A frequency conversion motor-generator test system and method

Abstract

The application discloses a frequency conversion motor-generator test system and method, and belongs to the technical field of frequency division power transmission and motors. The system comprises a motor-generator set and a frequency converter connected in parallel between a low-frequency bus and a power-frequency bus, and realizes comparison test of two variable frequency technical routes through switch switching. A multifunctional full-power converter simulates new energy power generation and driving set starting, a capacitor cabinet simulates submarine cable capacitance effect, and a measurement and control system integrates data acquisition and control. The test method sets the same conditions, compares operation data of a new energy station when a rotating frequency conversion set and a power electronic frequency converter are connected to a power grid, and verifies advantages of the rotating frequency conversion technology in voltage / frequency stability, reactive power support, rotational inertia support and harmonic suppression. The system provides a quantifiable comparison test platform for frequency division power transmission technology research, and solves the problem of insufficient stability of the existing power electronic frequency conversion technology.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power plant frequency division power transmission test, in particular to a frequency conversion motor-generator test system and method. BACKGROUND

[0002] With the development of offshore wind power to the middle and far sea, the demand for low-loss long-distance submarine power transmission is increasingly urgent. Among the current main power transmission methods, high-voltage power frequency alternating current transmission is limited by the submarine cable capacitance effect and is only suitable for near-shore wind farms (<70km); high-voltage flexible transmission requires the construction of an offshore converter platform, which is a huge investment; frequency division transmission has technical and economic advantages in the 50-150km range, but the power electronic frequency conversion method used in domestic demonstration projects has significant defects: ① poor voltage stability, low withstand voltage and current capacity of the converter, easy to cause the new energy station to be off the grid during power grid failure, and insufficient reactive power control capability, unable to provide effective voltage support; ② insufficient frequency stability, the converter has no inertia response capability, which reduces the system frequency stability. The existing technology lacks a direct comparison method for frequency division transmission technology, making it difficult to quantitatively evaluate the performance differences between rotary frequency conversion and power electronic frequency conversion. Therefore, the present application proposes a frequency conversion motor-generator test system, which realizes the comparison test of the two technical routes under the same working condition by parallelly arranging motor-generator sets and frequency converters, verifies the advantages of rotary frequency conversion technology in frequency stability, reactive power support, etc., and provides technical support for middle and far sea wind power transmission. SUMMARY

[0003] The present application aims to overcome the above-mentioned shortcomings of the prior art and provide a frequency conversion motor-generator test system and method.

[0004] The technical solution adopted by the present application is as follows:

[0005] A frequency conversion motor-generator test system includes: a low-frequency bus, a power frequency bus, a multi-functional full-power converter, a low-frequency transformer, a capacitor bank, a motor-generator set, a frequency converter, a synchronous motor excitation system, a power grid simulator, a resistive load, an LC load, a power frequency electrical cabinet, a low-frequency electrical cabinet, a synchronizing grid connection device, and a measurement and control system. The motor-generator set and the frequency converter are connected in parallel between the low-frequency bus and the power frequency bus, and switches are connected in series between the motor-generator set and both the low-frequency bus and the power frequency bus. Switches are also connected in series between the frequency converter and both the low-frequency bus and the power frequency bus. The switching of the switch enables the connection switching between the motor-generator set and the frequency converter; the multi-functional full-power converter is connected to the low-frequency bus through the low-frequency transformer to simulate the new energy power generation system and drive the motor-generator set to start; the capacitor cabinet is connected to the low-frequency bus to simulate the capacitance effect of submarine cables; the power grid simulator is connected to the power frequency bus to simulate the power frequency power grid; both resistive load and LC load are connected to the power frequency bus to simulate the load on the power grid side; the synchronous grid connection device is used to realize the grid connection of the new energy power station and the motor-generator set; the measurement and control system is used to collect data and control the entire test system.

[0006] Furthermore, the motor-generator set includes a low-frequency synchronous motor and a power frequency synchronous motor connected coaxially. The low-frequency synchronous motor is connected to a low-frequency bus, and the power frequency synchronous motor is connected to a power frequency bus. Frequency conversion is achieved by changing the number of poles of the low-frequency synchronous motor and the power frequency synchronous motor. A low-frequency circuit breaker is connected in series between the low-frequency synchronous motor and the low-frequency bus, and a synchronizing grid connection device and switch are connected in series between the power frequency synchronous motor and the power frequency bus.

[0007] Furthermore, the frequency converter is a power electronic frequency converter, with one end connected to the low-frequency bus via a low-frequency circuit breaker and the other end connected to the power frequency bus via a power frequency circuit breaker, used to simulate power electronic frequency division transmission technology.

[0008] Furthermore, at least two sets of multi-functional full-power converters are provided. Each set of multi-functional full-power converters is connected to the low-frequency bus through a corresponding low-frequency transformer, which is used to simulate the grid connection of one or more new energy units respectively.

