JP5851867B2 - Induction motor drive device - Google Patents

Description

  The present invention relates to a drive device for an induction motor, and more particularly to a drive device capable of operating an induction motor with high efficiency and high controllability over a wide operating range.

Conventionally, the following method is used as a method for driving an induction motor.
(1) V / F constant variable speed drive method using general-purpose inverter (2) Vector drive method for vector control of induction motor with speed sensor (3) Sensorless control for induction motor without speed sensor according to vector control Vector drive method (4) Direct connection drive method with direct commercial AC power supply without controller

A block diagram of the V / F constant variable speed driving method (1) is shown in FIG. FIG. 8B shows the voltage applied to the motor and the frequency setting. FIG. 8C is an equivalent circuit of a three-phase induction motor. In FIG. 8C, I _m is the exciting current of the motor. In the variable speed range, the V / F value and the torque boost value V ₀ in FIG. 8B are set so that the absolute value thereof is substantially constant. In this driving method, the slip of the induction motor varies depending on the motor load. As will be described later, the slip at which the motor efficiency is maximized with respect to the frequency (primary frequency) applied to the motor is uniquely determined, and thus the slip changes depending on the load.

FIG. 8D shows a block diagram of the vector driving method (2). A current vector diagram is shown in FIG. Vector control is a control method capable of separately setting and controlling the excitation current and torque current of the motor in FIG. Generally, the excitation current setting is set to be constant according to the electric motor to be driven, and high torque response is achieved by changing the torque current setting. In vector control, when the excitation current is set constant, the torque current is proportional to the slip frequency. Here, if the frequency converted value of the motor rotor speed is f _r , the slip frequency is f _s , and the primary frequency is f ₁ ,
f ₁ = f _s + f _r ---------------------------------------- (1)
It became. Since the slip frequency f _s is proportional to the torque component current, the primary frequency f ₁ varies with the torque component current even if the motor rotor speed _fr is constant. As will be described later, the slip that maximizes the motor efficiency with respect to the motor rotor speed is uniquely determined, whereby the primary frequency f ₁ is also determined.

  A block diagram of the sensorless vector driving method (3) is shown in FIG. For vector control with a normal speed sensor, the rotor speed is estimated using an internal constant of the motor instead of the speed sensor. This control method omits the speed sensor, and the control itself conforms to the vector control in (2) above. FIG. 8G shows a block diagram of the direct drive method (4). In this driving method, driving is performed by being directly connected to a commercial power source, driving is performed at a constant frequency and a constant voltage, and the motor rotor speed is also substantially constant.

  In the above driving methods (1) to (4), since the optimal control is not performed, the efficiency of the electric motor is not necessarily good. In the V / F constant variable speed driving method (1) above, a reduction in motor efficiency is inevitable. In particular, because of the constant excitation current, the efficiency drop at light load is extremely low. In the vector driving method of (2) above, the primary frequency changes regardless of the motor rotor speed, so that the motor efficiency decreases as in the V / F constant variable speed driving method of (1) above. In addition, because of the constant excitation current, the efficiency drop at light load is extremely low. In the sensorless vector driving method of (3) above, it cannot be said that the motor efficiency is considered in the same way as the vector driving method of (2) in terms of motor efficiency. In the direct drive method (4), as in the V / F constant variable speed drive method (1), the slip changes depending on the load, so a reduction in motor efficiency is inevitable. The same is true for the reduction in efficiency at light loads.

  Therefore, various drive methods have been devised that always keep the motor efficiency at the maximum by storing the slip frequency at which the motor efficiency is maximized for each operating condition and controlling it to operate at the optimum slip frequency. . The following are some examples of prior art related to the optimum driving method for induction motors.

  The “inverter device” disclosed in Patent Document 1 is capable of operating a motor at the highest efficiency point at all times with no simple operation and no useless operation. As shown to Fig.9 (a), it is an inverter apparatus which converts an alternating current power supply into a direct current power supply, converts the direct current into alternating current again, and drives a motor. The power factor when the motor is driven is detected by a power factor detector. The power factor that maximizes the efficiency at a certain frequency is stored in the memory in advance. The output voltage is controlled by comparing the power factor value stored in the memory with the power factor value detected by the detector. The memory stores a plurality of power factor values according to an arbitrary frequency. The power factor value in the memory is corrected according to the winding temperature of the motor.

