CN106443268A - Low-voltage ride-through capability detection device and method of low-voltage auxiliary engine frequency converter of thermal power plant - Google Patents

Abstract

The invention discloses low-voltage ride-through capability detection equipment for low-voltage auxiliary frequency converters in thermal power plants, including a three-phase input power supply, a device under test, a voltage sag generating device and a load, and the three-phase input power is electrically connected to the voltage sag generating device , the voltage sag generating device is electrically connected to the device under test, and the device under test is electrically connected to the load; the device under test is a low-voltage auxiliary machine inverter or a low-voltage auxiliary machine inverter system; the voltage sag The generating device includes two three-phase voltage-type PWM converters formed by "back-to-back" connection, the voltage sag generating device is used to generate voltage sag, and the voltage sag includes balanced voltage sag and unbalanced voltage sag, the load is a simulated load or an actual load; the invention can effectively and accurately measure the low-voltage ride-through capability of a low-voltage auxiliary machine inverter in a thermal power plant.

Description

Low-voltage ride-through capability detection equipment and method for low-voltage auxiliary frequency converters in thermal power plants

technical field

The invention relates to the technical field of low-voltage auxiliary machines in thermal power plants, in particular to a low-voltage ride-through capability detection device and method for frequency converters of low-voltage auxiliary machines in thermal power plants.

Background technique

Because of its irreplaceable advantages in control and energy saving, frequency converters have been widely used in various industries. However, due to the instability of the grid voltage, a new problem has arisen in the use of the inverter: the high and low voltage protection trip of the inverter (that is, low voltage ride through). Most frequency converters have poor high and low voltage ride-through capabilities, and some don't even have this capability. In recent years, there have been many incidents of system transient failures in thermal power plants across the country that caused thermal power units to shut down, causing system shocks or disconnection, large-scale power outages and load reduction, etc., causing major social and economic impacts.

Therefore, it is particularly important to transform low-voltage auxiliary frequency converters that do not have low-voltage ride-through capability, and it has also become an important method to improve the operating reliability of low-voltage auxiliary frequency converters in thermal power plants. Many thermal power plants have begun to transform the low-voltage auxiliary frequency converters of thermal power units that do not have low-voltage ride-through capability, but there are no relevant test methods and test equipment to verify whether the low-voltage ride-through capability of the transformed system meets the relevant requirements or is low. The level of voltage ride-through capability.

Contents of the invention

The technical problem to be solved by the present invention is to provide a low-voltage ride-through capability detection device and method for low-voltage auxiliary frequency converters in thermal power plants and a method for detecting low-voltage ride-through capabilities of low-voltage auxiliary frequency converters in thermal power plants. It can effectively and accurately measure the low-voltage ride-through capability of low-voltage auxiliary frequency converters in thermal power plants, and provide data support for thermal power plants to further improve the low-voltage ride-through capability of frequency converters.

For realizing above-mentioned technical purpose, the technical scheme that the present invention takes is:

Low-voltage ride-through capability detection equipment for low-voltage auxiliary frequency converters in thermal power plants, including a three-phase input power supply, a device under test, a voltage sag generator and a load, the three-phase input power is electrically connected to the voltage sag generator, and the voltage The sag generating device is electrically connected to the device under test, and the device under test is electrically connected to the load;

The device under test is a low-voltage auxiliary machine inverter or a low-voltage modified auxiliary machine inverter system;

The voltage sag generating device includes two three-phase voltage-type PWM converters formed by a "back-to-back" connection, the voltage sag generating device is used to generate a voltage sag, and the voltage sag includes a balanced voltage sag drops and unbalanced voltage dips,

The load is a simulated load or an actual load.

As a further improved technical solution of the present invention, the three-phase input power supply is electrically connected to the voltage sag generating device through the switch Q1, and the voltage sag generating device is electrically connected to the device under test through the switch Q2, and the device under test is connected through the The switch Q3 is electrically connected to the load.

