ADAPTIVE INTERVAL-CODE SYNCHRONIZING UNITS

The synchronizing units adaptive to instability of the mains voltage amplitude for the network forced power semiconductor converters are considered. In order to reduce switching and pulse interference in the synchronizing unit with tracing fixation of self-switching points the first-order aperiodic filters are used, regulated to the shift of input sinusoidal voltage to the angle of minus 30 or 60 electrical degrees that is determined by the level of interference from mains voltage. As a result the auxiliary three-phase voltage system is created which is processed further with the help of comparators and binary-decimal decoders. From the gained series of numbers the needed ones are chosen and com-bined by the function “OR”. The logic signal is gained as a result, the width of which corresponds to the required synchronization interval of the semiconductor converter. In the second case the synchronization signal affects the self-oscillating integrating sweep converters trans-ferring them to the forced switching mode with the mains voltage frequency. Together with this each of the synchronization channels gets the properties of the first-order aperiodic filters with time constant determined by the value of the amplitude and frequency of mains voltage. The closed-circuited structure of the sweep converters and the presence of the integrator in the direct control channel contribute to the high level of metrological characteristics of such synchronizing units. The waveform diagram of the synchronizing units and the recommendations concerning the choice of the parameters of their elements are given.


Introduction
Modern power systems both stationary and autonomic-based are characterized by the high level of interference with difficultly predicted parameters, often exceeding the allowable norms of interference and serving as destabilizing factors in the work of not only semiconductor converters (SC) but process installations in whole [1][2][3]. That is why the development of the SC control systems which can partly or fully adapt to the changing parameters of the power line is the actual task directed to reliability growth of The synchronizing units adaptive to instability of the mains voltage amplitude for the network forced power semiconductor converters are considered.
In order to reduce switching and pulse interference in the synchronizing unit with tracing fixation of selfswitching points the first-order aperiodic filters are used, regulated to the shift of input sinusoidal voltage to the angle of minus 30 or 60 electrical degrees that is determined by the level of interference from mains voltage. As a result the auxiliary three-phase voltage system is created which is processed further with the help of comparators and binary-decimal decoders. From the gained series of numbers the needed ones are chosen and combined by the function "OR". The logic signal is gained as a result, the width of which corresponds to the required synchronization interval of the semiconductor converter.
In the second case the synchronization signal affects the self-oscillating integrating sweep converters transferring them to the forced switching mode with the mains voltage frequency. Together with this each of the synchronization channels gets the properties of the first-order aperiodic filters with time constant determined by the value of the amplitude and frequency of mains voltage. The closed-circuited structure of the sweep converters and the presence of the integrator in the direct control channel contribute to the high level of metrological characteristics of such synchronizing units.
The waveform diagram of the synchronizing units and the recommendations concerning the choice of the parameters of their elements are given.
With the help of output units LE1-LE3, therefore, the signal "1" can be differentiated, the width of which will correspond to the required control interval of power inverters SC.
Together with this, both symmetric and asymmetric amplitude change of phase voltages does not bring a mistake to the synchronization process, because the SU makes pairwise (tracing) fixation of self-switching points of the signals "a", "b", "c" and time of their crossing the zero level ( fig. 2, b). The characteristic ( , ) fig. 3, which has been derived by means of simulation of the SU in software suite Matlab+Simulink, which shows that deviation of the synchronization process does not depend on signal amplitude of synchronization and is defined only by mains voltage frequency, that is why filters F A , F B , F C are used. Here power line frequency relative to its rated value S f .

The integrating interval-code synchronizing unit
In the systems with an abnormally distorted power line, for example, on objects with autonomicbased power systems it is recommended to use the SU based on principle of integrating sweeping conversion [7,[11][12][13][14]. Let us consider the above-mentioned variant of SU design applying to a three-phase bridge rectifier, for example, with a separate control [6,15].
The basis of SU ( fig. 4)  ISC A , ISC B , ISC C are present self-oscillating systems with frequency-pulse-width modulation [18][19][20][21] in initial state, where the output signal amplitude of the integrator I is limited by switching thresholds of RE and the signal has a sawtooth waveform. The inverting element IN is included to the diagram in order to correlate the outputs ISC A , ISC B , ISC C with further digital elements.
When AC voltage of the power line goes to an input, for example ISC A , and its amplitude outgoes the one of the output pulses of the RE in 2,0-4,0 times, the ISC switches to external synchronization mode, when the frequency of its output pulses is equal to the one of mains voltage. If the frequency of ISC A 's selfoscillations has been chosen to be equal to the one of mains voltage, then a phase-shift between the synchronization signal and the output pulses of the RE (of inverting element IN) becomes equal to minus 90 electrical degrees ( fig. 5, a-d) [14,16], and the ISC itself gets the properties of the first-order aperiodic filter [6][7]  parameters. It is worth taking into account that in comparison with the filters F A , F B , F C ( fig. 1) the ISC represents a closed system with an integrator in the direct channel of control that contributes to stability of time and temperature characteristics of synchronization channels [22]. Hereinafter we consider that ISC A forms the signal Q 0 of the low bit-position and ISC C -the signal Q 2 of the high bit position of the binary code ( fig. 5, b-d) which go to the decoder DC ( fig. 4).
Combining the corresponding numbers by the function "OR" with the help of the logical elements LE1-LE3 the pulses of the logical "1" will be formed on the output of the SU (fig. 5, f-h), the width of which corresponds to the intervals "1-4", "3-6" and "5-2" of self-switching points of the phases A, B, C in limits of which the control angle of thyristors in the bridge controlled rectifier is regulated.
The characteristic ( , ) for the SU with the ISC is practically similar to the one given in fig. 3. In this case during variations of synchronization voltage amplitude (of the power line) the integrator I aims at retaining average value of output pulses to be equal to zero, and as a result compensation of synchronization fault occurs.

Findings
1. The SU with tracing fixation of self-switching points of mains voltage is introduced, where with the help of first-order aperiodic filters the auxiliary threephase voltage system is generated, which is shifted relative to the main on minus 60 electrical degrees. As a result of pairwise comparison of mains voltages with the help of the comparators the number series is gained, from which the synchronization signal for the needed power diagram of the SC can be derived selectively. For the power line with the low level of interference time constant of smoothing filters can be chosen at the level of minus 30 electrical degrees.
2. High sensitivity of the comparator SU towards external interference and the open-circuited structure of the input filters that has a negative impact on the metrological characteristics of the synchronization channels can be considered as drawbacks of the comparing SU.
3. The integrating interval-code SU is considered, which is realized at the basis of the ISCs working in external synchronization mode with mains voltage frequency. In this case the synchronization channels get the properties of the adaptive first-order aperiodic filters with time constant determined by the mains voltage parameters. The recommendations concerning the choice of the synchronization conditions are given.
4. The integrating interval-code SU have higher metrological characteristics because of their closed-circuited structure and the presence of the integrator in the direct channel of control.