A method for calculating the capacity of a variable speed motor rotor converter

Abstract

The present invention discloses a method for calculating the capacity of a variable speed motor rotor converter, which belongs to the field of electrical engineering technology. The method comprises the following steps: according to the unit parameters, the relationship between the rotor current and the stator power is used to obtain the maximum excitation current Imax. According to the unit parameters, the relationship between the rotor voltage, the slip rate and the stator power is used to obtain the maximum excitation voltage Umax. Finally, the capacity of the rotor converter is calculated as the capacity design of the variable speed motor rotor converter. The present invention provides an accurate, convenient and fast calculation method for the capacity design of the variable speed motor rotor converter, and provides a reference for the engineering design and application of the variable speed motor and the rotor converter.

Description

Technical Field

[0001] The invention belongs to the technical field of electrical engineering, and in particular relates to a method for calculating the capacity of a variable speed motor rotor converter. Background Art

[0002] The variable speed motor is an asynchronous synchronous motor. In steady-state operation, its rotor excitation frequency can be controlled according to the motor speed. Therefore, when the pumped storage power station uses this motor, by controlling the rotor excitation frequency to adapt to the changes in head and flow, the entire power generation or pumping period has higher energy efficiency, expanding the power adjustable range during pumping conditions and increasing the service life of the water machine. In the dynamic process, the frequency of the power grid system and the speed of the motor rotor become a controllable flexible connection, which improves the stability of the motor and the reliability of the power grid operation.

[0003] The rotor converter is an important auxiliary equipment for variable speed motors. It provides the motor with adjustable rotor current in amplitude, frequency, phase and phase sequence to meet the stable operation of the motor. Usually, when calculating the capacity of the rotor converter, the rated excitation voltage and rated excitation current provided by the main engine manufacturer are used, and then an appropriate margin is added. However, for variable speed motors, different slip rates have a greater impact on the excitation voltage. Since the speed of the unit will change near the rated value during operation, the rotor converter capacity is calculated only by relying on the rated excitation voltage and rated excitation current provided by the main engine manufacturer. The result will often deviate from the actual usage. If the capacity is too small, it will directly affect the output capacity of the motor; if it is too large, it will affect the production cost of the equipment and lead to unnecessary waste. Therefore, it is necessary to study a more accurate calculation method. Summary of the invention

[0004] In order to solve the above-mentioned problem of calculating the capacity of a variable speed motor rotor converter, the present invention provides a method for calculating the capacity of a variable speed motor rotor converter, which more accurately calculates the capacity of the variable speed motor rotor converter to be closer to the actual working condition.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A method for calculating the capacity of a variable speed motor rotor converter comprises the following steps:

[0007] 1) According to the stator inductance, rotor inductance, mutual inductance and stator voltage, the maximum excitation current Imax is obtained by using the relationship between the rotor current and the stator power. This current is also the maximum current output by the rotor converter.

[0008] 2) According to the stator inductance, rotor inductance, mutual inductance, rotor resistance, stator voltage and maximum slip rate, the maximum excitation voltage Umax is obtained by using the relationship between rotor voltage and stator power. This voltage is also the maximum voltage output by the rotor converter.

[0009] 3) According to the formula The capacity of the rotor converter is calculated, where S is the capacity of the rotor converter.

[0010] Furthermore, in step 1), the relationship between the rotor current and the stator power is as follows:

[0011] 1a) In the synchronous coordinate system, when the d-axis is oriented to the direction of the stator flux, the scalar equations of the rotor current and stator power are shown in equation (1):

[0012]

[0013] Among them, P is the active power input to the motor, Q is the reactive power input to the motor, and L m is the mutual inductance of the motor stator and rotor, u s is the stator voltage, L s is the stator inductance, i ms is the general excitation current, i r is the rotor current;

[0014] 1b) According to the above equation and the maximum power operating range of the motor, the maximum excitation current Imax is obtained.

[0015] Furthermore, in step 2), the relationship between the rotor voltage and the stator power is as follows:

[0016] 2a) In the synchronous coordinate system, the d-axis is oriented to the direction of the stator flux. Since the motor operates in a steady-state condition, the differential variable can be ignored, and the rotor voltage is reduced from the differential equation to a constant equation. The scalar equations of the rotor voltage and stator power are obtained as shown in equation (2):

[0017]

[0018] Where:

[0019]

[0020] Among them, A, C, E, F, and M are the intermediate coefficients of the equation, which are related to the motor parameters. P is the active power input to the motor, Q is the reactive power input to the motor, and i ms is the universal excitation current, u r is the motor stator voltage, R r is the rotor resistance, ω sl is the stator-rotor speed difference, σ is L r is the rotor inductance, L s is the stator inductance, L m is the stator-rotor mutual inductance, u s is the stator voltage;

[0021] 2b) According to the above equation and the maximum power operating range of the motor, the maximum excitation voltage Umax is obtained.