As a further improved technical solution of the present invention, the simulated load is an energy feedback motor load composed of a motor and a generator, and the device under test is electrically connected to the motor in the energy feedback motor load through a switch Q3, and the motor Electrically connected to a generator that is electrically connected to a three-phase input power source.

As a further improved technical solution of the present invention, the simulated load is an energy-consuming motor load composed of a motor and a damping rotating wheel, and the device under test is electrically connected to the motor in the energy-consuming motor load through a switch Q3. The electric motor is electrically connected with the damping rotating wheel.

As a further improved technical solution of the present invention, the analog load is a power electronic analog load composed of two three-phase voltage-type PWM converters connected "back to back", and the device under test communicates with the power electronic analog load through switch Q3. The load is electrically connected, and the power electronic analog load is electrically connected to the three-phase input power supply.

As a further improved technical solution of the present invention, the actual load is a coal feeder.

As a further improved technical solution of the present invention, the low-voltage modified auxiliary machine inverter system is a low-voltage auxiliary machine inverter and a low-voltage ride-through device electrically connected to each other.

As a further improved technical solution of the present invention, the balanced voltage sag includes a voltage sag caused by a three-phase symmetrical short circuit, and the unbalanced voltage sag includes a voltage sag caused by a two-phase-to-ground short circuit and a voltage sag caused by a two-phase phase-to-phase short circuit. Voltage dips and single-phase-to-earth short-circuits.

For realizing above-mentioned technical purpose, another technical scheme that the present invention takes is:

A method for detecting low-voltage ride-through capability of a low-voltage auxiliary frequency converter in a thermal power plant, comprising the following steps:

(1) Confirm that switch Q1, switch Q2 and switch Q3 are all off;

(2) Close the switch Q1, check the working status of the voltage sag generating device, and set the output voltage of the voltage sag generating device to 380V;

(3) Close the switch Q2 and switch Q3, start the device under test and the load;

(4) The voltage sag generating device conducts low-voltage tests sequentially according to the characteristic quantities of voltage sags. The time interval between each two tests is not limited. Use an oscilloscope to collect the waveform of the input AC voltage and the output AC voltage of the device under test when the low voltage is low. The waveform of the voltage, the waveform of the DC bus voltage of the device under test and the waveform of the input AC voltage of the control circuit of the device under test;

(5) Send a stop command to the device under test, and observe whether the device under test stops output normally;

(6) If the device under test is a low-voltage auxiliary inverter system, perform step (7); if the device under test is a low-voltage auxiliary inverter system, make the low-voltage ride-through device send a fault signal, and observe whether the low-voltage auxiliary inverter is Normal stop output;

(7) If all the waveforms collected by the oscilloscope in step (4) do not fluctuate abnormally, the device under test works normally, and the devices under test in steps (5) and (6) output normally, then the device under test complies with Otherwise, it will be concluded that the tested equipment does not meet the requirements of the technical specification for low voltage ride through capability.

As a further improved technical solution of the present invention, it also includes the following steps: set the output fault types of the voltage sag generating device to three-phase symmetrical short circuit, two-phase ground short circuit, two-phase phase-to-phase short circuit, and single-phase ground short circuit in sequence, and detect Whether the device under test sends out an undervoltage fault signal, detect the low voltage ride-through capability of the device under test, draw the low voltage ride through capability curve of the device under test, and obtain the low voltage ride through capability of the device under test according to the low voltage ride through capability curve.

The invention can effectively and accurately determine whether the inverter of the low-voltage auxiliary machine in a thermal power plant meets the requirements of the low-voltage ride-through capability technical specification, and accurately obtain the level of the low-voltage ride-through capability of the tested equipment through the low-voltage ride-through capability curve, which is a further improvement for the thermal power plant. The low-voltage ride-through ability of the inverter provides data support; the tested equipment is a low-voltage auxiliary inverter or a low-voltage modified auxiliary inverter system, so the low-voltage auxiliary inverter or low-voltage modified auxiliary inverter system can be measured. Voltage ride-through capability; the load is a simulated load or an actual load, and the simulated load can realize load torque changes and simulate the electrical characteristics of a thermal power plant; the voltage sag generating device includes two three-phase voltage-type PWMs formed by a "back-to-back" connection The converter and the voltage sag generating device are power electronic, which can generate balanced voltage sag and unbalanced voltage sag, which provides a basis for testing the low voltage ride-through capability of the device under test.

