A dual-motor control system with series power supply of two neutral points

Abstract

The present application provides a dual-motor control system with double neutral points in series power supply, including a boost controller, a boost distributor, a first drive controller, a second drive controller, a first modulator and a second modulator; the boost controller outputs an equivalent duty ratio by tracking the target DC bus voltage; the boost distributor distributes the equivalent duty ratio to the average duty ratios of a first permanent magnet synchronous motor and a second permanent magnet synchronous motor using a preset distribution strategy; the two drive controllers respectively generate drive control quantities for the first permanent magnet synchronous motor and the second permanent magnet synchronous motor; the two modulators respectively generate actual control signals for the two permanent magnet synchronous motors and perform closed-loop control on the inverters of the two permanent magnet synchronous motors. The dual-motor control system provided by the present application can perform linked closed-loop control on two permanent magnet synchronous motors with double neutral points in series power supply.

Description

Technical Field

[0001] This application belongs to the technical field of electric drive control for electric vehicles, involves dual-motor drive control technology, and specifically provides a dual-motor control system with dual neutral points in series power supply. Background Technique

[0002] Dual-motor drive is a new type of electric drive mode for electric vehicles. When using dual-motor drive, the sum of the powers of two permanent magnet synchronous motors does not need to reach the power of a single motor to exceed the single motor in performance, and the high-efficiency range of the system can be significantly extended through different coupling methods (torque, speed, dual coupling), improving the efficiency of the motor under conditions such as high speed and light load; in addition, since the two permanent magnet synchronous motors can independently drive the wheels on both sides, the vehicle steering can be assisted through the speed difference and power distribution adjustment between the wheels, thus greatly improving the motion characteristics.

[0003] Currently, most existing dual-motor drive schemes use a DC / DC converter to boost the power supply voltage. The boosting principle of this scheme is intuitive and easy to implement, but it will increase additional devices such as switching tubes and inductors, resulting in an increase in the complexity and volume of the dual-motor drive system; in addition, a dual neutral point series power supply topology can also be used to achieve dual-motor drive. However, in existing research, the boosting mechanism has not been studied in depth, so simple open-loop control is used for the control of the three-phase currents of the two motors, and it cannot ensure independent and stable torque control of the two motors while boosting. Summary of the Invention

[0004] To solve the problems existing in the above-mentioned prior art, this application provides a dual-motor control system with dual neutral points in series power supply for closed-loop combined control of a first permanent magnet synchronous motor and a second permanent magnet synchronous motor with dual neutral points in series power supply, where the positive and negative poles of the power supply are respectively connected to the neutral points of the first permanent magnet synchronous motor and the second permanent magnet synchronous motor, and the two permanent magnet synchronous motors have the same DC bus voltage. This control system includes:

[0005] A boost controller, a boost distributor, a first drive controller, a second drive controller, a first modulator, and a second modulator;

[0006] The boost controller outputs an equivalent duty cycle by tracking the target DC bus voltage;

[0007] The boost distributor distributes the equivalent duty cycle into the average duty cycles of the first permanent magnet synchronous motor and the second permanent magnet synchronous motor using a preset distribution strategy;

[0008] The first drive controller and the second drive controller respectively generate drive control quantities for the first permanent magnet synchronous motor and the second permanent magnet synchronous motor by tracking the target torque;

[0009] The first modulator and the second modulator respectively generate actual control signals for the first permanent magnet synchronous motor and the second permanent magnet synchronous motor based on the average duty cycle and the drive control amount, and use the actual control signals to respectively perform closed-loop control on the inverters of the first permanent magnet synchronous motor and the second permanent magnet synchronous motor.

[0010] Further, the boost controller is a voltage-current double-loop controller, and its control parameters are determined through the following steps:

[0011] S1, establish a boost expression under the double-neutral-point series power supply structure;

[0012] S2, establish an equivalent boost model under the double-neutral-point series power supply structure based on the boost expression;

[0013] S3, obtain the small-signal mathematical model of the equivalent boost model;

[0014] S4, determine the voltage-loop control parameters and current-loop control parameters of the boost controller based on the small-signal mathematical model of the equivalent boost model.

[0015] Further, establish a boost expression under the double-neutral-point series power supply structure through the following steps:

[0016] Based on the circuit topology and averaging theory of the double-neutral-point series power supply structure, determine the 0-axis voltage expressions of the two permanent magnet synchronous motors:

[0017]

[0018] where, u bus is the DC bus voltage, N1 and N2 are the neutral points of the first permanent magnet synchronous motor and the second permanent magnet synchronous motor respectively, O is the grounding point, R S1 are respectively the 0-axis duty cycle, 0-axis voltage, neutral point potential, 0-axis current, 0-axis inductance and stator resistance of the first permanent magnet synchronous motor, R S2 are respectively the 0-axis duty cycle, 0-axis voltage, neutral point potential, 0-axis current, 0-axis inductance and stator resistance of the second permanent magnet synchronous motor;

[0019] Based on equal-power transformation, determine the expressions of the relationship between the 0-axis current and the neutral line current of the two permanent magnet synchronous motors and the expressions of the relationship between the average duty cycle of the three-phase inverter and the 0-axis duty cycle:

[0020]

[0021] where, i N is the neutral line current, They are the average duty cycles of the first permanent magnet synchronous motor and the second permanent magnet synchronous motor respectively;

[0022] Determine the expression for the neutral point potential of the two permanent magnet synchronous motors:

[0023]

[0024] Establish the expression for the supply power source voltage under the double neutral point series power supply structure as shown in the following formula:

[0025]

[0026] where, u in is the supply power source voltage;

[0027] When in steady state, ignoring the differential term and the stator resistance voltage drop, the boost expression under the double neutral point series power supply structure as shown in the following formula is obtained:

[0028]

[0029] where Δα h is the equivalent duty cycle.

