Electrolytic-capacitor-free Vienna rectifier unbalanced power and bipolar voltage cooperative control method

Abstract

The invention discloses an unbalanced power and bipolar voltage cooperative control method for a Vienna rectifier without an electrolytic capacitor, and belongs to the technical field of Vienna rectifier control. The invention aims to solve the problem of system control instability caused by violent bipolar voltage oscillation when a Vienna rectifier is connected with a load with a relatively large power level difference at a direct current side. Comprising the following steps: comparing an unbalanced power boundary with a real-time power unbalance degree, and if the unbalanced power boundary is smaller than the real-time power unbalance degree, selecting a bipolar voltage difference control mode; otherwise, selecting a bipolar voltage balance control mode; in the balance control mode, selecting the optimal clamping mode of intermittent pulse width modulation according to the comparison result of the midpoint voltage at the adjacent next moment and the voltage hysteresis boundary; and under a bipolar voltage difference control mode, calculating an optimal voltage unbalance degree, performing vector synthesis on two adjacent vectors in a voltage vector non-synthesis region, and obtaining a modulation wave after track optimization by calculating a duty ratio. According to the invention, grid-side current harmonics can be reduced.

Description

TECHNICAL FIELD

[0001] The application relates to a method for simultaneously controlling unbalanced power and bipolar voltage of an electrolytic capacitor-free Vienna rectifier and belongs to the technical field of Vienna rectifier control. BACKGROUND

[0002] The Vienna rectifier has become one of the mainstream topologies in medium and high power AC / DC converters due to its advantages of high power factor, low current harmonic and no risk of bridge arm shoot-through, and is widely used in electric vehicle fast charging systems, data center direct current power supply and rail transit traction power supply and the like. However, the bipolar voltage fluctuation as an inherent problem of three-level converters always exists.

[0003] To improve the power density of the system and prolong the service life of the device, a thin film capacitor with a small capacitance is used at the direct current side of the Vienna rectifier, but the reduction of the capacitance will lead to an increase in the bipolar voltage fluctuation, which further increases the voltage stress of the switching device and the thin film capacitor. In addition, when the Vienna rectifier is used as an electric vehicle charging device, different charging modes are required for different vehicles, and the Vienna rectifier needs to output different levels of bipolar direct current voltage. Usually, multiple post-stage converters or loads with constant power characteristics are connected, and the power demand has rapid fluctuation and obvious negative impedance characteristics. Therefore, to ensure the continuity of electric energy transmission and stable operation of the system, the Vienna rectifier needs to have a wide unbalanced power operating range to cope with the voltage fluctuation problem caused by the dynamic change of the bipolar direct current voltage output of multiple loads.

[0004] To reduce the negative impact of unbalanced loads on the control performance of the Vienna rectifier, the traditional methods mainly include a carrier modulation method based on zero sequence component injection and a model predictive control algorithm. The carrier modulation method based on zero sequence component injection calculates the optimal zero sequence component in different sectors to suppress the bipolar voltage fluctuation. The model predictive control algorithm selects the optimal voltage vector by comparing the cost functions corresponding to different voltage vectors to suppress the bipolar voltage fluctuation and the grid-side current harmonic.

[0005] However, when the unbalanced power further increases, the demand for the direct current component of the midpoint current also increases. However, the traditional method cannot meet the demand of the midpoint current, and the stability of the system cannot be maintained in the bipolar voltage balance mode, which eventually leads to system instability. Therefore, it is necessary to further study how to widen the unbalanced power operating range of the Vienna rectifier and suppress the bipolar voltage fluctuation. SUMMARY

[0006] To address the problem of severe bipolar voltage oscillations causing system instability when Vienna rectifiers are connected to loads with significantly different power levels on the DC side, this invention provides a method for coordinated control of unbalanced power and bipolar voltage in capacitor-free Vienna rectifiers.

