JP6031969B2 - Motor drive device - Google Patents

Description

  The present invention relates to a motor driving device in an interior permanent magnet synchronous motor (IPMSM) used for, for example, a compressor of an air conditioner.

  In driving a permanent magnet synchronous motor, since it is necessary to synchronize the rotation of the rotor and the rotating magnetic field generated by the stator coil, it is essential to detect the position (rotational position) of the rotor. However, due to factors such as cost and structural problems, various techniques of position sensorless driving for detecting the position of the rotor and driving the motor without using a position detecting sensor have been studied (for example, Patent Documents). 1 and 2).

  There are two methods for driving a motor that performs position sensorless driving, for example, a 120-degree energization method and a 180-degree energization method. The 120-degree energization method (rectangular wave energization method) energizes the 120-degree section of the 180-degree section, and detects rotor zero-crossing in the non-energized 60-degree section. It is a method to obtain. However, this 120-degree energization method is easy to control, but has a disadvantage in that fluctuation occurs in the output torque during one rotation, and noise, vibration and efficiency may be problematic.

  On the other hand, the 180-degree energization method (sine wave energization method) can suppress the above-mentioned problem. However, since the energization is always performed, there is no non-energization section like the 120-degree energization method, and the induced voltage zero crossing of the rotor. Cannot be obtained by detecting the position of the rotor. In addition to directly obtaining rotor position information using a sensor such as a Hall element, a method of estimating and controlling the rotor position by detecting motor current (for example, vector control: see Patent Document 1), rotor In many cases, a method of indirectly controlling rather than estimating the position information (for example, power factor control: see Patent Document 2) is employed. For example, Patent Document 1 proposes that the position of the rotor is estimated using a rotating coordinate system and the maximum torque control of the motor is performed. In the fourth embodiment described in Patent Document 2, the power factor control is performed by tabulating the relationship between the motor current and the power factor that maximizes the power consumption efficiency according to the torque obtained from the voltage. Proposed.

  As one method for realizing the 180-degree energization method, there is a method of continuing the operation by keeping the phase difference (power factor) between the motor applied voltage and the motor current constant as in Patent Document 2. Since the inverter applies a voltage to the motor, and the motor current that flows against the motor includes the rotor position information, the power factor control directly obtains the rotor position information (estimated by calculation). In other words, the motor is driven by indirect control (mainly adjusting the voltage amplitude). In the power factor control, what value is set as the target for this phase difference is important.

  By the way, in the above vector control, the motor current is separated into a torque current component that is proportional to the permanent magnet torque and an excitation current component that changes the magnitude of the magnetic flux. Improvement is possible.

  In the case of alternating current, if the voltage and current of each phase are handled in a three-phase fixed coordinate system, they always change as alternating current even in a steady state where there is no load torque fluctuation. It is difficult to let For example, a proportional-integral controller (PI controller) is generally used as the current controller. However, if the proportional control gain is increased to follow the current controller, it becomes unstable, and the integral control causes a phase delay. End up. Therefore, as a widely used coordinate system, there is a dq coordinate axis which is a rotating coordinate system. This is based on the direction of the magnetic flux by the magnet, and is a coordinate axis of a rotating coordinate system in which the coordinate axis also rotates as the rotor rotates. The d-axis is taken in the S → N pole direction of the magnet, and the q-axis is taken by shifting it by 90 degrees in the rotation direction from there. Even if it is an AC value in a fixed coordinate system, it can be handled as a DC value on this coordinate axis, and becomes a constant value in a steady state where there is no load torque fluctuation. Moreover, even if a PI controller is used, current control without steady deviation can be realized.

  FIG. 10 is an example of a basic block diagram of power factor control of the two-phase current detection method. As shown in FIG. 10, when information on the currents Iu and Iv is acquired from the U phase and V phase of the PWM inverter 28 and input to the three-phase current calculator 16, the current Iw is calculated and the currents Iu, Iv and Iw are A three-phase current value is obtained. Here, in the case of vector control, this current value is once converted into the dq coordinate axis that is a rotating coordinate system, but after a predetermined process, it is returned to the fixed coordinate system and sent to the PWM inverter 28 again. become.

JP 2009-291072 A JP 2008-199706 A

  By the way, in the above-mentioned Patent Document 1, the position of the rotor is estimated and the maximum torque control of the motor is performed. However, since a rotating coordinate system is used when estimating the rotor, complicated calculations such as coordinate conversion are required. . In Patent Document 2, since the relationship between the motor voltage of each phase and the power factor that maximizes the power consumption efficiency according to the torque obtained from the motor current is tabulated in advance, a memory is required. Depending on the amount of data, the accuracy of the required power factor may be reduced.