  The “induction motor control method” disclosed in Patent Document 2 is a method of reducing energy loss by driving at an optimum slip angular frequency that minimizes copper loss and iron loss. As shown in FIG. 9B, first, the copper loss and iron loss of the induction motor are calculated from the characteristic values of the primary side resistance, secondary side resistance, mutual inductance, secondary side reactance and iron loss resistance of the induction motor. The optimal slip angular frequency that minimizes the angle is calculated in correspondence with the rotation speed. Then, using this optimum slip angular frequency, the excitation current and the torque current are changed, and the output torque is controlled to a predetermined value corresponding to the torque command. Thus, since both the excitation current and the torque current are changed according to the torque command value while the slip angular frequency is maintained at the optimum slip angular frequency, the optimization control of the energy efficiency can be performed in the entire rotation range. Energy loss can be minimized in both high and low load regions.

  The “induction motor control device” disclosed in Patent Document 3 can have an arbitrary torque response with a simple configuration, and can drive an induction motor with the highest efficiency both in a transient state and in a steady state. As shown in FIG. 9 (c), the target torque Tm is calculated by the target torque calculator with respect to the torque command value Te 'given from the outside. The optimum slip frequency ω \ ochse for driving the induction motor with the highest efficiency is calculated by the optimum slip frequency calculation unit with respect to the target torque. An excitation current command value iφ \ och ′ and a torque current command value iT ′ are calculated by the vector control calculation unit from the target torque Tm and the optimum slip frequency ω \ ochse according to the vector control law.

  The “efficiency control method for induction motor” disclosed in Patent Document 4 calculates the slip of the induction motor and the optimum slip, maintains the slip at an optimum value corresponding to the fluctuation of the load torque, and converts the power. In cooperation with the motor, the voltage applied to the induction motor is controlled to obtain the maximum efficiency. As shown in FIG. 9 (d), the voltage signal of the power supplied from the power converter to the induction motor, the current signal and the frequency signal are separately detected in real time, and the slip and the optimum slip are calculated from these signals. Then, a new voltage command signal is transmitted to the power converter.

  The “induction motor control device” disclosed in Patent Document 5 drives an induction motor whose iron loss cannot be ignored, and enables maximum efficiency operation even if the motor constant changes due to temperature change during operation. To do. As shown in FIG. 10 (a), a calculation result of a predetermined function having a coefficient value as a constant of an induction motor including a constant related to iron loss is stored. A variable related to the predetermined function is input, and the ratio of the amplitude of the torque current command and the excitation current command is output. From this ratio and the torque command of the induction motor, the excitation current command is calculated by the current component command calculation means, and the d axis of the primary current on the orthogonal rotation coordinate axes (referred to as dq axes) rotating at the primary frequency. Output as component command. A torque current command for the induction motor is output as a q-axis component command for the primary current. The slip frequency of the induction motor is calculated from these outputs and added to the primary current to obtain the primary frequency. A primary current command is output in which the product of the outputs of the current component command calculation means is proportional to the torque command and the amplitude ratio is equal to a predetermined function value.

  The “induction motor control method” disclosed in Patent Document 6 is a method of quickly controlling slip so that the efficiency of the induction motor is always maximized with respect to load change and frequency change. As shown in FIG. 10B, the induction motor operation is controlled by an inverter. Detects slipping of induction motors that are controlled by an inverter. The optimum slip Sη \ ochMAX is calculated which has the maximum efficiency determined from the constant of the induction motor and the frequency given to the induction motor. Compare the optimal slip and induction motor slip. The voltage operation amount is obtained from the comparison result. The obtained voltage operation amount is applied to the output voltage command or the magnetic flux command, and the induction motor is operated with the optimum slip that provides the maximum efficiency.

