# CONTROL DEVICE AND CONTROL METHOD FOR INDUCTION MOTOR

A control device and a control method for an induction motor. The control device comprises: a magnetizing current adjusting unit used for calculating a magnetizing voltage instruction; a torque current adjusting unit used for calculating a torque voltage instruction; a flux linkage instruction angle generating unit calculating a flux linkage instruction angle according to a lower limit ω1th of a preset stator frequency, a stator frequency ω1, and a flux linkage estimation angle; and a motor stator voltage instruction calculating unit calculating, according to the magnetizing voltage instruction, the torque voltage instruction, and the flux linkage instruction angle, a stator voltage instruction for controlling a stator of the motor. The control system can be run outside an unstable area, and the stability of control by the control device is improved.

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**Description**

**BACKGROUND**

**Technical Field**

The present application relates to a field of motor technology, and in particular, to a control device and a control method for an induction motor.

**Description of Related Art**

When vector control is performed on a motor, it is sometimes difficult to install a sensor for detecting the rotor speed in the motor, or a sensor is not installed to reduce costs, and vector control is performed on the motor without a speed sensor.

a magnetizing current instruction calculating means **101** generates a magnetizing current instruction according to an inputted flux linkage instruction;

a magnetizing current adjusting means **103** obtains a magnetizing voltage instruction according to the magnetizing current instruction and a magnetizing current fed back by a park transformation means **110**;

a torque current instruction calculating means **116** generates a torque current instruction according to an inputted speed instruction value and a speed estimation value fed back by a speed estimating means **111**;

a torque current adjusting means **102** obtains a torque voltage instruction according to the torque current instruction and a torque current fed back by the park transformation means **110**;

an anti-Park-Clark transformation means **104** performs an anti-Park-Clark transformation on the magnetizing voltage instruction and the torque voltage instruction based on a flux linkage instruction angle and obtains a stator voltage instruction of three phases U, V, and W; and an inverter unit **200** generates three-phase stator voltages U, V, and W used for being inputted to a stator of a motor M according to the stator voltage instruction, so as to control the motor M.

As shown in **107** and **108**. A current/flux linkage estimating means **109**, based on the speed estimation value fed back by the speed estimating means **111** and the stator voltage and the current signal of the α-β coordinate system outputted by the Clark transformation means **107** and **108**, generates an estimation current and an estimation flux linkage. The speed estimating means **111**, according to the estimation current, the estimation flux linkage, and the current signal outputted by the Clark transformation means **108**, calculates a new speed estimation value.

As shown in **110** performs a Park transformation on the current signal outputted by the Clark transformation means **108** based on the flux linkage instruction angle and obtains the magnetizing current and the torque current.

As shown in **112** generates a slip frequency. A stator frequency calculating means **113**, according to the speed estimation value fed back by the speed estimating means **111** and the slip frequency, calculates a stator frequency ω_{1}. An integrator **117** integrates the stator frequency ω_{1 }and obtains the flux linkage instruction angle.

According to

In the control system shown in **111** may be located in an unstable area, that is, ω_{1}∈(−ω_{1th},ω_{1th}). When the speed estimation value ω_{1 }is located in the unstable area, it may cause the control system to lose control.

Patent Literature 1 discloses a control system for a motor capable of allowing the speed estimation value ω_{1 }calculated by the speed estimating means to be located outside the unstable area and thus accordingly preventing the control system from losing control.

**114** and a speed instruction correction amount calculating means **115** are added to the control system of

In **114** may, based on the speed instruction value inputted to the control system, the slip frequency calculated by the slip frequency calculating means **112**, and a stator frequency lower limit with, perform judgment and output a judging result. In **113** performs processing according to the judging result of **114**, so that the speed estimation value outputted by the stator frequency calculating means **113** is located outside the unstable area.

