SU1617575A1 - Frequency converter - Google Patents

Abstract

The invention relates to power converter technology and can be used in secondary power supply systems with a frequency below the mains frequency. The aim of the invention is to increase reliability by eliminating inrush currents. The converter contains two single-phase thyristor bridges 2–5 and 7–10, which are powered by a half-wave controlled rectifier on thyristor 12 with an output capacitor 11. The objective is achieved by the appropriate ratio of capacitor capacitance values and load parameters, as well as the corresponding thyristor control algorithms of the converter. 2 Il.

Description

The invention relates to a conversion technique and can be used to power receivers of non-industrial frequency, as well as in automation devices, telemechanics, communications, etc.

The purpose of the invention is to increase reliability by eliminating inrush currents.

In FIG. 1 is an electrical diagram of a frequency converter: FIG. 2 time diagrams explaining his work, in particular when dividing the frequency by two.

The converter contains a controlled inverter 1, formed by thyristors 2-5, connected by power buses in the opposite direction to a controlled inverter 6, formed by thyristors 710 (Fig. 1). A capacitor 11 is connected in parallel to the direct current terminals of inverters 1 and 6. For the charge of the capacitor 11 from the primary network, the controlled key element 12 is used in positive half-periods. The inductor 14 is connected in series with load 13 from the side of the inverter’s output terminals 14. Capacitor 11, inductor 14 and load 13 form an oscillatory circuit. To derive the relationship between the capacitance of the capacitor 11 and the inductance of the inductor 14, taking into account the impedance of the load 13, use the formula to calculate the frequency of the oscillatory circuit a_.

Ob = ^v 'l / LC -Rh / 4 L ² . ( ¹ ) where Wo is the natural conditional frequency of the oscillatory circuit;

L is the inductance of the oscillatory circuit;

C is the capacitance of the oscillatory circuit;

R _H - load resistance.

From the principle of operation of the converter, it follows that the frequency of the oscillating circuit is generally related to the frequency of the primary network supplying the converter (Fig. 2), as follows ^{0) 0} η - 0.5 η - 0.5 '( ^Ζ ' where η is an even number, by which the frequency of the primary network is divided;

a) c = 2 l f _c is the angular frequency of the primary network;

fc is the frequency of the primary network.

The load resistance R _H through the power and voltage of the fundamental harmonic (the frequency of this harmonic is equal to the load frequency f _H = fc / n) is expressed as

Rh = Zcos φ = -Y- cos φ = ——. (3) where Ζ is the load impedance for the fundamental;

cozy? - load power factor by the fundamental harmonic;

U is the effective value of the fundamental harmonic of the voltage at the load;

S, P - full and active power at the fundamental harmonic.

Similarly, the expression for the inductance of the oscillatory circuit is determined (taking into account the inductance of the load)

L ~ Unit + L _H , (4) where I — dr is the inductance of the inductor;

Lh - load inductance, v ι U ² , U ² sin 2 у?

X = Z · slny> = -р- cos φ sin φ = - · (5) where X is the inductive load resistance for the fundamental harmonic ^Lm О) n Wc '(θ' where Шн = 2πί _Η is the angular frequency of the current and voltage load.

Substituting expression (5) into formula (6), we obtain. n U ² sin 2 у?, _ х ^Lh ~ 2 Р No.

Substituting expression (7) into formula (4) we obtain, _,, n U ² sin 2 φ ^L - ^ ⁺ –2PT0T '

Substituting expressions (8) and (3) e expression (1) and taking into account (2), we find the ratio for the active-inductive load gd (P-0.5 f - P (2 PLjp-a * * n and ² sin 2 (9)

0¼ [4 (2 P ok Ldr + nU ² sln 2 φ) ² + (η - 0.5) ² and ⁴ co » ⁴

The control unit 15 (Fig. 1) contains a frequency adjuster synchronized with the network in the form of a rectangular pulse shaper 16 and a pulse frequency divider 16, single vibrators 18-19, delay assembly 20, pulse distributors 21-22, adders 23-24, and amplifier isolating nodes 25 -27.

A pulse shaper 16 converts a sinusoidal signal into rectangular pulses (Fig. 2c), and also performs galvanic isolation between the primary network and the control unit. As the shaper 16 can be used, for example, optoelectronic switches of logical signals or optoelectronic keys.

To divide the pulse frequency, a frequency divider 17 is used, which can be used as a pulse counter with a division coefficient selected depending on the output frequency of the converter (Fig. 2d).

Single vibrators 18 and 19 (for example, K155A ^G 3 integrated circuits) operate respectively on the leading and trailing edges of the output signal, the frequency divider (Fig. 2e _; and) and generate pulses of a given duration. The delay unit 20 is used to create a delay of the output pulses of the single-shot 18 in 90 el. (Fig. 2e). Two-channel distributors 21 and 22 are used to distribute the pulses between the output amplifying isolation nodes 25 and 26, Adders 23 and 24 are made of two-input ones and are used to sum the signals arriving from their inputs. vanically decoupled exits.

When dividing the frequency by two, the converter operates as follows:

Upon receipt of a positive half-wave of the primary network voltage Ui at the input t of the input at the moment t ₀ (Fig. 2 a), a control pulse (Fig. 2e) is applied to the control elec trode of the thyristor 12 (Fig. 1), the thyristor 12 opens, and from that moment until moment ti, the capacitor 11 is charged to the amplitude value of the voltage U? with the polarity indicated in FIG. 1.

