CN104682432A - Relay failure detection and filter capacitor protection method of photovoltaic grid-connected inverter - Google Patents

Abstract

The invention relates to the technical field of photovoltaic grid-connected inverters, in particular to a relay failure detection and filter capacitor protection method of a photovoltaic grid-connected inverter_invEffective value and same-phase network voltage V_gridThe difference between the absolute values of the effective values being less than a relay failure voltage threshold Δ V, i.e. | V_inv-V_gridIf the absolute value is less than delta V, the successive electric appliance is judged to be adhered, otherwise, the relay is normal; similarly, after the detection of the relay on the suction inversion side, the detection of the relay on the suction power grid side and the detection of the suction of the relays on the two sides are carried out in sequence, if each relay has no fault, grid connection is allowed, and if one relay has a fault, the system is stopped and is not connected to the grid. The invention accurately detects whether each relay is invalid, processes the voltage of the filter capacitor output by the inverter, eliminates the possibility that the current impact of the power grid to the filter capacitor is caused at the moment of grid connection of the inverter, improves the stability of the inverter system and prolongs the service life of the filter capacitor.

Description

Relay failure detection and filter capacitor protection method of photovoltaic grid-connected inverter

technical field

The invention relates to the technical field of photovoltaic grid-connected inverters, in particular to a relay failure detection and filter capacitor protection method of a photovoltaic grid-connected inverter.

Background technique

In the field of string photovoltaic grid-connected inverters and low-power photovoltaic grid-connected inverters, two sets of relays are used for grid-connection. The relay detection method commonly used in the industry is that the relay pulls in and the inverter is connected to the grid at the moment, and the inverter filter capacitor will not be charged, so that the grid energy is instantly poured into the filter capacitor at the moment the inverter is connected to the grid. This will generate a large current impact on the filter capacitor, which will easily lead to the failure of the filter capacitor and the reduction of its service life. Especially when the power of the inverter is large and the capacity of the filter capacitor is large, this inrush current may even cause the machine to fail to start normally.

Contents of the invention

In order to solve the above problems, the present invention provides a relay failure detection and filter capacitor protection method of a photovoltaic grid-connected inverter. While accurately detecting whether each relay fails, the output filter capacitor voltage of the inverter is processed. It eliminates the possibility of current impact on the filter capacitor caused by the power grid at the moment when the inverter is connected to the grid, improves the stability of the inverter system, and prolongs the life of the filter capacitor.

The present invention adopts the following technical scheme: the relay failure detection and filter capacitor protection method of photovoltaic grid-connected inverter, which is characterized in that it includes the following steps: (1) before closing any relay group, detect the voltage on the inverter side, if detected The effective value of a certain phase or multi-phase inverter voltage V _inv , the effective value of the same-phase grid voltage V _grid , and the relay failure voltage threshold ΔV meet: |V _inv -V _grid |<ΔV, then it is determined that the phase relay has been stuck and is not allowed The inverter is connected to the grid; otherwise, the phase relay is normal; (2) When the relay is detected to be normal in step (1), the inverter is turned on, and the inverter voltage with the same phase and amplitude as the grid voltage is sent out, and N power frequency After a cycle, after the voltage of the inverter output filter capacitor is established, turn on the relay group on the inverter side, continue to send out the inverter voltage of the above N power frequency cycles, release the electric energy of the filter capacitor, and detect the inverter voltage V after the release is completed. The difference between the effective value of _inv and the absolute value of the effective value of the same-phase grid voltage V _grid , when it is detected that the voltage of a certain phase or multiple phases meets: |V _inv -V _grid |<ΔV, it is determined that the relay on the grid side of the phase is stuck. Allow the inverter to be connected to the grid; otherwise, the grid-side relay is normal; (3) When the grid-side relay is detected to be normal in step (2), disconnect the inverter-side relay, turn on the inverter, and send a signal with the same phase and amplitude as the grid voltage. After N power frequency cycles, after the inverter output filter capacitor voltage is established, turn on the relay on the grid side, continue to send N power frequency cycle inverter voltage, and release the power of the filter capacitor. The release is complete Then detect the difference between the absolute value of the effective value of the inverter voltage V _inv and the effective value of the same-phase grid voltage V _grid , and when a certain phase or multiple phases are detected to satisfy: |V _inv -V _grid |<ΔV, then it is determined that the phase is inverted If the relay on the side of the inverter is stuck, the inverter is not allowed to be connected to the grid; otherwise, the relay on the inverter side is normal; (4) When the relay on the grid side is detected to be normal in step (3), turn on the inverter and send a signal that is in phase with the grid voltage. For the inverter voltage with the same amplitude, after N power frequency cycles, after the inverter output filter capacitor voltage is established, turn on the relay on the inverter side, continue to send out the inverter voltage for N power frequency cycles, and detect the inverter voltage The difference between the effective value of V _inv and the absolute value of the effective value of the same-phase grid voltage V _grid , when it is detected that one or more phases meet: |V _inv -V _grid |>ΔV, it can be concluded that the phase relay is receiving the open signal After that, it does not pick up, and it is determined that one of the relays of this phase has failed, and the inverter is not allowed to be connected to the grid; otherwise, the relay is normal, and the inverter starts to work in grid connection.

