JP5424250B2 - Motor control device - Google Patents

Description

  The present invention relates to a motor control device, for example, a motor control device that can drive a synchronous motor including a plurality of phase coils without using a sensor.

  An outdoor fan or the like of an air conditioner rotates by natural wind when the fan motor is not driven.

  Conventionally, a fan driving device using a brushless DC motor has been provided with a sensor for detecting the rotational position of a rotor such as a Hall element. Then, when the fan is started, a method of detecting the rotational position of the rotor based on the output signal of this sensor and controlling the energization to each switching element constituting the inverter in accordance with this rotational position has been adopted. Then, after the fan is temporarily stopped and the motor is positioned, starting is started. At this time, when the rotational speed of the fan rotating in the natural wind is high, the compressor is driven as it is without starting control of the fan.

  In recent years, when driving a motor, a sensorless motor control system that eliminates sensors such as Hall elements that detect the rotational position of the motor, reduces the number of parts, reduces reliability due to component failure, and reduces costs. Has been adopted.

  However, in the case of the fan motor described above, unlike the compressor, the load of the fan itself is light, so that it rotates freely by natural wind even when the operation is stopped. If you try to use a sensorless motor for such a motor, you can estimate the number of rotations from the value of the current flowing through the motor after startup, but before starting, control the startup from a state where the rotation state of the fan is not known at all Will be executed.

  In that case, when the motor starts when the natural wind is strong and the fan is rotating at a high speed, an excessive current flows through the switching elements constituting the winding and the inverter due to the induced voltage generated in the motor winding. There is a problem that the permanent magnet of the rotor is demagnetized or the switching element is destroyed, and it is necessary to stop the motor once.

  Therefore, when an FET or IGBT is used as a switching element in the inverter at the time of starting or before entering the start-up control, the driving power supply for the switching element for three phases constituting the positive side (hereinafter also referred to as the upper phase) arm. As described above, a system is employed in which a switching element constituting a negative side (hereinafter also referred to as a lower phase) arm is turned on, and a braking operation (regenerative braking) is performed with the motor short-circuited.

  In Japanese Patent Application Laid-Open No. 2005-124330, the current flowing through the element when detecting the short circuit state is detected, and if the protection level is exceeded, the switching element constituting the negative arm is returned to the off state to start A method for stopping is disclosed.

JP 2005-124330 A

  However, in the above method, if the typhoon is rotating at a high speed due to strong winds or the like during the typhoon, the switching element for the three phases forming the negative arm of the inverter is suddenly turned on at the moment. Since current flows, there is a problem that a high-speed CPU and a separate comparator are required to demagnetize the motor and protect the drive IC, which is costly.

  The present invention has been made to solve the above-described problems, and provides a motor control device capable of demagnetizing a motor and protecting a drive IC at a low cost with a simple method. The purpose is to do.

  A motor control device according to the present invention includes a sensorless multi-phase motor, an inverter in which switching elements are connected in a three-phase bridge, and supplies three-phase AC power to the motor, and current detection means for detecting a current flowing through the multi-phase motor. And a control device for controlling the inverter. The control device outputs a pulse signal that turns on the switching elements for three phases that form the negative arm of the inverter in order to short-circuit the arm during the starting operation. According to the current value detected by the current detection means, the duty ratio of the pulse signal for turning on the switching elements for three phases forming the negative arm of the inverter is adjusted.

  Preferably, the control device detects a zero cross cycle of the motor phase current of the multiphase motor by the current detection means, and ends the start-up operation when the motor rotation speed corresponding to the zero cross cycle is equal to or greater than a predetermined value.

  The motor control device according to the present invention suppresses overcurrent at the start-up operation and adjusts the duty ratio of the pulse signal applied to the negative side of the inverter according to the current value detected by the current detection means, thereby demagnetizing the motor. In addition, the driving IC can be protected. Also, only when it is determined that the current level is safe, the duty ratio of the pulse signal is gradually increased, and finally it is possible to execute a reliable braking operation by turning it on 100%. Become.

