Working point design method for flexible direct current bus frequency converter and permanent magnet synchronous motor

Abstract

According to the working point design method of the flexible direct-current bus frequency converter and the permanent magnet synchronous motor, the counter electromotive force of the permanent magnet synchronous motor at the rated rotating speed is close to the upper limit value of the direct-current bus voltage, it is guaranteed that the permanent magnet synchronous motor has the high port voltage and the low torque current requirement, the loss of an electric propulsion system is reduced, and the electric propulsion efficiency is improved. The electric propulsion system works at a high-efficiency working point with high voltage and small current; and on the other hand, the direct current bus voltage is adjusted through a modulation ratio constant method and a lookup table method until the modulation ratio stable tracking given value and the bus voltage stable tracking given value of the flexible direct current bus frequency converter are achieved, and then the efficient working point of the electric propulsion system is matched. The working points of the flexible direct current bus frequency converter and the permanent magnet synchronous motor are designed, so that the whole electric propulsion system operates in an efficient working area, the loss of the electric propulsion system is reduced, and the efficiency of the electric propulsion system is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronics and relates to a method for designing a motor operating point. Background Art

[0002] In new energy power systems such as electric vehicles, ship electric propulsion and rail transit, motor drivers, i.e. inverters, generally draw power from power batteries to drive motors, which have the advantages of high efficiency and cleanliness and broad application prospects. Permanent magnet synchronous motors can use permanent magnets to replace the excitation windings of traditional synchronous motors, without the need to install excitation windings and brushes. They have the advantages of simple structure, easy maintenance, high torque density and high power factor, and are widely used in defense, military industry, industrial production and other fields. However, with the consumption of energy, the power battery voltage, i.e. the DC bus voltage, will fluctuate in a wide range, affecting the system's operating point and working efficiency, which puts forward higher requirements for the design of the operating point of the electric propulsion system.

[0003] In the traditional design method, in order to ensure that the propulsion system can still operate at full power when the bus voltage is the lowest, the inverter and the motor must be designed to operate at full power at the minimum bus voltage. The principle of the traditional electric propulsion system operating point design is as follows: Figure 1 As shown in the figure, according to the traditional design concept, the designed motor must always maintain a low port voltage in the full speed range, that is, the line voltage peak is less than the minimum battery voltage, which requires the motor to have a small permanent magnet flux. However, when the electric propulsion system is actually running, the motor is at medium and low speeds most of the time, and the power bus voltage is at the middle value of its variation range most of the time, which leads to a very low DC bus voltage utilization rate of the system. In addition, the torque current demand is large under low bus voltage, resulting in greater losses in the electric propulsion system. Taking a small ship as an example, its battery voltage range is 350V-640V, and the maximum bus voltage is close to twice its minimum value. Therefore, the stator copper loss generated by the motor under the traditional electric propulsion system working point design concept may be as high as several times that under the optimal working point. Therefore, the traditional electric propulsion system working point design method makes it difficult to design the propulsion inverter and propulsion motor at the optimal working point, which restricts the efficiency improvement of the electric propulsion system.

[0004] Existing methods generally adjust the DC bus voltage by cascading a DC / DC converter in the front stage of the inverter, but there are still the following shortcomings: first, the DC / DC converter topology used for voltage stabilization generally adopts a single-arm chopper circuit, and the topology lacks universality for high-power occasions; second, the DC bus voltage is adjusted by the current and other operating parameter calibration methods, but this type of parameter calibration method is complex to implement and has weak universality; third, an artificial intelligence algorithm is used to adjust the bus voltage according to the training results of big data, but it is highly dependent on the historical data of a specific system and lacks engineering practicality. Summary of the invention

[0005] In order to solve the problems in the traditional electric propulsion system working point design method described in the background technology, such as very low DC bus voltage utilization rate, large loss of the electric propulsion system, difficulty in designing the propulsion inverter and the propulsion motor at the optimal working point, difficulty in improving the efficiency of the electric propulsion system, and poor universality and lack of engineering practicality of the existing design methods, the present invention provides a working point design method for a flexible DC bus inverter and a permanent magnet synchronous motor.

