FREQUENCY REVERSAL SYSTEM OF A SYNCHRONOUS-HYSTERESIS HYDRAULIC MOTOR

B. P. Soustin, Yu. A. Shurygin

(Presented by the scientific and technical seminar of the Research Institute of AEM)

Modern advances in the technology of developing mobile apparatus for space, scientific, military, and economic purposes impose high requirements on inertial-navigation systems. To reduce certain stationary and random errors, various autocompensation methods are used, for example, reversal of the kinetic moment \(H\) [1]. During operation over the interval \(t_1—t_2\) (Fig. 1), \(H\) must have high stability (up to \(0.005\%\)). The reversal interval \(t_2—t_5\) must be made minimal with unchanged losses. These conditions can be realized only through the use of static converters with frequency control, which make it possible to stabilize the output parameters with a high degree of accuracy and to vary them according to any law, up to a stepwise one.

Fig. 1

In the control system under study for a synchronous-hysteresis hydraulic motor, the static converter is implemented according to the principle of stepwise approximation of a sinusoidal voltage [2], whose form remains unchanged in all control modes and contains only harmonics that are multiples of \(12k \pm 1\), with a distortion factor of no more than 11%. The low voltage harmonics 11 and 13 create a pulsating torque with a 12-fold pulsation frequency, which, with a large moment of inertia of the rotor, causes speed pulsations on the order of \(0.0001\%\). The constancy of the har—

the harmonic content presupposes constancy of the losses from the higher harmonics over the entire frequency range when the motor current is stabilized.

The block diagram of the static converter is shown in Fig. 2 and includes: GPI — rectangular-pulse generator, FTI — clock-pulse shaper, P — interrupter, KPS — ring counting circuit, R and UM — expander and power amplifier for the control pulses, I\(_1\) and I\(_2\) — voltage inverters, BVT — output-transformer unit, ZOST — current-feedback link, RN — voltage regulator, NUV — uncontrolled rectifier, PrU — programming device, KG — quartz generator.

Fig. 2

The central element of the converter is the master oscillator ZG, consisting of GPI, FTI, P, KPS, RiUM, and controlling the operation of two three-phase bridge voltage inverters with a 30° electrical displacement. The GPI is made according to the circuit of a magnetic-transistor multivibrator with a frequency of \(\pm 12(\Delta f \div f_N + \Delta f)\). In the FTI, the rectangular voltage of the GPI is converted into clock pulses that control the ring counting circuit. Since the KPS is made on ferrite-thyristor cells, the interrupter P serves to switch off the thyristors. The ring counter consists of 12 cells; the output voltage of each cell is a narrow pulse with a frequency 12 times lower than the GPI frequency. These pulses are fed to expanders made on symmetrical flip-flops with separate input. At the output of the expanders, pulses of duration 180° are formed, shifted relative to one another by 30°. Pulses from P and UM are applied to the power transistors of the two inverters I\(_1\) and I\(_2\). The secondary windings of the BVT are connected so as to sum the voltage difference of two phases of one inverter with the voltage of one phase of the other. Figure 3 shows oscillograms of voltage and current, taken at a frequency of 500 Hz. In the channel function for current stabilization, consisting of ZOST and RN, the feedback is built on the principle of measuring the average value. The pulse regulator makes it possible to vary the voltage of the uncontrolled rectifier NUV in the range from \(0.1\,U_N\) to \(U_N\). At the moment of reversal, reducing the frequency by \(\Delta f\) leads to

Fig. 3

to a short-term current surge, i.e., overexcitation of the motor, and to the appearance of an additional asynchronous generator torque. Next, the frequency of the static converter is changed according to such a law that, over the interval \(t_2—t_3\), \(\Delta f=\mathrm{const}\). To preserve the linearity of the change in rotor speed and to maintain constant losses over the interval \(t_3—t_4\), dynamic braking is used. Over the interval \(t_4—t_5\), acceleration takes place in the opposite direction. At the instant \(t_4\), a frequency jump by the amount \(\Delta f\) also occurs, which promotes the appearance of an additional asynchronous motor torque. At the time \(t_5\), when the rotor speed reaches the rated value, the rectangular-pulse generator GPI is synchronized with the quartz generator KG with a frequency-maintenance accuracy of \(\pm 0.005\%\). As experimental studies have shown, exceeding the rated frequency by \(\Delta f\) at the instant \(t_5\) reduces the time required to enter synchronism. In the reversing mode, the stability of the stator current is \(\pm 1\%\).

Fig. 4

The change of frequency and the switching are performed by the program device PrU, the functional diagram of which is shown in Fig. 4 and which consists of three main blocks: a source of rising voltage, a source of falling voltage, and a switching unit. The frequency of the GPI is proportional to the rising (falling) voltage supplied from the program device. These signals are generated by the sawtooth-voltage generators GPI1 and GPI2. Disconnection of the PrU (point \(t_1\), Fig. 1) when the frequency rises to \(f_N+\Delta f\) is performed by means of comparator K, trigger Tr1, amplifier U1, and relay P2. The emitter followers EP1 and EP2 serve to match the output resistance of the sawtooth-voltage generators with the load. By means of resistor \(R_5\) (\(R_6\)), it is possible to vary the rise (fall) time of the frequency in the range from 30 sec to 10 min. The linearity of the sawtooth voltage is achieved by charging the capacitor with a constant current. The source of falling volta-

operates similarly, but then the increasing signal is inverted. K2, Tr2, U2, and R1 switch the circuit at time \(t_4\) (Fig. 1). Buttons Kn1 and Kn2 serve to obtain the initial state of the circuit, and Kn3 to start the program device. The flip-flop with counting input Tr3 and relay R3 carry out the phase reversal of A and B during reversing.

The constructed prototype of the static converter was tested and showed high operating qualities.

References

1. Inertial Navigation. Edited by K. F. O’Donnell. “Nauka,” 1969.
2. V. N. Lovushkin. Transistor DC Voltage Converters. “Energiya,” 1967.