Description of drawings

Figure 1 is a circuit topology diagram of a voltage sag generating device, which can also be used as a circuit topology diagram of a power electronic analog load.

Figure 2 is the wiring diagram of the preparatory stage for the low voltage ride-through capability test, and also the circuit wiring diagram for the low voltage ride-through capability test of the unmodified low-voltage auxiliary machine inverter.

Fig. 3 is a circuit wiring diagram of low voltage ride through capability detection when the low voltage ride through devices are connected in parallel and the low voltage ride through devices have no external energy storage.

Fig. 4 is a circuit wiring diagram of low voltage ride through capability detection when the low voltage ride through devices are connected in series and the low voltage ride through devices have external energy storage.

Fig. 5 is a circuit wiring diagram of low-voltage ride-through capability detection when a series UPS/DVR is used as a retrofit device.

Figure 6 is a circuit wiring diagram using an energy-consuming motor load.

Fig. 7 is a circuit wiring diagram using an energy regenerative motor load.

Fig. 8 is a circuit wiring diagram using energy feedback type power electronic analog load.

Figure 9 is the low-voltage ride-through capability curve drawn in the second test method.

detailed description

Below according to Fig. 1 to Fig. 9, the specific embodiment of the present invention is further described:

Low-voltage ride-through capability detection equipment for low-voltage auxiliary frequency converters in thermal power plants, including a three-phase input power supply, a device under test, a voltage sag generator and a load, the three-phase input power is electrically connected to the voltage sag generator, and the voltage The sag generating device is electrically connected to the device under test, and the device under test is electrically connected to the load;

The device under test can be a low-voltage auxiliary frequency converter that has low voltage ride-through capability without modification, or a low-voltage auxiliary frequency converter system that has been transformed through low voltage ride-through. There are mainly the following types of low-voltage auxiliary inverter systems: (1) As shown in Figure 3, a low-voltage ride-through device is connected in parallel with the low-voltage auxiliary inverter. The boost circuit in the low-voltage ride-through device converts the three-phase input power The residual voltage is boosted to 380V and input to the low-voltage auxiliary machine inverter. (2) As shown in Figure 4, connect the low-voltage ride-through device in series with the inverter of the low-voltage auxiliary machine, and connect the external energy storage. When the voltage sags, the boost circuit in the low voltage ride through device boosts the output voltage of the external energy storage to 380V to input the low voltage auxiliary machine inverter. (3) As shown in Figure 5, a UPS/DVR is connected in series between the low-voltage auxiliary machine inverter and the voltage sag generating device to ensure that the voltage input to the low-voltage auxiliary machine inverter is kept at the rated value at all times.

The voltage sag generating device includes two three-phase voltage-type PWM converters formed by a "back-to-back" connection, the voltage sag generating device is used to generate a voltage sag, and the voltage sag includes a balanced voltage sag Drop and unbalanced voltage sag, the voltage sag generating device is shown in Figure 1, the input filter inductor 1 is used to store energy, filter out high-frequency harmonics, reduce high-frequency current ripple, etc.; three-phase controllable rectification 2 Converting the input three-phase AC voltage into DC voltage, on the one hand, can increase the voltage at the DC bus to prepare for the detection of high voltage ride-through capability; Harmonic hazard; DC bus filter link 3 is used to store energy, ensure power balance between rectifier and inverter, and stabilize DC bus voltage; three-phase voltage type PWM inverter 4 input fault voltage type, residual voltage value, fault The voltage duration can generate corresponding SPWM waveforms in the control system, thereby controlling the switch tube to generate voltage sags of specified types and time, that is, the generation includes balanced voltage sags, unbalanced voltage sags, voltage interruptions, etc. The internal voltage fault provides test power for the low voltage ride-through test; 5 is an AC filter, which filters out the high-frequency harmonics generated by the three-phase voltage type PWM inverter 4 .