[0006] The method of the present invention comprises:

[0007] Based on the flexible DC bus inverter topology, according to the DC bus voltage variation range in actual applications and the rated current and rated speed of the permanent magnet synchronous motor, the constraint equation for the permanent magnet synchronous motor parameter design is established to make the back electromotive force at the rated speed of the permanent magnet synchronous motor close to the upper limit of the DC bus voltage, thus realizing the working point design of the electric propulsion system.

[0008] Based on the flexible DC bus inverter topology, the modulation ratio constant method is adopted. According to the modulation ratio u of the flexible DC bus inverter, s Modulation ratio deviation ΔU from the target modulation ratio d , adjust the DC bus voltage until the modulation ratio of the flexible DC bus inverter stably tracks the given value;

[0009] Based on the flexible DC bus inverter topology, the lookup table method is used to calculate the DC bus voltage. The DC bus voltage deviation ΔU from the actual value of the DC bus voltage dc , adjust the DC bus voltage until the bus voltage of the flexible DC bus inverter stably tracks the given value;

[0010] By combining the above-mentioned stable tracking of the given value by the modulation ratio of the flexible DC bus inverter and the stable tracking of the given value by the bus voltage of the flexible DC bus inverter, the working point design of the flexible DC bus inverter is realized.

[0011] Furthermore, the flexible DC bus inverter topology can be expanded according to the power level and the number of motor phases; the input side of the flexible DC bus inverter includes an input side capacitor for stabilizing the input voltage;

[0012] The flexible DC bus frequency converter comprises a buck-boost chopper module and an inverter speed regulation module, wherein the buck-boost chopper module and the inverter speed regulation module are cascaded in parallel with a bus support capacitor for stabilizing the DC bus voltage;

[0013] The buck-boost chopper module can be expanded to multiple levels according to power level requirements, and the power level can be improved by staggered parallel connection of multiple bridge arms; the buck-boost chopper module can also be simplified to a simple boost or buck chopper topology according to requirements; the inverter speed regulation module can be expanded to multiple phases according to load motor requirements, and drive permanent magnet synchronous motors with any number of phases ≥ 2.

[0014] Furthermore, in the working point design of the electric propulsion system, the stator resistance R of the permanent magnet synchronous motor and the d-axis inductance L d , q-axis inductance L q , permanent magnet flux ψ f Satisfy the constraint equations described in equations (1) and (2):

[0015]

[0016] Wherein, formula (1) is the stator voltage equation of permanent magnet synchronous motor; formula (2) is the parameter design constraint of permanent magnet synchronous motor; u d is the d-axis voltage of the permanent magnet synchronous motor, u q is the q-axis voltage of the permanent magnet synchronous motor; i d is the d-axis current of the permanent magnet synchronous motor, i q is the q-axis current of the permanent magnet synchronous motor, ω e is the electrical angular velocity of the permanent magnet synchronous motor, ω n is the rated electrical angular velocity of the permanent magnet synchronous motor, V dcmax is the upper limit of the inverter DC bus voltage, is the differential operator.

[0017] Furthermore, the modulation ratio constant method is:

[0018] The d-axis voltage generated by the current control loop is given by Q-axis voltage setting Calculate the modulation ratio u of the flexible DC bus inverter s , the modulation ratio u of the flexible DC bus inverter s Modulation ratio with target The modulation ratio deviation ΔU is obtained by subtracting d , ΔU d On the one hand, it is used to determine the buck-boost mode of the buck-boost chopper module, and on the other hand, it is sent to the PI regulator to obtain the current reference value of the buck-boost chopper module. After being evenly divided by each branch, the current i L1 to i LN The difference is sent to the PI regulator to obtain the duty cycle d of each branch of the buck-boost chopper module. L1 to d LN The buck-boost chopper module is based on the boost or buck mode and the duty cycle d of each branch. L1 to dLN Adjust the DC bus voltage so that the modulation ratio of the flexible DC bus inverter tracks the given value.

