RU2542672C1 - Method and device for phase control over variable voltage - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: this method comprises alternating connection of reactive load to supply circuit with the help of single half-wave control switches of serial circuit and its short-circuiting by single half-wave zero switches of parallel circuit. Then, the load is short-circuited at the start of existing voltage half-wave. Then, at preset control angle, control switch of previous half-period is switched on to provide for electromagnetic circuit power recuperation to the circuit. Proposed device control and zero switches are connected in pairs to bridge circuit, one diagonal of the latter being connected with supply circuit and another diagonal being connected with load via current transducer. Note here that control switches are shunted by inverter diodes.

EFFECT: expanded control range at inductive load irrespective of its parameters, reliable AC voltage controller.

2 cl, 2 dwg

Description

The invention relates to the field of electrical engineering, in particular to the regulation of alternating voltage and current, and can be used for deep voltage regulation in many industries, including welding plants and rectifiers.

A known method of phase regulation of the voltage at the load using a bipolar switch ("Automation devices on thyristors" / VA Skarzhepa, VV Morozov. - Kiev: Technique, 1974, Fig. 60 and 62, p. 97 and 100) , in which during each half-period of the mains voltage at a given moment the load is connected by closing the key, which opens at zero current value.

ограничивается критическим углом. Этот диапазон уменьшается с ростом индуктивной составляющей нагрузки.The disadvantages of this phase voltage regulation method are the limited regulation range, a high level of higher harmonics (distortion power), and additional reactive power consumption. Operating range of change of angle of inclusion $${\alpha }_{k\cdot \min }={\varphi }_n=arctg\frac{\omega \cdot L_H}{R_H}$$

limited to a critical angle. This range decreases with increasing inductive component of the load.

The intermittent current of the active-inductive load is calculated by the equation:

i _n = (U _m / Z _H ) · {sin (α-α _k ) -sin (α _K- φ _n ) · exp [- (α-α _k ) / tgφ _n ]},

_ω.where α = ω · t, α _k is the angle of regulation; $$Z_n=\sqrt{{\mathrm{<figure-callout\; id="2"\; label="R\; n"\; filenames="00000008.png"\; state="\{\{state\}\}">R\; </figure-callout>}}_n^{}+{\left(\omega \cdot L_n\right)}^2}$$

_ω .

In particular, with an active load and an inclusion angle α _K = 90 °, the powers reach the following values: active P ₍₁₎ = 50%, reactive Q ₍₁₎ = 32%, and distortion power (higher harmonics) N = 39%.

A known method of regulating the voltage at the load, selected as a prototype, by alternately connecting the reactive load to the supply network using the anti-parallel keys of the serial circuit, then shorting it with short anti-parallel keys of the parallel circuit and re-enabling one of the keys of the serial circuit (a. S. No. 541157 and A.S. No. 1686417).

Known AC voltage regulator with regulating and zero fully controllable switches, for example, on bipolar thyristors with cut-off diodes and switching capacitors installed between the thyristor electrodes of the same name, selected as a prototype (see A.S. No. 517122, or A.S. No. 1686417).

The disadvantage of the prototype method is that when phase voltage regulation by the angle of inclusion of the two-key controller on the anti-parallel thyristor switches with capacitive switching is not operational. It is not possible to lock the control key after changing the polarity of the mains voltage, since a short-circuited network loop is formed through the control thyristor key of the half-period that has arrived and the thyristor zero key of the previous half-cycle, especially in dynamic modes.

The main task in phase control is to expand the range of voltage regulation under inductive load regardless of its parameters and create a reliable AC voltage regulator that allows this method to be implemented.

