JPS6329516B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for driving an electric motor using a DC/DC switching converter in which a DC stabilized power source is switched on the primary side of a transformer and diode rectified on the secondary side. The method of generating AC power using a high-frequency inverter and converting this power to ordinary variable frequency/variable voltage power via a cycloconverter to drive an electric motor has been known for some time, but the equipment is complex and economical. It is not widely used due to lack of availability. Also,
A half-wave servo motor drive circuit that directly converts commercial power with a thyristor is also known, but this has poor control performance, for example, the servo bandwidth is about 2 to 3 Hz, and the biased magnetization of the power transformer becomes a problem. was. Here, the present invention aims to provide a motor drive system that satisfies compact equipment, low cost, power saving, and high performance at the same time, and is also a system that is most suitable for coreless DC servo motors such as print motors and cup motors. . FIG. 1 is a schematic diagram showing the principle of the present invention. TF is a transformer with a gap, Th _F is a thyristor for forward rotation, Th _R is a thyristor for reverse rotation, M is a DC servo motor, Tr is a transistor, D is a feedback diode, C is a smoothing capacitor, DS is a rectifier diode, S is a commercial power supply be. The primary side of the transformer TF is a typical flyback switch circuit, and the secondary side corresponds to a half-wave single-phase cycloconverter using a thyristor with a center tap.

[Table] In Table 1, 1 indicates the on state, 0 indicates the off state, and Th indicates either the thyristor Th _F or Th _R. Mode (100) represents the period during which electromagnetic energy is supplied from the power source S to the transformer TF. In mode (011), the transistor is turned off and this current is transferred to the feedback diode D, and at the same time the motor M
This shows a transient period in which the secondary voltage of the transformer TF is applied through the thyristor Th, and the current commutates from the primary to the secondary. Mode (010) represents a period in which current flows only through motor M. Mode (110) indicates a transient period in which the transistor Tr is turned on and the motor current commutates to the primary side. Mode (001) represents a period in which the transistor Tr is off and a feedback current is flowing through the diode D. Here, it is assumed that the transistor Tr is turned off instantaneously, so mode (111) does not enter. The basic control for driving this electric motor M is to store energy in mode (100) → commutate from the primary to secondary transformer in mode (011) → release energy in mode (010) → to release energy in mode (110). Commutation from transformer secondary to primary → Thyristor in mode (100)
The energy is returned to the power supply S in Th arc extinction → mode (001). This one cycle is set to, for example, 1 millisecond (m.sec), and this is repeated. When you want to accelerate the motor M in forward rotation, drive the gate of thyristor Th _F , and when you want to accelerate the motor M in forward rotation and reverse speed (reverse acceleration), drive the gate of thyristor Th _R with an impulse when entering mode (011). The waveforms of each current are as shown in Fig. 2 a and b. Figure 2a shows the current waveform when the motor M is running, and Figure 2b shows the current waveform when the motor M is braking.The hatched area is the time product of the current i flowing through the motor _M , and i _TR is the current flowing through the transistor Tr. i _D is the current flowing through the feedback diode D, t ₁ to t ₇ and t ₁₁ to t ₁₇ are the periods, and [T ₁₀₀ ] to [T ₀₀₀ ] are the respective modes (100) to
(000), T _C is the carrier period. The period T′ ₁₀₀ between t ₅ and t ₁₅ in mode (100) is set to be sufficiently longer than the turn-off time of the thyristor Th. From mode (010) to mode (110) so that T ₀₀₀ in period t ₇ and t ₁₇ of mode (000) does not always become zero.
Determine the transition point t _pff . t _pff = T _C − (T ₁₁₀ + T′ ₁₀₀ + T ₀₀₁ + T ₀₀₀ ) T′ ₁₀₀ +
Since the current of the motor M is zero during the period T ₀₀₁ +T ₀₀₀ , the motor terminal voltage correctly indicates the speed electromotive force. During this period, this voltage is compared with the speed command voltage, and a transistor Tr is proportional to this error.
