JPS6237090A - Drive system of single phase induction type electric motor - Google Patents

Abstract

PURPOSE:To start an electric motor by high starting torque by shifting the phase of currents fed to an auxiliary coil by 1/2pi from a power supply by using an inverter. CONSTITUTION:Alternating currents ACs are connected to a main coil 3 for an electric motor 1. An inverter drive circuit 5 is connected in parallel with the main coil 3, and an auxiliary coil 7 is connected to the output side of the inverter drive circuit 5. A current detecting coil 9 outputs detecting currents corresponding to AC currents fed to the main coil 3 to the inverter drive circuit 5. The detecting currents are employed as signal currents in order to shift the phase of the currents of the auxiliary coil by 1/2pi to the currents of the main coil on the starting of the electric motor 1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a drive system for a single-phase induction electric motor (hereinafter referred to as an electric motor).

[Prior Art] Conventionally, in an electric motor, a main coil connected in series to an AC power source, a current relay connected in series, a starting capacitor, and an auxiliary coil are connected in parallel. When the power switch is turned on, the current supplied to the auxiliary coil is shifted in phase with the alternating current supplied to the main coil by a capacitor, and is supplied while forming a rotating magnetic field, thereby connecting the main coil and the auxiliary coil. The starting torque of the electric motor is obtained by two-phase driving. When the electric motor reaches the required rotational speed and the current supplied to the main coil reaches the required value, the current relay returns to cut off the supply of auxiliary coil current to the auxiliary coil, and then the electric motor is connected to the main coil. It is driven in one phase by only one.

[Problems to be solved by the invention] However, in order to obtain a high starting torque when starting an electric motor, ideally the phase should be shifted by 1/2π with respect to the alternating current supplied to the main coil. It is necessary to supply current to the auxiliary coil. When the phase is shifted by a capacitor, the impedance of the auxiliary coil changes as the electric motor rotates, so it is difficult to maintain the phase shift by the capacitor to 1/2π. Therefore, it is difficult to start the electric motor with high starting torque in a short time, and the starting response of the electric motor is poor.

[Object of the Invention] In view of the above-mentioned conventional drawbacks, an object of the present invention is to make it possible to start an electric motor with a high starting torque, and to improve the starting response of the electric motor by varying the supplied electric power. An object of the present invention is to provide an electric motor drive method that can improve the performance.

[Means for Solving the Problems 1] Therefore, the present invention provides an electric motor in which an auxiliary coil is connected in parallel to a main coil, and a starting torque is obtained by the main coil and the auxiliary coil that are driven at the start of rotation. Until the required rotational speed is reached, an inverter-controlled auxiliary coil current is supplied to the auxiliary coil in synchronization with the alternating current supplied to the main coil by an inverter drive circuit so that the phase is shifted by 1/2π. After obtaining a starting torque, when the electric motor reaches a required rotational speed, the electric motor is driven in one phase by the main coil.

[Operation of the invention 1] Since the method of the present invention is configured as described above, when the electric motor starts rotating, the phase shifts by 1/2π in synchronization with the alternating current supplied to the main coil by the main coil and the inverter drive circuit. Since the electric motor is driven in two phases by the auxiliary coil to which the auxiliary coil current is supplied, the electric motor can be started with high rotational torque. Therefore, it is possible to improve the rotational responsiveness of the electric motor.

[Example] An embodiment of the present invention will be described below.

In FIG. 1 showing the circuit configuration of the electric motor according to the present invention and FIG. 2 showing the drive circuit configuration of the auxiliary coil, the main coil 3 of the electric motor 1 is supplied with an alternating current A having a required frequency.
C is connected. An inverter drive circuit 5 is connected in parallel to the main coil 3, and an auxiliary coil 7 is connected to the output side of the inverter drive circuit 5. The main coil 3 is provided with a current detection coil 9, and the current detection coil 9 outputs five detected currents corresponding to the alternating current supplied to the main coil 3 to the inverter drive circuit 5. The detected current is input to a synchronization circuit 15 to be described later, and when the electric motor 1 is started, the phase of the auxiliary coil current is adjusted to 172° with respect to the main coil current.
Used as a signal current for shifting by π.

