JP2012249342A - Motor driving system and method - Google Patents

Abstract

A shaft torsional vibration is generated in a generator shaft, and this vibration is transmitted to a motor drive inverter as a fluctuation in the generator terminal voltage, causing the motor terminal voltage to fluctuate and vibrate the motor shaft, and this vibration further vibrates the generator shaft. To provide an electric motor drive system capable of suppressing the vibration phenomenon without depending on special control.
A motor, a generator that generates electric power by driving the motor, a converter that converts electric power generated by the generator into electric power of a desired frequency, and electric power supplied from the converter. An electric motor and a driven device driven by the electric motor, an axial resonance frequency of a generator shaft that transmits the driving force of the prime mover to the generator, and the driving force of the electric motor as the driven The shaft resonance frequency of the motor shaft transmitted to the device is set to a different value.
[Selection] Figure 1

Description

  The present invention relates to a motor drive system and method optimal for preventing a resonance phenomenon caused by shaft torsional vibration of a generator shaft connecting a prime mover and a generator, and a motor shaft connecting a motor and a driven device.

  In recent years, from the viewpoint of energy saving, a technique for driving a rotary load such as a compressor, a fan, or a blower by an electric motor by converting electric power generated by a generator into a variable frequency by using a power converter has been widely used. For example, a system that has been directly driven by a steam turbine or a gas turbine until now has been electrified to be driven at a variable speed by an electric motor and a power converter, and depending on the system, a turbine generator is installed as a power supply facility. There is a case where the electric energy obtained here is converted into mechanical energy again by a power converter and an electric motor and driven at a variable speed. However, depending on the system configuration and control conditions, shaft torsional vibration may occur on the turbine generator shaft, possibly causing damage to the generator shaft.

  A large number of studies on shaft torsional vibration between turbine generators have been made in a DC power transmission system. For example, Japanese Patent Application Laid-Open No. 2000-224896 discloses a case where a turbine generator is linked to the vicinity of a DC converter station of a DC power transmission system. It has been shown that depending on the conditions of power control performed at the DC converter station, the shaft of the turbine generator vibrates due to interference between the DC power transmission system and the turbine generator. Also, shaft torsional vibration is related to the state of torque acting on the generator rotor, and the vibration phenomenon is detected from the frequency fluctuation of the bus voltage of the DC converter station of the DC power transmission system, and the control angle is changed to change the shaft torsional vibration. Technology to suppress this is shown.

  In addition to the DC power transmission system, for example, in Japanese Patent Application Laid-Open No. 11-27993, in a power conversion device and a power supply system using a power generation device constituted by a combination of an engine and a generator as a power source, the resonance frequency component of the power generation device is set. A control technology for a power converter that detects and suppresses vibration persistence and increase by interfering with the resonance frequency of the mechanical system of the power generator by detecting and canceling the vibration component of the power generator by the resonance frequency elimination circuit is shown. Yes.

JP 2000-224896 A JP-A-11-27993

  In the above invention, the shaft torsional vibration is generated in the generator shaft, and this vibration is transmitted to the motor drive inverter as the generator terminal voltage fluctuation, causing the motor terminal voltage to fluctuate and vibrate the motor shaft. The vibration phenomenon must be suppressed by using the control to change the control angle and the control to cancel the vibration component of the power generation device, the vibration must be suppressed, the accuracy of the system performing the control, There is a problem that the suppression effect of the resonance phenomenon in the case of malfunction or failure of the control device related to the system is lacking in reliability, and the vibration can be suppressed without depending on the special control by the system or the like. It is an object to provide a possible motor drive system and method.

  In order to solve the above problems, in the present invention, a prime mover, a generator that generates electric power by driving the prime mover, a converter that converts electric power generated by the generator into electric power of a desired frequency, and the converter An electric motor driven by the electric power supplied from the electric motor and a driven system driven by the electric motor. The shaft resonance frequency of the motor shaft that transmits the driving force of the motor to the driven device is set to a different value.

