RU2510123C1 - Method to control three-phase sinusoidal voltage - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: method to control three-phase sinusoidal voltage is based on alternation of connection of an excitation winding of a voltage booster or to a source of three-phase voltage or to a three-phase resistor. Switching is carried out by a three-phase semiconductor switch. At the same time the oscillating circuit, being formed by a serial winding of the voltage booster and the capacitor, is used to generate anti-distortions of current, and summing them with the current of the primary winding of the voltage booster, they provide a sinusoidal current of the network, sinusoidal voltage of the load.

EFFECT: reduced losses in loads in one or several power transformers and in a power transmission line and use of loss energy for production needs.

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Description

The invention relates to electrical engineering, in particular, to power electronics and can be used in power supply systems of industrial and agro-industrial enterprises, the consumers of which include electric heating plants for regulating or stabilizing three-phase voltage.

Known methods for regulating a three-phase voltage, which are based on the alternation of positive and negative voltage boost modes with a short-circuit mode of a voltage boost transformer using an electronic switch (see book Pulse AC voltage control B.K. Zharsky, V.V. Golubev Preprint - 96 IED AK Ukrainian SSR, Kiev, 1975 - 60 s). There is also a method of regulating a three-phase voltage, which, due to symmetrical and asymmetric alternations of the modes of voltage boost, volt-count and short-circuit, provides six-band regulation with improved harmonic composition of the three-phase voltage (RF Patent 2232078, MKI G05F 1/30, 7 Н02М 5/257. Three-phase regulation method voltage / BC Klimash (Russia) // Discovery. Inventions, 2002, No. 25, p. 573-574).

The disadvantage of all these methods is the distortion of the voltage shape of consumers and current forms in transformer equipment and in the network, as well as the complexity of the electronic switch and its control system.

Closest to the proposed one is a method based on the alternation of the voltage boost mode with a throttle mode with a frequency exceeding the mains frequency and a smooth transition from full voltage boost to full voltage subtraction with a given modulation depth, for example, ± 10%. Moreover, the upper limit of the voltage of consumers, which includes the main electric heating element, is determined by the transformation coefficient of the boost booster transformer, and the lower limit is the value of the additional resistance as, which is used by the additional electric heating element.

This method allows, with the help of a single transistor, to regulate or stabilize a three-phase voltage at the input of one or more transformer substations and for consumers. It implements regulation with high speed, using a simple power circuit and control system.

However, this method of regulation also has significant disadvantages, which consists in distorting the shape of the voltage in the power supply of consumers and the shape of the current in the power transformer of the substation and in the network.

The objective of the proposed method for regulating three-phase voltage is to preserve the sinusoidal form of the consumer supply voltage and the current form in the power transformer and in the network.

The solution of this problem is achieved by forming current anti-distortion for the primary winding of the boost transformer by means of an oscillating circuit created on the basis of this winding, and summing the current of the primary winding of the boost boost transformer with anti-distortion.

The technical result is to reduce losses among consumers in one or more power transformers and in power lines and the beneficial use of energy losses for production needs.

The essence of the proposed method is illustrated below by the description and the accompanying drawing, in which Fig. 1 shows the physical processes illustrating the process of forming the anti-distortion of the primary circuit current, summing them with the distorted primary current of the boost transformer by means of an oscillatory circuit, and providing a sinusoidal current in the substation power transformer and in the network and power supply voltage of consumers, and in Fig.2 - a device that implements the proposed method.

Figure 1 presents the mode of voltage boosting (figure 1, a), the mode of voltages (figure 1, b) and the following notation is introduced:

I _C = I ₁ = I _in + I _K is the current of the network and through the primary winding of the power transformer (the sum of the currents through the primary winding of the boost transformer and capacitor);

U _C is the mains voltage;

U _H - load voltage;

U _d - voltage boost;

I ₁ - current through the primary winding of the power transformer;

In - load current;

I _in - the current of the primary winding of the boost transformer;

U _K is the voltage across the capacitor;

I _K - capacitor current (anti-distortion current in the power transformer and in the network).

The indicated designations of physical processes were obtained in the Matlab environment using the model shown in Fig. 3.

