Design method of six-phase inverter with superposed alternating current and direct current

Abstract

The invention relates to the technical field of motor driving, and discloses an alternating current and direct current superposed six-phase inverter design method, which comprises the steps of superposing direct current excitation and alternating current armature current on the same winding through a six-phase inverter, constructing a double three-phase cascade inverter topology, modulating a magnetic circuit, performing dynamic field weakening control, performing double-loop PI control and activating a high output mode. And the function design of each module of the six-phase inverter, such as robustness optimization and efficiency optimization control, is adopted, so that wide-speed-range high-efficiency driving is realized. According to the invention, a six-phase AC-DC superposition inversion topology is provided, a traditional three-phase control algorithm is compatible, efficient superposition of AC and DC in the same winding is realized through a dual-three-phase cascade structure and a voltage superposition mechanism, a basis is provided for wide-speed-range operation of the motor, single-winding dual-function is realized through virtual current reconstruction, and the efficiency of the motor is improved. Six-phase current is converted into virtual three-phase current, interference of direct-current components on a control algorithm is eliminated, and meanwhile, control strategies such as a high-output mode and robustness optimization are combined, so that the motor can keep good performance under different working conditions.

Description

Technical Field

[0001] This invention belongs to the field of motor drive technology, specifically relating to a design method for a six-phase inverter with superimposed AC and DC currents. Background Technology

[0002] Driven by the global energy transition and the "dual carbon" goal, the new energy vehicle industry has entered a stage of rapid development. The performance of its core power system, the drive motor, directly determines the vehicle's range, power response, and operational stability. As a key power electronic device connecting the power battery and the drive motor, the inverter is the core link to achieve efficient power conversion and precise motor control. Its topology and control strategy have become key research directions for breaking through the performance bottleneck of the drive system.

[0003] Existing drive systems mostly use three-phase inverter topologies. Their core drawback is that they cannot achieve superposition control of AC and DC currents. They can only output AC armature current. If excitation is required, an independent excitation winding or a permanent magnet must be configured. This results in a complex system structure, insufficient control flexibility, and difficulty in adapting to the dynamic adjustment requirements of magnetic flux in a wide speed range.

[0004] Existing technologies optimize the local performance of inverters, but none of them have overcome the contradiction between "efficiency and torque density in a wide speed range". Either the torque output is insufficient under low-speed and high-load conditions, or the efficiency drops sharply in the high-speed range. Furthermore, they have not solved problems such as deterioration of control accuracy and multi-harmonic interference caused by magnetic circuit saturation, and cannot provide stable support for drive motors under all operating conditions.

[0005] In summary, traditional inverter topologies and control strategies are no longer adequate for the demands of next-generation high-performance drive motors. The industry urgently needs an inverter design that can achieve coordinated AC and DC current control, balance wide-speed-range efficiency and torque density, and possess high robustness to fill existing technological gaps and drive performance upgrades in new energy vehicle drive systems. Summary of the Invention The purpose of this invention is to utilize the working principle of a current superposition variable flux motor, and to superimpose DC excitation and AC armature current onto the same winding through a six-phase inverter. This invention constructs a dual three-phase cascaded inverter topology, and designs the functional modules of the six-phase inverter, including magnetic circuit modulation, dynamic field weakening control, dual-loop PI control, high output mode activation, robust optimization, and efficiency optimization control, thereby achieving high-efficiency drive over a wide speed range.

[0006] Based on the above concept, the technical solution adopted by this invention is as follows: The design method of a six-phase inverter with superimposed AC and DC currents includes superimposing DC excitation and AC armature current on the same winding in a six-phase inverter, constructing a dual three-phase cascaded inverter topology, magnetic circuit modulation, dynamic field weakening control, dual-loop PI control, high output mode activation, and robust optimization and efficiency optimization control, etc., to achieve high-efficiency drive over a wide speed range.

