Variable-speed controlling device for use with an induction motor

[0002] 1. Field of the Invention

[0003] The present invention relates to a variable-speed controlling device which calculates an AC (Alternating Current) voltage instruction value by using a primary angular frequency instruction value and a secondary magnetic flux instruction value, and drives an induction motor by providing this voltage instruction value to a power converting circuit such as an inverter, etc.

[0004] 2. Description of the Related Art

[0005] FIG. 1 is a block diagram showing the whole of a conventional variable-speed controlling device for use with an induction motor.

[0006] In this figure, a voltage instruction value calculating circuit 4 calculates voltage instruction values v_1d* and v_1q* in a rotating coordinate system (d-q axes) based on a primary angular frequency instruction value ω₁* and a secondary magnetic flux instruction value φ₂*, which are output from an instruction value generating circuit 3, and outputs the calculated values. Next, an integrator 5, to which ω₁* is input, calculates a phase angle instruction value θ*.

[0007] Here, assume that the rotating coordinate system rotates at an angular velocity equal to the primary angular frequency instruction value ω₁*, its d-axis is a coordinate axis matching the direction of the phase angle instruction value θ*, and its q-axis is a coordinate axis orthogonal to the d-axis.

[0008] A coordinate transforming circuit 7, to which the voltage instruction values v_1d* and v_1q* are input, performs a rotating coordinate transformation according to the phase angle instruction value θ*, and outputs an AC voltage instruction value vector v₁*. A power converting circuit 1 such as an inverter, etc. outputs an AC voltage of each phase according to the AC voltage instruction value vector v₁*, and drives an induction motor 2.

[0009] In the above described conventional variable-speed controlling device, a discrepancy may sometimes occur between a secondary magnetic flux instruction value φ₂* determined according to the direction of the phase angle instruction value θ* and the secondary magnetic flux occurring in the induction motor 2, due to a calculation error in the voltage instruction value calculating circuit 4, an error between the instruction value of the AC voltage output from the power converting circuit 1 and an actual value, or the like.

[0010] As a result, the magnetic flux according to an instruction value cannot be generated, which leads to a decrease in generated torque or in a motor efficiency, etc.

[0011] An object of the present invention is to provide a variable-speed controlling device for use with an induction motor, which comprises a means for compensating for the discrepancy between a secondary magnetic flux instruction value and a secondary magnetic flux actually occurring in an induction motor, realizes a satisfactory control by generating the secondary magnetic flux according to the instruction value, and can generate desired torque and improve a motor efficiency, so as to overcome the above described problems.

[0012] The variable-speed controlling device according to the present invention, for use with an induction motor, is configured to comprise a voltage instruction value calculating unit, an integrating unit, a power converting circuit, a current detecting unit, a voltage detecting unit, an induced voltage calculating unit, a primary angular frequency compensation amount calculating unit, and a compensating unit.

[0013] In a first aspect of the present invention, the voltage instruction value calculating unit calculates an AC voltage instruction value on d-q axes rotating coordinates rotating at an angular velocity equal to a primary angular frequency instruction value by using the primary angular frequency instruction value and a secondary magnetic flux instruction value. The integrating unit calculates a phase angle instruction value by integrating the primary angular frequency instruction value. The power converting circuit performs power conversion according to the AC voltage instruction value obtained from the AC voltage instruction value and the phase angle instruction value, and supplies an AC voltage to the induction motor. The current detecting unit detects the current of the induction motor. The induced voltage calculating unit calculates the d-axis component of the induced voltage vector of the induction motor from the AC voltage instruction value vector, the output of the current detecting unit, a first primary angular frequency instruction value, and a motor constant. The primary angular frequency compensation amount calculating unit calculates a primary angular frequency compensation amount from the first primary angular frequency instruction value and the calculation result of the d-axis component of the induced voltage vector from the induced voltage calculating unit. The compensating unit generates a second primary angular frequency instruction value provided to the voltage instruction value calculating unit and the integrating unit by adding the primary angular frequency compensation amount to the first primary angular frequency instruction value.

