On the Application of a Half-Wave Rectification Circuit in Inductor Generators

A. N. Korogodsky, A. D. Vlasov, V. I. Yurgenson

(Presented by the scientific seminar of the departments of electrical machines and general electrical engineering)

At the present time, considerable attention is being devoted to the development of contactless generator installations for tractors, distinguished by increased reliability and durability. The optimal type of tractor generator has been recognized as an inductor, homopolar, single-packet machine.

Since the rectifier is an integral part of the generator installation and accounts for a significant portion of its cost, the problem of choosing the optimal power-rectification circuit is highly relevant.

The use of a half-wave rectifier deserves serious attention because of its clear advantages over a bridge-type rectifier in a low-voltage consumer power-supply system, especially with the single-wire onboard electrical-equipment circuit that is used mainly on transport vehicles. The following advantages of the half-wave rectifier should be noted:

a) twice lower consumption of valves and lower losses in the rectifier at the same rectified power;

b) layout advantages—all the diodes can be placed on one heat-conducting panel or in one block not insulated from the machine housing electrically and, consequently, also thermally; in this connection, the problem of cooling the diodes is facilitated and the construction of a generator with a built-in rectifier is simplified.

The indicated advantages of the half-wave rectifier create prerequisites for increasing the efficiency of the generator installation, simplifying the design, reducing cost, and increasing reliability, provided that the generator in a half-wave rectification circuit will not be significantly inferior, in terms of consumption of active materials, to a generator used in a bridge rectification circuit.

In view of the foregoing, analysis of an inductor generator in a half-wave rectification circuit acquires special importance.

Interesting features of the physical process of an inductor machine arise with such an arrangement of the phase winding, when the phase inductance, unlike in classical synchronous machines, contains odd harmonics, including the fundamental. In this case the phase inductance at certain moments of time may be several times smaller than the average over a period and the maximum value of the inductance. It appears very tempting to use such a winding-connection circuit and rectification circuit in which the working interval falls within the region of minimum inductance of the phase winding, which creates

the prerequisites for a significant increase in the utilization of the generator in terms of electromagnetic power (a reduction of the armature-reaction flux). The simplest circuit implementing this possibility is a simple half-wave rectification circuit as applied to a unipolar generator, in which the phase winding is composed of coils mutually displaced along the stator bore by an electrical angle equal to, or a multiple of, 360 electrical degrees (Fig. 1). In this circuit the phase coils each embrace one stator tooth. The connection scheme of the coils in a phase provides the maximum depth of pulsation of the conductivity or inductance curve of the phase winding, while the polarity of the diodes and the direction of winding of the coils of the phase winding and of the excitation winding are coordinated in such a way that the pulsating m.m.f. of the phase winding coincides in direction with the excitation m.m.f. (the direction of the armature-reaction flux \(\Phi_{\text{ar}}\) coincides with the direction of the excitation flux). Owing to a definite combination of the commutation method inherent in the half-wave circuit (the phase current does not change sign with time) with the method of excitation characteristic of pulsating machines [1] (the magnetic flux does not change sign with time), a peculiar magnetizing effect occurs. When the polarity of the excitation current is changed, the working section moves into the region of maximum inductance of the phase winding, and the power taken from the armature decreases. Thus there is a fact paradoxical at first glance: a change in the polarity of excitation of an alternating-current generator affects its output. These features of inductor generators in the half-wave rectification circuit had not been discussed in the literature and were first discovered at AZTE. The design of a generator using the magnetizing effect has been recognized as an invention [2].

Investigations have shown that, in the rectification circuit and winding connection considered, greater power can be obtained from the active volume of an inductor generator than in a bridge rectification circuit, with a lower magnetic energy of excitation.

Fig. 1

The use of a half-wave rectification circuit in inductor generators requires a revision of the principal design ratios. In particular, the optimum width of the rotor tooth on the circumference is \((0.4—0.6)\tau\). When a single-layer coil winding is used, the width of the stator tooth must be equal to the width of the rotor tooth. It is advisable to make the rotor tooth thickening toward the base by beveling its leading wall and inclined against the direction of rotation. The consumption of armature copper in such a generator increases somewhat; in connection with this, in a number of cases it is expedient to increase the slot cross section, but the consumption

the copper in the field winding and the steel in the magnetic circuit of the excitation system are significantly reduced.

For an inductor generator in a half-wave rectification circuit, a large relative value of the short-circuit current is characteristic; therefore, in a number of cases the generator installation requires a special device for automatically limiting the load current.

Analysis of the indicated generators and their calculation can be carried out by graph-analytical integration of the machine’s differential equations, compiled using the method of the equivalent circuit of the magnetic chain in the active zone.

At AZTE, a tractor inductor generator with a built-in half-wave rectifier, G302B, has been developed. Its use instead of a generator with a bridge rectification circuit gives an annual saving of more than 0.5 million rubles by reducing the number of valves, lowering the consumption of copper in the field winding, and simplifying the design.

REFERENCES

1. V. V. Apsit. Classification of contactless synchronous machines. Contactless Electrical Machines, I. Publishing House of the Academy of Sciences of the Latvian SSR, 1961.

2. A. N. Korogodsky, S. L. Medovar, A. D. Vlasov, V. I. Yurtsenko et al. Multiphase inductor generator. Inventor’s Certificate No. 200654. Bulletin No. 17, 15/VIII 1967.