CN217508622U - Three-level inversion structure, inverter and photovoltaic power system - Google Patents
Three-level inversion structure, inverter and photovoltaic power system Download PDFInfo
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- CN217508622U CN217508622U CN202221432824.2U CN202221432824U CN217508622U CN 217508622 U CN217508622 U CN 217508622U CN 202221432824 U CN202221432824 U CN 202221432824U CN 217508622 U CN217508622 U CN 217508622U
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Abstract
The utility model discloses a three level contravariant structures, dc-to-ac converter and photovoltaic electrical power generating system belongs to inverter circuit topology field. The three-level circuit requires 5 power switching tubes, of which the power switch S 1 And S 4 ，S 2 And S 3 The switching timing of (2) is the same, so the number of driving circuits can be effectively reduced. The three-level circuit has only three working modes, and the direct-current power supply charges the first capacitor in the 0-level mode, so that the charging and discharging of the first capacitor can be ensured to be carried out under the switching frequency scale, and the voltage at two ends of the first capacitor is maintained to be stable; on the other hand, under the non-unit power factor, the charging circuit of the first capacitor is separated from the follow current circuit of the power grid, and the redundant electric energy of the first capacitor can be fed back to the direct current power supply, so that the voltage of the first capacitor of the circuit is stable in the full power factor range, and the circuit has excellent stable working performance in the full power factor range.
Description
Technical Field
The utility model relates to an inverter circuit topology field, concretely relates to three level contravariant structures, dc-to-ac converter and photovoltaic electrical power generating system.
Background
At present, non-isolated photovoltaic grid-connected inverter circuits with the capability of inhibiting leakage current are of three types, namely a two-level full-bridge inverter circuit with bipolar modulation, a half-bridge inverter circuit and a common-ground inverter circuit. Because the output voltage of the two-level full-bridge inverter circuit with bipolar modulation is two levels, the switching frequency must be increased or the filter capacity must be increased to reduce the distortion rate of the grid-connected current, so that the method is not beneficial to the improvement of the power density of the grid-connected inverter device. The half-bridge circuit outputs three levels of voltage level, so that the harmonic distortion rate of grid-connected current can be reduced without increasing the switching frequency or the capacity of a filter, however, the peak value of the inverter output is only half of the input direct-current voltage, which increases the design difficulty of the front-stage booster circuit of the inverter. The common-ground grid-connected inverter realizes natural suppression of leakage current, the peak value of output voltage is consistent with input direct-current voltage, and the voltage utilization rate is 100%, however, the current common-ground grid-connected inverter still has two problems, on one hand, the current common-ground inverter does not have expansion capability, and in order to further improve the output power quality and the output voltage gain, the filter capacity and the boosting capability of a preceding stage boosting circuit are still required to be increased; on the other hand, the conventional common ground type inverter often shows insufficient non-unit power factor processing capability during grid connection, that is, when the non-power factor angle is large, the terminal voltage fluctuation of the capacitor is large, which is not beneficial to the stable operation of a grid connection system.
SUMMERY OF THE UTILITY MODEL
Not enough to prior art, the utility model provides a three level contravariant structures, dc-to-ac converter and photovoltaic electrical power generating system.
The purpose of the utility model can be realized by the following technical scheme:
a three-level inverter structure comprising: the power supply comprises a first power switch tube, a second power switch tube, a third power switch tube, a fourth power switch tube, a fifth power switch tube, a first capacitor and an alternating current filter inductor;
the drain electrode of the first power switch tube is connected with the anode of the direct-current power supply; the source electrode of the first power switch tube is connected with the source electrode of the third power switch tube and the drain electrode of the fifth power switch tube; the drain electrode of the third power switch tube is connected with the anode of the first capacitor; the source electrode of the fifth power switch tube is connected with the drain electrode of the fourth power switch tube and the drain electrode of the second power switch tube; the negative electrode of the first capacitor is connected with the source electrode of the fourth power switch tube and one end of the alternating current filter inductor; the other end of the alternating current filter inductor is connected with one end of an alternating current distribution network; the other end of the alternating current distribution network is a common ground end; and the common ground end is connected with the source electrode of the second power switch tube and the negative electrode of the direct current power supply.
Further, the first power switch tube, the second power switch tube, the third power switch tube, the fourth power switch tube and the fifth power switch tube are at least one of a metal-oxide semiconductor field effect transistor, an insulated gate bipolar transistor and a silicon carbide field effect transistor.
