CN102072988A

CN102072988A - Access point voltage phase detection method of photovoltaic inverter by applying multiple zero-crossing points

Info

Publication number: CN102072988A
Application number: CN 201010550014
Authority: CN
Inventors: 李庆民; 龚宇雷; 段玉兵; 王辉; 谭兴国
Original assignee: Shandong University
Current assignee: Shandong University
Priority date: 2010-11-19
Filing date: 2010-11-19
Publication date: 2011-05-25
Anticipated expiration: 2030-11-19
Also published as: CN102072988B

Abstract

The invention relates to a phase detection method based on line inductance for the voltage of a photovoltaic inverter access point with multiple zero-crossing points. The method is simple and the calculation amount is small, and it can effectively detect the zero-crossing point of the actual grid voltage and determine its phase. It uses the unique characteristic that the multi-zero-crossing area of the voltage waveform at the access point of the photovoltaic inverter is strictly symmetrical to the actual grid voltage zero-crossing point, and accurately calculates the zero-crossing point of the actual grid voltage by detecting the front and rear time boundaries of the multi-zero-crossing area Time, and thus determine the specific phase of the grid voltage at the current moment.

Description

Phase detection method for photovoltaic inverter access point voltage with multiple zero-crossing points

技术领域technical field

本发明涉及一种基于线路电感的光伏逆变器接入点电压多过零点相位检测方法。The invention relates to a phase detection method based on line inductance for the voltage of a photovoltaic inverter access point with multiple zero-crossing points.

背景技术Background technique

光伏逆变器一般工作在最大功率跟踪(MPPT)状态，此时其输出电流跟踪电网交流电压的相位并保持同步，理想功率因数为1。为保证光伏逆变器的最大输出功率状态，其输出电流必须准确跟踪电网电压的相位。光伏逆变单元一般通过检测三相电压过零点的方式来实现电流与电压的相位同步，具有实时性好、跟踪迅速等优点。但实际线路电感并不为零，对于高频电力电子开关电路，其感抗远大于电阻，可近似为纯感抗。光伏逆变单元除含输出电感外，与电网之间还存在连接线路电感，因电流处于开关状态，将在线路电感上形成带有纹波的开关电压，致使光伏逆变器接入点的交流采样电压不再具有光滑的正弦波形。尤其当光伏逆变器的输出电流较大时，开关电压峰-峰值甚至超过网侧电压峰-峰值，且造成在一个周期内可能存在多个电压过零点。此时采用传统的检测电压过零点位置的方法来确定电压相位已不再有效，即使增加前置低通滤波器也不能完全消除开关电压的影响，且造成电压相位变化，检测误差较大。也有的光伏逆变单元采用锁相环(PLL)技术检测电网电压相位，尽管该方式可准确跟踪电网的频率，但并不能实现电压相位的准确跟踪。Photovoltaic inverters generally work in the maximum power tracking (MPPT) state. At this time, its output current tracks the phase of the AC voltage of the grid and maintains synchronization. The ideal power factor is 1. In order to ensure the maximum output power state of the photovoltaic inverter, its output current must accurately track the phase of the grid voltage. The photovoltaic inverter unit generally realizes the phase synchronization of current and voltage by detecting the zero-crossing point of the three-phase voltage, which has the advantages of good real-time performance and rapid tracking. However, the actual line inductance is not zero. For high-frequency power electronic switching circuits, the inductive reactance is much greater than the resistance, which can be approximated as pure inductive reactance. In addition to the output inductance of the photovoltaic inverter unit, there is also a connection line inductance between the photovoltaic inverter unit and the grid. Because the current is in the switching state, a switching voltage with ripples will be formed on the line inductance, resulting in the AC of the photovoltaic inverter access point. The sampled voltage no longer has a smooth sinusoidal waveform. Especially when the output current of the photovoltaic inverter is large, the peak-to-peak voltage of the switch even exceeds the peak-to-peak value of the grid-side voltage, and there may be multiple voltage zero-crossing points in one cycle. At this time, it is no longer effective to use the traditional method of detecting the voltage zero-crossing position to determine the voltage phase. Even adding a pre-low-pass filter cannot completely eliminate the influence of the switching voltage, and cause voltage phase changes, resulting in large detection errors. Some photovoltaic inverter units also use phase-locked loop (PLL) technology to detect the voltage phase of the grid. Although this method can accurately track the frequency of the grid, it cannot accurately track the voltage phase.

