A perturbation voltage generating device for grid-connected equipment port impedance characteristic measurement

Abstract

The application discloses a disturbance voltage generating device for grid-connected equipment port impedance characteristic measurement, comprising a rectifying unit, an inverting unit, an isolation unit, an output filter unit and a controller; the inverting unit comprises n groups of three-phase inverters; the isolation unit comprises three-phase transformers; the AC output ends of the three-phase inverters are respectively connected with the primary winding of the three-phase transformers; the secondary windings of the same phase of each three-phase transformer are connected in series to form a cascade branch, and the two ends of the cascade branch are connected to the output filter unit; the device realizes the inverting unit output voltage superposition through the secondary side cascade of the output side three-phase transformer, improves the equivalent switching frequency, realizes high-precision control output of a certain bandwidth range of harmonic voltage, can directly and accurately measure the wideband impedance characteristic of the grid-connected equipment port, effectively reduces the switching frequency of each group of inverters, improves the device output capacity, can reduce the insulation withstand voltage grade of the inverting unit and the rectifying unit to the ground, and makes the device smaller.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of grid-connected device testing, and in particular to a disturbance voltage generating device for measuring port impedance characteristics of a grid-connected device. BACKGROUND

[0002] With the increasing proportion of new energy power generation in the power system, the "double high" characteristics of high proportion of new energy and high proportion of power electronic devices are increasingly prominent, and the grid performance requirements of new energy power generation equipment are becoming higher and higher. Under this background, it is necessary to widely carry out research on the interaction characteristics, closed-loop effect and impedance characteristics of new energy power generation equipment and power grid, and to evaluate the adaptability, supportability and stability of new energy power generation equipment under various grid access conditions.

[0003] The existing new energy power generation impedance characteristic measuring devices have disturbance voltage injection type and disturbance current injection type, among which the disturbance voltage injection type device is divided into full voltage disturbance injection type and coupled voltage disturbance injection type. The full voltage disturbance injection type impedance characteristic measuring device generally uses a high-power inverter to simulate the grid voltage and harmonic disturbance voltage. During the test, the power generated by the measured device passes through the impedance characteristic measuring device entirely. Therefore, the capacity and volume of the full voltage disturbance injection type impedance characteristic measuring device are generally large. The coupled voltage disturbance injection type impedance characteristic measuring device generally uses a coupling transformer or a coupling capacitor to superimpose the harmonic disturbance voltage output by a small-capacity inverter in series on the grid voltage. In this scheme, the amplitude of the harmonic disturbance voltage is generally not high. During the test, only a small part of the power generated by the measured device passes through the impedance characteristic measuring device through the coupling branch. Compared with the full voltage disturbance injection type impedance characteristic measuring device, the capacity of the inverter in the coupled voltage disturbance injection type impedance characteristic measuring device can be greatly reduced, and the device volume is smaller, with very significant comprehensive advantages.

[0004] Chinese invention patent CN201811219105.0 discloses a high-voltage impedance characteristic measuring device based on a cascaded multi-level converter and a control method. The device includes a voltage disturbance injection unit, a signal processing unit, a wideband impedance calculation and monitoring unit, and a control unit. The voltage disturbance injection unit is composed of a plurality of power module units in cascade. Three phases are cascaded with n sub-power module units. Each unit takes power from the grid through a transformer with a ratio of k:1. Each phase is connected in series to the measured system after LC filtering to provide a voltage disturbance source. Each sub-power module unit is composed of a front-stage single-phase full-bridge rectifier and a rear-stage single-phase full-bridge inverter. In this invention patent, the DC link needs to be isolated by multiple paths, and the input uses a multi-winding transformer and a multi-path rectifier, so the system is complex. Moreover, the output voltage of the cascaded power module unit reaches 10kV, which will complicate the safety design of the power module unit.

