Unified power quality conditioner topological structure based on frequency division multiplexing technology and control method thereof

Abstract

The invention relates to a frequency division multiplexing technology-based unified power quality conditioner topological structure and a control method thereof, and the topological structure comprises a parallel AC side converter and a series AC side converter, the AC end of the parallel AC side converter is connected with a parallel AC side filter and a three-phase resonant cavity at the same time; the parallel AC side converter is multiplexed as a power frequency and high frequency output end and realizes energy interaction with the parallel AC side and the three-phase resonant cavity in a frequency division multiplexing mode, and a DC end of the parallel AC side converter is connected with a parallel AC side DC capacitor; the alternating-current end of the series alternating-current side converter is simultaneously connected with the series alternating-current side filter and the three-phase resonant cavity to be multiplexed as a power frequency and high-frequency output end, energy interaction with the series alternating-current side and the three-phase resonant cavity is realized in a frequency division multiplexing mode, and the direct-current end of the series alternating-current side converter is connected with the series alternating-current side direct-current capacitor. Compared with the prior art, the power density can be ensured, meanwhile, the equipment structure complexity is reduced, and the construction cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a unified power quality conditioner topology structure based on frequency division multiplexing technology and a control method thereof. Background Art

[0002] Due to the widespread application of a large number of power electronic devices, the nonlinear loads in the power transmission and distribution links and power terminals have increased significantly, causing the current and voltage waveforms of the power grid to change, resulting in harmonic pollution of the power grid, affecting the safe and stable operation of the power grid. Especially in the low-voltage distribution network in rural or urban areas, due to the long lines and diversified loads, there are many power quality problems such as low power factor, three-phase imbalance, unqualified voltage, harmonics, etc., which seriously affect the power supply quality. Unified Power Quality Conditioner (UPQC) is a power quality regulation device with comprehensive compensation function. It combines series active filters and parallel active filters, so as to give full play to the advantages of series and parallel active filters in power system applications, and has comprehensive power quality regulation functions. With the increasingly serious power quality problems today, this is undoubtedly a device with broad application prospects.

[0003] Traditional UPQC requires an industrial frequency transformer on the series AC side. The presence of the industrial frequency transformer seriously affects the power density of the equipment. For this reason, existing research has adopted a high-frequency isolation transformer on the DC port to significantly improve the power density of the equipment. The current conventional high-frequency isolated UPQC consists of three stages: a series AC side converter, a high-frequency isolated DC-DC, and a parallel AC side converter. Its structure is complex and the cost is high. Summary of the invention

[0004] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a unified power quality conditioner topology structure and control method based on frequency division multiplexing technology, which can reduce the complexity of the equipment structure and reduce the construction cost while ensuring the power density.

[0005] The object of the present invention can be achieved by the following technical solutions: a unified power quality conditioner topology based on frequency division multiplexing technology, including a parallel AC side converter and a series AC side converter, the AC end of the parallel AC side converter is simultaneously connected to the parallel AC side filter and the three-phase resonant cavity to be multiplexed as the industrial frequency and high-frequency output end, and energy interaction is achieved with the parallel AC side and the three-phase resonant cavity by frequency division multiplexing, and the DC end of the parallel AC side converter is connected to the parallel AC side DC capacitor;

[0006] The AC end of the series AC side converter is simultaneously connected to the series AC side filter and the three-phase resonant cavity to be multiplexed as the industrial frequency and high-frequency output end, and energy interaction is achieved with the series AC side and the three-phase resonant cavity through frequency division multiplexing. The DC end of the series AC side converter is connected to the series AC side DC capacitor.

[0007] Furthermore, one end of the parallel AC side filter is connected to the three-phase power grid, and the other end is connected to the AC end of the parallel AC side converter.

[0008] Furthermore, one end of the series AC side filter is connected to the three-phase power grid, and the other end is connected to the AC end of the series AC side converter.

[0009] Furthermore, a high-frequency transformer is embedded in the three-phase resonant cavity to achieve high-frequency isolation.

[0010] Furthermore, the parallel AC side filter adopts an L structure or an LCL structure.

[0011] Furthermore, the series AC side filter adopts an LC structure.

[0012] Furthermore, the parallel AC side converter adopts a three-phase full-bridge structure, wherein the power switch device adopts an IGBT power switch device, a SiC power switch device, a GaN power switch device or a MOSFET power switch device.

