A method for detecting relay sticking of a grid-connected converter

Abstract

The application discloses a relay sticking detection method of a grid-connected converter, and specifically comprises the following steps: step one, building a power unit level topology; step two, building a voltage sampling circuit; and step three, relay sticking detection. The method has the advantages that no additional voltage sampling circuit is added, and the resistance voltage division method is used for measurement, so that the hardware is simple and the cost is low; the output inverter voltage of the converter bridge arm side is not needed, so that the software is simple and easy to realize; and each relay only needs to be opened and closed once in the detection process, so that the number of actions is small, and the service life of the relay is prolonged.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of relay sticking detection method, and particularly relates to a relay sticking detection method of grid-connected converter. BACKGROUND

[0002] The AC side of the grid-connected converter is generally connected with the grid side through AC relays. After long-term use, the metal contacts in the relays are prone to sticking and cannot be disconnected in time, which may further cause secondary hazards. In addition, according to the domestic and foreign standards of the grid-connected converter, when the grid-connected converter fails, it must be reliably disconnected with the grid side. Therefore, the relays between the AC side of the grid-connected converter and the grid need to be redundantly designed. The current mainstream scheme is to use two groups of a total of six relays, that is, two relays per phase in series.

[0003] The traditional detection method is to first output inverter voltage on the bridge arm side of the grid-connected converter, then attract the first group of relays, and then detect the voltage difference between the two ends of the second group of relays. If the voltage difference is less than a certain threshold, it is considered that the second group of relays has sticking. Similarly, after disconnecting the first group of relays, the second group of relays is attracted, and the same method is used to detect whether the first group of relays has sticking.

[0004] The traditional detection method needs the bridge arm side of the grid-connected converter to first output inverter voltage, and the program control is complex. If the control is not good, it is easy to output large current and damage IGBT. In addition, if the sampling circuit for detecting the voltage between the two ends of the relay adopts an isolation scheme, the hardware is complex and the cost is high. If the resistance division method is used, an additional relay is also needed to disconnect the sampling resistor from the main circuit after the sticking detection is completed.

[0005] Another detection method is to sample the phase voltage on the bridge arm side. Although it does not need the grid-connected converter to output inverter voltage, it is only applicable to three-phase four-wire systems. Three-phase three-wire systems do not have a neutral line, and the neutral point constructed by the phase voltage sampling circuit is floating, so the phase voltage cannot be detected in the case of phase loss.

[0006] In summary, there is an urgent need for a simple, convenient and low-cost relay sticking detection method. SUMMARY

[0007] To solve the above problems, especially for the deficiencies of the prior art, the present application provides a relay sticking detection method of grid-connected converter.

[0008] To achieve the above purpose, the present application adopts the following technical means:

[0009] A relay sticking detection method of grid-connected converter, the specific method is as follows:

[0010] Step 1: Build a power unit level topology

[0011] The power unit is connected with A, B and C three-phase wires of the power grid, and L1 filter inductor, L2 filter inductor and L3 filter inductor are connected with the three-phase wires respectively; K1 front-stage relay and K2 rear-stage relay are connected with the A-phase wire connected with the L1 filter inductor; K3 front-stage relay and K4 rear-stage relay are connected with the B-phase wire connected with the L2 filter inductor; and K5 front-stage relay and K6 rear-stage relay are connected with the C-phase wire connected with the L3 filter inductor;

[0012] Step two, building a voltage sampling circuit

[0013] R1 resistor is connected with the A-phase wire between the L1 filter inductor and the K1 front-stage relay, and the R1 resistor is connected with R2 resistor in series; C1 filter capacitor is connected with the A-phase wire between the K1 front-stage relay and the K2 rear-stage relay; and C2 filter capacitor is connected with the A-phase wire between the K2 rear-stage relay and the power grid;

[0014] R3 resistor is connected with the B-phase wire between the L2 filter inductor and the K3 front-stage relay, and the R3 resistor is connected with R4 resistor in series; C3 filter capacitor is connected with the B-phase wire between the K3 front-stage relay and the K4 rear-stage relay; and C4 filter capacitor is connected with the B-phase wire between the K4 rear-stage relay and the power grid;