[0005] The Chinese invention patent CN201811219289.0 discloses a high-voltage large-capacity impedance characteristic measuring device and a disturbance control method thereof. The input of the high-voltage large-capacity wide-band voltage disturbance injection device adopts a multi-winding phase-shifting transformer. Each winding of the secondary side of the phase-shifting transformer is connected with an AC / DC / AC power sub-module for three-phase uncontrolled rectification. The AC / DC / AC power sub-module is composed of three-phase uncontrolled rectification, a DC side capacitor and a single-phase H bridge. The output of the device adopts a cascading mode of multiple AC / DC / AC power sub-modules. The output side of the device is connected with an LC output filter and is connected in series with a 10kV / 35kV coupling transformer to the 35kV side line of the new energy power generation equipment to be measured, thereby providing a voltage disturbance source. The patent needs multiple isolation of the DC link, adopts a multi-winding transformer and multiple rectifiers for input, and the system is complex. Moreover, when the power unit is three-phase isolated, high-frequency pulsation appears on the DC voltage, which affects the output voltage precision.

[0006] The above two patents realize multi-path isolated DC power supply through a multi-winding input transformer and multiple rectifiers, and realize direct cascading of the output end through corresponding multiple inverters. The present application can provide single DC power supply through a single input transformer and rectifier, simultaneously connect multiple inverters, and form multi-level output through cascading of the secondary side after isolation of multiple output transformers. SUMMARY

[0007] The technical problem to be solved by the present application is to provide a coupled voltage disturbance injection type impedance characteristic measuring device. The equivalent switching frequency is improved through the secondary side transformer group cascading mode of the output side, the harmonic voltage in a certain bandwidth range is realized with high-precision control output, the wide-band impedance characteristic of the port of the grid-connected equipment can be directly and accurately measured, the switching frequency of a single inverter can be effectively reduced, the output capacity of the device is improved, the insulation withstand voltage level and the ground safety distance of the inverter in the device are reduced, and the device is smaller in size.

[0008] To solve the above technical problem, the present application provides a disturbance voltage generating device for measuring the impedance characteristic of the port of a grid-connected equipment, which comprises a rectifying unit, a chopping unit, an inverting unit, an isolating unit and an output filtering unit.

[0009] The inverting unit comprises n groups of three-phase inverters, the isolating unit comprises n three-phase transformers, and the output filtering unit comprises three groups of filtering capacitors.

[0010] The three-phase transformer comprises a primary winding and a secondary winding.

[0011] The AC output end of each three-phase inverter is connected to the primary winding of the corresponding three-phase transformer.

[0012] The same phase of the secondary winding of each of the three-phase transformers is connected in series to form a cascade form, and is connected in series between the power grid and the measured device through the output filter unit.

[0013] The switch signal of each group of three-phase inverters of the inverter unit is obtained by closed-loop control of the amplitude of the disturbance voltage output by the disturbance voltage generating device: the disturbance voltage output by the disturbance voltage generating device is detected and the amplitude thereof is calculated, the calculated disturbance voltage amplitude is corrected through a regulator, a three-phase disturbance voltage given instantaneous value is generated according to the corrected disturbance voltage amplitude, a three-phase disturbance voltage modulation wave is obtained according to the three-phase disturbance voltage given instantaneous value and the direct current voltage corresponding to the inverter unit, and the switch signal of each group of three-phase inverters of the inverter unit is generated according to the three-phase disturbance voltage modulation wave.

[0014] Wherein n≥2.

[0015] Preferably, the rectifier unit comprises at least one two-level structure rectifier or multi-level structure rectifier, the AC side of the rectifier is connected to an AC power supply, and the DC side is connected in parallel to the DC side of the inverter unit.

[0016] Preferably, the chopper unit comprises a power module connected to the DC side of the inverter unit and an energy consumption unit, when the DC side voltage rises beyond a protection setting value, the power module is triggered to act, energy is released through the energy consumption unit to reduce the DC side voltage.

