CN204906217U - Gto photovoltaic inverter - Google Patents

Abstract

The utility model discloses a GTO photovoltaic inverter, including direct current circuit breaker, steady voltage electric capacity, three-phase contravariant bridge, wave filter, GTO and step-down device. The direct current breaker comprises a third switch, the voltage reduction device comprises a pre-charging resistor and a nonlinear resistor, one end of the pre-charging resistor is connected to the positive electrode of the voltage-stabilizing capacitor through a first wire, the other end of the pre-charging resistor is connected with a third wire through the first wire, one end of the nonlinear resistor is connected with the positive electrode of the voltage-stabilizing capacitor through a second wire, and the other end of the nonlinear resistor is grounded. A fourth switch is also arranged on the third lead, a second switch is arranged on the first lead and a second switch is arranged on the second lead. The utility model discloses a GTO photovoltaic inverter can improve photovoltaic inverter's the capacity of being incorporated into the power networks, reduce starting current, the impact to the electric wire netting when reducing photovoltaic inverter and starting.

Description

GTO Photovoltaic Inverter

technical field

The utility model relates to the field of solar power generation, in particular to a GTO photovoltaic inverter.

Background technique

Solar energy has the advantages of safety, cleanliness and resource universality, and can become the main renewable energy to replace fossil energy. Solar photovoltaic power generation has long been the focus of fierce competition among countries around the world in its development research, market development and industrialized manufacturing technology.

Figure 1 is a prior art photovoltaic inverter. As shown in Figure 1, the current photovoltaic inverter uses a three-phase inverter bridge. In order to limit the inrush current generated by the first startup of the photovoltaic inverter, first close the fuse F1, charge the voltage stabilizing capacitor through the pre-charging resistor R, and finally close the DC circuit breaker after the capacitor charging is completed.

However, such photovoltaic inverters have the following drawbacks.

First of all, when the AC circuit breaker uses the current passing through the coil, the magnetic flux is generated in the electromagnet, and the iron core realizes the closing and opening of the main circuit due to the action of the electric field force. Since the inverter will generate a large inrush current when it is started, it will cause a large voltage flicker to the grid-side voltage of the power supply. Large-scale ground photovoltaic power plants require electrical equipment to have a service life of 25 years. The AC circuit breaker is started and stopped every day, and the circuit breaker has been switched on and off more than 18,000 times during its entire life. In addition, AC circuit breakers are prone to mechanical failures such as screw loosening and contact wear during long-term high-frequency use, which will cause the inverter to stop operating and affect the power generation of photovoltaic power plants.

Secondly, in order to limit the inrush current generated by the first startup of the photovoltaic inverter, first close the fuse F1, charge the voltage stabilizing capacitor through the pre-charging resistor R, and finally close the DC circuit breaker after the capacitor charging is completed. However, due to the pre-charging process, the maximum withstand voltage of the voltage stabilizing capacitor is the open circuit voltage of the photovoltaic array, that is to say, the withstand voltage of the power device of the photovoltaic inverter must be greater than the open circuit voltage of the photovoltaic array. Therefore, when we design a string of photovoltaic arrays, the open circuit voltage of the photovoltaic modules in the string should not be greater than the withstand voltage of the inverter power device. Therefore, with the large-scale development of the photovoltaic industry, the existing small-capacity grid-connected photovoltaic inverter has become a bottleneck restricting the development of photovoltaic power stations to be intelligent and modular.

Utility model content

The purpose of this utility model is to provide a GTO photovoltaic inverter to improve the grid-connected capacity of the photovoltaic inverter and solve the problems of large starting current of the photovoltaic inverter, obvious impact on electrical equipment and high failure rate.

In order to achieve the above object, the utility model provides a GTO photovoltaic inverter, the GTO photovoltaic inverter includes a DC circuit breaker, a voltage stabilizing capacitor, a three-phase inverter bridge, a filter, a GTO and a step-down device, wherein , the DC circuit breaker includes a third switch (S ₁ ), the third switch (S ₁ ) is set on the third wire (L ₀ ), the step-down device includes a pre-charging resistor (R ₁ ) and a non- A linear resistor (R ₂ ), one end of the pre-charging resistor (R ₁ ) is connected to the positive pole of the voltage stabilizing capacitor through a first wire (L ₁ ), and the other end of the pre-charging resistor (R ₁ ) is connected to the positive electrode of the voltage stabilizing capacitor through a first wire (L 1 ). A wire (L ₁ ) is connected to the third wire (L ₀ ), one end of the non-linear resistor (R ₂ ) is connected to the positive pole of the voltage stabilizing capacitor through the second wire (L ₂ ), and the non-linear resistor The other end of the linear resistance (R ₂ ) is grounded, and a fourth switch (QB) is provided on the third wire (L ₀ ), and a second switch (QB) is provided on the first wire (L ₁ ). QB ₁ ) and a second switch (QB ₂ ) is provided on said second wire (L ₂ ).