  The present invention has been made in view of the above, and obtains a target phase difference based on a motor current obtained in a fixed coordinate system without using a data table and a rotational coordinate system and the rotational speed of the motor. It is an object of the present invention to provide a motor drive device capable of performing power factor control capable of obtaining a maximum torque.

  In order to solve the above-described problems and achieve the object, the present invention includes an inverter that converts direct current into alternating current and drives a motor, and a control unit that generates a PWM signal and performs PWM control of the inverter. Is a voltage / current phase difference calculator that calculates the phase difference between the motor voltage and the motor current, a motor voltage and a motor that can obtain the maximum torque from the motor current amplitude, the command rotational speed to the motor, and the motor constant stored in advance. A target phase difference generator for calculating a target phase difference of current, and an output voltage for calculating an amplitude of an output voltage based on a difference between the phase difference and the target phase difference for each carrier cycle for generating the PWM signal An amplitude generator, and the control unit determines the amplitude of the output voltage during a carrier cycle following the carrier cycle in which the amplitude of the output voltage calculated by the output voltage amplitude generator is calculated. Based characterized by PWM controlling the inverter.

  According to the present invention, in order to generate the torque necessary for power factor control with the minimum motor current, the target phase difference between the motor voltage and the motor current is obtained from the motor current, the motor speed, and the motor constant. Therefore, since a rotating coordinate system is not used, it is not necessary to perform complicated calculations such as coordinate conversion, so that the calculation process can be shortened. In addition, since calculation processing is performed for each PWM carrier cycle, it is not necessary to preliminarily prepare a table of target phase difference data, so that the synchronous motor can be efficiently controlled.

FIG. 1 is a diagram illustrating an example of a characteristic curve (constant current circle) of a current vector. FIG. 2 is a diagram illustrating an example of a characteristic curve (constant torque curve) of a current vector. FIG. 3 is a diagram illustrating an example of a characteristic curve (constant induced voltage ellipse) of a current vector. FIG. 4 is a diagram illustrating an example of the maximum torque / current control line. FIG. 5 is a block diagram showing an embodiment of a motor drive device according to the present invention. FIG. 6 is an example of a vector diagram on the dq coordinate axis, where (a) is a voltage vector diagram and (b) is a current vector diagram. FIG. 7 is a current vector diagram of state 1. FIG. 8 is a current vector diagram of state 2. FIG. 9 is a current vector diagram of state 3. FIG. 10 is a basic block diagram illustrating an example of power factor control of a conventional two-phase current detection method.

  Embodiments of a motor drive device according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

[Characteristic curve of current vector]
Before describing the power factor control contents of the present invention, first, various characteristic curves of the current vector will be described in order to explain the maximum torque / current control for generating the necessary torque with the minimum motor current. In addition, the meaning of the symbol in description is as showing below.

θvi ^* : target phase difference [rad]
ω: electrical angular angular velocity [rad / sec]
Iamp: current amplitude [A]
iu, iv, iw: U-phase current, V-phase current, W-phase current [A]
id, iq: d-axis current, q-axis current [A]
Ld, Lq: d-axis inductance, q-axis inductance [H]
Vo: induced voltage [V]
Ψa: Armature interlinkage magnetic flux [Wb]
Ra: Winding resistance [Ω]
Pn: Number of pole pairs

(A) Constant Current Circle The constant current circle shown in FIG. 1 is a current vector locus when the currents I are equal in magnitude, and is represented by the following equation.

(B) Constant torque curve The constant torque curve shown in FIG. 2 is a current vector locus in which the torque T is constant, and is expressed by the following equation.

(C) Constant Induced Voltage Ellipse The constant induced voltage ellipse shown in FIG. 3 is a current vector locus in which the induced voltage Vo generated in the armature becomes equal. When the angular velocity ω increases, the diameter decreases and is expressed by the following equation.

Next, a current vector control method (maximum torque / current control) will be described.
Maximum torque / current control is control that minimizes the current amplitude among current vectors that generate the same torque. Minimizing the current amplitude with the same torque means that the current vector is controlled at a point where the distance from the origin is the shortest with respect to the constant torque curve on the current vector plane. Therefore, the point at which the constant current circle contacts the constant torque curve is the operating point for maximum torque control. The current vector locus obtained by tracing this point is the maximum torque / current control line shown in FIG. This method (1) can generate the maximum torque with respect to the armature current, (2) the copper current is minimized because the current when the same torque is generated is minimized, and (3) the upper limit value of the current is considered In some cases, the maximum generated torque can be obtained.

The present invention does not use a rotating coordinate system when obtaining a target phase difference (hereinafter referred to as target phase difference θvi ^* ) in maximum torque / current control that generates a necessary torque by power factor control with a minimum motor current. The target phase difference θvi ^* is obtained by applying the following equation using the current amplitude Iamp and the electrical angular angular velocity ω obtained in the above.

