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CN104979846A - Method, equipment and system for controlling low voltage ride through of multilevel inverter - Google Patents

Method, equipment and system for controlling low voltage ride through of multilevel inverter Download PDF

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Publication number
CN104979846A
CN104979846A CN201410132281.6A CN201410132281A CN104979846A CN 104979846 A CN104979846 A CN 104979846A CN 201410132281 A CN201410132281 A CN 201410132281A CN 104979846 A CN104979846 A CN 104979846A
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voltage
phase
inverter
power frequency
current
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CN104979846B (en
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辛凯
郭海滨
刘云峰
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Huawei Technologies Co Ltd
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Huawei Technologies Co Ltd
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    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00Energy generation through renewable energy sources
    • Y02E10/50Photovoltaic [PV] energy
    • Y02E10/56Power conversion systems, e.g. maximum power point trackers

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Abstract

The invention provides a method, equipment and a system for controlling low voltage ride through of a multilevel inverter. The method, the equipment and the system are applied in an inverter for grid-connected operation of a photovoltaic power station. A DC current which is output from a solar pole plate of the photovoltaic power station is input to the inverter. The inverter inverts the DC current to AC current and feeds the AC current back to a power grid. The method comprises the steps of monitoring three-phase voltage of the power grid and determining whether an asymmetric fall of the power grid voltage occurs, wherein the asymmetric fall comprises a two-phase short-circuit fault and a single-phase grounding short-circuit fault; and if the asymmetric fall of the power grid voltage occurs, injecting a power-frequency common-mold voltage into a given three-phase grid-connected voltage of a PWM modulator, and outputting a PWM signal by a PWM controller according to the given three-phase power-connected voltage for controlling the switching state of a switch tube in the inverter. A power frequency fluctuation of a point current in a bust is reduced through controlling operation of the inverter. After the power frequency fluctuation of the point current in the current is reduced, the voltage stress which is bear by each switch tube is reduced, thereby preventing switch tube damage.

Description

A kind of multi-electrical level inverter low voltage traversing control method, equipment and system
Technical field
The present invention relates to electric and electronic technical field, particularly a kind of multi-electrical level inverter low voltage traversing control method, equipment and system.
Background technology
Along with petering out of the energy, solar energy is utilized now to generate electricity more and more.But what solar energy pole plate exported is direct current, and needing through inverter inversion is feed back to electrical network or load after alternating current.Therefore, inverter plays key effect in solar photovoltaic generation system.
In recent years, as the important indicator ensureing operation of power networks, in photovoltaic generating system, low voltage crossing (LVRT, the Low Voltage Ride Through) ability of inverter is more and more taken seriously.
LVRT refers to when power system accident or disturbance cause the Voltage Drop of photovoltaic electric station grid connection point, fall in scope and time interval in certain voltage, photovoltaic plant can ensure that off-grid does not run continuously, avoid the extension of electric network fault, photovoltaic combining inverter needs to send certain active power and reactive power simultaneously, to support power system restoration, thus " passing through " this low-voltage time (region).
LVRT is divided into symmetry fall (three phase short circuit fault) and asymmetricly to fall (two-phase short-circuit fault, single-phase grounding fault).
Introduce LVRT technology in prior art below.
See Fig. 1, this figure is the grid-connected inverters control block diagram in prior art with LVRT function.
In grid-connected inverters controls, first gather electrical network three-phase voltage (e a, e b, e c) and three-phase current (i a, i b, i c); By the component i that coordinate transform obtains under dq reference axis dand i q; Electric network voltage phase angle γ is obtained by phase-angle detection.
Wherein LVRT comprises LVRT detection module 100 and LVRT control module 200 two parts.LVRT detection module 100 realizes the real-time detection to grid voltage amplitude and phase place, returns testing result realizes active current and reactive current in LVRT process control to LVRT control module 200, LVRT control module 200.
Although the control block diagram shown in Fig. 1 can complete low voltage crossing by control inverter, in low voltage crossing process, there is larger fluctuation in bus mid point electric current.
Therefore, those skilled in the art need the control method and the equipment that provide a kind of multi-electrical level inverter low voltage crossing, when asymmetric falling occurs line voltage, can complete low voltage crossing smoothly, and reduce the fluctuation of bus mid point electric current.
Summary of the invention
The embodiment of the present invention provides a kind of multi-electrical level inverter low voltage traversing control method, equipment and system, successfully can complete low voltage crossing, and reduce the fluctuation of bus mid point electric current when asymmetric falling occurs line voltage.
First aspect, a kind of multi-electrical level inverter low voltage traversing control method is provided, be applied in the inverter of photovoltaic electric station grid connection operation, the direct current of the output of the solar energy pole plate of photovoltaic plant inputs to inverter, and DC inverter is, after alternating current, alternating current is fed back to electrical network by inverter; Comprise the following steps:
The three-phase voltage of monitoring electrical network, judges whether line voltage asymmetric falling occurs; Described asymmetric falling comprises two-phase short-circuit fault and single-phase grounding fault;
If there is asymmetric falling in line voltage, then in the given three-phase grid voltage inputing to PWM device, inject power frequency common-mode voltage, described PWM controller according to described given three-phase grid voltage output pwm signal with the on off state of control inverter breaker in middle pipe.
