A four-leg inverter system and a control method thereof

Abstract

The application discloses a four-bridge-arm inverter system and a control method thereof, and belongs to the field of motor control. The system comprises a target double three-phase motor and an inverter with four bridge arms. In the two groups of three-phase windings of the target double three-phase motor, one pair of windings with a phase difference of 180 degrees are directly connected and are not connected to the midpoint of a DC bus capacitor. The method comprises two methods. One is directly extending the space vector modulation of the four-switch inverter, which is equivalent to the control method of the four-bridge-arm inverter connected to the midpoint of the DC bus capacitor. The other is constructing a space voltage vector by using almost all switching states according to the new structure of the four-bridge-arm inverter not connected to the midpoint of the DC bus capacitor, namely the space vector modulation of the four-bridge-arm inverter. The application uses the four-bridge-arm inverter as a low-cost double three-phase inverter or a transition topology when the six-bridge-arm inverter is fault-tolerant, and simultaneously avoids the problem of fluctuation of the midpoint voltage of the DC bus capacitor existing in the traditional four-bridge-arm inverter topology.

Description

Technical Field

[0001] This invention belongs to the field of motor control, and more specifically, relates to a four-arm inverter system and its control method. Background Technology

[0002] Compared to traditional three-phase motors, multiphase motors offer higher efficiency, lower torque ripple, and greater fault tolerance, making them widely used in electric vehicles, all-electric ships, and wind power systems. The dual three-phase motor is the most common type of multiphase motor, consisting of two sets of armature windings with specific phase shift angles. Common dual three-phase motors include those with a 0° phase shift, 60° phase shift (symmetrical six-phase motor), and 30° phase shift. A 0° phase shift dual three-phase motor can be converted into a 180° phase shift dual three-phase motor by reversing one set of windings.

[0003] Dual three-phase motors are often driven by traditional six-arm inverters. However, in some low-cost applications, it is necessary to study dual three-phase inverter topologies that reduce switching devices. Currently, the most common dual three-phase inverter topologies that reduce switching devices are as follows: (1) nine-switch inverter topology; (2) five-arm inverter topology; (3) four-arm inverter topology.

[0004] A nine-switch inverter can independently control two three-phase loads, such as Figure 1 As shown, the nine-switch inverter has two operating modes: constant frequency (CF) mode, where the two three-phase outputs have the same frequency, and different frequency (DF) mode, where the two three-phase outputs have independent frequencies. Therefore, the nine-switch inverter can also be used to drive dual three-phase motors. Although the nine-switch inverter reduces three switching devices compared to a traditional six-arm inverter, it can only serve as a low-cost dual three-phase drive topology and cannot be used as a transition topology when one arm of a traditional six-arm inverter fails.

[0005] A five-bridge inverter drives two independent motors, such as Figure 2 As shown, in the three-phase windings of the two motors, one phase each shares a common bridge arm. The current in the common bridge arm is the total current of the two phases, therefore, it may face current overload problems. A five-bridge inverter can also drive dual three-phase motors and can serve as a fault-tolerant solution when one bridge arm of a traditional six-bridge inverter fails. In fact, compared to a traditional six-bridge inverter, a five-bridge inverter only reduces two switching devices, which is not a significant reduction.

[0006] Four-arm inverters are currently mostly used to drive two independent motors, such as Figure 3As shown, a four-arm inverter consists of four arms and two series-connected DC bus capacitors, with one phase of each motor connected to the midpoint of the DC bus capacitor. Compared to a traditional six-arm inverter, it reduces four switching devices. However, when the motors operate at low speeds or under heavy loads, the DC bus capacitor voltage fluctuates significantly, requiring a large capacitor to reduce voltage fluctuations, or to control the sum of the two-phase currents connected to the midpoint of the capacitors to be zero, thereby minimizing the DC bus capacitor voltage fluctuation. Essentially, a four-arm inverter can be viewed as two four-switch inverters. In a four-switch inverter system, DC bus capacitor midpoint voltage fluctuations reduce voltage utilization and generate torque ripple. Therefore, the performance of a four-arm inverter system is also affected by DC bus capacitor midpoint voltage fluctuations.