Further, the driving signals of the first power switch tube, the second power switch tube, the third power switch tube, the fourth power switch tube and the fifth power switch tube are generated by modulation waves and high-frequency triangular carrier modulation; the modulation wave is at 50Hz power frequency, and the frequency of the high-frequency triangular carrier wave is at 50 kHz.
Furthermore, the switching time sequences of the first power switch tube and the fourth power switch tube are the same and share one driving circuit; the second power switch tube and the third power switch tube have the same switching time sequence and share one driving circuit.
Furthermore, the three-level inversion structure further comprises an extension unit; the extension unit comprises the following structures:
the positive electrode of the (n-1) th capacitor is connected with the drain electrode of the (5 n-4) th power switch tube;
the source electrode of the 5n-4 th power switch tube is connected with the source electrode of the 5n-2 th power switch tube and the drain electrode of the 5n power switch tube;
the drain electrode of the 5n-2 power switch tube is connected with the anode of the nth capacitor;
the source electrode of the 5 nth power switch tube is connected with the drain electrode of the 5 nth-1 power switch tube and the drain electrode of the 5 nth-3 power switch tube;
the source electrode of the 5n-3 th power switch tube is connected with the negative electrode of the n-1 th capacitor;
the negative electrode of the nth capacitor is connected with the source electrode of the 5 nth-1 power switch tube and one end of the alternating current filter inductor; and the negative electrode of the nth capacitor is an output port of the expansion unit, and the other output port of the expansion unit is connected with the source electrode of the second power switch.
Further, the three-level inversion structure includes three working modes:
mode 1: turning on the first power switch tube, the fourth power switch tube and the fifth power switch tube, and providing forward voltage for the alternating current power distribution network by the direct current power supply; at this time, the current flowing through a loop formed by the direct-current power supply, the alternating-current filter inductor and the alternating-current power distribution network is equal to the current of the alternating-current power distribution network;
mode 2: switching on the first power switch tube, the second power switch tube, the third power switch tube and the fourth power switch tube; the potential of the point a and the potential of the point N are equal by a follow current branch circuit formed by the second power switch tube and the fourth power switch tube; the follow current loop of the alternating current distribution network is separated from the charging loop of the direct current power supply to the first capacitor; when the voltage across the first capacitor is charged to the direct current power supply, the potential is kept;
modality 3: switching on the second power switch tube, the third power switch tube and the fifth power switch tube to enable the first capacitor to be connected in series with the alternating-current power distribution network for discharging; at this time, the loop current flowing through the alternating current distribution network and formed by the second power switch tube, the third power switch tube, the fifth power switch tube, the first capacitor, the alternating current filter inductor and the alternating current distribution network is the current of the alternating current distribution network.
In a second aspect, the present invention further provides an inverter, including the three-level inverter structure as described in any one of the above embodiments.
A third aspect of the present invention provides a photovoltaic power system, including:
an optoelectronic device as a dc power supply for outputting a dc voltage;
an alternating current distribution network;
according to the inverter, the input end of the inverter is connected with the photoelectric device, the output end of the inverter is connected with the alternating current distribution network, and the inverter is used for converting the direct current voltage into the alternating current voltage and outputting the alternating current voltage to the alternating current distribution network.
The utility model has the advantages that:
the inverter circuit of the utility model can realize the direct connection of the zero line of the AC distribution network and the negative pole of the photovoltaic cell panel only by a small number of components, and form a common ground structure to realize the elimination of leakage current; the three-level circuit requires 5 power switching tubes, of which the power switch S 1 And S 4 ，S 2 And S 3 The switching time sequences are the same, so that the reduction of the number of driving circuits is realized, and the cost is reduced;
the charging and discharging of the first capacitor in the three-level circuit are only carried out in the negative half period of the alternating-current power distribution network and are carried out under the scale of switching frequency, so that the voltage at two ends of the first capacitor is stable; under the condition of non-unit power factor, the charging circuit of the first capacitor is separated from the follow current circuit of the alternating current distribution network, and the redundant electric energy of the first capacitor can be fed back to the direct current power supply, so that the voltage of the first capacitor is stable in the full power factor range. This inverter circuit possesses better expandable ability, and when extension unit increased to n, the contravariant output voltage level quantity increased to (2n +1), effectively improved contravariant output's electric energy quality, and output voltage's peak value is maximum n times of direct current input, has alleviateed boost circuit's pressure.