[0019] Furthermore, the lookup table method is:

[0020] The speed of the permanent magnet synchronous motor is ω re As input, the DC bus voltage given value is obtained according to the corresponding table of motor speed and DC bus voltage target value. Subtract it from the true value of the DC bus voltage to obtain the DC bus voltage deviation ΔU dc ; ΔU dc On the one hand, it is used to determine the buck-boost mode of the buck-boost chopper module, and on the other hand, it is sent to the PI regulator to obtain the current reference value of the buck-boost chopper module. After being evenly divided by each branch, the current i L1 to i LN The difference is sent to the PI regulator to obtain the duty cycle d of each branch of the buck-boost chopper module. L1 to d LN ; The buck-boost chopper module is based on the boost or buck mode and the duty cycle of each branch. L1 to d LN Adjust the DC bus voltage so that the bus voltage of the flexible DC bus inverter can stably track the given value.

[0021] Compared with the prior art, the present invention is based on a flexible DC bus inverter topology. On the one hand, a permanent magnet synchronous motor is designed in a targeted manner so that the back electromotive force of the permanent magnet synchronous motor at the rated speed is close to the upper limit of the DC bus voltage, ensuring that the permanent magnet synchronous motor has a higher port voltage and a lower torque current requirement, reducing the loss of the electric propulsion system, and making the electric propulsion system work at a high voltage, low current and high efficiency working point; on the other hand, the DC bus voltage is adjusted by a constant modulation ratio method and a lookup table method until the modulation ratio of the flexible DC bus inverter stably tracks a given value and the bus voltage stably tracks a given value, thereby matching the high efficiency working point of the electric propulsion system, ensuring that the electric propulsion system has high efficiency and preventing the permanent magnet synchronous motor from entering a weak magnetic field speed-up condition. The DC bus voltage adjustment method is easy to operate and can be flexibly selected and matched according to engineering requirements. In addition, the flexible DC bus inverter topology has good ductility and can be expanded to multi-phase and multiple according to power levels, or simplified to a simple boost or buck chopper topology according to requirements.

[0022] The present invention designs the working points of the flexible DC bus inverter and the permanent magnet synchronous motor so that the propulsion inverter and the propulsion motor can easily operate at the optimal working point, thereby improving the DC bus voltage utilization rate, allowing the electric propulsion system to operate under high voltage and low current conditions, thereby allowing the entire electric propulsion system to operate in a high-efficiency working area, reducing the loss of the electric propulsion system, and improving the efficiency of the electric propulsion system. At the same time, it can also achieve the effect of reducing output current harmonics and achieving the effect of reducing vibration and noise. The method of the present invention does not need to rely on historical data, is simple, has high versatility, wide universality, and strong engineering practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Design principles for the operating points of conventional electric propulsion systems.

[0024] Figure 2 This is the flexible DC bus inverter topology structure (boost-boost chopper) in the embodiment of the present invention.

[0025] Figure 3 This is the flexible DC bus inverter topology structure (boost chopper) in the embodiment of the present invention.

[0026] Figure 4 This is the flexible DC bus inverter topology structure (step-down chopping) in the embodiment of the present invention.

[0027] Figure 5 This is the working point design principle of the present invention.

[0028] Figure 6 The present invention discloses a method for regulating a DC bus voltage by adopting a constant modulation ratio method.

