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Longitudinal wave transmission lines. Part 2
In the of the previous part of this work, we got acquainted with the circuitry of a receiving-transmitting circuit for transmitting electrical energy by a longitudinal wave. Here we will consider the circuit design of the reactive energy amplifier included in the transmission circuit of this device. It determines the ratio of the energies of the longitudinal and transverse waves, which will then be distributed in the power transmission line, the reliability of the entire circuit. In addition, most of the active losses occur here.
Reactive Power Amplifier Circuitry
Only two options are proposed for consideration of the amplifier circuitry. The first is the classic ZVS driver, the simplicity and reliability of which can bribe even experienced radio electronics engineers. Its standard circuit is shown in Figure 6a, and the principle of operation is based on the classic multivibrator, when the first transistor is turned off by an open second transistor, and after the end of the oscillatory process in the LC circuit connected to it, the transistors change places: the first transistor opens, and the second is locked.
The circuit is automatically tuned to resonance, which is a huge advantage over others, where the generation is carried out by an external generator. The disadvantage of such a circuit is its very difficult start-up, and the more powerful the circuit, the larger the initial impulse is required for it. In fact, starting requires a large power capacitor and a powerful power button. Another way to start is a rather powerful power source (or battery), the power of which must be several times higher than the operating power of the driver.
Another disadvantage of this option is the use of chokes L1-L2, in which part of the reactive power is located. It heats up these elements and thus creates additional losses. Also, such circuitry, as a rule, operates from sufficiently low supply voltages (V1 according to the circuit).
Fig. 6. Comparison of ZVS-driver circuitry (a) and half-bridge version (b)
A much more flexible (second) variant of circuitry is offered by half-bridge or bridge circuits. Structurally, the half-bridge circuit is shown in Figure 6b, where there is an external master oscillator G1, a half-bridge amplifier DA1, which alternately opens transistors VT1-VT2, which causes the appearance of rectangular pulses at its output, with an amplitude equal to the value of the supply voltage V1. Further, these pulses, passing through the resonant circuit C1-L1 (Fig. 2-5), increase in amplitude, become sinusoidal and are already supplied to the power transmission line.
An embodiment of a half-bridge circuit with a generator is presented here.
The disadvantage of such a circuit design is obvious - manual adjustment of the resonant frequency is required, which, when the load and transmission line parameters change, can float within fairly wide limits. To eliminate this drawback, a phase-locked loop (PLL) is introduced into the circuit. In Figure 7a, it is depicted by the PLL block, which controls the frequency of the master oscillator G1. As a rule, PLL and G1 are assembled in a single microcircuit package.
Fig. 7. Half-bridge: with PLL (a), with PLL and overload protection (b)
The flexibility of the half-bridge option also lies in the fact that it makes it easy to introduce negative feedback to protect the output transistors from voltage surges in power lines. and all kinds of changes in load resistance, up to its short circuit. This is achieved using a low-resistance Rp and a PRT comparator circuit, which, in case of activation, temporarily disconnects the DA1 amplifier (Fig. 7b). Making the same feedback in the ZVS driver circuitry is problematic, since it will require an additional start after the protection is triggered.
State of the art
At the moment, taking into account all the advantages and disadvantages of the presented circuitry options, the authors see the optimal structural diagram for the longitudinal wave transmission line shown in Figure 8. It can operate at different supply voltages - from 12 to 500 V, automatically finds the resonant frequency of the entire system and has protection against overloads in power lines, up to a complete short circuit in the line.
Fig. 8. Optimal circuitry for longitudinal wave transmission lines
The problem of automatically changing the inductance L2, depending on the change in the load resistance Rn (according to formula 2), remains unsolved. One of the possible ways to solve it is to introduce feedback with the core of this coil according to the principle of a magnetic amplifier [1]: the higher the load current, the more it is necessary to enter this core into saturation. The same approach can solve the problem of maintaining a stable voltage across the load. Here, however, it should be noted that with relatively small changes in the resistance Rn, for example, 2 times, the circuit works quite stably even without adjusting this inductance.
Another theoretical and practical problem of longitudinal transmission lines is a rather large reactive energy circulating in LC1 (Fig. 1), which in practice can be several times higher than the active one obtained at the load. To maintain it, a coil L1 and a capacitor C1 corresponding to this power are required (Fig. 2-5).
Nevertheless, even at the current level of technology, this direction has great prospects today, for example, for the transmission of electrical energy from wind generators and solar stations to inverters, where rather thick wires are now used for this. If this distance is significant, then the use of a longitudinal wave transmission line can reduce the cost of non-ferrous metal many times, with the same transmitted power and the same losses.
Also, the authors see a promising direction to work on existing industrial electrical networks to transmit more power. In fact, we are talking about installing additional equipment at the transmitting and receiving ends of an industrial power transmission line to strengthen it. At the same time, the transmission line itself is not subject to any changes.
1. The presented power transmission line is not an alternative and replacement for the existing main and distribution electrical networks of medium and high voltage, including direct current lines. It can be used in cases when the transmission of electricity from a traditional network up to 1 kV 50 Hz for remote single low-power sources and consumers of electricity is impossible or not economically viable.
2. If the performance and safety of the presented power lines is confirmed, it can be used for:
  • piping of remote generation centers with a small unit capacity of RES installations (SPP, WPP, microHPP, etc.);
  • power supply of land, water / underwater and air infrastructure of consumers, in particular - for the purposes of power supply of the charging infrastructure of electric transport, highways of levitating vehicles, robotics;
  • organizing street lighting systems;
  • creation of chains for the export of surplus electricity from microgrid networks, active energy complexes.
3. With regard to the interests of power grid companies, this set of power transmission lines with appropriate scaling (both in terms of the number of parallel sets, and by the power of a single set) can be used if it is necessary to supply power to individual consumers, for example, private houses, individual households that do not have a centralized power supply, or as a backup power source for various consumers. Also, this power transmission line can be used in the construction of power supply circuits for the charging infrastructure of electric transport, highways of levitating vehicles, and unmanned aerial vehicles.
Materials used
  1. Wikipedia. Magnetic amplifier.