[0009] Furthermore, the synchronous grid connection device includes three sets. The first set of synchronous grid connection devices is used to connect the new energy power station to the low-frequency bus. The second set of synchronous grid connection devices is used to connect another new energy power station to the low-frequency bus. The third set of synchronous grid connection devices is used to connect the motor-generator set to the power frequency bus.

[0010] Further, the measurement and control system integrates data acquisition, control operation, protection interlocking and man-machine interaction functions, is used for monitoring the changes of each electrical quantity (speed, voltage, power, power angle) in the test system, and realizes the adjustment of the output torque of the multi-functional full-power converter and the field current of the synchronous motor excitation system.

[0011] Further, a frequency conversion motor-generator test method comprises the following steps:

[0012] S1: building a test system, connecting the motor-generator set and the frequency converter in parallel between the low-frequency bus and the power-frequency bus, and initializing the motor-generator set to be connected by a switch;

[0013] S2: setting the same test conditions, including the output parameters of the new energy side, the load parameters of the power grid side and the output parameters of the power grid simulator;

[0014] S3: starting the test system, building pressure and connecting to the grid by the multi-functional full-power converter to drag the motor-generator set, simulating the centralized sending of the new energy station through the rotating frequency conversion set, collecting and recording the operation data of the system under the active power regulation, the reactive power regulation, the new energy side fluctuation, the power grid side load / voltage / frequency fluctuation and the low voltage ride through;

[0015] S4: switching the switch to disconnect the motor-generator set and connect the frequency converter, simulating the centralized sending of the new energy station through the power electronic frequency converter under the same test conditions, collecting and recording the operation data under the same working condition;

[0016] S5: comparing and analyzing the two sets of operation data to verify the technical advantages of the motor-generator set in voltage stability, frequency stability, reactive power support and rotational inertia support.

[0017] Further, the system starting pressure building and grid connecting step comprises: dragging the power-frequency synchronous motor to the rated speed in the SFC mode by the multi-functional full-power converter and connecting to the power-frequency grid, inputting the low-frequency synchronous motor excitation to build pressure of the low-frequency bus, and then switching the multi-functional full-power converter to the low-frequency power generation mode and connecting to the low-frequency bus through the low-frequency transformer.

[0018] Further, the active power regulation step is: realizing the increase and decrease of the system active power by controlling the output torque of the multi-functional full-power converter; the reactive power regulation step is: realizing the increase and decrease of the low-frequency side or power-frequency side reactive power by adjusting the field current of the low-frequency synchronous motor or the power-frequency synchronous motor.

[0019] Further, the support ability of the motor-generator set and the frequency converter for voltage stability is compared when the voltage fluctuates at the grid side, the support ability of the two for frequency stability is compared when the frequency fluctuates at the grid side, and the transient reactive power support of the two is compared when the system is in low voltage ride through.

[0020] Therefore, by adopting the technical scheme, the present application has the following advantages:

[0021] The test system is designed in parallel connection of the motor-generator set and the frequency converter, so that the direct comparison test of the power electronic frequency division power transmission and the rotating frequency conversion technology is realized. Compared with the prior art, the present application has the following advantages: 1. In terms of voltage stability, the motor-generator frequency conversion system can provide large reactive power support for the wind power side and the grid side through synchronous motor excitation regulation, and the voltage fluctuation range is reduced compared with the converter system. Meanwhile, when the wind farm is out of operation, the motor-generator set can still be hung on the power frequency grid to operate in the phase modulation mode and provide reactive power support for the grid; 2. In terms of frequency stability, the moment of inertia of the motor-generator set can effectively inhibit the frequency change rate of the grid; 3. In terms of accident isolation, the mechanical shaft isolation between the motor and the generator can protect the new energy station from the influence of the electrical fault at the grid side; 4. In terms of harmonic suppression, the total harmonic distortion rate of the output current of the rotating frequency conversion technology is small; 5. In terms of comprehensive test function, the new energy output fluctuation, the grid load / voltage / frequency fluctuation and the low voltage ride through and other working conditions can be simulated, so as to provide quantitative comparison basis for the frequency division power transmission technology. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a schematic diagram of the experimental system of the present application;

[0023] Figure 2 is a schematic diagram of the system startup, pressure building and grid connection process of the present application.

[0024] Markings in the figure:

[0025] 1 - multifunctional full-power converter, 2 - transformer, 3 - capacitor cabinet, 4 - motor-generator set, 5 - frequency converter, 6 - grid simulator, 7 - LC load, 8 - synchronization and grid connection device, 9 - low frequency bus, 10 - power frequency bus, 11 - resistance load, 12 - low frequency circuit breaker. DETAILED DESCRIPTION

[0026] The present application will be described in detail below with reference to the accompanying drawings.