At time ti, the charge process of the capacitor 11 stops and the thyristor 12 closes. Subsequently, the charged capacitor 11 is discharged according to the oscillatory law for a period of time to a load 13 of the choke 14 from the moment n to the moment t4 (Fig. 2a, b) when the thyristors 2 and 3 of the controlled inverter ’and the thyristors 7 and 8 of the controlled inverter are opened

6. In this case, at the time ti open thyristors 2 and 3 and from that point until ^t .z (Fig. 2a, b) flows through the load 13 by positive half-wave sinusoidal current I (Fig. 26). The duration of the current flow is ensured by the choice of the capacitance of the capacitor 11 and the inductance of the inductor 14 according to the formula (9). At the end of the positive half-wave of current h, the thyristor 3 and 4 are closed, and the thyristors 7 and 8 of the controlled inverter 6 open, and from that moment until the moment 14 (Fig. 2a, 6), the negative half-wave of the discharge current flows through load 13. At the end of the negative half-wave of the current at the moment, the thyristors 7 and 8 are closed, and the thyristor 12 is opened, and from that moment until the moment t5, the capacitor 11 is again charged to the amplitude value of the voltage Ui with the same polarity. At time ts, the charge process stops and the thyristor 12 closes. From this moment, the condensation GOE 11 is discharged to the load 13 according to the vibrational law for one period until then (Fig. 2a. B) when the thyristors 4 and 5 of the controlled inverter 1 and the thyristors 9 :: 10 of the controlled inverter 2 are opened. the load proceeds in the prosthesis position compared with the first period. Further processes are repetitive.

To ensure that positive half-waves of current flow through thyristors 2 and 3 (9 and 10) and negative half-waves of current through thyristors 4 and 5 (7 and 8), control pulses arrive at their control electrodes, respectively, at time ti (t?) (Fig.

2.. L) and - <moment ta (t'i) (Fig. 2c. K).

The drift harmonics of the output current! G and voltages have a frequency fa two times m <.higher, hm hour of the ready fi network voltage (phi, -, 26). If the capacitor 1 ^{1 is} not charged for every l; -lo. ·:. 'Lal half-wave of the mains voltage Ι'ι, but after one, two, etc. with subsequent discharge and with the appropriate choice of capacitor 11 and inductance of inductor 14, the frequency will be divided by 4, 6, etc., respectively.

Carrying out the discharge of the capacitor 11, the attraction of one period allows one to eliminate the inrush of the charging current due to the fact that the initial voltage on the capacitor during charging has the same polarity as the primary voltage, and therefore, the difference. every time it only recharges. Reducing the inrush of the charging current allows G'Increase the reliability of the Converter.

The inrush of the charging current during the start-up of the converter is eliminated by traditional methods, for example, using the preliminary charge of the capacitor from the ps-external power source. For example, thyristors 2 and 9, 3 and 10, 4 and 7, 5 and 8 hl of the former can be counter-parallel connected and can be replaced by four triacs.

Claims (1)

Claim A frequency converter containing r a chain of a controllable key element and a capacitor enclosed to the input terminals, connected to the plates of this capacitor by a power bus with a single-phase bridge inverter with a choke in the output circuit, as well as a control unit including a frequency control unit, made in the form of a series interconnected rectangular pulser and frequency divider, the first one-shot, serially connected between β a delay unit and a first two-channel pulse distributor, three amplifier-decoupling units with several galvanically isolated outputs, the inputs of the control unit being connected to the input terminals of the converter for connecting to the primary network and the inputs of the rectangular pulse generator, the first output of the control unit is connected to the output of the first amplifier decoupling unit and controlled care of the key element, and the second and third, fourth and fifth outputs of the control unit connected respectively to the second and third outputs of the second and third amplifier-decoupling units are connected to the control inputs of the diagonally arranged thyristors of the bridge inverter, characterized in that, in order to increase reliability by eliminating the inrush of the charging current, it is additionally equipped with a second single-phase bridge inverter connected to the power buses in the opposite direction the first inverter, and the control unit of the converter is equipped with two two-input combiners and connected in series with each other by a second one-shot and in two-channel pulse distributor, the first inputs of the first and second adders connected respectively to the first and second outputs of the first pulse distributor, and the second inputs to the corresponding outputs of the second pulse distributor, the input of the second one-shot is connected to the interconnected output of the mentioned pulse frequency divider and the input the first one-shot, the output of which is connected to the inputs of the first amplifying-equating node and the delay node, the inputs of the second and third amplifying-decoupling of the connecting nodes are connected respectively to the outputs of the first and second adders, the sixth and seventh, eighth and ninth outputs of the control unit, connected respectively to the third and fourth outputs of the second and third amplifier-decoupling nodes, are connected to the control inputs of the diagonally arranged thyristors of the second inverter, and the capacitance values The capacitor and inductance Tsr of the inductor are interconnected by the relation + ⁺ -o.5f U ⁴ where η is an even number by which the frequency of the primary network is divided; P is the active power of the load at the fundamental harmonic; cut is the angular frequency of the primary network; U is the effective value of the voltage of the fundamental harmonic at the load; h! pf> is the angle between the active and reactive components of the current at the fundamental harmonic; cos φ is the load power factor for the fundamental harmonic.