  According to the present invention, there is an effect of suppressing the resonance phenomenon of shaft torsional vibration when the resonance frequencies of the generator shaft and the motor shaft match or approximate without depending on special control.

The structure of the electric motor drive device or system by Embodiment 1 of this invention. The 2 mass model block diagram which shows the vibration system of a turbine generator. Calculating model diagram of an electrical system damping coefficient D _e. Relationship between resonance ratio h and electrical damping coefficient. Electric motor or generator with variable shaft resonance frequency structure. An electric motor or generator with a variable shaft resonance frequency structure with improved versatility. The structure of the electric motor drive device or system by Embodiment 2 of this invention. The structure of the electric motor drive device or system by Embodiment 3 of this invention. A shaft-replaceable motor or generator. Motor or generator with variable shaft length structure. An electric motor or generator with a rotating body mounted on the drive shaft.

  Hereinafter, the best mode for carrying out the invention will be described with reference to the drawings.

Embodiment 1
FIG. 1 is an overall configuration diagram of the present invention. A gas turbine 1 and a generator 2 that converts mechanical energy of the gas turbine 1 into electric energy are coupled by a generator shaft 3. The inertial rotator 19 is an inertial rotator 19 for changing the shaft torsional resonance frequency of the generator shaft 3 by rotating integrally with the generator 2, and the generator shaft has a higher rigidity than the generator shaft 3. 18 is coupled to the generator 2. The fuel control device 14 controls the rotational force and the rotational speed of the gas turbine 1, the transformer 4 converts the output voltage of the generator 2 into a system voltage, and the transformer 5 converts the system voltage into the input voltage of the power converter. The transformer 4 and the transformer 5 are connected via the system 6. The power converter 7 converts the power output from the transformer 5 into desired power, a converter 15 including a diode bridge rectifier circuit that rectifies the three-phase received AC, a smoothing capacitor 17 that smoothes the converter output, The inverter 16 converts the smoothing capacitor voltage into a three-phase alternating current. The electric motor 8 is driven by the electric power output from the power converter, and the driven device 9 is driven by the electric motor 8. Further, the electric motor 8 and the driven device 9 are coupled by the electric motor shaft 10. The inertial rotating body 21 rotates integrally with the electric motor 8 to change the shaft torsional resonance frequency of the electric motor shaft 10 and is coupled to the electric motor 8 by the electric motor shaft 20 having higher rigidity than the electric motor shaft 10. Then, the power converter control device 11 operates the power converter 7 so that the output torque and speed of the electric motor 8 satisfy desired characteristics. The power converter output current detector (hereinafter referred to as current detector 12) detects and outputs the output current of the power converter 7, and outputs a power converter output voltage detector (hereinafter referred to as voltage detector 13). Detects the output voltage of the power converter 7. Output signals of the current detector 12 and the voltage detector 13 are input to a power converter control device 11, which performs various arithmetic processes and outputs a signal for operating the power converter 7. To do.

Here, the relational expression regarding the power source side vibration will be described. Fig. 2 shows the torsional vibration between the turbine and the generator in a two-mass system, where τ _G is the turbine torque, τ _L is the generator load torque, τ _s is the shaft torsion torque, ω ₁ is the turbine speed, omega ₂ the generator speed, K is the spring constant, D _m is the attenuation coefficient of the mechanical system, D _e is the attenuation coefficient of the electrical system, the unit is both a normalization amount p.u. at the rated point. T _a1 is the moment of inertia of the turbine, T _a2 is the moment of inertia of the generator, and each unit is seconds. In FIG. 2, D _e is the torque to reduce the speed increase of the generator, the load connected to the generator (including the controller), expresses the degree to which the electrically generated. From the state equation of the secondary vibration system obtained from FIG. 2, the characteristic equation of the system is Equation (1).

  Here, when the fourth item of the equation (1) is set to zero and approximated to the quadratic equation shown in the equation (2), the relationship of the equations (3) and (4) is established.

However, (3), (4) In the equation, the moment of inertia ratio that defines the n in (5), the acceleration time to rated speed that satisfies the T _a (6) below.

