CN101043175A - Three phase rectifying bridge DC side parallel type active electric power filter - Google Patents

Abstract

A type of three-phase commutating bridge direct current side parallel active filter is disclosed. The filter includes: capacitance, inductance, three low frequency bidirectional power switches and four high frequency bidirectional power switches. Thereinto: three low frequency bidirectional power switches are connected with three input ends of three-phase commutating bridge, and two serial bidirectional booster power transformer which consist of capacitance, inductance and four high frequency bidirectional power switches are paralleled in the direct current side of the whole commutating bridge. The invention suits for the harmonic wave management of three-phase commutating bridge especially. Comparing with the traditional dynamic current source electric filter, the invention reduces the number of high frequency source switches; and comparing with power density calibrator, the invention just processes the harmonic component of the load current, the processing current is smaller, and it can reduce the nominal capacity of harmonic wave management device greatly, and reduces the cost greatly too.

Description

Three-phase rectifier bridge DC side parallel active power filter

technical field

The invention belongs to the technical field of active power filters, in particular to a parallel active power filter.

Background technique

The rectifier bridge device widely used in the power system is the main source of harmonics. In order to suppress such harmonics, power factor correction (PFC) and shunt active power filter (APF) are commonly used at present, which are two main solutions for rectifier bridge load harmonic control. Among them, PFC controls harmonic pollution from the perspective of eliminating harmonic sources. PFC circuits of all structures need to handle all the output power, which limits their practical application. Especially for the three-phase system, a relatively mature three-phase PFC solution has not been found in the industry. APF is a dynamic and real-time compensation for load harmonics and reactive current. It only needs to deal with harmonics and reactive power. Compared with PFC, its processing power is small. At the same time, the compensation characteristics are less affected by grid impedance changes, and there is no danger of "harmonic amplification". Therefore, it is considered to be a promising method of harmonic control. However, since the current APFs are all installed on the AC side of the power grid, the voltage and current operate in four quadrants, requiring more high-frequency power switching devices, the cost of the main circuit is high, and the conventional APF needs to detect harmonic currents in real time and control the circuit Complexity also limits the application of parallel active power filter (APF).

DC-side shunt active power filters are used in high-voltage DC transmission and other fields to improve the filtering characteristics of passive filters and filter out the ripples of converter output DC voltage and current. However, it does not suppress the harmonics of the output current on the AC side; at the same time, the parallel active power filter on the DC side is also used in high-precision DC power supplies and high-response speed power supplies to improve the steady-state accuracy and accuracy of DC voltage or DC current. Dynamic performance, there is no compensation function for the input current on the AC side of the rectifier bridge. All active power filters on the DC side of the three-phase rectifier bridge are used to filter out harmonic components in the load, but there is no parallel active power filter on the DC side of the rectifier bridge for harmonic control of the incoming line current of the rectifier bridge. reporting and research.

Contents of the invention

The first object of the present invention is to provide a parallel active power filter with simple circuit, relatively low cost, and capable of controlling harmonics of the three-phase rectifier bridge load.

The second object of the present invention is to provide a control circuit suitable for the above-mentioned shunt active power filter.

In order to achieve the purpose of the first invention, the technical solution provided by the present invention is a parallel active power filter on the DC side of a three-phase rectifier bridge. The filter includes a bidirectional step-up power converter with a high frequency bidirectional power switch tube, a low frequency bidirectional power switch tube and a control circuit. There are two bidirectional step-up power converters of the present invention, each of which consists of an inductance, a high-frequency bidirectional power switch tube, and a capacitor connected in series in sequence, and between the inductor and the high-frequency bidirectional power switch tube Each of the connection points is tapped with another high-frequency bidirectional power switch tube to form a circuit. The two bidirectional step-up power converters are connected in series by connecting two capacitors and two tapped high-frequency bidirectional power switch tubes to a common connection point. The common connection point is connected to the AC side of the three-phase rectifier bridge and the AC grid through three low-frequency bidirectional power switch tubes. On the positive and negative output terminals of the DC side of the phase rectifier bridge.