[0007] Among the three dual-phase inverter topologies that reduce switching devices, the four-arm inverter reduces the most switching devices, but its performance is often affected by the fluctuation of the DC bus capacitor midpoint voltage. Summary of the Invention

[0008] To address the shortcomings and improvement needs of existing technologies, this invention provides a four-arm inverter system and its control method. The purpose is to utilize the four-arm inverter as a low-cost dual three-phase inverter or as a transitional topology for fault-tolerant operation of a six-arm inverter, while avoiding the DC bus capacitor midpoint voltage fluctuation problem present in traditional four-arm inverter topologies.

[0009] To achieve the above objectives, according to one aspect of the present invention, a four-arm inverter system is provided, comprising: a target dual three-phase motor to be driven and an inverter having four arms; the target dual three-phase motor includes a three-phase winding A1B1C1 and a three-phase winding A2B2C2, wherein the three phases of the three-phase winding A1B1C1 are A1 phase, B1 phase and C1 phase respectively, and the three phases of the three-phase winding A2B2C2 are A2 phase, B2 phase and C2 phase respectively, and the A1 phase, B1 phase and C1 phase windings are 180° phase shifted from the A2 phase, B2 phase and C2 phase windings respectively;

[0010] Phase A1 and phase A2 windings are connected together, and phases B1, C1, B2 and C2 windings are connected to the midpoints of the four bridge arms of the inverter, respectively.

[0011] In some alternative embodiments, the target dual three-phase motor is a dual three-phase motor with a phase shift of 180°.

[0012] In some alternative embodiments, the target dual three-phase motor is a dual three-phase motor with a phase shift of 180° formed by reversing one set of three-phase windings in a dual three-phase motor with a phase shift of 0°.

[0013] In some alternative embodiments, the target dual three-phase motor is a dual three-phase motor with a phase shift of 180° formed by renaming one set of three-phase windings in a dual three-phase motor with a phase shift of 60°.

[0014] According to another aspect of the present invention, a control method for the above-described four-arm inverter system is provided, comprising:

[0015] (S1) The two bridge arms connected to the B1 and C1 phase windings in the inverter are equivalent to a four-switch inverter, and the switching states of the B1 phase bridge arm and the C1 phase bridge arm are controlled according to the space vector modulation method of the four-switch inverter.

[0016] (S2) Control the switching states of phase B2 and phase C2 according to the switching states of phase B1 and phase C1, so that the switching state of phase B2 is always opposite to the switching state of phase B1, and the switching state of phase C2 is always opposite to the switching state of phase C1.

[0017] Among them, the B1 phase bridge arm, C1 phase bridge arm, B2 phase bridge arm and C2 phase bridge arm represent the bridge arms in the inverter that are connected to the B1 phase, C1 phase, B2 phase and C2 phase windings, respectively; the switching states of the bridge arms include the state where the upper tube is on and the lower tube is off, and the state where the upper tube is off and the lower tube is on, and these two states are opposite.

[0018] According to another aspect of the present invention, a control method for the above-described four-arm inverter system is provided, comprising:

[0019] (T1) The state where the upper transistor is on and the lower transistor is off in the bridge arm is defined as switch state "1", and the state where the upper transistor is off and the lower transistor is on is defined as switch state "0". The different states of the B1 phase bridge arm, C1 phase bridge arm, B2 phase bridge arm and C2 phase bridge arm in the inverter constitute the 16 switch states of the inverter from "0000" to "1111", and the corresponding 16 voltage vectors are denoted as v0 to v 15 ;

[0020] (T2) will combine voltage vectors v1 and v 11 Combined into a voltage vector Translate voltage vectors v8 and v 13 Combined into a voltage vector Put voltage vectors v4 and v 14 Combined into a voltage vector Combine voltage vectors v2 and v7 into a single voltage vector. Translate the voltage vectors v0, v3, v6, v9, v 12 v 15 v 1_11 v 8_13 v 4_14 and v 2_7As the basic voltage vector;

[0021] (T3) Based on the desired voltage vector u s The spatial angle θ is selected for synthesizing the desired voltage vector u. s The basic voltage vectors are determined, and the duration of each basic voltage vector is used as the duration of the corresponding switching state.