[0013] Furthermore, the series AC side converter includes three H-bridges, wherein the power switch devices are IGBT power switch devices, SiC power switch devices, GaN power switch devices or MOSFET power switch devices.

[0014] A control method for a unified power quality conditioner topology based on frequency division multiplexing technology includes a series side AC voltage control method and a parallel side AC current control method, which are used to correspondingly adjust the carrier phase difference of the series AC side converter and the carrier phase difference of the parallel AC side converter to achieve power size and direction regulation of high-frequency pulse electric energy.

[0015] Furthermore, the series side AC voltage control method specifically uses a series side voltage sensor to collect grid voltage information, determines the grid phase through a phase-locked loop technology, and then generates a standard grid voltage according to the grid phase, and makes a difference between the standard grid voltage and the actual grid voltage to serve as a series side voltage compensation reference value;

[0016] The parallel side AC current control method specifically uses the parallel side current sensor to collect grid current information, performs Park transformation on the grid current according to the grid phase, performs inverse Park transformation on the q-axis current obtained after Park transformation to obtain the active current component, and then makes a difference between the actual grid current and the active current component to serve as a parallel side current compensation reference value.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] The present invention proposes a unified power quality conditioner topology structure, including a parallel AC side converter and a series AC side converter, wherein the AC end of the parallel AC side converter is simultaneously connected to the parallel AC side filter and the three-phase resonant cavity, so as to be multiplexed as the power frequency and high frequency output end, and realizes energy interaction with the parallel AC side and the three-phase resonant cavity by frequency division multiplexing; the AC end of the series AC side converter is also simultaneously connected to the series AC side filter and the three-phase resonant cavity, so as to be multiplexed as the power frequency and high frequency output end, and realizes energy interaction with the series AC side and the three-phase resonant cavity by frequency division multiplexing. The series and parallel AC side converters adopt a high power frequency chopping method according to the corresponding AC modulation ratio instruction to chop the DC capacitor voltage of the AC side into a high power frequency mixed pulse electric energy with adjustable duty cycle. After the high power frequency mixed pulse electric energy passes through the three-phase resonant cavity, the high frequency fundamental component is separated from the high power frequency mixed pulse electric energy waveform by the three-phase resonant cavity, and only the high frequency electric energy is retained. Thus, low cost, high power density and high performance unified power quality regulation are achieved.

[0019] The present invention designs a series side AC voltage control method and a parallel side AC current control method to achieve unified power quality regulation, wherein the series side AC voltage control method uses a series side voltage sensor to collect grid voltage information, determines the grid phase through a phase-locked loop technology, and then generates a standard grid voltage according to the grid phase. The standard grid voltage is subtracted from the actual grid voltage to serve as a series side voltage compensation reference value; the parallel side AC current control method uses a parallel side current sensor to collect grid current information, performs Park transformation on the grid current according to the grid phase, and then performs an inverse Park transformation on the q-axis current obtained after the Park transformation to obtain an active current component, and then subtracts the actual grid current from the active current component to serve as a parallel side current compensation reference value. Thus, the phase difference of the carriers of the series and parallel AC side converters is correspondingly adjusted through real-time feedback, thereby accurately achieving the power size and direction regulation of high-frequency pulse electric energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the topological structure of the unified power quality conditioner in the present invention;

[0021] Figure 2It is a control block diagram of the unified power quality conditioner in the present invention. DETAILED DESCRIPTION

[0022] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] Example

[0024] like Figure 1 As shown, a unified power quality conditioner topology based on frequency division multiplexing technology includes:

[0025] Parallel AC side filter: The parallel AC side filter can adopt L, LCL and other structures, one end of which is connected to the three-phase grid, and the other end is connected to the three-phase full-bridge AC end of the AC side converter;

[0026] The parallel AC side converter consists of a three-phase full bridge. The AC end of the three-phase full bridge is multiplexed as the power frequency and high frequency output end. It is also connected to the parallel AC side filter and the three-phase resonant cavity. Energy interaction is achieved with the parallel AC side and the resonant cavity by frequency division multiplexing. The DC end of the three-phase full bridge is connected to the parallel AC side DC capacitor.

