CN106059356A - Electrolytic capacitor-free photovoltaic inverter capable of suppressing leakage current and control method for photovoltaic inverter - Google Patents

Abstract

The invention discloses a non-electrolytic capacitor photovoltaic inverter capable of suppressing leakage current and a control method thereof. The inverter consists of a photovoltaic cell array module, five power switch tubes, two power diodes, two identical DC storage It consists of an energy inductor, two identical filter inductors and a filter capacitor. The inverter topology of the present invention does not require electrolytic capacitors, has a long service life, and can realize single-stage inverter grid connection; among the five power switch tubes, four power switch tubes are in the power frequency mode, and one power switch tube is in the high frequency mode , and only one power switch tube is in the high-frequency mode at any time, which greatly reduces the loss of the power switch tube, and the system efficiency is high; the grid-connected inverter adopts the PWM modulation strategy based on the principle of area equivalent to ensure the Under the premise of quality, the inductance value of the DC energy storage is effectively reduced, and the volume and cost of the system are reduced; the topology and its control method can ensure a constant common-mode voltage, thereby effectively reducing the leakage current.

Description

A non-electrolytic capacitor type photovoltaic inverter capable of suppressing leakage current and its control method

technical field

The invention belongs to the field of photovoltaic grid-connected power generation, and in particular relates to a non-electrolytic capacitor photovoltaic inverter capable of suppressing leakage current and a control method thereof.

Background technique

Photovoltaic grid-connected power generation is mostly realized by low-frequency transformer isolation. Isolated grid-connected can realize electrical isolation between the grid and photovoltaic cells to ensure personal safety. At the same time, it can provide voltage matching, suppress the DC component of grid-connected current, and eliminate leakage current simply and effectively. However, the low-frequency transformer increases the volume, weight and cost of the system, and reduces the conversion efficiency. Therefore, the non-isolated grid-connected power generation method without transformers has quickly attracted the attention of researchers from various countries and the attention of the industry by virtue of its absolute advantages of high change efficiency, small size, light weight and low cost. However, the elimination of the transformer makes an electrical connection between the photovoltaic cell and the grid, which is likely to lead to a substantial increase in leakage current. The equipment causes serious conduction and radiation interference, increases grid-connected current harmonics and system loss, and even endangers equipment and personal safety. Therefore, the elimination of leakage current is a problem that must be solved for the wide application of non-isolated grid-connected inverters. It is of great significance to study the method of eliminating leakage current for the development of photovoltaic grid-connected power generation.

At present, the inverters on the market mainly adopt the voltage-type inverter topology. This inverter is a step-down inverter, that is, the voltage on the DC side must be greater than the peak value of the output voltage on the AC side. However, the photovoltaic panel The output voltage level is low and cannot be directly connected to the grid for power generation. Therefore, a boost circuit is often added to the front stage to obtain a higher DC side voltage and then connected to the grid, which adds a level of power conversion. The system structure becomes complicated, the control is difficult, and the conversion efficiency is low.

The current-source inverter and the voltage-source inverter are dual inverters. Compared with the voltage-source inverter, the application of the current-source inverter in the photovoltaic grid-connected system has the following advantages: (1) The current-source inverter itself has a boost characteristic, which can realize single-stage boost inverter; (2) In the current-source grid-connected inverter, the CL filter is the best structure for filtering switching harmonics. type LCL filter, the CL filter itself is a stable second-order system, the selection of parameters and structure is simple, and the filtering effect is good; (3) the current source inverter uses the inductor as the energy storage element, and the service life is longer; (5 ) In the current-type photovoltaic grid-connected inverter, it is easier to get timely protection when over-current and short-circuit protection occur, and the reliability is higher.

The disadvantage of the single-phase current-source inverter is that the DC current fluctuates greatly, and its fluctuation frequency is twice the frequency of the grid, which directly leads to a higher third harmonic in the grid-connected current, which seriously affects the current quality of the grid. The DC current is as smooth as possible, and a DC inductor with a large inductance is often connected in series on the DC side, resulting in an increase in system volume, increase in cost, and decrease in efficiency.

Therefore, it is very important to seek a transformerless single-phase current-mode inverter that can effectively suppress the leakage current and has a higher grid-connected current quality, which is of great significance for building a conservation-minded society.

Contents of the invention

The invention overcomes the shortcomings in the prior art, provides a non-electrolytic capacitor type photovoltaic inverter capable of suppressing leakage current, and proposes a PWM control method based on an area equivalent principle.

