existing series winding topology modulation method; Figure 10 These are the experimental measurement results of the four-arm voltage and the system common-mode voltage under the proposed constant common-mode voltage modulation method. The common-mode voltage is obtained by measuring the motor housing voltage to ground and can be considered a replica of the common-mode voltage (but with a smaller amplitude). It can be seen that the results obtained by the common-mode voltage calculation method proposed in this invention are consistent with the actual measurement results. Furthermore, compared with existing modulation methods, the housing-to-ground voltage measured using the constant common-mode voltage modulation method proposed in this invention is significantly suppressed and has a constant amplitude, thus effectively improving the common-mode characteristics.

[0105] Example 2

[0106] Taking a five-phase series winding topology as an example, the method of the present invention is described in detail below with reference to the accompanying drawings and specific examples:

[0107] Five-phase series winding topology as follows Figure 11 As shown, the wiring method is Δn = (5-1) / 2 = 2. To implement the constant common-mode voltage modulation method for this topology, the specific steps are as follows:

[0108] Determine the available bridge arm switch states for a five-phase series winding topology; a five-phase six-bridge arm series winding topology includes a total of 2 6= 64 available switching vector states. In order to suppress the zero-sequence voltage component of the series winding topology, the switching states of bridge arm Leg1 and bridge arm Leg6 need to be consistent, which actually includes 32 available switching states.

[0109] Based on the common-mode voltage calculation formula for a five-phase series winding topology:

[0110]

[0111] The common-mode voltage amplitude information for 32 available switching states was calculated, as shown in Table 2.

[0112] Table 2 Switching Vector States and CMV Amplitude of Five-Phase Series Winding Topology Inverter

[0113]

[0114] Select appropriate vector combinations for vector synthesis and modulation; according to the results in Table 2, under the existing series winding topology modulation method, the common-mode voltage of the five-phase series winding inverter is within (-0.5V). dc -0.3V dc -0.1V dc 0.1V dc 0.3V dc 0.5V dc The value varies between 0.5V, with the maximum absolute value being 0.5V. dc .

[0115] The distribution of each switch vector in the αβ plane of the five-phase series winding topology is as follows: Figure 12 As shown, the distribution of each switch vector in the xy plane of the five-phase series winding topology is as follows: Figure 13 As shown in Table 2, the numerical values ​​of the mapped vector lengths of each vector in the αβ plane and xy plane are calculated according to the generalized PARK transformation formula.

[0116] According to Table 2 and Figure 12 Result: Switch vector combination: (V 11 V 19 V 21 V 38 V 42 ),(V 25 V 36 V 50 V7,V 13 ),(V 54 V 23 V 27 V 44 V 46 ),(V 29 V 40 V 15 V52 V 58 The corresponding absolute values ​​of the common-mode voltages are all 0.1V. dc And the switch vector combination: (V 11 V 19 V 21 V 38 V 42 (Common-mode voltage -0.1V) dc ), (V 54 V 23 V 27 V 44 V 46 (Common-mode voltage 0.1V) dc Since all of them are long vectors, they are selected as the appropriate vector combinations for vector synthesis to achieve constant common-mode voltage modulation.

[0117] Using switch vector combination (V 54 V 23 V 27 V 44 V 46 For example, let the reference output vector be V. ref Let each switching cycle be T. s The duration of each vector action is T. 54 ,T 23 ,T 27 ,T 44 ,T 46 .

[0118] Switch vector combination (V) 54 V 23 V 27 V 44 V 46 ) in the αβ plane (fundamental wave plane) and the reference vector V ref The vector composition relationship is as follows Figure 14 As shown, the vector composition relationship of each vector in the xy plane (third harmonic plane) is as follows: Figure 15 As shown.

[0119] The combination of the reference vector and the switch vector satisfies the following constraints:

[0120]

[0121] The calculation yielded:

[0122]

[0123]

[0124]

[0125]

[0126]

[0127] Finally, based on the calculation results, during the switching modulation process, each switching transistor follows... Figure 16 Perform the action as shown. That is: in T 54 / 2,T 23 / 2,T 27 / 2,T 44 / 2,T 46 ,T 44 / 2,T 27 / 2,T 23 / 2,T 54 / 2 Within nine time segments, the switching states of the six bridge arms correspond to the switching vector V respectively. 54 V 23 V 27 V 44 V 46 V 44 V 27 V 23 V 54 .