From equations (3) and (4), the secondary system damping coefficient ζ and the secondary system natural vibration angular frequency ω _n are expressed by formulas (7) and (8), respectively, and are expressed by the electrical system damping coefficient _De. It can be seen that the vibration characteristics (ζ, ω _n ) of the system change.

Next, the electric system attenuation coefficient calculation unit 30 will be described with reference to FIG. In FIG. 3, the block surrounded by a broken line corresponds to the electric system attenuation coefficient calculation unit 30 in FIG. 2. In FIG. 3 and the following description, the generator output and generator load active power is P, the generator speed is ω ₂ , the generator terminal voltage is V, and the generator load torque is τ _L. Are P ₀ , ω ₂₀ , V ₀ , and τ _L0 , respectively, and the changes from the rated points are ΔP, Δω ₂ , ΔV, and Δτ _L , respectively. On the other hand, since the generator terminal voltage V is proportional to the generator speed ω ₂ assuming that the field is constant near the rated point, the conversion gain is V ₀ / ω ₂₀ . This corresponds to the generator terminal voltage calculation unit 40 and can be described by equation (9).

Since the right side of the equation (9) corresponds to V ₀ + ΔV, the equation (10) is established.

The load active power calculation unit 41 outputs the load active power P with respect to the generator terminal voltage V from the load characteristics. On the other hand, the generator load torque τ _L , the generator output P, and the generator speed ω ₂ have the relationship of equation (11), which corresponds to the generator load torque calculator 42.

Since the right side of the equation (11) corresponds to τ _L0 + Δτ _L , the equation (12) is established.

よって、電気系の減衰係数Ｄ_eは、（１２）式の変形により（１３）式で表現できる。

Therefore, the damping coefficient D _e of the electrical system can be expressed by equation (13) by the deformation of equation (12).

  Here, as an example, it is assumed that the load is a resistance load having a resistance value R [pu] in the load active power calculation unit 41.

At this time, the relationship of P = V ² / R and P ₀ = V ₀ ² / R is established. Therefore, when R is eliminated from these two equations and P is solved, equation (14) is obtained.

Since the right side of the equation (14) corresponds to P ₀ + ΔP, the equation (15) is established.

  Further, when Expressions (10) and (15) are substituted into Expression (13), Expression (16) is obtained.

In the normalization unit, the rated value is 1. Therefore, if P ₀ = ω ₂₀ = τ _L0 = 1 is substituted into the right side of the equation (16), D _e = 1. That is, when connecting a resistive load to the generator, the damping coefficient D _e of the electrical system will be 1. On the other hand, for example, considering an example in which a constant power load (ΔP = 0) is connected to the generator, ΔP = 0 is substituted into the equation (13), and D _e = −1. In this case, negative damping occurs, and generator torque is generated in a direction that promotes generator speed fluctuation (vibration). In particular, when the mechanical system damping coefficient D _m is small, the secondary system damping coefficient ζ is 0 or less, indicating that the system is divergent.

The above is the case where a resistive load or a constant power load is connected to the generator, but in an actual system, as shown in FIG. 1, a transformer, a power converter, an electric motor, a mechanical shaft, and a driven damping coefficient D _e of the electrical system is dictated by the characteristics of the device. In particular, the axial resonance frequency fn [Hz] on the generator side determined by the moment of inertia of the gas turbine 1 and the generator 2 and the spring constant of the generator shaft 3, the moment of inertia of the motor 8 and the driven device driven by the motor 8 damping coefficient D _e of the electrical system by the relationship of the axis resonant frequency fr of the motor side which is determined by the spring constant [Hz] of the motor shaft 10 is greatly influenced. For example, FIG. 4 is a graph in which the electrical attenuation coefficient _De for the system shown in FIG. 1 is plotted on the vertical axis, the resonance ratio h of fn and fr defined by equation (17) is plotted on the horizontal axis, and fn is selected as a parameter. It is.