[0007] The present invention provides a method for coordinated control of unbalanced power and bipolar voltage in a capacitorless Vienna rectifier, comprising:

[0008] The unbalanced power boundary is calculated based on the extreme components of the midpoint current and compared with the real-time power imbalance. The bipolar voltage control mode is selected based on the comparison result.

[0009] If the unbalanced power boundary is less than the real-time power imbalance, select the bipolar voltage difference control mode; otherwise, select the bipolar voltage balance control mode.

[0010] In the bipolar voltage balance control mode, a midpoint voltage prediction mechanism is used to predict the midpoint voltage at the next adjacent time step. Based on the comparison results between the midpoint voltage at the next adjacent time step and the voltage hysteresis boundary, the optimal clamping mode of discontinuous pulse width modulation is selected to achieve unbalanced power and bipolar voltage coordinated control.

[0011] In the bipolar voltage difference control mode, the optimal voltage imbalance is calculated based on the extreme components of the midpoint current and the active power. Simultaneously, the region where voltage vectors cannot be synthesized is determined based on the comparison between the maximum and minimum values ​​of the extreme components of the midpoint current. The vertical trajectory projection method is used to synthesize two adjacent vectors at the boundary of the region where voltage vectors cannot be synthesized. The two adjacent vectors include a mid-vector and a small vector. The duty cycle of the mid-vector is calculated. Based on the duty cycle of the mid-vector, the trajectory-optimized modulation wave of the region where voltage vectors cannot be synthesized is calculated, thereby realizing the coordinated control of unbalanced power and bipolar voltage.

[0012] According to the electrolytic capacitor-free Vienna rectifier unbalanced power and bipolar voltage coordinated control method of the present invention, the calculation method of the extreme component of the midpoint current is as follows:

[0013] ,

[0014] In the formula These are the extreme components of the midpoint current. For the net side Phase current, ; for Phase voltage modulation wave, This represents the zero-sequence voltage component that is equivalent to the superposition after clamping. Voltage imbalance;

[0015] The zero-sequence voltage component is equivalent to the superposition after clamping. maximum value and minimum value The expression is:

[0016] ,

[0017] In the formula For the maximum equivalent modulated wave, It is the minimum equivalent modulated wave;

[0018] Maximum equivalent modulated wave The fundamental value of the maximum equivalent modulated wave The maximum value, the minimum equivalent modulated wave The minimum equivalent modulated wave fundamental value The minimum value;

[0019] ,

[0020] ;

[0021] The zero-sequence voltage component is equivalent to the superposition after clamping. maximum value and minimum value The corresponding extreme components of the midpoint current were calculated. maximum value and minimum value .

[0022] According to the electrolytic capacitor-free Vienna rectifier unbalanced power and bipolar voltage coordinated control method of the present invention, combined with the extreme value component of the midpoint current. Constraint calculation of unbalanced power boundary:

[0023]

[0024] In the formula For unbalanced power boundary, To adjust the system.

[0025] According to the electrolytic capacitor-free Vienna rectifier unbalanced power and bipolar voltage coordinated control method of the present invention, in the bipolar voltage balance control mode, the midpoint voltage prediction mechanism is used to predict the midpoint voltage at the next adjacent moment, including:

[0026] ,

[0027] In the formula for Midpoint voltage at time, for Midpoint voltage at time, To control the cycle, The film capacitor capacitance value, The film capacitor capacitance value, The midpoint current at the moment.

[0028] The method for the electrolytic capacitor-free Vienna rectifier imbalance power and bipolar voltage cooperative control according to the application calculates the midpoint voltage prediction value of different clamping modes according to the relationship between the midpoint current and the duty cycle:

[0029] ,

[0030] In the formula The midpoint voltage at the moment in the maximum discontinuous pulse width modulation clamping mode , The midpoint voltage at the moment in the minimum discontinuous pulse width modulation clamping mode , The phase duty cycle in the maximum discontinuous pulse width modulation clamping mode , The phase duty cycle in the minimum discontinuous pulse width modulation clamping mode .