The load is a simulated load or an actual load. The simulated load can realize the change of load torque and simulate the electrical characteristics of a thermal power plant. The present invention proposes three possible solutions: one is an energy-consumption formula composed of a motor and its drag damping wheel. Motor load, simple equipment, easy to operate; second, the motor and its driven generator constitute an energy feedback motor load, the power generated by the generator is incorporated into the three-phase input power supply, and the power of the low-voltage auxiliary machine inverter can be adjusted by adjusting the power generated ; The third is the power electronic analog load composed of two three-phase voltage-type PWM converters connected "back to back". The topology is also shown in Figure 1. The AC output of the low-voltage auxiliary machine inverter is converted to The voltage is rectified and converted to a DC voltage higher than 540V, and the input voltage and current are controlled to form a specified phase relationship, which is used to simulate loads under various power factors; the three-phase voltage-type PWM inverter 4 is used to convert the DC power into the power grid The three-phase alternating current with the same frequency and phase, feeds the active power absorbed by the simulated load back to the three-phase input power supply, and the functions of other parts are the same as the voltage sag device. The actual load consists of auxiliary machines, conveyor belts and corresponding working fluids, and the actual load in this embodiment is the coal feeder.

Further, as shown in FIG. 1, the three-phase input power supply is electrically connected to the voltage sag generating device through the switch Q1, and the voltage sag generating device is electrically connected to the device under test through the switch Q2, and the device under test is connected through the The switch Q3 is electrically connected to the load.

Further, the simulated load is an energy regenerative motor load composed of a motor and its driven generator, as shown in Figure 7, the device under test is electrically connected to the motor in the energy regenerative motor load through a switch Q3 , the motor is electrically connected to a generator, and the generator is electrically connected to a three-phase input power supply.

Further, the simulated load is an energy-consuming motor load composed of a motor and the damping rotating wheel driven by it. As shown in FIG. connected, and the electric motor is electrically connected with the damping rotating wheel.

Further, the simulated load is a power electronic simulated load composed of two three-phase voltage-type PWM converters connected "back to back", as shown in Figure 8, the device under test communicates with the power electronic simulated The load is electrically connected, and the power electronic analog load is electrically connected to the three-phase input power supply.

Further, as shown in Fig. 2 to Fig. 5, the actual load is a coal feeder.

Further, the low-voltage modified auxiliary frequency converter system is a modified low-voltage auxiliary frequency converter, that is, a low-voltage auxiliary frequency converter and a low-voltage ride-through device electrically connected to each other.

Further, the balanced voltage sag includes a voltage sag of a three-phase symmetrical short circuit, and the unbalanced voltage sag includes a voltage sag of a two-phase-to-ground short circuit, a voltage sag of a two-phase phase-to-phase short circuit, and a single-phase to ground short circuit. voltage sag.

A method for detecting low-voltage ride-through capability of a low-voltage auxiliary frequency converter in a thermal power plant, comprising the following steps:

1. Preparation stage:

(a) Connect all test equipment according to Figure 2, and confirm that switch Q1, switch Q2 and switch Q3 are all in the off state;

(b) Close the switch Q1, check the working status of the voltage sag generating device, and set the output voltage of the voltage sag generating device to 380V;

(c) Close the switch Q2 and switch Q3, start the device under test and the load, and check whether the device under test and the load are operating normally;

(d) If it works normally, turn off switch Q1, switch Q2 and switch Q3. If abnormality or failure occurs, check the cause of the failure and eliminate the failure.

