Flexible loop closing device test system and test method

Abstract

The invention discloses a flexible loop closing device test system and test method, the test system comprises an adjustable AC power supply, a first fixed AC power supply, a second fixed AC power supply and a tested flexible loop closing device, one end of the flexible loop closing device is connected with the adjustable AC power supply, and the other end of the flexible loop closing device is connected with the first fixed AC power supply; the adjustable AC power supply comprises a multi-winding transformer and 3N AC-DC-AC power modules. The first fixed alternating current power supply and the second fixed alternating current power supply are alternating current power supplies with unadjustable output voltage and output frequency, the tested flexible loop closing device is connected between the power supplies, and the power flow between the power supplies is changed by adjusting the output voltage of the device. The invention further provides a test method of the interconnection device test system. The test system provided by the invention is low in cost, good in flexibility and high in reliability.

Description

Technical Field

[0001] The invention belongs to the field of power electronic power conversion, and in particular relates to a flexible loop closing device test system and a test method. Background Art

[0002] With the development of the distribution network, the load growth in some areas has exceeded expectations, causing overload in the power grid equipment. With the increase in the proportion of new energy, problems such as "power reverse transmission" have gradually become serious. At present, the traditional power grid's new point layout method is limited by line corridor resources and has high investment. There is an electromagnetic ring network problem in the interconnection line through the interconnection switch. Therefore, it is necessary to realize flexible power regulation and dynamic capacity expansion through flexible interconnection technology. It is necessary to provide reasonable nodes and paths for the consumption of new energy. In the field of large-capacity and high-power power electronic conversion technology, multi-level converters can realize flexible ring solutions by using modular cascade technology.

[0003] The flexible loop device realizes the function of partition interconnection and connects the two power supplies through power electronic equipment. How to verify the function and performance of the device through the test system and test method is the key to the engineering application of the device. The main difficulty lies in: the amplitude and phase difference of the two power supplies are different, and the factory usually does not have the test conditions for dual power supplies. Even if the dual power supply conditions are available, the amplitude and phase difference of the dual power supplies in the factory are fixed and cannot be adjusted according to the test requirements, and the verification effect cannot be achieved. On the other hand, in order to verify the transient performance of the device, it is necessary to simulate the situation where there is a fault in the power grid, that is, when the primary power supply drops, the voltage and current of the device are assessed, and it is difficult to simulate the drop in the real power grid. There is no suitable solution in the prior art to meet the above test requirements. In general, the prior art lacks a low-cost test solution that enables the test system to fully reproduce the real working conditions of the equipment. Summary of the invention

[0004] In view of the above technical problems, the technical problem to be solved by the present invention is to provide a low-cost flexible ring closing device test system that meets the test requirements.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] On the one hand, the present invention discloses a flexible loop device test system, the test system comprises an adjustable AC power supply, a first fixed AC power supply, a second fixed AC power supply and a flexible loop device to be tested, wherein one end of the flexible loop device is connected to the adjustable AC power supply, and the other end is connected to the first fixed AC power supply; the adjustable AC power supply comprises a multi-winding transformer and 3N AC / DC power modules, wherein N is an integer greater than or equal to 1, the primary side of the multi-winding transformer of the adjustable AC power supply is connected to the second fixed AC power supply, the multi-winding transformer comprises 3N secondary windings, which are connected one-to-one with the input ends of the AC / DC power modules, the output ends of the 3N AC / DC power modules are cascaded in three phases, each phase is composed of N modules to form a commutation chain, one end of the three-phase commutation chain is connected to form a common end, and the other end is connected to a reactor and then led out as the output end of the adjustable power supply; the first fixed AC power supply and the second fixed AC power supply are AC power supplies whose output voltage and output frequency are both unadjustable, the flexible loop device to be tested is connected between the power supplies, and the power flow between the power supplies on both sides is changed by adjusting the output voltage of the device.

[0007] More preferably,

[0008] The AC-DC-AC power module includes a rectifier unit, an inverter unit and a DC capacitor. The input end of the rectifier unit is connected to the secondary winding of the multi-winding transformer as the input end of the AC-DC-AC power module, and the output end is connected to the DC capacitor. The input end of the inverter unit is connected to the DC capacitor, and the output end serves as the output end of the AC-DC-AC power module.

[0009] More preferably,

[0010] The rectifier unit is a three-phase half-bridge rectifier circuit composed of 6 groups of power semiconductor devices or a full-bridge rectifier circuit composed of 4 groups of power semiconductor devices; the inverter unit is a full-bridge circuit composed of 4 groups of power semiconductor devices.

