JP2013021866A - Inverter device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inverter device with high reliability capable of precisely detecting lock of a motor regardless of instruction speed or load.SOLUTION: When a motor current increases to a level equal to or greater than a predetermined set value during a predetermined period of time from start of activation of a motor and before an estimated rotation speed does not reach a predetermined value, it is determined that the motor is locked.

Description

  Embodiments of the present invention relate to an inverter device used for an air conditioner, for example.

  Conventionally, when driving a brushless DC motor used for a fan motor or the like of an air conditioner, protection such as detecting a motor lock (restraint state) at an early stage of operation and stopping the motor is required. . As such lock detection means, a method is known in which a rotor position is detected from a voltage induced in each phase winding of a motor, and a lock is detected based on the rotor position (for example, Patent Document 1).

  On the other hand, the circuit for detecting the induced voltage of the motor is deleted to reduce the number of parts and at the same time to improve the motor efficiency. Sensorless vector control that estimates the rotor speed (= rotation speed) from the current flowing through each phase winding (called motor current) and controls the power supply to each phase winding so that the estimated rotor speed becomes the command speed. It is used. When such vector control is used, it is conceivable to detect the lock of the motor based on the motor current.

  That is, in vector control, the motor is started by forced commutation for forcibly switching energization of each phase winding, and then the rotor speed is estimated by vector control based on the motor current. However, even when the motor is locked, current flows through each phase winding of the motor. In vector control, a motor current is detected even if the motor is locked, and therefore a certain value is estimated as the rotor speed, and lock detection in this state cannot be performed. For this reason, the drive current to the motor is controlled to increase in order to bring the estimated rotor speed closer to the command speed. Despite this increase in drive current, the motor is locked, so the estimated rotor speed does not increase with the above value, and the drive current to the motor is controlled in an increasing direction. As a result, since the motor current reaches a certain set value, it can be determined as a lock of the motor.

  In the case of a fan motor, the motor current when the motor starts normally under high command speed or heavy load conditions is almost the same as the motor current when the motor is locked. There is a possibility of misjudging that As a countermeasure, if it is determined that the motor is locked when the motor current reaches a set value within a predetermined time from the start of startup, such erroneous determination can be prevented.

JP-A-8-88994

  However, in the vector control described above, the followability of the rotor speed with respect to the command speed is improved in a light load condition. Therefore, when the motor starts normally in a light load condition, a predetermined time has elapsed since the start of the start. However, there is a problem that the motor current reaches a set value for determining motor lock and erroneously determines that the motor is locked.

  An object of an embodiment of the present invention is to provide an inverter device with excellent reliability that can accurately detect a lock of a motor regardless of a command speed and a load.

  An inverter device according to an embodiment of the present invention converts a DC voltage into an AC voltage by switching and supplies it to a motor. The inverter unit detects a current flowing through the motor, and each phase winding of the motor. After starting the motor by forcibly switching energization, the rotation speed of the motor is estimated from the detection current of the detection means, and the control means for controlling the switching so that the estimated rotation speed becomes a command speed; When the detection current of the detection means rises above a predetermined set value within a predetermined time from the start of the start and before the estimated rotational speed reaches a predetermined value, the motor Determining means for determining that is locked.

The block diagram which shows the structure of one Embodiment. The flowchart which shows control of the motor control part in one Embodiment. The figure which shows the change of the motor current I at the time of normal of one Embodiment, and the estimated rotor speed R. FIG. The figure which shows the change of the motor current I at the time of lock | rock of one Embodiment, and the estimated rotor speed R. FIG.

Hereinafter, an inverter device according to an embodiment will be described with reference to the drawings.
As shown in FIG. 1, a rectifier circuit 3 is connected via an inductor 2 between an R phase and a T phase (ground phase) of a commercial AC power supply 1 of a three-phase four-wire system 400V that is widely used overseas. Is done. The rectifier circuit 3 rectifies the AC voltage of the commercial AC power source 1. A smoothing capacitor 4 is connected to the output terminal of the rectifier circuit 3, and a switching circuit 5 is connected to the smoothing capacitor 4. The switching circuit 5 has a plurality of switching elements, and converts the DC voltage supplied from the rectifier circuit 3 and the smoothing capacitor 4 into a three-phase AC voltage having a predetermined frequency by switching these switching elements. This three-phase AC voltage is supplied to each phase winding of the brushless DC motor 6 as drive power. The brushless DC motor 6 is used as a fan motor that drives an outdoor fan such as an air conditioner. The brushless DC motor 6 may drive an indoor fan of the air conditioner.

