CN103560520A - Unified power quality controller suitable for fault ride-through and control method - Google Patents

Abstract

The invention discloses a unified power quality controller suitable for fault ride-through and a control method. A UPQC is connected on the two sides of a photovoltaic power station exit transformer in a bridging mode, and the amplitude of an inverter exit voltage in a high voltage failure is compensated to keep the amplitude in a rated value. The harmonic component of a network voltage is compensated through a UPQC system, the exit voltage THD of a photovoltaic grid-connected inverter is close to 0, and the failure test speed and the response speed of the photovoltaic grid-connected inverter in a photovoltaic power station are improved. Reactive compensation benefits are provided by the UPQCs under the condition the volume design of meeting high voltage ride-through with a 1.3-time rated value. When a low voltage drops, the photovoltaic power station is matched to generate reactive power, the requirement of a power grid for photovoltaic power station reactive power can be met faster, and in a high voltage failure, an APF absorbs power grid reactive power to help to restore a power grid voltage.

Description

Be applicable to Unified Power Quality Controller and the control method of fault traversing

Technical field

The present invention relates to a kind of novel Unified Power Quality Controller (unified power quality conditioner, UPQC), relate in particular to a kind of Unified Power Quality Controller and control method that the high/low voltage of grid-connected photovoltaic power station passes through that be applicable to.

Background technology

In recent years, domestic photovoltaic plant installation total capacity constantly increases, and centralized photovoltaic generation is increasing on the impact of electric power system.The frequency of electrical network and amplitude effect being can not be ignored from grid-connected of photovoltaic plant.In the < < photo-voltaic power generation station access power system technology regulation > > that come into effect in June, 2013, stipulated that big-and-middle-sized photovoltaic plant should have low voltage ride-through capability.Line voltage power station when 0.9pu-1.1pu can normally be moved, and can keep at least continuous service 10 seconds at 1.1pu-1.2pu, and 1.2pu-1.3pu can be not less than 0.5 second by continuous service.Existing most of photovoltaic plant is when line voltage falls, and photovoltaic DC-to-AC converter output current is overcurrent not, has low voltage ride-through capability.And most of photovoltaic plant keeps grid-connected requirement while not considering in GB about high voltage fail, if meet the high voltage crossing requirement of GB, photovoltaic DC-to-AC converter by bear the highest 1.3 times to the overvoltage of normal working voltage, have a strong impact on the life-span of inverter switching device and increased switch conduction loss.During simultaneously general photovoltaic DC-to-AC converter normal operation, its modulation depth approaches 1.15, and line voltage rising may cause photovoltaic cell cannot operate in maximum power point even power oscillation can occur.Researcher has proposed a series of control algolithm for the high voltage crossing problem of blower fan.Method mainly contains several as follows: 1, utilize blower fan or power equipment (SVG, STATCOM) to electrical network absorb idle when keeping fault blower fan converter outlet voltage constant, and line reactance size is depended in the maintenance of converter output voltage.Reactance between general photovoltaic DC-to-AC converter outlet and point of common coupling (PCC) is less, needs very large reactive source capacity could keep Network Voltage Stability.2, regulate transformer voltage ratio, the regulation voltage that this scheme can not be level and smooth should not be applied.And other high voltage crossing schemes of such scheme and proposition are difficult to be used in single-phase and two-phase imbalance fault.

A kind of bucking-out system that effectively maintains voltage stabilization is UPQC.Utilizing UPQC to maintain the stable example of load side voltage is studied extensively and profoundly.Structure as shown in Figure 1, it can, when the high/low voltage failure of electrical network, keep load user's voltage and power stability.And being applied in photo-voltaic power generation station outlet side, UPQC to maintain the scheme of power station output voltage stabilization, do not obtain researcher's attention.Figure 2 shows that photovoltaic electric station grid connection schematic diagram, researcher is easy to expect by dynamic voltage compensator (dynamic voltage restorer, DVR) and active filter (active power filter, APF) be combined into Unified Power Quality Controller and be connected near the formation of PCC point as Fig. 3, the structure shown in 4.When this topology can effectively keep electrical network high voltage fail, inverter outlet voltage magnitude is constant.UPQC shown in Fig. 3, need to export series transformer at APF, and UPQC cost is higher.UPQC shown in Fig. 4 is connected in low-pressure side, and UPQC system has been saved a transformer, and under its inverter switching device withstand voltage prerequisite the same with Fig. 3, its larger grade of current rating, and inverter switching device loss is excessive, and system is difficult for realizing.

