CN111490525A - Open-phase detection and fault-tolerant control method for three-phase photovoltaic inverter - Google Patents

Abstract

The invention discloses a phase loss detection and fault-tolerant control method for a three-phase photovoltaic inverter, which specifically includes: performing topology transformation on the three-phase photovoltaic inverter; and detecting the operating state of the three-phase photovoltaic inverter. If it is running, it will carry out normal control. If it is abnormal operation, it will carry out fault phase detection and judgment; fault phase isolation and control switch triggering; carry out phase current reconstruction; PWM control output adjustment. The invention realizes phase-opening state detection based on the current vector variation law in the αβ coordinate system, and based on the phase current reconstruction technology, keeps the current vector trajectory in a circle, and realizes that the photovoltaic inverter can still operate amicably in the phase-opening state.

Description

A three-phase photovoltaic inverter phase loss detection and fault-tolerant control method

technical field

The invention relates to the technical field of three-phase photovoltaic inverter control, in particular to a three-phase photovoltaic inverter phase loss state detection and fault-tolerant operation control method.

Background technique

In recent years, with the intensification of the energy crisis, new energy power generation represented by photovoltaics and wind power has developed rapidly. New energy power generation has played an important role in alleviating the energy crisis, optimizing the existing energy structure, and reducing environmental pollution. Photovoltaic panels use solar energy to generate electricity. Since solar energy is theoretically inexhaustible and inexhaustible, the conversion rate of photovoltaic panels to solar energy should be improved as much as possible. The photovoltaic maximum power tracking technology is developed based on this. During the actual operation of photovoltaic power generation, it is inevitable that faults will occur, such as line short-circuit fault, disconnection fault, inverter bridge arm fault, etc. In this case, the traditional method is usually to let the photovoltaic inverter out of operation and wait for the fault to recover. Then put into operation again, which will cause a great waste of photovoltaic power generation resources during the fault period; in addition, for some weak grids where photovoltaic power generation accounts for the main proportion, such as power supply in remote areas, if the photovoltaic inverter is out of operation during the fault , it will produce a very large power disturbance, and in severe cases, it will cause grid instability and greatly reduce the reliability of grid operation. In order to improve the utilization rate of photovoltaics and ensure the reliability of power supply, for some less serious faults, such as single-phase short circuit, disconnection and single-arm failure of the inverter, the fault state can be detected in real time, and the control algorithm can be switched to make the inverter The device is in fault-tolerant operation and continues to deliver power to the grid or load. After a single-phase short-circuit fault, the phase can be tripped by a circuit breaker, and the same is true for the bridge arm of the inverter, so the fault types can be attributed to the disconnection fault (phase loss). In the state of open-phase operation, due to the asymmetry of the three-phase current, it will affect the three-phase load of the power grid, such as causing the torque ripple of the motor. Through the phase current reconstruction technology, the three-phase current vector trajectory is kept circular, which can effectively reduce the impact such as torque ripple.

SUMMARY OF THE INVENTION

The invention provides a three-phase photovoltaic inverter phase loss state detection and fault-tolerant operation control method. Based on the change law of the current vector in the αβ coordinate system, the phase loss state detection is realized. Based on the phase current reconstruction technology, the current vector trajectory is kept in a circular shape, so that the photovoltaic inverter can still operate amicably in the phase loss state.

The present invention is specifically a three-phase photovoltaic inverter phase loss detection and fault-tolerant control method. The three-phase photovoltaic inverter phase loss detection and fault-tolerant control method specifically includes the following steps:

Step (1), performing topology transformation on the three-phase photovoltaic inverter;

In step (2), the operating state of the three-phase photovoltaic inverter is detected. If it is in normal operation, normal control is performed, and if it is in abnormal operation, step (3) is entered;

Step (3), carry out fault phase detection and judgment;

Step (4), fault phase isolation and control switch triggering;

Step (5), carry out phase current reconstruction;

Step (6), PWM control output adjustment.