In order to achieve the second object of the invention, the present invention provides such a control circuit for the parallel-connected active power filter on the DC side of the three-phase rectifier bridge. The control circuit includes two current sensors connected in series at the positive and negative output ends of the DC side of the three-phase rectifier bridge, a phase detection circuit connected in parallel with the AC power grid, and a sensor connected in parallel with the two capacitors in series or with any one of them. A voltage sampling circuit, and a control and drive unit connected to the output terminals of the two current sensors, the output terminal of the phase detection circuit, and the output terminal of the voltage sampling circuit, the output terminals of the control and drive unit are respectively connected to three low-frequency bidirectional power The switch tube is connected with four high-frequency bidirectional power switch tubes for driving them.

The advantages of the present invention are as follows:

1. The present invention is particularly suitable for harmonic control of three-phase rectifier bridge loads.

When used to suppress the harmonic current injected into the grid by the front end of the rectifier bridge, the current absorbed by the entire rectifier bridge device from the grid can be close to a sine wave, and the power factor is approximately 1. Compared with the traditional AC-side active power filter, the number of high-frequency active switches can be reduced, so the circuit is relatively simple and the cost is relatively low; compared with the power factor corrector, the present invention only deals with the load current Harmonic components, the processed current is smaller, the rated capacity of the harmonic control device can be reduced, and the cost is also greatly reduced.

2. Since the present invention moves the traditional active power filter to the DC side of the three-phase rectifier bridge, the DC side APF only needs to operate in two quadrants of voltage and current, so the circuit structure of the DC side APF of the present invention can be simplified, It has the advantages of small processing power and a small number of active switches used, and the cost is greatly reduced, so that it can be widely used in industry.

The present invention will be further described below in conjunction with the accompanying drawings.

Description of drawings

Figure 1 - Schematic diagram of the active power filter on the DC side of the rectifier bridge

Figure 2 - Schematic diagram of the active power filter control circuit on the DC side of the rectifier bridge

Figure 3a - Three-phase voltage interval division diagram

Figure 3b - Timing Diagram of Low Frequency Bidirectional Switch Control

Figure 4 - Equivalent Circuit Diagram of Section II

Figure 5a - Phase a input current waveform diagram without DC side active power filter

Figure 5b - Phase b input current waveform without DC side active power filter

Figure 5c - Phase c input current waveform without DC side active power filter

Figure 6a——A-phase input current waveform diagram after adding DC side active power filter

Figure 6b - Phase b input current waveform diagram after adding DC side active power filter

Figure 6c——C-phase input current waveform diagram after adding DC side active power filter

Figure 6d——Current Waveform Diagram of Compensation Inductor L1 After Adding DC-side Active Power Filter

Figure 6e——Current Waveform Diagram of Compensation Inductor L2 After Adding DC-side Active Power Filter

Detailed ways

A three-phase rectifier bridge DC side parallel active power filter (refer to Figure 1). The filter includes a bidirectional step-up power converter with a high frequency bidirectional power switch tube, a low frequency bidirectional power switch tube and a control circuit. In the present invention, there are two bidirectional step-up power converters, each of which consists of an inductance (L1, L2), a high-frequency bidirectional power switch tube (Sp2, Sn2) and a capacitor ( Cp, Cn), and a circuit in which another high-frequency bidirectional power switch (Sp1, Sn1) is tapped at the junction of the inductor (L1, L2) and the high-frequency bidirectional power switch (Sp2, Sn2) constitute. The two bidirectional boost power converters are connected in series by connecting two capacitors (Cp, Cn) and two tapped high-frequency bidirectional power switches (Sp1, Sn1) to a common connection point; the The common connection point is connected to the AC side of the three-phase rectifier bridge ZLQ and the AC grid DW through three low-frequency bidirectional power switch tubes (Sa, Sb, Sc). The input ends of the two series connected bidirectional step-up power converters DCAPF located on one side of the two inductors (L1, L2) are respectively connected to the positive and negative output ends of the DC side of the three-phase rectifier bridge ZLQ.

