CN102072988B - Access point voltage phase detection method of photovoltaic inverter by applying multiple zero-crossing points - Google Patents

Abstract

The invention relates to an access point voltage phase detection method of a line inductance based photovoltaic inverter by applying multiple zero-crossing points, which is simple, has small computation quantity, and can effectively detect the zero-crossing points and determine the phase of an actual grid voltage. The zero-crossing point moment of the actual gird voltage is accurately calculated through detecting before-and-after boundaries of the multiple zero-crossing point region by utilizing a unique characteristic that a multiple zero-crossing point region of the access point voltage wave form of the photovoltaic inverter is in strict bilateral symmetry on the zero-crossing points of the actual grid voltage, and further the specific phase at the current time in the grid voltage is determined .

Description

Access point voltage phase detection method of photovoltaic inverter by applying multiple zero-crossing points

Technical field

The present invention relates to a kind of access point voltage phase detection method of photovoltaic inverter by applying multiple zero-crossing points based on line inductance.

Background technology

Photovoltaic DC-to-AC converter is generally operational in maximal power tracing (MPPT) state, and its output current was followed the tracks of the phase place of grid ac voltage and kept synchronous this moment, and the ideal power factor is 1.For guaranteeing the peak power output state of photovoltaic DC-to-AC converter, its output current must accurately be followed the tracks of the phase place of line voltage.The photovoltaic inversion unit is generally realized the phase-locking of electric current and voltage by the mode that detects Zero Crossing Point for Three Phase Voltage, have the advantages such as real-time is good, tracking is rapid.But the actual track inductance is also non-vanishing, and for the high-frequency power electronic on-off circuit, its induction reactance can be approximately pure induction reactance much larger than resistance.The photovoltaic inversion unit is except containing outputting inductance, and also there is the connection line inductance between the electrical network, because electric current is on off state, will at the switching voltage of line inductance formation with ripple, cause the AC sampling voltage of photovoltaic DC-to-AC converter access point no longer to have smooth sinusoidal waveform.Especially when the output current of photovoltaic DC-to-AC converter is larger, switching voltage peak-to-peak value even surpass the voltage on line side peak-to-peak value, and cause in one-period and may have a plurality of voltage over zero.Adopt the method for traditional detection voltage over zero position to determine that voltage-phase is no longer valid this moment, can not eliminate the impact of switching voltage fully even increase lowpass pre-filter, and cause voltage-phase to change, and detects error larger.The photovoltaic inversion unit that also has adopts phaselocked loop (PLL) technology for detection electric network voltage phase, although this mode can accurately be followed the tracks of the frequency of electrical network, can not realize the accurate tracking of voltage-phase.

Just present document finding for the coupling interaction impact of line inductance and inverter switching device process, not yet has the detection method of very effective voltage phase at access point of photovoltaic inverter, to realize the accurate synchronization of photovoltaic DC-to-AC converter output current and line voltage.

Summary of the invention

Purpose of the present invention is exactly for addressing the above problem, provide that a kind of method is easy, operand is little, can effectively detect and calculate the access point voltage phase detection method of photovoltaic inverter by applying multiple zero-crossing points based on line inductance of the actual zero crossing of line voltage, to determine its work phase place, finally realize based on the photovoltaic DC-to-AC converter output current of line inductance and the accurate synchronization of line voltage.

For achieving the above object, the present invention adopts following technical scheme:

A kind of access point voltage phase detection method of photovoltaic inverter by applying multiple zero-crossing points, photovoltaic DC-to-AC converter accessed electrical network after, be subjected to line inductance and with the switching voltage combined influence of ripple, a plurality of zero crossings zone must appear in the access point voltage waveform that obtains through sampling; Strict symmetrical exclusive feature behind the scope and time interval of calculating these zero crossing zones, was got the zero crossing that its central point can calculate actual electric network voltage about these many zero crossings zones presented about the zero crossing of actual electric network voltage; According to the time interval between current time and the actual electric network voltage over zero, can accurately obtain the electric network voltage phase of current time again.