Further, the topology transformation of the three-phase photovoltaic inverter in the step (1) is specifically:

For the three-phase three-wire photovoltaic inverter, in order to make the photovoltaic inverter in the state of lack of phase, the remaining two phases can be decoupled normally, install a neutral line with a control switch, and turn on the control switch by triggering it. The AC neutral point is connected to the DC neutral point of the inverter to realize phase current decoupling operation; in normal state, the control switch is closed, and the photovoltaic inverter operates under the three-phase three-wire system; for the three-phase four-wire photovoltaic system Inverter, no additional modification is required.

Further, the fault phase detection and judgment in the step (3) is specifically:

During normal operation, the current vector trajectory is a standard circle, and its radius is related to the load; when an open-circuit fault occurs in the photovoltaic inverter line, the current vector trajectory will become a semicircle, and its shape is determined by the open-circuit fault phase. The fault diagnosis can be realized by judging the slope of the current vector trajectory;

The three-phase current of the photovoltaic inverter satisfies i _a + i _b + i _c =0, and the three-phase current is transformed into the two-phase αβ static coordinate system by 3/2 coordinate transformation in the control system, and the space vector of the current is obtained, The transformation formula is as follows:

In the formula, i _a , i _b , and _ic are the output three-phase currents of the photovoltaic inverter, and i _α and i _β are the two-phase currents in the rectangular coordinate system;

The slope of the current vector trace is:

In the formula, n and n-1 are the nth and n-1th sampling values. Under normal circumstances, the current vector trajectory is a circle, and K is the change value. If one switch of the inverter is turned off, K is half a will be a constant value over the period; the faulty phase can be identified by judging the slope of the current vector trace.

Further, in the step (4), the fault phase isolation and the triggering of the control switch are specifically:

When the faulty phase is accurately determined, the control chip sends a fault signal to the relay or circuit breaker corresponding to the fault, isolates the fault in time, protects the inverter, and makes the system run stably; triggers the inverter center line thyristor switch to make the AC The neutral point is connected to the DC neutral point of the inverter to prepare for phase loss operation.

Further, the phase current reconstruction in the step (5) is specifically:

In the state of lack of phase, it is necessary to reconstruct the phase current, so that the current vector maintains a circular trajectory, so as to realize the fault-tolerant operation of the photovoltaic inverter; it is assumed that the three-phase current of the photovoltaic inverter is:

i _a =I _m cos(ωt)

When phase a is missing, the current control of phase bc should be:

When the b-phase is missing, the ac-phase current control should be:

When the c-phase is missing, the ab-phase current control should be:

Among them, I _mf is the phase current amplitude during open-phase operation, which is determined by the actual photovoltaic output and inverter capacity requirements.

Further, in the described step (6), the PWM control output adjustment is specifically:

The bridge arm switch corresponding to the fault is locked, and the corresponding modulation signal is obtained according to the control requirements of the reconstructed current, which is compared with the triangular wave to obtain the switch signal, which controls the normal bridge arm switch tube action of the inverter to realize the reconstructed current control.

Description of drawings

Figure 1 is the topology of the photovoltaic inverter;

Fig. 2(a), Fig. 2(b) and Fig. 2(c) are the current vector trajectories of the αβ coordinate system when the a bridge arm, the b bridge arm and the c bridge arm of the photovoltaic inverter are faulted respectively;

Fig. 3 is the control flow chart of the phase loss operation of the photovoltaic inverter.

Detailed ways

The specific embodiments of a three-phase photovoltaic inverter phase loss detection and fault-tolerant control method of the present invention will be described in detail below with reference to the accompanying drawings.

The invention provides the following three-phase photovoltaic inverter phase loss state detection and fault-tolerant operation control strategy technical solutions, which mainly include topology transformation, fault phase detection, fault phase isolation and control switch triggering, phase current reconstruction, PWM control output adjustment, etc. .