Apparently, the so-called AC grid DW can be either a mains power supply or an output of a generator. Those skilled in the art understand that, according to other conditions or requirements, the values of the two inductors ( L1 , L2 ) can be equal or unequal.

Furthermore, in the three branches of the three low-frequency bidirectional power switches (Sa, Sb, Sc), an inductor can be connected in series respectively, that is, an inductor can be connected in series at the three places a, b, and c in Figure 1 .

In addition, the three low-frequency bidirectional power switch tubes (Sa, Sb, Sc) can also be connected to two series-connected bidirectional step-up power converters DCAPF through an inductor connected in series at the common connection point, that is, in FIG. 1 An inductor is connected in series at e.

The above three-phase rectifier bridge DC side parallel-connected active power filter can use the existing control circuit adapted to it to control and drive each low-frequency and high-frequency bidirectional power switch tube therein. It is also possible to set a more adaptive control circuit for it, and the control circuit of the present invention is one of them. The control circuit (refer to Figure 2) includes two current sensors (CT1, CT2) connected in series at the positive and negative output ends of the DC side of the three-phase rectifier bridge ZLQ, a phase detection circuit VT connected in parallel to the AC grid DW, and a series Two capacitors (Cp, Cn) connected in parallel or with any one of the capacitors (Cp or Cn) in parallel with the voltage sampling circuit PT (due to the obviousness, the drawing of the voltage sampling circuit PT connected in parallel with any one of the capacitors (Cp or Cn) is omitted ), and a control and drive unit KZQDDL connected to the output terminals of two current sensors (CT1, CT2), the output terminal of the phase detection circuit VT, and the output terminal of the voltage sampling circuit PT, the output terminal of the control and drive unit KZQDDL They are respectively connected with three low-frequency bidirectional power switches (Sa, Sb, Sc) and four high-frequency bidirectional power switches (Sp1, Sp2, Sn1, Sn2) for driving them.

Further speaking, the phase detection circuit VT connected in parallel to the AC power grid DW can be connected to all three-phase lines of the AC power grid DW, or can only be connected to any two-phase lines, or can only be connected to any of the three-phase lines of the AC power grid DW. One phase line is connected (similarly due to obviousness, the accompanying drawings of the latter two cases are also omitted).

In the following, a further introduction will be made to the harmonic control process of the circuit disclosed in the above specific implementation manner.

The phase detection circuit VT of the present invention obtains the control sequence of three three-phase low-frequency bidirectional power switch tubes (Sa, Sb, Sc) by detecting the voltage of the power grid, and is divided into 6 intervals in each power frequency cycle of the power grid, and the three three-phase bidirectional The power switch tubes (Sa, Sb, Sc) work at twice the power frequency (refer to Fig. 3a, Fig. 3b). In any interval, the AC power grid DW, the three-phase rectifier bridge ZLQ and the parallel DC-side active power filter can be equivalent to two bidirectional boost power converters connected in series (refer to Figure 4, which only draws shows the equivalent circuit diagram in interval II). The current signal of the output terminal of the three-phase rectifier bridge ZLQ is obtained respectively through the current sensor (CT1, CT2), the voltage sampling circuit PT obtains the voltage signal of the DC side capacitance (Cp, Cn or Cp or Cn), and the control and drive unit KZQDDL can be controlled by PWM Mode produces the control signal of each high frequency bidirectional power switch tube (Sp1, Sp2, Sn1, Sn2), and drives the low frequency bidirectional power switch tube (Sa, Sb, Sc) and the high frequency bidirectional power switch tube ( Sp1, Sp2, Sn1, Sn2) on and off to realize the function of harmonic control. Fig. 5a, Fig. 5b, Fig. 5c are the waveform diagrams of input current (Ia, Ib, Ic) of three phases a, b, and c which are not connected to the filter of the present invention respectively. It can be seen from the three waveform diagrams that the input current waveform is close to a square wave, which contains a large number of harmonic components. Fig. 6a, Fig. 6b, and Fig. 6c are waveform diagrams of input currents (Ia, Ib, Ic) of phases a, b, and c after the filter of the present invention is connected. It is not difficult to find from the compared waveform diagrams that the input currents (Ia, Ib, Ic) of phase a, b, and c after treatment are very close to sine waves, and their power factors are approximately 1. Fig. 6d and Fig. 6e are waveform diagrams of the current (IL1, IL2) of the compensation inductance L1, L2 after the filter of the present invention is connected. From the latter two waveform diagrams, we can see the change process from harmonic control to sine wave.