  The “method for controlling an electric motor” disclosed in Patent Document 7 is an electric motor control method capable of optimizing the efficiency regardless of the load. As shown in FIG. 10 (c), the stator voltage frequency of the motor is determined by adding the optimum slip frequency of the motor and the desired rotational frequency of the rotor. The magnitude of the stator voltage is determined by subtracting the actual rotational frequency of the rotor and the desired rotational frequency. The desired stator frequency and magnitude is input to the pulse width modulation unit, which controls the inverter to supply the appropriate voltage to the motor. The operation of a motor with optimal slip is optimized for efficiency regardless of load.

  The “inverter device” disclosed in Patent Document 8 controls the induction motor so as to maintain the efficiency of the induction motor at the highest efficiency. As shown in FIG. 10 (d), alternating current is converted into direct current by a power forward converter. It is converted again to AC with a power inverter. The output voltage of the power reverse converter is detected by voltage detection means. The output current of the power inverter is detected by the current detection means. The phase difference between the output voltage and the output current is detected by the phase difference detection means. A pulse signal indicating the phase difference obtained by the phase difference detection means is received, and the time length of the pulse signal is measured by a microcomputer. The microcomputer obtains the slip amount of the induction motor from the phase difference, the output voltage, and a predetermined motor constant. Further, the efficiency of the induction motor is calculated from the slip amount, the output voltage, and a predetermined motor constant, and the phase difference and the output voltage are controlled to maintain the efficiency at the maximum value.

Japanese Unexamined Patent Publication No. 01-050792 Japanese Patent Laid-Open No. 02-023085 Japanese Unexamined Patent Publication No. 07-067399 Japanese Unexamined Patent Publication No. 08-317682 JP 09-262000 A Japanese Patent Laid-Open No. 10-032991 Japanese Patent Laid-Open No. 10-108488 Japanese Patent Laid-Open No. 11-235090

Tetsushima Shigehiko, “Illustrated induction motors: From basics to control” (published by Tokyo Denki University Press, November 1979), 90-100 pages, 170-176 pages.

  However, the conventional optimum driving method based on the optimum slip has the following problems. Since the operating range that can be driven with the maximum efficiency is not so wide, if the driving is always performed with the maximum efficiency, the driving can be performed only within a narrow operating range. Performing optimal control in response to drastic changes in operating conditions such as a wide range of load fluctuations, temperature changes, and a wide range of rotation speed changes from start to steady operation makes the control circuit quite complex, This is practically impossible because of the cost and complexity of adjustment. When the control circuit and control conditions are simplified, the efficiency is hardly increased. Furthermore, there is no known practical driving method for improving the efficiency in both power running drive and regenerative drive.

  The purpose of the present invention is to solve the above-mentioned conventional problems, drive the induction motor with the maximum efficiency in the widest possible operating range, and drive with a drive method with good controllability in the range where the maximum efficiency cannot be driven, In order to cope with fluctuations in the rotational speed and load factor, it is possible to drive with a good balance between efficiency and operability over a wide operating range of power running and regeneration.

  In order to solve the above problems, in the present invention, the induction motor is optimally driven from power running to regeneration based on the maximum efficiency slip value at which the motor efficiency is maximized and the maximum torque slip value at which the torque is maximized. Induction motor control apparatus provided with a feedback control means of the above, which is a chargeable / dischargeable DC power supply, and converts the DC power supply into AC in accordance with a voltage command and a frequency command, and applies to the induction motor and generates an AC current. A variable frequency inverter that converts DC to DC current and charges the DC power supply, a speed detector that detects the rotational speed, a voltage instruction means that instructs the variable frequency inverter to send a voltage command, a voltage command value and a power running regeneration command value, As a command voltage value, and as a feedback control means, it corresponds to the maximum efficiency slip value corresponding to the rotational speed and the stationary torque. Slip value storage means for holding the maximum torque slip value, means for obtaining the maximum efficiency slip value corresponding to the detected rotation speed, and the maximum efficiency slip value is output as the optimum slip value in the low voltage range of the indicated voltage value. An optimum slip value output means that outputs an intermediate slip value in the region and a maximum torque slip value in the high voltage region, a drive slip frequency calculation means that obtains a drive slip frequency from the optimum slip value corresponding to the indicated voltage value, and detection And a frequency adding circuit for adding a driving slip frequency to the rotational speed and instructing the variable frequency inverter as a frequency command.

