CN112583014A

CN112583014A - Mixed type active power filter device suitable for LCC-HVDC system

Info

Publication number: CN112583014A
Application number: CN202011580523.XA
Authority: CN
Inventors: 杜夏冰; 赵成勇; 杨勇平
Original assignee: North China Electric Power University
Current assignee: North China Electric Power University
Priority date: 2020-12-28
Filing date: 2020-12-28
Publication date: 2021-03-30

Abstract

The invention relates to a hybrid active filter device suitable for an LCC-HVDC system, which belongs to a novel harmonic control method in high-voltage direct current engineering; The active filter is connected in series with the topology of the active filter based on the cascaded H bridge, and the passive part bears most of the high voltage. This structure can effectively reduce the volume and capacity of the active filter. The hybrid active filter device uses the ip-iq method based on the instantaneous reactive power theory to detect the load harmonic current, and uses the quasi-proportional resonance controller to track the harmonic current, so that the active filter can dynamically output and load harmonic current. The equal and reverse compensation current can effectively filter out the harmonics of the power grid and achieve harmonic control.

Description

Mixed type active power filter device suitable for LCC-HVDC system

Technical Field

The invention relates to a mixed type active filter device suitable for an LCC-HVDC system, belonging to the application field of high-voltage direct current and power electronic devices.

Background

At present, the ultra-high voltage direct current engineering and the remote ultra-high voltage direct current engineering which are operated in China are high voltage direct current (LCC-HVDC) transmission engineering based on a power grid commutation converter. Each pole of the extra-high voltage direct current project is a double 12-pulse current conversion unit, 12k +/-1 times of characteristic harmonic waves can be generated in the operation process, a large number of passive filter banks need to be installed, the filters occupy a large area, the tracking speed is low, the dynamic adjustment capability is weak, and dynamic characteristics such as overvoltage in the load shedding process cannot meet the system operation requirements. Hybrid ac filter devices have attracted considerable attention for their superior performance as a means of suppressing harmonic pollution. However, in the existing filtering device, a two-level or three-level voltage source type inverter is generally adopted in an active filter part, but in a high-voltage power transmission system, the capacity of the device is limited, the requirement of harmonic compensation capacity is difficult to meet by adopting a traditional two-level inverter hybrid filtering device, and a two-level inverter is replaced by adopting a cascaded H-bridge converter, so that the free expansion of the compensation capacity of the active filter is realized under the limited device capacity, and the problem can be effectively solved. At present, the application development of the hybrid filter device in the LCC-HVDC system is still in the primary stage, the research on the topology, control method, stability and relay protection of the device is not mature, many problems need to be solved, and the research on the hybrid filter device suitable for the LCC-HVDC system has a great significance.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides a hybrid active filter device suitable for an LCC-HVDC system.

The invention aims to provide a hybrid active filter device suitable for an LCC-HVDC system, which can overcome the defects of more high-voltage direct-current transmission filter devices, large occupied area, large investment and poor filter effect.

The technical scheme adopted by the invention is as follows: a hybrid active filtering device formed by connecting a passive filter and an active filter in series is adopted, the voltage level at the outlet of a current converter of an LCC-HVDC system is high, and 12k +/-1 harmonic current is contained, so that the passive filter in the HAPF adopts an 12/24-time double-tuned filter, and the active filter is based on a cascaded H-bridge structure and can realize high-voltage and high-power output by increasing the number of cascaded submodules. The harmonic detection link adopts a harmonic detection method based on the instantaneous reactive power theory, namely i_p-i_qA method; the harmonic current compensation link adopts a plurality of quasi-proportional resonant controllers connected in parallel, can realize the harmonic current control of up to 37 times, and in the state, the modulated wave of the active filter does not contain the quasi-proportional resonant controllers connected with the power gridThe fundamental voltage with the same voltage phase, so that the power grid voltage is automatically borne by the passive filter; the dynamic reactive compensation link is realized by adjusting the d-axis voltage to enable the active filter to generate corresponding fundamental voltage.