In **115**, according to the stator frequency lower limit ω_{1th}, the speed instruction value, and the slip frequency, calculates a speed instruction correction amount and outputs different speed instruction correction amounts according to the judging result of **114**. As such, the torque current instruction calculating means in

Patent Literature 1: Japanese Patent Publication No. 2010-22096A

It should be noted that the above introduction to the technical background is only set forth to facilitate a clear and complete description of the technical solutions of the disclosure and to facilitate understanding of a person having ordinary skill in the art. It should not be considered that the above technical solutions are well-known to a person having ordinary skill in the art just because these solutions are described in the BACKGROUND section of the disclosure.

**SUMMARY**

The present application found out that in Patent Literature 1, the stator frequency calculating means **113**, the stator frequency lower limit implementation judging means **114**, and the speed instruction correction amount calculating means **115** are all required to be calculated according to the slip frequency. A slip frequency ω_{s }is generally calculated and obtained by adopting the following formula (1):

where i_{q }is a torque current, ψ_{r }is a rotor flux linkage, L_{m }is mutual inductance between a rotor and a stator, and R_{r }is resistance of the rotor.

From the above formula (1), it may be known that calculation accuracy of the slip frequency ω_{s }is significantly affected by the rotor resistance R_{r}. When the motor runs and generates heat, an error of the actual R_{r }compared to a nominal value may even increase to more than 20%. A calculation deviation of ω_{s }may increase significantly, and therefore, operation results of the stator frequency calculating means **113**, the stator frequency lower limit implementation judging means **114**, and the speed instruction correction amount calculating means **115** all have deviations. Therefore, the control system may still run in the unstable area, so as to cause the control system to lose control.

The present application provides a control device and a control method for an induction motor capable of avoiding the use of the slip frequency ω_{s}, which generates an error when being subjected to a resistance change, for calculation when the control device is used for performing vector control on the motor without a speed sensor, and accordingly, a control system can run outside an unstable area, and stability of control by the control device is improved.

According to an aspect of the embodiments of the present application, a control device for an induction motor is provided, and the control device includes:

a magnetizing current adjusting unit, used for calculating a magnetizing voltage instruction;

a torque current adjusting unit, used for calculating a torque voltage instruction;

a flux linkage instruction angle generating unit, calculating a flux linkage instruction angle according to a lower limit ω_{1th }of a preset stator frequency, a stator frequency ω_{1}, and a flux linkage estimation angle ∠{circumflex over (ψ)}_{r}; and

a motor stator voltage instruction calculating unit, calculating, according to the magnetizing voltage instruction, the torque voltage instruction, and the flux linkage instruction angle, a stator voltage instruction for controlling a stator of the motor.

According to another aspect of the embodiments of the present application, where the flux linkage instruction angle generating unit includes:

a frequency difference calculating unit, calculating a difference value between the lower limit ω_{1th }of the preset stator frequency and the stator frequency ω_{1};

an integral unit, integrating the difference value to obtain a flux linkage instruction angle correction amount; and

a correction unit, correcting the flux linkage estimation angle ∠{circumflex over (ψ)}_{r }by using the flux linkage instruction angle correction amount to obtain the flux linkage instruction angle.

According to another aspect of the embodiments of the present application, where a minimum value of the flux linkage instruction angle correction amount is 0, that is, a lower limit of the integral is 0.

According to another aspect of the embodiments of the present application, where the control device further includes:

a flux linkage estimation angle calculating unit, performing arctan calculation on flux linkages {circumflex over (ψ)}_{ra }and {circumflex over (ψ)}_{rb }based on an α-β coordinate system calculated based on a stator voltage signal, a stator current signal, and a speed estimation value of the motor to obtain the flux linkage estimation angle ∠{circumflex over (ψ)}_{r}.

According to another aspect of the embodiments of the present application, where the control device further includes:

a stator frequency calculating unit, deriving the flux linkage estimation angle ∠{circumflex over (ψ)}_{r }with respect to time to obtain the stator frequency ω_{1}.