In order to solve the above-mentioned technical problems, the present invention is achieved through the following technical solutions:

A non-electrolytic capacitor photovoltaic inverter that can suppress leakage current. The topology of the inverter includes a photovoltaic cell array module, five power switch tubes, two power diodes, two identical DC energy storage inductors, two The same filter inductor and a filter capacitor; one end of the first DC energy storage inductor is connected to the "+" end of the photovoltaic cell array module, and the other end is respectively connected to the anode of the fifth power switch tube and the first power diode. Anode connection; one end of the second DC energy storage inductor is connected to the "-" end of the photovoltaic cell array module, and the other end is respectively connected to the cathode of the fifth power switch tube and the cathode of the second power diode; the first power diode The cathode is respectively connected to the anode of the first power switch tube and the anode of the third power switch tube; the anode of the second power diode is connected to the cathode of the second power switch tube and the cathode of the fourth power switch tube respectively; " terminal is connected with the cathode of the first power switch tube and the anode of the second power switch tube, the "-" terminal of the filter capacitor is connected with the cathode of the third power switch tube and the anode of the fourth power switch tube, and the first filter inductor One end is connected to the "+" end of the filter capacitor, and the other end is connected to the "+" end of the grid; one end of the second filter inductor is connected to the "-" end of the filter capacitor, and the other end is connected to the "-" end of the grid. end connection.

The control method of the non-electrolytic capacitor type photovoltaic inverter capable of suppressing leakage current, the control method specifically includes the following content:

In the positive half cycle of the grid-connected current, the first power switch tube and the fourth power switch tube are always on, the second power switch tube and the third power switch tube are always off, and the fifth power switch tube is based on the area equivalent principle The PWM modulation controls its turn-on or turn-off; when the fifth power switch is turned off, the path of the grid-connected current is: "+" terminal of the photovoltaic cell array module → the first DC energy storage inductor → the first power diode → The first power switch tube → the first filter inductor → power grid → the second filter inductor → the fourth power switch tube → the second power diode → the second DC energy storage inductor → the "-" terminal of the photovoltaic cell array module → the photovoltaic cell array module " +" terminal; when the fifth power switch tube is turned on, the grid-connected current path is: "+" terminal of the first filter capacitor → first filter inductor → power grid → second filter inductor → "-" of the first filter capacitor "End → "+" end of the first filter capacitor;

In the negative half cycle of the grid-connected current, the first power switch tube and the fourth power switch tube are always off, the second power switch tube and the third power switch tube are always on, and the fifth power switch tube adopts the principle of area equivalent The PWM modulation controls its turn-on or turn-off; when the fifth power switch is turned off, the path of the grid-connected current is: "+" terminal of the photovoltaic cell array module → the first DC energy storage inductor → the first power diode → The third power switch tube → the second filter inductor → power grid → the first filter inductor → the second power switch tube → the second power diode → the second DC energy storage inductor → the "-" terminal of the photovoltaic cell array module → the photovoltaic cell array module " +" terminal; when the fifth power switch tube is turned on, the path of grid-connected current is: "-" terminal of the first filter capacitor → second filter inductor → power grid → first filter inductor → "+" of the first filter capacitor "End → "-" end of the first filter capacitor.

The fifth power switch adopts a PWM control strategy based on the area equivalent principle, and its modulation mechanism is as follows:

The carrier adopts a high-frequency triangular carrier, and the modulation wave signal is

$\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}\mathrm{<span\; class="notranslate">\; v</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&omega;\; LI</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&omega;</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; the\; tan</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; \&omega;\; C</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}\mathrm{<span\; class="notranslate">\; v</span>}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}<span\; class="notranslate">\; )</span>$

Where U _pv is the DC voltage output by the photovoltaic panel, U _g is the peak value of the grid voltage, ω is the fundamental angular frequency of the grid, L is the inductance value of the energy storage inductance on the DC side, C _f is the capacitance value of the filter capacitor, and I _c is the DC side The DC component of the inductor current.

The non-electrolytic capacitor photovoltaic inverter capable of suppressing the leakage current of the present invention belongs to the current type inverter and has a boost characteristic, that is, the output voltage U _pv of the photovoltaic cell array module does not need to be boosted and then connected to the inverter. It can realize grid-connected inverter when the AC voltage is lower than the peak value.