[0128] Based on the above steps, use vector combination (V) 54 V 23 V 27 V 44 V 46 During modulation, the common-mode voltage of the five-phase series-wound inverter system will remain constant at 0.1V. dc Similarly, using vector combination (V 11 V 19 V 21 V 38 V 42 During modulation, the common-mode voltage of the five-phase series winding topology inverter system will also remain constant at -0.1V. dc ;

[0129] Figure 16 This demonstrates the use of a switch vector combination (V) based on the proposed constant common-mode voltage modulation method in a five-phase series winding topology. 54, V 23 V 27 V 44 V 46 At time T, within a unit period s The switching operation mode of the six bridge arms was verified. The common-mode voltage remained constant at -0.1V. dc ;

[0130] Figure 17 This demonstrates the modulation method based on existing series winding topology in a five-phase series winding topology, within a unit period T. s Internally, the switching operation modes of the 6 bridge arms; the system output common-mode voltage is within (-0.5V). dc -0.3V dc -0.1V dc 0.1V dc 0.3V dc 0.5V dc The variation between these values ​​indicates that the proposed method significantly deteriorates compared to the model's performance.

[0131] The present invention provides a constant common-mode voltage modulation method and system applicable to multi-phase series winding topologies. It discloses for the first time a method for determining the common-mode voltage of multi-phase series winding topologies, which can suppress the common-mode voltage amplitude of N-phase series winding topologies to 1 / N of that of traditional modulation methods and keep it constant, thereby significantly reducing the common-mode electromagnetic interference of the system. In addition, the present invention is based on a software modulation scheme and does not rely on additional hardware at all, and has the advantages of strong applicability and low cost.

[0132] 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 constant common-mode voltage modulation method suitable for multiphase series winding topologies, characterized in that, include: S1. Determine the available bridge arm switch states for the multiphase series winding topology; S2. Calculate the average value of the voltage at each terminal of the winding under all available switching states to obtain the common-mode voltage corresponding to different switching states; S3. Select the switching states that have the same common-mode voltage amplitude and the smallest absolute value, combine them, and perform vector synthesis and modulation; The formula for calculating the common-mode voltage is: N N represents the number of phases in the series winding, where N is an odd number. This represents the voltage at the midpoint of each bridge arm.

2. The constant common-mode voltage modulation method applicable to multiphase series winding topology according to claim 1, characterized in that, The multiphase series winding topology includes N+1 bridge arms, each bridge arm including an upper bridge arm power switch device and a lower bridge arm power switch device. The upper node of the upper bridge arm power switch device in each bridge arm is connected to the DC bus voltage, the lower node of the lower bridge arm power switch device is connected to the power supply ground, and the lower node of the upper bridge arm power switch device is connected to the upper node of the lower bridge arm power switch device as the output node of the bridge arm.

3. The constant common-mode voltage modulation method applicable to multiphase series winding topology according to claim 2, characterized in that, For a series winding topology with N>3, step S3 includes: Determine the distribution of the vector combination corresponding to the selected switch state in the fundamental plane and the kth harmonic plane; k=3,5,…,N-2; A combination of relatively long switching vectors on the fundamental plane is selected for vector synthesis; Calculate the duration of action of the selected switch vector based on the reference vector; The action time of each switching vector satisfies the following: in the fundamental plane, the sum of the scalar multiplications of each switching vector and its action time is equal to the scalar multiplication of the reference vector and the unit period time, so as to synthesize the reference vector; In the k-th harmonic plane, within a unit period, the sum of the scalar products of each switching vector and its duration of action equals zero, in order to suppress the k-th harmonic; the sum of the durations of action of each switching vector equals a unit period. Within a unit cycle, each switching vector operates according to the calculated switching vector action time, synthesizes a reference vector, and maintains a constant common-mode voltage of the inverter system.

4. A constant common-mode voltage modulation method suitable for multiphase series winding topologies according to claim 2, characterized in that, For a three-phase series winding topology, step S3 includes: The duration of action of the selected switching vector is calculated based on the reference vector; the duration of action of each switching vector satisfies the following: in the fundamental plane, the sum of the scalar multiplications of each switching vector and its duration equals the scalar multiplication of the reference vector and the unit period time; the sum of the durations of action of each switching vector equals the unit period. Within a unit cycle, each switching vector operates according to the calculated switching vector action time, synthesizes a reference vector, and maintains a constant common-mode voltage of the inverter system.

5. A constant common-mode voltage modulator suitable for multiphase series winding topologies, characterized in that, include: A switch state selection module is used to determine the available bridge arm switch states of the multiphase series winding topology; The common-mode voltage calculation module is used to calculate the average value of the voltage at each terminal of the winding under all available switching states, so as to obtain the common-mode voltage corresponding to different switching states. The common-mode voltage modulation module is used to select and combine switching states that have the same common-mode voltage amplitude and the smallest absolute value for vector synthesis and modulation. The common-mode voltage is calculated using the following formula: N N represents the number of phases in the series winding, where N is an odd number. This represents the voltage at the midpoint of each bridge arm.

6. An inverter system with constant common-mode voltage, characterized in that, include: The modulator and multiphase series winding topology of claim 5; the multiphase series winding topology outputs a constant common-mode voltage under the control of the modulator.

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