In new GB, the response time of regulation photovoltaic plant dynamic reactive electric current after low voltage failure is not more than 30ms.Therefore improve efficiency and the speed of fault detect and reduce photovoltaic plant that to send the idle adjusting time most important, and voltage harmonic component in electrical network can affect photovoltaic inverting system phase-locked loop (phase-locked loop, PLL) to the detection speed of the high/low voltage failure of electrical network and precision, and then affect Whole Response speed and the precision of photovoltaic plant.Therefore the detection speed and the precision that how to improve PLL become the key factor that improves photovoltaic parallel in system transient response speed and precision.

Summary of the invention

The object of the invention is for overcoming the above problems, a kind of novel Unified Power Quality Controller that is applicable to photovoltaic plant fault traversing and control method are provided.UPQC is connected across the both sides of photovoltaic plant outlet transformer, and during compensation high voltage fail, the amplitude of inverter outlet voltage makes it maintain rated value.And the harmonic component of this UPQC system balance line voltage, photovoltaic combining inverter outlet voltage THD approaches 0, has improved fault detect speed and the response speed of photovoltaic combining inverter in photovoltaic plant.UPQC, in the Capacity design situation of the high voltage crossing of its satisfied 1.3 times of rated values, provides reactive power compensation benefit.During Low Dropout, coordinate photovoltaic plant to send out idle, make it meet quickly electrical network to the idle requirement of exerting oneself of photovoltaic plant, during high voltage fail, APF absorbs electric network reactive-load help and recovers line voltage.

To achieve these goals, the present invention adopts following technical scheme.

Be applicable to a Unified Power Quality Controller for fault traversing, comprise APF and DVR, its APF is partly connected in parallel on the low-pressure side of photovoltaic plant outlet transformer, and DVR is connected on the high-pressure side of photovoltaic plant outlet transformer.And APF coordinate photovoltaic plant electrical network low/send during high voltage fault (absorption) idle, DVR compensates the harmonic component of its line voltage and when high voltage fault, photovoltaic plant is exported to voltage compensation to rated value.

The present invention also provides a kind of control method that is applicable to the Unified Power Quality Controller of fault traversing, described DVR part both when high voltage fail bucking voltage amplitude to make photovoltaic plant outlet voltage be rated value, the harmonic voltage of compensation network side again.

Further, by detecting PCC place and the on high-tension side voltage V of photovoltaic plant outlet transformer _pcc, V _pv, the voltage V of the DVR that obtains connecting _dVR=V _pcc-V _pv, the reference signal V of DVR ^* _dVR=V ^* _pv-V _pcc, V wherein ^* _pvfor the on high-tension side reference signal of photovoltaic plant outlet transformer, the amplitude of reference signal and phase place are synchronizeed with electrical network nominal voltage signal.The control loop of compensation harmonic is taked rest frame, wherein resonant controller H _n(s) (n=5,7,11,13) expression formula is shown below:

$H_n\left(s\right)=2K_I{w}_c\frac{s+{\mathrm{<figure-callout\; id="2"\; label="w\; c\; s"\; filenames="HDA0000411704280000041.png,HDA0000411704280000051.png"\; state="\{\{state\}\}">w</figure-callout>}}_c}{s^{}}$

K wherein _ifor gain, w _cfor the shearing frequency of system, w _nfor the harmonic frequency of appointment, s is complex parameter.

As a further improvement on the present invention, described APF maintains the stable of UPQC direct-current chain electric capacity and no-power compensation function is provided.