[0027] In order to make the purpose, technical scheme and advantages of the present application more clear and explicit, the present application will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0028] Embodiment one

[0029] In this embodiment, as shown in Figure 1 A frequency conversion motor-generator test system includes a low-frequency bus, a power-frequency bus, a multifunctional full-power converter, a low-frequency transformer, a capacitor cabinet, a motor-generator set, a frequency converter, a synchronous motor excitation system, a power grid simulator, a resistance load, an LC load, a power-frequency electrical cabinet, a low-frequency electrical cabinet, a synchronous grid-connection device, and a measurement and control system. The motor-generator set and the frequency converter are arranged in parallel between the low-frequency bus and the power-frequency bus, and switches are connected in series between the motor-generator set and the low-frequency bus and the power-frequency bus. The frequency converter and the low-frequency bus and the power-frequency bus are connected in series, and the switching of the switches realizes the switching of the motor-generator set and the frequency converter. The multifunctional full-power converter is connected to the low-frequency bus through the low-frequency transformer, and is used to simulate a new energy power generation system and to drive the motor-generator set to start. The capacitor cabinet is connected to the low-frequency bus, and is used to simulate the capacitive effect of a submarine cable. The power grid simulator is connected to the power-frequency bus, and is used to simulate a power-frequency power grid. The resistance load and the LC load are both connected to the power-frequency bus, and are used to simulate a power grid side load. The synchronous grid-connection device is used to realize the grid-connection of a new energy station and the motor-generator set. The measurement and control system is used to collect data and control the entire test system.

[0030] Specifically, the low-frequency bus and the power-frequency bus are core electrical nodes of the system, and are arranged in parallel to form a parallel topology structure, and are used to transmit low-frequency electric energy and power-frequency electric energy, respectively. The low-frequency bus and the power-frequency bus are electrically connected through a busbar or a cable.

[0031] The motor-generator set and the frequency converter are arranged in parallel: both are connected across the low-frequency bus and the power-frequency bus to form a parallel branch. The motor-generator set is connected in series with a low-frequency circuit breaker between the low-frequency bus and the motor-generator set, and is connected in series with the synchronous grid-connection device and a power-frequency switch between the power-frequency bus and the motor-generator set. The frequency converter is connected in series with a low-frequency circuit breaker between the low-frequency bus and the frequency converter, and is connected in series with a power-frequency circuit breaker between the power-frequency bus and the frequency converter.

[0032] The multifunctional full-power converter: two groups (full-power converter A and full-power converter B) are arranged, and each group is connected to the low-frequency bus through an independent low-frequency transformer (low-frequency transformer A and low-frequency transformer B). The output end of the converter is electrically connected to the primary coil of the transformer, and the secondary coil of the transformer is connected to the low-frequency bus.

[0033] The capacitor cabinet: star or delta connection is adopted, and is directly connected in parallel to the low-frequency bus. The rated voltage of the capacitor group matches the voltage of the low-frequency bus.

[0034] The power grid simulator: is connected to the power-frequency bus through the power-frequency electrical cabinet. The input end is connected to an external power source, and the output end is fixedly connected to the power-frequency bus through a cable.

[0035] Resistive load and LC load: both are connected in parallel on the power frequency bus through power frequency switches, the resistive load uses an adjustable power resistance box, and the LC load is composed of adjustable inductance and capacitance in parallel.

[0036] Synchronization and grid connection device: three sets of synchronization devices are arranged respectively: synchronization and grid connection device A and B are connected in parallel on the low-frequency bus, and synchronization and grid connection device C is connected in series between the power frequency synchronous motor and the power frequency bus.

[0037] Measurement and control system: an industrial-grade PLC controller and an upper computer are combined in architecture, the PLC collects data of each electrical node through current transformers, voltage transformers and other sensors, and the upper computer is connected with the PLC through communication cable to realize human-computer interaction.

[0038] Working action

[0039] System start: full-power converter A is switched to SFC drag mode, and the power frequency synchronous motor is powered through the low-frequency transformer A, and after the motor reaches the rated speed, the synchronization and grid connection device C is actuated to connect the power frequency synchronous motor to the power frequency grid.

[0040] Mode switching: when switching from motor-generator set mode to frequency converter mode, first disconnect the low-frequency circuit breaker and power frequency switch on both sides of the motor-generator set, and then close the low-frequency circuit breaker and power frequency circuit breaker on both sides of the frequency converter.

[0041] Data acquisition: the measurement and control system collects real-time parameters such as speed, voltage, power, power angle of the motor-generator set, and operating data of the frequency converter.