Preferably, the relay failure voltage threshold ΔV is the maximum allowable error caused by sampling.

Preferably, the relay failure voltage threshold ΔV is 15V.

Preferably, the N value is 4.

A further improvement to the above technical solution is that the relay failure detection and filter capacitor protection method of the photovoltaic grid-connected inverter also includes step (5), specifically: after all relays have no faults, turn on the relay drive voltage and switch to Energy saving mode.

Preferably, the method for releasing the electric energy of the filter capacitor is: turning on the power tube of the inverter at a certain time sequence, forming a loop between the filter capacitor and the resistance on the line, thereby releasing the electric energy stored in the filter capacitor.

Compared with the prior art, the relay failure detection and filter capacitor protection method of the photovoltaic grid-connected inverter according to the present invention has the following beneficial effects:

1. This scheme not only effectively detects whether the relay is invalid, but also processes the output filter capacitor voltage of the inverter to a certain extent, eliminating the possibility of the current impact of the grid on the filter capacitor when the inverter is connected to the grid, and improving the efficiency of the inverter. System stability, extending the life of filter capacitors.

2. The relay failure detection method is accurate and can locate and detect any relay.

3. After the relay has no faults, turn on the drive voltage of the relay, which can ensure the reliable pickup of the relay and reduce the loss of the relay.

Description of drawings

Fig. 1 is a schematic diagram of a grid-connected three-phase photovoltaic grid-connected inverter in a relay failure detection and filter capacitor protection method of a photovoltaic grid-connected inverter according to an embodiment of the present invention;

2 is a schematic diagram of a grid-connected single-phase photovoltaic grid-connected inverter in a relay failure detection and filter capacitor protection method of a photovoltaic grid-connected inverter according to an embodiment of the present invention;

Fig. 3 is the relay driving waveform and the corresponding inverter voltage waveform in the relay failure detection and filter capacitor protection method of the photovoltaic grid-connected inverter according to the embodiment of the present invention;

Fig. 4 is a flowchart of a relay failure detection and filter capacitor protection method of a photovoltaic grid-connected inverter according to an embodiment of the present invention.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings.

Example:

Referring to Figures 1 and 4, the relay failure detection and filter capacitor protection method of the photovoltaic grid-connected inverter according to the present invention includes the following steps:

Taking the three-phase string photovoltaic grid-connected inverter system as an example, as shown in Figure 1, it includes four parts A, B, C, and D, where A is the photovoltaic array source and inverter power module, which is used for Invert the DC source of the photovoltaic array into a sinusoidal PWM wave, B is an LC filter system, which is used to convert the sinusoidal PWM wave output by the inverter into a sinusoidal wave, and C is a grid-connected relay group, which is used to establish the inverter and the grid Connection, D is the grid. L is the filter inductance of the inverter, C is the filter capacitor of the inverter, KM1, KM3, and KM5 are the relay groups on the inverter side, and KM2, KM4, and KM6 are the relay groups on the grid side.