In the first possible implementation of first aspect, before injecting power frequency common-mode voltage in the described given three-phase grid voltage to inputing to PWM controller, also comprise:
The amplitude of detection of grid three-phase voltage and phase place, and three-phase reactive current in asymmetric falling process and three-phase active current;
Amplitude and the phase place of described power frequency common-mode voltage is determined according to the amplitude of described electrical network three-phase voltage and phase place and three-phase reactive current and three-phase active current.
In conjunction with in first aspect and any one possible implementation above-mentioned, in the implementation that the second is possible, before injecting power frequency common-mode voltage in the described given three-phase grid voltage to inputing to PWM device, also comprise:
Detect positive bus-bar voltage and negative busbar voltage;
Positive and negative busbar voltage difference is obtained by described positive bus-bar voltage and negative busbar voltage;
Described positive and negative busbar voltage difference and reference voltage are compared, is determined amplitude and the phase place of described power frequency common-mode voltage by comparative result.
Second aspect, a kind of multi-electrical level inverter low voltage crossing control appliance is provided, be applied in the inverter of photovoltaic electric station grid connection operation, the direct current of the output of the solar energy pole plate of photovoltaic plant inputs to inverter, and DC inverter is, after alternating current, alternating current is fed back to electrical network by inverter; Comprise: judging unit and injection unit;
Described judging unit, for monitoring the three-phase voltage of electrical network, judges whether line voltage asymmetric falling occurs; Described asymmetric falling comprises two-phase short-circuit fault and single-phase grounding fault;
Described injection unit, during for judging that when judging unit asymmetric falling occurs line voltage, in the given three-phase grid voltage inputing to PWM device, inject power frequency common-mode voltage, described PWM controller according to described given three-phase grid voltage output pwm signal with the on off state of control inverter breaker in middle pipe.
In the first possible implementation of second aspect, also comprise: the first detecting unit and the first determining unit;
Described first detecting unit, for amplitude and the phase place of detection of grid three-phase voltage, and three-phase reactive current in asymmetric falling process and three-phase active current;
Described first determining unit, for determining amplitude and the phase place of described power frequency common-mode voltage according to the amplitude of described electrical network three-phase voltage and phase place and three-phase reactive current and three-phase active current.
In conjunction with in second aspect and any one possible implementation above-mentioned, in the implementation that the second is possible, also comprise: the second detecting unit, positive and negative busbar voltage difference obtain unit and the second determining unit;
Described second detecting unit, for detecting positive bus-bar voltage and negative busbar voltage;
Described positive and negative busbar voltage difference obtains unit, for obtaining positive and negative busbar voltage difference by described positive bus-bar voltage and negative busbar voltage;
Described second determining unit, for described positive and negative busbar voltage difference and reference voltage being compared, is determined amplitude and the phase place of described power frequency common-mode voltage by comparative result.
The third aspect, provides a kind of multi-electrical level inverter low voltage ride through control system, comprising: inverter, PWM device and controller;
Described inverter, the DC inverter for being exported by solar energy pole plate is that alternating current feeds back to electrical network;
Described PWM device, for output pwm signal under the control of the controller to the switching tube in inverter, the on off state of control switch pipe;
Described controller, for monitoring the three-phase voltage of electrical network, judges whether line voltage asymmetric falling occurs, and described asymmetric falling comprises two-phase short-circuit fault and single-phase grounding fault; If judge that line voltage occurs asymmetricly to fall, then in the given three-phase grid voltage inputing to PWM device, inject power frequency common-mode voltage.
In the first possible implementation of the third aspect, described controller, also for amplitude and the phase place of detection of grid three-phase voltage, and three-phase reactive current in asymmetric falling process and three-phase active current; Amplitude and the phase place of described power frequency common-mode voltage is determined according to the amplitude of described electrical network three-phase voltage and phase place and three-phase reactive current and three-phase active current.
In conjunction with in the third aspect and any one possible implementation above-mentioned, in the implementation that the second is possible, described controller, also for detecting positive bus-bar voltage and negative busbar voltage; Positive and negative busbar voltage difference is obtained by described positive bus-bar voltage and negative busbar voltage; Described positive and negative busbar voltage difference and reference voltage are compared, is determined amplitude and the phase place of described power frequency common-mode voltage by comparative result.
In conjunction with in the third aspect and any one possible implementation above-mentioned, in the implementation that the third is possible, described inverter is three-phase multi-electrical level inverter;
Described inverter is at least two parallel runnings.
Multi-electrical level inverter low voltage traversing control method, equipment and system that above technical scheme provides, judge line voltage occur asymmetric fall fault time, in given three-phase grid voltage, inject power frequency common-mode voltage.Because line voltage occurs asymmetric when falling fault, bus mid point electric current can produce power frequency fluctuation, in order to reduce the power frequency fluctuation of bus mid point electric current, therefore, just power frequency common-mode voltage was injected before PWM device, the pwm signal that such PWM device exports is exactly inject the later signal of power frequency common-mode voltage, because pwm signal is used for the on off state of control inverter breaker in middle pipe, is therefore reduced by the work of control inverter or reduces the power frequency fluctuation of bus mid point electric current.After the power frequency fluctuation of bus mid point electric current is reduced, the voltage stress that in inverter, each switching tube bears can reduce, and switching tube can not be caused like this to damage.
Accompanying drawing explanation
In order to be illustrated more clearly in the embodiment of the present invention or technical scheme of the prior art, be briefly described to the accompanying drawing used required in embodiment or description of the prior art below, apparently, accompanying drawing in the following describes is only some embodiments of the present invention, for those of ordinary skill in the art, under the prerequisite not paying creative work, other accompanying drawing can also be obtained according to these accompanying drawings.
