SUMMERY OF THE UTILITY MODEL
In order to solve the problem that exists among the prior art, the utility model provides an inverter current control system based on self-adaptation current harmonic restraines.
The utility model discloses a following technical scheme realizes:
an inverter current control system based on adaptive current harmonic suppression, comprising: signal detection and angle tracking module, current controller module, PWM signal output module, inverter module and filter module, wherein:
the input end of the signal detection and angle tracking module is connected to a three-phase power grid or a three-phase load, samples voltage and current signals, realizes angle tracking and signal conversion through a phase-locked loop, and outputs are respectively transmitted to the current controller module and the PWM signal output module;
the output of the current controller module is transmitted to the PWM signal output module, and the PWM signal output module generates a driving signal and outputs the driving signal to the inverter module to realize voltage modulation; the output end of the inverter module is connected with the filter module, and the inverter module filters the modulation voltage and generates corresponding three-phase current; the output of the filter module is transmitted to a three-phase grid or a three-phase load.
Furthermore, the current controller module is added with a self-adaptive harmonic fitting link to fit and compensate the current harmonic.
Preferably, the current controller module adopts a control structure that a PI controller and an adaptive harmonic fitting link are connected in parallel, fast non-static-error control of the inverter current is realized through the PI controller, and steady-state current harmonics are suppressed through the adaptive harmonic fitting link.
Preferably, the current controller module comprises: a first addition operation link, a proportional integral link, a self-adaptive harmonic fitting link, a proportional link and a second addition operation link; one input of the first addition operation link is from the processing result of the signal detection and angle tracking module, the other input end is input with the expected value of the current, and the output end is transmitted to one input of the proportional integral link and the adaptive harmonic fitting link; the other input end of the adaptive harmonic fitting link is from the processing result of the signal detection and angle tracking module, and the output is transmitted to one input of the second addition operation link; the output of the proportional-integral link is transmitted to one input of the second addition operation link; the input end of the proportion link is from the processing result of the signal detection and angle tracking module, and the output is sent to one input of the second addition operation link; the last input of the second addition operation link is the processing result from the signal detection and angle tracking module, and the output is transmitted to the PWM signal output module.
Preferably, the adaptive harmonic fitting link and the PI controller form a parallel structure, and the sum of the control quantity output by the adaptive harmonic fitting link and the PI controller and the constant coefficient feedforward decoupling term is used as the modulation quantity to be transmitted to the PWM signal output module.
Preferably, the current controller module further comprises a simplified adaptive harmonic fitting element, which requires only one of the cosine signal combination or the sine signal combination to be constructed.
Preferably, the adaptive harmonic fitting step comprises: storage and judge module, cosine signal combination, sine signal combination and addition operation link, wherein:
the output end of the storage and judgment module is connected with the cosine signal combination and the sine signal combination;
the cosine signal combination comprises one or more cosine signal modules, and the cosine signal combination output is transmitted to the addition operation link;
the sinusoidal signal combination comprises one or more sinusoidal signal modules, and the output of the sinusoidal signal combination is transmitted to an addition operation link.
The utility model discloses relative prior art has following advantage and effect:
(1) the utility model discloses add self-adaptation current harmonic fitting link on traditional PI control basis, combine together PI controller and self-adaptation harmonic fitting link, fit and compensate current harmonic, can restrain the current harmonic content in the inverter system effectively, improve inverter current's sine. The system has the advantages of easy parameter setting, no model dependence on design and strong stability, and can be simply and effectively applied to actual industrial fields, such as grid-connected inversion, variable-frequency speed regulation and the like.
(2) In the adaptive current harmonic fitting link, a series of sine and cosine signal combinations are adopted to fit the harmonic waves existing in the actual inverter, so that the real-time estimation and compensation of the harmonic wave signals are realized; amplitude information of sine and cosine signal combination can be acquired in a self-adaptive mode, and angle signals can be kept consistent with current signals through a phase-locked loop. Therefore, the utility model discloses a self-adaptation current harmonic fitting link is a strong, the high current loop harmonic fitting device of fitting precision of stability, has fine frequency adaptability, is particularly suitable for being used for the industry occasion of current frequency frequent change under the operating mode, if grid-connected inverter, variable frequency speed governing etc..
Detailed Description
The present invention will be described in further detail with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.
