JP2016146693A - Overload protection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an overload protecting device of a polyphase motor capable of easily controlling prevention of the overload applied to a polyphase motor which is in a stop state or a rotation operating state.SOLUTION: An overload protecting device 1 of a polyphase motor for controlling the overload applied to a polyphase motor 11 including a plurality of coils 25 comprises: a first load calculating unit 20 which calculates the first load applied to each coil 25 on the basis of a current value of each coil 25; a second load calculating unit 21 which calculates the second load applied to all the coils 25 on the basis of the current value of each coil 25; an overload determining unit 22 which determines the overload by comparing the first load and a first threshold value or the second load and a second threshold value; and a control unit 2 which controls the output of the polyphase motor 11. The control unit 2 decreases the output of the polyphase motor 11 when the first load exceeds the first threshold value or when the second load exceeds the second threshold value.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an overload protection device, and more particularly to an overload protection device for a multiphase motor that controls a load applied to a multiphase motor having a plurality of coils.

  There is a multiphase motor that rotates a rotor having a permanent magnet by a magnetic field generated in a plurality of coils. When the rotor is stopped or rotating while a load is applied to the multiphase motor, control is required to prevent overloading so that the current continues to flow and the multiphase motor is not damaged. As an apparatus for controlling a load applied to a multiphase motor, there is one described in Patent Document 1. According to the load control device for a multiphase motor described in Patent Document 1, a plurality of reference values corresponding to stop positions during one rotation of the rotor of the motor are set in advance, and a signal for detecting stop of the motor and the rotor A detection unit that detects a signal for detecting the stop position of the motor, and a comparison unit that compares any one reference value corresponding to the stop position with an overload amount that is summed up every predetermined sampling time. .

Japanese Patent Laid-Open No. 04-372521

The overload control device for a multiphase motor described in Patent Document 1 separately determines whether the rotor of the multiphase motor is rotating or stopped. Therefore, the overload control device for a multiphase motor described in Patent Document 1 has a complicated process for preventing overload. Further, there is a state in which a load is applied even if the rotor of the multiphase motor is rotating, and the overload control device for the multiphase motor described in Patent Document 1 prevents overload during rotation of the multiphase motor. There is a problem in controlling.
It is an object of the present invention to provide an overload protection device for a multiphase motor that can easily control the prevention of overload applied to the multiphase motor in a stopped or rotating operation state.

The present invention is a multiphase motor overload protection device for controlling a load applied to a multiphase motor having a plurality of coils,
A first load calculation unit that calculates a first load applied to each coil based on a current value of each coil;
A second load calculation unit that calculates second loads applied to all the coils based on the current values of the coils;
An overload determination unit configured to determine overload by comparing the first load with a first threshold, or to determine overload by comparing the second load with a second threshold;
A controller for controlling the output of the multiphase motor,
The control unit reduces the output of the multiphase motor when the first load exceeds a first threshold, and the multiphase motor when the second load exceeds a second threshold. Reduce the output of.

  In the present invention, the overload determination unit compares the first load applied to the coil of each phase with the first threshold to determine the overload, and therefore determines the overload in a state where the multiphase motor is stopped, The control unit can adjust the output of the multiphase motor. In addition, since the overload determination unit compares the second load applied to the coils of all phases with the second threshold value to determine the overload, the overload in the state where the multiphase motor is rotating is determined and controlled. Can adjust the output of the multiphase motor.

  According to the overload protection device of the present invention, it is possible to easily control overload applied to a multiphase motor that is in a stopped or rotating state.

It is the block diagram which showed the structure of the overload prevention apparatus. It is the graph which showed the electric current which flows into each phase of a motor. It is the graph which showed the relationship between an electric current and time. It is the flowchart which showed the process of the overload prevention apparatus. It is the figure which showed a part of circuit diagram of the modification of an overload prevention apparatus. It is the figure which showed a part of circuit diagram of the modification of an overload prevention apparatus.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the overload prevention device 1 is a device that prevents an overload of the motor 11. The overload prevention device 1 includes a control unit 2 that outputs current command values Idref and Iqref for controlling a current for driving the motor 11. The control unit 2 performs control to adjust the output of the motor based on the motor mechanical angle θm that is the rotation angle of the motor shaft. The control unit 2 controls the motor mechanical angle θm to follow the motor mechanical angle command θmref generated in the control unit 2 or given from the host.