Fig. 1 is the grid-connected inverters control block diagram in prior art with LVRT function;
Fig. 2 is multi-electrical level inverter low voltage traversing control method embodiment one flow chart provided by the invention;
Fig. 3 is that line voltage is for the inverter bus mid-point voltage wave pattern of B phase ground short circuit fault;
Fig. 4 is that asymmetric control block diagram when falling occurs line voltage provided by the invention;
Fig. 5 is multi-electrical level inverter low voltage traversing control method embodiment two flow chart provided by the invention;
Fig. 6 is multi-electrical level inverter low voltage traversing control method embodiment three flow chart provided by the invention;
Oscillogram when Fig. 7 is B relative ground circuit after injection power frequency common-mode voltage provided by the invention;
Fig. 8 is multi-electrical level inverter low voltage crossing control appliance embodiment one schematic diagram provided by the invention;
Fig. 9 is multi-electrical level inverter low voltage crossing control appliance embodiment two schematic diagram provided by the invention;
Figure 10 is multi-electrical level inverter low voltage crossing control appliance embodiment three schematic diagram provided by the invention;
Figure 11 is multi-electrical level inverter low voltage ride through control system embodiment one schematic diagram provided by the invention.
Embodiment
Below in conjunction with the accompanying drawing in the embodiment of the present invention, be clearly and completely described the technical scheme in the embodiment of the present invention, obviously, described embodiment is only the present invention's part embodiment, instead of whole embodiments.Based on the embodiment in the present invention, those of ordinary skill in the art, not making the every other embodiment obtained under creative work prerequisite, belong to the scope of protection of the invention.
For enabling above-mentioned purpose of the present invention, feature and advantage become apparent more, are described in detail the specific embodiment of the present invention below in conjunction with accompanying drawing.
It should be noted that; the embodiment of the present invention provides a kind of multi-electrical level inverter low voltage traversing control method, equipment and system; when there is asymmetric falling in line voltage; by injecting the fluctuation that power frequency common-mode voltage reduces bus mid point electric current in given three-phase voltage, and then the switching tube in protection inverter.
Embodiment of the method one:
See Fig. 2, this figure is multi-electrical level inverter low voltage traversing control method embodiment one flow chart provided by the invention.
The multi-electrical level inverter low voltage traversing control method that the present embodiment provides, be applied in the inverter of photovoltaic electric station grid connection operation, the direct current of the output of the solar energy pole plate of photovoltaic plant inputs to inverter, and DC inverter is, after alternating current, alternating current is fed back to electrical network by inverter; Comprise:
S201: the three-phase voltage of monitoring electrical network, judges whether line voltage asymmetric falling occurs; Described asymmetric falling comprises two-phase short-circuit fault and single-phase grounding fault;
It should be noted that, the method that the embodiment of the present invention provides is applicable to send in solar photovoltaic generation system asymmetric when falling fault.
Asymmetric fault of falling comprises: two-phase short-circuit fault, single-phase grounding fault.Such as, B phase ground short circuit fault, or, short trouble between A phase and B phase.
Be understandable that, this method is not suitable for symmetry and falls fault, and namely A phase, B phase and C phase three-phase are all short-circuited fault.
Such as, for three-level inverter, bus capacitor mid point electric current is determined by three-phase grid electric current and three-phase PWM switch function.When line voltage occur asymmetric fall fault time, there is larger fluctuation in bus capacitor mid point electric current, cause the fluctuation of upper and lower busbar voltage, specifically can see Fig. 3, this figure is that line voltage is for the inverter bus mid-point voltage wave pattern of B phase ground short circuit fault.
As can be seen from Figure 3, when ground short circuit fault occurs B phase, power frequency fluctuation (power frequency of China is 50Hz) will be produced on bus mid point electric current (in Fig. 3 corresponding inverter mid point electric current); Thus cause the power frequency fluctuation of inverter bus mid-point voltage.And by emulation and verification experimental verification; when there is asymmetric falling in line voltage; there is power frequency fluctuation in bus mid-point voltage; the voltage stress that the switching tube in inverter can be caused to bear when the fluctuation of bus mid-point voltage is larger is excessive or implement protection and cause LVRT failure, if increase the capacity of bus capacitor conversely, can increase system cost.
The present invention takes, when asymmetric falling occurs line voltage, to inject power frequency common-mode voltage, to reduce the fluctuation of bus mid point electric current.Fluctuation due to bus mid point electric current can produce the fluctuation of bus mid-point voltage, therefore, reduces the fluctuation of bus mid point electric current and then can reduce the fluctuation of bus mid-point voltage.
S202: if asymmetric falling occurs line voltage, then in the given three-phase grid voltage inputing to PWM device, inject power frequency common-mode voltage, described PWM controller according to described given three-phase grid voltage output pwm signal with the on off state of control inverter breaker in middle pipe.
Be understandable that, the object of injection power frequency common-mode voltage is the fluctuation in order to offset bus mid point electric current.
Specifically can see Fig. 4, this figure is the control block diagram of line voltage provided by the invention when there is asymmetric falling.
