CN114137306A - Grid-connected converter voltage phase detection method and system - Google Patents
Grid-connected converter voltage phase detection method and system Download PDFInfo
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Abstract
The invention discloses a grid-connected converter voltage phase detection method and a system, and belongs to the technical field of power electronics. Distorted and unbalanced voltage instantaneous value ea、eb、ecThe voltage vectors are combined and projected onto one VSF. And calculating the phase of the positive sequence fundamental voltage according to the space geometric relation of the voltage vector on the VSF. And adjusting the rotation speed and the steering of the VSF, and calculating the phase of the positive sequence/negative sequence m-order voltage according to the positive sequence fundamental voltage phase calculation method. The method solves the problem that the traditional phase detection method has errors when the power grid voltage distortion is unbalanced, and the adjustment process of the phase detection is simple without setting PI parameters. Compared with the SRF-PLL, the phase detection algorithm is not influenced by voltage distortion and unbalance, and can detect arbitrarily specified positive and negative sequence fundamental wave and harmonic voltage phases.
Description
Technical Field
The invention belongs to the technical field of power electronics, and relates to a voltage phase detection method and system for a grid-connected converter.
Background
A microgrid is a controllable system consisting of a plurality of Distributed Generators (DGs), an energy storage device and an on-site load, and has two operation modes, namely an island operation mode and a grid connection mode, wherein the DGs are usually connected into a power grid through a three-phase grid-connected inverter. In order to realize off/on-grid switching and inject current with unit power factor into the grid, the grid-connected converter needs to detect the voltage phase of a Point of Common Coupling (PCC). Due to the fact that a large number of grid-connected converters are connected into the microgrid, line impedance is generally not negligible, and therefore the PCC voltage contains background harmonics and a negative sequence and is expressed as distortion and unbalance. The voltage Phase detection of the three-Phase grid-connected converter usually adopts a Synchronous coordinate system-based software Phase-Locked Loop (SRF-PLL), when the voltage distortion is unbalanced, a negative sequence component of the SRF-PLL generates 2-frequency-doubled oscillation in a Synchronous coordinate transformation result, and even if a low-pass filter cannot completely eliminate the influence of the oscillation on the detection precision, the Phase detection result has an error.
Disclosure of Invention
The invention aims to overcome the defect that the voltage phase detection method of the grid-connected converter in the prior art is low in detection precision, and provides a voltage phase detection method and a system of the grid-connected converter.
In order to achieve the purpose, the invention adopts the following technical scheme to realize the purpose:
a voltage phase detection method for a grid-connected converter comprises the following steps:
step 1) synthesizing distorted and unbalanced voltage instantaneous values into voltage vectors, establishing a virtual synchronous coordinate system with adjustable rotating speed and steering, and then projecting the voltage vectors onto the virtual synchronous coordinate system;
step 2) extracting low-frequency components smaller than 0.5Hz from the coordinates of the voltage vector e on the virtual rotating coordinate system, and calculating the positive sequence fundamental voltage phase;
step 3) keeping the steering of the synchronous coordinate system unchanged, adjusting the rotating speed, projecting the voltage vector to the synchronous coordinate system, and calculating to obtain the phase of the positive sequence harmonic voltage;
and 4) adjusting the steering of the synchronous coordinate system, keeping the rotating speed unchanged, projecting the voltage vector into the synchronous coordinate system, and calculating to obtain the phase of the negative sequence harmonic voltage.
Preferably, step 1) is specifically:
step 101) setting the distorted and unbalanced voltage as:
step 102) synthesizes the distorted and unbalanced voltages into a voltage vector e,
step 103) establishing a virtual synchronous coordinate system with the rotating speed of omega't + gamma and the rotating direction of anticlockwise, wherein the coordinate of the voltage vector e on the stationary complex plane coordinate system is as follows:
step 104) because the included angle between e and the x axis is ω't + γ - θ, the coordinates of e on the virtual synchronous coordinate system are:
wherein E is an amplitude, m is a harmonic frequency, and theta is an initial phase angle; superscript + represents positive sequence, superscript-represents negative sequence; omega' is the power frequency angular velocity specified by the micro-grid, and gamma is the phase angle which changes randomly.