[0015] R5 resistor is connected with the C-phase wire between the L3 filter inductor and the K5 front-stage relay, and the R5 resistor is connected with R6 resistor in series; C5 filter capacitor is connected with the C-phase wire between the K5 front-stage relay and the K6 rear-stage relay; and C6 filter capacitor is connected with the C-phase wire between the K6 rear-stage relay and the power grid;

[0016] The other ends of the R2 resistor, the R4 resistor, the R6 resistor, the C1 filter capacitor, the C2 filter capacitor, the C3 filter capacitor, the C4 filter capacitor, the C5 filter capacitor and the C6 filter capacitor are connected together;

[0017] Step three, relay sticking detection

[0018] Ua is set as the A-phase bridge arm side voltage, Ub is set as the B-phase bridge arm side voltage, and Uc is set as the C-phase bridge arm side voltage;

[0019] A-phase relay sticking detection:

[0020] Close K1 front stage relay, K2 back stage relay, K3 front stage relay, K4 back stage relay, K5 front stage relay, K6 back stage relay, when Ua reaches peak U0, disconnect K3 front stage relay, K4 back stage relay, K5 front stage relay, K6 back stage relay, delay T1 seconds, record A phase bridge arm side voltage value U1 and calculate the RC circuit discharge time constant τ1 at this time, K2 back stage relay is disconnected at T1 time, delay T2 seconds, record A phase bridge arm side voltage value U2 and calculate the RC circuit discharge time constant τ2 at this time, τ1 and τ2 are same, then K2 back stage relay is stuck, τ1 and τ2 are not same, then K2 back stage relay is not stuck;

[0021] And disconnect K1 front stage relay, delay T3 seconds, record A phase bridge arm side voltage value U3, U3 at T3 time > 0V, then K1 front stage relay is stuck, U3 at T3 time = 0V, then K1 front stage relay is not stuck;

[0022] B phase relay sticking detection:

[0023] Close K1 front stage relay, K2 back stage relay, K3 front stage relay, K4 back stage relay, K5 front stage relay, K6 back stage relay, when Ub reaches peak U0, disconnect K1 front stage relay, K2 back stage relay, K5 front stage relay, K6 back stage relay, delay T4 seconds, record B phase bridge arm side voltage value U4 and calculate the RC circuit discharge time constant τ3 at this time, K4 back stage relay is disconnected at T4 time, delay T5 seconds, record B phase bridge arm side voltage value U5 and calculate the RC circuit discharge time constant τ4 at this time, τ3 and τ4 are same, then K4 back stage relay is stuck, τ3 and τ4 are not same, then K4 back stage relay is not stuck;

[0024] And disconnect K3 front stage relay, delay T6 seconds, record B phase bridge arm side voltage value U6, U6 at T6 time > 0V, then K3 front stage relay is stuck, U6 at T6 time = 0V, then K3 front stage relay is not stuck;

[0025] C phase relay sticking detection:

[0026] Close K1 front stage relay, K2 back stage relay, K3 front stage relay, K4 back stage relay, K5 front stage relay, K6 back stage relay, when Ub reaches peak U0, disconnect K1 front stage relay, K2 back stage relay, K3 front stage relay, K4 back stage relay, delay T7 seconds, record C phase bridge arm side voltage value U7 and calculate the RC circuit discharge time constant τ5 at this time, K6 back stage relay is disconnected at T7 time, delay T8 seconds, record C phase bridge arm side voltage value U8 and calculate the RC circuit discharge time constant τ6 at this time, τ5 and τ6 are same, then K6 back stage relay is stuck, τ5 and τ6 are not same, then K6 back stage relay is not stuck;

[0027] And disconnect K5 front stage relay, delay T9 seconds, record C phase bridge arm side voltage value U9, U9 at T9 moment > 0V, then K5 front stage relay sticking, U9 at T9 moment = 0V, then K5 front stage relay does not stick.

[0028] Further scheme of the present application is, the step three uses resistance voltage division method to measure voltage;

[0029] The setting method of the voltage Ua of the A-phase bridge arm side is as follows: the voltage U2 across R2 is collected by the DSP, and the bridge arm side voltage Ua is calculated

[0030] The setting method of Ub and Uc is the same as that of Ua.