According to another aspect of the embodiments of the present application, where the control device further includes:

a stator frequency calculating unit, performing arctan calculation on currents I_{a }and I_{b }based on an α-β coordinate system obtained based on a stator current flowing into the motor to obtain a current vector angle ∠I and performing a differential operation on the current vector angle ∠I next to obtain the stator frequency ω_{1}.

a speed instruction correction amount calculating unit, used for calculating a speed instruction correction amount according to the lower limit ω_{1th }of the preset stator frequency and the stator frequency ω_{1},

where the speed instruction correction amount is used for adjusting a speed instruction value, so as to calculate the torque voltage instruction.

According to another aspect of the embodiments of the present application, where the speed instruction correction amount calculating unit includes:

a first calculating unit, used for calculating a difference value between the lower limit ω_{1th }of the preset stator frequency and the stator frequency ω_{1}; and

a first determining unit, determining the speed instruction correction amount according to the difference value calculated by the first calculating unit. The following is further included:

a first proportional integral (PI) adjusting unit, performing a PI operation according to the difference value calculated by the first calculating unit and outputting a PI operation result,

where the first determining unit determines that the speed instruction correction amount is 0 when the PI operation result is less than 0,

where the first determining unit determines that the speed instruction correction amount is the PI operation result when the PI operation result is greater than or equal to 0.

According to another aspect of the embodiments of the present application, a control method for an induction motor is provided, and the control method includes:

calculating a magnetizing voltage instruction; and

calculating a torque voltage instruction.

A flux linkage instruction angle is calculated according to a lower limit of a preset stator frequency, a stator frequency, and a flux linkage estimation angle; and

according to the magnetizing voltage instruction, the torque voltage instruction, and the flux linkage instruction angle, a stator voltage instruction for controlling stator operation of the motor is calculated.

The effect of the present application is: capable of avoiding the use of the slip frequency ω_{s}, which generates an error when being subjected to a resistance change, for calculation, and accordingly, a control system can run outside an unstable area, and stability of control by the control device is improved.

With reference to the following description and accompanying drawings, specific embodiments of the present application are disclosed in detail, indicating the ways in which the principles of the present application can be adopted. It should be understood that the scope of the embodiments of the present application is not limited thereby. Within the spirit and scope of the terms of the appended claims, the embodiments of the present application include many changes, modifications, and equivalents.

**BRIEF DESCRIPTION OF THE DRAWINGS**

The included drawings are used to provide a further understanding of the embodiments of the present application, which constitute a part of the specification, are used to illustrate the embodiments of the present application, and together with the text description, explain the principle of the present application. Obviously, the drawings in the following description are only some embodiments of the present application, and for a person having ordinary skill in the art, other drawings can be obtained based on these drawings without creative labor. In the drawings:

**204** in the control device of Embodiment 1 of the present application;

**202***a; *

**201** of Embodiment 1 of the present application;

**116**;

**DESCRIPTION OF THE EMBODIMENTS**

With reference to the drawings, the foregoing and other features of the present application becomes apparent through the following description. In the specification and drawings, specific embodiments of the present application are specifically disclosed, representing some embodiments in which the principles of the present application can be adopted. It should be understood that the present application is not limited to the described embodiments. On the contrary, the present application includes all modifications, variations, and equivalents falling into the scope of the appended claims.

**Embodiment 1**

An embodiment of the present application provides a control device for an induction motor.

As shown in **30** for an induction motor controls a stator voltage inputted to a motor M according to a flux linkage instruction, a speed instruction value, and a stator frequency lower limit inputted to the control device **30**, so as to perform vector control on the motor M.

As shown in **30** for the induction motor includes: a magnetizing current adjusting unit **103**, a torque current adjusting unit **102**, a flux linkage instruction angle generating unit **204**, and a motor stator voltage instruction calculating unit **104**.

As shown in **103** may calculate a magnetizing voltage instruction according to a magnetizing current instruction and a magnetizing current.

The torque current adjusting unit **102** may calculate a torque voltage instruction according to a torque current and a torque current instruction. The flux linkage instruction angle generating unit **204** may calculate a flux linkage instruction angle according to a lower limit ω_{1th }of a preset stator frequency, a stator frequency ω_{1}, and a flux linkage estimation angle ∠{circumflex over (ψ)}_{r}.