[0014] In a second aspect of the present invention, the voltage instruction value calculating unit calculates an AC voltage instruction value on d-q axes rotating coordinates rotating at an angular velocity equal to the primary angular frequency instruction value by using the primary angular frequency instruction value and the secondary magnetic flux instruction value. The integrating unit calculates a phase angle instruction value by integrating the primary angular frequency instruction value. The power converting circuit performs power conversion according to the AC voltage instruction vector obtained from the AC voltage instruction value and the phase angle instruction value, and supplies an AC voltage to the induction motor. The current detecting unit detects the current of the induction motor. The voltage detecting unit detects the terminal voltage of the induction motor. The induced voltage calculating unit calculates the d-axis component of the induced voltage vector of the induction motor from the output of the voltage detecting unit, the output of the current detecting unit, the first primary angular frequency instruction value, and the motor constant. The primary angular frequency compensation amount calculating unit calculates the primary angular frequency compensation amount from the first primary angular frequency instruction value and the calculation result of the d-axis component of the induced voltage vector from the calculation of the induced voltage calculating unit. The compensating unit generates the second primary angular frequency instruction value provided to the voltage instruction value calculating unit and the integrating unit by adding the primary angular frequency compensation amount to the first primary angle frequency instruction value.

[0015] FIG. 1 is a block diagram showing the whole of a conventional variable-speed controlling device for use with an induction motor;

[0016] FIG. 2 is a vector diagram showing the relationship between an induced voltage and a magnetic flux;

[0017] FIG. 3 is a block diagram showing the configuration of a first preferred embodiment according to the present invention;

[0018] FIG. 4 is a block diagram showing the configuration of a second preferred embodiment according to the present invention;

[0019] FIG. 5 is a block diagram showing the configuration of a third preferred embodiment according to the present invention; and

[0020] FIG. 6 is a block diagram showing the principal part of a fourth preferred embodiment according to the present invention.

[0021] Hereinafter, preferred embodiments according to the present invention are described by referring to the drawings.

[0022] First of all, an equation of the voltage of an induction motor, which is observed in a d-q axes rotating coordinate system, is represented by the following expression 1. $\begin{array}{cc}\left[\begin{array}{c}{v}_{1d}\\ v_{1q}\\ 0\\ 0\end{array}\right]=\begin{array}{c}\left[\begin{array}{cccc}{R}_1+{\mathrm{pL}}_{\sigma }& -{\omega }_1{L}_{\sigma }& p& -{\omega }_1\\ {\omega }_1{L}_{\sigma }& R_1+{\mathrm{pL}}_{\sigma }& {\omega }_1& p\\ -R_2& 0& p+1/{\tau }_2& -{\omega }_1+{\omega }_2\\ 0& -R_2& {\omega }_1-{\omega }_2& p+1/{\tau }_2\end{array}\right]\begin{array}{c}\left[\begin{array}{c}{i}_{1d}\\ i_{1q}\\ {\phi }_{2d}\\ {\phi }_{2q}\end{array}\right]\end{array}\end{array}& \left[\mathrm{expression}1\right]\end{array}$

[0023] where v_1dis the d-axis component of a primary voltage, v_1qis the q-axis component of the primary voltage, i_1dis the d-axis component of a primary current, i_1qis the q-axis component of the primary current, φ_2dis the d-axis component of a secondary flux, φ_2qis the q-axis component of the secondary magnetic flux, R₁is the resistance of a primary (stator) winding, R₂is the resistance of a secondary (rotor) conductor, Lσ is a leakage inductance, ω₁is a primary angular frequency, ω₂is a secondary (rotor) angular frequency, τ₂is a secondary time constant, and p is a differential operator (=d/dt).

[0024] Considered here is the case where there are no errors between the voltage, the current, and the motor constant, which are used in the calculation of the expression 1 in a variable-speed controlling device, and those of the induction motor controlled. At this time, there is no discrepancy between the direction of the secondary magnetic flux φ₂of the induction motor and the secondary magnetic flux instruction value φ₂* of the variable-speed controlling device.

[0025] If the primary angular frequency instruction value ω₁* and the secondary magnetic flux instruction value φ₂* are given, φ_2d=φ_2q*, φ_2q=0, and ω₁=ω₁* can be set in the expression (1) The d-axis component v_1d* and the q-axis component v_1q* of the primary voltage instruction value are represented by an expression 2.

[0026] v_1d*=(R₁+pLσ)i_1d−ω₁*Lσi_1q  [Expression 2]

[0027] v_1q*=ω₁*φ₂*+(R₁+pLσ)i_1qω₁*Lσi_1d

[0028] Considered next is an induced voltage vector e₂=(e_2d,e_2q)^Tof the secondary circuit of the induction motor (hereinafter referred to as an induced voltage. ( )^Trepresents the transposed matrix of a matrix ( )).

