CN104953801B - Voltage-source type combining inverter current harmonics elimination device and method - Google Patents

Abstract

The present invention provides a kind of voltage-source type combining inverter current harmonics elimination device and method.The device includes：Net side sampler, for being sampled to obtain voltage on line side sampled signal to voltage on line side；First inverter sampler, is sampled to obtain contravarianter voltage sampled signal and inverter current sampled signal for the output voltage and output current to inverter；Voltage on line side processor, for N number of harmonic component of voltage on line side sampled signal to be separated with fundamental component；Phaselocked loop, amplitude and phase for detecting fundamental component；Power control loop, for calculating amplitude regulated quantity and phase adjusted amount；Reference signal synthesizer, for generating contravarianter voltage reference signal；And inverter control loop, for controlling inverter so that output voltage follows contravarianter voltage reference signal.According to the present invention it is possible to effectively suppress content of the voltage-source type combining inverter to the harmonic current of electrical grid transmission.

Description

Harmonic current suppression device and method for voltage source type grid-connected inverter

Technical Field

The invention relates to the technical field of inverter control, in particular to a harmonic current suppression device and method for a voltage source type grid-connected inverter.

Background

In recent years, with the increasing exhaustion of traditional fossil fuels such as coal and petroleum, the shortage of energy and environmental problems are increasing, so that the power generation technology of clean energy or renewable energy is gaining increasing attention and application. The rapid development of new energy and renewable energy is not only the need of protecting ecological environment, coping with climate change and realizing sustainable development, but also the main way of solving the civil electricity problem of people without electricity in remote areas of China.

Taking photovoltaic as an example, the main form of grid-connected power generation is to convert direct current generated by a photovoltaic cell panel into an alternating current form which can be accepted by a power grid by using an inverter taking a power electronic device as a core, and inject electric energy into the power grid. According to the characteristics of the output end of the inverter, the inverter can be classified into a current source type grid-connected inverter and a voltage source type grid-connected inverter. The current source type grid-connected inverter is developed earlier, the application range is wider, and the working principle is as follows: the inverter control loop only controls the output current of the inverter, the output voltage of the inverter is clamped by a power grid, meanwhile, the current control loop carries out maximum power tracking on the photovoltaic cell panel, and photovoltaic energy is injected into the power grid to the maximum extent. Because the solar irradiance has larger randomness, the output power fluctuation of the grid-connected system is larger, and the grid stability is not facilitated. The system has the advantages of simple control, good inverter output current waveform, and Total Harmonic Distortion (THD) of input current_i) Lower. However, the current source grid-connected inverter system cannot realize island operation and supply power for sensitive loads when the power grid fails. The voltage source type grid-connected inverter system is late, and the working principle is that the output of the inverter is controlledAnd the amplitude and the phase of the voltage control the active power and the reactive power transmitted to the power grid by the inverter according to the power transmission theorem. The voltage source grid-connected inverter system is characterized in that the outermost layer of an inverter control loop is voltage control, so that when a power grid fails, the voltage source grid-connected inverter system can be immediately disconnected and continue to provide electric energy for sensitive loads. In the grid-connected and off-grid conversion process of the voltage source type grid-connected inverter system, the structure of a control loop is not changed, the impact in the transition process is small, and the electric energy quality is high, so that the reliability of supplying power for sensitive loads can be improved by the voltage source type grid-connected inverter. However, the output impedance of the voltage source type grid-connected inverter is small and is easily influenced by the harmonic voltage on the grid side, so that the grid-connected current THD of the voltage source type grid-connected inverter is caused_iAnd the grid-connected current and power quality is influenced by the increase of the grid-connected current and power quality.

Therefore, it is desirable to provide a voltage source grid-connected inverter harmonic current suppression strategy to at least partially solve the above problems in the prior art.

Disclosure of Invention

In order to at least partially solve the problems in the prior art, according to one aspect of the present invention, a harmonic current suppression device for a voltage source grid-connected inverter is provided. The device includes: a grid-side sampler for sampling a grid-side voltage to obtain a grid-side voltage sampling signal; a first inverter sampler for sampling an output voltage and an output current of an inverter to obtain an inverter voltage sampling signal and an inverter current sampling signal; a grid-side voltage processor for separating N harmonic components of the grid-side voltage sampled signal from the fundamental frequency component, where N is an integer greater than or equal to 1; phase locked loop for detecting amplitude E of fundamental frequency component_baseAnd phase theta_base(ii) a A power control loop for calculating an amplitude adjustment amount Δ E and a phase adjustment amount Δ θ based on the inverter voltage sampling signal, the inverter current sampling signal, the target active power, and the target reactive power; reference signal synthesizer for amplitude basedValue E_basePhase theta_baseGenerating an inverter voltage reference signal by the amplitude adjustment quantity delta E, the phase adjustment quantity delta theta and the N harmonic components; and an inverter control loop for controlling the inverter to cause the output voltage to follow the inverter voltage reference signal.

Optionally, the grid side voltage processor comprises N sets of traps and subtractors. The N groups of wave traps are used for filtering N harmonic components in a one-to-one correspondence mode to obtain fundamental frequency components, wherein the central resonance angular frequency of each wave trap in each group of wave traps is the same as the angular frequency of the harmonic component corresponding to the group of wave traps. The subtractor is configured to subtract the fundamental frequency component from the net-side voltage sample signal to obtain N harmonic components.

Optionally, the apparatus further comprises a compensator. The compensator is configured to calculate an amplitude compensation quantity E for compensating for an influence of the N sets of traps on the fundamental frequency component based on the angular frequency of the fundamental frequency component and the transfer function of each of the N sets of traps_offsetAnd phase compensation amount theta_offsetAnd further for compensating quantities E based on the amplitudes, respectively_offsetAnd phase compensation amount theta_offsetFor the amplitude E_baseAnd phase theta_baseCompensation is performed.