Drawings
The present invention will be further described with reference to the accompanying drawings.
Fig. 1 is a schematic structural diagram of an expandable three-level inverter circuit according to the present invention;
fig. 2 is a schematic diagram of the driving signal of the power switch tube of the present invention;
FIG. 3 is a schematic diagram of the positive half cycle energy transfer mode of the AC distribution network voltage;
FIG. 4 is a diagram of a follow current mode of operation of the AC distribution network;
FIG. 5 is a working mode diagram of negative half-cycle energy transfer of AC distribution network voltage;
FIG. 6 is a waveform illustrating operation at unity power factor;
FIG. 7 is a graph of the operating waveform of the AC distribution network when the current leads the voltage by 90 °;
FIG. 8 is a graph of operating waveforms at 90 degrees current lag voltage of an AC distribution network;
FIG. 9 is a waveform of a first capacitor voltage at unity power factor;
FIG. 10 is a graph of the operating waveforms for AC distribution grid current leading voltage by 90 °;
FIG. 11 is a graph of operating waveforms at 90 degrees current lag voltage of an AC distribution network;
fig. 12 is an expanded circuit diagram of the circuit.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by a person of ordinary skill in the art without creative efforts belong to the protection scope of the present invention.
In the description herein, references to the description of "one embodiment," "an example," "a specific example," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
Referring to fig. 1, the present invention provides a three-level inverter circuit comprising: a first capacitor C 1 A first power switch tube S 1 A second power switch tube S 2 The third power switch tube S 3 The fourth power switch tube S 4 The fifth power switch tube S 5 AC filter inductor L 1 DC power supply V pv Single-phase alternating current distribution network u g 。
DC power supply V pv Positive pole and first power switch tube S 1 The drain electrodes are connected; first power switch tube S 1 Source and third power switch tube S 3 Source electrode of and fifth power switch tube S 5 The drain electrodes are connected; third power switch tube S 3 Drain and first capacitor C 1 The positive electrodes of the two electrodes are connected; fifth power switch tube S 5 Source and fourth power switch tube S 4 Drain electrode and second power switch tube S 2 The drain electrodes are connected; a first capacitor C 1 The negative pole of the inverter circuit is the output port a of the inverter circuit and the fourth power switch tube S 4 Source electrode and ac filter inductor L 1 One end of the two ends are connected; AC filter inductance L 1 And the other end of (b) is connected with an AC distribution network u g One end of the two ends are connected; AC distribution network u g The other end of the first power switch tube is the common ground end N of the inverter circuit and a second power switch tube S 2 Source and dc source V pv Are connected with each other.
FIG. 2 shows a three-level inverter circuit power switch tube driverDynamic signal diagram, in which the wave v is modulated M At power frequency (50 Hz), v tri A high frequency triangular carrier of 50 kHz. v. of M And v tri Modulation produces S 1 、S 2 、S 3 、 S 4 、S 5 The drive signal of (1). Wherein S is 1 And S 4 The switching sequences being identical and sharing a drive circuit, S 2 And S 3 The same switching time sequence of the driving circuit is shared, so that the driving quantity can be effectively reduced, the control is simplified, and the cost is reduced.
There are three modes of operation in this embodiment,
mode 1: as shown in FIG. 3, the energy transmission mode of the positive half period of the AC distribution network is realized by a DC power supply V pv For supplying a forward voltage to an AC distribution network, a first capacitor C 1 Does not participate in the work, in this state, the switch S is turned on 1 ,S 4 And S 5 At this time, switch S 1 、S 4 、S 5 DC power supply V pv And the current flowing through a loop formed by the alternating current filter inductor and the alternating current distribution network is equal to the current of the alternating current distribution network.
Mode 2: as shown in fig. 4, the freewheeling mode is shown. Switch-on power switch tube S 1 、S 2 、S 3 And S 4 At this time, S 2 、S 4 The potential of a point A and a point N are equal by the formed follow current branch, and the follow current loop of the AC distribution network and the DC power supply V pv For the first capacitor C 1 The charging circuits are separated from each other, when the first capacitor C 1 Charging voltage at two ends to V pv When the voltage is applied, the potential is maintained.