Compared with the prior art, the invention has the advantages that:

1. the hybrid filter device has better filtering performance, the traditional passive filter device can only filter harmonic waves on a tuning point, the filtering effect is greatly influenced by parameters, and the hybrid filter device can track most of times of harmonic waves and has stronger filtering performance. And the mixed active filter device generates harmonic current for compensation through the active filter to carry out filtering, so that the problems of ageing tuning point deviation and reduced filtering effect of passive filter equipment can be solved.

2. The device has small floor area and low cost, is limited by voltage fluctuation of an alternating current system, the capacity of the traditional passive filter and the reactive power compensation device is limited, and the number of the configured groups is usually as many as 16-20, so that the filter equipment and the reactive power compensation device occupy 1/3 of the floor area of the converter station. The hybrid active filter device has certain dynamic reactive power compensation capability, and can reduce voltage fluctuation caused by switching of the reactive power compensation device, thereby increasing the capacity of each group of capacitors, reducing the number of groups, saving occupied land and saving a large amount of investment.

3. The passive filter can be transformed on the existing engineering, a part of topology of the passive filter adopts a double-tuned filter of 12 times and 24 times in the engineering, the passive filter is more suitable for the actual engineering, and is suitable for occasions of high-voltage large-capacity harmonic filtering, and the filtering effect is good.

Drawings

The invention is further described below with reference to the accompanying drawings.

Fig. 1 shows a schematic structural diagram of a hybrid active filtering device suitable for an LCC-HVDC system, comprising an active filter, a passive filter and a control unit;

fig. 2 shows an equivalent circuit diagram of a hybrid active filter device. Generating and loading harmonic current i by controlling the action of internal switching device_LnEqual and opposite compensation currents i_FMake the power gridThe current does not contain harmonic components;

fig. 3 shows a control unit schematic of a hybrid active filter arrangement including harmonic detection, harmonic current tracking and reactive current tracking.

Detailed Description

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application.

A hybrid active filtering device structure suitable for LCC-HVDC system is shown in fig. 1, and includes an active filter, a passive filter and a control unit; the active filter comprises a submodule SM (full-control type device IGBT, diode, direct current side capacitor C) of an H-bridge structure_SM) An output inductor L_rEtc.; the passive filter comprises a high-voltage capacitor, an inductor and the like; the control unit comprises a current sensor, a harmonic detection link, a current control link and a carrier phase shift modulation link; the second diagram is an equivalent circuit diagram of the LCC-HVDC system and the hybrid active filter device, and the operation principle of the hybrid active filter device is explained from the circuit point of view. According to kirchhoff's law, the harmonic equivalent circuit can be represented by the following equation:

in the formula, Z_Sh，Z_Ch，Z_LCh，Z_LCChEquivalent impedances of an alternating current system, a reactive compensation device, a passive filter and the LCC are respectively; i is_Sh，I_Ch，I_Lh，I_FhThe current of an alternating current system, a reactive power compensation device, a hybrid filter device and an LCC load respectively; u shape_PCChIs the harmonic voltage of the AC bus. As can be seen from the above formula, as long as the compensation current output by the hybrid filter device is equal to the load harmonic current, the grid current does not contain harmonic content. Thus, the hybrid active filter device can be controlled to be a harmonic voltage source:

U_Fh(s)＝G_X(s)·[I_Lh(s)-I_Fh(s)]

wherein G is_XIs the transfer function of the harmonic current controller. The harmonic current controller may employ a quasi-proportional resonant controller,

in the formula, K_pIs a proportionality coefficient, K_rAs integral coefficient, ω_cTo cut off the angular frequency, omega₀Is the ac grid angular frequency.