Optionally, the wave traps for filtering harmonic components of the voltage on the same phase network side in the N sets of wave traps are connected in series.

Optionally, the apparatus further comprises a first Clark and Park transformation module for transforming the inverter voltage sampling signal and the inverter current sampling signal into dq coordinate system by Clark and Park transformation to obtain a transformed inverter voltage sampling signal and a transformed inverter current sampling signal. The power control loop includes a power calculation module and a power control module. The power calculation module includes: a power calculator for calculating instantaneous active power and instantaneous reactive power output by the inverter from the converted inverter voltage sampling signal and the converted inverter current sampling signal; a first low-pass filter for filtering high-frequency components in the instantaneous active power to obtain an average active power; and a second low pass filter for filtering high frequency components in the instantaneous reactive power to obtain an average reactive power. The power control module includes: a first subtractor for calculating an active power difference between the target active power and the average active power; a second subtractor for calculating a reactive power difference between the target reactive power and the average reactive power; a first proportional-integral-derivative (PID) controller for calculating a phase adjustment amount Δ θ based on the active power difference value; and a second PID controller for calculating the amplitude adjustment amount Δ E based on the reactive power difference.

Optionally, the reference signal synthesizer is specifically configured to: respectively connecting amplitude adjustment quantity delta E and phase adjustment quantity delta theta with amplitude E_baseAnd phase theta_baseAre combined to generate the inverter fundamental frequency reference signal u_b ^* _ase(ii) a And referencing the inverter fundamental frequency with a reference signal u_b ^* _aseAre superimposed with the N harmonic components to generate an inverter voltage reference signal.

Optionally, the reference signal synthesizer generates the inverter fundamental frequency reference signal based on the following formula

Wherein,andare respectively inverter fundamental frequency reference signalsThe components on the three phases abc.

Optionally, the apparatus further comprises a second inverter sampler for sampling an inductor current flowing through the inductor or a capacitor current flowing through the capacitor to obtain an inductor current or a capacitor current sampling signal, wherein the inductor and the capacitor constitute a filter of the inverter, and the filter is used for filtering a high frequency component in a voltage output by a three-phase full bridge circuit of the inverter. The inverter control loop includes: a second Clark and Park transformation module for transforming the inverter voltage sampling signal and the inductor current or capacitor current sampling signal to dq coordinate system by Clark and Park transformation to obtain a transformed inverter voltage sampling signal and a transformed inductor current or capacitor current sampling signal; a third Clark and Park transformation module for transforming the inverter voltage reference signal to a dq coordinate system by Clark and Park transformation to obtain a transformed inverter voltage reference signal; a voltage subtractor for calculating a voltage difference between the converted inverter voltage reference signal and the converted inverter voltage sampling signal; a proportional-integral-resonant hybrid (PIR) controller for calculating a current loop reference signal based on the voltage difference; a current subtractor for calculating a current difference between the current loop reference signal and the transformed inductor current or capacitor current sampling signal; a current controller for calculating a voltage modulation signal based on the current difference; an inverse Park and inverse Clark transformation module for transforming the voltage modulation signal to abc coordinate system by inverse Park and inverse Clark transformation to obtain a transformed voltage modulation signal; and a modulator for comparing the converted voltage modulation signal with a carrier signal to obtain a pulse width modulation signal, and driving the power switching devices in a three-phase full bridge circuit of the inverter with the pulse width modulation signal to make the output voltage identical to the inverter voltage reference signal.

Optionally, the transfer function of the proportional-integral-resonant hybrid controller in dq coordinate system is:

where s is Laplace operator, ω_baseIs the angular frequency, k, of the fundamental frequency component_pvAnd k is_ivRespectively proportional and integral parameters, k_{rv_n}And omega_nIs the resonance controller parameter, and n is 6k, where k is a positive integer.

According to another aspect of the invention, a harmonic current suppression method for a voltage source grid-connected inverter is provided. The method comprises the following steps: sampling the network side voltage to obtain a network side voltage sampling signal; separating N harmonic components of the grid-side voltage sampling signal from a fundamental frequency component, wherein N is an integer greater than or equal to 1; detecting the amplitude and phase of the fundamental frequency component; sampling the output voltage and the output current of the inverter to obtain an inverter voltage sampling signal and an inverter current sampling signal; calculating amplitude adjustment quantity and phase adjustment quantity based on the inverter voltage sampling signal, the inverter current sampling signal, the target active power and the target reactive power; generating an inverter voltage reference signal based on the amplitude, the phase, the amplitude adjustment, the phase adjustment, and the N harmonic components; and controlling the inverter to cause the output voltage to follow the inverter voltage reference signal.

According to the technical scheme provided by the invention, the phase and amplitude difference between the fundamental frequency component in the output voltage of the inverter and the fundamental frequency component of the network side voltage is controlled by the power control loop, so that the appointed fundamental frequency active and reactive current (power) can be transmitted to the power grid; meanwhile, the error between the harmonic component in the output voltage of the inverter and the harmonic component in the grid-side voltage can be reduced, so that the content of harmonic current transmitted to a power grid by the voltage source type grid-connected inverter can be effectively inhibited, and the complexity and the design difficulty of a grid-connected inverter system are greatly reduced.

In this summary, a number of simplified concepts are introduced that are further described in the detailed description section. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

The advantages and features of the present invention are described in detail below with reference to the accompanying drawings.