The utility model discloses inverter current control system's principle based on self-adaptation current harmonic restraines includes:
the design of the traditional inverter current control method depends on model precision, the performance of the traditional inverter current control method is influenced by frequency change, and the optimal control performance cannot be ensured. The utility model discloses on the basis of feedforward decoupling zero, adopt PI controller and the parallelly connected control structure of self-adaptation harmonic fitting link, realize the quick no static control of dc-to-ac converter electric current through the PI controller, further utilize self-adaptation harmonic fitting link in order to restrain the steady state current harmonic, improve the control effect of dc-to-ac converter on the whole.
The phase angle of the harmonic required by the adaptive harmonic fitting link is indirectly acquired through a phase-locked loop, corresponding cosine signal combination and sine signal combination are constructed according to the phase angle of the harmonic, fitting and compensation are carried out on the harmonic existing in an actual system, and the harmonic amplitude estimation value is corrected in real time according to the tracking error of the current. The design of the self-adaptive harmonic fitting link does not depend on a mathematical model of a controlled object, parameters are easy to set, and the self-adaptive harmonic fitting link can be suitable for different working frequencies.
The adaptive harmonic fitting link is simplified, only one group of cosine signal combination or sine signal combination needs to be constructed, and the calculation amount is only half of the original calculation amount. Although the fitting precision of the simplified adaptive harmonic fitting link is reduced, the calculation amount is greatly reduced. Therefore, the simplified adaptive harmonic fitting link is suitable for industrial occasions with lower precision requirements and poorer operational capability of the adopted chip.
Whether the adaptive harmonic fitting link is simplified or not is set by a storage and judgment module, the storage and judgment module selects proper sequence lengths of cosine signal combination and sine signal combination according to actual application requirements, and simultaneously judges whether the cosine signal combination and the sine signal combination are started independently or simultaneously so as to achieve balance of control effect and actual operation amount.
The self-adaptive current harmonic suppression is applied to a current loop of a three-phase grid-connected inverter system and used for reducing switching ripples and obtaining more ideal inverter current. In the actual operation process of the three-phase grid-connected inverter system, the influences of modulation ripples and dead zone effects generated by Space Vector Pulse Width Modulation (SVPWM) exist, and the generated voltage deviation is introduced into a current control loop, so that a common PI (proportional integral) controller of the grid-connected inverter system is difficult to completely respond, the harmonic content of grid-connected current is increased, and serious harmonic pollution is caused to a power grid. In order to restrain the influence of current harmonic wave, can add the utility model discloses a self-adaptation harmonic wave fitting link designs the current loop controller of grid-connected inverter system.
In the embodiment, the current controller module added with the adaptive harmonic fitting link is adopted to fit and compensate the current harmonic, so that the harmonic content of the current in the inverter system can be effectively inhibited, and the sine degree of the inverter current is improved. The adaptive harmonic fitting link is designed based on the Lyapunov stability principle, forms a parallel structure with the PI controller, and the sum of the control quantity output by the PI controller and the constant coefficient feedforward decoupling term is used as a modulation quantity to be transmitted to the PWM signal output module to realize the modulation of the voltage of the inverter.
The present invention will be described in further detail with reference to the accompanying drawings.
An inverter current control system based on adaptive current harmonic suppression, in one embodiment, as shown in fig. 1, comprises: the device comprises a signal detection and angle tracking module, a current controller module, a PWM (pulse width modulation) signal output module, an inverter module and a filter module.
Input of signal detection and angle tracking moduleThe end is connected to a three-phase power grid, voltage and current signals are sampled by a Hall voltage and current sensor, and angle tracking and signal conversion are realized by a phase-locked loop (PLL) to obtain corresponding voltage and current information (u)d、uq、id、iq) And angle information (theta), the outputs of which are respectively transmitted to the current controller module and the PWM signal output module.
The output of the current controller module is transmitted to the PWM signal output module, and the PWM signal output module generates 6 paths of PWM driving signals and outputs the signals to 6 IGBT switching tubes of the inverter module, so that voltage modulation is realized.
The output end of the inverter module is connected with the filter module, and the inverter module filters the modulation voltage and generates corresponding grid-connected current; the output of the filter module is transmitted to the three-phase grid.