The motor stator voltage instruction calculating unit **104** may calculate, according to the magnetizing voltage instruction, the torque voltage instruction, and the flux linkage instruction angle, a stator voltage instruction for controlling a stator of the motor. In an embodiment, the motor stator voltage instruction calculating unit **104** may perform an anti-Park-Clark transformation on the magnetizing voltage instruction and the torque voltage instruction based on the flux linkage instruction angle, so as to obtain the stator voltage instruction.

In this embodiment, the stator voltage instruction obtained by the motor stator voltage instruction calculating unit **104** may be inputted to an inverter unit **200**, so as to form three-phase stator voltages U, V, and W outputted to the motor.

In this embodiment, description of the magnetizing current adjusting unit **103**, the torque current adjusting unit **102**, the motor stator voltage instruction calculating unit **104**, and the inverter unit **200** may be found with reference to Patent Literature 1 mentioned in the BACKGROUND section.

According to the present embodiment, in the control device **30** for the induction motor, when calculating the flux linkage instruction angle, the flux linkage instruction angle generating unit **204** may perform calculation not based on a slip frequency ω_{s }of the motor. Therefore, a resistance change of a motor rotor is prevented from affecting a calculation result. Accordingly, the control device can be run outside an unstable area, and stability of control by the control device is improved.

**204** in the control device of Embodiment 1 of the present application. As shown in **204** includes a frequency difference calculating unit **204***a*, an integral unit **204***b*, and a correction unit **204***c. *

As shown in **204***a *calculates a difference value between the lower limit ω_{1th }of the preset stator frequency and the stator frequency ω_{1}. In an embodiment, the frequency difference calculating unit **204***a *may be a subtractor, and the calculated difference value is ω_{1th}−ω_{1}.

In this embodiment, the integral unit **204***b *may integrate the difference value to obtain a flux linkage instruction angle correction amount. In an embodiment, a minimum value of the flux linkage instruction angle correction amount is 0. For instance, an anti-saturation lower limit of the integral unit **204***b *is 0. That is, an integral result of the integral unit **204***b *is greater than or equal to 0.

In this embodiment, the correction unit **204***c *corrects the flux linkage estimation angle ∠{circumflex over (ψ)}_{r }by using the flux linkage instruction angle correction amount, to obtain the flux linkage instruction angle. In an embodiment, the correction unit **204***c *may be an adder, which adds the flux linkage instruction angle correction amount and the flux linkage estimation angle ∠{circumflex over (ψ)}_{r}, to obtain the flux linkage instruction angle.

In actual operation of the motor, an actual flux linkage angle and a stator frequency corresponds to each other. The flux linkage instruction angle may be accurately controlled through the flux linkage instruction angle generating unit **204**. Accordingly, it is equivalent to ensuring that the stator frequency ω_{1 }corresponding to the flux linkage angle controlled by the flux linkage instruction angle is always greater than or equal to the lower limit ω_{1th}, such that the control device **30** is prevented from operating in the unstable area.

In this embodiment, as shown in **30** may further include a flux linkage estimation angle calculating unit **203**. Herein, the flux linkage estimation angle calculating unit **203** may perform arctan calculation on flux linkages {circumflex over (ψ)}_{ra }and {circumflex over (ψ)}_{rb }based on an α-β coordinate system calculated based on a stator voltage signal, a stator current signal, and a speed estimation value of the motor M to obtain the flux linkage estimation angle ∠{circumflex over (ψ)}_{r}.

For instance, the flux linkage estimation angle calculating unit **203** may be obtain the flux linkage estimation angle ∠{circumflex over (ψ)}_{r }according to the following formula (2):

The flux linkage estimation angle ∠{circumflex over (ψ)}_{r }obtained by the flux linkage estimation angle calculating unit **203** may be inputted to the flux linkage instruction angle generating unit **204** for calculation.

According to the present embodiment, when calculating the flux linkage estimation angle ∠{circumflex over (ψ)}_{r}, the flux linkage estimation angle calculating unit **203** avoids using the slip frequency ω_{s }of the motor for calculation. Therefore, the resistance change of the motor rotor is prevented from affecting the calculation result.