<Formula for obtaining target phase difference θvi ^* >

  However,

Here, the target phase difference θvi ^* is a phase difference that maximizes the output torque at the current amplitude Iamp during operation at the electrical angular angular velocity ω.

Next, the derivation process (processes 1 to 3) of the above <expression for obtaining target phase difference θvi ^* > (expression 1) will be described.
<Process 1: Derivation of intersection of constant current circle and maximum torque / current control line>
Next maximum torque / current control formula

The intersection of the control line (maximum torque / current control equation) represented by

  From (Equation 2) and (Equation 3) above,

  With Ψa / (Lq−Ld) = C,

  Since we want to find the intersection of the second quadrant, select id <0,

Subsequently, iq is obtained.
From (Equation 3) and (Equation 4) above,

  Since iq exists in the second quadrant,

Than,

  Therefore, from the above (Expression 4) and (Expression 6), the d-axis current i'd and the q-axis current i'q at the intersection of the constant current circle and the maximum torque / current control line are

  However,

It can be expressed as.

<Process 2: Derivation of relational expression of constant power factor characteristics>
Consider the applied voltage vector shown in FIG. 6A and the current vector shown in FIG.

  The relationship between the voltage phase δ, the current phase β, and the dq component can be expressed by the following equation.

  Therefore, the phase difference is

It becomes.

  (Equation 8) above and the steady-state voltage equation of an embedded magnet synchronous motor

From

The phase difference δ−β can be expressed by the following equation.

<Process 3: Intersection power factor calculation>
In (Equation 9) above, since δ−β is the set target phase difference θvi ^* ,
Substituting δ−β = θvi ^* , id = id ′, iq = iq ′,

Can be derived.
However,

It is.

[Configuration of Motor Drive Device of the Present Invention]
Next, a schematic configuration of the motor drive device according to the present invention will be described.
As shown in the block diagram of FIG. 5, the motor driving device according to the present invention is a driving device for driving an embedded magnet type synchronous motor 30, and includes a carrier generator 8, an output rotation speed generator 10, and an output voltage phase. Generator 12, turbulence suppression controller 14, three-phase current calculator 16, current phase calculator 18, voltage-current phase difference calculator 20, target phase difference generator 22, output voltage amplitude generator 24, output voltage generator ( PWM generator) 26 and PWM inverter 28.

  The carrier generator 8 generates a PWM carrier necessary for generating a drive signal for driving the PWM inverter 28. It is also used for sampling to capture motor current data for each generated PWM carrier cycle.

  The output rotation speed generator 10 generates an output rotation speed based on a command rotation speed from a device (for example, a control unit of an air conditioner) equipped with this motor drive device.

  The output voltage phase generator 12 calculates the output voltage phase based on the output rotation speed from the output rotation speed generator 10 and the output voltage phase correction amount from the turbulence suppression controller 14.

  The turbulence suppression controller 14 calculates an output voltage phase correction amount based on the current phase θi from the current phase calculator 18. The power factor control is output voltage phase control, and the response is relatively slow and turbulent. Therefore, stabilization is achieved by adjusting the output voltage phase.

  The three-phase current calculator 16 calculates the W-phase current Iw from the U-phase and V-phase currents Iu and Iv detected for each period of the PWM carrier signal generated by the carrier generator 8, and calculates the current amplitude. Is.

  The current phase calculator 18 calculates the current phase θi from the U-phase, V-phase, and W-phase currents Iu, Iv, and Iw output from the three-phase current calculator 16. As a calculation method, for example, the method described in Patent Document 2 can be used.

  The voltage / current phase difference calculator 20 calculates a voltage / current phase difference from the output voltage phase θv output from the output voltage phase generator 12 and the current phase θi calculated by the current phase calculator 18 this time.

The target phase difference generator 22 includes the current amplitude from the three-phase current calculator 16, the output rotation speed from the output rotation speed generator 10, and motor constants (d-axis inductance Ld, q-axis inductance Lq, The target phase difference is generated from the armature interlinkage magnetic flux Ψa and the winding resistance Ra) by the magnet using the above-described <Expression for determining the target phase difference θvi ^* > (Expression 1).

<Equation for obtaining target phase difference θvi ^* > (Equation 1) is an electrical angular angular velocity ω, and the electrical angle represents an angle with 2π [rad] as one period of the magnetic field. Therefore, the electrical angle advances by the number of pole pairs while the rotor rotates once (rotation angle 360 ° = 2π). If the output rotation speed from the output rotation speed generator 10 is N rotations per second, the electrical angular angular velocity ω = N × 2π × pole pair number.

  The output voltage amplitude generator 24 corrects the difference between the phase difference calculated by the voltage / current phase difference calculator 20 and the target phase difference generated by the target phase difference generator 22 to calculate the output voltage amplitude.