In this embodiment, as shown in fig. 2, the current controller module includes: a first addition operation link, a proportional integral link, a self-adaptive harmonic fitting link, a proportional link and a second addition operation link; one of the inputs of the first addition operation unit is the processing result (current information) i from the signal detection and angle tracking moduledDesired value i of input current at the other input terminaldOutput signal edTransmitting the signal to one of the input of a proportional integral link and a self-adaptive harmonic fitting link; the other input end of the adaptive harmonic fitting link is from a processing result (angle information) theta of the signal detection and angle tracking module, and the output is transmitted to one input of the second addition operation link; the output of the proportional-integral link is transmitted to one input of the second addition operation link; the input end of the proportional link is from the processing result (current information) i of the signal detection and angle tracking moduleqThe output is sent to one input of the second addition operation link; processing result i of signal detection and angle tracking moduleqThe output is sent to one input of a second addition operation link through a proportion link omega L (omega is the angular frequency of the power grid); the last input of the second addition operation unit is the processing result (voltage information) u from the signal detection and angle tracking moduledAnd the output is transmitted to the PWM signal output module.
In this embodiment, the adaptive harmonic fitting step is shown in fig. 3, and includes: the device comprises a storage and judgment module, a cosine signal combination, a sine signal combination and an addition operation link. The storage and judgment module is used for selecting a proper sequence length N according to actual application requirements, simultaneously judging whether a cosine signal combination and a sine signal combination are started independently or simultaneously (namely judging whether an adaptive current harmonic suppression link or a simplified adaptive current harmonic suppression link is used), and connecting an output end with the cosine signal combination and the sine signal combination. The cosine signal combination and the sine signal combination respectively comprise N/3 cosine and sine signal modules, the amplitude value of each cosine signal module and the amplitude value of each sine signal module can be self-adaptive, and the phase angle of each cosine signal module and the phase angle of each sine signal module is set according to the processing result theta of the self-signal detection and angle tracking module, so that corresponding signals are generated and output to an addition operation link.
According to analysis of current harmonics on the alternating current side of the three-phase grid-connected inverter, under the influence of SVPWM modulation action and dead zone effect, a voltage deviation delta V is introduced into a current control loop, and the existence of the voltage deviation enables output current to generate corresponding harmonic components. Because the design of the current controller module is carried out on d and q axes, the voltage deviation Δ V is written into a fourier series form and is transformed into a d-q two-phase rotating coordinate system through coordinates, and the expression is obtained as follows:
wherein: Δ VdThe component of the voltage deviation Δ V on the d-axis, Δ VqIs the component of the voltage deviation Δ V on the q-axis, a1For DC gain, θPWMPhase lag for SVPWM modulation, n is the number of harmonics, k is a positive integer, an-1Is the amplitude of the (n-1) subharmonic, an+1Is the amplitude of the (n +1) th harmonic, and θ is the phase angle of the harmonic.
When the voltage value of the direct current side, the dead time and the sampling period are determined, the amplitude of each subharmonic component is constant, and the amplitude coefficient of each subharmonic component is reduced along with the increase of n.
If phase lag generated by SVPWM is ignored, expression (1) can be simplified as:
the current loop controlled object of the decoupled three-phase grid-connected inverter can be written into the following state space expression:
wherein:
is a differential amount of the d-axis current,
is the differential of the q-axis current; i.e. i
dIs a d-axis current component, i
qIs the q-axis current component; u. of
idControl rate of d-axis current, u
iqIs the control rate of the q-axis current; r is the sum of the resistance values of the switching loss resistor and the equivalent resistor of the filter inductor; l is the filter inductance value.
Since the control of the d-axis current and the q-axis current are independent of each other, the d-axis current control rate u is designed only by taking the d-axis current as an exampleidThe method is a form that a PI controller is connected with an adaptive harmonic fitting link in parallel, namely:
wherein: omega is the output of the adaptive harmonic fitting link; k is a radical of
p、k
iProportional coefficient and integral coefficient respectively;
setting the expected value of the d-axis current according to the actual situation, and obtaining the current value expected to be output by the whole control system; 0 is the lower integration limit and represents the
time 0; t is the upper integration limit and represents time t.
The self-adaptive harmonic fitting link adopts a trigonometric function sequence with the finite length of N to fit the voltage deviation in the formula (1), the phase angle theta of the required harmonic is obtained by a phase-locked loop (PLL), and the fitting value of theta can be expressed as follows:
wherein:
A1=[ad3(cos)… adN(cos)]T,A2=[ad3(sin)… adN(sin)]T
Φ1=[cos3θ … cosNθ]T,Φ2=[sin3θ … sinNθ]T
in the formula, adn(cos)Is an estimate of the magnitude of the cosine component of the nth harmonic on the d-axis, n being the number of fitted harmonics, adn(sin)For an estimate of the sinusoidal amplitude of the nth harmonic on the d-axis, A1Estimating the column vector of amplitudes for all cosine components, A1 TIs A1Transpose of phi1Column vectors, A, formed for all corresponding cosine signals2Estimating a column vector of amplitude values for all sinusoidal components, A2 TIs A2Transpose of phi2A column vector constructed for all corresponding sinusoidal signals.