[0011] More preferably,

[0012] A bypass switch is arranged in parallel at the output end of each inverter unit.

[0013] More preferably,

[0014] The flexible loop closing device under test is a series-parallel flexible loop closing device or a back-to-back flexible loop closing device composed of power semiconductor devices. The series-parallel flexible loop closing device includes a series part and a parallel part. The series part is a commutation chain composed of an H-bridge cascade, and the parallel part supplies energy for the series part; the back-to-back flexible loop closing device includes two AC-DC converters, the DC sides of the AC-DC converters are connected together, and the AC sides are respectively connected to AC power supplies.

[0015] More preferably,

[0016] A switch is also connected in series between the adjustable AC power source and the flexible loop-closing device under test and / or between the first fixed AC power source and the flexible loop-closing device under test.

[0017] More preferably,

[0018] The adjustable AC power supply also includes a control unit and a sampling unit. The sampling unit detects the AC voltage output by the first fixed AC power supply and sends the AC voltage sampling value to the control unit. The control unit sets the command value of the adjustable AC power supply output AC voltage according to the amplitude, frequency and phase of the AC voltage output by the first fixed AC power supply.

[0019] On the other hand, the present invention further discloses a test method based on the above-mentioned flexible loop closing device test system, wherein the test method includes a start-up method, and the start-up method includes the following steps:

[0020] Step 1: The first fixed AC power source is started;

[0021] Step 2: The second fixed AC power source is started;

[0022] Step 3: charging the DC capacitor in the AC / DC power module of the adjustable AC power supply;

[0023] Step 4: starting the rectifier unit in the AC / DC power module of the adjustable AC power supply to adjust the DC capacitor voltage to be stable;

[0024] Step 5: the inverter unit in the AC-DC-AC power module of the adjustable AC power supply is started, and the adjustable AC power supply outputs an AC voltage according to the command value of the output AC voltage;

[0025] Step 6: The flexible closed-loop device under test is started to adjust the current between the first fixed AC power source and the adjustable AC power source.

[0026] The present invention also discloses a test method based on the above-mentioned flexible loop closing device test system, wherein the test method includes a grid adaptability test method, and the grid adaptability test method includes the following steps:

[0027] Step 1: The first fixed AC power supply and the adjustable AC power supply in the flexible loop closing device test system are started;

[0028] Step 2: The flexible loop closing device under test is started, and the output current is controlled to be zero;

[0029] Step 3: The control unit of the adjustable AC power supply calculates the amplitude given value U2 and the phase given value θ2 of the AC voltage output by the adjustable AC power supply according to the amplitude U1 and the phase θ1 of the AC voltage output by the first fixed AC power supply and the voltage amplitude difference set value ΔU and the phase angle difference set value Δθ applied to the two ends of the flexible loop closing device under test; the calculation formula is:

[0030] U2=U1–ΔU;

[0031] θ2 = θ1 – Δθ;

[0032] Outputting an AC voltage according to the calculated amplitude given value U2 and phase given value θ2 of the AC voltage;

[0033] Step 4: After detecting the voltage difference and the phase angle difference, the flexible loop closing device under test adjusts its own output voltage and adjusts the current stability between the first fixed AC power source and the adjustable AC power source.

[0034] The present invention also discloses a test method based on the above-mentioned flexible loop closing device test system, characterized in that: the test method also includes a current blocking test method, including the following steps:

[0035] Step 1: The first fixed AC power supply and the adjustable AC power supply in the flexible loop closing device test system are started;

[0036] Step 2: The flexible loop closing device under test is started, and the output current is controlled to be zero first, and then gradually adjusted to the rated value;

[0037] Step 3: Adjust the output voltage of the adjustable AC power supply so that the output voltage drops rapidly to 0%-90% of the rated value;

[0038] Step 4: The voltage difference between the first fixed AC power source and the adjustable AC power source is applied to the flexible loop closing device under test, causing the current to rise rapidly;

[0039] Step 5: The power semiconductor device in the flexible loop closing device under test is quickly locked to block the current and detect the falling time of the current.

[0040] Compared with the prior art, the flexible ring closing device test system and test method described in the present invention have the following technical effects:

[0041] 1) The system proposed in the present invention designs a fixed power supply and an adjustable power supply. The adjustable power supply adopts a high-voltage frequency conversion technology solution. The input side is connected to a fixed power supply. A multi-winding transformer is used for isolation and then connected to multiple AC, DC, and AC power modules. The output sides of the AC, DC, and AC power modules are cascaded. By controlling the power semiconductor tip, the amplitude, phase, and frequency of the output voltage can be adjusted. The output voltage difference between the adjustable power supply and the fixed power supply is applied to both ends of the flexible loop device under test, which can fully simulate various types of working conditions of the two-way grid power supply.

