RU2431914C1 - Frequency converter control method - Google Patents

Abstract

FIELD: physics. ^ SUBSTANCE: in the method of controlling a frequency converter comprising a power supply filter, a single-phase rectifier, a clamp, a single-phase inverter on controlled rectifier diodes, a switching capacitor and switching inductor, which form a series resonant circuit with the load, control pulses are generated and successively transmitted to the rectifier diodes of the inverter, which form direct and inverse half-waves of alternating current in the load and they are switched on with frequency higher than the resonance frequency of the series resonant circuit. Instantaneous voltage across the output of the rectifier is measured. Frequency of switching on the rectifier diodes is controlled, respectively reduced and increased directly proportional to the measured instantaneous voltage across the output of the rectifier. ^ EFFECT: reduced current pulsation in the load of the frequency converter caused by pulsation of the output voltage of the single-phase rectifier. ^ 2 dwg

Description

The invention relates to a conversion technique and can be used in control systems with transistor frequency converters for electrical technologies, as well as in electronic ballasts for gas discharge lamps and drivers for powering high-power LEDs.

A known method of controlling a frequency converter containing a single-phase rectifier with a capacitive filter, a single-phase inverter on controlled valves, a choke, which forms a load with a series circuit, consisting in the fact that form and alternately supply control pulses to the inverter valves, forming the direct and reverse AC half-waves in load (Russian patent 2061292, MKI H05M 5/44. A method for controlling a frequency converter / EM Silkin - application. 09/22/92. Publish. 05/27/96. - Bull. No. 15).

The disadvantage of the control method is the high level of ripple of the load current of the frequency converter, due to ripple voltage at the output of the rectifier.

A known method of controlling a frequency converter containing a single-phase rectifier with a capacitive filter, a single-phase inverter on controlled gates, a switching capacitor and a switching inductor, which form a load with a series resonant circuit, which consists in generating and supplying control pulses to the inverter valves, forming a direct and reverse AC half-waves in the load, and they are turned on with a frequency close to the resonance frequency of the serial resonant circuit (Russian patent 202 5881, MKI Н02М 7/538. AC converter for inductor supply / EM Silkin et al. - Application 03.09.91. Publish. 30.12.94. - Bull. No. 24).

The disadvantage of the control method is the high level of ripple of the load current of the frequency converter, due to ripple voltage at the output of the rectifier.

A known method of controlling a frequency converter containing a line filter, a single-phase rectifier, a single-phase inverter on controlled gates, a switching capacitor and a switching inductor, forming a series resonant circuit with a load, which consists in generating and supplying control pulses to the inverter valves, forming a direct and reverse AC half-waves in the load, and they are switched on with a frequency close to the resonance frequency of the serial resonant circuit (AS USSR 1778896, MKI N02M 5/45. Frequency converter / Silkin EM et al. - Application. March 25, 91. Publish. August 1, 92. - Bull. No. 44).

This method of controlling a frequency converter is the closest in technical essence to the invention and is considered as a prototype.

The disadvantage of the control method is the high level of ripple load current of the frequency converter, due to ripple voltage at the output of a single-phase rectifier.

The invention is aimed at solving the problem of reducing current ripple in the load of the frequency converter, due to ripple of the output voltage of a single-phase rectifier, which is the purpose of the invention.

This goal is achieved by the fact that in the method of controlling a frequency converter containing a line filter, a single-phase rectifier, a clamp, a single-phase inverter on controlled gates, a switching capacitor and a switching choke, which form a load with a serial resonant circuit, which consists in generating and alternating pulses controls on the inverter valves forming the forward and reverse AC half-waves in the load; the inverter valves turn on with a frequency exceeding the resonance frequency after phase resonance circuit, measure the instantaneous voltage at the output of the rectifier, regulate, respectively, reduce and increase the frequency of switching on the inverter valves is directly proportional to the measured instantaneous voltage at the output of the rectifier.

A significant difference that characterizes the invention is the reduction of current ripple in the load of the Converter, due to ripple of the output voltage of a single-phase rectifier, smoothed by the action of the clamp. Measurement of the instantaneous voltage value at the output of the rectifier, regulation, respectively, decrease and increase, the switching frequency of the inverter valves is directly proportional to the measured instantaneous voltage at the output of the rectifier, operation at a frequency exceeding the resonance frequency of the series resonant circuit allows you to compensate for the dependence of the instantaneous load current on the output voltage ripples single phase rectifier.

The reduction of current ripple in the load of the converter due to ripple of the output voltage of a single-phase rectifier is a technical result due to new actions and the order of their implementation in the control method of the frequency converter, that is, the distinguishing features. Thus, the distinguishing features of the proposed method for controlling a frequency converter are essential.

Figure 1 shows a diagram of a device for implementing a method of controlling a frequency converter, figure 2 is a timing diagram of the processes in the circuit elements that explain the principle of control.

