Isolated single-phase integrated vehicle charging system topology circuit and control method thereof

Abstract

The application discloses a kind of topological circuits of isolated single-phase integrated vehicle charging system and control method thereof, comprising: open-winding permanent magnet synchronous motor, double three-phase inverter, power battery pack, bus capacitor, high-frequency transformer, winding switching switch K1, winding switching switch K2 and bus switching switch G1;Through the switching of winding switching switch K1, winding switching switch K2 and bus switching switch G1, the system works in driving mode or charging mode, and the control of the system is realized by combining driving and charging control method.The application realizes the electrical isolation of integrated vehicle charging system without increasing additional power devices and power frequency transformer, and improves the reliability and safety of charging.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of integrated vehicle charging technology for automobiles, and particularly relates to a topology circuit of an isolated single-phase integrated vehicle charging system and a control method thereof. BACKGROUND

[0002] At present, common charging of electric vehicles is generally realized by a vehicle-mounted charger or a non-vehicle-mounted independent charger. The non-vehicle-mounted charger generally directly charges the battery pack through a ground independent charging pile, and the charging power is generally above 50 kW, but the charging pile occupies a large space and has high construction cost and poor convenience. The vehicle-mounted charger charges the battery pack by converting the network-side alternating power source, which reserves a large charging power while taking into account the convenience and economy of charging. However, the vehicle-mounted charger is usually installed on the electric vehicle, which increases the weight of the automobile, occupies the limited space in the vehicle, and reduces the cruising range of the automobile, which is contrary to the goal of lightweight vehicle. Therefore, the integrated vehicle charging scheme of reusing the motor winding and the power device of the driving system of the electric vehicle has attracted continuous attention in the industry.

[0003] The integrated vehicle charging system usually changes the connection mode of the motor winding by switching the switch during charging of the automobile, reconfigures the motor winding and the driving system as an AC / DC converter, converts the network-side alternating power source into direct current that meets the voltage level of the electric vehicle charging, and thus realizes the integration of the driving charging system. Compared with the traditional vehicle-mounted charger, the integrated vehicle charging system realizes the charging effect of the vehicle-mounted charger by time-sharing reuse of the driving system and the motor winding, saves volume and weight, and has high practical value.

[0004] At present, since the integrated vehicle charging system usually does not have an electrical isolation function, a frequency transformer or a DAB converter needs to be attached to realize the electrical isolation of the charging system in actual application, which is contrary to the goal of high integration of the integrated charging system, and limits the large-scale development and application of the integrated charging system. Therefore, how to realize the isolated integrated vehicle charging system without increasing additional power devices and frequency transformers is a problem to be solved. SUMMARY

[0005] The present application provides a topology circuit of an isolated single-phase integrated vehicle charging system and a control method thereof, which realizes the electrical isolation of the integrated vehicle charging system without increasing additional power devices and frequency transformers, and improves the reliability and safety of charging.

[0006] Technical Solution: The topology circuit of the isolated single-phase integrated on-board charging system of the present invention includes: an open-winding permanent magnet synchronous motor, a dual three-phase inverter, a power battery pack, a bus capacitor, a high-frequency transformer, a winding switching switch K1, a winding switching switch K2, and a bus switching switch G1; the open-winding permanent magnet synchronous motor has three-phase windings, each phase winding has a center tap, dividing it into L... a1 L a2 L b1 L b2 L c1 L c2 The inverter has six winding sections; it is a dual three-phase inverter with a common bus structure and contains 12 switching transistors; the winding switching switch K1 has its fixed terminal connected to the three-phase winding L. a1 L b1 L c1 Connected, the switching terminals are located at the grid interface, the high-frequency transformer, and the three-phase winding L. a2 L b2 L c2 Inter-phase switching; the fixed terminal of the winding switching switch K2 is connected to the three-phase winding L a2 L b2 L c2 Connected, the switching terminal switches between the midpoint of the high-frequency transformer and the three-phase inverter bridge arm; the busbar switching switch G1 has its fixed terminal connected to the busbar, and its switching terminal is used to disconnect Q9 and Q... 10 Bridge arm, Q 11 and Q 12 The bridge arm and power battery pack achieve electrical isolation between the primary and secondary sides of the charging system; by switching the winding switching switch K1, winding switching switch K2 and bus switching switch G1, the system can operate in either drive mode or charging mode, and the system can be controlled by combining drive and charging control methods.