In this embodiment, as shown in **30** may further include a current/flux linkage estimating unit **109**, Clark transforming units **107** and **108**, and a speed estimating unit **111**.

A voltage detecting unit **105** detects the three-phase stator voltages U, V, and W actually outputted to the motor M to obtain the stator voltage signal. A current detecting unit **106** detects a current flowing through the stator of the motor M to obtain the stator current signal.

The Clark transforming units **107** and **108** perform Clark transformation on the stator voltage signal and the stator current signal to obtain a stator voltage and a stator current of the α-β coordinate system. The current/flux linkage estimating unit **109**, based on the speed estimation value fed back by the speed estimating unit **111** and the stator voltage signal and the stator current signal of the α-β coordinate system outputted by the Clark transforming units **107** and **108**, generates estimation currents and estimation flux linkages. The estimation flux linkages are represented as {circumflex over (ψ)}_{ra }and {circumflex over (ψ)}_{rb}, where {circumflex over (ψ)}_{ra }is an estimation flux linkage of an α axis, and {circumflex over (ψ)}_{rb }is an estimation flux linkage of a β axis. In this embodiment, the estimation flux linkages are represented as {circumflex over (ψ)}_{ra }and {circumflex over (ψ)}_{rb }and are inputted to the flux linkage estimation angle calculating unit **203** used for calculating the flux linkage estimation angle ∠{circumflex over (ψ)}_{r}.

In addition, the speed estimating unit **111** may, according to the estimation currents, the estimation flux linkages ({circumflex over (ψ)}_{ra }and {circumflex over (ψ)}_{rb}) and a stator current outputted by the Clark transforming unit **108**, calculate a new speed estimation value.

In this embodiment, as shown in **30** may further include: a stator frequency calculating unit **202**. The stator frequency calculating unit **202** may calculate the stator frequency ω_{1 }not based on the slip frequency ω_{s }of the motor. Therefore, the resistance change of the motor rotor is prevented from affecting the calculation result. Accordingly, the control device can be run outside the unstable area, and stability of control by the control device is improved.

As shown in **202** may derive the flux linkage estimation angle ∠{circumflex over (ψ)}_{r }with respect to time to obtain the stator frequency ω_{1}. For instance, the stator frequency calculating unit **202** may calculate the stator frequency ω_{1 }according to the following formula (3):

In addition, in this embodiment, the stator frequency calculating unit **202** may also adopt other manners to calculate the stator frequency ω_{1}.

For instance, in another embodiment, a stator frequency calculating unit **202***a *may perform arctan calculation on currents I_{a }and I_{b }based on the α-β coordinate system obtained based on a stator current flowing into the motor M to obtain a current vector angle ∠I and performs a differential operation on the current vector angle ∠I next to obtain the stator frequency ω_{1}.

**202***a*. As shown in _{U}, I_{V}, and I_{W }detected by the current detecting unit **106** are transformed into the currents I_{a }and I_{b }based on the α-β coordinate system by the Clark transforming unit **108**, where I_{a }is a current of the α axis, and I_{b }is a current of the β axis.

In this embodiment, the currents I_{a }and I_{b }are inputted to the stator frequency calculating unit **202***a*. The stator frequency calculating unit **202***a *includes: a current vector angle calculating unit **205** and a frequency calculating unit **202***a***1**.

As shown in **205** obtains the current vector angle ∠I according to the currents I_{a }and I_{b }where the current vector angle calculating unit **205** may calculate the current vector angle ∠I through, for example, the following formula (4):

In this embodiment, the frequency calculating unit **202***a***1** may derive the current vector angle ∠I calculated by the current vector angle calculating unit **205**, so as to calculate the stator frequency ω_{1}. For instance, the frequency calculating unit **202***al *may calculate the stator frequency ω_{1 }according to the following formula (5):

In this embodiment, as shown in **30** may further include a speed instruction correction amount calculating unit **201**. The speed instruction correction amount calculating unit **201** may calculate a speed instruction correction amount according to the lower limit ω_{1th }of the preset stator frequency and the stator frequency ω_{1}. Herein, the speed instruction correction amount is used for adjusting a speed instruction value inputted to the control device **30**, so as to calculate the torque voltage instruction.