2. Test phase:

Test method 1, to determine whether the low-voltage ride-through capability of a low-voltage auxiliary inverter or a modified low-voltage auxiliary inverter meets the requirements of the technical specification for low-voltage ride-through capability:

(1) According to whether the equipment under test has been modified or not and the three methods of modification, choose one of the wiring methods in Figure 2 to Figure 8 to connect all the test equipment, and confirm that the switch Q1, switch Q2, switch Q3 and switch Q4 are all is disconnected.

Figure 2 is suitable for low-voltage auxiliary frequency converters that have low-voltage ride-through capability without modification. The three-phase input power is electrically connected to the voltage sag generating device through the switch Q1, and the voltage sag generating device is connected to the low-voltage auxiliary device through the switch Q2. The low-voltage auxiliary machine inverter is electrically connected to the coal feeder through switch Q3, and the coal feeder control circuit power supply is electrically connected to the control system of the low-voltage auxiliary machine inverter, which is the control system of the low-voltage auxiliary machine inverter. Provide electrical energy.

Figure 3 is applicable to the retrofit method of connecting a low-voltage ride-through device in parallel with the low-voltage auxiliary inverter without external energy storage, and the three-phase input power supply is electrically connected to the voltage sag generating device through the switch Q1, and the voltage sag generating device is connected through the switch Q2 is electrically connected to the low-voltage auxiliary machine inverter and the low-voltage ride-through device, the low-voltage ride-through device is electrically connected to the low-voltage auxiliary machine inverter through the switch MCB, the low-voltage auxiliary machine inverter is electrically connected to the coal feeder through the switch Q3, and the uninterruptible power supply UPS It is electrically connected with the control circuit power supply of the coal feeder, and the control circuit power supply of the coal feeder is electrically connected with the control system of the low-voltage auxiliary machine inverter to provide electric energy for the control system of the low-voltage auxiliary machine inverter.

Figure 4 is applicable to the retrofit method of connecting the low-voltage ride-through device in series with the inverter of the low-voltage auxiliary machine, and externally connecting the external power supply. Q2 is electrically connected to the low-voltage auxiliary machine inverter, the external power supply is electrically connected to the low-voltage ride-through device through the switch MCB1, the low-voltage ride-through device is electrically connected to the low-voltage auxiliary machine inverter through the switch MCB2, and the low-voltage auxiliary machine inverter is connected to the low-voltage auxiliary machine inverter through the switch Q3. Coal electromechanical connection, uninterruptible power supply UPS is electrically connected to the control circuit power supply of the coal feeder, and the control circuit power supply of the coal feeder is electrically connected to the control system of the low-voltage auxiliary machine inverter to provide electric energy for the control system of the low-voltage auxiliary machine inverter.

Figure 5 is suitable for the transformation scheme of connecting UPS/DVR in series between the low-voltage auxiliary machine inverter and the voltage sag generating device, the three-phase input power supply is electrically connected to the voltage sag generating device through the switch Q1, and the voltage sag generating device passes through The switch Q2 is electrically connected to the UPS/DVR, the UPS/DVR is electrically connected to the low-voltage auxiliary machine inverter through the switch Q3, the low-voltage auxiliary machine inverter is electrically connected to the coal feeder through the switch Q4, and the uninterruptible power supply UPS is connected to the coal feeder control circuit power supply. Connection, the control circuit power supply of the coal feeder is electrically connected with the control system of the low-voltage auxiliary machine inverter, and provides electric energy for the control system of the low-voltage auxiliary machine inverter.

Figures 2 to 5 use the actual coal feeder as the load, and can also use the simulated load for laboratory testing. Taking the transformation method as an example, the low-voltage ride-through device is connected in parallel to the low-voltage auxiliary machine inverter without external energy storage, as shown in Fig. 6 is a wiring diagram when using an energy-consuming motor load, the low-voltage auxiliary frequency converter is electrically connected to the motor in the energy-consuming motor load through a switch Q3, and the motor is electrically connected to the damping rotating wheel. Fig. 7 is a wiring diagram when using an energy feedback motor load, the low-voltage auxiliary machine inverter is electrically connected to the motor in the energy feedback motor load through a switch Q3, the motor is electrically connected to a generator, and the generator is connected to three phase input power electrical connections. Fig. 8 is a wiring diagram when using an energy feedback type power electronic analog load, wherein the low-voltage auxiliary machine inverter is electrically connected to the power electronic analog load through a switch Q3, and the power electronic analog load is electrically connected to a three-phase input power supply through a switch Q4, The active power absorbed by the power electronics analog load is fed back to the three-phase input power supply.