  By configuring as described above, it is possible to operate with high efficiency and high controllability over a wide operating range of power running and regeneration in response to fluctuations in the rotational speed and load factor.

It is an L-type equivalent circuit of the three-phase induction motor controlled by the induction motor control apparatus in the Example of this invention. It is a graph showing the motor efficiency versus slip characteristic in the power running-regenerative region of the three-phase induction motor controlled by the induction motor control device in the embodiment of the present invention. It is the graph showing the slip of the applied frequency versus the maximum efficiency in the power running-regeneration area | region of the three-phase induction motor controlled by the induction motor control apparatus in the Example of this invention. It is the graph showing the slip frequency of the applied frequency vs. maximum efficiency in the power running-regeneration area | region of the three-phase induction motor controlled by the induction motor control apparatus in the Example of this invention. It is a graph showing the slip frequency of the motor rotor speed versus the maximum efficiency in the power running to regeneration region of the three-phase induction motor controlled by the induction motor control device in the embodiment of the present invention. It is a graph showing the slip and efficiency of a three-phase induction motor controlled by the induction motor control apparatus in the Example of this invention. It is a block diagram which shows the structure of the induction motor control apparatus in the Example of this invention. It is explanatory drawing of the conventional induction motor control apparatus. It is explanatory drawing of the conventional induction motor control apparatus. It is explanatory drawing of the conventional induction motor control apparatus.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to FIGS.

  The embodiment of the present invention holds the maximum efficiency slip value corresponding to the rotational speed and the maximum torque slip value corresponding to the stationary torque, obtains the optimal slip value corresponding to the applied voltage, and drives from the rotational speed and the optimal slip value. This is an induction motor control device that obtains a slip frequency, adds the drive slip frequency to the rotational speed, and instructs the variable frequency inverter as a frequency command.

  FIG. 1 shows an L-type equivalent circuit of a three-phase induction motor. FIG. 2 shows a graph of motor efficiency versus slip characteristics using the applied frequency as a parameter. FIG. 3 shows a graph of applied frequency versus maximum efficiency slip. FIG. 4 shows a graph of applied frequency versus maximum efficiency slip frequency. FIG. 5 shows a graph of the maximum efficiency slip frequency corresponding to the rotation speed. FIG. 6 shows a slip and efficiency graph. FIG. 6A is a graph showing efficiency and torque with respect to slip. FIG. 6B is a graph showing the optimum slip with respect to the applied voltage during power regeneration. FIG. 6C is a block diagram showing an example of the configuration of the feedback control means.

  FIG. 7 shows the configuration of the induction motor control device. FIG. 7A is an example in which a torque command is given for control. FIG. 7B is an example in which control is performed by giving a speed command. FIG.7 (c) is an example utilized for control of a generator. Each example includes a case where the induction motor is operated as a generator, but is simply expressed as an induction motor as meaning both the motor and the generator. In FIG. 7, a three-phase induction motor 1 is a three-phase induction motor. The speed detector 2 is a tachometer that detects the number of rotations (frequency) of the induction motor. The variable frequency inverter 3 drives a three-phase induction motor by converting a direct current into a three-phase alternating current according to a voltage command and a frequency command, and converts the generated alternating current into a direct current to charge a direct current power source. It is an inverter. The DC power supply 4 is a chargeable / dischargeable battery or a DC current source capable of reverse flow. Although a battery will be described as a representative example, it means that a direct current source is also included.

  The function and operation of the induction motor control apparatus in the embodiment of the present invention configured as described above will be described. First, an overview of functions of the induction motor control device will be described with reference to FIG. The induction motor control device includes feedback control means for optimally driving the induction motor based on a maximum efficiency slip value at which the motor efficiency is maximized and a maximum torque slip value at which the torque is maximized. The direct current power source is a chargeable / dischargeable battery or a direct current source capable of reverse flow. The variable frequency inverter converts a DC power source into AC in accordance with a voltage command and a frequency command, applies the AC power to the induction motor, converts the generated AC current into a DC current, and charges the DC power source. The rotation speed is detected by the speed detector. The voltage instruction means instructs a voltage command to the variable frequency inverter. The multiplier outputs the product of the voltage command value and the power running regeneration command value as an instruction voltage value.