Further, UPQC is according to compensation high voltage fail desired capacity, take the DVR, APF capacity perunit value of UPQC as H as example (the rated capacity Sn that fiducial value is photovoltaic plant).In meeting the limited field of UPQC capacity, it is idle and when high voltage, absorb electric network reactive-load that APF sends out certain when low voltage failure.During low voltage failure (DVR uncompensation voltage-drop UPQC is meritorious flowing through not), APF maximum can be sent the idle of H.During low voltage crossing, the idle reference signal I of APF ^* _qand the reference signal meritorious and idle component of photovoltaic plant electric current is respectively I _dref, I _qrefas follows:

A) voltage on line side U>0.9-2H/3;

I ^* _q＝-1.5*(0.9-k)I _N

I _qref＝0

$I_{\mathrm{dref}}=I_N\sqrt{1-2.25*{(0.9-k)}^2}$

B) voltage on line side 0.25<U<=0.9-2H/3;

I ^* _q＝-HI _N

I _qref＝I _N[-1.5*(0.9-k)+H]

$I_{\mathrm{dref}}=I_N\sqrt{1-2.25*{(0.9-k)}^2}$

C) voltage on line side U<=0.25;

I ^* _q＝-HI _N

I _qref＝1.05I _N+HI _N

I _dref＝0

I wherein _nfor photovoltaic output rated current, k is the perunit value (take electrical network rated value as fiducial value) of PCC place voltage during the high voltage fail rated value of 1.1 times (voltage higher than), and photovoltaic plant is entirely sent out and gained merit, and UPQC absorbs idle in right amount, and it is idle, and reference signal is as follows:

I ^* _q＝a*(k-1.1)I _N

Wherein a is reactive power compensation coefficient, and its occurrence determines by the capacity of APF, during high voltage fail, and the apparent power S of APF _aPFfor:

$\left|S_{\mathrm{APE}}\right|=\sqrt{{(1-1/k)}^2+a^2{(k-1.1)}^2}{P}_N$

P wherein _nfor photovoltaic output rated power (during normal operation, power factor (PF) approaches 1), from above formula, be not difficult to find out k and S _aPFbe directly proportional, a value is as follows:

$\left|S_{\mathrm{APE}}\right|\&le;{\mathrm{HP}}_N\&DoubleRightArrow;a=\sqrt{H^2-0.053}/0.2$

The apparent power S that export photovoltaic plant outlet transformer high-pressure side _outfor:

$\left|S_{\mathrm{out}}\right|=\sqrt{{{\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="HDA0000411704280000041.png,HDA0000411704280000051.png"\; state="\{\{state\}\}">P</figure-callout>}}^2}_{\mathrm{out}}+{{\mathrm{<figure-callout\; id="2"\; label="Q"\; filenames="HDA0000411704280000041.png,HDA0000411704280000051.png"\; state="\{\{state\}\}">Q</figure-callout>}}^2}_{\mathrm{out}}}=\sqrt{{(P_N/k)}^2+{[a*(k-1.1)P_N]}^2}$

$\&le;P_N\sqrt{H^2-1+2/k}\&le;{\mathrm{<figure-callout\; id="2"\; label="P\; N\; H"\; filenames="HDA0000411704280000041.png,HDA0000411704280000051.png"\; state="\{\{state\}\}">P</figure-callout>}}_N\sqrt{H^{}}\sqrt{{}^2+0.82},(1.1\&le;k\&le;1.3)$

The H of design is no more than 0.4, and transformer nonoverload now, so this Measures of Reactive Compensation can not bring transformer and circuit overload.

Innovative point of the present invention is: novel UPQC access infrastructure, and its APF partly accesses the low-pressure side of photovoltaic plant outlet transformer, and DVR is connected on the high-pressure side of photovoltaic plant outlet transformer.The voltage harmonic of UPQC compensation network side and to maintain photovoltaic plant outlet voltage when electrical network high voltage fail be rated value.The APF of UPQC partly coordinates photovoltaic plant to electrical network, to send out idle and absorb electric network reactive-load when the electrical network high voltage fail when low voltage failure of electric network to help to recover line voltage.

The present invention can directly be installed in photovoltaic plant outlet side to meet high voltage crossing requirement not needs photovoltaic plant is done to any transformation, the UPQC that compares general access high-voltage fence can save a transformer effectively.

The present invention can compensation network side voltage harmonic, improved the phase-locked speed of phase-locked loop and the fault detect speed of photovoltaic parallel in system in photovoltaic plant.During low voltage failure, APF part is sent out appropriate fast idle help photovoltaic plant and within the time of appointment, is sent the idle amount of national standard requirement.During high voltage fail, APF provides no-power compensation function, and absorption mesh side is idle, and help line voltage recovers.