[0030] Preferably, the equivalent boost model under the double neutral point series power supply structure includes an equivalent resistor R, an equivalent capacitor C, a first equivalent inverter unit, a second equivalent inverter unit, a first equivalent zero-axis resistor R1, a second equivalent zero-axis resistor R2, a first equivalent zero-axis inductor L1, and a second equivalent zero-axis inductor L2;

[0031] The first equivalent inverter unit includes a first upper switch tube A H and a first lower switch tube A L , and the second equivalent inverter unit includes a second upper switch tube B H and a second lower switch tube B L ;

[0032] where, the first end of the equivalent resistor R, the first end of the equivalent capacitor C, the first end of the first upper switch tube A H , and the first end of the second upper switch B H tube are connected to each other, and the second end of the equivalent resistor R, the second end of the equivalent capacitor C, the second end of the first lower switch tube A L , and the second end of the second lower switch tube B L are connected to each other;

[0033] The second end of the first upper switch tube A H is connected to the first end of the first lower switch tube A L , and the second end of the second upper switch tube B H is connected to the second end of the second lower switch tube B Lis connected to the first end, and the first equivalent zero-axis resistance R1, the first equivalent zero-axis inductor L1, the second equivalent zero-axis inductor L2, and the second equivalent zero-axis resistance R2 are connected in series between the second end of the first upper switching tube and the second end of the second upper switching tube in sequence.

[0034] Further, step S3 obtains the small-signal mathematical model of the equivalent boost model shown in the following formula by performing instantaneous value averaging operation, disturbance separation operation, and linearization operation on the equivalent boost model under the double neutral point series power supply structure:

[0035]

[0036] Among them, are respectively the AC components of the DC bus voltage, DC bus current, power supply voltage, duty ratio of the first equivalent inverter unit, and duty ratio of the second equivalent inverter unit in the small-signal mathematical model. V, I, D1, and D2 are respectively the DC components of the DC bus voltage, DC bus current, duty ratio of the first equivalent inverter unit, and duty ratio of the second equivalent inverter unit in the small-signal mathematical model, and V and the power supply voltage V in the small-signal mathematical model g satisfy the following relationship:

[0037]

[0038] Further, step S4 includes the following steps:

[0039] Perform Laplace transform on the small-signal mathematical model of the equivalent boost model:

[0040]

[0041] where s is the independent variable of the Laplace transform;

[0042] Based on the result of the Laplace transform, obtain the transfer function G vd (s) of the output voltage to the difference in duty ratios of the two inverter units, and the transfer function G id (s) of the power supply current to the difference in duty ratios of the two inverter units:

[0043]

[0044] Let Determine the transfer function G vi (s) of the output voltage to the power supply current shown in the following formula:

[0045]

[0046] Establish the current-loop open-loop transfer function G1(s) and the voltage-loop open-loop transfer function G2(s) shown in the following formula:

[0047]

[0048] Set the expected crossover frequency \(f\) c_i 、\(f\) c_v and phase margin Solve the following equation to obtain the voltage loop control parameters \(k\) v_p 、\(k\) v_i and current loop control parameters \(k\) i_p 、\(k\) i_i :

[0049]

[0050] where \(j\) is the imaginary unit.

[0051] Preferably, the equivalent duty ratio is allocated to the average duty ratios of the first permanent magnet synchronous motor and the second permanent magnet synchronous motor using a preset allocation strategy, specifically:

[0052] Centered on 0.5, the average duty ratio of the first permanent magnet synchronous motor and the average duty ratio of the second permanent magnet tube motor are respectively allocated as \(0.5 + \Delta\alpha\) h / 2 and \(0.5 - \Delta\alpha\) h / 2.

[0053] Furthermore, the actual control signal of the first permanent magnet synchronous motor is shown as follows:

[0054]

[0055] where are the actual duty ratio signals for controlling the A, B, and C phases of the inverter of the first permanent magnet synchronous motor respectively, are the drive control quantities of the A, B, and C phases of the inverter of the first permanent magnet synchronous motor generated by the first drive controller respectively;

[0056] The actual control signal of the second permanent magnet synchronous motor is shown as follows:

[0057]

[0058] where are the actual duty ratio signals for controlling the A, B, and C phases of the inverter of the second permanent magnet synchronous motor respectively, are the drive control quantities of the A, B, and C phases of the inverter of the second permanent magnet synchronous motor generated by the second drive controller respectively.

