CN1610230A - Three-phase power factor correcting circuit with AC boosting mode - Google Patents

Abstract

A three-phase power factor correction circuit in AC boost mode is used for inverter power supply. There is no 10KW high-power three-phase power factor correction circuit for continuous inductor current. Features of the present invention: three-phase grid star connection, output terminals Via, Vib, Vic are connected in series with one end of EMI and inductance La, Lb, Lc; the other end of La is connected with VD1 anode and one end of bidirectional power switch tube module Sa ; The other end of Lb is connected to the anode of VD3 and one end of Sb; the other end of Lc is connected to the anode of VD5 and one end of Sc; the rectifier bridge composed of diodes VD1 ~ VD6; capacitors C1 and C2 are connected in series; VD1, VD3, The cathode of VD5 is connected to the positive pole of C1; the anodes of VD2, VD4, VD6 and the negative pole of C2 together form the negative pole of electricity; the other end of Sa, Sb, Sc is connected to the negative pole of C1, the positive pole of C2, and the common connection of C1 and C2 The point and zero line are connected or independent; the invention simplifies the control, and improves the power factor of the arc welding inverter power supply using the capacitor filter rectifier circuit as the input stage from 0.6-0.7 to 0.98-1.

Description

A Three-Phase Power Factor Correction Circuit in AC Boost Mode

technical field

This technology belongs to the field of power electronics technology, and its main application scope is inverter arc welding power supply and other inverter power supplies.

Background technique

With the acceleration of industrialization worldwide, energy and environmental protection have been paid more and more attention. In addition to rationally developing energy and finding new energy sources to solve energy problems, self-tapping potential and improving energy utilization efficiency have also been mentioned in various industries. Environmental protection is no longer limited to the treatment of waste gas, waste water, waste residue, and noise. Electromagnetic pollution has been identified as the fifth largest source of pollution.

Harmonic pollution and radio frequency pollution are typical electromagnetic pollution. Electric processing of materials is the industry that consumes the most electricity, such as various casting, welding, forging, heat treatment and machining equipment, all use heat or kinetic energy converted from electric energy. The load conditions of material electric processing equipment are almost all highly nonlinear, such as high frequency induction heating, arc heating, electron beam heating, electrolysis, electroplating, and electrical equipment using rectified input (such as voltage regulating equipment, frequency conversion speed regulation and inverter variable power supply, etc.). These nonlinear loads make the power supply grid contain a large number of high-order harmonics. On the one hand, the power factor of the equipment is greatly reduced, resulting in a great waste of transmission loss and power supply capacity. On the other hand, it seriously pollutes the grid and affects the normal operation of other equipment. Make computer control equipment malfunction, and even cause power distribution accidents.

As a typical power electronic device, the inverter welding power supply has the advantages of small size, light weight, and good control performance, but it is essentially a large rectified power supply for the grid. The input current waveform of the inverter power supply is a sharp angle wave, as shown in Figure 1, which makes the power grid contain a large number of high-order harmonics. There is a serious phase shift between high-order voltage and current harmonics, resulting in a very low power factor of the welding machine. The problem of low-frequency harmonic distortion is a common problem in current power electronic equipment. The most effective way to solve it is to connect a harmonic suppression device at the input end of the equipment.

Power factor correction usually adds a Boost circuit after the bridge rectification, as shown in Figure 2, through the switching action of the power element, the input current becomes a sine wave that is almost in phase with the grid voltage, which can reduce the current distortion rate. To below 5%, the power factor can be improved to 0.99 or higher.

The basic principle of its work is: when the power switch tube S (controlled by the control circuit) is turned on, the input voltage Vin is all added to the inductor L, and as the input voltage Vin rises, the current through the inductor L also rises; when When the power tube is turned off, the inductor generates an induced voltage V _L with the same polarity as the input voltage. At this time, the voltage across the power tube is Vin+V _L , and the voltage is sent to the capacitor C through the diode D. In this way, the average current input to the inductor L will track the change of the sinusoidal voltage, and the current waveform is close to the sinusoidal wave with the same phase as the voltage, so that the power factor is close to 1. In order to realize the function of harmonic suppression, the output voltage Vo of the BoostPFC circuit must be greater than the peak voltage output by the rectifier. Moreover, the power tube is placed on the DC side of the rectifier bridge, the current passing through the power tube is DC, and only the power switch tube through which the unidirectional current passes is required.