[0022] (T4) Control the switching state of each bridge arm according to the determined switching state and duration, so as to synthesize the desired voltage vector with equal amplitude but opposite direction in the two sets of three-phase windings of the target dual three-phase motor.

[0023] Wherein, the B1 phase bridge arm, C1 phase bridge arm, B2 phase bridge arm, and C2 phase bridge arm represent the bridge arms in the inverter that are connected to the B1 phase, C1 phase, B2 phase, and C2 phase windings, respectively; the desired voltage vector u s The desired voltage vector of one set of three-phase windings of the target dual three-phase motor.

[0024] Further, step (T3) includes:

[0025] Determine the sector to which the spatial angle θ belongs, select the two fundamental voltage vectors v′ and v″ that constitute the two sides of the sector, and the two zero vectors v0 and v″ among the fundamental voltage vectors. 15 Used to synthesize the desired voltage vector u s ;

[0026] Based on the volt-second balance principle, the duration of each selected basic voltage vector is calculated and used as the duration of the corresponding switching state.

[0027] Furthermore, the formula for calculating the volt-second balance principle is as follows:

[0028]

[0029] Among them, T s Indicates the switching period; t′, t″, t0, and t 15 These represent the fundamental voltage vectors v′, v″, v0, and v, respectively. 15 The duration of action.

[0030] Furthermore, t0 = t 15 .

[0031] In summary, the technical solution conceived in this invention utilizes a four-arm inverter to drive a dual three-phase motor. Compared to a traditional six-arm inverter, this reduces four switching devices and can serve as a transition topology for fault-tolerant operation of a six-arm inverter. In the dual three-phase motor, a pair of windings with a 180° phase difference are directly connected and not connected to the midpoint of the DC bus capacitor. Therefore, compared to a traditional four-arm inverter, this invention effectively avoids the problem of voltage fluctuation at the midpoint of the DC bus capacitor, improves system performance and stability, and eliminates the need for two DC bus capacitors on the DC side of the inverter. Attached Figure Description

[0032] Figure 1 A schematic diagram of an existing nine-switch inverter topology;

[0033] Figure 2 This is a schematic diagram of an existing five-arm inverter topology;

[0034] Figure 3 Here is a diagram of an existing four-arm inverter topology;

[0035] Figure 4 This is a schematic diagram of a four-arm inverter system provided in an embodiment of the present invention;

[0036] Figure 5 The following are equivalent circuit diagrams for four switching states provided in the embodiments of the present invention: (a) is the equivalent circuit diagram when the switching states of the windings of phases B1, C1, B2 and C2 are “1”, “1”, “0” and “0” respectively; (b) is the equivalent circuit diagram when the switching states of the windings of phases B1, C1, B2 and C2 are “1”, “0”, “0” and “1” respectively; (c) is the equivalent circuit diagram when the switching states of the windings of phases B1, C1, B2 and C2 are “0”, “0”, “1” and “1” respectively; and (d) is the equivalent circuit diagram when the switching states of the windings of phases B1, C1, B2 and C2 are “0”, “1”, “1” and “0” respectively.

[0037] Figure 6 The following is a spatial distribution diagram of the voltage vector corresponding to different switching states provided in the embodiments of the present invention; wherein, (a) is a spatial distribution diagram of the voltage vector corresponding to different switching states acting on the three-phase winding A1B1C1, and (b) is a spatial distribution diagram of the voltage vector corresponding to different switching states acting on the three-phase winding A2B2C2.

[0038] Figure 7 The spatial distribution diagrams of the basic voltage vectors provided in the embodiments of the present invention are shown below; wherein, (a) is a spatial distribution diagram of the basic voltage vectors acting on the three-phase winding A1B1C1, and (b) is a spatial distribution diagram of the basic voltage vectors acting on the three-phase winding A2B2C2.

[0039] Figure 8 The diagram shows the voltage vector synthesis of the first sector provided in the embodiment of the present invention; wherein, (a) is a voltage vector synthesis diagram in the three-phase winding A1B1C1, and (b) is a voltage vector synthesis diagram in the three-phase winding A2B2C2. Detailed Implementation

[0040] 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.