Preferably, step 2) is specifically:
e is to beRAnd eISubstituting the value of (2) into the formula (4) to obtain:
extracting the coordinates of the positive sequence fundamental voltage on a virtual synchronous coordinate system as follows:
wherein omega-omega' is 0-0.5 Hz;
the phase angle of the positive sequence fundamental voltage is:
preferably, step 3) is specifically: the virtual synchronous coordinate system keeps the steering unchanged, the rotating speed is adjusted to be m omega't + gamma, wherein m represents the number of harmonic waves, the voltage vector e is projected to the virtual synchronous coordinate system, and the phase of the positive sequence m voltage is calculated; the method comprises the following steps:
step 301) firstly, calculating the coordinate of e on the virtual synchronous coordinate system as follows:
step 302) extracting the coordinates of the positive sequence m-time voltage on the virtual synchronous coordinate system as follows:
step 303) the phase of the positive m-times voltage is:
preferably, step 4) is specifically: the rotation direction of the virtual synchronous coordinate system is clockwise, the rotating speed is m omega't + gamma, wherein m represents the number of harmonic waves, the voltage vector e is projected to the virtual synchronous coordinate system, and the phase of the negative sequence m voltage is calculated; the method specifically comprises the following steps:
step 401) firstly, calculating the coordinates of e on the virtual synchronous coordinate system as follows:
step 402) extracting the coordinates of the negative sequence m-time voltage on the virtual synchronous coordinate system as follows:
step 403) the phase of the negative sequence m-times voltage is:
a grid-connected converter voltage phase detection system comprises:
a voltage measurement value acquisition unit for acquiring a distorted and unbalanced voltage instantaneous value;
a coordinate system establishing unit for establishing a virtual synchronous coordinate system;
the vector projection unit is respectively interacted with the voltage measurement value acquisition unit and the coordinate system establishment unit, and is used for synthesizing distorted and unbalanced voltage instantaneous values into voltage vectors and projecting the voltage vectors onto a virtual synchronous coordinate system;
the low-frequency component extraction unit is used for extracting low-frequency components smaller than 0.5Hz and further calculating a positive sequence fundamental voltage phase;
and the phase calculation unit is respectively interacted with the vector projection unit and the low-frequency component extraction unit and is used for adjusting a synchronous coordinate system and further calculating the phase of the harmonic sub-voltage.
Preferably, the phase calculation unit comprises a positive sequence module and a negative sequence module;
the positive sequence module is used for keeping the synchronous coordinate system unchanged in steering, adjusting the rotating speed, projecting a voltage vector to the synchronous coordinate system, and calculating to obtain the phase of the positive sequence harmonic voltage;
and the negative sequence module is used for adjusting the steering of the synchronous coordinate system, keeping the rotating speed unchanged, projecting the voltage vector into the synchronous coordinate system, and calculating to obtain the phase of the negative sequence harmonic voltage.
Preferably, the low frequency component extraction unit is specifically performed by a low pass filter.
Compared with the prior art, the invention has the following beneficial effects:
the invention discloses a voltage phase detection method for a grid-connected converter, which comprises the following steps: distorted and unbalanced voltage instantaneous value ea、eb、ecThe voltage vectors are synthesized and projected onto a virtual synchronous coordinate system (VSF). The rotation speed of the VSF is omega't + gamma, the rotation direction is anticlockwise, wherein omega' is the power frequency angular speed specified by the micro-grid, and gamma is a randomly changed phase angle. And calculating the phase of the positive sequence fundamental voltage according to the space geometric relation of the voltage vector on the VSF. And adjusting the rotation speed and the steering of the VSF, and calculating the phase of the positive sequence/negative sequence m-order voltage according to the positive sequence fundamental voltage phase calculation method. The invention solves the problem that the traditional phase detection method has errors when the power grid voltage distortion is unbalanced. In addition, the algorithm does not need to set PI parameters, so that the adjustment process of phase detection is simple; the voltage phase of any order of specified positive and negative sequences can be detected by applying the algorithm. Compared with SRF-PLL, the phase detection algorithmIs not affected by voltage distortion and unbalance; the PI parameter does not need to be set in the phase detection; any specified positive and negative sequence fundamental wave and harmonic voltage phase can be detected; the algorithm complexity is not increased obviously.