Preferably, the pre-charging resistor is an adjustable resistor.

Preferably, the step-down device further includes a first relay, and the first relay is used to control the opening and closing of the first switch (QB ₁ ).

Preferably, the voltage reducing device further includes a power supply, and the power supply is electrically connected to the first relay so as to provide electric energy for the first relay.

Preferably, the voltage reducing device further includes a first CPU module, and the first CPU module is electrically connected to the first relay so as to send instructions to the first relay.

Preferably, the input end of the GTO is electrically connected to the output end of the filter; and the GTO is set to control the conduction angle of the GTO so that the output voltage of the GTO photovoltaic inverter changes from zero to The value gradually increases until the GTOs are all turned on and the output voltage of the GTO photovoltaic inverter reaches the maximum value.

Preferably, the GTO photovoltaic inverter also includes an AC main contactor, the AC main contactor is set to be closed when the GTOs are all turned on, and the GTO is set to be The GTO is disconnected after the AC main contactor is closed.

Preferably, the AC main contactor is connected in parallel with the GTO.

Preferably, the GTO photovoltaic inverter also includes a control system, the control system includes a soft start module and a second CPU module, the soft start module is electrically connected to the second CPU module, and the soft start module The module includes a plurality of second relays, and the plurality of second relays are configured to receive instructions from the second CPU module and control the on and off of the GTO and the AC main contactor according to the instructions.

Preferably, the plurality of second relays include a class I relay, a class II relay and a class III relay, and the control system is configured to:

When the AC voltage at the input end of the GTO is at the same frequency and phase as the grid voltage to be connected to the output end of the GTO, the second CPU module sends an instruction to the relay of the first class, and the relay of the first class controls all The GTO is turned on, and the output voltage of the GTO gradually increases until all the GTOs are turned on; and

When the GTO photovoltaic inverter is running at the rated voltage, the second CPU module sends instructions to the second-type relay and the third-type relay respectively, so that the second-type relay controls the GTO to disconnect, so The above three types of relays control the closing of the AC main contactor, thereby completing the starting process of the GTO photovoltaic inverter.

Through the GTO photovoltaic inverter of the utility model, the grid-connected capacity of the photovoltaic inverter can be improved, the starting current can be reduced, the impact on the power grid when the photovoltaic inverter is started, the degree of equipment integration can be improved, and equipment capital can be saved , to ensure the stability and reliability of the system work, thereby improving the quality of power supply and the service life of equipment. At the same time, compared with the traditional photovoltaic inverter, the circuit breaker is omitted, and it is used in conjunction with the box-type substation to meet the selective characteristics of protection, save the occupied space of the equipment, and realize the integrated development of the equipment.

Description of drawings

Fig. 1 is a topological structure diagram of a photovoltaic inverter in the prior art.

Fig. 2 is a topological structure diagram of the GTO photovoltaic inverter of the present invention.

Fig. 3 is a schematic diagram of the control of the second CPU module of the GTO photovoltaic inverter of the present invention.

Fig. 4 is a control schematic diagram of the soft start module of the GTO photovoltaic inverter of the present invention.

Fig. 5 is a corresponding phase voltage diagram in the GTO voltage regulation circuit of the GTO photovoltaic inverter of the present invention.

Detailed ways

Preferred embodiments of the utility model will be described in detail below in conjunction with the accompanying drawings, so as to better understand the purpose, features and advantages of the utility model. It should be understood that the embodiments shown in the accompanying drawings are not intended to limit the scope of the utility model, but only to illustrate the spirit of the technical solutions of the utility model.

Glossary

Photovoltaic inverter: connect resistors and capacitors through power electronic devices, control the on-off of devices in the form of pulse width modulation, convert the direct current transmitted from the combiner box into alternating current, and complete the maximum power point tracking of photovoltaic modules at the same time, ensuring intelligent control and Anti-islanding effect, etc.

Pre-charging resistance: The voltage at both ends of the DC bus capacitor of the inverter is zero before charging, which is equivalent to a short circuit at the moment of charging the device, which will generate a large inrush current and easily cause damage to the power devices of the inverter. Therefore, a resistor needs to be connected in series with the charging circuit during the pre-charging process to limit the current. This resistor is called the pre-charge resistor.