Drawings

The following drawings of the invention are included to provide a further understanding of the invention. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings, there is shown in the drawings,

fig. 1a and 1b are a single-phase equivalent circuit diagram and a vector relationship diagram of a voltage source grid-connected inverter system respectively;

fig. 2a and 2b are a single-phase fundamental frequency component equivalent circuit diagram and a harmonic component equivalent circuit diagram of the voltage source grid-connected inverter system, respectively;

fig. 3 is a schematic block diagram of a voltage source grid-connected inverter harmonic current suppression device according to an embodiment of the present invention;

FIG. 4 is a schematic block diagram of a voltage source grid-tied inverter system according to one embodiment of the present invention;

figure 5 is a graph of amplitude-frequency and phase-frequency characteristics of a wave trap according to one embodiment of the present invention;

fig. 6 is a schematic diagram of the transformation of the output voltage and the output current of the voltage source grid-connected inverter from the abc coordinate system to the dq coordinate system according to one embodiment of the present invention;

fig. 7 is a flowchart of a harmonic current suppression method for a voltage source grid-connected inverter according to an embodiment of the present invention.

Detailed Description

In the following description, numerous details are provided to provide a thorough understanding of the present invention. One skilled in the art will recognize, however, that the following description is merely illustrative of a preferred embodiment of the invention and that the invention may be practiced without one or more of these specific details. In addition, some technical features that are well known in the art are not described in order to avoid confusion with the present invention.

The principle of harmonic current suppression of a voltage source grid-connected inverter according to an embodiment of the present invention is described below with reference to fig. 1a, 1b, 2a, and 2 b. In the following description, "inverter", "voltage source grid-connected inverter" refer to the same object, and they may be used interchangeably.

An equivalent circuit diagram of a voltage source grid-connected inverter system running in parallel with a three-phase balanced power grid can be obtained by analyzing any phase of the system, as shown in fig. 1 a. In the figure V_invFor outputting voltage vector, V, of voltage source type grid-connected inverter_gridIs a grid-side voltage vector, I is a grid-connected current vector, Z_line＝sL_line+R_lineThe impedance of an equivalent line between the output end of the voltage source type grid-connected inverter and a grid-connected point. In terms of circuit principles, the relationship between the vectors in FIG. 1a can be represented by a vector relationship diagram, as shown in FIG. 1 b. According to fig. 1b, an expression of active power P and reactive power Q transmitted to the grid by the voltage source grid-connected inverter can be obtained, as shown in the following formula:

in the formula (1), Δ φ is a vector V_invAnd vector V_gridThe phase difference of (a); z and theta are equivalent line impedance Z_lineAmplitude and phase. In the application of the voltage source grid-connected inverter, the line impedance is mainly inductive, that is, θ ═ pi/2, and Δ Φ is very small in the normal working process, that is: sin Δ φ ≈ Δ φ and cos Δ φ ≈ 1. Thus, equation (1) can be simplified to equation (2):

from the equation (2), it can be seen that the amplitude difference (V) between the output voltage of the voltage source grid-connected inverter and the grid-side voltage at the grid-connected point is controlled_inv-V_grid) And the phase difference delta phi can control the active power P and the reactive power Q transmitted to the power grid by the inverter. When the network side voltage only has a fundamental frequency component, the phase-locked loop can be used for detecting the network side voltage at the grid-connected point to obtain the instantaneous phase theta and the amplitude E of the network side voltage. Then two proportional-integral (PI) controllers are used as power controllers, and the power controllers are respectively based on an active power reference value (namely target active power) P of the inverter^*The difference value between the active power P actually output by the inverter and the reactive power reference value (target reactive power) Q of the inverter^*And the difference value between the actual output reactive power Q of the inverter is calculated, so that the phase adjustment quantity delta theta and the amplitude adjustment quantity delta E of the output voltage of the inverter are obtained. Finally, the inverter voltage reference signal is synthesized by the following formula (3), and the output voltage of the inverter is controlled by the inverter voltage current inner loop so as to follow the inverter voltage reference signalSo that the inverter transmits the specified active power and reactive power to the grid according to the principle described in equation (2).

When the voltage on the network side exists, the angular frequency is omega_harWhen the three-phase balanced harmonic voltage is disturbed, according to the linear superposition theorem, the graph of fig. 1a can be decomposed into a fundamental frequency component equivalent circuit diagram of a voltage source type grid-connected inverter system and an angular frequency of omega_harFig. 2a and 2b show equivalent circuit diagrams of harmonic components of (a). U in the figure_{ref_b}G_inv(jω_base) And u_{ref_h}G_inv(jω_har) Are respectively of voltage source typeThe fundamental frequency component and the angular frequency of the output voltage of the grid-connected inverter are omega_harA harmonic component of (a); u. of_grid(jω_base) And u_grid(jω_har) Fundamental frequency component and angular frequency of net side voltage are omega_harA harmonic component of (a); z_line(jω_base) And Z_line(jω_har) The fundamental frequency component and the angular frequency of the equivalent line impedance are omega_harThe harmonic component of (a). I (j omega)_base) And I (j ω_har) Fundamental frequency component and angular frequency of grid-connected current are omega_harThe harmonic component of (a).

According to fig. 2a, a fundamental frequency component amplitude expression of any one phase grid-connected current in the voltage source type grid-connected inverter system can be obtained as follows:

according to fig. 2b, an expression of the amplitude of the harmonic component of any one-phase grid-connected current in the voltage source grid-connected inverter system can be obtained as follows:

as can be seen from equation (4), in order to ensure that the voltage source grid-connected inverter can normally transmit fundamental frequency active power and reactive power to the power grid when harmonic voltage disturbance exists in the grid-side voltage, P/θ and Q/E droop control needs to be performed on the fundamental frequency component of the output voltage of the voltage source grid-connected inverter based on equation (2). As can be seen from equation (5), the harmonic current output by the voltage source grid-connected inverter and having the same angular frequency as the grid-side harmonic voltage can be reduced by reducing the absolute value of the molecules in the equation.