The detailed process of determining the actual zero crossing of line voltage is:

1) sets general zero crossing acquisition mode with common method, begin to carry out zero crossing for the sample waveform of photovoltaic DC-to-AC converter access point voltage and detect;

2) detect first zero crossing, be designated as moment point t1; Show that this moment, surveyed area entered the zero crossing regional extent;

3) detect next zero crossing, whether the spacing of judgement and a upper zero crossing is greater than the setting-up time value; If not, the punctum that clocks is t2, then explanation still is within this zero crossing regional extent, returns step 3); If so, illustrate that this zero crossing has been the initial zero crossing in next zero crossing zone, then changes next step over to;

4) calculating the nearest actual zero crossing of line voltage is (t1+t2)/2 constantly;

5) reset this zero crossing and constantly be t1;

6) determine the zero crossing phase place of actual electric network voltage; Judge access point voltage sample value between this zero crossing and the upper zero crossing whether for just, if so, the voltage zero-crossing point of power grid that then calculates constantly phase place is 0 degree, then changes step 3 over to); If not, the voltage zero-crossing point of power grid that then calculates constantly phase place is 180 degree, then returns step 3).

The invention has the beneficial effects as follows: can realize accurate calculating and tracking to the line voltage actual phase.Photovoltaic DC-to-AC converter is linked in the electrical network that contains line inductance, needs by measuring the access point voltage-phase so that output current and electric network voltage phase are synchronous.But the impact because of switching harmonics voltage, there is a plurality of zero crossings zone in the access point voltage that causes sampling to obtain at the near zero-crossing point of actual electric network voltage, be difficult to determine voltage-phase, cause effectively to realize the output current of photovoltaic DC-to-AC converter and the accurate synchronization of line voltage.The present invention by sampling photovoltaic DC-to-AC converter access point voltage waveform and detect its many zero crossings zone, strict symmetrical exclusive feature about utilizing its many zero crossings zone about the actual electric network voltage over zero, the center of getting many zero crossings zone constantly can be by calculating zero crossing and the phase place thereof that accurately defines actual electric network voltage.Interconnection technology for the photovoltaic DC-to-AC converter that contains larger line inductance, the present invention has thoroughly overcome the reciprocal effect of line inductance and photovoltaic DC-to-AC converter switching process, solved a difficult problem that is difficult to accurate detection of grid voltage-phase because of many zero crossings phenomenon, be easy to realize the accurate synchronization of photovoltaic DC-to-AC converter output current and line voltage, be operated in the maximum power output state to guarantee photovoltaic generation unit.

Description of drawings

Fig. 1 is photovoltaic inversion unit equivalent electrical circuit;

Fig. 2 a is in access point sampled voltage and the line voltage simulation waveform, access point sampled voltage and line voltage figure;

Fig. 2 b is in access point sampled voltage and the line voltage simulation waveform, access point sampled voltage and line voltage in single switch periods;

Fig. 3 a is in the voltage and electric current experimental waveform of grid integration point, access point voltage and output current wave figure;

Fig. 3 b is in the voltage and electric current experimental waveform of grid integration point, access point voltage and switching current oscillogram in single switch periods;

Fig. 4 is the detailed process based on the access point voltage phase detection method of photovoltaic inverter by applying multiple zero-crossing points of line inductance;

The Phase Tracking lab diagram of the grid-connected unit of Fig. 5.

Embodiment

The present invention will be further described below in conjunction with accompanying drawing and embodiment.

When considering line inductance the equivalent electrical circuit of photovoltaic inversion unit as shown in Figure 1, it adopts typical half-bridge topology.Among Fig. 1, PV is the photovoltaic cell group, C ₁And C ₂Be dc bus capacitor, Q ₁And Q ₂Be IGBT switching tube, V ₁Be the voltage detecting point of photovoltaic DC-to-AC converter access power distribution network, I ₁Be photovoltaic DC-to-AC converter output electric current measure point, L ₁Be the outputting inductance of inverter, L ₂Be line inductance, photovoltaic DC-to-AC converter passes through L ₂Voltage node V is connected to the grid _AC

1) the dynamic switch process of photovoltaic DC-to-AC converter

If flow through inductance L ₁And L ₂Electric current be i ₁, V ₁The voltage of point is u ₁Because of the switching frequency of power device far above power frequency, in a switch periods, photovoltaic cell group output voltage can be approximately a constant U _Dc, the ac bus voltage U _AcAlso can think constant.Switching tube Q ₁And Q ₂Switching signal complementary, they are alternate conduction in a switch periods.