Modality 3: as shown in fig. 5, the power switch tube S is turned on for the energy transfer mode of the negative half-cycle of the ac distribution network 2 、S 3 And S 5 Make the first capacitor C 1 The serial connection is connected into an alternating current distribution network to discharge, and at the moment, the discharge flows through a switch tube S 2 、S 3 、S 5 、C 1 And the loop current formed by the alternating current filter inductor and the alternating current distribution network is the current of the alternating current distribution network.
The inverter circuit works in a non-unit power factor working mode and a single modeThe bit power factor modes of operation are completely identical, as shown in fig. 3, 4 and 5. Under the condition of reactive power transmission, when the voltage of the alternating-current distribution network is positive and the network-entering current is negative, reactive energy is in load and direct-current power supply V pv The switching mode is shown in fig. 3; when the follow current mode 2 shown in fig. 4 is entered, the alternating current distribution network and the first capacitor C 1 Does not form a loop, and the first capacitor C 1 Directly connected in parallel with the DC power supply as the first capacitor C 1 DC power supply V when voltage at two ends is less than DC power supply pv Is a first capacitor C 1 Charging the first capacitor C 1 The voltage at two ends is greater than the DC power supply V pv At a voltage across, the first capacitor C 1 The electric energy is fed back to the DC power supply V pv In, hold the first capacitor C 1 The voltage at two ends is stable; when the ac distribution network voltage is negative and the network current is positive, the reactive energy is present in the load and the first capacitor C as shown in fig. 5 1 Is exchanged when the first capacitor C is used 1 The voltage across the capacitor will rise, but immediately following the next freewheel mode, the first capacitor C 1 The surplus electric energy will be fed back to the DC power supply, thereby always maintaining the first capacitor C 1 The voltage at the two ends is stable.
FIGS. 6, 7 and 8 are operation waveforms of the inverter circuit of the present embodiment at three-level output with unit power factor and non-unit power factor, where FIG. 6 is the inverter output u at unit power factor aN 、 u g 、i g Fig. 7 shows the time u when the incoming current leads the voltage of the ac distribution network by 90 deg aN 、u g 、i g Fig. 8 shows u when the incoming current lags behind the ac distribution network voltage by 90 deg aN 、u g 、i g The running waveform of (c). Wherein u is aN Peak voltage of and dc supply voltage V pv The voltage is 400V, u g Has a peak voltage of 311V and a network-in current i g The peak value is 6.43A, and the power frequency is 50 Hz. It can be seen that the inverter can stably output better electric energy quality under both unit power factor and extreme non-unit power factor.
FIG. 9, FIG. 10 andFIG. 11 shows the first capacitor C of the inverter circuit in this embodiment 1 The voltage waveforms are shown in fig. 9, fig. 10, and fig. 11, where the grid current leads the ac distribution network voltage by 90 °, and the grid current lags the ac distribution network voltage by 90 °. It can be seen that when the first capacitor C is used 1 At a switching frequency of 0.1mF and 50kHz, the first capacitor C has a unity power factor and an extreme non-unity power factor 1 The voltage of the inverter circuit is stabilized at 400V, and a stable high-quality grid-incoming current is output, so that the inverter circuit has the capability of transmitting reactive power to an alternating-current power distribution network to an excellent degree.
Fig. 12 is an extended circuit of the extended three-level inverter circuit according to the present embodiment. The capacitor of the extended inverter circuit works under the switching frequency scale, so that the voltage of the capacitor can be kept stable. It is noted that as the number of levels increases, there may be multiple switching modes for the same level, which is advantageous for achieving multiplication of the differential mode operating frequency. The extended circuit shown in fig. 12 satisfies equation (1), and can increase 2 levels and double the output voltage gain by adding one extended unit, i.e. by adding 5 switching tubes and 1 capacitor, where N represents the number of levels and N is the number of levels C Indicates the number of capacitors, N S Representing the number of switching devices, Ng representing the number of gate drives, G representing the output voltage gain, f DM Representing the equivalent differential-mode operating frequency, f, of the inverter S Represents the switching frequency;
the positive electrode of the (n-1) th capacitor is connected with the drain electrode of the (5 n-4) th power switch tube; the source electrode of the 5n-4 th power switch tube is connected with the source electrode of the 5n-2 th power switch tube and the drain electrode of the 5n power switch tube; the drain electrode of the 5n-2 th power switch tube is connected with the anode of the nth capacitor; the source electrode of the 5 nth power switch tube is connected with the drain electrode of the 5 nth-1 power switch tube and the drain electrode of the 5 nth-3 power switch tube; the source electrode of the 5n-3 th power switch tube is connected with the negative electrode of the n-1 th capacitor;
the negative electrode of the nth capacitor is connected with the source electrode of the 5 nth-1 power switch tube and one end of the alternating current filter inductor; the negative electrode of the nth capacitor is an output port of the expansion unit, and the other output port of the expansion unit is connected with the source electrode of the second power switch.
