Scheme for regulating the speed of rotation of a DC motor on the map. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Electric motors

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Karting is a fascinating and dynamic sport, in which competitions are held in circuit racing and track racing on ice. The machine that is used for this - a go-kart - has long become a rather complex device that uses expensive materials, complex technologies for manufacturing components and parts, and forced engines. Training and competitions can only be carried out on specially prepared tracks.

But boys always want to get on a four-wheeled, albeit not expensive, fast car that moves obedient to their will.

In the creative association “Prototyping and design of transport equipment” of the Dneprovskaya SUT-TSNTTM in Kiev, it was decided to produce an electric kart that could be driven not only on the highway, but also in the school gym or any other sufficiently large room. You can practice driving techniques, and winter is not a hindrance.

Electric karts had been built before, but in the described schemes the speed of movement was controlled by a rheostat or contactor. The first scheme suffered from large losses on the rheostat, the second – from jerks at start and during movement when changing modes. It became obvious that a smooth control circuit was needed for the DC motor used on the card.

Electronic engineer V.D. Lebedev undertook to help the circle members, and together they developed a pulse control circuit for engine speed, which is given below.

The principle of regulating the rotation speed of DC electric drives is based on regulating the average voltage value supplied to the motor. Pulse control allows you to create drives with high energy performance. Of the main advantages inherent in pulse regulators, the following can be noted: high speed when the control system is closed; high control accuracy while maintaining stability; high efficiency; smooth control of drive speed over a wide range; the ability to obtain large starting torques when the drive is switched to continuous power mode for a short time. Such systems include a transistor pulse-width converter PWB, designed to power the kart motor.

Figure 1 shows the block diagram of a transistor PWB. The power supply for the circuit is provided by an on-board battery pack (1) with an output voltage of 48 V and a capacity of at least 55 Ah.

The circuit contains a multivibrator (2) with a variable duty cycle of output pulse signals, a power amplifier (3), a powerful current switch (4), and an automatic gain control (AGC) circuit (5).

Switch on the SHIP with power contactor K1 (position 1). In position 2, the SPIKE is turned on and the battery is recharged when the kart is braking and moving by inertia. Figure 2 shows a schematic diagram of a PWB based on pulsed duty cycle control.

(click to enlarge)

The multivibrator (VT1 and VT2), depending on the position of the potentiometer R3, generates pulse signals with period T. They are amplified in the power amplifier VT3. In the extreme left position of the R3 engine, the multivibrator generates short-duration pulse signals with a period T, so the average current supplied to the bases of the VT3-VT12 current switch is small, and a minimum voltage is supplied to the motor. In the middle position of the R3 engine, the multivibrator generates pulses t=T/2 (meander), and a voltage close to U0/2 arrives at the motor.

In the extreme right position of the R3 engine, a constant voltage close to U0 is supplied to the engine. Thus, by smoothly changing the duration of the pulses generated by the multivibrator, you can smoothly change the number of revolutions of the PT drive motor. The constancy of engine speed when the load on the drive changes in all modes is maintained by the AGC circuit (VT4, VT5, VT6, VT7, VD2).

The intermittency of the current in the motor armature in pulse modes is eliminated by installing a choke Dr1 in its circuit, and the motor itself is shunted with a capacitor C3 and a diode VD1. Transistors VT2, VT3, VT4 have individual heat sinks. The current switch transistors are located on a common heat sink.

The Kruzhkovites have developed a drive (Fig. 3) from the gas pedal to the potentiometer R3 (1) for controlling the SHIP, which ensures sufficient durability of this unit.

The potentiometer is mounted using standard fasteners on the mounting panel. If necessary, the potentiometer slide is extended and its free end is fixed in the support bearing 4. Pulley 4 is fixed to the potentiometer slide close to the support 2 using a pin. The drive cable 7 is wound in two turns on pulley 2 and one end is fixed to the return spring 3, and the other - on the radius sector of pedal 5. Pedal 5 is equipped with an additional spring to return to its original position (energy recovery mode) (not shown in Fig. 3). In this case, contacts K1 (6) are switched. The force of the spring 3 is selected to the minimum necessary to eliminate the slipping of the cable 7 on the pulley 2. The radii of the sectors of the pedal 5 and pulley 2 are selected experimentally, depending on the required angular movement of the potentiometer R3.

In general, in our opinion, the above design is quite simple to manufacture and reliable in operation.

Authors: D.V.Lebedev, V.D.Lebedev

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