Stabilizing capacitor: a capacitor connected in parallel to the positive and negative terminals of the voltage source, which has a good filtering effect when used in chopper, inverter and other circuits; when the voltage changes, due to the role of capacitor energy storage, the voltage at both ends cannot change suddenly, ensuring stabilize the voltage.

GTO: The gate can turn off the thyristor. It is a component composed of PNPN four-layer semiconductors. It has three electrodes: anode A, cathode K and control level G. It can realize non-contact control of alternating current in the circuit.

GTO Photovoltaic Inverter: Photovoltaic inverter containing GTO (GTO).

The GTO photovoltaic inverter of the utility model usually includes a DC circuit breaker, a voltage stabilizing capacitor, a three-phase inverter bridge, a filter, a gate-pole turn-off thyristor (hereinafter referred to as GTO) and a voltage reducing device, wherein the DC circuit breaker The device includes a third switch (S ₁ ), the third switch (S ₁ ) is set on the third wire (L ₀ ), the step-down device includes a pre-charging resistor (R ₁ ) and a non-linear resistor (R ₂ ), One end of the pre-charging resistor (R ₁ ) is connected to the positive electrode of the voltage stabilizing capacitor through the first wire (L ₁ ), and the other end of the pre-charging resistor (R ₁ ) is connected to the third electrode through the first wire (L ₁ ). wire (L ₀ ), one end of the non-linear resistor (R ₂ ) is connected to the positive pole of the voltage stabilizing capacitor through the second wire (L ₂ ), the other end of the non-linear resistor (R ₂ ) is grounded, and at the There is also a fourth switch (QB) on the third wire (L ₀ ), a second switch (QB 1 ) on the first wire (L ₁ ), and a switch (QB ₁ ) on the second wire (L ₂ ). A second switch (QB ₂ ).

An embodiment of the GTO photovoltaic inverter of the present invention will be described in detail below with reference to FIG. 1 .

FIG. 1 is a topological structure diagram of a GTO photovoltaic inverter 100 of the present invention. As shown in FIG. 1 , a GTO photovoltaic inverter 100 includes a DC circuit breaker 10 , a voltage stabilizing capacitor 20 , a three-phase inverter bridge 30 , a filter 40 , a step-down device 50 , a GTO 60 and an AC main contactor 70 . Among them, the DC circuit breaker 10, the voltage stabilizing capacitor 20, the three-phase inverter bridge 30, and the filter 40 are electrically connected through wires in turn, and the output end of the filter 40 is electrically connected with the input end of the AC main contactor 70 and the input end of the GTO60 , the AC main contactor 70 and GTO60 are connected in parallel, the DC circuit breaker 10 is used to connect the photovoltaic modules, and the AC circuit breaker is used to connect to the power grid.

The step-down device 50 includes a first CPU module 51, a relay 52, a power supply 53, a pre-charging resistor R ₁ , a non-linear resistor R ₂ , a first wire L ₁ , a second wire L ₂ , a first switch QB ₁ , and a second switch QB ₂ and the fourth switch QB.

The DC circuit breaker 10 includes a plurality of switches, wherein the third switch S1 is arranged on the third wire _L0 , _one end of the pre _- charging resistor R1 is connected to the positive pole of the voltage stabilizing capacitor 20 through the _first wire L1, and the pre-charging resistor R The other end of ₁ is connected to the third wire _L0 through the first wire L1, _one end of the non-linear resistor R2 is connected to the positive pole of the voltage stabilizing capacitor ₂₀ through the _second wire L2, and the other end of the non _- linear resistor R2 is grounded , there is also a fourth switch QB on the third wire L ₀ , a first switch QB ₁ on the first wire L ₁ and a second switch QB _{2 on the second wire L 2 .} Among them, multiple switches of the DC circuit breaker 10 are first connected in parallel and then connected in series with the voltage stabilizing capacitor 20 through the third wire L ₀ , and the fourth switch QB is used to control the on-off of the DC circuit breaker 10 and the voltage stabilizing capacitor 20 .

Preferably, the pre-charging resistor R1 is _an adjustable resistor.

The power supply 53 is electrically connected to the first relay 52 so as to provide electric energy for the first relay 52, and the first CPU module 51 is electrically connected to the first relay 52 so as to send instructions to the first relay 52, and the first relay 52 is connected to the first CPU module 51. Instructs to control the opening and closing of the first switch QB ₁ .