**201** of an embodiment of the present application. As shown in **201** includes: a first calculating unit **201***a *and a first determining unit **201***c. *

Herein, the first calculating unit **201***a *is used for calculating the difference value between the lower limit ω_{1th }of the preset stator frequency and the stator frequency ω_{1}. The first determining unit **201***c *determines the speed instruction correction amount according to the difference value calculated by the first calculating unit **201***a. *

As shown in **201***a *may be a subtractor, and the calculated difference value is, for example, ω_{1th}−ω_{1}. When the difference value is less than 0, it means that ω_{1 }is located outside the unstable area, and at this time, the first determining unit **201***c *determines that the outputted speed instruction correction amount is 0. When the difference value is greater than or equal to 0, it means that ω_{1 }is located inside the unstable area, and at this time, the first determining unit **201***c *determines to output the difference value to act as the speed instruction correction amount.

In addition, in this embodiment, as shown in **201** may further include: a first proportional integral (PI) adjusting unit **201***b*. The first PI adjusting unit **201***b *may perform a proportional integral operation according to the difference value calculated by the first calculating unit **201***a *and outputs a PI operation result.

Herein, the first determining unit **201***c *may output the speed instruction correction amount according to the PI operation result. For instance, when the PI operation result is less than 0, the first determining unit **201***c *determines that the outputted speed instruction correction amount is 0. When the PI operation result is greater than or equal to 0, the first determining unit **201***c *determines that the outputted speed instruction correction amount is the PI operation result.

In **201***b*, stability of the outputted speed instruction correction amount may be improved.

According to the present embodiment, the speed instruction correction amount calculating unit **201** of the present application may calculate the speed instruction correction amount without depending on the slip frequency ωs of the motor. Therefore, the resistance change of the motor rotor is prevented from affecting the calculation result.

In this embodiment, as shown in **30** may further include a torque current instruction calculating unit **116**. The torque current instruction calculating unit **116** may, based on the inputted speed instruction value, the speed estimation value outputted by the speed estimating unit **111**, and the speed instruction correction amount outputted by the speed instruction correction amount calculating unit **201**, calculate the torque current instruction.

**116**. As shown in **116** includes an adder **116***a*, a subtractor **116***b*, and a second PI adjustor **116***c*. Accordingly, in the torque current instruction calculating unit **116**, the speed instruction value is added to the speed instruction correction amount, the speed estimation value is subtracted from a result of such addiction to obtain a difference value, and the difference value is subjected to a PI operation by the second PI adjustor **116***c*. A result of the PI operation by the second PI adjustor **116***c *is treated as the torque current instruction value to be outputted to the torque current adjusting unit **102**.

In this embodiment, description of other units in

In this embodiment, based on the related art, the torque current instruction calculating unit **116** is modified, and the speed instruction correction amount calculating unit **201**, the stator frequency calculating unit **202**, the flux linkage estimation angle calculating unit **203**, and the flux linkage instruction angle generating unit **204** are added. Accordingly, the stator frequency ω_{1 }may be controlled within a stable area (alternatively, outside the unstable area) without depending on the slip frequency ω_{s }of the motor, that is, it is ensured that ω_{1}≥ω_{1th}, and as such, stability of control by the control device is improved.

Effects of the control device of the present application are further described by an embodiment as follows. In the embodiment, rated voltage of the induction motor is 200V, rated power is 2.2 kW, the motor performs clockwise rotation, a load torque is −27.6 Nm, and a stable area boundary (i.e., the lower limit of the preset stator frequency) is ω_{1th}=0.5 Hz.

