CN101170284A - Single-phase unified power quality controller for electrified railway power supply - Google Patents

Abstract

The invention relates to a single-phase unified power quality controller for electrified railway power supply, belonging to the technical field of flexible AC power transmission and distribution. The invention includes a single-phase multi-winding transformer composed of a primary winding and n secondary windings. n voltage source converters connected in parallel with the secondary side windings; a single-phase chain-type H-bridge converter with n links connected to n voltage source converters through n capacitors, the H-bridge converter The AC port is directly connected to the traction grid through a reactor. The invention has the functions of active power control, reactive power compensation and harmonic compensation, which can solve the problems of unbalanced three-phase voltage, voltage fluctuation, low power factor and harmonic pollution in electric railway traction substation, and effectively reduce the Increase the capacity of traction transformers to increase the capacity and capacity of electric railways. It also has small footprint, low loss, and low cost; it can obtain good harmonic suppression characteristics and dynamic response characteristics. It is convenient for industrial production and improves device reliability.

Description

Single-phase unified power quality controller for electrified railway power supply

technical field

The invention belongs to the technical field of flexible AC transmission and distribution of power systems and power electronics, and relates to the treatment of large-capacity power electronic devices and user power quality problems, in particular, it provides a multi-winding transformer and chain H-bridge for power supply of electrified railways Unified Power Quality Controller (UPQC) device for structural converters.

Background technique

As a large-capacity single-phase load, electric locomotives will inject negative sequence current into the power supply system of electrified railways (referred to as electric railways), and cause power quality problems such as three-phase unbalanced voltage and voltage fluctuations in the power supply system. China's electric railway power supply system is a different-phase power supply mode. The commonly used phase sequence rotation technology and balancing transformer technology can only improve the influence of negative sequence current within a certain range, and usually cannot meet the relevant national power quality standards in practice. In addition, the inherent electrical phase separation link in the out-of-phase power supply mode is its weak link, and it has a great constraint on high-speed and heavy-load operation. The use of the same-phase power supply mode can avoid or reduce the phase separation link of the traction network, and then solve a series of problems caused by the electric phase separation, and greatly improve the transport capacity of the train. However, the disadvantage of the same-phase power supply scheme is that it is easy to cause negative sequence current, and the resulting imbalance problem is more serious than that of the out-of-phase power supply mode.

With the help of modern power electronics technology, negative sequence control can be implemented with a relatively small investment, so as to ensure the three-phase balance of the high-voltage side current of the traction transformer under various electric railway load conditions, and at the same time achieve the control goals of low harmonic content and high power factor . A lot of research has been carried out at home and abroad, and a series of types of power electronic control devices have been put into application. A large-capacity power balance regulator (Balance Converter Device, BCD) based on a self-shutoff power electronic switching device IGBT (Insulated Gate Bipolar Transistor) or IGCT (Integrated Gate Commutated Thyristor) is one of them. It can be seen in the following three scientific and technological documents: Document 1: Tetsuo UZUKA Shouji IKEDO Keiji UEDA, A Static Voltage Fluctuation Compensator for AC Electric Railway, PESC 2004 IEEE 35th Annual, Volume 3, Page(s): 1869-1873 Vol.3; 2: Zeng Guohong, Hao Rongtai, In-phase Power Supply System Based on Active Filter and Impedance Matching Transformer, Journal of Northern Jiaotong University, 2003, 25(3): 49-54; Document 3: Zeng Guohong, Hao Rongtai, Based on Active Filter and Si In-phase power supply system of Kete transformer, Journal of Northern Jiaotong University, 2003, 27(4): 84-90. Wherein, the power balance regulator described in Document 1 is applied to an out-of-phase power supply mode, and the power balance regulator described in Documents 2 and 3 is applied to an in-phase power supply mode.