  The feedback control means includes the following. The slip value storage means holds a maximum efficiency slip value corresponding to the rotation speed and a maximum torque slip value corresponding to the stationary torque. The maximum efficiency slip value corresponding to the detected rotation speed is obtained. The optimum slip value output means outputs the maximum efficiency slip value as the optimum slip value in the low voltage region of the indicated voltage value, outputs the intermediate slip value in the intermediate voltage region, and outputs the maximum torque slip value in the high voltage region. Output. The driving slip frequency calculating means obtains the driving slip frequency from the optimum slip value corresponding to the command voltage value. The frequency adding circuit adds the driving slip frequency to the detected rotational speed and instructs the variable frequency inverter as a frequency command.

  Next, the principle of the motor control method in the three-phase case will be described with reference to FIGS. The motor efficiency of the three-phase induction motor is calculated using the slip as a variable and the primary frequency as a parameter. Since the calculation result by the T-type equivalent circuit shown in FIG. 8C is not significantly different from the result calculated by the L-type equivalent circuit shown in FIG. 1, it is calculated by the L-type equivalent circuit of FIG. To do. The equivalent circuit is represented as one phase as a Y connection.

The primary voltage and V _1, the primary current and I _1, the secondary current and I _2, the exciting current and I _0, a slip and s, the primary frequency is f _1, the primary angular frequency as omega _1, the imaginary When the unit is j = √ (−1) and the primary voltage V ₁ is the reference phase, the following is obtained.
ω ₁ = 2πf ₁ ------------------------ (2)
I ₀ = V ₁ / (r ₀ + jω ₁ · L ₀ ) ------------------------ (3)
I ₂ = V ₁ / {(r ₁ + r ₂ s) + jω ₁ (l ₁ + l ₂ )} ---------------------- (4)
I ₁ = I ₀ + I ₂ ------------------------- (5)
Here, r ₀ is a resistance component representative of no-load loss. L ₀ is the excitation inductance. r ₁ is a primary resistance. l ₁ is the primary leakage inductance. r ₂ is a primary resistance of secondary resistance. l ₂ is a primary-converted secondary leakage inductance.

_Assuming that the primary input is P _input , the following is considered in consideration of the three phases.
P _input = 3 ・ V ₁・ I _1e ----------------------- (6)
I _1e = | I ₁ | cos (ψ) ---------------------- (7)
Here, cos (ψ) is the power factor on the primary side. I _1e is an effective component of the primary current, that is, a current in phase with the primary voltage V ₁ .

On the other hand, if the shaft output is P _output , this is also as follows in consideration of the three phases.
P _output = 3 {(1-s) / s} r ₂ | I ₂ | ² ----------------------- (8)
If the motor efficiency is η, η = 100 (P _output / P _input ) ----------------------- (9)
If the input power factor of the motor is PF again
PF = cos (ψ) = I _1e / | I ₁ | ----------------------- (10)
Refer to Non-Patent Document 1 for details of these equivalent circuits and calculation formulas.

Table 1 shows examples of three-phase induction motor constants.

The slip variable range has a primary frequency of 5 Hz to 60 Hz (5 Hz increments) as a parameter. Further, the drive side conditions are V / F = 4 (200 V / 50 Hz = 4, ie, 200 V at 50 Hz), and torque boost amount V ₀ = 0 [V]. There is a slip where the motor efficiency becomes maximum at each drive frequency. Moreover, it turns out that the slip which becomes the maximum value changes with drive frequencies.

  FIG. 2 shows characteristics when the sliding variable range is expanded to s: −1 to +1 to the regeneration region. As can be seen from FIG. 2, there is a slip where the motor efficiency reaches the maximum value also in the regeneration region, that is, the generator region. Moreover, it turns out that the slip which becomes the maximum value changes with drive frequencies. Hereinafter, the slip variable range is analyzed as s: −1 to +1.