就目前文献所见，针对线路电感与逆变器开关过程的交互耦合影响，尚未有非常有效的光伏逆变器接入点电压相位的检测方法，以实现光伏逆变器输出电流与电网电压的准确同步。As far as the current literature can see, there is no very effective detection method for the voltage phase of the photovoltaic inverter access point in view of the interactive coupling effect of the line inductance and the switching process of the inverter, so as to realize the balance between the output current of the photovoltaic inverter and the grid voltage. Sync exactly.

发明内容Contents of the invention

本发明的目的就是为解决上述问题，提供一种方法简便、运算量小、可有效检测和计算电网电压实际过零点的基于线路电感的光伏逆变器接入点电压多过零点相位检测方法，以确定其工作相位，最终实现基于线路电感的光伏逆变器输出电流与电网电压的准确同步。The purpose of the present invention is to solve the above problems, to provide a simple method, a small amount of calculation, which can effectively detect and calculate the actual zero-crossing point of the grid voltage. To determine its working phase, and finally realize the accurate synchronization of the output current of the photovoltaic inverter based on the line inductance and the grid voltage.

为实现上述目的，本发明采用如下技术方案：To achieve the above object, the present invention adopts the following technical solutions:

一种光伏逆变器接入点电压多过零点相位检测方法，将光伏逆变器接入电网后，受线路电感和带纹波的开关电压综合影响，经采样得到的接入点电压波形将必然出现多个过零点区域；这些多过零点区域关于实际电网电压的过零点呈现左右严格对称的独有特征，通过计算这些过零点区域的范围和时间间隔后，取其中心点即可计算得到实际电网电压的过零点；再根据当前时刻与实际电网电压过零点之间的时间间隔，可准确获得当前时刻的电网电压相位。A phase detection method for multiple zero-crossing point voltages at the access point of a photovoltaic inverter. After the photovoltaic inverter is connected to the grid, it is affected by the comprehensive influence of the line inductance and the switching voltage with ripple, and the voltage waveform of the access point obtained through sampling will There must be multiple zero-crossing areas; these multi-zero-crossing areas present a unique feature of strict symmetry with respect to the zero-crossing point of the actual grid voltage. After calculating the range and time interval of these zero-crossing areas, the center point can be calculated. The zero-crossing point of the actual grid voltage; and according to the time interval between the current moment and the actual grid voltage zero-crossing point, the grid voltage phase at the current moment can be accurately obtained.

确定电网电压实际过零点的具体过程为：The specific process of determining the actual zero-crossing point of the grid voltage is as follows:

1)以常用方法设置好一般的过零点捕获方式，针对光伏逆变器接入点电压的采样波形开始进行过零点检测；1) Set the general zero-crossing capture method in a common way, and start zero-crossing detection for the sampling waveform of the photovoltaic inverter access point voltage;

2)检测到第一个过零点，记为时刻点t1；表明此时检测区域已进入过零点区域范围；2) The first zero-crossing point is detected, which is recorded as time point t1; it indicates that the detection area has entered the zero-crossing point area at this time;

3)检测下一个过零点，判断与上一个过零点的间距是否大于设定时间值；如果不是，记时刻点为t2，则说明仍然处于本过零点区域范围之内，返回步骤3)；如果是，说明这一个过零点已是下一个过零点区域的起始过零点，则转入下一步骤；3) Detect the next zero-crossing point, and judge whether the distance from the previous zero-crossing point is greater than the set time value; if not, the timing point is t2, indicating that it is still within the range of this zero-crossing point, and return to step 3); if Yes, it means that this zero-crossing point is the initial zero-crossing point of the next zero-crossing point area, then go to the next step;