[0017] Preferably, the disturbance voltage generating device further comprises a controller, the controller is in communication connection with the inverter unit, and controls the inverter unit to output at least a harmonic voltage of 1-1000 Hz.

[0018] Preferably, the three-phase inverter is a two-level structure three-phase full-bridge PWM inverter or a multi-level structure three-phase full-bridge PWM inverter, the three-phase full-bridge PWM inverter comprises 6 bridge arms, each two of the bridge arms are taken as a group, and there are 3 groups in total, the AC output ends of the 3 groups of bridge arms are respectively connected to the two ends of the primary winding of one of the three-phase transformers; or, the three-phase inverter is a two-level structure three-phase half-bridge PWM inverter or a multi-level structure three-phase half-bridge PWM inverter, the three-phase half-bridge PWM inverter comprises 3 bridge arms, the AC output ends of the 3 bridge arms are respectively connected to one end of the primary winding of one of the three-phase transformers, and the other end of the primary winding of the three-phase transformer is connected together.

[0019] Preferably, the three-phase transformer adopts a three-phase four-core column structure or a three-phase five-core column structure or a three-phase group structure.

[0020] Preferably, the three-phase transformer adopts a three-phase three-core column structure.

[0021] Preferably, the AC power source connected with the rectifier unit is provided by a step-down transformer connected with the power grid.

[0022] Preferably, the AC power source connected with the rectifier unit is provided by a mobile power station, which includes a diesel generator or a storage power supply.

[0023] Preferably, the "closed-loop control of the output disturbance voltage amplitude of the disturbance voltage generator" specifically refers to:

[0024] receiving the user-set disturbance voltage amplitude, disturbance frequency and disturbance phase.

[0025] detecting the output disturbance voltage, and calculating the disturbance voltage amplitude at the user-set disturbance frequency by a fast Fourier transform method;

[0026] comparing the calculated disturbance voltage amplitude with the user-set disturbance voltage amplitude, and correcting the disturbance voltage amplitude;

[0027] generating three-phase disturbance voltage given instantaneous values according to the corrected disturbance voltage amplitude, the user-set disturbance frequency and the disturbance phase;

[0028] obtaining three-phase disturbance voltage modulation waves according to the three-phase disturbance voltage given instantaneous values and the DC voltage of the corresponding inverter unit;

[0029] generating the switching signals of the three-phase inverters in each inverter unit by carrier phase-shifted pulse width modulation according to the three-phase disturbance voltage modulation waves.

[0030] Preferably, the "comparing the calculated disturbance voltage amplitude with the user-set disturbance voltage amplitude, and correcting the disturbance voltage amplitude" includes:

[0031]

[0032] wherein, ΔU Aadj , ΔU Badj , ΔU Cadj is the product of the difference between the calculated disturbance voltage amplitude and the user-set disturbance voltage amplitude and the regulator gain coefficient K, U Aset , U Bset , U Cset is the user-set ABC three-phase disturbance voltage amplitude, U Afft , U Bfft , U Cfft is the ABC three-phase disturbance voltage amplitude at the user-set disturbance frequency calculated by the fast Fourier transform method from the sampled actual output voltage, and K is the regulator gain coefficient.

[0033] Preferably, the "generating three-phase disturbance voltage given instantaneous value according to the modified disturbance voltage amplitude, user-set disturbance voltage amplitude, disturbance frequency and disturbance phase" comprises:

[0034]

[0035] wherein θ Aset , θ Bset , θ Cset are ABC three-phase voltage phases, f set is the disturbance voltage frequency, u Aref , u Bref , u Cref are three-phase disturbance voltage given instantaneous values.