The simplified principle structure of the BCD device described in the above documents is shown in Fig. 1 . Two large-capacity voltage source converters V ₁ and V ₂ realize back-to-back electrical connection by sharing a DC side capacitor C. The AC sides of V ₁ and V ₂ are connected to single-phase transformers T ₁ and T ₂ respectively, and T ₁ and Ports x, y and z, w on the high voltage side of _T2 are respectively connected in parallel to the two-phase windings on the secondary side of the traction transformer. The capacitor C acts as a voltage support, and through the transformation of the switch network in the converters V ₁ and V ₂ , an equivalent control system with independently adjustable amplitude and phase can be obtained on the AC side of V ₁ and V ₂ . Voltage source, so that the BCD device can realize independent compensation for the reactive current and harmonic current of its x, y, z, w ports and the two-phase winding access point of the traction transformer secondary side; at the same time, the device can share The capacitor C controls the transfer of active power between V ₁ and V ₂ . The BCD device can realize the balance of the three-phase current on the high-voltage side of the traction transformer through the control and adjustment of the active power and the balance compensation of the reactive power, and achieve the purpose of compensating the negative sequence current as a whole.

The electric railway is a load of high voltage (27.5kV) and large capacity (several MVA to tens of MVA). The capacity range of its BCD device is generally between a few MVA and more than a dozen MVA. It has large device capacity, difficult electrical isolation, and output waveform quality requirements. High-level characteristics, it is necessary to select a suitable topology for the large-capacity voltage source converters V1 and V2 required by the BCD device. In order to realize V ₁ and V ₂ , in addition to direct series and parallel connection of power electronic switching devices, it also includes the application of multi-level converter technology and transformer-based converter series and parallel connection technology.

An embodiment of the BCD device described in the above-mentioned documents is shown in FIG. 2 . The AC sides of multiple voltage source converters V _L1 , V _L2 , ... V _Ln are respectively connected to the secondary windings S _L1 , S _L2 , ... S _L2 of the multi-winding transformer T ₁ to realize parallel connection; similarly, V _R1 , V The AC sides of _R2 and V _Rn are respectively connected to the secondary windings S _R1 , S _R2 , ... S _R2 of the multi-winding transformer T ₂ to realize parallel connection. The DC sides of the converters V _L1 , V _L2 , ... V _Ln and _VR1 , _VR2 , _VRn are electrically connected to both ends of the common capacitor C, and the V _L1 , V _L2 , ... V _Ln and _VR1 , _VR2 , V _Rn are two-level H-bridge converter topology or three-level diode mid-point clamped converter topology. Due to the limited withstand voltage range of these two topologies, in order to realize the voltage and capacity required by the BCD device, two multi-winding transformers are required to achieve voltage and capacity matching and electrical isolation. Therefore, the BCD scheme has the disadvantages of large footprint, high cost, and large loss. At the same time, the required passive filter has a large capacity, which makes it difficult to be applied in traction substations of electrified railways.

Contents of the invention

The purpose of the present invention is to solve the problems of power quality such as negative sequence, reactive power, and harmonics exceeding the standard in electrified railway traction substations, overcome the shortcomings of the existing technology, and propose a new type of single-phase unified electric energy for electrified railway power supply Quality controller (referred to as UPQC). Compared with the existing BCD scheme, the present invention saves a transformer, and has the advantages of small footprint, small loss and low cost. At the same time, under the same capacity level and lower switching loss conditions, a higher equivalent switching frequency can be obtained, and it has good waveform output characteristics and harmonic current suppression ability. Among them, the modular structure of the chain-type H-bridge converter enables the standardized production of UPQC in the industry, which is beneficial to reduce the production cost of UPQC; and facilitates the realization of redundant design to improve the reliability of UPQC operation.

The UPQC proposed by the present invention uses a single-phase multi-winding transformer to realize the parallel connection and electrical isolation functions of multiple voltage source converters, and is characterized in that it includes a single-phase multi-winding transformer composed of a primary winding and n secondary windings , n voltage source converters connected in parallel through the secondary winding of the transformer; a single-phase chain-type H-bridge converter of n links connected to the n voltage source converters through n capacitors, The AC port of the single-phase chain H-bridge converter with n chain links is directly connected to the traction grid through a reactor, wherein n is a positive integer ranging from 2 to 50.