(2) Close the switch Q1, and set the output voltage of the voltage sag generating device to 380V;

(3) Close all the switches, start the equipment under test and the load;

(4) Select "Technical Specifications for High and Low Voltage Ride-through of Auxiliary Machine Frequency Converters for Large Turbine Generator Sets" as the standard, and the voltage sag generating device will conduct low voltage tests sequentially according to the voltage sag characteristic quantities in Table 1. The time interval between the two tests is not limited. Use the oscilloscope to collect the waveform of the input AC voltage of the device under test, the waveform of the output AC voltage, the waveform of the DC bus voltage of the device under test, and the waveform of the control circuit of the device under test. Input AC voltage waveform and related data;

Table 1. The characteristic quantity of voltage sag required for the test

serial number Fault type residual pressure duration 1 Three-phase symmetrical short circuit 90%U _N 10s 2 Two-phase ground short circuit 90%U _N 10s 3 Short circuit between two phases 90%U _N 10s 4 Single-phase short circuit to ground 90%U _N 10s 5 Three-phase symmetrical short circuit 60%U _N 5s 6 Two-phase ground short circuit 60%U _N 5s 7 Short circuit between two phases 60%U _N 5s 8 Single-phase short circuit to ground 60%U _N 5s 9 Three-phase symmetrical short circuit 20% U _N 0.5s 10 Two-phase ground short circuit 20% U _N 0.5s 11 Short circuit between two phases 20% U _N 0.5s 12 Single-phase short circuit to ground 20% U _N 0.5s

The selection of residual voltage and duration refers to "Technical Specifications for High and Low Voltage Ride-through of Frequency Converters for Auxiliary Machines of Large Turbine Generator Sets".

(5) Send a stop command to the device under test, and observe whether the device under test stops output normally;

(6) If the device under test is a low-voltage auxiliary frequency converter, perform step (7); if the device under test is a low-voltage modified auxiliary frequency converter system, that is, a modified low-voltage auxiliary frequency converter, make the low-voltage ride-through device issue a fault signal, observe whether the low-voltage auxiliary machine inverter stops outputting normally;

(7) Give the test conclusion. If all the waveforms collected by the oscilloscope in step (4) have no abnormal fluctuations, the device under test is working normally, and the devices under test in steps (5) and (6) can output normally, It can be concluded that the tested equipment meets the requirements of the low voltage ride-through capability technical specification, that is, the low voltage ride-through capability of the tested equipment meets the requirements of the "Technical Specifications for High and Low Voltage Ride-through of Auxiliary Machine Frequency Converters of Large Turbine Generator Sets", otherwise if In other cases, it can be concluded that the equipment under test does not meet the requirements of the technical specification for low voltage ride-through capability.

Test method 2, draw the low-voltage ride-through capability curve of the low-voltage auxiliary inverter or the modified low-voltage auxiliary inverter within 20s:

(1) According to whether the equipment under test has been modified or not and the three methods of modification, choose one of the wiring methods in Figure 2 to Figure 8 to connect all the test equipment, and confirm that the switch Q1, switch Q2, switch Q3 and switch Q4 are all is disconnected.

(2) Close the switch Q1, and set the output voltage of the voltage sag generating device to 380V;

(3) Close all the switches, start the equipment under test and the load;

(4) Set the output fault types of the voltage sag generating device to three-phase symmetrical short circuit, two-phase ground short circuit, two-phase phase-to-phase short circuit and single-phase ground short circuit respectively, and check whether the equipment under test sends out an undervoltage fault signal, and detect Low-voltage ride-through capability of the device under test, draw the low-voltage ride-through capability curve of the device under test, and obtain the low-voltage ride-through capability of the device under test according to the low-voltage ride-through capability curve.