  The motor mechanical angle θm is obtained directly from the output from the angle detection unit (encoder) 12 connected to the control unit 2. The motor mechanical angle θm is calculated based on a motor electrical angle θe of a rotor (not shown). The motor electrical angle θe is obtained by dividing the motor mechanical angle θm by the number of motor pole pairs. The control unit 2 is provided with an output adjustment unit 2a. The output adjustment unit 2 a adjusts the current command values Idref and Iqref based on the overload determination result of the overload determination unit 22 connected to the control unit 2 as described later, and controls the output of the motor 11.

  A current control unit 3 is connected to the downstream side of the control unit 2. The current control unit 3 uses the d-axis voltage command values Vd, q so that the values of the d-axis current Id and the q-axis current Iq input from the second coordinate conversion unit 10 described later coincide with the current command values Idref, Iqref. The shaft voltage command value Vq is output. A first coordinate conversion unit 4 is connected to the downstream side of the current control unit 3.

  The first coordinate conversion unit (dq / αβ coordinate conversion unit) 4 converts the rotor dq coordinates into a stator (coil) αβ coordinate system. Both the dq coordinate and the αβ coordinate are orthogonal coordinates. The dq coordinates are converted into values expressed in the αβ coordinate system based on the voltage command values Vd and Vq. For the calculation of the coordinate conversion, a motor electrical angle θe of a rotor (not shown) output from an angle detection unit 12 described later is used. A first phase converter (αβ / UVW coordinate converter) 5 is connected to the downstream side of the first coordinate converter 4.

  The first phase converter 5 performs αβ / UVW coordinate conversion from the coordinates of the two-phase alternating current, and calculates each phase current command value Iuref, Ivref, and Iwref. A PWM (Pulse Width Modulation) circuit 6 is connected to the downstream side of the first phase converter 5. The PWM circuit 6 controls the motor 11 from each phase current command value Iuref, Ivref, and Iwref.

  In the PWM circuit 6, a pulse drive modulated gate drive signal for supplying a voltage corresponding to each phase current command value Iuref, Ivref and Iwref is formed. An inverter circuit 7 is connected to the downstream side of the PWM circuit 6. The inverter circuit 7 converts a direct current into a three-phase alternating current Iu, Iv, Iw based on the gate drive signal. The inverter circuit 7 is configured by, for example, switching elements 26 connected in a three-phase bridge (see FIG. 5). A DC voltage is supplied to the inverter circuit 7 from a DC power supply circuit (not shown). The gate drive signal input from the PWM circuit 6 is given to the gate of each switching element 26 (see FIG. 5) included in the inverter circuit 7.

  As a result, a PWM-modulated three-phase AC voltage that matches the voltage command values Vu, Vv, and Vw of each phase is generated. A motor 11 is connected to the downstream side of the inverter circuit 7. The motor 11 is, for example, a three-phase motor. The three-phase AC voltage output from the inverter circuit 7 is applied to each phase coil 25 (see FIG. 5) of the motor 11. That is, the motor 11 is rotationally driven by the three-phase alternating currents Iu, Iv, Iw that flow at the three-phase alternating voltage.

An A / D converter 8 is also connected to the downstream side of the inverter circuit 7. The A / D converter 8 detects the values of the three-phase alternating currents Iu, Iv, Iw output from the inverter circuit 7 and performs A / D conversion. The values of the three-phase alternating currents Iu, Iv, and Iw are directly measured by a current sensor (not shown). Generally, two-phase current values are measured, and the remaining one-phase current values are calculated according to the relationship of Equation (1).
Iu + Iv + Iw = 0 Formula (1)

  The values of the A / D converted three-phase alternating currents Iu, Iv, and Iw are converted into UVW / values by a second phase converter (UVW / αβ coordinate converter) 9 connected downstream of the A / D converter 8. αβ coordinate conversion is performed. That is, the values of Iu, Iv, and Iw are converted into two-phase current values Iα and Iβ by the second phase conversion unit 9. The two-phase current values Iα and Iβ are respectively converted into a d-axis current Id and a q-axis current Iq by a second coordinate conversion unit (αβ / dq coordinate conversion unit) 10 connected downstream of the second phase conversion unit 9. Converted. For this conversion, a motor electrical angle θe output from an angle detector 12 described later is used. The d-axis current Id and the q-axis current Iq are output to the above-described current control unit 3 connected to the downstream side of the second coordinate conversion unit 10.