4)计算最近的电网电压实际过零点时刻为(t1+t2)/2；4) Calculate the actual zero-crossing moment of the nearest grid voltage as (t1+t2)/2;

5)重新设置本次过零点时刻为t1；5) Reset the zero-crossing time to t1;

6)确定实际电网电压的过零点相位；判断本次过零点与上一个过零点之间的接入点电压采样值是否为正，如果是，则计算出的电网电压过零点时刻相位为0度，然后转入步骤3)；如果不是，则计算出的电网电压过零点时刻相位为180度，然后返回步骤3)。6) Determine the phase of the zero-crossing point of the actual grid voltage; judge whether the sampling value of the voltage at the access point between this zero-crossing point and the previous zero-crossing point is positive, and if so, the phase at the zero-crossing point of the calculated grid voltage is 0 degrees , and then go to step 3); if not, the calculated grid voltage zero-crossing moment phase is 180 degrees, and then return to step 3).

本发明的有益效果是：可实现对电网电压实际相位的准确计算与跟踪。光伏逆变器接入到含有线路电感的电网中，需要通过测量接入点电压相位使得输出电流与电网电压相位同步。但因开关纹波电压的影响，造成采样得到的接入点电压在实际电网电压的过零点附近存在多个过零点区域，难以确定电压相位，导致不能有效实现光伏逆变器的输出电流与电网电压的准确同步。本发明通过采样光伏逆变器接入点的电压波形并检测出它的多过零点区域，利用其多过零点区域关于实际电网电压过零点左右严格对称的独有特征，取多过零点区域的中心时刻即可通过计算准确界定实际电网电压的过零点及其相位。针对含有较大线路电感的光伏逆变器的并网技术，本发明彻底克服了线路电感和光伏逆变器开关过程的交互影响，解决了因多过零点现象而难以准确检测电网电压相位的难题，易于实现光伏逆变器输出电流与电网电压的准确同步，以保证光伏发电单元工作在最大功率输出状态。The beneficial effect of the invention is that the accurate calculation and tracking of the actual phase of the grid voltage can be realized. When the photovoltaic inverter is connected to the grid with line inductance, it is necessary to measure the voltage phase of the access point to synchronize the output current with the grid voltage phase. However, due to the influence of the switch ripple voltage, the sampled access point voltage has multiple zero-crossing areas near the zero-crossing point of the actual grid voltage, making it difficult to determine the voltage phase, resulting in the inability to effectively realize the output current of the photovoltaic inverter and the grid. Accurate synchronization of voltages. The present invention samples the voltage waveform of the photovoltaic inverter access point and detects its multi-zero-crossing area, and utilizes its unique feature that the multi-zero-crossing area is strictly symmetrical about the actual grid voltage zero-crossing point, and takes the multi-zero-crossing area The zero-crossing point of the actual grid voltage and its phase can be accurately defined by calculation at the central moment. For the grid-connected technology of photovoltaic inverters with large line inductance, the invention completely overcomes the interactive influence of line inductance and the switching process of photovoltaic inverters, and solves the problem that it is difficult to accurately detect the grid voltage phase due to the phenomenon of multiple zero crossings , it is easy to accurately synchronize the output current of the photovoltaic inverter with the grid voltage, so as to ensure that the photovoltaic power generation unit works at the maximum power output state.

附图说明Description of drawings

图1为光伏逆变单元等效电路；Figure 1 is the equivalent circuit of the photovoltaic inverter unit;

图2a为接入点采样电压与电网电压仿真波形中，接入点采样电压与电网电压图；Figure 2a is a graph of the sampling voltage at the access point and the grid voltage in the simulated waveform of the sampling voltage at the access point and the grid voltage;

图2b为接入点采样电压与电网电压仿真波形中，单开关周期内的接入点采样电压与电网电压；Figure 2b shows the sampling voltage of the access point and the grid voltage simulation waveforms, the sampling voltage of the access point and the grid voltage in a single switching cycle;