The following describes how the relay operates when the inverter is connected to the grid, so as to ensure the reliable and stable operation of the inverter system and accurately detect whether the relay fails. The specific implementation steps are as follows:

(1) Before closing any relay group, detect the voltage on the inverter side, if the absolute value difference between the effective value of a certain phase or multi-phase inverter voltage V _inv detected and the effective value of the grid voltage V _grid in the same phase is less than the relay failure voltage threshold ΔV, that is, |V _inv -V _grid |<ΔV, it is determined that the relay of this phase has been stuck, and the inverter is not allowed to be connected to the grid;

(2) After the detection in step (1) is passed, turn on the inverter and send out an inverter voltage with the same phase and amplitude as the grid voltage. After 4 power frequency cycles, after the voltage of the inverter output filter capacitor is established, turn on the inverter The relay group on the inverter side continues to send out the inverter voltage for 4 power frequency cycles, and releases the _electric energy of the filter capacitor through a certain strategy. The difference between the absolute value of the effective value of V _grid is the same as step (1). When a certain phase or multiple phases |V _inv -V _grid |<ΔV is detected, it can be determined that the relay on the grid side of this phase is stuck. Otherwise, Grid side relay is normal. If it is detected that there is no fault in the relay on the grid side, the relay on the inverter side is disconnected, and the detection process of step (3) is performed.

(3) Same as step (2), first turn on the inverter and send out an inverter voltage with the same phase and amplitude as the grid voltage. After 4 power frequency cycles, after the voltage of the inverter output filter capacitor is established, turn on the grid The relay on the side continues to send out the inverter voltage for 4 power frequency cycles, and releases the power of the filter capacitor through a certain strategy. After the power of the filter capacitor is released, the effective value of the inverter voltage V _inv and the effective value of the same-phase grid voltage V _grid are detected. The absolute value difference of , when a certain phase or multiple phases |V _inv -V _grid |<ΔV is detected, it can be determined that the relay on the inverter side of this phase is stuck, otherwise, the relay on the inverter side is normal. If it is detected that there is no fault in the relay on the inverter side, the detection process of step (4) will be carried out.

(4) Same as step (2), first turn on the inverter, and send out an inverter voltage with the same phase and amplitude as the grid voltage, after 4 power frequency cycles, after the voltage of the inverter output filter capacitor is established, turn on The relay on the inverter side continues to send out the inverter voltage for 4 power frequency cycles. In the third step, it is determined that the relay on the inverter side has no faults and has not disconnected the relay on the grid side. Therefore, after turning on the relay on the inverter side, the inverter The inverter is connected to the grid, and the difference between the absolute value of the effective value of the inverter voltage V _inv and the effective value of the same-phase grid voltage V _grid is detected. When a certain phase or multiple phases |V _inv -V _grid |>ΔV is detected, then It can be concluded that the relay of this phase has not been closed after receiving the opening signal, so it can be judged that one of the relays of this phase has failed. If the judging condition is not established, the relay is normal, the inverter starts to work in grid connection, and the whole relay detection process ends here.

Among them, the strategy for releasing the electric energy of the filter capacitor is: turn on the power tube of the inverter at a certain timing, and form a loop between the filter capacitor and the resistance on the line, thereby releasing the electric energy stored in the filter capacitor.

After the action of the relay is over and there is no fault, turn on the driving voltage of the relay and switch to the energy-saving mode, which can ensure the reliable pickup of the relay and reduce the loss of the relay.

What needs to be specially explained here is that at the moment when the two sets of relays are closed, there is already a voltage at the same frequency and the same amplitude as the grid voltage at both ends of the inverter filter capacitor, so there will be no impact on the filter capacitor.

The above relay failure voltage threshold ΔV is the maximum allowable error caused by sampling, which can be selected as ΔV=15V here.