[0036] After using the above device, the disturbance voltage generating device for grid-connected equipment port impedance characteristic measurement comprises a rectifying unit, a chopping unit, an inverting unit, an isolating unit and an output filter unit; the inverting unit comprises n groups of three-phase inverters; the isolating unit comprises n three-phase transformers; the output filter unit comprises three groups of filter capacitors; the three-phase transformer comprises a primary winding and a secondary winding; the AC output ends of each three-phase inverter are respectively connected to the primary windings of the corresponding three-phase transformers; the secondary windings of each three-phase transformer are connected in series in the same phase to form a cascade form, and are connected in series between the power grid and the measured device through the output filter unit; the amplitude of the disturbance voltage output by the disturbance voltage generating device is closed-loop controlled to obtain the switching signals of each group of three-phase inverters of the inverting unit; the disturbance voltage output by the disturbance voltage generating device is detected and its amplitude is calculated, the calculated disturbance voltage amplitude is modified through a regulator, three-phase disturbance voltage given instantaneous values are generated according to the modified disturbance voltage amplitude, three-phase disturbance voltage modulation waves are obtained according to the three-phase disturbance voltage given instantaneous values and the DC voltage corresponding to the inverting unit, and the switching signals of each group of three-phase inverters of the inverting unit are generated according to the three-phase disturbance voltage modulation waves; the disturbance voltage generating device for grid-connected equipment port impedance characteristic measurement realizes inverter unit output voltage superposition through the cascade of the output transformer group secondary side, greatly improves the equivalent switching frequency, realizes high-precision control output of a certain bandwidth range of harmonic voltage, can directly and accurately measure the wideband impedance characteristic of the grid-connected equipment port, at the same time, the cascade of the output transformer group secondary side can effectively reduce the switching frequency of a single inverter, improve the output capacity of the device, realize isolation from the high-voltage system through the output transformer group, reduce the insulation withstand voltage level and the safety distance of the inverter unit, the rectifying unit and the like in the device to the ground, and make the device smaller in size. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 System configuration diagram of a prior art high-voltage impedance measurement device based on a cascade multi-level converter

[0038] Figure 2 System configuration diagram of prior art high-voltage large-capacity impedance measurement device

[0039] Figure 3 System configuration diagram of the first embodiment of the disturbance voltage generating device for measuring the port impedance characteristics of grid-connected equipment according to the present application;

[0040] Figure 4 System configuration diagram of the fifth embodiment of the disturbance voltage generating device for measuring the port impedance characteristics of grid-connected equipment according to the present application;

[0041] Figure 5 System configuration diagram of the sixth embodiment of the disturbance voltage generating device for measuring the port impedance characteristics of grid-connected equipment according to the present application;

[0042] Figure 6 Control diagram of the seventh embodiment of the disturbance voltage generating device for measuring the port impedance characteristics of grid-connected equipment according to the present application. DETAILED DESCRIPTION

[0043] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and should not be used to limit the present application.

[0044] Embodiment 1

[0045] Please refer to Figure 3 , Figure 3 System configuration diagram of the first embodiment of the disturbance voltage generating device for measuring the port impedance characteristics of grid-connected equipment according to the present application;

[0046] The present embodiment discloses a disturbance voltage generating device for measuring the port impedance characteristics of grid-connected equipment, which comprises a rectifying unit, a chopping unit, an inverting unit, an isolating unit and an output filtering unit.

[0047] The inverting unit comprises n groups of three-phase inverters; the isolating unit comprises n three-phase transformers; and the output filtering unit comprises three groups of filtering capacitors.

[0048] The three-phase transformer comprises a primary winding and a secondary winding.

[0049] The AC output end of each three-phase inverter is connected to the primary winding of the corresponding three-phase transformer.

[0050] The secondary windings of each three-phase transformer are connected in series in the same phase to form a cascaded form, and are connected in series between the power grid and the measured equipment through the output filtering unit.