[0042] Parallel switching principle: through the on-off control of switching devices, the physical isolation and switching of the two variable frequency technology routes are realized to ensure that the comparison test is carried out under the same grid conditions. The motor-generator set uses the mechanical inertia of the synchronous motor (rotational inertia energy storage) to provide inertia response when the grid frequency fluctuates, while the frequency converter cannot realize this function because the power electronic devices have no rotational inertia. Rotational inertia energy storage

[0043] Capacitor simulation principle: the capacitive reactance of the capacitor cabinet is equivalent to the capacitive effect of the submarine cable, and when the low-frequency current passes through, the change rule of capacitive reactive power is consistent with the actual submarine cable, solving the problem that the capacitive effect of the submarine cable cannot be truly simulated in the prior art.

[0044] Beneficial effects: the structure realizes the direct comparison of power electronic frequency division transmission and rotary frequency conversion technology, and the synchronous motor set connected by the mechanical shaft can provide a large reactive power support capability (the reactive power support capability of the existing converter is relatively weak, and the capacity of the frequency converter needs to be increased), which improves the voltage stability of the system.

[0045] Further, the motor-generator set comprises a low-frequency synchronous motor and a power-frequency synchronous motor connected coaxially, the low-frequency synchronous motor is connected to a low-frequency bus, the power-frequency synchronous motor is connected to a power-frequency bus, frequency conversion is realized by changing the pole number of the low-frequency synchronous motor and the power-frequency synchronous motor, and a low-frequency circuit breaker is connected in series between the low-frequency synchronous motor and the low-frequency bus, and a synchronization grid-connection device and a switch are connected in series between the power-frequency synchronous motor and the power-frequency bus.

[0046] Specifically, the coaxial connection structure is that the low-frequency synchronous motor and the power-frequency synchronous motor are fixed coaxially through a rigid coupling, share the same main shaft, and the motor stators are independently installed in the casing, and the rotor core is fixed on the main shaft.

[0047] The pole number configuration is that the low-frequency synchronous motor is designed as 8 poles, and the power-frequency synchronous motor is designed as 20 poles, and the pole number ratio is 2:5.

[0048] The electrical connection is that the three-phase stator windings of the low-frequency synchronous motor are connected to the low-frequency circuit breaker on the low-frequency bus side through a cable, and the three-phase stator windings of the power-frequency synchronous motor are connected to the synchronization grid-connection device and the power-frequency switch on the power-frequency bus side through a cable.

[0049] The excitation system is that two independent excitation windings are embedded in the rotors of the low-frequency synchronous motor and the power-frequency synchronous motor respectively, and an excitation power supply supplies power to the excitation windings through a slip ring and a brush assembly.

[0050] The frequency conversion process is that when the main shaft speed n=300r / min, according to f=pn / 60, the low-frequency synchronous motor outputs a frequency f1=4×300 / 60=20Hz, and the power-frequency synchronous motor outputs a frequency f2=10×300 / 60=50Hz, realizing the conversion from 20Hz to 50Hz.

[0051] The excitation regulation is that when the power-frequency grid voltage decreases, the measurement and control system controls the excitation system to increase the excitation current of the power-frequency synchronous motor, so that it outputs inductive reactive power to suppress voltage drop; when the power-frequency grid voltage rises, the measurement and control system controls the excitation system to reduce the excitation current of the power-frequency synchronous motor, so that it absorbs inductive reactive power to suppress voltage rise.

[0052] The speed consistency principle is that the coaxial connection ensures that the speeds of the two motors are strictly consistent, meets the frequency conversion relationship f1 / f2=p1 / p2, and this mechanical coupling method is more stable than power electronic frequency conversion and is not affected by grid harmonics.

[0053] The inertia support principle is that the motor-generator set has a large rotational inertia (for example, the flywheel torque of a 200kW unit is The rotor kinetic energy can be used as an energy buffer pool to release / absorb rotor kinetic energy when the grid frequency fluctuates, play a damping role, and suppress frequency changes, while power electronic frequency converters do not have this capability.

[0054] The structure makes the system have natural damping characteristics, can keep synchronous operation when the power grid fails, avoids large-scale off-grid accidents, and realizes accurate frequency conversion through pole matching.

[0055] Further, the frequency converter is a power electronic frequency converter, one end of which is connected to the low-frequency bus through a low-frequency circuit breaker, and the other end is connected to the power frequency bus through a power frequency circuit breaker, which is used to simulate the power electronic frequency division power transmission technology.

[0056] Specifically, the power electronic frequency converter type: modular multilevel matrix converter (M3C), composed of IGBT power module three-phase bridge circuit, DC bus configuration film capacitor or electrolytic capacitor, for energy buffer and voltage stability.

[0057] Circuit breaker configuration: the low-frequency side of the frequency converter is connected to the low-frequency bus through a low-frequency circuit breaker, and the power frequency side is connected to the power frequency bus through a power frequency circuit breaker, and the circuit breaker is equipped with a relay protection device.

[0058] Filter device: M3C uses multi-level PWM, which has relatively small harmonic content compared to traditional frequency converters, but a small capacity LC filter is set at the output to suppress high-frequency harmonics to meet the grid requirements for new energy grid connection.