A method for controlling a frequency converter containing a line filter, a single-phase rectifier, a clamp, a single-phase inverter on controlled gates, a switching capacitor and a switching choke, which form a series resonant circuit with a load, is implemented by the following steps. Control pulses are formed and alternately fed to the inverter valves, which form the forward and reverse AC half-waves in the load. The inverter valves are turned on with a frequency exceeding the resonance frequency of the series resonant circuit. The instantaneous voltage at the rectifier output is measured. Regulate, respectively, reduce and increase, the frequency of inclusion of the inverter valves is directly proportional to the measured instantaneous voltage at the output of the rectifier.

A device diagram for implementing a method of controlling a frequency converter includes a line filter 1, a single-phase rectifier 2, a clamp 3, a single-phase inverter 4 on controlled gates, a switching capacitor 5 and a switching choke 6, which form a series resonant circuit with a load 7, the control unit of the device 8, input which is supplied with voltage from the output of the rectifier, and the outputs of the control unit of the device are connected to the control electrodes of the controlled inverter valves.

The device operates as follows. The control unit 8 generates and alternately delivers control pulses to the controlled valves of the inverter 4. The control unit 8 can be based on any of the known voltage-controlled oscillator circuits and output stages. The instantaneous voltage from the output of the rectifier 2 controls the generator of the control unit 8, as a result of which it is regulated, respectively decreases and increases, the switching frequency of the inverter 4 valves is directly proportional to the measured instantaneous voltage at the output of the rectifier 2. The alternating voltage of the supply network is converted to a constant by the rectifier 2. To ensure The electromagnetic filter 1 serves as the electromagnetic compatibility of the device with the mains. The rectified voltage from the output of a single-phase rectifier 2, which has high ripple, filtered clamp 3. The output of voltage clamp 3 also has a residual ripple (Figure 2). The clamp is made in the form of a ripple-limiting voltage device, similar to the known ones (diode-capacitive or diode-capacitive-resistive circuit). The voltage from the output of the clamp 3 is supplied to the input of the inverter 4 on the controlled valves. The inverter 4 valves turn on alternately. For the full cycle of operation of the valves forming the direct and reverse half-wave current in the load 7, a complete period of the output alternating current of the device is formed. An increase in the output frequency of the inverter 4 relative to the resonance frequency of the serial resonant circuit (detuning of the serial circuit) formed by the switching capacitor 5, the switching choke 6 and the load 7 leads to a decrease in the voltage levels at the switching capacitor 5 and the current through the load 7. This compensates for the increase in the current through the load 7, due to the increase in voltage at the output of the rectifier 2. The decrease in the output frequency of the inverter 4 relative to the resonance frequency of the series resonant circuit we (setting the circuit), formed by the switching capacitor 5, the switching inductor 6 and the load 7, leads to an increase in the voltage levels at the switching capacitor 5 and the current through the load 7. This compensates, respectively, the decrease in the current through the load 7, due to the decrease in the voltage at the rectifier output 2. Thus, the regulation of the output frequency of the inverter 4 (switching frequency of the valves) as a function of the level of the instantaneous output voltage of the rectifier 2 allows you to compensate for the change in the load current 7, due to fief change in inverter power supply 4, and reduce the ripple of the load current. The timing diagrams of FIG. 2 illustrate the operation of the device and the principle of controlling the frequency converter. The diagram of figure 2 shows the instantaneous voltage at the output of the rectifier 2, filtered by a clamp 3. The voltage is applied to the input of the control unit 8. The switching frequency of the inverter 4 valves also changes (directly proportionally).

Compared with the prototype, the use of the proposed method for controlling the frequency converter can significantly reduce the ripple of the load current due to ripple voltage at the output of a single-phase rectifier. The current through the load is stabilized by appropriate tuning and detuning (relative to the resonance frequency) of the series resonant circuit. When designing, for example, a control system for an electrotechnological installation, such stabilization can significantly reduce the requirements for circuit elements and, first of all, for power valves, increase the reliability of the device and the repeatability of technological processes. With regard to electronic ballasts for discharge lamps, in addition to the above, a noticeable decrease in the pulsations of the radiation of the lamps should be noted. Drivers for powering LEDs, made using the proposed control method, provide more stable operation of LED systems.

Compared with the prototype, ripple current loads can be reduced by more than 95% relative to the initial values without complicating the power part of the converter devices.

Claims (1)

A method of controlling a frequency converter containing a line filter, a single-phase rectifier, a clamp, a single-phase inverter on controlled gates, a switching capacitor and a switching choke, which form a load with a series resonant circuit, which consists of generating and supplying control pulses to the inverter valves forming a direct and the reverse AC half-wave in the load, and they are turned on with a frequency exceeding the resonance frequency of the serial resonant circuit, measure the instant apryazhenie at the output of the rectifier is controlled respectively decrease and increase the switching frequency of the inverter valves is directly proportional to the instantaneous voltage measured at the output of the rectifier.

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