RU2279178C1 - Three-phased controllable rectifier - Google Patents

Abstract

FIELD: power transformation equipment engineering, possible use in direct current power systems, for powering direct current electric engines, in power rectification plants, powered by electric energy sources of limited power.

SUBSTANCE: three-phased controllable rectifier consists of power gates block, assembled in accordance to three-phased bridge circuit, input and output filter, rectified voltage indicator and control system, which contains synchronization device, power gates block uses fully controlled gates (transistors) as keys, while control system includes saw-shaped voltage generator, control pulse generator, cyclic shift register, device for comparing phase voltages and circuit for selecting gates to be enabled. Output of saw-shaped voltage generator is connected to first input of control pulse generator, to second input of which output of rectified voltage indicator is connected. Output of control pulses generator is connected to input of cyclic shift register, having three outputs, by which it is connected to three of six inputs of circuit for selecting gates to be enabled. To remaining three inputs of circuit for selecting gates to be enabled outputs of device for comparing phase voltages are connected. By its three inputs device for comparing phase voltages is connected to phase voltages of power network. Six outputs of circuit for selecting gates to be enabled through synchronization device are connected to control outputs of power gates of power gate block.

EFFECT: power coefficient for three-phased controllable rectifier is always equal to one, decreased mass and dimensions of three-phased controllable rectifier.

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Description

The invention relates to power converting equipment and can be used in DC power supply systems, for powering DC electric drives, in power rectifier units powered by limited power sources of electric energy.

Known three-phase bridge uncontrolled rectifier [Rudenko B.C., Senko V.I., Chizhenko I.M. Basics of the conversion technology. Textbook for high schools. - M .: Higher. School, 1980, 424 pp.]. The main components of the rectifier are a step-down transformer and a block of power valves. The step-down transformer is designed to match the high supply voltage and low voltage at the output of the rectifier. The gates perform the conversion of the kind of current.

The main disadvantages of such a rectifier are the large mass and dimensions due to the use of a matching transformer, the low quality of the rectified voltage, which is reflected in the high level of ripple of the rectified voltage and the absence of its regulation and stabilization, as well as the low value of the power factor due to the high content of higher harmonics in the current spectrum consumed from the mains. Recent disadvantages determine the low level of electromagnetic compatibility of the specified rectifier with the mains and with the load.

The closest known is a three-phase bridge controlled rectifier [Rudenko B.C., Senko V.I., Chizhenko I.M. Basics of the conversion technology. Textbook for high schools. - M .: Higher. School, 1980, 424 pp.]. The main components of the rectifier are a step-down transformer, a block of power valves assembled according to a three-phase bridge circuit, input and output filters, a rectified voltage sensor and a control system. The control system includes: a zero-organ, phase shifting device, a pulse distributor and a matching device, which ensures coordination of the control system with the power unit.

As valves in a three-phase bridge controlled rectifier, power low-frequency, not fully controlled thyristor valves are used. As you know, not fully controllable valves allow you to control only the moment they are turned on (open), and the valves are locked regardless of the control system when blocking conditions occur. Therefore, the use of incompletely controlled gates does not allow flexible control of a three-phase bridge controlled rectifier and arbitrarily (efficiently) form the current consumed from the supply network and the rectified voltage.

According to the operating conditions, a three-phase bridge controlled rectifier consumes a current from the supply network, the shape of which differs from the sinusoidal one, i.e. the spectrum of the consumed current contains higher harmonic components. In addition, the first harmonic of the current lags in phase from the first harmonic of the supply voltage (φ ₁ ≠ 0). Moreover, the larger the control angle, the greater the distortion of the current shape (the higher harmonics in the current spectrum) consumed from the supply network, and the greater the phase shift between the first harmonics of the current and voltage.

As a result, the power factor of a three-phase bridge controlled rectifier calculated by the formula

where λ is the power factor;

P, S - active and full power consumed by the rectifier;

U ₁ , I ₁ and cosφ ₁ are the first harmonics of the current and voltage, as well as the phase shift angle between them;

U, I are the effective values of the total voltage and the total current of the rectifier, containing both the first and the highest harmonics;

γ _U , γ _i are the distortion coefficients of voltage and current, respectively, if there are no higher harmonics, then the distortion coefficients are equal to unity,

it will be approximately equal to 0.8 for a control angle of zero, and decreases to 0.5 for control angles of 60-70 electrical degrees. To ensure stable stabilization of the rectified voltage, three-phase bridge controlled rectifiers operate at control angles greater than 50 electrical degrees. Therefore, the value of the power factor of three-phase bridge controlled rectifiers is much less than unity.