Active power factor correction circuits are divided into single-phase power factor correction and three-phase power factor correction according to different application objects, and are divided into inductor current continuous mode (CCM) and inductor current discontinuous mode (DCM) according to the working mode of the circuit. Experts in the field of power electronics at home and abroad have conducted in-depth research on single-phase power factor correction technology. In the field of welding power supplies, there have been articles on power factor correction of single-phase low-power inverter welding power supplies in China. However, due to the high technical difficulty of the three-phase power factor correction circuit, it is difficult to realize the harmonic suppression of the three-phase circuit by the simple combination of the single-phase power factor correction circuit. Foreign scholars are only at the preliminary research stage. The working mode of the circuit generally adopts the inductive current discontinuous mode. The power switch of the circuit bears a relatively large current and voltage stress, which is only suitable for three-phase low-power equipment with stable loads. For the inductive current The continuous 10KW high-power three-phase power factor correction circuit has not yet been published. Domestic articles on three-phase power factor correction are seldom published, and they are all operated under the condition of small power output. With the advancement of device manufacturing technology and high-frequency power conversion technology, power factor correction technology has gradually penetrated into medium and high-power rectifier power supplies, so this method will definitely make a great contribution to the control of harmonic pollution, so new research must be done Harmonic suppression scheme suitable for high-power three-phase circuits.

Contents of the invention

The invention adopts the power factor correction circuit topology of the AC boost mode to replace the traditional capacitance filter diode rectification circuit.

A three-phase power factor correction circuit in AC boost mode, characterized in that, according to the three-phase balance rule, the inductance La, Lb, and Lc in the circuit are the same, the diodes VD1-VD6 are the same, the capacitors C1, C2 are the same, and the bidirectional power switch The tube modules Sa, Sb, and Sc are the same; the three-phase power grid is connected in star form, and its output terminals Via, Vib, Vic are serially connected with one end of the high-frequency EMI, that is, the Electro Magnetic Interference electromagnetic interference filter module and the inductors La, Lb, and Lc. The other end of La is connected together with the anode of VD1 and one end of bidirectional power switch module Sa; the other end of Lb is connected with the anode of VD3 and one end of bidirectional power switch module Sb; the other end of Lc is connected with VD5 The anode and one end of the bidirectional power switch tube module Sc are connected together; in the rectifier bridge composed of diodes VD1~VD6, the anode of VD1 is connected to the cathode of VD2, the anode of VD3 is connected to the cathode of VD4, the anode of VD5 is connected to the cathode of VD6 Connection; the DC side capacitors C1 and C2 for filtering are connected in series; the cathodes of VD1, VD3, VD5 and the positive pole of C1 are connected together to form the positive pole of the load power supply; the anodes of VD2, VD4, VD6 and the negative pole of C2 are connected in Together form the negative pole of the load power supply; the other end of the bidirectional power switch tube modules Sa, Sb, and Sc must be connected to the negative pole of C1 and the positive pole of C2, and the common connection point of C1 and C2 is connected to the neutral line of the three-phase grid or Independent of each other; the above-mentioned bidirectional power switch module is composed of one of the two ways shown in Figure 5, one way is to connect two power switch elements VT1 and VT2 with anti-parallel diodes, as shown in Figure 5 (a) As shown, the gates of VT1 and VT2 are connected together, the emitters are connected together, the collector of VT1 is connected with the cathode of D1 to form one end of the bidirectional power switch module, and the collector of VT2 is connected with the cathode of D2 to form a bidirectional power switch module. The other end of D1, D2 and the emitters of VT1 and VT2 are connected together; another way is shown in Figure 5(b), connecting a power switching element VT to a power switch element VT connected by D-1, D -2. The DC output terminal of the single-phase rectifier bridge composed of D-3 and D-4. The positive pole of the DC output terminal of the single-phase rectifier bridge is connected to the collector of VT, and the negative pole of the DC output terminal of the rectifier bridge is connected to the emitter of VT. The AC input terminals of the phase rectification bridge serve as two terminals of the bidirectional power switch module.