By adopting the invention, only four high-frequency power switches are needed, which can reduce the cost and the compensation capacity. The invention only needs four bidirectional power switch tubes, which can reduce the cost and compensation capacity of the three-phase rectifier bridge harmonic control device. The principle of selection of inductance, capacitance and each power switch tube in the present invention is the same as that of the existing filter, so the specific parameters are not disclosed.

Claims (5)

1. A three-phase rectifier bridge DC side parallel-connected active power filter, which includes a bidirectional step-up power converter with a high-frequency bidirectional power switch, a low-frequency bidirectional power switch and a control circuit, its characteristics In that, there are two bidirectional step-up power converters, each of which consists of an inductance (L1, L2), a high-frequency bidirectional power switch tube (Sp2, Sn2) and a capacitor ( Cp, Cn), and a circuit in which another high-frequency bidirectional power switch (Sp1, Sn1) is tapped at the junction of the inductor (L1, L2) and the high-frequency bidirectional power switch (Sp2, Sn2) Composition; the two bidirectional boost power converters are connected in series by connecting two capacitors (Cp, Cn) and two tapped high-frequency bidirectional power switches (Sp1, Sn1) to a common connection point , the common connection point is connected to the AC side of the three-phase rectifier bridge (ZLQ) and its AC grid DW through the three described low-frequency bidirectional power switch tubes (Sa, Sb, Sc), and the two bidirectional boost type in series The input ends of the power converter (DCAPF) on one side of the two inductors (L1, L2) are respectively connected to the positive and negative output ends of the DC side of the three-phase rectifier bridge (ZLQ). 2. The three-phase rectifier bridge DC side parallel-connected active power filter according to claim 1, characterized in that, on the three branches of the three low-frequency bidirectional power switch tubes (Sa, Sb, Sc), respectively There is an inductor each in series. 3. The three-phase rectifier bridge DC side parallel-connected active power filter according to claim 1 or 2, characterized in that the three low-frequency bidirectional power switches (Sa, Sb, Sc) are connected in series through a The inductor at the common connection point is connected to two series connected bidirectional boost power converters (DCAPF). 4. The three-phase rectifier bridge DC side parallel-connected active power filter according to claim 1, 2 or 3, characterized in that the control circuit comprises two series connected in the three-phase rectifier bridge (ZLQ ) A current sensor (CT1, CT2) at the positive and negative output ends of the DC side, a phase detection circuit (VT) connected in parallel to the AC power grid DW, connected in parallel with the two capacitors (Cp, Cn) in series or with any one of them A voltage sampling circuit (PT) connected in parallel with a capacitor (Cp or Cn), and connected to the output terminals of two current sensors (CT1, CT2), the output terminal of the phase detection circuit (VT), and the output terminal of the voltage sampling circuit (PT) A control and drive unit (KZQDDL), the output of the control and drive unit (KZQDDL) are respectively connected with three low-frequency bidirectional power switches (Sa, Sb, Sc) and four high-frequency bidirectional power switches (Sp1, Sp2 , Sn1, Sn2) are connected for driving them. 5. The three-phase rectifier bridge DC side parallel active power filter according to claim 4, characterized in that, the phase detection circuit (VT) connected in parallel to the AC power grid DW can be connected with the three phases of the AC power grid DW The phase lines are all connected, or only any two phase lines thereof, or only any one phase line thereof.

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