[0051] The switch signal of each group of three-phase inverters of the inverter unit is obtained by closed-loop control of the amplitude of the disturbance voltage output by the disturbance voltage generating device: the disturbance voltage output by the disturbance voltage generating device is detected and its amplitude is calculated, the calculated disturbance voltage amplitude is corrected by a regulator, three-phase disturbance voltage given instantaneous values are generated according to the corrected disturbance voltage amplitude, three-phase disturbance voltage modulation waves are obtained according to the three-phase disturbance voltage given instantaneous values and the DC voltage corresponding to the inverter unit, and the switch signal of each group of three-phase inverters of the inverter unit is generated according to the three-phase disturbance voltage modulation waves.

[0052] wherein n≥2.

[0053] In the embodiment, the rectifier unit comprises at least one two-level structure rectifier or multi-level structure rectifier, the AC side of the rectifier is connected to an AC power supply, and the DC side is connected in parallel to the DC side of the inverter unit.

[0054] The chopping unit comprises a power module connected to the DC side of the inverter unit and an energy consumption unit, when the DC side voltage rises beyond a protection setting value, the power module is triggered to act, energy is released through the energy consumption unit, and the DC side voltage is reduced.

[0055] Embodiment two

[0056] The embodiment is based on embodiment one, in the embodiment, the three-phase inverter is a two-level structure three-phase full-bridge PWM inverter or a multi-level structure three-phase full-bridge PWM inverter, the three-phase full-bridge PWM inverter comprises six bridge arms, each two bridge arms are taken as one group, and there are three groups in total, and the AC output ends of the three groups of bridge arms correspond to the two ends of the primary winding of one three-phase transformer respectively.

[0057] Embodiment three

[0058] The embodiment is based on embodiment one, in the embodiment, the three-phase inverter is a two-level structure three-phase half-bridge PWM inverter or a multi-level structure three-phase half-bridge PWM inverter, the three-phase half-bridge PWM inverter comprises three bridge arms, the AC output ends of the three bridge arms correspond to one end of the primary winding of one three-phase transformer respectively, and the other end of the primary winding of the three-phase transformer is connected together.

[0059] Embodiment four

[0060] The embodiment is based on the embodiment one, in the embodiment, the AC power supply is connected to the power grid through a step-down transformer, at this time, the operation of the rectifier unit will affect the voltage of the connection port of the disturbance voltage generating device and the measured device;Or the AC power supply is provided by a mobile power station, the mobile power station includes a diesel generator or a storage power supply, at this time, the operation of the rectifier unit will not affect the voltage of the connection port of the disturbance voltage generating device and the measured device, and the performance of the disturbance voltage generating device is more optimal.

[0061] Embodiment five

[0062] Please refer to Figure 4 , Figure 4 The system structure diagram of the disturbance voltage generating device for the grid-connected device port impedance characteristic measurement according to the embodiment five of the present application is shown in the figure.

[0063] The embodiment discloses a disturbance voltage generating device for grid-connected device port impedance characteristic measurement, which comprises a rectifier unit, an inverter unit, a chopping unit, an isolation unit and an output filter unit.

[0064] The inverter unit comprises n groups of three-phase inverters;The isolation unit comprises n three-phase transformers;The output filter unit comprises three groups of filter capacitors.

[0065] The three-phase transformer comprises a primary winding and a secondary winding.

[0066] The rectifier unit is composed of a two-level structure rectifier, the AC side of the rectifier is connected to the power grid through a step-down transformer, and the DC side is connected in parallel to the DC side of each group of three-phase inverters in the inverter unit.

[0067] The three-phase inverter is a two-level structure three-phase full-bridge PWM inverter, which comprises 6 bridge arms, wherein each two bridge arms are taken as a group, and a total of 3 groups are divided, wherein the AC output ends A1 and A2 of the first group of bridge arms correspond to the two ends of the primary side A-phase winding of a three-phase transformer, the AC output ends B1 and B2 of the second group of bridge arms correspond to the two ends of the primary side B-phase winding of the three-phase transformer, and the AC output ends C1 and C2 of the third group of bridge arms correspond to the two ends of the primary side C-phase winding of the three-phase transformer respectively. The same phase of the secondary winding of each three-phase transformer is connected in series to form a cascade form, and is connected in series between the power grid and the measured device through the output filter unit.