Beneficial effect of the present invention: the access infrastructure of controller of the present invention can directly be installed in photovoltaic plant outlet side with meet grid-connected new standard high voltage appearance pass through require and not needs photovoltaic plant is done to any transformation; Compare the UPQC of general access high-voltage fence, this access way can reduce by a three-phase transformer effectively; The harmonic component of its DVR partial-compensation electrical network is accelerated fault detect speed thereby make photovoltaic combining inverter ac output voltage approach the phase-locked speed of the sinusoidal PLL of raising simultaneously; APF is in good time send (absorption) idle, effectively meet electric network reactive-load requirement.

Accompanying drawing explanation

Fig. 1: UPQC access load-side schematic diagram.

Fig. 2: photovoltaic plant access electrical network schematic diagram.

The 11OKV side of Fig. 3: UPQC access photovoltaic plant.

The 10KV side of Fig. 4: UPQC access photovoltaic plant.

Fig. 5: the UPQC structure chart that is applicable to photovoltaic plant fault traversing.

Fig. 6: DVR control block diagram.

Fig. 7: APF control block diagram.

Embodiment

Below in conjunction with accompanying drawing and embodiment, the invention will be further described.

As shown in Figure 5, APF accesses the low-pressure side of 110KV transformer to topology of the present invention, the high-pressure side of DVR access 110KV transformer.

As shown in Figure 5, the voltage V of PCC place _pcc, the photovoltaic outlet voltage V after DVR compensation _pv, DVR takes the compensation of voltage same-phase, has:

$S_{\mathrm{out}}=P_{\mathrm{out}}+{\mathrm{jQ}}_{\mathrm{out}}=\frac{V_{\mathrm{pv}}}{V_{\mathrm{pcc}}}(P_g+{\mathrm{jQ}}_g)$

$P_g=P_{\mathrm{pv}},P_{\mathrm{APF}}=(1-\frac{V_{\mathrm{pv}}}{V_{\mathrm{pcc}}})P_{\mathrm{pv}}$

$Q_g=\frac{V_{\mathrm{pcc}}}{V_{\mathrm{pv}}}(Q_{\mathrm{pv}}+Q_{\mathrm{APF}})$

Wherein j is imaginary unit; S _outapparent power for the output of 110KV high voltage side of transformer; P _out, Q _outbe respectively the meritorious and reactive power of 110KV high voltage side of transformer; P _g, Q _gbe respectively the meritorious and reactive power of injecting grid side; P _pv, Q _pvfor gaining merit that photovoltaic plant sends; P _aPF, Q _aPFbe respectively the meritorious and reactive power that APF sends.UPQC system has bucking voltage amplitude and harmonic wave, and no-power compensation function, and its concrete control system is as follows.

1, DVR control system

The DVR part of UPQC both can be when high voltage fail bucking voltage amplitude to make photovoltaic plant outlet voltage be rated value (PCC place voltage moves higher than rated value DVR), harmonic voltage that again can compensation network side.DVR control block diagram as shown in Figure 6.By detecting the voltage V of PCC place and 110KV high voltage side of transformer _pcc, V _pv, the voltage V of release series connection DVR _dVR=V _pcc-V _pv, the reference signal V of DVR ^* _dVR=V ^* _pv-V _pcc, V wherein ^* _pvfor the reference signal of 110KV high voltage side of transformer, the amplitude of reference signal and phase place are synchronizeed with electrical network nominal voltage signal.The control loop of compensation harmonic is taked rest frame, specific strategy as shown in Figure 6, resonant controller H wherein _n(s) (n=5,7,11,13) expression formula is shown below:

$H_n\left(s\right)=2K_I{w}_c\frac{s+{\mathrm{<figure-callout\; id="2"\; label="w\; c\; s"\; filenames="HDA0000411704280000041.png,HDA0000411704280000051.png"\; state="\{\{state\}\}">w</figure-callout>}}_c}{s^{}}$

K wherein _ifor gain, w _cfor the shearing frequency of system, w _nfor the harmonic frequency of appointment, s is complex parameter.