  An angle detector 12 is connected to the motor 11 in order to detect the motor electrical angle θe. The angle detector 12 detects the motor mechanical angle θm from a motor rotor (not shown). The motor electrical angle θe is obtained by dividing the motor mechanical angle θm by the number of motor pole pairs. The angle detection unit 12 outputs the motor mechanical angle θm to the control unit 2. The angle detection unit 12 outputs the motor electrical angle θe to the first coordinate conversion unit 4 and the second coordinate conversion unit 10.

  Each phase integration unit (first load calculation unit) 20 is further connected to the downstream side of the A / D conversion unit 8. Each phase integrating unit 20 integrates the load of each phase of the motor 11 from the values of the A / D converted three-phase alternating currents Iu, Iv, Iw, and outputs each phase integrated value (first load).

  An all-phase integration unit (second load calculation unit) 21 is connected to the downstream side of the second coordinate conversion unit 10. The all-phase integrating unit 21 integrates all the phase current values of the motor 11 from the value of the q-axis current Iq output from the second coordinate conversion unit 10 and outputs an all-phase integrated value (second load).

  An overload determination unit 22 is connected to the downstream side of each phase integration unit 20 and all-phase integration unit 21. The overload determination unit 22 compares each phase integrated value with each phase load threshold (first threshold) to determine overload, or all phase integrated value and all phase load threshold (first threshold). 2) to determine overload. The overload determination unit 22 determines an overload in a state where the motor 11 is rotated, as well as an overload in a state where the motor 11 is stopped. The overload determination unit 22 outputs the determination result of the overload to the control unit 2 connected to the downstream side of the overload determination unit 22.

  The overload determination method of the overload determination unit 22 will be described. In the state where the motor 11 is rotating, since the current is dispersed in three phases, the temperature rise of each coil 25 (see FIG. 5) is delayed. When the motor 11 is stopped and torque is generated, current may concentrate on one phase, and the temperature of the coil 25 increases rapidly.

  As shown in FIG. 2, in a state where a current flows in each phase and the motor 11 is rotating, the effective value of the current in each phase is 1 / √2A in 2 seconds. Therefore, the temperature of the coil 25 of each phase rises due to the heat generated by this current value. On the other hand, when the motor 11 is stopped when the current value of the U phase is 1 A and the current values of the V phase and the W phase are 0.5 A and the current is supplied for 2 seconds, the effective value of the current of each phase is the U phase. Is 1A, the effective values of the V phase and the W phase are 0.5 A, the temperature of the U phase rises quickly, and the U phase is easily burned out.

  Therefore, it is necessary to use different threshold values in order to determine overload when the motor 11 is rotated and when it is stopped. As described above, when the motor 11 is stopped, the effective value of the current flowing in each phase is different. The overload determination unit 22 determines the overload in a state where the motor 11 is stopped by comparing the integrated value of the current of each phase (first load) with the load threshold of each phase (first threshold). . Specifically, overload is determined by the following method.

In order not to exceed the heat resistance temperature of the coil 25 when a current is passed through the one-phase coil 25, it is necessary to limit the time during which the current is passed. In general, current and time are in an inversely proportional relationship as shown in Equation (2) (see FIG. 3).
I × T = C1x Formula (2)
Each phase integration unit 20 calculates the first load L <b> 1 by integrating the current value by the equation (3) for each control cycle Ts of the motor 11.
L1 = Ix (t) × Ts Equation (3)

  Here, Ix (t): current [A] flowing in each phase every moment, control cycle Ts [s], C1x: first threshold (C1u = C1v = C1w). Then, the overload determination unit 22 determines that an overload occurs when the integrated value (first load) L1 exceeds C1 (first threshold value) in Equation (3). In this case, it is estimated that an excessive current flows through the one-phase coil 25.