Switching tube Q ₁(comprise the anti-paralleled diode conducting) when opening, establish V ₁The voltage of point is u ₁₁, can get:

$u_{11}={\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="HDA0000033092100000022.png,HDA0000033092100000051.png"\; state="\{\{state\}\}">L</figure-callout>}}_2\frac{{\mathrm{di}}_1}{\mathrm{dt}}+U_{\mathrm{ac}}=\frac{U_{\mathrm{dc}}}{2}-{\mathrm{<figure-callout\; id="1"\; label="L"\; filenames="HDA0000033092100000051.png"\; state="\{\{state\}\}">L</figure-callout>}}_1\frac{{\mathrm{di}}_1}{\mathrm{dt}}---\left(1\right)$

This moment photovoltaic DC-to-AC converter output current i ₁Rise V ₁The voltage of point is higher than ac bus voltage.

Solved by formula (1):

$u_{11}=\frac{L_1}{{\mathrm{<figure-callout\; id="1"\; label="L"\; filenames="HDA0000033092100000051.png"\; state="\{\{state\}\}">L</figure-callout>}}_1+L_2}{U}_{\mathrm{ac}}+\frac{L_2}{{\mathrm{<figure-callout\; id="1"\; label="L"\; filenames="HDA0000033092100000051.png"\; state="\{\{state\}\}">L</figure-callout>}}_1+L_2}\frac{U_{\mathrm{dc}}}{2}---\left(2\right)$

V ₁The current potential of point with respect to line voltage is:

$u_{11}-U_{\mathrm{ac}}=\frac{L_2}{{\mathrm{<figure-callout\; id="1"\; label="L"\; filenames="HDA0000033092100000051.png"\; state="\{\{state\}\}">L</figure-callout>}}_1+L_2}(\frac{U_{\mathrm{dc}}}{2}-U_{\mathrm{ac}})---\left(3\right)$

As switching tube Q ₂(comprise the anti-paralleled diode conducting) when opening, establish V ₁The voltage of point is u ₁₂, can get:

$u_{12}={\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="HDA0000033092100000022.png,HDA0000033092100000051.png"\; state="\{\{state\}\}">L</figure-callout>}}_2\frac{{\mathrm{di}}_1}{\mathrm{dt}}+U_{\mathrm{ac}}=-\frac{U_{\mathrm{dc}}}{2}-{\mathrm{<figure-callout\; id="1"\; label="L"\; filenames="HDA0000033092100000051.png"\; state="\{\{state\}\}">L</figure-callout>}}_1\frac{{\mathrm{di}}_1}{\mathrm{dt}}---\left(4\right)$

This moment photovoltaic DC-to-AC converter output current i ₁Descend V ₁The voltage of point is lower than ac bus voltage.

Solved by formula (4):

$u_{12}=\frac{L_1}{{\mathrm{<figure-callout\; id="1"\; label="L"\; filenames="HDA0000033092100000051.png"\; state="\{\{state\}\}">L</figure-callout>}}_1+L_2}{U}_{\mathrm{ac}}-\frac{L_2}{{\mathrm{<figure-callout\; id="1"\; label="L"\; filenames="HDA0000033092100000051.png"\; state="\{\{state\}\}">L</figure-callout>}}_1+L_2}\frac{U_{\mathrm{dc}}}{2}---\left(5\right)$

V ₁The current potential of point with respect to line voltage is:

$u_{12}-U_{\mathrm{ac}}=\frac{L_2}{{\mathrm{<figure-callout\; id="1"\; label="L"\; filenames="HDA0000033092100000051.png"\; state="\{\{state\}\}">L</figure-callout>}}_1+L_2}(-\frac{U_{\mathrm{dc}}}{2}-U_{\mathrm{ac}})---\left(6\right)$

V then ₁The peak-to-peak value of point voltage ripple is:

$u_{11}-u_{12}=\frac{L_2}{{\mathrm{<figure-callout\; id="1"\; label="L"\; filenames="HDA0000033092100000051.png"\; state="\{\{state\}\}">L</figure-callout>}}_1+L_2}{U}_{\mathrm{dc}}---\left(7\right)$

By formula (7) as can be known, V ₁The peak-to-peak value of point voltage ripple is proportional to dc voltage, and with the AC independent from voltage, and line inductance is larger, the peak-to-peak value of voltage ripple is larger.