Due to the adoption of the above technical solution, a non-electrolytic capacitive photovoltaic inverter capable of suppressing leakage current and its control method proposed by the present invention, compared with the prior art, has the following beneficial effects:

(1) This topology does not require electrolytic capacitors, has a long service life, and can realize single-stage inverter grid connection;

(2) Among the five power switch tubes, four power switch tubes are in power frequency mode, one power switch tube is in high frequency mode, and only one power switch tube is in high frequency mode at any time, which greatly reduces the loss of power switch tubes , the system efficiency is higher;

(3) The grid-connected inverter adopts a PWM modulation strategy based on the area equivalent principle, which effectively reduces the inductance value of the DC energy storage inductance and reduces the volume and cost of the system under the premise of ensuring the quality of the grid-connected current;

(4) The topology and its control method can ensure a constant common-mode voltage, thereby effectively reducing leakage current.

Description of drawings

Fig. 1 is a kind of topological structure of non-electrolytic capacitor type photovoltaic inverter that can suppress the leakage current of the present invention;

Fig. 2 is the driving waveform of a power switch tube in one cycle of a non-electrolytic capacitor type photovoltaic inverter capable of suppressing leakage current of the present invention;

Fig. 3 is working mode 1 of the present invention;

Fig. 4 is working mode 2 of the present invention;

Fig. 5 is the working mode 3 of the present invention;

Fig. 6 is working mode 4 of the present invention;

Figure 7 shows the waveforms of the output current before and after filtering when the DC inductor current fluctuates greatly, and the inverter adopts a modulation strategy based on the area equivalent principle;

Fig. 8 is a control block diagram of a closed-loop system of a non-electrolytic capacitor type photovoltaic inverter capable of suppressing leakage current in the present invention;

Fig. 9 is a simulation diagram of DC inductance current and grid-connected current of a non-electrolytic capacitor type photovoltaic inverter capable of suppressing leakage current according to the present invention;

Fig. 10 is a simulation diagram of the voltage across the parasitic capacitor and the common-mode current of a non-electrolytic capacitor type photovoltaic inverter capable of suppressing leakage current according to the present invention.

detailed description

The specific implementation manners of the present invention will be described in further detail below in conjunction with the accompanying drawings.

Fig. 1 shows the topological structure of a non-electrolytic capacitor photovoltaic inverter capable of suppressing leakage current of the present invention, which mainly consists of a photovoltaic cell array module, five power switch tubes, two power diodes, and two identical DC storage energy inductor, two identical filter inductors and a filter capacitor; _one end of the first DC energy storage inductor L1 is connected to the "+" end of the photovoltaic cell array module, and the other end is respectively connected to the fifth power switch tube S ₅ is connected to the anode of the first power diode D1; _one end of the _second DC energy storage inductor L2 is connected to the "-" end of the photovoltaic cell array module, and the other end is respectively connected to the _fifth power switch tube S5 The cathode is connected to the cathode of the second power diode D2 _; the cathode of the _first power diode D1 is respectively connected to the anode of the _first power switch S1 and the anode of the _third power switch S3; the _second power diode D2 The anode is respectively connected to the cathode of the _second power switch S2 and the cathode of the _fourth power switch S4; the "+" terminal of the filter capacitor C _f is connected to the cathode of the _first power switch S1 and the second power switch S ₂ , the "-" end of the filter capacitor C _f is connected to the cathode of the _third power switch S3 and the anode of the _fourth power switch S4, and one end of the first filter inductor L _f1 is connected to the "+" of the filter capacitor " end, and the other end is connected to the "+" end of the power grid; one end of the second filter inductor L _f2 is connected to the "-" end of the filter capacitor C _f , and the other end is connected to the "-" end of the power grid.

Through appropriate control, ensure that the grid-connected current and grid-connected voltage have the same frequency and phase, and realize grid-connected operation with unit power factor. C _pv is the parasitic capacitance between photovoltaic and ground, and its capacitance is related to factors such as external environmental conditions and the size and structure of photovoltaic panels, and is generally around 50-150nF/kW.