In addition, the rectified voltage of a three-phase bridge controlled rectifier, made on incompletely controlled valves, contains in its spectrum low-frequency harmonic components (from 300 Hz and above). Moreover, the ripple depth of the rectified voltage, and therefore the amplitude values of the higher harmonic components, depend on the control angle of the rectifier. The larger the control angle, the greater the depth of the ripple.

To reduce the ripple of the rectified voltage at the output of three-phase controlled and uncontrolled rectifiers set smoothing filters [Rudenko B.C. and other Fundamentals of the conversion technology. Textbook for high schools. - M .: Higher. school, 1980, 424 pp.], which provide filtering of the higher harmonic components of the rectified voltage and thereby provide a reduction in the ripple factor:

where K _n is the ripple coefficient of the rectified voltage;

U _d is the constant component of the rectified voltage;

U _m ⁽ⁿ⁾ is the amplitude value of the nth harmonic component of the rectified voltage,

and therefore, provide the electromagnetic compatibility of the rectifier with the load.

A distinctive feature of the output filters of three-phase bridge controlled rectifiers on incompletely controlled valves is that they are designed to filter low-frequency harmonic components (from 300 Hz). This leads to a large mass and dimensions of the constituent elements of the filter and the rectifier as a whole [Rudenko B.C., Senko V.I., Chizhenko I.M. Basics of the conversion technology. Textbook for high schools. - M .: Higher. School, 1980, 424 pp.].

As for the input filters of three-phase bridge controlled rectifiers, they are not designed to filter the low-frequency harmonic components of the current consumed by the rectifier from the mains, but are used only for filtering high-frequency harmonic components due to switching of the rectifier valves. Therefore, the input filter of a three-phase bridge controlled rectifier, firstly, does not remove the low-frequency harmonic components from the spectrum of the current consumed from the supply network and, therefore, practically does not increase the power factor of a three-phase controlled rectifier, and secondly, it has small mass and dimensions .

Thus, the main disadvantages of a three-phase bridge controlled rectifier are the large mass and dimensions, as well as the small value of the power factor, especially at large control angles. The last disadvantage is caused by the low level of electromagnetic compatibility of a three-phase bridge controlled rectifier with a power supply network.

The objective of the invention is the creation of a three-phase controlled rectifier, providing a high level of electromagnetic compatibility with the supply network, as well as its small weight and dimensions.

The technical result is the provision of a power factor of a three-phase controlled rectifier equal to unity and a decrease in the mass and dimensions of a three-phase controlled rectifier.

The technical result is achieved by the fact that in a three-phase controlled rectifier, consisting of a block of power valves assembled according to a three-phase bridge circuit, an input and output filter, a rectified voltage sensor and a control system containing a matching device, in the block of power valves are installed as keys fully controlled valves (transistors), and the control system includes a sawtooth voltage generator, a control pulse shaper, a cyclic shift register, a device in comparison of phase voltages and the circuit for selecting the valves included. Moreover, the output of the sawtooth voltage generator is connected to the first input terminal of the control pulse shaper, to the second input terminal of which the rectified voltage sensor output is connected. The output terminal of the control pulse shaper is connected to the input terminal of the cyclic shift register having three output terminals, by which it is connected to three of the six input terminals of the switching valves selection circuit. The remaining three input terminals of the circuit for selecting the valves to be connected are connected to the output terminals of the phase voltage comparison device. With its three input terminals, the phase voltage comparison device is connected to the phase voltages of the supply network. The six output terminals of the circuit for selecting the valves to be switched on through a matching device are connected to the control terminals of the power valves of the power valve block.

The use of fully controllable valves as part of a three-phase controlled rectifier, as well as the use of the above elements of the control system, allows flexible control of keys at a frequency several thousand times higher than the switching frequency in a three-phase bridge controlled rectifier. Thanks to the implemented algorithm of operation of a three-phase controlled rectifier, its input current has an almost sinusoidal shape with a phase shift angle relative to the first harmonic of the supply voltage equal to zero, and the rectified voltage contains only a constant component in its spectrum. The high-frequency components of the input current are closed on the input filter, and the high-frequency components of the rectified voltage are on the output filter. Since the input and output filters are designed to suppress harmonic components with numbers exceeding ten kilohertz, the reactive elements of the filters have a small mass and dimensions.