[0022] Further, in step 1b), the maximum excitation current Imax is obtained as follows:

[0023] Circle 1 is the stator power circle when the stator current is the rated value in the rectangular coordinate system with the horizontal coordinate Q and the vertical coordinate P;

[0024] Circle 2 is the locus of the scalar equations of the rotor current and stator power shown in equation (1) in a rectangular coordinate system with abscissa Q and ordinate P, and the center of circle O2 is the center of circle 2;

[0025] The maximum distance between the center O2 and a point on circle 1 is the line segment from the center O2 through the coordinate origin to circle 1. The length of this line segment is the maximum excitation current Imax.

[0026] Furthermore, in step 2b), the maximum excitation voltage Umax is obtained as follows:

[0027] Circle 1 is the stator power circle when the stator current is the rated value in the rectangular coordinate system with the horizontal coordinate Q and the vertical coordinate P;

[0028] Circle 3 is the trajectory of the rotor voltage equation shown in formula (2) at the maximum slip rate in the rectangular coordinate system with abscissa Q and ordinate P, and the center O3 is the center of circle 3;

[0029] The maximum distance between the center O3 and a point on circle 1 is the line segment from the center O3 through the coordinate origin to circle 1, and the length of this line segment is the maximum excitation voltage Umax.

[0030] The beneficial effects of the present invention mainly include:

[0031] 1. The present invention provides a rotor converter capacity calculation method that is closer to actual working conditions, and calculates the converter capacity by using the motor operation curve under multiple constraints such as stator voltage, stator current, rotor current, rotor voltage, slip rate and unit parameters.

[0032] 2. Avoid the mismatch between the converter and the motor operation, which affects the motor output, due to the converter capacity calculated solely using the rated excitation voltage and rated excitation current. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of an embodiment of a method for calculating the capacity of a variable speed motor rotor converter of the present invention;

[0034] Figure 2 It is a schematic diagram of the rotor voltage curve and rotor current curve of the variable speed motor;

[0035] Figure 2 Middle: Curve 1 is the power circle when the stator current is the rated value; Curve 2 is the rotor current circle, corresponding to the maximum rotor excitation current; Curve 3 is the rotor voltage circle when the slip rate is maximum, corresponding to the maximum rotor voltage. DETAILED DESCRIPTION

[0036] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

[0037] The present invention provides a method for calculating the capacity of a rotor converter that is closer to actual working conditions. The method uses a motor operating curve under multiple constraints such as stator voltage, stator current, rotor current, rotor voltage, slip rate, and unit parameters to calculate the maximum excitation voltage and maximum excitation current at the maximum slip rate, and uses these two values ​​to calculate the converter capacity.

[0038] like Figure 1 As shown, a method for calculating the capacity of a variable speed motor rotor converter according to an embodiment of the present invention comprises the following steps:

[0039] 1) According to the stator inductance, rotor inductance, mutual inductance and stator voltage, the maximum excitation current Imax is obtained by using the relationship between the rotor current and the stator power. This current is also the maximum current output by the rotor converter.

[0040] 2) According to the stator inductance, rotor inductance, mutual inductance, rotor resistance, stator voltage and maximum slip rate, the maximum excitation voltage Umax is obtained by using the relationship between rotor voltage and stator power. This voltage is also the maximum voltage output by the rotor converter.

[0041] 3) According to the formula The capacity of the rotor converter is calculated, where S is the capacity of the rotor converter.

[0042] Specifically, in step 1), the relationship between the rotor current and the stator power is as follows:

[0043] 1a) In the synchronous coordinate system, when the d-axis is oriented to the direction of the stator flux, the scalar equations of the stator power and rotor current are shown in equation (1):

[0044]

[0045] Among them, P is the active power input to the motor, Q is the reactive power input to the motor, and L m is the mutual inductance of the motor stator and rotor, u s is the stator voltage, L s is the stator inductance, i ms is the general excitation current, i r is the rotor current;

[0046] 1b) According to the above equation and the maximum power operating range of the motor, the maximum excitation current Imax is obtained.

[0047] Specifically, in step 2), the relationship between the rotor voltage and the stator power is as follows:

[0048] 2a) In the synchronous coordinate system, the d-axis is oriented to the direction of the stator flux. Since the motor operates in a steady-state condition, the differential variable can be ignored, and the rotor voltage is reduced from the differential equation to a constant equation, and the scalar equation of the stator power and the rotor voltage is obtained as shown in equation (2):

[0049]

[0050] Where:

[0051]

[0052] Among them, A, C, E, F, and M are the intermediate coefficients of the equation, which are related to the motor parameters. P is the active power input to the motor, Q is the reactive power input to the motor, and i ms is the universal excitation current, u r is the motor stator voltage, R r is the rotor resistance, ω sl is the stator-rotor speed difference, σ is L r is the rotor inductance, L s is the stator inductance, L m is the stator-rotor mutual inductance, u s is the stator voltage;

[0053] 2b) According to the above equation and the maximum power operating range of the motor, the maximum excitation voltage Umax is obtained.