[0007] Preferably, the structure employs two sets of independent three-phase inverters to form a dual three-phase cascaded structure, wherein the forward bias group corresponds to phases A, C, and E, and the output voltages are V, respectively. u +V dc V v +V dc and V w +V dc The negative bias group corresponds to phases B, D, and F, with output voltages of V respectively. u -V dc V v -V dc and V w -V dc , where V u V v and V w These are the AC voltages of phase U, phase V, and phase W in the three-phase AC voltage components, respectively. dc This is the DC bias voltage.

[0008] Preferably, the dual three-phase cascaded structure further includes a power module and a control core.

[0009] Preferably, the Hall current sensor acquires the current signals of phases A, B, C, D, E, and F in real time, including I... A I D I B I E I C and I F , Preferably, the current signal is transmitted to the DSP after filtering, amplification, and analog-to-digital conversion, according to I. U =I A +I D I V =I B +I E and I W =I C +I F The relationship reconstructs the six-phase current into a virtual three-phase current, eliminating the interference of the DC component on the control algorithm, where I U I V and I W These are the AC currents of the U-phase, V-phase, and W-phase components of the three-phase AC voltage, respectively.

[0010] Preferably, SVM modulation is performed on the positive and negative bias groups of the dual three-phase cascaded topology, with a phase offset angle of 30°.

[0011] Preferably, the reconstructed virtual three-phase current is subjected to Park transformation and decomposed into d-axis and q-axis currents.

[0012] Preferably, the d-axis current is dynamically adjusted using a PI controller to optimize the AC / DC current ratio. The d-axis current adjustment formula is as follows:

[0013]

[0014] in, For speed command, The actual measured speed of the encoder. For proportional gain, This is the integral gain.

[0015] Preferably, when the motor speed is greater than the base speed, the DC bias voltage is adjusted using a formula, the specific formula of which is:

[0016] in, As the reference speed, The weak magnetic coefficient, Simultaneously satisfying the constraints

[0017] and

[0018] Where L d L q These are right-angle axis inductors, and V is the dq-axis current. max For the maximum voltage, I max This is the maximum current.

[0019] Preferably, the six-phase inverter includes a data acquisition module, a control core, and a power module.

[0020] Preferably, the data acquisition module includes a Hall current sensor and a photoelectric encoder.

[0021] Preferably, the magnetic field modulation and DC component generate a 6-pole fixed magnetomotive force, and the AC component generates a 4-pole rotating magnetic field. The pole slots cooperate to generate a suitable modulated wave magnetic beam, driving the rotor to rotate synchronously.

[0022] Preferably, the robustness optimization addresses the magnetic circuit saturation problem during motor operation (e.g., magnetic flux density of the stator teeth ≥ 2T). A magnetic saturation compensation algorithm is introduced into the PI controller to dynamically adjust the inductance parameters, avoiding the deterioration of control accuracy due to the decrease in magnetic permeability, and ensuring that torque ripple is ≤ 5% under all operating conditions.

[0023] Preferably, the efficiency optimization control involves dynamically adjusting the AC / DC current ratio by real-time monitoring of copper and iron losses, employing a high ratio in the low-speed range (<3000 rpm). Increase torque density, reduce torque in high-speed range (>5000rpm) To reduce iron loss and achieve an efficiency of ≥85% across the entire speed range.

[0024] The beneficial effects of this invention are as follows: 1. This invention proposes a six-phase AC / DC superposition inverter topology that is compatible with traditional three-phase control algorithms. Through a double three-phase cascade structure and voltage superposition mechanism, it achieves efficient superposition of AC and DC currents in the same winding, providing a foundation for wide-speed-range operation of the motor. By reconstructing virtual current, it realizes dual functions of a single winding, converts the six-phase current into virtual three-phase current, eliminates the interference of DC components on the control algorithm, simplifies the control process, and reduces material costs by 40%.

[0025] 2. This invention improves high-speed efficiency by 20% through dynamic field weakening control, resolving the contradiction between "low-speed torque and high-speed efficiency". Combined with high-output mode and robust optimization control strategies, the motor can maintain good performance under different operating conditions. Various optimization measures are adopted to improve efficiency, reduce costs and suppress torque pulsation, such as selecting high-quality materials, optimizing winding design and improving control algorithms, so that the inverter has advantages such as high efficiency, low cost and low vibration. Attached Figure Description

[0026] Figure 1 This is a flowchart of the design steps of the present invention.