When judging asymmetric falling occurs, needing before PWM device, in given three-phase grid voltage, injecting power frequency common-mode voltage.As shown in Figure 4, given three-phase grid voltage is u a *, u b *and u c *; It should be noted that, the power frequency common-mode voltage of injection is a vector, comprises power frequency common-mode voltage amplitude and phase place.Amplitude and the phase place of the power frequency common-mode voltage injected are decided by the degree of depth of falling of line voltage.
In solar photovoltaic generation system shown in Fig. 4, comprise two inverters, these two inverter parallels.
Be understandable that, in solar photovoltaic generation system, only can comprise an inverter, also can comprise the inverter of multiple parallel running.
The method that the present embodiment provides is identical for the control of each inverter, injects identical power frequency common-mode voltage in each inverter.
To sum up, the multi-electrical level inverter low voltage traversing control method that the present embodiment provides, judge line voltage occur asymmetric fall fault time, in given three-phase grid voltage, inject power frequency common-mode voltage.Because line voltage occurs asymmetric when falling fault, bus mid point electric current can produce power frequency fluctuation, in order to reduce the power frequency fluctuation of bus mid point electric current, therefore, just power frequency common-mode voltage was injected before PWM device, the pwm signal that such PWM device exports is exactly inject the later signal of power frequency common-mode voltage, because pwm signal is used for the on off state of control inverter breaker in middle pipe, is therefore reduced by the work of control inverter or reduces the power frequency fluctuation of bus mid point electric current.After the power frequency fluctuation of bus mid point electric current is reduced, the voltage stress that in inverter, each switching tube bears can reduce, and switching tube can not be caused like this to damage.
The invention provides the control mode of two kinds of power frequency common-mode voltages, one is opened loop control, and another kind is closed-loop control, introduces in detail below in conjunction with specific embodiment.
Embodiment of the method two:
See Fig. 5, this figure is multi-electrical level inverter low voltage traversing control method embodiment two flow chart provided by the invention.
The method realizing multi-electrical level inverter low voltage crossing with opened loop control is introduced in the present embodiment.
S501 and S201 is identical, does not repeat them here.
S502: the amplitude of detection of grid three-phase voltage and phase place, and three-phase reactive current in asymmetric falling process and three-phase active current;
Due in operation of power networks process, three-phase voltage and the three-phase current information of electrical network can be gathered, therefore, just can judge whether asymmetric falling occurs by three-phase voltage.In addition, can determine by the information of voltage and current the amplitude and the phase place that need the power frequency common-mode voltage injected.
S503: amplitude and the phase place of determining described power frequency common-mode voltage according to the amplitude of described electrical network three-phase voltage and phase place and three-phase reactive current and three-phase active current.
S504: then inject power frequency common-mode voltage in the given three-phase grid voltage inputing to PWM device, described PWM controller according to described given three-phase grid voltage output pwm signal with the on off state of control inverter breaker in middle pipe.
It should be noted that, the method that the present embodiment provides, power frequency common-mode voltage is injected before being Fig. 4 PWM device in the position injecting power frequency common-mode voltage in given three-phase voltage.
The method that the present embodiment provides, do not need the voltage of detection or current feedback to compare to input and set-point or predetermined value, but directly determine the power frequency common-mode voltage that injects according to the voltage and current detected, belong to opened loop control, this control is fairly simple, and it is convenient to realize.By injecting power frequency common-mode voltage, can reduce the power frequency fluctuation of bus mid point electric current, thus reduce the voltage stress that in inverter, each switching tube bears, protection switch pipe is without prejudice.
Embodiment of the method three:
See Fig. 6, this figure is multi-electrical level inverter low voltage traversing control method embodiment three flow chart provided by the invention.
Realize the method for multi-electrical level inverter low voltage crossing with closed-loop control in the present embodiment.
S601 and S201 is identical, does not repeat them here.
S602: detect positive bus-bar voltage and negative busbar voltage;
S603: obtain positive and negative busbar voltage difference by described positive bus-bar voltage and negative busbar voltage;
Difference due to positive bus-bar voltage and negative busbar voltage can represent the fluctuation situation of bus mid point electric current, therefore, is used as feedback quantity by positive and negative busbar voltage difference, this feedback quantity and reference voltage is compared the fluctuation judging bus mid point electric current.
Be understandable that, described reference voltage is the voltage preset, and conveniently calculates, and can set reference voltage in the embodiment of the present invention is zero.
S604: described positive and negative busbar voltage difference and reference voltage are compared, is determined amplitude and the phase place of described power frequency common-mode voltage by comparative result.
S605: then inject power frequency common-mode voltage in the given three-phase grid voltage inputing to PWM device, described PWM controller according to described given three-phase grid voltage output pwm signal with the on off state of control inverter breaker in middle pipe.
It should be noted that, power frequency common-mode voltage is injected before being also Fig. 4 PWM device in the position injecting power frequency common-mode voltage in the present embodiment in given three-phase voltage.
In the present embodiment, adopt closed-loop control, obtain positive and negative busbar voltage difference by the positive bus-bar voltage that gathers and negative busbar voltage, positive and negative busbar voltage difference is fed back to input and reference voltage compares, determined amplitude and the phase place of the power frequency common-mode voltage of injection by comparative result.The closed-loop control that the present embodiment adopts, can be compared by the positive and negative busbar voltage difference of feedback and the reference voltage preset, can realize better like this controlling.
In order to the beneficial effect of the method that the above embodiment of the present invention provides is described better, illustrate below in conjunction with accompanying drawing.