Suppose that an angular frequency of n ω exists in the grid-side voltage_baseAnd the peak value is b_nThe harmonic voltage is expressed as follows:

equation (6) can be transformed by the following Clark and Park transformation equations represented by equation (7) and equation (8):

thus, an expression of three-phase balanced harmonic voltage in dq coordinate system is obtained, as shown in formula (9):

as can be seen from equation (9), the fundamental frequency component of the grid-side voltage is mapped as a direct current quantity on the dq axis. While all harmonic components are mapped to trigonometric function signals on the dq axis and cannot be cancelled. According to the difference of the positive sequence and the negative sequence of the original harmonic voltage signal, each harmonic component is mapped to a trigonometric function signal with different frequencies on a dq axis, wherein the positive sequence harmonic components of 1 st order, 4 th order, 7 th order and 10 th order are mapped to the corner frequency of (n-1) omega on the dq axis_baseThe trigonometric function signal of (a); the 2-, 5-, 8-and 11-th negative-sequence harmonic components are mapped to a dq-axis corner frequency of (n +1) ω_baseThe trigonometric function signal of (a).

It should be noted that, according to the difference of the harmonic voltage angular frequency at the network side, a corresponding resonant controller may be connected in parallel to a voltage loop controller (proportional-integral controller) of the voltage source type grid-connected inverter to form a PIR controller, so as to improve the tracking capability of the inverter control loop to the three-phase balanced harmonic voltage at the network side, further eliminate the harmonic voltage difference between the output end of the inverter and the grid-connected point, and contribute to reducing the harmonic current transmitted from the voltage source type grid-connected inverter to the power grid by reducing the molecular absolute value in the formula (5).

The invention is further described below in conjunction with fig. 3-7.

According to one aspect of the invention, harmonic current suppression is provided for a voltage source grid-connected inverter. Fig. 3 shows a schematic block diagram of a voltage source grid-connected inverter harmonic current suppression apparatus 300 according to an embodiment of the present invention.

The apparatus 300 includes a net-side sampler 301, a first inverter sampler 302, a net-side voltage processor 303, a phase locked loop 304, a power control loop 305, a reference signal synthesizer 306, and an inverter control loop 307.

The grid-side sampler 301 is configured to sample a grid-side voltage to obtain a grid-side voltage sampling signal. The first inverter sampler 302 is used for sampling the output voltage and the output current of the inverter to obtain an inverter voltage sampling signal and an inverter current sampling signal. The grid-side voltage processor 303 is configured to separate N harmonic components of the grid-side voltage sampled signal from the fundamental frequency component, where N is an integer greater than or equal to 1. The phase-locked loop 304 is used for detecting the amplitude E of the fundamental frequency component_baseAnd phase theta_base. The power control loop 305 is configured to calculate an amplitude adjustment amount Δ E and a phase adjustment amount Δ θ based on the inverter voltage sampling signal, the inverter current sampling signal, the target active power, and the target reactive power. The reference signal synthesizer 306 is configured to base the amplitude E on_basePhase theta_baseThe amplitude adjustment amount delta E, the phase adjustment amount delta theta and the N harmonic components generate an inverter voltage reference signal. The inverter control loop 307 is used to control the inverter such that the output voltage follows the inverter voltage reference signal.

For ease of understanding, the present invention is described in detail below with reference to FIG. 4. Fig. 4 is a schematic block diagram of a voltage source grid-connected inverter system according to an embodiment of the present invention. Fig. 4 shows a grid, a grid-connected inverter and a grid-connected inverter harmonic current suppression device associated therewith. It will be understood by those skilled in the art that fig. 4 is only an example of a grid-connected inverter system in which the present invention is implemented for clearly understanding the inventive concept of the present invention, but it is not to be construed as limiting the present invention.

In fig. 4, a grid side voltage processor 401, a phase locked loop 402, a power control loop 403, a reference signal synthesizer 404 and an inverter control loop 405 are shown, which correspond to the grid side voltage processor 303, the phase locked loop 304, the power control loop 305, the reference signal synthesizer 306 and the inverter control loop 307, respectively, of fig. 3.

In the embodiment shown in fig. 4, a net-side sampler (not shown) samples the net-side voltage to obtain a net-side voltage sample signal u_{grid_abc}. The network side voltage processor 401 samples the network side voltage sample signal u_{grid_abc}Is separated from the fundamental frequency component, where N is an integer greater than or equal to 1.

Alternatively, the grid side voltage processor 401 may include N sets of traps and subtractors. The N sets of traps are used to filter the N harmonic components in a one-to-one correspondence to obtain fundamental frequency components. The central resonant angular frequency of each trap in each set of traps is the same as the angular frequency of the harmonic component corresponding to that set of traps. The subtracter is used for sampling a signal u from a network side voltage_{grid_abc}The fundamental frequency component is subtracted to obtain N harmonic components.

Fig. 4 exemplarily shows the separation of the net-side voltage sample signal u using a set of traps and a subtractor_{grid_abc}Has a fundamental frequency component of and an angular frequency of ω_harIn the case of harmonic components. As shown in fig. 4, the network-side voltage processor 401 may further comprise a Demultiplexer (DEMUX) for sampling the network-side voltage sample signal u_{grid_abc}Splitting into abc triphases to give u_{grid_a}、u_{grid_b}And u_{grid_c}And then each is considered independently. In this case, a set of traps comprises three identical, central resonant angular frequencies ω_o＝ω_harWave trap G_notch(s). Central resonance angular frequency of omega_oThe transfer function of the trap of (2) is as shown in equation (10):

the central resonance angular frequency omega of the wave trap can be changed by changing the k and n values in the formula (10)_oThe width and depth of the attenuation frequency of the signal in the vicinity. For example, when k is 10 andthe amplitude-frequency characteristic and the phase-frequency characteristic of the trap having a center resonance frequency of 550Hz are shown in fig. 5.