And (3) ensuring the global stability of the system in a large range by adopting a Lyapunov second method, wherein the self-adaptive law of the amplitude coefficient can be obtained as follows:
wherein: e.g. of the type
dIs a current closed loop deviation; gamma-shaped
1And Γ
2The size of the diagonal matrix with each element larger than zero determines the convergence speed of the weight coefficient; sigma
1And σ
2A constant greater than zero, the magnitude of which can adjust the stability of the system;
the rate of change of the amplitude is estimated for the cosine component,
the rate of change of the amplitude is estimated for the sinusoidal components.
Since the control of the d-axis and q-axis currents is symmetrical, in order to simplify the design of the controller, the same control parameters are used in this embodiment. Therefore, the control rate u of the q-axis currentiqCan be designed as follows:
and designing the current loop controller according to the control rate and the self-adaptive law, so that the tracking error and the fitting harmonic weight of the closed loop system are consistent and bounded.
Further, the utility model provides a self-adaptation harmonic fitting link simplification method fits according to the voltage deviation in formula (2) promptly, and then the control rate of self-adaptation harmonic fitting link simplification method changes into:
comparing the formula (8) with the formula (7), it can be found that the PI controller and the adaptive harmonic fitting link are connected in parallel, two parts (including sine combination and cosine combination) are not simplified, and only one group is simplified. Because the simplified method only needs to use one group of cosine signal combination or sine signal combination, the operation amount is only half of the original operation amount. Although the fitting accuracy is reduced, the calculation amount is greatly reduced. Therefore, the simplification method is suitable for industrial occasions with lower precision requirements and poorer computing capability of the adopted chip.
The structure block diagram of the current control system of the present invention is shown in fig. 1. Form of parallel connection of PI controller and adaptive harmonic fitting link is combined with feedforward decoupling term omega Lid、ωLiqAnd ud、uqThe current controller module in fig. 1 is formed, and a block diagram of the structure of the current controller module is shown in fig. 2. Adaptive current harmonic suppression orThe simplified method is determined by the storage and decision module in fig. 3 (i.e., the adaptive harmonic fitting procedure can be simplified in form (4) and (7), or simplified in form (8), and the storage and decision module determines the type of the adaptive harmonic fitting procedure. Because the phase angle theta is obtained by the phase-locked loop, the phase-locked loop obtains the angle and then is used in the adaptive harmonic fitting link, the angle information of the internal cosine signal combination and sine signal combination is updated, the phase-locked loop can effectively adapt to different frequencies, and the control effect of the phase-locked loop is ensured. In addition, the PI controller and the adaptive harmonic fitting link correct the output of the closed-loop system according to the current tracking error, so that the design of a current controller module does not depend on a mathematical model of a controlled object, and the method has important significance for practical engineering application.
In this embodiment, the actual operation result of the inverter current control system with adaptive current harmonic suppression added and the corresponding comparison curve are shown in fig. 4, where: the control target of the current is 15A; the abscissa is time (unit: s); the ordinate represents the magnitude (unit: A) of the phase current a. As can be seen from fig. 4, the sine degree of the inverter current is significantly improved by adding the inverter current control system with adaptive current harmonic suppression.
Specifically, the inverter quiescent current in fig. 4 is subjected to a spectral analysis, the result of which is shown in fig. 5, wherein: the amplitude, frequency and total harmonic distortion value (THD) of the fundamental wave are plotted above the graph; the abscissa is the number of harmonics; the ordinate is the amplitude of the harmonic (as a percentage of the amplitude of the fundamental). As can be seen from fig. 5, the harmonic content of the inverter current is significantly reduced by adding the inverter current control system with adaptive current harmonic suppression.
In this embodiment, 3 rd, 6 th, 12 th and 18 th harmonic fitting modules are introduced, and a harmonic amplitude fitting curve of the adaptive harmonic fitting link is given in fig. 6 and 7, where: the abscissa is time (unit: s); the ordinate is the magnitude of the corresponding harmonic fit component. As can be seen from fig. 6 and 7, the adaptive harmonic fitting link introduced in this embodiment has good stability and high fitting accuracy.
According to the above embodiment, alright with realize well the utility model discloses. It is worth to say that, on the premise of the above structural design, in order to solve the same technical problem, even if some insubstantial changes or retouching are made in the utility model, the essence of the adopted technical scheme is still the same as the utility model, so it should be in the protection scope of the utility model.