From the graph of FIG. 4, h = 1 neighborhood, i.e., the fn = fr, D _e is seen to take a minimum value. Further, the resonance ratio h h ≦ 0.9 or, if you choose the range of h ≧ 1.1, with respect to fn of practically sufficient wide range (20 Hz from 2.5 Hz), it can be seen that ensures resistance load more D _e . Therefore, in the following, specific means for changing to h ≦ 0.9 or h ≧ 1.1 when h≈1 will be presented. Fr constituting the resonance ratio h can be expressed by the equation (18) in the case of two-inertia approximation. In the equation (18), JM is the moment of inertia of the motor 8, JL is the moment of inertia of the driven device 9, and KF is the spring constant of the motor shaft 10. Therefore, by increasing the equivalent JM in the equation (18), it is possible to reduce fr and avoid h≈1. In order to realize this, in the present embodiment, the electric motor 8 has a double-shaft structure shown in FIG. 5 and a structure in which an inertia rotating body can be attached to the shaft opposite to the driven object. An example of a variable shaft resonance frequency structure including the motor housing 50, the motor shaft 51, the inertia rotating body 52 for changing the shaft resonance frequency, and the motor shaft 53 as shown in FIG. At this time, with respect to the axial resonance frequency fn = 10 [Hz] on the generator side, the axial resonance frequency fr = 10 [Hz] on the electric motor side (JM = 105 [kg · m ² ], JL = 640 [kg · m] ² ], KF = 356110 [N · m / rad]). In this case, it is apparent from the equation (18) that fr = 9 [Hz] can be changed by mounting the inertia rotating body 52 having an inertia moment of 30 [kg · m ² ] on the motor shaft 53.

The above is the operation on the motor shaft for changing to h ≦ 0.9, but it is also possible to change to h ≧ 1.1 by giving the generator shaft side the same structure as in FIG. . For example, fn can be expressed by equation (19) in the case of 2-inertia approximation. In the equation (19), T _a1 is the moment of inertia of the turbine 1, T _a2 is the moment of inertia of the generator 2, and K is the spring constant of the generator shaft 3. Therefore, by increasing the equivalent T _a2 in the equation (19), fn can be decreased and changed to h ≧ 1.1.

  By the way, when the system shown in FIG. 1 is constructed, fn and fr are not always known at the design stage, and fn = fr may be noticed for the first time at the installation site. In this case, the moment of inertia of the inertial rotating bodies 18 and 21 cannot be determined in advance. Further, as in the second embodiment, there is a case where the resonance ratio h is desired to be set finely and accurately. Therefore, as shown in FIG. 6, the resonance ratio h can be set finely in the field by adopting a structure in which a plurality of inertial rotating bodies 52, 54, etc. can be mounted.

[Embodiment 2]
In the first embodiment, one generator and one motor are connected to each other. However, in this embodiment corresponding to a larger-scale plant, as shown in FIG. 7, there are i generators 2 and j motors 8, and these are connected to a common system. However, in FIG. 7, the reference numerals are the same as those in FIG. In this case, when the axial resonance frequency of the generator i is fn (i) and the axial resonance frequency of the motor j is fr (j), h (i, j) = fr (j) / fn (i) is defined. By satisfying h (i, j) ≦ 0.9 or h (i, j) ≧ 1.1 for all combinations of resonance ratios h (i, j), the electric system can be used in any operating state. the D _e is a calculation unit 30 of the damping coefficient is 1 or more, and ensure the stability of the system. As an example, consider a system in which three generators and three motors are connected to a common system. Specifically, the resonance frequency of each generator shaft is fn (1) = 10 [Hz], fn (2) = 8 [Hz], fn (3) = 11 [Hz], and the resonance frequency of each motor shaft is When fr (1) = 10 [Hz], fr (2) = 8 [Hz], and fr (3) = 9 [Hz], fn (1) = fr (1) = 10 [Hz], fn (2) = fr (2) = 8 [Hz], and h (1,1) = h (2,2) = 1. In such a case, fr (1) is changed from 10 [Hz] to 9 [Hz] and fr (2) is changed from 8 [Hz] to 7.2 [Hz] by the means described in the first embodiment. By doing so, the stability of the entire system can be ensured.