图3a为并网接入点的电压与电流实验波形中，接入点电压与输出电流波形图；Figure 3a is the waveform diagram of the voltage and output current of the access point in the voltage and current experimental waveforms of the grid-connected access point;

图3b为并网接入点的电压与电流实验波形中，单开关周期内的接入点电压与开关电流波形图；Figure 3b is the voltage and current waveform diagram of the access point in a single switching cycle in the voltage and current experimental waveforms of the grid-connected access point;

图4为基于线路电感的光伏逆变器接入点电压多过零点相位检测方法的详细流程；Fig. 4 is a detailed process of the phase detection method based on the line inductance of the photovoltaic inverter access point voltage with more than zero crossing points;

图5光伏并网单元的相位跟踪实验图。Figure 5 Phase tracking experiment diagram of photovoltaic grid-connected unit.

具体实施方式Detailed ways

下面结合附图与实施例对本发明做进一步说明。The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

考虑线路电感时光伏逆变单元的等效电路如图1所示，它采用典型的半桥拓扑结构。图1中，PV为光伏电池组，C₁和C₂为直流侧电容，Q₁和Q₂为IGBT开关管，V₁为光伏逆变器接入配电网的电压检测点，I₁为光伏逆变器输出电流检测点，L₁为逆变器的输出电感，L₂为线路电感，光伏逆变器通过L₂并入电网电压节点V_AC。Considering the line inductance, the equivalent circuit of the photovoltaic inverter unit is shown in Figure 1, which adopts a typical half-bridge topology. In Figure 1, PV is the photovoltaic cell group, C ₁ and C ₂ are DC side capacitors, Q ₁ and Q ₂ are IGBT switch tubes, V ₁ is the voltage detection point for the photovoltaic inverter to connect to the distribution network, and I ₁ is The output current detection point of the photovoltaic inverter, L ₁ is the output inductance of the inverter, L ₂ is the line inductance, and the photovoltaic inverter is connected to the grid voltage node V _AC through L ₂ .

1)光伏逆变器的动态开关过程1) Dynamic switching process of photovoltaic inverter

设流过电感L₁和L₂的电流为i₁，V₁点的电压为u₁。因功率器件的开关频率远高于工频，在一个开关周期内，光伏电池组输出电压可近似为一恒值U_dc，交流母线电压U_ac也可认为不变。开关管Q₁和Q₂的开关信号互补，它们在一个开关周期内交替导通。Suppose the current flowing through the inductors L ₁ and L ₂ is i ₁ , and the voltage at point V ₁ is u ₁ . Because the switching frequency of power devices is much higher than the power frequency, within a switching cycle, the output voltage of photovoltaic cells can be approximated as a constant value U _dc , and the AC bus voltage U _ac can also be considered constant. The switching signals of the switching tubes _Q1 and _Q2 are complementary, and they are turned on alternately within one switching period.

开关管Q₁开通时(包括反并联二极管导通)，设V₁点的电压为u₁₁，可得：When the switch tube Q ₁ is turned on (including the conduction of the anti-parallel diode), set the voltage at point V ₁ as u ₁₁ , and we can get:

${u u}_{1111} = = {L L}_{22} \frac{{di di}_{11}}{dt dt} + + {U u}_{ac ac} = = \frac{{U u}_{dc dc}}{22} - - {L L}_{11} \frac{{di di}_{11}}{dt dt} - - - - - - ((11))$

此时光伏逆变器的输出电流i₁上升，V₁点的电压高于交流母线电压。At this time, the output current i ₁ of the photovoltaic inverter rises, and the voltage at point V ₁ is higher than the AC bus voltage.