[0007] Furthermore, when the electric vehicle is in drive mode, the winding switching switch K1 and the three-phase winding L a2 L b2 L c2 The winding switching switch K2 is connected to the midpoint of the three-phase inverter bridge arm, therefore the three-phase winding L... a1 L b1 L c1 With three-phase winding L a2 L b2 L c2 Connected, three-phase winding L a2 L b2 L c2 Connected to the midpoint of the three-phase inverter bridge arm, and with the bus switching switch G1 closed, the DC power output from the power battery is converted into three-phase AC power through the common bus dual three-phase inverter to drive the open-winding permanent magnet synchronous motor.

[0008] Further, when the electric vehicle is in charging mode, the winding switching switches K1 and K2 are closed, the winding structure is reconfigured and connected to the single-phase power grid and the high-frequency transformer, and at the same time the bus switching switch G1 is disconnected, the system is reconfigured into a single-phase PWM rectifier and a dual active bridge converter; the single-phase power grid is connected to the winding L a1 and L b2 , the winding L b2 is connected to the winding L a2 , the winding L a2 is connected to the winding L b1 , the switching tubes Q1, Q2, Q3, Q4 and the windings L a1 , L a2 , L b1 , L b2 are reconfigured into the single-phase PWM rectifier; the high-frequency transformer is connected to the switching tubes Q7, Q8, Q9, Q 10 and the windings L c1 , L c2 , the switching tubes Q5, Q6, Q7, Q8 and the windings L c1 are reconfigured into the primary side full-bridge circuit, the switching tubes Q9, Q 10 , Q 11 , Q 12 and the windings L c2 are reconfigured into the secondary side full-bridge circuit, the primary side full-bridge circuit, the secondary side full-bridge circuit and the high-frequency transformer are reconfigured into the dual active bridge converter; the single-phase power grid alternating current passes through the PWM rectifier to output direct current, the multiplex bus capacitor is filtered to obtain high-voltage direct current, and the direct current is output through the dual active bridge converter in the rear stage to realize the isolation type single-phase integrated charging of the battery pack.

[0009] Correspondingly, a control method of a topology circuit of an isolation type single-phase integrated vehicle-mounted charging system, comprising the following steps:

[0010] Step 1, collect the single-phase power grid side voltage instantaneous value U g , the current instantaneous value I g , the power battery positive and negative electrode voltage U dc , the bus capacitor voltage U C ;

[0011] Step 2, calculate the phase angle θ g of U g by phase-locked loop, multiply the difference between the given value and the actual value of the bus capacitor voltage by the proportional integral controller and θ g , obtain the current given value of the power grid side, calculate the duty ratio of the switching tubes Q1, Q2, Q3, Q4 by modulating the current error through the proportional resonant controller, and the switching tubes Q1, Q4 are respectively complementary to the switching tubes Q2, Q3;

[0012] Step 3, the original side constant duty ratio is 0.5, the switch signal is generated, the switch tubes Q5, Q6, Q7 and Q8 are driven, the switch tubes Q5 and Q8 are complementary to Q6 and Q7 respectively; the difference between the given value and the actual value of the charging voltage of the high-voltage power battery is obtained after the proportional integral controller, the inter-bridge phase shift ratio is obtained, the original side switch signal is phase shifted, and the switch tubes Q9 and Q 10 , Q 11 , Q 12 are complementary to Q 12 , Q 10 and Q 11 respectively;

[0013] Step 4, the motor windings L a1 , L a2 , L b1 , L b2 are used as input inductors, the currents of the windings L a1 , L a2 and the windings L b1 , L b2 are equal in size and opposite in direction, the generated magnetic flux is offset; the turns ratio of the high-frequency transformer is 1:1, the windings L c1 , L c2 are connected to the same end of the transformer, the currents of the windings L c1 , L c2 are equal in size and opposite in direction, the generated magnetic flux is offset; the magnetic flux generated in the three-phase winding is zero, so that no electromagnetic torque is generated, and the motor rotor can be kept stationary.