[0031] The present application has the following beneficial effects:

[0032] The present application does not increase additional voltage sampling circuit, and uses resistance voltage division method for measurement, which is simple in hardware and low in cost; the output inverter voltage of the converter bridge arm side is not needed, which is simple in software and easy to realize; during the detection process, each relay only needs to be opened and closed once, so that the number of actions is small, and the service life of the relay is prolonged. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The present application is a relay sticking detection topology;

[0034] Figure 2 The present application is a detection flow chart of A-phase relay sticking;

[0035] Figure 3 The present application is a possible waveform diagram of Ua in the specific experiment. DETAILED DESCRIPTION

[0036] The technical solutions of the present application will be described clearly and completely in combination with the drawings. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0037] EMBODIMENT

[0038] A relay sticking detection method of a grid-connected converter, the specific method is as follows:

[0039] Step one, build power unit level topology

[0040] The power unit is connected to the grid via three-phase wires A, B, and C, which are connected to the grid. L1 filter inductor, L2 filter inductor, and L3 filter inductor are connected to the grid via three-phase wires. K1 pre-stage relay and K2 post-stage relay are connected to the A-phase wire connected to L1 filter inductor. K3 pre-stage relay and K4 post-stage relay are connected to the B-phase wire connected to L2 filter inductor. K5 pre-stage relay and K6 post-stage relay are connected to the C-phase wire connected to L3 filter inductor.

[0041] Step 2: Build the voltage sampling circuit

[0042] A resistor R1 is connected to the A-phase wire between the L1 filter inductor and the K1 pre-stage relay. The R1 resistor is connected in series with the R2 resistor. A filter capacitor C1 is connected to the A-phase wire between the K1 pre-stage relay and the K2 post-stage relay. A filter capacitor C2 is connected to the A-phase wire between the K2 post-stage relay and the power grid.

[0043] A resistor R3 is connected on the B-phase wire between the L2 filter inductor and the K3 pre-stage relay. The R3 resistor is connected in series with the R4 resistor. A C3 filter capacitor is connected on the B-phase wire between the K3 pre-stage relay and the K4 post-stage relay. A C4 filter capacitor is connected on the B-phase wire between the K4 post-stage relay and the power grid.

[0044] A resistor R5 is connected on the C-phase wire between the L3 filter inductor and the K5 pre-stage relay. The R5 resistor is connected in series with the R6 resistor. A C5 filter capacitor is connected on the C-phase wire between the K5 pre-stage relay and the K6 post-stage relay. A C6 filter capacitor is connected on the C-phase wire between the K6 post-stage relay and the power grid.

[0045] The other ends of resistors R2, R4, R6, and filter capacitors C1, C2, C3, C4, C5, and C6 are connected together.

[0046] Step 3: Relay adhesion detection

[0047] Let Ua be the voltage on the A-phase bridge arm side, Ub be the voltage on the B-phase bridge arm side, and Uc be the voltage on the C-phase bridge arm side.

[0048] Phase A relay adhesion detection:

[0049] Close K1 front stage relay, K2 back stage relay, K3 front stage relay, K4 back stage relay, K5 front stage relay, K6 back stage relay, when Ua reaches peak U0, disconnect K3 front stage relay, K4 back stage relay, K5 front stage relay, K6 back stage relay, delay T1 seconds, record A phase bridge arm side voltage value U1 and calculate the RC circuit discharge time constant τ1 at this time, K2 back stage relay is disconnected at T1 time, delay T2 seconds, record A phase bridge arm side voltage value U2 and calculate the RC circuit discharge time constant τ2 at this time, τ1 and τ2 are same, then K2 back stage relay is stuck, τ1 and τ2 are not same, then K2 back stage relay is not stuck;

[0050] And disconnect K1 front stage relay, delay T3 seconds, record A phase bridge arm side voltage value U3, U3 at T3 time >0V, then K1 front stage relay is stuck, U3 at T3 time =0V, then K1 front stage relay is not stuck;

[0051] B phase relay sticking detection:

[0052] Close K1 front stage relay, K2 back stage relay, K3 front stage relay, K4 back stage relay, K5 front stage relay, K6 back stage relay, when Ub reaches peak U0, disconnect K1 front stage relay, K2 back stage relay, K5 front stage relay, K6 back stage relay, delay T4 seconds, record B phase bridge arm side voltage value U4 and calculate the RC circuit discharge time constant τ3 at this time, K4 back stage relay is disconnected at T4 time, delay T5 seconds, record B phase bridge arm side voltage value U5 and calculate the RC circuit discharge time constant τ4 at this time, τ3 and τ4 are same, then K4 back stage relay is stuck, τ3 and τ4 are not same, then K4 back stage relay is not stuck;