V ₁Point and V _ACThe voltage simulation waveform at place is shown in Fig. 2 a, Fig. 2 b, and the experimental waveform of corresponding access point voltage and inverter output current is shown in Fig. 3 a, Fig. 3 b.In Fig. 3 a, voltage is the 100V/ lattice, and electric current is the 10A/ lattice; In Fig. 3 b, voltage is the 50V/ lattice, and electric current is the 10A/ lattice.By Fig. 2 a, Fig. 2 b and Fig. 3 a, Fig. 3 b as seen, because of the acting in conjunction of line inductance and switching process, cause sample amplitude when reproduced in power frequency period, to have a plurality of zero crossings, therefore, by detecting V ₁The access voltage over zero at place will produce very large phase error with the method for determining the current tracking phase place.Fig. 3 a is access point voltage waveform and the output current wave of photovoltaic DC-to-AC converter when adopting traditional zero crossing method for detecting phases, and obviously the two is seriously asynchronous.

2) utilize many zero crossings zone symmetrical feature to realize the new algorithm of phase-detection

For Fig. 2 a, establish

U _mBe voltage peak.At zero crossing moment t ₁And t ₄, make u ₁₁=0,

Then can obtain according to formula (2):

$\frac{L_1}{{\mathrm{<figure-callout\; id="1"\; label="L"\; filenames="HDA0000033092100000051.png"\; state="\{\{state\}\}">L</figure-callout>}}_1+L_2}{U}_m\cos \mathrm{\&omega;t}+\frac{L_2}{{\mathrm{<figure-callout\; id="1"\; label="L"\; filenames="HDA0000033092100000051.png"\; state="\{\{state\}\}">L</figure-callout>}}_1+L_2}\frac{{\mathrm{<figure-callout\; id="2"\; label="U\; dc"\; filenames="HDA0000033092100000022.png,HDA0000033092100000051.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{dc}}}{2}=0---\left(8\right)$

Further solve:

$\mathrm{\&omega;}{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="HDA0000033092100000051.png"\; state="\{\{state\}\}">t</figure-callout>}}_{\mathrm{1,4}}=2\mathrm{k\&pi;}\&PlusMinus;\arccos (-\frac{1}{U_m}\frac{L_2}{L_1}\frac{U_{\mathrm{dc}}}{2})---\left(9\right)$

$\mathrm{\&omega;}{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="HDA0000033092100000051.png"\; state="\{\{state\}\}">t</figure-callout>}}_1=2\mathrm{k\&pi;}-(\mathrm{\&pi;}-\arccos \left(\frac{1}{U_m}\frac{L_2}{L_1}\frac{U_{\mathrm{dc}}}{2}\right))---\left(10\right)$

For the moment of the zero crossing among Fig. 2 a t ₂And t ₃, make u ₁₂=0, in like manner can solve:

$\mathrm{\&omega;}{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="HDA0000033092100000022.png,HDA0000033092100000051.png"\; state="\{\{state\}\}">\; <figure-callout\; id="3"\; label="t"\; filenames="HDA0000033092100000022.png,HDA0000033092100000051.png"\; state="\{\{state\}\}">t</figure-callout>\; </figure-callout>}}_{\mathrm{2,3}}=2\mathrm{k\&pi;}\&PlusMinus;\arccos (\frac{1}{U_m}\frac{L_2}{{\mathrm{<figure-callout\; id="1"\; label="L"\; filenames="HDA0000033092100000051.png"\; state="\{\{state\}\}">L</figure-callout>}}_1}\&CenterDot;\frac{U_{\mathrm{dc}}}{2})---\left(11\right)$

$\mathrm{\&omega;}{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="HDA0000033092100000022.png,HDA0000033092100000051.png"\; state="\{\{state\}\}">t</figure-callout>}}_2=2\mathrm{k\&pi;}-\arccos \left(\frac{1}{U_m}\frac{L_2}{L_1}\frac{U_{\mathrm{dc}}}{2}\right)---\left(12\right)$

In Fig. 2 a, access point sampled voltage zero crossing t ₁And t ₂Between the actual electric network voltage over zero be

Convolution (10) and formula (12) as can be known, at t ₁And t ₂Between a plurality of zero crossing regional extents of access point voltage, strict symmetrical exclusive feature about the zero crossing of actual electric network voltage and about being.In like manner can push away, for t among Fig. 2 a ₃And t ₄Between a plurality of zero crossings zone of access point voltage, also the zero crossing about actual electric network voltage has strict symmetry characteristic.