[0042] 2) The present invention also provides a start-up sequence for each power supply in the test system and the flexible loop closing device under test, thereby ensuring the safety of the test process and meeting the working conditions of the tested product in actual power grid applications.

[0043] 3) The present invention also provides a test system current blocking test method, wherein the adjustable AC power supply can quickly reduce the output voltage to simulate a power grid failure, thereby evaluating the performance of the flexible loop closing device under test. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a structural schematic diagram of the flexible ring closing device test system of the present invention;

[0045] Figure 2 It is a schematic diagram of the AC, DC and AC power module of the adjustable AC power supply of the present invention;

[0046] Figure 3 It is a structural schematic diagram of an embodiment of a series-parallel flexible loop closing device;

[0047] Figure 4 It is a schematic diagram of the start-up process in the test method of the flexible loop closing device test system of the present invention;

[0048] Figure 5 It is a flow chart of the grid adaptability test method based on the flexible loop closing device test system;

[0049] Figure 6 The present invention is a flow chart of the current blocking test method of the loop closing device based on the flexible loop closing device test system. DETAILED DESCRIPTION

[0050] The specific implementation modes of the present invention will be further described in detail below in conjunction with the accompanying drawings.

[0051] like Figure 1 As shown, a flexible loop device test system, wherein the test system includes an adjustable AC power supply St, a first fixed AC power supply S1, a second fixed AC power supply S2 and a flexible loop device 1 to be tested, wherein one end of the flexible loop device is connected to the adjustable AC power supply, and the other end is connected to the first fixed AC power supply; the adjustable AC power supply includes a multi-winding transformer T1 and 3N AC / DC power modules 2, wherein N is an integer greater than or equal to 1, the primary side of the multi-winding transformer of the adjustable AC power supply is connected to the second fixed AC power supply, the multi-winding transformer includes 3N secondary windings, which are connected one-to-one with the input ends of the AC / DC power modules, the output ends of the 3N AC / DC power modules are cascaded in three phases, each phase is composed of N modules to form a commutation chain, one end of the three-phase commutation chain is connected to form a common end G, and the other end is connected to the reactor L and then led out as the output end of the adjustable power supply; the first fixed AC power supply and the second fixed AC power supply are AC power supplies whose output voltage and output frequency are not adjustable, the flexible loop device to be tested is connected between the power supplies, and the power flow between the power supplies is changed by adjusting the output voltage of the device.

[0052] Wherein: the AC-DC-AC power module includes a rectifier unit 3, an inverter unit 4 and a DC capacitor 5, the input end of the rectifier unit is connected to the secondary winding of the multi-winding transformer as the input end of the AC-DC-AC power module, and the output end is connected to the DC capacitor, the input end of the inverter unit is connected to the DC capacitor, and the output end serves as the output end of the AC-DC-AC power module.

[0053] Among them, the rectifier unit is a three-phase half-bridge rectifier circuit composed of 6 groups of power semiconductor devices or a full-bridge rectifier circuit composed of 4 groups of power semiconductor devices; the inverter unit is a full-bridge circuit composed of 4 groups of power semiconductor devices, and the inverter unit also includes a bypass switch 6.

[0054] The AC-DC-AC power module is implemented as follows Figure 2 shown.

[0055] The flexible loop-closing device under test is a series-parallel flexible loop-closing device or a back-to-back flexible loop-closing device composed of power semiconductor devices. The series-parallel flexible loop-closing device includes a series part 7 and a parallel part 8. The series part is a commutation chain composed of an H-bridge cascade, and the parallel part supplies energy to the series part. The back-to-back flexible loop-closing device includes two AC-DC converters, the DC sides of the AC-DC converters are connected together, and the AC sides are respectively connected to AC power supplies. Figure 3 The figure shows an embodiment of a series-parallel type flexible loop closing device.

[0056] Wherein: a switch K is also connected in series between the adjustable AC power supply and the flexible loop-closing device to be tested and / or between the first fixed AC power supply and the flexible loop-closing device to be tested.

[0057] Among them, the adjustable AC power supply also includes a control unit and a sampling unit. The sampling unit detects the AC voltage output by the first fixed AC power supply and sends the AC voltage sampling value to the control unit. The control unit sets the command value of the adjustable AC power supply output AC voltage according to the amplitude, frequency and phase of the AC voltage output by the first fixed AC power supply.