[0059] Frequency conversion process: when the low-frequency bus voltage is 380V / 20Hz, multi-level PWM modulation strategy is adopted to directly complete the conversion of 20Hz to 50Hz power in the matrix converter, and then it is connected to the power grid through the power frequency circuit breaker.

[0060] Fault protection: when the power grid has a short circuit fault, the circuit breaker trips within 50~100ms, cutting off the connection between the frequency converter and the power grid to prevent the converter module from overcurrent damage.

[0061] Power electronic frequency conversion principle: based on the fast switching (kHz level) of IGBT power module, the input / output side power conversion is directly completed through multi-level PWM modulation, and the control algorithm adopts vector control and sub-module voltage control, which can accurately adjust the output voltage and frequency.

[0062] Comparative advantage: after being connected in parallel with the motor-generator set, the harmonic characteristics of the two technologies can be directly compared to verify the harmonic suppression advantage of the rotary frequency conversion technology.

[0063] This setting provides a standard power electronic frequency division power transmission model for comparative tests, which facilitates quantitative analysis of the advantages of rotary frequency conversion technology in rotational inertia support (power electronic frequency converter rotational inertia support is 0, and 200kW motor-generator set can provide 0.6s of inertia support).

[0064] Further, the multi-functional full-power converter is provided with at least two groups, and each group of the multi-functional full-power converter is connected to a low-frequency bus through a corresponding low-frequency transformer, and is used for respectively simulating single or multiple new energy units to be connected to a grid.

[0065] Double-converter configuration: the full-power converter A and the converter B both adopt a back-to-back topology structure, and each converter is composed of a machine-side converter, a DC bus and a grid-side converter.

[0066] Low-frequency transformer connection: the grid-side output end of the full-power converter A is connected to a low-frequency transformer A, the grid-side output end of the converter B is connected to a low-frequency transformer B (parameters are the same as those of the transformer A), and the secondary windings of the two transformers are connected in parallel to a low-frequency bus.

[0067] Control interface: the control units of the two converters communicate with a measurement and control system through optical fibers and receive torque control instructions.

[0068] Single-unit simulation: the full-power converter A outputs a 380V / 20Hz voltage and is connected to the low-frequency bus through the low-frequency transformer to simulate the output of a single wind turbine unit.

[0069] Multiple-unit simulation: the full-power converter B works synchronously with the converter A, and the output powers of the two are superimposed to simulate multiple wind turbines to be connected to a grid.

[0070] Power superposition principle: the two converters are independently controlled, connected to the low-frequency bus through transformers, and realize linear superposition of power, so that different sizes of new energy stations can be simulated, and the stability of the system when multiple units are connected to a grid can be tested.

[0071] The arrangement enables the test system to cover full-scene testing from a single unit to a large station, and through the cooperative control of the double converters, random fluctuations of new energy output can be simulated, the adaptability of the rotating frequency conversion system can be verified, and the problem that the existing test platform cannot simulate multiple units to be connected to a grid is solved.

[0072] Further, the synchronous grid connection device includes three groups, the first group of the synchronous grid connection device is used for connecting a new energy station to a low-frequency bus, the second group of the synchronous grid connection device is used for connecting another new energy station to the low-frequency bus, and the third group of the synchronous grid connection device is used for connecting a motor-generator unit to a power-frequency bus.

[0073] Distribution of the three groups of synchronous devices: the synchronous grid connection devices A and B are installed in a control cabinet at the low-frequency bus side, the input ends are respectively connected to the output ends of the full-power converter A and the converter B, and the output ends are connected to the low-frequency bus through a cable; the synchronous grid connection device C is installed in a switch cabinet between a power-frequency synchronous motor and a power-frequency bus, the input end is connected to a stator winding of the power-frequency synchronous motor, and the output end is connected to the power-frequency bus.

[0074] Detection unit: Each group of synchronization device contains voltage transformer, current transformer, phase angle detection module, detection signal is transmitted to the control unit through shielded cable.

[0075] Actuator: The control unit of the synchronization device outputs the closing instruction to the corresponding circuit breaker operating mechanism to realize the automatic closing of the grid switch.

[0076] New energy station grid connection: When the amplitude difference of the full-power converter A output voltage and the low-frequency bus voltage is <5%, the phase angle difference is <5°, and the frequency difference is <0.2 Hz, the synchronization and grid connection device A sends a closing instruction to close the corresponding switch.

[0077] Motor-generator set grid connection: When the power frequency synchronous motor reaches the rated speed, the synchronization and grid connection device C detects the synchronization conditions with the power frequency grid, and closes the power frequency switch when the conditions are met.

[0078] Synchronization and parallel principle: Based on quasi-synchronization and parallel control, through closed-loop regulation, the voltage, frequency and phase at the moment of grid connection are strictly matched to minimize the impact current at the moment of grid connection and avoid electromagnetic shock to the system.

