LT6435B - Regulation method of three - phase induction motor with a phase rotor - Google Patents

Abstract

Proposed rotor current regulation method of a three-phase induction motor with a phase rotor and a device for the realization of this method, enabling the reduction of current losses in the rotor circuit by returning the emissions of electrical power in terms of alternate current to the network by an industrial type frequency converter; it is distinguished by high frequency, symmetrical, power factor correction capacitors (PFC) with inductive elements used at each rotor coil phase, ensuring the sinusoidal function of rotor currents and control of their gain, as well as torque power.

Description

Technical field

Electric machines and apparatus are used in industry and household.

State of the art

Induction three-phase motors with a phase rotor are known (Electrical Machines and Drive Systems. John Hindmarsh, Alasdair Renefrew. Third Edition, Newnes, 1996). By changing the impedance of the rotor circuit load chain rheostats, their rotational speed can be adjusted. The main disadvantages of adjustable actuators with such motors are the relatively large losses in the active impedance of the rotor circuit load rheostats and the phase lag of the rotor current due to the inductive impedance of the rotor in the rotor circuit. The phase lag of the rotor current decreases the generated torque and therefore requires a higher current to produce the same torque compared to the case where there is no phase lag. Both of these disadvantages are manifested by the greater the slip of the induction motor.

There is a known technical solution (JP 2005204490) which reduces the rotor loss of such an engine by activating a frequency converter in the rotor circuit, which converts the variable frequency electric power induced in the rotor to the electric power of the industrial frequency and returns it to the network. The increase in losses due to the influence of the inductive rotor impedance remains. In addition, there is a loss due to the higher harmonics of the rotor current that occur when the rotor windings are loaded with a diode bridge with a high capacitor below it, since the current in each phase of the rotor winding only flows when the phase voltage is higher than the other two. These current harmonics do not generate torque, but generate losses in the impedance of the rotor winding.

There is a known technical solution (CN 103582999) which can reduce the losses of an induction three-phase motor with a rotor by connecting a frequency converter in the rotor circuit, which converts the variable frequency electric power emitted by the rotor into the electric power of the industrial frequency. There is also a voltage boosting device in the rotor circuit, which in principle can be used to adjust the phase of the rotor current. However, the voltage boosting device only operates on one-way voltage, with only one half-life adjustment, so the loss reduction is only partial. Another disadvantage of this technical solution is that the energy is stored by the inductance of the rotor winding, whereas in the inductance of the current it is necessary for increasing the voltage, therefore the operation of the voltage increasing device causes the occurrence of harmonics. The four outputs of the rotor circuit are also a drawback, since an induction motor with four contact rotor rings is required, and standard induction three-phase motors with a phase rotor are manufactured with three contact rings.

The essence of the invention

Proposed method for regulating rotor current of an inductive three-phase motor with a phase rotor and a device for implementing the method, which allows to reduce the rotor circuit losses by returning the variable frequency electric power generated by the industrial frequency converter to the network rotor. PFCs with inductive elements that provide sinusoidal rotor currents and control the magnitude of these currents and thus the torque.

Brief description of the drawings

Fig. 1 is a schematic diagram of a device for controlling the rotor current of an induction three-phase motor with a phase rotor.

Fig. 2 - Current and electric drive in the rotor winding phase as a function of time.