Current transformers 7, 8, 9 are arranged as current detection means on a three-phase line between the switching circuit 5 and the brushless DC motor 6, and outputs of these current transformers 7, 8, 9 are supplied to the motor controller 10. . A display unit 11 is connected to the motor control unit 10. In the present embodiment, the current transformers 7, 8, and 9 are used as means for detecting the current flowing in the motor winding. Instead, the lower switching elements for the three phases in the switching circuit 5 are used. A shunt resistor may be inserted between the negative power sources, and the current may be detected based on a voltage drop across the shunt resistor. The inverter device is composed of all elements after the rectifier circuit 3. The motor control unit 10 controls switching of the switching circuit 5 to forcibly switch energization to each phase winding of the brushless DC motor 6, thereby starting the brushless DC motor 6 and after starting the brushless DC motor 6. Is detected based on the outputs of the current transformers 7, 8, and 9, and the rotor speed (= rotational speed) R of the brushless DC motor 6 is estimated from the motor current I. The switching of the switching circuit 5 is controlled so that the estimated rotor speed (= estimated rotational speed) R becomes the command speed Rt input from the outside, for example, the control circuit of the air conditioner. Control for forcibly switching energization of each phase winding is called forced commutation control. This forced commutation control is performed for a predetermined time t1 after receiving the start command, for example. Control based on detection of motor current I, conversion of detected motor current I to d-axis current Id and q-axis current Iq, estimation of estimated rotor speed R, and comparison between estimated rotor speed R and command speed Rt Is called vector control. This vector control is performed after the lapse of the predetermined time t1.

  In particular, in addition to the functions of forced commutation control and vector control, the motor control unit 10 determines determination means for determining the lock of the brushless DC motor 6, and notifies the fact when the determination means determines that the lock is determined. And control means for stopping the switching. The determination means determines that the motor current I has not reached the predetermined constant time t2 from the start of the activation of the brushless DC motor 6 and the estimated rotor speed R has not reached the predetermined constant value Rs. When it rises above a predetermined set value Is, it is determined that the brushless DC motor 6 is locked. The motor current I used for the lock determination is an instantaneous value of Iq in vector control.

  Next, the control operation of the motor control unit 10 will be described with reference to the flowchart of FIG.

  When a start command is input from the outside (YES in step 101), the motor control unit 10 starts a time count t (step 102) and executes forced commutation control until the time count t reaches a certain time t1. (NO in step 103 and step 104). The brushless DC motor 6 is activated by this forced commutation control. In general, the start command is determined when the command speed Rt rises from 0 to other rotational speeds.

  When the time count t reaches the predetermined time t1 (YES in Step 104), the motor control unit 10 detects the motor current I (Step 105), and shifts from forced commutation control to vector control (Step 106). By this vector control, the speed of the brushless DC motor 6 increases toward the command speed Rt.

  With the execution of vector control, the motor control unit 10 determines that the time count t has not reached the constant time t2 (YES in step 107) and the estimated rotor speed R has not reached the constant value Rs (in step 108). YES), it is determined whether or not the motor current I rises above the set value Is (step 109).

  FIG. 3 shows changes in the motor current I and the estimated rotor speed R when the brushless DC motor 6 starts normally. Under this normal condition, the motor current I does not reach the set value Is within the predetermined time t2. That is, while step 109 repeats NO before the motor current I reaches the set value Is, the determination of either the startup time determination step 107 or the rotation speed determination step 108 is NO, and the determination of step 109 Will not be made. In particular, once the determination of the startup time determination step 107 is NO, the process does not shift to YES unless it is stopped and started again. During this normal operation, when the motor control unit 10 receives a stop command and the command speed Rt becomes 0 from the outside (YES in step 112), the motor control unit 10 stops switching of the switching circuit 5 (step 111), and is brushless. The DC motor 6 is stopped.

