JPS607470B2 - Synchronous start method of synchronous motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to synchronizing a synchronous motor to an AC power system using a semiconductor power converter.

When starting a synchronous motor and connecting it to an AC power source, there are various starting methods such as using a damper winding or using an induction motor, but one method is a starting method using a semiconductor power converter. There is.

In this startup method, a synchronous motor is connected to an AC power source through a semiconductor power converter, and by controlling the amount of power supplied to the synchronous motor, the rotation speed of the synchronous motor is controlled. The position of the rotor relative to the stator of the motor is detected, and this detection signal determines the firing phase order of the semiconductor power converter, which supplies power to the armature windings of each phase of the synchronous motor. This is to accelerate the This starting method can be divided into three types, for example, constant current acceleration control, constant speed control, and comb distance control, depending on the control form until synchronization is performed. The converter control devices that perform such control are collectively referred to as a synchronous motor control device. The problems with starting this synchronous motor and synchronizing it to the AC power supply are shortening the startup time, ensuring synchronization, and preventing abnormal phenomena on the power supply side, the synchronous motor side, and the semiconductor power converter.
The aim is to suppress the input current and short-circuit current as much as possible. On the other hand, in order for a synchronous motor to be synchronously connected to the power supply system, the voltage difference, frequency difference, phase difference between the two, and the rate of change in the motor's rotational speed must fall within certain tolerance values. This is done by a remote control device. In addition, the synchronization detection device included in the synchronization control device detects whether or not the above-mentioned tolerance has been reached, and if the synchronization detection device has fallen within the tolerance and the conditions for synchronization are satisfied, the synchronization detection device Synchronization input signal #2
It looks like you'll get a 5. This synchronization signal connects the power supply system and the synchronous motor in parallel, and it is possible to synchronize the power supply by opening the circuit breaker, but the semiconductor power converter is operated in parallel with the power supply by turning on the parallel circuit breaker while it is in startup mode. Then,
If there is no isolation transformer on the input side of the semiconductor power converter, the firing phase of the semiconductor power converter creates a short circuit through the power supply side and motor side in parallel and through the disconnector, and the short circuit current is superimposed on the DC current and flows. The semiconductor power converter may be in an unfavorable state for the thyristor element in the semiconductor power converter, or if the phase of the power supply side is ahead of the phase of the terminal voltage of the synchronous motor when a parallel disconnector is turned on. There are drawbacks such as the possibility that the inverter that performs load commutation may fail in commutation. Therefore, in the present invention, the ignition pulse is generated after the current is attenuated by narrowing the power supply side control angle of the semiconductor power converter and operating the semiconductor power converter as an inverse converter using the synchronization input signal issued by the synchronization detection device. This solves the above problem by preventing short-circuit overcurrent and commutation failure when parallel circuit breakers are turned on.

The present invention will be explained below using the drawings as an example.

Figure 1 shows an example of a synchronous motor operating circuit. In the figure, 1
1 is an AC power supply, 2, 4, and 5 are breaker circuits, 3 is a semiconductor power converter, 6 is a synchronous motor, 7 is a constant speed signal generator, 8 is a constant distance control device, 9 is a rotor position detection of 6 It is a converter of signals into control signals. In addition, SI is a signal line of AC power supply voltage, S2
is the signal line for the armature terminal voltage of the synchronous motor, S3 is the signal line for the parallel signal, S4 is the signal line for the AC side current of 3, and S5 is the signal line for the 6
S6 is the control signal line converted in 9, and S7 is the control signal line that transmits the firing signal to 3.
Until synchronization is performed, 5 is open, 2 and 4 are closed, 6 is accelerated by 3, and 7 is reached. 5 is opened and 4 is opened in response to a signal that the synchronization conditions are satisfied. FIG. 2 illustrates the three types of control modes mentioned above as examples.

nM is the rotational speed of the synchronous motor rotor, iM is the armature current of the synchronous motor, ns is the reference rotational speed of the synchronous motor used in a constant speed control castle corresponding to a frequency level near the AC power supply frequency, and nso is the AC power supply The reference rotation speed of the synchronous motor, which corresponds to frequency, is the axis of time. In this figure, period A is constant current acceleration control, period B is constant speed control, and nM is ns.
・It is controlled so that During the period C, nM is controlled to become nso by a close signal, which is one of the signals generated at 7 in FIG. 1, in the close control mode. FIG. 3 shows that after the control mode of the synchronous motor is the uniform speed control shown in FIG. This is an example of a conventional case.