This goal is achieved by the fact that in the method of phase control of alternating voltage by alternately connecting the reactive load to the mains using the half-wave control keys of the serial circuit and then short-circuiting it with half-wave zero-parallel circuit keys at the beginning of each voltage half-cycle with the zero key of the previous half-cycle, short-circuit the load , then at a given angle of switching include the control key of the previous half-cycle , providing a circuit for the recovery of excess electromagnetic energy into the network, and at the moment the load current passes through zero, the regulating key of the incoming half-cycle is closed, creating an energy consumption circuit from the network.

The phase-voltage control device for alternating voltage, containing a control unit connected to a current sensor, and paired control and zero half-wave fully controlled keys, solves the problem by the fact that the control and zero keys are pairwise connected according to the bridge circuit, one diagonal of which is connected to the mains, and the other with a load through a current sensor, and in the opposite shoulders the control keys are shunted by reverse diodes.

As fully controlled keys, bipolar and field effect transistors of the MOSFET, IGBT type, lockable thyristors of the GTO, GCT, IGCT types or ordinary thyristors with cut-off diodes and capacitors installed between common points of connection of the thyristors with diodes can be used.

The invention is illustrated by the structural diagram of the voltage control device in figure 1 and timing diagrams with the algorithm of the controlled keys shown in figure 2.

The device (Fig. 1) is made on half-wave controlled keys: two control keys 1, 2 and two counter-connected zero keys 3, 4, which work in antiphase with keys 1, 2, while the control keys 1, 2 are shunted by reverse diodes 5 and 6, and all keys are connected in a bridge circuit.

The keys 1-4 are connected by one diagonal of the bridge to the supply network 7. Another diagonal formed by the same key electrodes is loaded on the active-inductive load 10 and the current sensor 8 connected to the control unit 9.

On figa indicated: oblique dashed line is the load voltage in the energy consumption mode, and the vertical dashed line is the mode of energy recovery in the supply network.

On fig.2d-g presents a zone of a closed state of the keys, explaining the method of regulating the voltage at the time of the start of connecting the load to the mains.

The onset half-cycle corresponds to the positive half-wave of the sinusoidal voltage of the network U _C (in Fig. 2, b, c, d - horizontal hatching), and the previous (second) half-period corresponds to the negative half-wave (Fig. 2, e, f, g - oblique hatching).

The essence of the phase method for regulating the output voltage 11 (figure 2) is as follows.

At the beginning of the onset of the half-cycle of the voltage of the network 7 from the moment α = 0, the signal from the control unit 9 closes the zero key 4 of the previous (second) half-cycle and through the diode 6 (figure 2, f) a short-circuited load circuit 10 is formed. The load current 12 continues to flow along the circuit consisting of a current 13 consumed from the network and an exponential current 14 flowing in a short-circuited load circuit (Fig. 2, a). The equations for the instantaneous currents obtained by the fitting method are as follows:

load current i _n (α) = i _s (α) + i _s (α),

,network current $$i_{\mathrm{from}}\left(\alpha \right)=\frac{k_2}{k_{\mathrm{one}}^2+\mathrm{one}}\left(k_{\mathrm{one}}\sin \alpha -\cos \alpha +\delta \cdot e^{-k_{\mathrm{one}}\alpha }\right)$$

,

.short-circuit current $$i_s\left(\alpha \right)=\frac{{\mathrm{<figure-callout\; id="2"\; label="k"\; filenames="00000008.png"\; state="\{\{state\}\}">k</figure-callout>}}_2\cdot \lambda }{k_{\mathrm{one}}^2+\mathrm{one}}\cdot e^{k_{\mathrm{one}}\alpha }$$

.

where k ₁ = R _n / L _n ; k ₂ = U _m / ω · L _n ; δ - coefficient taking into account the parameters

schemes and initial conditions of fitting; α = ω

For a given switching angle α = α _{K, the} signals from the control unit 9 simultaneously open the zero key 4, and close the control key 2 of the negative half-cycle voltage (the connection of the control and zero keys is indicated by a dashed line).