**801** is an actual rotation speed ω_{r }of a rotor of the motor M when the control device performs controlling according to this embodiment, a curve **802** is the stator frequency ω_{1 }of the motor M when the control device performs controlling according to this embodiment, a curve **803** is the slip frequency ω_{s }of the motor M, and a curve **804** is a stator frequency ω_{1}′ of the motor M when the control device performs controlling according to Patent Literature 1.

As shown in _{s }increases accordingly (as shown by the curve **803**). When the control device according to the present embodiment performs controlling, the speed instruction correction amount is automatically adjusted through PI, so that the actual speed ωr automatically increases, and w i is ensured to be stable at ω_{1th}. That is, the curve **802** does not drop, and overall stability of a control system is accordingly accomplished.

In contrast, when the control device using Patent Literature 1 performs controlling, in the case that Rr increases because of a temperature rise, since the slip frequency is still calculated based on a nominal value of Rr, the calculated slip frequency is smaller than the actual slip frequency. As such, the actually obtained ω_{1}′ may be lower than the stable area boundary ω_{1th }(as shown by the curve **804**), such that the motor may not be stably controlled.

**Embodiment 2**

Embodiment 2 of the present application provides a control method for an induction motor, and such control method corresponds to the control device **30** of Embodiment 1.

step **901**: calculating a magnetizing voltage instruction;

step **902**: calculating a torque voltage instruction;

step **903**: calculating a flux linkage instruction angle according to a lower limit of a preset stator frequency, a stator frequency, and a flux linkage estimation angle; and

step **904**: calculating, according to the magnetizing voltage instruction, the torque voltage instruction, and the flux linkage instruction angle, a stator voltage instruction for controlling stator operation of the motor.

Description related to each step of the control method may be found with reference to the description of corresponding units of Embodiment 1. Besides, the control method may further include steps other than the steps described in **30** of Embodiment 1.

According to this embodiment, the stator frequency ω_{1 }may be controlled within the stable area (alternatively, outside the unstable area) without depending on the slip frequency ω_{s }of the motor, that is, it is ensured that ω_{1}≥ω_{1th}, and as such, stability of control by the control device is improved.

A parameter calculation device described in combination with the embodiments of the present application may be directly implemented as hardware, a software module executed by a processor, or a combination of the two. The hardware module may be implemented by curing the software module by using a field programmable gate array (FPGA), for example.

The software module may be located in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, register, hard disk, removable disk, CD-ROM, or any other form of a storage medium known in the art. A storage medium may be coupled to the processor, so that the processor may read information from the storage medium and write information to the storage medium; alternatively, the storage medium may be a component of the processor. The processor and storage medium may be located in the ASIC. The software module may be stored in the memory of the mobile terminal, and may also be stored in a memory card that can be inserted into the mobile terminal. For instance, if an electronic apparatus uses a larger-capacity MEGA-SIM card or a large-capacity flash memory device, the software module may be stored in the MEGA-SIM card or a large-capacity flash memory device.

The parameter calculation device described in this embodiment may be implemented as a general-purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), and a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic device, discrete hardware component, or any appropriate combination thereof for performing the functions described in the present application. It may also be implemented as a combination of calculation apparatuses, for example, a combination of a DSP and a microprocessor, multiple microprocessors, one or a plurality of microprocessors in communication with the DSP, or any other such configuration.

The present application is described above in conjunction with specific embodiments, but it should be clear to a person of ordinary skill in the art that these descriptions are all exemplary and do not limit the protection scope of the present application. A person of ordinary skill in the art may make various variations and modifications to the present application according to the spirit and principle of the present application, and these variations and modifications are also within the scope of the present application.

## Claims

1. A control device for an induction motor, comprising:

- a magnetizing current adjusting unit, used for calculating a magnetizing voltage instruction;

- a torque current adjusting unit, used for calculating a torque voltage instruction;

- a flux linkage instruction angle generating unit, calculating a flux linkage instruction angle according to a lower limit ω1th of a preset stator frequency, a stator frequency ω1, and a flux linkage estimation angle ∠{circumflex over (ψ)}r; and

- a motor stator voltage instruction calculating unit, calculating, according to the magnetizing voltage instruction, the torque voltage instruction, and the flux linkage instruction angle, a stator voltage instruction for controlling a stator of the motor.

