RU2346416C1 - Device for controlled heating of silicon bars - Google Patents

Abstract

FIELD: chemistry; electro-chemistry.

SUBSTANCE: present invention pertains to the chemical industry, and particularly to silicon production in reactors of hydrogen reduction of polychorosilanes, and can be used for controlled heating of polycrystalline silicon bars in a reactor. The outcome is achieved by that, the rectifier unit of the input supply voltage of the device, consisting of two independent rectifiers, has a circuit which provides for serial or parallel connection of the rectifiers. A voltage of 1000 V is obtained from a series connection of the rectifiers, which is used in the initial period of growing silicon bars. Parallel connection of the rectifiers produces 500 V, used in the final stage of growing silicon bars, which uses more than 1000 A. Powerful transistor switches for controlling the heating current are controlled using a pulse-duration conversion method. Rectification of pulsed current of transistor switches is done using a power impedance coil, connected in series with the heated bar and a diode, reverse connected to the supply and closing the circuit of the impedance coil through the heated bar in the off-state period of the transistor switches. Control of the current regulator is done using a microprocessor system with an operator console. Initial heating of the silicon bars to working state is done using the operating voltage of the device through series connection and warming up parts of the silicon bars.

EFFECT: design of a device for controlling heating of silicon bars with high utilisation factor of electrical energy and high smoothing factor of direct current, used for heating the silicon bars.

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Description

The invention relates to the chemical industry, namely to the production of silicon in reactors for the hydrogen reduction of polychlorosilanes, and can be used for controlled heating of polycrystalline silicon rods in a reactor.

A device is known (US Patent No. 4562338, IPC Н05В 1/02, 1985) for heating polycrystalline semiconductor rods, including a power transformer and thyristors, connected in pairs to the terminals of the secondary winding of the power transformer, balanced transformer groups connected to the thyristor groups according to the scheme, providing direct current in the secondary winding of each balanced transformer with a semiconductor rod connected to it. The device provides an additional group of balanced transformers to ensure the supply of high voltage to the rods in the starting period.

The disadvantages of the known device described above are that it is not economical and does not provide stable DC characteristics on the rods.

A device is known ("Technology of semiconductor silicon" ./ Edited by E.S. Falkevich. M., "Metallurgy", 1992, pp. 219-220 - prototype) for heating silicon rods, including a power transformer, a group of controlled semiconductor rectifier bridges connected through switches to the secondary windings of the power transformer and connected in series with rods whose control inputs are connected to a pulse-phase control system. The disadvantage of this device is that it is not economical and does not provide stable DC characteristics on the rods.

The aim of the invention is to develop a device for the controlled heating of silicon rods with a high coefficient of electric energy and a high coefficient of smoothing DC used to heat silicon rods.

The technical result is achieved in that in a device for heating silicon rods containing a power transformer, to the secondary windings of which through a switching unit is connected a group of semiconductor rectifier bridges, and a pulse-phase control and current control unit connected in series with rectifier bridges and silicon rods, this switching unit rectifier bridges made according to the scheme, providing a series or parallel connection of rectifier bridges, the impulse block no-phase current control and regulation is implemented on power transistors connected in parallel and controlled by high-frequency pulses generated by a pulse-phase control circuit, while the device has a choke connected in series with a group of power transistors and a load channel consisting of silicon rods connected in series, a diode connected to the common output of the group of transistors in the opposite direction and closing the inductor current circuit through the rods during the closed state transistor switch, and a circuit for starting heating of silicon rods.

The proposed device for controlled heating of silicon rods is illustrated by drawings.

Figure 1 presents a diagram of the inclusion of semiconductor rectifier bridges.

Figure 2 presents a diagram of the inclusion of the main elements of an adjustable Converter.

Figure 3 presents a diagram of the inclusion of transistors and chokes of the power unit.

Figure 4 presents the voltage diagrams of transistors and chokes of the power unit.

Figure 5 presents a diagram of the load channel of the device on silicon rods.

The device contains a power transformer Tr1 with two independent secondary windings (see Figure 1), two semiconductor rectifier bridges D1 and D2, two normally open contactors K2 and K4 and one normally closed contactor K3, contactor K1, storage capacitor C1 (see Fig. .2), a load current controller, consisting of a block of power transistors T, an RC filter of high-frequency interference, a cooling panel of power transistors and diodes 2, a microprocessor control circuit of power transistors T, consisting of an operator console 9, a microcontrol 7, pulse-width modulator 10, driver control power transistor 8, current sensor 6, temperature sensor of the cooling panel 3, surface temperature sensor of the rods 4, power chokes Dr, block of diodes D3, smoothing capacitor C2, load block 5 (see Fig. .5), consisting of three silicon rods and two switches K5 and K6, connected in parallel to two silicon rods 11 and 12. The power transistor block (see Figure 3) consists of two groups of three power transistors T _A , T _B connected in parallel T _C and driven through the drive 8-phase pulse width modulator providing them alternately switch. Each group of transistors is connected to DR chokes, the second ends of which are connected to the load block (silicon rods) and to D3 diodes. All six block transistors and D3 diodes are located on the same heat sink panel 2.