[0059] An embodiment of the present application provides a dual-motor control system with dual neutral points in series power supply. First, a boost controller tracks the target DC bus voltage to output an equivalent duty cycle. Since the equivalent duty cycle is related to the difference between the average duty cycles of the two inverters, a wider boost range can be obtained compared to a single neutral point boost structure. Then, a boost distributor distributes the equivalent duty cycle to the average duty cycles of the two permanent magnet synchronous motors respectively, and combines them with the drive control quantities generated by the drive controller, finally realizing the linkage closed-loop control of the two permanent magnet synchronous motors with dual neutral points in series power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 It is a schematic diagram of a DC / DC boost drive structure for a dual-motor;

[0061] Figure 2 It is a schematic diagram of a dual neutral points in series power supply structure for a dual-motor;

[0062] Figure 3 It is a schematic diagram of the architecture of a dual-motor control system with dual neutral points in series power supply provided by an embodiment of the present application;

[0063] Figure 4 It is a flowchart for determining the control parameters of the boost controller provided by an embodiment of the present application;

[0064] Figure 5 It is a schematic diagram of an equivalent boost model of a dual neutral points in series power supply structure provided by an embodiment of the present application;

[0065] Figure 6 It is a schematic diagram of the current of an equivalent boost model of a dual neutral points in series power supply structure in the 11, 00 switch states provided by an embodiment of the present application;

[0066] Figure 7 It is a schematic diagram of the current of an equivalent boost model of a dual neutral points in series power supply structure in the 10, 01 switch states provided by an embodiment of the present application;

[0067] Figure 8 It is a timing diagram of the switch state distribution of an equivalent boost model of a dual neutral points in series power supply structure provided by an embodiment of the present application;

[0068] Figure 9 It is a schematic diagram of the voltage-current double-loop control of the boost controller provided by an embodiment of the present application;

[0069] Figure 10 It is a schematic diagram of the principle of dq-axis drive control provided by an embodiment of the present application;

[0070] Figure 11 It is the output result of the torque and speed of the two motors in Embodiment 1 of the present application;

[0071] Figure 12 This is the output result of the three-phase currents, neutral line current, and bus voltage of the two motors in Embodiment 1 of the present application;

[0072] Figure 13 This is the change situation of the bus voltage, neutral line current, and three-phase currents of the two motors in Embodiment 2 of the present application. Detailed implementation manners

[0073] Hereinafter, the present application will be further described based on preferred implementation manners with reference to the accompanying drawings.

[0074] In the description of the embodiments of the present application, it should be noted that if terms such as "upper", "lower", "inner", "outer", etc. are used to indicate the orientation or positional relationship, it is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship when the products in the embodiments of the present application are usually placed. This is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present application. In addition, in the description of the present application, in order to distinguish different units, the terms "first", "second", etc. are used in this specification, but these are not limited by the manufacturing sequence and should not be construed as indicating or implying relative importance. In the detailed description and claims of the present application, their names may be different.

[0075] The terms in this specification are used to describe the embodiments of the present application, but are not intended to limit the present application. It should also be noted that unless otherwise clearly defined and limited, if terms such as "set", "connected", "coupled" are used, they should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, a direct connection, or an indirect connection through an intermediate medium, and it can be the communication inside two elements. For those skilled in the art, the specific meanings of the above terms in the present application can be specifically understood.

[0076] As described in the background art, currently, the dual-motor drive scheme for electric vehicles can adopt Figure 1 the DC / DC boost drive architecture shown in Figure 2 and the drive architecture with dual neutral point power supply shown in

[0077] Figure 2 The shown Double Neutral Point Supply Structure (DNPSS), the positive and negative poles of the power supply are respectively connected to the neutral points of two permanent magnet synchronous motors (in the embodiments of the present application, for ease of description, the permanent magnet synchronous motor corresponding to the neutral point connected to the positive pole of the power supply is marked as the first permanent magnet synchronous motor, and the permanent magnet synchronous motor corresponding to the neutral point connected to the negative pole of the power supply is marked as the second permanent magnet synchronous motor), and the two permanent magnet synchronous motors have the same DC bus voltage.

[0078] This dual-motor drive structure can achieve torque output by controlling the dq-axis currents of the three-phase inverters on both sides. At the same time, by controlling the size of the zero-axis duty ratios on both sides, the bus voltage can be stabilized at the desired value. The drive and boost control can be regarded as decoupled, and this structure can also reduce the neutral line current ripple compared with the single neutral point power supply structure, so it has good application prospects.

[0079] However, for this structure, existing research has not clearly elaborated its boost mechanism, and simple open-loop control is used for the control of the three-phase currents, which cannot ensure stable torque control of the two motors while boosting.

[0080] Therefore, the present application provides a dual-motor control system with double neutral point series power supply to achieve closed-loop combined control of the two permanent magnet synchronous motors with double neutral point series power supply. Figure 3 It is a frame schematic diagram of the dual-motor control system with double neutral point series power supply provided by the present application.

[0081] As Figure 3 shown, this dual-motor control system includes a boost controller, a boost distributor, two drive controllers (the first drive controller, the second drive controller), and two modulators (the first modulator, the second modulator).