All power switches described in this embodiment are metal-oxide semiconductor field effect transistors (MOSFET for short), insulated gate bipolar transistors or silicon carbide field effect transistors.
The foregoing shows and describes the general principles, essential features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the above embodiments, and that the foregoing embodiments and descriptions are provided only to illustrate the principles of the present invention without departing from the spirit and scope of the present invention.
Claims (7)
1. A three-level inverter structure, comprising: the power supply comprises a first power switch tube, a second power switch tube, a third power switch tube, a fourth power switch tube, a fifth power switch tube, a first capacitor and an alternating current filter inductor;
the drain electrode of the first power switch tube is connected with the anode of the direct-current power supply; the source electrode of the first power switch tube is connected with the source electrode of the third power switch tube and the drain electrode of the fifth power switch tube; the drain electrode of the third power switch tube is connected with the anode of the first capacitor; the source electrode of the fifth power switch tube is connected with the drain electrode of the fourth power switch tube and the drain electrode of the second power switch tube; the negative electrode of the first capacitor is connected with the source electrode of the fourth power switch tube and one end of the alternating current filter inductor; the other end of the alternating current filter inductor is connected with one end of an alternating current distribution network; the other end of the alternating current distribution network is a common ground end; and the common ground end is connected with the source electrode of the second power switch tube and the negative electrode of the direct current power supply.
2. The tri-level inverter structure of claim 1, wherein the first power switch, the second power switch, the third power switch, the fourth power switch and the fifth power switch are at least one of metal-oxide semiconductor field effect transistors, insulated gate bipolar transistors and silicon carbide field effect transistors.
3. The three-level inverter structure according to claim 1, wherein the driving signals of the first power switch tube, the second power switch tube, the third power switch tube, the fourth power switch tube and the fifth power switch tube are generated by modulation wave and high-frequency triangular carrier modulation; the modulation wave is at 50Hz power frequency, and the frequency of the high-frequency triangular carrier wave is 50 kHz.
4. The three-level inverter structure of claim 3, wherein the first power switch tube and the fourth power switch tube have the same switching timing and share a driving circuit; the second power switch tube and the third power switch tube have the same switching time sequence and share one driving circuit.
5. The three-level inversion structure of claim 1, further comprising an expansion unit; the extension unit comprises the following structures:
the positive electrode of the (n-1) th capacitor is connected with the drain electrode of the (5 n-4) th power switch tube;
the source electrode of the 5n-4 th power switch tube is connected with the source electrode of the 5n-2 th power switch tube and the drain electrode of the 5n power switch tube;
the drain electrode of the 5n-2 th power switch tube is connected with the anode of the nth capacitor;
the source electrode of the 5 nth power switch tube, the drain electrode of the 5n-1 th power switch tube and the drain electrode of the 5n-3 th power switch tube;
the source electrode of the 5n-3 th power switch tube is connected with the negative electrode of the n-1 th capacitor;
the negative electrode of the nth capacitor is connected with the source electrode of the 5n-1 power switch tube and one end of the alternating current filter inductor; and the negative electrode of the nth capacitor is an output port of the expansion unit, and the other output port of the expansion unit is connected with the source electrode of the second power switch.
6. An inverter, characterized in that it comprises a three-level inverting structure according to any one of claims 1 to 5.
7. A photovoltaic power system, comprising:
the photoelectric device is used as a direct current power supply and is used for outputting direct current voltage;
an alternating current distribution network;
the inverter of claim 6, wherein the input of the inverter is connected to the photovoltaic device, the output of the inverter is connected to the AC distribution network, and the inverter is configured to convert the DC voltage into an AC voltage for output to the AC distribution network.
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