CONSTRUCTION OF CHARGE-DISCHARGE DEVICES WITH MUTUAL ENERGY EXCHANGE

S. K. ZEMAN, A. V. KYUZEV

(Presented by the Scientific and Technical Seminar of the Research Institute of AEM)

In accordance with the requirements of modern charging technology, in order to increase service life and improve the operational characteristics of storage batteries (SB), it is necessary systematically to carry out training cycles, consisting of a consecutive alternation of charge and discharge processes. To perform these technological operations with the least losses and the greatest productivity, it is desirable to use devices in which the named processes are combined in time and energy is exchanged between the discharged and charged batteries. Figure 1 shows possible variants of power-circuit diagrams of charge-discharge devices that satisfy these requirements.

Fig. 1.

The current in the discharge circuit is maintained at a prescribed level by changing the duration of closure of the controlled switch (K), implemented on a thyristor with forced commutation.

The magnitude of the current of the charging circuit is set by means of a regulated charging rectifier (CR), which, by adding current, makes it possible simultaneously to stabilize the discharge and charging currents. In this case the charging rectifier operates at voltages close to nominal and is loaded with small currents, as a result of which it has high energy characteristics (efficiency and \(\cos \varphi\)) and a comparatively small installed power. As the regulated charging rectifier (CR), any units may be used, including commercially produced charging devices implemented, for example, on controlled rectifiers, on rectifiers with ferromagnetic re—

ulators, etc. Figure 2 shows time diagrams explaining the operation of the device shown in Fig. 1, a. At time \(t_1\), when switch K is closed, the current due to the emf of the discharging group of storage batteries (DB) increases along the circuit DB–Ch–K (Fig. 2, a), and the voltage on the linear choke Ch is equal to the voltage

Fig. 2.

of this group (Fig. 2, b). In the circuit of the storage batteries being charged (CB), a current flows due to the voltage boost supplied by the charging rectifier (Fig. 2, c). At time \(t_2\), when switch K is opened, the emf of the discharging batteries is added to the self-induction emf of the linear choke and is applied to the group being charged (Fig. 2, b, 2, d), partially or completely blocking the CB. The current begins to flow through the circuit DB–Ch–D–CB (Fig. 2, c). The blocking diode D serves to prevent discharge of the group of batteries being charged.

The device shown in Fig. 1b operates in the same way as that described above, with the only difference that the current in the circuit of the discharging batteries is pulsed (Fig. 2, d).

Fig. 3.

The device described (Fig. 1, a) can readily be converted into a device for accelerated formation of electrodes, for example, of silver–zinc storage batteries by pulsed current. For this purpose it is sufficient to connect the charging rectifier CB in place of the discharging group of batteries DB (Fig. 3). The duration and repetition frequency of the current pulses are set by switch K, and the amplitude is regulated by CB. However, despite all the above-listed positive qualities, the devices shown in Fig. 1a, b have a substantial drawback—limited functional capabilities, since they are operable only when the voltage of the discharging group does not exceed the voltage of the group being charged.

Fig. 4.

Figure 4 shows the basic circuit diagram of the power section of a device that makes it possible to eliminate this drawback. The device contains a thyristor converter, constructed according to the circuit of a controlled rectifier, connected in series with a group of batteries being charged (ZB), a choke (Dr), and a diode D, to the terminals of which, in accordance with the source, a group of batteries being discharged (RB) is connected.

In the absence of the group of discharging batteries, the thyristor converter operates in rectifier mode, charging the group of batteries along the circuit ZV–ZB–Dr–D. Stabilization is carried out, on the basis of a signal from the current sensor DT through the control system SU, by changing the rectifier control angle. When a group of batteries is connected for discharge to the terminals of diode D, the diode is blocked and the emf of the discharging batteries is connected in series with the output voltage of converter ZV. If the voltage of the group of discharging batteries is less than the voltage of the charging batteries, the converter continues to operate in rectifier mode, but its control angle increases, and the output voltage decreases by the magnitude of the voltage across the group of discharging batteries. Accordingly, the power consumed by the rectifier from the network also decreases. If the voltage of the group of discharging batteries is greater than the voltage of the group of charging batteries, converter ZV switches to inverter mode; the current is still stabilized at the specified level, and the excess energy is returned to the network. If it is necessary to discharge batteries when no charging batteries are present, the terminals to which the charging batteries are connected must be short-circuited. In this case the converter operates in inverter mode, delivering energy to the network.

Thus, the device described is universal and can be used both as a charging device and as a discharging device. Its use is most expedient when there are two groups of batteries exchanging energy with each other. A device of this type

convenient for use in large charging facilities and at manufacturing plants, since their introduction will make it possible to increase significantly the productivity and quality of charging.

REFERENCES

1. V. V. Romanov, Yu. M. Khashev. Chemical current sources. Moscow, “Sovetskoe radio,” 1968.

2. S. K. Zeman. Automated AZAT-2M unit for charging automobile storage batteries. Proceedings of the VII Conference on Problems of Automation of Production, Tomsk, 1971.

3. Verfahren zum Laden und verlustlosen Entladen van mindestens zwei elektrischen Akkumulatoren. Patent No. 1101583, (FRG), 1961.