Relay adhesion detection method for grid-connected converter

Abstract

The invention discloses a relay adhesion detection method for a grid-connected converter. The method specifically comprises the following steps: step 1, establishing a power unit level topology; 2, building a voltage sampling circuit; and step 3, relay adhesion detection. The beneficial effects are that no extra voltage sampling circuit is added, a resistance voltage dividing method is adopted for measurement, hardware is simple, and cost is low; the bridge arm side of the converter does not need to output inversion voltage, software is simple, and implementation is easy; in the detection process, each relay only needs to be opened and closed once, the action frequency is small, and the service life of the relay is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of relay adhesion detection methods, and in particular to a relay adhesion detection method for a grid-connected converter. Background Art

[0002] The AC side of the grid-connected converter is generally connected to the grid side through an AC relay. After long-term use, it is easy to cause the metal contacts inside the relay to stick and fail to disconnect in time, which may cause secondary hazards. In addition, according to domestic and international standards for grid-connected converters, when a grid-connected converter fails, it must be reliably disconnected from 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 solution is to use two groups of six relays in total, that is, two relays in series per phase.

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

[0004] Traditional detection methods require the bridge arm side of the grid-connected converter to output the inverter voltage first, which is complex to program. If the control is not good, it is easy to output a large current to damage the IGBT. In addition, if the sampling circuit for detecting the voltage at both ends of the relay adopts an isolation solution, the hardware is complex and the cost is high. If the resistor voltage divider method is used, it is also necessary to use an additional relay to disconnect the sampling resistor from the main circuit after the adhesion detection is completed.

[0005] Another detection method is to sample the phase voltage on the bridge arm side. Although it does not require the grid-connected converter to output the inverter voltage, it is only applicable to the three-phase four-wire system. The three-phase three-wire system has no neutral line, and the neutral point constructed by the phase voltage sampling circuit is suspended, so the phase voltage cannot be detected in the absence of a phase.

[0006] In summary, there is an urgent need for a simple, convenient and low-cost relay adhesion detection method. Summary of the invention

[0007] In order to solve the above problems, especially to address the deficiencies in the prior art, the present invention provides a relay adhesion detection method for a grid-connected converter.

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

[0009] A method for detecting relay adhesion of a grid-connected converter, the specific method is as follows:

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

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

[0012] Step 2: Build a voltage sampling circuit

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

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

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

[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 3: Relay adhesion detection

[0018] Set Ua as the voltage on the bridge arm side of phase A, Ub as the voltage on the bridge arm side of phase B, and Uc as the voltage on the bridge arm side of phase C;

[0019] A phase relay adhesion detection:

[0020] Close the front relay K1, the rear relay K2, the front relay K3, the rear relay K4, the front relay K5, and the rear relay K6. When Ua reaches the peak value U0, disconnect the front relay K3, the rear relay K4, the front relay K5, and the rear relay K6. Delay T1 seconds, record the voltage value U1 on the bridge arm side of phase A, and calculate the RC circuit discharge time constant τ1 at this time. Disconnect the rear relay K2 at time T1, delay T2 seconds, record the voltage value U2 on the bridge arm side of phase A, and calculate the RC circuit discharge time constant τ2 at this time. If τ1 is the same as τ2, the rear relay K2 is adhered. If τ1 is different from τ2, the rear relay K2 is not adhered.

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

[0022] B phase relay adhesion detection:

[0023] Close the front relay K1, the rear relay K2, the front relay K3, the rear relay K4, the front relay K5, and the rear relay K6. When Ub reaches the peak value U0, disconnect the front relay K1, the rear relay K2, the front relay K5, and the rear relay K6. Delay T4 seconds, record the voltage value U4 on the bridge arm side of phase B, and calculate the discharge time constant τ3 of the RC circuit at this time. Disconnect the rear relay K4 at time T4, delay T5 seconds, record the voltage value U5 on the bridge arm side of phase B, and calculate the discharge time constant τ4 of the RC circuit at this time. If τ3 is the same as τ4, the rear relay K4 is adhered. If τ3 is different from τ4, the rear relay K4 is not adhered.

