One of significant disadvantages of a "classical" SPS is a low phase factor (Fp) equal to 0,3...0,4 and conditioned by impulse character of the consumed current from the system.
For the purpose of the Fp increase an active filter on the input of the invert circuit is used, which is sometimes called the Fp adjuster. For the filter power key control a range of well known firms ("Micro Linear", "Simens", "Motorolla") have developed special electronic chips providing quasi-continuous character of the line current and Fp increase up to 0,86 with simultaneous invert circuit constant-voltage regulation [2].
In [1,3] a modified algorithm of active filter control and the scheme of the algorithm realization are offered, that provides the Fp increase up to 0,95 and more meeting the hardest demands of the IEC (IEC-1000-3-2).
Notice that the SPS power part complication connected with the active filter application is made up with the fact that together with the Fp increase and invert circuit out voltage stabilizing treatment the filter condenser capacity value decreases by about 60 %.
Further SPS updating in terms of specific gravity decrease and loss enhancement, for example, has the following limitations:
- because of the invert circuit out voltage unbalance the power isolating transformer is performed gapped in the heart and is used only in the incremental hysteresis loop, that makes the bicyclic invert circuit bridge network be non-effective compared to a single-pulse one, and, finally, leads to the transformer mass-volume showings increase;
- the invert circuit out voltage line-locked frequency increase allows reducing the transformer and smoothing inductor frames, however, the power transistors´ losses increase at that. The last especially matters for powerful SPS.
The switching on the capacitors in series into the power transformation primary circuit allows excluding the invert circuit out voltage continuous component, and also, in some cases, reducing commutative losses in power transistors.
Two SPS networks with condensers in the invert power circuit are considered below: a half-bridge and full-bridge ones.
The half-bridge network provides a push-pull transformer work mode with a total absence of continuous component in the voltage curve. It allows using the heart without air isolation and with high degree of hysteresis loop rectangularity. Hence, the transformer frames and its losses can be reduced (at the same frequency) two-fourfold compared to the networks [2] without condensers.
The indisputable advantage of this network is the invert power circuit simplicity (push-pull mode is provided by only two power transistors). Respectively, the controlling system is also simplified.
The bridge network provides a push-pull transformer work mode and, respectively, its full use. The quantity of power transistors and outlets of the invert circuit controlling system in this network is twice as many, however, there is only one commutating capacitor and its band capacitance is eight times as much against the total capacitance of the capacitors in the half-bridge network.
Reduction of the compared versions to one and the same load gives absolutely identical both gain and rectified voltage regulation characteristics of the invert circuits. Voltages across power transistors in both versions are also identical and equal to the voltage of the invert circuit input; however, the current amount through the bridge invert circuit is twice as little. Hence, the total "installed capacity" of the power transistors in both networks is equal.
Conclusions:
- Including capacitors into the power transformer primary invert circuit gives an opportunity to apply the heart of this transformer without air isolation, with little field current and using on a complete hysteresis loop, that allows reducing its mass-volume showings essentially.
- In permanent output the current through invert circuit transistors has an intermittent nature, i.e. the transistors´ commutation is currentless, losses are minimal, that allows increasing the line-locked frequency and, respectively, decreasing mass-volume showings of the SPS.
- The two considered SPS networks with capacitors in the power circuit are identical on their voltage regulation characteristics, however, the bridge network (excepting the low power SPS) are preferable against the half-bridge one.
References:
- Magazinnik A.G., Magazinnik L.T., Magazinnik G.G. Secondary power sources phase factor correction. "Electrotechnics"/"Electrotechnica", № 5, 2001, pp. 40-42, Moscow.
- Pryanishnikov V.A. Electronics, 1998, p. 400.
- Patent № 2178234 РФ/RF. Secondary power source / Magazinnik L.T., Magazinnik G.G. Published 10.01.2002. Bulletin № 1. Priority from 13.02.2001.
The article is admitted to the V conference "Modern high technologies" February, 21-28st, 2007, Egypt (Hurgada), came to the editorial office on 27.04.07