FIG. 3 is a plot of slips in which the primary frequency is a variable and the motor efficiency at that time is maximized under the same conditions. It can be seen that the slip at which the maximum efficiency is uniquely determined by the primary frequency. If the slip frequency is f _s , the primary frequency is f ₁ , and the slip is s,
s = f _s / f ₁ ----------------------------------------- ( 11)
In other words, the slip s having the maximum efficiency is determined. In other words, the slip frequency f _s uniquely determining the maximum efficiency is determined by the primary frequency. FIG. 4 is a plot of the slip frequency f _s that achieves this maximum efficiency with the primary frequency as a variable. Regarding the motor efficiency, when the slip frequency that is uniquely maximum efficiency is determined by the primary frequency, the motor rotor speed is determined.

  Next, the relationship between the motor rotor speed and the slip frequency that maximizes the motor efficiency will be described with reference to FIG. When the motor rotor speed is determined, the slip frequency at which the motor efficiency is maximized is determined, and the primary frequency is determined in reverse from equation (1). FIG. 5 is a plot of motor rotor speed versus slip frequency at which motor efficiency is maximized.

Table 2 shows an example of the power running characteristics of the three-phase induction motor.

Table 3 shows an example of the regeneration characteristics of the three-phase induction motor.

  The relationship among slip, efficiency, and torque will be described with reference to Table 2, Table 3, and FIG. As shown in FIG. 6A, at the operating point where the efficiency is maximum, the output and torque are lower than the ratings. When the rated output is output, the efficiency is slightly reduced. Furthermore, it may be necessary to temporarily output a large output or torque, and in that case, the efficiency further decreases. It is useless from the viewpoint of effective use of the function of the motor to operate the induction motor only at the maximum efficiency. When operating with a large output or torque temporarily, the operability and the like are more important than the efficiency.

  As shown in FIG. 6B, in the case of a low applied voltage, driving is performed with a slip corresponding to the maximum efficiency. In the case of a high applied voltage, it is driven with a slip corresponding to the maximum torque. In the middle, the driving is performed so that the slip is increased according to the increase of the applied voltage. That is, the maximum efficiency slip value is the optimum slip value in the low voltage region, the maximum torque slip value is the optimum slip value in the high voltage region, and the intermediate slip value between the maximum efficiency slip value and the maximum torque slip value in the intermediate voltage region. Is the optimal slip value. An optimum slip value corresponding to the applied voltage is obtained, a drive slip frequency is obtained from the rotation speed and the optimum slip value, and is given to the variable frequency inverter as a frequency command. By doing so, it is possible to drive while achieving both efficiency and operability. The specific range of the low voltage region and the high voltage region is determined according to the balance between the characteristics, efficiency, and operability of the motor.

  As shown in FIG. 6C, the optimum slip value is obtained according to the rotation speed and the applied voltage, and the optimum slip frequency is obtained from the optimum slip value and the rotation speed. The drive frequency is obtained from the rotation speed and the optimum slip frequency, and given to the variable frequency inverter as a frequency command.

  Next, the operation of the induction motor control device will be described with reference to FIG. FIG. 7A shows a specific example in the case of controlling by giving a torque command. The induction motor control device includes feedback control means for optimally driving the induction motor based on a maximum efficiency slip value at which the motor efficiency is maximized and a maximum torque slip value at which the torque is maximized. A variable frequency inverter that charges and discharges a DC power source that can be charged and discharged, converts the DC power source into AC in accordance with a voltage command and a frequency command, applies it to the induction motor, and converts the generated AC current into a DC current. A speed detector for detecting the rotational speed, a voltage indicating means for instructing the variable frequency inverter with a voltage command corresponding to the torque command, and a product for outputting the product of the voltage command value and the power regeneration command value as the indicated voltage value And a feedback control means.

