SOME RESULTS OF AN EXPERIMENTAL STUDY OF AN AUTONOMOUS PULSED POWER SOURCE WITH AN INDUCTIVE-CAPACITIVE CONVERTER

F. P. Zverev, G. A. Sipailov, A. B. Tsukublin

(Presented to the scientific seminar of the Departments of Electrical Machines and General Electrical Engineering)

The pulsed use of electrical energy in modern technology has a fairly wide application. The main distinctive feature of pulsed systems is the accumulation of electrical or electromagnetic energy in a storage device over a relatively long time and its rapid delivery to the load.

Low-power pulsed systems \((W_{\text{stor}} = 10^2 \div 10^3\ \text{J})\), as a rule, are made autonomous; in them the primary source of energy is a low-voltage chemical battery of limited power, or a shaft for taking off mechanical power, which necessitates the creation of intermediate converting devices for charging the storage device. At the same time, in autonomous systems it is very important to ensure the highest efficiency of the storage-device charging process and the minimum weight and dimensions of the entire system as a whole.

Among such pulsed systems is an autonomous pulsed power source made according to the scheme synchronous generator—rectifier—storage capacitor \((\text{SG—R—SC})\) [1].

It is known [2] that the minimum energy expenditure and the highest charging efficiency correspond to a linear increase of the voltage on the capacitor during charging, i.e., charging with a constant current.

One of the ways of realizing such a charging mode of the storage capacitor is the use of an inductive-capacitive converter (ICC) as an intermediate link between the alternating-current generator and the rectifier, performing the role of converting a constant-voltage source into a constant-current source [3].

In the present article, some results are given of an experimental study of an autonomous pulsed power source (APPS) with an inductive-capacitive converter, the circuit of which is shown in Fig. 1.

As the alternating-current source, a low-power synchronous generator with electromagnetic excitation and a voltage regulator was used.

The ICC is made according to a three-phase T-shaped circuit with mutual-inductive coupling of the coils in the arms and is tuned to resonance at the frequency of the synchronous generator.

Below are the basic data of the experimental APPS installation:

Fig. 1. Schematic diagram of an autonomous pulsed-power source with an inductive-capacitive converter

Generator

Power
\(P = 500\ \text{W}\)

Voltage
\(N_{\text{d}} = 40\ \text{V}\)

Frequency
\(f_{\text{g}} = 500\ \text{Hz}\)

Rotational speed
\(n = 15\,000\ \text{rpm}\)

Inductive-capacitive converter

Inductance of the chokes
\(L_{\text{k}} = 0.9\ \text{mH}\)

Capacitance
\(C_{\text{n}} = 70\ \mu\text{F}\)

Coil coupling coefficient
\(k_{\text{c}} = 1.0\)

Coil quality factor
\(Q = 15\)

Matching transformer

Transformer type — three-phase, core-type

Transformation ratio
\(K_{\text{t}} = 25\)

Winding connection
\(\Delta/\Delta\)

Storage capacitor

Capacitance
\(C_{\text{H}} = 240\ \mu\text{F}\)

Rated voltage
\(U_{\text{cн}} = 3000\ \text{V}\)

Charging time
\(t_{\text{з}} = 0.2 \div 3.0\ \text{s}\)

Discharge time
\(t_{\text{р}} = 0.01\ \text{s}\)

The operating mode of the APPS is cyclic—“charge-discharge.”

The cyclic operating mode of the APPS and the variation of voltages and currents during the cycle over wide limits did not allow the use of pointer-type instruments in this circuit because of their large inertia. It also proved impossible to record the indicated quantities by direct recording of oscillograms and their subsequent decoding, because of the comparatively high frequency of the synchronous generator and the low repetition frequency of the discharge pulses (\(f'_{\min \text{ imp}} = 0.3\ \text{Hz}\)). Therefore, the following method was adopted for studying the energy characteristics of the APPS:

1. A harmonic analysis of currents and voltages was carried out, with recording of oscillograms of the changes during the charging process of all the most significant harmonic components. Calibration of the oscillograms by a reference voltage and current made it possible to determine the values of the fundamental harmonic, relative to which the amplitudes of the higher harmonic components were determined.