[Embodiment 3]
In carrying out the first and second embodiments, means for accurately estimating the resonance frequencies fn and fr of the generator shaft and the motor shaft are required. Therefore, in the present embodiment, an excitation torque applying means having a broadband frequency such as an M-sequence signal or white noise is provided to the motor 8 and the generator 2. In FIG. 8, a changeover switch 100 or 101 is provided which switches the application destination of the excitation torque to the generator or the motor. When the A side contact is selected, the excitation torque is applied to the generator side and the B side contact is selected. Then, the excitation torque is applied to the motor side. Further, the changeover switches 100 and 101 may be structured to be physically linked. On the other hand, the power converter control device 11 includes a current controller 102 including a PWM output, a current deviation calculator 104, an M-sequence signal or signal source 103 such as white noise, a generator control constant 107, and a motor control constant 106. , A control mode changeover switch 105 for the generator / motor. The generator control constant 107 and the motor control constant 106 include a winding inductance, a winding resistance, an induced voltage constant, an electrical rating value, etc. specific to the generator or the motor. If this configuration is used, when it is desired to estimate the axial resonance frequency of the generator, the control switches 100 and 101 are brought down to the A contact side, and then the generator control constant is selected by the control mode changeover switch 105. The generator shaft is vibrated. In this state, the resonance frequency fn of the generator shaft can be known by reading the signal of the speed detector or acceleration sensor separately attached to the generator shaft and performing FFT analysis. If the changeover switches 100 and 101 and the control mode changeover switch 105 are changed, the resonance frequency fr of the motor shaft can be similarly known.

[Embodiment 4]
In the first embodiment, the shaft resonance frequency is changed by attaching an inertial rotating body to the shaft of the electric motor 8 or the generator 2. In the present embodiment, the configuration shown in FIG. 9 allows the motor shaft 56 connecting the motor and the driven device to be exchanged, thereby changing the spring constant of the shaft itself and changing the shaft resonance frequency. Specifically, as shown in FIG. 9, the motor having a variable shaft resonance frequency structure includes an electric motor casing 50, an electric motor shaft 51, a driven device 58, and an electric motor shaft 56 that connects the electric motor and the driven device. When the motor 55 includes a coupling 55 that connects the motor shaft 51 and the motor shaft 56, and a coupling 57 that connects the motor shaft 56 and the driven device 58, the motor shaft 56 has different Young's modulus and shaft diameter. The shaft resonance frequency is changed by preparing a plurality of these in advance and exchanging them. By this operation, adjustment is performed so that the shaft resonance frequency on the motor shaft side and the shaft resonance frequency on the generator shaft side become different values.

  In the above specific examples, the example in which the drive shaft on the electric motor side can be replaced has been shown. Similarly, a system in which the drive shaft on the generator side can be replaced may be configured.

[Embodiment 5]
In the fourth embodiment, the shaft resonance frequency is changed by changing the shaft diameter of the motor shaft 56 that connects the motor and the driven device and the Young's modulus of the material. On the other hand, in the fifth embodiment, the spring constant of the drive shaft is changed by changing the axial length of the electric motor shaft 56 that connects the electric motor and the driven device with the configuration shown in FIG. To change. Specifically, as shown in FIG. 10, a horizontal rail 59 is installed on the floor surface of the motor housing 50, and a plurality of other drive shafts having different shaft lengths to be used as the motor shaft 56 are prepared in advance. The shaft resonance frequency is changed by adjusting with the horizontal rail 59 and exchanging with the other drive shaft. The change in the distance between the driven device 58 and the motor housing 50 due to the change in the axial length can be dealt with by fixing the motor housing 50 back and forth on the rail to the driven device 58. In the above specific examples, the example in which the drive shaft on the electric motor side can be replaced has been shown. Similarly, a system in which the generator is placed on a horizontal rail and the drive shaft on the generator side can be replaced is configured. May be.

