RU2212755C2 - Method for regulating torque of inductor-type electrical machine - Google Patents

Abstract

FIELD: electrical engineering; traction motors, variable-speed electrical machines and devices requiring high starting torque. SUBSTANCE: method for controlling torque of inductor-type electrical machine includes generation of unipolar current in phase winding by feeding voltage pulses to winding with aid of semiconductor frequency converter so as to prevent phase current drop to zero in the course of control. Torque is increased in inductor-type electrical machine due to dc component in current flowing through this winding. EFFECT: enhanced flexibility of electrical machine control; enhanced torque. 1 cl, 4 dwg

Description

 The invention relates to electrical engineering, and more specifically to methods of controlling induction electric machines having a gearless winding rotor and a gear stator, on which one or more phase windings are located, each of which is fed by unipolar current pulses from a semiconductor frequency converter. The proposed method of regulation can find a place in traction electric motors, in electric machines designed to operate in a wide range of speed changes, in devices that require a large starting torque.

 A known method of controlling an electric machine (see US patent 4707650 from 11.17.87). This source claims a microprocessor control system that generates control signals for the keys of the frequency converter.

 The control system allows you to adjust the intervals on and off keys depending on the speed of rotation of the electric machine and its operating mode (motor or generator mode). When the engine is operating at high frequencies, the control system implements a method for controlling torque by changing the angle of advance of turning on the keys. In this case, the engine runs in constant power mode. With an increase in the rotational speed above the critical one, the lead angle reaches its maximum value and the engine torque sharply decreases.

 The disadvantage of this method of regulating torque when operating at speeds higher than critical is a sharp decrease in the output power of an electric machine.

 There is also a method of increasing engine torque (see Russian patent 2034393, CL 6 N 02 K 19/06 from 12/14/92). The increase in engine torque occurs due to the magnetization of the magnetic system of an electric machine using permanent magnets placed in the grooves of the stator poles. The magnetization of each magnet is directed according to the magnetization of the pole. The magnetic flux in the tooth zone of such an engine is determined by the magnetic flux of the phase windings, fed by unipolar current pulses, and by the flux of permanent magnets. Given the quadratic dependence of the torque on the induction of the magnetic field, the torque upon excitation of the pole will be significantly higher than the braking torque on the permanent magnet with a de-energized coil. Torque control in such an engine is carried out by changing the lead angle and the key on and off intervals.

 The disadvantage of this method of increasing the engine torque is the complexity of the engine design due to the installation of permanent magnets, the inability to control the degree of magnetization. In addition, the installation of magnets is not possible in engines in which coils are placed on each stator tooth.

 The present invention is aimed at increasing the flexibility of controlling the induction motor and providing the possibility of further increasing the torque of the engine when operating at maximum speed.

A method of controlling the moment of an induction electric machine, which consists in generating a unipolar current in the phase winding of an electric machine using a semiconductor frequency converter by applying one or more voltage pulses to the winding, at the end of the voltage supply zone one or more voltage pulses of reverse polarity are applied, in which, according to this statement, change the parameters of the voltage pulses supplied to the winding so that the minimum value of the phase current was in the range 0.05I _max <I _min <0.45I _max , where I _max is the maximum value of the phase current, I _min is the minimum value of the phase current.

The invention is further explained with reference to the accompanying drawings, which show:
- figure 1 - diagram of the power circuits of one phase of the frequency Converter;
- figure 2 is a mechanical characteristic;
- figure 3 - phase current and phase voltage for the first embodiment;
- figure 4 - phase current and phase voltage for the second option.

To generate phase currents in the windings of the induction motor using a frequency converter, control signals are sent to turn on the keys T1 and T2 (see Fig. 1), the voltage of the power supply U is applied to the winding of the OD motor at time t ₁ and the current i starts to increase in it (see Fig. 3). At the end of the positive voltage supply zone (time t ₂ ), the keys T1 and T2 are closed, the negative voltage of the power supply is applied to the phase winding of the motor through the reverse diodes D1 and D2 and the current starts to quickly decrease to zero (time t ₃ ).