[0031] The method for selecting the optimal clamping mode of the discontinuous pulse width modulation according to the electrolytic capacitor-free Vienna rectifier imbalance power and bipolar voltage cooperative control method of the application is:

[0032] ,

[0033] In the formula The optimal clamping mode is represented, The minimum discontinuous pulse width modulation clamping mode is represented, The maximum discontinuous pulse width modulation clamping mode is represented, The current discontinuous pulse width modulation clamping mode is represented; The upper limit of the voltage hysteresis loop is represented, The lower limit of the voltage hysteresis loop is represented.

[0034] The method for calculating the optimal voltage imbalance degree according to the electrolytic capacitor-free Vienna rectifier imbalance power and bipolar voltage cooperative control method of the application is:

[0035] ,

[0036] In the formula The optimal voltage imbalance degree is represented, The real-time power imbalance degree is represented, The output active power is represented, The bus voltage is represented.

[0037] According to the electrolytic capacitor-free Vienna rectifier unbalanced power and bipolar voltage coordinated control method of the present invention, the judgment condition for determining the region where voltage vector cannot be synthesized is as follows:

[0038] ,

[0039] In the formula For the judgment coefficient, if , If the voltage vector is within the normal range, then the voltage vector is determined to be within the normal range; otherwise... , If the value is 0, it indicates that the voltage vector is located in the region where synthesis is not possible.

[0040] According to the electrolytic capacitor-free Vienna rectifier unbalanced power and bipolar voltage coordinated control method of the present invention, the calculation method of the duty cycle of the middle vector is as follows:

[0041] ,

[0042] In the formula The duty cycle of the mid-vector. For voltage vector Axis voltage component.

[0043] According to the electrolytic capacitor-free Vienna rectifier unbalanced power and bipolar voltage coordinated control method of the present invention, the calculation method of the modulation wave after trajectory optimization in the region where the voltage vector cannot be synthesized is as follows:

[0044] ,

[0045] In the formula for Modulated wave after phase trajectory optimization This represents the maximum value of the phase current on the grid side. This is the median value of the grid-side phase current. This represents the minimum phase current on the grid side.

[0046] The beneficial effects of this invention are as follows: The method of this invention can expand the operating range of unbalanced power and suppress bipolar voltage fluctuations. The bipolar voltage control mode is selected based on the relationship between the real-time power imbalance degree and the unbalanced power boundary. In the bipolar voltage balance control mode, the optimal clamping mode of discontinuous pulse width modulation is selected by combining the midpoint voltage prediction mechanism and the voltage hysteresis boundary. In the bipolar voltage difference control mode, the optimal voltage imbalance degree is calculated by combining the extreme components of the midpoint current and the active power. The region where the voltage vector cannot be synthesized is identified based on the magnitude of the extreme midpoint current, and the voltage vector error is reduced by combining the trajectory optimization method of the vertical projection of the voltage vector, thereby reducing grid-side current harmonics. Attached Figure Description

[0047] Figure 1 Circuit structure diagram of the electrolytic capacitorless Vienna rectifier of the present application;

[0048] Figure 2 Control block diagram of the unbalanced power and bipolar voltage collaborative control method of the electrolytic capacitorless Vienna rectifier of the present application;

[0049] Figure 3 Relationship diagram of real-time power unbalance degree , modulation degree and voltage unbalance degree when the capacitance C = 1000 μF;

[0050] Figure 4 Relationship diagram of real-time power unbalance degree , modulation degree and voltage unbalance degree when the capacitance C = 10 μF;

[0051] Figure 5 Relationship diagram of midpoint current extreme component , real-time power unbalance degree and voltage unbalance degree ;

[0052] Figure 6 Optimized schematic diagram of voltage vector trajectory under bipolar voltage difference control mode;

[0053] Figure 7 Steady-state experimental waveform diagram of the electrolytic capacitorless Vienna rectifier controlled by using the prior method;

[0054] Figure 8 Steady-state experimental waveform diagram of the electrolytic capacitorless Vienna rectifier controlled by using the method of the present application.