[0082] Among them, the input quantity of the boost controller includes the target DC bus voltage and u bus , and by comparing the difference between the two, the real-time tracking of the target DC bus voltage is achieved, and the equivalent duty ratio (i.e., the following α h1 -α h2 ) is output. This equivalent duty ratio is distributed by the boost distributor into the average duty ratio α h1 of the first permanent magnet synchronous motor and the average duty ratio α h2 of the second permanent magnet synchronous motor according to a preset distribution strategy.

[0083] The first drive controller (such as Figure 3The (shown by the dashed box in the upper left corner) receives the target torque Te1 of the first permanent magnet synchronous motor and tracks it in real time to generate the drive control quantity of the first permanent magnet synchronous motor. Correspondingly, the second drive controller (such as Figure 3 The (shown by the dashed box in the upper right corner) receives the target torque Te2 of the second permanent magnet synchronous motor and tracks it in real time to generate the drive control quantity of the second permanent magnet synchronous motor.

[0084] The first modulator (shown by the box below the first drive controller) generates the actual control signal of the first permanent magnet synchronous motor according to the received α h1 、 According to the preset modulation strategy (such as the ZSVIPWM modulation strategy). The above actual control signal is specifically the duty cycle signal for switching the switching states of the power devices of each phase of the first permanent magnet synchronous motor inverter ( Figure 3 Inverter 1 in it). By using the above actual control signal to control the switching states of the power devices of each phase, the closed-loop control of the inverter of the first permanent magnet synchronous motor can be achieved; correspondingly, the second modulator (shown by the box below the second drive controller) generates the actual control signal of the second permanent magnet synchronous motor according to the received α h2 、 According to the preset modulation strategy. And use the above actual control signal to achieve the closed-loop control of the inverter (Inverter 2) of the second permanent magnet synchronous motor.

[0085] The following will combine the accompanying drawings to detail the specific implementation manners of the above-mentioned functional units.

[0086] [Boost Driver and Its Design Process]

[0087] It is known that when a single permanent magnet synchronous motor is powered by a neutral point power supply topology, different multiples of boost effects can be achieved by changing the duty cycle of the switching signals of each switch tube of the three-phase inverter. For two permanent magnet synchronous motors powered by double neutral points in series, as Figure 2 shown, their neutral points are respectively connected to the positive and negative poles of the power supply. The boost mechanism is more complex than that of the single-motor neutral point power supply topology. Therefore, it is necessary to construct an effective boost model on the basis of clarifying the boost mechanism of this topology to ensure the reasonable setting of the control parameters of the boost driver so that it can accurately regulate the DC bus voltage.

[0088] In some embodiments of the present application, as Figure 4 shown, its control parameters are determined through the following steps:

[0089] S1. Establish the boost expression under the double neutral point series power supply structure;

[0090] S2. Establish the equivalent boost model under the double neutral point series power supply structure based on the boost expression;

[0091] S3. Obtain the small-signal mathematical model of the equivalent boost model;

[0092] S4. Determine the voltage loop control parameters and current loop control parameters of the boost controller based on the small-signal mathematical model of the equivalent boost model.

[0093] a. Derive the boost expression of the DNPSS structure

[0094] According to Figure 2 the topological structure, the average motor models of the first permanent magnet synchronous motor and the second permanent magnet synchronous motor can be expressed by equations (1) and (2):

[0095]

[0096] where, as Figure 2 shown, the subscript O represents the grounding point, the subscripts N1 and N2 represent the neutral points of the first permanent magnet synchronous motor and the second permanent magnet synchronous motor respectively, the subscripts A1, B1, C1 represent the connection points of the upper and lower switching tubes of each phase of the inverter of the first permanent magnet synchronous motor, and the subscripts A2, B2, C2 represent the connection points of the upper and lower switching tubes of each phase of the inverter of the second permanent magnet synchronous motor.

[0097] Furthermore, equations (3) and (4) can be obtained from the coordinate transformation formula:

[0098]

[0099] where, the subscripts d1, q1, 01 represent the d-axis, q-axis, and 0-axis components of the first permanent magnet synchronous motor respectively, and the subscripts d2, q2, 02 represent the d-axis, q-axis, and 0-axis components of the second permanent magnet synchronous motor respectively.

[0100] Then the 0-axis voltages of the first permanent magnet synchronous motor and the second permanent magnet synchronous motor can be expressed by equations (5) and (6):

[0101]

[0102] where, R S1 are respectively the 0-axis duty ratio, 0-axis current, 0-axis inductance, and stator resistance of the first permanent magnet synchronous motor, R S2 are respectively the 0-axis duty ratio, 0-axis current, 0-axis inductance, and stator resistance of the second permanent magnet synchronous motor.