2, APF control system

APF in parallel maintains the stable of UPQC direct-current chain electric capacity and no-power compensation function is provided.UPQC is with the desired Capacity design of compensation high voltage fail, and with the DVR of UPQC, APF capacity perunit value is that H is example (the rated capacity Sn that fiducial value is photovoltaic plant).In meeting the limited field of UPQC capacity, it is idle and when high voltage, absorb electric network reactive-load that APF sends out certain when low voltage failure.During low voltage failure (DVR uncompensation voltage-drop UPQC is meritorious flowing through not), APF maximum can be sent the idle of H.Control system as shown in Figure 7, during low voltage crossing, the idle reference signal I of APF ^* _qand the reference signal meritorious and idle component of photovoltaic plant electric current is respectively I _dref, I _qrefas follows:

A) voltage on line side U>0.9-2H/3;

I ^* _q＝-1.5*(0.9-k)I _N

I _qref＝0

$I_{\mathrm{dref}}=I_N\sqrt{1-2.25*{(0.9-k)}^2}$

B) voltage on line side 0.25<U<=0.9-2H/3;

I ^* _q＝-HI _N

I _qref＝I _N[-1.5*(0.9-k)+H]

$I_{\mathrm{dref}}=I_N\sqrt{1-2.25*{(0.9-k)}^2}$

C) voltage on line side U<=0.25;

I ^* _q＝-HI _N

I _qref＝1.05I _N+HI _N

I _dref＝0

I wherein _nfor photovoltaic output rated current, k is that the perunit value (the electrical network electrical network rated value of take is fiducial value) of PCC place voltage is during the high voltage fail rated value of 1.1 times (voltage higher than), photovoltaic plant is sent out meritorious entirely, and UPQC sends idle in right amount, and it is idle, and reference signal is as follows:

I ^* _q＝a*(k-1.1)I _N

Wherein a is reactive power compensation coefficient, and its occurrence determines by the capacity of APF, during high voltage fail, and the apparent power S of APF _aPFfor:

$\left|S_{\mathrm{APE}}\right|=\sqrt{{(1-1/k)}^2+a^2{(k-1.1)}^2}{P}_N$

P wherein _nfor photovoltaic output rated power (during normal operation, power factor (PF) approaches 1), from above formula, be not difficult to find out k and S _aPFbe directly proportional, a value is as follows:

$\left|S_{\mathrm{APE}}\right|\&le;{\mathrm{HP}}_N\&DoubleRightArrow;a=\sqrt{H^2-0.053}/0.2$

The apparent power S that 110KV high voltage side of transformer is exported _outfor:

$\left|S_{\mathrm{out}}\right|=\sqrt{{{\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="HDA0000411704280000041.png,HDA0000411704280000051.png"\; state="\{\{state\}\}">P</figure-callout>}}^2}_{\mathrm{out}}+{{\mathrm{<figure-callout\; id="2"\; label="Q"\; filenames="HDA0000411704280000041.png,HDA0000411704280000051.png"\; state="\{\{state\}\}">Q</figure-callout>}}^2}_{\mathrm{out}}}=\sqrt{{(P_N/k)}^2+{[a*(k-1.1)P_N]}^2}$

$\&le;P_N\sqrt{H^2-1+2/k}\&le;{\mathrm{<figure-callout\; id="2"\; label="P\; N\; H"\; filenames="HDA0000411704280000041.png,HDA0000411704280000051.png"\; state="\{\{state\}\}">P</figure-callout>}}_N\sqrt{H^{}}\sqrt{{}^2+0.82},(1.1\&le;k\&le;1.3)$

The H of design is no more than 0.4, and transformer nonoverload now, so this Measures of Reactive Compensation can not bring transformer and circuit overload.

Although above-mentioned, by reference to the accompanying drawings the specific embodiment of the present invention is described; but be not limiting the scope of the invention; one of ordinary skill in the art should be understood that; on the basis of technical scheme of the present invention, those skilled in the art do not need to pay various modifications that creative work can make or distortion still in protection scope of the present invention.

Claims (5)

1. be applicable to the Unified Power Quality Controller of fault traversing, comprise APF part and DVR part, it is characterized in that, its APF is partly connected in parallel on the low-pressure side of photovoltaic plant outlet transformer, and DVR is connected on the high-pressure side of photovoltaic plant outlet transformer; Described APF coordinate photovoltaic plant electrical network low/send during high voltage fault or absorb idlely, DVR compensates the harmonic component of its line voltage and when high voltage fault, photovoltaic plant is exported to voltage compensation to rated value.