1. Topological transformation

For the three-phase three-wire photovoltaic inverter, as shown in Figure 1, in order to make the photovoltaic inverter in the state of lack of phase, the remaining two phases can operate normally decoupling, it is necessary to install a neutral line with a control switch. By triggering the control switch to turn on, the AC neutral point is connected to the DC neutral point of the inverter to realize phase current decoupling operation; in normal state, the control switch is closed, and the inverter operates in a three-phase three-wire system. For three-phase four-wire system, no additional modification is required.

2. Fault phase detection

During normal operation, the current vector trajectory is a standard circle, and its radius is related to the load. When an open-circuit fault occurs in the photovoltaic inverter line, the current vector trajectory will become a semi-circle, and its shape is determined by the open-circuit fault phase. Through the time of one power frequency cycle, the shape of the current vector trajectory can be obtained, and then the fault phase position can be judged . As shown in Figure 2, fault diagnosis can be achieved by judging the slope of the current vector trajectory.

The three-phase current of the photovoltaic inverter satisfies i _a + i _b + i _c =0, and the three-phase current is transformed into the two-phase αβ static coordinate system by 3/2 coordinate transformation in the control system to obtain the space vector of the current. The transformation formula is as follows:

In the formula, i _a , i _b , and _ic are the output three-phase currents of the photovoltaic inverter, and i _α and i _β are the two-phase currents in the rectangular coordinate system.

The slope of the current vector trace is:

In the formula, n and n-1 are the nth and n-1th sampling values. Under normal circumstances, the current vector trajectory is a circle, and K is the change value. If one switch of the inverter is turned off, K is half a will be a constant value during the period. As shown in Fig. 2, Fig. 2(a), Fig. 2(b) and Fig. 2(c) respectively show the failure of the a bridge arm, the b bridge arm and the c bridge arm of the photovoltaic inverter.

3. Fault phase isolation and control switch triggering

When the faulty phase is accurately determined, the control chip sends a fault signal to the relay/circuit breaker corresponding to the fault, isolates the fault in time, protects the inverter, and makes the system run stably; The neutral point is connected to the DC neutral point of the inverter to prepare for phase loss operation.

4. Phase current reconstruction

In the state of lack of phase, it is necessary to reconstruct the phase current, so that the current vector maintains a circular trajectory and realizes the fault-tolerant operation of the photovoltaic inverter. Through the decoupling control of the two-phase normal current, the two-phase current amplitude is controlled to be equal, and the phase difference is 60 degrees. Assume that the three-phase current of the photovoltaic inverter is:

i _a =I _m cos(ωt)

When phase a is missing, the current control of phase bc should be:

When the b-phase is missing, the ac-phase current control should be:

When the c-phase is missing, the ab-phase current control should be:

Among them, I _mf is the phase current amplitude during open-phase operation, which is determined by the actual photovoltaic output and inverter capacity requirements.

5. PWM control output adjustment

The bridge arm switch corresponding to the fault is locked, and the corresponding modulation signal is obtained according to the control requirements of the reconstructed current, which is compared with the triangular wave to obtain the switch signal, which controls the normal bridge arm switch tube action of the inverter to realize the reconstructed current control.

6. The specific control process is shown in Figure 3.

Finally, it should be noted that the technical solutions of the present invention are only described in conjunction with the above embodiments, but not limited thereto. Those skilled in the art should understand that those skilled in the art can modify or equivalently replace the specific embodiments of the present invention, but these modifications or changes are all within the protection scope of the pending claims.