[0058] The present invention also provides a test method for the flexible loop closing device test system, characterized in that: the test method includes a start-up method, including the following steps:

[0059] Step 1: The first fixed AC power source is started;

[0060] Step 2: The second fixed AC power source is started;

[0061] Step 3: charging the DC capacitor in the AC / DC power module of the adjustable AC power supply;

[0062] Step 4: starting the rectifier unit in the AC / DC power module of the adjustable AC power supply to adjust the DC capacitor voltage to be stable;

[0063] Step 5: the inverter unit in the AC-DC-AC power module of the adjustable AC power supply is started, and the adjustable AC power supply outputs an AC voltage according to the command value of the output AC voltage;

[0064] Step 6: The flexible closed-loop device under test is started to adjust the current between the first fixed AC power source and the adjustable AC power source.

[0065] The startup method steps are as follows Figure 4 shown.

[0066] The test method includes a grid adaptability test method, which includes the following steps:

[0067] Step 1: The first fixed AC power supply and the adjustable AC power supply in the flexible loop closing device test system are started, and the series switch between the adjustable AC power supply and the flexible loop closing device under test and / or between the first fixed AC power supply and the flexible loop closing device under test is closed;

[0068] Step 2: The flexible loop closing device under test is started, and the output current, i.e., the current flowing through the connected reactor, is controlled to be zero;

[0069] Step 3: The control unit of the adjustable AC power supply calculates the amplitude given value U2 and the phase given value θ2 of the AC voltage output by the adjustable AC power supply according to the amplitude U1 and the phase θ1 of the AC voltage output by the first fixed AC power supply and the voltage amplitude difference set value ΔU and the phase angle difference set value Δθ applied to the two ends of the flexible loop closing device under test; the calculation formula is:

[0070] U2=U1–ΔU;

[0071] θ2 = θ1 – Δθ;

[0072] Output AC voltage according to the calculated AC voltage amplitude given value U2 and phase given value θ2

[0073] Step 4: After detecting the voltage difference and the phase angle difference, the flexible loop closing device under test adjusts its own output voltage and adjusts the current stability between the first fixed AC power source and the adjustable AC power source.

[0074] The steps of the grid adaptability test method are as follows: Figure 5 shown.

[0075] The test method further includes a current blocking test method, which includes the following steps:

[0076] Step 1: The first fixed AC power supply and the adjustable AC power supply in the flexible loop closing device test system are started;

[0077] Step 2: The flexible loop closing device under test is started, and the output current is controlled to be zero first, and then gradually adjusted to the rated value;

[0078] In a preferred embodiment of the present invention, the rated value is determined according to the rated current tolerance capability of the loop closing device under test;

[0079] Step 3: Adjust the output voltage of the adjustable AC power supply so that the output voltage drops rapidly to 0%-90% of the rated value.

[0080] Step 4: The voltage difference between the first fixed AC power source and the adjustable AC power source is applied to the flexible loop closing device under test, causing the current to rise rapidly;

[0081] Step 5: The power semiconductor device in the flexible loop closing device under test is quickly locked to block the current and detect the falling time of the current.

[0082] The current blocking test method steps are as follows Figure 6 shown.

[0083] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A flexible loop closing device test system, characterized in that: The test system includes an adjustable AC power supply, a first fixed AC power supply, a second fixed AC power supply and a flexible closed-loop device to be tested, wherein one end of the flexible closed-loop device is connected to the adjustable AC power supply, and the other end is connected to the first fixed AC power supply; the adjustable AC power supply includes a multi-winding transformer and 3N AC / DC power modules, wherein N is an integer greater than or equal to 1, the primary side of the multi-winding transformer of the adjustable AC power supply is connected to the second fixed AC power supply, the multi-winding transformer includes 3N secondary windings, which are connected one-to-one with the input ends of the AC / DC power modules, the output ends of the 3N AC / DC power modules are cascaded in three phases, each phase is composed of N modules to form a commutation chain, one end of the three-phase commutation chain is connected to form a common end, and the other end is connected to the reactor and then led out as the output end of the adjustable power supply; the first fixed AC power supply and the second fixed AC power supply are AC power supplies whose output voltage and output frequency are both unadjustable, and the flexible closed-loop device to be tested is connected between the power supplies, and the power flow between the power supplies on both sides is changed by adjusting the output voltage of the device.