由式(1)解得：Solved by formula (1):

${u u}_{1111} = = \frac{{L L}_{11}}{{L L}_{11} + + {L L}_{22}} {U u}_{ac ac} + + \frac{{L L}_{22}}{{L L}_{11} + + {L L}_{22}} \frac{{U u}_{dc dc}}{22} - - - - - - ((22))$

V₁点的电位相对于电网电压为：The potential of point _V1 relative to the grid voltage is:

${u u}_{1111} - - {U u}_{ac ac} = = \frac{{L L}_{22}}{{L L}_{11} + + {L L}_{22}} ((\frac{{U u}_{dc dc}}{22} - - {U u}_{ac ac})) - - - - - - ((33))$

当开关管Q₂开通时(包括反并联二极管导通)，设V₁点的电压为u₁₂，可得：When the switch tube Q ₂ is turned on (including the conduction of the anti-parallel diode), set the voltage at point V ₁ as u ₁₂ , and we can get:

${u u}_{1212} = = {L L}_{22} \frac{{di di}_{11}}{dt dt} + + {U u}_{ac ac} = = - - \frac{{U u}_{dc dc}}{22} - - {L L}_{11} \frac{{di di}_{11}}{dt dt} - - - - - - ((44))$

此时光伏逆变器的输出电流i₁下降，V₁点的电压低于交流母线电压。At this time, the output current i ₁ of the photovoltaic inverter drops, and the voltage at point V ₁ is lower than the AC bus voltage.

由式(4)解得：Solved by formula (4):

${u u}_{1212} = = \frac{{L L}_{11}}{{L L}_{11} + + {L L}_{22}} {U u}_{ac ac} - - \frac{{L L}_{22}}{{L L}_{11} + + {L L}_{22}} \frac{{U u}_{dc dc}}{22} - - - - - - ((55))$

${u u}_{1212} - - {U u}_{ac ac} = = \frac{{L L}_{22}}{{L L}_{11} + + {L L}_{22}} ((- - \frac{{U u}_{dc dc}}{22} - - {U u}_{ac ac})) - - - - - - ((66))$

则V₁点电压纹波的峰-峰值为：Then the peak-to-peak value of the voltage ripple at point _V1 is:

${u u}_{1111} - - {u u}_{1212} = = \frac{{L L}_{22}}{{L L}_{11} + + {L L}_{22}} {U u}_{dc dc} - - - - - - ((77))$

由式(7)可知，V₁点电压纹波的峰-峰值正比于直流侧电压，而与交流侧电压无关，且线路电感越大，电压纹波的峰-峰值越大。It can be seen from formula (7) that the peak-to-peak value of the voltage ripple at point _V1 is proportional to the DC side voltage and has nothing to do with the AC side voltage, and the larger the line inductance, the larger the peak-to-peak value of the voltage ripple.

V₁点和V_AC处的电压仿真波形如图2a、图2b所示，相应接入点电压和逆变器输出电流的实验波形如图3a、图3b所示。在图3a中，电压为100V/格，电流为10A/格；在图3b中，电压为50V/格，电流为10A/格。由图2a、图2b和图3a、图3b可见，因线路电感与开关过程的共同作用，造成采样点电压在工频周期内存在多个过零点，因此，通过检测V₁处的接入电压过零点以确定电流跟踪相位的方法将产生很大的相位误差。图3a为采用传统的过零点相位检测方法时光伏逆变器的接入点电压波形和输出电流波形，显然二者严重不同步。The voltage simulation waveforms at V ₁ and V _AC are shown in Figure 2a and Figure 2b, and the experimental waveforms of the corresponding access point voltage and inverter output current are shown in Figure 3a and Figure 3b. In Figure 3a, the voltage is 100V/div and the current is 10A/div; in Figure 3b, the voltage is 50V/div and the current is 10A/div. It can be seen from Fig. 2a, Fig. 2b and Fig. 3a, Fig. 3b that due to the combined effect of the line inductance and the switching process, the voltage at the sampling point has multiple zero-crossing points in the power frequency cycle. Therefore, by detecting the access voltage at _V1 The method of determining the current tracking phase by crossing the zero point will produce a large phase error. Figure 3a shows the input point voltage waveform and output current waveform of the photovoltaic inverter when the traditional zero-crossing phase detection method is adopted. Obviously, the two are seriously out of sync.

