JP5537123B2 - Synchronous motor restart method - Google Patents

Description

  The present invention relates to an inverter device for driving a synchronous motor, and more particularly to a restart method for smoothly shifting from a coasting state of a synchronous motor to operation by an inverter device.

  Conventionally, in a power converter that drives a motor that does not have a pulse generator, such as an encoder, at a variable speed, after the motor enters a free-run state due to an external factor such as a momentary power failure or operation of the power converter, In the case of restarting while the motor is rotating instead of starting from the start, if the motor speed and the output frequency of the power converter do not match, an excessive current flows and a restart failure state occurs. In order to avoid this, there is known a method for detecting the number of rotations of a motor in a free-run state and automatically restarting the power conversion device in synchronization with the rotation state of the motor.

  Patent Documents 1, 2, and 3 describe a method for restarting an induction motor. Due to the occurrence of an instantaneous power failure, the frequency number of the induction motor decreases according to inertia. The decrease in frequency is reflected as the frequency of the residual voltage of the induction motor. Therefore, the frequency of the residual voltage is monitored, and after the power supply is restored, the power converter performs control to achieve a predetermined frequency based on this and restarts. In order to detect the frequency of the induced voltage of the motor, the number of revolutions, the induced voltage, and the phase thereof are detected by converting the induced voltage into a pulse and detecting the cycle with a power converter, and the rotation state of the motor It is disclosed that restarting is performed.

  In an electric motor having a pulse generator such as an encoder, a method disclosed in Patent Document 4 is disclosed in which the motor rotation speed and phase are detected based on the frequency of a pulse generated by the pulse generator and restarted. However, in an electric motor without a pulse acquisition unit, another method such as a method of detecting the induced voltage is required. Further, in the synchronous motor, an excessive current is generated when the error between the phase and the number of rotations (output voltage) at the time of restart is large, so that a restart method with high accuracy is required.

  In addition, as a method for detecting the induced voltage of the motor, multiple circuits with a built-in power converter that convert the induced voltage appearing between the lines of the motor into pulses are provided, and the motor speed, phase, and direction of rotation are detected from the obtained pulses. In some cases, however, a method is used in which the motor is started in synchronism with the motor (up to the output frequency and phase of the power converter, and further in the rotational direction). The rotation speed detection pulse is converted from the Vuv, Vvw, Vuw motor line voltage, and the rotation direction can be determined by acquiring two or more line voltage pulses, and the rotation speed can be detected accurately. It is known that

  In addition, in order to make the detection circuit inexpensive in the induction motor, there is a case where only one of the motor line voltages is used, converted into a pulse, and the number of rotations is detected. . This is because the induced voltage of the induction motor has a characteristic of decaying with time when it shifts to the free-run state, and the induced voltage does not remain so much until the rotation changes as the rotation direction changes. It is because it is enough if you know.

JP-A-58-99286 Japanese Patent Laid-Open No. 55-8250 Japanese Patent Laid-Open No. 58-127592 JP 58-103666 A

  When applying the above technique to a synchronous motor, it is conceivable to use a method of detecting the number of rotations using only one line voltage in order to make the circuit inexpensive and compact by the same method. In this case, unlike the induction motor, the synchronous motor has a magnetic pole fixed to the rotor by a permanent magnet, and when the phase information is shifted, the detection error immediately appears as an increase in current. Unlike the induction motor, where the induced voltage after free run decays with time, in the case of a synchronous motor, it occurs when the rotor of the motor rotates even a little, so the rotation speed when the motor stops is zero. Even if the voltage drops in the vicinity, an induced voltage is generated in a situation where forward rotation and reverse rotation due to shaft vibration due to the influence of mechanical vibration and cogging torque are repeated.