On the interval α _K ≤α≤φ, the current 13 (12) of the load 10 flows counter to the voltage of the network 7 and drops to zero at α = φ with a speed depending on the time constant of the load. Excess electromagnetic energy is recovered into the network, while the control switch 2 is opened and the diode 6 is locked, open for half a period of current φ≤α≤π + φ.

At the moment α = φ of the transition of the current 12 through zero, the control switch 1 closes with a signal from the control unit 9 and the current 13 consumed from the network starts to flow through it and the diode 5.

In the interval α _K ≤α≤π, energy is consumed from the supply network, and the output voltage curve 11 is formed in the range of energy recovery and consumption zones. After changing the polarity of the voltage of the network 7 at the time α = π, the control key 1 is simultaneously opened and the zero key 3 is closed.

Since the voltage on the load in each half-cycle consists of two zones: the recovery zone and the zone of energy consumption from the network, a change in the reactive component of the load will only cause a change in these zones. In the range of these zones, the load is constantly connected to the network, so their relative duration does not affect the shape of the output voltage.

,The average and effective values of voltage 11 at the load are determined from the equations: $$U_{n\cdot \mathrm{from}R}=\frac{U_m}{\pi }\left(\mathrm{one}+\cos {\alpha }_k\right)$$

,

. $$U_n=\frac{{\mathrm{<figure-callout\; id="2"\; label="U\; m"\; filenames="00000008.png"\; state="\{\{state\}\}">U\; </figure-callout>}}_m}{\sqrt{2\pi }}\sqrt{\pi -{\alpha }_k+0,5\sin {\alpha }_k}$$

.

Current 14, caused by EMF of self-induction, decreases exponentially in the circuit: 10-8-5-3-10, scattering on the active resistances of the circuit.

At an angle α = π + α _K , a negative half-wave of the output voltage 11 begins to form, while the control key 1 closes again, forming an energy recovery circuit: 1-10-8-5 - (+) / (-) of the network 7 (Fig.2a , d).

From the moment α = π + φ, the regulating switch 2 and the diode 6 come into operation, through which the load current 12 flows in the range π + φ≤α≤2π.

Depending on the circuit and the type of keys used, instead of diodes 5 and 6, you can use controlled diodes - thyristors, unlocked by signals from the current sensor 8, as shown by the dotted line in figure 1.

From the above it follows that, unlike the prototype, when the phase voltage regulation at the time of closure of the control key in the proposed method, the control range does not depend on the nature of the load. With this method, there is a constant flow of the load current, as a result of which a free exchange of energy occurs between the network and the load.

The voltage signal from the current sensor 8 is compared with the reference voltage U _OP , and the difference signal from the control unit 9 affects the duration of the pulse control keys 1-4, and also acts on the protection system.

The device with such a scheme of connections and connections becomes reliable in operation, since there is no possibility of the appearance of through circuits of the short circuit of the network in static and dynamic modes through the control key of the incoming half-cycle and the zero key of the previous half-cycle of the network voltage. The energy performance of the device is higher here, because at intervals of a short-circuited load, current flows through it, but is not consumed from the network.

Claims (2)

1. The method of phase control of alternating voltage by alternately connecting the reactive load to the supply network using half-wave control keys of the serial circuit and then short-circuiting it with half-wave zero switches of the parallel circuit, characterized in that the load is short-circuited at the beginning of the voltage half-cycle by the previous half-cycle, then, at a given switching angle, the control key of the previous half-cycle is turned on, providing a recovery electromagnetic energy into the network, and at the moment the load current passes through zero, close the regulating key of the half-cycle that has come, creating a circuit for energy consumption from the network. 2. A device for phase regulation of alternating voltage, comprising a control unit that is connected to a current sensor, and paired control and zero half-wave fully controlled keys, characterized in that the control and zero keys are pairwise connected according to a bridge circuit, one diagonal of which is connected to the mains, and the other with a load through a current sensor, and in the opposite shoulders the control keys are shunted by reverse diodes.

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