[0055] Figure 1 M is the midpoint of three-phase grid voltage, is the three-phase grid voltage, is the three-phase grid current, is the inductance, is the resistance, is the six diodes forming the rectifier bridge; is the three-phase switch tube, is the switch tube associated diode, is the upper DC bus current, is the lower DC bus current, is the upper DC bus capacitor, is the lower DC bus capacitor, ; is the upper DC bus capacitor current, is the DC bus capacitor current; P is the top end of the DC bus, O is the midpoint of the DC bus capacitor, and N is the low end of the DC bus.

[0056] Figure 2 In is the grid-side current, and is the PO end and ON end voltage, and is the PO end and ON end active power, is the modulation wave in the balanced voltage control mode, is the axis voltage component of the voltage vector, d x is the duty cycle of the three-phase switch.

[0057] Figure 3 In is the upper limit of the unbalanced power boundary, is the lower limit of the unbalanced power boundary.

[0058] Figure 5 In is the maximum value of the midpoint current extreme component, is the minimum value of the midpoint current extreme component.

[0059] Figure 6 In PPN is a large vector, OPN and PON are medium vectors, and OPO, PPO, OON, and POO are small vectors, is the maximum voltage component of the beta axis, V ref is the reference voltage vector, regions 1 and 2 are voltage vector non-composition regions, and S1-S4 are different vector composition regions. DETAILED DESCRIPTION

[0060] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0061] DETAILED DESCRIPTION Figures 1 to 6 As shown in the drawings, the present application provides a method for simultaneously controlling unbalanced power and bipolar voltage of an electrolytic capacitor-free Vienna rectifier, comprising:

[0062] The unbalanced power boundary is calculated according to the midpoint current extreme component, and compared with the real-time power unbalance degree, and the bipolar voltage control mode is selected according to the comparison result;

[0063] If the unbalanced power boundary is less than the real-time power unbalance degree, a bipolar voltage difference control mode is selected; otherwise, a bipolar voltage balance control mode is selected.

[0064] In the bipolar voltage balance control mode, a midpoint voltage prediction mechanism is used to predict the adjacent next time midpoint voltage, and according to the comparison result of the adjacent next time midpoint voltage and the voltage hysteresis boundary, the optimal clamping mode of the discontinuous pulse width modulation is selected to realize the unbalanced power and bipolar voltage collaborative control.

[0065] In the bipolar voltage difference control mode, the optimal voltage unbalance degree is calculated according to the midpoint current extreme component and the active power; at the same time, the voltage vector non-synthetic region is determined according to the comparison relationship between the maximum and minimum values of the midpoint current extreme component; the vertical trajectory projection method is used to synthesize the two adjacent vectors at the boundary of the voltage vector non-synthetic region, the two adjacent vectors including a medium vector and a small vector; the duty cycle of the medium vector is calculated; the trajectory optimized modulation wave of the voltage vector non-synthetic region is calculated based on the duty cycle of the medium vector, realizing the unbalanced power and bipolar voltage collaborative control.

[0066] The embodiment combines the voltage vector vertical projection trajectory optimization method to reduce the voltage vector error, so as to reduce the grid-side current harmonics.

[0067] In the embodiment, the electrolytic capacitor-free Vienna rectifier usually controls the DC side voltage balance, at this time, the unbalanced power range boundary is mainly related to the midpoint current extreme value and the active power. Therefore, in order to widen the unbalanced power operating range, the unbalanced power boundary is calculated according to the midpoint current extreme component, and the bipolar voltage control mode is selected according to the size relationship between the real-time power unbalance degree and the unbalanced power boundary.