[0053] And disconnect K3 front stage relay, delay T6 seconds, record B phase bridge arm side voltage value U6, U6 at T6 time >0V, then K3 front stage relay is stuck, U6 at T6 time =0V, then K3 front stage relay is not stuck;

[0054] C phase relay sticking detection:

[0055] Close K1 front stage relay, K2 back stage relay, K3 front stage relay, K4 back stage relay, K5 front stage relay, K6 back stage relay, when Ub reaches peak U0, disconnect K1 front stage relay, K2 back stage relay, K3 front stage relay, K4 back stage relay, delay T7 seconds, record C phase bridge arm side voltage value U7 and calculate the RC circuit discharge time constant τ5 at this time, K6 back stage relay is disconnected at T7 time, delay T8 seconds, record C phase bridge arm side voltage value U8 and calculate the RC circuit discharge time constant τ6 at this time, τ5 and τ6 are same, then K6 back stage relay is stuck, τ5 and τ6 are not same, then K6 back stage relay is not stuck;

[0056] And disconnect K5 front stage relay, delay T9 seconds, record C phase bridge arm side voltage value U9, U9 at T9 moment >0V, then K5 front stage relay sticking, U9 at T9 moment =0V, then K5 front stage relay does not stick.

[0057] The voltage is measured by resistance voltage division method in step three, and the setting method of Ua of A phase bridge arm side voltage is as follows: the voltage U2 between R2 is collected by DSP, and the bridge arm side voltage Ub, Uc is calculated The setting method of Ub, Uc is same as the setting method of Ua.

[0058] Specific experiment

[0059] The grid phase voltage is 230V, R1=1MΩ, R2=2.5kΩ, C1=C2=15uF, T1=T2=T3=5s, and it can be seen from simulation that whether the relay sticks, Ua waveform has obvious change. After K3, K4, K5, K6 are disconnected, C1, C2 discharge through R1+R2, and Ua waveform is shown in the drawing. Figure 3 K2 is disconnected at T1 moment, if K2 sticks, Ua waveform is shown in the triangular curve, and the discharge time constant is unchanged. If K2 is disconnected, C1 discharges through R1+R2, the capacitance becomes small, the discharge time constant becomes small, the discharge accelerates, and Ua waveform is shown in the circular curve. K1 is disconnected at T2 moment, if K1 sticks, Ua waveform is shown in the star curve. If K1 is disconnected, Ua=0, and the waveform is shown in the pentagram curve.

[0060] The above description is made by way of example, but not limited to the embodiments. Based on the above description, other different forms of changes or variations can be made by those skilled in the art, and all the embodiments do not need to be exhausted, and the obvious changes or variations derived from the above description are still within the protection scope of the present application.