  On the other hand, FIG. 4 shows changes in the motor current I and the estimated rotor speed R when the brushless DC motor 6 is locked before starting. Even in the locked state, a current flows through each phase winding of the brushless DC motor 6. The vector control of the motor control unit 10 estimates a certain value as the rotor speed because the motor current I flows, and increases the drive current to the brushless DC motor 6 in an increasing direction so that the estimated rotor speed R approaches the command speed Rt. Control. However, in spite of this increase in drive current, the estimated rotor speed R does not increase at a substantially constant value, so the vector control of the motor control unit 10 controls the drive current to the brushless DC motor 6 in an increasing direction. To do. As a result, the motor current I reaches the set value Is within a certain time t2 (YES in Step 107) and the estimated rotor speed R is lower than the certain value Rs (YES in Step 108) (NO in Step 109). .

  When the brushless DC motor 6 is normally started in a situation where the command speed Rt is high or the fan load is heavy, the motor current I may reach the set value Is, but at this time, the motor current I becomes the set value Is. It reaches after a certain time t2. Since this fixed time t2 is added as a condition for lock determination, it is possible to prevent erroneous determination in a situation where the command speed Rt is high or a load is heavy.

  When the fan load is light, the followability of the rotor speed with respect to the command speed Rt is improved. Therefore, when the brushless DC motor 6 is normally started in such a situation, the motor current I is reduced before the predetermined time t2 has elapsed. The set value Is may be reached. However, in this case, the estimated rotor speed R exceeds the predetermined value Rs before the motor current I reaches the set value Is within the predetermined time t2 (YES in Step 107, NO in Step 108). Therefore, also in this case, the motor control unit 10 does not determine that the lock is set. As a result, it is possible to prevent an erroneous determination such that a lock determination is made despite being normal.

  The motor control unit 10 determines that the motor current I is not changed before the time count t reaches the constant time t2 (YES in Step 107) and the estimated rotor speed R does not reach the constant value Rs (YES in Step 108). Only when the value rises to the set value Is or higher (YES in Step 109), it is determined that the brushless DC motor 6 is locked, and the fact is notified to the user by the display on the display unit 11 (Step 110). Switching of the switching circuit 5 by the vector control is stopped (step 111). By stopping the switching, unnecessary driving of the brushless DC motor 6 in the locked state does not continue indefinitely, and the switching circuit 5 and other electric / electronic parts are not destroyed. The user can detect that the reason for the drive stop is the lock of the brushless DC motor 6 from the display on the display unit 11 and request repair.

  As described above, by setting three conditions for the lock determination of the brushless DC motor 6, the lock of the brushless DC motor 6 can be accurately detected regardless of the command speed Rt and the load. Thereby, the reliability as an inverter apparatus improves significantly.

  The above embodiment is presented as an example, and is not intended to limit the scope of the invention. The novel embodiment can be implemented in various other forms, and various omissions, rewrites, and changes can be made without departing from the spirit of the invention. In these embodiments and modifications, the scope of the invention is included in the gist, and is included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Commercial AC power source, 3 ... Rectifier circuit, 5 ... Switching circuit, 6 ... Brushless DC motor, 7, 8, 9 ... Current transformer, 10 ... Motor control part, 11 ... Display part

Claims (2)

In an inverter device that converts a DC voltage to an AC voltage by switching and supplies it to a motor,
Detecting means for detecting a current flowing through the motor;
After starting the motor by forcibly switching energization to each phase winding of the motor, the rotational speed of the motor is estimated from the detection current of the detection means, and the estimated rotational speed becomes the command speed. Control means for controlling the switching;
When the detection current of the detection means rises above a predetermined set value within a predetermined time from the start of the start and before the estimated rotational speed reaches a predetermined value, the motor Determining means for determining that is locked;
An inverter device comprising: 2. The inverter device according to claim 1, wherein when the determination unit determines that the lock is determined, the control unit notifies the fact and stops the switching.

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