The on-times t ₁ and t ₁₁ [T ₁₀₀ ] can be controlled. When the error is negative, select thyristor Th _F , and when it is positive, select thyristor Th _R. Further, if positive feedback of the motor induced voltage (speed electromotive force) emf is added to the control of the transistors Tr on-times t ₁ and t ₁₁ , this voltage, that is, emf compensation can be easily performed. FIG. 3 is a block diagram of one embodiment of the present invention. 10 is a timing generation circuit, 11 is an error amplifier, 12 is a voltage divider, 13 is a pulse width generation circuit, 1
4 is an OR circuit, 15 is a monostable multi, 16 is an inverter circuit, 17 is a transistor drive circuit, 18 and 19 are thyristor drive circuits, and 20 is a speed command. FIG. 4 is a timing chart showing the operation of each part of this embodiment. a and b are the outputs of the timing generation circuit, c and d are the outputs of the pulse width generation circuit, e is the output of the transistor drive circuit (transistor drive pulse),
f and g are the outputs of the thyristor drive circuits 18 and 19 (thyristor firing pulses), i _TR is the transistor
Tr current, i _D is diode D current, i _M is motor M current, and e _M is motor M voltage. Thus, the timing generation circuit 10 creates a carrier and also causes commutation of the thyristor Th _F or Th _R. First, when the timing generation circuit 10 generates a pulse a (time 401), the pulse width generation circuit 13 generates a pulse width signal c, 401 to 402, which is proportional to the speed error voltage which is the input voltage at time 401 of the pulse a.
and the polarity d (0 or 1) of the speed error voltage is generated. The pulse width signal c drives the transistor Tr via the OR circuit 14, and the current i _TR of the transistor Tr
gradually increases from 0 (time 401), and at the end of the pulse width (time 402), the transistor Tr is turned off, and the current in the gapped transformer TF is commutated to the diode D. Also, at the end of the pulse width C (time 402), the monostable multiplier 15 with a certain time width is activated, and the thyristor Th _F or Th _R is triggered depending on the polarity of the speed error voltage. In the time chart shown in Figure 4, the thyristor Th _F is triggered to power the motor.
The motor braking pattern is drawn using thyristor Th _R. Therefore, at the same time as the current of the gapped transformer TF commutates to the diode D (time 402),
The thyristor Th _F is also commutated to generate a current i _M in the motor M. The motor current i _M increases until the current in diode D decays to zero (time 403). Diode D
When the current attenuates to zero, the slope of the motor current i _M determined by the induced voltage and resistance of the motor M, the inductance of the transformer TF, and the inductance of the motor M attenuates (403 to 405). Next, a pulse b having a certain time width 405 to 406 is generated by the timing generation circuit 10 to drive the transistor Tr again, but at this time no firing pulse is given to the thyristor Th _F or Th _R. When the transistor Tr is turned on (at time 40
5), a reverse voltage is applied to the motor M, and the motor current i _M
Attenuates to zero (time 406), and the thyristor Th _F turns off. Pulse width b is thyristor
The pulse width is sufficient to turn off _ThF . Next, when the transistor Tr is turned off (time 407), this current is commutated to the diode D, and the diode current i _D flows in opposition to the power supply S, so that it rapidly attenuates (407-408). If the thyristor Th _F turns off (time 406),
The motor voltage e _M is only the induced voltage proportional to the rotation speed (406 to 410, 414 to 418, 422
~425) is compared with the speed command 20 and amplified by the error amplifier 11 to generate the next timing pulse a.
Prepare for. The voltage divider 12 functions to set a gain when giving positive feedback to the motor induced voltage in order to compensate for the motor current i _M attenuating during power running and increasing during braking. In other words, the speed error voltage is made larger than the actual value during power running, and is made smaller during braking. Note that this shows that the brake was applied at time 425. This circuit allows for good control without the need for a speed generator, and by increasing the frequency of the carrier, the external size of the transformer TF can be made smaller.