[0014] Advantages: compared with the prior art, the application has the following remarkable advantages: without increasing additional power devices and power frequency transformers, the electrical isolation of the integrated vehicle-mounted charging system is realized, and the reliability and safety of the charging are improved; on the basis of the open winding drive system of the electric vehicle, the stator winding of the drive motor is reused, the high-frequency transformer and the switching switch are added, the isolation type integrated vehicle-mounted charging system is obtained, when the system is switched from the drive operation mode to the charging operation mode, the stator winding, the drive system and the high-frequency transformer are reconstructed into a single-phase PWM rectifier cascaded double active bridge converter topology through the switching switch, the torque ripple suppression of the reused winding motor is realized through the magnetic flux balance method, the inductance current is controlled to realize the power factor correction, the phase shift control method is used to realize the isolation charging of the power battery, the system integration and control performance are improved, and the integrated design of the drive and charging functions is realized. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 It is the topological circuit structure diagram of the isolation type single-phase integrated vehicle-mounted charging system for electric vehicles.

[0016] Figure 2The topology diagram of the application in driving state.

[0017] Figure 3 The topology diagram of the application in charging state.

[0018] Figure 4 The equivalent circuit diagram of the application in charging mode.

[0019] Figure 5 The total control block diagram of the application in charging mode.

[0020] Figure 6 The waveform diagram of the front-stage bus capacitor voltage and the power battery charging voltage in the application.

[0021] Figure 7 The grid-side voltage and current waveform diagram of the application in steady-state charging.

[0022] Figure 8 The harmonic analysis result diagram of the grid-side current of the application in steady-state charging.

[0023] Figure 9 The transformer primary and secondary voltage difference and transformer inductance current waveform diagram of the application in steady-state charging.

[0024] Figure 10 The current and system torque waveform diagram of the three-phase two-section winding of the application in charging. DETAILED DESCRIPTION

[0025] As Figure 1 shown in the figure, a topology circuit of an isolated single-phase integrated vehicle-mounted charging system for electric vehicles comprises an open-winding permanent magnet synchronous motor, a double three-phase inverter, a power battery pack, a bus capacitor, a high-frequency transformer, winding switching switch K1, winding switching switch K2 and bus switching switch G1.

[0026] The open-winding permanent magnet synchronous motor has three-phase windings, each phase winding has a center tap, which is divided into L a1 , L a2 , L b1 , L b2 , L c1 , L c2 six-section windings; the double three-phase inverter is a common bus structure and contains 12 switching tubes.

[0027] The open-winding permanent magnet synchronous motor has three-phase windings, each phase winding has a center tap, which is divided into L a1 , L a2 , L b1 , L b2 , L c1 , L c2Six segments winding; the double three-phase inverter is common bus structure, including 12 switch tubes;

[0028] The fixed end of the winding switch K1 is connected with the three-phase winding L a1 , L b1 , L c1 , and the switching end switches among the power grid interface, the high-frequency transformer and the three-phase winding L a2 , L b2 , L c2 The fixed end of the winding switch K2 is connected with the three-phase winding L a2 , L b2 , L c2 , and the switching end switches between the high-frequency transformer and the three-phase inverter bridge arm midpoint; the fixed end of the bus switch G1 is connected with the bus, and the switching end is used for disconnecting Q9 and Q 10 bridge arms, Q 11 and Q 12 bridge arms and the power battery pack, realizing the electrical isolation of the primary and secondary sides of the system;

[0029] The isolation type single-phase integrated vehicle charging system for electric vehicles can work in the driving mode or the charging mode through the switching of the winding switch K1, the winding switch K2 and the bus switch G1, and realizes the control of the system in combination with the driving and charging control methods.

[0030] As shown in Figure 2 , when the electric vehicle is in the driving mode, the winding switch K1 is connected with the three-phase winding L a2 , L b2 , L c2 , the winding switch K2 is connected with the three-phase inverter bridge arm midpoint, thus the three-phase winding L a1 , L b1 , L c1 is connected with the three-phase winding L a2 , L b2 , L c2 , the three-phase winding L a2 , L b2 , L c2 is connected with the three-phase inverter bridge arm midpoint, and the bus switch G1 is closed at the same time, so that the direct current output by the power battery is inverted into three-phase alternating current by the common bus double three-phase inverter to drive the open-winding permanent magnet synchronous motor.