The preferred single-phase multi-winding transformer of the present invention adopts a split connection method, and the mutual impedance between each secondary winding and the primary winding is completely equal. When a transformer with a large number of windings is required, it can also be obtained by connecting multiple single-phase multi-winding transformers in parallel.

The voltage source converters all adopt a single-phase two-level H-bridge structure. The voltage source converters connected in parallel adopt the pulse distribution control technology of carrier phase shift (which belongs to the conventional technology and does not belong to the content of the present invention), so that the primary side of the multi-winding transformer can obtain good harmonic suppression characteristics.

The single-phase chained H-bridge converter is composed of multiple single-phase two-level H-bridge converters (called a chain link) in series, and each link is sequentially connected to the secondary winding side of the single-phase multi-winding transformer. A voltage source converter is electrically connected "back-to-back" through DC capacitors. The AC side of the single-phase chain-type H-bridge converter is directly connected to the power supply arm of the traction grid (voltage level is 27.5kV) through the connection reactor. The single-phase chain-type H-bridge structure converter adopts the carrier phase-shift control technology (which belongs to the conventional technology and does not belong to the content of the present invention), so that the final synthesized output voltage harmonics of all chain links can cancel each other, so that the output side can obtain Good harmonic suppression characteristics.

The present invention can adopt the control technology based on current tracking (belongs to conventional technology, and does not belong to the content of the present invention), so as to ensure that the present invention realizes compensation for the reactive current and harmonic current at the access point of the two-phase winding on the secondary side of the traction transformer and Control the transfer of active current while maintaining the average voltage of each independent DC capacitor within the set range. Energy-based voltage equalization control ensures mutual equalization of independent DC capacitor voltages.

The working principle of the present invention is briefly described as follows:

In the out-of-phase power supply mode, when the load of the electric iron in the power supply arm connected to the two-phase winding on the secondary side of the traction transformer is unbalanced, UPQC absorbs active current from the side with the lighter load of the electric iron (referred to as the rectifier side), and passes through the shared The DC capacitor is transmitted to the heavy load side of the electric railway (called the inverter side); at the same time, a small part of active current is absorbed from the power supply arm of the traction grid to supplement the loss of the device, so as to maintain the constant voltage of the DC capacitor. In the same-phase power supply mode, the side of the UPQC connected to the power supply arm of the traction network works in the inverter state, and the other side works in the rectification state. By controlling the transfer of active current, UPQC balances the active power of the two-phase load on the secondary side of the traction transformer connected to it. The rectifier side and inverter side of UPQC ensure that the voltage of each independent capacitor remains within a certain range through coordinated control, and the active power absorbed by the rectifier side meets the needs of the inverter side at all times, avoiding sudden rises and drops in capacitor voltage. Based on The voltage equalization control of energy ensures the equalization of capacitor voltages on the DC side of each group of converters.

When UPQC is applied in the same-phase power supply mode or the out-of-phase power supply mode when the load of one-phase power supply arm is no-load, the rectifier side converter adopts power factor correction technology, that is, the current waveform is controlled and the phase closely follows the voltage change, so that only the rectifier side Absorb pure active current to avoid reactive and harmonic current generated by UPQC itself.

The power factor of DC electric locomotives is generally about 0.8, and the reactive current generated by such electric railway loads can be compensated by UPQC. UPQC detects the reactive current on the secondary side of the traction transformer, and then generates a reactive compensation current corresponding to the amplitude and phase and injects it into the access point of the two-phase winding on the secondary side of the traction transformer, so that only pure active current flows through the traction transformer , The power factor is above 0.99.

Most of the harmonic current injected by DC electric locomotive into the electric railway power supply system can be compensated by UPQC. The principle of UPQC harmonic current compensation is similar to the principle of reactive current compensation. Based on the current tracking control technology, UPQC can compensate most of the harmonic current generated by the load, so that the current injected into the electric railway power supply system by the traction transformer after compensation is approximately pure fundamental current .

After UPQC controls active current transfer and compensates reactive current and harmonic current, three-phase symmetrical fundamental active current flows through the high-voltage side of the traction transformer, which not only solves the existing power quality problems, but also significantly improves the capacity utilization of the traction transformer Rate.