Claims (6)

1. A three-phase photovoltaic inverter phase loss detection and fault-tolerant control method, characterized in that the three-phase photovoltaic inverter phase loss detection and fault-tolerant control method specifically comprises the following steps: Step (1), performing topology transformation on the three-phase photovoltaic inverter; In step (2), the operating state of the three-phase photovoltaic inverter is detected. If it is in normal operation, normal control is performed, and if it is in abnormal operation, step (3) is entered; Step (3), carry out fault phase detection and judgment; Step (4), fault phase isolation and control switch triggering; Step (5), carry out phase current reconstruction; Step (6), PWM control output adjustment. 2 . The method for phase loss detection and fault-tolerant control of a three-phase photovoltaic inverter according to claim 1 , wherein the topology transformation of the three-phase photovoltaic inverter in the step (1) is specifically: For the three-phase three-wire photovoltaic inverter, in order to make the photovoltaic inverter in the state of lack of phase, the remaining two phases can be decoupled normally, install a neutral line with a control switch, and turn on the control switch by triggering it. The AC neutral point is connected to the DC neutral point of the inverter to realize phase current decoupling operation; in normal state, the control switch is closed, and the photovoltaic inverter operates under the three-phase three-wire system; for the three-phase four-wire photovoltaic system Inverter, no additional modification is required. 3 . The method for phase loss detection and fault-tolerant control of a three-phase photovoltaic inverter according to claim 2 , wherein the step (3) for detecting and judging the faulty phase is specifically: During normal operation, the current vector trajectory is a standard circle, and its radius is related to the load; when an open-circuit fault occurs in the photovoltaic inverter line, the current vector trajectory will become a semicircle, and its shape is determined by the open-circuit fault phase. The fault diagnosis can be realized by judging the slope of the current vector trajectory; The three-phase current of the photovoltaic inverter satisfies i _a + i _b + i _c =0, and the three-phase current is transformed into the two-phase αβ static coordinate system by 3/2 coordinate transformation in the control system, and the space vector of the current is obtained, The transformation formula is as follows:

In the formula, i _a , i _b , and _ic are the output three-phase currents of the photovoltaic inverter, and i _α and i _β are the two-phase currents in the rectangular coordinate system; The slope of the current vector trace is:

In the formula, n and n-1 are the nth and n-1th sampling values. Under normal circumstances, the current vector trajectory is a circle, and K is the change value. If one switch of the inverter is turned off, K is half a will be a constant value over the period; the faulty phase can be identified by judging the slope of the current vector trace. 4. The method for phase loss detection and fault-tolerant control of a three-phase photovoltaic inverter according to claim 3, characterized in that, in the step (4), the fault phase isolation and control switch triggering are specifically: When the faulty phase is accurately determined, the control chip sends a fault signal to the relay or circuit breaker corresponding to the fault, isolates the fault in time, protects the inverter, and makes the system run stably; triggers the inverter center line thyristor switch to make the AC The neutral point is connected to the DC neutral point of the inverter to prepare for phase loss operation. 5 . The method for phase loss detection and fault-tolerant control of a three-phase photovoltaic inverter according to claim 4 , wherein the reconstruction of the phase current in the step (5) is as follows: 6 . In the state of lack of phase, it is necessary to reconstruct the phase current, so that the current vector maintains a circular trajectory, so as to realize the fault-tolerant operation of the photovoltaic inverter; it is assumed that the three-phase current of the photovoltaic inverter is: i _a =I _m cos(ωt)

When phase a is missing, the current control of phase bc should be:

When the b-phase is missing, the ac-phase current control should be:

When the c-phase is missing, the ab-phase current control should be:

Among them, I _mf is the phase current amplitude during open-phase operation, which is determined by the actual photovoltaic output and inverter capacity requirements. 6 . The method for phase loss detection and fault-tolerant control of a three-phase photovoltaic inverter according to claim 5 , wherein, in the step (6), the PWM control output adjustment is specifically: The bridge arm switch corresponding to the fault is locked, and the corresponding modulation signal is obtained according to the control requirements of the reconstructed current, which is compared with the triangular wave to obtain the switch signal, which controls the normal bridge arm switch tube action of the inverter to realize the reconstructed current control.

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