If t among Fig. 2 a ₁And t ₂Between the zero crossing of actual electric network voltage be t constantly ₀, then can be got by the left-right symmetric characteristic:

$t_0={\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="HDA0000033092100000051.png"\; state="\{\{state\}\}">t</figure-callout>}}_1+\frac{t_2-{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="HDA0000033092100000051.png"\; state="\{\{state\}\}">t</figure-callout>}}_1}{2}=\frac{{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="HDA0000033092100000022.png,HDA0000033092100000051.png"\; state="\{\{state\}\}">t</figure-callout>}}_2+{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="HDA0000033092100000051.png"\; state="\{\{state\}\}">t</figure-callout>}}_1}{2}---\left(13\right)$

In like manner can try to achieve t ₃And t ₄Between the actual electric network voltage over zero constantly (be made as t _T) be:

$t_T=\frac{{\mathrm{<figure-callout\; id="3"\; label="t"\; filenames="HDA0000033092100000022.png,HDA0000033092100000051.png"\; state="\{\{state\}\}">t</figure-callout>}}_3+t_4}{2}---\left(14\right)$

The power frequency period of historical facts or anecdotes border line voltage is:

T＝t _T-t ₀ (15)

Constantly can determine its accurate phase place by the actual electric network voltage over zero of extrapolating.Slower because of the phase place variation of line voltage, can by measuring a plurality of zero crossings of line voltage, then be weighted average mode to improve the phase-detection accuracy.

Be that many zero crossings zone of zero is between many zero crossings zones of 180 degree with phase place at the actual electric network voltage-phase, long non-zero crossing zone of a time interval is arranged, can easily the zone of zero crossing more than two be separated thus.When the interval between two adjacent zero crossing zones becomes suddenly large, illustrate that this zero crossing has been the initial zero crossing in next many zero crossings zone.

Fig. 4 has provided the specific algorithm process flow diagram of realizing voltage zero-crossing point of power grid and phase-detection.

Above-mentioned phase-detection new algorithm based on the symmetrical feature of access point sampled voltage zero crossing, principle is simple and calculated amount is little, has a preferably effect in the situation that the photovoltaic DC-to-AC converter dc voltage is not too high.

3) photovoltaic DC-to-AC converter current tracking experiment

Because of the impact of line inductance and switching process, only adopt traditional voltage over zero method for detecting phases, can not realize the phase-locking of photovoltaic inversion unit access point voltage and output current, this is confirmed by the experimental result of Fig. 3 a.Based on the little electrical network experiment porch of the 10kW that sets up, the concrete voltage-phase new detecting method that proposes of using of this patent, carry out experimental study and obtained the many groups of waveforms that access point voltage and output current, shown in Figure 5 is one group of experimental waveform wherein, wherein access point voltage is the 100V/ lattice, and output current is the 10A/ lattice.

Can find out, the voltage-phase detection method that adopts the present invention to propose, the inverter output current can be followed the tracks of the phase place of alternating voltage exactly, is beneficial to the maximum power output of realizing the photovoltaic inversion unit.

Claims (1)

1. an access point voltage phase detection method of photovoltaic inverter by applying multiple zero-crossing points is characterized in that, determines that the detailed process of the actual zero crossing of line voltage is:

1)The zero crossing acquisition mode is set, begins to carry out zero crossing for the sample waveform of photovoltaic DC-to-AC converter access point voltage and detect;

2) detect first zero crossing, be designated as moment point t1; Show that this moment, surveyed area entered the zero crossing regional extent;

3) detect next zero crossing, whether the spacing of judgement and a upper zero crossing is greater than the setting-up time value; If not, the punctum that clocks is t2, then explanation still is within this zero crossing regional extent, returns step 3); If so, illustrate that this zero crossing has been the initial zero crossing in next zero crossing zone, then changes next step over to;

4) calculating the nearest actual zero crossing of line voltage is (t1+t2)/2 constantly;

5) reset this zero crossing and constantly be t1;

6) determine the zero crossing phase place of actual electric network voltage; Judge access point voltage sample value between this zero crossing t1 and the upper zero crossing t2 whether for just, if so, the voltage zero-crossing point of power grid that then calculates constantly phase place is 0 degree, then changes step 3) over to; If not, the voltage zero-crossing point of power grid that then calculates constantly phase place is 180 degree, then returns step 3).

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