Step (4) in test method 2 is as follows:

(a): Set the output fault type of the voltage sag generating device as a three-phase symmetrical short circuit, and the residual voltage is X _k %U _N ( X _k =10 k , k =0,1,2,3,4,5,6 ,7,8), the duration is 20s. The timing starts from the moment when the fault voltage is generated, and ends when the inverter of the low-voltage auxiliary machine sends out the undervoltage fault signal. This period of time is recorded as t _k . Record in sequence until k =8 or t _k =20s.

(b): Set the output fault types of the voltage sag generating device to two-phase ground short circuit, two-phase phase-to-phase short circuit and single-phase ground short circuit in turn, the residual voltage is X _k %U _N , and the duration is t _k , respectively Perform three tests. If the inverter of the low-voltage auxiliary machine in the three tests does not send an undervoltage fault signal, it is considered that the low-voltage ride-through capability of the device under test is T _{k =} t _k under X _k %UN. If at a certain moment (< t _k ) the frequency converter sends out an undervoltage fault signal, then the low voltage ride-through capability of the device under test is T _{k =} under X _k %UN.

(c): Draw the low-voltage ride-through capability curve of the low-voltage auxiliary inverter or the modified low-voltage auxiliary inverter. The typical drawing results are shown in Figure 9. The area above the curve represents the low-voltage ride-through capability of the inverter The X-axis in Figure 9 represents the time, and the Y-axis represents the residual pressure.

The invention can effectively and accurately determine whether the inverter of the low-voltage auxiliary machine in a thermal power plant meets the requirements of the low-voltage ride-through capability technical specification, and accurately obtain the level of the low-voltage ride-through capability of the tested equipment through the low-voltage ride-through capability curve, which is a further improvement for the thermal power plant. The low-voltage ride-through ability of the inverter provides data support; the tested equipment is a low-voltage auxiliary inverter or a low-voltage modified auxiliary inverter system, so the low-voltage auxiliary inverter or low-voltage modified auxiliary inverter system can be measured. Voltage ride-through capability; the load is a simulated load or an actual load, and the simulated load can realize load torque changes and simulate the electrical characteristics of a thermal power plant; the voltage sag generating device includes two three-phase voltage-type PWMs formed by a "back-to-back" connection The converter and the voltage sag generating device are power electronic, which can generate balanced voltage sag and unbalanced voltage sag, which provides a basis for testing the low voltage ride-through capability of the device under test.

The scope of protection of the present invention includes but is not limited to the above embodiments. The scope of protection of the present invention is based on the claims. Any replacement, deformation, and improvement that are easily conceived by those skilled in the art for this technology fall within the scope of the present invention. protected range.

Claims (10)