[0029] By transforming the first and the second lines of the above described expression 1, the d-axis component e_2dand the q-axis component e_2qof the induced voltage are represented by the following expression (3). Here, v_1dand v_1qin the expression 3 can be obtained from the AC voltage instruction value vector v₁* input to the power converting circuit or the terminal voltage detection value of the induction motor.

[0030] e_2q=ω₁Φ_2d+pΦ_2q=v1q−(R₁₊pLσ)i_1q−ω₁Lσi_1d  [Expression 3]

[0031] Considered next is the above described case where a discrepancy occurs between the direction of the secondary magnetic flux φ₂of the induction motor and the secondary magnetic flux instruction value φ₂* of the variable controlling device due to a calculation error of the AC voltage instruction value, or the like.

[0032] FIG. 2 is a vector diagram showing the relationship between the induced voltage e₂and the secondary magnetic flux φ₂.

[0033] In this figure, d-q axes are coordinate axes used in the internal calculations of a variable-speed controlling device, while d_m-q_maxes are coordinate axes based on the secondary magnetic flux φ₂of the induction motor.

[0034] Since the induced voltage e₂is orthogonal to the secondary magnetic flux φ₂, the d-axis component e_2dof the induced voltage e₂is “0” if no discrepancy exists between the coordinate axes (d-q axes) of the variable-speed controlling device and those (d_m-q_maxes) of the induction motor. If the discrepancy exists, e_2d≠0.

[0035] Furthermore, assuming that an axial discrepancy angle is Δθ as shown in FIG. 2, the signs of Δθ and e_2dhave the relationship represented by an expression 4 depending on the (positive/negative) sign of the primary angular frequency instruction value ω₁*.

[0036] Suppose that ω₁*>0.  [Expression 4]

[0037] If Δθ>0, e_2d>0

[0038] If Δθ<0, e_2d<0

[0039] Suppose that ω₁*<0.

[0040] If Δθ>0, e_2d<0

[0041] If Δθ<0, e_2d>0

[0042] Accordingly, a proportional operation or a proportional integration operation, which uses the d-axis component e_2dof the induced voltage e₂as an input, is performed, a signal (primary angular frequency compensation amount) Δω₁obtained by adding the sign data of a first (original) primary angular frequency instruction value ω₁* to the result of the operation, is compensated for the first primary angular frequency instruction value ω₁*, and its result is used as a second primary angular frequency instruction value ω₁** for the input to the voltage instruction value calculation and the phase angle instruction value calculation, so that the operation for reducing the axial discrepancy angle Δθ to “0” can be implemented.

[0043] Expressions 5 and 6 are the calculation expressions of the signal Δω₁and the second primary angular frequency instruction value ω₁**. This is an example where the proportional integration operation is performed by using e_2das an input. In the expression 5, sgn(ω₁*) is the sign data of ω₁*. If ω₁*≧0, sgn(ω₁*)=1. If ω₁*<0, sgn(ω₁*)=−1. Additionally, K_pis a proportional gain, and T_Iis an integration time constant.

[0044] Δω₁=sgn(ω₁*)·K_p{e_2d+(1/T_I)∫e_2ddt}  [Expression 5]

[0045] ω₁**=ω₁*−Δω₁  [Expression 6]

[0046] As described above, the present invention pays attention to the fact that the d-axis component e_2dof the induced voltage e_2ddoes not become “0” if there is an axial discrepancy between the coordinate axes of a variable-speed controlling device and those of an induction motor, and if a discrepancy occurs between the direction of the secondary magnetic flux φ₂of the induction motor and the secondary magnetic flux instruction value φ₂* of the variable-speed controlling device, and aims at adjusting the primary angular frequency instruction value in order to reduce the axial discrepancy angle to “0”.