  In this case, if the line voltage is detected in two or more phases, the rotation direction can be determined from their phase order, so there is no particular problem, but as described above, only the line voltage is detected in one phase. Since the direction of rotation is unknown, it may be erroneously detected as if rotating at a high frequency. In this case, since a high frequency and a voltage corresponding to the high frequency are applied to the substantially stopped motor, an excessive current jump occurs, and the power converter immediately shuts off the output for protection and cannot be restarted.

  The objective of this invention is providing the power converter device which prevented the restart failure by the detection after the induced voltage in the rotation speed zero vicinity at the time of restart.

In order to achieve the above object, for example, among each line of the output terminal connected to the synchronous motor , a voltage detector that detects a line voltage between two phases, and a line voltage detected from the voltage detector A pulse converter for converting a signal based on the frequency component, a magnitude of the induced voltage estimated based on the frequency component converted by the pulse converter, and a magnitude of the induced voltage detected by the voltage detector, And a control circuit that determines a method for starting the synchronous motor based on the comparison result .

  According to the present invention, if at least one-phase line voltage can be detected, phase detection accuracy and malfunction at low speed can be prevented, and restart can be performed without a current jump. Therefore, an inexpensive and compact output circuit has high accuracy. A restart method can be provided.

1 is a schematic configuration diagram of a power converter according to Example 1. FIG. It is an example of the pulse conversion from an induced voltage. It is an example from a voltage detection circuit to MCU. It is an example of the line voltage detection delay by a filter circuit. It is an example of the line voltage detection delay by the hysteresis of a comparator. It is a malfunction prevention explanatory drawing of this invention.

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

  The description of this embodiment will be described with reference to FIGS.

FIG. 1 is a block circuit diagram showing an embodiment according to the present invention.
The DC voltage charged in the smoothing capacitor 3 is converted into an AC voltage by the inverter circuit 2 and applied to the synchronous motor 1 to be driven.

Further, the voltage detection circuit 4 divides the induced voltage generated in an arbitrary phase (the U phase and the V phase in FIG. 1) into a line voltage when the synchronous motor 1 is in a free-run state. It is a circuit to output. The pulse conversion circuit 5 is a rotation speed detection circuit that converts the voltage detected by the voltage detection circuit 4 into a pulse wave synchronized with the rotation speed and outputs it to detect the rotation speed.
Reference numeral 6 denotes a control circuit that performs PWM control of the semiconductor switching elements constituting the inverter circuit 2. In the first embodiment of the present invention, the motor is in a free-run state due to an external factor such as an instantaneous power failure and a user operation, and the inverter circuit When output is shut off, PWM output is started by restart command. The control circuit 6 is composed of, for example, an MCU, and the output of the voltage detection circuit 4 is input to the AD converter of the MCU, and the voltage pulse output of the pulse conversion circuit 5 is input to the input port of the MCU, so that the number of revolutions of the induced voltage is increased. Let the MCU recognize the phase and size. FIG. 2 is a diagram showing the correspondence between the induced voltage and the converted pulse. The MCU calculates an output frequency and an output voltage from the current rotation speed and voltage phase of the synchronous motor detected from the voltage detection circuit 4 and the pulse conversion circuit 5.

The detected rotational speed, that is, the rotational frequency can be obtained from (Equation 1) using one pulse period of FIG.
(Equation 1) f = 1 / T
Here, the rotation frequency is f and the pulse period is T.
Further, the magnitude of the induced voltage in the free-run state can be calculated from (Equation 2).
(Equation 2) V = 2πf × Ke × √3 / √2
Here, the line voltage V, the frequency f, and the induced voltage constant Ke specific to the motor.

  FIG. 3 shows a path from detection of the induced voltage to input of a signal to the MCU. Normally, when the phase of the induced voltage is input, it is converted into a pulse shape, input to the MCU port, and recognized by the MCU. There is a delay in circuit and processing between the actual induced voltage phase and the output command phase.