[0079] Advantages of hierarchical grid connection: Three groups of synchronization devices are independently controlled, which can realize the batch grid connection of new energy stations, simulate the expansion process of actual power grid, while the existing technology can only realize one-time grid connection of single unit and cannot test the stability of step-by-step grid connection.

[0080] This configuration ensures the safety and stability of the grid connection process, with small voltage fluctuation during grid connection, providing standardized grid connection conditions for comparative tests, making the comparison results of the two technical routes more reliable.

[0081] Further, the measurement and control system integrates data acquisition, control operation, protection interlocking and human-computer interaction functions, which are used to monitor the changes of various electrical and mechanical quantities (speed, voltage, current, power, power angle, frequency) in the test system, and realize the adjustment of the output torque of the multi-functional full-power converter and the excitation current of the synchronous motor excitation system.

[0082] Hardware architecture: Two-layer architecture of "PLC + host computer" is adopted, PLC selects Siemens S7-1500 series, equipped with analog input module, analog output module, digital input / output module; the host computer uses industrial computer.

[0083] Sensor network: Current transformers, voltage transformers and speed encoders are installed at each electrical node, and sensor signals are connected to the AI module of PLC through shielded twisted pair.

[0084] Control interface: PLC communicates with full-power converter, excitation system and synchronization and grid connection device through bus to realize real-time control.

[0085] Power regulation: When the active power needs to be increased, the host computer sends a torque increase command to the full-power converter, and the converter output torque increases at a rate of 10% / s until it reaches the target value.

[0086] Reactive power regulation: When the grid voltage drops, the PLC calculates the required reactive power compensation and outputs an excitation current adjustment signal to the excitation system. The excitation current responds within 100ms (adjustment rate ≥ 10A / ms).

[0087] Real-time control principle: A PLC controller with a scanning period of 1ms is used to realize real-time monitoring and control of the system through a high-speed communication bus, with a control delay of <5ms, meeting the requirements of transient process testing.

[0088] Fault protection principle: The measurement and control system has multiple protection logic (overcurrent protection, overvoltage protection, loss of excitation protection). When an anomaly is detected, a trip command is issued within 10ms to cut off the fault circuit.

[0089] This system realizes full automation control and data acquisition during the test process, can accurately reproduce various working conditions (such as voltage drop depth 20%-80% adjustable, drop duration 0.1-1s adjustable), provides a controllable test environment for comparative tests, and solves the problem of insufficient precision of manual operation.

[0090] Further, a frequency conversion motor-generator test method,

[0091] System setup: According to the system diagram, connect the components, Figure 1 Connect the motor-generator set's low-frequency circuit breaker and power frequency switch, disconnect the frequency converter's two side circuit breakers, and form the motor-generator set access state.

[0092] Condition setting: Set the output power of full-power converter A and converter B to 100kW / 20Hz, and the grid simulator output voltage to 380V / 50Hz.

[0093] Rotary frequency conversion mode test:

[0094] Full-power converter A drags the power frequency synchronous motor to 300r / min in SFC mode, and the synchronization and grid connection device C acts and enters the power frequency grid.

[0095] Put in the low-frequency synchronous motor excitation, charge the capacitor cabinet to make the low-frequency bus voltage rise to 380V.

[0096] Converter A and converter B switch to power generation mode, connect through the low-frequency transformer to the low-frequency bus, and record the initial operation data after the system stabilizes.

[0097] Adjust the converter output torque to gradually increase the active power from 10kW to 100kW, and record the power change curve.

[0098] Power electronic frequency conversion mode test: Disconnect the low-frequency circuit breaker and power frequency switch of the motor-generator set, close the circuit breakers on both sides of the frequency converter, repeat the above test conditions, and record the data under the same operating conditions.

[0099] Data Comparison: Compare the speed fluctuation and voltage fluctuation during active power adjustment under the two modes.

[0100] Comparative test principle: By keeping the output parameters of the new energy side and the load parameters of the grid side consistent, and only changing the frequency conversion link (motor-generator set or power electronic frequency converter), a single variable comparison is achieved, which conforms to the principles of scientific testing.

[0101] Transient process simulation principle: By setting a voltage drop (such as a sudden voltage drop of 50% lasting 0.5s) using a power grid simulator, the system recovery time under two modes (recovery time of rotary frequency converter mode and recovery time of power electronic frequency converter mode) is observed to verify the transient reactive power support capability.

[0102] This method can quantitatively compare the key performance indicators of the two technical routes, providing data support for engineering applications and solving the problem of the lack of intuitive comparison methods in existing technologies.

[0103] Furthermore, the system starts building pressure, such as... Figure 2 The grid connection steps shown include: driving the power frequency synchronous motor to its rated speed and connecting it to the power frequency grid in SFC mode through a multi-functional full-power converter; energizing the low-frequency synchronous motor to build up voltage on the low-frequency bus; then switching the multi-functional full-power converter to low-frequency generation mode and connecting it to the low-frequency bus through a low-frequency transformer.