It is a figure explaining the whole structure of the fan control system according to Embodiment 1 of this invention. It is a figure explaining the structure of the principal part of the outdoor unit 117. FIG. It is a figure explaining schematic structure of the motor control apparatus according to the embodiment of the present invention. It is a figure explaining the operation | movement at the time of start-up according to Embodiment 1 of this invention. It is a figure explaining the waveform of the U-phase current according to Embodiment 2 of the present invention. It is a figure explaining the operation | movement at the time of starting according to Embodiment 2 of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

(Embodiment 1)
The overall configuration of the fan control system according to the first embodiment of the present invention will be described using FIG.

  Referring to FIG. 1, here, a configuration of a refrigeration cycle apparatus is shown as an example of a fan control system.

  Specifically, an inverter 52 is connected to the AC power source 51. The inverter 52 rectifies and smoothes the alternating current, converts the obtained direct current into alternating current of variable voltage and variable frequency, and outputs it. A compressor 53 constituting a refrigeration cycle is connected to the inverter 52.

  The refrigeration cycle includes a compressor 53, a four-way valve 54, an outdoor heat exchanger 55, an expansion valve 56, an indoor heat exchanger 57, an outdoor fan 58 and an indoor fan 59.

  As will be described later, the outdoor fan 58 includes a fan 8F and a motor 8M, and includes an inverter 110 for controlling the motor 8M.

  The inverter 110 is accompanied by a current detection circuit 111 that detects the winding current of the motor 8M.

  A speed control circuit 112 is provided to control the speed of the indoor fan 59. Further, it includes a control unit 113 that controls the inverters 52 and 110 and gives a speed command to the speed control circuit 112. The control unit 113 includes a light receiving unit 114 that receives a signal from the remote control device 116 and an abnormality. An abnormality display unit 115 is connected. The control unit 113 includes a microcomputer unit (hereinafter abbreviated as MCU), and executes arithmetic processing described later.

The configuration of the main part of the outdoor unit 117 will be described with reference to FIG.
Referring to FIG. 2, an outdoor heat exchanger 55 is disposed, a compressor 53 is disposed on the right side, and an outdoor fan 8 that drives a fan 8F by a motor 8M is mounted inside the outdoor heat exchanger 55. The heat exchange of the outdoor heat exchanger 55 is promoted by sucking outside air from the directions of arrows A and B and discharging it in the direction of arrow C.

  A schematic configuration of the motor control device according to the embodiment of the present invention will be described with reference to FIG.

  With reference to FIG. 3, a motor control device including an inverter 110 connected to the motor 8M and a control unit 113 that drives the inverter 110 will be described.

  AC power supply 4 is connected to converter circuit 3. The converter circuit 3 rectifies and smoothes alternating current and supplies a direct current voltage to the inverter unit 2. In the inverter unit 2, for example, six switching elements Q1 to Q6 made of IGBT are connected in a three-phase bridge. That is, a series connection circuit of switching elements Q1 and Q4, a series connection circuit of switching elements Q2 and Q5, and a series connection circuit of switching elements Q3 and Q6 are connected in parallel, and one end thereof is connected to the positive electrode of converter circuit 3. The other end is connected to the negative electrode of the converter circuit 3.

  Resistors R1 to R3 are provided between the switching elements Q4, Q5, Q6 and the negative electrode of the converter circuit 3, respectively.

  In order to detect the current flowing through each phase winding of the motor 8M, the switching elements Q4 and Q5 are connected to the switching elements Q4 and Q5 based on resistors R1 to R3 provided between the emitters of the switching elements Q4 and Q5 and the negative electrode of the converter circuit 3. Operational amplifiers AP1 and AP2 for amplifying the generated voltages are provided.

  A current detection circuit 111 is configured based on the operational amplifiers AP1 and AP2 and the resistors R1 to R3.

  Among these, the switching elements Q1 to Q3 constitute an upper phase arm, and the switching elements Q4 to Q6 constitute a lower phase arm.