[0068] Then, the bipolar voltage is controlled according to the voltage control mode selected by the unbalanced power judgment mechanism. When the bipolar voltage balance control mode is selected, in order to avoid the high-frequency oscillation of the midpoint voltage at the voltage hysteresis, the optimal clamping mode of the discontinuous pulse width modulation is selected to further suppress the bipolar voltage fluctuation by combining the midpoint voltage prediction mechanism and the voltage hysteresis boundary.

[0069] With the increase of power imbalance, when the imbalance power boundary is exceeded, the bipolar voltage control mode is switched from the balanced voltage control mode to the difference voltage control mode. When the bipolar voltage difference control mode is selected, the optimal voltage imbalance is calculated by combining the midpoint current extreme component and the active power, which maximizes the imbalance power operating range on the basis of ensuring the control performance of the Vienna rectifier; the bipolar voltage imbalance will cause the amplitude and direction of the voltage vector in the space vector diagram to change, resulting in the emergence of a voltage vector synthesis error increase area. The embodiment identifies the voltage vector synthesis error area according to the size of the midpoint current extreme value, and reduces the voltage vector error by combining the trajectory optimization method of the voltage vector perpendicular projection, so as to reduce the grid-side current harmonics.

[0070] Figure 2 The control block diagram of the imbalance power and bipolar voltage cooperative control method for the electrolytic capacitor-free Vienna rectifier. First, the capacitor voltage control mode is selected according to the imbalance power operating range judgment mechanism, when it is within the imbalance power boundary, the balanced voltage control mode is selected, and the bipolar voltage fluctuation suppression ability is enhanced through midpoint voltage prediction to avoid repeated oscillation at the voltage hysteresis boundary. When the imbalance power boundary is exceeded, the Vienna rectifier faces the risk of instability, and needs to be switched to the difference voltage control mode. Due to the constant power characteristic of the load, the required midpoint current direct current component can be regulated by independently controlling the size of the bipolar voltage, and the optimal voltage imbalance is obtained under the constraint of the midpoint current direct current component extreme value and the active power, so as to realize the widening of the imbalance power boundary. Finally, the voltage vector synthesis error is reduced by identifying the non-synthesizable area and introducing the voltage vector trajectory optimization strategy in it, so as to realize the bipolar voltage fluctuation suppression and the grid power quality improvement.

[0071] To analyze the influence of capacitor capacitance and voltage imbalance on the imbalance power boundary, the midpoint current extreme component is combined to obtain Figure 3 and Figure 4 .

[0072] From the relationship between the required component of the midpoint current and the voltage and power imbalance of Figure 5 , it can be seen that the imbalance power range allowed when the voltage is balanced is small.

[0073] Figure 6 The voltage vector trajectory optimization schematic diagram under the bipolar voltage difference control mode, by selecting the vector with the maximum voltage component on the β axis for vector synthesis, the vectors participating in voltage vector synthesis in sector II-1 are OPO and OPN, and the vectors participating in voltage vector synthesis in sector II-2 are POO and PON, and the synthesized voltage vector is the green trajectory in the figure.

[0074] When connecting Vienna rectifiers to loads of different power ratings, the required DC component of the midpoint current... The calculation method is as follows:

[0075] ,

[0076] In the formula This represents the grid-side voltage amplitude.

[0077] Furthermore, the maximum and minimum midpoint current clamped by the DPWM (Discontinuous Pulse Width Modulation) strategy are related to the superimposed zero-sequence components. The calculation method for the extreme components of the midpoint current is as follows:

[0078] ,

[0079] In the formula These are the extreme components of the midpoint current. For the net side Phase current, ; for Phase voltage modulation wave, This represents the zero-sequence voltage component that is equivalent to the superposition after clamping. Voltage imbalance; This is a sign function for the grid-side current, used to determine the polarity of the current;

[0080] The zero-sequence voltage component is equivalent to the superposition after clamping. maximum value and minimum value The expression is:

[0081] ,

[0082] In the formula For the maximum equivalent modulated wave, It is the minimum equivalent modulated wave;

[0083] Maximum equivalent modulated wave The fundamental value of the maximum equivalent modulated wave The maximum value, the minimum equivalent modulated wave The minimum equivalent modulated wave fundamental value The minimum value;

[0084] ,

[0085] ;

[0086] The zero-sequence voltage component is equivalent to the superposition after clamping. maximum value and minimum value The corresponding extreme components of the midpoint current were calculated. maximum value and minimum value .