[0027] A parallel AC side DC capacitor, wherein the parallel AC side DC capacitor is connected to the DC end of the parallel AC side converter, and the output of the DC end of the parallel AC side converter is controlled to a stable voltage by using the voltage of the parallel AC side DC capacitor;

[0028] A three-phase resonant cavity, one end of the three-phase resonant cavity is connected to the AC end of the parallel AC side converter, and the other end is connected to the AC end of the series AC side converter;

[0029] A high-frequency transformer is embedded in the three-phase resonant cavity and is used to achieve high-frequency isolation of the circuit;

[0030] The series AC side converter consists of three H-bridges. The AC ends of the three H-bridges are multiplexed as power frequency and high frequency output ends, and are connected to the series AC side filter and the three-phase resonant cavity at the same time. Energy interaction is achieved with the series AC side and the resonant cavity by frequency division multiplexing. The DC end of the three-phase full bridge is connected to the series AC side DC capacitor.

[0031] The AC side filter is connected in series, and the AC side filter is connected in parallel, which is composed of three LC filters, one end of which is connected to the three-phase grid, and the other end is connected to the three H-bridge AC terminals of the AC side converter;

[0032] The series AC side DC capacitor is connected to the DC end of the series AC side converter, and the series AC side DC capacitor is used to control the output of the DC end of the series AC side converter to a stable voltage.

[0033] This solution is designed to connect a three-phase resonant cavity in series between the series-parallel AC side AC link and the high-frequency transformer. The three-phase resonant cavity is used to separate the high-frequency fundamental component from the high-frequency mixed pulse power waveform generated by the series-parallel AC side converter, so that only high-frequency power flows to the high-frequency transformer.

[0034] In practical applications, the power switch devices in the series AC side converter and the parallel AC side converter can be selected from any one of IGBT power switch devices, SiC power switch devices, GaN power switch devices or MOSFET power switch devices. The power switch devices of the series AC side converter and the parallel AC side converter use the same high-frequency switching frequency. The series AC side converter and the parallel AC side converter use high power frequency chopping according to their respective AC modulation ratio instructions to chop the AC side DC capacitor voltage into high power frequency mixed pulse electric energy with adjustable duty cycle. After the high power frequency mixed pulse electric energy passes through the three-phase resonant cavity, only the remaining high-frequency electric energy passes through the high-frequency transformer, and only the remaining power frequency electric energy passes through the AC side filter.

[0035] The control block diagram of the unified power quality conditioner is as follows: Figure 2 As shown, the power size and direction of the high-frequency pulse electric energy can be regulated by adjusting the carrier phase difference between the series AC side converter and the parallel AC side converter.

[0036] Specifically, for the parallel AC side converters:

[0037] It is necessary to ensure that the voltage of the DC capacitor on the parallel AC side is stable, and at the same time, it is necessary to ensure that the output current can compensate for the reactive current and harmonic current of the power grid.

[0038] The DC capacitor voltage on the parallel AC side adopts feedback control. Its voltage regulator calculates the active current given instruction on the parallel AC side based on the voltage given value and feedback value.

[0039] At the same time, the current sensor collects the grid current i pabc , according to the grid phase, the grid current is Park transformed. The q-axis current obtained after Park transformation is Park inversely transformed to obtain the active current component i active , the difference between the actual grid current and the active current component is used as the parallel side current compensation reference value

[0040]

[0041] The active current is given Reactive power and harmonic compensation current Add them together to get the sum, and get the output current given by the AC port on the parallel side:

[0042]

[0043] Output current setting and AC current feedback value i pabc The difference is made, and the modulated wave is obtained through the current regulator. After SPWM adjustment, the output PWM wave drives the power switching device of the parallel side module.

[0044] For the series side converter:

[0045] It is necessary to ensure that the output voltage can compensate for the grid voltage so that the compensated output voltage is the rated voltage of the grid. At the same time, it is necessary to ensure that the voltage of the DC capacitor on the series AC side is stable.

[0046] The voltage sensor collects the grid voltage v abc , determine the grid phase through phase-locked loop technology. According to the grid phase, generate the standard grid voltage V rate ∠θ, the standard grid voltage V rate The difference between ∠θ and the actual grid voltage is used as the reference value for series side voltage compensation

[0047]

[0048] The voltage regulator is based on the voltage given value and voltage feedback v abc Get the AC current given Current setting and AC current feedback value i sabc The difference is made, and the modulated wave is obtained through the current regulator. After SPWM modulation, the output PWM wave drives the power switching device of the series side module.