Further, a Low Pass Filter (LPF) is applied to extract the coordinates of the positive-sequence fundamental voltage from the coordinate values of e on the VSF. Because the voltage vector e contains a direct current component and harmonic components of respective orders in the coordinate values of VSF. Since the rotation speed and the rotation direction of the VSF are the same as those of the positive sequence fundamental voltage vector, the direct current component contained in the coordinate of e corresponds to the positive sequence fundamental component in e, and can be extracted by applying the LPF alone.
The invention also discloses a voltage phase detection system of the grid-connected converter,
drawings
FIG. 1 is a schematic block diagram of a novel phase detection method for grid-connected converter with grid voltage distortion and unbalance according to the present invention;
FIG. 2 is a schematic diagram of a virtual synchronous coordinate system;
FIG. 3 is a virtual synchronous coordinate system for detecting negative sequence voltage phases;
FIG. 4 is a three-phase voltage waveform diagram when the grid voltage distortion is unbalanced;
FIG. 5 is a waveform diagram of the A-phase grid voltage, the A-phase positive-sequence fundamental voltage and phase detection thereof;
FIG. 6 is a waveform diagram of the A-phase grid voltage, the A-phase positive sequence 5 th harmonic voltage and its phase detection;
FIG. 7 is a waveform diagram of the A-phase grid voltage, the A-phase negative-sequence fundamental voltage and its phase detection;
FIG. 8 is a waveform diagram of the phase A positive-sequence fundamental voltage and its phase detection experiment;
FIG. 9 is a waveform diagram of the phase A positive sequence 5 th harmonic voltage and its phase detection experiment;
fig. 10 is a waveform diagram of three-phase voltage and phase detection experiment thereof when the network voltage is distorted and unbalanced.
Detailed Description
The invention is described in further detail below with reference to the accompanying drawings:
the grid-connected converter provided by the invention is suitable for a novel phase detection method for the distortion and unbalance of the grid voltage, the detection schematic block diagram is shown in fig. 1, and the detailed implementation mode is as follows:
step 2, Low Pass Filter (LPF) is applied to slave exAnd eyExtracting low-frequency components smaller than 0.5Hz, and calculating a positive sequence fundamental voltage phase;
and 3, the VSF is not changed in rotation direction, and the rotating speed is adjusted to be m omega't + gamma, wherein m represents the number of harmonic waves. Projecting the voltage vector e to VSF, and calculating the phase of the positive sequence m-time voltage;
and 4, the rotation direction of the VSF is clockwise, the rotation speed is m omega't + gamma, and m represents the number of harmonic waves. The voltage vector e is projected to the VSF, and the phase of the negative sequence m-order voltage is calculated.
Example 2
1. The acquisition of the positive sequence fundamental voltage phase is implemented according to the following steps:
1) let the distortion and unbalanced voltage be:
in the formula, E is an amplitude value, m is a harmonic frequency, and theta is an initial phase angle; the superscript + represents positive sequence, and-represents negative sequence.
2) Applying equation (2) synthesizes the voltages distorted to be unbalanced into a voltage vector e. e can be viewed as a vector composite of positive and negative sequence fundamental and harmonic voltages, with the magnitude and phase angle being time-varying.