2. A flexible loop closing device test system according to claim 1, characterized in that: The AC-DC-AC power module includes a rectifier unit, an inverter unit and a DC capacitor. The input end of the rectifier unit is connected to the secondary winding of the multi-winding transformer as the input end of the AC-DC-AC power module, and the output end is connected to the DC capacitor. The input end of the inverter unit is connected to the DC capacitor, and the output end serves as the output end of the AC-DC-AC power module.

3. A flexible loop closing device test system according to claim 2, characterized in that: The rectifier unit is a three-phase half-bridge rectifier circuit composed of 6 groups of power semiconductor devices or a full-bridge rectifier circuit composed of 4 groups of power semiconductor devices; the inverter unit is a full-bridge circuit composed of 4 groups of power semiconductor devices.

4. A flexible loop closing device test system according to claim 2 or 3, characterized in that: A bypass switch is arranged in parallel at the output end of each inverter unit.

5. A flexible loop closing device test system according to claim 1, characterized in that: The flexible loop closing device under test is a series-parallel flexible loop closing device or a back-to-back flexible loop closing device composed of power semiconductor devices. The series-parallel flexible loop closing device includes a series part and a parallel part. The series part is a commutation chain composed of an H-bridge cascade, and the parallel part supplies energy for the series part; the back-to-back flexible loop closing device includes two AC-DC converters, the DC sides of the AC-DC converters are connected together, and the AC sides are respectively connected to AC power supplies.

6. A flexible loop closing device test system according to claim 1, characterized in that: A switch is also connected in series between the adjustable AC power source and the flexible loop-closing device under test and / or between the first fixed AC power source and the flexible loop-closing device under test.

7. A flexible loop closing device test system according to claim 1, characterized in that: The adjustable AC power supply also includes a control unit and a sampling unit. The sampling unit detects the AC voltage output by the first fixed AC power supply and sends the AC voltage sampling value to the control unit. The control unit sets the command value of the adjustable AC power supply output AC voltage according to the amplitude, frequency and phase of the AC voltage output by the first fixed AC power supply.

8. A test method based on the flexible loop closing device test system according to any one of claims 1 to 7, characterized in that: The test method includes a startup method, which includes the following steps: Step 1: The first fixed AC power source is started; Step 2: The second fixed AC power source is started; Step 3: charging the DC capacitor in the AC / DC power module of the adjustable AC power supply; Step 4: starting the rectifier unit in the AC / DC power module of the adjustable AC power supply to adjust the DC capacitor voltage to be stable; Step 5: the inverter unit in the AC-DC-AC power module of the adjustable AC power supply is started, and the adjustable AC power supply outputs an AC voltage according to the command value of the output AC voltage; Step 6: The flexible closed-loop device under test is started to adjust the current between the first fixed AC power source and the adjustable AC power source.

9. A test method based on the flexible loop closing device test system according to any one of claims 1 to 7, characterized in that: The test method includes a grid adaptability test method, which includes the following steps: Step 1: The first fixed AC power supply and the adjustable AC power supply in the flexible loop closing device test system are started; Step 2: The flexible loop closing device under test is started, and the output current is controlled to be zero; Step 3: The control unit of the adjustable AC power supply calculates the amplitude given value U2 and the phase given value θ2 of the AC voltage output by the adjustable AC power supply according to the amplitude U1 and the phase θ1 of the AC voltage output by the first fixed AC power supply and the voltage amplitude difference set value ΔU and the phase angle difference set value Δθ applied to the two ends of the flexible loop closing device under test; the calculation formula is: U2=U1–ΔU; θ2 = θ1 – Δθ; Outputting an AC voltage according to the calculated amplitude given value U2 and phase given value θ2 of the AC voltage; Step 4: After detecting the voltage difference and the phase angle difference, the flexible loop closing device under test adjusts its own output voltage and adjusts the current stability between the first fixed AC power source and the adjustable AC power source.

10. A test method based on the flexible loop closing device test system according to any one of claims 1 to 7, characterized in that: The test method also includes a current blocking test method, comprising the following steps: Step 1: The first fixed AC power supply and the adjustable AC power supply in the flexible loop closing device test system are started; Step 2: The flexible loop closing device under test is started, and the output current is controlled to be zero first, and then gradually adjusted to the rated value; Step 3: Adjust the output voltage of the adjustable AC power supply so that the output voltage drops rapidly to 0%-90% of the rated value; Step 4: The voltage difference between the first fixed AC power source and the adjustable AC power source is applied to the flexible loop closing device under test, causing the current to rise rapidly; Step 5: The power semiconductor device in the flexible loop closing device under test is quickly locked to block the current and detect the falling time of the current.

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