Pulse control of the magnetic flux of the DCT of independent excitation
In the pulsed control of the magnetic flux, the DFT of independent excitation Llo6 and the key K are included in the excitation winding circuit (Figure 4.25).
Fig. 4.25. Scheme of pulsed magnetic flux control (a) and mechanical characteristics of DPT for pulsed control (b)
The well is settled within 0 & lt; at & lt; 1. For y = 1 R, is shunted by the To, which corresponds to the natural mechanical characteristic 1, Fig. 4.25. For y = 0 A, is constantly introduced into the chain OB, /"and F decreases, and the speed & lt;% increases - (artificial characteristic, line 2, Figure 4.25) .
Pulse regulation of the voltage at the armature of the independent excitation DCT
For pulsed control U on the anchor according to the scheme, the family of mechanical characteristics is shown in Fig. 4.26.
Fig. 4.26. Scheme of impulsive regulation of U at the anchor (a) and mechanical characteristics of the DPT for pulsed control (b)
With the constant key K (y = 1) always closed, the current in the anchor flows under the action U of the network natural mechanical characteristic), with the open K - under the action of EMF, closing through the diode V, while the current has pulsing character. By adjusting the duty ratio y, get artificial characteristics, at y = 0, the voltage U is not applied (dynamic braking circuit) and the mechanical characteristic passes through the origin.
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For small loads, the intermittent current mode is possible, which occurs at the following speed and current limit values:
where is the electromechanical time constant of the anchor chain.
Only in the region of discontinuous currents, the mechanical characteristics are not rectilinear, in the working load range the equation of the mechanical characteristic has the form:
Using thyristor keys for pulse control
Various thyristor switches are used for pulse regulation. The principle of operation of thyristor keys for impulse resistance control R will be considered according to the scheme (Figure 4.27). Thyristor VS 1 acts as a key. When opening, KS1 shunts the resistance R, when closing, inserts resistance R. To close KSI, the control electrode from the NRFU needs to provide a higher cathode potential in comparison with the anode potential. The ego is achieved by including an additional thyristor VS2 and switching elements C, L K, a CD diode, a low-power direct current source U , and the diode of the CD,.
If the thyristor KS1 is open in the initial position, and KS2 is closed and the capacitor C is loaded with the + on the lower plate, then to close the KS1, it is necessary to remove the control pulse from the KSI and feed it to the KS2 that opens, then the plus voltage of the SK will be applied to the cathode KS1, and to the anode - minus and VS 1 will close. The capacitor Sk will be charged through an open VS2 with a plus on the top plate.
Fig. 4.27. Pulse resistance control scheme
If you remove the control pulse from VS2, it will close by the end of the recharge. Then, when the impulse is applied to VSI , it will reopen by shunting A, and the capacitor will be recharged along the chain C ^ -VS-VD ^ -L K until the potential of the bottom plate C, becomes positive. For the initial charge C, the source is (/ ", VD" and R. "
For pulse voltage regulation, the thyristor key scheme shown in Fig. 4.28. The initial charge of the capacitor Q is from U Q (+ on the top plate).
Fig. 4.28. Pulse voltage regulation circuit
When the control pulse is applied to the KS1, it opens and a voltage is applied to the motor. At the same time, the capacitor starts to charge C through VS 1, VD , L,. with the + on the top plate, so when you apply a pulse to KS2, VSI will close. By changing the duty cycle of the control pulses VSI, with the help of the NRFB, impulse voltage regulation is provided in accordance with the KS2 pulse input.
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