Wave trap G_notch(s) will shift the angular frequency to ω_harSo as to obtain the values u of fundamental frequency components on three phases abc at the output ends of the three wave traps_{base_a}、u_{base_b}And u_{base_c}. As shown in fig. 4, the grid side voltage processor 401 may further include a Multiplexer (MUX) connected to the trap, which may couple u to u_{base_a}、u_{base_b}And u_{base_c}Synthesized as a fundamental frequency component u_{base_abc}. The subtracter can subtract u_{grid_a}、u_{grid_b}、u_{grid_c}Are respectively connected with u_{base_a}、u_{base_b}And u_{base_c}By subtraction to calculate the angular frequency ω_harThe value u of the harmonic component of (a) on the three phases abc_{harmonic_a}、u_{harmonic_b}And u_{harmonic_c}. The network-side voltage processor 401 may further comprise a multiplexer connected to the subtractor, which may couple u to the subtractor_{harmonic_a}、u_{harmonic_b}And u_{harmonic_c}Synthesized as harmonic component u_{harmonic_abc}。

Sampling the network side voltage_{grid_abc}The process of separating the fundamental frequency component and the harmonic component in (a) can be expressed by the following equation (11):

optionally, the wave traps for filtering harmonic components of the voltage on the same phase network side in the N groups of wave traps are connected in series. When harmonic voltage disturbance of a plurality of frequency points exists in network side voltage, the harmonic voltage of each frequency point can be filtered one by utilizing a structure that a plurality of groups of wave traps with different central resonance angular frequencies are connected in series, and a network side voltage sampling signal u is filtered by the structure shown in formula (12)_{grid_abc}Is separated from the harmonic component.

Optionally, the apparatus may further comprise a compensator (not shown). The compensator is configured to calculate an amplitude compensation amount Eo for compensating for an effect of the N sets of traps on the fundamental frequency component based on the angular frequency of the fundamental frequency component and a transfer function of each of the N sets of traps_ffset and phase compensation amount θ o_ffset. The compensator is further used for respectively compensating the quantity Eo based on the amplitude value_ffsetAnd phase compensation amount θ o_ffsetFor the amplitude E_baseAnd phase theta_baseCompensation is performed. It will be appreciated that when the above trap is employed, the trap G_notch(s) not only sampling the net side voltage with a signal u_{grid_abc}Has an angular frequency of ω_harThe harmonic component of (a) is filtered, and a network side voltage sampling signal u is also filtered_{grid_abc}Has an effect on the fundamental frequency component of (a). The influence is reflected when the fundamental frequency component of the network side voltage sampling signal needs to be detected and the output voltage of the inverter and the fundamental frequency component of the network side voltage sampling signal need to be synchronized before the grid-connected switch of the voltage source type grid-connected inverter system is closed. The influence of the wave trap on the fundamental frequency signal is compensated to reduce the error generated in the synchronization process, so that the overlarge impact current at the closing moment of the grid-connected switch can be avoided, and further the damage to the inversion can be avoidedA device.

The compensator calculates an amplitude compensation Eo_ffsetAnd phase compensation amount θ o_ffsetThe procedure of (2) is as follows.

First, s is equal to j ω_baseTransfer function G of band-in trap_notch(s), as follows:

in the formula of omega_baseThe angular frequency of the fundamental frequency component of the net side voltage sample signal. Then converting the formula (13) into a complex mode and complex angle form, and simplifying to obtain:

G_no_tch(jω_base)＝|g_notch|∠θ_notch(14)

in the formula (14), the compound represented by the formula (I),

therefore, the phase compensation amount θ o of the fundamental frequency component can be obtained_ffsetAnd the amplitude compensation amount Eo_ffset：

When multiple sets of wave traps are connected in series, the phase compensation quantity theta o of fundamental frequency component_ffsetAnd the amplitude compensation amount Eo_ffsetAs shown in the following formula:

when calculating the amplitude compensation quantity E of the fundamental frequency component_offsetAnd phase compensation amount theta_offsetOf fundamental frequency components by means of compensatorsThe amplitude and phase are compensated. The amplitude and phase of the fundamental frequency component may be detected using a phase locked loop 402, as described below.

The phase locked loop 402 is used to detect the amplitude E of the fundamental frequency component_baseAnd phase theta_base. Using a phase locked loop 402 to couple the fundamental frequency component u outputted from the network side voltage processor 401_{base_abc}Performing operation to obtain fundamental frequency component u_{base_abc}Phase of (a)_baseAnd amplitude E_base. By performing the operation of the following equation (17), the fundamental frequency component u not affected by the trap can be obtained_{base_abc}Phase of (a)_baseAnd amplitude E_baseThe value of (c):

in formula (17), θ'_baseAnd E'_baseRespectively represent the compensated phase theta_baseAnd the compensated amplitude E_base. Although different signs are used in equation (17) to represent the phases and amplitudes before and after compensation for the convenience of description, it is understood that θ ″ 'in the embodiment in which compensation is performed'_baseAnd E'_baseI.e., the phase theta input to the subsequent reference signal synthesizer 404_baseAnd amplitude E_base。

With continued reference to fig. 4, a first inverter sampler samples the output voltage and output current of the inverter to obtain an inverter voltage sampling signal u_CabcAnd an inverter current sampling signal i_Oabc. Power control loop 403 is based on inverter voltage sampling signal u_CabcInverter current sampling signal i_OabcTarget active power P^*And target reactive power Q^*An amplitude adjustment amount Δ E and a phase adjustment amount Δ θ are calculated.

Optionally, the apparatus may further include a first Clark and Park transformation module 406, configured to transform the inverter voltage sampling signal u by Clark and Park transformation as shown in equations (7) and (8)_CabcAnd an inverter current sampling signal i_OabcTransforming into dq coordinate system to obtain transformed inverter voltage sampling signal u_CdqAnd a converted inverter current sampling signal i_OdqAs shown in fig. 6.