2. the control method that is applicable to the Unified Power Quality Controller of fault traversing as claimed in claim 1, is characterized in that, it is rated value that described DVR part bucking voltage amplitude when high voltage fail makes photovoltaic plant outlet voltage; DVR is partly by detecting PCC place and the on high-tension side voltage V of transformer B _pcc, V _pv, the voltage V of the DVR that obtains connecting _dVR=V _pcc-V _pv, the reference signal V of DVR ^* _dVR=V ^* _pv-V _pcc, V wherein ^* _pvfor the reference signal of high voltage side of transformer, the amplitude of reference signal and phase place are synchronizeed with electrical network nominal voltage signal.

3. the control method that is applicable to the Unified Power Quality Controller of fault traversing as claimed in claim 2, is characterized in that, the harmonic wave of described DVR partial-compensation grid side, and the control loop of compensation harmonic is taked rest frame, wherein resonant controller H _n(s) (n=5,7,11,13) expression formula is shown below:

$H_n\left(s\right)=2K_I{w}_c\frac{s+w_c}{s^2+2w_{c}s+{w^2}_n+{w^2}_c}$

K wherein _ifor gain, w _cfor the shearing frequency of system, w _nfor the harmonic frequency of appointment, s is complex parameter.

4. the control method that is applicable to the Unified Power Quality Controller of fault traversing as claimed in claim 1, is characterized in that, described APF maintains the stable of UPQC direct-current chain electric capacity and no-power compensation function is provided; UPQC is according to compensation high voltage fail desired capacity, take UPQC DVR, APF capacity perunit value as H be example; In meeting the limited field of UPQC capacity, APF sends idle and when high voltage, absorbs electric network reactive-load when low voltage failure; During low voltage failure, APF maximum can be sent the idle of H; During low voltage crossing, the idle reference signal I of APF ^* _qand the reference signal meritorious and idle component of photovoltaic plant electric current is respectively I _dref, I _qrefas follows:

A) voltage on line side U>0.9-2H/3;

I ^* _q＝-1.5*(0.9-k)I _N

I _qref＝0

$I_{\mathrm{dref}}=I_N\sqrt{1-2.25*{(0.9-k)}^2}$

B) voltage on line side 0.25<U<=0.9-2H/3;

I ^* _q＝-HI _N

I _qref＝I _N[-1.5*(0.9-k)+H]

$I_{\mathrm{dref}}=I_N\sqrt{1-2.25*{(0.9-k)}^2}$

C) voltage on line side U<=0.25;

I ^* _q＝-HI _N

I _qref＝1.05I _N+HI _N

I _dref＝0

I wherein _nfor photovoltaic output rated current, k is the perunit value of PCC place voltage.

5. the control method of the Unified Power Quality Controller that is applicable to fault traversing as described in claim 1 or 4, is characterized in that, during high voltage fail, photovoltaic plant is sent out meritorious entirely, and UPQC absorbs idle, and it is idle, and reference signal is as follows:

I ^* _q＝a*(k-1.1)I _N

Wherein a is reactive power compensation coefficient, the apparent power S of APF _aPFfor:

$\left|S_{\mathrm{APE}}\right|=\sqrt{{(1-1/k)}^2+a^2{(k-1.1)}^2}{P}_N$

P wherein _nfor photovoltaic output rated power, k and S _aPFbe directly proportional, a value is as follows:

$\left|S_{\mathrm{APE}}\right|\&le;{\mathrm{HP}}_N\&DoubleRightArrow;a=\sqrt{H^2-0.053}/0.2$

The apparent power S that export photovoltaic plant outlet transformer high-pressure side _outfor:

$\left|S_{\mathrm{out}}\right|=\sqrt{{P^2}_{\mathrm{out}}+{Q^2}_{\mathrm{out}}}=\sqrt{{(P_N/k)}^2+{[a*(k-1.1)P_N]}^2}$

$\&le;P_N\sqrt{H^2-1+2/k}\&le;P_N\sqrt{H^2+0.82},(1.1\&le;k\&le;1.3)$

Design H is not more than 0.4, and its transformer and circuit can not transship.

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