  Further, the external connection of the U, V, and W phases of the motor 8M in which the interconnection point of the switching elements Q1 and Q4, the interconnection point of the switching elements Q2 and Q5, and the interconnection point of the switching elements Q3 and Q6 are star-connected. Connected to the conductor.

  As will be described later, a PWM signal (also referred to as a PWM pulse) that is an on / off control signal of the switching element created by the MPU 113 is input to the gates of the switching elements Q1 to Q6.

  The current detection circuit 111 detects voltages V1 and V2 generated when U and V-phase currents flow through the resistors R1 and R2, respectively, while the switching elements Q4 and Q5 are on.

Control unit 113 includes a three-phase PWM control unit 15 and a PWM creation unit 17.
The three-phase PWM control unit 15 calculates a U-phase current Iu, a V-phase current Iv, and a W-phase current Iw, which are three-phase currents, based on the voltages V1 and V2 input via the operational amplifiers AP1 and AP2. W-phase current Iw is calculated based on U-phase current Iu and V-phase current Iv. W-phase current Iw is calculated by-(Iu + Iv).

  The three-phase PWM control unit 15 receives a start / stop command, a rotation speed command, and the like, and sends a PWM pulse width (DUTY ratio) command corresponding to the command to the PWM creation unit 17. The start / stop command, the rotation speed command, and the like are generated by a command generation unit of the control unit 113 (not shown) based on a signal received by the light receiving unit 114 from the remote control device 116, for example. Alternatively, the activation command is a case where the command or the like is given when the control unit 113 reads the data stored in the non-volatile storage device when the fan control system is activated, regardless of the remote control device 116 or the like. May be.

  The PWM creation unit 17 outputs a PWM signal corresponding to the received PWM pulse width (DUTY ratio) of each phase. In this example, as an example, the PWM pulse cycle is 50 μs (PWM pulse frequency 20 kHz).

  By switching the switching elements Q1 to Q6 by the PWM signal from the PWM creating unit 17 of the control unit 113, an appropriate driving voltage is applied to the motor, and the motor 8M can be set to a desired rotation speed.

Regarding the present embodiment configured as described above, the operation at the time of activation will be described.
If the outdoor fan is in a stopped state, no voltage is induced in the phase winding of the motor, so the current of the inverter switching element is zero.

  Therefore, if it is stopped, there is no problem even if it starts immediately, but if the outdoor fan is rotating by natural wind, a voltage is induced in the winding of the motor, and if the switching element is turned on, When a sine wave current flows through the phase winding of the motor and an overcurrent flows, the motor may be demagnetized or the drive IC may be destroyed.

With reference to FIG. 4, the operation at the time of startup according to the first embodiment of the present invention will be described.
First, by receiving an activation command from the outside in the fan stop state, the three-phase PWM control unit 15 starts an operation of braking the motor 8M that is free-running by an external wind or the like. The processing shown below is mainly processing executed in the three-phase PWM control unit 15 and the PWM creation unit 17 of the control unit 113.

  Specifically, in step S2, the three-phase PWM control unit 15 starts outputting PWM pulses to the switching elements Q4 to Q6 constituting the lower phase arm. Specifically, the PWM generation unit 17 is instructed to apply a PWM pulse having the same value and an appropriate DUTY ratio, for example, a PWM pulse having an DUTY ratio of 10% as an initial value to the gate.

  As a result, the PWM creating unit 17 applies a PWM pulse with a DUTY ratio of 10%, for example, to the gates of the switching elements Q4 to Q6 constituting the lower phase arm. As will be described later, finally, a PWM pulse with a DUTY ratio of 100% is applied. In this example, as an example, since the PWM pulse period is 50 μs (PWM pulse frequency 20 kHz), when the DUTY ratio is 10%, as an example, a PWM pulse whose “H” level period during which the switching element is turned on is 5 μs. Applied.