[0027] Figure 2 This is a feature diagram of the six-phase inverter system of the present invention. Detailed Implementation

[0028] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0029] like Figures 1 to 2 As shown, the present invention includes the design of various modules of a six-phase inverter, such as superimposing DC excitation and AC armature current on the same winding through a six-phase inverter, constructing a dual three-phase cascaded inverter topology, magnetic circuit modulation, dynamic field weakening control, dual-loop PI control, high output mode activation, robust optimization and efficiency optimization control, etc., to achieve wide-speed-range high-efficiency drive.

[0030] In this embodiment, two independent three-phase inverters are cascaded into a dual three-phase structure. The dual three-phase cascaded inverter topology has alternating positive and negative bias windings, which can support independent control of the AC and DC voltage input of the six-phase windings. Complex current superposition is achieved through the voltage combination of different windings, providing diverse driving methods for the motor.

[0031] In this embodiment, the DC component generates a 6-pole fixed magnetomotive force, and the AC component generates a 4-pole rotating magnetic field. Coupling is achieved through a 10-pole, 12-slot pole-slot configuration. Utilizing this pole-slot configuration and magnetic field modulation principle, a suitable modulated wave magnetic flux can be generated to drive the rotor to rotate synchronously. This eliminates the need for an independent excitation winding, simplifying the motor structure and increasing the winding occupancy rate.

[0032] In this embodiment, the output terminal of the positive bias group of the dual three-phase cascaded inverter topology is connected to the A / C / E phase windings of the motor, and the output voltage is set to V. u +V dc V v +V dc and V w +V dc The output terminal of the negative bias group is connected to the B / D / F phase windings of the motor, and the output voltage is set to V. u -V dc V v -V dc and V w -V dc V u V v and V w The three-phase AC voltage components generated by SVM modulation, initial V dc =0.5V; The DSP (Digital Signal Processing) sends an initialization signal to the power module to detect the status of the six-phase winding circuit. If a phase (such as phase A) fails, it automatically switches to "degraded operation mode" to maintain the basic drive function through the remaining five-phase windings, ensuring that the system is not interrupted.

[0033] In this embodiment, the Hall current sensor acquires the current signals I of phases A / B / C / D / E / F in real time. A I D I B I E I C and I F The acquisition frequency is synchronized with the control cycle (100μs / time); the acquired current signal is processed by an RC filter circuit (filter frequency 20kHz) and an operational amplifier (amplification factor 10 times) before being transmitted to the ADC unit of the DSP to complete the conversion of analog signal to digital signal.

[0034] DSP according to relation IU =I A +I D I V =I B +I E and I W =I C +I F The calculation reconstructs the six-phase current into a virtual three-phase current; at the same time, a digital filtering algorithm (moving average filtering, window length 10) is enabled to further reduce noise interference and ensure that the reconstructed current error is ≤1%.

[0035] In this embodiment, the SVM modulation execution DSP generates SVM modulation waves for the positive and negative bias groups respectively, and synchronously controls the switching transistor drive signals of the two inverter groups through a timer, thereby controlling the three-phase voltage command (V) of the negative bias group. u V v V w By superimposing a 30° electrical angle phase shift, the switching operations of the two sets of inverters are staggered, ultimately reducing DC link ripple by 60% and harmonic current ratio to <15%. For the reconstructed virtual three-phase current (I U I V I W Perform the Park transformation to decompose it into d-axis currents (I). d (direct axis, corresponding to excitation current) and q-axis current (I) q (Intersecting axis, corresponding torque current).