1. Low-voltage ride-through capability detection equipment for low-voltage auxiliary frequency converters in thermal power plants, characterized in that it includes a three-phase input power supply, a device under test, a voltage sag generator and a load, and the three-phase input power and voltage sag generator Electrically connected, the voltage sag generating device is electrically connected to the device under test, and the device under test is electrically connected to the load; The device under test is a low-voltage auxiliary machine inverter or a low-voltage modified auxiliary machine inverter system; The voltage sag generating device includes two three-phase voltage-type PWM converters formed by a "back-to-back" connection, the voltage sag generating device is used to generate a voltage sag, and the voltage sag includes a balanced voltage sag and unbalanced voltage dips; The load is a simulated load or an actual load. 2. The low-voltage ride-through capability detection device for low-voltage auxiliary frequency converters in thermal power plants according to claim 1, characterized in that: the three-phase input power supply is electrically connected to the voltage sag generating device through a switch Q1, and the voltage sag The generating device is electrically connected to the device under test through the switch Q2, and the device under test is electrically connected to the load through the switch Q3. 3. The thermal power plant low-voltage auxiliary machine frequency converter low-voltage ride-through capability detection device according to claim 2, characterized in that: the simulated load is an energy feedback motor load composed of a motor and a generator, and the device under test The switch Q3 is electrically connected to the motor in the energy feedback motor load, the motor is electrically connected to the generator, and the generator is electrically connected to the three-phase input power supply. 4. The thermal power plant low-voltage auxiliary machine frequency converter low-voltage ride-through capability detection device according to claim 2, characterized in that: the simulated load is an energy-consuming motor load composed of a motor and a damping wheel, and the tested The device is electrically connected to the motor in the energy-consuming motor load through the switch Q3, and the motor is electrically connected to the damped rotating wheel. 5. The thermal power plant low-voltage auxiliary machine inverter low-voltage ride-through capability detection device according to claim 2, characterized in that: the simulated load is composed of two three-phase voltage-type PWM converters connected "back-to-back" The power electronic analog load, the device under test is electrically connected to the power electronic analog load through the switch Q3, and the power electronic analog load is electrically connected to the three-phase input power supply. 6. The detection device for low-voltage ride-through capability of low-voltage auxiliary frequency converters in thermal power plants according to claim 1, wherein the actual load is a coal feeder. 7. The detection device for low-voltage ride-through capability of low-voltage auxiliary inverters in thermal power plants according to claim 2, characterized in that: the low-voltage modified auxiliary inverter system is a low-voltage auxiliary inverter and a low-voltage ride-through device. 8. The detection device for low-voltage ride-through capability of low-voltage auxiliary frequency converters in thermal power plants according to claim 1, characterized in that: the balanced voltage sag includes a voltage sag of a three-phase symmetrical short circuit, and the unbalanced voltage sag Including the voltage sag of two-phase-to-ground short circuit, the voltage sag of two-phase phase-to-phase short-circuit and the voltage sag of single-phase-to-ground short circuit. 9. A method for detecting equipment for low-voltage ride-through capability of a low-voltage auxiliary machine frequency converter in a thermal power plant as claimed in claim 7, comprising the following steps: (1) Confirm that switch Q1, switch Q2 and switch Q3 are all off; (2) Close the switch Q1, check the working status of the voltage sag generating device, and set the output voltage of the voltage sag generating device to 380V; (3) Close the switch Q2 and switch Q3, start the device under test and the load; (4) The voltage sag generating device conducts low-voltage tests sequentially according to the characteristic quantities of voltage sags. The time interval between each two tests is not limited. Use an oscilloscope to collect the waveform of the input AC voltage and the output AC voltage of the device under test when the low voltage is low. The waveform of the voltage, the waveform of the DC bus voltage of the device under test and the waveform of the input AC voltage of the control circuit of the device under test; (5) Send a stop command to the device under test, and observe whether the device under test stops output normally; (6) If the device under test is a low-voltage auxiliary inverter system, perform step (7); if the device under test is a low-voltage auxiliary inverter system, make the low-voltage ride-through device send a fault signal, and observe whether the low-voltage auxiliary inverter is Normal stop output; (7) If all the waveforms collected by the oscilloscope in step (4) do not fluctuate abnormally, the device under test works normally, and the devices under test in steps (5) and (6) output normally, then the device under test complies with Otherwise, it will be concluded that the tested equipment does not meet the requirements of the technical specification for low voltage ride through capability. 10. The method for detecting low-voltage ride-through capability of a low-voltage auxiliary frequency converter in a thermal power plant according to claim 9, further comprising: setting the output fault types of the voltage sag generating device to three-phase symmetrical short circuit in sequence , two-phase ground short circuit, two-phase phase-to-phase short circuit and single-phase ground short circuit, detect whether the device under test sends out an undervoltage fault signal, detect the low voltage ride-through capability of the device under test, and draw the low voltage ride through capability curve of the device under test, according to The low voltage ride through capability curve shows the level of the low voltage ride through capability of the device under test.