Figure 3 shows the relay driving waveform and the inverter voltage waveform at the same time. The top is the relay driving waveform on the inverter side, the high level is on, the low level is off, the middle is the grid side relay driving waveform, and the bottom is Below is the corresponding phase inverter voltage waveform.

This method is also applicable to two-phase and single-phase (Figure 2) photovoltaic grid-connected inverters, and the method is the same as the above steps.

The above-mentioned embodiments only express several implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but should not be construed as limiting the patent scope of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent for the present invention should be based on the appended claims.

Claims (6)

1. the relay failure of photovoltaic combining inverter detects and filter capacitor guard method, it is characterized in that, comprises the steps:

(1) before closed any relay group, the voltage of inverter side is detected, as a certain phase that detects or multi-phase inverter voltage V _inveffective value and homophase line voltage V _grideffective value, relay failure voltage threshold Δ V meet: | V _inv-V _grid| < Δ V, then judge the adhesion of this phase relay, do not allow grid-connected inverters; Otherwise this phase relay is normal;

(2) when step () detects that relay is normal, open inverter, send and the inverter voltage of line voltage same-phase with amplitude, after N number of power frequency period, after inverter output filter capacitor Voltage Establishment, open the relay group of inverter side, continue the inverter voltage sending above-mentioned N number of power frequency period, the electric energy of release filter capacitor, detects inverter voltage V after release _inveffective value and homophase line voltage V _gridthe difference of the absolute value of effective value, when detecting that a certain phase or ployphase voltages meet: | V _inv-V _grid| < Δ V, then judge the relay adhesion of this phase grid side, do not allow grid-connected inverters; Otherwise grid side relay is normal;

(3) when step (two) detects that grid side relay is normal, disconnect inverter side relay, open inverter, send and the inverter voltage of line voltage same-phase with amplitude, after N number of power frequency period, after inverter output filter capacitor Voltage Establishment, open the relay of grid side, continue the inverter voltage sending N number of power frequency period, the electric energy of release filter capacitor, detects inverter voltage V after release _inveffective value and homophase line voltage V _gridthe difference of the absolute value of effective value, when a certain phase or heterogeneous satisfied being detected: | V _inv-V _grid| < Δ V, then judge the relay adhesion of this phase inverter side, do not allow grid-connected inverters; Otherwise inverter side relay is normal;

(4) when step (three) detects that grid side relay is normal, open inverter, send and the inverter voltage of line voltage same-phase with amplitude, after N number of power frequency period, after inverter output filter capacitor Voltage Establishment, open the relay of inverter side, continue the inverter voltage sending N number of power frequency period, detect inverter voltage V _inveffective value and homophase line voltage V _gridthe difference of the absolute value of effective value, when a certain phase or heterogeneous satisfied being detected: | V _inv-V _grid| > Δ V, then can conclude the not adhesive after receiving start signal of this phase relay, judge that one of them relay of this phase lost efficacy, do not allow grid-connected inverters; Otherwise then relay is normal, and inverter starts grid-connected work.

2. the relay failure of photovoltaic combining inverter detects and filter capacitor guard method according to claim 1, it is characterized in that: described relay failure voltage threshold Δ V is the limits of error caused of sampling.

3. the relay failure of photovoltaic combining inverter detects and filter capacitor guard method according to claim 2, it is characterized in that: described relay failure voltage threshold Δ V is 15V.

4. the relay failure of photovoltaic combining inverter detects and filter capacitor guard method according to claim 1, it is characterized in that: described N value is 4.

5. the relay failure of photovoltaic combining inverter detects and filter capacitor guard method according to claim 1; it is characterized in that: also comprise step (five); specifically: all after relay fault-free, open relay driving voltage, switch to energy saver mode.

6. the relay failure of photovoltaic combining inverter detects and filter capacitor guard method according to claim 1; it is characterized in that; the method of release filter capacitor electric energy is: the power tube opening inverter with certain sequential; resistance on filter capacitor and circuit is formed loop, thus discharges the electric energy that filter capacitor stores.