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

[0025] C phase relay adhesion detection:

[0026] Close the front relay K1, the rear relay K2, the front relay K3, the rear relay K4, the front relay K5, and the rear relay K6. When Ub reaches the peak value U0, disconnect the front relay K1, the rear relay K2, the front relay K3, and the rear relay K4. Delay for T7 seconds, record the voltage value U7 on the bridge arm side of phase C, and calculate the discharge time constant τ5 of the RC circuit at this time. Disconnect the rear relay K6 at time T7, delay for T8 seconds, record the voltage value U8 on the bridge arm side of phase C, and calculate the discharge time constant τ6 of the RC circuit at this time. If τ5 is the same as τ6, the rear relay K6 is adhered. If τ5 is different from τ6, the rear relay K6 is not adhered.

[0027] And disconnect the K5 front-stage relay, delay T9 seconds, record the voltage value U9 on the C-phase bridge arm side, if U9>0V at T9, the K5 front-stage relay is stuck, if U9=0V at T9, the K5 front-stage relay is not stuck.

[0028] A further solution of the present invention is that in step three, the voltage is measured using a resistance voltage division method;

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

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

[0031] Beneficial effects of the present invention:

[0032] The present invention does not add an additional voltage sampling circuit and adopts a resistance voltage division method for measurement, so the hardware is simple and the cost is low; it does not require the inverter bridge arm side to output an inverter voltage, so the software is simple and easy to implement; during the detection process, each relay only needs to be opened and closed once, the number of actions is small, and the service life of the relay is extended. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a topological diagram of relay adhesion detection of the present invention;

[0034] Figure 2 The present invention is a flow chart for detecting adhesion of the A-phase relay;

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

[0036] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] Example

[0038] A method for detecting relay adhesion of a grid-connected converter, the specific method is as follows:

[0039] Step 1: Build the power unit level topology

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

[0041] Step 2: Build a voltage sampling circuit

[0042] The A-phase wire between the L1 filter inductor and the K1 front-stage relay is connected with an R1 resistor, the R1 resistor is connected in series with an R2 resistor, the A-phase wire between the K1 front-stage relay and the K2 rear-stage relay is connected with a C1 filter capacitor, and the A-phase wire between the K2 rear-stage relay and the power grid is connected with a C2 filter capacitor;

[0043] The B-phase wire between the L2 filter inductor and the K3 front-stage relay is connected with an R3 resistor, the R3 resistor is connected in series with an R4 resistor, the B-phase wire between the K3 front-stage relay and the K4 rear-stage relay is connected with a C3 filter capacitor, and the B-phase wire between the K4 rear-stage relay and the power grid is connected with a C4 filter capacitor;

[0044] The C-phase wire between the L3 filter inductor and the K5 front-stage relay is connected with an R5 resistor, the R5 resistor is connected in series with an R6 resistor, the C-phase wire between the K5 front-stage relay and the K6 rear-stage relay is connected with a C5 filter capacitor, and the C-phase wire between the K6 rear-stage relay and the power grid is connected with a C6 filter capacitor;

[0045] 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;

[0046] Step 3: Relay adhesion detection

[0047] Set Ua as the voltage on the bridge arm side of phase A, Ub as the voltage on the bridge arm side of phase B, and Uc as the voltage on the bridge arm side of phase C;

[0048] A phase relay adhesion detection:

[0049] Close the front relay K1, the rear relay K2, the front relay K3, the rear relay K4, the front relay K5, and the rear relay K6. When Ua reaches the peak value U0, disconnect the front relay K3, the rear relay K4, the front relay K5, and the rear relay K6. Delay T1 seconds, record the voltage value U1 on the bridge arm side of phase A, and calculate the RC circuit discharge time constant τ1 at this time. Disconnect the rear relay K2 at time T1, delay T2 seconds, record the voltage value U2 on the bridge arm side of phase A, and calculate the RC circuit discharge time constant τ2 at this time. If τ1 is the same as τ2, the rear relay K2 is adhered. If τ1 is different from τ2, the rear relay K2 is not adhered.