[0047] In one embodiment of the present invention, a variable-speed controlling device includes a voltage instruction value calculating unit to calculate an AC voltage instruction value on d-q axes rotating coordinates rotating at an angle velocity equal to a primary angular frequency instruction value by using the primary angular frequency instruction value and a secondary magnetic flux instruction value; an integrating unit to calculate a phase angle instruction value by integrating the primary angular frequency instruction value; a power converting circuit to perform power conversion according to the AC voltage instruction value vector obtained from the AC voltage instruction value and the phase angle instruction value, and to supply an AC voltage to an induction motor; a current detecting unit to detect the current of the induction motor; an induced voltage calculating unit to calculate the d-axis component (the axis component in the same direction as that of the phase angle instruction value) of the induced voltage vector of the induction motor from the AC voltage instruction value vector, the output of the current detecting unit, a first primary angular frequency instruction value, and a motor constant; a primary angular frequency compensation amount calculating unit calculating the primary angular frequency compensation amount from the first primary angular frequency instruction value and the calculation result of the d-axis component of the induced voltage vector from the induced voltage calculating unit; and a compensating unit to generate a second primary angular frequency instruction value provided to the voltage instruction value calculating unit and the integrating unit by adding the primary angular frequency compensation amount to the first primary angular frequency instruction value.

[0048] In another embodiment, the induced voltage calculating unit calculates the d-axis component of the induced voltage vector from the output of a terminal voltage detecting unit of the induction motor, the output of the current detecting unit, the first primary angular frequency instruction value, and the motor constant.

[0049] The primary angular frequency compensation amount calculating unit may perform a proportional operation by using the d-axis component of the induced voltage vector as an input, and calculates a primary angular frequency compensation amount by multiplying the result of the operation and the sign data of the first primary angular frequency instruction value. The primary angular frequency compensation amount calculating unit can also perform a proportional integration operation by using the d-axis component of the induced voltage vector as an input, and calculates a primary angular frequency compensation amount by multiplying the result of the operation and the sign data of the first primary angular frequency instruction value. Another alternative may be that the primary angular frequency compensation amount calculating unit performs a proportional operation by using the d-axis component of the induced voltage vector as an input, and calculates a primary angular frequency compensation amount by multiplying the result of the operation and the sign data of the first primary angular frequency instruction value or primary angular frequency compensation by using the d-axis component of the induced voltage vector, and calculates a primary angular frequency compensation amount by multiplying the result of the operation and the sign data of the first primary angular frequency instruction value.

[0050] According to the invention recited in claim 6, the above described position discrepancy amount calculating unit performs a proportional integration operation by using the d-axis component of the induced voltage vector, and calculates a position discrepancy amount by multiplying the result of the operation and the sign data of the first primary angular frequency instruction value, in the variable-speed controlling device recited in claim 2.

[0051] The present invention can further include a voltage instruction value calculating unit for calculating an AC voltage instruction value on d-q axes rotating coordinates rotating at an angular velocity equal to a primary angular frequency instruction value by using the primary angular frequency instruction value and a secondary magnetic flux instruction value; an integrating unit for calculating a phase angle instruction value by integrating the primary angular frequency instruction value; a power converting circuit for performing power conversion according to the AC voltage instruction value vector obtained from the AC voltage instruction value and the phase angle instruction value, and supplying an AC voltage to an induction motor; a current detecting unit for detecting the current of the induction motor; an induced voltage calculating unit for calculating the d-axis component (the axis component in the same direction as that of the phase angle instruction value) of an induced voltage vector of the induction motor from the AC voltage instruction value vector, the output of the current detecting unit, a first primary angular frequency instruction value, and a motor constant; a primary angular frequency compensation amount calculating unit calculating a primary angular frequency compensation amount from the first primary angular frequency instruction value and the calculation result of the d-axis component of the induced voltage vector from the induced voltage calculating unit; and a compensating unit for generating a second primary angular frequency instruction value provided to the voltage instruction value calculating unit and the integrating unit by adding the primary angular frequency compensation amount to the first primary angular frequency instruction value.

[0052] Hereinafter, the preferred embodiments according to the present invention are further described in detail, by referring to the drawings.

[0053] In FIG. 3, the instruction value generating circuit 3 outputs a primary angular frequency instruction value ω₁* (a first primary angular frequency instruction value ω₁*) and a secondary magnetic flux instruction value Φ₂*. The primary angular frequency instruction value ω₁* is input to a compensator 12 implemented by an adder, a primary angular frequency compensation amount Δω₁, which will be described later, from a primary angular frequency compensation amount calculating circuit 11 is subtracted therefrom, and a second primary angular frequency instruction value ω₁** is output. The voltage instruction value calculating circuit 4 calculates the voltage instruction values v_1d* and v_1q* on the d-q axes by using Φ₂* and ω₁** as inputs. The integrator 5 calculates the phase angle instruction value θ* by integrating ω₁**. The coordinate transforming circuit 7 performs coordinate transformation according to θ* for v_1d* and v_1q*, and calculates the AC voltage instruction value vector v₁*. The power converting circuit 1 such as an inverter, etc. generates an AC voltage of each phase based on this vector v₁*, and drives the induction motor 2.