Power control loop 403 may include a power calculation module 4031 and a power control module 4032. The power calculation module 4031 may include a power calculator for sampling the signal u from the transformed inverter voltage_CdqAnd a converted inverter current sampling signal i_OdqAnd calculating instantaneous active power P and instantaneous reactive power Q output by the inverter. In the power calculation step, instantaneous active power P and instantaneous reactive power Q transmitted to the grid by the voltage source grid-connected inverter are calculated by using an instantaneous power theorem, as shown in the following formula:

the power calculation module 4031 may also include a first low pass filter G_LPF(s) and a second low-pass filter G_LPF(s) for filtering the high frequency components in the instantaneous active power P and the instantaneous reactive power Q to obtain an average active power P and an average reactive power Q, respectively, where the formula is as follows:

the power control module 4032 may include a first subtractor, a second subtractor, a first proportional-integral-derivative (PID) controller, and a second PID controller. The first subtracter is used for calculating the target active power P^*And an active power difference value between the average active power p, the first PID controller is configured to calculate a phase adjustment amount Δ θ based on the active power difference value, and the phase adjustment amount Δ θ is a phase adjustment amount for an output voltage of the inverter. Similarly, the second subtracter is used for calculating the target reactive power Q^*With an average reactive power qThe difference in reactive power between. The second PID controller is configured to calculate a magnitude adjustment amount Δ E, which is a magnitude adjustment amount for the output voltage of the inverter, based on the reactive power difference. The above calculation process is shown in equation (20):

in the formula (20), k_pp、k_pi、k_pdProportional, integral and differential parameters of the first PID controller are respectively; k is a radical of_qp、k_qi、k_qdThe proportional, integral and derivative parameters of the second PID controller, respectively.

With continued reference to FIG. 4, the reference signal synthesizer 404 is configured to base the magnitude E on_basePhase theta_baseGenerating an inverter voltage reference signal by an amplitude adjustment amount delta E, a phase adjustment amount delta theta and N harmonic components

Alternatively, the reference signal synthesizer 404 may combine the amplitude adjustment Δ E and the phase adjustment Δ θ output by the power control loop 403 with the amplitude E output or compensated by the phase locked loop 402_baseAnd phase theta_baseCombined to generate an inverter fundamental frequency reference signalThe calculation is shown as a trigonometric function of equation (21):

as shown in fig. 4, the reference signal synthesizer 404 may include an adder and a reference signal generator, both of which may be employed to implement the generation of the inverter fundamental frequency reference signal described aboveThe calculation process of (2). In fig. 4, the inverter fundamental frequency reference signal output by the reference signal generatorAs its components on three phases abcAnd

reference signal synthesizer 404 may further be used to reference the inverter fundamental frequency to a signalIs superimposed with the N harmonic components to generate an inverter voltage reference signalAs shown in fig. 4, the reference signal synthesizer 404 may further include demultiplexers, adders and multiplexers. The demultiplexer demultiplexes the harmonic component u output from the network side voltage processor 401 or the compensator_{harmonic_abc}Decomposition into the three phases abc to give u_{harmonic_a}、u_{harmonic_b}And u_{harmonic_c}. The adder being obtained at the output of the reference signal generatorAndare respectively connected with u_{harmonic_a}、u_{harmonic_b}And u_{harmonic_c}Are superimposed, as shown in equation (22), and then pass through a multiplexer to generate a complete three-phase inverter voltage reference signal

Optionally, the apparatus may further comprise a second inverter sampler (not shown) for sampling an inductor current flowing through the inductor 411 or a capacitor current flowing through the capacitor 412 to obtain an inductor current sampling signal i_LabcOr capacitance current sampling signal i_CabcWherein the inductor 411 and the capacitor 412 constitute a filter of the inverter 410, the filter being used for filtering high frequency components in the voltage outputted by the three-phase full bridge circuit 413 of the inverter 410.

The inverter control loop 405 may include a second Clark and Park conversion module 4051, a third Clark and Park conversion module 4052, a voltage subtractor 4053, a PIR controller 4054, a current subtractor 4055, a current controller 4056, an inverse Park and inverse Clark conversion module 4057, and a modulator 4058.

The second Clark and Park conversion module 4051 is configured to convert the inverter voltage sampling signal u by Clark and Park_CabcAnd an inductor current sampling signal i_LabcOr capacitance current sampling signal i_CabcTransforming into dq coordinate system to obtain transformed inverter voltage sampling signal u_CdqAnd a converted inductor current sampling signal i_LdqOr capacitance current sampling signal i_Cdq. The third Clark and Park conversion module 4052 is configured to convert the inverter voltage reference signal by Clark and ParkTransforming into dq coordinate system to obtain transformed inverter voltage reference signal

Voltage subtractor 4053 is used to calculate a converted inverter voltage reference signalAnd a converted inverter voltage sampling signal u_CdqDifference e between the voltages_dq. The PIR controller 4054 is configured to determine a voltage difference e based on the voltage difference_dqCalculating current loop reference signalIn fig. 4, a block 4054 shows the internal architecture of the PIR controller 4054. The transfer function of the PIR controller in the dq coordinate system is shown in formula (23):

in the formula (23), s is Laplace operator, ω_baseAt the angular frequency, k, of the fundamental frequency component_pvAnd k is_ivRespectively proportional and integral parameters, k_{rv_n}And omega_nIs a resonance controller parameter and n is 6k, where k is a positive integer, i.e. n is 6,12,18 …

The proportional-integral element in equation (23) enables the inverter control loop 405 to implement steady-state error-free control of the dc component in the dq coordinate system, that is: the diagonal frequency is omega under the abc coordinate system_baseSteady state, error-free control of the fundamental frequency component of (a); the resonance link can enable the inverter control loop to realize the diagonal frequency of n omega under the dq coordinate system_baseThe steady state homodyne control of the trigonometric function signal of (a), namely, the realization of the diagonal frequency of (n +1) omega under the abc coordinate system_baseHas a three-phase balanced positive sequence harmonic voltage component or angular frequency of (n-1) omega_baseThe three-phase balanced negative sequence harmonic voltage component of (1) is stably tracked without difference.