[0103] According to the equal-power transformation, the zero-axis currents of the two permanent magnet synchronous motors shown in Equation (7-1) can be obtained. The relationship with the neutral line current i N , and the average duty ratios of the two permanent magnet synchronous motors shown in Equation (7-2) (i.e., the average duty ratio of the inverter) The relationship with the zero-axis duty ratio is as follows:

[0104]

[0105]

[0106] The two neutral point potentials can be expressed by Equations (8) and (9):

[0107]

[0108]

[0109] According to (8) and (9), the expression (10) of the power supply voltage u in can be obtained:

[0110]

[0111] In the steady state, ignoring the differential term and the stator resistance voltage drop, the boost expression (11) for boosting the power supply voltage u in to the DC bus voltage u bus in the double-neutral-point power supply topology can be obtained:

[0112]

[0113] Δα h in the above formula is defined as the equivalent duty ratio. It can be seen from Equation (11) that for the double-neutral-point series power supply topology, by controlling the equivalent duty ratio Δα h , that is, the difference between the average duty ratios and of the inverters of the two permanent magnet synchronous motors, the boost multiple of the DC bus voltage can be controlled. That is, when ignoring the differential term and the stator resistance voltage drop, it has the characteristic equivalent to the boost duty ratio in the single-motor neutral point boost drive architecture as a whole.

[0114] b. Establish an equivalent boost model

[0115] According to the above boost expression (11), which reflects the relationship between the DC bus voltage and the difference in the average duty cycles of the two inverters. Obviously, different from the neutral point boost method of a single motor, the closer the average duty cycles of the two inverters are, the higher the boost effect can be obtained. Therefore, compared with the single neutral point boost structure, this topology can achieve a wider boost range.

[0116] In addition, during the actual control process, in order to achieve a better response effect, it is necessary to determine the type and control parameters of the boost controller according to the above boost mechanism. Therefore, it is necessary to first establish an equivalent boost model for the double neutral point series power supply structure.

[0117] In some embodiments, as Figure 5 shown, the equivalent boost model under the double neutral point series power supply structure includes an equivalent resistance R, an equivalent capacitance C, a first equivalent inverter unit, a second equivalent inverter unit, a first equivalent zero-axis resistance R1, a second equivalent zero-axis resistance R2, a first equivalent zero-axis inductor L1, and a second equivalent zero-axis inductor L2.

[0118] Specifically, the first equivalent inverter unit includes a first upper switch tube A H and a first lower switch tube A L , and the second equivalent inverter unit includes a second upper switch tube B H and a second lower switch tube B L ; among them, the first end of the equivalent resistance R, the first end of the equivalent capacitance C, the first end of the first upper switch tube A H , and the first end of the second upper switch B H are connected to each other, and the second end of the equivalent resistance R, the second end of the equivalent capacitance C, the second end of the first lower switch tube A L , and the second end of the second lower switch tube B L are connected to each other; the second end of the first upper switch tube A H is connected to the first end of the first lower switch tube A L , the second end of the second upper switch tube B H is connected to the first end of the second lower switch tube B L , and the first equivalent zero-axis resistance R1, the first equivalent zero-axis inductor L1, the second equivalent zero-axis inductor L2, and the second equivalent zero-axis resistance R2 are connected in series between the second end of the first upper switch tube and the second end of the second upper switch tube in sequence.

[0119] Figure 5 In the equivalent boost model shown, A H A L , B H B L are complementary and symmetric to each other. For example, taking 1 to represent the upper tube on and 0 to represent the lower tube on (such as the 10 switch state, representing A H and B LWhen it is turned on, there are a total of four switching states: 11, 00, 10, and 01.

[0120] c. Derive the small-signal mathematical model of the equivalent boost model

[0121] Based on the above equivalent boost model, its small-signal mathematical model can be established, and based on this, a voltage-current double-loop controller can be designed to improve the boost dynamic performance.

[0122] The establishment of the small-signal model generally consists of three steps: instantaneous value averaging, disturbance separation, and linearization.

[0123] I. Instantaneous value averaging, that is, for various variables x(t), as shown in Equation (12), the average value over a switching period Ts is used to replace the instantaneous value to eliminate high-frequency switching ripples:

[0124]

[0125] As Figure 6 shown, in the 11 and 00 switching states, the circuits corresponding to the two switching states are exactly the same. According to Kirchhoff's voltage law and current law, the following equations (13) and (14) can be established:

[0126]

[0127] Among them, v(t), i(t), v g (t), i C (t) are the DC bus voltage, source current, source voltage, and current of capacitor C, respectively.

[0128] Similarly, as Figure 7 shown, in the 10 and 01 states, the circuits corresponding to the two switching states are basically the same, only the direction of the capacitor is opposite. It can be analyzed in the same way. And when the carriers of the two permanent magnet synchronous motors on both sides are in phase, the 01 state does not appear. Here, only the circuit in the 10 state is analyzed, and equations (15) and (16) can be established:

[0129]

[0130]

[0131] II. Disturbance separation:

[0132] Separate the DC quantity and the AC quantity for consideration. Taking the case where the carriers are in phase as shown in Figure 8 as an example, calculate the switching time of each state to obtain Equation (17):

[0133]

[0134] Among them, D1 and D2 respectively represent the DC components of the duty cycles of the first equivalent inverter unit and the second equivalent inverter unit in the small-signal mathematical model.

[0135] The variables of concern are divided into DC components and AC components:

[0136]

[0137] Among them, the DC components of each variable are represented by capital letters, and the AC components of each variable are represented by lowercase letters with a caret.