[0087] Combining the extreme components of the midpoint current Constraint calculation of unbalanced power boundary:

[0088]

[0089] In the formula For unbalanced power boundary, To adjust the system.

[0090] Furthermore, in the bipolar voltage balance control mode, to further suppress bipolar voltage fluctuations, a midpoint voltage prediction mechanism needs to be introduced. This mechanism predicts the midpoint voltage at the next adjacent time step, including:

[0091] ,

[0092] In the formula for Midpoint voltage at time, for Midpoint voltage at time, To control the cycle, This refers to the capacitance value of the thin-film capacitor. for Midpoint current at time t.

[0093] Based on the relationship between the midpoint current and the duty cycle, the predicted midpoint voltage values ​​for different clamping modes are calculated:

[0094] ,

[0095] In the formula In maximum discontinuous pulse width modulation clamping mode Midpoint voltage at time, In minimum discontinuous pulse width modulation clamping mode Midpoint voltage at time, In maximum discontinuous pulse width modulation clamping mode Phase duty cycle, In minimum discontinuous pulse width modulation clamping mode Phase duty cycle.

[0096] The method for selecting the optimal clamping mode for discontinuous pulse width modulation is as follows:

[0097] ,

[0098] In the formula Indicates the optimal clamping mode. This indicates the minimum discontinuous pulse width modulation clamping mode. This indicates the maximum discontinuous pulse width modulation clamping mode. This indicates that the current discontinuous pulse width modulation clamping mode will be maintained; This is the upper limit of the voltage hysteresis. This is the lower limit of the voltage hysteresis loop.

[0099] Furthermore, when bipolar voltage difference control is selected, based on the extreme components of the midpoint current... maximum value The optimal voltage imbalance that maintains the real-time power imbalance can be obtained. The calculation method for the optimal voltage imbalance is as follows:

[0100] ,

[0101] In the formula For optimal voltage imbalance, For real-time power imbalance, To output active power, This is the bus voltage.

[0102] The criterion for determining the region where voltage vectors cannot be synthesized is:

[0103] ,

[0104] In the formula For the judgment coefficient, if , If the voltage vector is within the normal range, then the voltage vector is determined to be within the normal range; otherwise... , If the value is 0, it indicates that the voltage vector is located in the region where synthesis is not possible.

[0105] When the bipolar voltage is unbalanced, it will cause regions in the space vector diagram where the voltage vector cannot be synthesized. The trajectory optimization method of vertical projection of voltage vector can reduce the voltage vector synthesis error and suppress grid-side current distortion.

[0106] Let the duty cycle of the median vector be... Then the duty cycle of the smaller vector is The method for calculating the duty cycle of the vector is as follows:

[0107] ,

[0108] In the formula The duty cycle of the mid-vector. For voltage vector Axis voltage component.

[0109] The method for calculating the modulated wave after trajectory optimization in the region where voltage vector synthesis is not possible is as follows:

[0110] ,

[0111] wherein is the modulated wave after phase trajectory optimization, is the maximum value of the grid-side phase current, is the intermediate value of the grid-side phase current, is the minimum value of the grid-side phase current.

[0112] The calculation method of the voltage vector projection coefficient in the vertical trajectory projection method is as follows:

[0113] ,

[0114] wherein is the voltage vector projection coefficient, is the axis reference voltage component of the voltage vector, is the axis reference voltage component of the voltage vector.