2)利用多过零点区域对称特征实现相位检测的新算法2) A new algorithm for phase detection using the symmetrical features of multiple zero-crossing areas

针对图2a，设U_m为电压峰值。在过零点时刻t₁和t₄，令u₁₁＝0，For Figure 2a, set U _m is the peak voltage. At zero-crossing times t ₁ and t ₄ , let u ₁₁ =0,

则根据式(2)可得到：Then according to formula (2), we can get:

$\frac{{L L}_{11}}{{L L}_{11} + + {L L}_{22}} {U u}_{m m} cos cos ωt ωt + + \frac{{L L}_{22}}{{L L}_{11} + + {L L}_{22}} \frac{{U u}_{dc dc}}{22} = = 00 - - - - - - ((88))$

进一步解得：Further solution:

$ω ω {t t}_{1,4 1,4} = = 22 kπ kπ &PlusMinus; &PlusMinus; arccos arccos ((- - \frac{11}{{U u}_{m m}} \frac{{L L}_{22}}{{L L}_{11}} \frac{{U u}_{dc dc}}{22})) - - - - - - ((99))$

$ω ω {t t}_{11} = = 22 kπ kπ - - ((π π - - arccos arccos ((\frac{11}{{U u}_{m m}} \frac{{L L}_{22}}{{L L}_{11}} \frac{{U u}_{dc dc}}{22})))) - - - - - - ((1010))$

针对图2a中的过零点时刻t₂和t₃，令u₁₂＝0，同理可解得：For the zero-crossing moments t ₂ and t ₃ in Fig. 2a, set u ₁₂ =0, similarly, it can be solved as follows:

$ω ω {t t}_{2,3 2,3} = = 22 kπ kπ &PlusMinus; &PlusMinus; arccos arccos ((\frac{11}{{U u}_{m m}} \frac{{L L}_{22}}{{L L}_{11}} \cdot \cdot \frac{{U u}_{dc dc}}{22})) - - - - - - ((1111))$

$ω ω {t t}_{22} = = 22 kπ kπ - - arccos arccos ((\frac{11}{{U u}_{m m}} \frac{{L L}_{22}}{{L L}_{11}} \frac{{U u}_{dc dc}}{22})) - - - - - - ((1212))$

在图2a中，接入点采样电压过零点t₁和t₂之间的实际电网电压过零点为

结合式(10)和式(12)可知，在t₁和t₂之间接入点电压的多个过零点区域范围，关于实际电网电压的过零点而呈左右严格对称的独有特征。同理可推得，针对图2a中t₃和t₄之间接入点电压的多个过零点区域，也关于实际电网电压的过零点具有严格的对称特性。In Figure 2a, the actual grid voltage zero-crossing point between _t1 and _t2 of the sampling voltage zero-crossing point at the access point is

Combining equations (10) and (12), it can be seen that the multiple zero-crossing ranges of the access point voltage between _t1 and _t2 have a unique feature of strict symmetry with respect to the zero-crossing point of the actual grid voltage. In the same way, it can be deduced that for multiple zero-crossing regions of the access point voltage between _t3 and _t4 in Fig. 2a, the zero-crossing point of the actual grid voltage also has strict symmetric characteristics.

设图2a中t₁和t₂之间实际电网电压的过零点时刻为t₀，则由左右对称特性可得：Assuming that the zero-crossing moment of the actual grid voltage between t ₁ and t ₂ in Figure 2a is t ₀ , it can be obtained from the left-right symmetry characteristics:

${t t}_{00} = = {t t}_{11} + + \frac{{t t}_{22} - - {t t}_{11}}{22} = = \frac{{t t}_{22} + + {t t}_{11}}{22} - - - - - - ((1313))$

同理可求得t₃和t₄之间的实际电网电压过零点时刻(设为t_T)为：In the same way, the actual grid voltage zero-crossing moment between _t3 and _t4 (set as t _T ) can be obtained as:

${t t}_{T T} = = \frac{{t t}_{33} + + {t t}_{44}}{22} - - - - - - ((1414))$

故实际电网电压的工频周期为：Therefore, the power frequency period of the actual grid voltage is:

T＝t_T-t₀ (15)T=t _T -t ₀ (15)

由推算出的实际电网电压过零点时刻即可确定其准确相位。因电网电压的相位变化较慢，可通过测量电网电压的多个过零点，而后进行加权平均的方式以提高相位检测准确度。The exact phase can be determined from the calculated zero-crossing moment of the actual grid voltage. Because the phase change of the grid voltage is slow, the phase detection accuracy can be improved by measuring multiple zero-crossing points of the grid voltage and then performing weighted average.