  The output voltage generator (PWM generator) 26 outputs the output voltage amplitude value calculated by the output voltage amplitude generator 24 from the carrier generator 8 on the condition of the input DC voltage value and the phase of the output voltage phase generator 12. The PWM carriers are compared and Up, Vp, and Wp, which are PWM signals of the upper arm side switching elements U, V, and W of the PWM inverter 28, are output, respectively. Further, the output Up, Vp, Wp signals are subjected to NOT operation, and the PWM signals of the lower arm side switching elements U, V, W of the PWM inverter 28 are output as Un, Vn, Wn.

  The PWM inverter 28 supplies a three-phase AC voltage from the U phase, V phase, and W phase for driving the motor 30 to the motor 30 in accordance with a signal from the output voltage generator (PWM generator) 26.

[Example of Control Operation by Motor Drive Device of the Present Invention]
Next, an example of the control operation by the motor drive device of the present invention will be described with reference to FIGS. In the present invention, maximum torque / current control is performed to generate torque necessary for power factor control with a minimum motor current.

<State 1 (P1)>
Based on the command rotational speed, the output rotational speed generator 10 generates the output rotational speed, and using this, the output voltage phase generator 12 calculates the output voltage phase θv. The current amplitude calculated by the three-phase current calculator 16 is I3, and the voltage-current phase difference calculator 20 is calculated from the current phase θi calculated by the current phase calculator 18 and the voltage phase θv calculated by the output voltage phase generator 12. The current vector when the voltage-current phase difference calculated in (4) is θ4 is assumed to be in the state of P1 in FIG. At this time, P1 is deviated from the target maximum torque / current control line.

The target phase difference generator 22 calculates a target phase difference at which the maximum torque can be obtained with the current amplitude I3. At this time, the current amplitude Iamp in <Formula for obtaining target phase difference θvi ^* > (Formula 1) is I3.

  Since the solution of this equation is the intersection of the maximum torque / current control line in FIG. 7 and the constant current circle I3, the target phase difference is θ6.

  The output voltage amplitude generator 24 corrects the difference between the phase difference θ4 calculated by the voltage / current phase difference calculator 20 and the target phase difference θ6 generated from the target phase difference generator 22 so that the target phase difference θ6 is obtained. An output voltage amplitude is generated and output to the output voltage generator 26, and the motor is controlled via the PWM inverter 28.

<State 2 (P2)>
Actually, when the load torque is constant and control is performed so that the target phase difference θ6 is obtained, the curve moves on the constant torque curve τ5 and moves to P2 as shown in FIG. 8, but on the target maximum torque / current control line. Is still a little off.

  As shown in FIG. 9, using the current value I6 of P2, the next target phase difference is obtained by the target phase difference generator 22 in the same manner as described above, and the motor is controlled. By performing this operation for each PWM carrier cycle, control is performed so that the current vector converges on the maximum torque / current control line even in power factor control.

  Therefore, according to the present invention, the target torque difference between the motor voltage and the motor current is determined by the maximum torque / current control that generates the torque necessary for the power factor control with the minimum motor current. Since the fixed coordinate system is used based on the motor constant, the synchronous motor can be efficiently controlled only by the fixed coordinate system without using the rotating coordinate system.

DESCRIPTION OF SYMBOLS 8 Carrier generator 10 Output rotation speed generator 12 Output voltage phase generator 14 Disturbance suppression controller 16 Three phase current calculator 18 Current phase calculator 20 Voltage current phase difference calculator 22 Target phase difference generator 24 Output voltage amplitude generation 26 Output voltage generator (PWM generator)
28 PWM inverter 30 Motor

Claims (1)

An inverter that converts direct current to alternating current to drive a motor, and a controller that generates a PWM signal and performs PWM control of the inverter;
The control unit includes a voltage / current phase difference calculator that calculates a phase difference between a motor voltage and a motor current, a motor that obtains a maximum torque from an amplitude of the motor current, a command rotational speed to the motor, and a motor constant stored in advance. A target phase difference generator for calculating a target phase difference between the voltage and the motor current, and an output voltage amplitude based on the difference between the phase difference and the target phase difference for each carrier cycle for generating the PWM signal An output voltage amplitude generator that
The target phase difference generator calculates the target phase difference based on the following equation:
The control unit performs PWM control of the inverter based on the amplitude of the output voltage during a carrier cycle next to a carrier cycle in which the amplitude of the output voltage calculated by the output voltage amplitude generator is calculated. A motor drive device.

However, θvi ^* : target phase difference ω: electrical angular angular velocity Iamp: current amplitude iu, iv, iw: U-phase current, V-phase current, W-phase current i ′d, i′q: d-axis current, q-axis current Ld , Lq: d-axis inductance, q-axis inductance Ψa: armature interlinkage magnetic flux by magnet Ra: winding resistance

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