  Accordingly, switching elements Q4 to Q6 are turned on for a very short period of time, and the motor is short-circuited, so that a braking operation (regenerative braking) is performed.

Next, the three-phase PWM control unit 15 waits for a predetermined period (step S4).
For example, the predetermined period is set to about 3 ms as an example.

  Then, after waiting for a predetermined period, the three-phase PWM control unit 15 determines whether or not the absolute value of each phase current exceeds a threshold value, for example, 1A (step S6).

  When the three-phase PWM control unit 15 determines that the absolute value of each phase current does not exceed the threshold value (YES in step S6), the process proceeds to the next step S8.

  On the other hand, if the three-phase PWM control unit 15 determines that the absolute value of each phase current exceeds the threshold value (NO in step S6), the three-phase PWM control unit 15 returns to step S4 again and maintains the DUTY ratio in the above process. repeat.

  Next, in step S8, the three-phase PWM control unit 15 determines whether or not the current DUTY ratio has reached 100%.

  In step S8, when the current DUTY ratio reaches 100%, the three-phase PWM control unit 15 ends the braking operation (end).

  On the other hand, in step S8, if the current DUTY ratio is not 100%, the three-phase PWM control unit 15 increases the DUTY ratio by + 1% and returns to step S2. In accordance with an instruction from the three-phase PWM control unit 15, the PWM creation unit 17 applies a PWM pulse to the gates of the switching elements Q4 to Q6 constituting the lower phase arm. Then, the above process is repeated.

  Accordingly, when the PWM pulse is applied and the absolute value of each phase current does not exceed the threshold value, the DUTY ratio gradually increases.

Then, when the DUTY ratio reaches 100%, the braking operation ends.
The threshold value to be compared with the absolute value of each phase current in step S6 is set to 1A in this example, but is not limited to this, and a sufficient margin is secured from the demagnetizing current of the motor and the maximum rated value of the driving IC. Set the value to

  Further, the initial DUTY ratio, the ratio of the DUTY ratio to be increased, and the predetermined period in step S4 are set to appropriate values depending on the number of revolutions caused by the headwind and the motor constant.

  By this processing, initially, the switching elements Q4 to Q6 are turned on for a very short period, and the current flowing through the motor is about 1/10 of the case where the DUTY ratio is 100%.

  Since the motor is in a short-circuited state, a braking operation is performed, and if each phase current value in the short-circuited state is large, a PWM pulse that maintains a low DUTY ratio is applied, so that the motor is excessive in the short-circuited state. It is possible to avoid a current flowing through the motor to demagnetize the motor or to destroy a circuit element such as a driving IC, and a safe starting operation can be performed.

(Embodiment 2)
In the first embodiment described above, the method of gradually increasing the DUTY ratio of the PWM pulse to be applied in the braking operation executed in the starting operation has been described. However, in this example, the rotational speed of the motor during the braking operation is described. The case of detecting the will be described.

The waveform of the U-phase current according to the second embodiment of the present invention will be described using FIG.
Referring to FIG. 5, for example, after the braking operation is started, a cycle T1 (s) from the first zero cross of the U-phase current to the next zero cross is measured by a timer inside the microcomputer. If the motor has a relative number of 4 poles, the rotational speed of the motor is expressed by the following equation.

N (rpm) = 60 / (2 × 4 × T1)
As a result, the rotational speed of the motor can be grasped based on the zero-cross cycle T1.

  In this example, the case where the current phase to be detected is the U phase will be described. However, the phase is not limited to the U phase, and may be either the V phase or the W phase.

  In addition, if the phase in which the first zero cross is detected is used after the start of the braking operation, it is possible to detect the rotational speed earliest.

  Further, in order to avoid the influence of the distortion of the phase current waveform due to the magnetic hysteresis characteristic of the motor, the calculation may be performed not from the first zero cross but from the second or third zero cross period.

Using FIG. 6, the operation at the time of startup according to the second embodiment of the present invention will be described.
First, by receiving an activation command from the outside in the fan stop state, the three-phase PWM control unit 15 starts an operation of braking the motor 8M that is free-running by an external wind or the like.