See Fig. 7, oscillogram when this figure is B relative ground circuit after injection power frequency common-mode voltage provided by the invention.
Fig. 7 with Fig. 3 is compared and can find out, the opened loop control provided by the embodiment of the present invention or closed-loop control, inject power frequency common-mode voltage in given three-phase voltage after, the fluctuation of bus mid-point voltage and electric current when effectively reducing asymmetric falling.
As can be seen from Figure 3, the perunit value of inverter mid point electric current (bus mid point electric current) is probably 1, and in the figure 7, the perunit value of inverter mid point electric current (bus mid point electric current) is probably 0.5.
Apparatus embodiments one:
Based on the multi-electrical level inverter low voltage traversing control method that above embodiment provides, present invention also offers a kind of multi-electrical level inverter low voltage crossing control appliance, introduce in detail below in conjunction with accompanying drawing.
See Fig. 8, this figure is multi-electrical level inverter low voltage crossing control appliance embodiment one schematic diagram provided by the invention.
The multi-electrical level inverter low voltage crossing control appliance that the present embodiment provides, be applied in the inverter of photovoltaic electric station grid connection operation, the direct current of the output of the solar energy pole plate of photovoltaic plant inputs to inverter, and DC inverter is, after alternating current, alternating current is fed back to electrical network by inverter; Comprise: judging unit 800 and injection unit 900;
Described judging unit 800, for monitoring the three-phase voltage of electrical network, judges whether line voltage asymmetric falling occurs; Described asymmetric falling comprises two-phase short-circuit fault and single-phase grounding fault;
It should be noted that, the control appliance that the embodiment of the present invention provides is applicable to send in solar photovoltaic generation system asymmetric when falling fault.
Asymmetric fault of falling comprises: two-phase short-circuit fault, single-phase grounding fault.Such as, B phase ground short circuit fault, or, short trouble between A phase and B phase.
Be understandable that, this method is not suitable for symmetry and falls fault, and namely A phase, B phase and C phase three-phase are all short-circuited fault.
Such as, for three-level inverter, bus capacitor mid point electric current is determined by three-phase grid electric current and three-phase PWM switch function.When line voltage occur asymmetric fall fault time, there is larger fluctuation in bus capacitor mid point electric current, cause the fluctuation of upper and lower busbar voltage, specifically can see Fig. 3, this figure is that line voltage is for the inverter bus mid-point voltage wave pattern of B phase ground short circuit fault.
As can be seen from Figure 3, when ground short circuit fault occurs B phase, power frequency fluctuation (power frequency of China is 50Hz) will be produced on bus mid point electric current (in Fig. 3 corresponding inverter mid point electric current); Thus cause the power frequency fluctuation of inverter bus mid-point voltage.And by emulation and verification experimental verification; when there is asymmetric falling in line voltage; there is power frequency fluctuation in bus mid-point voltage; the voltage stress that the switching tube in inverter can be caused to bear when the fluctuation of bus mid-point voltage is larger is excessive or implement protection and cause LVRT failure, if increase the capacity of bus capacitor conversely, can increase system cost.
The present invention takes, when asymmetric falling occurs line voltage, to inject power frequency common-mode voltage, to reduce the fluctuation of bus mid point electric current.Fluctuation due to bus mid point electric current can produce the fluctuation of bus mid-point voltage, therefore, reduces the fluctuation of bus mid point electric current and then can reduce the fluctuation of bus mid-point voltage.
Described injection unit 900, during for judging that when judging unit asymmetric falling occurs line voltage, in the given three-phase grid voltage inputing to PWM device, inject power frequency common-mode voltage, described PWM controller according to described given three-phase grid voltage output pwm signal with the on off state of control inverter breaker in middle pipe.
It should be noted that, injection power frequency common-mode voltage is the fluctuation in order to offset bus mid point electric current.
Be understandable that, in solar photovoltaic generation system, only can comprise an inverter, also can comprise the inverter of multiple parallel running.
The equipment that the present embodiment provides is identical for the control of each inverter, injects identical power frequency common-mode voltage in each inverter.
To sum up, the multi-electrical level inverter low voltage crossing control appliance that the present embodiment provides, judge line voltage occur asymmetric fall fault time, in given three-phase grid voltage, inject power frequency common-mode voltage.Because line voltage occurs asymmetric when falling fault, bus mid point electric current can produce power frequency fluctuation, in order to reduce the power frequency fluctuation of bus mid point electric current, therefore, just power frequency common-mode voltage was injected before PWM device, the pwm signal that such PWM device exports is exactly inject the later signal of power frequency common-mode voltage, because pwm signal is used for the on off state of control inverter breaker in middle pipe, is therefore reduced by the work of control inverter or reduces the power frequency fluctuation of bus mid point electric current.After the power frequency fluctuation of bus mid point electric current is reduced, the voltage stress that in inverter, each switching tube bears can reduce, and switching tube can not be caused like this to damage.
Apparatus embodiments two:
Embodiments provide two kinds of different control appliances, a kind of is the control appliance of open loop control mode, and another kind is the control appliance of close-loop control mode, introduces respectively below, first introduces the control appliance of open loop control mode.
See Fig. 9, this figure is multi-electrical level inverter low voltage crossing control appliance embodiment two schematic diagram provided by the invention.