[0068] The switch signal of each group of three-phase inverters of the inverter unit is obtained by closed-loop control of the amplitude of the disturbance voltage output by the disturbance voltage generating device: the disturbance voltage output by the disturbance voltage generating device is detected and its amplitude is calculated, the calculated disturbance voltage amplitude is corrected by a regulator, three-phase disturbance voltage given instantaneous values are generated according to the corrected disturbance voltage amplitude, three-phase disturbance voltage modulation waves are obtained according to the three-phase disturbance voltage given instantaneous values and the DC voltage corresponding to the inverter unit, and the switch signal of each group of three-phase inverters of the inverter unit is generated according to the three-phase disturbance voltage modulation waves.

[0069] wherein n≥2.

[0070] In the embodiment, the disturbance voltage generating device further comprises a controller, which is in communication connection with the inverter unit and controls the inverter unit to output a harmonic voltage comprising at least 1-1000 Hz.

[0071] In the embodiment, the three-phase transformer adopts a three-phase four-core column structure or a three-phase five-core column structure or a three-phase group structure.

[0072] Embodiment six

[0073] Please refer to Figure 5 , Figure 5 System structure diagram of the disturbance voltage generating device for grid-connected equipment port impedance characteristic measurement according to the sixth embodiment of the present application;

[0074] The present embodiment discloses a disturbance voltage generating device for grid-connected equipment port impedance characteristic measurement, which comprises a rectifier unit, an inverter unit, a chopping unit, an isolation unit and an output filter unit.

[0075] The inverter unit comprises n groups of three-phase inverters; the isolation unit comprises n three-phase transformers; and the output filter unit comprises three groups of filter capacitors.

[0076] The three-phase transformer comprises a primary winding and a secondary winding.

[0077] The rectifier unit is composed of a two-level structure rectifier, the AC side of the rectifier is connected with an energy storage power supply, and the DC side is connected in parallel with the DC side of each group of three-phase inverters in the inverter unit.

[0078] The three-phase inverter is a three-phase half-bridge PWM inverter with two-level structure, which comprises three bridge arms, and the AC output ends of the three bridge arms are respectively connected to one end of the primary winding of one three-phase transformer, and the other end of the primary winding of the three-phase transformer is connected together.

[0079] The switch signals of each group of three-phase inverters of the inverter unit are obtained by closed-loop control of the amplitude of the disturbance voltage output by the disturbance voltage generating device: the disturbance voltage output by the disturbance voltage generating device is detected and the amplitude thereof is calculated, the calculated disturbance voltage amplitude is corrected by a regulator, a three-phase disturbance voltage given instantaneous value is generated according to the corrected disturbance voltage amplitude, a three-phase disturbance voltage modulation wave is obtained according to the three-phase disturbance voltage given instantaneous value and the DC voltage corresponding to the inverter unit, and the switch signals of each group of three-phase inverters of the inverter unit are generated according to the three-phase disturbance voltage modulation wave.

[0080] Wherein n≥2.

[0081] In the embodiment, the disturbance voltage generating device further comprises a controller, which is in communication connection with the inverter unit and controls the inverter unit to output at least a harmonic voltage of 1”1000 Hz.

[0082] In the embodiment, the three-phase transformer adopts a three-phase three-core column structure.

[0083] Embodiment Seven

[0084] Please refer to Figure 6 , Figure 6 The control diagram of the disturbance voltage generating device for measuring the port impedance characteristics of the grid-connected device according to Embodiment Seven of the present application.