Current subtractor 4055 for calculating current loop reference signalWith the transformed inductor current sampling signal i_LdqOr capacitance current sampling signal i_CdqThe difference in current between. The current controller 4056 is configured to calculate a voltage based on the current differenceModulated signal u_dq. The inverse Park and inverse Clark transformation module 4057 is used for transforming the voltage modulation signal u through inverse Park and inverse Clark_dqTransformed into abc coordinate system to obtain a transformed voltage modulated signal u_abc. anti-Park and anti-Clark transformation equations are shown in equations (24) and (25):

after the calculation of the inverse Park and inverse Clark conversion module 4057, the modulation signal u required by the three-phase full-bridge circuit 413 of the inverter 410 under the abc coordinate system is obtained_abc. Then, the transformed modulation signal u_abcInput to a modulator 4058. The modulator 4058 is used for modulating the transformed voltage modulation signal u_abcCompares with the carrier signal to obtain a Pulse Width Modulation (PWM) signal, and drives the power switching devices in the three-phase full bridge circuit 413 of the inverter 410 with the PWM signal to output the voltage u_CabcAnd an inverter voltage reference signalIn the same way, i.e. the inverter voltage reference signal is obtained on the capacitor 412The same output voltage u_Cabc。

As can be seen from the above description, there is a phase and amplitude difference between the fundamental frequency component in the output voltage of the inverter and the fundamental frequency component of the grid-side voltage. According to the harmonic current suppression device of the voltage source type grid-connected inverter provided by the invention, the phase and amplitude difference between the fundamental frequency component in the output voltage of the inverter and the fundamental frequency component of the grid-side voltage is controlled by the power control loop, so that the appointed fundamental frequency active and reactive current (power) can be transmitted to the power grid according to the correlation principle described in the formula (2); meanwhile, the error between the harmonic component in the output voltage of the inverter and the harmonic component in the grid-side voltage can be reduced by adopting the device, the content of the harmonic current transmitted to the power grid by the voltage source type grid-connected inverter can be effectively inhibited according to the correlation principle of the formula (5), and the complexity and the design difficulty of a grid-connected inverter system are greatly reduced.

According to another aspect of the invention, a harmonic current suppression method for a voltage source grid-connected inverter is provided. Fig. 7 shows a flow diagram of a voltage source grid-connected inverter harmonic current suppression method 700 according to one embodiment of the invention. The method 700 includes the following steps.

In step S701, the grid-side voltage is sampled to obtain a grid-side voltage sampling signal.

In step S702, N harmonic components of the net side voltage sample signal are separated from the fundamental frequency component, where N is an integer equal to or greater than 1.

In step S703, the amplitude and phase of the fundamental frequency component are detected.

In step S704, the output voltage and the output current of the inverter are sampled to obtain an inverter voltage sampling signal and an inverter current sampling signal.

In step S705, an amplitude adjustment amount and a phase adjustment amount are calculated based on the inverter voltage sampling signal, the inverter current sampling signal, the target active power, and the target reactive power.

In step S706, an inverter voltage reference signal is generated based on the amplitude, the phase, the amplitude adjustment amount, the phase adjustment amount, and the N harmonic components.

In step S707, the inverter is controlled so that the output voltage follows the inverter voltage reference signal.

By reading the above description of the harmonic current suppression device of the voltage source grid-connected inverter, a person skilled in the art can understand the steps, features and advantages of the harmonic current suppression method of the voltage source grid-connected inverter, and details are not described herein again.

The present invention has been illustrated by the above embodiments, but it should be understood that the above embodiments are for illustrative and descriptive purposes only and are not intended to limit the invention to the scope of the described embodiments. Furthermore, it will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, and that many variations and modifications may be made in accordance with the teachings of the present invention, which variations and modifications are within the scope of the present invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims (10)

1. A harmonic current suppression device for a voltage source grid-connected inverter comprises:

a grid-side sampler for sampling a grid-side voltage to obtain a grid-side voltage sampling signal;

a first inverter sampler for sampling an output voltage and an output current of an inverter to obtain an inverter voltage sampling signal and an inverter current sampling signal;

a grid-side voltage processor for separating N harmonic components of the grid-side voltage sampled signal from a fundamental frequency component, where N is an integer greater than or equal to 1;

a phase-locked loop for detecting the amplitude E of the fundamental frequency component_baseAnd phase theta_base；

A power control loop for calculating an amplitude adjustment amount Δ E and a phase adjustment amount Δ θ based on the inverter voltage sampling signal, the inverter current sampling signal, a target active power, and a target reactive power;

a reference signal synthesizer for synthesizing a reference signal based on the amplitude E_baseThe phase theta_baseGenerating an inverter voltage reference signal by the amplitude adjustment amount Δ E, the phase adjustment amount Δ θ and the N harmonic components; and

an inverter control loop for controlling the inverter to cause the output voltage to follow the inverter voltage reference signal.

2. The apparatus of claim 1, wherein the net-side voltage processor comprises:

n sets of traps for filtering the N harmonic components in a one-to-one correspondence to obtain the fundamental frequency components, wherein a central resonance angular frequency of each trap in each set of traps is the same as an angular frequency of a harmonic component corresponding to the set of traps; and

a subtractor for subtracting the fundamental frequency component from the net-side voltage sample signal to obtain the N harmonic components.

3. The apparatus of claim 2, further comprising a compensator for calculating an amplitude compensation quantity E for compensating for an effect of the N sets of traps on the fundamental frequency component based on the angular frequency of the fundamental frequency component and the transfer function of each of the N sets of traps_offsetAnd phase compensation amount theta_offsetAnd further for compensating quantities E based on said amplitudes, respectively_offsetAnd the phase compensation amount theta_offsetFor the amplitude E_baseAnd the phase theta_baseMake up forAnd (6) compensating.