A three-phase power factor correction circuit in AC boost mode, characterized in that the diodes in the rectifier bridge composed of diodes VD1-VD6 are diodes with fast recovery characteristics.

A three-phase power factor correction circuit in AC boost mode, characterized in that the power switching elements VT1 and VT2 and the power switching element VT are MOSFETs or IGBTs.

A three-phase power factor correction circuit in an AC boost mode, characterized in that the inductance range of the inductance La, Lb, and Lc is 1mH-7mH, the capacitance range of the filter capacitor is 470uF-3300uF, and the switch of the power device The frequency can be in the range of 15KHz to 25KHz.

The whole circuit is composed of three sets of AC Boost circuits. At every instant when the circuit works, these three sets of AC Boost circuits work simultaneously, and each phase of the power supply provides energy to the output terminal, which is different from that of conventional diode rectifiers. is different. From the perspective of the entire circuit structure, the boost inductor and the power switch are placed on the input side of the three-phase rectifier bridge in turn, and the AC input voltage of the rectifier is increased by changing the closed state of the bidirectional power switch tube, and at the same time, the AC input voltage of each phase is increased. The input inductor current directly tracks the sine wave waveform, which is different from the inductor current tracking the half-wave sine wave in the single-phase harmonic suppression circuit. This circuit also uses this characteristic of the circuit to realize the harmonic suppression of the input current of the three-phase circuit.

The basic principle of the circuit work of the present invention is: taking phase a as an example, when Via is positive, a single-phase Boost PFC circuit is composed of La, Sa, VD1, and C1; when Via is negative, it is composed of La, Sa, VD2, C2 forms a single-phase Boost PFC circuit, and so on for the other two phases. In this way, at any moment, each phase is connected with a Boost PFC circuit, and the circuit control method can adopt any mature single-phase power factor correction control method, such as average current control. These three sets of AC booster circuits can use the same control circuit, and each set of circuits uses its own current feedback loop and the same voltage feedback loop to form a multi-closed loop system with three current feedback inner loops and one voltage feedback outer loop. .

The invention is a three-phase power factor correction circuit of AC boost mode, which is characterized in that the diodes used in the rectification bridge adopt diodes with fast recovery characteristics instead of the diodes used in common rectification bridges. The purpose is to reduce the power loss caused by diode rectification, further improve the power factor of the system and the stability of the system.

The present invention is a three-phase power factor correction circuit of AC boost mode, which is characterized in that when the inductors La, Lb, and Lc are selected, the current passing through the inductor works in a continuous conduction mode according to the design principle of the Boost boost circuit, and the inductance The range is 1mH-7mH, the capacitance range of the filter capacitor is 470uF-3300uF, and the switching frequency of the power device can be in the range of 15KHz to 25KHz. The midpoints of the series filter capacitors C1 and C2 and the common ends of the bidirectional power switch must be connected together, and their common points and the neutral line of the power grid can be connected to each other or independent of each other. The design method of each current loop is exactly the same as the design method of the average current control single-phase Boost PFC circuit current inner loop. The design of the voltage outer loop is slightly different from that of the single-phase Boost PFC circuit. Since the frequency of the ripple of the output capacitor is three times the frequency of the grid power supply, the selection of its bandwidth can be appropriately relaxed according to the needs of the system response to increase the voltage. The closed-loop response speed of the loop.