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

[0051] B phase relay adhesion detection:

[0052] Close the front relay K1, the rear relay K2, the front relay K3, the rear relay K4, the front relay K5, and the rear relay K6. When Ub reaches the peak value U0, disconnect the front relay K1, the rear relay K2, the front relay K5, and the rear relay K6. Delay T4 seconds, record the voltage value U4 on the bridge arm side of phase B, and calculate the discharge time constant τ3 of the RC circuit at this time. Disconnect the rear relay K4 at time T4, delay T5 seconds, record the voltage value U5 on the bridge arm side of phase B, and calculate the discharge time constant τ4 of the RC circuit at this time. If τ3 is the same as τ4, the rear relay K4 is adhered. If τ3 is different from τ4, the rear relay K4 is not adhered.

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

[0054] C phase relay adhesion detection:

[0055] Close the front relay K1, the rear relay K2, the front relay K3, the rear relay K4, the front relay K5, and the rear relay K6. When Ub reaches the peak value U0, disconnect the front relay K1, the rear relay K2, the front relay K3, and the rear relay K4. Delay for T7 seconds, record the voltage value U7 on the bridge arm side of phase C, and calculate the discharge time constant τ5 of the RC circuit at this time. Disconnect the rear relay K6 at time T7, delay for T8 seconds, record the voltage value U8 on the bridge arm side of phase C, and calculate the discharge time constant τ6 of the RC circuit at this time. If τ5 is the same as τ6, the rear relay K6 is adhered. If τ5 is different from τ6, the rear relay K6 is not adhered.

[0056] And disconnect the K5 front-stage relay, delay T9 seconds, record the voltage value U9 on the C-phase bridge arm side, if U9>0V at T9, the K5 front-stage relay is stuck, if U9=0V at T9, the K5 front-stage relay is not stuck.

[0057] In step 3, the voltage is measured by the resistor voltage divider method. The setting method of the voltage Ua of the bridge arm side of phase A is as follows: the voltage U2 across R2 is collected by DSP, and the voltage Ua of the bridge arm side is calculated. The setting method of Ub and Uc is the same as that of Ua.

[0058] Specific experiments

[0059] The grid phase voltage is 230V, R1=1MΩ, R2=2.5kΩ, C1=C2=15uF, T1=T2=T3=5s. Through simulation, it can be seen that the Ua waveform changes significantly when the relay is stuck. After K3, K4, K5, and K6 are disconnected, C1 and C2 discharge through R1+R2, and the Ua waveform is shown in Figure 3 As shown. Disconnect K2 at T1, if K2 sticks, the Ua waveform is shown as the triangle curve, and the discharge time constant remains unchanged. If K2 is disconnected, C1 discharges through R1+R2, the capacitance becomes smaller, the discharge time constant becomes smaller, the discharge is accelerated, and the Ua waveform is shown as the circular curve. Disconnect K1 at T2, if K1 sticks, the Ua waveform is shown as the star curve. If K1 is disconnected, Ua=0, and the waveform is shown as the five-pointed star curve.

[0060] The examples given in the present invention are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here, and the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

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

2. The method for detecting relay adhesion of a grid-connected converter according to claim 1, It is characterized by: In the step 3, the voltage is measured by using a resistance voltage division method; The setting method of the voltage Ua of the bridge arm side of phase A is as follows: the voltage U2 across R2 is collected by DSP, and the voltage Ua of the bridge arm side is calculated. The setting method of Ub and Uc is the same as that of Ua.

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