Figure 2 shows the mechanical characteristic of the induction motor. In the range of rotational speeds 0-ω _{1, the} engine can operate with a constant torque (curve 1), in the range of rotational frequencies ω ₁ -ω _cr - the engine runs in constant power mode (curve 2), at a speed above ω _cr - the output power of the machine decreases sharply (curve 3). With a decrease in the supply voltage, this effect is exacerbated, there is an even greater decrease in the engine output (curve 4). Eliminate the decrease in output power by introducing a special bias mode. Figure 2 (curve 5) shows the mechanical characteristic of the engine at a speed above ω _kr obtained using the magnetization mode.

The bias mode can be created by:
- increase the duration of the positive voltage pulses supplied to the winding;
- introducing a zero pause in the zone of action of the negative voltage pulse;
- reducing the amplitude of the negative voltage pulses, or increasing the amplitude of the positive voltage pulses supplied to the winding.

 It should be noted that when operating in the magnetization mode, the advance angle of the supply of the first positive voltage pulse must be at least 70 electrical degrees, and the greater the degree of magnetization, the greater the advance angle. For the motor mode, the lead angle is counted from the position at which the stator tooth is opposite the rotor groove; for the generator mode, the angle is counted from the position at which the stator tooth is located against the rotor tooth.

To create a bias mode using the first option, at time t _{4, the} voltage of the power supply U is applied to the winding of the OD motor, and the current i begins to increase in it (Fig. 3). At the end of the voltage supply zone (time t ₅ ), the keys T1, T2 are closed, and the time t ₅ is selected so that the time interval (t ₅ -t ₄ ) is longer than the time interval (t ₂ -t ₁ ). A negative voltage of the power supply is applied to the phase winding of the motor through the reverse diodes D1 and D2 and the current begins to decrease rapidly in it. At time t ₆ , a positive voltage pulse is again applied to the winding, despite the fact that the phase current of the motor has not decreased to zero. Further supply of positive voltage pulses of increased duration will cause an even greater increase in the minimum phase current, and hence the motor torque. Upon reaching the required torque, by regulating the duration of a positive voltage pulse (t ₅ -t ₄ ), stabilize, for example, the engine speed.

To create a bias mode using the second option, at time t _{1, the} voltage of the power supply U is applied to the motor winding OD, and the current i starts to increase in it (Fig. 4). At the end of the voltage supply zone (time t ₂ ), the keys T1, T2 are closed, the negative voltage of the power source is applied to the phase winding of the motor through the reverse diodes D1 and D2 and the current begins to quickly decrease in it. At time t ₃ (with a non-zero phase current), an impulse is formed to additionally turn on the key T2, the current decrease is slowed down, since the winding is shorted through T2 and D1. At time t ₄ , a positive voltage pulse is again applied to the winding, despite the fact that the phase current of the motor has not decreased to zero. Further supply of negative voltage pulses with a specially introduced zero pause in the voltage (t ₄ -t ₃ ) will cause an even greater increase in the minimum phase current, and hence the motor torque. The introduction of a zero pause can be carried out at any time in the zone of action of a negative voltage pulse (t ₄ -t ₂ ). To reduce switching losses in the frequency converter, it is advisable to additionally switch on the switch at the end of the zone of operation of the negative voltage pulse. In this case, the switching of the minimum phase current occurs.

 To create a bias mode using the third option, the amplitude of the positive pulses must be greater than the amplitude of the negative voltage pulses. When a positive voltage pulse is applied to the winding, current begins to increase in it. After applying a negative voltage pulse of lower amplitude, the phase current does not have time to decrease to zero. By changing the ratio of the amplitudes of the positive and negative voltage pulses, the degree of magnetization of the motor is regulated.

 The described options for creating a bias mode are also valid for the generator mode. At the same time, changing the degree of magnetization, regulate the output electric power in the generator mode.

 The technical effect of the present invention consists in expanding the range of torque control when operating at high speeds due to more flexible control of the keys of the frequency converter and creating a bias mode in which the phase current of the induction machine does not decrease to zero.

Claims (1)

A method of controlling the moment of an induction electric machine, which consists in generating a unipolar current in the phase winding of an electric machine using a semiconductor frequency converter by applying one or more voltage pulses to the winding, at the end of the voltage supply zone one or more reverse voltage pulses are applied, characterized by the fact that they change the parameters of the voltage pulses supplied to the winding so that the minimum value of the phase current is in range 0.05I _max <I _min <0.45I _max , where I _max is the maximum value of the phase current, I _min is the minimum value of the phase current.

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