FIG. 3 shows a schematic diagram of a control unit of a hybrid active filter device, which first obtains a load current and a compensation current signal through isolation, a current sensor and A/D conversion, and passes through i_p-i_qDetecting harmonic current and reactive current, tracking the reactive current to be compensated by PI controller, tracking harmonic current by quasi-proportional resonant controller, and controlling the action of internal switch device to generate and load harmonic current i_LnEqual and opposite compensation currents i_FTherefore, the power grid current does not contain harmonic components. The modulation wave of the active filter does not contain fundamental wave voltage which is in phase with the grid voltage, so that the grid voltage is automatically borne by the passive filter; the dynamic reactive compensation link is realized by adjusting the d-axis voltage to enable the active filter to generate corresponding fundamental voltage. The transfer function of the harmonic detection link is as follows:

in the formula, ζ and ω_nThe damping ratio and the cut-off frequency of the high-pass filter, respectively.

Finally, it should be noted that: the described embodiments are only some embodiments of the present application and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

Claims

1. Is suitable forHybrid active filtering device of LCC-HVDC system, characterized by: the device comprises an active filter (1), a passive filter (2) and a control unit (3); the active filter comprises a submodule SM (full-control type device IGBT, diode, direct current side capacitor C) of an H-bridge structure_SM) An output inductor L_rEtc.; the passive filter comprises a high-voltage capacitor, an inductor and the like; the control unit comprises a current sensor, harmonic detection, current control and carrier phase shift modulation.

2. A hybrid active filtering device suitable for use in an LCC-HVDC system in accordance with claim 1, wherein: the voltage level at the outlet of the converter of the LCC-HVDC system is high, the converter contains 12k +/-1 times of harmonic current, the passive filter has a structure of a 12-order and 24-order double-tuned filter, and the passive filter has a certain tuning bandwidth and can provide a low-impedance path for the 11, 13, 23 and 25 times of harmonic current. Meanwhile, the passive filter bears most fundamental wave voltage, the number of modules of the cascade H-bridge active filter can be reduced, and the manufacturing cost of the filter is greatly reduced.

3. A hybrid active filtering device suitable for use in an LCC-HVDC system in accordance with claim 1, wherein: the active filter is based on a cascade H-bridge structure, and high-voltage and high-power output can be realized by increasing the number of cascade submodules. The active filter is equivalent to a controlled current source, and generates a load harmonic current i by controlling the action of an internal switching device thereof_LnEqual and opposite compensation currents i_FTherefore, the power grid current does not contain harmonic components.

4. A hybrid active filtering device suitable for use in an LCC-HVDC system in accordance with claim 1, wherein: the control unit of the device consists of a current transformer, a harmonic detection link, a harmonic and reactive current control link and a modulation link. The harmonic current controller adopts quasi-proportional resonance control, the gain of an ideal resonance controller at the resonance frequency is infinite, the gains at other frequencies are quickly attenuated, and the zero steady-state error control can be realized by a sinusoidal signal with the same frequency as the resonance frequency. Aiming at 12k +/-1 harmonic waves on the alternating current side of the LCC-HVDC system, the current controller adopts a plurality of quasi-proportional resonant controllers connected in parallel, and the characteristic subharmonic current control of up to 37 times can be realized. And the reactive power controller adopts PI tracking control, and can realize dynamic reactive compensation.

5. A hybrid active filtering device suitable for use in an LCC-HVDC system in accordance with claim 1, wherein: the traditional passive filter can only filter harmonic waves on a tuning point, and the cascade H-bridge HAPF can track most of harmonic waves, so that the filter has stronger filtering performance; the existing projects are mostly filtered by adopting a plurality of groups of double-tuned passive filters, and the existing projects can be directly modified by adopting a mixed type active alternating current filtering device; the capacity of the traditional passive filter and the reactive power compensation device is limited by the voltage fluctuation of an alternating current system, and the number of the configured groups is usually as many as 16-20, so that the filter equipment and the reactive power compensation device occupy 1/3 of the floor area of the converter station. The cascade H bridge HAPF has certain dynamic reactive power compensation capability, and can reduce voltage fluctuation caused by switching of the reactive power compensation device, thereby increasing the capacity of each group of capacitors, reducing the number of the groups, saving occupied land and saving a large amount of investment.