[0104] Furthermore, the active power adjustment steps are as follows: by controlling the output torque of the multi-functional full-power converter, the active power of the system is increased or decreased; the reactive power adjustment steps are as follows: by adjusting the excitation current of the low-frequency synchronous motor or the power frequency synchronous motor, the reactive power on the low-frequency side or the power frequency side is increased or decreased.

[0105] This power regulation method achieves independent control of active and reactive power. During active power regulation, the speed fluctuation is <0.5%, and during reactive power regulation, the voltage fluctuation is <1%, which meets the requirements of high-precision comparative tests and can clearly demonstrate the advantages of motor-generator sets in reactive power support.

[0106] Furthermore, when the grid-side voltage fluctuates, the ability of the motor-generator set and the frequency converter to support voltage stability is compared; when the grid-side frequency fluctuates, the ability of the two to support frequency stability is compared; and when the system experiences low voltage ride-through, the transient reactive power support effect of the two is compared.

[0107] The contrast test intuitively shows the significant advantages of the rotating frequency conversion technology in the stability support of the power grid, especially in the low voltage ride through scene, avoids the chain failure caused by the converter off-grid, provides a more reliable technical solution for the long-distance wind power transmission, and solves the stability problem of the existing power electronic frequency division power transmission technology in the power grid fault.

[0108] The above merely describes preferred embodiments of the application and is not intended to limit the application. Any modification, equivalent replacement, and improvement made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A frequency conversion motor-generator test system, characterized by, The utility model relates to a test system for new energy power grid integration test, including: Low frequency bus, power frequency bus, multi -functional full -power converter, low frequency transformer, capacitor cabinet, motor -generator set, frequency converter, synchronous motor excitation system, power grid simulator, resistance load, LC load, power frequency electrical cabinet, low frequency electrical cabinet, synchronization grid -connected device and control system, the motor -generator set with the frequency converter is parallelly connected and is arranged between the low frequency bus with the power frequency bus, and the motor -generator set with the low frequency bus and the power frequency bus all have switches in series, the frequency converter with the low frequency bus and the power frequency bus all have switches in series, realize the access switching of the motor -generator set with the frequency converter through the switching of the switch, the multi -functional full -power converter is connected to the low frequency bus through the low frequency transformer, is used for simulating new energy power generation system and drags the motor -generator set start, the capacitor cabinet is connected in the low frequency bus, is used for simulating submarine cable capacitance effect, the power grid simulator is connected in the power frequency bus, is used for simulating power frequency power grid, the resistance load with the LC load all are connected in the power frequency bus, are used for simulating power grid side load, the synchronization grid -connected device is used for realizing new energy field station and the grid -connected of motor -generator set, the control system is used for gathering data and controlling whole test system, The synchronization grid -connected device includes three groups, the first group synchronization grid -connected device is used for connecting new energy field station to the low frequency bus, the second group synchronization grid -connected device is used for connecting another new energy field station to the low frequency bus, the third group synchronization grid -connected device is used for connecting the motor -generator set to the power frequency bus.

2. A frequency conversion motor-generator test system as recited in claim 1, wherein: The motor -generator set includes coaxial connection's low frequency synchronous motor and power frequency synchronous motor, the low frequency synchronous motor is connected to the low frequency bus, the power frequency synchronous motor is connected to the power frequency bus, realizes frequency conversion through changing the pole number of the low frequency synchronous motor with the power frequency synchronous motor, and the low frequency synchronous motor with the low frequency bus is in series with low frequency circuit breaker, the power frequency synchronous motor with the power frequency bus is in series with synchronization grid -connected device and switch.

3. A frequency conversion motor-generator test system as recited in claim 1, wherein: The frequency converter is power electronic frequency converter, and one end is connected to the low frequency bus through low frequency circuit breaker, and the other end is connected to the power frequency bus through power frequency circuit breaker, and is used for simulating power electronic frequency division power transmission technology.

4. A frequency conversion motor-generator test system as recited in claim 1, wherein: The multi -functional full -power converter is provided with at least two groups, and each group multi -functional full -power converter is connected to the low frequency bus through corresponding low frequency transformer, and is used for simulating single or multiple new energy unit grid -connected respectively.

5. A frequency conversion motor-generator test system as recited in claim 1, wherein: The control system integrates data acquisition, control operation, protection interlock and man -machine interaction function, is used for monitoring the change of each electrical quantity (rotational speed, voltage, power, power angle) in the test system, and realizes the adjustment of multi -functional full -power converter output torque, the synchronous motor excitation system excitation current.