The control method of the non-electrolytic capacitor type photovoltaic inverter capable of suppressing leakage current, the control method specifically includes the following content:

In Fig. 2, when the photovoltaic grid-connected inverter of the present invention works in the positive half cycle of the grid-connected current, the _first power switch S1 and the _fourth power switch S4 are always on, and the second power switch S ₂ and the _third power switch S3 are always off, and the _fifth power switch S5 adopts PWM modulation based on the principle of area equivalent to control its on or off; in Fig. 3, when the _fifth power switch S5 When shutting down, That is, the voltage across the parasitic capacitance C _pv of the photovoltaic system is At this time, the common-mode voltage Ucm= _{Upv /} 2; in Fig. 4, when the _fifth power switch S5 is turned on, That is, the voltage across the parasitic capacitance C _pv of the photovoltaic system is At this time, the common mode voltage U _cm =U _pv /2;

When the photovoltaic grid-connected inverter of the present invention works in the negative half cycle of the grid-connected current, the _second power switch S2 and the _third power switch S3 are always on, and the _first power switch S1 and the fourth power switch S1 _The switch tube S4 is always off, and the _fifth power switch tube S5 adopts PWM modulation based on the principle of area equivalent to control its on or off; in FIG. 5, when the _fifth power switch tube S5 is off, That is, the voltage across the parasitic capacitance C _pv of the photovoltaic system is At this time, the common-mode voltage Ucm= _{Upv /} 2; in Fig. 6, when the _fifth power switch S5 is turned on, That is, the voltage across the parasitic capacitance C _pv of the photovoltaic system is At this time, the common-mode voltage U _cm = U _pv /2.

Table 1 lists the switching states of the four operating modes and the corresponding voltages across C _pv and the common-mode voltage. where U _m , and ω are the amplitude, phase and frequency of the grid voltage, respectively, ON means the switch is turned on, and OFF means the switch is turned off.

Table 1 Common mode voltage comparison table under different working modes

It can be seen from Table 1 that the common-mode voltage is constant, and the voltage across the parasitic capacitance C _pv does not contain high-frequency components. Since the system leakage current i _leak =C _p v(dUC _pv /dt), according to the above analysis, this topology can effectively reduce small leakage current.

For single-phase current-source inverters, the DC inductor current has certain fluctuations, and its fluctuation frequency is twice the frequency of the power grid, that is, i _L (t) = I _c + Ksin (2ωt + φ) (K is the amplitude of the AC component value), at this time, if the SPWM modulation strategy is adopted, the AC component in the inductor current will be fed to the grid, making the grid-connected current contain a large number of third harmonics, which seriously affects the quality of the grid-connected current.

The _fifth power switching tube S5 in the present invention adopts a PWM modulation strategy based on the principle of area equivalent, and in the case of large fluctuations in the DC inductor current, the pulse current area output by the inverter is equal to the desired output sine wave The area in the corresponding interval remains equal, so that the influence of the double frequency ripple of the inductor current on the grid-connected current is eliminated, and the quality of the grid-connected current is guaranteed. At this time, the modulation wave adopted by the _fifth power switch tube S5 is not sine wave, but

$\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; K</span>}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&omega;</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&phi;</span>}<span\; class="notranslate">\; )</span>}$

As shown in Figure 7, the grid-connected current after filtering is

${\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; \&lsqb;</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; K</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&omega;</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&phi;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; *</span>\frac{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; K</span>}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&omega;</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&phi;</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; MI</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>$

It can be seen from the above that after adopting the present invention, under the premise of ensuring the quality of the grid-connected current, the DC inductor current is allowed to fluctuate to a certain extent, so the DC inductor value can be effectively reduced.

Fig. 8 shows the system closed-loop control block diagram provided by the present invention, but it is not used as a limitation of the present invention. First, the output voltage U _pv and output current I _pv of the photovoltaic panel are collected, and the reference current I _c is given after MPPT, which is adjusted by feedback Then multiplied with the modulating wave r(t) to obtain the grid-connected given current, adjusted with the grid-connected feedback current and then compared with the triangular wave to obtain the PWM pulse, and then distribute the obtained pulse to each switch tube, the modulated wave signal is

$\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}\mathrm{<span\; class="notranslate">\; v</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&omega;\; LI</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&omega;</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; the\; tan</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; \&omega;\; C</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}\mathrm{<span\; class="notranslate">\; v</span>}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>$

Where U _PV is the DC voltage output by the photovoltaic panel, U _g is the peak value of the grid voltage, ω is the fundamental angular frequency of the grid, L is the inductance value of the DC side, C _f is the capacitance value of the filter capacitor, and I _c is the inductor current of the DC side The DC component of , that is, the reference current of the DC side given by MPPT.

Fig. 9 is a simulation diagram of the DC inductor current and the grid-connected current of the photovoltaic inverter according to the present invention. It can be seen that the DC inductor current fluctuates greatly, but the grid-connected current still maintains a good sine.