2. The control device for an induction motor according to claim 1, wherein the flux linkage instruction angle generating unit comprises:

- a frequency difference calculating unit, calculating a difference value between the lower limit ω1th of the preset stator frequency and the stator frequency ω1;

- an integral unit, integrating the difference value to obtain a flux linkage instruction angle correction amount; and

- a correction unit, correcting the flux linkage estimation angle ∠{circumflex over (ψ)}r by using the flux linkage instruction angle correction amount to obtain the flux linkage instruction angle.

3. The control device for an induction motor according to claim 2, wherein

- a minimum value of the flux linkage instruction angle correction amount is 0.

4. The control device for an induction motor according to claim 1, wherein the control device further comprises:

- a flux linkage estimation angle calculating unit, performing arctan calculation on flux linkages {circumflex over (ψ)}ra and {circumflex over (ψ)}rb based on an α-β coordinate system calculated based on a stator voltage signal, a stator current signal, and a speed estimation value of the motor to obtain the flux linkage estimation angle ∠{circumflex over (ψ)}r.

5. The control device for an induction motor according to claim 1, wherein the control device further comprises:

- a stator frequency calculating unit, deriving the flux linkage estimation angle ∠{circumflex over (ψ)}r respect to time to obtain the stator frequency ω1.

6. The control device for an induction motor according to claim 1, wherein the control device further comprises:

- a stator frequency calculating unit, performing arctan calculation on currents Ia and Ib based on an α-β coordinate system obtained based on a stator current flowing into the motor to obtain a current vector angle ∠I and performing a differential operation on the current vector angle ∠I next to obtain the stator frequency ω1.

7. The control device for an induction motor according to claim 1, wherein the control device further comprises:

- a speed instruction correction amount calculating unit, used for calculating a speed instruction correction amount according to the lower limit ω1th of the preset stator frequency and the stator frequency ω1,

- wherein the speed instruction correction amount is used for adjusting a speed instruction value, so as to calculate the torque voltage instruction.

- wherein the speed instruction correction amount is used for adjusting a speed instruction value, so as to calculate the torque voltage instruction.

8. The control device for an induction motor according to claim 7, wherein the speed instruction correction amount calculating unit comprises:

- a first calculating unit, used for calculating a difference value between the lower limit ω1th of the preset stator frequency and the stator frequency ω1; and

- a first determining unit, determining the speed instruction correction amount according to the difference value calculated by the first calculating unit.

9. The control device for an induction motor according to claim 8, wherein the speed instruction correction amount calculating unit further comprises:

- a first proportional integral (PI) adjusting unit, performing a proportional integral operation according to the difference value calculated by the first calculating unit and outputting a proportional integral operation result,

- wherein the first determining unit determines that the speed instruction correction amount is 0 when the proportional integral operation result is less than 0,

- wherein the first determining unit determines that the speed instruction correction amount is the proportional integral operation result when the proportional integral operation result is greater than or equal to 0.

10. A control method for an induction motor, comprising:

- calculating a magnetizing voltage instruction;

- calculating a torque voltage instruction;

- calculating a flux linkage instruction angle according to a lower limit of a preset stator frequency, a stator frequency, and a flux linkage estimation angle; and

- calculating, according to the magnetizing voltage instruction, the torque voltage instruction, and the flux linkage instruction angle, a stator voltage instruction for controlling stator operation of the motor.

**Patent History**

**Publication number**: 20210297027

**Type:**Application

**Filed**: Sep 10, 2019

**Publication Date**: Sep 23, 2021

**Applicant**: OMRON Corporation (KYOTO)

**Inventors**: Yutao WANG (Shanghai), Shaofeng LIU (Shanghai)

**Application Number**: 17/266,621

**Classifications**

**International Classification**: H02P 21/30 (20060101); H02P 21/18 (20060101); H02P 21/14 (20060101); H02P 21/22 (20060101);