[0054] An induced voltage calculating circuit 10 calculates a d-axis component e_2dof the induced voltage e₂of the induction motor 2 based on the above described expression 3 by using as inputs the AC voltage instruction value v₁* and a current detection value i₁obtained from a current detector 6.

[0055] This d-axis component e_2dand the first primary angular frequency instruction value ω₁* are input to the position discrepancy amount calculating circuit 11, which calculates the primary angular frequency compensation amount Δω₁by using the above described expression 5. This primary angular frequency compensation amount Δω₁is input to the compensator 12 with the signs (either of the signs?) shown in FIG. 3, and subtracted from the first primary angular frequency instruction valued ω₁*, so that the second primary angular frequency instruction value ω₁** is calculated.

[0056] As a result, as represented by the expression 4, control for reducing the axial discrepancy angle Δθ to “0” according to the d-axis component e_2dof the induced voltage e₂and the sign of the first primary angular frequency instruction value ω₁* is enabled, whereby the coordinate axes (d-q axes) of the variable-speed controlling device and those (d_m-q_maxes) of the induction motor can be aligned.

[0057] FIG. 4 is a block diagram showing the configuration of a second preferred embodiment according to the present invention.

[0058] In this preferred embodiment, a terminal voltage detection value v₁from a voltage detector 9 is used as a replacement of the AC voltage instruction value vector v₁* shown in FIG. 3 for the calculation of the d-axis component e_2dof the induced voltage e₂in the induced voltage calculating circuit 10, and the remaining configuration is similar to that shown in FIG. 3.

[0059] Since the fundamental operations performed in this preferred embodiment are the same as those shown in FIG. 3, their explanations are omitted here to avoid repetition.

[0060] FIG. 5 illustrates the principal part of a third preferred embodiment according to the present invention, and shows the configuration of the primary angular frequency compensation amount calculating circuit 11 shown in FIG. 3 or 4.

[0061] The primary angular frequency compensation amount calculating circuit 11 is configured by a P (Proportional) adjuster 20 to which the d-axis component e_2dof the induced voltage e₂is input, a sign calculating circuit 22 to which the first primary angular frequency instruction value ω₁* is input, and a multiplier which multiplies the outputs of the P adjuster 20 and the sign calculating circuit 22. As stated earlier, the sign calculating circuit 22 outputs “1” being sign data sgn (ω₁*) if ω₁*≧0, and outputs “−1” being sign data sgn (ω₁*) if ω₁*<0.

[0062] The multiplier 21 calculates the primary angular frequency compensation amount Δω₁according to the calculation of the following expression 7, and uses the primary angular frequency compensation amount Δω₁for the compensation of the first primary angular frequency instruction value ω₁*.

[0063] [Expression 7]

[0064] Δω₁=sgn(ω₁*)·K_p·e_2d

[0065] FIG. 6 shows the principal part of a fourth preferred embodiment according to the present invention, and illustrates the configuration where a primary angular frequency compensation amount calculating circuit 11A comprises a PI (Proportional Integration) adjuster 20A.

[0066] Calculation of the primary angular frequency compensation amount Δω₁, in this preferred embodiment is the one represented by the expression 5, and the primary angular frequency compensation amount Δω₁calculated based on the expression 5 is output from the multiplier 21.

[0067] As described above, according to the present invention, attention is paid to the d-axis component of an induced voltage vector if an axial discrepancy exists, and a second primary angular frequency instruction value is generated by compensating the first primary angular frequency instruction value for the position discrepancy amount obtained with a proportional operation or a proportional integration operation by using the d-axis component and the sign of the first primary angular frequency instruction value, whereby the axial discrepancy angle between a variable-speed controlling device and an induction motor is reduced to “0”, and the induction motor can be variable-speed-controlled with high efficiency by generating the magnetic flux or the torque according to an instruction value.