[0029] Figure 7 The present invention adopts a method for adjusting a DC bus voltage by using a lookup table method. DETAILED DESCRIPTION

[0030] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0031] The flexible DC bus inverter topology can be expanded according to the power level and the number of motor phases; the input side of the flexible DC bus inverter includes an input side capacitor for stabilizing the input voltage; the flexible DC bus inverter includes a buck-boost chopper module and an inverter speed regulation module, and the buck-boost chopper module and the inverter speed regulation module are cascaded in parallel with a bus support capacitor for stabilizing the DC bus voltage; the buck-boost chopper module can be expanded to multipleization according to the power level requirements, and the power level can be improved by staggering and paralleling multiple bridge arms; the buck-boost chopper module can also be simplified to a simple boost or buck chopper topology according to the requirements; the inverter speed regulation module can be expanded to multi-phase according to the load motor requirements, and drive permanent magnet synchronous motors of any number of phases with a phase number ≥ 2.

[0032] In this embodiment, the flexible DC bus inverter topology is as follows: Figure 2 As shown in the figure, taking the dual buck-boost chopper and six-phase inverter bridge arm as an example, the flexible DC bus inverter topology can be expanded according to the power level and the number of motor phases in actual application. The flexible DC bus inverter includes a buck-boost chopper module and an inverter speed regulation module. The dual buck-boost chopper module consists of 8 switch tubes S1, S2, S3, S4, S5, S6, S7, S8 with anti-parallel diodes, and 2 chopper inductors L1 and L2. The inverter speed regulation module contains 6 bridge arms, each of which adopts the traditional two-level topology structure. The 6 bridge arms have a total of 12 switch tubes S with anti-parallel diodes. A1 , S A2 , S B1 , S B2 , S C1 , S C2 , S U1 , S U2 , S V1 , S V2 , S W1 , S W2 The input side of the flexible DC bus inverter includes an input side capacitor C IN , used to stabilize the input voltage; the bus support capacitor C is connected in parallel at the cascade connection between the buck-boost chopper module and the inverter speed regulation module DC , which is used to stabilize the DC bus voltage. At the same time, the flexible DC bus inverter topology can be expanded to multi-phase and multiplex according to the power level, or it can be simplified to a simple boost or buck chopper topology according to the needs, such as Figure 3 , Figure 4 shown.

[0033] Working point design method of flexible DC bus inverter and permanent magnet synchronous motor, working point design principle is as follows Figure 5 As shown, the details are as follows.

[0034] based on Figure 2The flexible DC bus inverter topology shown in the figure establishes the constraint equations for the permanent magnet synchronous motor parameter design according to the DC bus voltage variation range in actual applications, as well as the rated current and rated speed of the permanent magnet synchronous motor, so that the back electromotive force at the rated speed of the permanent magnet synchronous motor is close to the upper limit value of the DC bus voltage, and the working point design of the electric propulsion system is realized, so that the propulsion system works at a high-voltage, low-current and high-efficiency working point.

[0035] Specifically, in the working point design of the electric propulsion system, the stator resistance R of the permanent magnet synchronous motor and the d-axis inductance L d , q-axis inductance L q , permanent magnet flux ψ f Satisfy the constraint equations described in equations (1) and (2):

[0036]

[0037] Wherein, formula (1) is the stator voltage equation of permanent magnet synchronous motor; formula (2) is the parameter design constraint of permanent magnet synchronous motor; u d is the d-axis voltage of the permanent magnet synchronous motor, u q is the q-axis voltage of the permanent magnet synchronous motor; i d is the d-axis current of the permanent magnet synchronous motor, i q is the q-axis current of the permanent magnet synchronous motor, ω e is the electrical angular velocity of the permanent magnet synchronous motor, ω n is the rated electrical angular velocity of the permanent magnet synchronous motor, V dcmax is the upper limit of the inverter DC bus voltage, is the differential operator.

[0038] based on Figure 2 The flexible DC bus inverter topology shown in the figure starts from the perspective of bus voltage regulation and proposes two DC bus voltage regulation methods. The DC bus voltage is adjusted by reasonably controlling the buck-boost chopper module to make the inverter speed regulation module work at a higher modulation ratio, such as above 0.9, but the permanent magnet synchronous motor will not enter the weak magnetic speed-up condition, which not only ensures low output current and high efficiency, but also avoids the adverse effects of long-term deep weak magnetic operation of the permanent magnet synchronous motor that may cause motor demagnetization.