The rectifier circuit 11 of the inverter drive circuit 5 rectifies the supplied alternating current into a direct current, and the four power transistors Tr1 to Tr4 and the auxiliary coil 7 are bridge-connected to the output side of the rectifier circuit 11. Note that the rectifier circuit 11
A regenerative capacitor 13 is connected in parallel to the output side of the . A synchronous circuit 15 is connected to the current detection coil 9, and the synchronous circuit 15 outputs a synchronous current whose phase is shifted by 1/2π with respect to the frequency of the main coil current supplied to the main coil 3. A waveform shaping circuit 17 is connected to the synchronous circuit 15, and the waveform shaping circuit 17 shapes the synchronous current into a rectangular wave. A central processing unit (hereinafter referred to as CPU) 19 is connected to the waveform shaping circuit 17 . A ROM 21 and a RAM 23 are connected to the CPU 19, respectively.
21 has a program memory area 25 and a speed data memory area 27. The program memory area 2
5 stores program data for inverter control of the auxiliary coil 7. Further, the speed data memory area 27 stores speed data that determines the timing of interrupting the drive of the auxiliary coil 7. The RAM 23 has two timer areas, and the timer area 29 measures the frequency according to the period of the auxiliary coil current controlled by the inverter.

A rectifier circuit 18 is connected to the current detection coil 9, and the rectifier circuit 18 rectifies the input 1c signal current into a direct current. An A/D conversion circuit 20 is connected to the rectifier circuit 18, and the A/D conversion circuit 20 converts the input DC current into digital data according to the rotation speed of the electric motor 1, and outputs the digital data to the CPU 19. do.

A pulse generation circuit 31 is connected to the CPU 19.

The pulse generating circuit 31 generates a PWM-controlled pulse signal whose phase is shifted by 172π from the phase of the alternating current supplied to the main coil 3 and in synchronization with the frequency of the main coil current. The pulse width of this pulse signal is PWM controlled so that the combined effective value waveform of the auxiliary coil current supplied to the auxiliary coil 7 approximates a sine wave as shown in FIG. 3, which will be described later.

Drive circuits 33a to 33d are connected to the pulse generating circuit 31. The drive circuits 338 to 33d drive the power transistors Tr1 - based on the input pulse signals.
A base current is sequentially applied to the bases of power transistors Tr"4, Tr2-Tr3, and the power transistors Tr1-Tr4
, Tr2-Tr3 are set to 0 according to the pulse width of the pulse signal.
Perform N-OFF control.

The drive circuits 33a to 33d are composed of a light emitting element and a light receiving element (none of which are shown). Based on the pulse signal, the power transistor T
By sequentially applying r1 to the bases of Tr4, Tr2 and Tr3, power transistors Tr1 to Tr4
, Tr2-Tr3 are controlled ON-OFF.

Next, a driving method of the electric motor configured as described above will be explained with reference to FIG.

In FIG. 3 showing current waveforms supplied to the main coil 3 and the auxiliary coil 7, when the power switch 4 is turned on, alternating current is supplied to the main coil 3 and the inverter drive circuit 5. At this time, the inverter drive circuit 5 rectifies the supplied alternating current into a direct current by the rectifier circuit 11, and then
It is applied between the emitters and collectors of power transistors Tr1 to Tr4. The CPU 19 also generates a pulse generator circuit 31 at a frequency corresponding to the main coil current in synchronization with a rectangular wave whose phase is shifted by 172π from the main coil current by the synchronization circuit 15 and whose waveform has been shaped by the waveform shaping circuit 17. drive As shown in FIG.
Pulse signals for PWM control of the auxiliary coil current supplied to the auxiliary coil 7 are sequentially output to the drive circuits 33a to 33d at timings whose phases are shifted by 1/2π. The drive circuits 33a to 33d transfer the base current to the power transistors Tr1, Tr4, Tr2 according to the pulse signal.
- The power transistors Tr1 to Tr4 and Tr2 to Tr3 are sequentially ON-OFF controlled according to the pulse width.