[0041] In this invention, the terms "first," "second," etc. (if present) in the invention and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0042] To address the technical problem that the performance of traditional four-arm inverter systems driving dual three-phase motors is affected by fluctuations in the midpoint voltage of the DC bus capacitor, this invention provides a four-arm inverter system and its control method. The overall approach is to utilize the phase shift characteristics of the windings in the dual three-phase motor, selecting two windings with a 180° phase difference from each other in two sets of three-phase windings and directly connecting them without connecting them to the midpoint of the DC bus capacitor. This ensures effective motor driving while avoiding the impact of fluctuations in the midpoint voltage of the DC bus capacitor. Based on this, a corresponding control method is proposed.

[0043] This invention is applicable to dual three-phase motors with two windings having a 180° phase shift, such as dual three-phase motors with a 180° phase shift, dual three-phase motors with a 0° phase shift, and dual three-phase motors with a 60° phase shift. Among these motors, dual three-phase motors with a 180° phase shift can be directly driven. Other motors can be modified to be dual three-phase motors with a 180° phase shift through certain processing before being driven. For example, for a dual three-phase motor with a 0° phase shift, one set of three-phase windings can be reversed to form a dual three-phase motor with a 180° phase shift; for a dual three-phase motor with a 60° phase shift, one set of three-phase windings can be renamed to form a dual three-phase motor with a 180° phase shift. Without loss of generality, in the following embodiments, a dual three-phase motor with a 180° phase shift is used as the target dual three-phase motor to be driven for description.

[0044] It should be noted that in this invention, the two sets of three-phase windings in the motor are equivalent; one set can be arbitrarily designated as three-phase winding A1B1C1, and the other set as three-phase winding A2B2C2. The following is an example.

[0045] Example 1:

[0046] A four-arm inverter system, such as Figure 4 As shown, it includes: a target dual three-phase motor to be driven and an inverter with four bridge arms; the target dual three-phase motor includes three-phase windings A1B1C1 and A2B2C2, the three phases of the three-phase windings A1B1C1 are A1 phase, B1 phase and C1 phase respectively, and the three phases of the three-phase windings A2B2C2 are A2 phase, B2 phase and C2 phase respectively, and the A1 phase, B1 phase, and C1 phase windings are 180° phase shifted from the A2 phase, B2 phase, and C2 phase windings respectively; the midpoints of the two sets of windings are denoted as N1 and N2 respectively;

[0047] Phase A1 and phase A2 windings are connected together, and phases B1, C1, B2 and C2 windings are connected to the midpoints of the four bridge arms of the inverter, respectively.

[0048] In this embodiment, two windings with a 180° phase difference from each other in the two sets of three-phase windings of the dual three-phase motor are directly connected and not connected to the midpoint of the DC bus capacitor. Therefore, the problem of DC bus capacitor midpoint voltage fluctuation that exists in the traditional four-bridge inverter topology can be effectively avoided. The following is a detailed explanation:

[0049] The fundamental current of a two-phase three-phase motor with a 180° phase shift during normal operation can be expressed as:

[0050]

[0051] In the formula, i A1 i B1 and i C1 Let i represent the phase currents of A1, B1, and C1 in the three-phase winding A1B1C1. A2 i B2 and i C2 Let I represent the phase currents of phases A2, B2, and C2 in the three-phase winding A2B2C2. m Let θ be the phase current amplitude. i Given the phase angle of phase current A1, it is clear that the sum of the two-phase currents with a phase difference of 180° in both sets of three-phase windings is zero, that is:

[0052]

[0053] like Figure 4 As shown, the voltage u to ground at the common connection point A of the A1 and A2 phase windings is... AO It can be represented as:

[0054]

[0055] In the formula, U dc C is the amplitude of the DC bus voltage on the DC side of the inverter, and C is the capacitance of the DC bus capacitor.

[0056] According to formula (3), the voltage at the midpoint of the capacitor is... As changes occur in the vicinity, the fluctuation component depends on the magnitude of the phase currents in phases A1 and A2.