[0036] Dynamically adjust I according to the d-axis current adjustment formula. d Optimize the AC / DC current ratio to ensure current tracking error ≤5%. The specific formula for adjusting the d-axis current is as follows:

[0037]

[0038] in, For speed command, The actual measured speed of the encoder. For proportional gain, Integral gain In this embodiment, the photoelectric encoder provides real-time feedback of the motor speed. ,when At speeds above 5000 rpm (base speed), the DSP initiates dynamic field weakening control and calculates V according to the formula. dc Adjustment amount

[0039] in, As the reference speed, The weak magnetic coefficient, Simultaneously satisfying the constraints

[0040] and

[0041] Where L d L q These are right-angle axis inductors, and V is the dq-axis current. max For the maximum voltage, I max Maximum current In this embodiment, DSP real-time calculation If the value is close to Or or near Triggering limiting logic: Decrease d-axis current command or increase d-axis current command. If the constraints are broken SiCMOSFETs have a built-in detection circuit that directly turns off the switching transistor, preventing device damage.

[0042] When the DSP calculates the load torque ≥40 N·m based on the current signal, it triggers the high output mode and controls the DC-DC converter to output V. dc Increase I simultaneously from 0.5V to 2.0V. d To enhance air gap magnetic flux, combined with I q Vector optimization increases the motor's output torque at 1000 rpm from 20 N·m to 50 N·m; when V dc When the voltage is ≥1.0V, the DSP calls the pre-stored "magnetic flux density-inductance mapping table" to dynamically adjust L. d L q Parameters are used to avoid deterioration in control accuracy due to magnetic saturation.

[0043] In this embodiment, a dual-loop PI control is designed, constructing a dual closed-loop control structure with current and speed loops. Taking the dq-axis current as the controlled object, a feedforward compensation algorithm is embedded in the DSP to suppress 20%-30% of the second harmonic in the six-phase current, controlling the current ripple to within 5%. This is based on feedback from the photoelectric encoder. Adaptively adjust PI parameters, increase K in the low-speed domain p Reduced to 0.8, improving torque response speed; K is reduced in the high-speed weak magnetic field domain. i To a minimum of 0.05, avoid speed overshoot; when the load changes by ±20%, the speed loop compensates for speed fluctuations through parameter adjustments, ensuring a steady-state speed error ≤ ±0.5%. The DSP monitors copper and iron losses in real time and dynamically adjusts I... d / I q Proportional, low-speed domain uses high Id / I q Increase torque density; reduce I in high-speed domain d Reduce iron loss and ultimately achieve an efficiency of ≥85% across the entire speed range and ≥90% in the high-speed range.

[0044] In this embodiment, robustness optimization addresses the magnetic circuit saturation problem during motor operation (e.g., stator tooth magnetic flux density ≥ 2T). A magnetic saturation compensation algorithm is introduced into the PI controller to dynamically adjust the inductance parameters, avoiding the deterioration of control accuracy due to the decrease in magnetic permeability, and ensuring that torque ripple is ≤ 5% under all operating conditions (at rated load).

[0045] In this embodiment, efficiency optimization control dynamically adjusts the AC / DC current ratio by real-time monitoring of copper and iron losses, employing a high ratio in the low-speed range (<3000 rpm). Increase torque density, reduce torque in high-speed range (>5000rpm) To reduce iron loss, achieve an efficiency of ≥85% across the entire speed range, and improve vibration suppression by 10dB compared to switched reluctance motors.

[0046] As is known from common technical knowledge, this invention can be implemented through other embodiments that do not depart from its spirit or essential characteristics. Therefore, the disclosed embodiments described above are merely illustrative and not exhaustive. All modifications within the scope of this invention or its equivalents are included in this invention.