4. The apparatus of claim 2, wherein traps of the N sets of traps for filtering harmonic components of a voltage on a same phase network side are connected in series.

5. The apparatus of claim 1,

the apparatus further comprises a first Clark and Park transformation module for transforming the inverter voltage sampling signal and the inverter current sampling signal into dq coordinate system by Clark and Park transformation to obtain a transformed inverter voltage sampling signal and a transformed inverter current sampling signal;

the power control loop includes:

a power calculation module, comprising:

a power calculator for calculating instantaneous active power and instantaneous reactive power output by the inverter from the converted inverter voltage sampling signal and the converted inverter current sampling signal;

a first low-pass filter for filtering high-frequency components in the instantaneous active power to obtain an average active power; and

a second low pass filter for filtering high frequency components in the instantaneous reactive power to obtain an average reactive power; and

a power control module, comprising:

a first subtractor for calculating an active power difference between the target active power and the average active power;

a second subtractor for calculating a reactive power difference between the target reactive power and the average reactive power;

a first proportional-integral-derivative controller for calculating the phase adjustment amount Δ θ based on the active power difference value; and

a second proportional-integral-derivative controller for calculating the magnitude adjustment Δ E based on the reactive power difference.

6. The apparatus of claim 1, wherein the reference signal synthesizer is specifically configured to:

respectively connecting the amplitude adjustment quantity delta E and the phase adjustment quantity delta theta with the amplitude E_baseAnd the phase theta_baseCombined to generate an inverter fundamental frequency reference signalAnd

reference the inverter fundamental frequencyAre superimposed with the N harmonic components to generate an inverter voltage reference signal.

7. The apparatus of claim 6, wherein the reference signal synthesizer generates the inverter fundamental frequency reference signal based on the following equation

$\left\{\begin{array}{c}{u}_{base\_a}^{*}=(\mathrm{\Δ}E+E_{base})\sin (\mathrm{\Δ}\mathrm{\θ}+{\mathrm{\θ}}_{base})\\ u_{base\_b}^{*}=(\mathrm{\Δ}E+E_{base})\sin (\mathrm{\Δ}\mathrm{\θ}+{\mathrm{\θ}}_{base}-\frac{2\mathrm{\π}}{3})\\ u_{base\_c}^{*}=(\mathrm{\Δ}E+E_{base})\sin (\mathrm{\Δ}\mathrm{\θ}+{\mathrm{\θ}}_{base}+\frac{2\mathrm{\π}}{3})\end{array}\right.,$

Wherein,andrespectively the inverter fundamental frequency reference signalThe components on the three phases abc.

8. The apparatus of claim 1,

the device further comprises a second inverter sampler, which is used for sampling an inductive current flowing through an inductor or a capacitive current flowing through a capacitor to obtain an inductive current or capacitive current sampling signal, wherein the inductor and the capacitor form a filter of the inverter, and the filter is used for filtering high-frequency components in the voltage output by a three-phase full bridge circuit of the inverter;

the inverter control loop includes:

a second Clark and Park transformation module for transforming the inverter voltage sampling signal and the inductor current or capacitor current sampling signal to dq coordinate system by Clark and Park transformation to obtain a transformed inverter voltage sampling signal and a transformed inductor current or capacitor current sampling signal;

a third Clark and Park transformation module for transforming the inverter voltage reference signal to dq coordinate system by Clark and Park transformation to obtain a transformed inverter voltage reference signal;

a voltage subtractor for calculating a voltage difference between the converted inverter voltage reference signal and the converted inverter voltage sample signal;

a proportional-integral-resonant hybrid controller for calculating a current loop reference signal based on the voltage difference;

a current subtractor for calculating a current difference between the current loop reference signal and the transformed inductor current or capacitor current sampling signal;

a current controller for calculating a voltage modulation signal based on the current difference;

an inverse Park and inverse Clark transformation module for transforming the voltage modulated signal by an inverse Park and inverse Clark transformation into an abc coordinate system to obtain a transformed voltage modulated signal; and

a modulator for comparing the converted voltage modulation signal with a carrier signal to obtain a pulse width modulation signal and driving power switching devices in a three-phase full bridge circuit of the inverter with the pulse width modulation signal to make the output voltage the same as the inverter voltage reference signal.

9. The apparatus of claim 8, wherein the transfer function of the proportional-integral-resonant hybrid controller in dq coordinate system is:

$G_{dqv}\left(s\right)=k_{pv}+\frac{k_{iv}}{s}+\underset{n}{\Σ}\frac{k_{rv\_n}s}{s^2+{\mathrm{\ω}}_{n}s+{(n\·{\mathrm{\ω}}_{base})}^2},$

where s is Laplace operator, ω_baseIs the angular frequency, k, of the fundamental frequency component_pvAnd k is_ivRespectively proportional and integral parameters, k_{rv_n}And omega_nIs the resonance controller parameter, and n is 6k, where k is a positive integer.

10. A harmonic current suppression method for a voltage source grid-connected inverter comprises the following steps:

sampling the network side voltage to obtain a network side voltage sampling signal;

separating N harmonic components of the grid-side voltage sampling signal from a fundamental frequency component, wherein N is an integer greater than or equal to 1;

detecting the amplitude and phase of the fundamental frequency component;

sampling the output voltage and the output current of the inverter to obtain an inverter voltage sampling signal and an inverter current sampling signal;

calculating an amplitude adjustment quantity and a phase adjustment quantity based on the inverter voltage sampling signal, the inverter current sampling signal, the target active power and the target reactive power;

generating an inverter voltage reference signal based on the magnitude, the phase, the magnitude adjustment, the phase adjustment, and the N harmonic components; and

controlling an inverter to cause the output voltage to follow the inverter voltage reference signal.