In the AC step-up three-phase power factor correction circuit, a more important switching element is the design of the bidirectional power switch module. Considering factors such as cost, it is usually thought of using a thyristor as the base component of a bidirectional power switch module, but the operating frequency of the thyristor cannot be very high, and it is a half-controlled device, which is not suitable for the application of power factor correction circuits. Therefore, we must construct a bidirectional switch using other existing switching elements. There are two ways to form a bidirectional switch, and one of them can be used during the test. One is to connect two controllable switching elements with anti-parallel diodes, as shown in Figure 5(a), the gates and emitters of VT1 and VT2 are connected, and the collector of VT1 is connected with the cathode of VD1 to form At one end of the bidirectional switch, the collector of VT2 is connected to the cathode of D2 to form the other end of the bidirectional switch, and the anodes of D1 and VD2 are connected together with the emitters of VT1 and VT2. In this way, the same set of driving circuits can be used for the two power switching elements. Its working principle is: when the current is forward, the current flows through VT1 and D2; when the current is reverse, the current flows through VT2 and D1, realizing the bidirectional flow of current. Another method is to connect a power switching element to the DC output terminal of a single-phase rectifier bridge (the positive pole of the DC output terminal of the rectifier bridge is connected to the collector of VT, the negative pole of the DC output terminal of the rectifier bridge is connected to the emitter of VT), and the AC input terminal As two terminals of two bidirectional switches, as shown in Fig. 5(b). Its working principle is: when the current is forward, the current flows through D-1, VT, and D-4; when the current is reversed, the current flows through D-2, VT, and D-3, realizing the bidirectional flow of current. These two methods of realizing bidirectional switching have their own advantages and disadvantages. The method in Figure 5(a) uses fewer components, but the conduction voltage is reduced. The method in Figure 5(b) uses more components, but only one can be used. Control switching elements, the conduction voltage drop is one diode drop higher than the method shown in Figure 5(a). The use of these two bidirectional power switches can simplify the design of the control system of the present invention, and only three driving signals are needed to complete the control. When constructing the above two bidirectional switch modules, MOSFET or IGBT can be selected as the basic components for designing bidirectional power switches according to the power output.

Description of drawings

Fig.1 Typical waveform (a) and frequency spectrum (b) of input current of high-power arc welding inverter power supply

Figure 2 Schematic diagram of single-phase BoostPFC circuit

Figure 3 Block diagram of three-phase power factor correction circuit in AC boost mode

Figure 4 Schematic structure diagram of three-phase power factor correction circuit in AC boost mode

Figure 5 Design schematic diagram of two bidirectional switches

Figure 6 The input current waveform of the three-phase power factor correction circuit in AC boost mode

Figure 7 Phase voltage and phase current waveforms of three-phase power factor correction in AC boost mode

Figure 8 Input voltage current (a) and frequency spectrum (b) of AC boosted arc welding inverter power test

Detailed ways

Using the design of the present invention, a 400A arc welding inverter power supply with harmonic suppression function has been developed, and its input stage adopts a three-phase power factor correction circuit of AC boost mode (inductance value is 3mL, DC side capacitor C1 , C2 is 2200uF, the rectifier bridge adopts diode rectification with fast recovery characteristics, the base part of the bidirectional power switch module adopts IGBT (BSM150GB120DN2)), the power output range is 10kW～15kW, and the power converter adopts a full bridge inverter circuit. Arc welding inverter power supply with low harmonic distortion is the development trend of welding power supply. Generally speaking, this welding machine consists of two parts: one is the harmonic suppressor, which can also be called a voltage pre-regulator or power factor correction stage, and the other is the power converter, which is the traditional arc welding inverter power supply. Remove the input rectification filter part. Each of these two parts is an independent system, but the harmonic suppressor is to control the load characteristics of the power supply relative to the grid, so as to reduce the harm of the harmonics of the power supply to the grid, and make full use of the capacity of the power supply system. The power converter is to convert the energy of the grid into the form required by the load. For the arc welding inverter power supply, it is low voltage and high current. Therefore, the harmonic suppressor is the input to control the entire welding machine system, and the power converter is the output to control the welding machine system. The combination of these two parts is a welding power source with low harmonic distortion.