These distinctive features of a three-phase controlled rectifier make it possible: firstly, to provide a power factor of the rectifier (formula 1) equal to unity; and secondly, to reduce the mass and dimensions of a three-phase controlled rectifier by eliminating a three-phase power transformer from its composition, as well as by reducing the mass and dimensions of the output filter.

Thus, the set of essential features of the invention set forth in the claims, helps to achieve the desired technical result.

Figure 1 presents the structural diagram of a three-phase controlled rectifier.

2 and 3 are timing diagrams explaining its operation.

A three-phase controlled rectifier (Fig. 1) consists of an input filter 1, a block of power valves 2 assembled according to a three-phase bridge circuit, an output filter 3, a control system 4, and a rectified voltage sensor 5. A load 6 is connected to the rectifier.

The control system 4 includes: a device for comparing phase voltages 7, the input terminals of which are connected to the phase conductors of the supply network, and the output terminals to three input terminals of the selection circuit of the included valves 8; matching device 9, connected by its input terminals to the output terminals of the selectable valves 8 selection circuit, and by the output terminals to the control terminals of the power valves 10, 11, 12, 13, 14, 15 of the power valve block 2; a sawtooth voltage generator 16 connected to the first input terminal of the control pulse shaper 17, made on the basis of a comparator, to the second input terminal of which the output voltage sensor 5 is connected, and a cyclic shift register 18 connected by the input terminal to the pulse generator 17, and the output terminals with the other three input terminals of the selectable valves 8 selection circuit.

The rectifier operates as follows.

The sawtooth voltage generator 16 generates a sawtooth voltage at the conversion frequency (Fig. 2, curve 1, a). The conversion frequency is determined by the capabilities of the element base of the rectifier and can range from units of kilohertz to hundreds of kilohertz. For clarity, the principle of operation of the rectifier in the time diagrams of figure 2, the conversion frequency is chosen equal to about 3 kHz.

A sawtooth voltage is supplied to one of the inputs of the comparator, which is part of the control pulse shaper 17. The voltage from the rectified voltage sensor 5 is supplied to the second input of the same comparator (Fig. 2, curve 1, b), which is proportional to the rectified voltage of the rectifier. In the comparator, two signals are compared and at its output, a sequence of logical zeros and ones is formed according to the result of the comparison. Moreover, at intervals where the sawtooth voltage is greater than the voltage of the rectified voltage sensor, a logical unit signal is generated at the output of the comparator, and a logical zero signal is generated at the remaining intervals. As a result, at the output of the control pulse generator 17, a pulse sequence is obtained (Fig. 2, curve 2). The pulse frequency determines the switching frequency of the valves, and the width of each pulse corresponds to the open time of the corresponding pair of transistors. Since the open time of the transistors is proportional to the value of the rectified voltage, then, by changing the duty cycle of the pulses, the rectified voltage of the three-phase controlled rectifier is regulated.

The generated pulse sequence arrives at the cyclic shift register 18, which distributes the received pulses alternately across three channels. The first channel (figure 2, curve 3) controls the connection of the interphase voltage U _AB to the load, the second channel (figure 2, curve 4) controls the voltage U _BC , and the third channel (figure 2, curve 5) controls the voltage U _CA The signals of the cyclic shift register are fed to the selection circuit of the included valves 8.

Simultaneously with the signals from the cyclic shift register 18 (Fig. 1), the signals from the device for comparing the phase voltages 7 are supplied to the selectable valves 8 selection circuit. These signals are also fed through three channels (Fig. 2, curves 7-9) in the form of logical zeros and units. The first channel (figure 2, curve 7) has a unit potential if the interfacial voltage u _ab (figure 2, curves 6) is positive, and zero potential if it is negative. The potential of the second channel (figure 2, curve 8) reflects the sign of the phase-to-phase voltage u _bc (figure 2, curves 6), and the potential of the third channel (figure 2, curve 9) reflects the sign of the phase-to-phase voltage u _ca (figure 2, curves 6).