The circuit configuration shown in FIG. 3 will be described as an example of the semiconductor power converter shown in FIG. 1. In the figure, 31, 32, and 33 constitute the semiconductor power converter 3, and 31 is 31 1, 312, 31
A forward converter consisting of 3,315,316 thyristor arms, 32 is a DC reactor, 33 is 331,33
This is an inverse converter composed of 2,333,334,335,336 thyristor arms. In FIG. 3, if the firing control angle of the thyristor of the forward converter 31 is in the constant speed control mode and the parallel breaker is turned on, for example, the control angle (Q control angle) of the daily converter 31 is 30 degrees, inverse converter 33
When the control angle (y control angle) of In the figure, a short circuit is formed through the parallel circuit breakers as shown by the arrows, and a short circuit overcurrent flows. The solid arrow indicates a short circuit on the power supply side, and the dashed arrow indicates a short circuit on the motor side. or,
If the phase on the power supply side is ahead of the phase of the terminal voltage of the synchronous motor, the commutation margin angle of the inverter will decrease by the phase difference at the moment the parallel circuit breaker is turned on, resulting in commutation failure. may occur. As an embodiment of the synchronization device according to the present invention for solving the above problems, FIG. 4 shows operational waveforms at the time of synchronization.

A is the envelope waveform of the beat waveform formed by the frequency difference between the power supply side and the motor side, and B is the synchronization closing signal #25 issued by the above-mentioned synchronization device, and this signal causes the closing signal of the parallel breaker. At the same time, the firing control angle of the forward converter is narrowed down. C is a DC voltage waveform, D is a DC current waveform, and these are operating waveforms when the ignition phase of the forward converter is narrowed down to zero the DC current from when the synchronization start signal of B is output.
E is the signal that terminates the ignition pulse and is generated after the current has decayed. Further, this signal may be generated either by detecting that the current has attenuated or after a preset time since the current decay time can be determined from the current value and circuit constant. F indicates the point in time when the parallel sword was thrown. According to this invention, as is clear from the explanation of FIG. It is possible to prevent short circuits from being formed and to prevent commutation failures.

Furthermore, the method according to the present invention is also superior in terms of protection, since it operates as a backup to cut off the ignition pulse even when the circuit that normally throttles the ignition phase of the converter is inactive. In this case, during the period after the current attenuates and the parallel disconnector is turned on, power is not supplied to the motor, so the speed decreases slightly, but in large-capacity machines, GD2 is large and the speed attenuation rate is predetermined. This will not be a problem if the synchronization input signal is issued taking into account the shift in the phase difference.

As described above, according to the present invention, the synchronization closing signal is used as the closing signal for the parallel switch and disconnector, and at the same time, the firing phase angle of the converter is narrowed down and the firing pulse is cut off. It is possible to suppress the risk of commutation failure due to short-circuit overcurrent at the time of breaker closing, and is effective in improving the stability of synchronous closing.

[Brief explanation of drawings]

FIG. 1 is an operation system diagram of a synchronous motor, FIG. 2 is a representative example of an operation control system for a synchronous motor, FIG. 3 is an explanatory diagram of conventional synchronization, and FIG. 4 is an explanatory diagram of synchronization according to the present invention. In the figure, 1 is a bus connected to an AC power supply, 2, 4, and 5 are cross-connectors, 3 is a semiconductor power converter, 6 is a synchronous motor, 7 is a constant speed signal generator, and 8 is a constant speed control device. , 9 is a converter for converting the rotor position detection signal of 6 into a control signal. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. A synchronous motor is connected to an AC power source and this power source through a semiconductor power converter, and the rotation speed of the synchronous motor is controlled by controlling the magnitude and frequency of the power supplied to the synchronous motor by controlling the semiconductor power converter. The power is controlled so that the frequency of the voltage applied to the armature of the synchronous motor is equal to the frequency of the AC power supply voltage, and the synchronization signal generated by the synchronization detection device included in the synchronization device is used to
In a synchronous motor synchronization method for synchronizing a synchronous motor to an AC power source, the ignition phase angle of the semiconductor power converter is narrowed down by the synchronization signal, and the semiconductor power converter is used as an inverse converter. A method for synchronizing a synchronous motor, characterized in that the input current of the synchronous motor is made zero, and then the ignition pulse of the semiconductor power converter is cut off, and then the synchronous motor is synchronously applied to the AC power supply.