Features and beneficial effects of the present invention:

The invention is a high-power power electronic device based on a self-turn-off switching device IGBT or IGCT and a pulse width modulation technology (PWM), and the power capacity range is between several MVA to more than ten MVA. It can be applied to electric railway traction substations adopting out-of-phase power supply mode and in-phase power supply mode, to solve the problem of negative sequence current injection caused by unbalanced load of electric railway, low power factor and harmonics caused by DC driven electric locomotive load pollution problem. It has the functions of suppressing the three-phase voltage unbalance and three-phase voltage fluctuation of the substation, realizing dynamic reactive power compensation and harmonic compensation, stabilizing the voltage of the traction network and improving the transport capacity of the electrified railway.

The invention fully utilizes the application advantages of the chain-type H-bridge structure converter in the high-voltage field of power electronics. The single-phase chain-type H-bridge structure converter used by UPQC is directly connected to the power supply arm of the 27.5kV traction grid, which saves a transformer, so it occupies a small area, has low losses and lower costs. The only multi-winding step-up transformer that realizes the electrical isolation on both sides of the UPQC and the parallel connection of the voltage source converters of each winding; at the same time, the electrical isolation between the parallel converters is beneficial to each of the chained H-bridge converters. Control of link capacitor voltage. The large-capacity chain-type H-bridge structure converter realized by connecting multiple chain links in series, the IGBT or IGCT in each chain link adopts a lower switching frequency, so that the chain-type converter can obtain a higher equivalent switching frequency, so that While obtaining better harmonic current suppression characteristics and dynamic response characteristics, UPQC can also maintain low switching loss and improve the operating efficiency of the device. The chain structure is easy to implement redundant design. When a link fails, the link can be bypassed, and through proper control to ensure the normal operation of UPQC, improving the reliability of UPQC. Each chain link in the chain structure is a modular structure, which is suitable for industrial production and is conducive to reducing the manufacturing cost of UPQC.

This device has the functions of active power control, reactive power compensation and harmonic compensation at the same time, which is an effective extension of the current active filter and STATCOM device control functions. It can effectively solve the problems of three-phase voltage fluctuation and three-phase voltage imbalance, low power factor, and harmonic pollution in traction substations, and can significantly improve the transportation capacity and transportation capacity of electric railways.

Description of drawings

FIG. 1 is a schematic diagram of an existing BCD device based on a double-transformer isolation structure.

FIG. 2 is a structural diagram of a BCD device with a double-transformer isolation structure that realizes parallel connection of converters through a single-phase multi-winding transformer.

Fig. 3 is a structural diagram of an UPQC device based on a single-phase multi-winding transformer and a chained H-bridge converter according to the present invention.

Fig. 4 is a schematic structural diagram of an embodiment of the i-th voltage source converter connected in parallel through a single-phase multi-winding transformer of the present invention.

Fig. 5 is a schematic structural diagram of an embodiment of a single-phase chain-type H-bridge converter with n chain links according to the present invention.

Fig. 6 is a schematic diagram of the application of the present invention in the electric railway traction substation in different phase power supply mode

Fig. 7 is a schematic diagram of the application of the present invention in the same-phase power supply mode electric railway traction substation

Detailed ways

The present invention is described in detail as follows in conjunction with accompanying drawing and embodiment:

The overall structure of the single-phase unified power quality controller (UPQC) device for electrified railway power supply of the present invention is as shown in Figure 3, and this device comprises single-phase multi-winding transformer 1 (by primary side winding P _R and n secondary windings S _R1 , S _R2 , ... S _Rn ), n voltage source converters 2 connected in parallel through the secondary winding of transformer 1; a total of n chain links connected to n voltage source converters 2 through n capacitors The single-phase chain-type H-bridge converter 3 of the single-phase chain-type H-bridge converter 3 with n chain links, the AC ports x', y' of the single-phase chain-type H-bridge converter 3 with n chain links are connected to the reactor 4 and then connected to the traction grid through the x, y ports Direct connection, (n is a positive integer between 2 and 50).