[Embodiment 6]
In Embodiment 1, the electric motor 8 has a double-shaft structure, and the axial resonance frequency is changed by mounting an inertial rotating body on the shaft opposite to the driven object. On the other hand, in the sixth embodiment, with the configuration shown in FIG. 11, by mounting an inertia rotating body on the drive target side shaft, the moment of inertia of the motor is changed and the shaft resonance frequency is changed. Specifically, in FIG. 11, as the inertial rotating body 60 to be mounted on the motor shaft 56, a plurality of objects having different moments of inertia are prepared in advance and replaced to change the shaft resonance frequency.

DESCRIPTION OF SYMBOLS 1 Gas turbine 2 Generator 3,18 Generator shaft 4,5 Transformer 6 System 7 Power converter 8 Electric motor 9,58 Driven device 10,20,51,53,56 Motor shaft 11 Power converter controller 12 Power conversion Output current detector 13 power converter output voltage detector 14 fuel control device 15 converter 16 inverter 17 smoothing capacitors 19, 21, 52, 54, 60 inertial rotating body 30 calculating unit 40 for electric system damping coefficient of generator terminal voltage Calculation unit 41 Load active power calculation unit 42 Generator load torque calculation unit 50 Motor housing 55, 57 Coupling 59 Horizontal rail 100, 101 Changeover switch 102 Current controller 103 Signal generation source 104 Current deviation calculator 105 Control mode switching Switch 106 Constant for motor control 107 Constant for generator control

Claims (12)

A motor, a generator that generates electric power by driving the motor, a converter that converts electric power generated by the generator into electric power of a desired frequency, and an electric motor that is driven by electric power supplied from the converter; In an electric motor drive system composed of a driven device driven by the electric motor,
An electric motor drive characterized in that the axial resonance frequency of the generator shaft that transmits the driving force of the prime mover to the generator and the axial resonance frequency of the electric motor shaft that transmits the driving force of the electric motor to the driven device have different values. system.   2. The motor drive system according to claim 1, wherein a value obtained by dividing the shaft resonance frequency of the generator shaft by the shaft resonance frequency of the motor shaft takes a value of 0.9 or less or 1.1 or more.   3. The electric motor drive system according to claim 1, wherein a length of the electric motor shaft is adjusted to change an axial resonance frequency of the electric motor shaft.   3. The electric motor drive system according to claim 1, wherein a length of the generator shaft is adjusted to change a shaft resonance frequency of the generator shaft.   3. The motor drive system according to claim 1 or 2, wherein one or a plurality of inertial rotating bodies are attached to the motor shaft, and the shaft resonance frequency of the motor shaft is changed.   3. The electric motor drive system according to claim 1, wherein a single or a plurality of inertial rotating bodies are attached to the generator shaft, and an axial resonance frequency of the generator shaft is changed.   3. The electric motor drive system according to claim 1, wherein a shaft resonance frequency of the electric motor shaft is changed by changing a material or a shaft diameter of the electric motor shaft.   3. The motor drive system according to claim 1, wherein the shaft resonance frequency of the generator shaft is changed by changing a material or a shaft diameter of the generator shaft.   9. The motor drive system according to claim 1, further comprising a power converter control device that estimates an axial resonance frequency of the generator shaft or the motor shaft.   The power converter control device according to claim 9, wherein the power converter control device applies an excitation torque having a broadband frequency including an M-sequence signal or white noise to the generator shaft or the motor shaft, and the shaft resonance of the generator shaft or the motor shaft. An electric motor drive system characterized by estimating a frequency.   The power converter control device according to claim 9, wherein the power converter control device includes a current controller that issues a current command to the inverter, a signal generation source that generates a current signal for performing the current command, and an output current of the inverter. An electric motor drive system comprising: a deviation calculator that calculates a deviation of the current signal.   Transmitting a driving force of a prime mover to a generator via a generator shaft and causing the generator to generate power; converting power generated by the generator into power of a desired frequency by a converter; and the converter Driving the electric motor with electric power supplied from the motor, and transmitting the driving force of the electric motor to the driven device via an electric motor shaft having an axial resonance frequency different from the axial resonance frequency of the generator shaft. An electric motor driving method comprising a step of driving an apparatus.

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