Fig. 6 is the inductance current test waveform of the three-phase power factor correction circuit in AC boost mode, and Fig. 7 is the phase voltage and phase current waveform of the three-phase power factor correction circuit. It can be seen that the input current of the AC boost mode is close to the standard sine wave, but there is a little distortion at the current zero crossing point. This is because the power factor circuit has a certain inductance relative to the power grid, and the phase of the inductor current lags behind When the power supply voltage and current cross the zero point, the current feedback loop cannot track the upper reference current. At the same time, the inductor current is intermittent near the zero crossing point, which causes a certain distortion of the inductor current at the zero crossing point. With such a topology, this Disadvantages are unavoidable. Figure 8 shows the test results of power factor and current harmonics using a FLUKE harmonic tester. It can be seen that the power factor of the welding machine has reached 0.99, and the current harmonic distortion rate is below 5%, which fully complies with the IEC61000-3-2 standard.

Claims (4)

1, a kind of three-phase power factor correcting circuit of AC boosting mode is characterized in that, according to the three-phase equilibrium criterion, inductance L a in the circuit, Lb, Lc are identical, diode VD1～VD6 is identical, and capacitor C 1, C2 are identical, and two-way power switch tube module Sa, Sb, Sc are identical; The star-like connection of three phase network, its output Via, Vib, Vic and high frequency E MI are that the end of Electro Magnetic Interference emi-filter module and inductance L a, Lb, Lc adopts connected in series successively; The end of the other end of La and the anode of VD1, two-way power switch tube module Sa links together; The end of the other end of Lb and the anode of VD3, two-way power switch tube module Sb links together; The end of the other end of Lc and the anode of VD5, two-way power switch tube module Sc links together; In the rectifier bridge of being made up of diode VD1～VD6, the anode of VD1 is connected with the negative electrode of VD2, the anode of VD3 is connected with the VD4 negative electrode, the anode of VD5 and the negative electrode of VD6 are connected; Capacitor C 1 and C2 polyphone join; The negative electrode of VD1, VD3, VD5 and the positive pole of C1 are joined together to form the positive pole of electric; The anode of VD2, VD4, VD6 and the negative pole of C2 are joined together to form the negative pole of electric; The other end of two-way power switch tube module Sa, Sb, Sc must and the negative pole of C1, the positive pole of C2 connect, the points of common connection of C1, C2 and the zero line of three phase network link together or are separate; Above-mentioned two-way power switch module is made of one of dual mode shown in the accompanying drawing 5, a kind of mode is power switch component VT1 and the VT2 butt joint that has the inverse parallel diode with two, shown in accompanying drawing 5 (a), the grid of VT1 and VT2 connects together, emitter is connected together, the collector electrode of VT1 and the negative electrode of D1 are connected to form an end of two-way power switch module, the collector electrode of VT2 and the negative electrode of D2 are connected to form the other end of two-way power switch module, and the emitter of the anode of D1, D2 and VT1, VT2 links together jointly; Another kind of mode is shown in accompanying drawing 5 (b), a power switch component VT is connected on the dc output end of a single-phase rectification bridge of forming by D-1, D-2, D-3, D-4, the positive pole of this single-phase rectification bridge dc output end connects the collector electrode of VT, the negative pole of rectifier bridge dc output end connects the emitter of VT, and this single-phase rectification bridge ac input end is as two terminals of two-way power switch module.

2, the three-phase power factor correcting circuit of a kind of AC boosting mode according to claim 1 is characterized in that, the described diode of being made up of in the rectifier bridge diode VD1～VD6 adopts the diode with fast recovery characteristics.

3, the three-phase power factor correcting circuit of a kind of AC boosting mode according to claim 1 is characterized in that, described power switch component VT1 and VT2 and power switch component VT adopt MOSFET or IGBT.

4, according to the three-phase power factor correcting circuit of the described a kind of AC boosting mode of claim 1, it is characterized in that, described inductance L a, Lb, Lc inductance value scope are 1mH-7mH, the capacitance swing of filter capacitor C1, C2 is 470uF-3300uF, and the switching frequency of power switch component VT1 and VT2 and power switch component VT is in 15KHz arrives the 25KHz scope.

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