[0057] In this embodiment, since there is a 180° phase shift between the A1 phase winding and the A2 phase winding, according to formula (2), i A1 +i A1 =0, therefore The voltage to ground at the common connection point A of the A1 and A2 phase windings. AO Will be a constant This avoids the impact of capacitor midpoint voltage fluctuations on system control performance.

[0058] Since there is no need to provide the midpoint of the DC bus capacitor in this embodiment, there is no need to use two bus capacitors, thereby reducing the design cost of the system.

[0059] Example 2:

[0060] The control method for the four-arm inverter system provided in Embodiment 1 above includes:

[0061] (S1) The two bridge arms connected to the B1 and C1 phase windings in the inverter are equivalent to a four-switch inverter, and the switching states of the B1 phase bridge arm and the C1 phase bridge arm are controlled according to the space vector modulation method of the four-switch inverter.

[0062] (S2) Control the switching states of phase B2 and phase C2 according to the switching states of phase B1 and phase C1, so that the switching state of phase B2 is always opposite to the switching state of phase B1, and the switching state of phase C2 is always opposite to the switching state of phase C1.

[0063] Among them, the B1 phase bridge arm, C1 phase bridge arm, B2 phase bridge arm and C2 phase bridge arm represent the bridge arms in the inverter that are connected to the B1 phase, C1 phase, B2 phase and C2 phase windings, respectively; the switching states of the bridge arms include the state where the upper tube is on and the lower tube is off, and the state where the upper tube is off and the lower tube is on, and these two states are opposite.

[0064] In this embodiment, the modulation signal expression of the equivalent four-switch inverter in step (S1) is:

[0065]

[0066] In the formula, U m Let θ be the amplitude of the modulated signal. m The phase angle of the modulated signal; This is the modulation signal corresponding to phase B1 bridge arm. These are the modulation signals corresponding to the C1 phase bridge arm;

[0067] Optionally, this embodiment involves... and The two modulation signals are sampled symmetrically according to a rule, and the resulting PWM signals are used as control signals for the B1 and C1 phase bridge arm switches, respectively, thereby determining the switching state of the B1 phase bridge arm and the C1 phase bridge arm; Optionally, in this embodiment, the state in which the upper tube is on and the lower tube is off in the bridge arm is defined as switch state "1", and the state in which the upper tube is off and the lower tube is on is defined as switch state "0".

[0068] In this embodiment, the two sets of three-phase windings in the dual three-phase motor have a 180° phase shift. Therefore, it is necessary to synthesize voltage vectors of equal magnitude and opposite direction in the two sets of three-phase windings. After determining the switching states of phase B1 and phase C1 in step (S1), the switching states of phase B2 and phase C2 can be controlled accordingly. The switching states of phase B2 are always opposite to those of phase B1, and the switching states of phase C2 are always opposite to those of phase C1, thus achieving control of the dual three-phase motor. Specifically, when the switching states of phases B1 and C1 are both "1", the switching states of phases B2 and C2 are both "0". The equivalent circuit diagram under this switching state is shown below. Figure 5 As shown in (a); when the switching states of phases B1 and C1 are "1" and "0" respectively, then the switching states of phases B2 and C2 are "0" and "1" respectively. The equivalent circuit diagram under this switching state is as follows. Figure 5 As shown in (b); when the switching states of phases B1 and C1 are both "0", then the switching states of phases B2 and C2 are both "1". The equivalent circuit diagram under this switching state is as follows. Figure 5 As shown in (c); when the switching states of phases B1 and C1 are "0" and "1" respectively, then the switching states of phases B2 and C2 are "1" and "0" respectively. The equivalent circuit diagram under this switching state is shown in Figure 1. Figure 5 As shown in (d);

[0069] This embodiment ensures that the switching states of phases B2 and B1 are opposite, and the switching states of phases C2 and C1 are also opposite. Therefore, the four-arm inverter only uses the aforementioned four switching states. Figure 5 As shown in the equivalent circuit, the voltage to ground at the connection point A of A1 and A2 is... Therefore, this control method is equivalent to the control method of connecting the four-arm inverter to the midpoint of the DC bus capacitor. That is to say, based on the control method provided in this embodiment, although the winding is not connected to the midpoint of the DC bus, the same control effect can be achieved.