Principle diagram of the device

An example of a device schematic diagram is shown in Fig. 1. There are three symmetrical voltage-boosting power factor correctors in the diagram. The portion of the diagram that makes up each corrector is delineated by a contour line for visual representations and is numbered 1, 2, or 3. Each corrector consists of two parts: positive and negative half-power power factor correctors. For example, in the corrector numbered 1, the positive-phase rotor phase-voltage corrector consists of a low-capacitance capacitor C1, the energy of which must be sufficient for one pulse of the phase corrector, energy-saving choke L1, diode D2, preventing industrial frequency inverter power return to power factor corrector circuit, field effect transistor with n channel performing transistor key function and its shunt diode protecting against reverse voltage. In the other two correctors, the positive half-power corrector respectively comprises elements C3, L3, D8, Q3, D9 in the second corrector and C7, L5, D14, Q5, D15 in the third corrector. The negative half-rotor phase voltage boosting corrector, which is part of the numbered corrector number 1, consists of: a low-capacitance capacitor C2, which must have enough energy stored per pulse of the phase corrector, energy-saving choke L2, diode D6, return to the power factor corrector circuit, a field effect transistor with a p channel, performing the function of a transistor key and a shunt diode protecting it from reverse voltage. In the other two correctors, respectively, the portion of the negative half-time corrector comprises elements C5, L4, D12, Q4, D10 in the second corrector and C8, L6, D113, Q6, D16 in the third corrector. During the positive half-life in each rotor winding phase, the corresponding positive-half-phase corrector charges the high-capacitance capacitor C4, and during the negative half-life, in each rotor winding phase, the corresponding negative-half-phase corrector charges the high-capacitance C6. Because everything is symmetrical, both capacitors charge equally and the frequency converter can be connected to both positive, negative and middle outputs, and only to positive and negative. Diodes D1, D7, and D13 allow the current to flow into their respective positive half-phase correctors during the respective half-life and prevent current from flowing into them during the negative half-life. Diodes D5, D11 and D17 D13 allow negative current to flow through their respective negative half-phases and prevent current from flowing into them during the positive half-period.

How the device works

This device works as follows:

Suppose, at the first moment of observation, that the positive half-life of the phase rotor winding phase to which the rising power factor corrector consisting of elements C1, L1, D2, Q1, and D3 is applied, begins. As current flows through diode D1, the voltage of capacitor C1 increases. The transistor key Q1 opens by shortening the capacitor through the inductance L1 and, as the current through the inductance increases (Fig. _{L L} 2), the electrical energy stored in the capacitor is transformed into increasing magnetic field energy in the inductance L1. When the key is closed, the magnetic field energy accumulated in the inductance L1 turns into electrical energy again; a self-induction electric motor is generated which is proportional to the current velocity and is directed in such a direction as to maintain current:

di e = —L - dt

Here: e is the instantaneous self-induction electromotive value, volts, L inductance, Henri, i is the instantaneous current value, Amperes, t is the time in seconds, the minus sign represents the direction opposite to the current direction if the current differential is positive and the direction coinciding with the current direction. , if the current differential is negative. The key closing and opening intervals are adjusted such that the inductive current pulse envelope, and thus the mean current Ir, are in the form of a positive half-life of a sinusoidal function whose initial phase coincides with that of the corresponding phase of the rotor winding. Since the inductance of the rotor winding is significantly higher than the inductance L1, the practically filtered sinusoidal current Ir, which has an initial phase coinciding with the initial phase of E _R , interacts with the magnetic field generated by the stator and thus produces the maximum possible moment .

At the end of the positive half-life of the electric drive, when the electric drive changes its sign, diode D1 closes by disconnecting the rising positive voltage power factor corrector consisting of elements C1, L1, D2, Q1, and D3, and diode D4 opens by activating of elements C2, L2, D4, Q2, and D6, and everything is repeated in the same way, only the rotor electromotive force, the current L pulses and the average rotor current are the opposite sign. And the initial phase again coincides with the initial phase of E _R , only in the negative half-life.

Claims (3)

1. A method of controlling the rotor current of an inductive three-phase motor with a phase rotor, wherein the current is controlled by reducing rotor circuit losses, without the use of high frequency symmetrical voltage-boosting power factor correctors with inductive elements for rotor winding phases and sinusoidal control of rotor currents. the magnitude and initial phase of these currents, and thus the torque magnitude. 2. The method of controlling the rotor current of an induction three-phase motor according to claim 1, characterized in that it comprises three symmetrical voltage-boosting power factor correctors, each of which comprises two parts: positive and negative half-life power factor correctors, which are stored in high-capacitance electrical energy. the inverter is returned to the grid as industrial frequency energy. 3. A method of controlling the rotor current of an inductive three-phase motor according to claims 1, 2, wherein the positive half-rotor phase voltage is passed to the rising positive voltage correctors in each phase by direct-acting diodes D1, D7 and D13 blocking the negative half-rotor phase voltage respectively. the negative half-rotor phase voltage to the rising negative-voltage correctors in each phase is missed by inverted diodes D5, D11 and D17, which block the positive half-rotor phase voltage.