[0031] As shown in Figure 3 and Figure 4 , when the electric vehicle is in the charging mode, the winding switches K1 and K2 are closed, the winding structure is reconfigured and connected with the single-phase power grid and the high-frequency transformer, and the bus switch G1 is disconnected at the same time, so that the system is reconfigured into a single-phase PWM rectifier and a double active bridge converter; the single-phase power grid is connected with the winding La1 and L b2 Connected, winding L b2 With winding L a2 Connected, winding L a2 With winding L b1 Connected, the switching transistors Q1, Q2, Q3, Q4 and winding L a1 L a2 L b1 L b2 Reconstructed into the single-phase PWM rectifier; high-frequency transformer and switching transistors Q7, Q8, Q9, Q... 10 and winding L c1 L c2 Connected, switching transistors Q5, Q6, Q7, Q8 and winding L c1 Reconstructed into a primary-side full-bridge circuit, with switching transistors Q9 and Q... 10 Q 11 Q 12 and winding L c2 The primary-side full-bridge circuit, the secondary-side full-bridge circuit, and the high-frequency transformer are reconstructed into the dual active bridge converter. The single-phase AC power from the mains is output as DC power through the PWM rectifier, filtered by the bus capacitor to obtain high-voltage DC power, which is then output as DC power through the subsequent dual active bridge converter to achieve isolated single-phase integrated charging of the battery pack.

[0032] like Figure 5 As shown, a charging control method for an isolated single-phase integrated on-board charging system for electric vehicles is described, wherein the motor winding L is connected in series. a1 L a2 L b1 L b2 Power factor correction is achieved by controlling the phase of the inductor current; output voltage control of the single-phase PWM rectifier is achieved by controlling the amplitude of the inductor current; and the output voltage of the rectifier is controlled by controlling the switching transistors Q5, Q6, Q7, Q8 and Q9, Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, Q9, Q1 ...1, Q2, Q1, Q1, Q1, Q2, Q1, Q1, Q1, Q2, Q1, Q1, Q2, Q1, Q1, Q1, Q2, Q1, Q1, Q2, Q1, Q1, Q1, Q2, Q1, Q1, Q2, Q1, Q1, Q2, Q1, Q1, Q2, Q1, Q1, Q2, Q1, Q 10 Q 11 Q 12 The phase shift angle is used to control the output voltage of the dual active bridge converter; the current of each phase winding is controlled to achieve magnetic flux balance and suppress torque ripple in the multiplexed winding motor; this control strategy includes the following steps:

[0033] (1) Collect the instantaneous voltage U of the single-phase grid side. g Instantaneous current value I g Power battery positive and negative terminal voltage U dc Bus capacitor voltage U C ;

[0034] (2) Calculate U using a phase-locked loop g phase angle θ gThe difference between the bus capacitance voltage given value and the actual value is multiplied by θ after passing through a proportional-integral controller to obtain a grid-side current given value. g The current error is calculated by a proportional-resonant controller after the current error passes through a proportional-resonant controller to obtain the duty cycles of the switching tubes Q1, Q2, Q3, and Q4. The switching tubes Q1 and Q4 are complementary to Q2 and Q3, respectively.

[0035] (3) The primary side constant duty cycle is 0.5. The switching signals are generated to drive the switching tubes Q5, Q6, Q7, and Q8. The switching tubes Q5 and Q8 are complementary to Q6 and Q7, respectively. The difference between the charging voltage given value and the actual value of the high-voltage power battery is obtained after passing through a proportional-integral controller to obtain the inter-bridge phase shift ratio. The primary side switching signal is phase-shifted to obtain the switching tubes Q9, Q 10 , Q 11 , Q 12 . The switching tubes Q9 and Q 12 are complementary to Q 10 and Q 11 .

[0036] The control of the current of each phase winding realizes the balance of magnetic flux and suppresses the torque ripple of the multiplex winding motor. The characteristic is that the series motor windings L a1 , L a2 , L b1 , L b2 are used as input inductors, the currents of the windings L a1 , L a2 and the windings L b1 , L b2 are equal in size and opposite in direction, and the generated magnetic flux is offset. The turns ratio of the high-frequency transformer is 1:1, and the windings L c1 , L c2 are connected to the same name terminal, so that the currents of the windings L c1 , L c2 are equal in size and opposite in direction, and the generated magnetic flux is offset. The magnetic flux generated in the three-phase winding is zero, so that no electromagnetic torque is generated, and the motor rotor can be kept stationary.