Figure 2 introduced the following notation:

Power 1 and booster 2 transformers, a semiconductor switch 3 with a control system 4, a filter-compensating capacitor block 5, an electric heater 6 with a main 7 and an additional 8 elements, load 9, which includes the most critical consumers for voltage quality, network 10.

The method operates as follows.

In each phase, the first harmonic is isolated from the primary winding current of the boost-up transformer by summing the current of this winding with anti-distortions, which are obtained in the oscillatory circuit formed by the primary winding inductance of the boost-up transformer 2 and a capacitor. The energy to maintain the generation of anti-distortion comes from the secondary circuit of the boost booster transformer and is added to the oscillatory circuit using an electronic key in a pulsed manner. When the semiconductor key is fully turned on and completely turned off, the capacitor of the oscillatory circuit does not participate in the operation, due to the fact that its resistance is many times greater than the primary winding of the boost transformer. With this method of regulation, the additional active energy during voltage addition is directed from the network to the load, and during voltage subtraction, the excess load energy is consumed by additional resistance.

With a reduced voltage in the network 10, the semiconductor switch 3 is turned on, and the boost transformer increases the voltage at the input of the power transformer 1 and at the load 9 to a predetermined level by inducing in the primary winding of the boost transformer 2 an EMF in phase with the mains voltage 10. In the full voltage boost mode, an additional element 8 of electric heater 6 is shorted by an open semiconductor switch 3 and de-energized, i.e. auxiliary heater is off.

With increasing voltage in the network 10, the device reduces the duration of the conductive state of the semiconductor switch 3 within each switching period of the load voltage. In this case, a change in the magnitude and direction of the main magnetic flux of the booster transformer is induced on the primary winding, which is in phase with respect to the voltage of the EMF network, thereby preserving the voltage at load 9. At the same time, an additional heater element 8 comes into operation at intervals of the locked state of the semiconductor switch 3 6.

The resistance value of the additional heating element 8 is selected from the condition of ensuring the lower limit of stabilization, at which the semiconductor switch 3 is completely turned off. An additional heating element 8 in the full-voltage mode performs the role of protecting the three-phase semiconductor switch 3 from overvoltage.

Verification of the functioning of the method was performed as a result of numerical experiments on a block-modular mathematical model in a Matlab environment.

The block modular mathematical model is shown in figure 3. It consists of a three-phase network and load, power (CT) and boost booster (VDT) transformers, main (EN1) and additional (EN2) heating elements, a semiconductor switch made on an IGBT transistor, a semiconductor switch control system (SU-TK) included in the diagonal of a three-phase bridge diode rectifier (LW), a capacitor (C) of the oscillatory circuit.

The results of experiments that were performed without a capacitor and with it are presented in figure 4 and figure 5. They show the unity of the nature of the occurrence of distortions of the input current (figure 4) and the output voltage (figure 5) and a method for eliminating them. Figure 4 shows the shape of the network current in one phase without an oscillatory circuit (curve 1) and with an oscillatory circuit (curve 2). Figure 5 - forms of load stresses of one phase without an oscillatory circuit (a) and with an oscillatory circuit (b).

The oscillation circuit completely eliminates distortions in the input current curve in the entire range of voltage regulation (stabilization) of consumers. With this method, the consequence of current filtering is to eliminate distortion in the output voltage curve.

The proposed method, as more advanced, can find application for regulating and stabilizing a three-phase sinusoidal voltage. The most appropriate field of application is agricultural enterprises, the consumers of which include electric heating plants.

Claims (1)

A method for regulating a three-phase sinusoidal voltage, based on the alternation of the boost mode and the throttle mode of the boost transformer, by closing and opening one end of the secondary winding of the boost transformer, to which the additional resistance is also connected, while its other ends are connected to the secondary winding of the power transformer, and the primary windings of the boost and power transformer are connected in series and connected to the network, while opening and the secondary winding of the booster transformer is clamped, for example, with a three-phase semiconductor switch, and the upper control limit is set by the transformation coefficient of the booster transformer, and the lower additional resistance, characterized in that they generate current distortions for the primary winding of the booster transformer by means of an oscillating circuit created on the basis of this winding, and summarize the primary current of the boost booster transformer with anti-distortion.

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