In the multi-winding transformer 1 shown in Fig. 3, the n secondary windings are exactly the same, that is, the mutual impedance between the n secondary windings S _R1 , S _R2 , ... S _Rn and the primary winding _PR is exactly the same, so that The n voltage source converters 2 connected in parallel through the secondary winding of the transformer 1 can achieve a good current sharing effect, and the control only needs to ensure that the amplitude and phase of the fundamental voltage generated by the n parallel voltage source converters are the same That's it. The multi-winding transformer can adopt the split connection method (belonging to the conventional technology, and does not belong to the content of the present invention). The split connection method of the secondary winding makes the mutual impedance very large, which is about 2 times the mutual impedance of the primary side and the secondary side. times. In this way, the mutual influence between the windings is very small during control, which can effectively reduce the circulating power between the windings caused by the control pulse error. The control of n voltage source converters connected in parallel adopts carrier phase shift control technology. While satisfying the same fundamental voltage amplitude and phase generated by each converter, the characteristic harmonic voltages of each converter are mutual due to carrier phase shift. There is a certain phase angle difference between them, thus canceling each other out. This makes the primary side of the transformer obtain good harmonic suppression characteristics.

The embodiment structure of n voltage source converters of the present invention is shown in Fig. 4 (since each voltage source converter has the same structure, only the structure of the i-th voltage source converter is shown in the figure). The voltage source converter of this embodiment is a single-phase two-level H-bridge structure, including two bridge arms, wherein each bridge arm is composed of two upper and lower insulated gate bipolar transistors (IGBT) S ₁ , S ₂ Composed of S ₃ , S ₄ and their antiparallel diodes D ₁ , D ₂ and D ₃ , D ₄ . The midpoints A _i and B _i of the two bridge arms are respectively connected to both ends of the i-th winding S _Ri of the transformer _. The bus bar is the positive pole, and the lower end bus bar is the negative pole.

The n-link single-phase chain-type H-bridge converter of the present invention is shown in Figure 5, and its feature is that any link L _i is a single-phase two-level H-bridge converter as shown in Figure 4, each A chain link L _i includes a DC capacitor C _i and two bridge arms connected in parallel with the capacitor. Each bridge arm is composed of two upper and lower IGBTs and their anti-parallel diodes. The IGBT switches S ₁ and S ₃ are connected to the positive pole of the capacitor C _i , and the IGBT switches S ₂ and S ₄ are connected to the negative pole of the capacitor C _i . Through the capacitor C _i , the chain link L _i shares the DC bus bar of the voltage source converter V _i , forming a "back-to-back" structure. The chain connection method of each chain link is: the midpoint of the bridge arm where the IGBT switches S ₁ and S ₂ in the chain link L i is connected to the midpoint of the bridge arm where _the IGBT switches S ₃ and S ₄ are located in the chain link L _i-1 , and the chain link L The midpoint of the bridge arm where the IGBT switches S ₃ and S ₄ are located in _i is connected to the midpoint of the bridge arm where the IGBT switches S ₁ and S ₂ are located in the chain link L _i+1 . The middle point x' of the bridge arm on the left side of the chain link L ₁ and the middle point y' of the bridge arm on the right side of the chain link L _n are respectively connected to the connection reactance jX ₁ and jX ₂ , as shown in FIG. 3 .

The embodiment of a 20MVA UPQC of the present invention is described in detail as follows in conjunction with Fig. 3:

According to the voltage level of the access system and the withstand voltage level of the IGBT used, the number n of chain links of the chain-type H-bridge converter can be determined. The H-bridge converter chain link composed of 6500V/600A IGBT, because the DC voltage fluctuates, the average value of the DC side voltage can be about 2800V. The voltage level of the traction power supply arm of the electric railway is 27.5kV, so 14 single-phase H-bridge converter chain links need to be connected in parallel to the load power supply arm. In order to ensure a certain redundancy, 15 single-phase H-bridge converters can be selected The converter chain links are connected in series to form a 15-link single-phase H-bridge converter. Correspondingly, it can be determined that the number of secondary windings of the single-phase multi-winding transformer and the number of voltage source converters connected in parallel with it are both 15, and each voltage source converter in parallel is also composed of 6500V/600A IGBT. The transformation ratio of the primary side and the secondary side of the multi-winding transformer is 15:1, and the capacity is selected as 10MVA. In this embodiment, considering the large number of secondary windings, three single-phase transformers with a capacity of 3.3 MVA and 5 secondary windings can be used to form a single-phase multi-winding transformer with a capacity of 10 MVA by connecting the primary sides in parallel.