[0037] Based on the above-mentioned isolation type single-phase integrated vehicle charging system topology and control strategy for electric vehicles, an isolation type single-phase integrated vehicle charging system is built in Matlab / Sumink software, mainly including a mathematical model of an open-winding permanent magnet synchronous motor with a center tap, a double three-phase inverter model, a single-phase PWM rectifier control model, and a double active bridge converter control model. The key parameters in the simulation verification process are shown in Table 1:

[0038] Table 1 Key parameter table

[0039]

[0040]

[0041] The simulation duration is set to 1s, as shown in the figure, which is the voltage waveform of the capacitor of the front bus and the charging voltage waveform of the power battery, and it can be seen that the charging voltage build-up time of both is less than 0.1s, the voltage fluctuation is small in the steady state, and it has good dynamic performance and steady-state performance. Figure 6

[0042] As shown in the figure, the steady-state waveform is intercepted from 0.2s to 0.3s, and the voltage waveform and the current waveform of the grid side are shown, respectively, it can be seen that the current has high sinusoidal degree, and the phase is basically consistent with the voltage, realizing the PFC function, and meeting the power requirement of the grid. Figure 7 Figure 8 Figure 7 As shown in the figure, the steady-state waveform is intercepted from 0.2s to 0.3s, and the voltage waveform and the current waveform of the grid side are shown, respectively, it can be seen that the current has high sinusoidal degree, and the phase is basically consistent with the voltage, realizing the PFC function, and meeting the power requirement of the grid. Figure 8 As shown in the figure, the steady-state waveform is intercepted from 0.2s to 0.3s, and the voltage waveform and the current waveform of the grid side are shown, respectively, it can be seen that the current has high sinusoidal degree, and the phase is basically consistent with the voltage, realizing the PFC function, and meeting the power requirement of the grid.

[0043] As shown in the figure, the steady-state waveform is intercepted from 0.2s to 0.3s, and the voltage waveform and the current waveform of the grid side are shown, respectively, it can be seen that the current has high sinusoidal degree, and the phase is basically consistent with the voltage, realizing the PFC function, and meeting the power requirement of the grid. Figure 9 As shown in the figure, the steady-state waveform is intercepted from 0.2s to 0.3s, and the voltage waveform and the current waveform of the grid side are shown, respectively, it can be seen that the current has high sinusoidal degree, and the phase is basically consistent with the voltage, realizing the PFC function, and meeting the power requirement of the grid.

[0044] Through the above contents, the feasibility of the isolation type single-phase integrated vehicle charging system topology and its control strategy for electric vehicles proposed in the application is verified. The isolation type single-phase charging system realizes the electrical isolation of the integrated vehicle charging system without increasing additional power devices and power frequency transformers, thereby improving the reliability and safety of the charging. At the same time, by increasing the high-frequency transformer in the driving system, the stator winding of the open-winding permanent magnet motor and the driving circuit are reconstructed into a single-phase PWM rectifier and a dual active bridge converter, the torque ripple suppression is realized through the magnetic flux balance method, the power factor correction is realized through the inductance current control, and the isolation charging of the power battery is realized through the phase shift control, thereby improving the system integration and control performance, and realizing the integrated design of driving and charging.​​​