When you need to turn on the GTO photovoltaic inverter, follow the steps below:

(1) Close the second switch QB ₂ and the third switch S ₁ , the voltage between the nodes ① and ② decreases from the open circuit voltage to the voltage U ₁ , where the value of the voltage U ₁ can be a real-time calculated value or a preset value fixed value, but not lower than the lowest normal operating voltage of the system;

(2) Close the first switch QB ₁ and precharge the voltage stabilizing capacitor 20 through the precharging resistor R ₁ , where the first relay 52 can be activated by sending a signal through the CPU module, so that the first relay 52 can control the switch QB ₁ closure;

(3) After the pre-charging is completed, close all the switches of the DC circuit breaker 10;

(4) closing the fourth switch QB;

(5) After the GTO photovoltaic inverter runs stably for a time t, the second switch QB ₂ is turned off, thereby completing the start-up.

The improvement of the grid-connected capacity of the GTO photovoltaic inverter of the present invention will be described below by comparing with the traditional photovoltaic inverter.

The input and output performance parameters of the photovoltaic inverter are shown in Table 1 and Table 2, respectively, and the parameters of the connected photovoltaic modules are shown in Table 3.

Table 1 PV inverter input parameters

Maximum DC input power (kW) MPPT voltage range (VDC) Maximum input DC current (A) 825 450～820 1600

Table 2 Photovoltaic inverter output parameters

Rated output power (kW) Maximum output power (kW) Rated working voltage (V) Rated output frequency (Hz) 750 810 315 50

Table 3 Performance parameters of photovoltaic modules

Rated power (kW) Open circuit voltage (V) Working voltage (V) 310 45.45 37.00

If a traditional photovoltaic inverter is used to connect photovoltaic modules in series, then the number N _max of photovoltaic modules connected to each string should satisfy the following formula:

45.45N _max ≤820(1)

The solution of formula (1) is;

_Nmax = 18(2)

If the photovoltaic inverter of the present utility model is used to connect photovoltaic modules in series, the open circuit voltage is reduced from 45.45V to the working voltage of 37.00V, then the number N _max connected to each string of photovoltaic modules should satisfy the formula (3)

37.00N _max ≤820(3)

The solution of formula (3) is:

_Nmax = 22(4)

Then the rated power of the photovoltaic inverter can be increased to

$\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 750</span>}<span\; class="notranslate">\; *</span>\frac{\mathrm{<span\; class="notranslate">\; twenty\; two</span>}}{\mathrm{<span\; class="notranslate">\; 18</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 916.6</span>}\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

It can be seen from formula (5) that the grid-connected capacity of the photovoltaic inverter of the present invention is obviously improved. Compared with traditional photovoltaic inverters, the grid-connected capacity has increased by 22.2%.

In another embodiment, the GTO photovoltaic inverter of the present invention further includes a control system, the control system includes a second CPU module 81 and a soft start module 82, and the soft start module 82 is connected to the second CPU module 81 through terminals. The terminals correspond to the soft-start state or action functions realized by the control system, and Table 1 is the terminal function table.

Table 1

terminal Function 001 GTO closing and opening state 002 GTO closing 003 GTO opening 004 Closing and opening state of the main contactor 005 Main contactor closed 006 main contactor open 007 main contactor alarm

Fig. 3 is a schematic diagram of the control of the second CPU module 81, and Fig. 4 is a schematic diagram of the control of the soft start module 82, as shown in Figs. The four types of relay J4 and multiple circuits A1, A2, A3, B1, B2, B3, B4, the opening and closing actions of the AC main contactor 70 and GTO60 are completed by controlling each relay.

When the soft-start photovoltaic inverter 100 starts, the control system detects whether the AC voltage coming out of the filter 40 is the same frequency and phase as the grid voltage to be incorporated through the GTO60. When the voltage of the power grid incorporated into GTO60 is at the same frequency and phase, the second CPU module sends a command 002 to the first-class relay J1, and the first-class relay J1 acts after receiving the command to close the control switch, the circuit where A1 is located is turned on, GTO60 starts, and GTO60 The output voltage gradually increases until GTO60 is fully turned on. After the GTO photovoltaic inverter 100 works at the rated voltage, the second CPU module sends command 003 to the second type relay J2, and sends command 005 to the third type relay J3, so that the second type relay J2 controls the disconnection of GTO60, and the third type relay J3 controls The AC main contactor 70 is closed, and the starting process of the GTO photovoltaic inverter 100 is completed.

Figure 5 is the corresponding phase voltage diagram in the voltage regulating circuit of GTO60. Taking a certain phase voltage as an example, the output voltage characteristics of the GTO photovoltaic inverter 100 will be analyzed below. As shown in Figure 5, where U is the input voltage of GTO60, α is the firing angle, is the freewheeling angle, θ is the conduction angle.