Claims

1. A design method for a six-phase inverter with superimposed AC and DC currents, characterized in that, Includes the following steps: Step 1 A dual three-phase cascaded structure is formed by two sets of independent three-phase inverters, where the forward bias group corresponds to phases A, C, and E, and the output voltages are V respectively. u +V dc V v +V dc and V w +V dc The negative bias group corresponds to phases B, D, and F, with output voltages of V respectively. u -V dc V v -V dc and V w -V dc Its structure also includes a power module and a control core; Among them, V u V v and V w These are the AC voltages of phase U, phase V, and phase W in the three-phase AC voltage components, respectively. dc This is the DC bias voltage; Step 2 The current signals of phases A, B, C, D, E, and F are acquired in real time by Hall current sensors, filtered, amplified, and converted from analog to digital before being transmitted to the DSP. (Press I...) U =I A +I D I V =I B +I E and I W =I C +I F The relationship reconstructs the six-phase current into a virtual three-phase current, eliminating the interference of the DC component on the control algorithm; Among them, I U I V and I W I represents the AC currents of phases U, V, and W in the three-phase AC voltage components. A I B I C I D I E and I F These are the currents in phases A, B, C, D, E, and F; Step 3 SVM modulation is applied to the positive and negative bias groups of the dual three-phase cascaded topology, with a 30° phase offset angle set to stagger the switching actions of the two inverter groups. The reconstructed virtual three-phase current is subjected to Park transformation, decomposed into d-axis and q-axis currents. The d-axis current is dynamically adjusted using a PI controller to optimize the AC / DC current ratio. The d-axis current adjustment formula is as follows: in, For speed command, The actual measured speed of the encoder. For proportional gain, This is the integral gain. Step 4 When the motor speed is greater than the base speed, the DC bias voltage is adjusted using the following formula: in, As the reference speed, The weak magnetic coefficient, This is the DC bias voltage; Simultaneously satisfying the constraints and Where L d L q These are right-angle axis inductors, V max For the maximum voltage, I max This is the maximum current.

2. The design method for a six-phase inverter with superimposed AC and DC currents according to claim 1, characterized in that, In step 1, the positive and negative bias windings of the dual three-phase cascaded inverter topology are distributed alternately, supporting independent control of the AC and DC voltage input of the six-phase windings, and are compatible with the traditional three-phase control algorithm. In the event of a single-phase fault, it can achieve degraded operation.

3. The design method for a six-phase inverter with superimposed AC and DC currents according to claim 1, characterized in that, In step 2, Hall current sensors are connected in series on each branch of the six-phase winding. The collected current signals are processed by the analog-to-digital conversion unit of the DSP and then a virtual three-phase current reconstruction operation is performed. During the reconstruction process, a digital filtering algorithm is used to further reduce noise interference.

4. The design method for a six-phase inverter with superimposed AC and DC currents according to claim 1, characterized in that, In step 4, the constraint condition monitoring for dynamic field weakening control is completed in real time via DSP. The calculated value is close to , or when I d Approaching I max At this time, the DSP triggers the limiting logic, reducing the d-axis current command or increasing the field weakening coefficient. Meanwhile, the overvoltage and overcurrent detection circuits built into the SiC MOSFET power module directly turn off the switching transistors when the constraints are exceeded.

5. A design method for a six-phase inverter with superimposed AC and DC currents, characterized in that, By superimposing DC excitation and AC armature current onto the same winding in a six-phase inverter, the design of various modules of the six-phase inverter, including dual three-phase cascaded inverter topology, magnetic circuit modulation, dynamic field weakening control, dual-loop PI control, high output mode activation, robust optimization, and efficiency optimization control, is constructed.

6. The design method for a six-phase inverter with superimposed AC and DC currents according to claim 5, characterized in that, The six-phase inverter includes a data acquisition module, a control core for executing SVM modulation and vector control algorithms, and a power module with a withstand voltage of 600V. The data acquisition module includes a Hall current sensor and a photoelectric encoder.

7. The design method for a six-phase inverter with superimposed AC and DC currents according to claim 5, characterized in that, The high-output mode activation increases the DC bias current synchronously by increasing the DC voltage activation, thereby enhancing the air gap magnetic flux. Combined with the vector optimization of the AC armature current, this significantly improves the electromagnetic torque.

8. The design method for a six-phase inverter with superimposed AC and DC currents according to claim 5, characterized in that, The magnetic field modulation includes a DC component generating a 6-pole fixed magnetomotive force and an AC component generating a 4-pole rotating magnetic field. The coupling is achieved through a 10-pole, 12-slot pole-slot combination, driving the rotor to rotate synchronously.

9. The design method for a six-phase inverter with superimposed AC and DC currents according to claim 5, characterized in that... By designing a dual-loop PI control, a dual closed-loop control structure of current loop and speed loop is constructed. The current loop takes the dq-axis current as the control object and adjusts the AC / DC current ratio in real time through the PI controller to ensure that the winding current quickly tracks the command value.

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