[0039] Specifically, based on Figure 2 The flexible DC bus inverter topology structure shown in FIG. 1 adopts a method of adjusting the DC bus voltage by using a constant modulation ratio method. Figure 6 As shown, the d-axis voltage generated by the current control loop is given by Q-axis voltage setting Calculate the modulation ratio u of the flexible DC bus inverter s , the modulation ratio u of the flexible DC bus inverter s Modulation ratio with target The modulation ratio deviation ΔU is obtained by subtracting d , ΔU d On the one hand, it is used to determine the buck-boost mode of the buck-boost chopper module, and on the other hand, it is sent to the PI regulator to obtain the current reference value of the buck-boost chopper module. After being evenly divided by each branch, the current i L1 to i LN The difference is sent to the PI regulator to obtain the duty cycle d of each branch of the buck-boost chopper module. L1 to d LN The buck-boost chopper module is based on the boost or buck mode and the duty cycle d of each branch. L1 to d LN Adjust the DC bus voltage so that the modulation ratio of the flexible DC bus inverter tracks the given value.

[0040] Specifically, based on Figure 2 The flexible DC bus inverter topology structure shown in FIG. 1 is a method for adjusting the DC bus voltage using a lookup table method. Figure 7 As shown, the speed of the permanent magnet synchronous motor ω re As input, the DC bus voltage given value is obtained according to the corresponding table of motor speed and DC bus voltage target value. Subtract it from the true value of the DC bus voltage to obtain the DC bus voltage deviation ΔU dc ; ΔU dc On the one hand, it is used to determine the buck-boost mode of the buck-boost chopper module, and on the other hand, it is sent to the PI regulator to obtain the current reference value of the buck-boost chopper module. After being evenly divided by each branch, the current i L1 to i LN The difference is sent to the PI regulator to obtain the duty cycle d of each branch of the buck-boost chopper module. L1 to d LN ; The buck-boost chopper module is based on the boost or buck mode and the duty cycle of each branch. L1 to d LN Adjust the DC bus voltage so that the bus voltage of the flexible DC bus inverter can stably track the given value.

[0041] Finally, by combining the above-mentioned flexible DC bus inverter modulation ratio stable tracking given value and flexible DC bus inverter bus voltage stable tracking given value, the flexible DC bus inverter is made to operate at a high efficiency operating point, realizing the operating point design of the flexible DC bus inverter.

[0042] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A method for designing the working point of a flexible DC bus frequency converter and a permanent magnet synchronous motor, characterized in that: include: Based on the flexible DC bus inverter topology, according to the DC bus voltage variation range in actual applications and the rated current and rated speed of the permanent magnet synchronous motor, the constraint equation for the permanent magnet synchronous motor parameter design is established to make the back electromotive force at the rated speed of the permanent magnet synchronous motor close to the upper limit of the DC bus voltage, thus realizing the working point design of the electric propulsion system. Based on the flexible DC bus inverter topology, the modulation ratio constant method is adopted. According to the modulation ratio u of the flexible DC bus inverter, s Modulation ratio deviation ΔU from target modulation ratio d , adjust the DC bus voltage until the modulation ratio of the flexible DC bus inverter stably tracks the given value; Based on the flexible DC bus inverter topology, the lookup table method is used to determine the DC bus voltage U d * c The DC bus voltage deviation ΔU from the actual value of the DC bus voltage dc , adjust the DC bus voltage until the bus voltage of the flexible DC bus inverter stably tracks the given value; By combining the above-mentioned stable tracking of the given value by the modulation ratio of the flexible DC bus inverter and the stable tracking of the given value by the bus voltage of the flexible DC bus inverter, the working point design of the flexible DC bus inverter is realized.