[0138] According to equations (13), (15), (17), and (18), through integration by parts, equation (19) is obtained:

[0139]

[0140] By making the DC components corresponding equal, equation (20) is obtained:

[0141]

[0142] At steady state, the differential component is zero: V g -(D1 - D2)V = 0, and equation (21) can be obtained:

[0143]

[0144] This is consistent with the boost expression (11) of the DNPSS structure derived previously.

[0145] By making the AC components corresponding equal, equation (22) is obtained:

[0146]

[0147] Similarly, for equations (14) and (16), the same treatment is performed, and equation (23) is obtained:

[0148]

[0149] By making the DC components corresponding equal, equation (24) is obtained:

[0150]

[0151] At steady state, the differential components of the system are zero, and equations (25) and (26) are obtained:

[0152]

[0153]

[0154] By making the AC components corresponding equal, equation (27) is obtained:

[0155]

[0156] III. Linearization:

[0157] When the amplitude of the AC small signal is much smaller than the DC value, the second-order differential components in Equations (23) and (27) can be discarded, and the following differential equation (28) can be obtained:

[0158]

[0159] d. Determine the control parameters of the boost controller

[0160] By establishing the above small-signal mathematical model, the boost controller can be designed and its control parameters can be determined. In the embodiments of the present application, as Figure 9 shown, the boost controller adopts a voltage-current double-loop controller architecture, and its control parameters can be determined based on the transfer function characteristics of its voltage outer loop and current inner loop

[0161] First, perform a Laplace transform on Equation (28) to obtain Equation (29):

[0162]

[0163] where s is the independent variable of the Laplace transform.

[0164] The transfer function G vd (s) of the difference in the duty cycles of the two inverter units can be obtained through Equation (29), and the transfer function G id (s) from the power supply current to the difference in the duty cycles of the two inverter units:

[0165]

[0166]

[0167] According to Equations (21) and (26), let The transfer function G vi (s) from the output voltage to the power supply current can be obtained:

[0168]

[0169] The PI parameter tuning can be designed according to the desired crossover frequency and phase margin of the open-loop transfer function of the two control loops. Among them,

[0170] The open-loop transfer function of the current loop is as shown in Equation (33):

[0171]

[0172] The open-loop transfer function of the voltage loop is as shown in Equation (34):

[0173]

[0174] According to the open-loop transfer function, the PI parameters can be designed based on the desired crossover frequency f c_i 、f c_v and phase margin Specifically, list the following equation (35) and solve it to obtain the voltage-loop control parameters k v_p 、k v_i of the boost controller and the current-loop control parameters k i_p 、k i_i :

[0175]

[0176] In the above formula, j is the imaginary unit.

[0177] [Distribute the average duty cycle]

[0178] The boost controller outputs an equivalent duty cycle Δα by tracking the target bus DC voltage h . Obviously, for each determined value of Δα h , different can be respectively allocated to the first permanent magnet synchronous motor and the second permanent magnet synchronous motor. For example, when Δα h = 0.3, one can choose or However, since the upper and lower limits of the average duty cycle of each permanent magnet synchronous motor are both [0, 1], if the allocated to the two permanent magnet synchronous motors deviates from the median value, although it can meet the constraint of making , it will cause the zero-sequence voltage of one side of the motor to be too large, reducing the DC voltage utilization rate of the corresponding motor and thus reducing the power output ability.

[0179] Therefore, in some preferred embodiments of the present application, as Figure 3 shown, the preset distribution strategy adopted by the boost distributor is specifically: centered on 0.5, the average duty cycle of the first permanent magnet synchronous motor and the average duty cycle of the second permanent magnet tubular motor are respectively allocated as 0.5 + Δα h / 2 and 0.5 - Δα h / 2.

[0180] Through this distribution strategy, the duty cycles of the two-side inverters are symmetric about 0.5, controlling the zero-sequence voltages of the two-side inverters to shift in opposite directions at the same speed. Such an operation is simple and can achieve good control.

[0181] [Drive controller and its design process]

[0182] The first drive controller and the second drive controller are used to track the target torques Te1 and Te2 of the first permanent magnet synchronous motor and the second permanent magnet synchronous motor and form drive control quantities for the first permanent magnet synchronous motor. Specifically, the torque command Te1 is obtained by combining the dq-axis current distribution strategy and Then it is compared with the actual value, and the control quantity u * d1 、u * q1 and u * d2 、u * q2 are further obtained through PI control. After coordinate transformation, the drive control quantities of each phase of the inverters of the two permanent magnet synchronous motors are obtained and

[0183] Figure 10 Figure 5 shows a schematic diagram of the principle of dq-axis drive control in some embodiments. As Figure 10 shown, the drive controller can adopt a traditional internal model controller architecture. The transfer function of the PI controller is:

[0184]

[0185] where K p_d 、K p_q are the proportional gains of the d-axis and q-axis PI controllers respectively, and K i_d 、K i_q are the integral gains of the d-axis and q-axis PI controllers respectively.

[0186] According to the principle of internal model control, the transfer function of the controller should be:

[0187]

[0188] where α is the control bandwidth designed for the dq-axis current loop.