The connection modes of the device of the present invention applied to traction substations in out-of-phase power supply mode and in-phase power supply mode are shown in Fig. 6 and Fig. 7 . In Fig. 6, the AC side x, y, z, and w ports of the UPQC of the present invention are respectively connected to two points b, c and a, c of the two power supply arms of the traction transformer T, so that one of the two secondary phases of the traction transformer T The phase winding ob is connected in parallel with the other phase winding oa through UPQC. In Fig. 7, one phase winding bc of the two secondary phases of the traction transformer is also connected in parallel with the other phase winding oa through UPQC. The difference from the out-of-phase power supply mode is that in the same-phase power supply mode, the x and y ports of UPQC are connected to the secondary winding bc of the traction transformer and connected to the power supply arm of the traction network at the same time, while the z and w ports are only connected to the other phase winding oa of the transformer It is not electrically connected to the power supply arm of the traction network. When applied in out-of-phase power supply mode, according to the difference in the load of the electric iron at points a and b of the power supply arms at both ends of the phase split point S, UPQC has a bidirectional flow of active power, that is, the ports x, y, z, and w can be used as rectifiers The side can also be used as the inverter side. When applied to the same-phase power supply mode, the active power is only a single-phase flow, and the z and w ports are the rectification side and the x and y ports are the inverter side. In order to ensure the normal and stable operation of UPQC, the instantaneous active power is measured and calculated, and through the coordinated control of the rectifier side and the inverter side, the voltage of each independent capacitor is kept within a certain range, and the active power absorbed by the rectifier side meets the requirements of the inverter at all times. The demand on the side should not cause excess and shortage, so as to avoid the sharp rise or fall of the DC side voltage and endanger the safety of the UPQC device.

Claims (6)

1. single-phase unified electric energy quality controller that is used for electrified railway power supply, it is characterized in that, comprise by a former limit winding and n the single-phase multi winding transformer that the secondary winding constitutes n voltage source converter of the secondary winding parallel connection by described transformer; The single-phase chain type H bridge current transformer of n the chain link that links to each other with a described n voltage source converter by n electric capacity, the interchange port of the single-phase chain type H bridge current transformer of this n chain link is by reactor and drawing electric network direct connection, and wherein n is the positive integer of span between 2-50.

2. controller as claimed in claim 1 is characterized in that, described multi winding transformer adopts division formula connection, and each the secondary winding and the mutual impedance between the winding of former limit of described multi winding transformer are identical.

3. controller as claimed in claim 1 is characterized in that, the phase-shifting carrier wave control technology is adopted in the control of n voltage source converter of described parallel connection, makes the former avris of transformer obtain good harmonic wave suppression characteristic.

4. controller as claimed in claim 1, it is characterized in that, described voltage source converter adopts single-phase two level H-bridge structures, this structure comprises two brachium pontis, and wherein each brachium pontis is formed by two insulation gate pole bipolar transistors up and down and with the diode of each insulation gate pole bipolar transistor reverse parallel connection respectively.

5. controller as claimed in claim 1 is characterized in that, arbitrary chain link L of the single-phase chain type H bridge construction of described n chain link current transformer _iBe single-phase two level H-bridge structures, this structure comprises two brachium pontis, and wherein each brachium pontis is formed by two insulation gate pole bipolar transistors up and down and with the diode of each insulation gate pole bipolar transistor reverse parallel connection respectively.

6. controller as claimed in claim 1 is characterized in that, described single-phase many windings transformation adopts a plurality of many windings single-phase transformers to be formed in parallel.

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