As the circuit delay, for example, when the frequency of the line voltage is high as shown in FIG. 4, the phase shift is increased by the filter circuit for noise removal, so that a phase delay occurs.
For example, the time constant of a low-pass filter such as an RC circuit can be calculated from (Equation 3).
(Equation 3) Tc = R × C
Here, the time constant Tc, the resistance value R, and the capacitor capacitance C.

The phase error by the low-pass filter, that is, the phase angle can be calculated from (Equation 4).
(Equation 4) Φ = −arctan (ωTc)
Here, Φ is a phase angle, Tc is a circuit time constant, ω is an angular frequency, and the frequency f has a relationship of ω = 2πf.
The phase error due to the filter is determined by the circuit time constant and the driving frequency, and can be corrected by linear approximation or polynomial approximation of the arctan function.

Further, as shown in FIG. 5, when the line voltage is small, a delay occurs due to a hysteresis component by a comparator that prevents malfunction of pulse conversion. This increases as an error when the line voltage is small, but the fluctuation of the line voltage obtained from the equation (2) depends only on the fluctuation of the frequency, and can be accurately corrected by linear approximation or polynomial approximation. Since the delay due to these circuits is determined in advance at the time of circuit design, the delay is calculated at the time of design and corrected.
Further, as a processing delay, an operation delay at the time of output occurs in the MCU due to phase data based on port information and processing speed. This is mainly due to delays such as transfer between software tasks and register updates, and the delay time is almost determined so that correction is possible. By correcting these delays and outputting, it is possible to perform restart without increasing current due to phase shift from at least one-phase line voltage.

  In addition, as shown in FIG. 6, when the shaft vibrates in a low speed region and appears as a line voltage, the induced voltage estimated from the detected rotation frequency and the line voltage are detected within a half cycle. Compared with the peak induced voltage, if the difference is a predetermined value (for example, the calculated difference is within a range of ± 10% of the induced voltage), it is started by a start command and is outside the above range. In this case, the detection is performed again, and the timing is delayed until the condition is satisfied, or the start is stopped, or the start is performed from 0 Hz, thereby preventing erroneous restart.

  In addition, the conversion pulse circuit of FIG. 1 may generate pulse information inside the MCU from the induced voltage value taken into the MCU and use it as the rotation speed. At this time, since it is necessary to add a filter and hysteresis as a noise countermeasure as in the circuit, correction is performed in the same manner.

DESCRIPTION OF SYMBOLS 1 ... AC motor, 2 ... Inverter part, 3 ... Smoothing capacitor, 4 ... Line voltage detection circuit, 5 ... Pulse conversion circuit, 6 ... Control circuit

Claims (4)

Among each line of the output terminal connected to the synchronous motor, a voltage detector that detects a line voltage between two phases;
A pulse converter that converts a signal based on the line voltage detected from the voltage detector into a frequency component;
The magnitude of the induced voltage estimated based on the frequency component converted by the pulse converter is compared with the magnitude of the induced voltage detected by the voltage detector, and a method for starting the synchronous motor is determined based on the comparison result. A control circuit;
A power conversion device comprising: The power conversion device according to claim 1,
In the control circuit, the magnitude of the induced voltage estimated based on the frequency component converted by the pulse converter, and the magnitude of the peak induced voltage detected within a half cycle of the line voltage detected by the voltage detector. And a method of starting the synchronous motor is determined based on the comparison result. The power converter according to claim 1 or 2,
In the control circuit, when the difference between the magnitude of the induced voltage estimated based on the frequency component converted by the pulse converter and the magnitude of the induced voltage detected by the voltage detector is within a predetermined range, the synchronous motor A power conversion device characterized by starting. The power converter according to claim 1 or 2,
In the control circuit, when the difference between the magnitude of the induced voltage estimated based on the frequency component converted by the pulse converter and the magnitude of the induced voltage detected by the voltage detector is not within a predetermined range, the voltage the detection by the detector again or stops starting of the synchronous motor, or a power conversion device which is characterized in that the starting of the synchronous motor from 0 Hz.

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