[0085] The embodiment is based on any one of Embodiments One to Six, and in the embodiment, the closed-loop control of the amplitude of the disturbance voltage output by the disturbance voltage generating device to obtain the switch signals of each inverter unit specifically comprises:

[0086] Receiving the disturbance voltage amplitude, disturbance frequency and disturbance phase set by the user;

[0087] Detecting the output disturbance voltage of the disturbance voltage generating device, and calculating the disturbance voltage amplitude at the set disturbance frequency by the fast Fourier transform method;

[0088] Comparing the calculated disturbance voltage amplitude with the disturbance voltage amplitude set by the user, and correcting the disturbance voltage amplitude according to the error, which comprises:

[0089]

[0090] wherein, ΔU Aadj , ΔU Badj , ΔU Cadj is the product of the difference between the calculated disturbance voltage amplitude and the user-set disturbance voltage amplitude and the regulator gain coefficient K, i.e. the corrected disturbance voltage amplitude, U Aset , U Bset , U Cset is the user-set ABC three-phase disturbance voltage amplitude, U Afft , U Bfft , U Cfft is the ABC three-phase disturbance voltage amplitude at the set disturbance frequency calculated by FFT sampling the actual output voltage, and K is the regulator gain coefficient;

[0091] According to the corrected disturbance voltage amplitude, the user-set disturbance voltage amplitude, the disturbance frequency and the disturbance phase, a three-phase disturbance voltage given instantaneous value is generated, comprising:

[0092]

[0093] wherein, θ Aset , θ Bset , θ Cset is the ABC three-phase voltage phase, f set is the disturbance voltage frequency, u Aref , u Bref , u Cref is the three-phase disturbance voltage given instantaneous value;

[0094] According to the three-phase disturbance voltage given instantaneous value and the DC voltage of the corresponding inverter unit, a three-phase disturbance voltage modulation wave is obtained:

[0095]

[0096] wherein, V dcA , V dcB and V dcC is the DC voltage of the corresponding inverter unit;

[0097] According to the three-phase disturbance voltage modulation wave component, and after carrier phase-shifted PWM modulation, the switching signal of the three-phase inverter in each inverter unit can be obtained.

[0098] The disturbance voltage generating device for grid-connected equipment port impedance characteristic measurement realizes inverter unit output voltage superposition through output transformer group secondary side cascade, greatly improves equivalent switching frequency, realizes high-precision control output certain bandwidth range harmonic voltage, can directly and accurately measure wide frequency impedance characteristic of grid-connected equipment port, simultaneously, through output transformer group secondary side cascade, switching frequency of single inverter can be effectively reduced, output capacity of the device is improved, through output transformer group, isolation with high-voltage system is realized, insulation withstand voltage grade and safety regulation distance of the inverter unit, rectifier unit and the like in the device to ground are reduced, so that the device is smaller in size.

Claims

1. A perturbation voltage generating device for grid connected equipment port impedance characteristic measurement, characterized in that, The rectifying unit, the chopping unit, the inverting unit, the isolating unit and the output filter unit are included. The inverting unit includes n groups of three-phase inverters, and the isolating unit includes n three-phase transformers, wherein n≥2. The output filter unit includes three groups of filter capacitors. The three-phase transformer includes a primary winding and a secondary winding. The AC output ends of the three-phase inverters are respectively connected to the primary windings of the corresponding three-phase transformers. The same phase of the secondary windings of each three-phase transformer is connected in series to form a cascade form, and is connected in series between the power grid and the measured device through the output filter unit. The switch signals of the three-phase inverters of the inverting unit are obtained by closed-loop control of the amplitude of the disturbance voltage output by the disturbance voltage generator, including: Receiving the user-set disturbance voltage amplitude, disturbance frequency and disturbance phase; Detecting the disturbance voltage output by the disturbance voltage generator, and calculating the disturbance voltage amplitude at the set disturbance frequency by the fast Fourier transform method; Comparing the calculated disturbance voltage amplitude with the user-set disturbance voltage amplitude, and correcting the disturbance voltage amplitude; Generating a three-phase disturbance voltage given instantaneous value according to the corrected disturbance voltage amplitude, the user-set disturbance voltage amplitude, the disturbance frequency and the disturbance phase; Generating a three-phase disturbance voltage modulation wave according to the three-phase disturbance voltage given instantaneous value and the DC voltage of the corresponding inverting unit; Generating the switch signals of the three-phase inverters in each inverting unit through carrier phase-shifted pulse width modulation according to the three-phase disturbance voltage modulation wave.