  The feedback control means includes the following. The slip value storage means holds the maximum efficiency slip value corresponding to the rotation speed and the maximum torque slip value corresponding to the stationary torque. The maximum efficiency slip value corresponding to the detected rotation speed is obtained. The optimum slip value output means outputs the maximum efficiency slip value as the optimum slip value in the low voltage region of the indicated voltage value, outputs the intermediate slip value in the intermediate voltage region, and the maximum torque slip in the high voltage region. Output the value. The driving slip frequency calculating means obtains the driving slip frequency from the optimum slip value corresponding to the command voltage value. The frequency adding circuit adds the driving slip frequency to the detected rotational speed and instructs the variable frequency inverter as a frequency command.

  Since the applied voltage for controlling the torque does not affect the efficiency, if the maximum efficiency slip frequency with respect to the motor rotor speed is determined, the motor is operated at the maximum efficiency. When the applied voltage is 0 to Vm, it is driven with the maximum efficiency slip value. In the region where the applied voltage is high, the drive is performed with the maximum torque slip value. In the middle, the driving is performed by changing the slip value so as to increase as the applied voltage increases.

  FIG. 7B shows a specific example in the case of controlling by giving a speed command. It consists of a DC power supply, variable frequency inverter, speed detector, feedback control means, PID controller for speed control, and the like. The voltage instruction means instructs the variable frequency inverter with a voltage command generated based on the speed command and the detected speed. A product of a power running regenerative command value and a voltage command value generated based on the speed command and the detected speed is generated by a multiplier and output as a command voltage value. In the low voltage region of the command voltage value, the maximum efficiency slip value is output as the optimum slip value, in the intermediate voltage region, the intermediate slip value is output, and in the high voltage region, the maximum torque slip value is output. A drive slip frequency is obtained from the optimum slip value corresponding to the command voltage value, and the drive slip frequency is added to the detected rotational speed to instruct the variable frequency inverter as a frequency command.

  Although the example of the driving drive of an electric vehicle is shown, it is not restricted to this. There are many cases where the load of the motor constantly fluctuates. An example is electric vehicle travel drive. When accelerating, the maximum electric power is often required, but not so much at constant speed. If the electric motor can be continuously operated at the maximum efficiency against such load fluctuations, the travel distance will be increased. Further, when the brake is decelerated, the regenerative energy can be efficiently recovered to the power source side by controlling so as to be the curve of FIG. 5, and the travel distance is further increased.

  FIG. 7C shows a specific example in the case of a generator. It comprises a DC power supply, a variable frequency inverter, a speed detector, and feedback control means. A voltage command corresponding to the power generation command is instructed to the variable frequency inverter. The product of the voltage command value and the regenerative command value is output as the command voltage value. In the low voltage region of the command voltage value, the maximum efficiency slip value is output as the optimum slip value, in the intermediate voltage region, the intermediate slip value is output, and in the high voltage region, the maximum torque slip value is output. A drive slip frequency is obtained from the optimum slip value corresponding to the command voltage value, and the drive slip frequency is added to the detected rotational speed to instruct the variable frequency inverter as a frequency command. This is an example when used for wind power generation or hydroelectric power generation. When an induction motor is used as an induction generator and maximum efficiency is achieved, it is possible to generate power at a low cost, and power generation efficiency is also increased.

  As described above, in the embodiment of the present invention, the induction motor drive device holds the maximum efficiency slip value corresponding to the rotation speed and the maximum torque slip value corresponding to the stationary torque, and the optimum slip value corresponding to the applied voltage. The drive slip frequency is calculated from the rotation speed and the optimal slip value, and the drive slip frequency is added to the rotation speed to instruct the variable frequency inverter as a frequency command. Therefore, it can be operated with high efficiency and high controllability over a wide operating range of power running and regeneration.

  The induction motor driving device of the present invention is optimal as a driving device for controlling the torque or the rotational speed of the induction motor. Moreover, it is suitable also as a control apparatus of an electric vehicle or a wind power generator.