[0115] As shown in FIG. 1, in combination with the voltage vector projection coefficient, the distance of the reference voltage vector to the line segment AB can be obtained as Figure 6 , which can be equivalent to the reference voltage vector synthesis error u err , and the expression is as follows:

[0116] .

[0117] Verification experiment: the following experiment is used to verify the effectiveness of the present application.

[0118] The effectiveness of the unbalanced power and bipolar voltage collaborative control method is verified on a Vienna rectifier platform without electrolytic capacitor. The parameter settings of the experimental platform are as follows: grid frequency 50 Hz, input inductance 3 mH, switching frequency 50 kHz, and DC side capacitor capacity 10 μF.

[0119] Figure 7 is a steady-state experimental waveform diagram without using the unbalanced power and bipolar voltage collaborative control algorithm proposed in the present application. Figure 8 is a steady-state experimental waveform diagram using the unbalanced power and bipolar voltage collaborative control algorithm proposed in the present application. As can be seen from Figure 7 and Figure 8 , when the unbalanced power is not used in the method of the present application, as the unbalanced power increases, when it exceeds the boundary, the bipolar voltage oscillates violently, and finally the bipolar voltage diverges, triggering the Vienna rectifier protection shutdown. After using the method of the present application, as the unbalanced power increases, when it exceeds the boundary, the bipolar voltage switches to the differential voltage control mode, and the Vienna rectifier can stably operate under a larger unbalanced power condition. Figure 8 ​For the experimental results comparison chart under different power imbalance degrees after adopting the method of the present application, it can be seen that the voltage vector trajectory optimization method realizes the suppression of bipolar voltage fluctuation and the improvement of grid-side power quality.

[0120] While the application has been described with reference to particular embodiments thereof, it should be understood that these are merely illustrative examples of the principles and application of the application. It will thus be appreciated that numerous modifications can be made to the illustrative embodiments and that other arrangements can be devised without departing from the spirit and scope of the present application as defined by the appended claims. It will be understood that the features described in relation to separate embodiments can be used in combination with other features described herein. It will be further understood that features described in relation to one embodiment can be used in combination with features described in relation to another embodiment.

Claims

1. A method for coordinated control of unbalanced power and bipolar voltage in a capacitor-free Vienna rectifier, characterized in that, include: The unbalanced power boundary is calculated based on the extreme components of the midpoint current and compared with the real-time power imbalance. The bipolar voltage control mode is selected based on the comparison result. If the unbalanced power boundary is less than the real-time power imbalance, select the bipolar voltage difference control mode; otherwise, select the bipolar voltage balance control mode. In the bipolar voltage balance control mode, a midpoint voltage prediction mechanism is used to predict the midpoint voltage at the next adjacent time step. Based on the comparison results between the midpoint voltage at the next adjacent time step and the voltage hysteresis boundary, the optimal clamping mode of discontinuous pulse width modulation is selected to achieve unbalanced power and bipolar voltage coordinated control. In the bipolar voltage difference control mode, the optimal voltage imbalance is calculated based on the extreme components of the midpoint current and the active power. Simultaneously, the region where voltage vectors cannot be synthesized is determined based on the comparison between the maximum and minimum values ​​of the extreme components of the midpoint current. The vertical trajectory projection method is used to synthesize two adjacent vectors at the boundary of the region where voltage vectors cannot be synthesized. The two adjacent vectors include a mid-vector and a small vector. The duty cycle of the mid-vector is calculated. Based on the duty cycle of the mid-vector, the trajectory-optimized modulation wave of the region where voltage vectors cannot be synthesized is calculated, thereby realizing the coordinated control of unbalanced power and bipolar voltage.