  Specifically, in step S12, the three-phase PWM control unit 15 starts outputting PWM pulses to the switching elements Q4 to Q6 constituting the lower phase arm. Specifically, the PWM generation unit 17 is instructed to apply a PWM pulse having the same value and an appropriate DUTY ratio, for example, a PWM pulse having an DUTY ratio of 10% as an initial value to the gate.

  As a result, the PWM creating unit 17 applies a PWM pulse with a DUTY ratio of 10%, for example, to the gates of the switching elements Q4 to Q6 constituting the lower phase arm. As will be described later, finally, a PWM pulse with a DUTY ratio of 100% is applied.

  Accordingly, switching elements Q4 to Q6 are turned on for a very short period of time, and the motor is short-circuited, so that a braking operation (regenerative braking) is performed. Further, the rotation speed detection flag is set to clear (OFF).

  Then, the three-phase PWM control unit 15 clears (initializes) the interval timer and starts the timer (step S14).

  Next, the three-phase PWM control unit 15 determines whether or not the rotation speed detection flag is on (ON) (step S15). If it is determined in step S15 that the rotation speed detection flag is not turned on (ie, is turned off) (NO in step S15), the process proceeds to the next step S16.

  On the other hand, when it is determined that the rotation speed detection flag is ON (YES in step S15), the process proceeds to step S28.

  Then, when the three-phase PWM control unit 15 determines that the rotation speed detection flag is not on (ie, off), that is, is off (OFF), it next determines whether or not a zero-cross cycle has been detected. (Step S16).

  If it is determined that the zero-cross cycle has been detected, the process proceeds to the next step S18. If it is determined that the zero-cross cycle has not been detected, the process proceeds to step S28.

  If it is determined that the zero-cross cycle has been detected (YES in step S16), the rotational speed is calculated according to the zero-cross cycle in the short-circuit state, and the rotational speed detection flag is set to ON (step S18). When the rotation speed is once calculated according to the zero cross cycle by setting the rotation speed detection flag to ON, the rotation speed detection flag is turned on in step S15 and the process proceeds to step S28 without calculating the rotation speed. move on. The calculation of the rotation speed in this example is used to determine whether or not the rotation is abnormal, and it is sufficient if the rotation speed is once calculated to determine whether or not the rotation is abnormal. With this process, it is possible to adjust the duty ratio at a high speed by omitting the calculation of the rotation speed from the next time onward.

  Then, the three-phase PWM control unit 15 next determines whether or not the rotational speed exceeds 200 rpm (step S20).

  If the three-phase PWM control unit 15 determines that the rotational speed exceeds 200 rpm, the process proceeds to step S22.

  In step S22, the three-phase PWM control unit 15 stops applying the PWM pulse to the switching elements Q4 to Q6 constituting the lower phase arm. For example, the PWM generation unit 17 is instructed to stop the generation of PWM pulses. Alternatively, it instructs to output a signal for turning off the switching element.

  Then, it waits for a predetermined period (step S24). For example, the predetermined period can be set to about several seconds depending on the system.

  Then, after waiting for a predetermined period, the process returns to step S12 again, and the same processing as described above is repeated from the initial state.

  That is, after starting the braking operation, the rotational speed is calculated. If the rotational speed is equal to or higher than the predetermined rotational speed, it is determined that it is not suitable for an unreasonable start-up and waits for a while. Then, after a predetermined period has elapsed, restart is executed.

  On the other hand, if it is determined in step S20 that the rotational speed does not exceed 200 rpm, it is next determined whether or not the interval timer has exceeded 3 ms (step S28).

  If it is determined that the interval timer has exceeded 3 ms, the process proceeds to the next step S30. On the other hand, if it is determined that the interval timer does not exceed 3 ms, the process returns to step S15 and the above-described processing is repeated.