6. A method for testing a frequency conversion motor-generator, applied to the frequency conversion motor-generator testing system of claim 2, characterized in that: The utility model relates to a test system for new energy power grid integration test, including: Low frequency bus, power frequency bus, multi -functional full -power converter, low frequency transformer, capacitor cabinet, motor -generator set, frequency converter, synchronous motor excitation system, power grid simulator, resistance load, LC load, power frequency electrical cabinet, low frequency electrical cabinet, synchronization grid -connected device and control system, the motor -generator set with the frequency converter is parallelly connected and is arranged between the low frequency bus with the power frequency bus, and the motor -generator set with the low frequency bus and the power frequency bus all have switches in series, the frequency converter with the low frequency bus and the power frequency bus all have switches in series, realize the access switching of the motor -generator set with the frequency converter through the switching of the switch, the multi -functional full -power converter is connected to the low frequency bus through the low frequency transformer, is used for simulating new energy power generation system and drags the motor -generator set start, the capacitor cabinet is connected in the low frequency bus, is used for simulating submarine cable capacitance effect, the power grid simulator is connected in the power frequency bus, is used for simulating power frequency power grid, the resistance load with the LC load all are connected in the power frequency bus, are used for simulating power grid side load, the synchronization grid -connected device is used for realizing new energy field station and the grid -connected of motor -generator set, the control system is used for gathering data and controlling whole test system, The synchronization grid -connected device includes three groups, the first group synchronization grid -connected device is used for connecting new energy field station to the low frequency bus, the second group synchronization grid -connected device is used for connecting another new energy field station to the low frequency bus, the third group synchronization grid -connected device is used for connecting the motor -generator set to the power frequency bus. The motor -generator set includes coaxial connection's low frequency synchronous motor and power frequency synchronous motor, the low frequency synchronous motor is connected to the low frequency bus, the power frequency synchronous motor is connected to the power frequency bus, realizes frequency conversion through changing the pole number of the low frequency synchronous motor with the power frequency synchronous motor, and the low frequency synchronous motor with the low frequency bus is in series with low frequency circuit breaker, the power frequency synchronous motor with the power frequency bus is in series with synchronization grid -connected device and switch. The frequency converter is power electronic frequency converter, and one end is connected to the low frequency bus through low frequency circuit breaker, and the other end is connected to the power frequency bus through power frequency circuit breaker, and is used for simulating power electronic frequency division power transmission technology. The multi -functional full -power converter is provided with at least two groups, and each group multi -functional full -power converter is connected to the low frequency bus through corresponding low frequency transformer, and is used for simulating single or multiple new energy unit grid -connected respectively. The control system integrates data acquisition, control operation, protection interlock and man -machine interaction function, is used for monitoring the change of each electrical quantity (rotational speed, voltage, power, power angle) in the test system, and realizes the adjustment of multi -functional full -power converter output torque, the synchronous motor excitation system excitation current. Including following steps: S1: building the test system, connecting the motor-generator set and the frequency converter in parallel between the low-frequency bus and the power-frequency bus, and initializing the motor-generator set through a switch; S2: setting the same test conditions, including new energy side output parameters, power grid side load parameters, and power grid simulator output parameters; S3: starting the test system, driving the motor-generator set to build pressure and connect to the grid through the multifunctional full-power converter, simulating the centralized sending of the new energy station through the rotating frequency converter set, collecting and recording the operating data of the system under active power regulation, reactive power regulation, new energy side fluctuation, power grid side load / voltage / frequency fluctuation, and low voltage ride through; S4: switching the switch to disconnect the motor-generator set and connect the frequency converter, simulating the centralized sending of the new energy station through the power electronic frequency converter under the same test conditions, collecting and recording the operating data under the same operating conditions; S5: comparing and analyzing the two sets of operating data to verify the technical advantages of the motor-generator set in voltage stability, frequency stability, reactive power support, and rotational inertia support.

7. A method of testing a frequency converted motor-generator as defined in claim 6, wherein: The step S3 includes: driving the power-frequency synchronous motor to the rated speed in SFC mode through the multifunctional full-power converter and connecting to the power-frequency grid, inputting the low-frequency synchronous motor excitation to build pressure on the low-frequency bus, and then switching the multifunctional full-power converter to the low-frequency power generation mode and connecting to the low-frequency bus through the low-frequency transformer.

8. A method of testing a frequency converted motor-generator as defined in claim 6, wherein: The active power regulation step is to control the output torque of the multifunctional full-power converter to increase or decrease the system active power; the reactive power regulation step is to adjust the excitation current of the low-frequency synchronous motor or the power-frequency synchronous motor to increase or decrease the reactive power on the low-frequency side or the power-frequency side.

9. A method of testing a frequency converted motor-generator as defined in claim 6, wherein: When the voltage fluctuates on the power grid side, compare the voltage stability support capability of the motor-generator set and the frequency converter; when the frequency fluctuates on the power grid side, compare the frequency stability support capability of the two; when the system is in low voltage ride through, compare the transient reactive power support of the two.

Images