Claims

1. A topology circuit for an isolated single-phase integrated on-board charging system, characterized in that, include: The components include an open-winding permanent magnet synchronous motor, a dual three-phase inverter, a power battery pack, a high-frequency transformer, winding switching switches K1 and K2, and a bus switching switch G1. The open-winding permanent magnet synchronous motor has three-phase windings, each with a center tap, dividing it into L phases. a1 L a2 L b1 L b2 L c1 L c2 There are six windings in total; the winding switching switch K1 has its fixed terminal connected to the three-phase winding L. a1 L b1 L c1 Connected, the switching terminals are located at the grid interface, the high-frequency transformer, and the three-phase winding L. a2 L b2 L c2 Inter-phase switching; the fixed terminal of the winding switching switch K2 is connected to the three-phase winding L a2 L b2 L c2 Connected, the switching terminal switches between the midpoint of the high-frequency transformer and the three-phase inverter bridge arm; the busbar switching switch G1 has its fixed terminal connected to the busbar, and its switching terminal is used to disconnect Q9 and Q... 10 Bridge arm, Q 11 and Q 12 The bridge arm and power battery pack achieve electrical isolation between the primary and secondary sides of the charging system; by switching the winding switching switch K1, winding switching switch K2 and bus switching switch G1, the system can operate in drive mode or charging mode. The dual three-phase inverter has a common bus structure and contains 12 switching transistors. When the electric vehicle is in drive mode, the winding switching switch K1 and the three-phase winding L a2 L b2 L c2 The winding switching switch K2 is connected to the midpoint of the three-phase inverter bridge arm, therefore the three-phase winding L... a1 L b1 L c1 With three-phase winding L a2 L b2 L c2 Connected, three-phase winding L a2 L b2 L c2 Connected to the midpoint of the three-phase inverter bridge arm, and with the bus switching switch G1 closed, the DC power output from the power battery is converted into three-phase AC power through the common bus dual three-phase inverter to drive the open-winding permanent magnet synchronous motor. It also includes the bus capacitor. When the electric vehicle is in charging mode, winding switching switches K1 and K2 are closed, reconfiguring the winding structure and connecting to the single-phase power grid and high-frequency transformer. At the same time, bus switching switch G1 is opened, and the system is reconfigured into a single-phase PWM rectifier and a dual active bridge converter; the single-phase power grid and winding L a1 and L b2 Connected, winding L b2 With winding L a2 Connected, winding L a2 With winding L b1 Connected, the switching transistors Q1, Q2, Q3, Q4 and winding L a1 L a2 L b1 L b2 Reconstructed into the single-phase PWM rectifier; high-frequency transformer and switching transistors Q7, Q8, Q9, Q... 10 and winding L c1 L c2 Connected, switching transistors Q5, Q6, Q7, Q8 and winding L c1 Reconstructed into a primary-side full-bridge circuit, with switching transistors Q9 and Q... 10 Q 11 Q 12 and winding L c2 The primary-side full-bridge circuit, the secondary-side full-bridge circuit, and the high-frequency transformer are reconstructed into the dual active bridge converter. The single-phase AC power from the mains is output as DC power through the PWM rectifier, filtered by the bus capacitor to obtain high-voltage DC power, which is then output as DC power through the subsequent dual active bridge converter to achieve isolated single-phase integrated charging of the battery pack.

2. The control method for the topology circuit of the isolated single-phase integrated on-board charging system as described in claim 1, characterized in that, Includes the following steps: Step 1: Collect the instantaneous voltage value U of a single-phase grid side. g Instantaneous current value I g Power battery positive and negative terminal voltage U dc Bus capacitor voltage U C ; Step 2: Calculate U using a phase-locked loop. g phase angle θ g The difference between the given value and the actual value of the bus capacitor voltage is passed through a proportional-integral controller and then compared with θ. g Multiply to obtain the grid-side current setpoint. After the current error is passed through the proportional resonant controller, the duty cycle of the switching transistors Q1, Q2, Q3, and Q4 is obtained through modulation calculation. Switches Q1 and Q4 are complementary to Q2 and Q3, respectively. Step 3: Generate a primary-side switching signal with a constant duty cycle of 0.5 to drive switches Q5, Q6, Q7, and Q8. Switches Q5 and Q8 are complementary to Q6 and Q7, respectively. The difference between the given and actual charging voltage of the high-voltage power battery is processed by a proportional-integral controller to obtain the inter-bridge phase shift ratio. The primary-side switching signal is then phase-shifted to obtain the phase shift ratios of switches Q9 and Q1. 10 Q 11 Q 12 Switching transistors Q9 and Q 12 respectively with Q 10 Q 11 Complementary conduction; Step 4, Series connection of motor winding L a1 L a2 L b1 L b2 As the input inductor, the winding L a1 L a2 and winding L b1 L b2 When currents are equal in magnitude but opposite in direction, the resulting magnetic flux cancels out; the high-frequency transformer has a turns ratio of 1:1, and winding L... c1 L c2 Connect the transformer to the same-name terminal, so that winding L... c1 L c2 When the currents are equal in magnitude and opposite in direction, the resulting magnetic fluxes cancel each other out. The magnetic fluxes generated in the three-phase windings are all zero, so no electromagnetic torque is generated, and the motor rotor remains stationary.

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