[0049] Series AC side DC capacitor voltage v s The voltage regulator is controlled by the carrier phase difference in the SPWM modulation of the series-parallel side. With feedback value v s , calculate the carrier phase difference. The SPWM modulation on the series-parallel side generates carriers with different phases according to the carrier phase difference, and outputs PWM waves to drive the series-parallel side converters.

[0050] In summary, this scheme proposes a unified power quality conditioner topology structure and control method based on frequency division multiplexing technology, which can reliably achieve low-cost, high power density and high-performance unified power quality regulation.

Claims

1. A unified power quality conditioner topology based on frequency division multiplexing technology, characterized in that: It includes a parallel AC side converter and a series AC side converter, wherein the AC end of the parallel AC side converter is simultaneously connected to the parallel AC side filter and the three-phase resonant cavity to be multiplexed as an industrial frequency and high-frequency output end, and energy interaction is achieved with the parallel AC side and the three-phase resonant cavity in a frequency division multiplexing manner, and the DC end of the parallel AC side converter is connected to the parallel AC side DC capacitor; The AC end of the series AC side converter is simultaneously connected to the series AC side filter and the three-phase resonant cavity to be multiplexed as the industrial frequency and high-frequency output end, and energy interaction is achieved with the series AC side and the three-phase resonant cavity through frequency division multiplexing. The DC end of the series AC side converter is connected to the series AC side DC capacitor.

2. According to claim 1, a unified power quality conditioner topology structure based on frequency division multiplexing technology is characterized in that: One end of the parallel AC side filter is connected to the three-phase power grid, and the other end is connected to the AC end of the parallel AC side converter.

3. The unified power quality conditioner topology structure based on frequency division multiplexing technology according to claim 1 is characterized in that: One end of the series AC side filter is connected to the three-phase power grid, and the other end is connected to the AC end of the series AC side converter.

4. The unified power quality conditioner topology structure based on frequency division multiplexing technology according to claim 1 is characterized in that: A high-frequency transformer is embedded in the three-phase resonant cavity to achieve high-frequency isolation.

5. The unified power quality conditioner topology structure based on frequency division multiplexing technology according to claim 1 is characterized in that: The parallel AC side filter adopts an L structure or an LCL structure.

6. The unified power quality conditioner topology structure based on frequency division multiplexing technology according to claim 1 is characterized in that: The series AC side filter adopts an LC structure.

7. The unified power quality conditioner topology structure based on frequency division multiplexing technology according to claim 1 is characterized in that: The parallel AC side converter adopts a three-phase full-bridge structure, wherein the power switch device adopts an IGBT power switch device, a SiC power switch device, a GaN power switch device or a MOSFET power switch device.

8. The unified power quality conditioner topology structure based on frequency division multiplexing technology according to claim 1 is characterized in that: The series AC side converter includes three H-bridges, wherein the power switch devices are IGBT power switch devices, SiC power switch devices, GaN power switch devices or MOSFET power switch devices.

9. A control method for a unified power quality conditioner topology structure based on frequency division multiplexing technology, applied to a unified power quality conditioner topology structure based on frequency division multiplexing technology as claimed in claim 1, characterized in that: It includes a series side AC voltage control method and a parallel side AC current control method, which are used to correspondingly adjust the carrier phase difference of the series AC side converter and the carrier phase difference of the parallel AC side converter to achieve power size and direction regulation of high-frequency pulse electric energy.

10. The control method of the unified power quality conditioner topology structure based on frequency division multiplexing technology according to claim 9, characterized in that: The series side AC voltage control method specifically uses a series side voltage sensor to collect grid voltage information, determines the grid phase through a phase-locked loop technology, and then generates a standard grid voltage according to the grid phase, and makes a difference between the standard grid voltage and the actual grid voltage to serve as a series side voltage compensation reference value; The parallel side AC current control method specifically uses the parallel side current sensor to collect grid current information, performs Park transformation on the grid current according to the grid phase, performs inverse Park transformation on the q-axis current obtained after Park transformation to obtain the active current component, and then makes a difference between the actual grid current and the active current component to serve as a parallel side current compensation reference value.

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