2. The method for coordinated control of unbalanced power and bipolar voltage in a capacitorless Vienna rectifier according to claim 1, characterized in that, The method for calculating the extreme components of the midpoint current is as follows: ， In the formula These are the extreme components of the midpoint current. For the net side Phase current, ; for Phase voltage modulation wave, This represents the zero-sequence voltage component that is equivalent to the superposition after clamping. Voltage imbalance; The zero-sequence voltage component is equivalent to the superposition after clamping. maximum value and minimum value The expression is: ， In the formula For the maximum equivalent modulated wave, It is the minimum equivalent modulated wave; Maximum equivalent modulated wave The fundamental value of the maximum equivalent modulated wave The maximum value, the minimum equivalent modulated wave The minimum equivalent modulated wave fundamental value The minimum value; ， ； The zero-sequence voltage component is equivalent to the superposition after clamping. maximum value and minimum value The corresponding extreme components of the midpoint current were calculated. maximum value and minimum value .

3. The method for coordinated control of unbalanced power and bipolar voltage in a capacitorless Vienna rectifier according to claim 2, characterized in that, Combining the extreme components of the midpoint current Constraint calculation of unbalanced power boundary: In the formula For unbalanced power boundary, To adjust the system.

4. The method for coordinated control of unbalanced power and bipolar voltage in a capacitorless Vienna rectifier according to claim 3, characterized in that, In bipolar voltage balance control mode, the midpoint voltage prediction mechanism is used to predict the midpoint voltage at the next adjacent time step, including: ， In the formula for Midpoint voltage at time, for Midpoint voltage at time, To control the cycle, This refers to the capacitance value of the thin-film capacitor. for The current at the midpoint at any given moment.

5. The method for coordinated control of unbalanced power and bipolar voltage in a capacitorless Vienna rectifier according to claim 4, characterized in that, Based on the relationship between the midpoint current and the duty cycle, the predicted midpoint voltage values ​​for different clamping modes are calculated: ， In the formula In maximum discontinuous pulse width modulation clamping mode Midpoint voltage at time, In minimum discontinuous pulse width modulation clamping mode Midpoint voltage at time, In maximum discontinuous pulse width modulation clamping mode Phase duty cycle, In minimum discontinuous pulse width modulation clamping mode Phase duty cycle.

6. The method for coordinated control of unbalanced power and bipolar voltage in a capacitorless Vienna rectifier according to claim 5, characterized in that, The method for selecting the optimal clamping mode for discontinuous pulse width modulation is as follows: ， In the formula Indicates the optimal clamping mode. This indicates the minimum discontinuous pulse width modulation clamping mode. This indicates the maximum discontinuous pulse width modulation clamping mode. This indicates that the current discontinuous pulse width modulation clamping mode will be maintained; This is the upper limit of the voltage hysteresis. This is the lower limit of the voltage hysteresis loop.

7. The method for coordinated control of unbalanced power and bipolar voltage in a capacitorless Vienna rectifier according to claim 8, characterized in that, The optimal voltage imbalance is calculated as follows: ， In the formula For optimal voltage imbalance, For real-time power imbalance, To output active power, This is the bus voltage.

8. The method for coordinated control of unbalanced power and bipolar voltage in a capacitorless Vienna rectifier according to claim 7, characterized in that, The criterion for determining the region where voltage vectors cannot be synthesized is: ， In the formula For the judgment coefficient, if , If the voltage vector is within the normal range, then the voltage vector is determined to be within the normal range; otherwise... , If the value is 0, it indicates that the voltage vector is located in the region where synthesis is not possible.

9. The method for coordinated control of unbalanced power and bipolar voltage in a capacitorless Vienna rectifier according to claim 8, characterized in that, The method for calculating the duty cycle of the medium vector is as follows: ， In the formula The duty cycle of the mid-vector. For voltage vector Axis voltage component.

10. The method for coordinated control of unbalanced power and bipolar voltage in a capacitorless Vienna rectifier according to claim 9, characterized in that, The method for calculating the modulated wave after trajectory optimization in the region where voltage vector synthesis is not possible is as follows: ， In the formula for Modulated wave after phase trajectory optimization This represents the maximum value of the phase current on the grid side. This is the median value of the grid-side phase current. This represents the minimum phase current on the grid side.

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