[0070] Example 3:

[0071] The control method for the four-arm inverter system provided in Embodiment 1 above includes:

[0072] (T1) The state where the upper transistor is on and the lower transistor is off in the bridge arm is defined as switch state "1", and the state where the upper transistor is off and the lower transistor is on is defined as switch state "0". The different states of the B1 phase bridge arm, C1 phase bridge arm, B2 phase bridge arm and C2 phase bridge arm in the inverter constitute the 16 switch states of the inverter from "0000" to "1111", and the corresponding 16 voltage vectors are denoted as v0 to v 15 ;

[0073] The spatial distributions of the voltage vectors corresponding to different switching states acting on three-phase windings A1B1C1 and A2B2C2 are as follows: Figure 6 As shown in (a) and (b) in the table, each voltage vector may have different amplitudes and phases in the two sets of three-phase windings, as shown in Table 1.

[0074] Considering that the two sets of three-phase windings are 180° out of phase, when synthesizing the desired voltage on one set of three-phase windings using voltage vectors, it should be ensured that the same voltage vector can be used to synthesize a desired voltage vector with equal amplitude and opposite direction on the other set of three-phase windings; according to Figure 6 As shown in Table 1, among the 16 voltage vectors, due to v5 and v 10 The effects are the same in both sets of three-phase windings, which is not conducive to synthesizing the desired voltage vectors with equal amplitude and opposite direction in both sets of three-phase windings. Therefore, these two voltage vectors will not be used; v1 and v 11 When acting for the same amount of time, the combined vector magnitudes in the two sets of three-phase windings are equal and opposite in direction; v8 and v 13 When acting for the same amount of time, the combined vector magnitudes in the two sets of three-phase windings are equal and opposite in direction; v4 and v 14 When applied for the same duration, the combined vector magnitudes in the two sets of three-phase windings are equal and opposite in direction; when applied for the same duration, the combined vector magnitudes in the two sets of three-phase windings are equal and opposite in direction. Therefore, these four pairs of voltage vectors will be combined into four voltage vectors for use.

[0075] (T2) will combine voltage vectors v1 and v 11 Combined into a voltage vector Translate voltage vectors v8 and v 13 Combined into a voltage vector Put voltage vectors v4 and v 14 Combined into a voltage vector Combine voltage vectors v2 and v7 into a single voltage vector. Translate the voltage vectors v0, v3, v6, v9, v 12 v 15 v1_11 v 8_13 v 4_14 and v 2_7 As the basic voltage vector;

[0076] After steps (T1) and (T2), this embodiment selects effective basic voltage vectors to ensure that when the desired voltage is synthesized on the three-phase winding A1B1C1 using the voltage vector, the same voltage vector can be used to synthesize the desired voltage with the same amplitude and opposite direction on the three-phase winding A2B2C2.

[0077] The spatial distributions of the 10 selected basic voltage vectors acting on the two sets of three-phase windings are as follows: Figure 7 As shown in (a) and (b); according to Figure 7 It can be seen that these 10 basic voltage vectors divide the space into 8 sectors, that is... Figure 7 Sectors I to VIII are defined in the three-phase winding A1B1C1. The spatial angle ranges corresponding to each sector are as follows:

[0078] Sector I: Sector II: Sector III: Sector IV: Sector V: Sector VI: Sector VII: Sector VIII:

[0079] In control, the corresponding sector can be determined based on the angular range to which the spatial angle of the desired voltage vector belongs;

[0080] (T3) Based on the desired voltage vector u s The spatial angle θ is selected for synthesizing the desired voltage vector u. s The basic voltage vectors are determined, and the duration of each basic voltage vector is used as the duration of the corresponding switching state.

[0081] Taking sector I of the three-phase winding A1B1C1 as an example, refer to... Figure 7 As shown in (a), the two fundamental voltage vectors constituting the two sides of this sector are v3 and v2, respectively. 1_11 Desired voltage vector u s In a switching cycle T s The schematic diagram of the synthesis is as follows: Figure 8 As shown, according to the volt-second balance principle, we have:

[0082]

[0083] In the formula, t0, t3, t 1_11 , t15 They are vectors v0, v3, and v 1_11 and v 15 Duration of action;

[0084] according to Figure 8 From the geometric relationships in the diagram, we can obtain:

[0085]

[0086] will|u s |=U s , Substituting equation (5) into equation (6) yields:

[0087]

[0088] In the formula, U s Represents the desired voltage vector u s The amplitude; from equation (7), the amplitude of each basic voltage vector in one switching cycle T can be obtained. s The duration of action of a basic voltage vector is the duration of its corresponding switching state.