Claims

1. A method for detecting relay adhesion in a grid-connected converter, characterized in that, The specific method is as follows: Step 1: Build the power unit level topology The power unit is connected to the grid via three-phase wires A, B, and C, which are connected to the grid. L1 filter inductor, L2 filter inductor, and L3 filter inductor are connected to the grid via three-phase wires. K1 pre-stage relay and K2 post-stage relay are connected to the A-phase wire connected to L1 filter inductor. K3 pre-stage relay and K4 post-stage relay are connected to the B-phase wire connected to L2 filter inductor. K5 pre-stage relay and K6 post-stage relay are connected to the C-phase wire connected to L3 filter inductor. Step 2: Build the voltage sampling circuit A resistor R1 is connected to the A-phase wire between the L1 filter inductor and the K1 pre-stage relay. The R1 resistor is connected in series with the R2 resistor. A filter capacitor C1 is connected to the A-phase wire between the K1 pre-stage relay and the K2 post-stage relay. A filter capacitor C2 is connected to the A-phase wire between the K2 post-stage relay and the power grid. A resistor R3 is connected on the B-phase wire between the L2 filter inductor and the K3 pre-stage relay. The R3 resistor is connected in series with the R4 resistor. A C3 filter capacitor is connected on the B-phase wire between the K3 pre-stage relay and the K4 post-stage relay. A C4 filter capacitor is connected on the B-phase wire between the K4 post-stage relay and the power grid. A resistor R5 is connected on the C-phase wire between the L3 filter inductor and the K5 pre-stage relay. The R5 resistor is connected in series with the R6 resistor. A C5 filter capacitor is connected on the C-phase wire between the K5 pre-stage relay and the K6 post-stage relay. A C6 filter capacitor is connected on the C-phase wire between the K6 post-stage relay and the power grid. The other ends of resistors R2, R4, R6, and filter capacitors C1, C2, C3, C4, C5, and C6 are connected together. Step 3: Relay adhesion detection Let Ua be the voltage on the A-phase bridge arm side, Ub be the voltage on the B-phase bridge arm side, and Uc be the voltage on the C-phase bridge arm side. Phase A relay adhesion detection: Close the K1 pre-stage relay, K2 post-stage relay, K3 pre-stage relay, K4 post-stage relay, K5 pre-stage relay, and K6 post-stage relay. When Ua reaches its peak value U0, disconnect the K3 pre-stage relay, K4 post-stage relay, K5 pre-stage relay, and K6 post-stage relay. After a delay of T1 seconds, record the voltage value U1 on the A-phase bridge arm side and calculate the RC circuit discharge time constant τ1 at this time. At time T1, disconnect the K2 post-stage relay. After a delay of T2 seconds, record the voltage value U2 on the A-phase bridge arm side and calculate the RC circuit discharge time constant τ2 at this time. If τ1 and τ2 are the same, then the K2 post-stage relay is stuck. If τ1 and τ2 are different, then the K2 post-stage relay is not stuck. Disconnect the K1 pre-stage relay, delay for T3 seconds, and record the voltage value U3 on the A-phase bridge arm side. If U3 > 0V at time T3, then the K1 pre-stage relay is stuck. If U3 = 0V at time T3, then the K1 pre-stage relay is not stuck. B-phase relay adhesion detection: Close the K1 pre-stage relay, K2 post-stage relay, K3 pre-stage relay, K4 post-stage relay, K5 pre-stage relay, and K6 post-stage relay. When Ub reaches its peak value U0, disconnect the K1 pre-stage relay, K2 post-stage relay, K5 pre-stage relay, and K6 post-stage relay. After a delay of T4 seconds, record the voltage value U4 on the B-phase bridge arm side and calculate the RC circuit discharge time constant τ3 at this time. At time T4, disconnect the K4 post-stage relay. After a delay of T5 seconds, record the voltage value U5 on the B-phase bridge arm side and calculate the RC circuit discharge time constant τ4 at this time. If τ3 and τ4 are the same, then the K4 post-stage relay is stuck. If τ3 and τ4 are different, then the K4 post-stage relay is not stuck. Disconnect the K3 pre-stage relay, delay for T6 seconds, and record the voltage value U6 on the B-phase bridge arm side. If U6 > 0V at time T6, then the K3 pre-stage relay is stuck. If U6 = 0V at time T6, then the K3 pre-stage relay is not stuck. C-phase relay adhesion detection: Close the K1 pre-stage relay, K2 post-stage relay, K3 pre-stage relay, K4 post-stage relay, K5 pre-stage relay, and K6 post-stage relay. When Ub reaches its peak value U0, disconnect the K1 pre-stage relay, K2 post-stage relay, K3 pre-stage relay, and K4 post-stage relay. Delay for T7 seconds, record the voltage value U7 on the C-phase bridge arm side, and calculate the RC circuit discharge time constant τ5 at this time. At time T7, disconnect the K6 post-stage relay. Delay for T8 seconds, record the voltage value U8 on the C-phase bridge arm side, and calculate the RC circuit discharge time constant τ6 at this time. If τ5 and τ6 are the same, then the K6 post-stage relay is stuck. If τ5 and τ6 are different, then the K6 post-stage relay is not stuck. Disconnect the K5 pre-stage relay, delay for T9 seconds, and record the voltage value U9 on the C-phase bridge arm side. If U9 > 0V at time T9, then the K5 pre-stage relay is stuck. If U9 = 0V at time T9, then the K5 pre-stage relay is not stuck.

2. The relay adhesion detection method for a grid-connected converter according to claim 1, Its characteristics are: In step three, the voltage is measured using the resistance voltage divider method; The method for setting the voltage Ua on the A-phase bridge arm side is as follows: The voltage U2 across R2 is acquired by the DSP, and the bridge arm side voltage is calculated. The setting methods for Ub and Uc are the same as those for Ua.

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