1 Three-phase induction motor 2 Speed detector 3 Variable frequency inverter 4 DC power supply

Claims (3)

An induction motor control device having feedback control means for optimally driving an induction motor from power running to regeneration based on a maximum efficiency slip value at which the motor efficiency is maximized and a maximum torque slip value at which the torque is maximized. The chargeable / dischargeable DC power supply and the variable power supply that converts the DC power supply into AC and applies it to the induction motor according to the voltage command and frequency command, and converts the generated AC current into DC current to charge the DC power supply. Outputs the product of the voltage command value and the power regeneration command value as the command voltage value, the frequency inverter, the speed detector that detects the rotation speed, the voltage command means that commands the voltage command corresponding to the torque command to the variable frequency inverter The multiplier and the feedback control means include a maximum efficiency slip value corresponding to the rotational speed and a maximum torque slip corresponding to the stationary torque. Slip value storage means for holding the value, means for obtaining the maximum efficiency slip value corresponding to the detected rotational speed, and the maximum efficiency slip value is output as the optimum slip value in the low voltage region of the indicated voltage value, and in the intermediate voltage region The optimum slip value output means that outputs the maximum slip value in the high voltage range, the drive slip frequency calculation means that calculates the drive slip frequency from the optimum slip value corresponding to the indicated voltage value, and the detected rotation speed An induction motor control device comprising: a frequency addition circuit for adding a drive slip frequency to the variable frequency inverter to instruct the variable frequency inverter as a frequency command. An induction motor control device having feedback control means for optimally driving an induction motor from power running to regeneration based on a maximum efficiency slip value at which the motor efficiency is maximized and a maximum torque slip value at which the torque is maximized. The chargeable / dischargeable DC power supply and the variable power supply that converts the DC power supply into AC and applies it to the induction motor according to the voltage command and frequency command, and converts the generated AC current into DC current to charge the DC power supply. A frequency inverter, a speed detector for detecting the rotational speed, a voltage instruction means for instructing the variable frequency inverter to generate a voltage command based on the speed command and the detected speed, and a speed command and a detected speed A multiplier that outputs the product of the power regeneration command value and the voltage command value as the indicated voltage value, and the feedback control means that supports the rotational speed Slip value storage means for holding the maximum efficiency slip value corresponding to the maximum torque slip value corresponding to the stationary torque, means for obtaining the maximum efficiency slip value corresponding to the detected rotational speed, and a low indicated voltage value as the optimum slip value. The optimum slip value output means that outputs the maximum efficiency slip value in the voltage range, the intermediate slip value in the intermediate voltage range, and the maximum torque slip value in the high voltage range, and the optimum slip value corresponding to the indicated voltage value An induction motor control device comprising: a drive slip frequency calculating means for obtaining a slip frequency; and a frequency addition circuit for adding the drive slip frequency to the detected rotational speed and instructing the variable frequency inverter as a frequency command. An induction motor control device having feedback control means for optimally driving an induction motor from power running to regeneration based on a maximum efficiency slip value at which the motor efficiency is maximized and a maximum torque slip value at which the torque is maximized. The chargeable / dischargeable DC power supply and the variable power supply that converts the DC power supply into AC and applies it to the induction motor according to the voltage command and frequency command, and converts the generated AC current into DC current to charge the DC power supply. Outputs the product of the voltage command value and the regenerative command value as the command voltage value, the frequency inverter, the speed detector for detecting the rotation speed, the voltage command means for commanding the voltage command corresponding to the power generation command to the variable frequency inverter As the multiplier and the feedback control means, the maximum efficiency slip value corresponding to the rotation speed and the maximum torque slip value corresponding to the stationary torque are obtained. The slip value storage means to hold, the means for obtaining the maximum efficiency slip value corresponding to the detected rotational speed, and the maximum slip value is output as the optimum slip value in the low voltage region of the indicated voltage value, and the intermediate slip in the intermediate voltage region. The optimum slip value output means that outputs the value and outputs the maximum torque slip value in the high voltage range, the drive slip frequency calculation means that calculates the drive slip frequency from the optimum slip value corresponding to the indicated voltage value, and the detected rotational speed An induction motor control device comprising: a frequency addition circuit that adds a slip frequency and instructs a variable frequency inverter as a frequency command.

Images