在实际电网电压相位为零的多过零点区域与相位为180度的多过零点区域之间，有一个时间间隔较长的非过零点区域，由此可方便地将两个多过零点区域分开。当两个相邻过零点区域之间的间隔突然变大时，说明该过零点已是下一个多过零点区域的起始过零点了。Between the multi-zero-crossing region where the actual grid voltage phase is zero and the multi-zero-crossing region where the phase is 180 degrees, there is a non-zero-crossing region with a long time interval, which can easily separate the two multi-zero-crossing regions . When the interval between two adjacent zero-crossing areas suddenly becomes larger, it means that the zero-crossing point is already the initial zero-crossing point of the next multi-zero-crossing area.

图4给出了实现电网电压过零点与相位检测的具体算法流程图。Figure 4 shows the specific algorithm flow chart for realizing grid voltage zero-crossing point and phase detection.

上述基于接入点采样电压过零点对称分布特征的相位检测新算法，原理简单且计算量小，在光伏逆变器直流侧电压不太高的情况下具有较好的应用效果。The above-mentioned new phase detection algorithm based on the symmetrical distribution characteristics of the zero-crossing point of the sampling voltage at the access point has a simple principle and a small amount of calculation, and has a good application effect when the DC side voltage of the photovoltaic inverter is not too high.

3)光伏逆变器电流跟踪实验3) Photovoltaic inverter current tracking experiment

因线路电感和开关过程的影响，仅采用传统的电压过零点相位检测方法，并不能实现光伏逆变单元接入点电压和输出电流的相位同步，这已为图3a的实验结果所证实。基于所建立的10kW微电网实验平台，本专利具体应用所提出的电压相位检测新方法，开展了实验研究并得到了多组接入点电压和输出电流的波形，图5所示是其中一组实验波形，其中接入点电压为100V/格，输出电流为10A/格。Due to the influence of line inductance and switching process, only using the traditional voltage zero-crossing point phase detection method cannot realize the phase synchronization of the input point voltage and output current of the photovoltaic inverter unit, which has been confirmed by the experimental results in Figure 3a. Based on the established 10kW micro-grid experimental platform, this patent specifically applied the proposed new method of voltage phase detection, carried out experimental research and obtained multiple sets of access point voltage and output current waveforms, one of which is shown in Figure 5 Experimental waveform, where the voltage at the access point is 100V/div, and the output current is 10A/div.

可以看出，采用本发明提出的电压相位检测方法，逆变器输出电流可准确地跟踪交流电压的相位，利于实现光伏逆变单元的最大功率输出。It can be seen that with the voltage phase detection method proposed by the present invention, the output current of the inverter can accurately track the phase of the AC voltage, which is beneficial to realize the maximum power output of the photovoltaic inverter unit.

Claims

1. many zero crossings of photovoltaic DC-to-AC converter access point voltage method for detecting phases, it is characterized in that: after photovoltaic DC-to-AC converter is inserted electrical network, be subjected to the switching voltage combined influence of line inductance and band ripple, a plurality of zero crossings zone must appear in the access point voltage waveform that obtains through sampling; The exclusive feature of strict symmetry about these many zero crossings zones present about the zero crossing of actual electric network voltage, the scope and time by calculating these zero crossing zones at interval after, get the zero crossing that its central point can calculate 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.

2. many zero crossings of photovoltaic DC-to-AC converter access point voltage method for detecting phases as claimed in claim 1 is characterized in that, determines that the detailed process of the actual zero crossing of line voltage is:

1) sets general zero crossing acquisition mode with common method, begin to carry out zero crossing at 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 a judgement and a last 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 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 be t1 constantly;

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