  Then, when the interval timer exceeds 3 ms, it is determined whether or not the absolute value of each phase current exceeds a threshold, for example, 1A (step S30).

  When it is determined that the absolute value of each phase current does not exceed the threshold value, the process proceeds to the next step S32.

  On the other hand, if it is determined that the absolute value of each phase current exceeds the threshold value, the process returns to step S14, and the above process is repeated with the DUTY ratio maintained. That is, the interval timer is cleared and the timer is started.

In step S32, it is determined whether or not the current DUTY ratio has reached 100%.
In step S32, when the current DUTY ratio becomes 100%, the braking operation is ended (END).

  On the other hand, if the current DUTY ratio is not 100% in step S32, the three-phase PWM control unit 15 increases the DUTY ratio by + 1% (step S34). Then, the process returns to step S14 again, the interval timer is cleared, and a PWM pulse with a 1% increase in the DUTY ratio is output, and the same operation as described above is repeated.

  The threshold value to be compared with the absolute value of each phase current in step S30 is set to 1A in this example, but is not limited to this, and a sufficient margin is secured from the demagnetizing current of the motor and the maximum rated value of the driving IC. Set the value to

  The initial DUTY ratio, the ratio of the DUTY ratio to be increased, the interval timer in step S28, and the like are set to appropriate values depending on the number of rotations caused by the headwind and the motor constant.

  That is, when the rotational speed is measured before the adjustment of the DUTY ratio of the PWM pulse described above, the motor is rotating backward or forward at a high speed that is not suitable for the adjustment of the DUTY ratio. Therefore, it is possible to prevent the motor from being overloaded and to apply a high load to the motor, and to take appropriate measures to wait until the rotation is settled.

  In Embodiment 2 of the present invention, the motor current can be prevented from flowing suddenly even in the reverse rotation free-run state due to the influence of the back wind at the start of the fan or the like. IC destruction can be avoided.

  Further, only when it is determined that the current level is safe, the switching DUTY ratio is gradually increased, and finally, 100% ON state is achieved, so that reliable braking is possible.

  Furthermore, by detecting the zero-crossing period of the motor phase current, the rotational speed can be estimated, and excessive starting and braking can be quickly suppressed.

  The above functions can be realized at low cost without using a motor position sensor, an induced voltage detection circuit, or a high-speed CPU.

  In each of the above-described embodiments, the air conditioner as a refrigeration cycle apparatus has been described. However, the present invention is not limited to an air conditioner, but may be applied to other refrigeration cycle apparatuses such as a water heater whose main part is similarly configured. It is possible to apply.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  8M motor, 2 inverter unit, 3 converter circuit, 4, 51 AC power supply, 8F fan, 15 3-phase PWM control unit, 17 PWM creation unit, 52, 110 inverter, 53 compressor, 54 four-way valve, 55 outdoor heat exchanger , 56 expansion valve, 57 indoor heat exchanger, 58 outdoor fan, 59 indoor fan, 111 current detection circuit, 112 speed control circuit, 113 control unit, 114 light receiving unit, 115 abnormality display unit, 116 remote control device.

Claims (2)

Sensorless multi-phase motor,
An inverter having a switching element connected in a three-phase bridge and supplying three-phase AC power to the motor;
Current detection means for detecting current flowing in the multiphase motor;
A control device for controlling the inverter,
The control device includes:
Outputting a pulse signal having a predetermined duty ratio for turning on the switching elements for three phases forming the negative arm of the inverter in order to short-circuit the arm at the start-up operation;
After that, every time a predetermined period elapses, a pulse signal of the predetermined duty ratio is output until the current value detected by the current detection means becomes less than the predetermined value, and when the current value is less than the predetermined value, the duty ratio of the pulse signal Adjust the motor control device. The control device includes:
Detecting a zero-cross cycle of the motor phase current of the multiphase motor by the current detection means;
The motor control device according to claim 1, wherein when the motor rotation speed corresponding to the zero cross cycle is equal to or greater than a predetermined value, the start-up operation is terminated.

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