[0054] Specifically, in step 1b), the maximum excitation current Imax is obtained as follows:

[0055] As attached Figure 2 As shown, circle 1 is the stator power circle when the stator current is the rated value, the center O2 is the center of the rotor current equation, and the maximum length between the center and circle 1, that is, the line segment from O2 passing through the coordinate origin to circle 1, is the maximum excitation current Imax.

[0056] Specifically, in step 2b), the maximum excitation voltage Umax is obtained as follows:

[0057] As attached Figure 2 As shown, circle 1 is the stator power circle when the stator current is the rated value, the center O3 is the center of the rotor voltage equation at the maximum slip rate, and the maximum length between the center of the circle and circle 1, that is, the line segment from O3 passing through the coordinate origin to circle 1, the length of this line segment is the maximum excitation voltage Umax.

[0058] The above embodiments are only for illustrating the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for calculating the capacity of a variable speed motor rotor converter, comprising the following steps: 1) According to the stator inductance, rotor inductance, mutual inductance and stator voltage, a scalar equation of the first stator power and the rotor current is obtained by using the relationship between the rotor current and the stator power. According to the scalar equation of the first stator power and the rotor current and the maximum power range of the motor, a maximum excitation current Imax is obtained, which is also the maximum current output by the rotor converter; 2) According to the stator inductance, rotor inductance, mutual inductance, rotor resistance, stator voltage and slip rate, the relationship between the rotor voltage and the stator power is used to obtain the scalar equation of the second stator power and the rotor voltage. According to the scalar equation of the second stator power and the rotor voltage and the maximum power range of the motor, the maximum excitation voltage Umax is obtained, which is also the maximum voltage output by the rotor converter; 3) According to the formula The capacity of the rotor converter is calculated, where S is the capacity of the rotor converter.

2. A method for calculating the capacity of a variable speed motor rotor converter according to claim 1, characterized in that: In step 1), the relationship between the rotor current and the stator power is as follows: 1a) In the synchronous coordinate system, when the d-axis is oriented to the direction of the stator flux, the scalar equations of the first stator power and rotor current are obtained as shown in equation (1): Among them, P is the active power input to the motor, Q is the reactive power input to the motor, and L m is the mutual inductance of the motor stator and rotor, u s is the stator voltage, L s is the stator inductance, i ms is the general excitation current, i r is the rotor current; 1b) According to the scalar equation of the first stator power and rotor current and the maximum power range of the motor, the maximum excitation current Imax is obtained.

3. The method for calculating the capacity of a variable speed motor rotor converter according to claim 1, characterized in that: In step 2), the relationship between the rotor voltage and the stator power is as follows: 2a) In the synchronous coordinate system, the d-axis is oriented to the direction of the stator flux. Since the motor operates in a steady-state condition, the differential variable is ignored, and the rotor voltage is reduced from the differential equation to a constant equation. The scalar equation of the second stator power and rotor voltage is obtained as shown in formula (2): Where: Among them, A, C, E, F, and M are the intermediate coefficients of the equation, which are related to the motor parameters. P is the active power input to the motor, Q is the reactive power input to the motor, and i ms is the universal excitation current, u r is the motor stator voltage, R r is the rotor resistance, ω sl is the stator-rotor speed difference, σ is L r is the rotor inductance, L s is the stator inductance, L m is the stator-rotor mutual inductance, u s is the stator voltage; 2b) According to the scalar equation of the second stator power and the rotor voltage and the maximum power range of the motor, a maximum excitation voltage Umax is obtained.

4. A method for calculating the capacity of a variable speed motor rotor converter according to claim 2, characterized in that: In step 1b), the method for obtaining the maximum excitation current Imax is specifically as follows: Circle 1 is the stator power circle when the stator current is the rated value in the rectangular coordinate system with the horizontal coordinate Q and the vertical coordinate P; Circle 2 is the locus of the scalar equations of stator power and rotor current shown in equation (1) in a rectangular coordinate system with abscissa Q and ordinate P, and the center of circle O2 is the center of circle 2; The maximum distance between the center O2 and a point on circle 1 is the line segment from the center O2 through the coordinate origin to circle 1. The length of this line segment is the maximum excitation current Imax.

5. The method for calculating the capacity of a variable speed motor rotor converter according to claim 3, characterized in that: In step 2b), the method for obtaining the maximum excitation voltage Umax is specifically as follows: Circle 1 is the stator power circle when the stator current is the rated value in the rectangular coordinate system with the horizontal coordinate Q and the vertical coordinate P; Circle 3 is the trajectory of the rotor voltage equation shown in formula (2) at the maximum slip rate in the rectangular coordinate system with abscissa Q and ordinate P, and the center O3 is the center of circle 3; The maximum distance between the center O3 and a point on circle 1 is the line segment from the center O3 through the coordinate origin to circle 1, and the length of this line segment is the maximum excitation voltage Umax.

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