A compact device can be realized. Figures 5a and 5b are block diagrams of other embodiments of the invention. Capacitors Cm, C _n1 , C _n2 ,
By connecting C _n3 , the inductance of motor M can be canceled. D _P and D _N are diodes, T _rP and T _rN are transistors, and Th _F1 , Th _F2 , Th _R1 , Th _R2 , and Th ₁₁ to Th ₁₆ are thyristors. Transistors T _rP and T _rN are base driven at the same time. And thyristor Th _F1 and Th _F2 , thyristor
Add a gate pulse to either Th _R1 or Th _R2 at the same time (half-wave DC servo amplifier). thyristor
Th ₁₁ to _{Th 16} are driven by an inverter (half waveform 3φ cycloconverter). By the way, in the control method of the present invention, the thyristor
Transistor for extinguishing Th _F or Th _R
Instead of keeping the Tr on point [mode (010) and (110) transition point 405, 413, 421,...] constant, a Hall element is inserted into the gap of the transformer TF, this current is detected, and this current Control can be performed to determine the longest flow period according to the current flow period. Although the present invention mainly describes the motor M as a DC motor, it is clear that the invention can also be applied to an AC motor. Conventional high-performance DC servo motor drive circuits that control the pulse width of transistors have complex bridge structures, especially for low voltage (24V)
In the following motors, the transformers, diodes, filters, etc. used to create the DC constant voltage source that is the power source are large, resulting in large dimensions, weight, and cost. However, the present invention is constructed based on the same concept as a line-operated switching regulator that operates directly from a commercial power source without using a transformer, and because the transformer, diode, filter, etc. operate at high frequency, it is compact and can be used with a servo motor. Since the drive section uses a thyristor to perform only polarity switching, it is simple and can be realized at low cost. Moreover, since the operation is a half-wave cycloconverter whose pulse width is controlled on the primary side, if the pulse frequency is increased to 1KHz or more, it will be possible to
Not only can it provide control performance comparable to that of a PWM servo amplifier, but it also has the advantage of eliminating the need for a DC tachogenerator because motor speed electromotive force can be easily detected and utilized.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the principle of the present invention, Figure 2a
2b is a current waveform diagram when the motor is running, FIG. 3 is a block diagram of an embodiment of the present invention, and FIG. 4 is the operation of each part of the embodiment. Timing chart showing Figure 5a,
b is a block diagram of another embodiment of the invention. S... Commercial power supply, DS... Rectifier diode, C,
C _n , C _n1 ~ C _n2 ... Capacitor, T _r , T _rP , T _rN ... Transistor, TF... Transformer with gap, Th _F ,
Th _F1 , Th _F2 , Th _R , Th _R1 , Th _R2 , Th ₁₁ ~ _{Th 16} ...
Thyristor, M...Motor, 10...Timing generation circuit, 11...Error amplifier, 12...Voltage divider, 13...
Pulse width generation circuit, 14... OR circuit, 15... Monostable multi, 16... Inverter circuit, 17
...Transistor drive circuit, 18, 19...Thyristor drive circuit, 20...Speed command.

Claims (1)

[Scope of Claims] 1. A transformer with a gap, a switch circuit that connects and disconnects the energy supplied from a DC power source to the primary winding of the transformer with a gap, and a diode that returns the energy of the primary winding to the DC power source. and controls the drive of the motor by a thyristor circuit connected to the secondary winding of the gapped transformer and the switch circuit, wherein the switch circuit is turned on when a pulse a is sent out at a certain point in time. and after a period of time proportional to the deviation between the induced voltage of the motor and the speed command voltage of the motor detected during a period when no motor current is flowing through the motor,
Turning off the switch circuit, igniting the thyristor circuit to flow the motor current according to the deviation, and turning on the switch circuit at pulse b before pulse a at the next point in time. and extinguishing the thyristor element by commutating the motor current to the primary side of the gapped transformer and applying a reverse bias voltage between the anode and cathode of the thyristor element in the thyristor circuit, A motor drive system characterized in that the switch circuit is turned off after the forward blocking ability of the thyristor element is restored.