The multi-electrical level inverter low voltage crossing control appliance that the present embodiment provides, except comprising judging unit 800 in apparatus embodiments one and injection unit 900, also comprises: the first detecting unit 1000a and the first determining unit 1000b;
Described first detecting unit 1000a, for amplitude and the phase place of detection of grid three-phase voltage, and three-phase reactive current in asymmetric falling process and three-phase active current;
Due in operation of power networks process, three-phase voltage and the three-phase current information of electrical network can be gathered, therefore, just can judge whether asymmetric falling occurs by three-phase voltage.In addition, can determine by the information of voltage and current the amplitude and the phase place that need the power frequency common-mode voltage injected.
Described first determining unit 1000b, for determining amplitude and the phase place of described power frequency common-mode voltage according to the amplitude of described electrical network three-phase voltage and phase place and three-phase reactive current and three-phase active current.
It should be noted that, the control appliance that the present embodiment provides, power frequency common-mode voltage is injected before being Fig. 4 PWM device in the position injecting power frequency common-mode voltage in given three-phase voltage.
The control appliance that the present embodiment provides, do not need the voltage of detection or current feedback to compare to input and set-point or predetermined value, but directly determine the power frequency common-mode voltage that injects according to the voltage and current detected, belong to opened loop control, this control is fairly simple, and it is convenient to realize.By injecting power frequency common-mode voltage, can reduce the power frequency fluctuation of bus mid point electric current, thus reduce the voltage stress that in inverter, each switching tube bears, protection switch pipe is without prejudice.
Apparatus embodiments three:
See Figure 10, this figure is multi-electrical level inverter low voltage crossing control appliance embodiment three schematic diagram provided by the invention.
Introduce the control appliance with close-loop control mode below.
The multi-electrical level inverter low voltage crossing control appliance that the present embodiment provides, except comprising judging unit 800 in apparatus embodiments one and injection unit 900, also comprise: the second detecting unit 1000c, positive and negative busbar voltage difference obtain unit 1000d and the second determining unit 1000e;
Described second detecting unit 1000c, for detecting positive bus-bar voltage and negative busbar voltage;
Described positive and negative busbar voltage difference obtains unit 1000d, for obtaining positive and negative busbar voltage difference by described positive bus-bar voltage and negative busbar voltage;
Difference due to positive bus-bar voltage and negative busbar voltage can represent the fluctuation situation of bus mid point electric current, therefore, is used as feedback quantity by positive and negative busbar voltage difference, this feedback quantity and reference voltage is compared the fluctuation judging bus mid point electric current.
Be understandable that, described reference voltage is the voltage preset, and conveniently calculates, and can set reference voltage in the embodiment of the present invention is zero.
Described second determining unit 1000e, for described positive and negative busbar voltage difference and reference voltage being compared, is determined amplitude and the phase place of described power frequency common-mode voltage by comparative result.
It should be noted that, power frequency common-mode voltage is injected before being also Fig. 4 PWM device in the position injecting power frequency common-mode voltage in the present embodiment in given three-phase voltage.
In the present embodiment, adopt closed-loop control, obtain positive and negative busbar voltage difference by the positive bus-bar voltage that gathers and negative busbar voltage, positive and negative busbar voltage difference is fed back to input and reference voltage compares, determined amplitude and the phase place of the power frequency common-mode voltage of injection by comparative result.The closed-loop control that the present embodiment adopts, can be compared by the positive and negative busbar voltage difference of feedback and the reference voltage preset, can realize better like this controlling.
A kind of multi-electrical level inverter low voltage traversing control method provided based on above embodiment and equipment, present invention also offers a kind of multi-electrical level inverter low voltage ride through control system, describe in detail below in conjunction with embodiment.
System embodiment one:
See Figure 11, this figure is multi-electrical level inverter low voltage ride through control system embodiment one schematic diagram provided by the invention.
The multi-electrical level inverter low voltage ride through control system that the present embodiment provides, comprising: inverter 1100, PWM device 1200 and controller 1300;
Described inverter 1100, the DC inverter for being exported by solar energy pole plate is that alternating current feeds back to electrical network;
Described PWM device 1200, for output pwm signal under the control of the controller to the switching tube in inverter, the on off state of control switch pipe;
Described controller 1300, for monitoring the three-phase voltage of electrical network, judges whether line voltage asymmetric falling occurs, and described asymmetric falling comprises two-phase short-circuit fault and single-phase grounding fault; If judge that line voltage occurs asymmetricly to fall, then in the given three-phase grid voltage inputing to PWM device, inject power frequency common-mode voltage.
It should be noted that, the method that the embodiment of the present invention provides is applicable to send in solar photovoltaic generation system asymmetric when falling fault.
Asymmetric fault of falling comprises: two-phase short-circuit fault, single-phase grounding fault.Such as, B phase ground short circuit fault, or, short trouble between A phase and B phase.
Be understandable that, this method is not suitable for symmetry and falls fault, and namely A phase, B phase and C phase three-phase are all short-circuited fault.
Such as, for three-level inverter, bus capacitor mid point electric current is determined by three-phase grid electric current and three-phase PWM switch function.When line voltage occur asymmetric fall fault time, there is larger fluctuation in bus capacitor mid point electric current, causes the fluctuation of upper and lower busbar voltage.
When judging asymmetric falling occurs, needing before PWM device, in given three-phase grid voltage, injecting power frequency common-mode voltage.As shown in Figure 4, given three-phase grid voltage is u a *, u b *and u c *; It should be noted that, the power frequency common-mode voltage of injection is a vector, comprises power frequency common-mode voltage amplitude and phase place.Amplitude and the phase place of the power frequency common-mode voltage injected are decided by the degree of depth of falling of line voltage.