The device operates as follows.

Before starting the operation of the converter, the power capacitor C1 is charged to a voltage of 700 V. After this, the contactor K1 of supplying the supply voltage to the power transformer Tr1 of the rectifier unit of the converter is turned on.

In the initial period of operation from the power rectifier unit, a voltage of 1000 V is supplied to the power transistor unit. For this, the contactor K3 is closed in the power rectifier (Figure 2) and the contactors K2 and K4 open. Contactors K2, K3 and K4 are switched simultaneously. Two rectifiers of 500 V each are connected in series and give a voltage of 1000 V to the storage capacitor and power transistors.

The current in the load (silicon rod) is controlled by a block of power transistors T and chokes Dr controlled by a three-phase pulse-width modulator (PWM) 10 through driver 8. The magnitude of the current in the load depends on the shape of the transistor control pulse. The longer the pulse to open the transistor, the greater the current in the load. The pulse duration depends on the magnitude of the current reference and the selected carrier frequency. In manual control mode, the current value is set from the operator panel 9 by pressing the appropriate control buttons on the monitor screen, and in automatic mode, the current value is determined by the program controller by the specified temperature of the rod surface. The PWM carrier frequency is selected at 15 kHz, which ensures almost complete absence of converter noise in the sound range. The operation of a three-phase PWM is illustrated in FIG. 4. Figure 1 shows the original pulse-width transistor control signal. On the diagrams 2, 3 and 4 shows the currents of the transistors T _A , T _B and T _C. Figure 5 shows the current through the diode D3. The source of current through the diode is the energy of the inductor Dr, accumulated during the open state of the power transistor T. Figure 6 shows the nature of the current in the load channel - silicon rods. The choice of three-phase control of power transistors allowed to reduce the heat load on each transistor.

The constant nature of the current in the load is achieved through the use of a power inductor Dr and a diode D3, turned on in the opposite direction to the power transistor. Additional smoothing of the direct current at the load is carried out by a filtering capacitor C2.

The silicon rod of the load channel (Figure 5) consists of three specially prepared (alloyed) silicon rods 11, 12 and 13, connected in series. In the starting mode, when the silicon rods are cold and the resistance of each of them is about 25 Ohms, the scheme for starting heating of the rods is turned on. In this case, the contactors K5 and K6 are turned on, which shunt two of the three rods. There is heating and "breakdown" of the rod 13 by the operating voltage of the Converter. Its resistance in this state becomes an order of magnitude smaller. Accordingly, the voltage on it also drops. Next, the K6 switch turns off. A second rod 12 is connected to the device. Heating and breakdown of the second rod occur together with the first. Then the K5 switch turns off. The third rod 11 is connected to the device. It heats up and breaks down. Thus, for the starting heating of the rods, an additional high-voltage power supply or a special heating circuit of silicon rods is not required. After thermal “breakdown” of the rods and bringing them to the required temperature, the process of growing silicon begins.

During the process of growing silicon rods, as their diameter grows, their resistance decreases and, consequently, the voltage drop across the rods decreases. When the voltage at the rods is less than 500 V, the K2-K4 contactors are switched in the power rectifier unit (Fig. 1) and the rectifiers are switched to the parallel mode of two 500 V rectifiers. A voltage of 500 V is set at the input of the controller-converter. This mode decreases load on the diodes of power rectifiers; heat losses on power transistors and chokes are reduced without reducing the current on silicon rods.

The inventive device provides a high degree of use of electric energy, allows to obtain high quality DC power on the rods.

Depending on the size of the hydrogen reduction reactor of polychlorosilanes, the device may contain several load channels with silicon rods and, accordingly, several channels of controlled heating of silicon rods.

Claims (1)

A device for controlled heating of silicon rods containing a power transformer, to the secondary windings of which a group of semiconductor rectifier bridges is connected through a switching unit, and a pulse-phase control and current control unit connected in series with silicon rods, characterized in that the switching unit of semiconductor rectifier bridges is made according to the scheme, providing series or parallel connection of rectifier bridges, a pulse-phase control unit and the current control contains a group of power transistors with an RC circuit for suppressing impulse noise connected in parallel and controlled by high-frequency pulses generated by a pulse-phase control circuit, while the device has a choke connected in series with a group of power transistors and a load channel consisting of several silicon rods, a filtering capacitor connected in parallel to the load channel and a diode connected to the common output of the group of transistors in the opposite direction and the closure conductive circuit inductor current through the load channel during a closed state of the transistor switch, wherein the traffic channel comprises switches which shunt a part of the silicon rods during their successive start heating.

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