For example, when forming a positive component of the auxiliary coil current, the power transistors Tr1 and Tr4 are used, and when forming a negative component, the power transistor Tr2 is used.
・Double r3 is controlled ON-OFF.

As a result, the auxiliary coil current is applied to the auxiliary coil 7 with a phase shift of 1/2π from the main coil current and PWM-controlled at a frequency synchronized with the frequency of the main coil current. As a result, when the electric motor 1 starts rotating,
It is driven by two phases: a main coil 3 and an auxiliary coil 7 supplied with an auxiliary coil current whose phase is shifted by 1/2π with respect to the main coil current. As a result, it is possible to form an ideal rotating magnetic field and start the electric motor 1 with high starting torque. Furthermore, when the electric motor 1 starts rotating, PWM
By varying the pulse width of the controlled pulse signal, the electric power supplied to the auxiliary coil 7 can be changed to improve the rotation start-up characteristics of the electric motor 1.

The rotational speed of the electric motor 1 is determined based on the current detected by the current detection coil 9 in the speed data memory area 2.
When the required rotation speed stored in 7 is reached, the CPU 1
9 cuts off the supply of auxiliary coil current to the auxiliary coil 7. As a result, the electric motor 1 is driven in one phase only by the main coil 3.

In this way, in this embodiment, when the electric motor 1 starts to rotate, the phase of the auxiliary coil current supplied to the auxiliary coil 7 is reliably shifted by 172π with respect to the main coil current to form an ideal rotating magnetic field. The starting torque of No. 1 can be increased. Furthermore, since a large capacity capacitor as in the conventional case is not required, it is possible to downsize the drive device.

In the above explanation, a synchronization signal whose phase is shifted by 172π is formed by the synchronization circuit 15 based on the detected current from the current detection coil 9 corresponding to the frequency of the main coil current, and the auxiliary coil current is controlled by the inverter using the synchronization signal. However,
The auxiliary coil current may be controlled by the CPU so that the phase thereof is shifted by 172π with respect to the frequency of the main coil current without providing a synchronization circuit.

Furthermore, in the above explanation, the auxiliary coil current is subjected to PWM control as shown in Fig. 3, but as shown in Fig. 4, the auxiliary coil current is PWM controlled to form an alternating current that approximates the main coil current. It may be something that does.

Furthermore, in the above description, the current detection coil 9 detects the rotation speed of the electric motor 1 and switches from two-phase drive using the main coil 3 and auxiliary coil 7 to one-phase drive using only the main coil 3. The rotation speed detection means may be an alternating current generator (tacho generator), an encoder, or the like.

[Effects of the Invention] As described above, the present invention provides an electric motor that can start the electric motor with a high starting torque and that can vary the amount of electric power supplied to improve the starting response of the electric motor. It is possible to provide a drive system.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing the circuit configuration of the electric motor, Fig. 2 is a block diagram showing the drive circuit configuration of the auxiliary coil, Fig. 3 is an explanatory diagram showing the operation, and Fig. 4 shows a modified embodiment of the present invention. It is an explanatory diagram. In the figure, 1 is an electric motor, 3 is a main coil, 5 is an inverter drive circuit, and 7 is an auxiliary coil.

Claims (1)

[Claims] (1) In a single-phase induction electric motor in which an auxiliary coil is connected in parallel to the main coil, and the starting torque is obtained from the main coil and the auxiliary coil that are driven at the start of rotation, In between,
After obtaining starting torque by supplying an inverter-controlled auxiliary coil current to the auxiliary coil so that the phase is shifted by 1/2π in synchronization with the alternating current supplied to the main coil by an inverter drive circuit, the electric motor is activated. A drive system for a single-phase induction electric motor that is characterized by one-phase drive by the main coil when the required rotational speed is reached.