In solar photovoltaic generation system shown in Fig. 4, comprise two inverters, these two inverter parallels.
Be understandable that, in solar photovoltaic generation system, only can comprise an inverter, also can comprise the inverter of multiple parallel running.
The control system that the present embodiment provides is identical for the control of each inverter, injects identical power frequency common-mode voltage in each inverter.Be understandable that, same PWM device 1200 and same controller 1300 during multiple inverter, can be shared.
To sum up, the multi-electrical level inverter low voltage ride through control system that the present embodiment provides, controller 1300 judge line voltage occur asymmetric fall fault time, in given three-phase grid voltage, inject power frequency common-mode voltage.Because line voltage occurs asymmetric when falling fault, bus mid point electric current can produce power frequency fluctuation, in order to reduce the power frequency fluctuation of bus mid point electric current, therefore, just power frequency common-mode voltage was injected before PWM device 1200, the pwm signal that such PWM device 1200 exports is exactly inject the later signal of power frequency common-mode voltage, because pwm signal is used for the on off state of control inverter 1300 breaker in middle pipe, is therefore reduced by the work of control inverter 1300 or reduce the power frequency fluctuation of bus mid point electric current.After the power frequency fluctuation of bus mid point electric current is reduced, the voltage stress that in inverter 1300, each switching tube bears can reduce, and switching tube can not be caused like this to damage.
The invention provides the control mode of two kinds of power frequency common-mode voltages, one is opened loop control, and another kind is closed-loop control, introduces in detail below in conjunction with specific embodiment.
System embodiment two:
The operation principle that controller realizes in the mode of opened loop control controlling is introduced in the present embodiment.
The present embodiment middle controller, also for amplitude and the phase place of detection of grid three-phase voltage, and three-phase reactive current in asymmetric falling process and three-phase active current; Amplitude and the phase place of described power frequency common-mode voltage is determined according to the amplitude of described electrical network three-phase voltage and phase place and three-phase reactive current and three-phase active current.
Due in operation of power networks process, three-phase voltage and the three-phase current information of electrical network can be gathered, therefore, just can judge whether asymmetric falling occurs by three-phase voltage.In addition, can determine by the information of voltage and current the amplitude and the phase place that need the power frequency common-mode voltage injected.
The control system that the present embodiment provides, do not need the voltage of detection or current feedback to compare to input and set-point or predetermined value, but directly determine the power frequency common-mode voltage that injects according to the voltage and current detected, belong to opened loop control, this control is fairly simple, and it is convenient to realize.By injecting power frequency common-mode voltage, can reduce the power frequency fluctuation of bus mid point electric current, thus reduce the voltage stress that in inverter, each switching tube bears, protection switch pipe is without prejudice.
System embodiment three:
The operation principle that controller realizes in the mode of closed-loop control controlling is introduced in the present embodiment.
The present embodiment middle controller, also for detecting positive bus-bar voltage and negative busbar voltage; Positive and negative busbar voltage difference is obtained by described positive bus-bar voltage and negative busbar voltage; Described positive and negative busbar voltage difference and reference voltage are compared, is determined amplitude and the phase place of described power frequency common-mode voltage by comparative result.
Difference due to positive bus-bar voltage and negative busbar voltage can represent the fluctuation situation of bus mid point electric current, therefore, is used as feedback quantity by positive and negative busbar voltage difference, this feedback quantity and reference voltage is compared the fluctuation judging bus mid point electric current.
Be understandable that, described reference voltage is the voltage preset, and conveniently calculates, and can set reference voltage in the embodiment of the present invention is zero.
In the present embodiment, adopt closed-loop control, obtain positive and negative busbar voltage difference by the positive bus-bar voltage that gathers and negative busbar voltage, positive and negative busbar voltage difference is fed back to input and reference voltage compares, determined amplitude and the phase place of the power frequency common-mode voltage of injection by comparative result.The closed-loop control that the present embodiment adopts, can be compared by the positive and negative busbar voltage difference of feedback and the reference voltage preset, can realize better like this controlling.
It should be noted that, the inverter in the control system that above embodiment provides can be three-phase multi-electrical level inverter; Be such as three-level inverter, five-electrical level inverter etc.In addition, described inverter also can be an inverter, also can be the inverter of multiple parallel running, such as, be two inverter parallels.
The topology of inverter can be T-shaped or I type.
It should be noted that the control system that the above embodiment of the present invention provides, owing to reducing the fluctuation of bus mid point electric current, therefore also reduces the capacitance of bus capacitor simultaneously.Because in identical bus mid point current fluctuation situation, the capacitance of bus capacitor is larger, and the fluctuation of bus mid-point voltage is less.The above is only preferred embodiment of the present invention, not does any pro forma restriction to the present invention.Although the present invention discloses as above with preferred embodiment, but and be not used to limit the present invention.Any those of ordinary skill in the art, do not departing under technical solution of the present invention ambit, the Method and Technology content of above-mentioned announcement all can be utilized to make many possible variations and modification to technical solution of the present invention, or be revised as the Equivalent embodiments of equivalent variations.Therefore, every content not departing from technical solution of the present invention, according to technical spirit of the present invention to any simple modification made for any of the above embodiments, equivalent variations and modification, all still belongs in the scope of technical solution of the present invention protection.