It can be seen from Figure 5 that the conduction angle θ, firing angle α and freewheeling angle The functional relationship between them is:

Let the expression of voltage U be:

U＝U _m sinωt(2)

At this time, the expression of GTO60 output voltage effective value U _L is

Equation (3) simplifies to

It can be seen from formula (4) that when the freewheeling angle When it is a constant, the output voltage of the GTO can be changed only by changing the size of the GTO firing angle α, and the requirement that the output voltage of the inverter can be changed according to a predetermined rule can be realized.

Therefore, by controlling the conduction angle of the GTO The output voltage of the GTO photovoltaic inverter can be gradually increased from zero until the output voltage of the GTO photovoltaic inverter reaches the maximum value after all the GTOs are turned on.

Through the GTO photovoltaic module 100 of the utility model, the capacity of the photovoltaic inverter can be increased, the starting current can also be reduced, the impact on the power grid when the photovoltaic inverter is started, the degree of equipment integration can be improved, equipment capital can be saved, and the system can be guaranteed Work stability and reliability, thereby improving the quality of power supply and service life of equipment. Compared with the traditional photovoltaic inverter, the circuit breaker is omitted, and it is used in conjunction with the box-type substation to meet the selective characteristics of protection, save the occupied space of the equipment, and realize the integrated development of the equipment.

The preferred embodiments of the utility model have been described in detail above, but it should be understood that after reading the above teaching content of the utility model, those skilled in the art can make various changes or modifications to the utility model. These equivalent forms also fall within the scope defined by the appended claims of this application.

Claims (6)

1. A kind of GTO photovoltaic inverter, it is characterized in that, described GTO photovoltaic inverter comprises DC circuit breaker, stabilizing capacitor, three-phase inverter bridge, filter, GTO and step-down device, wherein, described DC The circuit breaker includes a third switch (S ₁ ), the third switch (S ₁ ) is arranged on the third wire (L ₀ ), and the step-down device includes a pre-charging resistor (R ₁ ) and a non-linear resistor (R ₂ ), one end of the pre-charging resistor (R ₁ ) is connected to the positive pole of the voltage stabilizing capacitor through the first wire (L ₁ ), and the other end of the pre-charging resistor (R ₁ ) is connected to the positive pole of the voltage stabilizing capacitor through the first wire (L 1 ). ₁ ) connected to the third wire (L ₀ ), one end of the non-linear resistor (R ₂ ) is connected to the positive pole of the voltage stabilizing capacitor through the second wire (L ₂ ), and the non-linear resistor (R ₂ ) the other end is grounded, and a fourth switch (QB) is provided on the third wire (L ₀ ), a second switch (QB ₁ ) is provided on the first wire (L ₁ ) and A second switch (QB ₂ ) is provided on said second wire (L ₂ ). 2. The GTO photovoltaic inverter according to claim 1, wherein the input end of the GTO is electrically connected to the output end of the filter; and the GTO is configured to control the conduction of the GTO angle, so that the output voltage of the GTO photovoltaic inverter gradually increases from zero until the output voltage of the GTO photovoltaic inverter reaches a maximum value after the GTOs are all turned on. 3. The GTO photovoltaic inverter according to claim 2, characterized in that, the GTO photovoltaic inverter also includes an AC main contactor, and the AC main contactor is set so that when the GTOs are all turned on, The AC main contactor is closed, and the GTO is arranged to open when the AC main contactor is closed. 4. The GTO photovoltaic inverter according to claim 3, wherein the AC main contactor is connected in parallel with the GTO. 5. The GTO photovoltaic inverter according to claim 3, characterized in that, the GTO photovoltaic inverter also includes a control system, the control system includes a soft start module and a second CPU module, and the soft start module It is electrically connected with the second CPU module, and the soft start module includes a plurality of second relays, and the plurality of second relays are configured to receive instructions from the second CPU module and control the GTO and the The conduction and disconnection of the AC main contactor. 6. The GTO photovoltaic inverter according to claim 5, characterized in that, the plurality of second relays comprise a class one relay, a class two relay and a class three relay, and the control system is set to: When the AC voltage at the input end of the GTO is at the same frequency and phase as the grid voltage to be connected to the output end of the GTO, the second CPU module sends an instruction to the relay of the first class, and the relay of the first class controls all The GTO is turned on, and the output voltage of the GTO gradually increases until all the GTOs are turned on; and When the GTO photovoltaic inverter is running at the rated voltage, the second CPU module sends instructions to the second-type relay and the third-type relay respectively, so that the second-type relay controls the GTO to disconnect, so The above three types of relays control the closing of the AC main contactor, thereby completing the starting process of the GTO photovoltaic inverter.