3) A rotation speed ω't + γ is established, turning to a counter-clockwise VSF. Wherein omega' is the power frequency angular velocity specified by the micro-grid, and gamma is a phase angle which changes randomly. According to the spatial geometry shown in 2, eRAnd eIComprises the following steps:
4) since e is at an angle ω't + γ - θ to the x-axis, its coordinates on the VSF are:
5) e is to beRAnd eISubstituting the value of (2) into the formula (4) to obtain:
6) LPF is used for extracting the coordinates of the positive sequence fundamental voltage on the VSF (the allowable frequency deviation of the power grid with the national power grid specified capacity below 300 ten thousand kilowatts is +/-0.5 Hz, so that omega-omega' is 0-0.5 Hz):
7) although gamma changes randomly in each detection process, once determined, gamma is a known quantity, so ω't + gamma is a known quantity. According to the spatial geometry shown in fig. 2, the phase angle of the positive sequence fundamental voltage is:
the m-order positive sequence harmonic voltage phase is acquired specifically according to the following steps:
1) from the calculation method of claim 1 and the spatial geometry shown in fig. 2, the coordinates of e on the VSF are found as:
2) LPF is applied to extract the coordinates of the positive sequence m-order voltage on the VSF as:
3) according to the spatial geometry shown in fig. 2, the phases of the positive sequence m-th order voltages are:
the m negative sequence voltage phases are acquired specifically according to the following steps:
1) from the calculation method of claim 1 and the spatial geometry shown in fig. 3, the coordinates of e on the VSF are found as:
2) LPF is applied to extract the coordinates of the negative sequence m times of voltage on the VSF as:
3) according to the spatial geometry shown in fig. 3, the phases of the negative sequence m voltages are:
to verify the effectiveness of the algorithm, simulations were performed on MATLAB/Simulink, with the grid voltage consisting of a positive sequence fundamental voltage superimposed with a negative sequence fundamental voltage of 0.2pu and a positive sequence 5 th harmonic voltage of 0.05 pu.
The experiments were carried out under different conditions and the results were: the method comprises the steps of obtaining a three-phase voltage oscillogram (see fig. 4) when the grid voltage is distorted and unbalanced, obtaining a voltage phase and a voltage actual phase by applying the algorithm of the invention according to the results of the oscillograms, and obtaining a voltage phase and a voltage actual phase completely consistent according to the results of the oscillograms. Therefore, the novel phase detection method provided by the invention can accurately detect the phase information of fundamental wave, harmonic wave and negative sequence voltage from distorted and unbalanced voltage.
The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.
Claims (8)
1. A voltage phase detection method for a grid-connected converter is characterized by comprising the following steps:
step 1) synthesizing distorted and unbalanced voltage instantaneous values into voltage vectors, establishing a virtual synchronous coordinate system with adjustable rotating speed and steering, and then projecting the voltage vectors onto the virtual synchronous coordinate system;
step 2) extracting low-frequency components smaller than 0.5Hz from the coordinates of the voltage vector e on the virtual rotating coordinate system, and calculating the positive sequence fundamental voltage phase;
step 3) keeping the steering of the synchronous coordinate system unchanged, adjusting the rotating speed, projecting the voltage vector to the synchronous coordinate system, and calculating to obtain the phase of the positive sequence harmonic voltage;
and 4) adjusting the steering of the synchronous coordinate system, keeping the rotating speed unchanged, projecting the voltage vector into the synchronous coordinate system, and calculating to obtain the phase of the negative sequence harmonic voltage.
2. The grid-connected converter voltage phase detection method according to claim 1, wherein the step 1) is specifically as follows:
step 101) setting the distorted and unbalanced voltage as:
step 102) synthesizes the distorted and unbalanced voltages into a voltage vector e,
step 103) establishing a virtual synchronous coordinate system with the rotating speed of omega't + gamma and the rotating direction of anticlockwise, wherein the coordinate of the voltage vector e on the stationary complex plane coordinate system is as follows:
step 104) because the included angle between e and the x axis is ω't + γ - θ, the coordinates of e on the virtual synchronous coordinate system are:
wherein E is an amplitude, m is a harmonic frequency, and theta is an initial phase angle; superscript + represents positive sequence, superscript-represents negative sequence; omega' is the power frequency angular velocity specified by the micro-grid, and gamma is the phase angle which changes randomly.