Claims (10)

1. a multi-electrical level inverter low voltage traversing control method, it is characterized in that, be applied in the inverter of photovoltaic electric station grid connection operation, the direct current of the output of the solar energy pole plate of photovoltaic plant inputs to inverter, and DC inverter is, after alternating current, alternating current is fed back to electrical network by inverter; Comprise the following steps:
The three-phase voltage of monitoring electrical network, judges whether line voltage asymmetric falling occurs; Described asymmetric falling comprises two-phase short-circuit fault and single-phase grounding fault;
If there is asymmetric falling in line voltage, then in the given three-phase grid voltage inputing to PWM device, inject power frequency common-mode voltage, described PWM controller according to described given three-phase grid voltage output pwm signal with the on off state of control inverter breaker in middle pipe.
2. multi-electrical level inverter low voltage traversing control method according to claim 1, is characterized in that, before injecting power frequency common-mode voltage, also comprises in the described given three-phase grid voltage to inputing to PWM controller:
The amplitude of detection of grid three-phase voltage and phase place, and three-phase reactive current in asymmetric falling process and three-phase active current;
Amplitude and the phase place of described power frequency common-mode voltage is determined according to the amplitude of described electrical network three-phase voltage and phase place and three-phase reactive current and three-phase active current.
3. multi-electrical level inverter low voltage traversing control method according to claim 1, is characterized in that, before injecting power frequency common-mode voltage, also comprises in the described given three-phase grid voltage to inputing to PWM device:
Detect positive bus-bar voltage and negative busbar voltage;
Positive and negative busbar voltage difference is obtained by described positive bus-bar voltage and negative busbar voltage;
Described positive and negative busbar voltage difference and reference voltage are compared, is determined amplitude and the phase place of described power frequency common-mode voltage by comparative result.
4. a multi-electrical level inverter low voltage crossing control appliance, it is characterized in that, be applied in the inverter of photovoltaic electric station grid connection operation, the direct current of the output of the solar energy pole plate of photovoltaic plant inputs to inverter, and DC inverter is, after alternating current, alternating current is fed back to electrical network by inverter; Comprise: judging unit and injection unit;
Described judging unit, for monitoring the three-phase voltage of electrical network, judges whether line voltage asymmetric falling occurs; Described asymmetric falling comprises two-phase short-circuit fault and single-phase grounding fault;
Described injection unit, during for judging that when judging unit asymmetric falling occurs line voltage, in the given three-phase grid voltage inputing to PWM device, inject power frequency common-mode voltage, described PWM controller according to described given three-phase grid voltage output pwm signal with the on off state of control inverter breaker in middle pipe.
5. multi-electrical level inverter low voltage crossing control appliance according to claim 4, is characterized in that, also comprise: the first detecting unit and the first determining unit;
Described first detecting unit, for amplitude and the phase place of detection of grid three-phase voltage, and three-phase reactive current in asymmetric falling process and three-phase active current;
Described first determining unit, for determining amplitude and the phase place of described power frequency common-mode voltage according to the amplitude of described electrical network three-phase voltage and phase place and three-phase reactive current and three-phase active current.
6. multi-electrical level inverter low voltage crossing control appliance according to claim 4, is characterized in that, also comprise: the second detecting unit, positive and negative busbar voltage difference obtain unit and the second determining unit;
Described second detecting unit, for detecting positive bus-bar voltage and negative busbar voltage;
Described positive and negative busbar voltage difference obtains unit, for obtaining positive and negative busbar voltage difference by described positive bus-bar voltage and negative busbar voltage;
Described second determining unit, for described positive and negative busbar voltage difference and reference voltage being compared, is determined amplitude and the phase place of described power frequency common-mode voltage by comparative result.
7. a multi-electrical level inverter low voltage ride through control system, is characterized in that, comprising: inverter, PWM device and controller;
Described inverter, the DC inverter for being exported by solar energy pole plate is that alternating current feeds back to electrical network;
Described PWM device, for output pwm signal under the control of the controller to the switching tube in inverter, the on off state of control switch pipe;
Described controller, for monitoring the three-phase voltage of electrical network, judges whether line voltage asymmetric falling occurs, and described asymmetric falling comprises two-phase short-circuit fault and single-phase grounding fault; If judge that line voltage occurs asymmetricly to fall, then in the given three-phase grid voltage inputing to PWM device, inject power frequency common-mode voltage.
8. multi-electrical level inverter low voltage ride through control system according to claim 7, is characterized in that, described controller, also for amplitude and the phase place of detection of grid three-phase voltage, and three-phase reactive current in asymmetric falling process and three-phase active current; Amplitude and the phase place of described power frequency common-mode voltage is determined according to the amplitude of described electrical network three-phase voltage and phase place and three-phase reactive current and three-phase active current.
9. multi-electrical level inverter low voltage ride through control system according to claim 7, is characterized in that, described controller, also for detecting positive bus-bar voltage and negative busbar voltage; Positive and negative busbar voltage difference is obtained by described positive bus-bar voltage and negative busbar voltage; Described positive and negative busbar voltage difference and reference voltage are compared, is determined amplitude and the phase place of described power frequency common-mode voltage by comparative result.
10. the multi-electrical level inverter low voltage ride through control system according to any one of claim 7-9, is characterized in that, described inverter is three-phase multi-electrical level inverter;
Described inverter is at least two parallel runnings.
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