Figure 10 shows the simulation diagram of the voltage across the parasitic capacitor of the photovoltaic inverter and the common-mode current of the present invention. It can be seen that the voltage across the parasitic capacitor does not contain high-frequency components, which verifies the analysis in Table 1, and the leakage current is very small.

Claims (3)

1. one kind can be suppressed leakage current no electrolytic capacitor type photovoltaic DC-to-AC converter, it is characterised in that: the topological structure bag of this inverter Include photovoltaic battery array module, five power switch pipes, two power diodes, two identical direct current energy storage inductors, two Identical filter inductance and a filter capacitor composition；One end of first direct current energy storage inductor and photovoltaic battery array module "+" end connects, and its other end is connected with the anode of the 5th power switch pipe and the anode of the first power diode respectively；Second is straight Stream energy storage inductor one end connect with the "-" end of photovoltaic battery array module, its other end respectively with the 5th power switch pipe The negative electrode of negative electrode and the second power diode connects；The negative electrode of the first power diode respectively with the anode of the first power switch pipe Connect with the anode of the 3rd power switch pipe；The anode of the second power diode respectively with the negative electrode and of the second power switch pipe The negative electrode of four power switch pipes connects；Filter capacitor "+" hold the negative electrode with the first power switch pipe and the second power switch pipe Anode connect, the anode connection of the "-" end of filter capacitor and the negative electrode of the 3rd power switch pipe and the 4th power switch pipe, the One end of one filter inductance and filter capacitor "+" end connects, its other end and electrical network "+" hold and be connected；Second filter inductance One end connect with the "-" end of filter capacitor, its other end is connected with the "-" end of electrical network.

A kind of control method suppressing leakage current no electrolytic capacitor type photovoltaic DC-to-AC converter, it is special Levy and be: this control method specifically includes following content:

In grid-connected current positive half period, the first power switch pipe and the 4th power switch pipe are constantly on, the second power switch Pipe and the 3rd power switch pipe turn off always, and the 5th power switch pipe uses PWM based on area equivalent principle to control it On or off；When the 5th power switch pipe turns off, the path of grid-connected current is: photovoltaic battery array module "+" end → the One direct current energy storage inductor → the first power diode → the first power switch pipe → the first filter inductance → electrical network → the second filtering Inductance → the 4th power switch pipe → the second power diode → the second direct current energy storage inductor → photovoltaic battery array module "-" end → photovoltaic battery array module "+" end；When the 5th power switch pipe conducting, the path of grid-connected current is: the first filter capacitor "+" end the → the first filter inductance → electrical network → the second filter inductance → the first filter capacitor "-" end → the first filter capacitor "+" end；

In grid-connected current negative half-cycle, the first power switch pipe and the 4th power switch pipe turn off always, the second power switch Pipe and the 3rd power switch pipe are constantly on, and the 5th power switch pipe uses PWM based on area equivalent principle to control it On or off；When the 5th power switch pipe turns off, the path of grid-connected current is: photovoltaic battery array module "+" end → the One direct current energy storage inductor → the first power diode → the 3rd power switch pipe → the second filter inductance → electrical network → the first filtering Inductance → the second power switch pipe → the second power diode → the second direct current energy storage inductor → photovoltaic battery array module "-" end → photovoltaic battery array module "+" end；When the 5th power switch pipe conducting, the path of grid-connected current is: the first filter capacitor "-" end → the second filter inductance → electrical network → the first filter inductance → the first filter capacitor "+" end the → the first filter capacitor "-" end.

One the most according to claim 1 can suppress leakage current no electrolytic capacitor type photovoltaic DC-to-AC converter, it is characterised in that the Five power switch pipes use PWM control strategy based on area equivalent principle, and its modulation scheme is as follows:

Carrier wave uses the triangular carrier of high frequency, and modulation wave signal is

$r\left(t\right)=\frac{sin\left(\mathrm{\&omega;}t\right)}{1+\frac{U_{pv}}{2{\mathrm{\&omega;LI}}_c}sin(2\mathrm{\&omega;}t+\mathrm{\&theta;})},\mathrm{\&theta;}={\tan }^{-1}\left(\frac{{\mathrm{\&omega;C}}_f{U}_g^2}{2U_{pv}{I}_c}\right)$

Wherein U_pvFor the DC voltage of photovoltaic battery panel output, U_gFor line voltage peak value, ω is electrical network first-harmonic angular frequency, and L is DC side energy storage inductor inductance value, C_fFor filter capacitor capacitance, I_cDC component for DC side inductive current.