[0089] It is easy to understand that for the synthesized basic voltage vector v 1_11 The two corresponding voltage vectors v1 and v 11 The duration of action t1 and t 11 All are v 1_11 Half of, that is

[0090] v0 and v 15 These are two zero vectors in the basic voltage vector, and the durations of these two zero vectors are equal, i.e., t0 = t 15 At this time, the current ripple of the three-phase output is relatively small; as a preferred implementation, in this embodiment, it is preferable to set t0 = t 15 In other embodiments of the present invention, t0 and t 15 It can also be set arbitrarily under the premise of satisfying equation (7).

[0091] The voltage vector synthesis in other sectors is similar and will not be explained in detail here.

[0092] (T4) Control the switching state of each bridge arm according to the determined switching state and duration, so as to synthesize the desired voltage vector with equal amplitude but opposite direction in the two sets of three-phase windings of the target dual three-phase motor.

[0093] Wherein, the B1 phase bridge arm, C1 phase bridge arm, B2 phase bridge arm, and C2 phase bridge arm represent the bridge arms in the inverter that are connected to the B1 phase, C1 phase, B2 phase, and C2 phase windings, respectively; the desired voltage vector u s The desired voltage vector of one set of three-phase windings of the target dual three-phase motor.

[0094] This embodiment utilizes a novel structure where the four-arm inverter is not connected to the midpoint of the DC bus capacitor. By constructing a space voltage vector using almost all switching states, it effectively controls the four-arm inverter system.

[0095] Table 1 Voltage Vectors of Four-Arm Inverters

[0096]

[0097]

[0098] 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 control method for a four-arm inverter system, characterized in that, The four-arm inverter system includes: a target dual three-phase motor to be driven and an inverter with four arms; the target dual three-phase motor includes a three-phase winding A1B1C1 and a three-phase winding A2B2C2, wherein the three phases of the three-phase winding A1B1C1 are A1 phase, B1 phase and C1 phase respectively, and the three phases of the three-phase winding A2B2C2 are A2 phase, B2 phase and C2 phase respectively, and the A1 phase, B1 phase, and C1 phase windings are 180° phase shifted from the A2 phase, B2 phase, and C2 phase windings respectively; Phase A1 winding and phase A2 winding are connected together, and phases B1, C1, B2 and C2 winding are respectively connected to the midpoints of the four bridge arms of the inverter. The control method includes: (S1) The two bridge arms connected to the B1 phase and C1 phase windings in the inverter are equivalent to a four-switch inverter, and the switching states of the B1 phase bridge arm and the C1 phase bridge arm are controlled according to the space vector modulation method of the four-switch inverter. (S2) Control the switching states of phase B2 and phase C2 according to the switching states of phase B1 and phase C1, so that the switching state of phase B2 is always opposite to the switching state of phase B1, and the switching state of phase C2 is always opposite to the switching state of phase C1. Wherein, the B1 phase bridge arm, C1 phase bridge arm, B2 phase bridge arm and C2 phase bridge arm represent the bridge arms in the inverter that are connected to the B1 phase, C1 phase, B2 phase and C2 phase windings, respectively; the switching states of the bridge arms include the state where the upper tube is on and the lower tube is off, and the state where the upper tube is off and the lower tube is on, and these two states are opposite.

2. The control method for the four-arm inverter system as described in claim 1, characterized in that, The target dual three-phase motor is a dual three-phase motor with a phase shift of 180°.

3. The control method for the four-arm inverter system as described in claim 1, characterized in that, The target dual three-phase motor is a dual three-phase motor with a phase shift of 180° formed by reversing one set of three-phase windings in a dual three-phase motor with a phase shift of 0°.