The selection circuit of the included valves 8 (Fig. 1), comparing the signals from the cyclic shift register 18 about the sequence and time of connecting interphase voltages to the load with information from the comparison device 7 about the polarity of the corresponding voltage, generates control signals for the power valves (Fig. 2, curves 10 -fifteen). Moreover, the curves 10, 11, 12, 13, 14 and 15 correspond to the control signals of the valves 10, 11, 12, 13, 14 and 15. These signals are transmitted through six channels to the matching device 9 (figure 1).

The coordination device 9 is intended for matching control signals generated by the control system with the signals of the rectifier power circuit for voltage and power, and also, if necessary, for galvanic isolation of the power circuit and control system, i.e. at the output of the matching device, the waveform will remain the same as at its input.

Ultimately, the control signals 10-15 (figure 2), acting on the valves 10-15 (figure 1) of the block of power valves 2, provide consumption of input currents i _a , i _b and i _c , the form of which is shown in curves 16- 18 (FIG. 2). At the same time, at the output of the power valve unit 2, a rectified voltage u _{d is formed} , the shape of which is shown in diagram 19 (figure 2). The currents i _a ', i _b ' and i _c 'and the voltage u _d ' correspond to the mode of operation of the rectifier without input and output filters.

2 shows rectifier diagrams for a reduced conversion frequency. To obtain instantaneous values of the rectifier currents and voltages at the real conversion frequency, Fig. 3 shows timing diagrams similar to diagrams 6, 16-19 (Fig. 2) for a conversion frequency of 15 kHz. In addition, figure 3 shows a three-phase voltage system u _a , u _b , u _c (curve 2).

As can be seen from the time charts 3-5 (figure 2), the shape of the currents consumed by the power valve block 2 (figure 1) of the rectifier differs from the sinusoidal (currents i _a ', i _b ' and i _c '). However, the use of an input filter 1 (Fig. 1) provides filtering of high-frequency harmonics in the input circuits of the rectifier.

As a result, currents consumed from the mains rectifier for each phase (Figure 3, curves 3-5) are substantially sinusoidal _{(i a, i b, i} c) and in phase with the supply voltages u _a, u _a, u _c ( figure 3, curves 2), i.e. cosφ1 = 0.

This means that the power factor of the proposed rectifier, calculated by the formula 1, will be almost equal to unity. Consequently, the rectifier will provide full electromagnetic compatibility with the mains.

The use of an output filter provides smoothing of the rectified voltage of the rectifier. As a result, the rectified voltage of the rectifier will contain only a constant component u _d , which, in turn, means that the ripple coefficient of the rectified voltage calculated by formula 2 will be zero, i.e. The rectifier will provide full electromagnetic compatibility with the load.

Moreover, the mass and dimensions of the output filter of the proposed rectifier will be significantly lower than the mass and dimensions of the analogue. This is because the harmonic frequency of the proposed rectifier is one to two orders of magnitude higher than the frequency of the harmonic spectrum of the analog. And, as you know [Rudenko B.C., Senko V.I., Chizhenko I.M. Basics of the conversion technology. Textbook for high schools. - M .: Higher. school, 1980, 424 pp.], the electrical parameters and dimensions of the reactive elements of the high-pass filter are significantly lower than the low-pass filter. Therefore, the mass and dimensions of the filter for the proposed rectifier will be significantly less than that of the analogue.

Therefore, the reduction in the mass and dimensions of the proposed rectifier in comparison with the analogue is ensured not only due to the absence of a power matching transformer, but also by reducing the mass and dimensions of the output filter.

Claims (1)

A three-phase controlled rectifier, consisting of a block of power valves assembled according to a three-phase bridge circuit, an input and output filter, a rectified voltage sensor and a control system containing a matching device, characterized in that fully controlled valves are installed as keys in the block of power valves - transistors, and the control system includes a sawtooth voltage generator, a control pulse shaper, a cyclic shift register, a phase voltage comparison device and a circuit for selecting the valves to be turned on, the output of the sawtooth generator being connected to the first input terminal of the control pulse generator, the output of the rectified voltage sensor connected to the second input terminal, and the output terminal of the control pulse generator connected to the input terminal of the cyclic shift register having three output terminals with which it is connected to three of the six input terminals of the circuit for selecting the included valves, to the other three input terminals of the circuit for selecting the included vents leu connected to the output terminals of the phase voltage comparison device which three of its input terminals connected to phase conductors of a power line, and six output terminals included selection circuits valves via a matching device connected to the control gates of power terminals of power valve block.

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