  The overload determination unit 22 outputs a determination result to the control unit 2 connected to the downstream side of the overload determination unit 22 when the integrated value L1 exceeds the first threshold C1 and is determined to be an overload. Thereafter, the control unit 2 performs control so as to decrease the outputs of all the coils 25 when the first load L1 exceeds the first threshold C1. In this case, since one of the phases exceeds the first threshold C1, current flows in each phase (torque is generated) with the motor 11 stopped.

  Therefore, the control unit 2 performs control so as to decrease the current command value Iqref in order to decrease the output of the motor 11 (Idref is normally 0). The overload determination unit 22 compares the first load L1 with the first threshold value C1, and determines that it is not an overload when the first load L1 falls below the first threshold value C1. Thereafter, the control unit 2 normally controls the motor 11. In order to reduce the output of the motor 11, the control unit 2 controls the output adjustment unit 2 a to perform torque suppression, speed suppression, operation suppression, and the like of the motor 11.

On the other hand, when the motor 11 is rotated as described above, the effective values of the currents of the respective phases are equal. The overload determination unit 22 determines an overload in a state where the motor 11 is rotated by comparing an integrated value of the currents of all phases (second load) with a threshold value of the loads of all phases (second threshold value). . Specifically, the overload is determined by the following method. In a state where the first load of each phase does not exceed the first threshold value, it is determined whether or not the integrated value (second load) of the currents of all phases of the motor 11 exceeds the second threshold value. The all-phase integrating unit 21 calculates the second load L2 by integrating the q-axis current Iq obtained from the currents Iu, Iv, and Iw of each phase through phase conversion and coordinate conversion for each control period Ts.
L2 = Iq (t) × Ts (4)

  The overload determination unit 22 compares the second load L2 with the second threshold C2, and determines that the load is overloaded when the second load L2 exceeds the second threshold C2. In this case, the motor 11 generates torque while rotating. Thereafter, the control unit 2 performs control so as to reduce the speed command and the torque command in order to reduce the output of the motor 11. The overload determination unit 22 compares the second load L2 with the second threshold C2, and determines that it is not an overload when the second load L2 falls below the second threshold C2. Thereafter, the control unit 2 normally controls the motor 11.

  Next, a process in which the overload prevention device 1 prevents the motor 11 from being overloaded will be described.

  As shown in FIG. 4, each phase integrating unit 20 calculates a first load L <b> 1 applied to the coil 25 of each phase, and the all phase integrating unit 21 is a second load L <b> 2 applied to the coil 25 of all phases. Is calculated (S100). The overload determination unit 22 determines the overload by comparing the first load L1 and the first threshold C1, or determines the overload by comparing the second load L2 and the second threshold C2. (S101). When it is determined that the first load L1 exceeds the first threshold C1 and is overloaded, or when the second load L2 exceeds the second threshold C2 and is determined to be overloaded (S101: Yes) The control unit 2 reduces the output of the motor 11 (S102).

  When it is determined that the first load L1 does not exceed the first threshold C1 and is not overloaded, or when the second load L2 does not exceed the second threshold C2 and is determined not to be overloaded (S101: No), the control unit 2 normally controls the motor 11 (S103). Thereafter, the control unit 2 determines whether or not the control of the motor 11 is finished (S104), and when it is judged that the control is finished (S104: Yes), when the control of the motor 11 is finished and it is judged that it is not finished (S104: No), it returns to step S100.

  As described above, according to the overload prevention device 1, the overload determination unit 22 compares the first load L1 applied to the coil 25 of each phase with the first threshold C1 to determine overload. The overload with the phase motor stopped can be determined, and the output of the multiphase motor can be adjusted by the control unit. Further, since the overload determination unit 22 determines the overload by comparing the second load L2 applied to the coils of all phases and the second threshold value C2, the overload in the state where the motor 11 is rotating is determined. The controller 2 can adjust the output of the motor 11. Thereby, the overload protection device 1 can easily control the prevention of the overload applied to the motor 11 in a stopped or rotating operation state.