4. The control method for the four-arm inverter system as described in claim 1, characterized in that, The target dual-three-phase motor is a dual-three-phase motor with a phase shift of 180° formed by renaming one set of three-phase windings in a dual-three-phase motor with a phase shift of 60°.

5. A control method for a four-arm inverter system, characterized in that, The four-arm inverter system includes: a target dual three-phase motor to be driven and an inverter with four arms; the target dual three-phase motor includes a three-phase winding A1B1C1 and a three-phase winding A2B2C2, wherein the three phases of the three-phase winding A1B1C1 are A1 phase, B1 phase and C1 phase respectively, and the three phases of the three-phase winding A2B2C2 are A2 phase, B2 phase and C2 phase respectively, and the A1 phase, B1 phase, and C1 phase windings are 180° phase shifted from the A2 phase, B2 phase, and C2 phase windings respectively; Phase A1 winding and phase A2 winding are connected together, and phases B1, C1, B2 and C2 winding are respectively connected to the midpoints of the four bridge arms of the inverter. The control method includes: (T1) The state where the upper transistor is on and the lower transistor is off in the bridge arm is defined as switch state "1", and the state where the upper transistor is off and the lower transistor is on is defined as switch state "0". The different states of the B1 phase bridge arm, C1 phase bridge arm, B2 phase bridge arm, and C2 phase bridge arm in the inverter constitute the 16 switch states "0000" to "1111" of the inverter, and the corresponding 16 voltage vectors are denoted as follows: v 0~ v 15 ; (T2) will change the voltage vector v 1 and v 11 Combined into a voltage vector , to the voltage vector v 8 and v 13 Combined into a voltage vector , to the voltage vector v 4 and v 14 Combined into a voltage vector , to the voltage vector v 2 and v 7. Combined into a voltage vector , to the voltage vector v 0、 v 3. v 6. v 9. v 12 , v 15 , v 1_11 , v 8_13 , v 4_14 and v 2_7 As the basic voltage vector; (T3) Based on the desired voltage vector u s spatial angle θ Selecting the desired voltage vector for synthesis u s The basic voltage vectors are determined, and the duration of each basic voltage vector is used as the duration of the corresponding switching state. (T4) Control the switching state of each bridge arm according to the determined switching state and duration, so as to synthesize the desired voltage vectors with equal amplitude and opposite direction in the two sets of three-phase windings of the target dual three-phase motor. Wherein, the B1 phase bridge arm, C1 phase bridge arm, B2 phase bridge arm, and C2 phase bridge arm represent the bridge arms in the inverter that are connected to the B1 phase, C1 phase, B2 phase, and C2 phase windings, respectively; the desired voltage vector u s Let be the desired voltage vector of one set of three-phase windings of the target dual three-phase motor.

6. The control method for the four-arm inverter system as described in claim 5, characterized in that, The target dual three-phase motor is a dual three-phase motor with a phase shift of 180°.

7. The control method for the four-arm inverter system as described in claim 5, characterized in that, The target dual three-phase motor is a dual three-phase motor with a phase shift of 180° formed by reversing one set of three-phase windings in a dual three-phase motor with a phase shift of 0°.

8. The control method for the four-arm inverter system as described in claim 5, characterized in that, The target dual-three-phase motor is a dual-three-phase motor with a phase shift of 180° formed by renaming one set of three-phase windings in a dual-three-phase motor with a phase shift of 60°.

9. The control method according to any one of claims 5 to 8, characterized in that, The step (T3) includes: Determine the spatial angle θ The sector to which it belongs is selected by choosing the two fundamental voltage vectors that constitute the two sides of the sector. v 'and v ", and the basic voltage vector v 0 and v 15 Used to synthesize the desired voltage vector u s ; Based on the volt-second balance principle and the sine theorem, the duration of action of each selected basic voltage vector is calculated and used as the duration of the corresponding switching state.

10. The control method as described in claim 9, characterized in that, The formula for calculating the volt-second balance principle is: in, T s Indicates the switching cycle; t ′、 t "、 t 0 and t 15 These represent the basic voltage vectors. v ′、 v "、 v 0 and v 15 The duration of action.

11. The control method as described in claim 10, characterized in that, t 0= t 15 。

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