3. The grid-connected converter voltage phase detection method according to claim 2, wherein the step 2) is specifically:
e is to beRAnd eISubstituting the value of (2) into the formula (4) to obtain:
extracting the coordinates of the positive sequence fundamental voltage on a virtual synchronous coordinate system as follows:
wherein omega-omega' is 0-0.5 Hz;
the phase angle of the positive sequence fundamental voltage is:
4. the grid-connected converter voltage phase detection method according to claim 2, wherein the step 3) is specifically: the virtual synchronous coordinate system keeps the steering unchanged, the rotating speed is adjusted to be m omega't + gamma, wherein m represents the number of harmonic waves, the voltage vector e is projected to the virtual synchronous coordinate system, and the phase of the positive sequence m voltage is calculated; the method comprises the following steps:
step 301) firstly, calculating the coordinate of e on the virtual synchronous coordinate system as follows:
step 302) extracting the coordinates of the positive sequence m-time voltage on the virtual synchronous coordinate system as follows:
step 303) the phase of the positive m-times voltage is:
5. the grid-connected converter voltage phase detection method according to claim 2, wherein the step 4) is specifically: the rotation direction of the virtual synchronous coordinate system is clockwise, the rotating speed is m omega't + gamma, wherein m represents the number of harmonic waves, the voltage vector e is projected to the virtual synchronous coordinate system, and the phase of the negative sequence m voltage is calculated; the method specifically comprises the following steps:
step 401) firstly, calculating the coordinates of e on the virtual synchronous coordinate system as follows:
step 402) extracting the coordinates of the negative sequence m-time voltage on the virtual synchronous coordinate system as follows:
step 403) the phase of the negative sequence m-times voltage is:
6. a grid-connected converter voltage phase detection system is characterized by comprising:
a voltage measurement value acquisition unit for acquiring a distorted and unbalanced voltage instantaneous value;
a coordinate system establishing unit for establishing a virtual synchronous coordinate system;
the vector projection unit is respectively interacted with the voltage measurement value acquisition unit and the coordinate system establishment unit, and is used for synthesizing distorted and unbalanced voltage instantaneous values into voltage vectors and projecting the voltage vectors onto a virtual synchronous coordinate system;
the low-frequency component extraction unit is used for extracting low-frequency components smaller than 0.5Hz and further calculating a positive sequence fundamental voltage phase;
and the phase calculation unit is respectively interacted with the vector projection unit and the low-frequency component extraction unit and is used for adjusting a synchronous coordinate system and further calculating the phase of the harmonic sub-voltage.
7. The grid-connected converter voltage phase detection system according to claim 6, wherein the phase calculation unit comprises a positive sequence module and a negative sequence module;
the positive sequence module is used for keeping the synchronous coordinate system unchanged in steering, adjusting the rotating speed, projecting a voltage vector to the synchronous coordinate system, and calculating to obtain the phase of the positive sequence harmonic voltage;
and the negative sequence module is used for adjusting the steering of the synchronous coordinate system, keeping the rotating speed unchanged, projecting the voltage vector into the synchronous coordinate system, and calculating to obtain the phase of the negative sequence harmonic voltage.
8. The grid-connected converter voltage phase detection system according to claim 6, wherein the low frequency component extraction unit is specifically performed by a low pass filter.
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| CN102305886A (en) * | 2011-05-31 | 2012-01-04 | 浙江大学 | Fundamental voltage synchronous signal detection method during harmonic distortion and unbalance of network voltage |
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| CN107102204A (en) * | 2017-04-27 | 2017-08-29 | 西安理工大学 | Suitable for line voltage distortion and unbalanced voltage-phase detection method |
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Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR20060065742A (en) * | 2004-12-10 | 2006-06-14 | 경북대학교 산학협력단 | Device of detecting phase of system voltage using virtual two phase voltage |
| EP1790520A2 (en) * | 2005-11-29 | 2007-05-30 | Denso Corporation | Control apparatus and method for electric vehicles |
| CN102305886A (en) * | 2011-05-31 | 2012-01-04 | 浙江大学 | Fundamental voltage synchronous signal detection method during harmonic distortion and unbalance of network voltage |
| CN105743109A (en) * | 2016-04-19 | 2016-07-06 | 大连理工大学 | Phase-locked loop applicable to power grid voltage unbalance and distortion states |
| CN107102204A (en) * | 2017-04-27 | 2017-08-29 | 西安理工大学 | Suitable for line voltage distortion and unbalanced voltage-phase detection method |
Non-Patent Citations (1)
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