[0189] Comparing Equation (35) and Equation (36), the parameters of the PI controller can be tuned to:

[0190]

[0191] [Generate actual control signal]

[0192] The average duty cycles α h1 and of the first permanent magnet synchronous motor and the average duty cycles α h2 and After that, the first modulator and the second modulator respectively determine the actual control signals for each phase of the inverters of the first permanent magnet synchronous motor and the second permanent magnet synchronous motor based on the following equations (38) and (39):

[0193]

[0194]

[0195] Wherein, are the actual duty cycle signals for controlling the A, B, and C phases of the inverter of the first permanent magnet synchronous motor respectively, are the actual duty cycle signals for controlling the A, B, and C phases of the inverter of the second permanent magnet synchronous motor respectively.

[0196] According to the above actual duty cycle signals, the switching tubes of the inverters of the two permanent magnet synchronous motors can be switched on and off, and the boost-drive control of the two permanent magnet synchronous motors can be realized.

[0197] [Embodiment 1]

[0198] This embodiment is a simulation embodiment, and a dual-motor control system with double neutral points in series is constructed using the system architecture shown in Figure 3 The system simulation parameters are shown in Table 1.

[0199] Table 1 Embodiment 1 Simulation Parameter Settings

[0200] Parameter Symbol Value Unit Number of pole pairs p0 4 - Stator resistance Rs 0.07 Ω d-axis inductance Ld 1.7 mH q-axis inductance Lq 3.4 mH 0-axis inductance L0 2.4 mH Permanent magnet flux linkage ψf 0.0553 Wb Switching frequency fw 10 kHz Supply voltage uin 60 V Target bus voltage ubus 120 V

[0201] Figure 11 shows the output results of the torque and speed of the two motors. Through Figure 11 it can be seen that by using the dual-motor control system provided by the present application, the torque can be continuously and stably output, and good control of the two motors on both sides can be achieved.

[0202] Figure 12 shows the output results of the three-phase currents, neutral line current, and bus voltage of the two motors. Through Figure 12 it can be seen that the three-phase currents have good sinusoidality, and the ripple amplitude of the neutral line current is relatively small, about 2A.

[0203] [Embodiment 2]

[0204] This embodiment simulates the dual-motor control during the dynamic regulation of the motor speed. Among them, the input power supply u in is 60V, the target value is 120V, and the two motors simultaneously experience the acceleration and deceleration processes at 0.1s and 0.25s, Figure 13 shows the bus voltage tracking, neutral line current, and the changes in the three-phase currents of the two motors, as shown in Figure 13As shown, the magnitude of the busbar voltage remains stable throughout the process, and the neutral line current fluctuates very little.

[0205] The specific implementation manners of the present application have been introduced in detail above. For those skilled in the art of this technology, without departing from the principle of the present application, several improvements and modifications can still be made to the present application, and these improvements and modifications also fall within the protection scope of the claims of the present application.