2. The perturbation voltage generating device for grid-tied equipment port impedance characteristic measurement according to claim 1, characterized in that, The rectifying unit includes at least one two-level structure rectifier or multi-level structure rectifier, the AC side of the rectifier is connected to an AC power supply, and the DC side is connected in parallel to the DC side of the inverting unit.

3. The perturbation voltage generating device for grid-tied equipment port impedance characteristic measurement according to claim 1, characterized in that, The chopping unit includes a power module connected to the DC side of the inverting unit and an energy consumption unit, when the DC side voltage rises above the protection setting value, the power module is triggered to act, and the energy consumption unit releases energy to reduce the DC side voltage.

4. The perturbation voltage generating device for grid-tied equipment port impedance characteristic measurement of claim 2, wherein: The disturbance voltage generator further includes a controller, which is in communication connection with the inverting unit and controls the inverting unit to output at least a harmonic voltage of 1-1000 Hz.

5. The perturbation voltage generating device for grid-tied equipment port impedance characteristic measurement according to any one of claims 1 to 4, characterized in that, The three-phase inverter is a two-level structure three-phase full-bridge PWM inverter or a multi-level structure three-phase full-bridge PWM inverter, which includes six bridge arms, every two bridge arms are taken as a group, and there are three groups in total, and the AC output ends of the three groups of bridge arms are respectively connected to the two ends of the primary winding of one three-phase transformer.

6. The perturbation voltage generating device for grid-tied equipment port impedance characteristic measurement according to claim 5, characterized in that, The three-phase transformer adopts a three-phase four-core column structure or a three-phase five-core column structure or a three-phase group structure.

7. The perturbation voltage generating device for grid-tied equipment port impedance characteristic measurement according to any one of claims 1 to 4, characterized in that, The three-phase inverter is a two-level structure three-phase half-bridge PWM inverter or a multi-level structure three-phase half-bridge PWM inverter, which includes three bridge arms, and the AC output ends of the three bridge arms are respectively connected to one end of the primary winding of one three-phase transformer, and the other end of the primary winding of the three-phase transformer is connected together.

8. The perturbation voltage generating device for grid-tied equipment port impedance characteristic measurement according to claim 7, characterized in that, The three-phase transformer adopts a three-phase three-core column structure.

9. The perturbation voltage generating device for grid-tied equipment port impedance characteristic measurement according to claim 2, characterized in that, The AC power supply is connected to the power grid through a step-down transformer.

10. The perturbation voltage generating device for grid-tied equipment port impedance characteristic measurement according to claim 2, characterized in that, The AC power supply is provided by a mobile power station, which includes a diesel generator or a storage power supply.

11. The perturbation voltage generating device for grid-tied equipment port impedance characteristic measurement according to claim 1, characterized in that, The "generating three-phase disturbance voltage given instantaneous values according to the corrected disturbance voltage amplitude, user-set disturbance voltage amplitude, disturbance frequency, and disturbance phase" includes: where θ Aset , θ Bset , θ Cset are the ABC three-phase voltage phases, f set is the disturbance voltage frequency, u Aref , u Bref , u Cref are the given instantaneous values of the three-phase disturbance voltage, U Aset , U Bset , U Cset are the user-set ABC three-phase disturbance voltage amplitudes, ΔU Aadj , ΔU Badj , ΔU Cadj are the products of the difference between the calculated disturbance voltage amplitudes and the user-set disturbance voltage amplitudes and the regulator gain coefficient K, i.e. the corrected disturbance voltage amplitudes.

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