2. The working point design method of the flexible DC bus frequency converter and the permanent magnet synchronous motor according to claim 1 is characterized in that: The flexible DC bus inverter topology structure can be expanded according to the power level and the number of motor phases; the input side of the flexible DC bus inverter includes an input side capacitor for stabilizing the input voltage; The flexible DC bus frequency converter comprises a buck-boost chopper module and an inverter speed regulation module, wherein the buck-boost chopper module and the inverter speed regulation module are cascaded in parallel with a bus support capacitor for stabilizing the DC bus voltage; The buck-boost chopper module can be expanded to multiple levels according to power level requirements, and the power level can be improved by staggered parallel connection of multiple bridge arms; the buck-boost chopper module can also be simplified to a simple boost or buck chopper topology according to requirements; the inverter speed regulation module can be expanded to multiple phases according to load motor requirements, and drive permanent magnet synchronous motors with any number of phases ≥ 2.

3. The working point design method of the flexible DC bus frequency converter and the permanent magnet synchronous motor according to claim 1 is characterized in that: In the working point design of the electric propulsion system, the stator resistance R of the permanent magnet synchronous motor and the d-axis inductance L d , q-axis inductance L q , permanent magnet flux ψ f Satisfy the constraint equations described in equations (1) and (2): Wherein, formula (1) is the stator voltage equation of the permanent magnet synchronous motor; formula (2) is the parameter design constraint of the permanent magnet synchronous motor; u d is the d-axis voltage of the permanent magnet synchronous motor, u q is the q-axis voltage of the permanent magnet synchronous motor; i d is the d-axis current of the permanent magnet synchronous motor, i q is the q-axis current of the permanent magnet synchronous motor, ω e is the electrical angular velocity of the permanent magnet synchronous motor, ω n is the rated electrical angular velocity of the permanent magnet synchronous motor, V dcmax is the upper limit of the inverter DC bus voltage, is the differential operator.

4. The working point design method of the flexible DC bus frequency converter and the permanent magnet synchronous motor according to claim 1 is characterized in that: The constant modulation ratio method is: The d-axis voltage generated by the current control loop is given by Q-axis voltage setting Calculate the modulation ratio u of the flexible DC bus inverter s , the modulation ratio u of the flexible DC bus inverter s Modulation ratio with target The modulation ratio deviation ΔU is obtained by subtracting d , ΔU d On the one hand, it is used to determine the buck-boost mode of the buck-boost chopper module, and on the other hand, it is sent to the PI regulator to obtain the current reference value of the buck-boost chopper module. After being evenly divided by each branch, the current i L1 to i LN The difference is sent to the PI regulator to obtain the duty cycle d of each branch of the buck-boost chopper module. L1 to d LN The buck-boost chopper module is based on the boost or buck mode and the duty cycle d of each branch. L1 to d LN Adjust the DC bus voltage so that the modulation ratio of the flexible DC bus inverter tracks the given value.

5. The working point design method of the flexible DC bus frequency converter and the permanent magnet synchronous motor according to claim 1 is characterized in that: The lookup table method is: The speed of the permanent magnet synchronous motor is ω re As input, the DC bus voltage given value is obtained according to the corresponding table of motor speed and DC bus voltage target value. Subtract it from the true value of the DC bus voltage to obtain the DC bus voltage deviation ΔU dc ; ΔU dc On the one hand, it is used to determine the buck-boost mode of the buck-boost chopper module, and on the other hand, it is sent to the PI regulator to obtain the current reference value of the buck-boost chopper module. After being evenly divided by each branch, the current i L1 to i LN The difference is sent to the PI regulator to obtain the duty cycle d of each branch of the buck-boost chopper module. L1 to d LN ; The buck-boost chopper module is based on the boost or buck mode and the duty cycle of each branch. L1 to d LN Adjust the DC bus voltage so that the bus voltage of the flexible DC bus inverter can stably track the given value.

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