Claims

1. A dual-motor control system with dual neutral point series power supply, used for closed-loop joint control of a first permanent magnet synchronous motor and a second permanent magnet synchronous motor with dual neutral point series power supply, wherein the positive and negative poles of the power supply are respectively connected to the neutral points of the first permanent magnet synchronous motor and the second permanent magnet synchronous motor, and the two permanent magnet synchronous motors have the same DC bus voltage, characterized in that: include: A boost controller, a boost distributor, a first drive controller, a second drive controller, a first modulator and a second modulator; The boost controller outputs an equivalent duty cycle by tracking the target DC bus voltage; The boost distributor distributes the equivalent duty cycle as an average duty cycle of the first permanent magnet synchronous motor and the second permanent magnet synchronous motor using a preset distribution strategy; The first drive controller and the second drive controller respectively generate drive control quantities of the first permanent magnet synchronous motor and the second permanent magnet synchronous motor by tracking the target torque; The first modulator and the second modulator respectively generate actual control signals of the first permanent magnet synchronous motor and the second permanent magnet synchronous motor based on the average duty cycle and the drive control amount, and use the actual control signals to perform closed-loop control on the inverters of the first permanent magnet synchronous motor and the second permanent magnet synchronous motor respectively; The boost controller is a voltage-current dual-loop controller, and its control parameters are determined by the following steps: S1, establish the boost expression under the double neutral point series power supply structure; S2, establishing an equivalent boost model under a double neutral point series power supply structure based on the boost expression; S3, obtaining a small signal mathematical model of the equivalent boost model; S4, determining a voltage loop control parameter and a current loop control parameter of the boost controller based on a small signal mathematical model of the equivalent boost model; The voltage boost expression under the double neutral point series power supply structure is established through the following steps: Based on the circuit topology and average theory of the double neutral point series power supply structure, the 0-axis voltage expression of the two permanent magnet synchronous motors is determined: Among them, u bus is the DC bus voltage, N1 and N2 are the neutral points of the first permanent magnet synchronous motor and the second permanent magnet synchronous motor respectively, O is the grounding point, R S1 are the 0-axis duty cycle, 0-axis voltage, neutral point potential, 0-axis current, 0-axis inductance and stator resistance of the first permanent magnet synchronous motor, respectively. R S2 are the 0-axis duty cycle, 0-axis voltage, neutral point potential, 0-axis current, 0-axis inductance and stator resistance of the second permanent magnet synchronous motor respectively; Based on equal power conversion, the expression of the relationship between the 0-axis current and the neutral line current of the two permanent magnet synchronous motors and the expression of the relationship between the average duty cycle of the three-phase inverter and the 0-axis duty cycle are determined: Among them, i N is the neutral current, are the average duty cycles of the first permanent magnet synchronous motor and the second permanent magnet synchronous motor respectively; The expression for determining the neutral point potential of two permanent magnet synchronous motors is: The expression of the power supply voltage under the double neutral point series power supply structure is established as shown in the following formula: Among them, u in is the power supply voltage; Ignoring the differential term and stator resistance voltage drop in steady state, the boost expression under the double neutral point series power supply structure is obtained as shown in the following formula: where Δα h is the equivalent duty cycle; The equivalent boost model under the dual neutral point series power supply structure includes an equivalent resistor R, an equivalent capacitor C, a first equivalent inverter unit, a second equivalent inverter unit, a first equivalent zero-axis resistor R1, a second equivalent zero-axis resistor R2, a first equivalent zero-axis inductor L1 and a second equivalent zero-axis inductor L2; The first equivalent inverter unit includes a first upper switch tube A H and the first lower switch tube A L The second equivalent inverter unit includes a second upper switch tube B H And the second lower switch tube B L ; Among them, the first end of the equivalent resistor R, the first end of the equivalent capacitor C, the first upper switch tube A H The first end of the second upper switch B H The first ends of the tubes are connected to each other, the second end of the equivalent resistor R, the second end of the equivalent capacitor C, the first lower switch tube A L The second end of the second lower switch tube B L The second ends of the ??are connected to each other; The first upper switch tube A H The second end of the first lower switch tube A L The first end is connected to the second upper switch tube B H The second end of the second lower switch tube B L A first end of the first upper switch tube is connected, a first equivalent zero-axis resistor R1, a first equivalent zero-axis inductor L1, a second equivalent zero-axis inductor L2, and a second equivalent zero-axis resistor R2 are sequentially connected in series between the second end of the first upper switch tube and the second end of the second upper switch tube; Step S3 performs instantaneous value averaging operation, disturbance separation operation and linearization operation on the equivalent boost model under the double neutral point series power supply structure to obtain a small signal mathematical model of the equivalent boost model as shown in the following formula: in, are the AC components of the DC bus voltage, DC bus current, power supply voltage, duty cycle of the first equivalent inverter unit, and duty cycle of the second equivalent inverter unit in the small signal mathematical model, respectively. V, I, D1, and D2 are the DC components of the DC bus voltage, DC bus current, duty cycle of the first equivalent inverter unit, and duty cycle of the second equivalent inverter unit in the small signal mathematical model, respectively. V is proportional to the power supply voltage V in the small signal mathematical model. g The following relations are satisfied:

2. The dual-motor control system with dual neutral point series power supply according to claim 1 is characterized in that: Step S4 further comprises the following steps: The small signal mathematical model of the equivalent boost model is Laplace transformed: Where s is the independent variable of Laplace transform; Based on the result of pull-type conversion, the transfer function G from the output voltage to the difference in duty cycle of the two inverter units is obtained as shown in the following formula: vd (s), and the transfer function G from the power supply current to the difference in duty cycle of the two inverter units id (s): make Determine the output voltage to supply current transfer function G as shown below vi (s): The current loop open-loop transfer function G1(s) and the voltage loop open-loop transfer function G2(s) are established as shown in the following equations: Set the desired crossover frequency f c_i 、f c_v and phase margin Solve the following equation to obtain the voltage loop control parameter k of the boost controller: v_p , k v_i and current loop control parameter k i_p , k i_i : Here, j is an imaginary unit.

3. The dual-motor control system with dual neutral point series power supply according to claim 1, characterized in that: The use of a preset allocation strategy to allocate the equivalent duty cycle as an average duty cycle of the first permanent magnet synchronous motor and the second permanent magnet synchronous motor is specifically: Centered on 0.5, the average duty cycle of the first permanent magnet synchronous motor and the average duty cycle of the second permanent magnet motor They are respectively distributed as 0.5+Δα h / 2 and 0.5-Δα h / 2.

4. The dual-motor control system with dual neutral point series power supply according to claim 1, characterized in that: The actual control signal of the first permanent magnet synchronous motor is shown as follows: in, are respectively actual duty cycle signals for controlling phases A, B, and C of the inverter of the first permanent magnet synchronous motor, A, B, and C phase drive control quantities of the inverter of the first permanent magnet synchronous motor generated by the first drive controller respectively; The actual control signal of the second permanent magnet synchronous motor is shown as follows: in, are respectively actual duty cycle signals for controlling phases A, B, and C of the inverter of the second permanent magnet synchronous motor, The A, B, and C phase drive control quantities of the inverter of the second permanent magnet synchronous motor are respectively generated by the second drive controller.

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