  Note that the present invention is not limited to the above-described embodiment, and can be modified as appropriate without departing from the spirit of the present invention. For example, in the above embodiment, a current sensor is used to measure the values of Iu, Iv, and Iw of each phase. However, as shown in FIG. 5, a shunt resistor 30 is added to the lower arm of each phase. The values of Iu, Iv, and Iw may be obtained by inserting and measuring the voltage applied thereto. Alternatively, as shown in FIG. 6, a shunt resistor 31 is inserted into the ground line G of the inverter circuit 7 and a voltage applied thereto is measured. Then, a two-phase current value obtained by sampling twice within a period of 1 PWM may be measured, and the remaining one-phase current value may be calculated from the relationship of Expression (1).

In addition, in the determination of overload, each phase current command value Iuref, Ivref, and Iwref may be used instead of the value of each phase current Iu, Iv, Iw. The current command Iqref may be used instead of the current Iq for all phases. In the above embodiment, the current is simply integrated, but the effective value of the current may be used. Here, n samples at the effective current Ie (n), if the _{t s} is the sampling time,
^{_{Ie (n) = √ ((}} I 1 2 t s + I 2 2 t s + ... + I n 2 t s) / (t s + t s + ... + t s))
^{_{= √ ((I 1 2 t}} s + I 2 2 t s + ... + I n 2 t s) / nt s)
= √ ((I ₁ ² + I ₂ ² +... + I _n ² ) / n) (5)
Is required. In order to obtain the square root, both sides of equation (5) are squared to obtain equation (6).
Ie (n) ² = (I ₁ ² + I ₂ ² +... + I _n ² ) / n Formula (6)
From equation (6), equation (7) is obtained when n + 1 samples.
Ie (n + 1) ² = (I ₁ ² + I ₂ ² +... + I _{n + 1} ² ) / (n + 1) (7)

Saving the current values (I ₁ , I ₂ ,..., I _n ) from the start of control at each calculation makes the calculation complicated, and is simplified using the following equation (8).
Ie (n + 1) ² −Ie (n) ²
= I ₁ ² + I ₂ ² +... + I _{n + 1} ² ) / (n + 1) − (I ₁ ² + I ₂ ² +... + I _n ² ) / n
= I _{n + 1} ² / (n + 1) −Ie (n) ² / (n + 1) (8)
From this, equation (9) is obtained.
Ie (n + 1) ² = I _{n + 1} ² / (n + 1) + Ie (n) ² −Ie (n) ² / (n + 1)
= I _{n + 1} ² / (n + 1) + nIe (n) ² / (n + 1) (9)

  From equation (9), it is only necessary to know the effective value at time n, the current value at time n + 1, and the time from the start of control (sampling number). Regarding the square of the effective value, a graph similar to the graph of the relationship between current and time as shown in FIG. 3 may be created in advance from temperature measurement or the like and used for determination of overload.

DESCRIPTION OF SYMBOLS 1 ... Overload protective device 2 ... Control part 2a ... Output adjustment part 3 ... Current control part 4 ... Coordinate conversion part 5 ... Phase conversion part 6 ... Circuit 7 ... Inverter circuit 8 ... Conversion part 9 ... Phase conversion part 10 ... Coordinate conversion Unit 11 ... Motor 12 ... Angle detection unit 20 ... Each phase integration unit 21 ... All phase integration unit 22 ... Overload judgment unit 25 ... Coil 26 ... Switching element 30 ... Shunt resistor 31 ... Shunt resistor G ... Ground line

Claims (1)

A multiphase motor overload protection device for controlling a load applied to a multiphase motor having a plurality of coils,
A first load calculation unit that calculates a first load applied to each coil based on a current value of each coil;
A second load calculation unit that calculates second loads applied to all the coils based on the current values of the coils;
An overload determination unit configured to determine overload by comparing the first load with a first threshold, or to determine overload by comparing the second load with a second threshold;
A controller for controlling the output of the multiphase motor,
The control unit reduces the output of the multiphase motor when the first load exceeds a first threshold, and the multiphase motor when the second load exceeds a second threshold. Overload protection device that reduces the output of

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