2. From the known amplitude of the first harmonic and the relative values of the spectral components, the effective values of the measured current and voltage quantities were determined in accordance with expressions (1) and (2).

\[ I_{\text{eff}}=\frac{I_{1m}}{\sqrt{2}}\sqrt{1+\sum_{k=3}^{n}\left(\frac{I_{km}}{I_{1m}}\right)^2} \tag{1} \]

\[ U_{\text{eff}}=\frac{U_{1m}}{\sqrt{2}}\sqrt{1+\sum_{k=3}^{n}\left(\frac{U_{km}}{U_{1m}}\right)^2}. \tag{2} \]

1. The instantaneous value of the active power was determined by recording oscillograms with the aid of measuring power loops by the two-wattmeter method.

Using the method described, the relationships between currents, voltages, and powers in all elements of the system were experimentally investigated, and the operating characteristics of the AIGM were plotted (Figs. 2–5).

Fig. 2. Operating characteristics of the AIGM generator when operating into a capacitance

Fig. 3. Operating characteristics of the inductive-capacitive converter of the AIGM when operating into a capacitance

Analysis of the oscillograms and operating characteristics of the AIGM shows that

1) the use of the ICC as an intermediate link substantially increases the efficiency of the charging process; the average value of the efficiency, experimen-

Fig. 4. Load parameters during operation of the AIPM into a capacitance

Fig. 5. Efficiency of the system and the amount of energy stored by the storage unit

...of the experimental AIPM installation, for a charging time \(t_3 = 3\) sec, was \(\eta_{\text{av}} = 0.74\), which considerably exceeds the efficiency of a charging device with limiting inductances \((\eta_{\text{av}} \cong 0.6)\) or with active resistance in the charging-circuit chain (after the rectifier) \((\eta_{\text{av}} \leq 0.5)\) [1, 2];

2) tuning the IEC to resonance at the frequency of the supply voltage ensures a practically unchanged value of the current at the output of the IEC (Fig. 3), relative stability of the charging current and, correspondingly, a practically linear increase of the voltage on the storage capacitance during the charging process (Fig. 4);

3) the high values of the generator power factor (Fig. 2) during the charging process \((\cos \varphi_{g,\text{av}} = 0.86)\) show that, with proper tuning, the IEC practically does not consume reactive power;

4) the use of the IEC accounts for the absence of dips in the generator output voltage, which are unavoidable when a synchronous generator is connected to a discharged capacitance, either directly through a rectifi-

... both through limiting inductances or resistances; this circumstance is very significant for autonomous pulsed systems, in which the generator, in addition to operating into a capacitive storage unit, can also be used to supply other consumers requiring voltage stability.

The results of the harmonic analysis are given in the table.

Table

Content of higher harmonics in the voltage and current curves during the storage-unit charging process

Harmonic analysis of the currents and voltages at the generator output, of the ICC, and of the matching transformer shows that

1) the shapes of the current and voltage curves are deformed during the charging process; moreover, the curves contain no harmonics that are multiples of the number of phases of the system, nor do they contain even harmonics;

2) in all cases, the most significant of the higher harmonics are the 5th and 7th; their variation over the charging time is shown in the table;

3) the content of higher harmonics in the generator output-voltage curve throughout the entire charging time does not exceed 10%, which once again indicates the possibility of using the AIIM generator to supply other consumers;

4) the shapes of the phase-current curves of all elements of the AIIM, as well as of the phase voltages of the ICC and the matching transformer, are significantly distorted (up to 20–30%), which must be taken into account when designing the elements of an autonomous pulsed-power source with an inductive-capacitive converter.

REFERENCES

1. A. I. Bertinov et al., “Energetics of the process of charging a capacitor from an alternating-current generator through a rectifier,” Elektrichestvo, No. 8, 1967.

2. P. M. Mostov, I. L. Neuringer, and D. S. Rigney, “Optimum capacitor charging efficiency for space systems,” Proceedings of the 9th R. E. Mau, 1961.

3. D. I. Milyakh et al., Inductive-capacitive converters of voltage sources into current sources. Publishing House “Naukova Dumka,” Kiev, 1964.